college.cengage.comcollege.cengage.com/coursemate/earth_science/... · web viewtraditionally, we...

Answers to BRIEF REVIEW QuestionsEssentials 6th

Chapter 1: THE ORIGIN OF THE OCEAN

1. Why did I write that there’s one world ocean? What about the Pacific and Atlantic oceans, the “Seven Seas?”

Traditionally, we have divided the ocean into artificial compartments called oceans and seas, using the boundaries of continents and imaginary lines such as the equator. In fact there are few dependable natural divisions, only one great mass of water. Because of the movement of continents and ocean floors (about which you’ll learn more in Chapter 3) the Pacific and Atlantic Oceans and the Mediterranean and Baltic Seas, so named for our convenience, are in reality only temporary features of a single world ocean. In this book we refer to the world ocean, or simply the ocean, as a single entity, with subtly different characteristics at different locations but with very few natural partitions. This view emphasizes the interdependence of ocean and land, life and water, atmospheric and oceanic circulation, and natural and man-made environments.

2. Which is greater: the average depth of the ocean or the average height of the continents above sea level?

If Earth's contours were leveled to a smooth ball, the ocean would cover it to a depth of 2,686 meters (8,810 feet). The volume of the world ocean is presently 11 times the volume of land above sea level -- average land elevation is only 840 meters (2,772 feet), but average ocean depth is 4½ times greater!

3. Is most of Earth’s water in the ocean?

Most of Earth’s water lies in the crust. It’s not present in great hollow reservoirs, but rather is bound to the rocky material. About 1/40th of a cubic mile of this water escapes each year as steam from volcanic vents, deep-ocean seeps, and other places.

4. Can the scientific method be applied to speculations about the natural world that are not subject to test or observation?

Science is a systematic process of asking questions about the observable world, and testing the answers to those questions. The scientific method is the orderly process by which theories are verified or rejected. It is based on the assumption that nature "plays fair" -- that the answers to our questions about nature are ultimately knowable as our powers of questioning and observing improve.

1 | P a g e


By its very nature, the scientific method depends on the application of specific tests to bits and pieces of the natural world, and explaining, by virtue of these tests, how the natural world will react in a given situation. Hypotheses and theories are devised to explain the outcomes. The tests must be repeatable -- that is, other researches at other sites must be able to replicate the experiments (tests) with similar results. If replication is impossible, or if other outcomes are observed, the hypotheses and theories are discarded and replaced with new ones. Figure 1.4 shows the process.

Can these methods be applied to speculations about the natural world that are not subject to test or observation? By definition, they cannot.

5. What is the nature of “truth” in science? Can anything be proven absolutely true?

Nothing is ever proven absolutely true by the scientific method. Hypotheses and theories may change as our knowledge and powers of observation change; thus all scientific understanding is tentative. The conclusions about the natural world that we reach by the process of science may not always be popular or immediately embraced, but if those conclusions consistently match observations, they may be considered true.

6. What if, at the moment you shake the keys, the wires under the hood are jostled by a breeze and fall back into place? What if the car starts when you try it again? Can you see how superstition might arise?

For an interesting perspective on this question, find some back issues of Skeptical Inquirer magazine. Also, author Michael Shermer has written extensively on the issue of irrational superstition and the alarming rise of illogical and superstitious thought in American society.

7. Can scientific inquiry probe further back in time than the “Big Bang?”

No. Spacetime began at the origin of the universe, so the concept of “before” is meaningless when applied to the period preceding that astonishing moment.

8. What element makes up most of the detectable mass in the universe?

Hydrogen

9. Outline the main points in the condensation theory of star and planet formation.

The life of a star begins when a diffuse area of a spinning nebula begins to shrink and heat up under the influence of its own weak gravity. Gradually, the cloudlike sphere flattens and condenses at the center into a knot of gases called a protostar. The fusion process begins – the

2 | P a g e


star “turns on.” Much of the outer material eventually became planets, the smaller bodies that orbit a star and do not shine by their own light.

10. Trace the life of a typical star.

After fusion reactions begin, the star becomes stable— neither shrinking nor expanding, and burning its hydrogen fuel at a steady rate. Over a long and productive life, the star converts a large percentage of its hydrogen to atoms as heavy as carbon or oxygen. This stable phase does not last forever, though. The life history and death of a star depend on its initial mass. When a medium-mass star (like our sun) begins to consume carbon and oxygen atoms, its energy output slowly rises and its body swells to a stage aptly named red giant by astronomers. The dying giant slowly pulsates, incinerating its planets and throwing off concentric shells of light gas enriched with these heavy elements. But most of the harvest of carbon and oxygen is forever trapped in the cooling ember at the star’s heart.

11. How are the heaviest elements (uranium or gold) thought to be formed?

From the deaths of ancient stars.After a long and productive life, an average star converts a large percentage of its

hydrogen to atoms as heavy as carbon or oxygen. When a medium-mass star begins to consume these heavier atoms, its energy output slowly rises and its body swells to a stage aptly named red giant by astronomers. The dying giant slowly pulsates, throwing off concentric shells of light gas enriched with these heavy elements. But most of the harvest of carbon and oxygen is forever trapped in the cooling ember at the star’s heart.

The dying phase of a massive star is more interesting. The end begins when its depleted core collapses in on itself. This rapid compression causes the star’s internal temperature to soar. When the infalling material can no longer be compressed, the energy of the inward fall is converted to cataclysmic expansion called a supernova. The explosive release of energy in a supernova is so sudden that the star is blown to bits, and its shattered mass is accelerated outward at nearly the speed of light. The explosion lasts only about 10 seconds, but in that short time the nuclear forces holding apart individual atomic nuclei are overcome—and atoms heavier than iron are formed. The gold of your rings, the mercury in a thermometer, and the uranium in nuclear power plants were all created during such a brief and stupendous flash. The atoms produced by a star through millions of years of orderly fusion, and the heavy atoms generated in a few moments of unimaginable chaos, are sprayed into space.

Every chemical element heavier than hydrogen—most of the atoms that make up the planets, the oceans, and living creatures—was manufactured by the stars.

12. What is density stratification?

Density is mass per unit of volume. Early in its formation, the still-fluid Earth was sorted

3 | P a g e


by density -- heavy elements and compounds were driven by gravity towards its center, lighter gases rose to the outside. The resulting layers (strata) are arranged with the densest at and near the Earth's center, the least dense as the atmosphere. The process of density stratification lasted perhaps 100 million years, and ended 4.6 billion years ago with the formation of Earth's first solid crust. For a preview of the result, see Figure 3.6.

13. How old is Earth?

Many lines of evidence interlock to suggest Earth is about 4.6 billion (4,600 million) years old.

Radiometric dating (described in an appendix) is a powerful technique based on the discovery that unstable, naturally radioactive elements lose particles from their nuclei and ultimately change into new stable elements. The radioactive decay occurs at a predictable rate, and measuring the ratio of radioactive to stable atoms in a sample provides its age. Using radiometric dating, researchers have identified small zircon grains from western Australian sandstone that are 4.2 billion years old. The zircons were probably eroded from nearby continental rocks and deposited by rivers. (Older crust is now unidentifiable, having been altered and converted into other rocks by geological processes.)

Observing the rates of mountain-building and erosion also provides clues. If we assume the processes we observe occur now at rates similar to rates in the past, we can extrapolate suggestions of age. Even the rate at which heat leaks from within Earth can provide data.

One of the most interesting methods of age-dating searches for cosmic-ray traces in metallic meteorites that have fallen from space. It is likely these objects are remnants of the cores of failed planets, or from material ejected from Earth that ended up in our moon. The density of the traces suggests how long it has been since the objects formed.

The moon itself has provided clues. Its angular momentum and orbital shape can tell of its early formation and subsequent movements, and samples brought back by Apollo astronauts have confirmed an age similar to (but slightly younger than) Earth.

14. How was the moon formed?

About 30 million years after its initial formation, a planetary body somewhat larger than Mars smashed into the young Earth and broke apart. The metallic core fell into Earth’s core and joined with it, while the rocky mantle was ejected to form a ring of debris around Earth. The debris began condensing soon after and became our moon. The newly formed moon, still glowing from heat generated by the kinetic energy of infalling objects, is depicted in Figure 1.13.

15. Is the world ocean a comparatively new feature of Earth, or has it been around for most of Earth’s history?

A few million years after the moon-forming impact, Earth cooled enough to allow the

4 | P a g e


upper clouds to form droplets. Hot rains fell toward Earth, only to boil back into the clouds again. As the surface became cooler, water collected in basins and began to dissolve minerals from the rocks. Some of the water evaporated, cooled, and fell again, but the minerals remained behind. The salty world ocean was gradually accumulating.

These heavy rains may have lasted about 20 million years. Large amounts of water vapor and other gases continued to escape through volcanic vents during that time and for millions of years thereafter. The ocean grew deeper. Evidence suggests that Earth’s crust grew thicker as well, perhaps in part from chemical reaction with oceanic compounds. Although most of the ocean was in place about 4 billion years ago, ocean formation continues very slowly even today.

16. Is Earth’s present atmosphere similar to or different from its first atmosphere?

In a sense, there have been three atmospheres: the original atmosphere blown away by the ignition shock of the sun, the reducing atmosphere that outgassed from within the Earth, and the oxidizing atmosphere that has resulted from the work of photosynthesizing plants and plant-like organisms.

