ARCTIC REGION AND ANTARCTICA ISSUES AND RESEARCH
ANTARCTICA: THE MOST INTERACTIVE ICE-AIR-OCEAN ENVIRONMENT
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ARCTIC REGION AND ANTARCTICA ISSUES AND RESEARCH
ANTARCTICA: THE MOST INTERACTIVE ICE-AIR-OCEAN ENVIRONMENT
JASWANT SINGH AND
H.N. DUTTA EDITORS
Nova Science Publishers, Inc. New York
Copyright © 2011 by Nova Science Publishers, Inc. All rights reserved. No part of this book may be reproduced, stored in a retrieval system or transmitted in any form or by any means: electronic, electrostatic, magnetic, tape, mechanical photocopying, recording or otherwise without the written permission of the Publisher. For permission to use material from this book please contact us: Telephone 631-231-7269; Fax 631-231-8175 Web Site: http://www.novapublishers.com NOTICE TO THE READER The Publisher has taken reasonable care in the preparation of this book, but makes no expressed or implied warranty of any kind and assumes no responsibility for any errors or omissions. No liability is assumed for incidental or consequential damages in connection with or arising out of information contained in this book. The Publisher shall not be liable for any special, consequential, or exemplary damages resulting, in whole or in part, from the readers‘ use of, or reliance upon, this material. Any parts of this book based on government reports are so indicated and copyright is claimed for those parts to the extent applicable to compilations of such works. Independent verification should be sought for any data, advice or recommendations contained in this book. In addition, no responsibility is assumed by the publisher for any injury and/or damage to persons or property arising from any methods, products, instructions, ideas or otherwise contained in this publication. This publication is designed to provide accurate and authoritative information with regard to the subject matter covered herein. It is sold with the clear understanding that the Publisher is not engaged in rendering legal or any other professional services. If legal or any other expert assistance is required, the services of a competent person should be sought. FROM A DECLARATION OF PARTICIPANTS JOINTLY ADOPTED BY A COMMITTEE OF THE AMERICAN BAR ASSOCIATION AND A COMMITTEE OF PUBLISHERS. Additional color graphics may be available in the e-book version of this book. LIBRARY OF CONGRESS CATALOGING-IN-PUBLICATION DATA Antarctica : the most interactive ice-air-ocean environment / editors, Jaswant Singh, H.N. Dutta. p. cm. -- (Arctic region and Antarctica issues and research) Includes bibliographical references and index. ISBN 978-1-61324-402-9 (eBook) 1. Antarctica--Environmental conditions. 2. Antarctica--Geography. 3. Natural history--Antarctica. 4. Extreme environments--Antarctica. 5. Ecology--Antarctica. 6. Climatic changes--Environmental aspects--Antarctica. I. Singh, Jaswant, Ph. D. II. Dutta, H. N. GE160.A6A59 2011 919.8'9--dc22 2010046843
Published by Nova Science Publishers, Inc. † New York
CONTENTS Foreword
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Preface
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About the Editors
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Contributors
xiii
Acknowledgments
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Chapter 1
Antarctica: Continent Dedicated to Science P.K. Purohit 1 , Soumi Bhattacharya2 and A.K. Gwal2
Chapter 2
An Insight into the Ocean-Ice-Air Interactions over the East Antarctic Marine Boundary Layer: Unique Phenomena H. N. Dutta1 , Pawan K. Sharma2, N.C. Deb3 and Laxmi Bishnoi4
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Land-Ice-Air-Ocean Interactions in the Schirmacher Oasis, East Antarctica Khwairakpam Gajananda1 , H. N. Dutta2 and Victor E Lagun3
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Effects of UV-B Radiations on Terrestrial Ecosystem of Antarctica and Their Defense Mechanisms Jaswant Singh, Rudra P. Singh and Anand K. Dubey
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Chapter 3
Chapter 4
Chapter 5
Chapter 6
Chapter 7
Chapter 8
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Ultraviolet Radiation Stress: Response and Protective Strategies of Antarctic Flora Sanghdeep Gautam and Jaswant Singh
107
Antarctic Mosses, Limiting Factors and Their Distribution Rudra P. Singh and Jaswant Singh
131
Affinities of Lichen Flora of Indian Subcontinent VIS-À-VIS Antarctic and Schirmacher Oasis Dalip K. Upreti and Sanjeeva Nayaka
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Water Relation of Some Common Lichens Occurring in Schirmacher Oasis, E. Antarctica
163
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Contents Sanjeeva Nayaka1 , Dalip K. Upreti1 and Ruchi Singh2
Chapter 9
Chapter 10
Chapter 11
Chapter 12
Index
Solar Wind Influence on Atmospheric Processes in Winter Antarctica O.A.Troshichev , V.Ya.Vovk and L.V.Egorova
173
Atmospheric Observations at Dome C, Antarctic Plateau, One of the Coldest Place in the World S. Argentini and I. Pietroni
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Impact of Individual Responsibility in Changing Global Warming? Nitosh Kumar Brahma
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Navigation with Global Positioning System in Antarctic Circle Rajesh Tiwari 1 , Smita Tiwari 1, P. K. Purohit 2 and A. K. Gwal 3
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FOREWORD The Indian Antarctic program started in the year 1981-82 and soon it was realized that Antarctica holds strongly coupled ice-air-ocean interactive system in the world. Dr. Ram Manohar Lohia Avadh University had an opportunity to participate in four Indian Scientific Expeditions to Antarctica in collaboration with the National Physical Laboratory, New Delhi. I am happy to see the results from the various Indian Antarctic expeditions being poured in the form of a book, which deals with a complex subject of ice-air-ocean interaction over the icy continent. I am also happy to note that there are contributions from Italian and Russian Antarctic stations supporting the SCAR spirit. Antarctica holds the most efficiently coupled ice-air-ocean interaction system which has led to many unique natural phenomena both over the Southern Ocean and over the Antarctic continent itself. In fact, it is the efficient coupling in Antarctica that would help it to maintain and sustain the much debated global change in various ways. I am sure; the book will fill up the gap of scientific results particularly from the east Antarctic regions and the understanding on the ice-air-ocean interactive processes over the Antarctic continent and would inspire the younger generation to formulate their projects for future expeditions to Antarctica from the world over. As an academician, I compliment the authors (Dr. Jaswant Singh & Dr. H.N. Dutta) and all the Authors of various chapters for integrating their knowledge for the advancement of Antarctic science & technology. I wish authors would continue their efforts in future in elevating Antarctic research for the benefit of humanity, which is facing multiplicity of complex problems at the global level. (Prof. R.C. Saraswat)
PREFACE Antarctica is the coldest, windiest, driest and the shiniest continent on Earth, which is surrounded by the stormiest and biologically the most productive oceans in the world. To a first time visitor, Antarctica is seen like a fantasyland and an ivory vastness bisected by ethereal mountains. In addition, this place contains many scientific mysteries like aurora, polar shadows, mirage, katabatic winds, severe cyclones, ozone hole and many other geophysical phenomena. The continent covers an area of 14x106 km which is about 10% of the land surface on earth. Antarctica holds a pristine environment and the world's largest stock of fresh water in the form of a frozen thick ice sheet. Antarctica pushes ice, cold fresh water and cold air mass from its interior towards the Southern Ocean in order to maintain cool around it and to lead many atmospheric/oceanic processes. But the ocean around Antarctica transports back only the air laden with rich water vapor and some minor constituents present in the air. The water vapor condenses to cause snowfall both over the Antarctic continent and over the ocean itself. The snowfall not only maintains the equilibrium for Antarctica to retain its physical strength and shape, it is absolutely necessary to maintain pristine environment. Antarctic environment is the least polluted and is having the highest atmospheric visibility. Antarctica is a magnificent display of interaction between air and the various phases of water in a pristine environment. This interaction has led to the formation of many unique features and many scientific mysteries, which are yet to be explored. Antarctica is now emerging as an important key in the understanding of global environmental concerns. Its unique features have provided scientists with special opportunities to investigate the origin of the continents, the pollution of the globe, ozone hole and changes in world climate. Lack of scientific data remains a major problem for researchers in many areas of Antarctic science; it is basically due to vast size of the continent, inhospitable conditions and the logistic support to sustain the efforts. The contributors are eminent scientists, expedition members and technologists, who have directly experienced the vastness of this continent to realize the Mother Nature‘s craftsmanship in carving the most efficiently, coupled system of ice-air-ocean in the world. The book shall be useful to almost all the planners and researchers working in the area of Antarctic science and technology as it encompasses chapters specifically devoted to Antarctic science, land-ocean-ice-air interaction, influence of solar wind on atmospheric processes, atmospheric observation at Dome C, navigation with global positioning system in
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Preface
Antarctic circle, effects of UV-B radiations on terrestrial ecosystem, Antarctic lichen and mosses and adaptations of Antarctic flora to survive under extreme environmental conditions. Advances made in recent years have been provided in this book which will be helpful in understanding of Antarctic climate and environmental changes. The book provides up-to-date information on Antarctic ice-air-ocean environment. It is hoped that the book shall benefit the polar scientific community in general and shall stimulate further advancement in the polar science.
ABOUT THE EDITORS
Dr. Jaswant Singh, Associate Professor at the Department of Environmental Sciences of Dr. R.M.L. Avadh University, Faizabad U.P., India and having twenty years of active research career. He has been engaged in teaching to postgraduate students and research on current issues of environmental pollution and management. He has successfully completed six major research projects in the capacity of Principal investigator and edited a book ―Natural Resource management and conservation‖. Currently working on the effects of UV-B radiations on Antarctic cryptrogams and their adaptive strategies to survive under harsh environmental conditions. He has participated in the 22nd and 24th Indian scientific expedition to Antarctica.
Dr. H. N. Dutta is leading Roorkee Engineering & Management Technology Institute, Shamli as Director (R&D) promoting Antarctic research. Prior to this assignment, he served at the National Physical Laboratory, New Delhi from 1976 to 2007, where he worked as the Convener of CSIR Steering Committee on Antarctic Research and led a group on PBL studies over Antarctica. He himself participated in three Indian Scientific Expeditions to Antarctica and carried out multidisciplinary investigations over the Schirmacher Oasis, where India has established its Maitri station. As part of the Indian Antarctic program, Dr. Dutta designed, developed and established a monostatic acoustic sounder at the Maitri station and later on, he became the first in the world to establish shipborne acoustic sounders onboard various ships probing PBL over east Antarctic Ocean. As part of these studies, Dr. Dutta has many unique distinctions to his credit-technology transfer of Antarctic acoustic sounder to a private company for its production, utilizing Antarctic data for taking an international patent, publishing papers in refereed journals and producing several PhD‘s on the Antarctic environment. Dr. Dutta has received many distinctions and honors for his scientific and technological contributions.
CONTRIBUTORS Anand K. Dubey Department of Environmental Sciences, Dr. R.M.L. Avadh University, Faizabad224001, U.P., India. Prof. A. K. Gwal Space Science Laboratory, Department of Physics, Barkatullah University, Bhopal 462026, India. Dr. Dalip K. Upreti Lichenology Laboratory, National Botanical Research Institute, Rana Pratap Marg, Lucknow – 226001, U.P., India. Prof. Dipl.-Ing. Nitosh Kumar Brahma Department of Chemical Engineering, Indian Institute of Technology, Kharagpur721302, W.Bengal, India. Dr. H. N. Dutta Shri Balwant Institute of Technology, Sonepat-131001, India. Dr. I. Pietroni ISAC-CNR via del Fosso del Cavaliere, 100, 00133 Roma, Italy. Dr. Jaswant Singh Department of Environmental Sciences, Dr. R.M.L. Avadh University, Faizabad-224001, U.P. India. Dr. Khwairakpam Gajananda Department of Environmental Science, Faculty of Science, Addis Ababa University,P.O. Box 1176,Addis Ababa, Ethiopia Dr. L. V. Egorova Arctic and Antarctic Research Institute, St. Petersburg, 199397, Russia.
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Contributors Dr. Laxmi Bishnoi, Government Girl's P. G. College, Gurgaon-122 001, India. Dr. N.C. Deb Indian Statistical Institute, 203 B.T. Road, Kolkata-700 108, India. Dr. O. A. Troshichev Arctic and Antarctic Research Institute, St. Petersburg, 199397, Russia. Dr. Pawan K. Sharma Department of Chemistry, Kurukshetra University, Kurukshetra-132 119, India. Dr. P. K. Purohit National Institute of Technical Teachers Training and Research, Shamla Hills, Bhopal462026, India. Dr. Rajesh Tiwari Electrical, Electronics and Computer Engineering Newcastle University, Newcastle Upon Tyne, NE1 7RU, UK. Rudra P. Singh Department of Environmental Sciences, Dr. R.M.L. Avadh University, Faizabad224001, India. Dr. Ruchi Singh Plant Physiology Laboratory, National Botanical Research Institute, Rana Pratap Marg, Lucknow – 226001, U.P., India. Sanghdeep Gautam Department of Environmental Sciences, Dr. R.M.L. Avadh University, Faizabad224001, India. Dr. Sanjeeva Nayaka Lichenology Laboratory, National Botanical Research Institute, Rana Pratap Marg, Lucknow – 226001, U.P., India.
Dr. Smita Tiwari Electrical, Electronics and Computer Engineering, Newcastle University, Newcastle Upon Tyne, NE1 7RU, UK. Dr. S. Argentini ISAC-CNR via del Fosso del Cavaliere, 100, 00133 Roma, Italy.
Contributors
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Dr. Soumi Bhattacharya Space Science Laboratory Department of Physics, Barkatullah University, Bhopal462026, India. Dr. Victor E Lagun Arctic and Antarctic Research Institute, St. Petersburg-199397, Russia. Dr. V. Ya. Vovk Arctic and Antarctic Research Institute, St. Petersburg, 199397, Russia.
ACKNOWLEDGMENTS On behalf of all the authors, the editors are thankful to the National Centre for Antarctic and Ocean Research, Goa (Ministry of Earth Sciences, Government of India, New Delhi) for providing us an opportunity to participate in various Indian Scientific Expeditions to Antarctica. These endeavors have given us a personal experience to bring before the world a volume of scientific work for a better understanding of the ice-ocean-air interactions over Antarctica. The editors would also like to express their sincere thanks to the authorities of the National Physical Laboratory, (Council of Scientific and Industrial Research, New Delhi) and Dr. R.M.L. Avadh University, Faizabad, U.P. for wholeheartedly supporting the Indian Antarctic program and our personal participation. The editors would like to express thanks all the authors who have provided their scientific contributions in the form of various chapters. The views expressed in this book are solely of authors and are not to be attributed to their respective governments and institutions. In this series of acknowledgements, we sincerely express gratefulness to our families for their moral and emotional support while the work was being carried out over the icy continent. The editors particularly wish to thank Nova Science Publishers, Inc. and their staff members for their collective efforts in finalizing and publishing this book. At the end, we would definitely like to thank our readers and we are sure, there might be many shortcomings but we will be very happy to receive suggestions and the criticism to improve ourselves.
Editors
In: Antarctica: The Most Interactive Ice-Air-Ocean Environment ISBN: 978-1-61122-815-1 Editors: Jaswant Singh, H.N. Dutta © 2011 Nova Science Publishers, Inc.
Chapter 1
ANTARCTICA: CONTINENT DEDICATED TO SCIENCE P.K. Purohit 1 *, Soumi Bhattacharya2 and A.K. Gwal2 ABSTRACT Antarctica is a land of extremes: it is the highest, driest, coldest, windiest continent. It is the last continent to be explored and exploited. The continent is known to have many unusual, interesting and unexplored features. Antarctica is not only a place of curiosity for scientist but is a place of interest to layman also. In many ways Antarctica is a ―Scientist Paradise‖. Science is the principal human activity in Antarctica. Being away from polluted places and human interference, unique physical properties, geographical locations, easy for analysis of radio waves, effect of solar radiation‘s, Global warming, effect of magnetic flux on poles, excess of charged particles and ionized gasses in the environment above poles makes it an important place for research. Polar atmospheric conditions affects the atmosphere of the whole earth and provides important information to world related to weather and environment. It is a pristine laboratory and its ice core archives climate history of the past. The unique nature of the region provides a living laboratory where scientists can measure the effects of changes in the environment and climate change.
Keywords: Antarctica, Blizzard, Continent, Earth History, Scientists Paradise.
*
E-mail:
[email protected], Fax and Phone Numbers +91-755-2661600 National Institute of Technical Teachers‘ Training And Research, Shamla Hills, Bhopal-462026, India 2 Space Science Laboratory, Department of Physics, Barkatullah University, Bhopal-462026, India
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P.K. Purohit, Soumi Bhattacharya and A.K. Gwal
INTRODUCTION The universe has seven continents namely Asia, Africa, North America, South America, Antarctica, Europe and Australia. Among all continents on the basis of shape and size Antarctica occupies the fifth place. Antarctica is the remotest, isolated and frozen continent of the Earth, with a very inhospitable terrain and a very harsh climate. Antarctica is arguably the most untouched region on the planet that makes it one of the world's most important places to do scientific research. Prolonged stay and research on this continent is fraught with dangers. Antarctica being called as the heaven for scientist and has several unsolved mysteries concealed within it. It is a universally accepted fact that this is the largest pollution free research lab available to the mankind. Antarctica occupies an area between South Pole and Antarctic Circle from 65S and 90S. Antarctic convergence zone lies southward from 50 south and comprises of all islands presents beyond 50 but the actual zone is beyond 66.5 south. This island is banked by water on all sides being Atlantic Ocean, Pacific Ocean and Indian Ocean. Being the highest, coldest, driest, windiest continent it is engulfed by ice to almost 97.6 % and the rest 2.4% part of this continent comprises of iceless part of land. Almost forming one- tenth part of the earth and its area is 14million sq. km. The features of suspense and thrill possessed by this continent fascinate the world. Antarctica is also known as the land of midnight sun, most unbearable weather, house of hail and snowstorms, land of the penguins, a frozen desert, fascinating continent and South Pole with all its attractive features attracts one and all.
Figure1. Map depicting geographical position of Antarctica.
Antarctica: Continent Dedicated to Science
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Figure 2. Mountain of ice in Antarctica.
Two hundred million years ago Antarctica was joined with Africa, Australia, India, New Zealand and South America forming the super continent- Gondwanaland. Forces within the Earth affecting the crust caused these continents to separate and drift apart. Thirty million years ago the continents as we know them today, reached their approximate present positions. Humans didn't even catch a glimpse of Antarctica until 250 years ago. And only in the last 90 years have people begun to explore this vast polar desert in earnest. After conquering the South Pole and the discovery of Antarctica this land happens to be the centre of interest for the scientists to quench their aspirations, and this land no longer remained lonesome. Initially Antarctica was not a frozen land around 70 million years ago and the environment was as similar to other warm islands. There were flora and fauna on the land. But little is known about it today. A new scientific era has already begun with the discovery of Antarctica. India has been sending scientific expeditions to Antarctica every year since 1981-82, and has collected a wealth of data in various areas of science. With the establishment of Dakshin Gangotri in 1983-84 and Maitri in 1988-89, India is now directly involved in polar research.
WHAT IS ALL HIDDEN IN ANTARCTICA? It is very difficult to find out the different minerals that lie under the thick layer of ice, covering the continent. From the samples obtained from mountains it can be enlisted that Antarctica has almost all the minerals that are present in South Africa and South America. On the analysis of the core of land there are chances of iron oxide and coal being present in large quantities. Several other minerals are present there but in very small proportions having very low commercial value. A decade earlier it was decided by the members of the Antarctic treaty that for the coming fifty years the mineral ores comprising of hydrocarbons, oil and gas would not be extracted from here. But the water from the glacier could be utilized. It is believed that in the future we would be able to find more deposits of oil and natural gas. The extremely cold temperature of the continent, the thick layer of ice being harder than iron, being very far from other continents, the problem due to transportation, to cross the enraged and frothy oceans, big glaciers, the split of ice shelf forming icebergs that flow in the ocean, the water of ocean being frozen, the icebergs which can collide and break the ships to pieces, all these act as obstacles to the natural extractions of these minerals.
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P.K. Purohit, Soumi Bhattacharya and A.K. Gwal
The fossils of the past atmospheric inhabitants lie in the layers of ice. Due to excess of ice the plant samples are well protected waiting to be unearthed. Antarctica is a vital area of attraction not only due to its scientific value but also due to its geopolitical and commercial values. Its comprises of valuable minerals like copper, gold, zinc, manganese, tin, uranium various gases and oil. But the mining of minerals and commercial usage are not allowed at present. The water bodies have species that may possess some commercial usage. Nature has bestowed on the Antarctica some ornamental and natural blessing, which are of prime importance due to their geographical and scientific values. It is very surprising to enlist that the ice of Antarctica holds about 90% of pure water of the world. Several such icebergs melt here every year. Scientists are making an analysis of expenditure regarding transportation of these icebergs by huge ships to fulfill the requirements of drinking water. A single small iceberg has the potential to fulfill the water requirement of a metro town in prime countries. An iceberg that broke form this continent in 1963 is perhaps the largest ever known iceberg with a length of 335 kms and width being 97 kms. It floated for 12 years before losing its existence. In the interior regions extremely low temperatures, several months of complete darkness, fierce winds and blowing snow combine to make life virtually impossible. Antarctica is the harshest in the world. Wind chills freeze exposed skin in seconds; blizzards can reduce visibility to a few feet, months of darkness and seemingly endless expanses of snow and ice. Most of Antarctica is covered with vast areas of snow and ice, which reflect about 75% of the incoming solar radiation.
THE FASCINATING CONTINENT The human interest in Antarctica has been to compute the origin of scientific inquisitiveness occurring here. Initially the inquisitiveness was limited only up to finding the geographical locations. As far as possible the initial expedition‘s team has tried to gather samples and data regarding weather, flora and fauna. Several deep secrets of nature are enclosed in the continent. As a challenge to science this place is a fort of unsolved mysteries. The continent being free form pollution and being called as world‘s largest laboratory why does it captivate the scientists of the world? Being away from polluted places, unique physical properties, geographical locations, easy for analysis of radio waves, effect of solar radiation‘s, effect of magnetic flux on poles, excess of charged particles and ionized gasses in the environment above poles makes it an important place for research. Solar radiations and the highly energetic charged particles having ionization power present in the upper atmosphere are responsible for magnetic storms and form aurora affecting the transmission of radio waves. These entire phenomenons can be studied here very well and in fact scientists are undertaking these studies in greater detail. Polar atmospheric conditions affects the atmosphere of the whole earth and provides important information to world related to weather and environment. During winter nights, at the time of absence of solar radiations and absence of direct ionization is a special property of Polar Regions. This continent offers a golden chance of analyzing effects of geo-magnetism on structure and mechanism of ionosphere. During
Antarctica: Continent Dedicated to Science
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summer season when Antarctica has continues day for few months that causes ionization at a constant rate in the upper atmosphere due to solar radiations and excessive heat. A regular measurement of geo-magnetic activities at the permanent research centers of all the nations is being carried out. The data records pertaining to this is being properly analyzed and utilized for navigation purposes. Information can be obtained regarding the movement of magnetic poles. One can perform a complete analysis related to these phenomena‘s and it could be utilized for social welfare. North and south poles are maintaining the energy balance of the world. The energy from atmosphere and oceans coming to the poles loses its identity and converts to thermal radiations. The cold winds in this region combines with hot air of lower latitudes to form clouds thereby regulating the global environment. To predict the changes in atmosphere in the future it is necessary to analyze the trend in the past. This continent is ideal for such types of analysis. The ice that has been accumulating from years withholds natural secrets amongst its layers. Antarctica is a ―Scientists Paradise‖. Science is the Principle human activity in Antarctica. It is a pristine laboratory and its ice core archives climate history of the past. The unique nature of the region provides a living laboratory where scientists can measure the effects of changes in the environment. Ongoing research is crucial to the understanding and monitoring of the global warming, ozone depletion and atmospheric pollution. The important research work associated with this place is the discovery of ozone hole, gradual increase in temperature of Earth, information regarding presence of antifreeze chemical in the body of fishes. Atmospheric research is one of the areas for which Antarctica provides a rich ground. The fundamental knowledge gained here is currently being used for practical applications and has potential promise for future applications as well. Antarctic ecosystems are ideal for biological research due to many factors. Few life forms survive above the ice because of harsh environmental conditions. A simple, land-based ecosystem is easier to study here. Thick Antarctic ice sheets provide one of the best records for past climate change. Ice cores can reveal patterns of mean air temperature, evidence of major volcanic eruptions and composition of the atmosphere. Antarctica and the surrounding areas are natural laboratories for scientific research that cannot be done anywhere else on Earth. Geophysicists can take advantage of Antarctica's ideal conditions to study the effects of solar radiation on the Earth's magnetic field. The geographical location of Antarctica has been a field of special interest for the Indian scientists. Pacific and Atlantic Ocean meet both the poles of earth but Indian Ocean has land in the north and Antarctic Ocean in the south. Indian Ocean captures the enormous energy available here and carries it across to the country. This continent is called as key of the weather of the world. Information regarding weather, climate and water can be obtained from this continent. Because of its geographical location it‘s the best and static location for atmospheric researches. Scientists pertaining to geography and environmental study have accepted this as their prime research area. This land is primarily useful for researches pertaining to pure and applied science areas.
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Figure 3. Scientists taking metrological observations and UVB measurements.
IDEAL PLACE FOR SCIENTIFIC INVENTIONS Antarctica is a land of extremes yet these extremes offer spectacle and beauty. It is the last continent to be explored and exploited – the continent about which still least is known has many unusual, interesting and beautiful features. The scientists of various nations working in Antarctica undertake in depth research and measures ozone, ultraviolet radiations, carbon dioxide, carbon monoxide and Green house gases. In our atmosphere at a height of 30 to 50 km ozone layer is present. This layer protects life on earth by preventing harmful UV radiations of sun and upper atmosphere to reach earth surface. In the beginning of the century people could not imagine that this gas only being 0.03% is responsible to maintain the environmental balance and probably this unawareness has been the reason for ozone depletion. During the period of 1969 to 1989 a fall in ozone by 3% was observed. In the year 1985, British Antarctic survey scientist J. Farman declared a startling and disturbing discovery, ozone levels in the stratosphere over the South Pole were dropping precipitously during September and October every year as the sun reappears at the end of long polar winter. This ozone depletion phenomenon has been occurring at least since 1960s but was not recognized because earlier researchers programmed their instruments to ignore changes in
Antarctica: Continent Dedicated to Science
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ozone levels that were presumed to be erroneous. It was also informed that in 1970 the thickness of this layer was almost double than is 1981 and the rate of ozone depletion had picked up pace. The exceptionally cold temperatures in Antarctica play a role in ozone losses. The cooled air gets settled on the poles because of which chlorine gets accumulated on troposphere. During summer season at Antarctica the sun is present for all 24 hours. The reaction of chlorine and ozone continue to occur all the time in presence of sunlight. This depletes the ozone layer. During September and October the hole widens to cover the whole of Antarctica and southern Australia. Hole in ozone layer has been observed on North Pole also. Springtime ozone hole in Antarctica provides favorable atmospheric conditions for observing the celestial dome. This window enables scientists to probe the structure of the Sun and the universe with novel precision. Evidence for levels of global pollution by industry, agriculture and transport sectors is frozen into the Antarctic ice. Antarctic 4.75 km thick ice sheet is a record of past climate for the last 5,00,000 years. Antarctica is a vital area of attraction not only due to its scientific value but also due to its geopolitical and commercial values. The winter season here is from April to September and summers are from October to March. In the winter season this continent doubles itself as the ocean around these freezes. As it occupies positions on the pole hence it has nearly six months of darkness and six months of day. Indian station Maitri located on Shrimachar Mountain has day from 22nd November to 24th January and continuous night from 31st May to 20th July. This continent is hit by most severe adversity of climate. The minimum temperature recorded here is -89.2C at the Vostok centre of Russia in 1983. The wind velocity and velocity of storms recorded here has been 320 km/h. The windstorms and hailstorms continue for days together. Calamities like breaking of ice, breaking of ice shelf, formation of icebergs and its flow into the waters for Kms together, formations of rifts in ice, render an utmost challenging and almost impossible working environment to people engaged in researches here. The reflection of sunrays due to ice almost renders the researchers to continue their work and increases the chances of getting lost. Antarctic can be compared to a desert also. Any area of land that has less than 254 mm (10 inches) rain than it is called as desert. There is almost no rainfall here even if rain falls it is in the form of snow. Hence it‘s called as a cold desert. During winter season the area of sea ice increases to 20 million sq. kms, which is larger than the total area of the continent. Every year almost 85% of this part melts in the summer seasons. The whole game is of the weather; even a smallest flaw in understanding the climate can turn disastrous. There must be a thousand mysteries that lie unsolved in Antarctica. The more mysteries that are unfolded the more hidden mysteries line up. There are countless mysteries in Antarctica being almost impossible to count. It is strange but a fact that Antarctica plays a vital role in the weather and climate mechanism of the whole earth. A key role is played by Polar Regions in regulating the climate of the world. To derive facts and figures related to such issues an in-depth analysis of the climatic mechanism at Antarctica has to be done. About 97.6% of ice of this continent inclusive of the oceanic ice is very sensitive towards the global warming. The ice holds enormous reserve of water inside it. The risk of increase in sea level may arise by melting of this ice. The whole coastal region is surrounded by winds hence sudden changes of weather
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are natural. The climate of this place is considered to be the most hazardous amongst all continents. The strong winds due to gravitation give birth to storms, which flow from lower regions of the continent to upper regions. Keeping the diversity and importance of the weather and climate of this region January Ist, 1957-58 was celebrated as International geophysical year. Along with these celebrations all the nations started the race of exploration of this quiet Zone. A non-governmental organization named SCAR (Scientific committee on Antarctic Research) was set up in 1958. The committee acts as a regulator for nations doing research here and also establishes co-operation between these nations. A new avenue was opened in the field of Metrology in Antarctica after establishment of IGY and SCAR. Antarctica has day for 24 hours in summer and 24 hours of night in winter. We know that the earth revolves around the sun and simultaneously rotates on its axis also. The earth is tilted 23½ on its axis. During revolution half of the earth that faces sun has day and the other half portion that lies in the dark has night. Antarctica lies on the south pole of the Earth and when there is day on the North Pole the South Pole has complete night. The Earth‘s South and North Pole plays an important role in research of global weather and climate because heat from lower latitudes is transported to high latitudes through meteorological process and is than radiated from polar latitudes at larger wavelengths. Analysis of meteorological data‘s collected here is of paramount importance in modeling of global weather and climate. The weather of Antarctica is made up of uncertainties, nonconsistencies and hindrances. There is no similarity and balance in the climatic factors here. Many nations have set up static or permanents centers in the white continent and have established their laboratories regarding weather and climate. The environmentalists here conduct research on weather related factors of this place. Antarctica affects the atmospheric and oceanic cycle inside the southern hemisphere hence has an impact on the atmosphere and weather of the world. The ice here acts as a heat absorber, thereby regulates the sea level. To know the environment of the world completely it‘s essential to know about energy balance of this white continent. This frozen ice has detained mysteries of climate of past several thousands year. To calculate weather of a particular place the data of surroundings is essential. To predict weather of an area the data both of the surface and upper atmosphere of various regions is required. There are huge uninhabited areas as well as a major area is occupied by water hence the complete zone cannot be inspected and no related data‘s can be obtained. The various weather satellites set up by several nations have achieved laurels in the area of weather predictions. To give exact prediction of weather this place is only partially suitable. The climate here depends on the weather of the sea, which is devoid of any static laboratories. The ice of Antarctica is a key factor of the weather mechanism of earth. The whole continent is surrounded by ice, which spreads to 18 million sq. kms during winters and melts to two sq. kms during the summer season. The ice is quiet sensitive to these changes of weather. To collect figures and samples from this ice covered regions is difficult and hazardous but has been eased by remote sensing. From time to time scientists were able to extract huge ice cores to analyze the life structures and climate of the past. This would help in knowing the changes of the atmosphere
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that has undergone in the past. This information is related with changes in temperature, carbon dioxide, ozone level, atmospheric pressure etc. Low pressure group of air move southward from 500 to 700 along with regular wind. At times its a group of 5 to 6 slabs at low pressure which have impact on surrounding of Antarctica move eastward at a speed of 90 km/hour. Cold winds towards the coastal region gives rise to high velocity snowstorms, which may occur for a few hours or several moths altogether. In the early years information was collected to derive normal conditions but now permanent laboratories have been constructed to assist research. Research using hi-tech devices was initiated only in the sixties. International Antarctic Analysis centre was set up to analyze the data available with all the nations collected from work of several years. The data held was also published so that it could be used to unravel mysteries of weather. Later use of satellite was made to predict weather, climate, pressure, temperature, humidity, direction and velocity of wind etc. Correct information of all these factors was available only because of the satellites used. After the use of these technologies it became easy to know about the location of low-pressure area. To know the climatic hazards of this region information for research is being made available through world climate research program and World Meteorological Organization. Today efforts are being made to know the degree to which weather can be predicted and the human activities affects the weather. Some scientists belonging to member nations of SCAR are conducting research pertaining to movement of ice, its thickness, energy flux and activities in the atmosphere. The layer of ice serves as a mirror to solar radiations coming from the top and reflects these rays back into the atmosphere. There by this continent shreds energy in the form of radiations and acts like a global energy sink affects the weather. To know in detail about the weather and climate total devotion and carefulness in required. It is essential requirement to analyze the surroundings of Antarctica and the ocean and also to analyze the reactivity and effect on oceanic waters. Weather experts in various centers have analyzed pieces of ice to know chemical reactions along with freezing and changes in atmosphere several decades before. Russian scientists have analyzed the freezing rate, atmospheric temperature of oxygen, percentage of compounds of hydrocarbon in an ice slab extracted from 2000 mts under ice. With more human intervention for research the carbon dioxide percentage has increased causing an increase in the green house effect due to which an increase in the warmth of the continent is observed. On analysis of pieces of ice from the layer for the gases enclosed a rise in percentage of CO2 has been proved. Two hundred years ago the percentage of CO2 was 200 ppm, which went upto 280 ppm hundred years ago and now it has risen to 340 ppm. Many years ago the reason for low CO2 percentage was dissolution of CO2 in cold water, which has better dissolution capacity than hot water. Thus the glaciers were more static pertaining to low CO2. In the recent years almost all nations have established their automatic weather stations in this region. Implementing the modern hi-tech devices information regarding Antarctic and the rest of the world can be predicted at least a week before. This white continent has become an inseparable part of the climate and weather mechanism of the globe. It is even possible to calculate the weather of high latitudes easily. From the first expedition, India had started gathering information related to weather for research purposes. Regular per minute inspection of the velocity of air, state of clouds, visibility, humidity, vapour etc. by the Indian metrology department is going on. The
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laboratories have all self-start and automatic devices. These laboratories experimenting on diffused solar radiations, surface ozone, total ozone, ultra violet radiation, measurement of Green House Gases etc. The prior prediction of weather is useful especially for scientists who perform research work in the Antarctic fields. The average temperature of Antarctica is - 490C. On the southern pole the sun shines for 24 hours and for nearly 6 months but if one feels that a little warmth can be felt due to sun it is wrong. The outside world avails information regarding Antarctic from data‘s available through satellite. Satellite can be used to obtain information regarding temperature of water, ice layer on water, construction and expansion of ozone layer. The recording of the climate of this region started in 1950. Through the data and pictures available from satellite the state of clouds, velocity and movement of storms, formation of ice and its distribution and various environmental processes can be updated. Various global climatic models clearly indicate that there would be enormous changes in the climate of Antarctica during the next 100 years which would cause an increase in temperature that would in turn increase the snow melt. The available climatic models have failed to produce reliable data of the changes in weather hence more research is required in this field. Several experiments have proved that there are certain changes occurring in the upper atmosphere. In ionosphere in the F- region (300 kms) the peak of concentration of electron density from the past 38 years has come down by 8 kms. In the lower atmosphere due to increase in concentration of green house gases the temperature has increased but the upper atmosphere has become relatively colder. The various theoretical analyses have shown that the layers have decreased. Southern ocean acts like a sink in global carbon cycle. The layers of ice, oceanic ice and oceans are active factors of climate. The polar plates being formed over Antarctica render it coolest. There is extreme cold due to flow of cold air. The air flows from cold mountains at a height of 9000 feet downwards and flows towards the coastal region. The rotation of earth deflects the air to left side. Researchers believe that these cold winds have major effects up to long distances. In the coastal areas the wind velocity is 150 meters per hour. The 5 meter thick ice of this continent deposited from 5 lakhs years encloses the climate of the past. These gas bubbles enclosed in the ice are a witness of pollution caused by environmental gases, industrialization, atomic bomb and fertilizers used for crops. The future climate and weather can be predicted on the basis of research on theses factors. Every year during winters about 7 million sq. kms of ice deposits around Antarctica, which melts during summers. This is the biggest event associated with weather. Scientists have discovered two more sub glacial lakes, raising renewed speculation of the existence of living ecosystems below the ice. The one lake is called "90°E" because it lies along that longitude and is now the second biggest sub glacial lake in Antarctica, while the other is named after the Russian station above the lake called Sovetskaya. These lakes were known of before but this is the first time that scientists have been able to assess their size using satellites and ground penetrating radar equipment. Scientists and experts coming to Antarctica are conducting research on various problems. Zoologists are analyzing the behavior of animals residing here and are trying to find out reasons due to which they can survive in this hostile environment. Some scientist has discovered very small plants growing inside rocks. The biologist‘s analyzes water of lakes covered to find out fecal coli form and other chemical contaminations. Environmental and weather experts analyze the climate of Antarctica and trying to discover reasons of the
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alterations regarding the unpredictability of weather. Geologists are performing critical analysis of the rocks and mountains ranges to find out the history of earth. They have been very successful in discovering minerals and ores. Glaciologists have analyzed the Antarctic ice and have gathered ice samples. Physicists have done research on southern magnetic poles and wind. They have gathered vital information regarding the ozone layer and its depletion. For Astrologist this area is matchless as during summers the sunlight is available for days together.
LIFE IN EXTREME ENVIRONMENT Although it seems quite unbelievable that even under such adverse climatic conditions life is possible but this fact is absolutely true. The Antarctic continent where earlier human settlement was beyond imagination is now a home to numerous permanent bases where the scientists conduct research and experiments throughout the year. In spite of the dangerous weather and hostile environmental conditions plants survive here. Almost 350 species of plants are found here all of which represent lichen, algae and moss. The natural flora and fauna does not have a big influence on the environment. The continent has absence of higher order plants. The higher order plants refer to those that markedly exhibit flowers, leaves, root system and fruits. The research regarding the vegetation of this place started after 1960. This was done after the predominant plants of this region were collected in large numbers as samples and were grouped into species to do a selective analysis. Many important conclusions were drawn after studying the plant density, life cycle, behavior and chemical characteristics. The outstanding feature of analysis was how the plants have sustained the adverse conditions and survived. These plants being green are producers prepare food through the process of photosynthesis for consumers. In the barren valleys of Antarctica a few rocks are found which leave space for air and moisture within them. Some of these rocks being translucent allow light to penetrate as a result some primitive type of vegetation is able to grow and survive. The namesake greenery is due to green colored ground algae, during summers this alga shows a little growth. The cold temperature and snow cover during winters curb the growth of these algae. The prevailing darkness during winters does not allow the photosynthesis to take place. In the Antarctic Peninsula some green grass can be spotted, as the temperature of this region is little warmer. Here as compared to marine life forms the terrestrial life forms are in great minority. This plays a vital role in the Antarctic food chain. During the summer season due to longer days it shows tremendous growth in the water under the floating ice. Marine microorganisms consume this. The microorganisms are intern consumed by krill and other small fishes. Lichens are abundantly growing on bare rocks and display different colors such as orange, dark brown, black etc. Their rate of growth is very slow almost being approximately 1cm in a century. These can survive in dry and passive region for long periods and are able to perform photosynthesis at even very low temperature at – 200C also. Creatures found on this continent comprises of seals, whales, penguins, krill, petrel, skua, mite‘s etc. All activities within the Antarctica continent and the waters around it are regulated and governed by a unique treaty called ―Antarctic Treaty.‖ The need of this treaty was felt to
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provide a constituted outlook to the research happening here so that it could benefit all nations.
WHO OWNS ANTARCTICA? All activities within the Antarctic continent and the waters around it are regulated and governed by a unique treaty called ―Antarctic Treaty.‖ The need of this treaty was felt to provide a constituted outlook to the research happening here so that it could benefit all nations. The Antarctic treaty was made on December 1, 1959 but was enforced on June 23, 1961. Antarctica is an international conservation and research area managed by a group of countries all of which are signatories to the Antarctic Treaty. Hence no individual, organization or country owns Antarctica. The scientists working here on environmental conservation issues are given full freedom. The scientists came here through their national research programmes but the tourists who visit this place are also given a guideline, which they have to follow. For years to come Antarctica would remain a fabulous place for the tourist and a challenge to the scientific community. Antarctic research may be a long way from home, but it is an outstanding and most pertinent in present day context of Global warming and climate change.
REFERENCES Chaturvedi, A:. Rochak avam Romanchak Antarctica: Prabhat Prakashan, Delhi, pp.1-256, ISBN No.81-7315-532-1, (2006). Khare, N.: Dharkta Mahadeep, NCAOR, Goa (2000). Girija R.:-Atmospheric research from Antarctica, the Indian contribution, pp. 1-104, IIG Bombay (1993). Purohit, P.K.: Antarctic: Vigyan Avam Chunotion., Madhya Pradesh Hindi Granth Acadamy Bhopal, pp. 1-116,(2004). Purohit, P.K.: Antarctic: Aakarshan Kyon? Indira Publishing House Bhopal, pp.1-175, ISSN No.818910703-8, (2005). Purohit, P.K.: Antarctic: Where the Silence Speaks, Indira Publishing House Bhopal, pp. 1180, ISSN No. 8189107-14-3 (2006).
In: Antarctica: The Most Interactive Ice-Air-Ocean Environment ISBN: 978-1-61122-815-1 Editors: Jaswant Singh, H.N. Dutta © 2011 Nova Science Publishers, Inc.
Chapter 2
AN INSIGHT INTO THE OCEAN-ICE-AIR INTERACTIONS OVER THE EAST ANTARCTIC MARINE BOUNDARY LAYER: UNIQUE PHENOMENA H. N. Dutta1 *, Pawan K. Sharma2, N.C. Deb3 and Laxmi Bishnoi4 ABSTRACT Antarctica is a magnificent display of interaction between air and the various phases of water in a pristine environment. This interaction has led to the formation of many unique features over the Antarctic continent, which is surrounded by an equally magnificent ocean known as the Southern Ocean. India‘s interaction with the Southern Ocean effectively started with the launch of Indian Scientific Expeditions to Antarctica in the year 1991 and as part of these expeditions, India made several attempts to install various types of shipborne acoustic sounders onboard various ships, which were part of these expeditions. The present Chapter deals with the understanding of the marine boundary layer over the east Antarctic region as probed by a shipborne acoustic sounder installed onboard the ship Megdalena Oldendroff, which sailed to Antarctica as part of the 21 st Indian Scientific Expedition in the year 2002 from South Africa to Antarctica. In the entire period from 22 January –March 3, 2002, which is of 984 hours in terms of duration, the system recorded data only for 476 hours, which is 48.37% and the rest of the data contained windy conditions, system maintenance etc. Even with this limited data, it is clear that most of the time, the marine boundary layer remains stable and the thickness of the ground based inversion was about 150 m although its ranged varied between 50-325 m. Similarly, in the case of thermal convection, the plume rise has recorded variability between 100-450m and most of the plumes reached up to a height of 300 m. *
E-mail:
[email protected] Roorkee Engineering and Management Technology Institute, Shamli-247774, U.P. India 2 Pawan K. Sharma, Department of Chemistry, Kurukshetra University, Kurukshetra-132 119, India 3 N.C. Deb, Indian Statistical Institute, 203 B.T. Road, Kolkata-700 108, India 4 Laxmi Bishnoi, Government Girl's P.G.College, Gurgaon-122 001, India 1
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Keywords: Acoustic sounder, Marine boundary layer, Shipborne, Southern Ocean.
1. INTRODUCTION Antarctica is a magnificent display of interaction between air and the various phases of water (vapor, liquid and solid) in a pristine atmosphere, where the direct solar energy reaches the Pole for six months of the year at very low elevation angle, and for the other six months of the year, it is dark. This has already led to the formation of a dome shaped, permanent ice cap, which is about 4 km thick in the interior of the continent, having an area of about 14.5 m km2 (or a circle with a radius of about 2000 km). Antarctica is surrounded from all around by an equally magnificent ocean called as the Southern Ocean and both the Antarctic continent and its surrounding ocean are connected through the most efficiently coupled ocean-ice-air system (Bailey, 2000; Schellenberg et al., 2002; Liu et al., 2004; Hall and Visbeck, 2002; Parkinson, 2004; Simmonds and King, 2004; Naithani, 1995). The Southern Ocean is dominated by a yearly variation of sea ice; its maximum area is about 19 million km2 in late winter and the minimum about 4 million km2 during late summer (Arrigo and Thomas, 2004). The moment sea ice forms, it reflects the solar radiation, thus enhances the sea ice growth. Also, being a poor conductor of heat (Van den Broeke et al., 2006; Lefebvre and Goosse, 2008), it separates the warm ocean water and the colder atmosphere and thus stops the transfer of heat from ocean to atmosphere and vice versa. Moreover, when sea ice forms, brine is rejected into the underlying ocean creating a layer of saline, dense water decreasing the vertical stability at the base of the oceanic mixed layer (Kwok and Comiso, 2002). Subsequently, entrainment causes a negative feedback between the ocean and sea ice, whereby the deeper, warmer ocean water is brought to the surface, increasing oceanic heat flux and inhibiting sea ice growth (Martinson, 1990; Marsland and Wolff, 1998). The heat flux is greatest initially when brine rejected by the rapidly growing ice sets up thermohaline convection in the underlying water. As the rate of ice growth and brine rejection decreases, so does the convection and the heat flux to the lower ice boundary drops off. During summer, sea ice melts mostly by warming of the ocean mixed layer through heat input (mainly solar radiation) in open water areas (Ohshima and Nihashi, 2005). Also, a large number of low pressure areas in summer result ocean swells and high winds breaking the ice into large pieces that move under the influence of wind and currents. (Fast-ice is sea-ice that is held fast to the continent.) Pack ice can change in a matter of hours from being open and navigable to densely packed and impassible. The large seasonal fluctuation of the sea ice cover affects the exchange of energy, mass and momentum between the ocean and atmosphere, and is extremely important in controlling the existence of Antarctic continent and its interaction with the whole globe (Lefebvre and Goosse, 2005, 2008; Simmonds, 2003; Thattermann and Levermann, 2009; Busalacchi, 2004; Meskhidze and Nenes, 2006; Ito et al., 2010; Ved Parkash, 2008; Liss et al., 2004). The Southern ocean's circulation system has another unique feature known as the Antarctic Circumpolar Current (ACC), which is both the longest and the strongest current in the ocean carrying a volume transport of 130 Sv (1 Sverdrup=1 Sv=1×106 m3 s−1) along a
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24 000 km path encircling Antarctica (Gille, 1994). The ACC is also unique because no continental barriers exist in the latitudes spanning Drake Passage (the gap between South America and the Antarctic Peninsula), which allows the current to close upon itself in a circumpolar loop and is the primary means of inter-basin exchange of heat, carbon dioxide, chemicals, biology and other tracers. Despite its essential role in the climate system, the ACC remains one of the most poorly understood currents in the ocean (Thompson, 2008). At the same time, deep waters in the Southern Ocean are rich in dissolved inorganic carbon (DIC) and depleted in oxygen. When circulation brings these waters into the mixed layer, the soluble gases are exchanged at the air-sea interface. The formation of deep mixed layers combined with high biological productivity make the Southern Hemisphere extra-tropical oceans an important component of the global carbon cycle (Bishop and Wood, 2009).
2. INTERACTION BETWEEN THE MAIN ANTARCTIC CONTINENT AND THE SOUTHERN OCEAN The interaction between the Southern Ocean and the Antarctic continent (Dierer et al., 2005; van Ommen and Morgan, 2010) has already led Antarctica to be the coldest (due to the thickest dome shaped ice cover on Earth), windiest (again due to thick dome shaped ice cover and by the least polluted pristine environment), driest (due to low temperature, water vapor freezes into ice and whatever is left, it is pushed towards the ocean by the katabatic winds. Also, the katabatic winds make the icy surface harder, as evaporation causes cooling, thus help in maintaining stability of the dome shaped ice) and the least polluted (pristine environment-the frequent snowfall cleans the atmosphere and almost all the particulate matters are pulled down and buried under the ice forever). Also, the pristine environment helps the radiative energy-Infrared/heat energy to escape to the sky without any hindrance, leading to the formation of steep surface based inversions in the lowest atmosphere resting on the icy slopes of Antarctica. This air mass is pulled by the gravity and flows out of the periphery of the continent as the unidirectional, highly consistent winds, called as katabatic winds. These winds trigger / force or create warm-air advection for creating atmospheric cyclones over the ocean, with the result, Antarctica is surrounded all around by the stormiest ocean in the world (Fyfe, 2003; Kalnay et al., 1996; Lin and Simmonds, 2002; Carrasco et al., 2003; Gajananda, 2002). These cyclones, in-turn, pump moisture over the continent, leading to the snowfall (Genthon and Krinner, 2001; Guo et al., 2003; Gajananda et al., 2004, 2007) and churn the oceanic water, creating trillions and trillions of water droplets, thus rendering a perfect turbulent transfer of air into the ocean and the transfer of the oceanic gases, water vapor, pollutants, microorganisms etc. into the air (Gajananda et al., 2004; Gajananda and Dutta, 2005; Lim and Simmonds, 2007; Bargagli, 2008). All these microorganisms, various pollutants, sea salt particles, oceanic gases and water vapor have invaded the periphery of Antarctica and form an important subject of investigations over the ocean and oasis regions of Antarctica (Honjo, 2004; Gajananda et al., 2004, 2007; Kerminen et al., 2000; Ved Parkash, 2008). Antarctic continent and its surrounding ocean are connected with each other basically in four ways:
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H. N. Dutta, Pawan K. Sharma, N.C. Deb et al. 2.1. Ice interaction: The ice from the main continent is slowly pushed towards the ocean due to gravity and a part of this ice breaks in various forms to maintain the cool over the Southern Ocean (Joughin and Tulaczyk, 2002; Ng and Conway, 2004; Rignot, 2006). It is important to note that the Antarctic continent pushes ice into the surrounding ocean, while the ocean creates snowfall over the entire continent and over the ocean itself. 2.2. Water interaction: During local summer, over the main continent, when the upper portion of the ice melts, the water either gets collected in depressions, forming pools/lakes or tries to cut the ice to create trenches, crevasses, tunnels etc. flowing out of the continent towards the periphery. The water gets collected in the form of lakes / ponds etc. over the oasis regions or flows towards the ocean (Naithani, 1995; Gajananda, 2002; Gajananda et al., 2003). The formation of water alters the surface albedo and wherever, water gets collected, it dissolves more and more ice. Also, at the periphery of the continent, the lower portion of the shelf ice gets dissolved in the relatively warm oceanic water (Vaughan and Doake, 1996). In any case, over the past millions of years, there has been a perfect equilibrium between the ice melting during summer and freezing during the winter period. In fact, there should be more deposition of ice during winter than the melting during summer, so that the net balance is positive, but confirmatory results are still awaited (Wingham et al., 2006; Ramillien et al., 2006). 2.3 Air interaction: The third interaction is through the air, which is the lightest form in terms of density and specific heat compared to water and ice. Over the main continent, due to pristine atmosphere, the icy surfaces emit infrared energy to the sky, resulting in the formation of surface based inversion. With the result, the air resting over the icy slopes becomes much heavier than the air aloft, thus it is pulled by the gravity towards the periphery of the continent. As the air move towards the periphery, its velocity increases tremendously and it pushes the lower atmospheric water vapor towards the periphery. This unidirectional moving cold and dry air mass is known as katabatic winds (Kumar, 2002). It is important to note that although the katabatic flow carries very cold and dry air, its remarkable strength may disrupt the surface temperature inversion by vertically mixing the cold surface layer with the upper and warmer atmospheric layers, causing a surface warming (König-Langlo et al., 1998). In addition to this mechanism, also the frictional and adiabatic heating of the katabatic flow may contribute to warming the near-surface air. Over the Southern ocean, the relatively cooler, dry katabatic winds trigger many phenomena, including the formation of sea ice over open ocean areas and pushing it away from the periphery of the continent. Also, the katabatic winds trigger the formation of cyclones over lower latitudes. These cyclones, in turn, lead to snowfall over the continent and the entire loss of ice in various forms gets compensated. The intensity of katabatic winds is more pronounced during local winter, as the cooling of the icy surfaces is the highest. 2.4. Radiation interaction: The snowfall during winter covers almost all the portions of Antarctica, so that in local summer, the Sun rays get reflected as part of the survival strategy of Antarctica and its surrounding (Naithani, 1995; Gajananda, 2002; Pirazzini, 2004). Also, during snowfall periods, the entire atmosphere becomes
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cleaner, as the suspended particulate matter in the air is brought down by the falling snow flakes and buried in the ice (Wang et al., 2008; Boucher et al., 2003; Eisele et al., 2008; Stohl and Sodemann, 2010; Gajananda et al., 2004, 2007). This cleaning of the atmosphere is essential for the radiative part to be efficiently active over the entire Southern Ocean. The cleaning of the atmosphere also happens even during summer, when the cyclones lead to snowfall. This is an absolutely essential component of the entire Southern Ocean environment as for the formation of the sea ice, it is necessary that the radiative energy must escape to sky without any hindrance or modification etc. (Chamberlain et al., 2000; Lawrence et al., 2004; Naithani et al., 1994). In summer, cyclones may also result in some rainfall events at the periphery of the continent (Deb et al., 1999; Ved Parkash, 2008). In fact, over the past thousands of years, the loss of Antarctic ice had been lower than the total amount it gained and that‘s how, Antarctica is holding its physical structure and is participating in the controlling the global temperature and many other important features. Even in the past, there has been no change in the snowfall over the continent since the IGY (Monaghan et al., 2006) and Antarctica seems to be stable in some respect (Gudmundsson and Jenkins, 2009). However, many signals or worries are related to the global warming, which makes the subject of ocean-ice-air interaction to be an important science subject (van de Berg et al., 2006; Justino et al., 2010; Peck, 2005; van den Broeke, 2008; Bindschadler, 2006; Steig et al., 2009; Gille, 2008; Zazulie et al., 2010; Atkinson et al., 2004). In fact, to strengthen our knowledge about various aspects of Antarctica, many programs are in progress (Rignot, 2002; Frey et al., 2009). Once the katabatic winds are forced to blow over the ocean, they move up the relatively warm and humid air. As this humid air moves up, it moves into a region of low pressure and cools. The associated water vapor also cools to form water droplets or directly into snow, releasing latent heat. This release of latent heat creates a low pressure area, with the result; more air is sucked into this region. Thus, it triggers the formation of a well defined or well developed cyclone over the ocean, which has to move towards the continent. The cyclonic air from the ocean side is relatively much warmer than the existing Antarctic air, leading to warming of the atmosphere, which is more noticeable in winter months (Naithani, 1995; Gajananda, 2002). In fact, there are events over Antarctica, wherein a widespread warming has been observed both during local summer and winter seasons (Enomoto et al., 1998; Deb et al., 1999; Van As et al., 2007). In summer, the katabatic winds are weaker but the number of lows per month is higher in summer due to advection of water vapor (Naithani, 1995; Kumar, 2002; Carrasco, 2003; Ved Parkash, 2008). At the same time, the invaded moisture by the cyclones may lead to the formation of fog over the periphery of the continent (Gera et al., 2002; Walden et al., 2003; Gajananda et al., 2003; Gajananada et al., 2007). These cyclones approaching from lower latitudes (moving from west to east), become the main sources of heat for the atmosphere, and the atmosphere-surface heat transfer takes place through turbulent mixing and longwave radiation, the latter is dominated by clouds. The cyclones are also responsible for warming of planetary boundary layer around the periphery of the continent during winter.
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Also, the cyclones replenish the loss of ice in the form of fresh snowfall all over the continent and around the ocean. The freezing ice in winter and the falling snow cover almost all the exposed parts even at the periphery of Antarctica, thus prepare the entire continent to be ready to reflect the falling Sun‘s energy during the local summer. The atmospheric research in Antarctica is increasingly important as many processes taking place in the atmosphere are still barely understood (Anisimov et al., 2007). This is particularly true for exchange of gases and particles between ocean and atmosphere, an area of study which is currently receiving much attention (Meskhidze and Nenes, 2006; Zorn et al., 2008). Since the Antarctic atmosphere is absolutely clear, aerosol particles play an important role in the atmosphere because of their effects on the radiation budget and consequently on climate and climate change, which is in particular true for aerosols from marine environments (O‘Dowd et al., 2007). Currently, the focus is on their formation and understanding which gaseous compounds participate in it (O‘Dowd et al., 2007) and the atmospheric processes over the most complex situation caused by the water, ice and air (Andreas et al., 2004; Bishnoi et al., 2005; Dutta et al., 2004 ). In the present Chapter, we shall concentrate only on the atmospheric phenomena, which have been captured by a shipborne acoustic sounder deployed onboard the ship Megdalena Oldendroff, which sailed along the periphery of the east Antarctic ocean in the year 2002.
3. SODAR MEASUREMENTS The group at the National Physical Laboratory, New Delhi had established an acoustic sounder (sodar) at the Indian Antarctic station, Maitri (70.76o S; 11.73o E; elevation 117m) in the year 1990-91 (Dutta et al., 1991; Dutta and Naithani, 1994; Naithani and Dutta, 1995; Gajananda et al., 2004, 2007; Kumar et al., 2007; Gera et al., 2010). This development had made India as the sixth country in the world to have a boundary layer program over Antarctica and since then, attempts have been made to install a sodar system onboard the ships sailing to Antarctica as part of various Indian Antarctic expeditions (Dutta et al., 1993, 1999, 2004, 2007; Bishnoi et al., 2005). The most successful attempt for shipborne operation was made during the 21st Indian Scientific Expedition in the year 2002, when the system was installed onboard the ship Megdalena Oldendroff, which sailed from South Africa to Antarctica. The team established it successfully and operated PC controlled system as shown in Figure 1. Figure 1 shows photograph of the antenna mounted onboard the ship and that of Dr Pawan Kurmar Sharma who installed and operated the system successfully. The system was placed on the ship around January 19, 2002 and after making several checks, it finally started functioning from January 22, 2002. At the same time, the ship was sailing; its pathway is shown in Figure 2. The ship actually sailed to the German Antarctic station, Neumayer, which is situated on the shelf itself. It is important to note that the ship cannot be anchored along the shelf during the cyclonic conditions for various reasons and therefore it is kept in motion. The square shown in Figure 2. indicates that the ship remained in this area from February 3 to March 11, 2002.
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Figure 1. Shipborne acoustic sounder antenna onboard the ship Megdalena Oldendroff and Dr Pawan Kumar Sharma operating the system electronics.
Figure 2. It indicates latitude and longitude that ship followed during its journey in Antarctica. The box indicates that the ship remained in this area from February 3 to March 11, 2002.
4. BASIC PLANETARY BOUNDARY LAYER STRUCTURES In the entire period from 22 January –March 3, 2002, which is of 984 hours, the system recorded data only for 476 hours, which is 48.37% and the rest of the data contains windy conditions, system maintenance etc.
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Out of this useful data of 476 hours, 69.9% of the time, it was surface based inversion, followed by thermal convection for 15.3% of the time and elevate inversion for 14.7% of the time (Figure 3). This indicates that even during sunny hours, it is the stability in the lower atmosphere, which dominates the lower marine planetary boundary layer close to the periphery of the east Antarctic continent.
Thermal convection 15.3% Elevated inversion 14.7% Surface based inversion 69.9%
Figure 3. Out of the total 476 hours of noise free recording by the shipborne acoustic sounder, surface based inversions dominated the occurrence followed by elevated layers and the thermal convection.
4.1 Surface Based Inversion (Stable Atmospheric Structure) Surface based inversions are the most common feature of the Antarctic environment along the shelf. On acoustic sounder records, it is seen as a thick patch with one end sticking to the ground and another showing a flat upper surface under the most stable conditions; otherwise, wind may lead to some turbulence or undulations at the upper boundary. An example of the surface based inversion is given in Figure 4. The surface based inversion is caused by the radiative cooling of the surface. The surface based inversion depicts two important parameters: (i) Thickness of the ground based inversion, and (ii) The thermal gradient The thickness can be directly read from the facsimile chart with a precision of about 10m, while the thermal gradient can be judged from the colors depicted in the chart. The Figure 4. shows that the surface based layer has about 275 m as the thickness, which is varying at different timings. This variability is caused by the radiative processes influenced by the prevailing wind. Also, many thermal gradients are imbedded in the inversion, as the depiction is not just one dark patch, rather, there are many colors are an integral part of it. This shows that there must be some wind blowing at the site, which intensified at 0645 hrs. Moreover, the lighter wind was blowing throughout the record as can be seen by the green colored vertical
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lines, indicating wind noise. The surface based inversion thickness is an important parameter and is plotted in Figure 5. This shows that surface based inversions have a high variability in terms of thickness, which can as low as just 50 m or as high as 325m. Of course, the most probable thickness lies around 150 m. However, it is important to note that the data given in this figure cannot be taken for any strong or definite conclusion, these are just preliminary observations actually meant to show that the shipborne acoustic sounder can function normally even under the most adverse Antarctic conditions, recording variability in the thermal structures of the lowest PBL.
Figure 4. An example of a surface based inversion recorded by a shipborne Acoustic sounder observed over the southern ocean along the eastern coast of Antarctica. This echogram directly gives the thickness of inversion and is an important parameter in many atmospheric applications.
Figure 5. Statistical distribution of thickness of surface based inversion in various categories. The SBI thickness has a high variability but is most probable around 150 m.
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4.2. Thermal Convection Thermal convection is an important phenomenon that is rare in the Antarctic environment but it has its own importance in transporting fine particles and biological material from the oceanic surfaces to upper atmospheric regions. In this region, since the velocity is high, it helps transportation to much longer distances (Gajananda et al., 2004). On an acoustic sounder system, thermal convection is seen as inverted cones, caused by the thermal heating of the lowest surfaces, leading to mach warmer air close to the surface of earth/ ocean than the air aloft. With the result, the warmer air rises upwards, leading to the formation of what are called thermal plumes on the acoustic sounder echograms. The thermal plumes represent region of direct vertical mixing for the fine particulate matter or biological microorganisms (Gajananda et al., 2004) and are essential to be recorded on a long-term basis in order to detect signals like global warming. In the Antarctic ocean, these may not be just caused by the thermal heating of the oceanic upper surfaces by the Sun, but the warm oceanic water compared to the adjoining air, can also lead to such a situation. The reasons of formation may be many but the most important parameter to be measured is the height up to which these thermal go. Figure 6. shows a case of thermal convection as recorded and depicted by an echogram. Many papers have been published on the interpretations of these records. In this photograph (Figure 6), the clarity of thermal plumes is seen to diminish as soon as the background winds become stronger beyond 2130 hrs. Actually, winds distort the vertical movement and also lead to generation of noises on the acoustic sounder record, these two effects combined together, make them indiscernable. The plumes are seen to be going well up to a height of 350m between 1800-1900 hrs and have a high day to day variability. This has been measured on hourly basis and is plotted in Figure 7. Similarly, in the case of thermal convection, the plume rise has variability between 100450m but most of the plumes reach up to a height of 300 m (Figure 7). It is important to note that over ocean, the development of thermal plumes may not just due to the surface heating of the upper oceanic surfaces but it can also be due to the warm water, after all, thermals indicate only relativeness in the surface and upper air temperatures.
Figure 6. Thermal plumes are an important atmospheric phenomenon in the Antarctic atmosphere as they represent surface air to be much warmer than the air aloft. The warmer surface air rushes up to form an inverted cone on the acoustic sounder echograms. The height up to which these thermal go represents the thermal mixing in the atmosphere.
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Figure 7. The occurrence of thermal convection in various height ranges as recorded by the shipborne acoustic sounder over the east Antarctic coast. As expected, it has a high variability but the most probable height attained by the plumes is around 300 m. This is an important finding and shall be useful in many models.
Figure 8. Elevated inversions in the Antarctic environment are an expected phenomenon in the PBL Shipborne acoustic sounder has revealed a variety of these layers, which have shown a high degree of variability in the height but thickness is generally between 50-80 m.
4.3. Elevated Layers / Inversions Another important feature for any site in the world is the presence of an elevated layer, which is basically a stable layer but suspended in the air (Naithani, 1995; Kumar, 2002). It may be caused by a number of atmospheric phenomenon and the most common among them are the presence of a high pressure zone, which suppresses the air towards the earth. The other cause can be the wind shear, which means two air masses of different origin may lead to the appearance of this situation (Naithani, 1995).
