Investigating Earth’s Oceans (Introduction to Earth Science)

Published in 2012 by Britannica Educational Publishing (a trademark of Encyclopædia Britannica, Inc.) in association with Rosen Educational Services, LLC 29 East 21st Street, New York, NY 10010. Copyright © 2012 Encyclopædia Britannica, Inc. Britannica, Encyclopædia Britannica, and the Thistle logo are registered trademarks of Encyclopædia Britannica, Inc. All rights reserved. Rosen Educational Services materials copyright © 2012 Rosen Educational Services, LLC. All rights reserved. Distributed exclusively by Rosen Educational Services. For a listing of additional Britannica Educational Publishing titles, call toll free (800) 237-9932. First Edition Britannica Educational Publishing Michael I. Levy: Executive Editor, Encyclopædia Britannica J.E. Luebering: Director, Core Reference Group, Encyclopædia Britannica Adam Augustyn: Assistant Manager, Encyclopædia Britannica Anthony L. Green: Editor, Compton’s by Britannica Michael Anderson: Senior Editor, Compton’s by Britannica Sherman Hollar: Associate Editor, Compton’s by Britannica Marilyn L. Barton: Senior Coordinator, Production Control Steven Bosco: Director, Editorial Technologies Lisa S. Braucher: Senior Producer and Data Editor Yvette Charboneau: Senior Copy Editor Kathy Nakamura: Manager, Media Acquisition Rosen Educational Services Alexandra Hanson-Harding: Editor Nelson Sá: Art Director Cindy Reiman: Photography Manager Matthew Cauli: Designer Introduction by Krista West Library of Congress Cataloging-in-Publication Data Investigating earth’s oceans / edited by Michael Anderson. p. cm.—(Introduction to earth science) “In association with Britannica Educational Publishing, Rosen Educational Services.” ISBN 978-1-61530-546-9 (eBook) 1. Oceanography--Juvenile literature. I. Anderson, Michael. GC21.5.I58 2011 551.46—dc22 2010049489 On the cover, page 3: Coral reefs are made up of the colorful skeletons of tiny sea animals. The reefs create underwater habitats that are essential for many fish and other marine organisms. Shutterstock.com Interior background ©www.istockphoto.com / Island Effects

C ON T E N T S

Introduction

Chapter 1 The World Ocean

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Chapter 2 Physical and Chemical Oceanography

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Chapter 3 Biological Oceanography

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Chapter 4 Geological Oceanography

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76 77 81 85 86

Conclusion Glossary For More Information Bibliography Index

INTRODUCTION “

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nowledge of the oceans is more than a matter of curiosity,” President John F. Kennedy told Congress in 1961. “Our very survival may hinge upon it.” Half a century later, these words still ring true. Scientists now understand that the oceans play two major roles on Earth. Most of the life on the planet lives in the oceans. The oceans also regulate climate by moving and storing heat. Between these two roles, the oceans have been integral in making Earth what it is today. Ocean exploration by the United States officially began in 1807, when President Thomas Jefferson created a government agency called the United States Coast Survey to study the country’s coastlines. These early scientists concentrated on mapping the edge of the sea and the character of the seafloor. They took the temperature of the world’s oceans, determined the direction of water currents, and cataloged life-forms. Over the next hundred years, the development of new technologies governed our exploration of the oceans. Getting to the remote parts of the oceans is difficult, so scientists had to invent ways to reach these places. Dredges (large scoops used to scrape the deep sea for life) and early forms of sonar were among the inventions that helped early scientists study ocean life and layout.

Introduction

Bathers relax at the pebble and sand beach beside turquoise waters at Porto Katsiki, on the island of Lefkada, Greece. Sean Gallup/Getty Images

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Today, some two centuries later, the functions of the original United States Coast Survey fall to the National Oceanic and Atmospheric Administration (NOAA), which conducts research on the oceans and the atmosphere. Modern researchers continue to build upon the knowledge of the early ocean explorers by studying sea life and the seafloor as well as the physical characteristics and chemical composition of seawater. This research helps us get to know the oceans better, which in turn helps us to better monitor their health. Scientific exploration in the past two centuries has answered many questions about the sea. One of the most impressive aspects of the oceans is their vastness. We now know that 71 percent of the planet is covered with ocean—and that accounts only for surface area. To really get a sense of the size of the ocean, it helps to consider the volume of the planet’s biosphere. The biosphere is all parts of Earth that can support life, including the land, the oceans, and part of the atmosphere. Imagine that the volume of Earth’s biosphere is contained in a 32-ounce (1-liter) soda cup. Of the biosphere in this cup, almost 30 ounces (.88 liter) are ocean. Given the immense size of the oceans, it is

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Introduction

not surprising that they hold a lot of life. Of the 33 animal phyla (or categories of animals) on Earth, 30 consist of ocean dwellers. If you’re interested in learning more about the oceans and why they need to be protected, this book is a great place to start. As you read, keep in mind that this is just a small sampling of what scientists have learned about the oceans so far. And, even though people have studied the oceans for centuries, there will always be more to learn.

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CHAPTER 1

The World Ocean

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t has been called the new frontier. The great body of water embracing Earth’s continents is also known as the world ocean. Its major subdivisions are the Pacific, the Atlantic, the Indian, and the Arctic oceans. Some people divide the world ocean into the North Pacific, South Pacific, North Atlantic, South Atlantic, Indian, Arctic, and Antarctic—a total of seven. The term seven seas, however, originated with medieval

Major features of the ocean basins.

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The World Ocean

Arabic geographers who knew only the waters of Europe and Asia. Around the borders of the oceans lie partially enclosed seas and gulfs, such as the Mediterranean, Caribbean, Baltic, Black, Red, and North seas, the Gulf of Mexico, and the Persian Gulf. The landlocked Caspian Sea was part of a great ocean in an earlier geologic era. Gulfs are generally described as extensions of oceans or seas. The Gulf of Mexico is larger than most seas. Straits are narrow passageways connecting two large bodies of water, such as the Strait of Gibraltar between the Atlantic Ocean and the Mediterranean Sea. Oceans, seas, gulfs, and straits cover about 71 percent of Earth’s surface. No other known planet is as watery as Earth. The Atlantic, Pacific, Indian, and Arctic oceans cover 129,428,700 square miles (335,218,800 square kilometers). The Pacific Ocean is the largest. It occupies almost one third of Earth’s total area. The oceans are not evenly distributed over Earth’s surface. About 43 percent of their total area lies in the Northern Hemisphere and 57 percent in the Southern Hemisphere. The word ocean is derived from Oceanus— in Greek mythology one of the Titans. He was a son of Uranus (the sky) and Gaea (Earth),

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the first rulers of the world. Oceanus personified the river that the Greeks believed encircled the flat Earth. The oceans influenced the formation of Earth’s land surface as it is known today.

A Roman mosaic from 3rd century DEA/G.Dagli Orti/ Getty Images

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depicts the god Oceanus.

The World Ocean

During several periods of Earth’s history large parts of North America were covered by the ocean. Most of the limestone, sandstone, and shale on land was deposited as sediment on the bottom of ancient, shallow seas. Chalk, such as that found in England and the U.S. states of Texas and Kansas, was formed on seabeds from the shells of sea creatures. The oceans also affect climate. Water has a high capacity for storing heat. It warms more slowly than land, and it also cools more slowly. Thus the coasts of the continents have cooler summers and warmer winters than the inland areas. One example of this moderating effect is the Gulf Stream, a warm current in the North Atlantic flowing from Gulf of Mexico northeast along United States coast to Massachusetts and then eastward toward Europe. The oceans are also the birthplace of storms that affect climate throughout the world.