The volcanic venting of volatile substances including water vapor -- outgassing -- gave rise to the present ocean. As hot water vapor rose, it condensed into clouds in the cool upper atmosphere. Recent research suggests that millions of tiny icy comets colliding with the Earth may also have contributed to the accumulating mass of water vapor, this ocean-to-be.

17. Are the atoms and basic molecules that compose living things different from the molecules that make up nonliving things? Where were the atoms in living things formed?

No, atoms are atoms. An atom of carbon in a living object is indistinguishable from an atom of carbon in a rock. Other than primordial hydrogen and some helium, all the elements were made in and by stars. As Carl Sagan was fond of saying, “We are, all of us, bits of stardust.”

18. How old is the oldest evidence for life on Earth? On what are those estimates based?

The oldest fossils yet found, from northwestern Australia, are between 3.4 billion and 3.5 billion years old (Figure 1.16). They are remnants of fairly complex bacteria-like organisms, indicating that life must have originated even earlier, probably only a few hundred million years after a stable ocean formed. Evidence of an even more ancient beginning has been found in the form of carbon-based residues in some of the oldest rocks on Earth, from Akilia Island near Greenland. These 3.85-billion-year-old specks of carbon bear a chemical fingerprint that many researchers feel could only have come from a living organism. Life and Earth have grown old together; each has greatly influenced the other.

19. Was Earth’s atmosphere rich in oxygen when life originated here?

5 | P a g e


No. The present oxygen-rich atmosphere has resulted from the work of photosynthesizing plants and plant-like organisms. Life (as we know it) could not have evolved in a highly oxidizing atmosphere.

20. The particles that make up the atoms of your body have existed for nearly all of the age of the universe. Look again at Figure 1.9. What could be next?

The ultimate recycling, that’s what! It is arresting to think that the atoms you are using to comprehend this sentence were formed in titanic explosions, have cycled through space and time, and will – eventually – be ejected back into space to condense into some new object.

21. Where would you look for water in our solar system?

Water has been found on Mars (as ice), and there are tremendous quantities of water in the atmospheres of Jupiter and Saturn.

22. If we encounter life elsewhere, would we expect its chemistry and appearance to resemble life on Earth?

For starters, let's look at stars. Most stars visible to us are members of multiple-star systems. If the Earth were in orbit around a typical multiple-star system, we would be close to at least one of the host stars at certain places in our orbit, and too far away at others. Also, not all stars -- in single or multiple systems -- are as stable and steady in energy output as our sun. If we were in orbit around a star that grew hotter and cooler at intervals, our situation would be radically different than it is at the moment.

Next, let's look at orbital characteristics. Our Earth is in a nearly circular orbit at just the right distance from the sun to allow liquid water to exist over most of the surface through most of the year.

Next, consider our planet's cargo of elements. We picked these up during the accretion phase. At our area of orbit there was an unusually large amount of water (or chemical materials that would led to the formation of water).

So, with a stable star, a pleasant circular orbit that is well placed, and suitable and abundant raw materials, we are a water planet. This marvelous combination is probably not found in many places in the galaxy.

The course of evolution of life on any planet depends on the materials and energy available. Because water planets are probably very rare, I shouldn’t expect alien life to resemble what we see on Earth – indeed, we may have difficulty recognizing truly foreign life forms if or when we encounter them.

Chapter 2: A HISTORY OF MARINE SCIENCE6 | P a g e


1. What advantages would a culture gain if it could use the ocean as a source of transport and resources?

Any coastal culture skilled at raft building or small boat navigation would have economic and nutritional advantages over less skilled competitors. From the earliest period of human history, understanding and appreciating the ocean and its life-forms benefited coastal civilizations.

2. How was the culture of the Library of Alexandria unique for its time? How was the size and shape of Earth calculated there?

The great Library at Alexandria constituted history's greatest accumulation of ancient writings. As we have seen, the characteristics of nations, trade, natural wonders, artistic achievements, tourist sights, investment opportunities, and other items of interest to seafarers were catalogued and filed in its stacks. Manuscripts describing the Mediterranean coast were of great interest.

Traders quickly realized the competitive benefit of this information. Knowledge of where a cargo of olive oil could be sold at the greatest profit, or where the market for finished cloth was most lucrative, or where raw materials for metalworking could be obtained at low cost, was of enormous competitive value. Here perhaps was the first instance of cooperation between a university and the commercial community, a partnership that has paid dividends for science and business ever since.

After their market research was completed, it is not difficult to imagine seafarers lingering at the Library to satisfy their curiosity about non-commercial topics. And there would have been much to learn! In addition to Eratosthenes' discovery of the size of the Earth (about which you read in the chapter), Euclid systematized geometry; the astronomer Aristarchus of Samos argued that Earth is one of the planets and that all planets orbit the sun; Dionysius of Thrace defined and codified the parts of speech (noun, verb, etc.) common to all languages; Herophilus, a physiologist, established the brain was the seat of intelligence; Heron built the first steam engines and gear trains; Archimedes discovered (among many other things) the principles of buoyancy on which successful shipbuilding is based.

The last Librarian was Hypatia, the first notable woman mathematician, philosopher, and scientist. In Alexandria she was a symbol of science and knowledge, concepts the early Christians identified with pagan practices. After years of rising tensions, in 415 A.D. a mob brutally murdered her and burned the Library with all its contents. Most of the community of scholars dispersed and Alexandria ceased to be a center of learning in the ancient world.

The academic loss was incalculable, and trade suffered because ship owners no longer had a clearing house for updating the nautical charts and information upon which they had come to depend. All that remains of the Library today is a remnant of an underground storage room. We shall never know the true extent and influence of its collection of over 700,000 irreplaceable scrolls.

Historians are divided on the reasons for the fall of the Library. But we know there is no record that any of the Library's scientists ever challenged the political, economic, religious, or

7 | P a g e


social assumptions of their society. Researchers did not attempt to explain or popularize the results of their research, so residents of the city had no understanding of the momentous discoveries being made at the Library at the top of the hill. With very few exceptions, the scientists did not apply their discoveries to the benefit of mankind, and many of the intellectual discoveries had little practical application. The citizens saw no practical value to such an expensive enterprise. Religious strife added elements of hostility and instability. As Carl Sagan pointed out, "When, at long last, the mob came to burn the Library down, there was nobody to stop them."1

As for speculations on historical impact had the Library survived, some specialists have suggested that much of the intellectual vacuum of the European Middle Ages might have been “sidestepped,” in a sense, if the information processing and dissemination processes centered at the Library had continued. Instead of the subsequent fragmentation and retraction, one wonders if continued academic stimulation might have reinvigorated the West? Also, had the Library lasted longer, one wonders if researchers there might have discovered the intellectual achievements of China, a civilization much advanced at the time.

3. What were the stimuli to Polynesian colonization? How were the long voyages accomplished?

The ancestors of the Polynesians spread eastward from Southeast Asia or Indonesia in the distant past. Although experts vary in their estimates, there is some consensus that by 30,000 years ago New Guinea was populated by these wanderers and by 20,000 years ago the Philippines were occupied. By around 500 B.C. the so-called cradle of Polynesia -- Tonga, Samoa, the Marquesas and the Society islands -- was settled and the Polynesian cultures formed.

For a long and evidently prosperous period the Polynesians spread from island to island until the easily accessible islands had been colonized. Eventually, however, overpopulation and depletion of resources became a problem. Politics, intertribal tensions, and religious strife shook their society. When tensions reached the breaking point, groups of people scattered in all directions from the Marquesas and Society Islands during a period of explosive dispersion. Between 300 and 600 A.D. Polynesians successfully colonized nearly every inhabitable island within the vast triangular area shown in Figure 2.5. Easter Island was found against prevailing winds and currents, and the remote islands of Hawaii were discovered and occupied. These were among the last places on Earth to be populated.

Large dual-hulled sailing ships, some capable of transporting up to 100 people, were designed and built for the voyages. New navigation techniques were perfected that depended on the positions of stars barely visible to the north. New ways of storing food, water, and seeds were devised. In that anxious time the Polynesians honed and perfected their seafaring knowledge. To a skilled navigator a change in the rhythmic set of waves against the hull could indicate an island out of sight over the horizon. The flight tracks of birds at dusk could suggest the direction of land. The positions of the stars told stories, as did the distant clouds over an unseen island. The smell of the water, or its temperature, or salinity, or color, conveyed information, as did the direction of the wind relative to the sun, and the type of marine life clustering near the boat. The sunrise colors, sunset colors, the hue of the moon -- every nuance had meaning, every detail had been passed in ritual from father to son. The greatest Polynesian

1 Sagan, C. 1980. Cosmos. New York: Random House.

8 | P a g e


minds were navigators, and reaching Hawaii was their greatest achievement.

4. What stimulated the Vikings to expand their exploration to the west? Were they able to exploit their discoveries?

Norwegian Vikings began to explore westward as European defenses against raiding became more effective. Though North American was colonized by A.D. 1000, the colony had to be abandoned in 1020. The Norwegians lacked the numbers, the weapons, and the trading goods to make the colony a success.

5. What innovations did the Chinese bring to geology and ocean exploration? Why were their remarkable exploits abruptly discontinued?