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An example of this layer is shown in Figure 8, wherein an elevated layer is seen to be persisting continuously for several hours. Again, the interest will be in the height and the thickness of such layers (Naithani, 1995; Kumar, 2002). In Antarctica, flow of katabatic winds close to the undulating surface of earth may lead to the formation of elevated layers (Naithani, 1995; Kumar, 2002). With the available scanty data, it is not advisable to draw a figure depicting various height ranges for the elevated layers, but, most of the layers have been between 250-350 m altitudes. It is important to note that over the Indian Antarctic station, Maitri, numerous studies have been made during 1990-96 period and a variety of elevated inversions associated with a number of phenomena have been identified (Naithani, 1995; Deb, 2009). Here, since the observational period was too short, we have not been able to really record a variety of these layers.
5. NORMAL ATMOSPHERIC PHENOMENA The acoustic sounder structures observed during the experimental period recorded a variety of structures, indicating the fact that during summer, the atmospheric conditions are variable over space and time. Figure 9. shows variable structures observed on January 24, 2002, it shows a highly variable surface based inversion, with clear jumps in the structure dynamics at 0430-0530 hrs. At the same time, the presence of elevated layer indicates that there may be two different sources of airflow. Unfortunately, we were not carrying out any supporting measurements of temperature either in the oceanic water or in the air, with the result, its interpretation is difficult. But, the observed structures are a testimony to the variability. However, this variability is created by the fact that over ocean, the water surface is highly variable in terms of type of sea ice, its age and its strength embedded over open ocean spaces. Undoubtedly, the open ocean spaces are at a much higher temperature than the areas covered by a variety of sea ice. This type of variability may not be seen on daily basis, Figure 10. shows the facsimile recorded on February 10, 2002, in which surface based inversion is predominantly present in the lower atmosphere. However, dull thermal convection seems to be appearing during 10001400 hrs. At the same time, the surface based inversion is spiky, which means, vertical movement of wind or turbulence is present in the lower atmosphere. At the same time, there have been a number of incidences of high wind speeds, again indicating atmospheric variability
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Figure 9. Highly variable facsimile picture shows a turbulent planetary boundary layer over the Southern Ocean.
Figure 10. Dominance of surface based inversion is the key for the survival of Antarctica but patches of thermal convection are indicators of atmospheric variability over the ocean.
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6. UNUSUAL PLANETARY BOUNDARY LAYER PHENOMENA Apart from the mixed types of structures, there have been two extremely important and unusual incidences over the east Antarctic region. These are discussed below:
6.1. Prolonged Persistence of Thermal Convection Figures 11 a-b show that there was a special case of thermal convection on February 2-3, 2002, wherein convection persisted continuously for almost 2 days, although there were timings when the winds were high.
Figure 11 a. An extremely important and unusual event of continuous thermal convection over the east Antarctic ocean is a subject of great scientific value and needs in-depth investigations.
This is something unique as if we see the sunlight hours, the convection can only be expected during the peak sunlight hours and that too, if we presume that there was no mixing over the ocean. On the other hand, if the oceanic water is warmer than the air, then the thermal convection can be sustained on a prolonged basis. In any case, thermal convection indicates that the surface is at least 3-4oC warmer than the air aloft and the horizontal mixing is low. It is the time when surface of ocean transports its heat to the atmosphere.
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Figure 11.b. Dull thermal convection continuing from the previous day, is again an extremely important phenomenon and calls of well planned PBL studies over the east Antarctic Ocean, which is holding many natural secrets. The most important part is that even under high winds beyond 1030 hrs., dull convection continued till 2115 hrs.
Unfortunately, we had no support of any other simultaneous data and therefore, it is difficult to comment but on the basis of the published results and the data downloaded from the Antarctic data websites, some light can be thrown as discussed below:
6.1.1. Discussion It is important to note that there was a surprising event over the east Antarctic region in early 2002, when the break-up of the Larsen B ice shelf was observed (http://www.coolantarctica.com/Antarctica%20fact%20file/science/global_warming.htm). This event has been attributed to the effects of global warming. That it occurred is beyond dispute and that it is a result of the warming of the Antarctic Peninsula where it is situated is also beyond dispute. What remains unclear is whether or not this is a taste of things to come and an indicator of an Antarctic-wide phenomena or simply a localized result of the localized warming of the Antarctic Peninsula region alone. The Larsen B ice shelf was about 220m thick (720 feet) and during a 35 day period in early 2002 lost about 3,250 km2 of ice into the ocean. It is thought to have been in existence for at least 400 years prior to this and probably as long as 12,000 years since the end of the last ice age. Such disintegration in such a short time period is therefore an extremely significant event. What now remains of the Larsen B is about 40% of what was there in 1995. It had been breaking up at what was considered to be a rapid rate anyway before this major event. The break-up is thought to be a consequence of higher temperatures and large amounts of summer melt-water running down crevasses in the ice shelf so speeding the disintegration process.
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Overall in the Antarctic Peninsula, seven ice shelves have between them declined in area by about 13,500 km2 since 1974. This melting on such a large scale cannot be explained just on the basis of warming of the air, it has to be basically warming of the water, which had dissolved the whole mass of ice. This warming or warm water must have been below the ship on February 2-3, leading to the formation of thermal convection observed for over 24 hours. A series of Southern Hemisphere experiments have been performed to study turbulent convection on a continental shelf–slope placed in a large rotating tank filled with fresh water (Liang et al., 2008). The upward ocean heat transport is generated by oceanic advection, diffusion, and convective overturning. In the Southern Ocean, convection occurs along the continental shelves of Antarctica as well as in the open ocean owing to ice formation and associated salt rejection (Baines and Condie 1998). Bitz et al. (2006) have demonstrated the strong influence of sea ice on convection and the upward ocean heat transport through freshwater transport, which makes the surface waters more stable in a greenhouse warming scenario. In support of the thermal convection, it is important to note that the synoptic pictures show that there was certainly warming over the investigation area (Figure 12).
Figure 12. Rising layer is a common phenomenon over the land and is well understood. But, over ocean and that too in Antarctica, where the ocean is the most turbulent and winds are strong, this is something unique and needs in-depth investigation.
6.2. The Rising Layer Another important and unique event is the rising layer observed on January 23, 2002 (Figure 13). The rising layer phenomenon over ocean /ice looks to be unique, as we cannot expect that over ocean, the heat will not be dissipated by the mixing of the water due to winds and thermal gradients. Of course, over land, the surface based inversion created at nigh starts moving up under the influence of solar heating of the earth‘s surface. As this inversion layer rises, underneath are the thermal plumes.
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Figure 13. Rising layer over Antarctic ocean is a unique feature on acoustic sounding as it hard to expect that the oceanic/ icy surface will not transfer energy to its own medium, rather only the upper surface will get warmer to create convection and sustain it for at least 6 hours.
In fact, it is the thermal plumes, which lift the inversion at the same time, erode it from the lower side of the inversion. In the case of brisk heating, the plumes may penetrate into the inversion and may break it within a short span of time. On the other hand, like in winter, it may take several hours or the upward moving inversion may not break at all, it may remain as a suspended layer throughout the day and then return back to ground in the evening as the heating subsides (Dutta et al., 1994; Choudhury and Mitra, 2004; Kumar et al., 2010). Over the Indian Antarctic station Maitri, an acoustic sounder was deployed in the year 1990 and here also, over a period of six years, some incidences of rising layer were noticed but such cases were not very prominent (Naithani, 1995). On the other hand, on the ship, a case of rising layer was observed and it very unique as over ocean, it cannot be expected that either ocean or ice will behave like Earth. In the ocean, some amount of mixing will always be expected and over the ice, the melted water under solar heating shall always dissolve more ice. But under exceptional circumstances, it is just possible that the energy exchange underneath the water or ice gets limited and the energy exchange takes place between the wet /icy surface and the air. But, it would certainly require a high pressure area over the observational site to ensure calm weather (calm ocean) and low winds.
6.2.1. Discussion We have scanned the whole literature to get a support for our observation but there is nothing that can be quoted with firmness. However, it is important to note that for a rising layer, the heating has to be continuous on the ground to support the development of thermal plumes underneath the rising layer. This will only be available if the mslp is high so that the atmosphere is clear to form the steep inversion and in the morning to receive the heat to warm up or erode the inversion. The atmosphere, of course, has to be still.
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Figure 14. Isobaric contours of surface msl recorded on January 22, 2002 indicate high Pressure zone (marked as H) around the ship position.
Figure 15. The sea ice erosion along the eastern coast of Antarctica has been severe in the months of January-March, 2002. Sreenivasan and Majumdar (2006).
This support is available for the synoptic pictures as seen in Figure 14. It is clear from this figure that there was indeed a high pressure area or zone between two consecutive cyclones. This is what normally happens in Antarctica (Naithani, 1995; Kumar, 2002; Gajananda et al., 2004; Ved Parkash, 2008) and the weather is altogether different in two regimes (the low pressure area and the high pressure area). The other support is from the surface temperature (Figure 15), which shows the warming over the eastern zone of Antarctica and relatively open ocean so that its albedo is low.
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Actually, the whole month of January was getting warmer as is seen from the published work of Sreenivasan and Majumdar (2006), wherein authors have reported the unusual melting and the figures are presented here as Figure 15. The calculated estimates are given in Table 1. Table 1. Sea ice areal extents and depletion statistics
Date
15.1.2002 23.1.2002
Area of Sea ice depletion Million km2
Weekly depletion Million km2
5.023 4.348
1.160 0.675
Average Weekly rate of depletion km2/day 165714 84375
CONCLUSION Antarctica is the least explored and still a mysteries continent on Earth; through acoustic sounding of the atmosphere, we have explored two of its unique secrets for the first time in the history of mankind. Both of these events throw a light on the need to continue acoustic sounding program with better coordination and planning for giving a proper interpretation for the better understanding of the water-ice-air-radiation interactions over Antarctica. After all, Antarctica holds the largest fresh water stock on Earth, the key to absorb CO2, millions of unique species and much more for the betterment of mankind on Earth.
ACKNOWLEDGMENTS The authors are grateful to Dr. B.S. Gera, who supported the development of shipborne acoustic sounder in India. Authors would like to thank members of various Indian Scientific Expedition teams, who helped in the installation of acoustic sounders onboard various ships sailing over east Antarctica. Thanks are also due to the Chairman, CSIR-SCAR for selecting and providing field support to various NPL Antarctic teams.
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O‘Dowd C D., Y J. Yoon, W. Junkerman, P. Aalto, M. Kulmala, H. Lihavainen and Y. Viisanen: Airborne measurements of nucleation mode particles I: coastal nucleation and growth rates; Atmos. Chem. Phys. 7, 1491-1501 (2007). Ohshima, K.I. and S. Nihashi, A simplified ice–ocean coupled model for the Antarctic ice melt season. J. of Phys. Oceanogra. 35, 188-201 (2005). Parkinson, C.L.: Southern Ocean sea ice and its wider linkages: insights revealed from models and observations. Antarctic Sci. 16, 387-400 (2004). Peck, L.S.: Prospects for surviving climate change in Antarctic aquatic species, Frontiers in Zoology. 2 doi: 10.1186/1742-9994-2-9 (2005). Pirazzini, R.: Surface albedo measurements over Antarctic sites in summer. J. Geophy. Res. 109, D20118, doi:10.1029/2004JD004617 (2004). Ramillien, G., A. Lombard, A. Cazenave E.R. Ivins, M. Llubes, F. Remy and R. Biancale: Interannual variations of the mass balance of the Antarctica and Greenland ice sheets from GRACE. Glob. and Plan. Change. 53, 198-208 (2006). Rignot, E.: East Antarctic glaciers and ice shelves mass balance from satellite data. Annals of Glaciol. 34, 217-227 (2002). Rignot, E.: Changes in ice dynamics and mass balance of the Antarctic ice sheet. Phil. Trans. R.. Soc. 364, 1637-1655 (2006). Schellenberg, B.A., T.L. DeLiberty, C.A. Geiger, J. Silberman and A.P. Worby: Investigation of seasonal sea-ice thickness variability in the Ross Sea, Proceedings of the 13th Symposium on Global and Climate Variations, American Meterological Society, Orlando, Florida, January 13-17, 130-132 (2002). Simmonds, I. and J.C. King: Global and hemispheric climate variations affecting the Southern Ocean. Ant. Sci. 16, 401-413 (2004). Simmonds, I.: Modes of atmospheric variability over the Southern Ocean. J. Geoph. Res. 108(C4), 8074. doi:10.1029/2000JC000542 (2003). Sreenivasan, G. and T.J. Majumdar: Mapping of Antarctic sea ice in the depletion phase: an indicator of climatic change? Curr. Sci. 90, 851-857 (2006). Steig, E.J., D.P. Schneider, S.D. Rutherford, M.E. Mann, J.C. Comiso and D.T. Shindell: Warming of the Antarctic ice-sheet surface since the 1957 International Geophysical Year. Nat. 457, 459-462 (2009). Stohl, A. and H. Sodemann: Characteristics of atmospheric transport into the Antarctic troposphere. J. Geophy. Res., 115, DO2305, doi:10.1029/2009JD012536 (2010). Thattermann, T. and A. Levermann: Response of Southern Ocean circulation to global warming may enhance basal ice shelf melting around Antarctica, Climate Dynamics, Published online, August 26, DOI: 10.1007/s00382-009-0643-3 (2009). Thompson, A.F.: The atmospheric ocean: eddies and jets in the Antarctic Circumpolar Current. Phil. Trans. R.. Soc. A. 366, 4529-4541 (2008). Van As, D., M.R. van den Broeke and M.M. Helsen: Strong-wind events and their impact on the near-surface climate at Kohnen Station on the Antarctic Plateau. Antarcatic. Sci.., doi:10.1017/S095410200700065X (2007). Van de Berg, W.J., M.R. van den Broeke, E. van Meijgaard and C.H. Reijmer: Reassessment of the Antarctic surface mass balance using calibrated output of a regional atmospheric climate model. J. of Geoph. Res., 111 D11104. doi: 10.1029/2005JD006495 (2006). Van den Broeke, M., C., Reijmer, D. Van As and W. Boot: Daily cycle of the surface energy balance in Antarctica and the influence of clouds. Int. J. Climatol., 26, 1587-1605 (2006).
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In: Antarctica: The Most Interactive Ice-Air-Ocean Environment ISBN: 978-1-61122-815-1 Editors: Jaswant Singh, H.N. Dutta © 2011 Nova Science Publishers, Inc.
Chapter 3
LAND-ICE-AIR-OCEAN INTERACTIONS IN THE SCHIRMACHER OASIS, EAST ANTARCTICA Khwairakpam Gajananda1 *, H. N. Dutta2 and Victor E Lagun3 ABSTRACT Study of the land-ice-air-ocean interaction over the Schirmacher Oasis (SO) of east Antarctica was carried out during the years 1999-2000. The research revealed that a unique ecosystem prevails over this oasis, where all the physical and biological components interact in a complex pattern. SO ecosystem is heterogeneous in nature and the estimated biomass production is low at a value of 22.5 gm m-2. The lakes are oligotrophic in nature and are of fresh water lakes. Food chain of SO is very simple and short and the energy cycle is poor due to less sunlight during austral winter. The diversity of the flora and fauna is poor and is dominated by poikilohydric microorganisms. About 34 species of primitive flora were observed and only 6 primitive invertebrate fauna were recorded. Only four species of birds were observed in SO. The migratory birds from subAntarctic islands may introduce some non-indigenous forms of plants, animals and microorganisms species to SO, but only cold tolerant variety of organisms survived. Average organic carbon content of the oasis is 1.58%, which is poor in comparison to other ecosystem of the world. The microbial enzyme activity or dehydrogenase activity is 0.008 mg TPF g soil-1 day-1 suggesting a very less microbial activity for substrate decomposition. Experimental investigation suggested that the climate at Maitri is dominated by the extreme contrasts between the seasonal inputs of solar radiation. SO experiences sub-zero mean temperature throughout the year except in the peak summer months (December and January). Pressure (average 986.5 mb) forms half yearly cycle and influenced for the formation of cyclones. The humidity and precipitation are low but have significant relationship for the growth of microorganisms. Convective atmospheric phenomena during austral summer have the potential for dispersal of the microorganisms *
E-mail:
[email protected], Mobile: +251-910448842 Department of Environmental Science, Faculty of Science, Addis Ababa University, P.O. Box 1176,Addis Ababa, Ethiopia 2 Roorkee Engineering and Management Technology Institute, Shamli-247774, U.P. India 3 Arctic and Antarctic Research Institute, St. Petersburg-199397, Russia 1
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Khwairakpam Gajananda, H. N. Dutta and Victor E Lagun in this oasis. The study suggested that the ecosystem of SO must have grown with some control of atmospheric parameters and high UV-B doses in Antarctica. Climatic parameters are limiting the survival of normally living organisms, except for cold hardiness ones. The diminutive forms of plants and animal of SO are the result of less availability of nutrient, food and harsh conditions for growth and survival. Therefore, only the cold tolerant varieties of microorganisms have evolved with time in this oasis.
1. INTRODUCTION Antarctica presents the most efficient and the most interactive land-ice-air-ocean system in the world (Dutta et al., 2007). The land-ice-air-ocean interactive system supports extreme climatic conditions in the interior of the continent. With the result, only micro flora and fauna have been able to evolve with time and survive, forming one of the most important subjects in Antarctica for human understanding (Gajananda 2003). In Antarctica, only Oasis regions get deglaciated during local summer and therefore, present the most favourable conditions for the survival, growth and function of the micro flora and fauna in the otherwise harsh climatic conditions. The deglaciation of the east Antarctic oasis might have started very rapidly, close to the Pleistocene/Holocene boundary, probably favoured by marine transgression, sea level falls and climatic warming (Melles et al., 1997). Antarctic continental soils are arid, saline and lacking in organic matter, whereas maritime soils, in wetter environment, range from structure-less lithosols to frozen peat (Hall and Walton, 1992). Two important factors in the development and diversity of terrestrial communities are water availability and the period of exposure since deglaciation. The retreat of ice sheets offers new sites for colonization by microbes, plants and animals. The interactions between snow line, freeze-thaw cycles, wet-dry cycles and the length of the summer are considered as critical in determining the extent and rate of localized changes in weathering and pedogenesis (Gajananda 2007). The implications of higher temperatures and differing precipitation regimes are considered in relation to weathering, soil development and the establishment and development of terrestrial communities of flora and fauna. A study on this subject will provide a good model of how present soils and communities developed at the end of the last glacial age. The east Antarctic region, has relatively young terrestrial and inland water ecosystems, dominated by a few or single species. These ecosystems offer a great deal of information about species adaptation and reproduction. Moreover, the coastal region is ideal for the study of dispersal and colonization across great expanses of ice and ocean (Gajananda 2003). The 8 major coastal oases of Antarctica provide the migration and immigration of organisms during austral summer. The migratory birds and Penguins migrate from various sub-Antarctic islands to these regions in summer, bringing with them various forms of seeds, propagules of plants, spores and minute invertebrates. The atmospheric boundary layer dynamics over Antarctica has been studied at many stations by acoustic sounding technique, which provides an in-depth knowledge of the PBL dynamics (Argentini et al., 1996; Gera et al., 1997; Naithani and Dutta, 1995). Acoustic sounder finds applications in the areas of fog monitoring (Beran and Hall 1974; Gajananda et al., 2007). The coastal Antarctic planetary boundary layer (PBL) experiences varying external influences both from the interior of the continent and due to the moving depressions/cyclones along the coast (Wendler and Kodama, 1994; Carrasco and Bromwich, 1997). The influence
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from the interior of the continent is dominated by katabatic flow of winds of varying intensities, often depositing snow/ice in the form of blowing snow, drift and blizzards (Du and Bromwich, 1992; Argentini et al., 1996; Braaten, 1997). However, cyclones push relatively warm and moist air towards the interior of the continent, leading to foggy weather condition (Naithani and Dutta 1995) and coreless nature of temperature variation over Antarctica (Wendler and Kodama, 1994; Naithani and Dutta, 1995). In the driest and coldest habitats, especially where fog and dew are major water sources, desiccation-tolerant algae or cyanobacteria, bryophytes, lichens may form the only vegetation (Alpert and Oliver 2002). At the same time, thermal convection over the ocean transports fine living materials and propagules (Gajananda et al., 2004b). During summer, the atmospheric processes and the local solar heating make the Antarctic boundary layer to be one of the most dynamical regions (Kottmeier et al., 1993; Williams and Hacker, 1992 and 1993). It can be mentioned here that the increasing scientific activities and tourisms over Antarctica has introduced new and alien species and also unwanted materials are increasing day by day. The extent of its impact on this pristine environment is yet to be ascertained precisely. Strictly speaking, vegetation should be considered to be part of the climate system on all timescales. Thus, this study presents a detailed investigation on almost all aspects of climatic/atmospheric phenomena in the Schirmacher region that influence both the terrestrial and aquatic ecology or are directly responsible for ecological control and development of this region. Results obtained from the analysis of the samples collected over the Schirmacher Oasis (SO hereafter) during the period December 1999 to January 2000 have been discussed. At the same time, support of the personal observations related to the number of ecological study and the simultaneous measurements of the atmospheric parameters, during the above period have been utilized. Since various ecological factors affect the functioning of life forms in a holistic manner (i.e. all the factors operate in conjunction and not in isolation), it becomes difficult to understand the mechanism of the nature of influence by an individual factor. To understand this mechanism of environmental influences, it is essential to study the effect of each individual factor separately, thus, by taking into account the concept of an analytical approach; the following paper has been organized accordingly.
2. MATERIAL AND METHODS The SO is mainly comprised of the Precambrian age strata consisting of acidous gneiss and crystalline slates with intrusions of gabbro-norites, gabbro-diorites and pegmatite veins. Gouging traces of the ice sheet glaciation are observed everywhere as these are preserved in the form of individual spurs, ―sheep-back rocks‖ and glacial striation at the surface of cliffs, etc. indicating that in the past, the glacier covered the Oasis. Weak development of the weathering forms on the rock surfaces and fresh traces of glacial impact indicate recent ice disappearance. The weathering of rocks releases minerals, an essential component for the survival and development of the eco-system. It may be noted that the weathering of rocks leads to the formation of sandy soil, which cannot support normal forms of plant and animal lives. At the same time, brown or black rocks absorb solar energy, leading to a much higher temperature of the rock surfaces, thus providing a better habitat for the unique micro flora and fauna of Antarctica. The channels of temporary water flows appearing in the summer months
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Khwairakpam Gajananda, H. N. Dutta and Victor E Lagun
interconnect many lakes. The depth of channel entrenchment is different comprising 8-10 m in the break segments. In mid-summer during the period of intense melting of snowfields and the glacial slope adjoining the SO, the area of some lakes significantly increases. Numerous small lakes appear with an area of up to several tens of square meters. By genesis, the lakes of glacial origin dominate. There are many relict lakes-lagoons located at the boundary between the Oasis and the ice shelf. Both shallow (3-5 m) and deep lakes (20 to 120 m) are encountered. Water in the lakes has very low mineral and small hardness. Figure 1. gives the sampling locations, fresh water lakes, rocky areas, ice shelves, polar icecaps with the two adjacent east Antarctic researches stations namely Maitri and Novolazarevskaya. SO can be classified as a true cold desert of Antarctica (Wharton 1993). In this oasis average annual precipitation (expressed in terms of water) is between 50-150mm (Schwerdtfeger 1979). Heavy snowfall occurs when cyclonic storms over the surrounding seas push in relatively warm and moist air over the continent. This moist air freezes and is deposited as snow over the areas. The region has almost continuous daylight during the local summer and darkness during the winter. The continental character dominates climate of the SO, except in local summer when it is predominated by the intensity of solar radiation heating the exposed rocks. The weather forms depend on the position of the circumpolar trough, solar parameters, flow of katabatic winds and the position of various cyclones along the periphery of Antarctica. The circumpolar trough has a biannual movement, leading to the surface pressure level to be the highest during summer and winter periods. In contrast to the seasons normally observed over the Northern hemisphere, the seasons of Antarctica have been divided as given in table 1. The relative air humidity, on an average does not exceed 52% in a year. Under such conditions, strong evaporation and melting of snow occurs, which is probably, one of the decisive factors ensuring the existence of the oasis under the current climatic conditions. Table 2. shows the average climatic characteristics of the SO, calculated from the meteorological data recorded during 1990-96 at Maitri, Antarctica.
Figure 1. Location of the study sites in east Antarctica.
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Table 1. Different seasons of Schirmacher Oasis S No. 1.
Seasons Summer
2.
Autumn
3.
Winter
4.
Spring
Months of the season December, January and February December-January are totally sunny over the Schirmacher region Circumpolar trough is towards the periphery of Antarctica March, April and May Surface temperature is on the declining phase Circumpolar trough moves away from the continent and by Winter, it again returns close to the periphery of Antarctica. June, July and August June and July are totally dark over the SO Circumpolar trough is near to the Antarctic continent September, October and November Surface temperature is on the inclining phase Circumpolar trough starts moving towards the Southern Ocean and again in summer, it returns back to the periphery of Antarctica.
Table 2. Average climatic parameters recorded over the Schirmacher Oasis during 1990-96 Direct annual radiation Total annual radiation Absorbed annual radiation Annual radiation balance Average annual temperature Mean annual atmospheric pressure at sea level Mean annual wind speed Prevailing wind direction Mean annual relative air humidity Annual precipitation quantity Number of days with snow storms for a year Mean annual absolute air humidity Mean annual total cloudiness
43.9 kcal/cm2 93.8 kcal/cm2 69.6 kcal/cm2 23.9 kcal/cm2 -11°C 988.0 mb 10.2 m/s ESE 52% 309 mm 88 days 0.07 hPa 5.8 points
The group at the National Physical Laboratory (NPL), New Delhi has been primarily working on the Atmospheric Boundary Layer (ABL) over the SO since 1989-90. During the years 1990-1997, a monostatic acoustic sounder or Sodar was operated at the Maitri, Station (Naithani and Dutta 1995). The Sodar measurements indicate stable atmospheric condition throughout the year (~95%), except in summer, when thermal convection predominates during the noon hours (~5%). The stable atmosphere is basically due to the extreme transparency of the atmosphere, leading to the cooling of the icy surfaces. However, heating of the dry, rocky region, especially in the warmer hours of the day, causes the thermal convection. In the Antarctic environment, penetration of UV light is much deeper. However, it is influenced by the influx of suspended particulate material, sea salt etc. by the cyclones churning and pushing the warm, moist oceanic air towards the continent.
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Khwairakpam Gajananda, H. N. Dutta and Victor E Lagun
2.1. Atmospheric Measurements The techniques used for studying the atmospheric parameters are broadly classified into the following two categories: 1. Direct or in-situ measurement techniques, and 2. Remote sensing techniques. The direct sensing techniques include surface instruments, instrumented towers, free rising balloons, radiosonde etc and the remote sensing techniques include Sodar, satellites data, UV-B, radiosonde etc. Depending upon the meteorological parameters to be measured, both of these techniques have their own importance and are at times complementary or supplementary to one another. The precise and accurate measurements of meteorological parameters need appropriate combination of the direct and the remote sensing techniques for a better understanding of the atmospheric dynamics. The Indian Antarctic program is relatively new as the permanent Antarctic station Maitri was established only in the year 1988-89. At present both the direct and remote sensing instruments are in use at the Maitri station.
2.2. Ecological Samples Collection and Analysis In the SO the exposed landmass filled with glacial water in the streams and lakes offers a relatively warmer habitat for the development of its own ecosystem. A continuous cycle of freezing and melting in winter and summer brings a large amount of change in physicochemical and biological properties of the waters, bottom sediments and over the rocky structures. In the SO, 14 sites that were showing the growth of some biological organisms were selected for studying some important ecological parameters. Collection of water, soil, flora and fauna and records of migratory birds such as Skua, Petrels and Penguins etc. were performed at these 14 locations of the SO (figure 1). Table 3. gives the descriptions of these sites. This work has been one of the most important tasks that have been undertaken at the Maitri and over the surrounding region. The water, soil and biological samples from all the 14 different locations covering almost entirely the oasis region were studies of their physicochemical analysis. It can be mentioned here that sampling is seriously limited by the harsh weather conditions in Antarctica. It is pertinent to mention here that SO is a rocky terrain with high and low undulations, sparse nunataks and depressions, slippery ice sheets, falling glacier walls, severe blizzards etc. Sampling was also often interrupted by adverse weather conditions.
2.3. Sampling Techniques The collection of samples was done during the last week of December 1999 to 31 January 2000, which was the only favourable period for growth of flora and fauna. Samples of water and soil, flora including lichens, algae and mosses, and birds litter were collected from the study sites such as moist and dried lakes, running streams and rocky sandy soil areas, all
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along the length of SO. The temperature was recorded at the site of collection using simple thermometer during the sampling session and compared with the daily station temperature records at Maitri. From all the 14 sites, samples of soil, water (wherever available), rocks and biological samples were collected in triplicate. The sampling and analysis were carried out based on the standard methods. Table 3. Description of the 14 sampling sites at the Schirmacher Oasis Site No. 1
Habitat type Swampy lake bank
2
Lake bank
Site No. 3
Habitat type Hilly rocky area
4
Swampy lake bank
5
Hilly and rocky area
6
Glacier melt water, lake bank Rocky area near Skua nest Near Maitri station, Zub lake bank Small dried lake, swampy area Glacier melt water, stream, small lake Dried lake, swampy and sandy area Near Novolazarevskaya lake Hilly rocky area
Algae and tardigrades dominate Mosses and mites dominate
Transition of continental ice and SO rocks
Lichen dominate
7 8 9 10 11 12 13 14
Flora and Fauna Algae, protozoans and mites dominate Algae, protozoans and mites dominate Flora and Fauna Lichen and mites dominate Algae, protozoans and mites dominates Lichen and mites dominate
Algae and mites dominate Mosses and protozoans dominate Algae and tardigrades dominate Mosses and mites dominate Algae and protozoans dominate Lichen and mites dominate
Remark Little human activities Little human activities Remark Little human activities Little human activities Little human activities Little human activities Moderate human activities High activities of human Little human activities Little human activities Little human activities High activities of human Little human activities Little human activities
3. RESULTS AND DISCUSSION Figure 2. shows the schematic flow diagram of the interactive mechanism, in which, energy (heat and momentum) flows from one form to another to support the survival of some life forms and development of Antarctic environment with time (adapted from Dutta et al., 2007).
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Khwairakpam Gajananda, H. N. Dutta and Victor E Lagun
Figure 2. Most efficiently coupled Land-Ice-Air-Ocean Interaction System in the World. It maintains itself strongly but gets influenced by the global changes. (Dutta et al., 2007).
In the process, cyclones churn the ocean to mix the oxygen in the oceanic water, promoting high rate of biological production. Also, due to the cyclones, long exposure of the high UV-B doses to the biological organisms is avoided due to creation of turbulent mixing in the ocean, as well as, due to the development of thick clouds and precipitation. High doses of UV-B radiations in Antarctica might also be playing a role in degrading the dead organic matter, thereby releasing various nutrients, which could be readily used by planktons, thereby rendering Antarctic Ocean as the most productive ocean in the world. At the same time, the
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cold oceanic water has much higher capacity to retain dissolved oxygen, the most essential component in the production, growth and function of organisms, as well as to support krills and various types of fishes in the southern ocean (Dutta et al., 2007). Under natural conditions, it is found that living organisms are affected by the sum total of all ecological factors and not by any individual factor. All these factors interact and are interrelated to each other, forming a complex process. Variations in one may affect the other in measurable quantities.
3.1. Structure and Function of the SO Ecosystem The SO ecosystem is a unique and fragile ecosystem with very low species diversity both from plant and animal kingdom, non-existence of higher life forms, domination of the biotic component by lower forms of plants and invertebrate organisms surviving since millions of years. The nutrient and energy exchanges in this oasis are poor due to low productivity and low diversity of flora and fauna, and extreme environmental factors. At this juncture, it is important to mention that the main factors limiting life in the SO ecosystem are the sub-zero temperatures, severe katabatic winds, drift, blizzards, extremely low humidity, snowfall, low availability of liquid water and poor sun light even during summer months, high doses of UV radiation etc. Despite the extreme environment, some forms of life have been found in the soils, streams, lakes, rocks, glacial lake ices, and melted water pools. Microorganisms such as the prokaryote dominate while a few varieties of eukaryotes prefer less stressful sites. The flora of the oasis is dominated with several species of algae, lichen and mosses. The total faunal biodiversity of the oasis consist of nearly 10 mostly microscopic species, permanently inhabiting the region. These species include protozoans, rotifers, nematodes, tardigrades, insects, and mites; there are no land-based vertebrates. The poorly developed soils and low nutrient water bodies contain bacteria, algae, yeast, and fungi. These microorganisms interact among themselves and with their nonliving environment for both food and nutrition. Over the thousands of years, SO has resulted in the development and sustenance of one of the simplest ecosystems in the world, leading to very high species endemism in this region. The lake ecosystem in the oasis varies from brackish to freshwater in nature, depending upon the distance from the coast. In SO, the hill slopes remain covered with ice in winter, but in summer, melted water gets accumulated in the depression areas between the hills, forming lakes of various sizes. However, the quantity of water in the lakes depends on the quantity of melting water, which varies from year-to-year. The majority of the lakes are archaic, possessing no outflow, and the annual ablation rate is generally balanced by the summer ephemeral inflow of glacial meltstreams. Some lakes are very shallow, small in size and are subjected to periodic drying. In winter, all these lakes freeze. The lakes, ponds and swampy areas surveyed during the study were of fresh water in nature, varying in physical area from 1.5 sq m to 2.1 sq km; depth ranges from 1.2 to 8 m. At the same time, it has also been found that the surrounding of the lakes peripheries provides a better habitat for the organisms. Figure 3. shows possible interaction between five principal components of the environment (energy, soil nutrients, organisms, water and air) prevailing over the oasis. From this figure, we infer that the ecological factors alone cannot sustain in this interactive system, rather they are a part of the whole system (Gajananda 2003).
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Khwairakpam Gajananda, H. N. Dutta and Victor E Lagun
Figure 3. Simplified patterns of energy and nutrient exchange in the Schirmacher Oasis.
Consequently, looking at the roles of inorganic components which involve in material cycling, the organic compounds linking the biotic and abiotic component, climate, the prevailing organisms of the ecosystem (structure) and their holistic interaction or links in a complex pattern for energy, nutrients, food chain, evolution and control (function) etc in the SO ecosystem, give a meaningful study in terms of the traditional way of ecosystem analysis by both the structural and functional concept (Figure 3).
3.2. Biotic (Living Matter) The biological environment of Antarctica is composed of two distinct and very different ecosystems: a terrestrial ecosystem (mainly over the Oasis regions), and a marine ecosystem. Marine organisms are widely distributed around Antarctica, often in patches with high population densities. Some marine mammals, such as seals and sea birds, spend some time both on land and at sea. Sea birds also supply land-based plants with vital nutrients, but terrestrial organisms provide no nutrients for marine flora or food for marine fauna. The micro faunal density at SO was found to be high in moss associated sediments. This could be related to the availability of rich organic matter in the moss beds (Davis, 1980). The SO soil has very low organic content. SO represents a typical terrestrial ecosystem, with low organism densities and abundance. It is important to note that due to higher population densities, greater complexity, and greater continuity, the marine ecosystem of Antarctica is probably somewhat more resilient to
Land-Ice-Air-Ocean Interactions in the Schirmacher Oasis, East Antarctica
49
impacts than is the land-based ecosystem. The biotic component of the oasis is expressed in terms of their energy exchanges and trophic position such as producers, consumers and decomposers.
3.2.1. Producers The producers of the SO are comprised of all non vascular plants. Based on the study and collection of all the vegetated sites in the 14 study areas of SO, a total of 34 species were recorded consisting of mostly lichens, algae and mosses. The Oasis is represented by individual rare patches of lichens on rocky substrates and by moss mats on silt. A total of about 19 species of lichen have been reported in the Oasis (Pandey and Upreti 2000). In the present study 17 species of lichens were recorded. Diatoms were found to be present in waters of lakes of the oases. The algal-flora of lakes in the oasis consists of about 11 species and most of them belong to the phytoplanktonic groups dominated by cyanobacteria. On the land, the producers such as lichen, mosses and algae were found mostly on damp soils, surface of rocks, and beneath the rock surface. Wherever moisture availability is high the populations of producers are also high. As the primary productivity is very less, they may support a small fraction of living consumers. Description of the species found in the SO performing the roles of primary producers are: (i) Algae. The algal species at the SO occupied distinct levels of habitats; (a) in association with mosses (b) on damp soils (c) on quartz rocks in the water pools and (d) lake bottoms. The submerged rocks, which are directly exposed to sunlight, favored the growth of thin reddish brown to blue-green encrustation. These crusts were composed of both N2 and non-N2-fixing species. The cyanobacterial patches only covered with high amount of mucilage were abundant on the soil surface near the edge of the stream and were also observed in the depressions created on turning the small rocks and stones in slow running streams. Glacier does not support growth of algae and cyanobacteria. The pond and upper stream support less growth of algae and cyanobacteria. However, their growth was abundant and readily visible on the surface of the rocks, boulders and weathered soil of the middle portion of the stream of site no. 2. Algae are also found under rocks, particularly light-coloured quartz stones, where the microclimate is more favourable than in the surrounding sand or soil. This strategy enables them to scrape a humble living in this harsh environment. The species richness of algae was highest in the streams. Analysis of SO lake water showed the presence of Oscillatoria, Chroococcus, Synechocystis and some diatom species. Phormidium frigidum constitutes an important and dominant species of algal flora, which is non-N2-fixing species. Table 4. shows the different types of algae found at the SO. Majority of the algae recorded at the SO possess tough and collared mucilage. These properties of algae may help in two possible ways (a) light filtration and (b) increasing water retention capacity. Komarek and Ruzicka (1966) found that the ice-covered lakes of SO were highly productive due to algae. The main component of flora is the Phormidium species, which forms large fan shaped colonies supersaturating the water with oxygen. (ii) Lichens. Lichens are the most widespread flora of the SO. Lichens such as Rhizocarpon flavum, Acarospora gwynnii, Xanthoria elegans, Buellia pallida,
50
Khwairakpam Gajananda, H. N. Dutta and Victor E Lagun Lecidia cancariformis, Lecanora fuscobrumnea, Umbilicaria aprina dominate in the oasis. It is interesting to note that lichens are found growing even on rock surfaces, where availability of nutrients is low. This is due to the fact that many of these rocks are porous; so as to retain little amount of water. The lichens released some weak acids themselves, resulting in the dissolution of some nutrients from the rocks (Pandey and Upreti, 2000; Stoutjesdijk and Barkman, 1991; Upreti and Pant, 1995). At the same time, rock surfaces become much warmer under sunlight than the soil itself, leading to a favorable conditions for lichens to grow. Under the microscope, it has been observed that the lichens penetrate the upper transparent coat of the rock. In all the samples collected, lichens are present mainly in the water free rocky samples. Their population density is high in the oasis. Lichen population and density are more favourable in humid environment. They are found in abundance in all the forms of soil substrates. Lichens are known to be the initial colonizers of bare rocks starting the succession process. The growth of lichens on the rocks of SO indicates that they might be having the way for some more forms of life by creating gradually a little more congenial conditions for growth in years to come. Table 5. gives the various descriptions and the dispersal potential of the lichen communities over SO. (iii) Mosses. The moss species available over the SO are given in Table 6. the most dominant one is Bryum argenteum, which is capable of photosynthesis in low light and low temperature. Photosynthesis of this moss can start within a few hours of thawing after a prolonged period of freezing and almost immediately following short snowfall periods. Moss (Bryum species) has been found to be associated with algae such as Nostoc species and Stigonema species. Moss turfs are seen mainly on the icemelt water streams from the glaciers. They tend to grow more on the places with finer sand than the coarse sand with pebbles (Table 6). Maximum biomass of the Zub Lake has been estimated as ~40.63 gm m-2 and it comprises mainly of moss turfs (Gajananda 2003). The moss habitat forms the substratum for the micro invertebrates such as tardigrades, nematodes and rotifers. Only in site no. 9 (Figure 1), mosses were not observed. This may be due to the fact that the sample was collected from water free dry lake region of SO. Mosses were found in abundance in other samples. In terms of density and population moss Bryum argenteum is amongst the dominant flora of the SO.
3.2.2. Consumers The real consumers of the oasis are mainly the primary consumers composed of invertebrate micro-fauna. These micro-fauna have adapted to the extreme living conditions throughout the years. However, some of the larger birds (Skua, Snow Petrels, Storm Petrels and stray Penguins) migrate to this region only during the local summer. All the birds depend on the sea for their food except Skua, which also feeds on the dead remains of Penguins, Petrel and their chicks. Thus, Skua acts as a detritivore and scavenger. It may be noted that these birds except Penguins, migrate purposely towards the oasis region, while Penguins come by mistake, losing their sense of direction. Instead of moving towards the coast in search of food, they move towards the continent. The death of such Penguins serves the purpose of the scavenger bird Skua and the remains add to nutrient pool of the oasis. The invertebrate terrestrial fauna of SO mainly inhabited in the soil and in vegetation. They range from protozoa (single-celled creatures), rotifers, tardigrades and nematodes to arthropods
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51
(mainly mites and springtails, midge). The largest invertebrate found is the wingless midge (Belgica antarctica), which grows to 12 mm long. The distribution of tardigrades, nematodes and rotifers are more near surface soil area. The occurrence of micro fauna on the top layers of the soil may be due to a slight rise in temperature due to sunshine, availability of food etc. They may also migrate up and down in the soil. Further studies might reveal the local variations due to temperature and light difference the occurrence of these fauna in the soil. Heywood (1979) has also shown that many invertebrates are plant feeders. It may be stated here, that the species reported in 8 lakes and 4 swampy areas of SO are those that are distributed widely in Antarctic lakes with similar behavioural pattern that is thriving well in sediments rich in micro flora and organic matter. Densities of these micro fauna vary from 20,000 to more than 14 million animals per m2 (Bonner and Walton, 1985). Ingole et al., (1987) observed a maximum tardigrade density of 140 per m2 and 272 per m2 of nematodes at Zub Lake. However, a maximum of 35 per m2 of Tardigrades, 21 per m2 of nematodes and 10 per 2 m of rotifers were observed in the present study, which is much lower than at the bottom of the lake in SO. The low density of micro-fauna in the present study may be due to less food availability (moss growth) on the land. Population density of these micro-fauna is reported to show variations with light, temperature, level of blizzard, relative humidity and food, these being the major determinants (Fleeger and Hummon, 1975; Morgan, 1977). All of the Antarctic animals have adapted to life in extremely cold conditions. The springtails and mites live under rocks in the SO. A brief description of the primary consumers of SO is provided as follows. Table 4. Taxonomic assessment, identification, habitats descriptions and the dispersal potential of the algal communities of Schirmacher Oasis, East Antarctica S No.
Algal class, order and species
Habitat descriptions
Shapes and sizes (μm), color
Forms of possible dispersal
Comments
1
Class: Cyanophyceae Order: Nostocales Calothrix gracilis Lyngbya aeustuarii Nostoc commune Oscillatoria limosa Phormidium frigidum Schizithrix Order: Chroococcales Aphanocapsa Aphanothece nidulans Gloeocapsa kuetzingiana
Found in all the sites; fresh water lakes, streams, swamps, ponds etc. association with lichen and mosses; forming green scum; black epilithic crusts on rock surfaces
Ellipsoidal, Spherical, irregular; motile or non motile; 1-90; both unicellular or multicellular; colonial
Independent dispersal of spores and cysts may occur; vegetative cells, spores and cysts
Generally aggregated, chlorophyll present, thallus undifferentiated thalloid plant body
52
Khwairakpam Gajananda, H. N. Dutta and Victor E Lagun Table 4. (Contnued) S No.
Algal class, order and species
Habitat descriptions
Shapes and sizes (μm), color
Forms of possible dispersal
Comments
Spherical, ellipsoidal, irregular 1-80
Same
Same
Order: Chlorococcales Chlorococcum 3
Class: Baccilariophycea e Order: Pennales Hantzschia Pinnularia borealis
Table 5. Taxonomic assessment, identification, habitats, descriptions and the dispersal potential of the lichen communities of Schirmacher Oasis, East Antarctica S No.
Lichen class, order and species
Sites, Habitat descriptions and date
Shapes and sizes (μm), colour Spherical, irregular; 35-70; yellowish green
Forms of possible dispersal Independent dispersal of ascospores; Soredia, Isidia
Comments
1
Acarospora A. gwynnii A. williamsi
2
Alectoria A.minuscule
Very common on shady place, moraine and rocks; generally absent in habitats close to melt water; Near Russian and Indian Stations Cracks and surface of rocks, rocks inside water
Same
Same
Moraine, amongst pebbles, rocks
Same
Same
Carbonea C. capsulata
Grow on rocks of small depressions, Near Russian station along the lake.
White mat with compressed areolate
Same
5
Lecidea L.cancariformis
Same; black apothecia
Same
6
Lecanora L.fuscobrumnea
Very common, endolithic lichen, grow in dry rocky surface, mostly on the leeward sides of rocks, along the dried stream Grow on rocks, sheltered place,
Same; Fruticose; forms varicose masses; filamentous Same; umbilicate thallus; crustose and saxicolous Same; amorphous thallus; apothecia on the tops and sides of the stipes Same
3
Buellia B.pallida
4
yellowdark brown disc,
Same
Squamulose areolate and crustose; thallus fragments very common
Same; lichen with crowded mats of apothecia
Land-Ice-Air-Ocean Interactions in the Schirmacher Oasis, East Antarctica S No.
Lichen class, order and species
Sites, Habitat descriptions and date
7
Lepraria Lepraria membranacea
8
Physcia P.caesia
9
Polycauliona P. murrayi
Very common lichen of SO, grow on moist place, decayed mosses Common and luxuriant lichen; Pebbles and small rocks Common lichen on rocks, sandy soils, well watered areas
8
Porpidia P.species
9
Rhizocarpon R.flavum R.species
10
Rinodina R.Species
11
Umbilicaria U.aprina U.decussata
12
Xanthoria X.elegans
Stones, pebbles, Rocks; leeward sides of rocks Rocks, stones, pebbles; streams, ponds, lakes
Most common lichen on rocks; decayed mosses tufts, algae etc. Most common lichen on rocks, stream, lakes, ponds, sandy soil; elevated well sunlight area Sandy soil near Novolazarevskaya lake
53
Shapes and sizes (μm), colour Powdery, Yellow colored
Forms of possible dispersal Same
Comments
Same; whitish,
Same
Same; foliose lichen
Orangeblack circular hapteron Same; black apothecia Same; yellowblack and white-black colored Same; black granular
Same
Same; fruticose lichen; erect tufts
Same
Same
Same
Same
Same
Same; varicose lichen
Thallus 0.1 cm to 18 cm diameter
Same
Same; foliose lichen; cosmopolitan
Same; red lichen
Same
Same; lobate lichen
Same
Table 6. Taxonomic assessment, identification, habitats, descriptions and the dispersal potential of the mosses (bryophytes) communities of Schirmacher Oasis, East Antarctica S No.
Mosses family, Genus and species
Sites, Habitat descriptions and date
Shapes and sizes (μm), colour
1.
Bryaceae Bryum argenteum(Hedw.) Bryum pseudotriquetreum (Hedw.)
Very Common; moist soils, sheltered place of rocks; banks of lakes, ponds and swampy areas; close to snow banks; biogenic remains; birds nest remains etc.
Globose, tetrahedral, Variable in length; 10-25; yellowish brown to brownish, red stem, deep green
Forms of possible dispersal Spores, Gemmae
Comments
Sporophyte present; seta 1.5-4.5 cm long; whitish colour; capsulated; vegetative fragments dispersal observed
54
Khwairakpam Gajananda, H. N. Dutta and Victor E Lagun Table 6. (Continued)
S No.
Mosses family, Genus and species
Sites, Habitat descriptions and date
Shapes and sizes (μm), colour
2.
Pottiaceae Bryoerythrophyllu m recurviroste (Hedw.) Pottia cf. heimii (Hedw)
Not common; banks of lakes, ponds and swampy areas; close to snow banks; around the nest remains etc.
3.
Ditrichaceae Cedratondon purpureus (Hedw.)
Common; Same as Sl No. 1
4.
Grimmiaceae Grimmia sps.
Common; Same as S No. 1.
Globose and tetrahedral; 10-25; reddish green to brown, yellowish green to green, reddish nerves Globose, tetrahedral, Variable in length; 10-25; brownish green, yellow, reddish Globose, tetrahedral, Variable in length; 6-20; brownish green, green turfs
Forms of possible dispersal Gemmae, vegetative fragments
Comments
Gemmae, vegetative fragments
Non Sporophyte vegetative fragments dispersal observed
Gemmae, vegetative fragments
Non Sporophyte; vegetative fragments dispersal observed
NonSporophyte; vegetative fragments dispersal observed.
3.2.2.1. Primary Consumers The primary consumers of the SO are very less in comparison to others ecosystem types. The primary consumers comprise of minute organisms, which consume very little amount of food available in this oasis. Table 7. shows the various primary consumers of the oasis. During the present investigation, six different micro faunal groups viz., Protozoa, Nematoda, Rotifera, Tardigrada, Collembola and Mites have been recorded from SO area (Table 7). Some groups of parasitic insects are also found in this region. It is found that nematodes and protozoans have higher range of adaptability in this harsh environmental condition. Table 7. shows that most of the micro-faunal groups were found from ice free areas, except mites, which were not found in ice-free water. Collembola was not found in sites mostly covered with ice water. All the micro faunal groups were found in both running and stagnant water except mites, which were available only in running water. Thus from the present data (Table 7) it may be concluded that Protozoa, Rotifera and Nematoda were distributed in generalized way and in all different conditions of the water and moss habitat type. (i) Protozoa. Maximum number of Testacids Protozoan species (7 sps) followed by 6 sps of Rhizopods have been observed in SO. Amongst ciliates, Oxytricha fallax is found in all the lakes. Testacids Corythion dubium was found to be most dominant and cosmopolitan, followed by Assulina muscorum and Arcella Sp. One genus (Parmulina Penard) of protozoan species of Schirmacher area is cosmopolitan to soil
Land-Ice-Air-Ocean Interactions in the Schirmacher Oasis, East Antarctica
55
and moss dwelling forms. However, earlier workers found that several species are endemic to SO. (ii) Rotifer. The Rotifers are a group of small usually microscopic, Pseudocoelomate animals. They are also called ‗Rotatoria‘ or wheel animalcules. Only one species viz., Philidina gregaria has been observed and collected from SO. (iii) Tardigrada. Tardigrades have well defined head and four trunk segments with 4 pairs of short legs bearing claws, which are used to walk along underwater surfaces. Tardigrades have the ability to ‗hibernate‘ (cryptobiosis) in which they can survive extreme thermal condition, exposure to highly toxic chemicals, drying out, etc. In this process, they are capable of withstanding very cold condition (-900 C) by passing into a state of very low metabolic activity. This phenomenon is also referred to as anabiosis. The body surface is covered with ornamented plates, sometimes bearing spines or hairs. Many species have eyes. The mouth is terminal or ventroterminal. Sexes are separate and the females are oviparous. Development is direct, the cuticle being moulted. Two species of tardigrades are found in SO, namely Hypsibius ckhilenesis and Macrobiotus polaris. The ability to tolerate severe desiccation, anhydrobiosis survival etc are the advantages for the widespread distribution of many species of tardigrades. In spite of the short summer season tardigrades multiply quickly and become very abundant. They reproduce by parthenogenesis. (iv) Nematoda. Three species of nematodes are found in SO viz. Tylenchorhychus sp., Dorylaimoides sp and Rhabditis. Hazra (1994) recorded 5 genera from SO for the first time. The genus Tylenchorhynchus and Dorylaimoides, which occur widespread in the Indian continent, might have been transported along with agricultural products to the SO especially in the Zub lake area (Venkataraman 1998). (v) Springtail (Collembola). Two species out of two families viz., Isotomidae and Entomobryidae were observed from SO. Isotomidae is larger and have slender body, they can jump actively, whereas smaller type Entomobryidae is dorso-ventrally flattened with broad oval abdomen and moves slow to hide in the soil. The body segments are more obvious in larger type. The springtails were collected from soil with micro-plants. They mainly inhabited the soils where little growth of plants is possible. The population densities of larger and smaller types of springtails were counted as 6 to 28 and 12 to 56, respectively in 100 gm of soil sample. So far 20 species of springtails have been reported from the Antarctic continent (Laws, 1977). (vi) Mites. Mites, which belong to the spider family, are the commonest land animals. It is the world‘s most southerly indigenous animal found as far south as 850 S. Two species of mite‘s viz., Tyrophagus sp and another unidentified species of family Scutacaridae from SO have been reported by earlier workers (Mitra, 1999). Many of the mites avoid freezing by a physical process known as ‗super-cooling‘, whereby their body fluids are maintained in a liquid state in temperatures below their normal freezing point (Pan and Shimada 1991). Their ability to synthesize glycerol, antifreeze, enables them to survive temperatures of –350 C (Block et al., 1994). The population varied from 7 to 76 in 100 gm soil. Acarina represents the principal Arthropod group and these mites are large and relatively well-known group in the region. (vii) Insects. Compared to other regions, insects are scarce and much smaller in size over the oasis. The type of living habitat for most of them has been found to be
56
Khwairakpam Gajananda, H. N. Dutta and Victor E Lagun parasitic, like lice, which live in the feathers and fur of birds and seals, where they remain protected from the harsh climate for most of the time. Collembola (springtails) are the only free-living insects, which feed on algae and fungi, and remain dormant in winter. However, some of the parasitic insects do fall on the surface from feathers of the birds, but they do not survive during the freezing periods. Table 7. Primary consumers of SO S No.
Microconsumers (species)
Habitat descriptions
1
Protozoa
2
Rotifer
Most dominant sps, lakes, soil, moss dwelling forms Partly freshwater but prefer moist terrestrial moss-water habitat
3
Tardigrada
4
Nematoda
5
Springtail (Collembola)
6
Insects
7
Mites
Non-planktonic; Found in aquatic mosses and algae, mud, ponds and lakes. Active tardigrades found even in droplets and film of water on terrestrial wet mosses. Not common; found in soils, plants and dead organic materials, terrestrial moist soil, moss-fresh-water etc. Found mostly in soil; damped place with small amount of micro flora Scarce; Parasitic; found mainly inside the stations; birds feathers etc. Commonest land animals
Shapes and sizes (μm), color
Comments
Small microscopic, ½ mm long; reddish color.
Also known as ‗rotatoria‘ or wheel animalcules Commonly known as ‗water bear‘; Cryptobiosis; reproduce by parthenogenesis
About 1 mm long
About 0.6 mm long, 0.03 mm wide and weighs about 0.55 micrograms About 0.65mm to 1.25 mm long; white in color Smaller compare to mainland parasites
About 0.3 mm long; whitish in color; oval shape with dorsally convex body
Only free living insect Mostly parasitic to birds
World‘s most southernly indigenous animal; process of "supercooling"
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3.2.2.2. Secondary Consumers Birds: Penguins (Emperor, King, and Adélie), petrels (Snow, Wilson's storm, Blackbellied storm, and Gray-backed storm), Brown Skua, and Arctic Tern were seen during the study period. Most typical and abundant bird of the oasis is the Adélie penguins and Brown Skua. Their description and habitat are given as follows: (i) (i). Penguins. Penguins are the common flightless, aquatic birds of the southern hemisphere. The largest species are the Emperor Penguin, which may attain a height of more than 120 cm (48 in), and the King Penguin, from 91 to 97 cm (36 to 38 in) in height. Adelie penguins are the most widespread penguins in Antarctica and they are smaller than Emperor and King Penguins. All these species of penguins are found on the Antarctic ice. They evolved from earlier flying ancestors but have become highly specialized for swimming. Their wings resemble the paddles of other swimming vertebrates. The ability to withstand intense cold is one of the penguin's greatest advantages. Most penguins have small feet, wings, and heads. The relatively small body parts in comparison to the bird‘s volume results in excellent heat conservation. In addition, many penguins have a thick insulating layer of fat under the skin. The emperor penguin, which may weigh 27 to 32 kg, appears to be the best equipped of all. Penguins usually walk or hop and toboggan along on their breasts, pushing with wings and feet. Penguins feed on fish, cuttlefish, crustaceans, and other small sea animals. On land, they make colonies (rookeries), which often numbered in the hundreds of thousands. The greatest concentrations of penguins are seen in rookeries, where the birds gather to breed. The emperor penguin breeds in one of the world's most inhospitable regions during one of the coldest periods of the year, laying and incubating its eggs in temperatures as low as -620 C. Most species of penguin lay a clutch of two eggs, which are white or greenish in colour. Incubation periods vary according to species. The Adélie‘s incubate their eggs in the open nests formed of stones or sticks. King and Emperor penguins build no nests; in these species the bird holds its single egg on the top of its feet, hunching down over it so that a fold of abdominal skin covers and warms the egg. In general, both sexes incubate the eggs and feed the young. The male Adélie penguin usually fasts while incubating the eggs for the first two weeks, allowing the female to return to the sea to feed and bathe. The male has been known to fast during the entire time that the nesting territory is established and defended, courtship takes place, and the eggs are laid and incubated. Most penguin chicks are covered with a sooty-grey down at hatching, although some have a pattern of soft greys and whites. Natural enemies of the penguin include leopard seals, killer whales and in the case of young chicks and eggs, Skuas. Today, the populations of penguins have increased due to lesser human perturbation. Scientific classification: Penguins make up the order Sphenisciformes. The king penguin is classified as Aptenodytes patagonica, the emperor penguin as Aptenodytes forsteri. The six other species that have yellowish feather crests on the sides of their heads make up the genus Eudyptes. The Adelie Penguin as Pygoscelis adeliae. (ii) Skua (Catharacta macromicii). Skuas are brown coloured predatory sea birds. The lower side of the wing feathers are light colour and flashy. Their beak is like the common kites and is strongly hooked. The beak is covered at the base with a flat horny sheath. The black feet are like that of the common duck and are strongly
58
Khwairakpam Gajananda, H. N. Dutta and Victor E Lagun clawed. They have a rapid, sustained and powerful flight, which enables them to prey on many birds. Skuas prey on chicks and eggs, particularly those of penguins and take a heavy toll of small petrels. Skuas characteristically are territorial bird; they defend intruders of their territories by raising and squalling with open wings over the back. The females are larger than males and are more aggressive and rapacious. Females are particularly aggressive in defending their young chicks from intruders. The Skuas fight, dive, squall, flap and acrobat to ward off the intruders.
3.2.3. Decomposers At the present study the decomposer assessment could not be undertaken. However, some earlier workers have reported the following microorganisms. Bacteria, yeasts and fungi: The dominant species of bacteria present in SO are the gram-positive rod identified as Pseudomonas fluoresceus, P. putida and P. syringae and gram-positive cocci as Micrococcus genus Arthrobacter (Shivaji et al., 1989a, 1989b). Matondkar and Prabhu (1986) reported bacterial counts in peripherial lake sediments in January 1985 to range from 21x105 numbers g-1 of dry sediment. In loam and moss soil, their concentration varied from 12x102 to 2.5 x 103 and 10 x 102 to 1.2 x 103 per g dry weight respectively. Moss algae and moist soil were rich in bacterial counts as compared to dry sand. Evans et al., 1997 has reported bacterial counts to vary from (1 to 25) 106 per g dry weight in some of the Antarctic lake sediments and majority of the bacteria as psychrotrophs. On the other hand phylogeny of obligately anaerobic, coiled bacterium from Ace Lake, Antarctica, was isolated by Franzmann and Rohde, (1991); Franzmann and Dobson (1993), which they believed to have been introduced by humans. Franzmann et al., (1991) also found that Carnobacterium funditum and Carnobacterium alterfunditum are psychrotrophic, lactic acid-producing bacteria found at anoxic waters in Ace Lake, Antarctica. Matondkar and Prabhu (1986) studied the effect of temperature on bacterial population of SO, and found that temperature has minimal effect on these microorganisms indicating their high degree of tolerance to low temperature. Shivaji, et al., 1989c isolated fungal populations and found Penicilium species, consisting of P. olivicolor, P. corylophulum, P. viridicatum, P. chrysogenum, P. waksmanii, and P. camemberti to dominate the fungi. Few colonies of Fusarium oxysporum and Paecilumyces variotii were also reported. Similarly, in the soil samples of SO, 8 strains of yeasts Rhodotorula rubra, one Bullera alba, one diamorphic Candida humicola and one C. famata and the remaining two tentatively identified as C. ingeniosa and C. auricularia was reported (Ray et al., 1989). In the dry valleys elsewhere in Antarctica various yeast strains such as Cryptococcus, Candida, Rhodotorula and others have been reported (Vishniac and Kurtzman, 1992; Vishniac 1993).
3.3. Food Chain and Food Web Food chains and food webs are the basic units of ecosystem, since all the energy and materials cycling take place around them. The food webs of SO can be represented as follows (Figure 4). The food chains and webs are much simpler at SO terrestrial ecosystem as compared to any other ecosystem, particularly in view of the non-existence of higher organisms of plant or animal kingdom. The only higher animals include some migratory birds.
Land-Ice-Air-Ocean Interactions in the Schirmacher Oasis, East Antarctica
59
Figure 4. Simplified Food Webs of the Terrestrial Ecosystem of Schirmacher Oasis.
The carbohydrates produced by the algae and mosses through photosynthesis are the main source of food for the primary consumers like mites, tardigrades, protozoans, rotifers and midges etc. More information is needed on the actual decomposition process in the Antarctic ecosystem where temperature is very low. The primary production is very little and as such the proportion of plant biomass passing into detritus component is presumably quite low as most of the primary production is grazed by the herbivores. Detailed investigations are required to understand the energy flow and nutrient cycling through the terrestrial ecosystem at SO through the simple food chain. During the Antarctic winter when it is dark, there is no photosynthesis by many of the producers. The plant eating primary consumers living on algae grew only during the summer.
3.4. Characteristics of SO Community 3.4.1. Frequency Distribution The data collected for ecological community study with the help of ‗line transect method‘ during the months of December 1999 to January 2000 are given in Table 8. For preparing the frequency diagram of the SO the values were counted and calculated as % of the total species for five different classes as laid down by Raunkiaer’s (1934). The law of frequency is given as: > A>B>C=D<E < The % values of normal frequency diagram of different frequency classes are: A=53, B=14, C=9, D=8 and E=16. From table 8, the % frequency of different classes was calculated as follows: Calculation of Frequency Class (%):
60
Khwairakpam Gajananda, H. N. Dutta and Victor E Lagun i)
Frequency Class A % = (No. of sampling sampling units) x 100 = (11/25) x 100 = 44 ii) Frequency Class B % = (No. of sampling sampling units) x 100 = (8/25) x 100 = 32 iii) Frequency Class C % = (No. of sampling sampling units) x 100 = (3/25) x 100 = 12 iv) Frequency Class D % = (No. of sampling sampling units) x 100 = (3/25) x 100 = 12
unit of species occurrence/Total no. of unit of species occurrence/Total no. of unit of species occurrence/Total no. of unit of species occurrence/Total no. of
Table 8. Frequency of plant species in Schirmacher Oasis (estimated by ‘Line Transect’ method) S No.
Vegetation Groups
Name of Species
Frequency (%)
I
Algae
II
Lichen
III
Mosses
Lyngbya aeustuarii Nostoc commune Oscillatoria limosa Phormidium fragile Aphanothece nidulans Chlorococcum Pinnularia borealis Acarospora gwynnii Buellia pallida Carbonea capsulata Lecidea cancariformis Lepraria membranacea Physcia caesia Polycauliona murrayi Rhizocarpon flavum Rinodina Species Umbilicaria aprina Umbilicaria decussata X.elegans Bryum argenteum Bryum pseuotriquetreum Bryoerythrophyllum Recurviroste Cedratondon purpureus Grimmia sps. Unknown
60 60 80 80 20 40 40 40 40 20 30 20 10 30 20 10 30 30 10 60 20 10
Frequency class To which species belongs C C D D A B B B B A B A A B A A B B A C A A
20 20 70
A A D
IV
Unknown
The above-calculated values are plotted and compared with the normal frequency classes (Figure 5.a and b). From the figure 5.b. it is clear that values of frequency classes B, C and D of figure 5.b. is comparatively higher than the respective values in normal frequency diagram (Figure 5.a). Thus, the plant community of the SO is heterogeneous in character. It can also be mentioned here that the value of frequency class E in figure 5.b is nil. Thus, none of the
Land-Ice-Air-Ocean Interactions in the Schirmacher Oasis, East Antarctica
61
species showed 80-100% constancy. This indicates that the SO environment does not provide suitable habitat for any species to occur homogenously. The heterogeneity is linked to microenvironments in the oasis providing congenial conditions for growth, both spatially and temporally. Also from table 8 it is found that the dominant algal species are Oscillatoria limosa and Phormidium fragile both of which are blue green algae, the moss species are dominated by Bryum argenteum and the lichen species by Acarospora gwynnii. It is important to note here that amongst all the plant groups, algal species dominate, whereas, the occurrences of moss and lichen species is lesser, which could be because the study sites are mostly aquatic in nature and it is true that out of 14 selected sampling 8 sites are just the banks of lakes, two dried lakes and four swampy areas. Some unknown species also occurred, which seemed to be some moss in close association with some lichen or algae, and could not be identified. It is very interesting to note that all the algal mats were dominantly consisting of cyanobacteria or blue green algae. Heterocystous cyanobacteria capable of independent nitrogen fixation like Nostoc Commune were mostly present on ice surface and lake bank over snowmelt. Pinnate diatom Pinnularia was found on surface layers of lift-off and often seen sliding between blue green algal mats. The only green algae found in the present transect study was Chlorococcum. This is in contrast to many other reports from snow regions where Chlorophyta members are present in abundance. Earlier Ling and Seppelt (1993) reported Chloromonas Subroleosa belonging to chlorophyta from Antarctica, which gave a red color to the snow attributed to the development of pigment in the species.