Oceanographic Research The scientific study of all aspects of the oceans is called oceanography. The major branches of this study are concerned with the physical nature of the oceans, their chemical and mineral constituents, the great variety of living things that inhabit

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â•…

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The World Ocean

the oceans, and the geological structure of the ocean floor. Oceanography is also concerned with the technical and economic potentials of the oceans. Oceanographic research is very expensive. Usually it is undertaken by governmental and international organizations or by large universities. The first purely scientific oceanographic expedition ranks as one of the greatest ever undertaken. From 1872 to 1876 the British research vessel HMS Challenger cruised around the world. The famous 50-volume report of the Challenger Expedition formed the basis of the modern science of oceanography. Much research was carried on during World War II. Since then there has been more exploration of the ocean than in all previous history. Many large organizations study the oceans. The Intergovernmental Oceanographic Commission of the United Nations Educational, Scientific, and Cultural Organization (UNESCO) encourages international cooperation in ocean research and sponsors numerous long-term expeditions Sailors examine a haul aboard the HMS Challenger during its scientific voyage around the world. Time Life Pictures/Getty Images

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Divers perform scientific examinations of coral in the waters off St. Croix, U.S. Virgin Islands. NOAA/Department of Commerce. OAR/ National Undersea Research Program (NURP);Virgina Institute of Marine Science

and research projects. In the United States a government agency called the National Oceanic and Atmospheric Administration (NOAA) includes the Office of Ocean Exploration and Research, which conducts deep-sea exploration. Other major U.S. institutions include the University of California’s

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Scripps Institution of Oceanography at La Jolla and the Woods Hole Oceanographic Institution at Woods Hole, Mass. The laboratory of the Marine Biological Association of the United Kingdom is an important facility in Plymouth, Eng.

Branches of Oceanography The field of oceanography is traditionally divided into four major areas of research: physical, chemical, biological, and geological. Physical oceanographers describe the physical state of the sea, particularly the distribution of water masses, the conditions that form them, and the great currents that disperse and mix them. Chemical oceanographers study the chemical constituents of seawater and their consequences on biological, geological, and physical processes in the marine environment. Biological oceanographers study the plants, animals, and other organisms that live in the sea. Geological oceanographers are concerned with the geological structure and mineral content of the ocean floor as well as with phenomena ranging in scale from the planetary to that of individual sediment particles.

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The World Ocean

Oceanography is the sum of these several branches. Oceanographic research entails the sampling of seawater and marine life for close study, the remote sensing of oceanic processes with aircraft and Earth-orbiting satellites, and the exploration of the seafloor by means of deep-sea drilling and seismic surveys. In a seismic survey, waves of energy are used to determine the density of rocks in the crust below the ocean bottom.

Crew members aboard a drilling ship inspect a rock core during a scientific expedition that succeeded for the first time in drilling through the upper oceanic crust. JOI Alliance/IODP

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CHAPTER 2

Physical and Chemical Oceanography

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he field of physical oceanography involves the study of seawater’s properties, such as temperature and density. Physical oceanographers also study the movement of seawater (waves, currents, and tides) and the interactions between ocean waters and the atmosphere. Chemical oceanographers identify the dissolved elements in seawater and the ocean’s numerous chemical and biochemical cycles. They also devise models to explain the origin and development of the oceans.

Minerals in Seawater Billions of years ago, Earth was enveloped in clouds so thick that sunlight could not penetrate them and was so hot that no moisture could fall to its surface. As Earth cooled, rain began to fall continuously for centuries, pouring into the deep ocean basin and Research diver deploying self-contained instrument package. Courtesy of NOAA

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carrying with it the minerals of the continents, including the salts. Today the salt in the oceans would cover the continents with a 500-foot-thick (150-meter-thick) layer. The solid material carried to the oceans by rivers is deposited mainly near the shore, often forming such great river deltas as that of the Mississippi. Dissolved materials gradually mix throughout the oceans and become part of the great salt content of the seas. There is much more salt in seawater than in river water. Comparison of the percentages of the various salts present indicates that there is a significant difference in composition between the two kinds of water. The rivers of today are probably similar to those that existed in the past. The differences in composition of river water and seawater are due largely to chemical reactions that take place in the oceans. Most of these reactions remove material from seawater. Living organisms, for example, consume some of the elements as food, then die and sink to the ocean floor. This radar image of the Mississippi River delta, taken from the space shuttle Endeavour in 1995, shows where the river enters into the Gulf of Mexico along Louisiana’s coast. NASA/ JPL-Caltech

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This dead organic material is chemically “sticky” and may draw rare elements from the water. The mineral particles suspended in river water settle at the mouths of the rivers or are carried out to sea, where they settle to the ocean floor. They, like the organic material, remove elements from the seawater solution as they settle. Materials dissolved in ocean water may also be removed by chemical reactions between them and substances in the seafloor. These reactions, in turn, form new minerals. Also, some of the dissolved salts are blown out of the water by the wind, along with the ocean spray. Most of the chloride (a component of salt) in river water is in the process of being returned to the ocean after a windborne escape.

Trace and Abundant Elements The chemical elements that are easily removed from seawater by the processes mentioned, leaving only small amounts in solution, are called trace elements. It is probable that every element that exists on land is also present in ocean water,

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though many elements are too scarce to be measured. The most abundant elements in the oceans are hydrogen and oxygen. Together they make up water, and they also exist separately in the sea as dissolved gases. Also abundant are sodium, magnesium, calcium, and potassium, as well as such compounds as sulfates and chlorides. These substances become well mixed into the

This image of an H2O water molecule shows the oxygen atom as red, the hydrogen atoms as white, and the chemical bonds between the atoms as gray. Shutterstock.com

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oceans and are always found in the same proportions. They consistently make up fixed percentages of the dissolved materials in any sample of seawater. The rare elements, especially those which are nutrients for plants and other living things, are found in varying amounts.

The Formation of Seawater The chemical processes involved in the formation of seawater can be described in terms of Earth’s geochemical balance. Originally, Earth’s crust was composed of igneous rock (rock formed by the solidification of molten material, called magma). Then, over long periods of geological time, the oceans and the great layers of sedimentary rock (rock that is made up of accumulated pieces of older, broken down rocks) were formed. So, by considering the differences in composition between igneous and sedimentary rocks and estimating the amount of rock which has been changed from igneous to sedimentary, it is possible to calculate the total amounts of the various elements which have been delivered to the oceans.

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The elements sodium, magnesium, potassium, and calcium are metals and commonly form cations (or positively charged ions) in solution. A significant fraction of these four elements is left in seawater, but some other metals, such as iron and aluminum, have been almost entirely removed. The elements chlorine, bromine, sulfur, and boron are also present in the ocean, in quantities much too abundant to have been derived from the weathering of rocks. They are nonmetals and tend to form anions (negatively charged ions) in solution. These elements are found in volcanic gases, and it seems certain that they were delivered to the oceans through billions of years of volcanic eruptions. It is not possible to estimate what fraction of these anions has been removed from the seas.