In addition to the compass, the Chinese invented the central rudder, watertight compartments, fresh water distillation for shipboard use, and sophisticated sails on multiple masts, all of which were critically important for the successful operation of large sailing vessels. The Chinese intentionally abandoned oceanic exploration in 1433. The political winds had changed, and the cost of the “reverse tribute” system was judged too great.

6. If he was not a voyager, why is Prince Henry of Portugal considered an important figure in marine exploration?

Prince Henry the Navigator, third son of the royal family of Portugal, was a European visionary who thought ocean exploration held the key to great wealth and successful trade. Prince Henry established a center at Sagres for the study of marine science and navigation. Although he personally was not well traveled, captains under his patronage explored from 1451 to 1470, compiling detailed charts wherever they went. Henry’s explorers pushed south into the unknown and opened the west coast of Africa to commerce. He sent out small, maneuverable ships designed for voyages of discovery and manned by well-trained crews. For navigation, his mariners used the compass—an instrument (invented in China in the fourth century BCE.) that points to magnetic north. Henry’s students knew the Earth was round (but because of the errors of Claudius Ptolemy they were wrong in their estimation of its size).

7. What were the main stimuli to European voyages of exploration during the Age of Discovery? Why did it end?

There were two main stimuli: (1) encouragement of trade, and (2) military one-upsmanship.

Trade between east and west had long been dependent on arduous and insecure desert caravan routes through the central Asian and Arabian deserts. This commerce was cut off in 1453 when the Turks captured Constantinople. An alternate ocean route was desperately needed.

9 | P a g e


As we have seen, Prince Henry of Portugal thought ocean exploration held the key to great wealth and successful trade. Henry's explorers pushed south into the unknown and opened the West coast of Africa to commerce. He sent out small, maneuverable ships designed for voyages of discovery and manned by well-trained crews.

Christopher Columbus was familiar with Prince Henry's work, and "discovered" the New World quite by accident while on a mission to encourage trade. His intention was to pioneer a sea route to the rich and fabled lands of the east made famous more than 200 years earlier in the overland travels of Marco Polo. As "Admiral of the Ocean Sea," Columbus was to have a financial interest in the trade routes he blazed. As we saw, Columbus never appreciated the fact that he had found a new continent. He went to his grave confident that he had found islands just off the coast of Asia.

Charts that included the properly-identified New World inspired Ferdinand Magellan, a Portuguese navigator in the service of Spain, to believe that he could open a westerly trade route to the Orient. In the Philippines, Magellan was killed and his crew decided to continue sailing west around the world. Only 18 of the original 250 men survived, returning to Spain three years after they set out. But they had proved it was possible to circumnavigate the globe.

The seeds of colonial expansion had been planted. Later, the empires of Spain, Holland, Britain, and France pushed into the distant oceanic reaches in search of lands to claim. Military strength might depend on good charts, knowledge of safe harbors in which to take on provisions, and friendly relations with the locals. Exploration was undertaken to insure these things.

But that gets ahead of the story. The Magellan expedition's return to Spain in 1522 -- the end of the first circumnavigation -- technically marks the end of the first age of European discovery.

8. Capt. James Cook has been called the first marine scientist. How might that description be justified?

Captain James Cook's contributions to marine science are justifiably famous. Cook was a critical link between the vague scientific speculations of the first half of the eighteenth century and the industrial revolution to come. He pioneered the use of new navigational techniques, measured and charted countless coasts, produced maps of such accuracy that some of their information is still in use, and revolutionized the seaman's diet to eliminate scurvy. His shiphandling in difficult circumstances was legendary, and his ability to lead his crew with humanity and justice remains an inspiration to naval officers to this day.

While Captain Cook received no formal scientific training, he did learn methods of scientific observation and analysis from Joseph Banks and other researchers embarked on HMS Endeavour. Because his observations are clear and well recorded, and because his speculations on natural phenomena are invariably based on scientific analysis (rather than being glossed over or ascribed to supernatural forces), some consider him the first marine scientist.2 But, to be rigorously fair, perhaps his explorational and scientific skills should be given equal weighting.

2 For more information on Cook as scientist, see Richard Hough's biography: Hough, R. 1994. Captain James Cook. New York: W. W. Norton.

10 | P a g e


9. Why was determining longitude so important? Why is it more difficult than determining latitude? How was the problem solved?

Longitude is east-west position. Longitude is more difficult to determine than latitude (north-south position). One can use the North Star as a reference point for latitude, but the turning of Earth prevents a single star from being used as an east-west reference. The problem was eventually solved by a combination of careful observations of the positions of at least three stars, a precise knowledge of time, and a set of mathematical tables to calculate position.

10. What were Matthew Maury’s contributions to marine science? Benjamin Franklin’s?

Maury was the first person to sense the worldwide pattern of surface winds and currents. Based on his analysis, he produced a set of directions for sailing great distances more efficiently. Maury’s sailing directions quickly attracted worldwide notice: He had shortened the passage for vessels traveling from the American east coast to Rio de Janeiro by 10 days, and to Australia by 20. His work became famous in 1849 during the California gold rush— his directions made it possible to save 30 days on the voyage around Cape Horn to California.

Franklin published, in 1769, the first chart of any current. His studies of the voyaging records of mail carriers (he was postmaster of the Colonies) convinced him a “river”flowed in the north Atlantic. Discussions with his cousin, Tim Folger, sealed the deal.

11. What was the first purely scientific oceanographic expedition, and what were some of its accomplishments? What contributions did the earlier, hybrid expeditions make?

The expeditions of Cook, Wilkes, the Rosses, de Bougainville, Wallis, and virtually all other runners-up to HMS Challenger were multi-purpose undertakings: military scouting, flag-waving, provision hunting, and trade analysis were coupled with exploration and scientific research.

The first sailing expedition devoted completely to marine science was conceived Charles Wyville Thomson, a professor of natural history at Scotland's University of Edinburgh, and his Canadian-born student of natural history, John Murray. They convinced the Royal Society and the British Government to provide a Royal Navy ship and trained crew for a "prolonged and arduous voyage of exploration across the oceans of the world." Thomson and Murray even coined a word for their enterprise: Oceanography.

HMS Challenger, the 2,306 ton steam corvette chosen for the expedition, set sail on 7 December 1872 on a four-year voyage that took them around the world and covered 127,600 kilometers (79,300 nautical miles). Although the Captain was a Royal Naval officer, the six-man scientific staff directed the course of the voyage.

The scientists also took salinity, temperature, and water density measurements during these soundings. Each reading contributed to a growing picture of the physical structure of the deep ocean. They completed at least 151 open water trawls, and stored 77 samples of seawater for detailed analysis ashore. The expedition collected new information on ocean currents, meteorology, and the distribution of sediments; the locations and profiles of coral reefs were charted. Thousands of pounds of specimens were brought to British museums for study.

11 | P a g e


Manganese nodules, brown lumps of mineral-rich sediments, were discovered on the seabed, sparking interest in deep sea mining.

This first pure oceanographic investigation was an unqualified success. The discovery of life in the depths of the oceans stimulated the new science of marine biology. The scope, accuracy, thoroughness, and attractive presentation of the researchers' written reports made this expedition a high point in scientific publication. The Challenger Report, the record of the expedition, was published between 1880 and 1895 by Sir John Murray in a well-written and magnificently illustrated 50-volume set; it is still used today. The Challenger expedition remains history's longest continuous scientific oceanographic expedition.

12. What was Sir John Murray’s main contribution to the HMS Challenger expedition and to oceanography?

The Challenger Report, the record of the expedition, was published between 1880 and 1895 by Sir John Murray in a well-written and magnificently illustrated 50-volume set; it is still used today. It was the 50 volume Report, rather than the cruise itself, that provided the foundation for the new science of oceanography.

13. Why were oceanographic conditions at Earth’s poles of interest to scientists?

Scientific curiosity, national pride, new ideas in shipbuilding, questions about the extent and history of the southern polar continent, and the quest to understand weather and climate – not to mention great personal courage -- led in the early years of the last century to the golden age of polar exploration.

14. How is the echo sounder an improvement over a weighted line in taking soundings? Which expedition first employed an echo sounder? Can you think of a few things that might cause echo sounding to give false information?

In 1925 the German Meteor expedition, which criss-crossed the south Atlantic for two years, introduced modern optical and electronic equipment to oceanographic investigation. Its most important innovation was to use an echo sounder, a device which bounces sound waves off the ocean bottom, to study the depth and contour of the seafloor. The echo sounder revealed to Meteor scientists a varied and often extremely rugged bottom profile rather than the flat floor they had anticipated.

Meteor scientists knew that the speed of sound through seawater varied with temperature, salinity and pressure. Because an echo sounder’s accuracy is based on knowledge of the speed of the sound pulses through seawater, compensating estimates were made. Even with the need to estimate, echo sounding is more accurate than discovering depth by dropped lines (that tend to drift with the currents).

12 | P a g e


15. What stimulated the rise of oceanographic institutions?

Individuals and voyages are most prominent in the first half of this century. Captain Robert Falcon Scott's British Antarctic expedition in HMS Discovery (1901-1904) set the stage for the golden age of Antarctic exploration. Roald Amundsen's brilliant assault on the south pole (1911) demonstrated that superb planning and preparation paid great dividends when operating in remote and hazardous locales. The German Meteor expedition, the first "high tech" oceanographic expedition, showed how electronic devices and sophisticated sampling techniques could be adapted to the marine environment. And certainly the individual contributions of people like Jacques Cousteau and Emile Gagnan (inventors in 1943 of the "aqualung," the first scuba device) and Don Walsh and Jacques Piccard (pilots of Trieste to the ocean's deepest point in 1960) are important.