Figure 5. A and B. Shows the Raunkiaer‘s normal frequency diagram and the frequency diagram of the Schirmacher Oasis community. Frequency classes B, C and D of diagram B are relatively higher than A, thus the community is heterogeneous.
62
Khwairakpam Gajananda, H. N. Dutta and Victor E Lagun
Rare occurrence of green algae and dominance of blue green algae in the SO of Antarctica suggests that these cyanobacterial species are better adapted to the prevailing extremities of climatic conditions in Antarctica. The prokaryotic cell wall struture consist of diaminopimellic acid and muramic acid presumably provides better resistance to the cells. It also seems likely that the green algae are not so efficient in withstanding the freezing and thawing. In an experiment conducted by Bidigare et al., (1993), samples of red and green Chlamydomonas (Chlorophyta) when exposed to freezing and thawing resulted in lysis of the green cells whereas the red cells survived, which was due to increased membrane fluidity. Cyanobacteria containing phyco-cyanin (blue pigment) and phyco-erythrin (red pigment) seem to have more resistance to the stress conditions of Antarctica.
3.4.2. Plant Biomass (Standing Crop) Biomass or the standing crop present in a population at any given time is expressed as weight per unit area and is given in Table 9. for various study sites of SO. The estimated standing crop (dry weight) or biomass per square meter of SO varies from 6.25 to 45.31 gm-2 in various study sites. Various methods have been used by different workers to estimate the net primary production of an ecosystem and mostly a time-series data of harvest method is employed. However, Antarctic ecosystem is unique as it experiences long periods about two months of complete dark followed by two months of complete light. Again, it is during the summer period (December to February) that the snowmelts and favourable periods for some plant growth set in. Thus, the data on standing crop of biomass collected in the present study on December 31, 1999 to January 18, 2000 represent the peak growth and peak biomass and have therefore been considered as an estimate of net primary production (NPP) of the SO ecosystem (Odum 1971). Table 9. Peak Plant Biomass (gm-2) in terms of fresh weight and dry weight for the vegetation at different study sites of Schirmacher Oasis (the values are mean of three replicates)
Site No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Biomass (gm-2) Fresh weight 11.5 15.35 12.5 9.54 14.5 26.7 8.5 21.75 7.5 21.75 17.45 8.5 11.6 21.8
Dry Weight 2.8 3.25 2.95 2.2 3.45 7.25 1 6.5 1.2 6.2 4.65 1.2 2.46 5.3
Moisture Content % 310.71 372.31 323.73 333.64 320.29 268.28 750 234.62 525 250.81 275.27 608.33 371.54 311.32
17.5 20.31 18.44 13.75 21.56 45.31 6.25 40.63 7.5 38.75 29.06 7.5 15.38 33.13
Mean (±1 S.E)
14.92 (± 4.30)
3.60 (± 4.32)
375.42 (± 4.31)
22.50 (± 4.32)
Biomass per unit area
Land-Ice-Air-Ocean Interactions in the Schirmacher Oasis, East Antarctica
63
It must, however, be mentioned here, that these values of NPP are highly biased because they correspond to the study sites where conditions are favourable for growth. Even during summer, there are large areas bearing no vegetation at all. The present estimates of NPP therefore give an estimate of the potential of production of SO under the prevailing conditions. The average NPP value of the SO (22.5 gm-2), when compared to other stressful ecosystems of the world is still found to be very little.
3.5. Abiotic Component (Standing State) The study of abiotic components of the SO consists of rocks, ice, snow, and various inorganic nutrients, soil, melted water, sunlight and the climatic parameters. The soil over the SO has been classified as dry, polar desert soil, with a variety of textures and their occurrence has been found to be limited to the deglaciated (ice-free) area. Organic compound, such as ‗humus‘ (that links the biotic and abiotic component of the ecosystem), is extremely poor in this region. In table 10. the analysis of the various water, soils and biological samples for determining the ‗standing state‘ of the ecosystem and the atmospheric condition of the particular dates are given. Table 10. shows the physicochemical analysis of water (0 to 1m depths), biological and organic carbon of soils collected during December 1999 to January 2000, from 14 different sites with the atmospheric condition of the particular dates of SO. The results of the various analyses presented in table 10 are given below.
3.5.1. Physicochemical Analysis of Waters and Soils Samples: The average value of pH in the water of 14 different sites is 7.5, indicating that the water bodies are slightly of alkaline nature. This alkaline nature may be due to the photosynthesis by the algae and diatom mat present at the bottom of the lake (Gajananda and Dutta, 2005). The average Ca and Mg content of all the lakes have been measured to be 17.6 and 4.8 mg l-1, respectively. Dissolved Oxygen is also high at the value of 7.5 mg l-1. The DO, pH, Ca and Mg contents indicate that the lakes are well aerated and offer to be sources of freshwater supply to the oasis (Gajananda et al 2004a). Over the SO, these few important parameters of physicochemical characteristics of freshwater lakes were correlated with the available fauna (Table 10). 3.5.2. pH, Dissolved Oxygen and Conductivity pH in the surface waters ranged from 6.9 to 8.20, showing alkaline nature of the lakes. In site no. 4 (table 10), the pH in the surface water was high, while in site no. 8 the reverse was observed. Such changes may reflect the chemical composition of the bedrock sediments of each of the lakes and also human perturbances. The DO of lakes ranges between 6.1 to 8.4 mg l-1. The maximum was recorded from site no. 8. The conductivity of the lakes varied between 8-15μ mhos cm-1 (Gajananda et al., 2004a). The DO levels of the lakes indicate high quality water. The high DO levels can also be due to good photosynthetic activity of the algae present in the water (Gajananda et al., 2004a).
Table 10. Physicochemical analyses of the various water, soils and biological samples and the atmospheric conditions of the particular dates S. No 1 2 3 4
Ecological Parameters Surface Air Temp. (0C) MSL Pressure (mb) Wind Speed (m/s) UV-B (MED/Hr)
Dates and sites of the samples collected Dec. 30, 1999 Jan. 7, 2000 I II III IV V
Jan. 13, 2000 VII VIII
IX
Jan. 28, 2000 X XI
XII
Jan. 29, 2000 XIII XIV
Average
VI
-2.63
-2.63
-2.63
0.2
0.2
0.2
2.5
2.5
2.5
-2.0
-2.0
-2.0
-3.2
-3.2
-0.87
986.57
986.57
986.57
978.96
978.96
978.96
981.25
981.25
981.25
981.9
981.9
981.9
986.3
986.3
982.76
3.77
3.77
3.77
5.76
5.76
5.76
4.50
4.50
4.50
4.11
4.11
4.11
3.08
3.08
4.32
0.798
0.798
0.798
2.282
2.282
2.282
2.1
2.1
2.1
0.946
0.946
0.946
1.718
1.718
1.55
5
DO mg l-1
8.2
7.8
7.9
6.1
7.6
6.6
8.4
8.1
8.2
6.5
7.9
6.2
7.8
7.6
7.5
6 7 8 9 10
pH PO4 mg l-1 NH4 mg l-1 NO2 mg l-1 NO3 mg l-1
7.2 0.16 0.36 0.45 0.56
7.8 0.42 0.01 0.06 0.78
7.4 0.24 0.24 0.22 0.98
8.2 0.12 0.12 0.18
7.3 0.04 0.12 0.32 0.12
7.6 0.56 0.03 0.14 0.32
7.5 0.32 0.34 0.46 0.51
6.9 1.28 0.93 0.94 0.94
7.7 0.61 0.56 0.76 0.12
7.8 0.93 0.01 0.07 0.23
7.8 0.07 0.23 0.82 2.40
7.1 1.26 0.99 0.19 2.20
7.0 0.07 0.17 0.21 0.09
7.4 0.08 0.06 0.05 0.16
7.5 0.44 0.31 0.3 0.69
11
Ca mg l-1
22.6
2.1
3.1
25.0
32.0
14.3
10.5
37.5
29.0
2.5
6.4
48.5
10.2
2.2
17.6
12
Mg mg l-1 Chlorides mg l-1 Chlorophyll mg m-3 Primary Productivity mgC m-3 hr-
4.2
3.1
1.3
3.0
16.4
2.5
3.5
15.2
2.3
2.4
1.1
9.3
1.3
1.1
4.8
0.016
0.022
0.018
0.022
0.011
0.008
0.041
0.052
0.021
0.026
0.056
0.052
0.001
0.000
0.0
0.264
0.632
0.046
0.050
0.457
0.132
0.241
0.060
0.415
0.122
0.711
0.910
0.058
0.260
0.31
0.72
4.15
1.13
0.62
3.26
2.70
1.13
4.26
1.85
2.80
0.65
4.33
0.89
0.55
2.074
1.36
1.77
1.43
1.36
1.70
1.63
1.43
1.77
1.57
1.63
1.36
2.58
1.36
1.16
1.582
13 14
15
1
16
Organic Carbon %
S. No
17
18
Ecological Parameters Sediment Organism density individuals m-2 Dehydrogen ase activity μg/ g soil/24 hr
Dates and sites of the samples collected Dec. 30, 1999 Jan. 7, 2000 I II III IV V
Jan. 13, 2000 VII VIII
IX
Jan. 28, 2000 X XI
XII
Jan. 29, 2000 XIII XIV
Average
VI
1730
520
2205
1100
1115
1680
1750
1820
1050
1250
410
430
1630
380
1219
0.007
0.011
0.008
0.003
0.01
0.009
0.009
0.012
0.011
0.009
0.003
0.016
0.008
0.001
0.008
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Khwairakpam Gajananda, H. N. Dutta and Victor E Lagun
3.5.3. Ammonia, Phosphate, Nitrate and Nitrite Analysis for ammonia shows variation from 0.01 to 0.99 μM respectively, in different sites. Concentration ratio of PO4:NO3 ranged from 0.44 to 0.69. Ammonia in these waters probably acts as source of nitrogen for the growth of non-nitrogen fixing algal species. In surface water, nitrate is nutrient taken up by plants and assimilated into cell protein (Gajananda 2007). Maximum concentration of phosphate, ammonia, NO3 and Nitrite is found to be 1.28, 0.93, 0.94 and 0.94 mg l-1 at site no. 8 i.e. near Maitri station (table 10). An input of these nutrients seems to have taken place through anthropogenic activities (Gajananda 2007). 3.5.4. Calcium, Magnesium, Chloride Content and Chlorophyll a The average concentration of Calcium, Magnesium, Chloride, and Chlorophyll a are 17.6, 4.8, 0.0 mg l-1 and 0.31mg m-3, respectively (table 10). Calcium and magnesium dissolves out of almost all rocks and is, consequently, detected in many lakes and streams water. As it has been mention in the earlier that the SO rock comprises of metamorphic and igneous rocks, calcium and magnesium contribution to hardness of water is low. As there is no intrusion of seawater or geological formation to contribute for the chloride concentration in the lakes the average chloride content is very low (Gajananda 2007). Chlorophyll a aids in the assimilation of nutrients into cell biomass by harnessing the energy of sunlight. Its concentration is related to the quantity of the cell carbon. The concentration varies with water depth depending on the penetration of light (necessary for algal photosynthesis) and whether there is sufficient turbulence to mix the algae within the water column. Concentration of chlorophyll a (chl. a) in the surface waters in all lakes remained below 0.91 mg m-3 (Gajananda 2007). 3.5.5. Organic Carbon and Sediment Organism Density Organic carbon content of the soil samples ranged from 1.16 to 2.58 %. The soil covered with the vegetation (moss or algae) showed high organic carbon content compared to those without vegetation. The average total organic carbon content in the soil is 1.58%. Table 10. shows the result of the analysis of the soil samples collected from 14 sites of SO (Figure 1). The organic matter in the soil is contributed by the algae, lichens, mosses and the soil fauna. The greatest soil TOC content (site 12, 2.58%) is likely to be due to trampling of the microbiotic crusts through human activity, whereby a large amount of organic materials may have penetrated below ground. The average TOC content of 1.58% in the open soils of the SO, when considered against the amount of plant biomass present, can be regarded as significant in comparison with other Antarctic continental and maritime soils. The sediment organism density was found to be around 1219 individual m-2 in the SO, indicating a very low amount of fauna in the oasis (Gajananda 2003). 3.5.6. Enzyme Activity (Dehydrogenase Activity) Dehydrogenase activity (g soil-1 day-1) is an index of total soil metabolic activity and the oxidation-reduction reactions mediated by microorganisms in the soil. It is often correlated with soil fertility and even soil microbial population (Sethi et al., 1990). Also the dehydrogenase activity is dependent on the substrates availability (Schleifer et. al., 1972). The DHA values in the 14 studies sites of SO are found to be low and are about 10 times less than
Land-Ice-Air-Ocean Interactions in the Schirmacher Oasis, East Antarctica
67
that of marginal soils in sub-tropics (Malik et al., 1995). The DHA value shows a relationship with soil organic carbon. The low DHA in SO soils indicates that there is very limited microbial activity in the soil, which in turn, affects the decomposition process and Cmineralization. Relatively higher DHA values on the site 12 may be attributed to the inputs of the organics matter coming from the Russian Station Novolazarevskaya (Gajananda 2007).
3.6. Climatic Parameters of SO Ecosystem Weather and climate, determine to a large degree, the distribution of plants and animals, and of whole biocoenoses, not only on a continental scale but also on the regional scale. Climate governs both the distribution of plants and animals and the soil conditions, which are important for their inter-relationship. Secondly, vegetation influences both the soil and smallscale climatic conditions (the microclimate) (Stoutjesdijk and Barkman, 1991). During local summer over SO, the sun is available for 24 hours for 2 months and during this period, temperature is the highest, winds are the lowest, moisture is inducted in the form of snowfall, fog and at times by drizzle (light rain). Therefore, the most important functions of the biological life cycle took place during this period and in the later period i.e. local Antarctic winter, biological life becomes dormant. The only negative factor that prevails during summer is the high doses of UV-B radiations. Of course, our study reveals that UV-B intensity in MED/hr is negatively correlated with the productivity over SO. In fact, interaction of UV-B energy with the micro flora and fauna is still a subject of concern, which needs indepth studies. The atmospheric boundary layer (ABL), which extends from the surface to a height of about 1 km or so is the most important part for all the plants and animals to survive and is generally known as ‗biosphere‘ (Stoutjesdijk and Barkman, 1991). The ABL of Antarctica usually remains stable all round the year (Naithani and Dutta, 1995; Gajananda et. al., 2002b). Extreme stability is found in the winter months while extreme instability is reached to a lesser extent during polar summer (Naithani and Dutta 1995). Over the SO, katabatic winds, temperature, humidity, total solar radiation, UV doses, formation of inversions and cyclones etc. are the most important atmospheric parameters controlling the development of the habitats (Gajananda et. al., 2002c). Thus, considering the impact of the climate on plants and animals involved a complex factor. For instance, understanding the temperature at the surface of a plant not only need to study the air temperature, air humidity, radiation and wind, but also on the transpiration of the plant. Therefore, it is obvious that plants and animals are in interaction with their natural environment (Odum 1971). To link the ecosystem and the atmosphere it is important to study the various climatic factors such as temperature, humidity of air, winds, pressures, precipitations, evaporation rates, solar energy and UV doses etc. All these factors are discussed individually as follows:
3.6.1. Temperature Temperature plays a key role in the survival, growth, locomotory activity, life cycle, oxygen consumption rates, water balance, osmoregulatory ability, psychrophilic forms, fatty acid synthesis and other metabolic characters of plants and animal (Block et al 1994; Klok and Chown 1997; Moller and Dreyfuss 1996).
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Khwairakpam Gajananda, H. N. Dutta and Victor E Lagun
A perusal of the literatures shows a wide range of the effects of temperature on the flora and fauna of Antarctica. Many earlier workers had studied various aspects of temperature and their roles in determining the organisms‘ survival, evolution of super cooling ability and habitat distribution etc. Booth (1990) used various climatological data to describe the climatic requirements of plants and for numerical methods and models to indicate the decisive climatic factors for plant distribution. In another study of temperature dependences of three species of free-living Antarctic fellfield nematodes exhibited differing degrees of both strategies of cold-hardiness, freeze-tolerance and freeze-avoidance (Pickup 1990). The adaptation and acclimation of growth and photosynthesis of some Antarctic freshwater algae to low temperatures had been studied (Nagashima et al 1993; Eggert and Wiencke 2000). Both low temperature and water are limiting factors in the Antarctic terrestrial environment; these two factors have profound effect on the rate of photosynthetic response to the Antarctic moss Polytrichum alpestre to low temperatures (Kennedy 1993a-b). Franzmann (1997) found that cells of Methanogenium frigidum isolated from the perennially cold, anoxic hypolimnion of Ace Lake in the Vestfold Hills were psychrophilic, which exhibit most rapid growth at 150 C and no growth at temperatures above 18 to 200 C. The growth and consumption rates of bacteriovorous Antarctic naked marine amoebae grew at temperatures down to –20 C and showed optimal growth at 20 C and the growth efficiencies were low, typically <2%, which suggest that amoebae incur high energetic costs for life at low temperatures (Mayes et al 1997). Crustose lichen Buellia frigida growing on rock at Cape Geology were well adapted to the combination of hydration, low temperatures and strong light (Kappen et al 1998). Studies carried out on the cyanobacterium Nostoc commune by Kashyap et al (1991) over SO shows the influences of temperature on the nitrogen fixation. Matondkar and Prabhu (1986) also found that in SO the effect of temperature on bacterial populations is significant. At SO, the animals recorded were all of very small size. The small size also seems to be an adaptation to the prevailing low temperature. Todd and Block (1997) and Pickup (1990) showed greater super-cooling ability in small-sized classes of insects due to accumulation of cryoprotectants. Freezing intolerance is much more widespread throughout the invertebrates than freezing tolerance, but that switching from being tolerant to intolerant of body ice formation may occur in natural populations under snow cover (Block et al., 1994). In Antarctica the organisms are eurythermal, which can survive temperature in a very wide range. One good example was given by Nicolaus et al (1998), who found that bacterium Alicyclobacilli isolated from an unexplored geothermal soil in Antarctica: Mount Rittmann, were thermoacidophilic, showing an optimum temperature of -630 C and an optimum pH of 3.5 to 4.0. These bacteria were able to grow in the temperature range -45 to 700 C. Thus, in Antarctica both cold tolerant and thermophilic organisms can survive. Thus, from the above discussions it is clear that temperature plays a great role in all the life forms of plants and animals. It seems to affect shape, size, and volume, short or long life cycles etc. The plants as well as animals present at SO have adaptations to face the low temperature and are tolerant to freezing. Also, the snow present at Antarctica plays great role in providing suitable niches to the organisms through its various physical properties. The data of Maitri and the Novolazarevskaya are complimentary to each other giving an opportunity to study long-term variation or time series analysis of both temperature and pressure.
Land-Ice-Air-Ocean Interactions in the Schirmacher Oasis, East Antarctica
69
Figure 6. Seasonal average temperature from 1961 to 2001 recorded at Novolazarevskaya, Antarctica. Full data sets of annual temperature (dark squares) with summer values highlighted as open squares. Solid trend lines represent annual and dashed lines are of summer only.
Figure 6 shows the temperature trend of the Novolazarevskaya station for the last four decades. The data pertains to the year 1961 to 2001. The monthly average surface air temperature observed at this station shows that the temperature has significantly increased during the last four decades by [1.11 0C (P<0.01)], which is at the rate of about 0.27 0C per decade. The summer (December-February) of this period also shows a significant rise in temperature by about [0.99 0C (P=0.05)], which is at the rate of about 0.24 0C per decade increase. In the year February 1996 a widespread warming over east Antarctica was reported (Gajananda et al., 2002d). Hence, in the SO, the surface air temperature enhancement will certainly affect the function of ecosystem dynamics in future.
3.6.2. Atmospheric Pressure Atmospheric pressure seems to be of lesser ecological significance on the terrestrial ecosystem of SO. Though it has found that in terms of plants and animals life it has played some secondary role. In plants the osmosis of cell is influenced by pressure, similarly in animals low or high-pressure can reduce or increase the rate of transfer of energy within the tissue (Stoutjesdijk and Barkman, 1991). The surface air pressure variation over the SO (Figure 7) depicts a semi-annual pressure variation. The highest pressure is observed during the local summer (December-January) and in winter months (June-July), while the minimum pressure is observed during the two transition seasons (March-April and September-October). The annual average pressure of 986.5 mb is observed and forms half yearly cycle, influencing the formation of cyclones. The semi-annual variation in pressure has been explained by movement of the circumpolar trough (Streten, 1983; Naithani and Dutta 1995). At any particular time, the Antarctic trough is occupied by decaying depressions originating at lower latitudes. During local summer and in the local winter seasons, over Antarctica, the circumpolar trough moves away from the continent, thus average pressure increases. It is closest to the continent in autumn and spring seasons, thereby leads to minima.
70
Khwairakpam Gajananda, H. N. Dutta and Victor E Lagun
Figure 7. Monthly average msl pressure observed at Novolazarevskaya from 1961 to 2001.
In Antarctica specially, pressure plays a vital role in the development and maintenance of flora and fauna indirectly by affecting cloud formation, precipitation etc. The high and lowpressure systems around the circumpolar trough develop in severe cyclone. These cyclones push towards the continent and result in the formation of clouds, moisture, warmer air and precipitation over the continent periphery (Bromwich 1997). The cyclones also churn the ocean, thereby mixing the water with atmospheric oxygen, resulting into very high production of Southern ocean. Likewise, over the continent periphery, warmer air, precipitation, churning of lake water etc. gives a better habitat for plants and animals.
3.6.3. Wind Velocity and Direction Winds are the most effective vectors for the transportation of the spores and propagules of organisms to the Antarctic environment (Broady and Smith, 1994). In the SO, Singh and Agarwal (1998) estimated the settling rate of one bacterium per two hours of the exposed plates over the region. The reported bacteria and fungi were also present in the soil of this oasis. In Antarctica, earlier workers have studied unintentional dispersal of non-indigenous biota by human activities and dispersal by natural agents (wind, birds) (Smith, 1996). In the absence of higher life forms of plant kingdom, wind does not play a very significant role on the terrestrial ecosystem at SO. However, the wind direction does play an important role on dispersal of spores of the mosses and lichens. Smith (1996) also reported the unintentional dispersal of non-indigenous biota by human activities, and dispersal by natural agents (wind, birds) into and within the Antarctic, which contravened the measures of the Antarctic Treaty for the control of introduced biota. Over the SO, the average wind speed is 10.2 m/s coming from mostly SE and ESE direction. The biological effect of wind can be summarized as follows: (a) mechanical damage, especially in combination with air-borne salt, sand or ice crystals; increased transpiration; (b) reduction of dew formation; (c) supply of air pollutants; (d) hindrance of insect or bird dispersal and flight. All these effects vary from organism to organism. On the other hand, wind promotes the dispersal of pollen, spores, seeds, cysts and small animals, as well as bird flights. Heise and Heise (1949) carried out study of the influence of winds aloft on the distribution of pollens and moulds in the upper atmosphere.
Land-Ice-Air-Ocean Interactions in the Schirmacher Oasis, East Antarctica
71
Gajananda et al 2004b also reported the potential dispersal of microorganisms over SO earlier.
3.6.4. Humidity and Precipitation Evaporation depends on air humidity. Humidity not only determines the speed of evaporation, but also the ultimate water content of organisms. If the organisms cannot compensate for water losses through water uptake from the water bodies, soil and air (plants) or drinking (animals), they start desiccating. Desiccation of organisms is the most important part deciding their survival rate. Both evaporation rate and water content of organisms are important ecological factors. Although the RH at SO is low yet due to abundant water availability in the form of snow water, the vegetation present at SO show very high moisture content as revealed by the fresh weight and dry weight differences. In the SO the humidity level is very low (52%), thus have a profound effect on the development and metabolic characteristics of the flora and fauna. As has been stated above the moisture of the air is more important than rain for microorganisms such as lichen and mosses, this decreased humidity enhances desiccation of cell protoplasm‘s of the flora and fauna of the SO. But the algal species like Nostoc commune, Oscillatoria, Lyngbya etc. show a high degree of desiccation tolerance. 3.6.5. Solar Radiation (Direct and Diffused) Light between 400 and 700nm is used in photosynthesis by green plants. This ‗photosynthetically active radiation‘ or PAR makes up about half of the energy provided by solar radiation (Ross 1975). Photochemical effects at the upper end of the visible spectrum are found both with near red (λ 600 –700 nm) and far red (λ 700 – 800 nm), especially for germination.
Figure 8. Albedo (%) of various vegetation types and other surfaces values.
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Khwairakpam Gajananda, H. N. Dutta and Victor E Lagun
The amount of solar radiation reflected by the soil surface or by vegetation varies considerably. Green plant cover reflects little of the visual spectrum but much above 700 nm (near infra-red). Albedo (%) of various vegetation types and other surfaces values are given in figure 8. (after Stoutjesdijk and Barkman, 1991). From this figure, we see that water has a low albedo, but at low solar elevations, specular reflection strongly increases the albedo. The albedo of fresh snow is the highest found on earth and approached the albedo of an ideal white surface. The net radiation is the amount of energy available for the warming of soil and air and for evaporation. Clearly, the net radiation will differ markedly from point to point; a bare surface which is greatly warmed by the sun will receive a low net radiation and, conversely, a strongly transpiring crop with the same albedo as the bare surface, remaining cool, will have a high net radiation. Also, when there is a strong wind, the net radiation received by bare sand will be greater than under still conditions, when the surface is considerably warmed up. The warming of the atmosphere by the soil surface can be extended to hundreds of meters in the course of a sunny day. Naturally, thermal convection is dependent on the intensity of solar radiation (at night there is no convection at all) and on the characteristics of the landscape: a strong convection above dry ground, but less above vegetation using a large part of the energy received for evaporation.
3.6.6. UV-B Radiation Most organisms do not possess UV-B receptors; they cannot avoid deleterious wavelength radiation that (according to new measurements) penetrates deeper into the water column than what has been previously measured. New action spectra indicate that, in addition to DNA, other targets absorb UV-B radiation including intrinsic proteins of the photoreceptor and photosynthetic apparatus (Gajananda et al., 2002a). The inability to adjust their position within the water column causes massive inhibition of photosynthesis, measured both in field and laboratory studies. Only in a few cases have potential UV-B-inducible screening pigments been identified (Hader, et al., 1991). In situ incubations of natural phytoplankton assemblages in Antarctic waters indicated that UV-B under the ozone hole (150 DU) impaired photosynthesis by about 4.9 % while UV-A was responsible for about 6.2 % inhibition (Hansen- Holm et al., 1993a and 1993b). Similar ratios were found for tropical waters (Helbling et al., 1994), and screening of most UV <378 nm results in an increase in photosynthesis by 10 to 20 %. The Antarctic ecosystem may serve as a model system to measure continuous changes in UV radiations in relation to biological systems. The dominants of blue green algae at SO seems to be due to their better adaptation under high UV doses (Figure 9). Thomas and Duval (1995) reported green coloured algae to be more sensitive to UV. Duval et al., (1999) also reported that there is tendency in the green algae Chlamydomonas nivalis to develop carotenoids for better protection against UV. The phycobiliproteins and carotenoids present in Cyanobacteria seem to give them better protection against the harmful UV-B radiations. The studies suggest that the ecosystem of SO must have grown with some control of atmospheric parameters and high UV-B doses in Antarctica. The maximum UV-B radiation of 3.998 MED/hr was recorded on December 1, 1998 and 2.806 MED/hr was recorded on October 27, 1999, both of which fall almost in the middle of austral spring period (Figure 9). The UV-B recorded on the average during the year 1999 was lower than in the year 1998. In both the years the threshold limit of UV-B (1 MED/hr) was crossed during both spring and summer. Thus, a profound effect on the flora and fauna is likely.
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Figure 9. Graph showing the maximum daily values during the noontime for the period 1st February, 1998 to 31st January, 2000 observed over Maitri, Antarctica.
A comprehensive long term program involving the study of ecosystem under both prolonged low UV-B conditions and high UV-B conditions should be drawn, so as to understand the relationship and scientific mechanisms through which the ecosystem of SO has survived. Although many studies, but not all (Tosserams and Rozema 1995, Gehrke et al. 1995), suggest that photosynthesis and plant growth can be reduced by elevated levels of UV-B radiation, data on plant biomass and rates of net primary productivity, i.e. the standing stock of living matter expressed as g dry weight per unit ground area, and growth expressed as g dry weight per unit ground area per unit time, are difficult to find for natural ecosystems and forests. However, a review (Rozema et al. 1997a) suggests that there is little impact of UV-B radiation on the primary production of terrestrial ecosystems. The high doses of UV-B radiations in the Antarctic ecosystem also result in strong photooxidation of chlorophyll-a of green algae causing damage to the algal cells whereas other pigments are more protective against UV. This could be another reason why the species dominating the SO ecosystem consisted of cyanobacteria. Lichens, which are the symbiotic associations of cyanobacteria and fungi mainly, occupied hilly and rocky terrians. Due to their highly adaptive features of nutrient absorption by heterotrophic fungi and photosynthesis by algal partner, they are the common pioneer species reported for starting autotrophic succession on bare rocks.
3.6.7. Snow Snow cover changes the thermal budget at the surface of the earth. Fresh snow reflects solar radiation, not only the visible light but also shorter and longer wave radiation, up to 95% (Figure 8). Older snow has a lower reflection because of the snow turning into ice and due to accumulation of dust. However, for long-wave (heat) radiation snow acts as an ideal black surface, with absorption of 99.5 % and only 0.5% reflected. Older snow partly turns into ice and becomes more transparent. A fresh snow cover of 20 cm transmits only 3% of the solar radiation between 400 and 700 nm, but an older snow cover of the same depth transmits
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13% (Geiger 1965). Under icy snow a sort of greenhouse effect may occur. In Antarctica temperatures of +130 C were measured on lichens growing under an icy snow cover, with an air temperature of –90 C (Lange and Kappen 1972). Because of the small amount of heat from the soil during a clear and still night snow can cool off rapidly at the surface, causing very low night temperatures. Moreover, high radiation intensities during the day (both from direct and reflected sunlight) may lead to relatively high temperatures in the middle of the day. As a result, plants growing above the snow may be subjected to very large temperature differences, with a damaging effect. A particular characteristic of snow is its insulating effect, protecting soil and vegetation from frost. On top of the snow cover it is much colder than on the bare ground; underneath the snow it is much warmer. Many plants in alpine and arctic/Antarctic environments with winter temperatures of –20 to –50 0 C, would be killed in temperate regions because of the severe frost with no protecting snow cover. Under a long-lasting snow covers many animals; both vertebrates and invertebrates can remain active for most of the winter (Merriam and Caldwell 1983). Lichens are photosynthetically active when they receive a great deal of light reflected by the snow on the ground. Creveld (1981) found that during winter lichen receives the highest light intensities because of snow reflection and called this adaptation as cheimophotophytic (cheimoon = winter). This is also true for Antarctic lichens. Snow offers an effective protection against low temperatures; on the other hand little solar radiation is passing through a thick layer of snow. Another ecological aspect of snow is that the snowmelts on the soil may be saturated with water. Thickness of the snow cover and time of melting are often varied spatially according to fixed patterns, which can be correlated with vegetation patterns found in the summer (Friedel 1961). Sheltered depressions and spaces behind obstacles receive a great deal of snow. In the SO snow remains longer on north slopes than on south ones. Variation in snow cover ranges from very short duration with strong frost and desiccating winter storms (Blizzards), to a relatively long duration, especially in SO. Stoutjesdijk and Barkman (1991) found that if the soil is snow-free for less than three weeks, no vegetation will develop. If the snow-free period lasts at least three weeks the moss dominated. If the snow-free period is still longer, and the winter is cold, the limiting effect of frost on the vegetation is considerable. Clearly, lichens growing in snow-free places in high mountains and polar areas have to tolerate very low temperatures. In the SO the average summer temperature is –9.83 0C, the average winter temperature is –300C. Lichens occurring here tolerate temperatures of –750C, even in wet conditions (according to laboratory experiments of some workers). They can assimilate at –20 0C and have their photosynthetic optimum at low light intensities and very low temperatures of 0-50 C (Lange and Kappen 1972; Gjessing and Ovstedal 1989). The dark colour of lichens above the snow cover may be related to their heat requirement. Solar radiation, because of the high reflection from snow, has little influence on snowmelt. As soon as objects appear above the snow, plants or stones, melting proceeds much faster. These objects release heat through conduction and radiate heat, which is fully absorbed by the snow. In this way holes arise in the snow around patches of mosses, algae‘s and lichens, providing the essential water for these plants. The extreme low temperature of Antarctica resulting in the thick snow cover forms an important part of the climate system and affects greatly the ecology of the region. The snow cover seems to mediate the SO ecosystem in the following ways:
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a) The snow has a great potential of acting as an energy bank by storing latent heat of fusion and sublimation and crystal bonding forces (Gubler, 1985). The intake and release of energy throughout the year seems to be responsible for the variability in habitat conditions leading to heterogeneity of the ecosystem composition at the SO. b) The snow has a porous medium with large air content with a high insulation capacity. The insulation plays an important role in giving protection to the microorganisms. c) The snow acts as a reservoir of water during the summer and provides habitat and food resources to the various primitive plant forms, invertebrates and microbes. Permafrost: Permanently frozen ground underlies some 25% of the earth's land surface, which is widespread in Antarctica. Permafrost is believed to form gradually over very long time intervals (105 years), occurring continuously where mean annual air temperature is <-70 C. Along the margins, where it is thin and discontinuous, permafrost degradation can be monitored. Changes in the permafrost and the overlying summer active layer can have important effects on hydrological regimes, ecological and geomorphological conditions, and structures (Koster and Nieuwenhuijzen, 1992; Nelson et al., 1993).
3.6.8. Energy Balance and Water Relations, Dew Formation, Fog and Hoarfrost During the day high temperatures of the lower air layers promote energy exchange, while at night the situation is reversed: the colder and heavier air is not easily mixed with higher warmer layers of air and consequently the atmosphere is stable. Nyberg (1938) found that at 1 mm above the snow on still clear nights there was an unmistakable effect of turbulence. As stated above, the vapour pressure profile indicates the beginning of dew formation, which has been left out of consideration in the energy balance because it is negligible in energy terms. The occurrence of extremely low minima above bad conduction soil has received more attention than the absence of such minima above rock surfaces, although both phenomena are biologically important. For many organisms, which cannot take up water from the soil, the presence of liquid water can be very important, from dew or from precipitation. For mosses and lichens dew may be essential. These organisms can absorb water up to saturation from a dry starting position and retain this water. In mosses dew is also important for fertilization, allowing the spermatozoids to swim to the archegonia. Rocks are a similarly extreme environment for mosses, algae and lichens, as deserts are for higher plants. Some epiphytic species are only found at the foot of hills and do not grow higher up the glacier where the nocturnal radiation fog reaches. Dew is of special importance for the micro flora on the surface of leaves of vascular plants (Ruinen 1961). For many animals, dew is an important source of water. The relationship between fog and lichen flora in the Antarctica is one of the good examples. Fog is important as a source of water for organisms, which cannot take up water from the substrate, such as lichens on rocks. It is also important for lichens to be able to photosynthesize continuously in the daytime, which requires sufficient light and moist (but not wet) conditions. Fog here is more favourable to lichens than rain, i.e. especially fog in the daytime. In climates with mainly night fog and drought during the day lichens do not thrive, because respiration at night continues and is not compensated for sufficiently by photosynthesis (a so-called negative photosynthetic balance). In the SO, for example, the number of days with fog is generally low throughout the years. In the same direction the epiphytic lichen flora is considerably impoverished. Thus, maps of fog frequency are
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important if one wants to know whether the fog habitually occurs at night or in the daytime and affects lichen flora. A prolonged presence of elevated layer in the planetary boundary layer over SO will enhance fog duration (Gajananda et al., 2002e). Figure 10. shows the Sodar echogram of the foggy boundary layer in SO during January 1996.
Figure 10. Facsimile pictures of foggy and non-foggy days during 8–10 January 1996 at Maitri. Formation of fog started at around 21 : 15 h (UTC).
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For many organisms, which cannot take up water from the soil, the presence of liquid water can be very important, from dew or from precipitation. For mosses and lichens fog may be essential. These organisms can absorb water up to saturation from a dry starting position and retain this water. In mosses, fog is also important for fertilization, allowing the spermatozoids to swim to the archegonia. Clouds form when air is supersaturated with respect to water or ice (Gajananda et al., 2007). Fog is a potentially significant source of water in the desert environment, and also a far more predictable source of moisture than rainfall (Gajananda et al., 2007). There is, however, no evidence for direct uptake of fog condensation on leaves by plants. Any leaf structure capable of absorbing water on the leaves is also a potential route via which water can evaporate. Thus, there would be little benefit for plants in a hyper-arid environment to absorb fog moisture directly from the leaves. A more likely route whereby plants could benefit from fog moisture would be by absorbing condensation on the sand surface and as a result of stem flow. This route would facilitate the uptake of both fog and dew condensation on the soil surface. Certain plants growing in the fog zone of the Namib have well-developed superficial root networks or efficient mycorrhizal relationships to be able to benefit from alternative moisture sources such as fog and dew. In the Namib Desert lichens grow in great diversity on west facing slopes and surfaces where they are able to draw moisture from the sea fogs. If it were not for the fog the plants would have no source of water (Lange 2003). Dawson (1998) has clearly documented the importance of fog drip for soil moisture and root uptake. In the Arctic, foggy weather cut down the photosynthetic rates, but the net amount of carbon fixed by the end of growing season is high at about 174 g C per m2 per season (Billings and Peterson 1992). Gas exchange is completed by small pores in the leaf surface called stomata. Most desert plants have few stomata on the bottom side of the leaf, protected by deep depressions. The relationship between fog and lichen flora in the Antarctica is one of the good examples. Fog is important as a source of water for organisms, which cannot take up water from the substrate, such as lichens on rocks. It is also important for lichens to be able to photosynthesize continuously in the daytime, which requires sufficient light and moist (but not wet) conditions. Fog here is more favourable to lichens than rain, i.e. especially fog in the daytime. In climates with mainly night fog and drought during the day lichens do not thrive, because respiration at night continues and is not compensated for sufficiently by photosynthesis (a so-called negative photosynthetic balance). In the SO, for example, the number of days with fog is generally low throughout the years. In the same direction the epiphytic lichen flora is considerably impoverished. Thus, maps of fog frequency are important if one wants to know whether the fog habitually occurs at night or in the daytime and affects lichen flora (Gajananda et al., 2007). In SO the solar heating of the ground and formation of thermal plumes had less effect on the formation and dissipation of the fog episode. The dissipation of fog was only after the katabatic wind started flowing from the interior of the continent. Therefore, this type of fog can be regarded as advection fog (figure 10). It is also likely that due to changing climate over Antarctica, frequent fog may occur in the near future. The monostatic acoustic sounding data in association with the study of microbiotic crusts retention of atmospheric moisture especially during foggy period will help in understanding the complex physiological and metabolic characters of the various microbiota of Antarctica. The cytological mechanisms of the microbiotic communities of SO, which used fog moisture are unclear. Therefore, research on this aspect will be fruitful.
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3.6.9. Thermal Convection Convection is the vertical transfer of energy by the actual movement of the heated substance and is sometimes called sensible heat transfer processes. Sodar operation in the monostatic mode detects thermal structures associated with atmospheric phenomena (Gajananda et al., 2002f). Two types of thermal convection/plumes have been recorded at the Maitri station. In the first case, thermal plumes formed during free convection (well mixed Atmospheric Boundary Layer) due to the solar heating of the ground, which are conical in shape and seen as a rising layer, have been observed all over the Antarctic continent (Gajananda et al., 2004). In any case, these plumes lead to thermally driven vertical transport or uplifting air masses from the rocky surface of SO upto an altitude of 200–300 meters (Figure 11), representing a much warmer habitat on the ground (Gajananda, 2002f; Gajananda et al., 2004). As SO comprises of a rocky surface surrounded by polar ice, the uplifting air masses are more prevalent than the descending air masses, which are more common above lakes and seas (Stoutjesdijk and Barkman, 1991). The convective activity is mainly confined in the summer season between 1200 to 1400 hr and is the most favourable period for the dispersal of microorganisms. Surface based inversions are the most predominant feature on Sodar echograms and have been observed for about 94.37% of the time, clearly dominating over the convective activity which has been observed for only 5.63 % of the time (Figure 11).
Figure 11. Facsimile chart showing thermal plumes on January 10, 1996 at Maitri. It shows plumes around 0945 to 2200 hrs.
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Short spells of winter warming enhancing surface air temperature by even 15 0C have been measured. Such warming events may play an important role in the sustenance of microorganisms from totally desiccating their body fluids (Gajananda 2004b). These convective or unstable atmospheric conditions in the lower atmospheric boundary layer may help carry upward the spores/pollens of the micro-flora in the SO and facilitate their dispersive capacity to a larger distance (Gajananda et al., 2004).
4. CONCLUSION From the above studied, it is clear that Antarctica provides a unique platform for understanding the climatic processes in a complex environment. Study of land-ice-air-ocean interaction over the SO reveals that a unique ecosystem prevails over this oasis, where all the physical and biological components interact in a complex pattern. The conclusions drawn from the present research are summarized as: 1. The climate at Maitri is dominated by the extreme contrasts between the seasonal inputs of solar radiation. It experiences sub-zero mean temperature throughout the year except in the peak summer months (December and January). The surface wind regime (annual mean 10.2 m/s) is dominated by katabatic wind component from the southeast direction (110 to 1800), which is the direction of maximum slope around the Maitri site. Pressure (annual average 986.5 mb) forms half yearly cycle and influenced for the formation of cyclones. The humidity and precipitation are although low but have significant relationship for the growth of microorganisms. Surface albedo also has great effect on the warming and cooling of the surface of SO and in formation of atmospheric convection. 2. The monthly average surface air temperature observed at Novolazarevskaya station shows that the temperature has significantly increased during the last four decades by 1.11 0C (P<0.01), which is at the rate of about 0.27 0C per decade. The summer (December-February) of this period also shows a significant raise in temperature by about 0.99 0C (P=0.05), which is at the rate of about 0.24 per decade increase. Hence, in the SO the surface air temperature enhancement will certainly affect the function of ecosystem dynamics. 3. The ecosystem of SO must have grown with some control of high UV-B doses. The threshold limit of UV-B (1 MED/hr) was crossed during both spring and summer for the study period. Thus, a profound effect on the flora and fauna is likely. A comprehensive long term program involving the study of ecosystem under both prolonged low UV-B conditions and high UV-B conditions should be drawn, so as to understand the relationship and scientific mechanisms through which the ecosystem of SO has survived. 4. Thick snow cover forms an important part of the climate system and affects the ecology of the region. The snow acts as an energy bank by storing latent heat of fusion and sublimation and crystal bonding forces. The intake and release of energy throughout the year seems to be responsible for the variability in habitat conditions leading to heterogeneity of the ecosystem composition at the SO. The snow has a
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Khwairakpam Gajananda, H. N. Dutta and Victor E Lagun porous medium with large air content with a high insulation capacity playing an important role in giving protection to the microorganisms. The snow acts as a reservoir of water during the summer and provides habitat and food resources to the various primitive plant forms, invertebrates and microbes. 5. Our observation of fog layer within 300–400 m continuously for about 24 h due to the influence of oceanic air is an important feature for the microbiota of this cold and dry region. In the austral summer over the SO, there is 24 h sunshine and no rainfall except during rare occasions. Thus, fog here will be more favourable to the lichens than rain, i.e. especially fog during austral summer. However, in the SO, the number of days with fog is generally low throughout the year. Correspondingly, the epiphytic lichen floras are also considerably impoverished. As there is little or no rainfall, localized fogs contributed atmospheric moisture to the few poikilohydric microbiotic crusts as their sole water source. Organisms, which cannot take up water from the soil, dew and precipitation, are important. For mosses and lichens fog may be essential. These organisms can absorb water up to saturation from a dry starting position and retain this water. In mosses fog is important for fertilization, allowing the spermatozoids to swim to the archegonia. 6. The type of fog in SO are advection fog. In future it is predicted that frequent fog may occur in Antarctica. The cytological mechanisms of the microbiotic communities of SO, which used fog moisture are unclear and research on this aspect will be fruitful. 7. The convective or unstable atmospheric conditions in the lower atmospheric boundary layer help carry upward the spores/pollens of the micro-flora in the SO and facilitate their dispersive capacity to a larger distance. In Antarctica, katabatic winds represent atmospheric conditions when microorganisms are forcefully transported from the interior towards the icy periphery and the ocean, but the rocky oases regions may provide a shelter/protection for their survival and growth. In the present model of coupled mechanism, thermal convection over the ocean transports fine living materials and propagules towards the interior of the continent during local summer.
It is clear from the above points that all the climatic parameters are limiting the survival of living organisms in SO. The floral diversity in SO is poor and dominated by primitive poikilohydric groups of producers (algae, mosses and lichens) forming thin crusts on the soils surface. It also exhibits a very narrow spectrum of micro-floras in two distinct ecosystems i.e. terrestrial and aquatic. With the abiotic factors limiting life forms, the following conclusions are made: 1. The energy cycle and food chain are poor and short in SO due to less sunlight during austral winter and lack of higher organisms. 2. About 34 species of primitive flora were observed and only 6 primitive invertebrate fauna were recorded. Only four species of birds were observed in SO. The algal species are dominated by blue green algae (cynobacteria) and green algae are not frequent. Lichens are the most wide spread species in this oasis. Mosses have less species diversity but their frequency over the oasis is large.
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3. Sub-antarctic Island‘s migratory birds may introduce some non-indigenous forms of plants, animals and micro-organism species, but only cold tolerant variety of organisms survive. 4. The SO ecosystem is heterogeneous in nature with primitive plant life forms occupying some suitable niches at some less stressful microhabitats. The flora and fauna, which comprises the ecological equivalents of the SO, can be regarded as endemic species. 5. The estimated average biomass or NPP is low at a value of around 22.5 gm m-2 (range 6.25 to 45.31 gm-2). The lakes are oligotrophic in nature and are of fresh water lakes. 6. The average organic carbon content of the oasis is 1.58%, which is poor in comparison to other ecosystem of the world, indicating lesser amounts of detritus organic C or humus. 7. Dehydrogenase activity (DHA) was low and the average was 0.008 mg Triphenyl formazan (TPF) g soil-1 day-1, suggesting a very less microbial activity of substrate decomposition. The low DHA in SO also suggests that anaerobic oxidation of organic C is poor. The primitive plant compositions and the small DHA suggest that the SO is in the primary stage of ecological successions. The diminutive forms of plants and animal in SO is the results of less availability of nutrient, food and harsh climatic conditions for growth and survival. This might have resulted into the evolution of the cold hardiness, UV-B tolerant species of micro-floras and faunas with times. The biotic and abiotic component of SO, which interact in a cyclic and intricate manner are yet to be fully understood. Our present study provide baseline information and data for undertaking a long-term land-ice-air-ocean interaction research at SO. However, further study on the sustenance, growth, metabolic functions, reproduction and survival of the micro flora and fauna in the present climatic change scenario penetrating the periphery of Antarctica is highly recommended.
ACKNOWLEDGMENTS We are grateful to the Director, National Physical Laboratory (NPL), New Delhi and to the Secretary, Ministry of Earth Sciences, Government of India for providing us an opportunity to work at the Indian Antarctic station, Maitri. We also thank the Director (Dr. Rasik Ravindra), National Centre for Antarctic and Ocean Research (NCAOR), Goa for the supports and logistics helps. The constructive criticisms rendered by Professor Anubha Kaushik, Guru Jambheshwar University, Hisar is thankfully acknowledged. The Leader (Dr. Ajay Dhar) and Members of the 18th and 19th Indian Scientific Expedition to Antarctica (InSEA) who helped in surveying the SO is thankfully acknowledged. Thanks are also due to IMD at Antarctica and to Dr. Risal Singh and Mr. Shambhu Nath of NPL, New Delhi who provided data of the harsh polar environment. The financial assistance to one of the author (KG) under CSIR-SRF, DOD-SRF (DOD/12-MMDP/8–97-MRC CELL) and deputation as a Wintering Member of the 18th InSEA (1998–2000) by NPL, New Delhi, is acknowledged with thanks.
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In: Antarctica: The Most Interactive Ice-Air-Ocean Environment ISBN: 978-1-61122-815-1 Editors: Jaswant Singh, H.N. Dutta © 2011 Nova Science Publishers, Inc.
Chapter 4
EFFECTS OF UV-B RADIATIONS ON TERRESTRIAL ECOSYSTEM OF ANTARCTICA AND THEIR DEFENSE MECHANISMS Jaswant Singh*, Rudra P. Singh and Anand K. Dubey ABSTRACT The terrestrial environments of Antarctica are among the most extreme on earth challenging the very existence of life itself. The major voyages were carried out to the Antarctica for scientific observations and investigations by several countries. Presently, the thinning of springtime ozone layer due to release of chlorofluorocarbons in earth atmosphere causes the increased UV-B radiation over Antarctica is a serious cause of concern among environmentalists. The long term predictions of future UV-B levels are difficult and uncertain and UVB have significant effects on organisms at the different trophic levels. Antarctic continent is mostly dominated by cryptogamic plants which are distributed in different parts of the icy continent. The long term UV-B studies carried out under field conditions showed plant responses to higher UV-B levels and effects tends to increase or cumulative in nature. This chapter provides information of UV-B effects in field based studies and adaptive responses to UV-B radiations and how the enhanced UV-B altered the concentrations and distribution of photosynthetic pigments in plants.
Keywords: Antarctica, Ozone hole, UV-B, Pigments, Antarctic Flora, Adaptive strategies.
*
E-mail:
[email protected], Mobile+919415717168 Dept. of Environmental Sciences, Dr. R.M.L Avadh University Faizabad-224001,. (U.P.), India
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INTRODUCTION Till 1830, Antarctica remains as an unsolved puzzle for researchers. Later on number of expeditions to this continent were carried out by the explorers and scientists, from different countries basically for collecting flora and fauna from the different parts of the icy continent. In the year, 1948 the British, Australian, New Zealand, conducted Antarctic research expeditions for exploring the biodiversity of flora along with meteorological analysis at Antarctica. Antarctica is almost entirely (99.68 %) covered by permanent ice and has a surface area of 13,830,000 sq. km., which include several massive floating ice-shelves, which is some what similar to the area of Arctic Ocean (British Antarctic Survey 2004). Three major national voyages were carried out the Antarctica between 1837 and 1843; an important object for each was the determination of the position of the South Magnetic pole. The French naval expedition (1837-1840) visited the South Orkney Islands, South Shetlands, Trinity peninsula, Orleans Strait and Joinville Island. The International Polar Commission was formed at a conference in Hamberg, 1889 and a second conference was held in Berne, 1880 and a third in Sankt Peterburg, 1881, (Headland 2005). The international polar year conducted from 1st August 1882 to 31st August 1883, and 12 countries established 14 scientific stations in polar regions for co-coordinated Scientific observations. Three national expeditions, from Britain, Germany and Sweden set out in 1901 after much careful planning, the intended to explore different part of Antarctica and coordinate their geophysical and meteorological observations (Headland 2005). India‘s interest in Antarctica arises mainly from its ―Gondwana land connection‖, the lack of any land barrier between the Indian and Antarctic Ocean is also of great significance. India‘s first research station ―Dakshin Gangotri‖ commissioned in the year 1984 and second research station ―Maitri‖ commissioned in the year 1988-89 over the exposed rocks of Schirmacher Oasis of Queen Maud Land area in east Antarctica (Figure 1). The Schirmacher Oasis (700 45‘58‖S) is one of the small, snow / ice covered during the winter (June-August) and spring (September-November) seasons, typical desert near the shore of East Antarctica, with a width of 1.6 Km and length of about 20 Km with east-west orientation.
Figure 1. Map of Antarctica (www.nationsonline.org/oneworld/map/antarctica_map.htm).
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It‘s composed of with mainly high grade of metamorphic rocks, the fresh water lakes, ponds, pools cover a total area of 35 square km, and the altitude varies from 0 to 228m with an undulated surface. Climatic conditions are similar to other East Antarctica ice-free areas with annual temperature of -100C, January is the warmest month (-0.60C) and August is the coldest (10.10C), (Francisco et al. 2004). Recently India started to build its third station at Larsemann Hills, (69o20‘S to 69o30‘S Lat.; 75o55‘E to76o30‘E. long) in Prydz Bay, is an ice-free oasis on the Ingrid Christensen coast, of East Antarctica.
OZONE DEPLETION AND ULTRAVIOLET RADIATIONS Most of the ozone (about 90%) is located in the stratosphere (8-18 km) and only 10% in troposphere (below 8 km). Ozone in the stratosphere is very important as it acts as a shield for the mother Earth and protects life from harmful UV radiations coming from sun. One cannot think of any form of life in the absence of stratospheric ozone. Stratospheric ozone depletion has been recorded throughout from the temperate to polar regions (Blumthaler and Ambach 1990; Lubin and Jensen 1995). However, the ozone in the troposphere is a green house gas, trapping the long wave radiation in 9.6 nm bands affecting the energy budget of the earth-atmosphere system. Atmospheric ozone has two types of effects on the temperature balance of the earth, it absorbs solar ultraviolet radiations, which heats the stratosphere and it also absorbs infrared radiation emitted by the earth‘s surface effectively trapping heat in the troposphere. Therefore, the climate impact of change in ozone concentration is important and varies with altitude at which these ozone changes occur. Depletion of stratospheric ozone, resulting from anthropogenic atmospheric pollution has led to increased ultraviolet radiation at earth‘s surface as well as spectral shifts to the more biologically damaging shorter wavelengths (Frederick and Snell 1988). A decrease in the concentration of stratospheric ozone enhances the incoming solar UV-B radiation, which is detrimental to over all growth of the plant and various other metabolic processes of the organisms (Caldwell et al 1998), may cause changes in pigments concentrations, nucleic acids and proteins (Jansen et al 1998). Ecologists are interested to know how Antarctic flora is surviving over the harsh environmental conditions such as ultraviolet radiation stress, coldness and nutrient poor soils etc. The response of terrestrial plants to UV-B radiation is an active subject of research by molecular biologist, physiologist and environmentalists. Research during the past three decades has been largely focused on stratospheric ozone depletion and the resultant increase in irradiances of UV-B at the earth‘s surface and has greatly increased our understanding of how UV-B radiation affects Antarctic flora and their defense mechanism. Recovery of the Antarctic ozone hole is currently predicted by 2050, but it remains a topic of intense research interest (McKenzie et al 2003).
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Jaswant Singh, Rudra P. Singh and Anand K. Dubey Table 1. Distribution of Antarctic Flora in different regions of Antarctica SN 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
27
Lichens Umbilicaria, decussata Acarospora gwynnii Buellia pallida Lecidea cancriformis Lecanora fuscobrunnea Physcia caesia Rhizocarpon flavum Rinodina olivaceobrumea Umbilicaria antarctica Xanthoria elegans Usnea antarctica Sphaerophorus globosus Parmelia saxatilis Turgidosum complicatulum Pseudephebe minisciila Rizoplaca melanopthalma Carhonea capsulata Pseudephebe miniscula Bryophytes Bryum argenteum Bryum pseudotriquetrum Ceratodon perpureus Grimmia antarctici Sanionia uncinata Lichens Andrea regularis Cephaloziella varians Schistidium antarctici Algae Entomeneis kjellmannii
28
Berkeleya adeliense
29
Nitzschia stellata
30 31
Prasiola crispa Choricystis minor
32 33 34 35 36
Phormidium sp Lyngbyasp sp Oscillatoria sp Nodularia sp Anabaena sp
19 20 21 22 23 SN 24 25 26
Location Schirmacher Oasis Schirmacher Oasis Schirmacher Oasis Schirmacher Oasis Schirmacher Oasis Schirmacher Oasis Shirmacher Oasis Schirmacher Oasis Schirmacher Oasis Schirmacher Oasis Schirmacher Oasis Schirmacher Oasis Schirmacher Oasis Antarctic Peninsula Schirmacher Oasis Schirmacher Oasis Schirmacher Oasis Schirmacher Oasis
References Czeczuga 1996 Dodge 1973 Dodge 1973 Dodge 1973 Dodge 1973 Czeczuga 1996 Dodge 1973 Dodge 1973 Lamb 1964 Czeczuga et al. 1986b Lamb 1964 Czeczuga et al. 1986b Czeczuga 1996 Lud et al. 2001 Upreti et al. 2000 Upreti et al. 2000 Upreti et al. 2000 Upreti et al. 2000
Antarctic Peninsula Windmill Islands Windmill Islands Windmill Islands Antarctic Peninsula Location Antarctic Peninsula Antarctic Peninsula Windmill Islands
Green et al. 2000 Markham et al. 1990 Robinson et al. 2006 Robinson et al. 2005 Newsham 2002; 2003 References Newsham 2002; 2005 Newsham et al. 2002 Robinson et al. 2006
Cape Evans Ross Island Cape Evans Ross Island Cape Evans Ross Island Windmill Islands South Shetland Archipelago Mc Murdo Mc Murdo Mc Murdo Mc Murdo Mc Murdo
Ryan et al. 2002 Ryan et al. 2002 Ryan et al. 2002 Post and Larkum 1993 Zidarova 2006 Quesada et al. 1998 Quesada et al. 1998 Quesada et al. 1998 Quesada et al. 1998 Quesada et al. 1998
Effects oF UV-B Radiations on Terrestrial Ecosystem of Antarctica… SN 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51
Lichens Chlorell vulgaris Chlorococcum sp Phormidium uncinatum Oscillatoria sp Aphanothece sp Urospora sp Cylindrocapsa geminella Calothrix brevissuna Chrococcus macrococcus Gloeocapsa sp Lyngbya martensiana Nostoc commune Stigonema sansabaricus Higher Plants Deschampsia antarctica Colobanthus quitensis
Location Schirmacher Oasis Schirmacher Oasis Schirmacher Oasis Schirmacher Oasis Schirmacher Oasis Schirmacher Oasis Schirmacher Oasis Schirmacher Oasis Schirmacher Oasis Schirmacher Oasis Schirmacher Oasis Schirmacher Oasis Schirmacher Oasis
References Shukla et al. 1999 Shukla et al. 1999 Shukla et al. 1999 Shukla et al. 1999 Shukla et al. 1999 Shukla et al. 1999 Shukla et al. 1999 Shukla et al. 1999 Shukla et al. 1999 Shukla et al. 1999 Shukla et al. 1999 Shukla et al. 1999 Shukla et al. 1999
Antarctic Peninsula Antarctic Peninsula
Xiong et al. 2000 Xiong et al. 2000
Table 2. Important Pigments in Antarctic Plants SN
Lichens
1
Umbilicaria, decussata Acarospora gwynnii Buellia pallida
2 3 4 5 6
7 8 9 10
11
Lecidea cacriformis Lecanora fuscobrunnea Physcia caesia
Rhizocarpon flavum Rinodina olivaceobrumea Umbilicaria antarctica Xanthoria elegans Usnea antarctica
Photosynthetic Pigments
Other pigments
References
β-Carotene, Lutein, Cathaxanthin, Astaxanthin β-Carotene, Lutein, Hydroxyechinenone β-Carotene, Lutein, Zeaxanthin β-Carotene, Lutein,
Czeczuga 1996
α-Carotene, β-Carotene, Lutein β-Carotene, βCryptoxanthin, Lutein, Astaxanyhin β-Cryptoxanthin, Canthaxanthin, Lutein, β-Carotene, Lutein, Zeaxanthin, Canthaxanthin β-Carotene, βCryptoxanthin, Lutein, β-Carotene, βCryptoxanthin, Lutein, Asthaxanthin β -Carotene, βCryptoxanthin, Lutein, Hydroxyechinenone
Czeczuga, 1996
Czeczuga 1996 Czeczuga 1996 Czeczuga 1996
Czeczuga 1996
Czeczuga 1996 Czeczuga 1996 Czeczuga 1996 Czeczuga 1996
Czeczuga 1996
93
94
Jaswant Singh, Rudra P. Singh and Anand K. Dubey Table 2 (Continued) SN
Lichens
12
Sphaerophorus globosus Parmelia saxatilis Turgidosum coplicatulum Bryophytes Bryum argenteum
Other pigments
References
Astaxanthin, Adonixanthin
Czeczuga 1996
β-Carotene, βCryptoxanthin, Lutein β-Carotene, Lutein, Neoxanthin, Violaxanthin
Czeczuga 1996
Chl a, Chl b.,
Violaxanthin, β- Carotein
Bryum pseudotriquetrum Ceratodon perpureus Grimmia antarctici
Chl a, Chl b.,
Violaxanthin, β- Carotein
Chl a, Chl b.,
Violaxanthin, β- Carotein
Chl a, Chl b.,
Violaxanthin, β- Carotein
Sanionia uncinata Andrea regularis
Chl a, Chl b.,
Chl a, Chl b., Chl a, Chl b.,
25
Cephaloziella varians Schistidium antarctici Algae Entomeneis kjellmannii Berkeleya adeliense Nitzschia stellata
Neoxanthin, Lutein, Zeaxanthin, β,β- Carotene Neoxanthin, Violaxanthin, Lutein, Zeaxanthin Neoxanthin, Lutein, Zeaxanthin, β,β- Carotene Anthocyanin
Markham et al. 1990 Robinson et al. 2002; 2006 Dunn 2000 Robinson 2002 Dunn 2000 Robinson 2002; 2005 Newsham et al. 2002 Newsham 2003
26
Prasiola crispa
Chl a, Chl b.,
Mycosporine like amino acids Mycosporine like amino acids Mycosporine like amino acids Violaxanthin
27 28
Choricystis minor Phormidium sp
Chl a, Chl b., Chl a.,
29
Lyngbya sp
Chl a.,
30
Oscillatoria sp
Chl a.,
31
Nodularia sp
Chl a.,
13 14
15 16 17 18
19 20 21 22
23 24
Photosynthetic Pigments
Chl a, Chl b.,
Chl a, Chl b.,
β-carotene MAAs (porphyra-334) βCarotene MAAs (porphyra-334) βCarotene MAAs (porphyra-334) βCarotene MAAs (porphyra-334) βCarotene
Lud et al. 2001
Newsham et al. 2002; 2005 Robinson et al. 2006 Ryan et al. 2002 Ryan et al. 2002 Ryan et al. 2002 Post and Larkum 1993 Zidarova 2006 Quesada et al. 1998 Quesada et al. 1998 Quesada et al. 1998 Quesada et al. 1998
Effects oF UV-B Radiations on Terrestrial Ecosystem of Antarctica… SN
Lichens
32
Anabaena sp
33
Palmaria decipiens Phyllophora antarctica Porphyra endiviifolium Iridaea cordata
34 35 36
37 38
Higher Plants Deschampsia antarctica Colobanthus quitensis
Photosynthetic Pigments Chl a.,
Other pigments
References
MAAs (porphyra-334) βCarotene
Quesada et al. 1998 Dhargalkar 2004 Dhargalkar 2004 Dhargalkar 2004 Dhargalkar 2004
Chl a, Chl b.,
Orientin, Luteolin
Chl a, Chl b.,
Orientin, Luteolin
Ruhland et al. 2001 Ruhland et al. 2001; Lud et al. 2001
Chl a., Chl a., Chl a., Chl a.,
95
ANTARCTIC FLORA AND THEIR PIGMENTS Historically, Antarctic plants were growing under the low UV-B levels on the earth but now because of ozone depletion, they are exposed to some of the highest concentrations with little time for evolutionary adjustment and acclimation (Madronich et al. 1995). In continental Antarctic, environmental conditions are extremely hostile to terrestrial vegetation with extreme cold, UV irradiance, strong wind and drought (Green et al. 1999). In Antarctic ecosystems, snow cover can offer protection from excess photosynthetically active radiation (PAR) and also damaging UV-B radiation (Marchand 1984). Away from the Antarctic Peninsula the vegetation is composed of entirely of poikilohydric organism, the occurrence of which depends on the distribution of available water. The brief spring and summer season thought to be the main period of growth and productivity (Hovenden et al. 1994). Cryptogams are a major component of the vegetation in both polar regions their response to elevated UVB radiation is of particular interest. Very few species have been recorded from ice-free areas of the continent which is approximately 2%. Different types of flora survive there, the lichens are the major elements of Antarctica, mosses, fungi and algae have also shown their existence and are characterized by a high degree of adaptation on harsh environmental conditions. Soil of Antarctica has very less humus, but rich nitrogen and phosphorus are responsible to provide luxuriant growth to lichens and mosses on rocks in both dry and moist habitats, (Crittenden 1998). Cryptogams are poikilohydric, and as a result, during period of low water availability or freezing temperatures, they possess the ability to enter a dormant state of physiological inactivity through controlled dehydration of their cells (Robinson 2003). The photosynthetic pigment contents in lichenized alga are chlorophyll a, chlorophyll b, carotenoid, phycocyanin, lutein and β-carotene as well as the lipid soluble antioxidant alphatocopherol (Table 2). Riley, (1997) explored the melanin in lichens and concluded that, melanin a predominantly indolic polymer is the major pigment present in surface of lichen, these are black in color naturally found in lichens growing in Antarctica. These black colors
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may be helpful to accumulate high photo energy from sun and retention in lower amount, these melanin help to protect lichen thallus against UV-radiation. Gauslaa and Ustvedt, (2003) explored the brightly orange color anthroquinone i. e. parietin found in lichens and discussed their role as UV screening compound and concluded that parietin may reduce the effect of UV radiations. UV-B absorbing pigments such as flavonoids are wavelength selective UV-B screens, which can accumulate rapidly in response to high UV-B radiation levels, Caldwell et al. (1983). Morphological changes includes reduced growth, where as reduced photosynthesis is also important parameter for measurement (Prasad et al. 2005). Several pigments like chlorophyll, carotenoid in lichens, algae, bryophytes, and green alga are the advance parameter rather than morphology and anatomy, to detect the effect of UV radiation on Antarctic flora. The pigment found, in photoautotrophic organisms have the interest to ecologist and biologist for a number of reasons, e. g. chlorophyll and their derivatives has been much used a parameter for the measurement of productivity. Their qualitative as well as quantitative measurements may be indicative of the climatic changes.