Salinity and Density of Seawater The salinity of ocean water is given as a percentage. It is defined as the ratio of the weight of salt in a given volume of water to the weight of the water. The usual notation is in parts per thousand indicated by the symbol 0⁄00. Thus, ocean water with a salinity

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of 35 0⁄00 has 3.5 pounds (1.6 kilograms) of salt in each 100 pounds (45.4 kilograms) of seawater. The salinity depends upon the balance maintained between the evaporation of water from the surface of the sea and the amount of freshwater that is being returned to the sea by rivers and rain. When seawater evaporates, the salt is left to form a more concentrated solution. In the central region of the oceans, therefore, if more water is lost by evaporation than is returned by rainfall, the surface salinity will be greater than it is in areas where rainfall is adequate to replace the water lost by evaporation. In coastal waters, the salinity at the surface is usually less than it is in the central ocean basins because the flow of fresh river water from the land dilutes the seawater. The density of seawater is determined by its temperature and salinity. Water becomes denser as it gets colder or saltier. The heaviest water, therefore, has both very low temperature and very high salinity.

How the Sun Affects the Ocean The Sun’s light penetrates many feet into the water, and far from land the ocean is

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deep blue and as transparent as pure distilled water. Along the coasts, however, the transparency of seawater is reduced by the growth of tiny plants and plantlike organisms called phytoplankton. Organic-decay products from dead organisms are also present. The living things of the sea that cannot swim against the current but rather drift are collectively called plankton. Most are microscopic. This organic matter gives coastal water its characteristic green color. The transparency of coastal seawater is also reduced by the sediment carried into it by rivers. As ocean water absorbs the Sun’s radiation, the surface layer becomes heated. This heat can be lost in several ways, the two most important being evaporation and radiation. An average of about 36 inches (91 centimeters) of water evaporates from the surface of the oceans each year. This amount is approximately equal to some 88,000 cubic miles (1,316,000 cubic kilometers). In some regions—such as off the coast of Labrador in Canada, where cold, dry air flows over the warmer air of the Gulf Stream—the evaporation rate in winter may be half an inch (1.27 centimeters) per day. The evaporation of one cubic inch (16 cubic centimeters) of

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water requires the same amount of heat that would have to be removed from 1,000 cubic inches (16,000 cubic centimeters) of water to cool it one degree Fahrenheit.

Waves Next to their vastness, the most striking feature of the oceans is the constant motion of

Surfers swim as a huge wave crashes onto Manly Beach in Sydney, Australia. Jean-Pierre Muller/ AFP/Getty Images

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Physical and Chemical Oceanography

their surfaces. Waves—ripples, ridges, and hollows moving over the water—are the cause of this choppy, rolling, or otherwise disturbed appearance. Wind is the most common cause of waves. Waves generated by the wind may range in height from less than an inch to as much as 60 feet (18 meters). Waves breaking against a shore are called surf. Other waves are caused by such geologic disturbances as earthquakes and volcanic eruptions beneath the oceans. Waves formed by underwater earthquakes are known as seismic sea waves or as tsunamis, their Japanese name. Tsunamis are sometimes incorrectly called tidal waves, but they have no relationship to the tides. Near seacoasts, tsunamis may become very large and cause great destruction, but in the deep open sea they cannot be detected by the eye. Waves are formed as variations in air pressure above the water force gusty winds downward upon the water’s surface, displacing the water. In addition, the wind tends to drag water particles along in the direction of its movement—that is, to exert a shearing force. Waves are generated by the combined effect of the downward and shearing forces of the wind upon the surface of the water. Scientists have not yet been able to determine to any certain degree the exact nature of this composite action.

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The Ocean and the Seasons The temperatures of the oceans may vary by time of day and season. On a clear day in March, for example, the ocean surface becomes heated; after the Sun sets, the same amount of heat may be lost. During spring and summer, more heat is absorbed than is lost, and the temperature of the ocean’s surface layer increases. The wind and waves mix the heat downward, causing a sharp thermocline. A thermocline is an oceanic water layer in which the temperature decreases rapidly with increasing depth. In autumn, more heat is lost to the atmosphere than is gained by the ocean. It takes more heat to raise the temperature of a given volume of water one degree Fahrenheit than it does to raise the temperature of the same volume of sand one degree. This, together with the fact that the warmed water is mixed many tens of feet deep, makes the oceans huge reservoirs of heat. Heat is stored in summer and slowly given up in winter. The surface of the sea is usually warmer than the adjacent land in winter and cooler than the land in summer. The oceans

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Thermohaline circulation transports and mixes the water of the oceans. In the process it transports heat, which influences regional climate patterns. The density of seawater is determined by the temperature and salinity of a volume of seawater at a particular location. The difference in density between one location and another drives the thermohaline circulation.

therefore have a moderating effect upon the climates of coastal cities. Cities farther inland generally experience greater seasonto-season variations in climate.

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During the summer months, the mixing of seawater may carry the heat of the Sun’s radiation to a depth of several hundred feet. However, this is only a small part of the total ocean depth. Below this layer of seasonal change the oceans are cold and dark. Since cold water is heavier than warm water, the world’s oceans below a few thousand feet contain water that originally sank

The frigid sea near the continent of Antarctica is the source of much of the cold water in the depths of the world’s oceans. Torsten Blackwook/ AFP/Getty Images

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either close to the Antarctic continent or far to the north in the Atlantic Ocean off Greenland. Occasionally, water becomes very heavy because of its high salinity. An example of this is the Mediterranean Sea. The water flowing outward through the Strait of Gibraltar has greater salinity than the adjacent water of the Atlantic Ocean, and because it is heavier, it sinks. This Mediterranean flow can be tracked as a tongue of high-salinity water most of the way across the Atlantic Ocean.

Water Masses Water having a characteristic temperature and salinity is called a water mass. The measurement of temperature and salinity is one method oceanographers use to trace the movement of water masses. For example, in the Atlantic Ocean the cold, low-salinity Antarctic Bottom Water can be tracked as it moves northward along the seafloor. However, it is easier to track the low-salinity tongue of Antarctic Intermediate Water, which moves northward at a depth of about 3,000 feet (900 meters).

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Tides Another type of movement of ocean water is the tides. The tides are the regular rise and fall of the ocean’s water level. They are seen most prominently along coasts and in harbors and bays. In mid-ocean the difference between high water and low water is perhaps two or three feet (about half a meter to a meter). But along the shores of continents, especially in gradually narrowing bays, the difference may be much greater. In most places, the tide rises and falls twice a day, reaching a maximum height called high tide on each rise and a minimum level called low tide on each fall. It takes a little more than six hours for rising waters to reach high tide and approximately another six hours for falling waters to reach low tide. This sequence is called the tidal cycle. The complete cycle takes 12 hours and 25 minutes and is then repeated. The amount of change in the water level during a tidal cycle is known as the tidal range. Tides are caused by the gravitational pull of the Sun and the Moon on Earth’s water. When the Sun, Moon, and Earth form a straight line (top), higher and lower tides than usual are generated. In contrast, when the lines between the Sun and Earth and the Moon and Earth are perpendicular to one another (bottom), high tides and low tides are moderated. Encyclopædia Britannica, Inc.