But the undeniable success story of late twentieth century oceanography is the successful rise of the great research institutions with broad state and national funding. Without the cooperation of research universities and the federal government (through agencies like the National Science Foundation, the National Oceanic and Atmospheric Administration, and others), the great strides that were made in the fields of plate tectonics, atmosphere-ocean interaction, biological productivity, and ecological awareness would have been much slower in coming. Along with the Sea Grant Universities (and their equivalents in other countries), establishments like the Scripps Institution of Oceanography, the Lamont-Doherty Earth Observatory, and the Woods Hole Oceanographic Institution, with their powerful array of researchers and research tools, will define the future of oceanography.

16. Satellites orbit in space. How can a satellite conduct oceanography research?

Satellites beam radar signals off the sea surface to determine wave height, variations in sea-surface contour and temperature, and other information of interest to marine scientists. Photographs taken from space can assist in determining ocean productivity, current and circulation patterns, weather prediction, and many other factors.

17. What role does field research play in modern oceanography?

Marine science is by necessity a field science: Ships and distant research stations are essential to its progress. The business of operating the ships and staffing the research stations is costly and sometimes dangerous, yet “ground truth” – verification of readings taken remotely – is an essential part of the scientific process.

Chapter 3: EARTH STRUCTURE AND PLATE TECTONICS1. What force did Wegener believe was responsible for the movement of continents?

13 | P a g e


He believed "centrifugal force" (inertia, actually) and tidal drag was the motive power for continental drift.

2. What were the greatest objections to Wegener’s hypothesis?

He was incorrect in believing "centrifugal force" and tidal drag was the motive power for continental drift. The continental tracks that would have proven his theory -- trailing scars left on the seabed by the movement of continents -- were never found. He also assumed that the continents had split only once, while we now know that the process of plate tectonics is a lengthy cycle, with lithospheric plates suturing and splitting over great spans of time. (The cycle has been called the Wilson Cycle in honor of the insights of Canadian geologist John Tuzo Wilson.)

Wegener’s main contributions were to draw attention to the diverse bits of evidence suggesting continents were once together, and to stimulate geophysical study of the underpinnings of continents.

3. What do we mean when we say something is dense?

Something is said to be very dense if it weighs a lot per unit of volume. Density is an expression of the relative heaviness of a substance.

4. How is density expressed (units)?

Density is usually expressed in grams per cubic centimeter (g/cm3).

5. How can seismic waves be used to “see” inside Earth?

Seismic waves form in two types: surface waves and body waves. Surface waves can sometimes be seen as an undulating wave-like motion in the ground. Surface waves cause most of the property damage suffered in an earthquake. Body waves (P waves and S waves) are less dramatic, but they are useful for analyzing Earth’s interior structure.

The time of transit through Earth, the changes in the “sound” of the waves (analogous to our hearing difference in the treble or bass in our stereo systems), the attenuation of the waves, and the later arrival of faint echos all can be used to analyze the interior.

6. List the Earth’s internal layers by physical characteristics.

Different conditions of temperature and pressure prevail at different depths, and these conditions influence the physical properties of the materials subjected to them. The behavior of a rock is determined by three factors: temperature, pressure, and the rate at which a deforming force (stress) is applied. This behavior, in turn, determines how (and if) rocks will move. We can classify the internal layers by physical properties as follows:

14 | P a g e


The lithosphere -- the Earth's cool, rigid outer layer -- is about 100 – 200 kilometers (60 - 125 miles) in thickness. It is comprised of the brittle continental and oceanic crusts and the uppermost cool and rigid portion of the mantle.

The asthenosphere is the thin, hot, slowly-flowing layer of upper mantle below the lithosphere. Extending to a depth of about 350 – 650 kilometers (220 - 400 miles) the asthenosphere is characterized by its ability to deform plastically under stress.

The lower mantle extends to the core. Though it is hotter than the asthenosphere, the greater pressure at this depth probably prevents it from flowing.

The core is divided into two parts: the outer core is a viscous liquid with a density about 4 times that of the crust, the inner core a solid with a maximum density of about 6 times crustal material.

As we saw in the chapter, recent research has shown that slabs of Earth's relatively cool and solid surface -- its lithosphere -- float and move independently of one another over the hotter, partially molten asthenosphere layer directly below. The physical properties of each make this possible, so classification by physical properties is more useful in explaining plate tectonics.

7. What is the relationship between crust and lithosphere? Between lithosphere and asthenosphere?

Lithosphere includes crust (oceanic and continental) and rigid upper mantle down to the asthenosphere. The velocity of seismic waves in the crust is much different from that in the mantle. This suggests differences in chemical composition, or crystal structure, or both. The lithosphere and asthenosphere have different physical characteristics: the lithosphere is generally rigid, but the asthenosphere is capable of slow plastic movement. Asthenosphere and lithosphere also transmit seismic waves at different speeds.

8. Why is Earth’s interior still hot? Shouldn’t it have cooled off by now?

Much of the heat inside Earth results from the decay of radioactive elements. Some of this internal heat journeys toward the surface by conduction.

9. How can continents be supported high above sea level?

A continent floats above sea level because the lithosphere gradually sinks into the deformable asthenosphere until it has displaced a volume of asthenosphere equal in mass to the continent’s mass.

10. How did a careful plot of earthquake locations affect the discussion of the Theory of Continental Drift (as it was first called)? What about the jigsaw-puzzle-like fit of continents around the Atlantic?

15 | P a g e


The jigsaw-puzzle fit of continents around the Atlantic and the distinctly non-random distribution of earthquakes stimulated vigorous discussion in geological circles. Hugo Benioff’s plots of earthquake activity surrounding the Pacific Ring of Fire demanded explanation, and researchers redoubled their efforts to discover the links after the conclusion of the Second World War.

11. How did an understanding of radioactive decay and radiometric dating and influence the debate?

Radiometric dating allowed rock sequences to be dated and their relative positions through time determined. Radiometric studies also solidified understanding of Earth’s age, assuring researchers that Earth was indeed older than 6,000 years and that time was sufficient for large-scale seafloor spreading.

12. What were the key insights that Hess and Wilson brought to the discussion?

Hess (and Dietz) suggested that new seafloor develops at the Mid-Atlantic Ridge (and the other newly discovered ocean ridges) and then spreads outward from this line of origin. Continents would be carried along by the same forces that cause the ocean to grow. This motion could be powered by convection currents. In 1965 John Tuzo Wilson integrated the ideas of continental drift and seafloor spreading into the overriding concept of plate tectonics.

13. Can you outline – in very simple terms – the action of Earth’s crust described by the Theory of Plate Tectonics?

Have a go at your own synthesis, and then compare your drawing with Figure 3.10.

14. What kinds of plate boundaries exist? Can you tell what happens at each provide examples?

The three types of plate boundaries that result from these interactions are called divergent, convergent, and transform boundaries, depending on their sense of movement.

15. About how fast do plates move?

Though spreading speeds can reach a rate of 18 centimeters (7 inches) a year along parts of the Pacific plate, most plates move more slowly, about 3 centimeters (1.3 inches) each year.

16. What causes most earthquakes and volcanoes?

16 | P a g e


A subducting plate's periodic downward lurches cause earthquakes and tsunami. Volcanoes often occur over a subducting plate or at divergent plate boundaries where the crust is stressed and thinned.

17. Is Earth’s magnetic field a constant? That is, would a compass needle always point north?

Earth’s magnetic field reverses at irregular intervals of a few hundred thousand years. In a time of reversal a compass needle would point south instead of north, and any particles of magnetic material falling below their Curie points in fresh seafloor basalt at a spreading center would be imprinted with the reversed field.

18. How can Earth’s magnetic field be “frozen” into rocks as they form?

A compass needle points toward the magnetic north pole because it aligns with Earth’s magnetic field (Figures 3.21). Tiny particles of an iron-bearing magnetic mineral called magnetite occur naturally in basaltic magma. When this magma erupts at mid-ocean ridges, it cools to form solid rock. The magnetic minerals act like miniature compass needles. As they cool to form new seafloor, the magnetic minerals’ magnetic fields align with Earth’s magnetic field. Thus the orientation of Earth’s magnetic field at that particular time becomes frozen in the rock as it solidifies. Any later change in the strength or direction of Earth’s magnetic field will not significantly change the characteristics of the field trapped within the now-solid rocks.

19. Can you explain the matching magnetic alignments seen south of Iceland (Figure 3.23)?

The alternating magnetic stripes represent rocks with alternating magnetic polarity—one band having normal polarity (magnetized in the same direction as today’s magnetic field direction), and the next band having reversed polarity (opposite from today’s direction). Researchers realized that the pattern of alternating weak and strong magnetic fields was symmetrical because freshly magnetized rocks born at the ridge are spread apart and carried away from the ridge by plate movement.