LICHENS The peculiarity of lichens is that they are not one homogenous organism but a symbiosis of two different partners. The fungal partner supplies the plant, water and nutritious salt, meanwhile the algal partner supplies the organic substances, like carbohydrate produce. With this ideal ―job-sharing‖ lichens can withstand hardest environmental conditions. Of all the plants, lichens are best adapted to survive in the harsh polar climatic conditions (Table 1). Some lichens have even been found only about 400 km from the South Pole. Lichens are colorful organisms owing to numerous combinations of algal and fungal pigments; color is often used in taxonomic studies to aid species identification. Some times the color of the thallus is used as a characteristic to discriminate related genera; however, color variation within species can be significant because of spatial and temporal variations through environmental factors (Gauslaa and Mc Evoy 2005). Among Antarctic flora, the lichen shows extensive diversity, thus it has taxonomical, ecological, environmental, interest of many lichenologist from various countries. According to Dodge (1973) there are 429 species of lichens occurring in Antarctica, while Hertel (1988) estimated only 160 crustose lichens in that area. Comparing the investigation to Indian context a single lichen genus Acarospora was recorded by Wafar and Untawale (1983), from Maitri area. Upreti (1999) collected lichens from Maitri region of Schirmacher Oasis, and enumerated about 23 species of lichens belonging to 16 genera. According to Friedmann (1982), in Antarctica, lichens are the major floral elements of terrestrial vegetation of the harsh climate, after the disappearance of macrolichens the rock inhabiting (saxicolous) crustose species forms the main component of the lichen vegetation. The crustose lichen develops a thin primitively organized thallus, which is completely affixed to the substratum over the whole lower surface or hidden in the uppermost layer of the rock. According to Hertel (1988), the crustose lichens can colonize, in extreme polar habitat better than the other macroscopically visible plants. The common genera of lichens, are reported in Table 1 are Acarospora, Buellia, Candellariella, Lecidea, Lecanora, Physcia, Rhizocarpon, Rinodina, Umbilicaria, Xanthoria, Turgidosculum, Usnia, etc are luxuriant growing in Antarctica (Czeczuga 1996; Lud et al. 2001; Lamb 1964; Dodge 1973).
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The poikilohydric nature of lichens and several secondary chemicals like atronorin, usnic acid, zeorin, triterpins are widely found, and help to protect against stress; thallus color of lichens i. e. orange, red, yellow, grey are also helpful during harsh environmental conditions. During stress conditions these secondary chemicals reach at upper cortex of lichens thallus to protect them (Elix, 1996). Leading to these types of studies Huneck (1999), justified that these secondary chemicals some time react with rock substratum and secrete powdery substance on upper surface called ―Pruna‖ these pruna shade the thallus to protect the thallus against temperature as well UV radiations. The darkness of melanin pigments are observed with the naked eye in intact Lobaria pulmonaria thallus again a natural light gradient reflects the level of solar exposure. The brownest thalli are observed in the most sun-exposed position and increasing pigmentation causes a reduced cortical transmittance, especially of UV and short wave visible radiation. A photo protective role for melanin compound should imply a higher resistance against excessive light in thalli where these pigments are abundant (Riley 1997). The melanic green algal lichens like Parmelia and Cetraria display predominantly Arctic / Alpine regions; this melanin shows the strongest protection at energy-rich wavelength, the percentage reduction in transmittance caused by melanin appears to be large in the UV range. The secondary medullary compounds, stictic and norstictic acid deposited in largest quantities in the photobiont layer may assist in UV protection (Bachereau and Asta 1997).
BRYOPHYTES Like the lichens, the bryophytes can be found in all areas capable of supporting plant life in the Antarctic, though they are not very widespread in distribution. Bryophytes, even those of open, exposed habitat have been seen as showing features that would generally be regarded as characteristic of shade plants. With lichens, bryophytes share the distinction of being the largest group of plants that occur in Antarctic region. In spite of general assumption that Joseph D. Hooker made the first collections of mosses in Antarctica during 1829-30. The bryophytes are also poikilohydric, depending on the presence of free water during the summer month for photosynthetic carbon gain and growth. Antarctic bryophyte communities are largely confined to the margins of melt lake at Casey (the Australian base in the Windmill Island region, 660 17‘S, 1100 32‘E) the three dominant moss species Ceratodon purpureus, Grimmia antarctici and Bryum pseudotriquetrum are found in the both pure and mixed communities (Selkirk and Seppelt 1987) and stream areas subject to snow accumulation. In addition to their role in energy storage compounds, simple sugars and polyols performs multiple roles in plant. They are thought to act as cryoprotctants, as osmotic regulator in the drought and salt stress plants, and as antioxidant (Popp and Smirnoff 1995). Various soluble carbohydrate are able to interact with the polar head groups of phospholipids, taking the place of water molecules and maintaining membrane integrity during desiccation (Crowe and Crowe 1986), polyols accumulate in higher plants in response to water stress. These molecules probably have multiple roles, as compatible solutes, scavengers of active oxygen species and as stabilizers of macromolecules (Loescher 1987; Smirnoff and Cumbes 1989; Popp and Smirnoff 1995). Differences in the response of the three moss species to desiccation, and the phenotypic plasticity in their response, was assessed by testing for
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differences in three parameters over two sites that differed in water availability; (1) the WC (water content) at full hydration, (2) the rates of drying over time, and (3) the relationship between the decline in chlorophyll fluorescence and relative WC. Initial rates of water loss were faster in moss obtained from the wet sites compared to that from the dry sites. Few mosses have been studied, to know the negative effects of UV radiation on growth and morphology in some high latitude species (Sonesson et al. 1996; Searles et al. 1999; 2002, Robson et al. 2003, Robinson et al. 2005). Short moss turf and cushion moss is found most frequently in sandy and gravelly soil. The extent of these moss communities depends on the availability of summer melt water, and ranges from the extensive moss which occurs around, melt lakes and along melt streams (Selkirk and Seppelt 1987). Mosses, like lichens, gather in colonies, which make them possible to collect and retain more water. They also lose less by evaporation and show a marked ability to use water rapidly whenever it becomes available. Mosses have also become well adapted to the almost continuous light during long day of a polar summer. The impact of ambient ultraviolet (UV-B) radiation on the endemic bryophyte, Grimmia antarctici, was studied over 14 months in East Antarctica. Over recent decades, Antarctic plants have been exposed to the largest relative increase in UV-B exposure as a result of ozone depletion. Although photosynthetic rates were not affected, there was evidence of UV effects on morphology Antarctic bryophytes possess UV-B absorbing pigments which should offer better protection under ambient UV-B radiation, these findings suggested that G. antarctici may be disadvantaged in some settings under a climate with continuing high levels of springtime UV-B radiation (Robinson et al. 2005). Recently, high concentrations of UV-B absorbing pigments have also been reported in two Antarctic mosses, Sanionia uncinata and Andreaea regularis, and one liverwort, Cephaloziella varians, with positive correlations between pigment accumulation and flux of natural solar UV-B radiation (Newsham et al. 2002, 2005, Newsham 2003), and investigated the effect of reduced UV and visible radiation on the pigment concentrations, surface reflectance and physiological and morphological parameters of the moss. Chlorophyll content was significantly lower in plants grown under near-ambient UV, while the relative proportions of photoprotective carotenoids, especially β-carotene and zeaxanthin, increased (Table 2). However, no evidence for the accumulation of UV-B absorbing pigments in response to UV radiation was observed. According to Paul (2001), the carotenoid concentration plays an important role in prolonged period of freezing. The Bryum argenteum produce more energy by photosynthesis in low light at 50C than it does at 150C or higher. Photosynthesis can start within few hours of thawing after a prolonged period of freezing, and almost immediately following short period, due to this reasons it may be survive there.
ALGAE Snow algae, which grows in semi permanent to permanent snow or ice in the alpine or polar region of the world. Their optimum growth temperature is generally below 100C. According to Green et al. (1999) more than 300 species of non-marine alga have been found in Antarctica, these algae successfully adapted to their harsh environment though the development of a number of adaptive features which includes pigments polyols (sugar
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alcohols, e. g. glycerin), sugar and lipid (oils), mucilage sheaths, motile stages and spore formation. Cyanobacteria (blue green algae) have a cosmopolitan distribution ranging from hot springs to Arctic and Antarctic regions characterized by high variability and the organisms need to adapt to various environmental factors (Rozema et al. 2002). Blue green and other algae are found growing in damp sand and gravel around lakes and pools along melt water streams or in low-lying areas. Other than blue and green algae may form extensive and spectacular red, yellow or green patches in area of permanent snow. These pigments protect the cells from the high light and ultraviolet radiation damage during the summer months. The pigments may take the form of iron tannin compounds, as M. berggrenii, or orange to red-pigmented lipids as in the majority of the snow algae. The cells of some species also secrete copious amount of mucilage, which unable them to adhere to one another and to snow crystal and to prevent the cell from being wash away by melt water. The mucilage also forms a protective cover and delays desiccation. It may have additional function as an ultraviolet shield. According to Sinha et al. (2005), Ultraviolet-B radiation reaching the earth surface due to depletion of stratospheric ozone layer have been shown to cause destruction of phycobiliproteins like phycoerythrin, phycocyanin, allophycocyanin, especially in blue green algae. In general, cyanobacteria are protected by mycosporine-like amino acids (MAAs) and scytonemins while terrestrial plants contain flavonoids (Table 2).
FUNGI In Antarctic conditions, fungi have been studied in little. Several mushrooms have been found on the west coast of the Antarctic peninsula, and on the South Shetlands. A few of the fungi in Antarctica are unique to the continent and responsible to deteriorate the quality of material but there is little study regarding pigments (Green et al. 1999).
HIGHER PLANTS Only two native vascular plants, the Antarctic hair grass Deschampsia antarctica and a cushion forming pearlwort, Colobanthus quitensis, survive south of 560 S. They occur in small clumps near the shore of the west coast of Antarctic Peninsula. Both plants can tolerate very harsh environmental conditions. The accumulation of UV-B absorbing pigments would be particularly useful in Antarctic plants because such passive screens could protect them from UV-B damage when physiological inactivity, due to desiccation or freezing, renders active repair mechanisms unavailable (Lovelock et al. 1995, Cockell and Knowland 1999). They continue to maintain their physiology at freezing point (Caldwell et al. 1998).
Ultraviolet Radiations and Adaptations in Plants According to Prasad et al. (2005), UV-B exposure to photosynthetic terrestrial plant Pisum sativum, is believed to enhance the generation of active oxygen species at various sites of photosynthetic and respiratory electron transport chain. The active oxygen species (AOS) i. e. hydrogen peroxide, superoxide radicals and hydroxyl radicals are highly reactive and can
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induce lipid and protein peroxidation and thus, these active oxygen species are suggested to affect the structural integrity and permeability of cellular mechanisms due to ultraviolet radiations. Almong et al. (1991) suggested that enhanced UV-B radiation causes a multitude of differing effects such as change in electron transport capability, chloroplast ultrastructure, level of photosynthetic and protective pigments and disturb the mechanism of photosynthesis in terrestrial plants. Among two photosystem, photosystem II appeared to be more sensitive to ultraviolet radiation than photosystem I. Significant reduction in chlorophyll content was noticed with increasing dose of UV-B and the suppression was more prominent on chlorophyll-a than chlorophyll-b in other words it shows decreasing trend in Chl a / Chl b ratio. This reduction could be due to chlorophyll destruction as reported in most of the UV-B exposed photosynthetic organisms in glass house study (Teramura and Sullivan 1994). In contrast to chlorophyll contents, carotenoid contents showed an enhancement with increasing dose of UV-B radiation. In order to avoid AOS induced damage during oxidative stress, plants evolve a complex antioxidant defense system (Kondo and Kawashima 2000). The antioxidative enzymes: superoxide dismutase, catalase, peroxidase, etc. and non-enzymatic antioxidants: ascorbate, carotenoids, flavonoids and a variety of phenolics are synthesized in stressed plants (Rao et al. 1996). UV-B may cause damage to nucleic acids, proteins, and lipids, and may affect photosynthesis, growth and development of plants (Jansen et al. 1998). According to Tevini et al. (1981), carotenoid acts as scavenger of singlet oxygen which is formed during intense light, protect chlorophyll from photo-oxidative damage therefore, increased carotenoid content following UV-B exposure could have a positive effect on protecting chlorophyll pigments. Interestingly, concentrations of UV-B absorbing compounds were higher and chlorophyll-b was lower under ambient UV-B radiation in two Antarctic vascular species, D. antarctica and C. quitensis, (Ruhland and Day 2000). There is also evidence to suggest that reductions in leaf area may be related to increases in insoluble levels of UV-B absorbing phenylpropanoids that contain epidermal cell elongation and subsequent leaf expansion. Studies have found that the ambient levels of UV-B can stimulate production of UV-B absorbing compounds (Hunt and Mc Neil 1999). It is important to study the effect of particular stress on the biological organisms, and to explore the pathway for signaling system i. e. defense mechanism at targeted organism and also explore the mechanism between photosynthetic pigments and defense. Among these it is also necessary that what type of defense be adopted by the organisms during adverse conditions. In Antarctica, there are intense ultraviolet radiations therefore, it is important to study the effect of ultraviolet radiation on flora and fauna and type of defense adopted for surviving organisms. Leading to these types of studies in Robson et al. (2003) using polyester film for the attenuation of ultraviolet radiation, which transmit a large percentage of the UVA radiation and found that photosynthetic pigment altered with UV-B radiations. Phoenix et al. (2002), have used polycarbonate filter that absorb both UV-A and UV-B radiation, in this experimental model the effect of ultraviolet radiation, in subarctic shrubs, reductions in UV-B radiation resulted in increased levels of UV-B absorbing compounds which was attributed to either increased secondary metabolism in absence of UV-B radiation or UV photo-oxidation of these pigments. Krizek and Mirceki (2004) reported that cellulose acetate film as sometime used for near-ambient control in UV-B exclusion or UV-B attenuation experiments can have toxic effects on plants and affect growth in dependently of their effect on UV radiation. The experiment of Robson et al. (2003) is not affected by this problem as Aclar film was used instead of cellulose acetate for in-vitro as well field study. Result of these UV-B experiments,
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added more information leading to effects of UV-B radiation on vegetation. Reduction in chlorophyll b concentration has been observed in the other species of plant in response to enhanced levels of UV-B (Strid et al. 1990, Deckmyn et al. 1994, Barsig and Malz 2000). These reductions may be associated with UV-B induced damage to photosystem II (Greenberg et al. 1989). Scientific investigations have shown that phytoplankton‘s are sensitive to current UV-B levels, which can reduce the rate of primary productions, (Smith et al. 1992, Vincent and Roy 1993). Bothwell et al. (1994) showed that UV-radiation reduced not only the photosynthesis and growth of benthic diatoms but also inhibited algal consumers. Ochs (1997) demonstrated the harmful effects of ultraviolet radiation on the grazing activity of heterotrophic flagellates on autotrophic pico-plankton. Keller et al. (1997), using a mesocosm approach, concluded that the enhancement of UV-B radiation during a winter / spring bloom did not affect the marine food web, trends of diminishing abundance of organisms were consistently observed at different trophic level in the enhance UV-B treatment.
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Hovenden M J, Jackson A E, and Seppelt R D, (1994) Field photosynthetic activity of lichens in the windmill Island Oasis, Wilkes Land, continental Antarctica. Physiologia Plantarum 90: 567-576. Headland R K, (2005) The Poles: information for exploration. Archives of natural history 32 (2): 207-220. Huneck S, (1999) The significance of lichens and their metabolites. Naturwissenschaften 86: 559-570. Hunt J E, Mc Neil, D L, (1999) The influences of present day level of ultraviolet-B radiation on seedlings of two Southern Hemisphere temperate tree species. Plant Ecology 143: 3950. Jansen M A K, Gaba V, and Greenberg B M, (1998) Higher plants and UV-B radiation: balancing damage, repair and acclimation. Trends in Plant Sci. 3: 131-135. Keller A, Hargraves P, Jeon H, Klein-Macphee G, Klos S, Oviatt C, and Zhceng J, (1997) Ultraviolet-B radiation enhancement does not affect marine trophic levels during a winter spring bloom. Ecoscience 4: 129-139. Kondo N, and Kawashima M, (2000) Enhancement of the tolerance to oxidative stress in cucumber (Cucumis sativus L.) seedlings by UV-B irradiation: possible involvements of phenolic compounds and antioxidative enzymes. J. Plant Res 113: 311-317. Krizek D T, Mirceki R M, (2004) Evidence for phytotoxic effects of cellulose acetate in UV exclusion studies. Environmental and Experimental Botany 51: 33-43. Loescher W H, (1987) Physiology and metabolism of sugar alcohols in higher plants. Physiologia Plantarum 70: 553–557. Lamb I M, (1964) Antarctic Lichens I. The genera Usnea, Ramelina, Himantormia, Alectoria, Cornicularia. Br. Antarct. Surv. Sci. Rep. 38: 1-34. Lovelock C E, Jackson A E, Melick D R, et al (1995) Reversible photoinhibition in Antarctic moss during freezing and thawing. Plant Physiology 109: 955-961. Lubin D and Jensen E H, (1995) Effect of clouds and stratospheric ozone depletion on ultraviolet radiation trends. Nature 377: 710-713. Lud D, Rozema J, Huiskes A, Maerdijk A, (2001) The effects of altered levels of UV-B radiation on an Antarctic grass and lichen. Plant Ecology 154: 89-99. Madronich S, Mc Kenzie R L, Caldwell M M, et al (1995) Changes in Ultraviolet radiation reaching the Earth‘s surface. Ambio 24: 143-152. Marchand P J, (1984) Light extinction under a changing snow cover. In: Winter Ecology of Small Mammals (ed. Merritt JF), Carnegie Museum of Natural History, Pittsburg, PA, USA pp 33-37. Markham K R, Franke A, Given D R, et al (1990) Historical Antarctic Ozone level trends from herbarium specimen flavonoids. Bulletin de Liaison Groupe du Polyphenols 15: 230-235. Mc Kenzie R L, Bjorn L O, Bais A, Ilyasd M, (2003) Changes in biologically active ultraviolet radiation reaching the Earth‘s surface. Photochemical and Photobiological Sciences 2: 5-15. NASA, (2008) www.toms.nsfc.nasa.gov Newsham K K, Hodgson D A, Murray A, et al (2002) Response of two Antarctic bryophytes to stratospheric ozone depletion. Global Change Biology 8: 972-983. Newsham K K, (2003) UV-B radiation arising from stratospheric ozone depletion influences the pigmentation of the moss Andreaea regularis. Oecologia 135: 327-331.
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Newsham K K, Geissler P A, Nicolson M J, et al (2005) Sequential reduction of UV-B radiation in the field alters the pigmentation of an Antarctic leafy liverwort. Environmental and Experimental Botany 54: 22-32. Ochs C A, (1997) Effect of UV radiation on grazing by two marine heterotrophic nanoflagellates on autotrophic picoplankton. J. Plankton Res. 19: 1517-1536. Paul N, (2001) Plant response to UV-B; time to look beyond stratospheric ozone depletion. New Phytologist 150: 1-8. Peter S S, Flint S D, Cadwell M M, (2001) A meta–analysis of plant field studies simulating stratospheric ozone depletion. Oecologia 127: 1-10. Phoenix G K, Gwynn-Jones D, Lee J A, Callaghan T V, (2002) Ecological importance of ambient solar ultraviolet radiation to a sub arctic health community. Plant Ecology 165: 263-273. Popp M, Smirnoff N, (1995) Polyol accumulation and metabolism during water deficit. In ‗Environment and plant metabolism-flexibility and acclimation‘. Bios Scientific Publishers: Oxford, UK (Ed. N Smirnoff) pp 199-215. Post A, Larkum A W D, (1993) UV-absorbing pigments, photosynthesis and UV exposure in Antarctica: comparison of terrestrial and marine algae. Aquatic Botany 45: 231-243. Prasad S M, Shrivastva G, Mishra V, Dwivedi R, Zeeshan M, (2005) Active oxygen species generation, oxidative damage and Antioxidant defense system in Pisum sativum exposed to UV-B irradiation. Physiol. Mol. Bio. Plant 11 (2): 303-311. Quesada A, Goff L, Karentz D, (1998) Effects of natural UV Radiation on Antarctic cyanobacterial mats. Polar Biology 11: 98-111. Rao M V, Paliyath G, and Ormrod D P, (1996) Ultraviolet-B and ozone-induced biochemical changes in antioxidant enzymes of Arabidopsis thaliana. Plant Physiol. 110: 125-136. Riley P A, (1997) Melanin: molecules in focus. Int. J. of Biochem and Cell Biol. 29 (11): 1235-1239. Robinson S A, Lovelock C E, (2002) Surface reflectance properties of Antarctic moss and their relationship to plant species, pigment composition and photosynthetic function. Plant Cell and Environment 25: 1239-1250. Robson T M, Panocotto V A, Flint S D, Ballare C L, Sala O E, Scopel A L, Cadwell M M, (2003) Six years of solar UV-B manipulations affect growth of Sphagnum and vascular plants in a Tierra del Fuego peatland. New Phytologist 160: 379-389. Robinson S A, Wasley J, and Tobin A K, (2003) Living on the edge- plants and global change in continental and maritime Antarctica. Global Change Biology 9: 1681-1717. Robinson S A, Turnbull J D, and Lovelock C E, (2005) Impact of changes in natural ultraviolet radiation on pigment composition, physiological and morphological characteristics of the Antarctic moss, Grimmia antarctici. Global Change Biology 11: 476-489. Robinson S A, Lovelock C E, Wasley J, (2006) Climate change manipulations show Antarctic flora is more strongly affected by elevated nutrients than water. Global Change Biology 12: 1800-1812. Rozema J, Bjorn L, Bornman J, et al (2002) The role of UV-B radiation in aquatic and terrestrial ecosystems–an experimental and functional analysis of the evolution of UV absorbing compounds. J. of Photochemistry and Photobiology B: Biology 66: 2–12.
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Ruhland C T, Day T A, (2000) Effect of ultraviolet-B radiation on leaf elongation, production and phenylpropanoid concentrations of Deschampsia antarctica and Colobanthus quitensis in Antarctica. Physiol. Plant. 109: 244-251. Ryan K G, McMinn A, Mitchell K A, Trenerry L, (2002) Mycosporine-Like Amino Acids in Antarctic Sea Algae, and Their Response to UVB Radiation. Z. Naturforsch 57c: 471477. Searles P S, Flint S D, Diaz S B, et al (1999) Solar ultraviolet-B radiation influence on Sphagnum bog and Carex fen ecosystems: first field season findings in Tierra del Fuego, Argentina. Global Change Biology 5: 225-234. Searles P S, Flint S D, Diaz S B, et al (2002) Plant response to solar ultraviolet-B radiation in a southern South American Sphagnum peatland. Journal of Ecology 90: 704-713. Selkirk P M, Seppelt R D, (1987) Species distribution within a moss bed in Greate Antarctica. Symposia Biologia Hungarica 35: 279-284. Sinha R P, Kumar A, Tyagi M B, Hader D P, (2005) Ultraviolet-B induced destruction of phycobiliproteins in cynobacteria. Physiol. Mol. Biol. Plant. 11 (2): 313-319. Smirnoff N, Cumbes Q J, (1989) Hydroxyl radical scavenging activities of compatible solutes. Phytochemistry 28: 1057-1060. Smith R C, et al (1992) Ozone depletion: Ultraviolet radiation and phytoplankton biology in Antarctic water. Science 255: 952-959. Sonesson M, Callaghan T V, and Carlsson B A, (1996) Effects of enhanced ultraviolet radiation and carbon dioxide concentration on the moss Hylocomium splendens. Global Change Biology 2: 67-73. Strid A, Chow W S, Anderson J M, (1990) Effect of supplementary ultraviolet-B radiation on photosynthesis in Pisum sativum. Biochem. Biophys. Acta 1020: 260-268. Shukla S P, Gupta R K, Kashyap A K, (1999) Algal colonization of Schirmacher Oasis, Antarctica. Fifteenth Indian Expedition to Antarctica, Scientific Report, Tech Pub No.13 Department of Ocean Development, India 109-116. Tevini M, Iwanzik W, Thoma U, (1981) Some effect of enhanced UV-B irradiation on the growth and composition of plants. Planta 153: 388-394. Teramura A H, and Sullivan J H, (1994) Effect of UV-B radiation on photosynthesis and growth of terrestrial plants. Photosynth. Res. 39: 463-473. Tobin A K, (2003) UV-B effects on crops. In: Modern Trends in Applied Terrestrial Ecology (ed. Ambasht RS), Kluwer / Plenum Press, New York USA pp 183-193. Upreti D K, Mukerji K G, Chamola B P, Upadhya R K, (1999) Studies on Antarctic Lichens: Biology of Lichens (eds.) Aravali Book International, New Delhi pp 333-342. Upreti D K, and Pandey V, (1994) Heavy metals of Antarctic Lichens I. Umbilicaria. Feddes Repetorium 105 (3-4): 197-199. Upreti D K, and Pandey V, (2000) Lichen flora of Schirmacher Oasis and Vettiyya Nunatak. Seventeenth Indian expedition to Antarctica, Scientific Report. Tech Pub No. IS, Department of Ocean Development, India 185-201. Vincent W F, and Roy S, (1993) Solar Ultraviolet-B radiation and aquatic primary production: Damage, protection, and recovery. Environ. Rev 1: 1-12. www.nationsonline.org/oneworld/map/antarctica_map.htm Wafar S, and Untawale A G, (1983) Flora of Dakshin Gangotri in Antarctic Scientific Report of Ist Indian Expedition to Antarctica. Technical pub. 1: 182-185.
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Xiong F S, Mueller E C, Day T A, (2000) Photosynthetic and respiratory acclimation and growth response of Antarctic vascular plants to contrasting temperature regimes. American Journal of Botany 87: 700-710. Zidarova R, Pouneva I, (2006) Physiological and Biochemical characterization of Antarctic Isolate Choricystis minor during oxidative stress at different temperatures and light intensities. Gen. Appl. Plant Physiol. Special Issue 109-115.
In: Antarctica: The Most Interactive Ice-Air-Ocean Environment ISBN: 978-1-61122-815-1 Editors: Jaswant Singh, H.N. Dutta © 2011 Nova Science Publishers, Inc.
Chapter 5
ULTRAVIOLET RADIATION STRESS: RESPONSE AND PROTECTIVE STRATEGIES OF ANTARCTIC FLORA Sanghdeep Gautam and Jaswant Singh* ABSTRACT Antarctica is place of adverse conditions- low temperature, low water availability, strong winds and high incidence of solar specially the UV radiation altogether constituting limiting factor for plant and animal life. Increases in ultraviolet radiation at the Earth‘s surface due to the depletion of the stratospheric ozone layer have increased interest in the mechanisms of various effects it can cause on organisms. DNA is certainly one of the key targets for UV-induced damage in a variety of organisms ranging from bacteria to humans. Absorption of UV-B radiation by plants can damage and disrupt key biological molecules. UV-B damage can manifest reduced photosynthesis, growth of the plants and photosynthetic productivity. Antarctic plants experiences UV-B stress and for their survival has shown various adaptive strategies. The first line of defence is to screen UV-B radiation before it reaches the cell, then to minimize damage within the cells through other protective strategies, and finally to repair damage once it has occurred. The survival of Antarctic plants under ‗ozone depletion‘ depends on their ability to acclimate, by employing photo protective mechanisms to avoid and repair UV-B damage.
1. INTRODUCTION Antarctica is a place like no other; as an intriguing habitat, it is a scientist's dream. It is a land where water is scarce, despite having more than two-thirds of the world's freshwater supply trapped in ice. Though it borders the world's major oceans, the Southern Ocean system is unique; it is a sea where average temperatures do not reach 2°C in summer, where even the water is so unusual that it can be identified thousands of kilometers away in currents that * Email:
[email protected] Department of Environmental Sciences, Dr. R.M.L. Avadh University, Faizabad-224001, U.P., India
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originated here. As the Earth, tilt on its rotational axis, makes its elliptical journey around the Sun each year, the Sun "sets" in April, not to be seen again until September. And the ice—an unimaginable, incomparable vastness of ice—appears in a dozen different varieties, at times and in places several thousand meters thick. There are two major ice sheets that change all the time. Antarctica is a remote and inhospitable continent. The climate is the coldest and driest known on Earth; nevertheless it is not uniform across the continent, and different climatic regions can be distinguished (Holdgate 1977; Onofri 1999; Øvstedal). The prevailing Antarctic conditions of low temperature, low water availability, frequent freeze–thaw cycles, low annual precipitation, strong winds, high sublimation and evaporation, high incidence of solar and especially ultraviolet radiation together constitute significant limiting factors for plant and animal life. As a consequence of these severe conditions, the Antarctic flora is almost entirely cryptogamic, only two vascular species occur, both of which are restricted to the relatively mild Antarctic Peninsula. Therefore, the biology of Antarctica, more than other continents, is dominated by microorganisms, with a high level of adaptation and able to withstand extreme conditions. Abundance and diversity of organisms decrease, along broad latitudinal gradients, from the maritime to the continental Antarctic zone and within the latter with increasing altitude and latitude from the coast to the Ice Slope Region (Pickard and Seppelt 1984; Kappen 1993).
2. DISTRIBUTION OF ANTARCTIC FLORA Antarctica has been divided into three phyto-geographic zones -continental, maritime and periantarctic (Stonehouse, 1989). The high-latitude, Continental Antarctic, is the most climatically severe zone. The northwest coast of Antarctic Peninsula and associated islands (including King George, South Shetlands, Sandwich and Orkney and Peter IØy) make up the relatively mild Maritime Antarctic (Figure 1). Despite the severe growth conditions, plants are found on the Antarctic continent, although many species, including the two Angiosperms, are restricted to the relatively mild maritime zone (Lewis Smith, 1984; Edwards and Smith, 1988; Hansom and Gordon, 1998; Longton, 1988). Outside the maritime zone, the remaining cryptogamic vegetation is primarily limited to a few small rocky outcrops along the coast, the dry valleys and inland nunataks. Exacerbating the extremely dry conditions are the subzero summer temperatures, which lock most water away as snow and ice, significantly limiting plant productivity (Hansom and Gordon, 1998). Antarctica has the most extensive and best developed terrestrial vegetation in continental Antarctica but the vegetation is restricted to six species of bryophytes and 27 lichen species (Lewis Smith 1988; Melick et al. 1994). The bryophytes are poikilohydric, depending on the presence of free water during the summer months for photosynthetic carbon gain and growth. Consequently, Antarctic bryophyte communities are largely confined to the margins of melt lakes and streams and areas subject to snow accumulation. At Casey (the Australian Antarctic Base in the Windmill Island region, 66°17S, 110°32E) the three dominant moss species Ceratodon purpureus, Grimmia antarctici and Bryum pseudotriquetrum are found in both pure and mixed communities (Selkirk and Seppelt 1987). The extent of these moss communities depends on the availability of summer melt water, and
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ranges from the extensive moss turves which occur around melt lakes and along melt streams to small isolated moss buttons which are found in moisture pockets on rocky outcrops. Of the three species, G. antarctici is common within melt lakes and streams, C. purpureus is often associated with drier sites, and B. pseudotriquetrum co-occurs with both G. antarctici and C. purpureus (Selkirk and Seppelt 1987) Despite limitations to growth , mosses have been reported from as far south as 84.1̊ S and although bryophyte fruiting events are rare in the continental Antarctic zone (Wise and Gressitt, 1965; Filson and Willis, 1975). In addition to the relatively conspicuous mosses and lichens, the continental Antarctic terrestrial vegetation includes groups that are often overlooked, including the chasmoendolithic algae, which occur only within rock fissures. These organisms are widespread in coastal regions of Antarctica and are believed to underlie up to 20% of the rock surface in some locations (Longton, 1985; Hansom and Gordon, 1998). Total plant group contributing to the biodiversity of the Antarctic landmass is provided in the table 1. Table. 1. Estimated contribution of plant groups to the terrestrial plant biodiversity of Antarctica Phytogeographic zone Continental Maritime Total
Angiosperms
Mosses
2 2
30 75 85
Liverwort s 1 25 26
Lichens 125 150 200+
Macrofung i 2 22+ 28
References Lewis Smith(1984) Lewis Smith(1984) Longton(1985)
Figure 1. Map of Antarctica. The Maritime Antarctic is the area to the left of the dashed line. The Periantarctic islands are found north of the limit of sea ice and bounded by the polar front. Locations where much of the research described in this review was conducted include Signy Island, Maritime Antarctic, Windmill Islands, Wilkes Land, Ross Island and Victoria Land ( Adapted from Robinson 2003).
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3. OZONE LOSS IN SOUTHERN HEMISPHERE Depletion of stratospheric ozone, resulting from anthropogenic, atmospheric pollution has led to increased ultraviolet (UV) radiation at the Earth‘s surface, as well as a spectral shift to the more biologically damaging shorter wavelengths (Frederick and Snell, 1988). As a consequence, Antarctica now experiences unseasonably high UV-B radiation through much of the spring, caused by the combined effects of the ‗ozone hole‘ and the approach of the natural annual radiation peak, the summer solstice (Frederick and Snell, 1988; Roy et al., 1994). The ‗ozone hole‘ which is defined as the average area with an ozone thickness of 220 DU, develops during the austral spring (September–November) and is closely linked with the polar vortex (Roy et al., 1994). Ozone depletion has recently extended into the mid-latitudes reaching South America and the south island of New Zealand (Stolarski et al., 1986; McKenzie et al., 1999). The largest ‗ozone holes‘ were recorded between 1998 and 2001(Figure 2), with areas twice that of Antarctica and minimum ozone thickness reaching 90DU at the south pole (NASA, 2002). In Antarctic ecosystems, snow cover can offer protection from excess photo-synthetically active radiation (PAR) and also damaging UV-B radiation (Marchand, 1984). Furthermore, the spectral composition of sunlight transmitted through snow is primarily between 450 and 600 nm, with shorter and longer wavelengths removed (Salisbury, 1984). However, these figures vary with the depth and density of snow cover. After snowmelt, submergence beneath water may reduce incident PAR. Water preferentially absorbs longer wavelengths and, although some attenuation of shorter wavelengths does occur, it offers only limited UV-B protection (Cockell and Knowland, 1999). In addition to changes in incident UV-B due to stratospheric ozone distribution and concentration, actual UV-B experienced on the ground is highly variable because it is strongly influenced by cloud cover, geometry and albedo (Bodeker, 1997).
Figure 2. Ozone hole area w.r.t to 220DU in Southern hemisphere from year 1999 to 2008 (NASA 2008).
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4. EFFECTS OF UV-B RADIATIONS ON PLANTS Absorption of UV-B radiation by plants can damage and disrupt key biological molecules, with an array of repercussions for the physiological functioning of the plant (Greenberg et al., 1997; Rozema et al., 1997; Jansen et al., 1998; Tobin, 2003). The first line of defence is to screen UV-B radiation before it reaches the cell, then to minimize damage within the cells through other protective strategies, and finally to repair damage once it has occurred (Stapleton, 1992). Since repair mechanisms are often incomplete, prevention of damage, through avoidance of UV-B absorption, should be more effective. Damage to biological molecules can occur through direct absorption of UV-B or indirectly as a result of the production of reactive oxygen species (ROS) (Figure 3). Although such molecular effects of UV-B damage can manifest as reduced photosynthesis and growth of the plants, photosynthetic productivity is unlikely to be significantly affected by increasing UV-B (Allen et al., 1998), and direct effects on plant communities are likely to be subtle (Caldwell et al., 1999). Vulnerability to UV-B damage is likely to be greater in plants occurring at high latitudes due to the fact that they have evolved under lower UV-B conditions (Caldwell et al., 1982; Barnes et al., 1987; Marchant, 1997). Prior to ozone depletion, polar plants were growing under the lowest UV-B levels on earth, and in the last few decades they have been exposed to similar levels as temperate plants, having little time for evolutionary adjustment and acclimation (Karentz, 1991).
Figure 3. Effects of UV-B radiation on plant cells, showing screening sites of damage.
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The annual occurrence of the ‗ozone hole‘ coincides with time of emergence from winter dormancy beneath the protective snow cover (Karentz, 1991; Adamson and Adamson, 1992; Wynn-Williams, 1994), exposing plants to sudden elevations of UV-B radiation in combination with increased PAR and greater temperature fluctuations. Bryophytes may be particularly susceptible to UV-B damage because of their simple structure, with most having leaves that are only one cell thick and lacking protective cuticles or epidermal layers (Richardson, 1981; Gehrke, 1998; Gwynn-Jones et al., 1999). Combined with the physiologically stressful effects of repeated freeze/thaw cycles, an intermittent water supply and limiting nutrients, polar bryophytes are likely to be sensitive to the additional stress imposed by elevated UV-B radiation (Robinson et al., 2003;Wasley et al., 2006 a, b). The survival of Antarctic plants under ‗ozone depletion‘ depends on their ability to acclimate, by employing photoprotective mechanisms to avoid and repair UV-B damage. Many of the effects induced by UV-B radiation allow for at least a duality of interpretations. The difference between damage, repair and acclimation can be subtle and it is not always possible to identify one particular mechanism as the explanation underlying a given phenomenon. For example, the UV-B induced degradation of the D1 protein of PSII can be seen either as damage or as a part of a repair mechanism leading to the substitution of the damaged components of PSII. A number of studies have found that photosynthetic activity (estimated by measuring gas exchange or chlorophyll fluorescence) does not appear to be strongly affected by either reduced or elevated UV-B treatments in the two Antarctic vascular species. However, growth was affected in a number of ways by exposure to UV-B. The major impact was a reduction in cell length, leading to shorter leaves. Less branching and fewer leaves per shoot led to reduced plant size and biomass, with effects more pronounced in C. quitensis than D. antarctica. Leaves were also thicker in plants exposed to UV-B. Perhaps the cost of producing and maintaining thicker leaves explains the reductions in growth that occur in the absence of effects on photosynthesis (Xiong and Day, 2001; Xiong et al., 2002). Long-term field studies showed similar but less pronounced impacts of UV-B radiation compared with similar length pot studies, but the latter showed high inter-annual variation and provided evidence of cumulative UV-B effects (Day et al., 2001). Exposure to UV-B accelerated plant development and led to greater numbers of reproductive structures in both species, although the weight of C. quitensis seed capsules declined with higher UV-B exposure. However, since these structures produced fewer spikelets and seeds, the overall reproductive effort was unchanged. In addition, although the final seeds produced under UVB exposure were smaller, their germination rates were unaffected (Day et al., 2001). In two Antarctic bryophyte species (Sanionia uncinata and Bryum argenteum), no reductions of net photosynthesis or chlorophyll fluorescence parameters were observed under current levels of UV-B. However, in the 7 day field UV-B enhancement study, effective photochemical quantum yield (FPSII) was reduced in S. uncinata. Studies of lichens in Antarctica have concentrated on the impact of excess visible radiation on photosynthesis and have found that, while photoinhibition was evident when lichens were water stressed (Hovenden et al., 1994), it was less likely to be a factor when lichens were fully hydrated (Kappen et al., 1998a). No significant effects of either screening or supplementation of UV-B have been observed. As with the excess PAR studies, it appears that lichens are far more sensitive to moisture content and temperature. Perhaps these factors, which are hard to control under screening treatments, have tend to obscure any potential impact of UV-B (Huiskes et al., 2001; Lud et al., 2001b).
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5. PLANTS PROTECTION MECHANISM Plants in nature are seldom affected by only a single stress factor such as UV-B radiation. Instead, plants are subjected to a combination of environmental stresses and their overall response to them can be very different from that induced by a single stress. For example, the effectiveness of UV-B radiation can be ameliorated (Teramura et al. 1990) or in some cases aggravated (Dube‘ et al. 1992) depending on the plant species and on the nature of the stress factor interacting with UV-B radiation (Bornman and Teramura, 1993; Caldwell et al. 1998). However, experiments in controlled environments are often necessary, providing valuable information on specific targets and mechanisms during relatively short time periods. They are also useful as predictive indicators for organism response in natural environments, but they should be verified as much as possible under field conditions.
5.1. UV Absorbing Compounds UV-absorbing compounds are widespread and are found in lower and higher plants, including aquatic and terrestrial life forms. One of the many roles of these compounds appears to be the protection of organisms from harmful effects of UV-B radiation by means of their direct absorption of these wavelengths. However, recent evidence suggests that some of the phenolic compounds may contribute to the decrease in active oxygen species by acting as antioxidants (Husain et al. 1987; Foyer et al. 1994; Markham et al. 1998; Olsson et al. 1998; Ryan et al. 2002). Although almost omnipresent, UV-absorbing molecules are chemically very different in the various plant groups, since, for instance, their degree of polymerisation and complexity decreases from higher plants to lower plants to cyanobacteria. The survival of Antarctic bryophytes under ozone depletion depends on their ability to acclimate to increasing UV-B radiation by employing photoprotective mechanisms to avoid or repair UV-B damage. UV-B absorbing pigments are widespread across the plant kingdom, due to their ability to absorb biologically damaging UV-B radiation while transmitting essential photosynthetically active radiation. A meta analysis of field studies revealed that the most striking and consistent response of plants to increased UV-B radiation was an increase in UV-B absorbing pigments, on average by 10% (Searles et al., 2001). A similar study of Arctic plants also showed increases in UV-B screening or radical scavenging compounds as the major response to increasing UV-B radiation (Dormann and Woodin, 2002). However, high latitude, southern hemisphere vascular plants do not show such consistent accumulation of UV-B absorbing compounds (Day et al., 2001; Giordano et al., 2003). The accumulation of UV-B absorbing pigments could be particularly useful in polar and alpine bryophytes, since when such plants are physiologically inactive during desiccation or freezing, passive screens would provide more effective protection from UV-B damage than repair mechanisms which require an active metabolism (Cockell and Knowland, 1999). The primary UV-B-absorbing pigments found in higher plants are flavonoid compounds, providing a broad UV-B screen (Swain, 1976). UV-B-absorbing pigments such as flavonoids are wavelength-selective UV-B screens, which can accumulate rapidly in response to high UV-B radiation levels (Caldwell et al., 1983). In addition to their UV-B-absorbing properties, some flavonoids (e.g. quercetin and kaempferol) with additional hydroxyl groups are thought to function as antioxidants, thus
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protecting plants against oxidative damage (Bornmann et al., 1997) (Figure 4). Accumulation in higher plants is primarily in the epidermis, screening physiologically important molecules below (Robberecht and Caldwell, 1978; Tevini et al., 1991; Vogt et al., 1991; Lois, 1994; Cuadra and Harborne, 1996; Bjerke et al., 2002; Buffoni-Hall et al., 2002). The accumulation of UV-B-absorbing pigments would be particularly useful in Antarctic plants because such passive screens could protect them from UV-B damage when physiological inactivity, due to desiccation or freezing, renders active repair mechanisms unavailable (Lovelock et al., 1995a, Lovelock et al., 1995b). UV-absorbing compounds have been investigated in a number of Antarctic terrestrial species from cyanobacteria to terrestrial plants. In general, cyanobacteria are protected by mycosporine-like amino acids (MAAs) and scytonemins, while terrestrial plants contain flavonoids (Rozema et al., 2002). Flavonoids are important UV-B absorbing pigments, which can be induced within hours in response to UV-B radiation, and are ubiquitous in higher plants (Cooper- Driver and Bhattacharya, 1998). They have been extracted from about half of the bryophyte species examined (Markham, 1990). Flavonoids from herbarium specimens of Antarctic Bryum argenteum were also shown to correlate with historical ozone levels suggesting the possibility that these were actively induced UV-B screens (Markham 1990). Recently, high concentrations of UV-B absorbing pigments have also been reported in two Antarctic mosses, Sanionia uncinata and Andreaea regularis, and one liverwort, Cephaloziella varians, with positive correlations between pigment accumulation and flux of natural solar UV-B radiation (Newsham et al., 2002, 2005; Newsham, 2003). Conversely, UV-B absorbing pigments decreased or showed no change in response to elevated UV-B levels in seven European, Arctic and South American moss species (Barsig et al., 1998; Gehrke, 1998, 1999; Searles et al., 1999; Niemi et al., 2002 a, b).
Kaempferol
Quercetin Figure 4. Molecular structure of kaempferol (above) and quercetin (below) found in some terrestrial and aquatic higher plants.
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As a result of these studies, it has been suggested that mosses are less likely to synthesize UV-B absorbing pigments than other plant groups and are potentially more vulnerable as a functional type (Gwynn-Jones et al., 1999). Although relatively few mosses have been studied, negative effects of UV radiation on moss growth and morphology have been reported for some high latitude species (Sonesson et al., 1996; Searles et al., 1999, 2002; Robson et al., 2003, Robinson et al., 2005). In many species, flavonoid synthesis is stimulated by exposure to UV-B radiation (Tevini et al. 1981; Staaij et al. 1995), which seems to act at the gene level by increasing the expression of the enzymes of the phenylpropanoid pathway (Hahlbrock et al. 1989; Kubasek et al. 1992) such as Chs, which encodes the enzyme chalcone synthase, and phenylalanine ammonia lyase (PAL). Lichens are exposed to the highest irradiance levels when desiccated (Lange et al. 1999), and in this state, active repair cannot take place. Therefore, lichens are probably more dependent on UV-B protection by screening compounds than the homeohydric plants. UVprotection in lichens has been tentatively ascribed to secondary compounds, also called lichen compounds (Fahselt 1994; Rikkinen 1995; Huneck 1999), a heterogeneous group of fungal compounds with varying biosynthetic pathways (Huneck and Yoshimura 1996). Most lichen compounds absorb strongly in the UV, and some, such as parietin, additionally absorb photosynthetically active radiation (PAR) (Solhaug et al. 2003; Hill and Woolhouse 1966). The widely distributed and common compounds parietin, atranorin, usnic acid, as well as the structurally less known fungal melanins, are cortical pigments, forming a screen above the photobiont. Most other compounds are located in the photobiont layer within the upper part of the medulla (Fahselt and Alstrup 1997). The cortical lichen compounds in particular have a strong potential to protect the photobiont in lichens against adverse effects of UV-B radiation (Dietz et al. 2000) found that pigmentation of the cortex, rather than changes in reflectance and cortex thickness was the most important factor determining percent transmitted PAR in nine investigated lichen species.
6. PROTECTION FROM UV-B INDUCED DNA DAMAGE IN THE DESICCATED STATE Although tolerance of solar radiation and either drought stress or desiccation are associated in many plants. Bryophytes are protected from UV-B induced DNA damage in the desiccated state and since a previous study had shown that lichen thalli accumulate more damage when desiccated (Buffoni-Hall et al. 2003). Desiccation tolerant mosses and lichens can often tolerate exposure to both high PAR and UV-B (Seel et al. 1992a; Seel et al. 1992b; Tákacs et al. 1999; Heber et al. 2000) and this tolerance can manifest differentially in the hydrated and desiccated state. For example, the photosynthetic apparatus of the desiccation tolerant moss species, Tortula ruralis, is more tolerant of photoinhibition when the moss is desiccated than when it is hydrated, but even when hydrated this species was able to tolerate elevated UV-B for 8 days with no significant decline in Fv/Fm (Tákacs et al. 1999). In Antarctic mosses the tolerance to UV-B induced DNA damage, and the extent to which desiccation is protective, fits with the degree of desiccation tolerance and hence the hydrological habitat of each species (Robinson et al. 2000; Wasley et al. 2006), as well as with its relative accumulation of UV-B absorbing compounds (Lovelock and Robinson 2002;
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Dunn and Robinson 2006; Clarke and Robinson 2008). The fact that these mosses are so well protected when dry is suggestive of passive protection, as enzymatic repair processes are unlikely to be active in desiccated organisms (Buffoni-Hall et al. 2003). Passive protection mechanisms would also be effective when these mosses are frozen and could thus be particularly beneficial to polar and alpine plants. Protection from UV-B when desiccated could be due to morphological changes upon drying, which reduce light levels in the cell. Desiccation tolerant plants typically reduce exposed leaf area when dry by folding or curling of leaves (Davey and Ellis-Evans 1996; Proctor and Tuba 2002). This reduces transmission of PAR into the cell by between 40-60% in a range of moss species including B. pseudotriquetrum and T. ruralis (Seel et al. 1992a). UV-B is likely to be similarly reduced which would contribute considerable protection at the molecular level. Based on relative turf densities, desiccation of these three mosses results in reductions in size ranging from 25% in S. antarctici to 40 to 50% in B. pseudotriquetrum and C. purpureus respectively (Wasley et al. 2006). When moss cells shrink upon desiccation, cytoplasm volume is reduced, concentrating cellular contents including UV-B screening compounds and possibly increasing the attenuation of UV-B. In most ecosystems, periods of high insolation (and associated UVB stress) cause desiccation in bryophytes as they equilibrate leaf turgor with that of their surroundings (Gehrke 1999). The reverse is true in the Antarctic environment however, where the major water source is snow-melt, which is maximal during periods of high insolation, and can coincide with elevated UV-B as a result of ozone depletion. Thus if desiccation is a major strategy for protection from UV-B these plants may still be at risk from high UV-B during ozone depletion, especially when this coincides with spring melt.
7. DNA DAMAGE BY UV-B RADIATIONS AND REPAIR MECHANISM DNA is the primary cellular target of UV-B radiation. DNA strongly absorbs UV-C and UV-B regions of the spectrum, with the peak absorption for around 260 nm and the maximum absorption of DNA in intact plants near 280 nm (Quaite et al. 1992). Longer wavelengths (UV-A, 315-400 nm) play a role in the formation of lesions, although to a lesser extent (Quaite et al. 1992). UV-B-induced DNA damage can be classified into two major categories: cyclobutane pyrimidine dimers (CPDs), which make up approximately 75% of the damage and pyrimidine-(6-4)-pyrimidinone photoproducts [(6-4) photoproducts], constituting the rest (Mitchell et al. 1993) (Figure 5). CPDs are covalently linked to two adjacent pyrimidines on the same DNA strand and are very stable photoproducts unlike the 6-4 photoproducts, which isomerise into Dewar photoproducts in the presence of UV-A radiation (Matsunaga et al. 1993). Both types of dimmers block DNA replication and transcription, and can lead to the death of the cell. CPDs are the most abundant and most cytotoxic lesions but the 6–4PPs have more serious mutagenic effects (Lindahl and Wood 1999, Matsunaga et al. 1993)(Figure 6). UV sources which contains UV-B and UV-A, produce a Dewar isomers since the photoisomerization is most efficient around 320 nm, corresponding to the UV absorption maximum of 6–4PPs. (Taylor et. al. 1990). Both classes of lesions distort the DNA helix. Sequences which promote bending and unwinding at favourable sites for damage formation, e.g., CPDs form at higher yields in single-stranded DNA and at the flexible ends
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of poly (dA)-(dT) tracts, but not in their rigid centre (Becker and Wang 1989, Lyamichev 1991). CPD formation is less when the bending of the DNA is towards the minor groove (Pehrson and Cohen, 1992). One of the transcription factors which have a direct effect on DNA damage formation and repair is the TATA-box binding protein (TBP). TBP induces the selective formation of 6– 4PPs in the TATA-box, where the DNA is bent, but CPDs are formed at the edge of the TATA-box and outside, where the DNA is not bent (Aboussekhra and Thoma, 1999). Every CPD acts as a block to transcription and replication, and only a small fraction of dimers results in a mutation (Britt 1995, 1996). These DNA lesions, if unrepaired, interfere with DNA transcription and replication and leading to misreading of the genetic code and leads to mutations and death. Plants uses two broad strategies to minimise the amount of damage caused by UV-B radiation: decreasing the penetration of UV-B radiation within the tissue and repairing the damage caused by the radiation that succeeded in penetrating into the tissue. One way of decreasing the penetration of UV-B radiation in the tissue is by the accumulation of UV-absorbing pigments, as described in the previous section. Evidence that UV-absorbing pigments are important for the protection of the DNA come from various studies in which plants that are genetically deficient in these pigments were shown to be much more sensitive to UV-induced DNA damage than their respective wild types (Li et al. 1993; Stapleton et al. 1994).
Figure 5. Formation of the UV-induced CPD and 6,4 photoproducts (ncbi.nlm.nih.gov).
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Figure 6. Formation of the UV-induced second most frequently occurring 6–4 photoproducts and their Dewar valence isomers. 6–4 photoproducts are formed at 5_-T–C-3_, 5_-C–C-3_, 5_-T–T-3_ but not at 5_-C–T-3_ sites in DNA (cosmobiousa.com).
7.1. DNA Repair Mechanisms The accurate transmission of genetic information from one cell to its daughters is the key for the survival of organisms. This key transmission requires (i) extreme accuracy in replication of DNA and precision in chromosome distribution, and (ii) the ability to survive spontaneous and induced DNA damage while minimizing the number of heritable mutations (Zhou and Elledge 2000). To achieve this goal organisms have developed efficient DNA repair mechanisms in order to minimise the lethal effects of DNA lesions. Specialized repair proteins plays important role. These specialized proteins scan the genome continuously for the presence of DNA lesions. Lesion recognition protein finds a mismatched base, if any, an apurinic or apyrimidinic site, or structurally altered bases, it triggers an efficient DNA repair, which ultimately leads to the restoration of the genetic information (Carell and Epple 1998).
7.2. Photo Reactivation This is one of the simplest and oldest repair systems consisting of a single enzyme: photolyase. DNA lesions formed by UV, many organisms containing the photolyase enzyme which specifically binds to CPDs (CPD photolyase) or 6– 4PPs (6–4 photolyase) reverses the damage using the energy of light, a process known as photo reactivation (Figure 7. and Figure 8) (Sancar 1994, 1996, Kim et. al. 1994, Todo et. al.1997, Thoma 1999). CPD photolyases have been reported in bacteria, fungi, plants, invertebrates and many vertebrates. DNA photolyases are found in a number of archaebacteria, they are considered to be ancient repair proteins, which have helped in the evolution of life on Earth (Carell and Epple 1998). DNA photolyases are monomeric flavin-dependent repair enzymes with a molecular weight of between 50 and 65 kDa. Ten to twenty enzyme molecules are believed to scan the genome for UV lesions in every cell nucleus. DNA photolyases consists of two chromophores. One of the chromophores (which can be either 5,10-methenyltetrahydrofolate or 8-hydroxy-5-
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deazariboflavin, with absorption maxima of 380 and 440 nm, respectively) is a lightharvesting antenna absorbing the blue-light photon and transfers excitation energy to the active (catalytic) cofactor, which is invariably a two electron- reduced flavin–adenine dinucleotide (FADH). Flavin in the excited state donates an electron to the CPD, splitting the cyclobutane ring, and the electron is transferred back to the flavin concomitantly with the generation of the two canonical bases (Thoma 1999). CPD photolyases recognize CPDs with a selectivity similar to that of sequence specific DNA-binding proteins, which suggests that they could compete with histones for DNA accessibility in a manner similar to transcription factors (Sancar et. al.1987). Once photolyase binds to CPD, the efficiency of photo reactivation is extremely high: approximately one dimer split for every blue-light photon absorbed (Britt 1996). Although the general light-driven splitting mechanism of photo reactivation is well understood, a number of aspects of the repair process remain obscure such as (i) how repair enzymes recognize single DNA lesions with high precision in a structurally heterogeneous mega base prokaryotic or even chromatin-containing eukaryotic genome, (Roberts 1995, Reinisch et. al. 1995, Nelson and Bestor 1996) (ii) how the initial reduction of FAD to FADH takes place.
Figure 7. Formation of the most toxic and mutagenic DNA lesion, cyclobutane–pyrimidine dimers by UV radiation. Dimers can form between two adjacent pyrimidines and their photoreactivation by the enzyme photolyase in the presence of light.
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Figure 8. Repair of pyrimidine dimers with photolyase. Energy derived from absorbed light is used to reverse the photoreaction that caused the lesion. The two chromophores methenyltetrahydrofolylpolyglutamate (MTHFpolyGlu) and FADH_, perform complementary functions. On binding of photolyase to a pyrimidine dimer, repair proceeds as follows (Principles of Lehninger fourth edition). 1 A blue-light photon (300 to 500 nm wavelength) is absorbed by the MTHFpolyGlu, which functions as a photoantenna. 2 The excitation energy passes to FADH_ in the active site of the enzyme. 3 The excited flavin (*FADH_) donates an electron to the pyrimidine dimer (shown here in a simplified representation) to generate an unstable dimer radical. 4 Electronic rearrangement restores the monomeric pyrimidines, and 5 the electron is transferred back to the flavin radical to regenerate FADH.
Based on site-directed mutagenesis (Heelis et. al.1990, Li et. al.1991) and EPR investigations (Essenmacher et. al. 1993) it was suggested that the formation of FADH_ results from a temporary photo-reduction and requires an electron transfer from a distant tryptophan to the light-excited FAD radical quartet state. In addition, by using time-resolved absorption spectroscopy it has been shown in E. coli DNA photolyase that the excited FAD radical abstracts an electron from a nearby tryptophan in 30 ps. After subsequent electron transfer along a chain of three tryptophans, the most remote tryptophan (as a cation radical) releases a proton to the solvent in about 300 ns, showing that electron transfer occurs before
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proton dissociation (Aubert et. al 2000). A similar process may take place in photolyase-like blue-light receptors, (iii) how the enzymes mediate the energy and electron transfer processes in order to achieve repair with almost maximal efficiency (quantum yield = 0.7–0.9), and (iv) in view of the lack of any knowledge of how photolyases recognize their substrate, the different cleavage rates observed for dimers possessing different configurations and constitutions remain obscure (Kim et. al 1993).
CONCLUSION Climate change has already impacted on Antarctic plants. Temperature changes in Antarctic have led to changes in the distribution of native plants. The current levels of UV-B have been shown to reduce growth of the plant species, suggesting that ozone depletion may be having a negative effect on these plants. Although negative effects of UV-B are ameliorated by UV-screening compounds in many Antarctic plants. Comprehensive predictions are complicated by both the lack of certainty in the prediction of changes to abiotic variables, and by the lack of long-term studies investigating recent changes to the flora. The effects of UV-B radiation on DNA damage and repair in natural environments are not known clearly as yet and require further research. Furthermore, lichens are usually regarded as individuals, although they are a symbiotic entity involving at least two partners. The high resilience of desiccated mosses to DNA damage suggests that passive screening maybe more important than repair in these species. Further investigations are required on the effects of UV-B radiation on the DNA of the single symbiotic partners in order to assess whether the fungus constitutes an effective shield protecting the photobiont against DNA damage.
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Mitchell DL, Karentz D, (1993) The induction and repair of DNA photodamage in the environment In: Young, AR, Björn, LO, Moan, J, Nultsch, W, (eds), Environmental UV photobiology. Plenum Press, New York, pp. 345-377. NASA (2002) Total Ozone Mapping Spectrophotometer. http://toms.gsfc.nasa.gov/ Nelson H. C. M and Bestor T. H, (1996) Base eversin and shuffling by DNA methyltransferases, Chem. Biol. 3, 419–423. Newsham K (2003) UV-B radiation arising from stratospheric ozone depletion influences the pigmentation of the moss Andreaea regularis. Oecologia, 135, 327-331. Newsham K, Hodgson D, Murray A. et al. (2002) Response of two Antarctic bryophytes to stratospheric ozone depletion. Global Change Biology, 8, 972-983. Newsham KK, Geissler P, Nicolson M. et al. (2005) Sequential reduction of UV-B radiation in the field alters the pigmentation of an Antarctic leafy liverwort. Environmental and Experimental Botany, 54, 22-32. Niemi R, Martikainen P, Silvola J. et al. (2002a) Responses of two Sphagnum moss species and Eriophorum vaginatum to enhanced UV-B in a summer of low UV intensity. New Phytologist, 156, 509-515. Niemi R, Martikainen P, Silvola J. et al. (2002b) Elevated UV-B radiation 680 alters fluxes of methane and carbon dioxide in peatland microcosms. Global Change Biology, 8, 361371. Olsson LC, Veit M, Weissenbök G, Bornman JF, (1998). Differential flavonoid response to enhanced UV-B radiation in Brassica napus. Phytochemistry, 49: 1021-1028. Onofri S (1999) Antarctic microfungi. In: Seckbach J (ed) Enigmatic microorganisms and life in extreme environments. Kluwer Academic publishers, Dordrecht, Boston, London, pp 323–336. Øvstedal DO, Lewis Smith RI (2001) Lichens of Antarctica and South Georgia. In: Øvstedal DO, Lewis Smith RI (eds) A guide to their identification and ecology. Studies in Polar Research, University of Cambridge, pp 4–5. Pehrson J. R and Cohen L. H (1992) Effects of DNA looping on pyrimidine dimer formation, Nucleic Acid Res. 20, 1321–1324. Pickard J, Seppelt RD (1984) Phytogeography of Antarctica. Journal of Biogeography, 11, 83–102. Proctor MCF, Tuba Z (2002) Poikilohydry and homiohydry: antithesis or spectrum of possibilities. New Phytologist 156, 327-349. Quaite FE, Sutherland BM, Sutherland JC (1992). Action spectrum for DNA damage in alfalfa lowers predicted impact of ozone depletion. Nature, 358: 576-578. Reinisch K. M., Chen L, Verdine G. L and Lipscomb W. N (1995) The crystal structure of HaeIII methyltransferase covalently complexed to DNA: an extrahelical cytosine and rearranged base pairing, Cell, 82, 143–153. Richardson DHS (1981) The Biology of Mosses. Blackwell Scientific Publication, Oxford. Rikkinen J (1995) What‘s behind the pretty colours? A study on the photobiology of lichens. Bryobrothera 4:1–239. Robberecht R, Caldwell MM (1978) Leaf epidermal transmittance of ultraviolet radiation and its implications for plant sensitivity to ultraviolet-radiation induced injury. Oecologia, 32, 277–287. Roberts R. J On base flipping, Cell, (1995), 82, 9–12.