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Between these two water masses, most of the depth is filled by Atlantic Deep Water, which takes on its characteristic temperature and salinity in the north and moves southward, mixing slowly with the surrounding water.

Mixing of the Oceans The exact manner in which deep water masses move is still unknown to oceanographers, as are their speeds of movement. Their movement is slow, but probably not steady. It is possible that water masses move in whirls and eddies very much as smoke rises from a slowly burning fire. The oceans of the world are interconnected and flow through the great southern ocean surrounding Antarctica. By way of the Antarctic Ocean the water from the Atlantic Ocean can flow into the Indian and Pacific oceans. Consider a hypothetical experiment. If a cubic mile (4.2 cubic kilometers) of seawater halfway between the surface and the seafloor in the middle of the Atlantic Ocean were dyed red, the movement of the individual molecules of water could be traced. The cube

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Major surface currents of the world’s oceans. Subsurface currents also move vast amounts of water, but they are not known in such detail. Encyclopædia Britannica, Inc.

would probably drift slowly southward at a speed of about 50 miles (80 kilometers) a year. But it would mix with the surrounding water at a much faster rate. Because the density of seawater increases with depth, the water mixes horizontally more easily than vertically. In time, the red cube would become a pink disk with a vertical dimension of perhaps 2 miles (3 kilometers) and a horizontal diameter of about 1,000 miles (1,600 kilometers). Pink water that reached the surface

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The Sound Channel in the Sea Sound waves travel better through water than do light and radio waves. This fact is employed by ships at sea to locate the position of submarines or schools of fish. The technique of using high-frequency sound waves with sonar devices is called echo ranging. The method is similar to the way in which the position of an airplane or a ship is found by echo ranging using radio waves with radar devices. Sound can travel much farther in the ocean than in the air. One reason for this is the sound channel which exists in the deep ocean. The velocity of sound increases with increasing temperature and pressure. There is a depth in the ocean at which the velocity of sound is at a minimum. Sound energy becomes trapped in this low-velocity sound channel. The sound channel extends continuously through most areas of the world’s oceans. For example, if a small explosive charge is detonated in the sound channel near San Francisco, Calif., the sound can be detected by a hydrophone suspended in the sound channel near the Hawaiian islands, some 2,500 miles (4,000 kilometers) away. (A hydrophone is a device for converting sound waves into electrical signals that is used primarily for detecting sound waves from an underwater source.)

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would mix with the surrounding water faster than would the water that was two miles (3.2 kilometers) deep. The dyed water would eventually find its way to the Antarctic Ocean and then to the Pacific Ocean and the Indian Ocean. Finally, all ocean waters would become pale pink as the dyed molecules found their way into oceans at all depths. How long would this take? Some oceanographers believe the mixing process would require at least a thousand years.

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CHAPTER 3 Biological Oceanography

B

iological oceanography is the study of the populations of plants, animals, and other organisms of the sea. It deals especially with the distribution of these living communities, their numerical growth, how one population affects another, and how they are influenced by the environment in which they live. For instance, the number of fish caught by commercial fishing fleets in a certain area of the continental shelf may depend upon the amount of fish food present in a particular year. What is this fish food? Some kinds of fish feed on zooplankton, or plankton consisting of tiny animals and animal-like organisms in the upper waters. The zooplankton may be more numerous in some years than in others. This is due to variations in the abundance of phytoplankton, the plankton consisting of plants and plantlike living things on which the zooplankton in turn feed, to variations in currents, or to variations in the temperature of the water.

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Other kinds of fish eat animals which live on the bottom of the ocean. When conditions favor the growth of these bottom-dwelling animals, the fishes also increase in number.

Three Kinds of Sea Life Scientists divide the life of the sea into three groups. One group consists of the animals that are able to swim strongly enough to move against a current. This group, called

The animals called sea stars are commonly called starfish, but they are not actually fish. There are about 1,600 species spread throughout the world’s oceans. Karl Weatherly/Photodisc/Thinkstock

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the nekton, is made up for the most part of fishes, but also includes squid and whales. Another group, the benthos, is composed of all the animals, plants, and other organisms which live on or in the sea bottom. This group includes seaweeds, crabs, worms, starfishes, and similar marine life. These two groups may seem to include all the living things in the ocean. However, the third group—which is the least noticeable and was the last to be discovered—is the most important of all. This group is the plankton, which consists of thousands of kinds of mostly tiny living things. They do not, as is often supposed, lie on the ocean surface. Instead, they are suspended in the water at various depths. Planktonic organisms are therefore carried throughout the oceans by the currents. The portion of plankton consisting of plants and plantlike organisms, such as algae and some bacteria, is called phytoplankton. Many of these organisms are single-celled and so small that they cannot be seen without a microscope. Most of the zooplankton, which comprises the animals and animallike organisms, such as protozoans, are only a fraction of an inch in size, though some— such as the larger jellyfishes—are a foot or more in diameter.

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Plankton is very important because only plants, algae, and some bacteria can use sunlight to manufacture the carbohydrates that all animals need in their food, through a process called photosynthesis. In order to obtain carbohydrates, animals must eat either photosynthetic organisms or other animals that have eaten photosynthetic organisms. However, sunlight penetrates only a short distance into the sea, and most ocean water is in absolute darkness. There is not enough light there for photosynthesis to occur. Without phytoplankton, most of the ocean would be a vast liquid desert, unable to support any life. The phytoplankton that float in the well-lighted upper layers of the ocean undergo photosynthesis, thereby making the nutrients needed for nearly all other life-forms in the sea. During spring and summer the surface waters of the oceans have an abundance of blooms of these mostly minute organisms. The growth of phytoplankton frequently removes all nutrient elements—principally nitrogen, phosphorus, and silicon—from the surface waters. In spring and summer, the surface waters are warm and light and do not easily mix with the cold, heavy deep water. So new nutrients are not available to the surface waters.

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The tiny plants and plant like organisms called phytoplankton are the principal food source of the sea. Ablestock.com/Thinkstock

Upwelling and Downwelling Eventually the blooms fail for lack of food, and the organisms die and sink into the depths. As they descend, bacteria attack and partially destroy their remains. The nutrient elements are then liberated and return to the solution in the depths. Upwelling is a process of vertical water motion whereby subsurface water and its suspended nutrients are carried

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toward the surface. The most pronounced coastal upwellings are found off the western United States, Peru, Morocco, South Africa, western Africa, Western Australia, and south of the Aleutian chain. The reverse process, downwelling, completes the cyclical movement of bodies of water. Downwelling and upwelling do not necessarily occur in the same areas. As a result of upwelling, extensive fishing and kelp areas are found off the African and North and South American continents, large bird populations produce huge deposits of guano in Peru,

Upwelling typically results when offshore winds blow surface waters out to sea and deeper waters rise to replace them. Downwelling occurs when onshore winds cause surface waters to pile up and sink. Copyright Encyclopædia Britannica, Inc.; rendering for this edition by Rosen Educational Services

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which people mine for fertilizer, and near the Antarctic Convergence in the Atlantic there is an unusually large standing crop of plankton that supports krill, the main food of whales. Such coastal areas are also provided with nutrient-rich waters for mariculture, or the farming of organisms in the sea.