20. How does the long chain of Hawaiian volcanoes seem to confirm the Theory of Plate Tectonics?

The northern Pacific contains an “assembly line” chain of islands which extends from the old eroded volcanoes of the Emperor Seamounts to the still-growing island of Hawaii. The Pacific Plate is moving northwest relative to a mantle plume anchored in the mantle below.

21. Earth is 4,600 million years old, and the ocean nearly as old. Why is the oldest ocean floor so young -- rarely more than 200 million years old?

17 | P a g e


The light, ancient granitic continents ride high in the lithospheric plates, rafting on the moving asthenosphere below. In subduction, heavy basaltic ocean floor (and its overlying layer of sediment) plunges into the mantle at a subduction zone to be partially remelted, but the light granitic continents ride above, too light to subduct. The subducting plate may be very slightly more dense than the upper asthenosphere on which it rides, and so is pulled downward into the mantle by gravity. Because the ocean floor itself acts as a vast "conveyor belt" transporting accumulated sediment to subduction zones where the seafloor sinks into the asthenosphere, no marine sediments (or underlying crust) are of great age. The ocean floor is recycled; the continents just jostle above the fray. Figure 3.22, showing accreting terranes, demonstrates this nicely.

22. Do you live on a terrane?

Changes are good that you live on a terrane. If you live in North America, check Figure 3.27.

23. Can you suggest areas for future research in plate tectonics?

A review of the bulleted list in this section will provide food for thought. What other questions come to mind?

24. In your opinion, how has an understanding of plate tectonics revolutionized geology?

It’s difficult to underestimate the effect our understanding of plate tectonics has had on all areas of science. Coal in the Antarctic? Latitudinal variations in the Australian Barrier Reef? Similar fossils across separated continents? The relative youth of the seabed? Earthquake distribution (and prediction)? It’s hard to know where to stop!

Chapter 4: OCEAN BASINS1. How was bathymetry accomplished in years past? How do scientists do it now?

The simplest methods involved lowering a weight on a line. The length of line is measured, and the depth determined. Sometimes the weight was tipped with wax to retrieve a sample of bottom sediment. Scientists now use beams of sound to measure depth (see next answer).

2. Echo sounders bounce sound off the seabed to measure depth. How does that work?

Echo sounders sense the contour of the seafloor by beaming sound waves to the bottom and measuring the time required for the sound waves to bounce back to the ship. Unlike a simple echo sounder, a multibeam system may have as many as 121 beams radiating from a ship’s hull.

18 | P a g e


3. Satellites orbit in space. How can a satellite conduct oceanographic research? Why does the surface of the ocean “bunch up” over submerged mountains and ridges?

Satellites cannot measure ocean depths directly, but they can measure small variations in the elevation of surface water using radar beams. This is useful because the pull of gravity varies across Earth’s surface depending on the nearness (or distance away) of massive parts of Earth. An undersea mountain or ridge “pulls” water toward it from the sides, forming a mount of water over itself, and that mount is detected by the orbiting satellite.

4. How would you characterize the general shape of an ocean basin?

Ocean basins are not bathtub-shaped. The submerged edges of continents form shelves at basin margins, and the center of a basin is often raised by a ridge.

5. If you could walk down into the seabed, the transition from granite to basalt would mark the true edge of the continent and would divide ocean floors into two major provinces. What are they?

Try drawing a diagram of a typical ocean basin’s cross-section. Now look at Figure 4.9. Did your drawing include the continental margin (continental shelf + continental rise) and the deep ocean floor? Did you remember to raise the center of the deep floor to indicate a mid-ocean ridge? The true edge of a continent is marked by the transition from granite to basalt?

6. How does a continental margin differ from a deep-ocean basin?

The transition to basalt marks the true edge of the continent and divides ocean floors into two major provinces. The submerged outer edge of a continent is called the continental margin. The deep seafloor beyond the continental margin is properly called the ocean basin.

7. What are the features of the continental margins?

The continental margin is characterized by thick (and less dense) granitic rock of the continents. Near shore the features of the ocean floor are similar to those of the adjacent continents because they share the same granitic basement. Relatively thin (and denser) basalt forms the adjacent deep seafloor.

8. How is an active tectonic margin different from a passive tectonic margin?

19 | P a g e


Continental margins facing the edges of diverging plates are called passive margins because relatively little earthquake or volcanic activity is now associated with them. Continental margins near the edges of converging plates (or near places where plates are slipping past one another) are called active margins because of their earthquake and volcanic activity.

9. How do the widths of continental shelves differ between active margins and passive margins?

The width of a shelf is usually determined by its proximity to a plate boundary. The shelf at a passive margin is usually broad, but the shelf at the active margin is often very narrow.

10. How has sea level varied with time? Is sea level unusually high or low at present?

Figures 4.15 provides a graph of sea level through time. Sea level is high at the moment, and is rising as the ocean warms.

11. What are submarine canyons? Where are they found, and how are they thought to have been formed?

Submarine canyons cut into the continental shelf and slope, often terminating on the deep-sea floor in a fan-shaped wedge of sediment. Most geologists believe that the canyons have been formed by abrasive turbidity currents plunging down the canyons.

12. Where would you look for a continental rise? What forms continental rises?

Along passive margins, the oceanic crust at the base of the continental slope is covered by an apron of accumulated sediment called the continental rise. Sediments from the shelf slowly descend to the ocean floor along the whole continental slope, but most of the sediments that form the continental rise are transported to the area by turbidity currents.

13. What are typical features of deep-ocean basins?

Deep-ocean basins consist mainly of the oceanic ridge systems and the adjacent sediment-covered (abyssal) plains. Basin edges may be rimmed by trenches or aprons of sediments that have fallen along the continental shelves. The abyssal plains are sometimes punctuated by islands, hills, and volcanoes.

14. What is the extent of the mid-ocean ridge system? Are mid-ocean ridges always literally in mid-ocean?

20 | P a g e


Oceanic ridges are Earth’s most remarkable and obvious feature. They stretch 65,000 kilometers. Although these features are often called mid-ocean ridges, less than 60% of their length actually exists along the centers of ocean basins.

15. Draw a cross section through an active mid-ocean ridge. Where are the hydrothermal vents located? Where is new seabed being formed?

Check Figure 4.22 after you make your drawing.

16. What are fracture zones? What causes these lateral breaks?

Fracture zones extend outward from the ridge axis. They are seismically inactive areas that show evidence of past transform fault activity. While segments of a lithospheric plate on either side of a transform fault move in opposite directions from each other, the plate segments adjacent to the outward segments of a fracture zone move in the same direction.

17. What are abyssal plains? What is unique about them?

Abyssal plains are flat, featureless expanses of sediment-covered ocean floor found on the periphery of all oceans. Abyssal plains are extraordinarily flat.

18. Why are abyssal plains relatively rare in the Pacific?

Because the extensive system of trenches along the active margins of the Pacific trap much of the sediments flowing off the continents, preventing them from building the broad, flat abyssal plains typical of the Atlantic. There are a few abyssal plains in the Pacific (notably adjacent to China and Southeast Asia), but none approaches the extent of, say, the Canary Abyssal Plain west of the Canary Islands in the North Atlantic, with an area of 900,000 square kilometers (350,000 square miles).

19. How do guyots form? How were lines of guyots and sea-mounts important in deciphering plate tectonics?

Guyots are flat-topped seamounts that once were tall enough to approach or penetrate the sea surface. The flat top suggests that they were eroded by wave action when they were near sea level. Movement of the lithosphere away from spreading centers has carried them outward and downward to their present positions.

20. How are the ocean’s trenches formed? How are earthquakes related to their formation?

21 | P a g e


A trench is an arc-shaped depression in the deep-ocean floor that forms where a converging oceanic plate is subducted. Earthquakes are understandably associated with subduction zones.

21. Why are trenches and island arcs curved? Is the descent to the bottom steeper on the convex side of the arc or on the concave side? Why do you think most trenches are in the western Pacific?

Trenches are curved because of the geometry of plate interactions on a sphere. The convex sides of these curves generally face the open ocean. The trench walls on the island side of the depressions are steeper than those on the seaward side, indicating the direction of plate subduction. Trenches are prevalent in the western Pacific because that is an area of vigorous plate subduction.

22. How do you think graphics like The Grand Tour have assisted our understanding of geological processes?

These large-scale remote sensing techniques have allowed researchers to (quite literally) see the big picture. For the first time, global processes may been in context in relation to one another. For example, in Figure 4.27, look at the area numbered “9” just south of the tip of South America. Notice how the tip of the continent – along with the adjacent northern tip of Antarctica’s Palmer Peninsula -- has been nudged to the east. The South Sandwich Trench marks the easternmost terminus of the large feature. The relationship of all these was unclear until images like this Figure provided the “aha” moment.

Chapter 5: OCEAN SEDIMENTS

1. What is sediment?

Sediment is particles of organic or inorganic matter that accumulate in a loose, unconsolidated form.

2. Why are very few areas of the seabed completely free of sediments?

The marine processes that generate sediments are widespread. Sediment particles may consist of the remains of once-living organisms, bits of windblown dust, volcanic ash, etc.

3. The ocean is more than 4 billion years old, yet marine sediments are rarely older than about 180 million years. Why?

22 | P a g e


As you learned in Chapter 3, tectonic processes form and destroy the seabed over time. Because of subduction, seabed older than about 180 million years is rare.

4. What types of particles compose most marine sediments?

Most marine sediments are made of finer particles: sand, silt, and clay.