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Robinson SA, Turnbull JD and Lovelock CE (2005) Impact of changes in natural ultraviolet radiation on pigment composition, physiological and morphological characteristics of the Antarctic moss, Grimmia antarctici. Global Change Biology, 11, 476-489. Robinson SA, Wasley J, Popp M, Lovelock CE (2000) Desiccation tolerance of three moss species from continental Antarctica. Australian Journal of Plant Physiology 27, 379-388. Robinson SA, Wasley J, Tobin AK (2003) Living on the edge –plants and global change in continental and maritime Antarctica. Global Change Biology, 9, 1681–1717. Robson TM, Pancotto VA, Flint SD et al. (2003) Six years of solar UV-B manipulations affect growth of Sphagnum and vascular plants in a Tierra del Fuego peatland. New Phytologist, 160, 379-389. Roy CR, Gies HP, Tomlinson DW (1994) Effects of ozone depletion on the ultraviolet radiation environment at the Australian stations in Antarctica. Ultraviolet radiation in Antartica: measurements and biological effects. Antarctic Research Series, 62, 1–15. Rozema J, Bjorn L, Bornman J et al. (2002) The role of UV-B radiation in aquatic and terrestrial ecosystems – an experimental and functional analysis of the evolution of UVabsorbing compounds. Journal of Photochemistry and Photobiology B: Biology, 66, 2-12. Rozema J, Staaij Jvd, Bjorn LO et al. (1997) UV-B as an environmental factor in plant life: stress and regulation. Trends in Ecology and Evolutionary Science, 12, 22–28. Ryan KG, Ewald EE, Swinny E, Markham KR, Winefield C, (2002). Flavonoid gene expression and UV photoprotection in transgenic and mutant Petunia leaves, Phytochemistry, 59: 23-32. Salisbury FB (1984) Light conditions and plant growth under snow. In: The Winter Ecology of Small Mammals (ed. Meritt JF), Carnegie Museum of Natural History, Pittsburg. Sancar G. B, Smith F. W, Reid R, Payne G, Levy M and Sancar A (1987). Action mechanism of Escherichia coli DNA photolyase.I. Formation of the enzyme-substrate complex, J. Biol. Chem. 262, 478–485. Sancar, No ―end of history‖ for photolyases, Science, (1996), 272, 48–49. Sancar, Structure and function of DNA photolyase, Biochemistry, (1994), 33, 2–9. Searles P, Flint S and Caldwell M (2001) A meta-analysis of plant field studies simulating stratospheric ozone depletion. Oecologia, 127, 1-10. Searles PS, Flint SD, Diaz SB. et al. (2002) Plant response to solar ultraviolet-B radiation in a southern South American Sphagnum peatland. Journal of Ecology, 90, 704-713. Searles PS, Flint SD, Diaz SB.et al. (1999) Solar ultraviolet-B 705 radiation influence on Sphagnum bog and Carex fen ecosystems: first field season findings in Tierra del Fuego, Argentina. Global Change Biology, 5, 225-234. Seel WE, Baker NR, Lee JA (1992a) Analysis of the decrease in photosynthesis on desiccation of mosses from xeric and hydric environments. Physiologia Plantarum 86, 451- 458. Seel WE, Hendry GAF, Lee JA (1992b) The combined effects of desiccation and irradiance on mosses from xeric and hydric habitats. Journal of Experimental Botany 43, 10231030. Selkirk PM, Seppelt RD (1987) Species distribution within a moss bed in Greater Antarctica. Symposium Biologica Hungary, 25, 279–284. Solhaug KA, Gauslaa Y, Nybakken L, Bilger W (2003) UVinduction of sun-screening pigments in lichens. New Phytol. 158:91–100.
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In: Antarctica: The Most Interactive Ice-Air-Ocean Environment ISBN: 978-1-61122-815-1 Editors: Jaswant Singh, H.N. Dutta © 2011 Nova Science Publishers, Inc.
Chapter 6
ANTARCTIC MOSSES, LIMITING FACTORS AND THEIR DISTRIBUTION Rudra P. Singh and Jaswant Singh* ABSTRACT Antarctica is an unique, southern most continent and is known for extreme cold conditions. The life on this continent is very difficult, only some of the micro flora and specialized fauna are surviving here due to natural acclimatization and survival mechanisms. The lichens are dominant flora of Antarctica followed by mosses, algae and fungi. The Antarctic climatic conditions such as lowest temperature, precipitation, high wind speeds and UV-B radiations influences the Antarctic life. Mosses are the important cryptogamic plants, poikilohydric in nature and adapted strategies for survival. About 250 species of mosses were recorded from Antarctica (sub-Antarctic, maritime Antarctic and continental Antarctic) while the number of aquatic mosses is just 16. The most favorable habitats of the maritime Antarctic is dominated by cryptogamic communities of carpet and turf-forming mosses. Antarctic bryophytes responds rapidly to ozone dependent increase in solar UV-B by synthesizing UV-B screening pigments and carotenoids in tissues and the pigmentation provides protection from potentially deleterious effects of UV-B radiation.
Keywords: Antarctica, Aquatic mosses, Bryophytes, Terrestrial mosses.
INTRODUCTION In Antarctica only cold adapted plants and animals survive, such as Penguins, seals, many types of lichen, moss and algae. The bryophytes, because of their poikilohydric nature and alternative strategy of adaption, are one of the very few plant groups which grow in *
E-mail:
[email protected], Mobile +919415717168 Department of Environmental Sciences, Dr. R M L. Avadh University, Faizabad-224001, U.P., India
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Antarctica. As such, their role in habitat modification, nutrient cycling, primary production and providing shelter and security to associated invertebrate animals assume a particular significance, Incidentally, barring just two species of vascular plants, viz. Deschampsia antaractica, a grass belonging to family Poaceae, and Colobanthus quitensis, a pearlwort of family Caryophyllaceae reported to be occurring in Antarctica (Seppelt and Broadly, 1988). Other groups of plant recorded from the icy continent include lichens, fungi, algae and bacteria. Thus the Antarctic continent, with its off-lying Islands, is unique in being the only major landmass almost entirely vegetated by cryptogams, with the lichens predominating in drier, more exposed situations, while the bryophytes dominant in the more sheltered and moister habitats. The Antarctic flora in general is impoverished due to both, harsh environment and isolation of the continent because of vast, cold and turbulent oceanic barrier of the southern sea. Various biogeographical schemes have been suggested as a means of classifying Antarctic terrestrial environment but there is currently a general recognition of three biogeographical zones within the Antarctic as a whole, the sub-, maritime and continental Antarctic (Smith, 1984; Longton, 1988). The sub-Antarctic zone includes isolated Islands and archipelagos at high latitudes in the Southern Ocean. Most, with the exception of South Georgia, Heard and McDonald Islands are close to or north of the oceanic Polar Frontal Zone. These Islands are under strong maritime influence, which limits and buffers temperature variation year round, as they are not normally impacted by pack or fast ice. The Maritime Antarctic is also a region under strong Maritime influence from the Southern Ocean, in this case with the influence being more seasonal in nature and limited to the short Antarctic summer period. It includes the western coast of the Antarctic Peninsula to c. 72 ºS, the South Shetland, South Orkney and South Sandwich Islands, and the isolated Bouvetoya and Peter Ioya. The central mountain spine, eastern coast and the more southern elements of the Antarctic Peninsula are not included, and therefore the term ―Maritime Antarctic‖ does not include all or even a majority of the geological region of West Antarctica. The continental Antarctic is the largest biogeographical zone in terms of area, including all of East Antarctica, the Balleny Islands, and those parts of the Antarctic Peninsula not included in the Maritime Antarctic. By contrast with the other two zones, terrestrial habitats of the continental Antarctic are very limited in extent and more isolated, although they include coastal rocky regions superficially similar to those of the maritime Antarctic. With one exception i.e., formation of the extensive ice-free cold deserts of Victoria Land (Lyons et al., 1997). Air temperature in the continental Antarctic are more extreme than those of the maritime and sub-Antarctic although, as in all zones, microhabitat temperature may be more variable, in particular with snow cover giving protection from winter thermal minima. During the brief summer, absorption of energy by rocks and soil can lead to melting and free water being available even at the most southern ice-free locations. The continental Antarctic bryoflora is characterized by just a few species of bryophytes generally wide distribution belonging to 8-10 genera only, viz. Bryoerythropyllum, Bryum, Cephaloziella, Ceratodon, Dicranella, Didymodon, Grimmia, Plagiothecium, Pottia and Sarconeurum. Bryum is the luxirount growing moss genus occurring in Antarctica, because of great phenotypic plasticity exhibited by it in response to extreme environmental conditions, coupled with general lack of sporophytes make this as taxonomically most difficult and confused genus in the continent. Sarconeurum, a monotypic moss genus widely distributed in Antarctica and Southern South Amrica (Green, 1975; Matteri, 1982), shows the southern
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most distribution by any bryophyte, being recorded at 82° 42'S latitude (Wise and Gressit, 1965).
HISTORY OF ANTARCTIC BOTANY Scientific reports only came out when there were scientific expeditions to Antarctica with the aim of exploring not only the marine but the terrestrial environment. Difficulties on land were overwhelming especially because of freezing temperatures and strong winds. Infact, this was a land for adventurers made by laymen, hunters and sailors, who used to send their collections to specialists for identification. Systematic botany was first presented in a study by J. Torrey. He, in 1823, described what appears to the first botanical finding in Antarctica: a new species of Usnea (Lichen). J. Eight was the first scientist to collect the lichens, mosses, sea algae and grasses, between 1829-1830. J.D. Hooker carried out collection on the newly discovered Cock burn Island, close to Trinity Peninsula, in 1843, while participating in Ross‘s Antarctic Expedition and the results were published by Wilson and Hooker, (1847). After J.D. Hooker‘s expedition, new collections in Antarctica were carried out by E. Racowitza, a botanist who included 15 species and two varieties of mosses, described by Cardot (1900-1901), and three species of liverwort on the west coast of the Antarctic Peninsula, which were examined by Stphani, (1901). Fenton and Smith, (1982) described the ecology of the tall turf- forming mosses and their distributions over Signy Island and South Orkney Island. The genetic diversity, mutagenesis and dispersal of Antarctic mosses were well documented in the review of Skotnicki et al., (2000). Recently biologist and botanist are participating in the expedition from all over world and making excellent contributions in the floral biodiversity of icy continent.
ANTARCTIC BRYOPHYTES AND THEIR DISTRIBUTION The cryptogrammic plants are the main Antarctic flora which survives under harsh environmental conditions. Bednarek-Ochyra et al., (2000) and Lewis Smith, (1984), reported that most of the mosses are distributed in maritime Antarctic, and continental Antarctic. Maritime Antarctic (North) have maximum moss species (100-115 species) and are dispersed under South Sandwich Island, South Orkney Island, South Shetland, west coast of Antarctic Peninsula to 65 0S, North coast of Peninsula to 65 0S while in the South maritime Antarctic have 40-50 species of mosses, dispersed on west coast of Antarctic Peninsula and offshore Islands from 68 0S to c. 72 0S and east coast of Antarctic peninsula from 65 0S. Continental Antarctic (coastal and slope areas) recorded 20-30 species of mosses and are distributed over eastern Antarctica and western south of 72 0S. Latter on Convey, (2006) reported current Antarctic biodiversity knowledge under three biogeographical zones of Antarctica, the maximum 250 moss species were reported from sub-Antactic zone, while 100 from maritime and 25 from continental Antarctic zone. The bryophyte found in Antarctica, can be subdivided in to two big taxonomic groups: the Hepaticae, 27 species and the Mosses (Musci) of which there are at least 100-110 species (Putzke and Pereira, 2001). The distribution of Antarctic bryophytes are as follows.
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Amblystegiaceae
Campyliadelphus polygamus (B.S.G.) Kanda [ syn: Compylium polygamus (schimp. In B.S. and G.) lange in g. Jens]- South Shetland Island Orthotheciella varia (Hedw.) Ochyra [ syn: Amblystegium subvarium Broth].Bipolar Sanionia uncinata (Hedw.) Loeske with S. uncinata (Hedw.) Loeske var. georgicouncinata (C. muell) Putzke and Pereira C.N. – Bipolar, found in all main Island Warnstorfia laculosa (C. Muell.) Ochyra and Matteri (Calliergidium austrostramineum is syn.)- Circumsubantarctic Warnstorfia sarmentosa (Wahlenb.) Hedenas (Calliergon sarmentosum is syn.)Bipolar
Andreaeaceae
Andreaea acceminata Mitt. Andreaea depressinervis Card. Andreaea gainii Card. – West Antarctic endemic (found in all the main Islands of the South Shetland and in the continent) Andreaea regularis Muell. South temperate and Antarctic (found in all main Island of the south Shetland and in the continent)
Bartramiaceae
Bartramia patens Bird.- Amphiatlantic south temperate Conostomom megellanicum Sull.- American south temperate, south Georgia, south Orkney and south Shetland
Brachytheciaceae
Brachythecium austro-glareosum (C. Muell.) kindb.- continent Brachythecium austro-salebrosum (C. Muell) kindb.- Pan south temperate, South Shetland Island and Antarctic continent Brachythecium glaciale B.S.G. [all collections identified as B. subpilosum (Hook. F. ae wils.) Jaeg probably correspoods to this species]- Bipolar Brachythecium subpilosum (Hook.f. et Wils) Jaeg- South Shetland Island
Bryaceae
Bryum amblyodon G. Muell- Bipolar, South Shetland Island and Antarctic continent
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Bryum argenteum Hedw.- Worldwide, South Shetland Island and Antarctic continent Bryum dichotomum Hedw. Only on Deception Island Bryum orbiculatifolium Card. Et. Borth – Shetland Island Bryum pallescens Schlieich Ex. Schwaegr- Bipolar, South Shetland Island and Antarctic continent Bryum psudotriquetrum (Hedw.) Schwaegr Bryum urbanskyi Broth (probably= Bryum psudotriquetrum)- South Shetland Island Pohlia cruda (Hedw) Lindb.- Bipolar, South Shetland Island and Antarctic continent Pohlia drummondii (C. Muell) A. L. Andrews in Gront [syn: Pohlia inflexa (C. Muell.) wijk. Et. Marg]- Bipolar, South Shetland Island and Antarctic continent Pohlia nutans (Hedw) Lindb- Bipolar, South Shetland Island and Antarctic continent Pohlia wahlenbergii (web. Et Mohr.) Andrews- Bipolar, South Shetland Island
Dicranaceae
Anisothecium cardotii (R. Br. ter.) Ochyra [syn: Dicranella cardotii (R. Brown ter.) Dixon]- South America, Australia and New Zeland, Subantarctic Island (King George Island- For a single locality in Ezeurra Inlet. Anisothecium hookeri (C. Muell.) Broth. [syn: Dicranella hookeri (C.Muell.) Card.]- South Shetland (Only Deception Island) and Antarctica (Victoria Land) need to revised more carefully Chorisodontium caiphyllum (Hook. F. et wills.) Broth.- Southern South America, New Zeland, Antarctic Peninsula and Southern Shetland Island (all the main Island) Kiaeria pumila (Mitt. In Hook. F.) Ochyra – Southern South America, Subantarctic Island and Southern Shetland Island (only in King George Island), Antarctic continent
Ditrichaceae
Campylopus pyriformis (Schulz) Bird- Central Victoria land, Antarctica, in Fumaroles- also in south America (Brazil and Paraguay) and Africa other species were cited to Deception Island Ceratodon antacticus Card.- Widespread Ceratodon grossiretis Card.- Widespread Ceratodon purpureus (Hedw.) Bird.- Widespread (Bipolar) Distichum capillaceum (Hedw.) B.S.G.- Widespread (Bipolar) Ditrichum conicum (Mont.) Mitt.- South America, Subantarctic Island and South Shetland Island (only in Deception Island near Furnaroles) Ditrichum gemmiferum Ochyra and Lewis. Smith- Deception Island Ditrichum hyalinum (Mitt) Kuntze (sin: D. austro-georgicum C. Muell.)- South America, South Shetland (Liringstone and King George Island) and Antarctic continent
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Ditrichum lewis and Smithii Ochyra- America, South Shetland (Liringstone and King George Island) and Antarctic continent.
Encalyptaceae
Encalypta rhaptocarpa Schwaerge (= E. patogonica Broth) Encalypta procera- Antarctic continent
Grammiaceae
Grimmia reflexidens C. Musell Grimmia lawiana J.H. willis and Grimmia plagiopoda are reported but needs revision- South America, east Africa, Bipolar, and Antarctic continent Racomitrium sudeticum (Funck) Bruch and Schimp. In BSG. (syn: R.austrogeorgicum Par.)- Bipolar, South Shetland and Antarctic continent Racomitrium pachydictyon Card. Schistidium amblyophyllum (C. Muell.) Ochyra and Hertel [syn: Schistidium hyalinecuspidatum (C. Muell.) B.G. Bell]- South America, Subantarctic Island and South Shetland Island Schistidium antarctici (Card) L.I. Saviez and Smironova [belongs here all reports of Schistidium opocarpum (Hedw.) B.S.G. to the Antarctica]- Antarctic Endemic Schistidium cupulare (C. Muell) Ochyra- Amphiatlantic, Subantarctic Island and in the South Shetland Island (only in King George Island) Schistidium folcatum (Hook. F. at. Wils) B. Bremer.- Amphiatlantic, Subantarctic Island and in the South Shetland Island (only in King George Island) Schistidium halinae Ochyra.- Livingstone and King George Island (endemic to west Antarctica) Schistidium occultum (C. Muell) Ochyra and Malteri- Southern South America, Antarctic Peninsula, South Shetland Island Schistidium rivulare (Bird) Pobp.- Aquatic, Bipolar, South Shetland Island and Antarctic continent Schistidium steerei Ochyra.- Antarctic endemic known only from the South Shetland Island (martel and Ezeurra Inlets in king George Island) Schistidium urnulacerum (C. Muell.) B.G. Bell- South Georgia and South Shetland Island
Hypnaceae
Hypnum revolutum (mitt) Lindb Platydictya jungermannioides (Bird.) Crum (rare)- only in King George Island
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Meesiaceae
Meesia uliginosa Hedw. (syn: Ceratodon kinggeorgicus Kand)- Bipolar, South Shetland and Antarctic continent
Orthotrichaceae
Muellerialla crassifolia (Hook f. et wils) Dus. Orthotrichum rupestre Schleich. Ex. Schwaegr
Plagiotheciaceae
Plagiothecium ovalifolium Card. Plagiothecium georgieo antarcticum (C. Muell) Kindb (syn: Plagiothecium simonovi Sav. L. jub. and Smirn.)
Polytrichaceae
Notoligotrichum trichodon (Hook f. et. Wils.) G.L. Smith- South America and Antarctica (known only from a single locality on Potter Peninsula, King George Island) Polytrichum alpinum (Hedw) G. L. Smith- Bipolar, South Shetland Island and Antarctic continent Polytrichum strictum Bird (Syn- P. alpestre Hoppe)- Bipolar, South Shetland Island and Antarctic continent Polytrichum juniperinum Hedw- Bipolar, South Shetland Island and Antarctic continent Polytrichum piliferum Hedw- Bipolar, South Shetland Island and Antarctic continent
Pottiaceae
Bryoerythrophyllum recurvirostrum (Hedw.) chem.- Antarctic continent Didymodon gelidus Card- South Shetland Island and Antarctic continent Hennediella heimii (Hedw) Zand [syn: P. hemi (Hedw) Hamp]- Bipolar Hennediella antarctica (Angstz) Ochyra and Matteri (syn: Pottis austoo- georgica Card)- Bipolar, South Shetland Island and Antarctic continent Stegonia latifolia (Schwaegr in Schult) Vent in Broth- Bipolar (extremely rare and only in King George Island). o Syntrichi filaris (C. Muell.) Zand [syn: Tortula filaris (C. Muell) Broth]Amphiatlantic, Subantarctic, South Shetland Island and Antarctic Peninsula
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Syntrichia princeps (De Not.) Mitt. (syn: Tortula princeps De Not)- Bipolar, South Shetland Island and Antarctic continent Syntrichia sacicola (Card) zand (syn: Tortulasaricols Card)- Amphiatlantic, Subantarctic and South Shetland Island Sarconeurum glaciale (C. Mull.) Card et Bryhm- Tierradel Fuego, Antarctic continent and South Shetland Island (only in Deception Island) Sarconeurum tortelloides C.W. Greene
Seligeraceae
Dicranoweisia brevipes (C. Muell) Card [including those reported as D. antarctica (C. Mull) kindb]- Australia (SE), Subantarctic Island, Southern South America, Antarctic Peninsula and Southern Shetland Island Dicranoweisia crispula (Hredw) Midde.- Bipolar, infrequent in the south Shetland Island and Antarctic Peninsula Dicranoweissia grimmiacca (C. Mull.) Broth- Amphiatlantic and Antarctic Peninsula Holodontrium strictum (Hook f. et milts) Ochyra- Southern South America up to equator (Known only from a single locality at filders peninsula King George Islandprobably introduced)
ANTARCTIC AQUATIC MOSSES Bryophytes occurs in a diverse range of terrestrial and in aquatic habitats. Ignatov and Kurbatova, (1990), reviewed the occurrence of aquatic bryophytes, especially in deep lakes in the world and listed about 85 taxa of mosses and liverworts. These aquatic bryophytes, which grow on bottom substrata in lakes and streams, and permanently in submerged conditions, have often been found in high altitude (Light and Smith, 1976) or high latitude regions (Longton, 1988) where the environmental conditions are very severe for macrophytes and aquatic seed plants. In the Antarctic region, 16 taxa of mosses are known as aquatic plants at the bottom of lakes (Table-1). In the maritime Antarctic 6 taxa of mosses have been reported in large number from lakes on Signy Island (Light and Heywood, 1973; Priddle and Dartmall, 1978; Priddle, 1979) and 5 taxa of mosses are known from lakes on Alexander Island (Light and Heywood, 1975). Even in some ice free areas in East-Antarctica, the most severe terrestrial habitat on Earth, 5 taxa of aquatic mosses have been reported (Savich-Lyubitskaya and Smirnova, 1960; Kasper et al., 1982; Seppelt, 1983; Kanda and Iwatsuki, 1989). In the Soya Coast region, 4 taxa of aquatic mosses have been reported by Imura et al., (2003) which are B. pseudotriquetrum (Kanda and Ohtani, 1991), Bryum sp. (Kanda and Mochida, 1992), H. heimii (Kanda and Ohtani, 1991 as Pottia heimii) and Leptobryum sp. (Imura et al., 1992; Kanda and Iwatsuki, 1989 as Dicranella sp.). Most of the work on aquatic mosses are reports on their occurrences in particular lakes, or taxonomical treatments. Only Kanda and Mochida, (1992), discussed the distribution of aquatic mosses at Skarvsnes, one of the ice free areas Soya Coast region in East Antarctica.
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Table 1. Distribution of aquatic mosses in different lakes of Antarctica Aquatic mosses Signy Island Alexander Island East Antarctica Ambrystegium sp. (1) Calliergon sarmentasum (1,2,3) Campylium sp. (1) Drepanocladus sp. (1) Drepanocladus cf. aduncus (1,2) Pohlia nutans (1) Bryum sp. (4) Campylium polygyamum (4) Dicranella sp. (4) Distichium capillaceum (4) Bryum psudotriquetrum (4) (5-12) Bryum sp. (11) Leptobryum sp. (11-16) Henediella heimii (10) Plagiothecium simonowii (17) Plagiothecium georgico-antarcticum (17) (1) Light and Heywood (1973), (2) Priddle (1979), (3) Priddle and Dartmall (1978), (4) Light and Heywood (1975), (5) Savich-Lubitskaya and Smirnova (1959), (6) Savich-Lyubiskaya and Simirnova (1960), (7) Kesper et al., (1982), (8) Seppelt (1983), (9) Kanada and Iwatsuki (1989), (10) Kanda Ohtani (1991), (11) Kanda and Mochida (1992), (12) Imura et al., (1999), (13) Nakanishi (1977), (14) Ochi (1979), (15) Imura et al., (1992), (16) Tewari and Pant (1996), (17) Savich-Lyubitskaya and Smirnova (1964).
The aquatic moss vegetation were found at the bottom of lakes from 2.0 to 14.5m in depth, and were most vigorous from 3 to 5m. In shallow areas, less than 2m in depth, moss vegetation were not found, probably due to ice action, there were only fragments of algal mats. Bodin and Nauwerck, (1968), noted that ice movement in summer is the main reason to explain the absence of aquatic moss colonies in the shallow water zone down to about 2m depth. The deepest record of aquatic mosses in the east Antarctica is 32.3m, where P. georgicoantarcticum was found in lake Glubokoye, Schirmacher Oasis, Dronning Maud Land (Savich-Lyubitskaya and Smirnova, 1964).
SURVIVAL OF MOSSES AND LIMITING FACTORS Antarctic harsh environmental conditions causes difficulties for survival of flora and only about 2% of continental Antarctica is ice-free. Despite these difficulties, Antarctic terrestrial vegetation offers exceptional opportunities for gaining novel insights into both the mechanisms of plant survival under extreme conditions, and plant genetic evolution, especially in response to increased UV irradiation and climate change. These plants also provide a glimpse of the wide scope of adaptation and evolution in pristine habitats once thought to be incompatible with life.
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1. Survival of Mosses under UV-B Radiations The potential biological significance of seasonal ozone depletion is linked with the associated increase in shorter wavelength i. e., UV-B radiation, reaching the Earth‘s surface. During periods of maximum ozone loss (typically October and November, during the austral spring) the intensity of UV-B radiation at ground level is similar to that normally experienced in mid-summer. However, early in the spring, exposed biota may be unable to respond, as they are yet to resume normal physiological activity after winter. The survival of Antarctic bryophytes under UV-B radiations depends on their ability to acclimate to increasing UV-B radiation by employing photoprotective mechanisms to avoid or repair UV-B damage (Jansen et al., 1998). UV-B absorbing pigments are widespread across the plant kingdom, due to their ability to absorb biologically damage UV-B radiation while transmitting essential photosynthetically active radiation (Cockell and Knowland, 1999). A meta analysis of field studies revealed that most striking and consistent response of plants to increased UV-B radiation was an increase in UV-B absorbing pigments, on average by 10% (Searles et al., 2001). The accumulation of UV-B absorbing pigment could be particularly useful in polar and alpine bryophytes, since when such plants are physiologically inactive during desiccation or freezing, passive screens would provide more effective protection from UV-B damage than repair mechanisms which require an active metabolism (Cockell and Knowland, 1999). The primary UV-B absorbing pigments found in higher plants are flavonoid compounds, providing a broad UV-B screen (Swain, 1976). The accumulation of UV-B absorbing pigments would be particularly useful in Antarctic plants because such passive screens could protect them from UV-B damage when physiological inactive, due to desiccation or freezing, renders active repair mechanism unavailable (Lovelock et al., 1995a, b; Cockell and Knowland, 1999). UV-absorbing compounds have been investigated in a number of Antarctic terrestrial species from cynobacteria to terrestrial plants. Flavonoids are important UV-B absorbing pigments, which can be induced within hours in response to UV-B radiation, and are ubiquitous in higher plants (Cooper-Driver and Bhattacharya, 1998). They have also been extracted from about half of the bryophyte species examined (Markham, 1990). Flavonoids from herbarium specimens of Antarctic B. argenteum were also shown to correlate with historical ozone levels suggesting the possibility that these were actively induced UV-B screens (Markham, 1990). Recently, high concentrations of UV-B absorbing pigments have also been reported in two Antarctic mosses, S. uncinata and A. regularis, and one liverwort, C. varians, with positive correlations between pigment accumulation and flux of normal solar UV-B radiation (Gehrke, 1998, 1999; Searles et al., 1999; Niemi et al., 2002 a, b). As a result of these studies, it has been suggested that mosses are less likely to synthesize UV-B absorbing pigments than other plant group and are potentially more vulnerable as a functional type (Gwynn-Jones et al., 1999). Although relatively few mosses have been studied, negative effects of UV radiation on moss growth and morphology have been reported for some high latitude species (Sonesson et al., 1996; Searles et al., 1999, 2002; Robson et al., 2003; Robinson et al., 2005). In many species, flavonoid synthesis is stimulated by exposure to UV-B radiation (Tevini et al., 1981; van de Staaij et al., 1995; Olsson et al., 1998), which seems to act at the gene level by increasing the expression of the enzymes of the phenylpropanoid pathway (Hahlbrock et al., 1989; Kubasek
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et al., 1992) such as Chs, which encodes the enzyme chalcone synthase, and phenylalanine ammonia lyase (PAL).
2. Low Temperature and Photosynthesis in Antarctic Mosses Antarctic and sub-Antarctic photosynthetic autotrophs maintain photosynthesis at low temperatures, with some being active well below 0ºC. Prevailing low temperatures throughout the Antarctic biome are generally considered to limit net photosynthesis (Pn) for most of the growing season (Xiong et al., 1999). However, photosynthetic organs can reach relatively high temperatures and show much greater fluctuations than seen in diurnal air temperature, e.g. +20°C above ambient on the continent (Longton, 1974; Melick and Seppelt, 1994). During summer photosynthetic organs often achieve temperatures well above zero and optimum temperatures for photosynthesis are correspondingly higher, rating from 10-12°C in D. antarctica from Signy Islands and the Antarctic Peninsula (Edwards and Smith, 1988; Xiong et al., 1999), 12°C in Poa cookii from Marion Island (Bate and Smith, 1983), 15°C in Pringlea antiscorbutica at Îles Kerguelen (Aubert et al., 1999), 190C in C. quitensis from Signy Island (Edwards and Smith, 1988) and up to 20-25ºC in a variety of maritime moss (S. glaciale, B. argenteum, A. regularis, and A. depressinervis) species (Rastorfer, 1972; Green et al., 1999, 2000; Schroeter et al., 1997; Pannewitz et al., 2003). Some species additionally show plasticity in their optimal temperature. When grown at temperatures above those experienced in the field, the optimal temperature for Drepanocladus uncinatus (now known as S. uncinata) remained at 15 ºC, whilst that for Polytrichum alpestre increased from 5-10 ºC to 15ºC (Collins, 1977). The relative importance of temperature and irradiance to photosynthetic rates varies. In the two Maritime Antarctic vascular plants (D. antarctica and C. quitensis) net photosynthetic rates are negligible at canopy air temperatures greater than 20 ºC, rather than high irradiance responsible for this photosynthetic depression (Xiong et al., 1999). However, it has also been demonstrated for these species that increasing vegetative growth outweighs decreases in photosynthetic rates under 20°C day time temperatures (Xiong et al., 2000).
3. Antarctic Mosses under Changing Water Availability On the Antarctic continent most water is permanently locked up as ice and snow, while large areas are accurately described as frigid desert, receiving very low or no direct precipitation and experiencing chronically low relative humidity. Organisms living here must therefore be able to survive long periods of freezing and consequent drought, year round. In the summer, water may become available from snowmelt and around melt lakes, however, this water supply is transient and repeated freeze thaw events still occur. In the maritime and sub-Antarctic, water is less limiting, although the maritime region experiences extended periods of freezing during winter and rainfall plays a more important role. Throughout the region water availability thus varies spatially and temporally, with large variation occurring from year to year. At a broad scale, levels of tolerance of desiccation therefore vary across the Antarctic biome and among species, with the maritime region supporting some desiccationsensitive species, particularly in hydric habitats (Davey, 1997a,b,c; Robinson et al., 2000;
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Lange and Kappen, 1972). Continental Antarctic bryophytes, whilst less tolerant of increasing aridity than lichens and also have the ability to survive desiccation. Species-specific differences in tolerance of desiccation have been detected for three moss species from the Windmill Islands, East Antarctica (Robinson et al., 2000; Wasley et al., 2006) with two cosmopolitan species (B. pseudotriquetrum, C. purpureus) able to metabolise at lower turf water content than the endemic G. antarctici, and S. antarctici. B. pseudotriquetrum also shows greater plasticity than the other species, with plants from drier sites showing greater tolerance of desiccation that those from wetter sites, in addition to seasonal changes in desiccation tolerance (Robinson et al., 2000; Wasley et al., 2006). The ability to survive repeated desiccation and freezing events is probably related to the high concentrations of soluble carbohydrates found in these species (Melick and Seppelt, 1994) and in particular the presence of compounds such as stachyose and trehalose in B. pseudotriquetrum (Robinson et al., 2000; Wasley et al., 2006). In contrast C. purpureus has a much higher proportion of fatty acids/soluble carbohydrates. All three species have a high proportion of their fatty acids in polyunsaturated forms (> 67%), a feature characteristic of cold tolerant higher plants (Zuñiga et al., 1996; Wasley et al., 2006). Quantifying the relative importance of lipids versus soluble carbohydrates in these freeze tolerant plants stands out as an interesting target for further study, it may be that lipids are a safer storage compound, since soluble carbohydrates are known to leak from bryophytes during desiccation-rehydration and freeze thaw cycles (Melick and Seppelt, 1992). Water is less likely to be limiting in the relatively moist Maritime Antarctic. On Signy Island, whilst some xeric species are occasionally water-limited (Davey, 1997c), more generally photosynthesis is not water-limited (Collins, 1977). When the photosynthetic rates of a range of xeric and hydric species from this Island were compared under laboratory conditions, no difference among habitats was detected (Convey, 1994). Maritime moss (A. regularis, A. depressinervis, P. alpestre, and B. algens) species from a variety of habitats (hydric, mesic, xeric) also experience increased penetration of light into the turf as drying occurs, counteracting at least in the short term the loss of productivity during periods of desiccation (Davey and Rothery, 1996). Water availability has been shown to influence turf and gametophyte morphology in a range of continental and maritime Antarctic mosses (A. regularis, P. alpestre, B. algens, Grimmia lawiana and G. antarctici) and this, in turn, can affect water relations (Nakanishi, 1979). In general, gametophyte shoots are shorter and turf denser in drier sites (Gimingham and Smith, 1971; Wasley, 2004; Wasley et al., 2006). Indeed, the changes in plant morphology and growth patterns that are reported as the norm in many long-term environmental manipulation experiments, often implicitly assumed to relate primarily to temperature increase, may equally well be explained by changes in microclimate humidity and soil moisture. In general, continental Antarctic mosses (G. lawiana, Grimmia plagiopodia, Coscinodon psudocribrosus and C. bolivianus) can survive repeated freeze-thaw events (Melick and Seppelt, 1992), whilst maritime species appears to be less tolerant (Davey, 1997b). The pattern of exposure to freezing is also important - repeated freeze-thaw cycles cause a greater reduction in gross photosynthesis than constant freezing over the same time period (Kennedy, 1993). Tolerance of freeze-thaw events involves interactions with other environmental parameters, in particular that of water availability. For example, desiccation before freezing reduces damage to the photosynthetic apparatus, while protection from freeze-thaw events can be provided by snow cover acting as an insulator (Lovelock et al., 1995a,b).
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Xiong, F. S., Mueller, E. C. and Day, T. A.: Photosynthetic and respiratory acclimation and growth response of Antarctic vascular plants to contrasting temperature regimes, American Journal of Botany, 87, 700-710 (2000). Zuñiga, G. E., Alberdi, M. and Corcuera, L. J.: Non-structural carbohydrates in Deschampsia antarctica Desv. from South Shetland Islands, maritime Antarctic, Environmental and Experimental Botany, 36, 393-398 (1996).
In: Antarctica: The Most Interactive Ice-Air-Ocean Environment ISBN: 978-1-61122-815-1 Editors: Jaswant Singh, H.N. Dutta © 2011 Nova Science Publishers, Inc.
Chapter 7
AFFINITIES OF LICHEN FLORA OF INDIAN SUBCONTINENT VIS-À-VIS ANTARCTIC AND SCHIRMACHER OASIS Dalip K. Upreti* and Sanjeeva Nayaka ABSTRACT Affinities of Indian subcontinent lichen flora with lichens of Antarctic and Schirmacher Oasis are discussed in detail. Out of 439 taxa of lichens known from the Antarctica and South Georgia 76 are similar to Indian subcontinent and 68 with the Schirmacher Oasis, while 18 species are common in both subcontinent and Schirmacher Oasis. The genus Cladonia with 17 species showed the maximum affinities of Antarctic lichens. Most of the Indian subcontinent lichens which exhibited affinities with Antarctica are known mostly from temperate and alpine regions of the subcontinent.
Keywords: Diversity, distribution, similarity, geographical isolation, speciation.
INTRODUCTION Lichens are one of the most widely distributed groups of organisms in the world; exhibit their presence in almost all the habitats available. They have an ability to grow on rock, stones, bark, leaves and various man made substrates including glass plane, iron rods and plastics. The dry and sterile rock surfaces where other group of plants unable to grow, but lichens colonizes successfully on them and flourish. Lichens exhibit broadest range of habitats as they occur both in dry hot and cold desert, from low sea level region to highest mountains. *
Email:
[email protected], Mobile: +919450400264 Lichenology Laboratory, National Botanical Research Institute (NBRI-CSIR), Rana Pratap Marg, Lucknow – 226001, U.P., India
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The Antarctic regions is a well known extreme environment for plant life, as the temperatures are low, there are long periods of frost and snow cover and frequent winds that causes abrasion and evaporation. Lichens, because of their high resistance to freezing and their ability to endure long periods of inactivity in a frozen state, can survive in this environment (Kappen 1973). In the past few decades a large number of lichenological investigations on Antarctic lichens were carried out in different regions of the world, thus resulted a fairly clear picture of the diversity and distribution of lichens in the region. Øvstedal and Smith (2001) provided the detailed diversity and biogeography of the lichen biota in Antarctica. Accordingly, South Georgia which is represented by 194 species of lichen has 47 exclusive species not known from Antarctic biome. The Antarctic Peninsula has greatest diversity of 268 taxa. The South Orkeys and South Shethland Islands are represented by 221 and 211 taxa.
MATERIALS AND METHODS The enumeration of lichens known from different regions of Antarctica and Schirmacher Oasis (SO), East Antarctica are compiled from the investigation provided by Lindsay (1977) and Øvstedal and Smith (2001). The inventory of Indian subcontinent lichens provided by Awasthi (2000) was used for tracing out the affinities of subcontinent lichens with Antarctic lichens. All the information available on lichens of SO in the last five decades is consolidated in Table 1, while Table 2. enumerates the affinities of lichens occurring in Antarctica, Indian subcontinent and SO. Table 1. Occurrence of lichens in Schirmacher Oasis, E. Antarctica (Cr = Crustose, Fo = Foliose, Fr = Fruticose, En = Endemic, Bi = Bipolar, Co = Cosmopolitan) Lichen taxa 1 2 3 4 5
6
7
Growth Form Acarospora. flavocordia Castello and Nimis Cr Cr A. gwynnii C.W. Dodge and E.D. Rudolph Cr A. macrocyclos Vain. Cr A. williamsii Filson Amandinea coniops (Wahlenb.) M. Choisy ex Cr Scheid. - Lecidea coniops Wahenb. - Buellia coniops (Wahlenb.) Th. Fr. A. petermannii (Hue) Matzer, H. Mayerhofer Cr and Scheid. - Lecanora petermanii Hue - Rinodina petermanii (Hue) Darb. - Beltraminia petermannii (Hue) C.W. Dodge A. punctata (Hoffm.) Coppins and Scheid. Cr - Lecidea punctata Hoffm. - Buellia punctata (Hoffm.) A. Massal.
Distribution En En En En Bi
Nayaka Olech and et al 2009 Singh 2010 + + + + + + +
En
+
-
Co
-
+
Affinities of Lichen Flora of Indian Subcontinent… Lichen taxa 8 9
10 11 12 13 14 15 16 17 18 19
20 21 22 23
24 25 26
27 28
29 30
31
Growth Form Cr
Arthonia molendoi (Frauenf.) R. Sant. - Tichothecium molendoi Frauenf. A. rufidula (Hue) D. Hawksw., R. Sant. and Cr Øvstedal - Charcotia rufidula Hue Cr Bacidia johnstonii C.W. Dodge Cr B. stipata I.M. Lamb Cr Buellia darbishirei I.M. Lamb B. frigida Darb. Cr Cr B. grimmiae Filson Cr B. grisea C.W. Dodge and G.E. Baker Cr B. illaetabilis I.M. Lamb. Cr B. lingonoides R. Filson B. pallida Dodge and Baker Cr Cr B. papillata (Sommerf.) Tuck. - Lecidea papillata Sommerf. - Tetramelas papillatus (Sommerf.) Kalb. B. pycnogonoides C.W. Dodge and G.E. Baker Cr Cr B. subfrigida May. Inoue Cr Caloplaca athallina Darb. C. citrina (Hoffm.) Th. Fr. Cr - Verrucaria citrina Hoffm. - Pyrenodesmia mawsonii C.W. Dodge Cr C. frigida Søchting Cr C. lewis-smithii Søchting and Øvstedal C. saxicola (Hoffm.) Nordin Cr - Psora saxicola Hoffm. - Gasparrinia murorum Tornab. Fo Candelaria murrayi Poelt Candelariella flava (C.W. Dodge and G.E. Cr Baker) Castello and Nimis - Huea flava C.W. Dodge and G.E. Baker - C. antarctica R. Filson - C. hallettensis (J.S. Murray) Øvestedal - Protoblastenia citrina C.W. Dodge Cr Carbonea assentiens (Nyl.) Hertel - Lecidea assentiens Nyl. Cr C. vorticosa (Flörke) Hertel - Lecidea sabuletorum var. vorticosa Flörke - L. vorticosa (Flörke) Körb. - L. capsulata C.W. Dodge and G.E. Baker - C. capsulata (C.W. Dodge and G.E. Baker) Hale Cr Lecania cf. racovitzae (Vain.) Darb.
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Distribution Bi
Nayaka Olech and et al 2009 Singh 2010 +
En
-
+
En En En En En En En En En Bi
+ + + + + -
+ + + + + + + + +
En En En Co
+ +
+ + + +
En En Bi
+
+ + +
En En
+
+ +
En
+
-
Bi
+
+
En
-
+
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Dalip K. Upreti and Sanjeeva Nayaka Table 1. (Continued) Lichen taxa
- Lecanora. racovitzae Vain. 32 Lecanora epibryon (Ach.) Ach. - Lichen epibryon Ach. - L. broccha Nyl. 33 L. expectans Darb. 34 L. fuscobrunnea C.W. Dodge and G.E. Baker 35 L. geophila (Th. Fr.) Poelt - Placodium geophillum Räsänen 36 L. cf. mawsonii C.W. Dodge 37 L. mons-nivis Darb. 38 L. orosthea (Ach.) Ach. - Lichen orostheus Ach. 39 L. polytropa (Hoffm.) Rabenh. - Verrucaria polytropa Ehrh. 40 L. sverdrupiana Øvstedal 41 Lecidea andersonii Filson 42 L. auriculata Th. Fr. 43 L. cancriformis C.W. Doge and G.E. Baker - L. phillipsiana R. Filson 44 L. lapicida (Ach.) Ach. - L. lapicida Ach. - L. rupicida Vain. 45 L. cf. placodiiformis Hue 46 Lecidella siplei (C.W. Dodge and G.E. Baker) May Inoue - Lecidea siplei C.W. Dodge and G.E. Baker 47 L. stigmatea (Ach.) Hertel and Leuckret - L. stigmatea Ach. 48 Lepraria cacuminum (A. Massal.) Kümmerl. and Leuckert - Diploicia cacuminum A. Massal. 49 L. neglecta (Nyl.) Erichs. - Lecidea neglecta Nyl. 50 Physcia caesia (Hoffm.) Furner. - Lichen caesius Hoffm. - P. wainioi Räsänen 51 P. dubia (Hoffm.) Lettau - Lobaria dubia Hoffm. 52 Pleopsidium chlorophanum (Wahlenb.) Zopf. - Parmelia chlorophana Wahlenb. - Acarospora chlorophana (Wahlen.) Mass. - Biaterella antarctica J.S. Murray - B. cerebriformis (C.W. Dodge) R. Filson 53 Pseudephebe minuscula (Nyl. Ex Arnold) Brodo and Hawks. - Imbricaria lanata var. minuscula Arnold
Growth Distri- Nayaka Olech and Form bution et al 2009 Singh 2010 Cr
Bi
+
-
Cr Cr Cr
En En Bi
+ + +
+ + +
Cr Cr Cr
En En Bi
+
+ + +
Cr
Bi
+
-
Cr Cr Cr Cr
En En Co En
+ + +
+ + +
Cr
Co
+
-
Cr Cr
En En
+
+ +
Cr
Bi
+
+
Cr
Co
+
+
Cr
Bi
+
-
Fo
Co
+
+
Fo
Co
+
+
Cr
Bi
+
+
Fr
Bi
+
+
Affinities of Lichen Flora of Indian Subcontinent… Lichen taxa
153
Growth Distri- Nayaka Olech and Form bution et al 2009 Singh 2010
- Parmelia minuscule (Nyl. ex Arnold) Nyl. 54 Rhizocarpon geminatum Körb. Cr 55 R. geograhicium (L.) DC Cr - Lichen geographicus L. - R. flavum C.W. Doge and G.E. Baker 56 R. nidificum (Hue) Darb. Cr - Lecidea nidifica Hue 57 Rhizoplaca melanophthalma (Ram.) Leuckert and Cr Poelt - Squamaria melanophthalma Ram. - L. melanophthalma (Ram.) Ram. 58 Rinodina endophragmia I.M. Lamb. Cr 59 R. olivaceobrunnea C.W. Dodge and G.E. Baker Cr 60 Sarcogyne privigna (Ach.) A. Massal Cr - Lecidea privigna Ach. 61 Umbilicaria africana (Jatta) Krog and Swinscow Fo - Gyrophora caplocarpa var. africana Jatta 62 U. antarctica Frey and I.M. Lamb Fo 63 U. aprina Nyl. Fo - Omphalodiscus spongiosus (C.W. Dodge and G.E. Baker) Llano var. subvirginis (Lamb et Frey) Golubk. 64 U. decussata (Vill.) Zahlbr. Fo - Lichen decussatus Vill. - Omphalodiscus decussatus (Vill.) Schol. var. discolor Lynge 65 U. vellea (L.) Ach. Fo - L. velleus L. 66 Usnea antarctica Du. Rietz Fr 67 U. sphacelata R. Br. Fr - U. sulphrea Th. Fr. 68 Xanthoria elegans (Link) Th. Fr. Fo - Lichen elegans Link - Gasparrinia elegans Stein apud Cohn 69 X. mawsonii Dodge Fo
Bi Co
+
+ +
En
+
-
Bi
+
+
Bi Bi Co
+ + +
+ + +
Co
+
+
En Co
+ +
+ +
Bi
+
+
Co
+
-
Co Bi
+ +
+ -
Co
+
+
En
+
+
Table 2. Affinities of Antarctic lichens with Indian subcontinent lichen flora and lichens of SO S. No. 1 2 3 4 5
Antarctica Acarospora badiofusca (Nyl.) Th. Fr. A. flavocordia Castello and Nimis A. gwynnii C.W. Dodge and E.D. Rudolph A. macrocyclos Vain. A. williamsii Filson
India + -
SO + + + +
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Dalip K. Upreti and Sanjeeva Nayaka Table 2. (Continued)
S. No. 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48
Antarctica Amandinea coniops (Wahlenb.) M. Choisy ex Scheid. A. petermannii (Hue) Matzer, H. Mayerhofer and Scheid. A. punctata (Hoffm.) Coppins and Scheid. Arthorhaphis alpina (Schaer.) R. Sant. Arthonia molendoi (Frauenf.) R. Sant. A. rufidula (Hue) D. Hawksw., R. Sant. and Øvstedal Bacidia johnstonii C.W. Dodge B. stipata I.M. Lamb Bryonora castanea (Hepp) Poelt Buellia darbishirei I.M. Lamb B. frigida Darb. B. grimmiae Filson B. grisea C.W. Dodge and G.E. Baker B. illaetabilis I.M. Lamb. B. lingonoides R. Filson B. pallida Dodge and Baker B. papillata (Sommerf.) Tuck. B. pycnogonoides C.W. Dodge and G.E. Baker B. subfrigida May. Inoue Caloplaca athallina Darb. C. cerina (Ehrh. ex Hedw.) Th. Fr. C. citrina (Hoffm.) Th. Fr. C. exsecuta (Nyl.) Dalla Torre C. holocarpa (Hoffm.) Wade C. frigida Søchting C. lewis-smithii Søchting and Øvstedal C. saxicola (Hoffm.) Nordin Candelaria murrayi Poelt Candelariella aurella (Hoffm.) Zahlbr. C. flava (C.W. Dodge and G.E. Baker) Castello and Nimis C. vitellina (Ehrh.) Müll. Arg. Carbonea assentiens (Nyl.) Hertel C. vorticosa (Flörke) Hertel Cetraria aculeata (Schreb.) Fr. C. islandica (L.) Ach. Chrysothrix chlorina (Ach.) J.R. Laundon Cladia aggregate (Sw.) Nyl. Cladonia bellidiflora (Ach.) Schaer C. carneola (Fr.) Fr. C. chlorophaea (Flörke ex Sommerf.) Spreng. C. deformis (L.) Hoffm. C. fimbriata (L.) Fr. C. galindezii Øvstedal
India + + + + + + + + + + + + + + + + + + + + + +
SO + + + + + + + + + + + + + + + + + + + + + + + + + + + -
Affinities of Lichen Flora of Indian Subcontinent… S. No. 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93
Antarctica C. gracilis (L.) Wild. C. mitis Sandst. C. phyllophora Hoffm. C. pleurota (Flörke) Schaer. C. pocillum (Ach.) O.J. Rich. C. pyxidata (L.) Hoffm. C. rangiferina (L.) Webber C. scabriuscula (Delise) Nyl. C. squamosa (Scop.) Hoffm. C. subsubulata Nyl. Collema tenax (Sw.) Nyl. Lecania racovitzae (Vain.) Darb. Lecanora epibryon (Ach.) Ach. L. expectans Darb. L. frustulosa (Dicks.) Ach. L. fuscobrunnea C.W. Dodge and G.E. Baker L. geophila (Th. Fr.) Poelt L. mawsonii C.W. Dodge L. mons-nivis Darb. L. orosthea (Ach.) Ach. L. polytropa (Hoffm.) Rabenh. L. sverdrupiana Øvstedal Lecidea andersonii Filson L. atrobrunnea (Ramond) Schaer. L. auriculata Th. Fr. L. cancriformis C.W. Doge and G.E. Baker L. lapicida (Ach.) Ach. L. placodiiformis Hue Lecidella elaeochroma (Ach.) M. Choisy L. siplei (C.W. Dodge and G.E. Baker) May Inoue L. stigmatea (Ach.) Hertel and Leuckret Lecidoma demissum (Rutstr.) Gotth. Schneid. and Hertel Lepraria cacuminum (A. Massal.) Kümmerl. and Leuckert L. neglecta (Nyl.) Erichs. Leproloma vouaux (Hue) J.R. Laundon Megaspora verrucosa (Ach.) Hafellner and V. Writh Ochrolechia tartarea (L.) A. Massal. Parmelia saxatilis (L.) Ach. P. sulcata Taylor Peltigera didactyla (With.) J.R. Laundon P. rufescens (Weis) Humb. Pertusaria coccodes (Ach.) Nyl. Phaeophyscia endococcina (Körb.) Moberg Phaeorrhiza nimbosa (Fr.) H. Mayrhofer and Poelt Physcia caesia (Hoffm.) Furner.
155 India + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
SO + + + + + + + + + + + + + + + + + + + +
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Dalip K. Upreti and Sanjeeva Nayaka Table 2. (Continued)
S. No. 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126
Antarctica P. dubia (Hoffm.) Lettau Physconia muscigena (Ach.) Poelt Placynthiella icamalea (Ach.) Coppins and P. James Pleopsidium chlorophanum (Wahlenb.) Zopf. Protoparmelia badia (Hoffm.) Hafellner Pseudephebe minuscula (Nyl. Ex Arnold) Brodo and Hawks. Psilolechia lucida (Ach.) M. Choisy Rhizocarpon badioatrum (Flörke ex Spreng.) Th. Fr. R. disporum (Hepp) Müll. Arg. R. geminatum Körb. R. geograhicium (L.) DC R. nidificum (Hue) Darb. R. superficiale (Schaer.) Malme Rhizoplaca melanophthalma (Ram.) Leuckert and Poelt Rinodina endophragmia I.M. Lamb. R. olivaceobrunnea C.W. Dodge and G.E. Baker Sarcogyne privigna (Ach.) A. Massal Sporastatia testudinea (Ach.) A. Massal. Stereocaulon alpinum Laurer Tephromela atra (Huds.) Hafellner ex Kalb Umbilicaria africana (Jatta) Krog and Swinscow U. antarctica Frey and I.M. Lamb U. aprina Nyl. U. decussata (Vill.) Zahlbr. U. krascheninnikovii (Savicz) Zahlbr. U. thamnodes Hue Usnea antarctica Du. Rietz U. sphacelata R. Br. Verrucaria maura Wahlenb. in Ach. V. muralis Ach. Xanthoria candelaria (L.) Th. Fr. X. elegans (Link) Th. Fr. X. mawsonii Dodge
India + + + + + + + + + + + + + + + + + + + + + + + -
SO + + + + + + + + + + + + + + + + +
RESULTS AND DISCUSSION Distribution Pattern of Antarctic Lichens The Antarctic lichens exhibit four categories of their distributional pattern (Rudolph 1967). 1. The Antarctic Peninsula (west coast): Usnea fasciata and Ramalina terebrata shows their similar pattern of distribution in west coast comprising of Antarctic Peninsula,
Affinities of Lichen Flora of Indian Subcontinent…
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South Shetland, South Georgia and outlying of Falkland Islands. Some members of the stipitate and crustose members of lichens also exhibit their restricted distribution in the west coast of the Antarctic Peninsula, South Shetland and South Orkney Islands are Bacidia stipitata, Catilaria corymbosa, Caloplaca regalis, Lecania brialmontii and Rinodina petermanii. The Antarctic Peninsula (west coast) exhibit occurrence of distinctive elements such as Cladonia rangiferina, Cornicularia aculenta, Cystocoleus niger, Himantormia lugubris, Massalengia cornosa, Pannaria hookeri, Parmelia gerlachei, P. ushuaiensis, Pseudophebe pubescens, Sphaerophorus globosus and Stereocaulon glabrum. Most of the species under this category exhibit a strong maritime tendency. 2. The Antarctic Peninsula (east coast): The Antarctic Peninsula possesses a continuous mountainous range of altitudinal variation of 1500 – 2500 m in height. Due to the height of the mountain range the climate divide between two coasts. The west coast has a strong maritime climate with relatively warm, wet winds but the east coast having extensive ice shelf provide a relatively cold, dry winds approaching that of continental Antarctica. Usnea sulphurea and U. fasciata dominates the area. Pseudophebe minuscule also occur in this region. 3. The Antarctic Peninsula Endemic: The stipitate crustose lichen species such as Bacidia stipata, Catilaria corymbosa, Caloplaca regalis, Lecania brialmontii and Rinodina petermanii are restricted to the west coast of the Antarctic Peninsula and South Shetland and South Orkeney Islands and have originated in this region (Lindsay 1975). 4. The Circumpolar Antarctic: Buellia frigida an endemic species of Antarctica and Xanthoria elegans a circumpolar species exhibit their scattered occurrence in this category. Though the Arctic and Antarctic lichens exhibit many similarities in their origins, however, the restricted nature of Antarctic lichen flora show little similarity with the Arctic. Out of the 45 genera of lichens known from the Arctic 20 are also known from the Antarctic. Out of 328 species of lichens recorded from Greenland (Lynge 1937), 47 are found in the Antarctic, while out of the 65 genera listed from the former region 46 are found in the later. The greater number of genera in common between Arctic and Antarctic supports the idea that at one time the polar lichen floras were basically similar, but the geographical isolation, especially that of Antarctica from other southern hemisphere continents, has led to differences through speciation.
Lichen Flora of Schirmacher Oasis, East Antarctica SO is a small ice-free landmass of 35 km2, located in Queen (Dronning) Maud Land area of continental east Antarctica (70.8° S and 11.8° E) and is surrounded by 10 nunataks (Figure 1). Lichens from SO have been collected since the year 1970s and Golubkhova and Simonov (1972) published the first comprehensive list of 21 lichen taxa form the area. Ritcher (1990) provided a list of 25 species of lichens collected by the Russian researchers from this area between the year 1979 and 1984. Further, Ritcher (1995) published a revised list of lichens comprising 26 species including the specimen collected during 1988-89.
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Figure 1. Map showing the location of Schirmacher Oasis and surrounding nunataks.
The National Botanical Research Institute (NBRI-CSIR) Lucknow, was identified by the Ministry of Earth Science, New Delhi as the centre for carrying out lichenological studies in SO in the year 1991. The organization participated for the first time in the 11th Indian Antarctic Expedition (IAE) during the year 1991-92 and reported a total of 26 lichen species (Upreti and Pant 1995, Upreti 1996, 1997). During 17th IAE Pandey and Upreti (2000) listed a total of 19 lichen species collected from the SO and the Vettiya nunatak. Mean while Gupta et al. (1999) of the Botanical Survey of India also collected some lichens form SO during 18th IAE and reported five more species. NBRI continued its participation in the 22nd IAE and more extensively and intensively explored the 31 sites of the whole stretch of SO together with seven nunataks located nearby and listed a total of 35 lichen species (Nayaka and Upreti 2005). The consolidation of published accounts on the SO lichens revealed the occurrence of total of 48 species in the area (Nayaka et al. 2009). Out of the 48 lichen species that occur in SO, 19 are cosmopolitan in distribution. Olech and Singh (2010) during 23rd IAE in 2003-04 made a detailed lichenological survey of the Oasis and reported 57 lichen taxa after adding 22 new addition to the Oasis. The consolidation of all the available lichenological studies revealed the occurrence of 69 species in the SO (Table 1). The species of lichen genus Buellia dominates the area with 10 species, followed by 9 species of Lecanora, 5 species each of Caloplaca and Umbilicaria. The crust forming species dominates the area with 54 species, while only 9 species are foliose, 4 are fruticose and single species of leprose form.
Affinities of Indian Lichen Flora with Lichens of SO and Antarctica Awasthi (2000) listed 2450 species of lichens from the Indian subcontinent. Most of the macrolichens (foliose and fruticose) are more or less fairly well worked out from India. However, some of the microliches (leprose, crustose and squamulose) are still in need of revisionary studies based on the modern concept of different lichen taxa available. In the last few decades a large number of microlichens from India are studied in detail and on the basis of their occurrence and distributional pattern, tentative observations can be made in respect of
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the affinities of the lichen flora of the subcontinent with neighbouring area and other regions including Antarctica. A large number of lichen species of the subcontinent are cosmopolitan in distribution. The eastern Himalayan lichen flora has many species common with the SinoJapanese and south-east Asian regions. Lichen species present in the western Himalayas exhibit a distinct affinity with the lichen flora of northern Europe. Though the Antarctic lichen flora exhibits a more restricted nature, however most of the lichen genera are known from Antarctica is also exhibit their occurrence in other regions of the world including Indian subcontinent. The SO is represented by the following 23 genera of lichens; Acarospora, Amandinea, Arthonia, Bacidia, Buellia, Caloplaca, Candelaria, Carbonea, Lecania, Lecanora, Lecidea, Lecidella, Lepraria, Physcia, Pleopsidium, Pseudophebe, Rhizocarpon, Rahizoplaca, Rinodina, Sarcogyna, Umbilicaria, Usnea and Xanthoria. Except the genus Pseudophebe all the 22 genera know from SO are also know from India and the Indian subcontinent. Out of the 69 species, so far known from SO, 19 species belonging to 13 genera are also known from India. The lichen taxa common between India and SO are Amandinea punctata, Caloplaca cerina, C. citrina, C. frigida, C. saxicola, Carbonea vorticosa, Lecanora polytropa, Lecidea auriculata, L. lapicida. Lecidella stigmatea, Physcia caesia, P. dubia, Pleopsidium chlorphanum, Rhizocarpon geographicum, Rhizoplaca melanophthalma, Sarcogyne privigna, Umbilicaria decussata, U. vellea and Xanthoria elegans. In India most of the lichen species which exhibit their occurrence in SO are mostly exhibit their restricted distribution in temperate and alpine regions of the Himalayas. Rhizocaron geographicum sometimes also found growing on rocks in higher altitudes of southern Indian region. Out of 439 taxa of lichens so far known from Antarctica and South Georgia (Øvstedal and Smith 2001, 2004) 76 species exhibit similarities with Indian subcontinent and 68 with the SO. Out of 76 Indian subcontinent lichen species common to Antarctica (Figure 2) the lichen genus Cladonia is represented by 64 species in the subcontinent, out of which 17 (47%) species are also known to occur in Antarctica. However, the SO is devoid of this genus as not a single species of Cladonia is known from there.
Lecidea 5%
Lecidella 5%
Parmelia 5%
Physcia 5% Xanthoria 5%
Caloplaca 12%
Cladonia 47%
Rhizocarpon 8% Umbilicaria 8%
Figure 2. Representation of some major Indian subcontinent lichens in Antarctica.
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The species of Phaeophyscia, Physcia and Physconia are widely distributed in Indian Himalayan regions are also known from Antarctica, while except for Physcia other two genera do not exhibit their representation in SO. Most of Indian species of Rhizocarpon show affinities to the Antarctic lichens as 5 species are commonly known from both the regions. It is interesting to note that Buellia, a crustose thalloid genus, most common in Antarctica and Indian subcontinent have different species, but not a single species of Antarctica occur in India. However, SO is represented 10 species of Buellia known from Antarctica. Most of the genera of lichens known from India are also reported from Antarctica. The greater number of genera is common between Indian subcontinent and Antarctica supports the idea that one time the Indian subcontinent and Antarctic lichen flora were basically similar, but the geographical isolation that of Antarctica from other southern hemisphere continents has led to difference through speciation.
ACKNOWLEDGMENTS We thank Director, National Botanical Research Institute, Lucknow for providing laboratory facilities, Ministry of Earth Science and Council of Scientific and Industrial Research, New Delhi for facilitating Antarctic expeditions.
REFERENCES Awasthi, D.D.: Lichenology in Indian Subcontinent. Bishen Singh Mahendra Pal Singh, Dehra Dun (2000). Golubkova, N.S. and I.M. Simonov: Lishayniki Oazisa Shirmakhera. Trudy Sovet Skoy East Antarkti Cheskoy Eksfeditsii Leningrad, 60, 317-327 (1972). Gupta, B.K., G.P. Sinha, and D.K. Singh: A note on lichens of Schirmacher Oasis, East Antarctica. Indian J. Forestry., 22(3), 292-294 (1999). Kappen, L.: Response to extreme environments. In: The lichens (Eds: V. Ahmadjian and M.E. Hale). Academic Press, New York. pp 311-380 (1973). Lindsay, D.C.: Lichens of cold deserts. In: Lichen Ecology (Eds: M.R.D. Seaward.). Academic Press, London. pp. 183-209 (1977). Lindsay, D.C.: The macrolichens of South Georgia. Brit. Antarct. Surv. Sci. Rep., 89, 1-91 (1975). Lynge, B.: Lichens from West Greenland, collected chiefly by Th. M. Fries. Meddr. Grønland., 118, 1-225 (1937). Nayaka, S. and D.K. Upreti: Schirmacher Oasis, East Antarctic, a lichenologically interesting region. Curr. Sci., 89(7), 1059-1060 (2005). Nayaka, S., D.K. Upreti and R. Bajpai: Diversity and adaptive response of lichens in Antarctica with special reference to Schirmacher Oasis. In: Frontiers in Fungal Ecology, Diversity and Metabolites (Ed. K.R. Sridhar.). I.K. Internataional Publishing House Pvt. Ltd., New Delhi. pp. 107-123 (2009). Olech, M. and S.M. Singh: Lichens and Lichenicolous Fungi of Schirmacher Oasis, Antarctica. National Centre for Antarctic and Ocean Research, Vasco da Gama (2010).
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Øvstedal, D.O. and R.I.L. Smith: Addition and corrections to the lichens of Antarctica and South Georgia. Cryptogamie Mycologie. 25(4), 323-331 (2004). Øvstedal, D.O. and R.I.L. Smith: Lichens of Antarctica and South Georgia. A guide to their identification and ecology. Cambridge University Press, U.K. (2001). Pandey, V. and D.K. Upreti: Lichen flora of Schirmacher Oasis and Vettiyya Nunatak. In: Scientific Report: Seventeenth Indian Expedition to Antarctica. Ministry of Earth Science, New Delhi. Technical Publication No. 15. pp. 185-201 (2000). Ritcher, W.: Biology. In: The Schirmacher Oasis, Queen Maud Land, East Antarctica and its surroundings (Eds: P. Bormann and D. Fritzsche.). Germany. 321-347 (1995). Ritcher, W.: The lichens of the Schirmacher Oasis (East Antarctica). Geodätische und Geophysikalische Veröffentlichungen, Reihe 1, Berlin 16, 471-488 (1990). Rudolph, E.D.: Lichen distribution. In: Terrestrial Life in Antarctica (Eds: V. Bushnell). Antarct. Map Fol. Ser., 5, 9-11 (1967). Upreti, D.K. and G. Pant: Lichen flora in and around Maitri region, Schirmacher Oasis, East Antarctica. In: Scientific Report: Eleventh Indian Expedition to Antarctica. Ministry of Earth Science, New Delhi. Technical Publication No. 9, pp. 229-241 (1995). Upreti, D.K.: Lecideoid lichens from the Schirmacher Oasis, East Antarctica. Willdenowia., 25, 681-686 (1996). Upreti, D.K.: Notes on some crustose lichens from Schirmacher Oasis, East Antarctica. Feddes Repertorium., 108(3-4), 281-286 (1997).