Phytoplankton The main components of phytoplankton (which is Greek for “plant wanderers”) are plantlike organisms that include diatoms, dinoflagellates, coccolithophorids, green algae, and cyanobacteria (formerly known as blue-green algae). Many of them are microscopic and single-celled. The growth of these organisms, which photosynthesize light, depends on a delicate balance between nutrient enrichment by vertical mixing, often limited by the availability of nitrogen, and the availability of light. Some of the thousands of kinds of phytoplankton swim feebly by lashing a whiplike thread appendage called a flagellum. The dinoflagellates are known for their bioluminescence, or phosphorescence, a “cold light” similar to that of fireflies. Since they emit a toxin, dinoflagellates can be extremely

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poisonous when present in great numbers. In plumes they are known to color the water red, brown, or even black. Red tides in the Gulf of Mexico and in Walvis Bay, Namibia, are often accompanied by mass mortality of fish, crabs, and other animals that wash up on the beach. A strong toxin of red tides, when accumulated in mussels and clams and consumed by humans, can lead to illness or death.

Zooplankton Zooplankton are animal-like forms of plankton. Among these are the larval and adult forms of some animal species and certain protozoans. During the temporary larval stages, some benthic and nektonic animals appear quite different from the adults into which they mature. These immature animals are able to populate new areas by drifting with the currents. Copepods are small crustaceans that are holoplankton, or organisms that are plankton throughout their life cycles. There are probably more copepods in the world than there are all other animals combined (though the animal-like protozoans are even more numerous). The primary herbivorous animals of the sea, copepods are vital to marine ecosystems.

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Diatoms Tiny one-celled organisms called diatoms are found by the billions in all the waters of Earth. The largest of them are barely visible to the unaided eye, and the smallest are less than a thousandth of an inch long. Biologists classify diatoms as golden or golden-brown forms of algae. Like other algae, diatoms have no leaves, stems, roots, or flowers, but the cell of every diatom contains chlorophyll, the substance that is responsible for the green color of leafy plants. Just as it does in plants, chlorophyll absorbs sunlight to help diatoms make sugars from carbon dioxide and water. Unlike diatoms, most plants next change these sugars

Magnification of a diatom reveals its beautiful symmetry. Eric Grave/Photo Researchers

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to cellulose to make their cell walls strong. Diatoms, on the other hand, take up dissolved silica from the water and form it into a pair of glassy shells adorned with intricate patterns. There are thousands of species of diatoms, each with its own shape. The two shells of a diatom fit together like the top and bottom of a box and are held together along the edges by a softer band called a girdle. Most diatoms float in the water or fasten themselves with a sort of jelly to stones or other water plants. Diatoms reproduce themselves by various methods. Sometimes the cell divides, the shells separate, and each half grows a new shell on its exposed surface. Two diatoms may combine after shedding their old shells. The united cells then separate into two new individuals, each of which grows a new pair of shells. Some species reproduce by means of spores. In cold waters, where diatoms are most plentiful, the dead and the discarded shells may form thick deposits on the bottom. After long ages, the shell deposits turn into a porous mineral mass called diatomite (also called diatomaceous earth, tripolite, and kieselguhr). Diatomite deposits are found on the sites of many ancient oceans and lakes. Diatomite is used as a chemical filter, particularly in the sugar industry, and in the preparation of heatinsulating materials and polishing compounds and for mixing with concrete.

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They graze off the aquatic pastures of phytoplankton and provide a link between the primary production of algae, plants, and cyanobacteria and the numerous large and small carnivores. Most copepods are minute but some can be as big as a grain of rice. Other abundant holoplankton are the single-celled foraminiferans and radiolarians.

A jellyfish has no skeleton, and more than nine-tenths of its body are jellylike. Shutterstock.com

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The foraminiferans have skeletons made of calcium carbonate (CaCO3), and radiolarians have skeletons made of silicon dioxide. Jellyfishes are among the largest planktonic organisms. Transparent arrowworms, or glass worms, are bottom dwellers with large jaws designed to seize copepods and other small animals.

Fish and Marine Mammals The majority of ocean fish are coastal, or littoral; very few are diadromous, living part of their lives in freshwater and part in the oceans. The familiar fish species caught for human consumption make up only a fraction of the world fish population. The most abundant fishes of the ocean—cyclostomes—are not commercially sought and live 1,000 to 3,000 feet (300 to 900 meters) below the surface. These small, transparent, and luminescent species are so abundant that, as a deep scattering layer, they reflect the sound waves of echo-ranging instruments. The marine mammals, also part of the nekton, include the seals, sea lions, sea otters, manatees, porpoises, and whales. Some whales consume zooplankton by straining

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Investigating Earth’s Oceans

Two orcas, or killer whales, swimming. Killer whales are the largest of the toothed whales. iStockphoto/Thinkstock

them through the water through horny plates (baleen or whalebone). The killer whale preys upon fishes, penguins, porpoises, seals, and sea lions.

Deep-Sea Life The largest ecosystem on Earth, and also the least explored, is the vast realm of the ocean known as the deep sea. It is home to billions

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Biological Oceanography

of organisms adapted to its extreme conditions: profound to total darkness, crushing pressures, and cold temperatures. Deep in the ocean, animal life tends to be sparse. Most of the animal species belong to groups that also live in shallower marine environments. These include many kinds of invertebrates, or animals without backbones,

A close view of a Humboldt squid at night in the Gulf of California, Mexico. Brian J. Skerry/National Geographic Image Collection/ Getty Images

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such as worms and squids, octopuses, clams, and other mollusks. More than a dozen families of marine fishes are represented. Most deep-sea animals are small. Certain types of invertebrates that live at great depths, however, such as giant squid, shrimp, and sea urchins, grow more than 10 times larger than relatives who live near the surface. Prey is scarce, and deep-sea fishes typically have huge mouths, expanding jaws, and large fangs to help them eat whatever animals they find. Many deep-sea animals have large eyes, presumably to take advantage of the little light that exists. In the deepest waters, animals with tiny eyes or no eyes are found. Bioluminescence, or the generation of light by living organisms, is common among deep-sea life. Such light may be produced by special cells within the organism or, in certain fishes, by bioluminescent bacteria that live within the fish’s body. Some animals have lights of different colors and on various parts of the body that flash on and off. Fishes and invertebrates may use bioluminescence to help attract a mate, to hide from or escape predators, or to lure prey. Some deep-sea organisms cluster around oceanic hot springs, or vents, that spew

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Anglerfish, like this one, live in the deepest parts of the sea. Peter David/Taxi/Getty Images

extremely hot water. The water is rich in minerals such as iron, manganese, zinc, copper, nickel, and other metals. Much sulfur also is present in the form of hydrogen sulfide. Although this chemical is lethal to most forms of life, bacteria and other

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microorganisms at the vents use it to make their own food. These microorganisms form the bottom of the food chain: some animals living near the vent eat the microbes or harbor them in their bodies, while other animals in turn eat those animals. Similar communities of organisms have been found around “cold seeps,” places where fluid rich in dissolved methane and other minerals seeps up through the ocean floor. The microorganisms at the base of a seep community obtain energy from methane or sulfur compounds and form a mat along the seep. Common seep animals include tube worms, clams, and mussels.

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CHAPTER 4 Geological Oceanography

G

eological oceanography is one of the broadest fields in the Earth sciences. Researchers in this branch of oceanography are involved in the study of the topography, structure, and geological processes of the ocean floor.