5. Which particles are most easily transported by water?

The smaller the particle, the more easily it can be transported by streams, waves, and currents.

6. How do well-sorted sediments differ from poorly sorted sediments?

Sediments composed of particles of mostly one size are said to be well-sorted sediments. Sediments with a mixture of sizes are poorly sorted sediments. Sorting is a function of the energy of the environment—the exposure of that area to the action of waves, tides, and currents.

7. What are the four main types of marine sediments?

Marine sediments are separated into four categories by source: terrigenous, biogenous, hydrogenous (or authigenic), and cosmogenous.

Terrigenous sediments are the most abundant. As the name implies, terrigenous sediment originates on the continents or islands near them. They are carried to the ocean in rivers and streams, or by winds as blowing dust, and dominate the continental margins, abyssal plains, and polar ocean floors.

Biogenous sediments, the next most abundant, consist of the hard remains of once-living marine organisms. The siliceous (silicon-containing) and calcareous (calcium carbonate-containing) compounds that make up these sediments of biological origin were originally dissolved in the ocean at mid-ocean ridges or brought to the ocean in solution by rivers. Biogenous sediments are found mixed with terrigenous material near continental margins, but are dominant on the deep ocean floor.

Hydrogenous sediments are minerals that have precipitated directly from seawater. The sources of the dissolved minerals include submerged rock and sediment, leaching of the fresh crust at oceanic ridges, material issuing from hydrothermal vents, or substances flowing to the ocean in river runoff. The most prominent hydrogenous sediments are manganese nodules, which litter abyssal plains, and phosphorite nodules, seen along some continental margins. Hydrogenous sediments are also called authigenic (authis = in place, "on the spot") because they were formed in the place they now occupy.

Cosmogenous sediments, which are of extraterrestrial origin, are the least abundant.

23 | P a g e


These particles enter the Earth's high atmosphere as blazing meteors or as quiet motes of dust. Their rate of accumulation is so slow that they never accumulate as distinct layers -- they occur as isolated grains in other sediments, rarely constituting more than 1% of any layer.

8. Which type of sediment is most abundant?

Terrigenous sediments are the most abundant. The largest terrigenous deposits form near continental margins.

9. Which type of sediment covers the greatest seabed area?

Biogenous sediments, though their total volume is less than that of terrigenous sediments.

10. Which type of sediment is rarest? Where does this sediment originate?

Cosmogenous sediments, which are of extraterrestrial origin, are the least abundant.

11. Do most sediments consist of a single type? (That is, are terrigenous deposits made exclusively of terrigenous sediments?)

Most sediment deposits are a mixture of biogenous and terrigenous particles, with an occasional hydrogenous or cosmogenous supplement. The dominant type gives its name to the mixture.

12. How do neritic sediments differ from pelagic ones?

Neritic sediments consist primarily of terrigenous material. Deep-ocean floors are covered by finer sediments than those of the continental margins, and a greater proportion of deep-sea sediment is of biogenous origin. Sediments of the slope, rise, and deep-ocean floor that originate in the ocean are called pelagic sediments.

13. Are neritic sediments generally terrigenous or biogenous?

The bulk of neritic sediments are terrigenous; they are eroded from the land and carried to streams, where they are transported to the ocean.

14. What is lithification? How is sedimentary rock formed?

24 | P a g e


Neritic sediments can undergo lithification: They are converted into sedimentary rock by pressure-induced compaction or by cementation.

15. Can you think of an example of lithified sediment on land?

Much of the Colorado Plateau, with its many stacked layers easily visible in the Grand Canyon, was formed by sedimentary deposition and lithification beneath a shallow continental sea beginning about 570 million years ago.

16. Why are Atlantic sediments generally thicker than Pacific sediments?

When averaged, the Atlantic Ocean bottom is covered by sediments to a thickness of about 1 kilometer, while the Pacific floor has an average sediment thickness of less than 0.5 kilometer.

17. How do turbidity currents distribute sediments? What do these sediments (turbidites) look like?

A turbidity current is a dilute mixtures of sediment and water that periodically rushes down the continental slope. The resulting deposits (turbidites) are graded layers of terrigenous sand interbedded with the finer pelagic sediments typical of the deep-sea floor.

18. What is the origin of oozes? What are the two types of oozes?

The organisms that contribute their remains to deep-sea oozes are small, single-celled, drifting, plantlike organisms and the single-celled animals that feed on them. The silica-rich residues give rise to siliceous ooze, the calcium-containing material to calcareous ooze.

19. What is the CCD? How does it affect ooze deposition at great depths?

At the calcium carbonate compensation depth (CCD), the rate at which calcareous sediments are supplied to the seabed equals the rate at which those sediments dissolve. Below this depth, the tiny skeletons of calcium carbonate dissolve on the seafloor, so no calcareous oozes accumulate.

20. How do hydrogenous materials form? Give an example of hydrogenous sediment.

Most hydrogenous sediments originate from chemical reactions that occur on particles of the dominant sediment. The most famous hydrogenous sediments are manganese nodules.

25 | P a g e


21. How are sediments studied?

Cameras are used to visualize the bottom, and direct samplers (clamshell, piston corers) are used to obtain specimens. Reflected sound can image strata beneath the surface covering.

22. How have studies of marine sediments advanced our understanding of plate tectonics?

The discovery that marine sediments are comparatively young (compared with terrestrial sediments) is a prime proof of the tectonic theory. Remember what happens at subduction zones!

23. Would you say the “memory” of the sediments is long or short (in geologic time)?

Because the deep sea sediment record is ultimately destroyed in the subduction process, the ocean's sedimentary "memory" does not start with the ocean’s formation as originally reasoned by early marine scientists.

24. How might past climate be inferred from studies of marine sediments?

Scientists now have instruments capable of analyzing very small variations in the relative abundances of the stable isotopes of oxygen preserved within the carbonate shells of microfossils found in deep sea sediments. These instruments allow them to interpret changes in the temperature of surface and deep water over time.

Chapter 6: WATER

1. Give an example of water in a very short, rapid part of a hydrologic cycle. A long and slow part? [Note: due to the author’s oversight, questions 1 and 2 are essentially identical. The answer to both is below question #2:]

2. Give an example of a very short, rapid hydrologic cycle. Long and slow?

A very short cycle could result from summer rainfall into a warm tidal pool. The water would quickly evaporate and return as vapor to the sky. A much longer cycle would result if that brief rainfall soaked into porous rocks, became trapped there, and was eventually subducted into

26 | P a g e


the mantle. Millions of years later, this water might escape into the atmosphere as steam from a volcanic vent.

3. How are atoms different from molecules?

Atoms cannot be broken into simpler substances by chemical means. A molecule is a group of atoms held together by chemical bonds.

4. What holds molecules together?

Molecules are held together by chemical bonds. Chemical bonds, the energy relationships between atoms that hold them together, are formed when electrons are shared between atoms or moved from one atom to another.

5. Why is water a polar molecule? What properties of water derive from its polar nature?

The water molecule has a positive end that attracts particles that have a negative charge, and a negative end (or pole) that attracts particles with a positive charge. When water comes into contact with compounds whose elements are held together by the attraction of opposite electrical charges (most salts, for example), the polar water molecule will separate that compound’s component elements from each other.

6a. Why does water look blue? [Note: due to the author’s oversight, there are two questions carrying the number 6. The answer to the second one is below.]

Hydrogen bonds selectively remove red light (changing its energy into heat). The remaining blue light travels farther through the water, and may strike objects to reflect back through the surface to your eyes.

6b. How is heat different from temperature?

Heat is energy produced by the random vibration of atoms or molecules. Heat is a measure of how many molecules are vibrating and how rapidly they are vibrating. Temperature records only how rapidly the molecules of a substance are vibrating. Temperature is an object’s response to an input (or removal) of heat.

7. What is meant by heat capacity? Why is the heat capacity of water unique?

27 | P a g e


Heat capacity is a measure of the heat required to raise the temperature of 1 gram of a substance by 1°C. Not all substances respond to identical inputs of heat by rising in temperature the same number of degrees. Water’s heat capacity is exceptionally high.

8. What factors affect the density of water? Why does cold air or water tend to sink? What role does salinity play?

Temperature and salinity affect water density. Cold, salty water tends to sink.

9. How is water’s density affected by freezing? Why does ice float?

Ice is less dense than liquid water—and thus floats—because the molecules are packed less efficiently.

10. What is the difference between sensible and nonsensible heat?

Sensible heat can be sensed by a temperature change measurable on a thermometer. Nonsensible heat is known as “latent.” (See next item.)

11. What’s the latent heat of fusion of water? The latent heat of vaporization? Why do we use the term latent?

Removing a calorie of heat from freezing water at 0°C (32°F) won’t change its temperature at all; 80 calories of heat energy must be removed per gram of pure water at 0°C (32°F) to form ice. This heat is called the latent heat of fusion.

At 540 calories per gram at 20°C (68°F), water has the highest latent heat of vaporization of any known substance.

The term latent applies to heat input that does not cause a temperature change but does produce a change of state (as from a liquid to a gas, or vice versa).

12. What is thermal inertia?

The tendency of a substance to resist a change in temperature with the gain or loss of heat energy is called thermal inertia.