In: Antarctica: The Most Interactive Ice-Air-Ocean Environment ISBN: 978-1-61122-815-1 Editors: Jaswant Singh, H.N. Dutta © 2011 Nova Science Publishers, Inc.
Chapter 8
WATER RELATION OF SOME COMMON LICHENS OCCURRING IN SCHIRMACHER OASIS, E. ANTARCTICA Sanjeeva Nayaka1 *, Dalip K. Upreti1 and Ruchi Singh2 ABSTRACT The lichens are classic examples of poikilohydric desiccation tolerant organisms. The existence of lichens in Antarctica is mainly due to their morpho-physiological adaptation to the extremes. In this communication water relation of six common lichens of Schirmacher Oasis growing in different water regime is presented. The elasticity modulus derived through psychrometric methods is utilized as marker of desiccation tolerance. It indicates the strechability of the cell wall and lesser the values of elasticity modulus higher would be the elasticity. The lichens growing in exposed and dry areas (Rhizoplaca melanophthalma, Umbilicaria decussata) had lesser elasticity modulus followed by ones growing in water drainage (Buellia frigida, U. aprina), while muscicolous (L. epibyron) and shade loving lichen (Xanthoria elegans) had higher values. Among all the lichens studied R. melanophthalma emerged as a better desiccation tolerant in Schirmacher Oasis by having comparatively lower osmotic potential at full turgor, lesser apoplastic fraction, elasticity modulus and water content at turgor loss point. The desiccation tolerance sequence of lichens studied are of following order; R. melanophthalma > U. decussata > U. aprina > B. frigida > X. elegans > L. epibryon. Further, the water holding capacity of U. aprina was maximum and ranged from 130.6 – 229.12 % of dry weight.
Keywords – PV curve, desiccation tolerance, stress physiology, adaptation.
*
E-mail:
[email protected],
[email protected],
[email protected], Mobile: +919305227203 Lichenology Laboratory 2 Plant Physiology Laboratory, National Botanical Research Institute (NBRI-CSIR), Rana Pratap Marg, Lucknow – 226001, U.P., India 1
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INTRODUCTION Lichen is a composite plant consisting of symbiotically associated fungal (mycobiont) and algal or cyanobacterial (photobiont) partners. The mycobiont is usually an ascomycete and in very few cases a basidiomycete, and a photobiont is usually a green alga but in about 10% of lichens a cyanobacterium. Lichens are strictly dependent on ambient moisture for their metabolic activities. Unlike homiohydric vascular plants lichens lack stomata, cuticle and water transport system such as roots, xylem vessel and tracheids. Hence, they can not actively regulate their water content and are called as poikilohydrous organism. The homiohydric organisms are desiccation sensitive and die when water content falls below a certain threshold, where as poikilohydric organism include both desiccation-sensitive and desiccation-tolerant species. Desiccation-tolerance is the ability to revive from the air-dried state when water is provided. It is also found in prokaryotes, algae and bryophytes, and occasionally in pteridophytes, but very rare in the vegetative tissues of angiosperms or in animal tissues. The vast majority of lichens are desiccation-tolerant. Under natural conditions, the life of most lichens is exposed to rapidly changing water contents and correspondingly rapidly changing physiological activity such as respiration and photosynthesis (Kranner et al. 2008). Antarctica is a land of extremes. About 98% of the continent is permanently covered with ice, while remaining 2% of ice-free land is restricted mostly to the periphery of the continent. These ice-free areas are the only habitat available for the growth lichens. Antarctica is the coldest continent with heat balances is everywhere negative (Engelskjön 1986). It is the windiest of the continents with the highest wind speed measured at d'Urville (327 km/h). The wind can act in three ways, by desiccation, wind-chill and ice-blast. The absolute humidity in the continent is 0.03%, lower than that of the Sahara Desert. Low average humidity combined with the extreme cold make the South Pole region the world's driest desert. It rains very rarely in maritime Antarctica, otherwise the snowfall, which averages less than one inch annually is the major precipitation in the continent. The sun does not shine at the South Pole for six months of the year. When the sun does shine, much less solar energy actually reaches the ground at the Pole because the sun's rays pass through a thicker layer of atmosphere than at the Equator. Also, due to the predominance of ice and snow covering Antarctica, most of the sun's rays that do reach the ground are reflected back into space leaving the continent cold with un-molten ice mass. The freshwater lakes in Antarctica are mostly confined to certain ice-free areas as Larsemann Hills, Schirmacher Oasis, Bunger Hills and Vestfold Hills. These lakes, which remain frozen for most of the year, are fed by glacier and snowmelt streams during the short austral summer months. Despite the restricted availability of liquid water and other extremes a total of 439 lichens do exist in Antarctica (Øvstedal and Smith 2001; 2004), which can be directly attributed to their adaptation to the stressor (Kappen 2000). The adaptive stimulus is clearly expressed in lichens as they are the most successful elements of the terrestrial biota in Antarctica and have obvious dominance in ice-free areas. They are superior to bryophytes and perhaps also to free living algae and fungi, particularly in harsher regions (Kappen 2004). Lichens together with bryophytes or alone form the largest amount of standing biomass in Antarctic landscapes with up to 950 kgm-2 in continental and up to 1300 gm-2 in maritime Antarctic habitats (Kappen 2000). Nayaka et al. (2009) discussed in detail the adaptive response of Antarctic lichens to various stress in factors. The water being a major constrain in Antarctica physiological
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adaptation to it is an interesting aspect for research. In the present study water relations of six common Antarctic lichens growing in different water regime in Schirmacher Oasis (SO) were studied in details. The aim of the study is to identify a lichen species that is physiologically better adapted to water stress in Antarctica. The aim is achieved by through psychrometric technique and measuring water holding capacity. This technique relies on water potential data from which pressure volume (PV) curve is constructed and various isotherms are derived. The PV isotherm is one of the widely used tools utilized for characterizing water status (Becket 1997). The PV isotherm has proved useful in assessing desiccation tolerance and the distribution of tree species in Malay-Thai peninsula (Baltzer et al. 2008). Many useful relations such as osmotic potential (OP) at full turgor, turgor loss point (TLP), relative water content (RWC) at TLP, elasticity modulus, solute concentration, symplastic, apoplastic and intercellular water contents can be measured with the help of PV curve.
MATERIALS AND METHODS Lichen Habitat and Species Selection Two important macro-habitats can be recognized in SO in relation to occurrence of lichens and source of water; 1). lake drainages, where water from one lake over flows to the another in summer, and 2). dry areas, where major source of water is snow melt. The lichens in SO are found growing on moraine, rock and moss in these habitats. Most of the lichens are directly exposed to sun while few are shade loving. A total of six lichens are selected for desiccation study and were identified by following Øvstedal and Smith (2001) (Table 1). The characteristics of the lichens are as follows; Buellia frigida Darb. – It is a crustose lichen, grey to blackish in colour, forms thick, circular patches on rocks. It is endemic to Antarctica, but one of the most common and wide spread lichens throughout the continent. In SO it is commonly occurs in lake drainages along with Umbilicaria aprina Nyl. and Rhizocarpon geographicum (L.) DC. It depends on lake drainage and snow melt for water. Lecanora epibryon (Ach.) Ach. – It is a crustose lichen with thick pale coloured thallus and prominent, circular apothecia found growing on moss. It is a bipolar species and also common in Antarctica. In SO it occurs in moist places near the lakes on the mosses. The snow melt and lake is its source of water. Rhizoplaca melanophthalma (Ram.) Leuckert and Poelt – It is a foliose lichen, yellow to yellow-green in colour, with prominent, crowded lecanorine apothecia, forms weakly lobate, smaller thallus on rock or moraine crusts. In very exposed habitats it appears grey-green to black. It is a cosmopolitan species and very common in Antarctica. In SO it occurs on rock and moraine crusts in exposed areas. Snow melt is its primary source of water. Umbilicaria aprina Nyl. – It is a foliose lichen, umblicate, usually monophyllous, 5 – 10 cm in size, dark grey to brown grey in colour. It is a cosmopolitan species and common in Antarctica. In SO it is the most prominent lichen, occurs mostly in lake drainage of lakes on rocks. Along with other species of Umbilicaria and Buellia it makes the lake drainage appear black in colour. The lake drain water is its major source of water. U. decussata (Vill.) Zahlbr. – It is a foliose lichen, umblicate, monophyllous, smaller in size, up to 3 cm in diam., button like, with wrinked upper surface and grows on rock. It is cosmopolitan in distribution, found in colder region and common in Antarctica. In SO it
Table 1. Antarctic lichen taxa analyzed for the water relation and their ecology
1 2 3 4 5 6
Sample
Habit
Habitat
Substratum
Buellia frigida Darb. Lecanora epibryon (Ach.) Ach. Rhizoplaca melanophthalma (Ram.) Leuckert & Poelt Umbilicaria aprina Nyl. U. decussata (Vill.) Zahlbr. Xanthoria elegans (Link) Th. Fr.
Crustose Crustose Foliose
Water drainage Dry area Dry area
Rock Moss Soil
Exposure to sun Exposed Partial shade Exposed
Foliose Foliose Foliose
Water drainage Dry area Dry area
Rock Rock Rock
Exposed Exposed Partial shade
Locality Priyadarshini Lake Near Circle lake North West of Maitri Priyadarshini Lake Vetehia nunatak Trishul Hill
Table 2. Water holding capacity and derivatives of PV curve for Antarctic lichens Sample 1 2 3 4 5 6
B. frigida L. epibryon R. melanophthalma U. aprina U. decussata X. elegans
Water holding capacity (% dry wt.) 70.9 – 110.57 90.62 – 145.24 120.83 – 187.2 130.6 – 229.12 115.51 – 220.62 148.42 – 208.22
OP at full Turgor (MPa) -1.02 ± 0.46 -0.90 ± 0.26 -0.90 ± 0.29 -0.64 ± 0.25 -1.63 ± 0.22 -0.85 ± 0.80
Apoplastic water fraction 12.0 ± 5.66 19.75 ± 7.50 12.29 ± 7.34 28.0 ± 8.3 21.38 ± 9.24 21.0 ± 5.31
Elasticity modulus (MPa) 6.42 ± 0.43 15.01 ± 5.12 3.98 ± 2.95 5.75 ± 3.03 4.55 ± 2.59 9.50 ± 4.50
Water content at TLP 61.75± 1.5 48.25 ± 5.91 67.43 ± 8.02 66.25 ± 3.4 58.75 ± 8.46 56.25 ± 2.2
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is found growing luxuriantly on rocks of Vitteheia and Baalsrudfjellet nunatak along with Pseudophebe minuscuala (Nyl. ex. Arnold) Brodo and D. Hawksw. Xanthoria elegans (Link) Th. Fr. – It is a foliose lichen, up to 5 cm in diam., orange in colour with radiating lobes. It is a cosmopolitan species very common in Antarctica. It is an attractive and very prominent due to its bright orange colouration. But in SO it is rare and found on rocks, in partially shaded, shelf facing side of Trishul Hill.
Water Holding Capacity About 10 –15 gm of fresh lichen samples were cleaned and kept immersed in water for 30 min to make it saturated. Then samples were blotted using paper towels to remove excess of water present over the thallus and the weight was taken. The samples were then kept in desiccator with silica crystals for 3 hrs and then transferred to hot air oven. The samples were dried for 70 hr at 50° C until the constant weight is attained. The water holding capacity is calculated as follows; Water holding capacity = [(Turgid weight – Dry weight)/Dry weight] x 100
Water Potential (Ψ) Measurement and Pressure Volume (PV) Curve About 15 – 20 mg of fresh samples of lichen were cleaned and kept in tap water for 15 30 min to make it fully turgid. Then samples were blotted using paper towels to remove excess of water present outside the thallus, quickly weighed and placed in chambers of Psypro Water Potential System. After equilibration for 4 hr chambers are connected to a Wescor HR-33T micro voltmeter and measured the water potential. Samples were then allowed to lose about 5–20% of their water and allowed to equilibrate again. Measurements were repeated until the water potential fell to below –5 MPa. Then the samples were dried for 70 hrs at 50° C in hot air oven and weight was taken. Psychrometer chambers were calibrated with standard solution 0.5 M of NaCl at 25° C. Values of Ψ are corrected to room temperature of 25° C. A total of 8 replicates were analyzed for each species. The water potential is represented as; Ψ = P – п, where P is turgor potential (TP) and п is osmotic potential. A PV curve was constructed by plotting 1/Ψ against relative water content (RWC) (Beckett 1995, 1997). The resulting curve is initially concave, but beyond the region where turgor is lost (i.e. where turgor no longer contributes to Ψ) the curve became linear. From the PV curve TP (P) was calculated at each Ψ as the difference between y-axis intercept value of the extrapolated linear portion of the curve and the actual Ψ (P = Ψ – п). The TP was then plotted as a function of RWC. The difference between total water content of the lichen thallus and the water content at which turgor starts falling is considered as inter cellular water. This intercellular water has to be deducted to actual water content within lichen. Hence, the RWCs for all the data were recalculated as follows; RWCc = [(Fresh weight – Dry weight) / (Turgid weight – Dry weight)] – Weight of intercellular water
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Figure 1. Representative PV curves of lichen species studied for water relations.
The PV curve reconstructed using RWCc and the OP (п) at full turgor is noted as the yintercept of the linear portion of the PV curve (Figure 1). Regression line going through this linear portion of the curve intercepts at x-axis and yields the symplastic and apoplastic fraction of water. Tissue elasticity was calculated from the relationship between Ψ and RWCc (Stadelmann 1984). The bulk elasticity modulus of tissue expresses the change in turgor of tissue cells for a unit change in the relative water content of the cells (e = dP/dr).
RESULTS The water holding capacity of Antarctic lichen varied from 70.9 – 229.12 % of dry of wt. (Table 2). The foliose lichen U. aprina, which has larger, thick thallus and grows on rock in lake drainages had maximum water holding capacity ranging from 130.6 – 229.12 % dry wt. However, a crustose lichen B. frigida, found in the same habitat but having smaller thallus has lower water holding potential which ranged from 70.9 – 110.57 % of dry wt. In general foliose lichens exhibited better water holding capacity in comparison to crustose.
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The Antarctic lichens exhibited varied level of desiccation tolerance as indicated by derivatives of PV curve in the present study (Table 2). The lichen growing in exposed areas, on moraine and rock are better desiccation tolerant, while muscicolous and shade loving ones are less tolerant. U. decussata had lowest OP (–1.63 ± 0.22 MPa) at full turgor and L. epibryon had lowest (48.25 ± 5.91) water content at turgor loss point. B. frigida had lowest apoplastic water while U. aprina had more (28.0 ± 8.3). The elasticity modulus of R. melanophthalma was lowest (3.98 ± 2.95 MPa) and it was maximum in muscicolous lichen L. epibryon (15.01 ± 5.12 MPa).
DISCUSSION The lichens, being exposed to frequent water stress have developed high degree of water holding capacity. They lack cuticle to impede entry of water in to the thallus. The spongy nature of the thallus tissue, presence of large intercellular spaces, the gelatinous sheath of algal cells and swollen hyphal wall allows them to hold good amount of water. The thalli often can absorb considerably more water during a prolonged immersion of several hours. The lichens are hygroscopic in nature and absorb moisture from the surroundings even at low humidity. The lichen can be hydrated and activated quickly by the snow, dew, mist or glacier meltwater and resume photosynthesis. Some lichens such as Umbilicaria having dark coloured thalii by absorbing sunlight become much warmer and can melt snow crystals deposited over them. Further, moistened thalli can reach an over-air temperature of nearly 23 K, which means that they can become as warm as 20˚C at maximum that induce maximal productivity. Some lichens are capable of gaining enough moisture from the humidity at the edge of a temporary snow patch on the rock without any visible melting process. Blum (1973) enumerated the water content (water holding capacity) of saturated thali of some lichens which ranged from 116 – 738 % of dry wt. (maximum in cyanolichen – Collema flaccidum (Ach.) Ach.). Umbilicaria pustulata (L.) Hoffm. held 201 % of dry wt. of water, in 5 min. of immersion, 203 % in 1 hr and 209 % in 15 hr. Similarly, Xanthoria parietina (L.) Beltr. held 178, 188 and 227 % of dry wt. of water in 5 min, 1 and 15 hr respectively. However, in case of Antarctic U. aprina, U. decussata and X. elegans their thallus reached full saturation within 30 min. of immersion with maximum of 229.12, 220.62 and 208 % of dry wt. of water respectively. This indicates the quicker response of Antarctic lichens when water is made available and an adaptation to combat water scarcity. The water holding capacity of crustose lichens in both the regions, i.e. main land (Blum 1973) as well as in Antarctica was lesser compared to foliose lichens. Unlike vascular plants, lichens can stay longer in desiccation state and their metabolic activity can recover after their tissues have been reduced to very low RWC. Such plants are called ‗‗resurrection plants‘‘ and have evolved desiccation tolerance (Alamillo and Bartels 2001, Bartels 2005; Tuba et al. 1998). The lichen can photosynthesize at low water potentials such as –20 MPa at –20˚C. Experiments in hot deserts have shown that lichens are able to photosynthesize even at low water potentials as low as –38 MPa (Nash et al. 1990). As soon as availability of moisture stops lichens thallus quickly desiccates, loses up to 97% of its water, and falls into an anabiotic state. Under low water potential photosynthesis rate will be low and can be considered as a means of keeping the photosynthetic apparatus intact and
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producing frost-protective carbohydrates than for actual dry matter. The psychrometric technique explores new possibilities to elucidating the water status of plants including cryptogams such as lichens, bryophytes, pteridophytes. According to several studies utilizing PV curve, an ideal desiccation tolerant lichen would have low OP at full turgor, lesser apoplastic water content, low RWC at turgor loss and more importantly less elasticity modulus. The low OP at full turgor indicates that the cell sap has low salt concentration and water potential would be high or near to zero. The lower apoplastic contents mean little quantity of water is present in the cell wall pores and more within in the cell (symplast), which contributes to high water potential. It is always necessary for a desiccation tolerant plant that it maintains turgidity of the cell even at lower amount of water. Hence, low RWC at turgor loss would be beneficial. Similarly, elasticity modulus indicates the stretchability of the cell wall. The low elasticity modulus value means high elasticity of cell wall and more tolerance for desiccation. Becket (1997) studied the PV isotherm of several poikilohydric plants including lichen Roccella hypomecha (Ach.) Bory., and also provided explanation for varied values of PV isotherms. The lichen R. hypomecha consisted low OP, low RWC at turgor loss, low elasticity modulus and low solute concentration. Proctor et al. (1998) studied the water contents of several bryophytes including a lichen Cladonia convoluta (Lam.) Cout., using PV relationship, where the lichen contained low OP, low RWC at TLC and low bulk elasticity modulus. In the present study all the lichens studied exhibited varied values for measured parameters. U. decussata had lowest OP (–1.63 ± 0.22 MPa) at full turgor, but slightly higher water content at TLP (58.75 ± 8.46) and apoplastic water (21.38 ± 9.24). B. frigida had lowest apoplastic water fraction (12.0 ± 5.66), but higher OP at full turgor (-1.02 ± 0.46 MPa). Similarly, L. epibryon had lowest water content at TLP (48.25 ± 5.91), but higher elasticity modulus (15.01 ± 5.12 MPa), apoplastic water content (19.75 ± 7.50) and OP at full turgor (-0.90 ± 0.26). Hence, it is has become necessary to relay on one strong parameter, compare other parameter accordingly and decide the desiccation tolerance of the lichens. The elasticity modulus is thought to be determined by the mechanical properties of cell walls (Cheung et al. 1975, Tyree and Hammel 1972). In leaf cells that have turgor elasticity modulus has a critical role in water relations. Advantage of the small elasticity modulus in the drought environment is that it contributes to the turgor maintenance of the leaf cells under conditions of low water content (Kozlowski et al. 1991). Hence, in the present study desiccation tolerances of lichens are compared based on their elasticity modulus. The lichens growing on moraine or rock in exposed areas are better desiccation tolerant and have lesser elasticity modulus. Among them R. melanophthalma exhibited lowest (3.98 ± 2.95) elasticity modulus indicating its highest desiccation tolerance. It is followed by U. decussata (4.55 ± 2.59), U. aprina (5.75 ± 3.03) and B. frigida (6.42 ± 0.43). It is obvious that lichens growing in exposed areas are the one who first experience the extremes of Antarctic conditions. They lose water either due to high irradiation, wind or low temperature and such conditions are very frequent in Antarctica. Hence, the cells of the lichens probably have become more stretchable or elastic. Where as in X. elegans, a lichen growing in partial shade at Trishul hill elasticity modulus is moderate (9.50 ± 4.50) indicating its medium level of desiccation tolerance. L. epibryon, a muscicolous lichen that grows in partial shade has highest elasticity modulus. The moss cushions acts like sponge and hold water for longer duration. Further, the mosses have many dead cells in their leaf tissue which again holds water. The moss in Antarctica usually grows in shaded area, between or under the rocks. The lichen by growing over them can obtain water for longer duration and hence developed less
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desiccation tolerance. In general, by considering all water relation parameters studied the foliose lichens R. melanophthalma can be considered as highly desiccation tolerant species. As discussed earlier it has low elasticity modulus, but also has comparatively lower low OP at full turgor (–0.90 ± 0.29 MPa), lower apoplastic water fraction (12.29 ± 7.34) and lower water content at TLP (67.43 ± 8.02). Further, water holding capacity of R. melanophthalma is considerably high which ranges from 120.83 – 187.2 % of dry wt.
CONCLUSION Among all the theories, the ‗adaptation‘ theory explains best the dominance of lichens in Antarctica. The lichens are adapted both morphologically as well as physiologically to the stress components of the continent. The water relation study carried out with the help of psychrometric method clearly indicates the differential levels of desiccation tolerance in Antarctic lichens. The habitat selection and restricted distribution of lichens is a clear strategy for the survival. Hence, X. elegans is found only on shelf facing side of Trishul hill in SO which receives shade at least for half a day during summer. The muscicolous lichen L. epibryon grows only on moss so that it gets water for longer duration. As per elasticity modulus desiccation tolerance is higher in sun exposed lichens, moderate in partially shaded and least in muscicolous. Hence, desiccation tolerance in Antarctic lichens is of following sequence; R. melanophthalma > U. decussata > U. aprina > B. frigida > X. elegans > L. epibryon. Further, water absorbance ability is faster and water holding capacity is higher which reaches up to 200% of their dry weight. Apparently, lichens did not develop ‗unique‘ adaptive mechanisms in the extreme Antarctic environment. The high desiccation tolerance and some morphological features of Antarctic lichens are also been observed in lichens growing in harsh climate of elsewhere (Kappen, 1988). However, the ability to tolerate stress, survive and evolve is high in Antarctic lichens.
ACKNOWLEDGMENTS We are thank full to the Director, National Botanical Research Institute for providing the necessary facilities, to Dr. U.V. Pathre for allowing us to utilize facilities of Plant Physiology Laboratory, to Council of Scientific and Industrial Research, New Delhi for financial assistance, to National Centre for Antarctic and Ocean Research, Vasco da Gama for selecting S.N. for 28th Indian Antarctic Expedition, to the leaders and members of the expedition for their cooperation during the collection of lichen samples, to Dr. Ajit Pratap Singh and members of Plant Physiology Laboratory for their cooperation during the study.
REFERENCES Alamillo, J. and D. Bartels: Effects of desiccation on photosynthesis pigments and the ELIPlike dsp 22 protein complexes in the resurrection plant Craterostigma plantagineum. Plant. Sci., 160, 1161-1170 (2001).
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Baltzer, J.L., S.J. Davies, S. Bunyavejchewin and N.S.M. Noor: The role of desiccation tolerance in determining tree species distributions along the Malay-Thai Peninsula. Funct. Ecol., 22, 221-231. (2008). Bartels, D.: Desiccation tolerance studied in the resurrection plant Craterostigma plantagineum. Integrative Comparative Biology., 45, 696-701 (2005). Beckett, R.P.: Pressure volume analysis of a range of poikilohydric plants implies the existence of negative turgor in vegetative cells. Annals of Bot. 79, 145-152 (1997). Beckett, R.P.: Some aspects of the water relations of lichens from habitats of contrasting water states studied using thermocouple psychrometry. Annals of Bot. 76, 211-217 (1995). Blum, O.B.: Water relations. In: The Lichens (Eds. V. Ahmadjian and M.E. Hale.). Academic Press, New York and London. pp. 381-400 (1973). Cheung, Y.N.S., T.M. Tyree and J. Dainty: Water relations parameters on single leaves obtained in a pressure bomb and some ecological interpretations. Can. J. of Bot. 42, 231235 (1975). Engelskjon, T.: Zonality of climate and plant distributions in some Arctic and Antarctic regions. Rapportserie Norsk Polarinstitutt, 30, 1-49 (1986). Kappen, L.: Ecophysiological relationships in different climatic regions. In: CRC Handbook of bchenology, Vol. II. (Ed. M. Galun.). CRC Press, Boca Raton, FL. 37-100 (1988). Kappen, L.: Some aspects of great success of lichens in Antarctica. Ant. Sci. 12(3), 314-324 (2000). Kappen, L.: The diversity of lichens in Antarctica, a review and comments. Biblioth. Lichenol., 88, 331-343 (2004). Kozlowski, T.T., P.J. Kramer and S.G. Pallardy: The physiological ecology of woody plants. Academic Press, New York, London (1991) Kranner, I., R.P. Beckett, A. Hochman and T.H. Nash III.: Desiccation tolerance in lichens: a review. Bryol. 111(4), 576-593 (2008). Nash III, T.H., A. Reiner, B. Demmig-Adams, E. Kilian, W.M. Kaiser and O.L. Lance: The effect of atmospheric desiccation and osmotic water stress on photosynthesis and dark respiration of lichens. New Phytol. 116, 269-276 (1990). Nayaka, S., D.K. Upreti and R. Bajpai: Diversity and adaptive response of lichens in Antarctica with special reference to Schirmacher Oasis. In: Frontiers in Fungal Ecology, Diversity and Metabolites (Ed. K.R. Sridhar.). I.K. Internataional Publishing House Pvt. Ltd., New Delhi. pp. 107-123 (2009). Øvstedal, D.O. and R.I.L. Smith: Addition and corrections to the lichens of Antarctica and South Georgia. Cryptogamie, Mycologie. 25(4), 323-331 (2004). Øvstedal, D.O. and R.I.L. Smith: Lichens of Antarctica and South Georgia. A guide to their identification and ecology. Cambridge University Press, U.K. (2001). Proctor, M.C.F., Z. Nagy, Z. Csintalan and Z. Takacs: Water-content components in bryophytes: analysis of pressure-volume relationships. J. of Exp. Bot. 49, 1845-1854 (1998). Stadelmann, E.J.: The derivation of the cell wall elasticity functions from the cell turgor potential. J. of Exp. Bot. 35, 859-868 (1984). Tuba, Z., M.C.F. Protor and Z. Csintalan: Ecophysiological responses of homoiochlorophyllous and poikilochlorophyllous desiccation tolerant plants: a comparison and an ecological perspective. Plant Growth Regulation. 24, 211-217 (1998). Tyree, M.T. and H.T. Hammel: The measurement of the turgor pressure and the water relations of plants by the pressure-bomb technique. J. of Exp. Bot. 23, 267-282 (1972).
In: Antarctica: The Most Interactive Ice-Air-Ocean Environment ISBN: 978-1-61122-815-1 Editors: Jaswant Singh, H.N. Dutta © 2011 Nova Science Publishers, Inc.
Chapter 9
SOLAR WIND INFLUENCE ON ATMOSPHERIC PROCESSES IN WINTER ANTARCTICA O.A.Troshichev *, V.Ya.Vovk and L.V.Egorova ABSTRACT The paper presents a summary of the experimental results demonstrating the strong influence of the interplanetary electric field on atmospheric processes in the central Antarctica, where the large-scale system of vertical circulation is formed during the winter seasons. The influence is realized through acceleration of the air masses, descending into the lower atmosphere from the troposphere, and formation of cloudiness above the Antarctic Ridge, where the descending air masses enter the surface layer. The cloudiness formation results in the sudden warmings in the surface atmosphere, since the cloud layer efficiently backscatters the long wavelength radiation from the ice sheet, but does not affect the adiabatic warming process of the descending tropospheric air masses. The acceleration is followed by a sharp increase of the atmospheric pressure in the near-pole region, which gives rise to the katabatic wind strengthening above the entire Antarctica. As a result, the circumpolar vortex about the periphery of the Antarctic continent correspondingly decays and the cold air masses flow out to the Southern ocean. The latter phenomena evidently destroys the regular relationships between the sea level pressure fluctuations in the Southeast Pacific high and the North Australian-Indonesian low. It seems that the El-Niño beginnings are related exactly to the anomalous atmospheric processes in the winter Antarctica.
Keywords: Solar wind, Antarctica, atmosphere, anomalous winds, El-Niño.
* Eg225 mail:
[email protected], Fax:+7-812-352-2688, Phone: 7-812-337-3134 Arctic and Antarctic Research Institute, St.Petersburg, 199397, Russia
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INTRODUCTION Existing models of the atmospheric variability and change do not take into consideration the short-term changes of solar activity. Indeed, the total energy, contributed by the solar wind and the cosmic rays in the Earth‘s atmosphere, is extremely insignificant in comparison with the total solar irradiance. But, as distinct from the total solar irradiance, the energy of solar wind and cosmic rays can increase in hundreds and more times in periods of high solar activity. The attempts to find the cause-effect relations between the solar activity variations and weather and climate changeability have a long story (Wilcox, 1975; Herman and Goldberg, 1978). The galactic cosmic rays (GCR) altered by solar wind were usually regarded as the most plausible agent of the solar activity influence on the Earth‘s atmosphere. The experimental data were presented showing the influence of the varying GCR flux on the Earth‘s weather and climate (Tinsley et al., 1989), on high cloud coverage (Pudovkin and Veretenenko, 1995), on temperature in the polar troposphere (Pudovkin et al., 1996, 1997), on the global total cloud cover (Svensmark and Friis-Christensen, 1997; Todd and Kniveton, 2001), on low cloud coverage (Marsh and Svensmark, 2003). These results suggest that just cloudiness variation affected by cosmic rays lead to changes in the atmospheric and meteorological characteristics. However, the hypothesis about the determining influence of the galactic cosmic rays on the cloudiness was not always supported by the subsequent, more detail research. It was indicated that the correlation with GCR disappears when the cloud coverage is decomposed in fractions by cloud type or height, by region (reduce for ocean basis), or by latitude (patterns in the tropical zone are better associated with concurrent El-Nino) (Farrar, 2000). A comprehensive study of the low cloud coverage for the last 120 years (Palle and Butler, 2002) revealed that the global cloudiness increased during the past century regardless of variations of GCR. The solar irradiance turned out to be correlated better and more consistently with low cloud cover than the cosmic ray flux (Kristjansson et al., 2002). As a result, the conclusion was maid that the mechanism linking the cosmic ray ionization and cloud properties cannot be excluded, but its high efficiency is not obvious (Harrison and Carslaw, 2003). At the same time it is well known that severe reductions in the galactic cosmic rays flux, known as Forbush decrease (FD), are related to the disturbed, high speed solar wind, emerging by the most intense solar flares. The disturbed solar wind is characterized by the largest changes in such parameters as the solar wind pressure PSW = m· n ·(VSW) 2 and the interplanetary electric field ESW = VSW x BZ (or simply the southward component of the interplanetary magnetic field (IMF BZS). The velocity VSW might vary with a factor of 2-3 at maximum, whereas the IMF BZ components might change the sign and increase by some factors of ten. The geoeffective solar wind parameters strongly affect (impact) the Earth‘s magnetosphere. It was noted that the FD beginnings at the Earth‘s orbit are recorded simultaneously with dramatic disturbances in the solar wind, and therefore, the atmospheric effects, assigned to Forbush decreases, can be, in reality, influenced by the geoeffective solar wind parameters (Troshichev et al., 2003). Figure 1. shows, as an example, response of the cloudiness above Vostok station (Antarctica) to Forbush decrease (left column) and to the IMF BZ minimum (right column) during the winter season of 1974-1992 (Troshichev et al., 2008). The list of 24 Forbush
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decreases was taken from the widely known analysis (Todd and Kniveton, 2001), but in our case the Forbush decrease maximum has been used as a key date in the epoch superposition method unlike to Todd and Kniveton (2001), who used the Forbush decrease beginning. Indeed, in many cases it is difficult to determine the FD beginning unambiguously, as a result the FD beginning dates sometimes are identified with as large a scatter as 5 days in various studies. On contrast, the Forbush event maximum is easily and uniquely identified by minimum in the galactic cosmic ray flux in each case. The same list has been used to separate the IMF BZ minimum dates, related to the FD events. Unfortunately, the IMF BZ data turned out to be available only for 15 events of 24. So, the left column in Figure 1. is for the data of cloudiness above Vostok, allocated relative to the FD maximum, whereas the right column is for the data allocated to the appropriate IMF BZ minimum.
Figure 1. Behavior of the average Forbush decrease (FD), the average interplanetary magnetic field (IMF) BZS component, and the appropriate cloudiness above Vostok for the most powerful FD events during the winter season of 1974-1992 (list of Todd and Kniveton, [2001]). A key date (t = 0) was taken as a day with FD maximum in the left column and a day with the IMF BZ minimum in the right column (from Troshichev et al.,2008).
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The results presented in the left column demonstrate that Forbush decrease coincides with increased cloudiness, which starts three days ahead of the key date (FD minimum) and reaches the 55 % maximum by the key date, the statistic significance being equal to 0.96. The results presented in the right column demonstrate, with no less evidence, that cloudiness above Vostok starts to increase one day before the IMF BZ minimum and reaches its maximum next day after the key date. The statistical significance in this case is less, ss=0.91, but we have to take into account that number of the available events was reduced in 1.5 times while examining the Bz indicator instead of Forbush decrease. This example clearly shows that changes of cloudiness may be successfully explained by Forbush decrease as well as by the IMF variations.
IMF VARIATIONS AS A DETERMINING FACTOR FOR THE CLOUDINESS ABOVE VOSTOK To demonstrate that variations in the interplanetary magnetic field by themselves can produce an effect on cloudiness we need to examine such solar wind disturbances, which were accompanied by the quite insignificant Forbush decreases. Taking into account that the Forbush decrease magnitude is negligible for the solar minimum epochs, the relation between the interplanetary magnetic field and the cloudiness above Vostok was examined for the years of the solar minimum (1974-1977 and 1985-1987) (Troshichev et al., 2008). The cloudiness at Vostok station was determined by two methods. The first method is based on estimation of cloudiness power in reports from the visual man-made observations (0 is for clear sky, 10 is for heavy cloudiness). The second method is based on measurement of the radiation balance (BR) value in MJ/m2 produced by balancer. It has been known that during the winter season, under conditions of the dark polar night, the radiation balance at Vostok is always negative. The larger negative BR values correspond to more intense radiation cooling, the less negative BR values indicate the cooling reduction as a consequence of the cloud layer formation above Vostok station. Figure 2. demonstrates the response of the radiation balance (second panel), the cloudiness balls (third panel) to the negative deviation in the daily averaged IMF Bz component (top panel) for three groups of BZ values: -2 < BZ < -1 nT (18 events), -2.5 < BZ < -2 nT (11 events), and BZ < -2.5 nT (13 events) in years of solar minimum (1974-1977, 19851987), the day of maximal negative BZ deviation being taken as a zero date (t = 0). One can see the evident response of cloudiness to influence of the interplanetary magnetic field: the greater the negative IMF BZ component, the larger is the cloudiness, the more pronounced is the reduction in the cooling. The cloudiness formation starts simultaneously with the negative BZ deviation (-1st day) and reaches the maximum at 0 or +1st day. It is important that statistical significance of all effects, being minor for the first BZ gradation, quickly grows with the increase of the negative BZ (in spite of the events number diminishing) and reaches 92% level in case of radiation balance for third BZ level. The crucial role of the interplanetary magnetic field was confirmed when examining the effects of the strong negative (ΔBZ<-2 nT) and positive (ΔBZ>2 nT) deviations of the IMF BZ component (Troshichev et al., 2008). As Figure 3. shows the intensification of the negative BZ deviation is followed, with a delay time of about 1 day, by the cloudiness enhancement
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and the corresponding warming in the ground layer, whereas the rise of the positive BZ deviation is followed by the opposite reaction: the cloudiness decays and the cooling starts on the ground layer. It should be reminded that Vostok is located at the ice dome at an altitude of 3.45 km above sea level, and, therefore, h=3.5 km corresponds to ground level at Vostok, whereas h= 6 km corresponds to an altitude of ~ 2.5 km above the ice sheet level. The results of the analysis (Troshichev et al., 2008), completed for conditions of the negligible Forbush decrease, demonstrate that the sign of the BZ component defines the trend of the cloudiness change (growth or decay), the cloudiness power being determined by the value of the southward IMF component. It seems reasonable to suggest that the formation of the cloud layer occurs at altitudes higher than ~ 5 km above the ice sheet.
Figure 2. Mean changes in cloudiness estimated from the radiation balance measurements (second panel) and by the visual man-made observations (third panel), obtained for three gradations of the negative deviation in the daily averaged IMF BZ component (-2
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Figure 3. Run of the daily averaged IMF BZ component for cases of strong negative and positive B Z deviations (upper panel) and the appropriate effects in the cloudiness (second panel) and in temperature at heights 3.5 km and 6 km above Vostok (third and forth panels) in years of the solar activity minimum 1974-1977 and 1985-1987 (from Troshichev et al., 2008).
A DISTINCTIVE FEATURES OF THE ATMOSPHERIC CIRCULATION ABOVE ANTARCTICA The Antarctic continent is dominated by the ice dome rising above 3.5 km in the Antarctic ridge area. A unique feature of the atmospheric circulation in the winter Antarctica is the continental-scale katabatic wind regime (Egger, 1985; Parish and Bromwich, 1987, 1991). It is a powerful drainage stream of the near-surface air masses flowing roughly radially from the Antarctic ridge to coastline (Figure 4). This drainage is determined by the negative air buoyancy supported by severe radiation cooling of the atmosphere on the ice sheet surface. Since mass continuity requires a permanent substitution of the air masses draining in the near-surface layer, the air masses are supplied from the troposphere over the Antarctic ridge area. As a result, a large-scale system of vertical (meridional) circulation is formed in the winter Antarctica (Figure 5). The system includes drainage of the air masses along the slope of the Antarctic ice sheet, ascending flow near the coast line, return movement in the lower and middle troposphere, and descending flow in the near-pole region (Parish and Bromwich, 1991).
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Figure 4. Drainage pattern of near-surface katabatic winds (from Parish and Bromvich, 1991). Location of the inner-continental stations Vostok, Dome C and South Pole is shown.
Figure 5. A conceptual scheme of the vertical mass circulation forced by the katabatic wind regime in Antarctica (from Parish and Bromwich, 1991).
The spatial structure of katabatic winds is one of the most stable atmospheric phenomena on the Earth (Schwerdtfeger, 1984). Phases of weak and strong katabatic winds alternate with each other at regular intervals from few days (Egger, 1985; James, 1989) to 30-50 days (Yasunari and Kodama, 1993). The model-based studies (Egger, 1985; James, 1989; Parish and Bromvich, 1991; Parish, 1992) showed that the Antarctic katabatic wind regime appears to be an important forcing mechanism for the circumpolar vortex around the periphery of the Antarctic continent. As the experimental study of Yasunari and Kodama (1993) demonstrates, the weak katabatic wind phase corresponds to a deep upper tropospheric circumpolar vortex, whereas the strong katabatic wind phase corresponds to a weak circumpolar vortex. Thus, the
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low atmosphere is not static above the Central Antarctic ridge: there is a powerful vertical channel, where the air masses go down from upper troposphere to the Antarctic ice sheet.
SUDDEN WARMINGS IN THE CENTRAL ANTARCTIC AND THEIR RELATION TO THE DISTURBED SOLAR WIND It was suggested (Troshichev and Janzhura., 2004) that superposition of the constant radiation cooling of air situated at the ice sheet and adiabatic warming of air masses, which arrive from above, maintains the atmosphere on the Antarctic ridge in the state of thermal quasi-equilibrium. A cloud layer formation at altitude about 5-10 km would efficiently backscatter the long wavelength radiation from the ice sheet, but it will not affect the adiabatic warming process, when the air masses go down from troposphere to the Antarctic ice dome. As a result of the reduction in the radiative cooling, the atmosphere should be warmer below the cloud and give rise to sudden warmings at ground level, which happen sometimes in the Central Antarctica during the winter seasons. The particular events of sudden warmings were studied in (Troshichev et al., 2003; Troshichev and Janzhura, 2004) on the basis of three sets of meteorological data: (1) daily meteorological observations (temperature, pressure and winds) at the ground level at Vostok station (h =3.45 km) for 1978-1992, (2) hourly temperature values derived from the 10-min observations provided by the automatic stations (AWS) at Dome C, South Pole and Vostok for 2000-2001, and (3) daily aerological measurements of temperature, pressure and winds above Vostok station (h =3.5–20 km) for 1978-1992. It was found that warmings came after large increases in the amplitude of the negative (southward BZS) component of the interplanetary magnetic field. The time of the maximum deviation in the solar wind parameter (BZS, or ESW, or PSW) was used as a key (―zero‖) date. The temperature variation (T) was calculated as the difference between the temperature values for the key moment and for the preceding and succeeding days (or hours). The results (Troshichev et al., 2004) demonstrated the clear correlation between BZ and T and between ESW and T. As Figure 6. shows, the correlation of the temperature variations with the electric field deviations ΔESW is markedly higher than with ΔBZ and can expressed as T [deg] = 3.5 - 0.0047ESW [nTkm/s], where ESW is regarded as negative for negative values of BZ. The correlation is best for larger values of the leaps in BZ, the regression line slope being determined by the end points (maximal negative or positive values ΔBZ). Figure 7. shows the statistical response of the ground hourly temperature T at stations Vostok, Dome C and South Pole to variations in ESW in 2000-2001 as a function of the duration of southward IMF (Troshichev and Janzhura, 2004). The abscissa axis presents the duration of events, the ordinate axis is for the number of successive hourly intervals with negative BZ< -2 nT. One can see that the increase in the ground temperature is determined by the power of the negative BZ action: the longer the BZS field exposure (and the higher electric field intensity) lasts, the larger is the temperature deviation and the shorter is the delay time
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between the key moment and the temperature change. At stations Vostok and Dome C a 15hours exposure affects the effective warming (up to T > +10) after 12 hours at a level of statistical significance equal to 0.99. However, the warming at station South Pole may be observed only under conditions of very strong interplanetary electric field, and this link is not statistically significant. The different effects in the ground temperature at stations Vostok and Dome C, on the one hand, and South Pole, on the other hand, are easily explained by their different locations relative to the katabatic wind system. Indeed, stations Vostok and Dome C are located on the Antarctic ridge, which is the region of the descending tropospheric air mass flow, whereas South Pole is located in the regions of the developed drainage stream. As the results (Troshichev and Janzhura, 2004) showed, there is a weak tendency to ground temperature decrease after the pressure pulses: the coolings at Vostok follow the large pressure pulses within 2 hours and last about the next 24 hours (Figure 8). However, we have to keep in mind that pressure pulses in the interplanetary shocks usually pass the Earth some hours (from 0 to 12) ahead of the interplanetary electric field disturbances. So, the isolated effects of the pressure increases can be seen, in principle, only whithin the first hours after the pressure pulses. When the electric field comes into play, the influences of the pressure pulses and interplanetary electric field would superpose on one another, and their combined effect in the temperature deviations is observed.
Figure 6. Correlation between daily changes in ground temperature (T) at Vostok station (1978-1992) and daily deviations in the interplanetary magnetic field BZ (upper panel) and in the geoeffective electric ESW field (lower panel) (from Troshichev et al., 2003).
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Figure 7. Character of temperature hourly changes T at stations Vostok, Dome C, and South Pole as a function of number of the hourly interval with B Z <-2nT. Dotted line marks the key moment. Rate of the warming is presented by dark signatures (from Troshichev and Janzhura, 2004).
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Figure 8. Response of the ground temperature T at Vostok to pulses in the solar wind dynamic pressure in 2000 – 2001, the key moment being determined by sharp increase in the dynamic pressure. (from Troshichev and Janzhura, 2004).
It is meaningful that the response in temperature to the ESW influence is quite opposite in the lower and upper troposphere. Figure 9. shows the profiles of the averaged daily temperature deviations above Vostok station for negative and positive variations of ESW (Troshichev et al., 2004). The temperature profile for the –1st day, preceding the zero day (i.e. day of the maximum ESW deviation), is taken as the level of reference for all succeeding days. The average warming at the ground level (h = 3.45-3.5 km) responds, within 1-2 days, to the negative step in ESW, but at altitudes more than 10 km a cooling is observed (upper panels). The opposite behaviour is typical of the positive step in ESW: the atmosphere gets cooler at ground level, and gets warmer at h > 10 km (lower panels). Such regularity would be observed if a cloud layer appears at altitudes 5-10 km under the influence of the negative ESW variations, and disappears under the influence of the positive ESW variations.
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Figure 9. Mean height profiles of the daily temperature deviations above Vostok under conditions of the negative and positive ESW changes (from Troshichev et al., 2003).
Impact of the Disturbed Solar Wind on Atmospheric Pressure The aerological data from Vostok station for 1978-1992 have been used to study relationship between the daily values of the interplanetary electric field and atmospheric pressure at altitudes h=3.5–20 km (Troshichev et al., 2004). A day of negative or positive leap in the interplanetary electric field has been taken as a key date in the epoch superposition analysis. The magnitudes of ΔESW (difference between daily values for the key date and for the preceding and succeeding days) were compared with the appropriate value of the atmosphere pressure. The results presented in Figure 10. show that atmospheric pressure at all altitudes from 0 to 15 km sharply increases in response to negative leap ΔESW and keeps this level in subsequent four days. In response to positive ΔESW the atmospheric pressure decreases at all altitudes at the zero day and then starts gradually to increase starting at 15 km
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at the first day and lowering to the ground level by the third day. In the context of the going down air masses flow it implies that the interplanetary electric field effectively accelerates or delays the descending tropospheric air masses.
Figure 10. Mean height profiles of the daily atmospheric pressure deviations above Vostok under conditions of the negative and positive ESW changes (from Troshichev et al., 2004).
To check this concept, the aerological measurements of the atmospheric winds at altitudes h = 0-25 km have been also analysed in (Troshichev, 2008). The only horizontal wind parameters were measured at the air balloons launched at Vostok, and just these data were used to extract information about changes in the vertical flow of air masses. Figure 11. shows the mean vertical profiles of the horizontal wind mean direction and mean speed for ―zero‖ day with large negative ESW leap, for preceding -1st day (level of reference), and for succeeding 1st, 2nd, and 4th days. One can see that the wind azimuths lay in range 270-290° at
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h= 15-25 km, 240-270° at h=10-15 km, and 210-240° at h=5-10 km, i.e. the horizontal winds blow approximately toward the East. To understand this regularity we have to remember that the masses falling vertically in the rotating Earth‘s system are deviated toward the East under the action of Corioles force. Speed of this deviating motion is determined by formula ve = ω x r , where ω is the angle speed of the Earth‘s rotation (ω = 1/240 °/s), and r is radius-vector in the point of observation (r ~ 880 km at latitude of Vostok station, φ = 82°). Taking into account these quantities and making allowance for angle ~ 8° between vectors ω and r, a rough measure of the deviation speed is obtained, ve ≈ 10 m/s. It is just mean value of the horizontal speed that was observed in aerological observations at altitudes 10-15 rm above Vostok station. Thus, we can suggest that direction and speed of the regular wind in the surface atmosphere at a top of the Antarctic ice dome is determined by deviating action of Corioles force on the descending air masses.
Figure 11. Dependence of the height profiles of the horizontal wind mean direction and mean speed above Vostok on the negative ΔESW influence. The wind profiles for the -1st day preceding the ΔESW impact (dotted lines) are taken as a level of reference (from Troshichev et al., 2004).
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In response to the negative ESW leap the wind horizontal speed decreases in a key (―zero‖) day at altitudes higher 12 km and sharply increases at altitudes from 5 to 12 km (up to 35 % at h = 8-9 km), the vertical wind profile for -1st day being taken as a level of reference. The opposite regularity is typical of the positive ESW leaps. By the forth day the wind speed recovers to the quiet level. Taking into account that Corioles acceleration should be directly dependent on speed of the descending air masses, we suggest that increase or decrease of the wind horizontal speed is indicative of acceleration or slowing-down of the descending air masses. In such a case we came to conclusion that formation of cloud layer at h=5-10 km is favourable to acceleration of the descending masses, whereas clear sky favours their slowing-down. The mechanism of this linkage is unclear. The acceleration (slowing-down) process should lead to the strong enhancement (or reduction) of the atmospheric pressure just for day of the negative (positive) ESW leap, as we have seen in Figure 10. It should be noted that the enhanced atmospheric pressure keeps during some days in the surface level (~ 3.5 km at Vostok station). One might expect that occurrence of the enhanced atmospheric pressure in the Central Antarctica will led to violation of the wind regime above the whole Antarctica.
ANOMALOUS WINDS AT THE ANTARCTIC STATIONS AND THEIR RELATION TO THE IMF BZ The wind azimuth distribution at each Antarctic station is a specific feature, which is determined by the large-scale katabatic wind system and by local orography at a particular coast stations. Two separated extremes in the wind occurrence are observed at the coast stations during the winter season. The main noticeable extreme at 60-120° corresponds roughly to the westward wind formed due to action of the Corioles force on the moving radially drainage flow. The secondary minor extreme nearby 180° corresponds to the anomalous wind flowing from the Antarctic coast toward equator. One wide and rather flat maximum in a range from 180º to 270° is typical of the near-pole station Vostok, but the high-speed winds (V > 6 m/s) are observed exclusively at azimuth around 200°. In view of it, the winds at Vostok station falling within the range 180-210° were examined as anomalous winds. Figure 12. shows directions of the main and anomalous winds plotted on the map of Antarctica for all 13 stations. Thus, two wind patterns are typical of the winter Antarctica: the main pattern is the regular circumpolar circle surrounding the continent, and the secondary pattern is system of the ―anomalous winds‖ flowing from Antarctica toward the equator. Analysis of relationship between the anomalous wind occurrence and changes in IMF BZ component demonstrated (Troshichev et al., 2008) that the anomalous winds were preceded by the southward IMF coupling with the magnetosphere. Figure 13. shows, as an example, behavior of the mean anomalous wind observed at near-pole station Vostok in 1981-1989, and the mean anomalous winds observed simultaneously at the coast stations Neumayer, Casey, Russkaya, situated, correspondingly, in the Atlantic, Indian and Pacific ocean sectors. The mean variation of the appropriate IMF BZ component was calculated separately for each station taking into account only the events with anomalous wind observed at this certain station. The day with anomalous wind occurrence at each particular station was taken as a zero date.
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One can see from Figure 13. that occurrence of the anomalous winds at the coast stations was preceded by the increase of southward IMF BZ and was delayed one-two days relative to the wind strengthening at Vostok. Not all wind violations starting at the Antarctic Ridge are extended to cover the overall coast area: only 82% of anomalous winds detected at Vostok reach Casey, located in the Indian ocean sector and as few as 41% reach Neumayer, located in the Atlantic sector.
Figure 12. Distribution of the regular (solid arrows) and anomalous (dashed arrows) winds at the Antarctic stations (from Troshichev et al., 2008).
Figure 13. Anomalous winds at stations Vostok, Neumayer, Casey and Russkaya in their relation to changes in the IMF BZ for winter seasons of 1981-1989, the day with anomalous wind occurrence at each particular station being taken as a key date (from Troshichev et al., 2008).
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It seems likely that extent of the coast station involvement in the process of the wind violation varies from one event to other. The anomalous winds at the coast stations, associated with high speed (V > 6m/s) anomalous wind at Vostok, were accompanied by the sharp reduction of the westward wind speed and by the succeeding wind turning toward the equator. This regularity corresponds to decay of the circumpolar vortex while increasing the katabatic winds, noticed in (Yasunari and Kodama, 1993). The efficiency of the anomalous winds influence on the circumpolar vortex turned out to be dependent on duration of the southward IMF action: the 3-days influence of southward IMF with average ΔBZ ~ 3 nT (10 events) preceded the anomalous winds, which were observed simultaneously at the all coast stations.
SOI AND ITS RELATION TO ANOMALOUS WIND SYSTEM IN ANTARCTICA Southern Oscillation (SO) is determined (Philander and Rasmussen, 1985) as a negative correlation between the sea level pressure fluctuations in the Southeast Pacific high and the North Australian-Indonesian low. A coupled system linking an anomalous warming of surface water in the eastern Pacific (El Niño) to an atmospheric branch SO, was named ENSO. During the years between warm events the opposite regularity often occurs and a cold phase of ENSO, the La Nina, exists (Van Loon and Shea, 1987). Nature of the ENSO action is unknown. Stable links between Southern Oscillation and atmospheric processes in Antarctica was revealed in many studies (Trenberth, 1980; Mo et al., 1987; Van Loon and Shea, 1985, 1987; Parish and Bromwich, 1987; Bromwich et al., 1993; Smith and Stearns, 1993). The conclusion was made, that propagation of the katabatic winds from Antarctica is a phenomenon that is accompanied by changes that involve the entire southern hemisphere (Bromwich et al., 1993). To characterize the phase and intensity of the ENSO activity the Southern Oscillation Index (SOI) is used. SOI presents difference between the monthly pressure anomalies at Tahiti (Central Pacific) and Darwin (North Australia) (Van Loon and Shea, 1987). The SOI is a nondimensional index, which is negative when ENSO is in a warm phase (El Niño events) and positive when ENSO is in a cold phase (La Nina events). One of the most intriguing feature of El Niño events is the seasonal regularity in their occurrence: formation of ENSO occurs mainly during the southern autumn-winter season (Van Loon and Shea, 1987). Troshichev et al. (2005) examined all large negative SOI deviations during 1868-2002 and separated them in two groups in accordance with their duration: the short-lived deviations, lasting less than 3 months (17 events), and long-lived deviations, lasting more 6 months (23 events). It turned out that the long negative deviations (Figure 14), which correspond to real El-Nino events, start usually between March and June, and their mean early variation (thick line) reaches the minimum in June and tends to restore in November/December. The short deviations of SOI can begin in any time of year and their mean monthly values are close to zero. To demonstrate the possible relation of SOI to the anomalous winds the mean angular distribution of the monthly winds (―the wind roses‖) at each station were examined for months preceding and succeeding the El-Niño beginning (Troshichev et al., 2005). The ElNiño events with sharp onset (decrease of SOI value more than 1 during the month) have
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been only included in the examination. The wind rose for the –4th month, preceding the ElNiño onset, has been taken as a level of reference for all succeeding months, and the appropriate ―differential wind roses‖, characterizing the changes in the wind azimuths for -3d, -2d, -1st, and zero (El-Niño onset) months have been constructed. Results of the analysis testified that the evident excess of winds above the level of reference was observed at angles 195-210° for Vostok, 185-215° for Russkaya, and 270-300° for Leningradskaya, which just correspond to azimuths of the anomalous winds at these stations. As Figure 15. shows, the anomalous winds are observed during -2d and -1st months, preceding the El-Niño onset, and did not typical of -3th and zero months (as well as of succeeding months, which are not shown in Figure 15).
Figure 14. Behavior of SOI index in course of large negative long-lived and short-lived SOI deviations during 1868-2002 (from Troshichev et al., 2005).
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Figure 15. Differential wind roses, characterizing the changes in wind occurrence in course of El-Niño events for stations Vostok (a), and Russkaya (b) (from Troshichev et al., 2005).
Availability of statistically significant relationships between the disturbed solar wind and anomalous winds above the Antarctica, on the one hand, and between the anomalous winds and SOI, on the other hand, makes it possible to suggest that linkage between the disturbed solar wind and development of SOI would be presented. Unfortunately, the monthly IMF data are very incomplete for years preceding 1998, and the relation of SOI to AE index (instead of IMF) was examined in (Troshichev et al., 2005). Only sharp SOI events, in which the monthly value of SOI (negative or positive) was changed by 1 or more, have been included in the analyses. The month of this sharp change has been taken as a zero date in the superposition analysis. Figure 16. shows behavior of SOI index for three types of changes in the southern oscillation: (a) sharp declination of SOI with subsequent keeping of negative value during many months (basically, it is real El-Niño events with sudden onset) observed in 1969, 1972, 1982, 1986, 1991, 1994, (b) sharp short-lived declination of SOI (1959, 1961, 1979, 1980, 1984, 1985), and (c) short-lived increase of SOI (1962, 1964, 1970, 1975). The low panel in Figure 16 presents the proper changes in AE index. One can see, that in case of long negative SOI deviations the mean magnetic activity starts to increase 2-3 months before the beginning of El-Niño and reaches maximum just in month of the beginning (s.s. = 0.96).
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Figure 16. Relationship between changes in monthly values of SOI and AE indices for long-lived negative deviation of SOI (a), and short-lived negative and positive deviation of SOI (b) (from Troshichev et al., 2005).
Figure 17. A conceptual sketch of generation of the electric currents in the low-latitude boundary layer, while the solar wind coupling with the magnetosphere (adopted from Troshichev, 1982). It is shown the magnetosphere dawn-dusk cross viewed from the Sun. The arrows denote the electric currents. The field-aligned currents, flowing in the southern and northern polar caps at the dawn side and flowing out at the dusk side, provide the polar cap electric voltage.
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On the contrary, in cases of short-term positive or negative deviations of SOI, the magnetic activity does not show the noticeable changes before and after the SOI impulses. These results make it possible to conclude, that changes, negative or positive, in the southern oscillation occur irrespective of the solar wind influence, but development of the veritable ElNiño events, happening during southern winter, is likely influenced by the intense and lasting disturbances in the interplanetary electric field and correlate with corresponding magnetic activity.
MECHANISMS SUGGESTED TO EXPLAIN THE SOLAR WIND INFLUENCE ON THE ATMOSPHERIC PROCESSES A suggestion about the influence of the interplanetary electric field on cloudiness in Antarctica was made in (Troshichev and Janzhura, 2004) and based on the well-established fact of the solar wind impacting the magnetosphere. While the magnetosphere – solar wind coupling the interplanetary electric field, bearing by solar wind, generates the field-aligned currents, connecting the boundary magnetosphere with the polar ionosphere. The fieldaligned currents flow into the polar ionosphere at the dawn side and flow out of the ionosphere at the dusk side, and provide the ―overhead‖ polar cap ionospheric potential. The corresponding impact scheme is presented in Figure 17, adopted from (Troshichev, 1982). Although some details of this process continue to be unknown, the linkage between the interplanetary electric field and the polar cap voltage is principally resolved and well defined. Sharp changes of the ionospheric potential should intensify or reduce the electric currents between the polar ionosphere and the surface, passing through the layer at 5-8 km, where the atmospheric conductivity sharply declines (Handbook of Geophysics, 1985). The connecting link between the polar cap voltage and the polar atmosphere is realized by the global electric circuit. There is a constant potential difference ~ 250 kV between the ionosphere and the Earth‘s surface, which is provided by the tropic thunderstorms. This potential drives the return downward currents (see Figure 18), which are most intense and variable in the polar areas (3-5 pA/m2) due to the effects of cosmic and magnetospheric energetic particles, and, what is more important, the influence of the polar cap voltage. The influence of the solar wind on the global electric circuit is well documented (Tinsley, 1996). The actual changes of the polar cap atmospheric electric field represent the combination of so-called Carnegie curve (describing the daily course of the tropic thunderstorms) and the deviations controlled by the ЕSW changes (Frank-Kamenetsky et al., 1999, 2001). It means that the interplanetary electric field affects the ―overhead‖ ionospheric potential above the station. According to Tinsley and Deen (1991) and Tinsley and Heelis (1993), who examined the cloud layer properties in relation to the global electric circuit, the space charges are accumulated at the boundary of sharp changes of atmospheric conductivity, in proportion to the downward current density through the cloud. It was shown that the ionosphere-Earth current density is modulated, particularly, by the polar cap ionospheric potential (Tinsley and Zhou, 2006). The changes in tropospheric ionization might affect the rate of freezing of supercooled water droplets in high clouds. Since the mechanism of electrofreezing acts irrespective of the solar irradiation input, it would be workable also in the near-pole region under conditions of the polar night.
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Figure 18. Diagram illustrating the global atmospheric electric circuit and the causes of its temporal and spatial variation (from [Tinsley and Zhou, 2006]). The vertical scale is greatly exaggerated below 120 km and greatly compressed above.
CONCLUSION Thus, the concept of the solar wind influence on processes in the Antarctic atmosphere seems to be convincingly verified with use of all available meteorological and aerological observations (Troshichev et al., 2003, 2004, 2005, 2008; Troshichev and Janzhura, 2004; Troshichev, 2008). The disturbed solar wind has a greater impact on atmosphere processes in the central Antarctica, where the large-scale system of vertical circulation is formed during the winter seasons. The impact is realized through the interplanetary electric field ESW, which influences the magnetosphere field-aligned currents, creating the appropriate polar cap electric voltage. The ionospheric electric potential strongly affects the global electric circuit, which is generated by the tropic thunderstorms and is closed mainly in polar caps. Two processes are brought into operation when the IMF BZS component and the appropriate electric field ESW strongly increase. The first of them is formation of the cloud layer above the Antarctic Ridge, where the air masses income into the central Antarctica from above troposphere. Under the usual conditions the atmosphere on the Antarctic ridge is in state of the thermal quasi-equilibrium owing to superposition of the adiabatic warming of the descending air masses and stable radiation cooling of air situated at the ice sheet. The cloud layer will efficiently backscatter the long wavelength radiation going from the ice sheet, but it will not affect the adiabatic warming process. As a result of the radiative cooling reduction, the atmosphere should be warm below the cloud layer and would be cool above the layer. Just such regularity is observed during specific events of the sudden warmings, happening from time to time in the central Antarctica. The second process is acceleration of the air masses incoming into the central Antarctica from troposphere. This process causes the sharp increase of the atmospheric pressure in the surface layer and gives rise to collapse of the regular large-scale wind system above the entire
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Antarctica. The draining winds are strongly strengthened and the circumpolar vortex about the periphery of the Antarctic continent correspondingly decays. Both processes are strongly linked and lead to the cold air masses flow out to the Southern ocean. The latter process evidently destroys the regular relationships between the sea level pressure fluctuations in the Southeast Pacific high and the North AustralianIndonesian low and promote the El-Niño beginning.
REFERENCES Bromwich, D.H., J.F. Carrasco, Z. Liu and R.Y. Tzeng: Hemispheric atmospheric variations and oceanographic impacts associated with katabatic surges across the Ross Shelf, Antarctica. J. Geophys. Res., 98(D7), 13045-13062 (1993). Egger, J.: Slope winds and the axisymmetric circulation over Antarctica. J. Atmos. Sci., 42, 1859-1867 (1985). Farrar, P.D.: Are cosmic rays influencing ocean cloud coverage – or is it only El Nino? Climate Change., 47, 7-15 (2000). Frank-Kamenetsky, A.V., G.B. Burns, O.A. Troshichev, V.O. Papitashvili, E.A. Bering and W.J.R. French: The geoelectric field at Vostok, Antarctica: its relation to the interplanetary magnetic field and the cross polar cap potential difference. J. Atmos. SolarTerr. Phys., 61, 1348-1356 (1999). Frank-Кamenetsky, A.V., O.A. Troshichev, G.B. Burns and V.O. Papitashvili: Variations of the atmospheric electric field in the near-pole region related to the interplanetary magnetic field. J. Geophys. Res., 106, 179-190 (2001). Handbook on Geophysics and the Space Environment, (Eds Jursa, A.S.). Air Force Geophysical Laboratory, USAF (1985). Harrison, R.G. and K.S. Carslaw: Ion-aerosol-cloud processes in the lower atmosphere, Rev. Geophys., 41, 1012-1026. doi: 10.1029/2002RG000114 (2003). Herman, J.R. and R.A. Goldberg: Sun, Weather, and Climate. NASA, Washington, D.C., 430 p. (1978). James, I.N.: The Antarctic drainage flow: Implications for hemispheric flow on the Southern Hemisphere. Antarct. Sci., 1, 279-290 (1989). Kristjansson, J.E., A. Staple, J. Kristiansen and E. Kaas: A new look at possible connection between solar activity, clouds and climate, Geophys. Res. Let., 29(23), 2107, doi:10.1029/2002GL015646 (2002). Marsh, N. and H. Svensmark: Galactic cosmic ray and El Nino-Southern Oscillation trends in International Satellite Cloud Climatology Project D2 low-cloud properties, J. Geophys. Res., 108(D6), 4195 doi: 10.1029/2001JD 001264 (2003). Mo, K.C., J. Pfaendtner and E. Kalnay: A GCM study on the maintenance of the June 1982 blocking in the southern hemisphere. J. Atmos. Sci., 44, 1123-1142 (1987). Palle, E. and C.J. Butler: The proposed connection between clouds and cosmic rays: cloud behavior during the past 50-120 years. J. Atmos. Solar-Terr. Phys., 64(3), 327-337 (2002). Parish, T.R. and D.H. Bromwich: The surface windfield over the Antarctic ice sheets: Nat., 328, 51-54 (1987).