The Continents and Ocean Basins The largest features of Earth’s surface are the continents and ocean basins. The four major ocean basins (Arctic, Atlantic, Indian, and Pacific) are bound by landmasses and major oceanic ridges. Each continent is rimmed by a submerged, gently sloping continental margin. This includes the relatively flat continental shelf, generally found at depths of less than 600 feet (180 meters) with a width of a few miles to more than 200 miles (320 kilometers). At the shelf break portion of the margin, there is a rise in the continental shelf before the continental slope begins its plunge to the

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The broad, gentle pitch of the continental shelf gives way to the relatively steep continental slope. The more gradual transition to the abyssal plain is a sediment-filled region called the continental rise. The continental shelf, slope, and rise are collectively called the continental margin. Depth is exaggerated here for effect. Encyclopædia Britannica, Inc.

deep-sea bottom. Deep submarine canyons frequently cut into the continental margin.

Rises and Ridges Rises and ridges, flanked by smaller basins, divide the major ocean basins. The

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The Atlantic Ocean, with depth contours and submarine features.

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Mid-Oceanic Ridge spans the length of the North Atlantic, South Atlantic, Indian, and South Pacific oceans for a combined distance of more than 40,000 miles (64,000 kilometers). This broad fractured swell, rising up to 9,000 feet (2,700 meters) above the ocean floor, usually contains a central rift valley that is the site of earthquake epicenters.

Volcanism Submarine volcanoes produce lava flows, volcanic ash, and fine-grained lava sediment on the seafloor. Ocean-ridge volcanism produces basaltic seafloor crust that sometimes builds plateaus, such as Iceland, that rise above sea level. Subsea earthquakes are associated with mid-oceanic ridge systems and subduction zones where tectonic plates converge. (For more information on tectonic plates, see the sidebar on page 65.)

Trenches Trenches are highly localized submarine gashes in Earth’s crust. In cross section, trenches are generally V-shaped with either a series of terracelike steps or a dramatic fall to the ocean floor. In deeper trenches, the

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Geological Oceanography

Ash rises into the air from an undersea volcanic eruption on March 19, 2009. The eruption took place on the islet of Hunga Ha’apai, 39 miles (63 kilometers) from Nuku’alofa, Tonga. AFP/Getty Images

steeper sides are toward land. Trenches lie mainly around the Pacific but also occur in the northern borders of the Indian Ocean, in the outer loops of the Caribbean, and in

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the Scotia Arc, an island system in the South Atlantic. They mark some of the deepest spots in the ocean: the Mariana Trench off the coast of Guam, the Tonga Trench in the South Pacific, and the Philippine Trench. Troughs are elongated depressions with contours more gradual than those of trenches. Some trenches are partially filled with sediments and appear as troughs.

Seamounts Isolated elevations that rise at least 3,000 feet (900 meters) above the surrounding deep-sea floor are called seamounts. Seamounts are very abundant and occur in all major ocean basins. Virtually every oceanographic expedition discovers new seamounts, and it is estimated that tens of thousands exist in the oceans of the world. Usually basaltic volcanoes, these undersea mountains often occur as long chains, as they do in the Hawaiian Islands. A seapeak is a seamount with a pointed summit. Guyots are flat-topped seamounts that became smooth-planed by the action of wind and water when the submarine volcanoes were at sea level.

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Plate Tectonics The theory, or idea, of plate tectonics says that Earth’s outer layer, or crust, is made up of large, moving pieces called plates. All of Earth’s land and water sit on these plates. Under the plates is a layer of melted rock called magma. The plates float on top of the magma. As the plates move they often come into contact with each other. One of three things happens at these plate boundaries. First, the plates may move past each other in opposite directions. Second, the plates may crash into each other. In this case the edge of one plate may slide under another plate and be destroyed. Or the two edges of the plates may rise up and form mountains. Third, magma may rise to the surface and force the plates to move apart. As the rising magma cools, it hardens to create new crust. Earthquakes and volcanoes often happen along plate boundaries. There are so many earthquakes and volcanoes at the edges of the Pacific Plate that this region is called the ring of fire. The plates have moved across Earth’s surface for hundreds of millions of years. As the plates move, the continents on them move, too. This movement is called continental drift. The continents continue to move today. Scientists believe that in about 250 million years they will join together again.

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Abyssal Hills Abyssal plains are flat areas of the seafloor about 10,000 to 20,000 feet (3,000 to 6,000 meters) below the water’s surface, generally near the continents. Rising from these plains are abyssal hills less than 3,000 feet (900 meters) high and about 10 times as wide. They are variously formed by volcanism, folding and faulting, and sediment draping over older buried seamounts or hills. The abyssal zone is the world’s largest ecological unit, occupying more than three quarters of the total area of the oceans and more than half of the area of the globe.

Oceanic Crust The oceanic crust is typically composed of three layers that overlie the mantle. Unconsolidated sediments, averaging about a third of a mile (a half-kilometer) in thickness, make up the top layer. Next is the consolidated volcanic layer, about a mile (1.6 kilometers) thick. It is thinner in shallow water and thicker in the Pacific than in the Atlantic Ocean. On the bottom is the basaltic

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Oceanic ridges offset by transform faults and fracture zones. The arrows show the direction of movement across the transform faults. Encyclopædia Britannica, Inc.

or oceanic layer, about 3 miles (5 kilometers) in thickness. It is principally composed of rocks rich in magnesium and iron, especially basalt. Surface hills are common in the oceanic layer. In some places the oceanic layer is not covered by the other two layers.

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Studies of the magnetic properties of minerals in the oceanic crust provide information about the structure and movements of the crust. Magnetic patterns on both sides of oceanic rift valleys show that new seafloor is produced at these rifts and moves horizontally away from the spreading centers. Over the past 200 million years, this process has produced all of the crust of the present seafloor.

Submarine Geological Processes The geological processes of the deep sea are relatively slow compared to those on land. A striking difference between land and sea is the lack of significant erosion in the deep sea. Sedimentary deposits accumulate in the deep sea at a rate of only a fraction of an inch every thousand years. Once deposited, marine sediments are unlikely to be eroded and redeposited because bottom currents are generally weak. Deep-sea sediments thus offer the most complete historical records of organic evolution, temperature changes during ice ages, and other geological patterns.

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Beaches Land bordering an ocean, sea, or lake is called a coast or shore. Coastal lands are classified according to the natural processes that formed them and according to the type and structure of the rock material that underlies them and that is acted upon by wind and water. Beaches are coastal lands that fall into the category called depositional landforms. Depositional landforms result from an accumulation of sediment along a coast. A beach consists of such sediments—sand, gravel, or crushed seashells and other organic matter, for example—that have been carried by waves and deposited on the coast. Beaches are formed because waves move toward land and away from it at unequal speeds. If wave movements were identical in speed and duration, the sediments would not be left behind onshore. There are three kinds of beaches. The first is a narrow strip of sediment, usually composed of sand and gravel, that borders a rocky or cliffy coast. The second type is a free beach, which is a fairly wide expanse of accumulated sediment; this is the familiar sort of place where people go to swim and sun themselves. The third type of beach is a sediment-covered barrier reef such as those that parallel the coasts of Texas and eastern Florida in the United States. These coastal barriers are normally anchored on slightly

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submerged bedrock or compact clay and may stretch for dozens, or even hundreds, of miles. These barriers separate lagoons from the open sea and are often cut into pieces by tidal inlets. In the temperate regions of the world, beach sands are primarily quartz. Some sands are feldspars, and a few contain heavier minerals. In the tropics, many beaches are covered with the skeletal remains of marine organisms and precipitated oolites (small, rounded calcium carbonate particles).