13. Why is the fact that ice floats important to Earth’s generally moderate climate?

More 12 million square miles of surface, thaws and refreezes in the polar ocean each year. Removing a calorie of heat from freezing pure water at 0°C (32°F) won’t change its temperature at all—80 calories of heat energy must be removed per gram of liquid water to form ice. Incoming solar heat melts ice in the local polar summer, but the ice melts and the ocean’s

28 | P a g e


temperature doesn’t change. The situation reverses in winter – the water freezes and again the temperature doesn’t change.

14. How is heat transported from tropical regions to polar regions?

Masses of moving air account for about two-thirds of the poleward transfer of heat; ocean currents move the other third.

15. How is seawater’s salinity expressed?

The total quantity (or concentration) of dissolved inorganic solids in water is its salinity. The ocean’s salinity varies from about 3.3% to 3.7% by mass.

16. Other than hydrogen and oxygen, what are the most abundant ions in seawater?

Other than hydrogen and oxygen, the most abundant ions in seawater are chloride, sodium, sulfate, magnesium, and calcium.

17. What are the sources of the ocean’s dissolved solids?

The ocean’s dissolved solids are derived from erosion and weathering of ocean basins and the contact of seawater with hot minerals at mid-ocean rifts.

18. What is the principle of constant proportions?

The Principle of Constant Proportions states the ratio of various salts in seawater is the same in samples from many places, regardless of how salty the water is.

19. How is salinity determined?

The chloride ion is abundant and comparatively easy to measure, and it always accounts for the same proportion of dissolved solids (55.04%), so marine chemists devised the concept of chlorinity to simplify measurement of salinity.

20. What is meant by “residence time”? Does seawater itself have a residence time?

Residence time is the average length of time an atom of an element spends in the ocean. Seawater itself has a residence time of about 4,100 years.

29 | P a g e


21. Which dissolves more gas per unit volume – cold seawater or warm seawater?

Unlike solids, gases dissolve most readily in cold water.

22. What happens when carbon dioxide dissolves in seawater?

Initially, carbon dioxide and water combine to form carbonic acid. Carbonic acid then rapidly dissociates into a bicarbonate ion and a hydrogen ion. Most of the carbon dioxide dissolved in seawater ends up as bicarbonate. Some of the bicarbonate and hydrogen ions will then combine to form carbonate ions and two hydrogen ions.

23. How do concentrations of oxygen and carbon dioxide vary with ocean depth?

In areas of rapid photosynthesis pH will rise because carbon dioxide is used by plants and plant-like organisms. Surface pH in warm productive water is usually around 8.5. At middle depths and in deep water, more carbon dioxide may be present than at the surface. With cold temperatures, high pressure, and no photosynthetic plants to remove it, this CO2 will lower the pH of water, making it more acid with depth.

24. How is pH expressed? What’s neutral?

The acidity or alkalinity of a solution is measured in terms of the pH scale, which measures the concentration of hydrogen ions in a solution. An excess of hydrogen ions in a solution makes that solution acidic. An excess of hydroxide ions makes a solution alkaline. A pH of 7 is neutral.

25. What is a buffer? How might seawater’s ability to act as a buffer be important?

A buffer is a group of substances that tends to resist change in the pH of a solution. Buffering prevents broad swings of pH when acids or bases are introduced into the ocean.

26. How is the ocean stratified by density? What names are given to the ocean’s density zones?

Seawater’s density increases with increasing salinity, increasing pressure, and decreasing temperature. The three strata (density zones) are the surface zone (or mixed layer), the pycnocline, and the deep zone.

30 | P a g e


27. What, generally, are the water characteristics of the surface zone? Do these conditions differ significantly between the polar regions and the tropics?

The surface zone consists of water in contact with the atmosphere and exposed to sunlight. It contains the ocean’s least dense water and accounts for only about 2% of total ocean volume. Conditions in the surface zone differ greatly with latitude.

28. What, generally, are the water characteristics of the deep zone? Do these conditions differ significantly between the polar regions and the tropics?

The deep zone lies below the pycnocline at depths below about 1,000 meters in mid-latitudes (40°S to 40°N). Conditions are consistent at all latitudes. This deep zone contains about 80% of all ocean water. Deep zone conditions are very similar everywhere in the ocean.

29. How is the pycnocline related to the thermocline and halocline?

The pycnocline is a zone in which density increases with increasing depth. It is a combination of the thermocline and halocline, zones in which density increases with depth as temperature falls and salinity rises.

30. How is a water mass defined?

A water mass is a body of water with characteristic temperature and salinity and therefore density.

31. How does the ocean’s density stratification limit the vertical movement of seawater?

The great difference in temperature, and therefore density, between surface water and deep water in the tropics makes the water column very stable and prevents an exchange of surface and deep water.

32. What factors influence the intensity and color of light in the sea?

Scattering occurs as light is bounced between air or water molecules, dust particles, water droplets, or other objects before being absorbed. The absorption of light is governed by the structure of the water molecules it happens to strike. When light is absorbed, molecules vibrate and the light’s electromagnetic energy is converted to heat. In the ocean, red light is converted to heat more efficiently than blue.

31 | P a g e


33. Intensities being equal, which color of light moves farthest through seawater. Least far? What happens to the energy of light when light is absorbed in seawater?

The top meter of ocean absorbs 71% of red light. The dimming light becomes bluer with depth because the red, yellow, and orange wavelengths are being absorbed. By 300 meters even the blue light has been converted into heat.

34. What factors affect the depth of the photic zone? Could there be a photocline in the ocean?

Even the clearest seawater is not perfectly transparent. In the very clearest tropical waters the photic zone may extend to a depth of 600 meters, but a more typical value for the open ocean is 100 meters. In contrast, light typically penetrates the coastal waters in which we swim only to about 40 meters. “Photocline” would refer to a rapid decrease in light with increasing depth. Local increases in turbidity could cause a photocline.

35. Which moves faster through the ocean—light or sound?

Light travels much faster than sound in both air and water.

36. How much faster is the speed of sound in water than in air?

The speed of sound is almost five times faster in water than in air, about 1,500 meters per second.

37. Is the speed of sound the same at all ocean depths?

The speed of sound in seawater increases as temperature and pressure increase. Sound travels faster at the warm ocean surface than it does in deeper, cooler water. Its speed decreases with depth, eventually reaching a minimum at about 1,000 meters. Below that depth, however, the effect of increasing pressure offsets the effect of decreasing temperature; so speed increases again.

38. What’s a sofar layer?

Sound waves bend toward layers of lower sound velocity and so tend to stay within this minimum-velocity zone. Therefore, loud noises made at this depth can be heard for thousands of kilometers. The minimum-velocity layer has come to be known as the sofar layer.

39. How does sonar work? What kinds of sonar systems are used in oceanographic research?

32 | P a g e


Active sonar, the projection and return through water of short pulses (pings) of high-frequency sound to search for objects in the ocean, is used to search for objects or ocean conditions of interest to researchers. Side-scan solar is among the most useful active sonar devices

Chapter 7: ATMOSPHERIC CIRCULATION

1. How is weather different from climate?

Weather is the state of the atmosphere at a specific time and place, while climate is the long-term average of weather in an area.

2. Which is denser at the same temperature and pressure: humid air or dry air?

Curiously, humid air is less dense than dry air at the same temperature—because molecules of water vapor weigh less than the nitrogen and oxygen molecules than the water vapor it displaces.

3. How does air’s temperature change as it expands? As it is compressed?

Air becomes cooler when it expands, and warms as it is compressed. Air descending from high altitude warms as it is compressed by the higher atmospheric pressure near Earth’s surface.

4. Can more water vapor be held in warm air or cool air?

Warm air can hold more water vapor than cold air (at the same atmospheric pressure).

5. What happens when air containing water vapor rises?

Water vapor in rising, expanding, cooling air will often condense into clouds because the cooler air can no longer hold as much water vapor. If rising and cooling continue, the droplets may coalesce into raindrops or snowflakes.

6. What is meant by thermal equilibrium? Is Earth’s heat budget in balance?

Over long periods of time the total incoming heat (plus that from earthly sources) equals the total heat radiating into the cold of space; so Earth is in thermal equilibrium. Some variation is observable over shorter time spans -- the current episode of global warning is an example.

33 | P a g e


7. How does solar heating vary with latitude? With the seasons?

Near the poles light approaches the surface at a low angle, favoring reflection. At tropical latitudes, sunlight strikes at a more nearly vertical angle, which distributes the same amount of sunlight over a much smaller area. Tropical latitudes thus receive significantly more solar energy than the polar regions. As Earth revolves around the sun, the constant tilt of its rotational axis causes the Northern Hemisphere to lean toward the sun in June but away from it in December. The sun therefore appears higher in the sky in the summer but lower in winter.

8. What is a convection current? Can you think of any examples of convection currents around your house?

A convection current is a single closed-flow circuit of rising warm material and falling cool material.

9. Describe the Coriolis effect to the next person you meet. Go ahead—give it a try!

Understanding Coriolis effect depends on communicating the idea that objects “inherit” their eastward momentum from their originating latitude. They bring that eastward movement with them as they move north of south. In a sense, the apparent motion of Coriolis effect is the difference in expected east-west position.

10. If all of Earth rotates eastward at 15º an hour, why does the eastward speed of locations on Earth vary with their latitude?