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Parish, T.R. and D.H. Bromvich: Continental-scale simulation of the Antarctic katabatic wind regime. J. Climate., 4, 135-146 (1991). Parish, T.R.: On the role of Antarctic katabatic winds in forcing large-scale tropospheric motions. J. Atmos. Sci., 49, 1374-1385 (1992). Philander, S.G. and E.M. Rasmusson: The southern oscillation and El-Nino, Adv. Geophys., 28(A), 197-215 (1985). Pudovkin, M.I. and S.V. Veretenenko: Cloudness decreases associated with Forbushdecreases of the galactic cosmic rays. J. Atmos. Terr. Phys., 57, 1349-1355 (1995). Pudovkin, M.I., S.V. Veretenenko, R. Pellinen and E. Kyro: Cosmic ray variation effects in the temperature of the high-latitude atmosphere. Adv. Space Research., 17(11), 165-168 (1996). Pudovkin, M.I., S.V. Veretenenko, R. Pellinen and E. Kyro: Meteorological characteristic changes in the high-latitudinal atmosphere associated with Forbush decreases of the galactic cosmic rays. Adv. Space Res., 20(6), 1169-1177 (1997). Schwerdtfeger, W.: Weather and Climate of the Antarctic, 261pp., Elsevier, New York (1984). Smith, S.R. and C.R. Stearns: Antarctic pressure and temperature anomalies surrounding the minimum in the southern oscillation index. J. Geophys. Res., 98, 13071-13083 (1993). Svensmark, H. and E. Friis-Christensen: Variation of cosmic ray flux and global cloud coverage - a missing link in solar climate relations, J. Solar-Terr. Phys., 59, 1225-1232 (1997). Tinsley, B.A.: Correlations of atmospheric dynamics with solar wind induced changes of airEarth current density into cloud tops. J. Geophys. Res., 101, 29701-29714 (1996). Tinsley, B.A., G.M. Brown, and P.H. Scherrer: Solar variability influences onweather and climate: possible connection through cosmic ray fluxes and storm intensification. J. Geophys. Res., 94, 14783-14792 (1989). Tinsley, B.A. and C.W. Deen: Apparent tropospheric response to MeV-GeV particle flux variations: a connection via eletrofreezing of supercooled water in high-level clouds? J. Geophys. Res., 96, 22283-22296 (1991). Tinsley, B.A. and R.A. Heelis: Correlations of atmospheric dynamics with solar activity: evidence for a connection via the solar wind, atmospheric electricity, and cloud microphysics. J. Geoph. Res., 98, 10375-10384 (1993). Tinsley, B.A. and L. Zhou: Initial results of a global circuit model with variable stratospheric and tropospheric aerosols, J. Geophys. Res., 111, 16205-16223 doi: 10.1029/2005JD006988 (2006). Todd, M. and D. Kniveton: Changes in cloud cover associated with Forbush decreases of galactic cosmic rays, J. Geophys. Res., 106, 32031-32041 (2001). Trenberth, K.E.: Planetary waves at 500 mb in the southern hemisphere. Mon. Weather Rev., 108, 1378-1389 (1980). Troshichev, O.A.: Polar magnetic disturbances and field-aligned currents. Space Sci. Reviews., 32, 275-360 (1982). Troshichev, O.A., L.V. Egorova and V.Ya. Vovk: Evidence for influence of the solar wind variations on atmospheric temperature in the southern polar region. J. Atmos. Solar-Terr. Phys., 65, 947-956 (2003).
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Troshichev O.A., L.V. Egorova and V.Ya. Vovk: Influence of the solar wind variations on atmospheric parameters in the southern polar region. Adv. Space Res., 34, 1824-1829 (2004). Troshichev, O. and A. Janzhura: Temperature alterations on the Antarctic Ice sheet initiated by the disturbed solar wind. J. Atmos. Solar-Terr. Phys., 66, 1159-1172 (2004). Troshichev, O.A., L.V. Egorova and V.Ya. Vovk: Influence of the disturbed solar wind on atmospheric processes in Antarctica and El-Nino Southern Oscillation. Mem. Soc. Astronomy of Italia., 76, 890-898 (2005). Troshichev, O., V. Vovk and L. Egorova: IMF associated cloudiness above near-pole station Vostok: impact on wind regime in winter Antarctica, J. Atmos. Solar Terr. Phys., 70, 1289-1300 (2008). Van Loon, H. and D.J. Shea: The Southern Oscillation, IV: The precursors south of 15°S to the extremesof the oscillation, Mon. Weather Rev., 113, 2063-2074 (1985). Van Loon, H. and D.J. Shea: The Southern Oscillation, VI, Anomalies of sea level pressure on the southern hemisphere and of Pacific sea surface temperature during the development of a warm event, Mon. Weather Rev., 115, 370-379 (1987). Wilcox, J.M.: Solar activity and weather, J. Atmos. Terr. Phys., 37, 237-243 (1975). Yasunari, T., and S. Kodama: Intraseasonal variation of katabatic wind over East Antarctica and planetary flow regime in the southern hemisphere. J. Geophys. Res., 98, 1306313070 (1993).
In: Antarctica: The Most Interactive Ice-Air-Ocean Environment ISBN: 978-1-61122-815-1 Editors: Jaswant Singh, H.N. Dutta © 2011 Nova Science Publishers, Inc.
Chapter 10
ATMOSPHERIC OBSERVATIONS AT DOME C, ANTARCTIC PLATEAU, ONE OF THE COLDEST PLACE IN THE WORLD S. Argentini * and I. Pietroni ABSTRACT Atmospheric field experiments were made during several years at the French-Italian plateau station of Concordia at Dome C (Lat. 75° 06.06 S, Long. 123° 20.74 E, 3250 m a.s.l.) in Antarctica. On 2005 Concordia became a permanent station, this allowed to carry out the one year atmospheric field experiment STABLEDC (Study of the STABLE boundary layer environmental at Dome C). The aim of STABLEDC was to study the processes occurring in the long-lived stable, and the weak convective atmospheric boundary layers, observed during winter and summer respectively, and to collect the relevant input parameters for atmospheric models. Both in situ and ground based remote sensing instruments were used to monitor meteorological parameters. This paper book summarize the main results from STABLEDC.
1. INTRODUCTION Antarctica has a fundamental role in the global climate system. However due to its remoteness and inaccessibility, relatively little is known about the processes occurring in the interior of the ice sheet. In the long Antarctic winter, with no short-wave radiation, the surface is cooled continuously through negative net long-wave radiation which is enabled by clear sky conditions and the very cold and dry overlying atmosphere. This energy loss is partially compensated by the turbulent and sub-surface heat fluxes which extract heat from both the atmosphere and the ice sheet, cooling the near surface air and snow. As a consequence of this *
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radiative cooling strong surface-based inversions develop. Phillpot and Zillman (1970) studied the climatology of the temperature inversion across the Antarctic continent, they found that the inversions over South Pole are on average about 20 K in winter, while those over the highest parts of the plateau are on average 25 K. Connolley (1996) gives an overview of the temperature inversion at 21 Antarctic stations (whose 3 in the interior); following Jouzel and Merlivat (1984) he derived a regression between the surface temperature and the inversion strength all over the Antarctic continent also showing the dependence of this relationship on the terrain slope. Other analyses were done to investigate the link between the near-surface winds and the temperature inversions (Dalrymple et al., 1966 and Lettau and Schwerdtfeger, 1967). Hudson and Brandt (2005) studied the surface-based inversion over the Antarctic plateau; they focused on the measurements from South Pole and Dome C, but the analyses were done for a short period and limited to the first 30 m of atmosphere at South Pole, and restricted to the summer season at Dome C. In presence of a surface slope, the denser and colder air masses of air adjacent to the surface are forced down-slope due to the horizontal pressure gradient, and deflected to the left by the Coriolis force. As a result the well known katabatic winds take place. The katabatic wind regime can be occasionally interrupted by the horizontal advection of warm air masses, or the presence of strong large-scale winds. On the other hand, during the Antarctic summer, the absorption of short-wave radiation introduces a diurnal cycle in the behaviour of the solar radiation. Although the amount of solar radiation available to heat the surface is limited by the high surface albedo the surface warming may cause a weak convection and the formation of a Convective Boundary Layer (hereafter CBL) during daytime (Mastrantonio et al., 1999, Argentini et al., 2005). Reliable measurements of the radiation balance at the surface on the Antarctic ice sheet are important to assess its role as heat sink in the climate system of the earth, as ground truth for satellite observations (e.g., to distinguish between clouds and the snow surface) and for validation of atmospheric models (King and Connolley 1997). They may also be used to develop albedo parameterizations of dry snow for atmospheric models or, for radiation parameterization in energy and mass balance and ice dynamical models (Van de Wal and Oerlemans 1997). A reliable estimate of the Surface Energy Balance (hereafter SEB) is not possible without an accurate measurement of the radiation components (Bintanja and van den Broeke 1995; Van As et al. 2005b) which can be affected by several problems related to snow properties and sun elevation angle. Long-wave fluxes dominate the surface heat budget in Antarctica because of the region‘s high solar albedo and prolonged periods of darkness. The Antarctic atmosphere is highly transmissive for solar radiation, especially in the high interior plateau where the atmosphere is thin and the concentrations of clouds, water vapour and aerosol are low. Even in full summer, when the solar zenith angles are large, the finegrained, dry and clean snow surface absorbs only 5–25% of the incoming short-wave radiation (Carroll and Fitch, 1981). On the other hand the snow, like most natural surfaces, has a high long-wave emissivity (ε≈0.98) (Wiscombe and Warren, 1980) so that it effectively looses heat in the form of long-wave radiation. In combination with an atmosphere that is cold, dry, thin, clear and clean, this leads to a pronounced (long-wave and all-wave) radiation deficit at the surface in winter. An average turbulent transport of sensible heat from the atmosphere to the surface compensate for this heat loss. This loss of energy makes the Antarctic ice sheet a major heat sink in the Earth‘s atmosphere and introduces a strong
Atmospheric Observations at Dome C, Antarctic Plateau, One of the Coldest Place… 201 coupling between the radiation balance and near-surface climate (Dutton et al., 1991; Stanhill and Cohen, 1997). Despite the number of observational studies of SEB carried out in Antarctica, only few measuring campaigns have been done during the winter and in the interior, due to the dearth of occupied stations on the polar plateau and the enhanced difficulty of maintaining instruments on robotic platforms. The above notwithstanding, the number of winter time experimental campaigns in Antarctica during the winter is slowly increasing, although with often unknown quality of data. A short history of the SEB studies from unmanned stations is available, from Weller, 1980; Carroll, 1982; King and Turner, 1997; Wendler et al., 1988; Bintanja and van den Broeke, 1995; Reijmer et al., 1999; Argentini et al., 2005; van As et al., 2005a. Some of these studies evidenced that the magnitude of the surface heat fluxes exhibit strong spatial and temporal variations, which reflect the differences in the prevailing meteorological conditions and in the state of the surface. King et al. (2006) describe the summer SEB at two contrasting Antarctic sites: the interior site of Dome C (75°S 123‘E) at 3306 m a.s.l and the coastal site at Halley (75°S, 26‘W) at 30 m a.s.l. At both stations, the short wave radiation produces a diurnal cycle in net radiation, which results in a diurnal cycle of surface temperature. Despite this similarity, the summer-time SEB differs significantly at the two sites for what regards the behaviour of the sensible heat flux. Convection signature is observed on acoustic radar echograms at the cold Dome C site, while is absent at Halley. This is due to the large summer-time net radiation at Halley generating melt, which limits the partitioning of the SEB into convection. Due to the extreme temperatures, dryness and the high altitude the Antarctic plateau is a potential ideal site for astronomical observations otherwise possible only from space. For this reason in the last years the optical turbulence over the Antarctic plateau has been object of studies by astronomers (for ex. Hagelin, 2008), the optical turbulence intensity depending on vertical gradients of the wind velocity and on the temperature inversion strength (Marks et al., 1999). A large atmospheric field experiment STABLEDC (Study of the STAble Boundary Layer Environmental at Dome C) was held at the French-Italian station of Concordia located on the Antarctic plateau at Dome C during 2004-2005. This was the first over wintering at Concordia. The aim of the field experiment was to test an observing system to study the processes occurring in the long-lived stable, and the weak convective atmospheric boundary layers, observed during winter and summer respectively, and to collect the parameters relevant for the atmospheric models. The results obtained during this experiment are shown in the following sessions.
2. SITE AND INSTRUMENTATION Concordia is a permanent station located at Dome C, Antarctica (74.1°S, 123.3°E, 3233 m a.s.l.), on the East Antarctic plateau approximately 1000 km from the nearest coast (Figure 1). It is jointly operated by the French IPEV (Institut Polaire Français Paul-Émile Victor) and Italian PNRA (Programma Nazionale Ricerche in Antartide) polar institutes. Dome C is set on a regional topographic maximum on the plateau where the local slopes do not exceed 1%.
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The climate consists of a synoptic coastal influence which brings relatively warm and cloudy air masses, and gravity driven flow occurring under cold, clear, sky conditions. Low wind speeds combined with frequent stable boundary layers and small surface roughness result most of the time in low atmospheric thermal turbulence at Dome C.
Figure 1. Position of Dome C (red dot DC) in Antarctica.
The annual mean wind speed is 3.4 m s-1 with extreme values up to 16 m s-1. Monthly mean temperatures were –39 °C in summer and –61 °C in winter. Most of the time, strong surface inversions occur at Dome C, creating a large cold air source feeding the katabatic winds observed in some zones of confluence along the East Antarctic coast. In situ and ground based remote sensing sensors were used to monitor the behaviour of the meteorological parameters. The instrumentation as well as the measurements done during the field experiment are listed in Table 1. Turbulence and radiation measurements were made in the period November 2004 January 2006. Turbulent heat and momentum fluxes were derived from eddy covariance measurements (Lee et al., 2004) using a Metek USA-1 sonic thermo-anemometer sampling at 10 Hz installed 3.6 m above the snow surface; long- and short-wave radiation components were measured using a Kipp and Zonen CNR-1 net radiation sensor system installed 1 m above the snow surface. The heat flux within the snowpack was measured at a depth of 50 mm using a Campbell Scientific HFP01 heat flux plate. A mini-SODAR (Sound Detection and Ranging) Doppler system (Mastrantonio et al., 1999) provided a continuous record of the structure of the atmospheric boundary layer along the year. A passive Meteorological Temperature Profiler (MTP-5P) (Kadygrov and Pick, 1998) was used for the remote measurement of the air temperature profile.
Atmospheric Observations at Dome C, Antarctic Plateau, One of the Coldest Place… 203 The instrumentation was placed approximately 1000 m South of the main base buildings. Since the dominant wind direction is from the sector 150°-210° this ensured an unobstructed fetch over the measurement site. In addition to the measurements described above, standard meteorological parameters provided by the AWS (Automatic Weather Stations), and radiosonde profiles (once a day) were available from other projects. Table 1. Sensor and measured micrometeorological variable SENSOR Radiometer mod.CNR-1 (Kipp and Zonen) with two pyranometers (CM3) up and down two pyrgeometers (CG3 ) up and down Conventional HFP01 heat flux plates 0, 5, 15, 30, 50 cm A sonic anemo-thermometer mod. USA-1 (Metek) and a fast response LICOR Lyman-alpha-hygrometer (only summer ) 13-m Tower : thermometers, hygrometers and wind probes at 1.25, 2.5, 5, 10 and 13 m A triaxial Doppler mini-SODAR Range 12 - 400 m , Resolution 13 m Micro-lidar 532 nm wavelength , Range 300 m Passive Microwave radiometer MTP5P by Kipp and Zonen. Range 0-600 m Radio soundings
MEASURE Radiative budget: - Incoming and outgoing short-wave and long-wave radiation. -Net Radiation -Albedo Sub-surface energy fluxes, snow temperature profiles: -Snow heat fluxes Energy budget: -Turbulent Fluxes (Heat, Latent, Momentum)
Surface layer profiles of mean variables
PBL measures : -Thermal structure of the ABL, Boundary layer depth, wind speed PBL measures: -Aerosols content; - Aerosol phase (liquid water or ice crystal), - Particles size PBL measures: - Temperature, Development and break down of atmospheric inversions Atmosphere: - Temperature; - Pressure; -Wind speed
For convenience, all subsequent results are presented with reference to local time. The terms ―night-time‖ and ―nocturnal‖ are referred to the periods of negative surface radiation balance.
3. THE CLIMATOLOGICAL SETTING The average values of the mean wind, temperature, and sensible heat flux for the period 15 November 2004 - 13 January 2006 and for the different seasons are shown in Table 2. The ―seasons‖ have been defined as follows: 1° Summer: 15 November 2004 - 1 February, 2005 2° Summer: 15 November 2005 - 13 January, 2006 Autumn: 1 February - 1 April, 2005
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The annual mean wind speed is 4.4 ms-1 with extreme values up to 12 ms-1. The mean annual temperature is –45 oC. The lowest temperatures (-72 °C was the minimum) are observed during the winter while the highest temperatures (-29 °C was the maximum) are observed during the summer. Table 2. Mean values of the wind speed, temperature and sensible heat flux for the measurement periods: summer, autumn, winter and spring Period
All
Summer
Autumn
Winter
Spring
Summer
Parameter
2004/12/14 to 2006/01/13
2004/12/14 to 2005/01/31
2005/02/01 to 2005/03/31
2005/04/01 to 2005/09/14
2005/09/15 to 2005/11/14
2005/11/15 to 2006/01/13
Mean wind speed (m/s)
4.4 ± 2.0
3.5 ± 1.6
4.2 ± 1.7
4.9 ± 2.0
4.8 ± 2.2
4.0 ± 2.0
Mean temperature (°C)
-44.8 ±12.2
-29.3 ± 4.7
-47.2 ± 7.8
-54.8 ± 6.9
-46.8 ± 7.6
-30.2 ± 5.7
Mean sensible heat flux (Wm-2)
-4.5 ± 10.4
3.2 ± 8.9
-4.8 ± 8.1
-10.6 ± 8.8
-6.1 ± 9.5
2.4 ± 9.0
Strong long-lived ground based inversions occur most of the time at Dome C with the exception of the summer days during the hours of maximum insulation (and positive values of net radiation). These inversions contribute to create a large cold air source producing and feeding the katabatic winds observed in most of the glaciers confluence zone along the East Antarctic coast. Few clouds are generally present in the sky above Dome C since cloud cover and precipitation decrease as one moves inland from the coast, and the frequency of occurrence of active weather systems is low (King and Turner, 1997). However Argentini et al. (2001) have shown that warming events are periodically observed at Dome C during the winter; during these periods the surface temperatures sometimes may reach the summer values. In correspondence of the warming events the wind direction changes from 180° (the most frequent wind direction) to 0° (which is from the coast), indicating that the warming events are correlated to phenomena originating along the coast (i.e. advection of warm air).
Atmospheric Observations at Dome C, Antarctic Plateau, One of the Coldest Place… 205
4. BEHAVIOUR OF SOME METEOROLOGICAL PARAMETERS 4.1. Wind Speed The frequency distribution of the wind is shown in the polar graph of Figure 2. The wind direction is separated in 12 intervals whereas the wind speed in 4 classes: 0-2 ms-1, 2-4 ms-1, 4-6 ms-1 and greater than 6 ms-1. Most of the time the winds blows from the sector 150°-300°, in this sector are also observed the strongest (greater than 4 ms-1) winds. The peak in this sector is observed between 180°-210°, that is from the continent. The wind (Figure 3) reaches the highest velocities (11 ms-1) during the winter warming events. The rest of the time the wind velocity periodically varies between 2 ms-1 and 7 ms-1. 0°
30 %
330°
30° 24 % 18 %
300°
60° 12 % 6%
0 v < 2 ms -1
90°
270° 2 v < 4 ms -1
4 v < 6 ms -1
240°
120°
v 6 ms -1
210°
150° 180°
Figure 2. Wind rose for four different velocity ranges.
The wind speed during the summer (Figure 4.a) exhibits a clear diurnal variation with a peak during the warmest hours of the day. As shown also by King et al. 2006, a little variation in wind speed occurs between 1900 and 0600 local time (LT). After 0600 LT, the wind speed increases gradually until local noon, when it is about 1.5 ms-1 higher than it was at 0600 LT. The wind speed then remains fairly constant until 1500 LT, after which it falls off at a rate somewhat faster than it increased during the morning, reaching its ―night-time‖ value at around 1900 LT.
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Speed (ms-1)
9 8 7 6 5 4 3 2 1
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan
Figure 3. Wind velocity behaviour at Concordia station from January 2005 to January 2006.
Figure 4. a-d. shows the diurnal behaviour of the wind speed for summer (a), autumn (b), winter (c) and spring (d). The diurnal variations observed at Dome C during the summer are typical of those seen at locations where a convective boundary layer develops in response to daytime heating. During the autumn the wind velocity is fairly constant around 4.2 ms-1 (Figure 4.b.), 5 ms-1 in winter (Figure 4.c.), and 4.8 ms-1 in spring (Figure 4.d.).
4.2. Temperature The temperature histogram in the range -70 °C / -20 °C at steps of 5 °C is shown in Figure 5. The ordinate axis gives the percentage of temperature values observed in a given temperature range. This frequency distribution shows two peaks. One peak is centred at -50 °C, the other between -35 °C and -20 C°. The peak at -50 °C corresponds to winter, spring and autumn temperatures. The secondary peak includes instead the summer values. Figure 6. shows the daily average of the 3-meters AWS (Automatic Weather Station) temperature. The temperature has a strong seasonal cycle with values varying between -20 °C, during the short summer, and -70 °C in the long and coreless winter. Period of warming events are evidenced during the winter, when the temperature in few cases may reach values typical of summer.
Atmospheric Observations at Dome C, Antarctic Plateau, One of the Coldest Place… 207 6 15/11 - 01/02 ( SUMMER )
(a)
5 4 3 6
Wind Speed (ms-1)
01/02 - 01/04 ( AUTUMN )
(b)
5 4 3 6 01/04 - 15/09 ( WINTER )
(c)
5 4 3 6 15/09 - 15/11 ( SPRING )
(d)
5 4 3
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
Time (Hour) Figure 4. Average diurnal cycles of the wind (a) summer, (b) autumn, (c) winter, (d) spring, at Concordia station from January 2005 to January 2006.
16
14
Occurrence (%)
12
10
8
6
4
2
0
-70
-65
-60
-55
-50
-45
-40
-35
-30
-25
Temperature (°C)
Figure 5. Temperature histogram at Concordia station from January 2005 to January 2006.
-20
22
23
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-10
Temperature (°C)
-20 -30 -40 -50 -60 -70 -80 N D
J
F M A M J J A S O N D Time (Months)
J
F
Figure 6. Temperature behaviour at Concordia station from January 2005 to January 2006.
The warming events last for about 5 days and have a periodicity of about 15 days. During these periods the temperature may increase of several degrees (Argentini et al., 2001). Carroll, 1982, Stone et al. 1990, Stone and Kahl, 1991 and Stone, 1993 on a study at South Pole evidenced that these warming events were mostly observed in presence of cloudiness. Neff (1999) analysing the periods of cooling and warming at South Pole correlated these phenomena to the variations in wind direction in the elevated layer toward Nord-East, sometimes this variation was accompanied by cloud advection from the West or from the Weddel sea. Carrol (1982) suggested two possible mechanisms: advection of warm air and/or vertical mixing of air from different layers. Othake (1978) analysed the particles trajectory across Antarctica; he showed that the warming was mostly due to the intrusion of warm and moist air and to the condensation of nuclei which originate from the Wedding sea and reach the pole producing a variety of clouds type. Schwerdtfeger and Weller (1977) related the surface warming to the variation of long-wave radiation emitted by clouds associated at moist air from the upper part of atmosphere. Figure 7.a-d. show the mean diurnal variation of the temperature at Dome C for summer (Figure 7.a.), autumn (Figure 7.b.), winter (Figure 7.c.), spring (Figure 7.d.). The sonic temperature behaviour is similar in summer, autumn and spring, with the peak of the temperatures 2–3 hours after the local noon. The amplitude of the diurnal temperature variation is ~10°C during the summer (the maximum and minimum temperatures are respectively -25°C and -35°C) and ~5°C during the spring and autumn (maximum temperature -45°C, minimum temperature -50°C ). During the winter the average value of the temperature is ~ -55°C.
Atmospheric Observations at Dome C, Antarctic Plateau, One of the Coldest Place… 209 -20 15/11 - 01/02 ( SUMMER )
-25
(a)
-30 -35 -40
Temperature (°C)
-40 01/02 - 01/04 ( AUTUMN )
-45
(b)
-50 -55 -60 -40 01/04 - 15/09 ( WINTER )
-45
(c)
-50 -55 -60 -40 15/09 - 15/11 ( SPRING )
-45
(d)
-50 -55 -60
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
Time (Hour)
Figure 7. Average diurnal cycles of the sonic temperature (a) summer, (b) autumn, (c) winter, (d) spring, Concordia station from January 2005 to January 2006.
Figure 8. shows the profiles for summer (a), autumn (b), winter (c) and spring (d) in the vertical range 0-300 m. Each figure contains three profiles corresponding at averages over different hours of the day. A ―diurnal‖ profile (averages between 1000 - 1400 LT), an ―all day‖ profile, and a ―nocturnal‖ profile (averages between 2200-0200 LT). An unstable profile is observed in summer when the sun elevation reaches a peak. For all the other hours/seasons a stable boundary layer is observed. The temperature increases of about 5° C in the first 100 meters during the summer and 20° C during the winter. The result of a detailed analysis of the potential temperature gradients over all the winter is given in Figure 9. The graph shows the density contour plots of potential temperature gradients in the first 150 m of atmosphere. It is evident that the temperature gradient generally ranges between 0.1 and 1 (°C/m). However the strongest gradients occur below 40 m. This result is in general agreement with the observations by Agabi et al., 2006.
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300 250
Diurnal Mean Nocturnal
a)
250
Height (m)
Height (m)
150
100
50
50
0 -40
-35 -30 -25 Temperature (°C)
0 -60
-20
300
-55
-50 -45 -40 Temperature (°C)
-35
-30
300
Diurnal Mean Nocturnal
c) 250
200
Diurnal Mean Nocturnal
d)
200
Height (m)
Height (m)
150
100
150
150
100
100
50
50
0 -70
b)
200
200
250
Diurnal Mean Nocturnal
-65
-60 -55 -50 Temperature (°C)
-45
-40
0 -60
-55
-50 -45 -40 Temperature (°C)
-35
-30
Figure 8. Temperature profiles diurnal (crossed line), averaged (black dotted line), nocturnal (black dotted line), during a) Summer, b) Autumn, c) Winter, d) Spring at Concordia station at Dome C from January 2005 to January 2006.
Figure 9. Iso-Colour zone graphic of potential temperature gradient during the 2005 winter at Dome C.
Atmospheric Observations at Dome C, Antarctic Plateau, One of the Coldest Place… 211
4.3. Sensible Heat Flux The sensible heat flux H0 = C p w 'T ' is derived directly from the turbulence data using the eddy correlation technique; in this equation is the air density ( = 0.95 Kg m-3 at Dome C), C p is the specific heat of dry air constant pressure (1005 J kg-1 K-l), w'T ' is the covariance of the potential temperature with the vertical wind velocity as measured by the ultrasonic anemometer. The sensible heat flux on average is negative (Figure 10). Positive values occur in full summer (months of December and January) and in a few cases in correspondence of the winter warming events. The minimum of the sensible heat flux is observed at the end of June - beginning of July. Carefully analysing the high frequency data we realized that when the temperature drops below – 70 °C the sonic anemometer does not work properly and the fluxes could not be estimated. 15 10
H0 (Wm-2)
5 0 -5 -10 -15 -20 -25 -30
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan
Figure 10. Sensible heat flux behaviour at Concordia station at Dome C from January 2005 to January 2006.
5. ANALYSIS OF RADIATIVE BUDGET The energy budget of a non-melting snow surface may be written as
Rnet H 0 H L G 0
(1)
where Rnet is the net radiation, H0 is the sensible heat flux, HL is the latent heat flux and G is the conductive heat flux through the snowpack. We use the sign convention that fluxes of
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energy directed towards the snow surface are positive. Rnet may be broken down into its components
Rnet SW SW LW LW = SWnet+LWnet (2) where SW↓ is the incoming short wave radiation, SW↑ is the reflected short-wave radiation, LW↓ is the incoming long-wave radiation, LW↑ is the outgoing long-wave radiation, SWnet and LWnet are the net short wave and the net long wave respectively. Careful quality control of these radiation data is essential due to the large absolute values generated by the instruments, from which a relatively small difference is extracted. The annual behaviour of the daily mean of the radiative budget components and the Radiation at Top Of Atmosphere (RTOA) for 2005 are shown in Figure 11. As expected an annual variation and a diurnal variability are present. The SW↓ reaches the peak value during the summer (480 Wm2 ) and decreases to 50 Wm2 at the beginning of the winter.
600 RTOA
-2
Radiation (W m )
500 400
SW SW LW LW
300 200 100 0
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Local Time (day)
Figure 11. Time series of daily mean of RTOA (black line), SW (--), SW (dot), LW (--), LW (circle) at Concordia station from January 2005 to January 2006.
Atmospheric Observations at Dome C, Antarctic Plateau, One of the Coldest Place… 213 100 SWnet LWnet Rnet
80
-2
Radiation (W m )
60 40 20 0 -20 -40 -60 -80 -100
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Local Time (month)
Figure 12. Time series of daily mean SWnet (dotted line), LWnet (star) and Rnet (circle) at Concordia station from January 2005 to January 2006.
The LW↓ ranges between 200 Wm2 (in summer) and 80 Wm2 in winter. In winter during cloudy days the LW↓ increases of 20-30 Wm2. The seasonal variation of LW↑ reflects the cycle of the surface temperature with maximum values (~ 200 Wm2) in summer and minimum values (~ 100 Wm2) in winter. During the summer the short-wave radiation absorption helps in reducing the intensity of the surface inversion, instead, during the winter, surface based inversion may also decrease during the warming events as the surface temperature increases. Figure 12. shows time series of SWnet, LWnet, and Rnet. The LWnet is the only component contributing to the net radiation during the winter. In summer LWnet and SWnet have opposite sign, as a result Rnet (20 Wm2), although small, is positive. For each season the diurnal cycle of the four components of the radiative budget is shown. The diurnal cycles of SW↓ is shown in Figure 13. The SW↓ peaks around local noon. During the summer the peak is about 800 W m-2. In spring and autumn the peak value reduces to 400 W m-2 while in the full winter night the SW↓ is zero. The diurnal variation of incoming long-wave radiation at Dome C is shown in Figure 14 a-d. A clear diurnal cycle is apparent at Dome C in the outgoing solar radiation for all seasons with the exception of the winter. This suggests that there is a diurnal cycle in temperature in the lower part of the atmospheric column at Dome C as well as at the surface. In summer such diurnal variability is consistent with our hypothesis of a diurnal CBL at Dome C. Outgoing long-wave radiation is simply related to snow surface temperature, Ts, through Stefan‘s law
LW Ts 4 (1 ) LW
(3)
where ε is the long-wave emissivity of the snow surface and ζ is Stefan‘s constant. Since ε is approximately constant and has a value close to unity, the first term on the right hand side of (5) dominates and variations in LW↑ closely follow those in Ts. The diurnal variation of LW↑ during the summer reflects the larger diurnal range in near-surface air temperature at Dome C. In the other seasons such variation it is not observed. Figure 15. a-d illustrate the diurnal variation of Rnet obtained by eq. 2 at Dome C. During the ―night time‖, Rnet at Dome C is typically -50 W m-2.
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1200 15/11 - 01/02 ( SUMMER )
(a)
Shortwave Radiation Down (Wm-2)
800 400 0 600 01/02 - 01/04 ( AUTUMN )
(b)
400 200 0
600 01/04 - 15/09 ( WINTER )
(c)
400 200 0
600 15/09 - 15/11 ( SPRING )
400
(d)
200 0 0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
Time (Hour)
Figure 13. Shortwave daily radiation down for (a) summer, (b) autumn, (c) winter and (d) spring at Concordia station from January 2005 to January 2006.
300 LW (a) LW
15/11 - 01/02 ( SUMMER )
200 100
Longwave Radiation (Wm-2)
0 300 01/02 - 01/04 ( AUTUMN )
(b)
200 100 0 300 01/04 - 15/09 ( WINTER )
(c)
200 100 0 300 15/09 - 15/11 ( SPRING )
(d)
200 100 0
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
Time (Hour)
Figure 14. Longwave radiation up and down for (a) summer, (b) autumn, (c) winter and (d) spring at Concordia station from January 2005 to January 2006.
Atmospheric Observations at Dome C, Antarctic Plateau, One of the Coldest Place… 215 100 15/11 - 01/02 ( SUMMER )
50
(a)
0 -50 -100
Net Radiation (Wm-2)
100 01/02 - 01/04 ( AUTUMN )
50
(b)
0 -50 -100 100 01/04 - 15/09 ( WINTER )
50
(c)
0 -50 -100 100 15/09 - 15/11 ( SPRING )
50
(d)
0 -50 -100
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
Time (Hour)
Figure 15. Diurnal cycle of net radiation for a) summer, b) autumn, c) summer, d) spring at Concordia station from January 2005 to January 2006.
A regular diurnal cycle is observed for all the seasons with the exception of the winter when there is not solar radiation. The peak of Rnet is about 80 W m-2 and 50 W m-2 during the spring and autumn respectively.
6. BOUNDARY LAYER STRUCTURE DURING THE YEAR The thermal structure of the atmosphere may be clearly shown by the mini-SODAR facsimile. The mini-SODAR facsimile represents the intensity of the acoustic backscattered echo within the mini-SODAR range. Being the main tracers the thermal fluctuations, it gives a picture of the thermal structure of the atmosphere. Figure 16.a. shows the 24-hour miniSODAR facsimile for 7 January, 2005. During the night the turbulent activity, if exists, is confined in a very shallow layer (< 50 m) that is below the first mini-SODAR range gate. From about 0700 LT the surface-based turbulent layer deepened and mini-SODAR returns characteristic of a growing CBL started to appear. These are a strong echo associated with the rising capping inversion at the top of the CBL with a ―spiky‖ echo structure associated with convective plumes below, indicative of strong mixing within the CBL. The capping inversion reached a maximum height of around 200 m by 1300 LT. Around 1500 LT the echoes associated with mixing within the CBL started to fade and by 1800 LT the capping inversion had disappeared, leaving only the shallow nocturnal layer. The rate at which a CBL grows is controlled to a large extent by the sensible heat flux from the underlying surface and the subsidence velocity at the top of the capping inversion. The mini-SODAR record in Figure 16.a is the typical thermal structure observed at Dome C over the entire summer. However as shown by Argentini et al. (2005), the depth of the CBL strongly depends on the amount of
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solar radiation reaching the surface, consequently its depth varies from November to end of February depending on the solar elevation angle. Figure 16.b shows the 1-hour averaged temperature profile for the same day of Figure 16.a at 1400 LT. A weak convective activity is observed close to the ground with a strong temperature inversion above this confirming the mini-SODAR observations. By contrast, mini-SODAR records during the winter show no echoes during the all day. The only exception is given by the days in which the arrival of perturbations produce a thermal fluctuation that is strong enough to be revealed by the miniSODAR. Figure 17.a gives as an example of the thermal structure for 21 July, 2005, no echoes are present during the entire day. Again if some echoes exists they are confined below the first mini-SODAR range gate. Some field experiments carried out by astronomers interested in ―site testing‖ to the estimate the atmospheric optical seeing at Dome (Agabi et al., 2006, Aristidi et al., 2005) have shown a poor ground seeing mainly due to a strong turbulent boundary layer confined in the first 20 m – 30 m close to the ground. In the future we then plan to set the mini-SODAR in a configuration which will allow to study the structure and depth of this shallow layer close to the ground.
600
b) 500
Height (m)
400 300
200 100
0 -25
-24.5
-24 -23.5 -23 Temperature (°C)
-22.5
-22
Figure 16. (a) Thermal structure of the atmosphere during summer as seen by mini-SODAR for day 7 January 2005, (b) temperature profile by MTP-5P for the same day at 1400 LT.
Atmospheric Observations at Dome C, Antarctic Plateau, One of the Coldest Place… 217
600
b) 500
Height (m)
400 300 200 100 0 -70
-65
-60 -55 -50 Temperature (°C)
-45
-40
Figure 17. (a) Thermal structure of the atmosphere during winter as seen by a mini-SODAR for day 21 July 2005, (b) temperature profile by MTP-5P for the same day at 1400 LT.
Figure 17.b. shows the 1-hour averaged temperature profile for the same day of Figure 8.a at 1400 LT. A strong ground-based inversion of the order of 0.125 °C/m is observed.
ACKNOWLEDGMENTS This research was supported by the Piano Nazionale Ricerche in Antartide (PNRA) in the frame of French-Italian ―Dome C‖ project. The authors would like to thank the logistics staff at Concordia for their support during the experimental fieldwork and all people which contributed to the field experiments. A special thank to Ing. Guillaume Dargaud overwintering at Concordia station during 2005, and to Sig. A. Conidi which participated to the summer field operations during STABLEDC. The authors also wish to thanks Dr. G. Mastrantonio, Dr. A. Viola, and Dr. Igor Petenko which contributed to some of the results showed in these papers, for useful comments, and all the work which has been done in the realization of STABLEDC.
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REFERENCES Agabi, A., E. Aristidi, M. Azouit, E. Fossat, F. Martin, T. Sadibekova, J. Vernin and A. Ziad: First Whole Atmosphere Nighttime Seeing Measurements at Dome C, Antarctica. The Publications of the Astronomical Society of the Pacific., 118(840), 344-348 (2006). Argentini, S., I. Petenko, G. Mastrantonio, V. Bezverkhnii and A. Viola: Spectral characteristics of East Antartica meteorological parameters during 1994. J. Geophys. Res., 106, 12463-12476 (2001). Argentini, S., A. Viola, A. Sempreviva and I. Petenko: Summer boundary-layer height at the plateau site of Dome C, Antarctic. Boundary-Layer Meteorol., 115, 409-422, 10.1007/s10546-004-5643-6 (2005). Aristidi, E., A. Agabi, E. Fossat, M. Azouit, F. Martin, T. Sadibekova, T. Travouillon, J. Vernin and A. Ziad: Site testing in summer at Dome C, Antarctica. Astronomy and Astrophysics., 444(2), 651-659 (2005). Bintanja, R. and M.R. van den Broeke: The Surface-Energy Balance of Antarctic Snow And Blue Ice. J. Appl. Meteorol., 34, 902-926 (1995). Carroll, J. J. and B.W. Fitch: Effects Of Solar Elevation And Cloudiness On Snow Albedo At The South-Pole. J. Geophysical Res., 86, 5271-5276 (1981). Carroll, J. J.: Long-term means and short-term variability of the surface energy balance components at the South Pole. J. Geophysical Res., 87, 4277-4286 (1982). Connolley, W.M.: The Antarctic temperature inversion. Int. J. Climatol., 16, 1333-1342 (1996). Dalrymple, P. C.: A physical climatology of the Antarctic Plateau. Studies in Antarctic Meteorology, (Eds. M.J. Rubin), Antarctic Research Series, 9, Amer. Geophys. Union., 195-231 (1966). Dutton E.G., R.S. Stone D.W. Nelson and B.G. Mendoca: Recent interannual variations in solar radiation, cloudiness and surface temperature at the South Pole. J. Clim., 4, 848-858 (1991). Hagelin, S., E. Masciadri, F. Lescaux and J. Stoesz: Comparison of the atmosphere above South Pole, Dome C and Dome A: first attempt. Mon. Not. R. Astron. Soc., 387, 14991510 (2008). Hudson, S.R. and R.E. Brandt: A look at the surface based temperature inversion on the Antarctic plateau. J. of Climate., 18, 1673-1696 (2005). Jouzel, J. and L. Merlivat: Deuterium and Oxygen 18 in precipitation modelling of the isotopic effects during snow formation. J. Geophys. Res., 89, 11749-11757 (1984). Kadygrov, E.N. and D.R. Pick: The potential for temperature retrieval from an angularscanning single-channel microwave radiometer and some comparisons with in situ observations. Meteorol. Appl., 5, 393-404 (1998). King, J.C. and W.M. Connolley: Validation of the surface energy balance over the Antarctic ice sheets in the UK Meteorological Office unified climate model. J. Climate., 10, 12731287 (1997). King, J.C. and J. Turner: Antarctic Meteorology and Climatology, 409 pp. Cambridge University Press, Cambridge. (1997).
Atmospheric Observations at Dome C, Antarctic Plateau, One of the Coldest Place… 219 King, J.C., S.A. Argentini and P.S. Anderson: Contrasts between the summertime surface energy balance and boundary layer structure at Dome C and Halley stations, Antarctica. J. Geophys. Res.-Atmos., 111, D02105 10.1029/2005jd006130 (2006). Lee, X., W. Massman and B. Law: Handbook of Micrometeorology, Kluwer Academic Publishers, Dordrecht (2004). Lettau, H.H. and W. Schwerdtfeger: Dynamics of the surface-wind regime over the interior of Antarctica. Antarct. J. U. S., 2, 155-158 (1967). Marks, R.D., J. Vernin, M. Azouit, J.F. Manigault and C. Clevelin: Measurement of optical seeing on the high Antarctic plateau. Astron. Astrophys. Suppl. Ser., 134, 161-172 (1999). Mastrantonio, G., V. Malvestuto, S. Argentini, T. Georgiadis and A. Viola: Evidence of a convective boundary layer developing on the Antarctic Plateau during the summer. Meteorol. and Atmospheric Physics., 71, 127-132 (1999). Neff, W. D.: Decadal time scale trends and variability in the tropospheric circulation over the South Pole. J. Geophys. Res., 104, 27217-27251 (1999). Othake, T.: Atmospheric ice crystals at the South Pole in summer. Antarct. J. U. S., 13, 174175 (1978). Phillpot, H.R. and J.W. Zillman: The surface temperature inversion over the Antarctic continent. J. Geophys. Res., 75, 4161-4169 (1970). Reijmer, C.H., W. Greuell and J. Oerlemans: The annual cycle of meteorological variables and the surface energy balance on Berkner Island, Antarctica. Annals of Glaciol., 29, 4954 (1999). Schwerdtfeger, P. and G., Weller: Radiative heat transfer processes in snow and ice‘, Meteorological Studies at Plateau Station, (Ed., J. A. Businger.). Antarctic Research Series., 25, Amer. Geophys. Union., 35-39 (1977). Stanhill, G. and S. Cohen: Recent changes in solar irradiance in Antarctica. J. Clim., 10, 1078-1086 (1997). Stone, R.S., G. E. Dutton and J.J. DeLuisi: Surface radiation and temperature variations associated with Cloudiness at the South Pole. Antarctic J. Rev., 24, 230-232 (1990). Stone, R.S. and J.D. Kahl: Variations in Boundary layer Properties associated with Clouds and Transient weather disturbance at the South Pole during winter. J. Geophysical Res., 96(D3), 5137-5144 (1991). Stone, R.S.: Properties of austral winter clouds derived from radiometric profiles at the South Pole. J. Geophysical Res., 98(D7), 12961-12971 (1993). Van As, D., M.R. van den Broeke, C. Reijmer and R. van De Wal: The summer surface energy balance of the high Antarctic plateau. Boundary-Layer Meteorol., 115, 289-317 (2005a). Van As, D., M. van den Broeke and R. van de Wal: Daily cycle of the surface layer and energy balance on the high Antarctic Plateau. Antarctic Sci., 17, 121-133 (2005b). Van de Wal and Oerlemans: Modelling the short-term response of the Greenland ice-sheet to global warming. Clim. Dyn., 13(10), 733-744 (1997). Weller, G.: Spatial and temporal variations in the South Polar surface Energy Balance. Monthly Weather Rev., 108, 2006-2014 (1980). Wendler, G., N. Ishikawa, Y. Kodama: The heat balance of the icy slope of Adelie Land, Eastern Antarctica. J. Appl. Meteorol., 27, 52-65 (1988). Wiscombe, W. and S. Warren: A model for the Spectral albedo of Snow. I: Pure snow. J. Atmosp. Sci., 37, 2712-2733 (1980).
In: Antarctica: The Most Interactive Ice-Air-Ocean Environment ISBN: 978-1-61122-815-1 Editors: Jaswant Singh, H.N. Dutta © 2011 Nova Science Publishers, Inc.
Chapter 11
IMPACT OF INDIVIDUAL RESPONSIBILITY IN CHANGING GLOBAL WARMING? Nitosh Kumar Brahma* ABSTRACT ―Global Warming‖ may be influenced by an individual contribution by burning of fossil fuel (energy), and the total carbon content of fossil fuel. The energy used globally may be determined by the measure of direct use of energy applicable to an individual. It must be counted in the form of total carbon dioxide (CO2) emission, influencing the increasing global warming and the ice melting. 75 % of the total global energy has been used by the developed nations, compared to developing nations. However the density of fine carbon particulates, floating at stratospheric layers, perhaps to be differentiated between developed and developing nations. Carbon(C) particles at stratospheric layers would perhaps be higher, in developing nation due to direct burn of coal. Thermodynamically this may be written in the form of entropy (S = Q/ T; or G = H – TS; or T S = H-G; S = H- G/ T or Q / T), moving towards the maximum orderly situation, i.e. S < O at frequent up and down chaos (small disorders), i.e. small delta S.> O; the fluctuation of environments. 0.1 degree of Celsius/ year could be a disaster for sustainability of earth and cannot be estimated at long perspective of earth cooling. The recycling of CO2 is however be considered for ultimate solution to control the increasing ―Global Warming‖, where third world countries would be seriously affected, due to vast uses of coal and agrocellulosic residues (ACR) as fuel and for generating nano- and pico- C- particles.
Keywords: Global warming, Ice-melt, Carbon dioxide, Greenhouse gases (GHG‘s).
*
E-mail:
[email protected] Faculty, Department of Chemical Engineering, Indian Institute of Technology, Kharagpur-721302, W.Bengal, India
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INTRODUCTION Global warming and ice melt is directly proportional to the rate of carbon burn of agrocellulose residues (ACR), coal and petroleum, partially differentiated in case of developing countries and developed nations. Freon and fossil fuel consumptions, perhaps to be considered more seriously, 1000 X time intensified, compared to the emission of CO2 caused by burning of coal and ACR. Due to increasing carbon dioxide (CO2) emission, the physicochemical properties of stratosphere, amplifying the stratospheric reflections and solar (sun) rays – heat. This is equally being important in case of GHG‘s (CH4, CO, N2 and CO2) effects in the history of mankind. The same phenomenon has happened on ancient earth, about 3.7 billions of years ago during ―Golden age of Reptiles‖, and caused the extinction of reptiles. Ice changes to liquid water, if warmed above 4oC to its melting point and Vis- a Vis changed to ice, if cooled to its freezing point. Earth's Polar Regions consists largely of ice and exhibit dramatic change in temperature. An increase of 0.1oC in temperature resulting from global warming may affect drastically the extent of polar ice and the habitats of polar region. However this will not affect the change of sea level, since the floating of ice follows the ―Archimedes principle‖, corresponding to the displacement of water. The melt of continental ice (such as glaciers and ice sheets) raises sea level. This happens because, ice on land when melts adds its water into the ocean which was not there before. This extra water raises sea level. For example, if the ice of Himalaya starts to melt it will affect the change of sea level of bay of Bengal and Indian ocean and subsequently the same will affect the increase of water level of Ganges and Bramhaputra belt and subsequenly may cause flood and the increase of wastewaters, compared to potable drinking water. Although the melting of ice doesn't significantly affect the sea level, if floats, there are other consequences which have to be considered. Ice melt may cause the variations in salinity and temperature drive, global ocean circulations, because the density of ocean water differs. Fresh water is less dense than salt water and warm water is less dense than cold water. This thermohaline circulation may sometimes refer the great ocean "conveyor belt" because it is one of earth's main mechanisms for transporting energy (Edgerton, 2008). The formation of sea ice, which is primarily made of pure water, leaves behind salt in the water beneath the ice, resulting saltier and colder water that sinks through the water below it, and thereby promoting the circulation. When ice melts, it adds fresh water to the ocean, decreasing salinity and affecting the circulation pattern. Any change to ocean circulation could have damaged the water cycle and weather patterns. In addition, a change in the temperature or salinity of ocean water disrupts the habitats and could have harmful effects on marine life forms that are sensitive to such changes. The loss of sea ice in Polar Regions also threatens the survival of certain species, such as the polar bear, which depend on the ice for hunting and breeding. Increasing population will cause the increasing global warming due to higher CO2 emissions. Socioengineering (SE) application shows its significant application to control population and global warming, in third world developing countries. Application of Microbial engineering (ME) and microbes may play a significant role to change the social impact in pollution abatement. So the reform of social– economical structure in third world in support of ME (microbial Engineering) may change the
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engineering concept of sociology, the exploitation of natural resources in an appropriate, ecofriendly and cost-effective applications. Such application may reduce the global warming. One example would be the reform of water resources, and their recycling, which is exponentially growing as basic demand, with increasing population. Although ME and SE are existing in two different boundaries, have shown their common interest in technological innovations to optimize the demand of food, health and shelter, the entropy (S) and chaos (Brahma and Basu, 2008). As per the "Darwin‘s Laws of Evolution‖, mankind belongs to the highest group of "Animal Kingdom" adapting to all kinds of environmental factors in the course of 50 billions of years in early earth evolution. The best example may be giving by ―The Golden Age of Reptiles" and their extinctions. This is to be considered seriously with the present global warming, ozone depletion, population and pollutions. Since food, shelter, health and biological essential demands are predominating. In addition to competition for better life, with material gains and consumptions the increasing population proportionally relates the increasing pollution. In this case the SE - application the reduction of population perhaps would be the best solutions to resolve the problem of present world crisis of global warming. SE and technological innovations essentially affect independent to color, race, religion, and population control. This will ultimately be imposed by Enforced appropriate technology (EAT) for specific technical applications Zero Effluent Discharge (ZED), waste to energy (WTE), Microbial Enhanced Technology (MET) perhaps would integrate SE along with ME. The global population and pollution will ultimately cross the boundaries of ―Life and engineering Interfacial Phenomena‖, where animate and inanimate reactions will predominate and perhaps will show the guideline to explain how the hybrid technology and innovations will be essential for clean environment. Clean water, air and soil will be essential to utilize ―Time and Energy‖ as ―Human Factor‖ (Brahma, 2004; 2007).
Important Observable Facts Global climate change is a major threat to biodiversity worldwide (Kondrat, 2004; Petry, 1995). One way it motivates the changing behavior of animals and is being documented by films. Since May 24, 2006, millions of people have seen Al Gore‘s films. Several countries have proposed such ‗AIT‘ films to schools in classrooms as part of their academic curricula. The purposes of the present set of studies have been evaluated to which AIT accomplishes its apparent goals, convincing at the same time the methods for reducing greenhouse gas emissions. Two studies were conducted; one is with a sample of the concept of AL Goers ―Global warming‖ and its relation to ice melt. Participants were randomly assigned to complete a survey either before or after watching AIT. The survey was designed to measure attitudes, beliefs, and behavioral intentions related to global warming. The results of both studies showed that watching ―An Inconvenient Truth‖ does increase the concern and motivation to reduce greenhouse gases. However, the results of the second study suggest that the willingness to take action does not necessarily be translated into action. Recommendations are made for how the movie should be used to create behavioral change (Brahma, 2004; 2007; 2008).
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Some Mathematical Derivations Earth is already showing many signs of worldwide climate change. To realize the fact, it would be interesting to design the concept of entropy, both an individual human aspects, industry and environmental aspects. First it is essential to know the climate is changing, as per the www.google.com. It is said, that; (a) Average temperatures have climbed 1.4 degrees Fahrenheit (0.8 degree Celsius) around the world since 1880, much of this in recent decades, according to NASA's Goddard Institute for Space Studies. (b) The rate of warming is increasing. The 20th century's last two decades were the hottest in 400 years and possibly the warmest for several millennia, according to a number of climate studies. The United Nations' Intergovernmental Panel on Climate Change (IPCC) reports that 11 of the past 12 years are among the dozen warmest since 1850. (c) The Arctic is feeling the effects of the most average temperatures in Alaska, western Canada, and eastern Russia and has risen at twice the global average. According to the multinational ―Arctic Climate Impact Assessment‖ report, it is said that between 2000 and 2004, there were some reduction of temperature profile and thereafter the climate observed the temperature rise. (d) Arctic ice is rapidly disappearing, and the region may have its first completely icefree summer by 2040 or earlier. Polar bears and indigenous cultures are already suffering from the sea-ice loss. (e) Glaciers and mountain snows are rapidly melting. For example, Montana's Glacier National Park now has only 27 glaciers, versus 150 in 1910. In the Northern Hemisphere, this has shown its impact a week earlier the incoming of spring and freezes the environment. (f) Coral reefs, which are highly sensitive to small changes in water temperature, suffered the worst bleaching since 1988. Seventy percent bleach rate is increased in last decades. Experts expect these sorts of events to increase in frequency and intensity in the next 50 years as sea temperatures rise. (g) An upsurge in the amount of extreme weather events, such as wild fire, heat wave and strong tropical storms, is also attributed in part to climate change by some experts. The report, based on the work of some 2,500 scientists in more than 130 countries, concluded that humans have caused all or most of the current planetary warming. Human-caused global warming is often called anthropogenic climate change. (h) Industrialization, deforestation, and pollution have greatly increased atmospheric concentrations of water vapor, carbon dioxide, methane, and nitrous oxide, all greenhouse gases that help trap heat near earth's surface. (i) Humans are pouring carbon dioxide into the atmosphere much faster than plants and ocean absorb it. These gases persist in the atmosphere for years, meaning that even if such emissions were eliminated today, it would not immediately stop global warming. (j) Some experts have pointed out, that natural cycles in Earth's orbit can alter the planet's exposure to sunlight, which may explain the current trend. Earth has indeed
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experienced warming and cooling cycles, roughly every hundred thousand years due to these orbital shifts, but such changes have occurred over the span of several centuries. Today's changes have taken place over the past hundred years or less. (k) Other recent research has suggested that the effects of variations in the sun's output are "negligible" as a factor in warming, but other, more complicated solar mechanisms could possibly play a role.
How the Above Points Would Be Realistic and How This May Be Controlled? A follow-up report by the IPCC, release in April- 2007 warned that global warming could lead to large-scale food and water shortages and have catastrophic effects on wildlife. The following points are relevant; (a) Sea level could rise between 7 and 23 inches (18 to 59 centimeters) by century's end. The IPCC's (United Nations' Intergovernmental Panel on Climate Change) February 2007 reports that the rises of just 4 inches (10 centimeters) could cause flood to many South Sea Islands and swamp up large parts of ―Southeast Asia‖. (b) Some hundred million people live within 3 feet (1 meter) of mean sea level, and much of the world's population is concentrated in vulnerable coastal cities. In the U.S., Louisiana and Florida are especially at risk. (c) Glaciers around the world could melt, causing sea levels to rise while creating water shortages in regions dependent on runoff for fresh water. (d) Strong hurricanes, droughts, heat waves, wildfires, and other natural disasters may become commonplace in many parts of the world. The growth of deserts may also cause food shortages in many places. (e) More than a million species face extinction from disappearing habitat, changing ecosystems, and acidifying of oceans. (f) The ocean's circulation system, known as the ocean conveyor belt, could be permanently altered, causing a mini-ice age in Western Europe and other rapid climate changes. (g) At some point in the future, warming could become uncontrollable by creating a socalled positive feedback effect. Rising temperatures could release additional greenhouse gases by unlocking methane in permafrost and undersea deposits, freeing carbon trapped in sea ice, and causing increased evaporation of water (Walter et al., 2006).
ALTERNATIVE CONCEPT Global warming is caused by green house gases (GHG‘s), which traps the sun‘s infrared rays in the earth‘s atmosphere, which in turn heat up the earth‘s atmosphere. This green house effect warming is called as ―Global warming‖. The effects of green house are visible more prominently in the recent years, with number of natural calamities on the rise in the whole
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world. The global warming has happened in the past few years and is evident from the rise in mean temperature of the earth‘s atmosphere. The main causes for the global warming are attributed to release of green house gases by human activities. The main gases contributing to green house effect are carbon dioxide, water vapor, methane and nitrous oxide. The largest producers of these gases are the thermal power plants, which burn the fossil fuels and produce these gases in large quantities. The second biggest sources of these green house gases are the road vehicles and industries (Archer, 2006; Brahma and Basu, 2008). The global warming has led to an increase in mean earth surface temperature and thus melting of polar ice. There are frequent melt down of glaciers that result in floods and other natural calamities. The melting of polar ice had lead to increase the mean sea level. And further increase in temperature may further melt the ice and lead to further increase in mean sea level, which will engulf low lands of the continents. The effect of global warming is very important for animal kingdom. Some animals have become extinct due to loss of their natural habitat or their inability to evolve to the rapid changes in the climate. Also there is a change in their life style because of the changes in the seasons. The migrating birds have changed their time of travel and also their place of migration. The effect of global warming can be seen on seasons too. There is shift in season cycle, as the summers are getting longer than the winters. This has affected the animals and made them to change their lifestyle accordingly, and those who failed to do so are perished or on the verge of extinction. The global warming is also responsible for the introduction of some new diseases. The bacteria are more effective and multiply much faster in warmer temperatures compared to cold temperatures. The same concept has been introduced by the author in the form microbial engineering (ME), affecting the environment and health. The increase in temperature has led to increase in the microbes that cause diseases; subsequently the survival attitudes of microbes from ambient temperature to mesophilic and to finally to thermophilic are increasing causing thereby pollution. Global warming is also affecting the crop production. The sudden change in temperatures or sudden set of rains destroys the crops productions. Also the flash floods and other natural calamities affect the crop. As a matter of fact, global warming changes the earth‘s atmosphere and is getting more unpredictable rainfalls in areas, where the scanty of rainfall or drought were predominated. The annual rainfall pattern may also be affected by ―Global Warming‖.
BASELESS COUNTER ARGUMENTS But there are some people, who believe that the global warming is a natural process and cannot disturb our ecosystem. The earth‘s mean surface temperature was even higher in a long time ecosystem. But the changes that are happening now are faster compared to earlier times. In this case the author will discuss the concept of entropy in form of S and S, small delta versus big delta. The skeptical view of global warming is that, that global warming is not an ecological trouble. It is trouble of population explosions. Some of the facts have been highlighted: (a) The Green house gases are the main culprits of the global warming. The green house gases like carbon dioxide, methane, and nitrous oxide are playing hazards in the
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present times. GHG‘s are the ingredients of the atmosphere that add to the greenhouse effect. (b) 0.7-meter increase of sea level may act as a problem of environmental adaptations, affecting directly to the ocean plankton, flora and fauna. Adaptation has an adverse to biodiversity. CO2, Freon and Chlorofluorocarbons are all contributing the disbalance of ecosystems effects and global warming. Environmental Protection Agency (EPA); analyze the reports of Global climate changes. Research Resources Defense Council indicates, that in their action plan, the sea rise and climate change may be caused due to rapid change of global warming and the change of Stratospheric Ozone structures. The same study was included in Washington Water Zone Management Program, where they have marked the potential threat areas of the earth surface.
Figure 1 .
Figure 2. a.
Figure 2. b. Figure 1. Figure 2. (a.b.) represents the sectors, which influence percentile the global warming, caused by various types of fossil fuel burns and the increasing propagation of warming with increasing the years. Figure 2.b. shows the separate effect of Greenhouse Gases.
CONCLUSION AND ENTROPY RELATED FUNCTIONS Entropy is defined by the measure of order. The concept of order may goes from macro-, micro- to nano- and finally to pico level of molecules. ―Atmospheric layers covered by Magnetosphere and Stratospheric layers‖ basically cover the surface of earth at least 3-10
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kilometer. GHG‘s like CH4, NOx, CO and CO2 may increase the effect. Among them CO2 may be considered as major culprit and may cause stratospheric hole as shown in Figure 3. Once the sufficient solar rays enters the earth atmosphere, automatically by the theory of light it will try to reflect, and be amplified in the cover of CO2 emitted GHG and will reflect back to the earth surface, causing ―Global Warming‖. The same will continue to change the entropy. Greeneries and plantations are prone to absorbed the sun ray, photosynthetically to make their food in the form of glucose and ultimately to cellulose, liberating at the same O2. This O2 is converting to O3 (Ozone) on the surface of ocean in presence of sunlight, that absorbs IR (Infrared) and thereby the reduction of thermal wave. However in case of GHG and CO2 this IR could perhaps be captured by CO2 to protect the reactions of O3 and reduce the photosynthetic activities of planktons, flora and fauna. Therefore it is essential, that greeneries and increase of plantation may capture CO2. Moreover sea planktons, algae and microbes are involved to capture CO2 as part of their biosynthetic process. Since there are variations of population on the surface of earth, CO2 emission may also vary accordingly i.e., CO2 emits form carbon (in fossil fuel) burning, might be different compared to CO2 emits by the burns of coal and ACR residues as fine particulates (Fick, 2004). This is a type of formulation to describe the increasing of entropy due to stratospheric hole and amplifications of sun-light as source of thermal energy, characterized by S = Q/ T. So the capturing of solar energy could be variable on the surface of the earth and may be influenced by CO2 emission. Alternative concept could be the increasing population and survivals demand. More population means more pollution, which automatically generate CO2 emission. Compared to developed nations, developing nations are consuming less energy, i.e., less consumptions and burns of fossil fuel. However they commit more CO2 emission, since they burn coal and ACR as direct source of their survivals and energy resources, generating at the same time, nano- and pico particles of CO2. From the part of population dense, it is also true that third world countries will suffer from various types of environmental hazards and global warming, compared to that of developed nations (Hasselmann, 1997). Developed nations are basically controlled by low dense population, free of pollution and cold atmosphere. So statistically even if they consume more energy, by burning fossil fuel, they are in position to emit less CO2 compared to developing thick populated nations. It might be true that to control cold, the developed nation burns coal in thermal power stations and use strategic measure to heat their automobiles, if compared to third world nations, where Freon‘s are used for cooling, emits CO2 , 10,00 times more than fossil fuel burn. This relies the change of entropy (Levi et.al., 1992). Entropy will influence the change of biological system, chaos in biodiversity and automatically the danger for the extinction of living system. Markovn relation; spatial propagation of Markov truncated electrostatic interactions, existing between one amino acid and the others at the protein 3D backbone, show, that there are the change of molecular interaction Figure 4.
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Figure 3. The progress of amplification has been demonstrated.
Figure 4. The molecular interaction of one amino acid at Z direction increases according to the order.
In doing so, the elements of (x, y, z, q) may be considered as the probabilities ‗(pij)‘ with which the amino acid ‗I‘ presents a ‗truncated‘ electrostatic interaction of energy ‗E ij ‘, with the amino acid ‗j‘ placed at a distance ‗d ij‘.