Swimmers enjoy the beach near Padstow, in Cornwall, England, as lifeguards patrol in an inflatable boat patrol. Matt Cardy/Getty Images

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Clastic Sedimentation Most clastic sediment—rock and soil eroded from the land—is first deposited on the continental shelf, mainly in tidal environments, in deltas, and along beaches. The rest of the sediment continues out to sea. Winds and currents carry fine-grained particles offshore where they ultimately settle to the ocean floor. Along the continental margins, sediment is carried by so-called turbidity currents, which flow downhill because they are denser than the surrounding water. These underwater avalanches help explain the formation of submarine canyons, continental rises, and the flat abyssal plains of the deepsea floor. Deposits of the rise and abyssal plain consisting of graded beds of sand, silt, and clay that have formed in this way are called turbidites.

Chemical and Biological Deposition Most of the near-shore and shallow-water sediments consist of calcium carbonate derived from the shells or hard coverings of dead marine animals. Some of the larger contributors include clams, mussels, oysters, scallops, snails, and slugs; smaller sources are

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the microscopic organisms of the sea, including those that make up coral and algal reefs. Deep-sea deposits are located in less than 13,000 feet (4,000 meters) of water, where much of the ocean floor is covered with an ooze (a deposit of soft mud) made of the shells of foraminiferans. Below this depth there is less calcium carbonate, and the falling shelled organisms begin to dissolve while settling or soon after coming to rest on the bottom. The depth of water below which calcium carbonate begins to dissolve is called the calcium carbonate compensation depth. Below the compensation depth, oozes containing skeletons made of silica form in many places. Oozes made of diatoms are found mostly in the Pacific and Antarctic oceans.

Mineral Resources of the Oceans All the sediments and wastes of the continents pour into the oceans. People mine some of the elements contained in ocean

Vibrantly colored soft coral reef, Red Sea, Egypt. Shutterstock.com

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This photo shows a Norwegian oil drilling rig in the North Sea. AFP/ Getty Images

water. Sodium chloride, or common table salt, and magnesium, a lightweight metal, are frequently obtained from the oceans. Progress has also been made in converting ocean water to fresh water by removing the sodium chloride. Another source of minerals is the ocean floor. Deposits of calcium phosphate, sometimes used as a fertilizer, cover parts of the

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ocean bottom. Diamonds, gold, tin, iron, and sulfur are mined from shallow-water deposits and beaches. Petroleum and natural gas are extracted from the continental shelf. Other minerals that are less commercially accessible or desirable can also be found on the ocean floor. Manganese nodules cover much of the ocean basins. Formed by chemical precipitation around a nucleus such as a shark’s tooth or a piece of volcanic ash, they consist primarily of alternating layers of manganese and iron oxides. Manganese, iron, copper, nickel, and cobalt are also present in high but varying concentrations.

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Conclusion

W

ithout the oceans, life as it is known today could not exist. Among other functions, they act as a great heat reservoir, leveling the temperature extremes that would otherwise prevail over Earth and expand the desert areas. The oceans provide the least expensive form of transportation known, and the coasts serve as major recreational sites. More importantly, the sea is a valuable source of food and a potentially important source of energy and minerals, all of which are required in everincreasing quantities by industrialized and developing countries alike. Because the oceans are so invaluable, the field of oceanography will remain a vital one. Greater knowledge of the world’s oceans enables scientists to more accurately predict, for example, long-term weather and climatic changes and also leads to more efficient exploitation of Earth’s resources. Oceanography is also crucial to understanding the effect of pollution on ocean waters and to the preservation of the quality of the oceans’ waters in the face of increasing human demands made on them.

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Glossary

abyssal Of or relating to the bottom waters of the ocean depths. basalt A dense, dark, often glassy-appearing volcanic rock. benthos Organisms that live on or in the ocean bottom. cation An atom or group of atoms that bears a positive electric charge. clastic Made up of pieces of preexisting rocks. deposition The act or process of depositing. flagellum A hairlike structure that some cells use for movement. foraminiferans Microscopic one-celled organisms. When they die, their shells sink and form an ooze that covers about 30 percent of the seafloor. Hardening of these deposits produce limestone and chalk. Gulf Stream Warm current in the North Atlantic flowing from the Gulf of Mexico northeast along the coast of the United States and then eastward to Europe. igneous rock Rock that is formed by the solidification of magma. ion An atom or group of atoms that carries a positive or negative electric charge as a result of having lost or gained one or more electrons.

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krill Small, shrimplike crustaceans that are an important source of food for fish, squid, whales, seabirds, and other animals, especially around Antarctica. They swim in large swarms and can grow to be about 2.5 inches (6 centimeters) long. littoral The area along the shore between the high-tide and low-tide levels. It is the habitat for such sea life as clams, oysters, mussels, and seaweed. nekton Free-swimming aquatic animals that move independent of wave and current action. pelagic Of, relating to, living, or occurring in the open sea. photosynthesis The process by which green plants and certain other organisms transform light energy into the chemical energy needed for life. plankton Passively floating or weakly swimming microscopic animal and plant life living in a body of water. sediment Matter, such as dirt or rocks, that is deposited by water. seismic Of, subject to, or caused by an earthquake; also: of or relating to an earth vibration caused by an earthquake or some other force.

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Glossary

shearing A force causing two parts of a body that touch along a boundary to slide relative to one another in a direction parallel to their plane of contact. silicon A nonmetallic element that is the second most abundant element on Earth. It makes up about 28 percent of Earth’s crust. The most common form of silica is quartz, which includes sand and flint. subduction The process in which a denser tectonic plate sinks below another plate and into Earth’s mantle as the two plates converge. thermocline A region in a body of water which separates warmer surface water from cold deep water and in which temperature decreases rapidly with depth. topography The configuration of a place, usually as shown on maps and charts, especially revealing the relative positions and elevations of its natural features. trench A long, narrow, and usually steepsided crack cut into the ocean floor. turbidity currents Underwater avalanches made up of large masses of sediment that create a dense, watery mixture, then flow down an ocean canyon to deposit a layer of sand in deep water.

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unconsolidated Loosely arranged; not stratified or layered. upwelling A process in which deeper water and the nutrients it contains rise to the surface, allowing phytoplankton and zooplankton to reproduce rapidly and provide abundant food for other sea creatures.

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Environmental Protection Agency (EPA) Ariel Rios Building 1200 Pennsylvania Avenue NW Washington, DC 20460 (202) 272-0167 Web site: http://www.epa.gov/ebtpages/ wateaquaticecosystoceans.html The EPA offers information about projects to promote awareness of various ecological topics such as oceans, coasts, and watersheds, as well as project ideas for students who would like to take action on environmental issues in their own communities.

For More Information

Bamfield Marine Sciences Centre 100 Pachena Road Bamfield, BC V0R 1B0 Canada (250) 728-3301 Web site: http://www.bms.bc.ca A variety of resources from Bamfield Marine Sciences Centre, a teaching and research facility focusing on marine and coastal environments.