(1) The ‗truncated‘ electrostatic interactions are those, which occur between amino acids at a cut-off distance (din) shorter than the half of the sum of their van der Waals radius. Here, a shifting function (δij) was used to indicate the presence (δij = 1) or absence (δij = 0) of the ‗truncated‘ electrostatic interaction between aminoacids ‗I‘ and ‗j‘ occurs by the above interactions (Fick, 2004; Molina and Uriarte, 2004; Nordhaus and Shellenberger, 2007;
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Philander, 2009). The theory of Doom guard Factotum states that ―Entropy‖ leads everything in the multiversity to its ultimate doom. And Entropy always wins. It can be delayed, but never defeated. Energy consumption will not decrease, so humanity needs to find a way to control its needs for energy, so ―Global Warming‖ can be controlled if the energy consumptions are reduced. The humanity also needs to find more efficient ways to generate energy. These two things would help a lot towards controlling this problem, but anyway, the increase of heat will continue. (Hasselmann, 1997) cited further that as I believe in the laws of thermodynamics, and I don't believe in a perpetual energy source 100% efficient, the only way to solve this problem would be to produce energy using sources outside the Earth. The most straightforward answer for this comment is the use of ―Solar Energy‖. That is the only actual way of reducing ―Global Warming‖ on Earth currently approached. The Sun is like a battery, there is no known way of pulling more energy than it generates, but it produces energy enough to sustain life on Earth for billions of years yet. Using the ―Sun‖ energy we can lower the ―Entropy‖ (S) of the Earth, and in this way we can reduce the problem of increasing ―Global Warming‖ of the planet. Eventually the Sun's Entropy will reach the values so high that it will become a red giant, almost enveloping the Earth orbit, and destroying this beautiful planet, and all traces of civilization here‖(Hasselmann, 1997; Willium, 2008; Nordhaus and Shellenberger, 2007; Pétry, 1995). In the present chapter author has described the said concept in the form of big and small delta ( and ). In India there are sufficient program have been initiated by Prime Minister Council of Climate Change, wherein the NAVARATNA companies are earmarked. Two percent of their profit to be invested in the control program of ―Global warming‖ as part of CSR (Corporate Social Responsibility). Global warming can also be captured, recently by catalytic membrane process, by increasing the culture of algae, either in algal ponds, or in photo bioreactor, various biodiesel programme can be initiated. We can surely create a lot of power plants in our planet, which can generate enough energy to sustain the earth‘s life, interplanetary energy transfer methods, yet unknown, to bring this energy from one place of earth to other, through microwave propagation. Big Bang could also be used as a clean energy source in plasma fusion. There are many possibilities, but currently the only feasible one, is to rely on biodiesel, and the use of solar radiation as a source of energy. Photovolticells, Fuel cells and solar cookers are falling in these categories. While most of the energy generated on earth comes from earthly sources, there will still be heat being generated and the ―Entropy‖ will still be increased. This is an Entropy factor to describe ―Global Warming‖. It can be delayed but never defeated. So, let‘s embrace ―Global Warming‖, because we cannot run away from it, yet. Solar power is somewhat a reality, that human being use it to sustain humanity and mankind on the earth. There is a long and winding road ahead of us before humanity can use the ―Sun‖ as its most important source of energy again. Decay, Death and Destruction will be always in our doorsteps, one way or another, so being used to it. So it might be concluded, that to prevent flood, to prevent ice melt and to prevent ―Global warming‖ mankind can really develop, several possibility and among them the use of solar and wind energy and the reductions of population, recycling and NCER (Nonconventional Energy Resources) would be essential and as an utmost factor (Philander, 2009).
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REFERENCES Archer, D.: Global warming Understanding the Forecast, Blackwell. 256 (2006). Brahma, N.K.: Sustainable design in Chemical and Bioprocess Industries, Recoveries and recycling for Ecofriendly applications. NIT. Rourkela, September 27-29 (2004). Brahma, N.K.: Zero-effluent Discharge and Global warming: the role of MBST, UV and Microbial Engineering, OISOZED All India Seminar on ―Zero Effluent Discharge‖. IEI22-23 December (2007). Brahma, N.K. and S. Basu: Sequestration and Conversion of CO2: The way to recover Global Warming, Chemical Business. Nov.ISSN:0970-3136-.Issue: 22(11), 24 (2008). Edgerton, L.T.: ―The rising tide‖ global warming and world sea levels. Island Press. Publisher Place, Washington, DC (USA) (2008). Fick, S.: Global warming impact is already evident in Canada. In the Northwest Territories, warmer-than-usual, Reader's Digest Association (Canada), Canadian Geographic Enterprises, Science, p 40-43 (2004). Hasselmann, K.: Are we seeing global warming? Science, 276, 914-915 (1997). Levi, B. G., D.W. Hafemeister. and R.A. Scribner: Global warming: physics and facts: Washington, D.C., published by American Institute of Physics, Science, 311 (1992). Molina, R. and E. Uriarte: Markov entropy backbone electrostatic descriptors for predicting proteins biological activity. Bioorganic and Medicinal Chemistry., 14, 4691-4695 (2004). Nordhaus, T. and M. Shellenberger: Break through: from the death of environmentalism to the politics of possibility -Political Science, 142 (2007). Pétry, F.: Sustainability issues in agricultural and rural development policies, Vol.2. Policy Analysis Division, FAO, 1.45-1.50. (1995). Philander, S. G.: Encyclopedia of Global Warming and Climate Change. Nature, page 59 (2009). Willium, M. J.: Entropy shows that Global warming should cause increase viability in the weather, Global warming, American Physical Society, Vol.17: (2008). Walter, K.M., S.A. Zimov, J.P. Chanton, D. Verbyla and F.S. Chapin: "Methane bubbling from Siberian thaw lakes as a positive feedback to climate warming". Nature., 443(7107), 71-75 (2006).
In: Antarctica: The Most Interactive Ice-Air-Ocean Environment ISBN: 978-1-61122-815-1 Editors: Jaswant Singh, H.N. Dutta © 2011 Nova Science Publishers, Inc.
Chapter 12
NAVIGATION WITH GLOBAL POSITIONING SYSTEM IN ANTARCTIC CIRCLE Rajesh Tiwari 1 *, Smita Tiwari 1, P. K. Purohit 2 and A. K. Gwal 3 ABSTRACT The solar energetic charged particles from the Sun carry a tremendous amount of energy in the form of solar wind which hits the earth magnetic field. However, the magnetic field of the earth protects earth‘s atmosphere from this incoming charged particles of sun. In spite of it, some of the charged particles (called plasma) enter the magnetosphere on the day side of the earth eventually drifted and elongates the magneto tail. The elongated magneto tail reconnects across the neutral sheet, thus those charged follows the magnetic lines of earth and drifted to high latitude of earth. This return flow of plasma is associated with the sudden onset of auroral storm in the ionosphere at E layers. The auroras are visualized as green, yellow or purple curtains. The oval curtains cover the higher latitude and are known as auroral ovals. Generally, the location of the auroral oval is between 60˚ and 70˚ N or S. The radio waves propagating through auroral oval get degraded in terms of signal strength. This research studies the effect of auroral storms on GPS-based navigation. The experiment was conducted with GISTM (GPS Ionospheric Scintillation and TEC Monitoring) based NovAtel 4004A GPS receiver installed on board of M. V. Emerald, a Russian cargo ship during its journey from Indian Bay (69.60˚ S, 12.43˚ E) to Larsemann Hills (69.06˚ S, 76.03˚ E). Position error was computed and correlated with auroral activities during eight nights of the journey within the Antarctic Circle. During the eight nights, it was found that mean energy flux of aurora above 7 keV of energy degraded the SNR (Signal to Noise Ratio) of GPS signal. This degraded signal produced a few meters of error in GPS-based navigation.
*
E-mail:
[email protected], Phone No: +441912227272 Electrical, Electronics and Computer Engineering, Newcastle University, Newcastle Upon Tyne, NE1 7RU, UK 2 National Institute of Technical Teachers‘ Training and Research, Shamla Hills, Bhopal, India 3 Department of Physics, Barkatullah University, Bhopal, India 1
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INTRODUCTION The Global Positioning Systems (GPS) developed by US for air-land- and marinenavigation, which primarily available for US DoD (Department of Defence) and latter on it is made available for civilian users. Nowadays most of the navigation services uses GPS tool for movement. However, the most important element of GNSS services is safety measure which does get affected when GPS signal passes through the ionospheric irregularities. The ionospheric irregularities lower group velocity, or speeds up the phase velocity of the transionospheric GPS signals. The delay or acceleration of the signal produces a range error, eventually affecting the position solution obtained from the GPS receiver. The aurora storm is common phenomena at high latitude which creates ionospheric irregularities and eventually degradation in GPS performance.
AURORA The sun continuously emits charged particles in the form of solar radiation known as solar wind whose speed ranges from a few hundred to one thousand km/sec. In addition to solar wind thrust, the earth is exposed to the interplanetary magnetic field (IMF) of ~5-10 nT, most of which lies in a heliospheric equatorial plane. The earth‘s magnetic field protects the earth from the solar wind carrying ~40 TW of solar energy flux at ~50 Re (Re is radius of the earth) from the center of the earth. However, a fraction of the solar wind energy (~0.4 TW) enters the magnetosphere, known as leak in (Gordon, 1998) moreover, the amount of leak in energy depends upon the direction of IMF, if IMF is parallel to the earth‘s magnetic field, then a very small fraction of solar wind energy manages to get into the magnetosphere while in the case anti parallel IMF, the maximum amount of solar wind energy flows enters the magnetosphere. Figure 1. depicts the anti parallel IMF with earth‘s magnetic field and Figure 1. (A) illustrate the flow of energy as indicated by solid arrow which elongates the magnetic field lines of the earth, termed magnetotail. The field lines reconnect at the magnetotail and trap the energy. The trapped energy in the earth‘s magnetic field is accelerated along the magnetic field toward the higher-latitude illustrated in Figure 1.(B) and then strikes the atmosphere to form the aurora. The aurora is visible at night in the form of dancing of green, yellow, or purple lights. The shape of aurora is oval (or annulus) and therefore, it is referred to as the auroral oval. This oval, or annulus, is centered over the magnetic pole during quiet times. The annulus grows when the magnetosphere is disturbed. The location of the auroral oval is generally between 60º and 70º N or S. The auroral arc extends equatorward and maximum at 67º of geomagnetic latitude at midnight illustrated in Figure 2. (A), while at noon it extends towards pole up to 77º latitude (Feldstein, 1963).
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Figure 1. A represents open magnetic lines. B represents the closed magnetic lines.
Figure 2. A. Represents the equatorward extension of aurora in midnight. B. Energy precipitation (E0) due to aurora, recorded in South Pole at 16:00 UT from TIMED satellite.
Figure 2.(B) depicts an example of auroral precipitate energy at high latitude due to auroral storm. The auroral precipitate energy at South Pole obtained from TIMED satellite at 16:00 UT time seems to be maximum (between 7 keV to 10 keV) at midnight. The large precipitate of auroral energy affects the electron density of the ionosphere. A strong enhancement in TEC (Total Electron Content) was recorded on March 31, 2001 due to strong auroral precipitate energy (Foster and Vo, 2002). The enhanced TEC adds extra phase modulation to the satellite signal during propagation through auroral oval. The extra phase modulation to signal generates a random fluctuation of phase in the original signal. The random fluctuation of phase or amplitude of the signal, termed as scintillation (Hey et al., 1946) is very common in the higher latitude due to auroral storms. The phase scintillation of GPS signal was correlated with auroral activity in the arctic (Smith et al., 2008). The strong scintillation not only degrades the signal but may lose lock of the satellite. This problem is severe during the solar maximum cycle (Skone and Canon, 1999) observed RMSE (Root Mean Square Error) of positional error from 60 to 80 cm during solar maximum period. The
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next solar maximum cycle is expected around 2013, therefore, scientists and engineers have been alerted to model its effects. This research will find the threshold value of the auroral precipitate energy which may affect the GPS-based navigation at high latitude. The experiment was conducted on a Russian cargo ship, the M. V. Emerald from Indian Bay (69.60º S, 12.43º E) to Larsemann Hill (69.06º S, 76.03º E). The ship‘s route was selected within the Antarctic Circle so as to observe auroral oval.
MEASUREMENT OF AURORA Ground-Based Measurement When the highly energized solar particle hits the magnetosphere, the geomagnetic field of Earth is disturbed. The aurora is produced by the disturbed magnetic field line of the earth, so in order to take advantage of this effect, magnetometer stations were installed across the world at high and mid latitudes. The average value of variation of Horizontal component (H) of earth magnetic field obtained from installed magnetometer gives an idea about the occurrence of aurora. The commonly used magnetic index to represent magnetic storm is Kp, and it is global index obtained every three hours. When Kp > 5, it is considered to severe case of geomagnetic storm; Kp < 4 is a geomagnetic quiet condition; and Kp = 4 is moderate case. The distribution aurora is not based on luminosity but on the measurement particle energy (Hardy et al., 1985). Handy studied the zones of electrons and ion flux in terms of Magnetic Local Time (MLT) at all level of geomagnetic activity quantified by Kp. Chubb and Hicks in 1970 used Kp to study the level and mechanism of aurora; according to them, the equator boundary of the oval expands about 1.7º equatorward per unit of Kp on the day side of the earth and 1.3º on the night-side while it moves by 1º-3º of latitude during Substorm time (Chubb and Hicks, 1970).
Satellite-Based Measurement Satellites with image capturing equipment (ultraviolet image sensing) are sent into the polar orbit to capture the snapshot of the atmosphere during their passes. Several projects of NASA‘s is based on studying auroral activity; the TIMED (Thermosphere, Ionosphere, Mesosphere, Energetic, and Dynamic) mission is one of them. TIMED is aGlobal Ultraviolet Imager (GUVI) that provides cross-track scanned images of the Earth‘s ultraviolet airglow and auroral emission in the Far Ultraviolet (FUV) at wavelengths 115.0 to 180.0 nm, scanning imaging spectrograph that provides horizon-to-horizon images at five wavelength intervals (TIMED webpage http://www.timed.jhuapl.edu, 2008). It provides information of the ionosphere and thermosphere by monitoring all three regions: daytime mid-latitude, night-time low- to mid-latitude ionosphere and the high-latitude auroral zone, these regions are then characterized by energy and flux of the electrons (TIMED webpage http://www.timed.jhuapl.edu, 2008).
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EXPERIMENTAL SETUP AND METHODOLOGY The experiment was conducted on board of a Russian cargo ice class ship, the M. V. Emerald Sea, from Indian Bay (69.60º S, 12.43º E) on 27 February, 2007 to Larsemann Hills (69.06º S, 76.03º E) on 06 March, 2007. A NovAtel -602 GPS antenna installed on the deck of the ship as shown in Figure 3.(A) and is connected to GISTM based NovAtel 4004A GPS receiver installed in the radio room of the ship. The NovAtel -602 GPS antenna is choke ring designed used to minimize the multipath effect and the GPS receiver is operating on L1 C/A code and L2 carrier signal has 12 channels which can lock 12 satellites at a time. The GPS receiver has been logged with the following log command: GPGGA, GPGSV at 1 Hz rate, which we consider as positional file in ASCII format while the raw ionospheric file is binary file. The positional file provides position of the receiver in Real Time Kinematic (RTK) mode, satellite geometry, number of locked satellite along with their elevation angle, azimuth angle and their SNR (signal to noise ratio). The ionosphere file provides the TEC and ionospheric scintillation over phase and amplitude in binary format. The ship path followed during the experiment is shown in Figure 3.(B) and the figure represents that the ship remained in Antarctic circle throughout the experiment in order to observe aurora. The IPP (Ionospheric Pierce Point) at 300 km computed so as to identify the traces of GPS satellite in auroral oval. The position solution and IPP computed from receiver are transformed in MLT (Magnetic Local Time) frame of reference using coordinate transformation model (Alfven and Falthammar, 1963). The energy precipitation from the aurora was generated from TIMED satellites at the same time as the experiment; the direct polar plot of mean energy flux (E0) Vs MLT is archived from the TIMED web page.
Figure 3. A. Experimental set on the ship and GPS signal are shown passing through aurora. B. The red line indicate the ship path from Indian Bay (69.60º S, 12.43º E) to Larsemann Hill (69.06º S, 76.03º E).
REAL TIME KINEMATIC POSITIONING The real kinematic position is the process of estimating the position of any object in motion. Several parameters are used to estimate the position solution and error in any one
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parameter can degrade the position solution. In this study the position of the ship is estimated in real time using constant velocity and a constant acceleration model. In marine navigation, the precise position solution is very important. The GPS provides a position solution that does not degrade over time. However, the case may be different when there is an ionospheric storm. In real time kinematics, it is difficult to obtain a high precision position solution, because the stochastic properties of the system depend on factors, such as the ship‘s dynamic status and physical environment (e.g., rolling and pitching of ship on a rough sea), which are not always fixed. Therefore, efficient Kalman filtering algorithms have become an attractive research topic. In this study, the efficient Kalman modelling is not an issue because the Kalman filter algorithm has been used to estimate the position solution in real time. In this study, only the ionospheric condition related to aurora is correlated with the positional error obtained from the GPS receiver. The positional error of the ship in real time is computed in three steps. In the first step, the positional solution is computed by the software of receiver; in the second step, the position solution is estimated using constant velocity and constant acceleration model and filtering out the noises using Kalman filter. (The algorithm of the second stage is described in the next paragraph.) In the third stage, the position error is computed by taking the difference of the estimated positional solution from model with Kalman filter and position solution obtained from GPS in Cartesian coordinate frame. A constant velocity and acceleration model is used here to measure the update of positions, because it is assumed that the velocity of ship cannot be changed within a minute. A 9-dimensional state vector contains three components of position (x, y, z), three components of velocity (vx, vy, vz) and three components of acceleration (ax, ay, az). The average of velocity and acceleration for a minute is taken as a constant velocity and acceleration of the model for the next epoch, and each epoch is recorded at 1 sec. Figure 4. explains the real kinematic state of the ship; consider the ship is at point P at time t1 after one minute of initial stage the ship reached point Q. The velocity and acceleration obtained for 1 min are averaged to have one constant value which would be used to compute the position of the ship in next epoch therefore our first computation is at 1min 1 sec. When the ship reached to point R then the model will take the average value of velocity and acceleration obtained between points Q and R. The probable noises are filtered out through the Kalman filter model.
Kalman Filter The filter estimates the process state at some time and then obtains feedback in the form of (noisy) measurements. The mathematical process of Kalman filter falls into two groups: Time Update equations and Measurement Update equations. The time update equations are responsible for projecting forward solution by using the current state and error covariance estimates to obtain a priori estimates for the next time. The second is the measurement update equations, and it is responsible for the feedback (i.e. for incorporating a new measurement into a priori estimate to obtain an improved a posteriori estimate). Figure 5. shows the algorithm of the Kalman filter.
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Figure 4. Real Time Position for Ship.
Figure 5. Kalman filter algorithm.
The state model can be written as:
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RESULTS AND DISCUSSION The mean energy spectrum of precipitating electron varies from eV to tens of keV, which is responsible for ionization in the E and F region of ionosphere. The lower mean energy ionizes the F layer; while, the E layer is ionized by the high level of mean energy (Kintner et al., 2002). The TEC value obtained from GPS depends upon these two layers therefore it is important to study the auroral effect on GPS to improve the accuracy of GPS based navigation during auroral storms. These regions are more interesting because they are accompanied by ionospheric irregularities that cause scintillations (Basu et al., 1985; 1993). The result of the research has been classified into two groups: one group represents a case study in which the ship was under the auroral oval region and the consequent effect on position solution; the second group describes when the ship was not under the influence of aurora. The horizontal error of both cases is taken into consideration so as to represent the effect of aurora on position solution. The position solution obtained here for both cases was taken for 24 hours to clarify the understanding of the effect of aurora. The whole day analysis of position error leads to a better understanding and produces consistency in our solution, because the auroral event lasts for 20 – 30 minutes of interval but it may range up to several hours during highly disturbed geomagnetic storms. The third group is statistical analysis of the result obtained during the ship vogue from source to final destination.
GPS POSITIONAL SOLUTION IN ACTIVE AURORA On 28th February 2007, TIMED spacecraft observed an aurora at three intervals when the ship was in the night time zone (according to MLT). The recorded time of auroral oval region by TIMED spacecraft is at 17:55, 19:32, and 21:09 UT (Figure 6) whose MLT times are 19:20, 20:37 and 22:28 respectively. The solid blue arrow with red boundary indicates the position of the ship within auroral activity as shown in the upper panel of the Figure 6. The IPP of locked PRNs are illustrated in the lower panel of Figure 6. The IPP illustrated in the lower panel of the Figure 6 indicates the signal of the locked PRNs actually passed through the auroral activity. Due to the presence of aurora activity, the number of satellite locked is 5 between 17:30 UT to 18:30 UT. Compared to the MLT and the IPP it was found that few of the PRN passed through the auroral oval. The SNR of the locked satellite are illustrated in Figure 7. and it indicates the most of the PRNs (4, 9, 12, 17, 20, and 28) signal passed through the aurora has very low SNR value. Out of 10 locked PRN, 5 were found to have SNR below 15dB, but the required SNR is 23 dB. (Senior and Honary, 2003) found that the fading of low frequencies is due to D layer of the ionosphere. However, the signal degrades at GPS L1 frequency due to diffraction of the signal from the precipitation of auroral energy (Titheridge, 1971). The fast moving auroral arcs are the evidence of particle precipitation that could cause ionospheric irregularities that affect the GPS signals in terms of fading of the GPS signal (Smith et al., 2008). Previous studies of the production and decay of plasma density from auroral precipitation in the F region calculate a production rate of 5–10 min and a decay rate of 10–20 min (Sojka
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and Schunk, 1986). The work in demonstrates the correlation of TEC derived from GPS with TIROS precipitating energy flux over 0.3–20 keV (Coker et al., 1995). They mentioned that short enhancement of TEC correlates with the precipitating electron flux. Aarons et al. (2000) have used Polar UVI data to study the production of fluctuations in GPS signal produced by TEC variations correlate well with increased TEC. Similar studies is seen in (Pi et al., 1997) where author considered worldwide GPS network to investigate GPS TEC fluctuations and present a case showing high-latitude TEC fluctuations in the evening and early morning during a magnetic storm. The TEC fluctuation can be produced by precipitating electron flux. The sum of this evidence is that TEC fluctuations occur in the same regions as active auroral displays. The tracking performance of GPS receiver can be degraded by the fluctuation of TEC and during periods of enhanced ionospheric activity in the high latitude auroral region is very significant (Skone, 2001). Figure 6 represents the case when the GUVI energy flux is approximately equal to 10 keV and when the GPS satellites are in the line of sight and the degradation in position solution is greater. The first panel of Figure 8 represents northing and easting error; the second and third panels represent the total number satellites locked and HDOP, respectively. Results show that when aurora activity is observed, a corresponding strong fluctuation in horizontal position is recorded. The evidence of enhanced TEC degrades the SNR of the signal and the degraded signal causes significant positional error. These variations are associated with smaller intensifications in the auroral oval, which are often observed as precursors to the more intense expansive phase velocity (Murphree et al., 1991). Due to high auroral activity the number of satellite locked also decreases and reaches the minimum number of 4 between 19:00 UT and 20:00 UT. With the decreases number of satellites, the geometry is affected and increased HDOP is also a source of positional error (Position Accuracy = HDOP x User Range Error). The easting error in Figure 8. shows one-to-one correlation with the PRNs affected by the auroral storm. Figure 8. also illustrates that the positional solution is smooth when there is no auroral storm.
GPS POSITIONAL SOLUTION IN QUIET AURORA Another event was selected when the auroral oval was not found in the line of sight of locked GPS satellites. The auroral oval was traced by TIMED satellite at 11:37 UT and 13:16 UT, illustrated in the upper panel of Figure 9. The corresponding MLT has been representing in polar plots with latitude circle. Based on the above mentioned time (UT), the position of ship was computed to find its position according to MLT at 11:37 UT. At two time periods, 11:37 UT and 13:16 UT, the ship was found around 14:00 MLT position within 65 degree of latitude circle.
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Figure 6. The upper panel represents the auroral precipitate energy and the lower represents the IPP of the GPS satellite passing through the aurora (computed in MLT reference).
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An estimation of position of ship is purely based on MLT confined within the auroral plot, as indicated by the solid red arrow. The IPP of total number of visible satellite are illustrated in the lower panel of Figure 9. During this event the maximum number of locked satellites was 7. Figure 10. illustrates the effect of the SNR of the signal and the SNR value obtained indicate no degradation of the signal in the absence of aurora. The horizontal position errors are illustrated in the upper panel of Figure 11, the results show negligible horizontal position errors in terms of easting and northing. The second panel of the Figure 11. illustrates the number of locked satellites, and the third panel represents HDOP to study the satellite geometry. The results show that in the absence of auroral activity the position accuracy was fair and good. Though position error was recorded high around 06:00 UT to 15:00 UT due to the low number of satellites locked (4), the HDOP increased to 8. As mentioned in the previous section, the big value of HDOP is also responsible for positional error. Therefore, the positional error obtained is due to bad geometry.
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STATISTICAL STUDY OF POSITIONAL ERROR To have a clear picture of positional error during auroral activity, we compute the statistics of absolute position error for complete ship journey. We divide the data into groups, according to auroral activity. In the first group, auroral activity is present and in the other, auroral activity is absent. For this purpose we compute mean, standard deviation and maximum value for the two groups (Table 1). From the table we found that on the days when auroral activity was present, the maximum horizontal and vertical error was more than 6 m and standard deviation was greater than 1; this is very high. In the absence of aurora, the position error is less than 4 m and standard deviation is less than 0.4. Due to the high auroral activity, the mean number of satellite locked is 5; as a result, the maximum HDOP is 7, which increases the probability of poor geometry. On the other hand, due to the absence of auroral activity in the Antarctic region, the mean number of satellites locked is greater than 9, which is sufficient for good geometry; therefore the maximum value of HDOP is 3.
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SUMMARY AND CONCLUSION We established strong correlations between GPS performance and auroral phenomena in the Antarctic region during the ship‘s movement. The precipitating energy flux over 0.3–20 keV correlated well with GPS-derived TEC (Coker et al., 1995). The auroral E region is the main source of TEC-induced phase fluctuations. The auroral activities are common at high latitudes. The performance of the GPS receiver degraded at high latitudes during auroral activities. Therefore, the higher the auroral energy, the higher the dynamic auroral arcs. TEC fluctuations produced by discrete auroral arcs will be more common and larger in the night side auroral ionosphere (Basu et al., 1993). The L1 ranging errors of at least 2 m will be introduced by auroral arcs into navigation systems for differential and augmentation (Kintner et al., 2002). In aurora region, degradation accuracy is of concern for communication and navigation. This issue is a concern for reliable operation of safety-critical GPS systems, such as marine DGPS (Differential Global Positioning System) services or SBAS (Satellite-Based Augmentation Systems) for aviation applications. During ionospheric disturbances over high latitude regions, users experience degraded position errors, and sometimes exceed tolerable limits. Our study shows that the precipitating energy flux over 7 keV energy degraded the position solution. Table 1. Statistics of Position Error during Auroral Activity Statistics Observations Horizontal Error (m) Vertical Error (m) HDOP No. of Satellite
Auroral Activity Present Mean Std Max 7.2 1. 5 8.9 7.5 1.4 6.4 5.4 1.7 7.0 4.9 1.1 11.0
Auroral Activity Absent Mean Std Max 2.5 0.5 3.3 2.6 0.4 3.1 1.6 0.2 3.0 9.1 0.1 11.0
ACKNOWLEDGMENTS The authors wish to acknowledge the financial support from NCAOR, Goa, Ministry of Earth Science, Govt. of India, under the Space Weather Programme at Antarctica. The authors also acknowledge the TIMED mission for providing aurora data.
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INDEX A abatement, 222 absorption spectroscopy, 120 access, 248 accessibility, 119 acclimatization, 131 acid, 62, 67, 97, 115, 229 active oxygen, 97, 99, 113 active site, 120 adaptability, 54 adaptation, 40, 68, 72, 74, 82, 95, 108, 139, 146, 163, 164, 169, 171 adaptations, viii, 68, 227 adenine, 119, 128 adjustment, 95, 111 advancement, viii adverse conditions, 11, 100, 107 adverse effects, 115 adverse weather, 44 aerosols, 18, 196 Africa, 2, 3, 135, 136 age, 24, 28, 40, 41, 222, 225 agriculture, 7 Air Force, 195 air pollutants, 70 air temperature, 5, 22, 67, 69, 74, 75, 79, 141, 169, 202, 213 Alaska, 224 Alaskan North Slope, 82 alcohols, 99, 103 alfalfa, 126 algae, 11, 41, 44, 47, 49, 50, 53, 56, 58, 59, 61, 62, 63, 66, 68, 72, 74, 75, 80, 82, 83, 84, 85, 87, 95, 98, 99, 104, 109, 129, 131, 133, 164, 228, 230 algorithm, 238, 239 alien species, 41 alpha-tocopherol, 95 alters, 16, 104, 126, 146
amino, 94, 99, 114, 228, 229 amino acid, 94, 99, 114, 228, 229 amino acids, 94, 99, 114, 229 ammonia, 66, 115, 141 amplitude, 85, 180, 208, 235, 237 anatomy, 96 ancestors, 57 antioxidant, 95, 97, 100, 104 antithesis, 126 appropriate technology, 223 aquatic habitats, 138 Arabidopsis thaliana, 104, 125 Argentina, 105, 127, 146, 147 arthropods, 50 Asia, 2 assessment, 34, 51, 52, 53, 58, 82, 84 assimilation, 66 atmosphere, 1, 4, 5, 6, 8, 9, 10, 14, 15, 16, 17, 18, 20, 22, 24, 27, 30, 31, 33, 34, 43, 67, 70, 72, 75, 84, 86, 89, 91, 164, 173, 174, 178, 180, 183, 184, 186, 193, 194, 195, 196, 199, 200, 208, 209, 215, 216, 217, 218, 224, 225, 227, 228, 233, 234, 236 atmospheric pressure, 9, 43, 173, 184, 185, 187, 194 autecology, 124 authorities, xv automobiles, 228 avoidance, 68, 111
B bacteria, 47, 58, 68, 70, 83, 107, 118, 132, 226 bacterium, 58, 68, 70, 83 banks, 53, 54, 61, 143 barriers, 15 base, 14, 57, 97, 118, 119, 126, 203 base pair, 126 behavioral change, 223 behavioral intentions, 223 bending, 116
250
Index
benthic diatoms, 101 Big Bang, 230 biochemistry, 101, 123 biodiesel, 230 biodiversity, 47, 90, 109, 133, 223, 227, 228 biogeography, 150 biological activity, 231 biological samples, 44, 45, 63, 64 biological systems, 72 biomass, 32, 34, 39, 50, 59, 62, 66, 73, 81, 84, 112, 129, 145, 164 biosphere, 67 biosynthesis, 145 biosynthetic pathways, 115 biotic, 47, 48, 49, 63, 81 birds, 39, 40, 44, 48, 50, 53, 56, 57, 58, 70, 80, 81, 226 bleaching, 224 body fluid, 55, 79 bonding, 75, 79 branching, 112 Brazil, 135 breeding, 222 Britain, 90 bryophyte, 97, 98, 108, 112, 114, 125, 128, 133, 140, 145 burn, 133, 221, 222, 226, 228 buttons, 109
C cabbage, 143 cadmium, 123 calcium, 66 campaigns, 201 carbohydrate, 96, 97 carbohydrates, 59, 101, 121, 142, 143, 145, 148, 170 carbon, 6, 9, 10, 15, 32, 34, 39, 63, 66, 67, 77, 81, 97, 105, 108, 126, 128, 143, 146, 147, 221, 222, 224, 225, 226, 228 carbon dioxide, 6, 9, 15, 34, 105, 126, 128, 146, 147, 221, 222, 224, 226 carbon monoxide, 6 carefulness, 9 carotene, 94, 95, 98 carotenoids, 72, 82, 98, 100, 102, 131 case study, 241 cation, 120 cellulose, 100, 103, 222, 228 chaos, 221, 223, 228 chemical, 5, 9, 10, 11, 63, 222 chemical characteristics, 11 chemical properties, 222 chemical reactions, 9
chemicals, 15, 55, 97 China, 86 chlorine, 7 chlorophyll, 51, 66, 73, 95, 98, 100, 101, 102, 112 chloroplast, 100 chromosome, 118 circulation, 14, 33, 34, 36, 85, 173, 178, 179, 194, 195, 219, 222, 225 cities, 225 civilization, 230 clarity, 22 classes, 59, 60, 61, 68, 116, 205 classification, 57 clean energy, 230 cleaning, 17 cleavage, 121 climate, vii, viii, 1, 2, 5, 7, 8, 9, 10, 12, 15, 18, 36, 37, 39, 41, 42, 48, 56, 67, 74, 77, 79, 84, 86, 91, 96, 98, 108, 121, 123, 128, 139, 143, 157, 171, 172, 174, 195, 196, 199, 200, 201, 202, 218, 223, 224, 225, 226, 227, 231 climate change, 1, 5, 12, 18, 36, 121, 128, 139, 143, 174, 223, 224, 225, 227 climates, 75, 77 climatic factors, 8, 67, 68 CO2, 9, 31, 32, 85, 124, 128, 221, 222, 227, 228, 231 coal, 3, 221, 222, 228 coastal region, 7, 9, 10, 40, 84, 109 colonization, 40, 84, 105 combined effect, 110, 127, 181 commercial, 3, 4, 7 communication, 163, 247 communities, 40, 50, 51, 52, 53, 77, 80, 82, 86, 97, 98, 108, 111, 131, 143, 144, 145 community, viii, 12, 34, 59, 60, 61, 84, 104, 146 compatibility, 87 competition, 223 complexity, 48, 113 composition, 5, 63, 75, 79, 101, 104, 105, 110, 125, 127, 128, 143, 146, 147 compounds, 9, 18, 97, 99, 100, 101, 104, 113, 115, 116, 121, 122, 127, 140, 142, 143 computation, 238 condensation, 77, 208 conduction, 74, 75 conductivity, 63, 193 conductor, 14 conference, 90 configuration, 216 conservation, ix, 12, 57, 87 consolidation, 158 constant rate, 5 constituents, vii
251
Index construction, 10 consumers, 11, 49, 50, 51, 54, 56, 59, 101 consumption, 68, 85, 230 consumption rates, 68, 85 contamination, 32 Continental, 32, 108, 109, 133, 142, 144, 196 contour, 209 convention, 211 convergence, 2 cooling, 15, 16, 20, 43, 55, 56, 68, 79, 176, 177, 178, 180, 183, 194, 199, 208, 221, 225, 228 cooperation, 171 coordination, 31 copper, 4 correlation, 87, 174, 180, 189, 211, 242 correlations, 247 cortex, 97, 115, 123 cosmic ray flux, 174, 175, 196 cosmic rays, 174, 195, 196 cost, 112, 223 courtship, 57 covering, 3, 44, 164 critical analysis, 11 criticism, xv crop, 62, 72, 87, 226 crop production, 226 crops, 10, 105, 128, 226 crust, 3, 158 crystal structure, 126 crystalline, 41 crystals, 70, 167, 169, 219 Cuba, 144 culture, 230 curricula, 223 cuticle, 55, 164, 169 cycles, 40, 108, 112, 125, 142, 145, 207, 209, 213, 224 cycling, 33, 48, 58, 59, 132 cyclones, vii, 15, 16, 17, 18, 31, 39, 40, 42, 43, 46, 67, 69, 70, 79, 85 cytoplasm, 116 cytosine, 126
D danger, 228 data set, 69 decay, 177, 189, 241, 248 decomposition, 39, 59, 67, 81, 82, 84 defence, 107, 111 deficit, 104, 200 deforestation, 224 degradation, 75, 102, 112, 234, 242, 244, 247 dehydration, 95, 143
deposition, 16 deposits, 3, 10, 123, 225 depression, 47, 141 depth, 6, 7, 26, 28, 35, 40, 42, 47, 66, 67, 73, 110, 139, 202, 203, 215 derivatives, 96, 166, 169 desiccation, 41, 55, 71, 87, 97, 99, 113, 115, 116, 127, 128, 140, 141, 142, 163, 164, 165, 169, 171, 172 destruction, 99, 100, 105 developed nations, 221, 222, 228 developing countries, 222 developing nations, 221, 228 deviation, 176, 177, 180, 183, 186, 192, 246 dew, 41, 70, 75, 77, 80, 169 DHS, 126 diffraction, 241, 248 diffusion, 28 disaster, 221 diseases, 226 displacement, 222 dissociation, 121 dissolved oxygen, 47 distribution, 10, 21, 35, 51, 55, 67, 68, 70, 84, 89, 95, 97, 99, 105, 110, 118, 121, 124, 125, 127, 132, 133, 138, 145, 149, 150, 156, 158, 159, 161, 165, 171, 187, 189, 236 diversity, 8, 39, 40, 47, 77, 80, 82, 96, 108, 147, 150, 172 DNA, 72, 107, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129 DNA damage, 115, 116, 117, 118, 121, 122, 126, 129 DNA lesions, 117, 118, 119, 122, 128 DNA repair, 118, 121, 125 DOI, 34, 35, 36 dominance, 62, 164, 171 drainage, 163, 165, 166, 178, 181, 187, 195 dream, 107 drinking water, 4, 222 drought, 37, 75, 77, 95, 97, 115, 141, 170, 226 dry matter, 170 drying, 47, 55, 98, 116, 128, 142 DS-1, 83 duality, 112
E ecology, 41, 74, 79, 84, 126, 133, 144, 145, 147, 161, 166, 172 ecosystem, viii, 5, 34, 39, 44, 47, 48, 54, 58, 59, 62, 63, 67, 69, 70, 72, 73, 74, 75, 79, 81, 83, 84, 85, 122, 123, 143, 146, 226 editors, iv, xv
252
Index
effluent, 231 egg, 57 elasticity modulus, 163, 165, 168, 169, 170, 171 electric current, 192, 193 electric field, 173, 174, 180, 181, 184, 193, 194, 195 electricity, 196 electron, 10, 99, 119, 120, 123, 235, 241, 242, 248 electrons, 236 elongation, 100, 105 emission, 221, 222, 228, 236 enemies, 57 energy, 5, 8, 9, 14, 15, 16, 17, 18, 29, 39, 41, 45, 47, 48, 49, 58, 59, 66, 67, 69, 71, 72, 75, 78, 79, 80, 91, 96, 97, 98, 118, 120, 121, 132, 164, 174, 199, 200, 211, 212, 219, 221, 222, 223, 228, 229, 230, 233, 234, 235, 236, 237, 241, 242, 243, 245, 247 energy consumption, 230 energy transfer, 230 engineering, 222, 223, 226 entropy, 221, 223, 224, 226, 228, 231 environment, iv, vii, viii, ix, 1, 3, 4, 5, 7, 8, 10, 11, 13, 15, 17, 20, 22, 23, 32, 40, 41, 43, 45, 47, 48, 49, 50, 61, 67, 68, 70, 75, 77, 79, 81, 84, 85, 98, 116, 124, 126, 127, 132, 133, 146, 150, 170, 171, 223, 224, 226 environmental aspects, 224 environmental change, viii, 123, 144 environmental conditions, viii, ix, 5, 11, 91, 95, 96, 97, 99, 132, 133, 138, 139 environmental control, 143 environmental factors, 47, 96, 99, 223 environmental influences, 41 Environmental Protection Agency (EPA), 227 environmental stress, 113 environmental stresses, 113 environmentalism, 231 enzyme, 39, 115, 118, 119, 120, 127, 141 enzymes, 100, 103, 104, 115, 118, 119, 121, 140 epidermis, 114 EPR, 120 equilibrium, vii, 16 equipment, 10, 236 ERA, 35 erosion, 30 eukaryotic, 119 Europe, 2, 159 evaporation, 15, 42, 67, 71, 72, 98, 108, 150, 225 evidence, 5, 77, 98, 100, 112, 113, 176, 196, 241, 242 evolution, 32, 48, 68, 81, 85, 86, 104, 118, 122, 127, 139, 143, 223 excision, 128
excitation, 119, 120 exclusion, 100, 103 exploitation, 223 exposure, 40, 46, 55, 97, 98, 99, 100, 104, 112, 115, 123, 128, 140, 142, 180, 224 external influences, 40, 85 extinction, 103, 125, 222, 225, 226, 228 extreme cold, 10, 95, 131, 164
F FAD, 119, 120 families, xv, 55 fat, 57 fatty acids, 142 fauna, 39, 48, 50, 51, 63, 66, 80, 84, 85, 86, 87, 131 fertility, 66 fertilization, 75, 77, 80 fertilizers, 10 films, 223 filters, 101, 122, 124 filtration, 49 financial, 81, 171, 247 financial support, 247 fish, 57 fixation, 143 flavonoids, 96, 99, 100, 103, 113, 122, 124, 125, 128, 145, 147 flexibility, 104 flight, 58, 70 flights, 70 floods, 226 flora, viii, 3, 4, 11, 39, 40, 41, 44, 47, 48, 49, 50, 51, 56, 67, 68, 70, 71, 72, 75, 77, 79, 80, 81, 86, 87, 90, 91, 95, 96, 100, 102, 104, 105, 108, 121, 128, 131, 132, 133, 139, 143, 146, 149, 153, 157, 159, 160, 161, 227, 228 flora and fauna, 3, 4, 11, 39, 40, 41, 44, 47, 67, 68, 70, 71, 72, 79, 81, 90, 100, 227, 228 flowers, 11 fluctuations, 112, 141, 173, 189, 195, 215, 242, 247 fluorescence, 98, 112, 124 food, 11, 40, 47, 48, 50, 51, 54, 58, 59, 75, 80, 81, 101, 223, 225, 228 food chain, 11, 48, 58, 59, 80 food web, 58, 101 force, 15, 186, 187, 200 formation, vii, 7, 10, 13, 14, 15, 16, 17, 18, 22, 24, 28, 35, 39, 41, 66, 67, 68, 69, 70, 75, 77, 79, 99, 116, 117, 120, 121, 125, 126, 132, 173, 176, 177, 180, 187, 189, 194, 200, 218, 222 formula, 186 fossils, 4 fragments, 52, 53, 54, 139
253
Index freedom, 12 freezing, 9, 16, 18, 44, 50, 55, 56, 62, 68, 95, 98, 99, 103, 113, 125, 133, 140, 141, 142, 145, 150, 193, 222 frequency distribution, 205, 206 freshwater, 28, 47, 56, 63, 68, 86, 107, 164 frost, 74, 150, 170 fruits, 11 fuel consumption, 222 functional analysis, 104, 127 fungi, 47, 56, 58, 70, 73, 86, 95, 99, 118, 131, 132, 164 fungus, 121 fusion, 75, 79, 230
G gametophyte, 142 gene expression, 127 genes, 124, 144, 145 genetic code, 117 genetic diversity, 133 genetic information, 118 genome, 118, 119 genus, 54, 55, 57, 58, 96, 132, 146, 149, 158, 159, 160 geography, 5, 86 geometry, 110, 237, 242, 244, 246 Georgia, 87, 126, 132, 134, 136, 149, 150, 157, 159, 160, 161, 172 Germany, 90, 125, 161 germination, 71, 112 global climate change, 121 global scale, 82 global warming, 5, 7, 17, 22, 27, 33, 35, 36, 82, 219, 221, 222, 223, 224, 225, 226, 227, 228, 231 glucose, 228 glycerin, 99 glycerol, 55 google, 224 GPS, 233, 234, 235, 236, 237, 238, 241, 242, 243, 245, 247, 248 gracilis, 51, 155 graph, 205, 209 grass, 11, 99, 103, 125, 132, 143, 144 grasses, 133 gravitation, 8 gravity, 15, 16, 202 grazing, 101, 104 green alga, 61, 62, 72, 73, 80, 86, 96, 97, 99, 164 greenhouse, 28, 34, 74, 223, 224, 225, 227 greenhouse gases, 223, 224, 225 growth, 11, 14, 36, 39, 40, 44, 47, 49, 50, 51, 55, 61, 62, 63, 66, 67, 68, 73, 79, 80, 81, 83, 87, 91, 95,
97, 98, 100, 102, 104, 105, 106, 107, 108, 111, 112, 115, 121, 127, 128, 129, 140, 141, 142, 143, 146, 147, 148, 164, 177, 225 growth rate, 36 growth temperature, 98 Guangzhou, 86
H habitat, 41, 44, 47, 50, 54, 55, 57, 61, 68, 70, 75, 78, 79, 85, 96, 97, 107, 115, 132, 138, 164, 168, 171, 225, 226 habitats, 41, 49, 51, 52, 53, 67, 95, 123, 125, 127, 131, 132, 139, 141, 142, 149, 164, 165, 172, 222 hair, 99, 144 hardness, 42, 66 harmful effects, 101, 113, 222 harvesting, 119 hazards, 9, 226, 228 health, 104, 143, 223, 226 heat loss, 200 heat transfer, 17, 78, 219 height, 6, 10, 13, 22, 23, 24, 34, 57, 67, 157, 174, 184, 185, 186, 215, 218 hemisphere, 8, 42, 57, 110, 113, 157, 160, 189, 195, 196, 197 heterogeneity, 61, 75, 79 high winds, 14, 27 histogram, 206, 207 histones, 119 history, iv, 1, 5, 11, 31, 86, 103, 127, 147, 201, 222 Holocene, 40, 86 hot springs, 99 House, 10, 12, 160, 172 human, 1, 4, 5, 9, 11, 40, 45, 57, 63, 66, 70, 82, 224, 226, 230 human activity, 1, 5, 66, 82 humidity, 9, 39, 42, 43, 47, 51, 67, 71, 79, 141, 142, 164, 169 humus, 63, 81, 95 Hungary, 127 hunting, 222 hurricanes, 225 hyaline, 136 hybrid, 223 hydrocarbons, 3 hydrogen, 99, 125 hydrogen peroxide, 99 hydroxyl, 99, 113 hydroxyl groups, 113 hypothesis, 174, 213
254
Index
I ideal, 5, 40, 72, 73, 96, 170, 201 identification, 51, 52, 53, 87, 96, 126, 133, 161, 172 identity, 5 image, 236 images, 236, 247 imagination, 11 IMF, 174, 175, 176, 177, 178, 180, 187, 188, 189, 191, 194, 197, 234 immersion, 169 immigration, 40 Impact Assessment, 224 impulses, 193 in vitro, 125 incidence, 107, 108 income, 194 India, ix, xi, xii, xiii, xv, 1, 3, 9, 13, 18, 31, 34, 35, 39, 81, 85, 89, 90, 91, 105, 107, 131, 149, 153, 154, 155, 156, 158, 160, 163, 221, 230, 231, 233, 247 individuals, 65, 121 induction, 126, 128 industrialization, 10 industries, 226 industry, 7, 224 ingredients, 227 inhibition, 72, 84, 122 insects, 47, 54, 55, 68 institutions, xv insulation, 75, 80, 204 integrity, 97, 100 interface, 15 interference, 1 intervention, 9 intrusions, 41 inversion, 13, 16, 20, 21, 24, 25, 29, 30, 200, 201, 213, 215, 217, 218, 219 invertebrates, 40, 50, 51, 68, 74, 75, 80, 118 ionization, 4, 174, 193, 241 iron, 3, 99, 149 irradiation, 103, 104, 105, 128, 147, 170, 193 islands, 2, 3, 39, 40, 108, 109 isolation, 41, 132, 149, 157, 160 isomers, 116, 118, 125 isotherms, 165, 170 isotope, 33 issues, iv, ix, 7, 12, 87, 231 Italy, xi, xii, 34, 86, 199
J Jamaica, 87
Japan, 86 Jordan, 32
K kaempferol, 113, 114
L laboratory studies, 72 lactic acid, 58, 83 lakes, 10, 16, 39, 42, 44, 47, 49, 51, 53, 54, 56, 61, 63, 66, 78, 81, 85, 91, 98, 99, 108, 138, 139, 141, 144, 145, 164, 165, 231 landscape, 72 landscapes, 145, 146, 164 Late Pleistocene, 86 laws, 230 leaching, 145 lead, vii, 16, 17, 20, 22, 23, 24, 74, 78, 116, 132, 174, 187, 195, 225, 226 legs, 55 Lepidoptera, 85 lesions, 116, 118 lice, 56 lichen, viii, 11, 47, 49, 50, 51, 52, 53, 61, 68, 71, 74, 75, 77, 80, 82, 85, 95, 96, 101, 102, 103, 108, 115, 122, 124, 125, 131, 145, 149, 150, 153, 157, 158, 160, 163, 165, 166, 167, 168, 169, 171 life cycle, 11, 67, 68 light, 11, 27, 31, 47, 49, 50, 51, 57, 62, 66, 67, 68, 73, 74, 75, 77, 97, 98, 99, 100, 102, 106, 116, 118, 119, 120, 122, 123, 124, 142, 144, 228 lipids, 99, 100, 142 living conditions, 50 logistics, 81, 217 Louisiana, 225 low temperatures, 4, 68, 74, 83, 85, 141 luminosity, 236 lutein, 95 lying, 99, 132 lysis, 62
M macroalgae, 102 macromolecules, 97 magnesium, 66 magnetic field, 5, 174, 175, 176, 180, 181, 195, 233, 234, 236 magnetism, 4 magnetosphere, 174, 187, 192, 193, 194, 233, 234, 236 magnitude, 176, 201
255
Index majority, 47, 58, 99, 132, 164 mammal, 87 mammals, 48 man, 149, 176, 177 management, ix manganese, 4 manipulation, 142 marine environment, 18 mass, vii, 14, 15, 16, 28, 34, 36, 37, 164, 178, 179, 181, 200 materials, 41, 56, 58, 66, 80, 147 matrix, 240 matter, iv, 14, 17, 22, 67, 73, 226 measurement, 5, 10, 44, 96, 143, 172, 176, 200, 202, 203, 204, 236, 238 measurements, 6, 24, 35, 36, 41, 43, 44, 72, 82, 86, 96, 127, 128, 177, 180, 185, 200, 202, 203, 238, 248 mechanical properties, 170 medulla, 115 melanin, 95, 97 melt, 4, 10, 28, 36, 45, 47, 50, 52, 97, 98, 99, 108, 116, 141, 165, 169, 201, 221, 222, 223, 225, 226, 230 melting, 7, 16, 28, 31, 36, 42, 44, 47, 74, 132, 169, 211, 221, 222, 224, 226 melts, 7, 8, 10, 14, 16, 222 membranes, 101 meta analysis, 113, 140 meta-analysis, 123, 127 metabolism, 101, 103, 104, 113, 124, 140, 143, 144 metabolites, 102, 103, 124 metals, 105 meter, 10, 62, 225, 227 microbial communities, 147 microbiota, 77, 80 microclimate, 49, 67, 125, 142 microcosms, 126, 146 microenvironments, 61 micrograms, 56 microhabitats, 81 microorganism, 34, 84 microorganisms, 11, 15, 22, 39, 47, 58, 66, 71, 75, 78, 79, 80, 83, 102, 108, 126 microscope, 50 migration, 40, 226 mineralization, 67 mission, 236, 247 mixing, 16, 22, 27, 29, 70, 85, 208, 215 MLT, 236, 237, 241, 242, 243, 244, 245 model system, 72 modelling, 32, 35, 218, 238 models, 10, 23, 34, 36, 68, 174, 199, 200, 201
modulus, 163, 166, 170 moisture, 11, 15, 17, 49, 67, 70, 71, 77, 80, 109, 112, 142, 164, 169 moisture content, 71, 112 molecular biology, 124, 144 molecular weight, 118 molecules, 97, 104, 107, 111, 113, 114, 118, 227 momentum, 14, 36, 45, 202 monoclonal antibody, 125 Montana, 224 Morocco, 83 morphology, 96, 98, 115, 140, 142, 248 motivation, 223 mutagenesis, 120, 133, 147 mutant, 127 mutation, 117 mutations, 117, 118
N NaCl, 167 natural disaster, 225 natural disasters, 225 natural gas, 3 natural resources, 223 navigation system, 247 negative effects, 98, 115, 121, 140 nematode, 84 Netherlands, 123, 144, 146 neutral, 233 New Zealand, 3, 90, 102, 110, 125, 144 nitrogen, 33, 61, 66, 68, 95 nitrogen fixation, 61, 68 nitrous oxide, 224, 226 Nitzschia, 92, 94 non-enzymatic antioxidants, 100 North America, 2 Norway, 82 NPL, 31, 33, 43, 81 nucleation, 36, 147 nuclei, 208 nucleic acid, 91, 100 nucleus, 118 nutrient, 40, 47, 48, 50, 59, 66, 73, 81, 91, 132 nutrients, 46, 47, 48, 50, 63, 66, 104, 112, 128 nutrition, 47
O obstacles, 3, 74 oceans, vii, 3, 5, 10, 15, 107, 225 oil, 3, 4 operations, 217 opportunities, vii, 139
256
Index
orbit, 174, 224, 230, 236 ores, 3, 11 organic compounds, 48 organic matter, 40, 46, 48, 51, 66 organism, 48, 66, 70, 81, 95, 96, 100, 113, 164 organs, 141 oscillation, 33, 191, 193, 196, 197 osmosis, 69 oxidation, 32, 66, 73, 81, 100 oxidative damage, 100, 104, 114 oxidative stress, 100, 103, 106 oxygen, 9, 15, 46, 49, 67, 70, 99, 100, 104 oxygen consumption, 67 oxygen consumption rate, 67 ozone, vii, 5, 6, 7, 9, 10, 11, 72, 84, 89, 91, 95, 98, 99, 102, 103, 104, 107, 110, 111, 112, 113, 116, 121, 123, 124, 125, 126, 127, 128, 129, 131, 140, 223
P P. sulcata, 155 Pacific, 2, 5, 173, 187, 189, 195, 197, 218 Paraguay, 135 parallel, 234 parasites, 56 parthenogenesis, 55, 56 pasture, 83 peat, 40 percentile, 227 periodicity, 208 permeability, 100 peroxidation, 100 petroleum, 222 phenolic compounds, 103, 113 phenylalanine, 115, 141 phosphate, 66 phospholipids, 97 phosphorus, 95 photosynthesis, 11, 50, 59, 63, 66, 68, 71, 72, 73, 75, 77, 83, 84, 85, 86, 96, 98, 100, 101, 102, 104, 105, 107, 111, 112, 121, 127, 129, 141, 142, 143, 144, 146, 164, 169, 171, 172 photosynthesize, 75, 77, 169 phycocyanin, 95, 99 phycoerythrin, 99 physical environment, 238 physical properties, 1, 4, 68 physical structure, 17 physicochemical characteristics, 63 physics, 231 Physiological, 106, 122 physiology, 87, 99, 101, 146, 163 phytoplankton, 72, 84, 101, 105
pigmentation, 97, 102, 103, 104, 115, 126, 131 pioneer species, 73 plankton, 101, 227 plant growth, 62, 73, 127 plants, 10, 11, 39, 40, 47, 48, 49, 55, 56, 66, 67, 68, 69, 70, 71, 74, 75, 77, 81, 82, 86, 87, 89, 91, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 111, 112, 113, 114, 115, 116, 117, 118, 121, 122, 123, 124, 127, 128, 129, 131, 133, 138, 139, 140, 141, 142, 144, 146, 147, 148, 149, 164, 169, 172, 224 plasticity, 97, 132, 141, 142 plastics, 149 platform, 79 playing, 46, 80, 226 polar, vii, viii, 3, 6, 8, 10, 42, 63, 67, 74, 78, 81, 83, 90, 91, 95, 96, 97, 98, 109, 110, 111, 112, 113, 116, 140, 145, 157, 174, 176, 192, 193, 194, 195, 196, 197, 201, 205, 222, 226, 236, 237, 242, 248 polarization, 123, 248 politics, 231 pollen, 70 pollutants, 15 pollution, vii, ix, 2, 4, 5, 7, 10, 82, 91, 110, 222, 223, 224, 226, 228 polycarbonate, 100 polymer, 95 ponds, 16, 47, 51, 53, 54, 56, 91, 230 pools, 16, 47, 49, 91, 99 population, 48, 50, 55, 58, 62, 66, 84, 222, 223, 225, 226, 228, 230 population control, 223 population density, 50 positive correlation, 98, 114, 140 positive feedback, 225, 231 power plants, 226, 230 precipitation, 39, 40, 42, 43, 46, 70, 75, 77, 79, 80, 108, 131, 141, 164, 204, 218, 235, 237, 241, 248 preparation, iv pressure gradient, 200 prevention, 111 principles, 247 probability, 246 probe, 7 producers, 11, 49, 59, 80, 226 profit, 230 project, 34, 217 prokaryotes, 164 prokaryotic cell, 62 propagation, 189, 227, 228, 230, 235
257
Index protection, 72, 74, 75, 80, 95, 97, 98, 105, 110, 113, 115, 116, 117, 131, 132, 140, 142 protective mechanisms, 107 protective role, 97, 125 proteins, 72, 91, 100, 118, 231 protoplasm, 71 publishing, ix, xv pure water, 4, 222 pyrimidine, 116, 119, 120, 126
Q quality control, 212 quartz, 49 quasi-equilibrium, 180, 194 quercetin, 113, 114
R race, 8, 223 radar, 10, 201, 248 Radiation, v, 16, 71, 72, 83, 85, 104, 105, 107, 123, 144, 203, 212 radiation damage, 99, 128 radical formation, 123 radicals, 99 radio, 1, 4, 233, 237, 248 radius, 14, 186, 229, 234 rainfall, 7, 17, 77, 80, 141, 226 reaction center, 102 reactions, 66, 223, 228 reactive oxygen, 111 reactivity, 9 real time, 238 reality, 174, 230 receptors, 72, 121 recognition, 118, 132 recommendations, iv recovery, 105 recycling, 221, 223, 230, 231 reform, 222, 223 regenerate, 120 regions of the world, 150, 159 regression, 180, 200 regression line, 180 rehydration, 142, 143 rejection, 14, 28 religion, 223 remote sensing, 8, 33, 44, 199, 202 repair, 99, 103, 107, 111, 112, 113, 115, 116, 117, 118, 119, 120, 121, 122, 124, 126, 128, 140, 144 replication, 116, 117, 118 reproduction, 40, 81
requirements, 4, 68 researchers, viii, 6, 7, 90, 157 residues, 221, 222, 228 resilience, 121 resistance, 62, 97, 125, 150 resources, 75, 80, 87, 228 respiration, 75, 77, 82, 85, 123, 143, 164, 172 response, 32, 68, 85, 91, 95, 97, 98, 101, 104, 105, 106, 113, 122, 125, 126, 127, 129, 132, 139, 140, 146, 147, 148, 160, 164, 169, 172, 174, 176, 180, 183, 184, 187, 196, 203, 206, 219 restoration, 118 risk, 7, 116, 225 rods, 149 room temperature, 167 root, 11, 77 root system, 11 roots, 164 rotifers, 47, 50, 51, 59 roughness, 202 runoff, 225 rural development, 231 Russia, xi, xii, xiii, 7, 39, 173, 224
S safety, 234, 247 salinity, 222 salt concentration, 170 saturation, 75, 77, 80, 169 scale system, 173, 178, 194 scarcity, 169 scatter, 175 scavengers, 97 school, 223 science, viii, 3, 4, 5, 17, 27, 32, 35 scientific observation, 89 scope, 139 sea level, 7, 8, 40, 43, 149, 173, 177, 189, 195, 197, 222, 225, 226, 227, 231 seasonal changes, 142 seasonal flu, 14 secondary metabolism, 100 secrete, 97, 99 security, 132 sediment, 58, 66 sediments, 44, 48, 51, 58, 63, 86 seed, 112, 138 seedlings, 103, 123, 124, 128, 145 selectivity, 119 sensing, 44, 82, 236, 248 sensitivity, 32, 101, 102, 126 sensors, 202 seta, 53
258
Index
shade, 97, 163, 165, 166, 169, 170, 171 shape, vii, 2, 56, 68, 78, 88, 234 shear, 23 sheep, 41 shelter, 80, 132, 223 shoot, 112 shoots, 142 showing, 20, 44, 63, 68, 73, 78, 97, 111, 120, 142, 158, 174, 200, 224, 242 shrubs, 100 signals, 17, 22, 234, 241, 248 signs, 224 silica, 167 simulation, 196 simulations, 34 skin, 4, 57 social welfare, 5 sociology, 223 software, 238 SOI, 189, 190, 191, 192, 193 solution, 167, 221, 234, 237, 238, 241, 242, 247 South Africa, 3, 13, 18, 85 South America, 2, 3, 15, 105, 110, 114, 127, 135, 136, 137, 138, 144, 146 Southeast Asia, 225 Spain, 83 specialists, 133 speciation, 149, 157, 160 species richness, 49 specific heat, 16, 211 speculation, 10 spin, 123 spine, 132 sponge, 170 spore, 99 Spring, 43, 204, 210 St. Petersburg, xi, xii, xiii, 39 stability, 14, 15, 20, 35, 67, 85 stabilizers, 97 staff members, xv standard deviation, 246 state, 9, 10, 55, 63, 95, 115, 119, 120, 123, 124, 150, 164, 169, 180, 194, 201, 238, 239 states, 172, 230, 240 statistics, 31, 246 sterile, 149 stimulus, 164 stomata, 77, 164 storage, 97, 142 storms, 4, 7, 8, 10, 42, 43, 74, 233, 235, 241, 248 stress, 62, 91, 97, 100, 107, 112, 113, 115, 116, 122, 123, 124, 127, 163, 164, 169, 171, 172
structure, 4, 7, 24, 34, 40, 48, 77, 84, 88, 101, 112, 114, 121, 145, 179, 202, 203, 215, 216, 217, 219, 222, 248 style, 226 substitution, 112, 178 substrate, 39, 75, 77, 81, 121, 127 substrates, 49, 50, 66, 149 succession, 50, 73 Sun, 7, 16, 18, 22, 108, 192, 195, 230, 233 supplementation, 112 suppression, 100 surface area, 90 surface energy, 37, 203, 218, 219 surface layer, 16, 61, 173, 178, 194, 219 survival, 16, 25, 40, 41, 45, 55, 67, 68, 71, 80, 81, 107, 112, 113, 118, 131, 139, 140, 171, 222, 226 survival rate, 71 suspense, 2 sustainability, 221 Sweden, 87, 90 symbiosis, 96 synthesis, 67, 115, 140
T target, 116, 142 taxa, 138, 149, 150, 151, 152, 153, 157, 158, 166 TBP, 117 teams, 31 techniques, 44, 248 technologies, 9 technology, viii, ix, 223 technology transfer, ix temperature, 3, 5, 7, 9, 10, 11, 15, 16, 17, 24, 31, 34, 39, 41, 43, 45, 50, 51, 58, 59, 67, 68, 69, 74, 79, 84, 85, 86, 91, 97, 102, 106, 107, 108, 112, 122, 131, 132, 141, 142, 144, 146, 147, 148, 170, 174, 178, 180, 181, 182, 183, 184, 196, 197, 200, 201, 203, 204, 206, 208, 209, 210, 211, 213, 216, 217, 218, 219, 222, 224, 226 temperature dependence, 68 terrestrial ecosystems, 73, 101, 104, 122, 127, 143, 147 territorial, 58 territory, 57 testing, 97, 216, 218 TGA, 124 thermal energy, 228 thermodynamics, 230 thinning, 89 thymine, 124, 125 time periods, 113, 242 time series, 68, 102, 213
259
Index tin, 4 tissue, 69, 117, 168, 169, 170 total energy, 174 toxic effect, 100 trajectory, 208 transcription, 116, 117, 119 transcription factors, 117, 119 transformation, 237 transgression, 40 translation, 84 transmission, 4, 116, 118 transparency, 43 transpiration, 67, 70 transport, 7, 14, 28, 34, 36, 78, 99, 164, 200 transportation, 3, 4, 22, 70 treatment, 101 triggers, 17, 118 tropical storms, 224 tryptophan, 120, 125 tundra, 82 turbulence, 20, 24, 66, 75, 85, 201, 202, 211 turbulent mixing, 17, 46 turgor, 116, 163, 165, 167, 168, 169, 170, 172
U United Kingdom, xii, 33, 82, 85, 104, 218, 233 ultrastructure, 100 uniform, 108 unique features, vii, 13 United, 84, 224, 225 United Nations, 84, 224, 225 universe, 2, 7 uranium, 4 USA, 101, 102, 103, 105, 128, 202, 203, 231 USSR, 144 Ultra-Violet (UV), v, viii, ix, 6, 40, 43, 44, 46, 47, 64, 67, 72, 73, 79, 81, 84, 87, 89, 91, 95, 97, 98, 99, 100, 101, 102, 103, 104, 105, 107, 110, 111, 112, 113, 115, 116, 117, 118, 119, 121, 122, 123, 124, 125, 126, 127, 128, 131, 139, 140, 143, 144, 145, 146, 147, 231, 248 UV irradiation, 139 UV light, 43, 122 UV radiation, 6, 47, 72, 91, 96, 97, 98, 100, 104, 107, 115, 119, 122, 125, 128, 140 UV-radiation, 96, 101
V valence, 118, 128 Valencia, 83 validation, 32, 200
vapor, vii, 14, 15, 84 variables, 121, 123, 144, 203, 219 variations, 36, 51, 84, 96, 174, 176, 180, 183, 195, 196, 197, 201, 206, 208, 213, 218, 219, 222, 225, 228, 242 varieties, 40, 47, 108, 133 vector, 186, 238, 239 vegetation, 11, 34, 41, 50, 62, 63, 66, 67, 71, 72, 74, 84, 87, 95, 96, 101, 108, 121, 122, 124, 125, 139, 145 vehicles, 226 velocity, 7, 9, 10, 16, 22, 174, 201, 205, 206, 211, 215, 234, 238, 239, 242 ventilation, 35 vertebrates, 47, 57, 74, 85, 118 Viking, 248
W Washington, 145, 195, 227, 231, 248 waste, 223 water ecosystems, 40 water quality, 34, 84 water resources, 223 water shortages, 225 water vapor, vii, 15, 16, 17, 224, 226 wavelengths, 8, 91, 110, 113, 116, 236 wealth, 3 weather patterns, 222 web, 135, 237 websites, 27 Western Australia, 37 Western Europe, 225 whales, 11, 57 wild type, 117 wildlife, 225 wind speeds, 24, 131, 202 windstorms, 7 workers, 55, 58, 62, 68, 70, 74 worldwide, 223, 224, 242, 248
X xylem, 164
Y Yale University, 82 yeast, 47, 58 yield, 112, 121
Z zinc, 4