Fisheries and Oceans Canada (DFO) Communications Branch

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200 Kent Street 13th Floor, Station 13E228 Ottawa, ON K1A 0E6 Canada (613) 993-0999 Web site: http://www.dfo-mpo.gc.ca/oceans/ oceans-eng.htm Fisheries and Oceans Canada promotes the safe and sustainable use and development of Canada’s oceans and fresh waters. This Web site offers extensive information about the ocean and the creatures that live in it. National Oceanic and Atmospheric Administration (NOAA) 1401 Constitution Avenue NW Room 5128 Washington, DC 20230 (301) 713-1208 Web site: http://www.noaa.gov NOAA provides information about opportunities to advance environmental literacy, including workshops for educators and scholarships and internships for students.

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For More Information

Smithsonian Ocean Portal C/O National Museum of Natural History Smithsonian Institution 10th Street & Constitution Avenue, NW Washington, DC 20560-0135 (202) 633-2950 Web site: http://ocean.si.edu From the origins of the oceans to current issues, the Ocean Portal from the Smithsonian Museum’s National Museum of Natural History offers extensive content, both for students and teachers, about the ocean and the life it contains. Windows to the Universe National Earth Science Teachers Association PO Box 3000 Boulder, CO 80307 (720) 328-5350 Web site: http://windows2universe.org/ earth/Water/ocean.html This Web site for teachers and students provides concise overviews of numerous ocean-related topics, such as ocean motions, ocean chemistry, and ocean life.

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Web Sites Due to the changing nature of Internet links, Rosen Educational Services has developed an online list of Web sites related to the subject of this book. This site is updated regularly. Please use this link to access the list: http://www.rosenlinks.com/ies/ocean

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Bibliography

Berkenkamp, Lauri. Discover the Oceans: The World’s Largest Ecosystem (Nomad, 2009). Burns, L.G. Tracking Trash: Flotsam, Jetsam, and the Science of Ocean Motion (Houghton, 2007). Careers in Focus: Oceanography (Ferguson, 2010). Chamberlin, W.S., and Dickey, T.D. Exploring the World Ocean (McGraw, 2008). Crist, D.T., and others. World Ocean Census: A Global Survey of Marine Life (Firefly Books, 2009). Garrison, Tom. Oceanography: An Invitation to Marine Science, 6th ed. (Brooks/Cole, 2007). Nichols, C.R., and others. Recent Advances and Issues in Oceanography (Greenwood, 2003). Nouvian, Claire, ed. The Deep: The Extraordinary Creatures of the Abyss (Univ. of Chicago Press, 2007). Parker, Bruce. The Power of the Sea: Tsunamis, Storm Surges, Rogue Waves, and Our Quest to Predict Disasters (Macmillan, 2010). Sverdrup, K.A., and Armbrust, E.V. An Introduction to the World’s Oceans (McGraw, 2009).

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Index

A abyssal hills, 66 algae, 44, 45, 48, 50, 52, 73 Antarctic Ocean, 10, 35, 38, 41, 73 Arctic Ocean, 10, 11, 59 arrow worms, 53 Atlantic Ocean, 10, 11, 35, 38, 48, 59, 66

B Baltic Sea, 11 barrier reefs, 69–70 beaches, explained, 69–70 benthos, 44, 49 bioluminescence, 48, 56 Black Sea, 11

C calcium carbonate compensation depth, 73 Caribbean Sea, 11, 63 Caspian Sea, 11 cations vs. anions, 27 Challenger Expedition, 15 chemical and biological deposition, 71, 73 clams, 49, 56, 58, 71 clastic sedimentation, 71 cold seeps, 58 continental drift, 65 continents and ocean basins, 22, 59–60 copepods, 49, 52, 53

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crabs, 44, 49 cyclostomes, 53

D deep-sea life, 54–58 diatoms, explained, 50–51 drilling, deep-sea, 19

E earthquakes, 31, 62, 65 echo ranging, 40, 53 elements, 24–26, 27, 43, 45, 46

F fish and marine mammals, 40, 42–43, 44, 47, 49, 53–54, 75 foraminiferans, 52, 53, 73 free beaches, 69

G Gulf of Mexico, 11, 13, 49 Gulf Stream, 13, 29 guyots, 64

H holoplankton, 49, 52 hydrophones, 40

I ice ages, 68 igneous vs. sedimentary rock, 26

Index

Indian Ocean, 10, 11, 38, 41, 59, 62, 63 Intergovernmental Oceanographic Commission, 15

J jellyfish, 44, 53

M manatees, 53 Mariana Trench, 64 mariculture, 48 Marine Biological Association, 17 Mediterranean Sea, 11, 35 Mid-Oceanic Ridge, 62 minerals, 17, 20–24, 51, 57, 58, 67, 68, 70, 73–75, 76 Mississippi River Delta, 22 mussels, 49, 58, 71

N National Oceanic and Atmospheric Administration (NOAA), 16 nekton, 43–44, 49, 53 North Atlantic Ocean, 10, 13, 62 North Pacific Ocean, 10 North Sea, 11

O ocean, origin of word, 11–12

oceanic crust, 19, 62, 66–68 oceanography biological, 17, 20, 42–58 branches, 17, 19 geological, 17, 59–75 overview, 10–19, 76 physical and chemical, 17, 20–41 research, 13–17, 19, 64 octopuses, 56 Office of Ocean Exploration and Research, 16 oysters, 71

P Pacific Ocean, 10, 11, 38, 41, 59, 63, 65, 66, 73 penguins, 54 Persian Gulf, 11 Philippine Trench, 64 photosynthesis, 45, 48 phytoplankton, 29, 42, 44, 45, 48–49, 52 plankton, 29, 42, 44–45, 48, 49, 53 plate tectonics, explained, 65 porpoises, 53, 54

R radiolarians, 52, 53 Red Sea, 11 red tides, 49 ring of fire, 65 rises and ridges, 60, 62

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S scallops, 71 Scotia Arc, 64 Scripps Institution of Oceanography, 16–17 sea life, three kinds of, 43–45 sea lions, 53, 54 seals, 53, 54 seamounts, 64, 66 sea otters, 53 seapeaks, 64 sea urchins, 56 seawater, formation of, 17, 26–27 movement of, 17, 20, 28, 30–31, 32, 34, 35, 36–37, 38–39, 41, 44, 45, 46–48, 49, 68, 69, 71 salinity and density of, 20, 22, 27–28, 35, 38, 39 seasons and, 13, 32–35, 45 sunlight and, 28–30, 34, 45, 48 seven seas, origin of term, 10–11 sharks, 75 shrimp, 56 slugs, 71 snails, 71 sound channels, 40 South Atlantic Ocean, 10, 62, 64

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South Pacific Ocean, 10, 62, 64 squids, 44, 56 starfish, 44 Strait of Gibraltar, 11, 35 submarine geological processes, 68

T thermocline, 32 tides, explained, 31, 36–37 Tonga Trench, 64 trenches, 62–64 tsunamis, 31

U UNESCO, 15–16 upwelling vs. downwelling, 46–48

V volcanism, 27, 31, 62, 64, 65, 66, 75

W Walvis Bay, 49 water masses, 17, 35, 38 waves, explained, 30–31 whales, 44, 48, 53–54 Woods Hole Oceanographic Institution, 17

Z zooplankton, 42, 44, 49, 53