The angular velocity of Earth is 15° an hour (think of the pie slice of Figure 7.10). But the linear velocity depends on latitude. See how much farther Quito must travel to make it around Earth in one day in that Figure?

11. How many atmospheric circulation cells exist in each hemisphere?

Three air circulation cells exist in each hemisphere.

12. How does the Coriolis effect influence atmospheric circulation?

Instead of continuing all the way from equator to pole in a continuous loop in each hemisphere, air rising from the equatorial region moves poleward and is gradually deflected

34 | P a g e


eastward; that is, it turns to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. This eastward deflection is caused by the Coriolis effect.

13. What happens to air flow between circulation cells? (Hint: What causes Earth’s desert climates?)

The great deserts of both hemispheres, dry bands centered around 30° latitude, mark the intersection of the Hadley and Ferrel cells. Air falls toward Earth’s surface in these areas, causing compressional heating.

14. Draw the general pattern for the atmospheric circulation of the Northern Hemisphere (without looking at Figure 7.13). Now locate these features: the doldrums (or ITCZ), the horse latitudes, the prevailing westerlies, and the trade winds.

Do your drawing without looking at the Figure, and then check your accuracy.

15. What’s a monsoon? Do we experience monsoons in the continental United States?

Heating of the great landmass of Asia draws vast quantities of warm, moist air from the Indian Ocean. Winds from the south drive this moisture toward Asia, where it rises and condenses to produce a months-long deluge (a monsoon). Monsoons occur in North America as warming and rising air over the South and West draws humid air and thunderstorms from the Gulf of Mexico.

16. What are the two kinds of large storms? How do they differ? How are they similar?

Large storms are either tropical cyclones or extratropical cyclones. Tropical cyclones (sometimes called hurricanes or typhoons) form in a single tropical air mass. Extratropical cyclones (named because they form outside the tropics) are the frontal storms familiar to winter residents of mid-latitude continents. Extratropical cyclones form at a front between two air masses.

17. What is an air mass? How do air masses form?

An air mass is a large body of air with nearly uniform temperature, humidity, and therefore density throughout. Air pausing over water or land will tend to take on the characteristics of the surface below.

18. What causes an extratropical cyclone? How are air masses involved?

35 | P a g e


Energy is required to mix air masses. Since that energy is not always available, a dense air mass may slide beneath a lighter air mass, lifting the lighter one and causing its air to expand and cool. Water vapor in the rising air may condense. All of these effects contribute to turbulence at the boundaries of the air masses and can lead to the formation of an extratropical cyclone.

19. What’s a weather front? Is it typical of tropical or extra-tropical cyclones?

The boundary between air masses of different density is called a front. Fronts are typical of extratropical cyclones.

20. Why do extratropical cyclones rotate counterclockwise in the Northern Hemisphere?

This apparent anomaly is caused by the Coriolis deflection of winds approaching the center of a low-pressure area from great distances. In the Northern Hemisphere there is rightward deflection of the approaching air. The edge spin given by this approaching air causes the storm to spin counterclockwise in the Northern Hemisphere.

21. What causes the greatest loss of life and property when a tropical cyclone reaches land?

Three aspects of a tropical cyclone can cause property damage and loss of life: wind, rain, and storm surge. Of these, storm surge is the most devastating.

22. What things were unique about the 2005 Atlantic hurricane season?

A record 27 tropical cyclones formed, and 15 of these became hurricanes. Three hurricanes reached Category 5 strength. One of these was hurricane Katrina, cause of the costliest natural disaster to befall the United States.

23. Of a tropical cyclone’s three most dangerous properties (wind, rain, storm surge), which of Katrina’s characteristics caused the greatest loss of life? Of property?

Storm surge caused the greatest loss of life and property when Katrina struck the Gulf coast. The storm surge in Bay St. Louis was 10.4 meters, or 34 feet, high.

24. How do large tropical cyclones affect the human-built coastal zone? The natural coastal zone?

36 | P a g e


The effects of a large tropical cyclone on a built-up area were clearly seen in the city of New Orleans. Much of the city was built on land below sea level, and when the levees failed because of storm surge stress, much of the city flooded. The natural coast was also affected. Salt water driven inland by storm surge killed marsh grasses along the Louisiana and Mississippi coasts. In Louisiana alone, more than 260 square kilometers (100 square miles) of wetlands were torn apart, their ability to support a rich variety of species essentially destroyed.

25. Is there a proven link between global warming and the apparent growing intensity of Atlantic hurricanes?

Althought there is a strong suggestion of a relationship between the growing greenhouse and intensification of tropical cyclones, researchers are unable to link the two with certainty

Chapter 8: OCEAN CIRCULATION1. What causes the two major types of ocean currents?

Surface currents are wind-driven movements of water at or near the ocean’s surface, and thermohaline currents are the slow deep density-driven currents that affect the vast bulk of seawater beneath the pycnocline.

2. About what percentage of the world ocean is involved in wind-driven surface currents?

About 10% of the water in the world ocean is involved in surface currents driven by wind friction.

3. What is a gyre? How many large gyres exist in the world ocean? Where are they located?

A gyre is a circuit of wind-driven current flow around the periphery of an ocean basin. There are six major gyres in the world ocean: North and South Pacific, North and South Atlantic, Indian Ocean, and the West-Wind Drift (Antarctic Circumpolar Current).

4. Why does seawater in most surface currents flow around the periphery of ocean basins? How is Coriolis effect involved?

Water flow in a gyre is dynamically balanced between the downhill urge of the pressure gradient and the uphill tendency of Coriolis deflection (see again Figure 8.7 and 8.12).

5. Compare and contrast western boundary currents to eastern boundary currents.

37 | P a g e


Western boundary currents tend to be hot, fast, and deep. Eastern boundary currents are cold, slow, and shallow.

6. Name a western boundary current. An eastern boundary current.

Western boundary currents (at the western edge of an ocean basin) include the Gulf Stream, the Kuroshio Current, and Brazil Current.

Eastern boundary currents (at the eastern edge of an ocean basin) include the California Current, the Canary Current, and the Peru Current.

7. What is meant by “westward intensification?” Why are western boundary currents so fast and deep?

Let’s use a Northern Hemisphere example. Due to the Coriolis effect—which increases as water moves farther from the equator—eastward-moving water on the north side of a gyre is turned sooner and more strongly toward the equator than westward-flowing water at the equator is turned toward the pole. So the peak of the hill described in Figure 8.7 is not in the center of the ocean basin, but closer to its western edge. Its slope is steeper on the western side. If an equal volume of water flows around the gyre, this means the current on the eastern boundary is spread out and slow, and the current on the western boundary is concentrated and rapid.

8. What is the relationship between surface currents and the climate of adjacent continents?

Warm water flows to higher latitudes, transfers heat to the air and cools, moves back to low latitudes, absorbs heat again, and the cycle repeats. The greatest amount of heat transfer occurs at mid-latitudes, where about 10 million billion calories of heat are transferred each second.

9. How does wind blowing over a surface current influence the climate downwind?

If a continent is downwind of a mass of warm water, the atmosphere will transfer some of the heat to the continent. For example, the mild climates of Edinburgh, Dublin, and London are due to eastward-moving air only recently in contact with the relatively warm North Atlantic Current.

10. How can wind-driven horizontal movement of water induce vertical movement in surface water?

The friction of wind blowing from the north along the ocean surface causes the water

38 | P a g e


next to the west coast of a continent to begin moving. Coriolis effect deflects the water to the right (in the Northern Hemisphere), and the resultant Ekman transport moves it offshore. Deep water then rises (moves vertically) to replace the seaward-moving surface water.

11. How is the Coriolis effect involved in equatorial upwelling?

Though the Coriolis effect is weak near the equator (and absent at the equator), water moving in the currents on either side of the equator is deflected slightly poleward and replaced by deeper water (Figure 8.13). Thus, equatorial upwelling occurs in these westward-flowing equatorial surface currents.

12. Which way does wind typically blow over the tropical Pacific? How does this flow change during an El Niño event?

The trade winds blow from the normally high-pressure area over the eastern Pacific (near Central and South America) to the normally stable low-pressure area over the western Pacific (north of Australia). However, for reasons that are still unclear, these pressure areas change places at irregular intervals.

13. What is the Southern Oscillation? How is this related to El Niño?

In the Southern Oscillation, winds across the tropical Pacific reverse direction and blow from west to east—the trade winds weaken or reverse.

14. Why do fisheries on South America’s west coast decline—often dramatically—in El Niño years?

Upwelling within the nutrient-laden Peru Current is responsible for the great biological productivity of the ocean off the coasts of Peru and Chile. Although upwelling may continue during an ENSO event, the source of the upwelled water is nutrient-depleted water in the thickened surface layer approaching from the west (Figure 8.18). When the Peru Current slows and its upwelled water lacks nutrients, fish and seabirds dependent on the abundant life it contains die or migrate elsewhere.

15. How is La Niña different from El Niño?

La Niña is the usual configuration of equatorial winds in the Pacific basin.

16. How might weather in the western United States be affected by El Niño?

39 | P a g e


Greater evaporation of water from the warm ocean surface, combined with an increased number of winter storms steered into the western United States by the southward-trending jet stream, can double rainfall amounts and increase coastal erosion.

17. What drives the vertical movement of ocean water?

The slow circulation of water at great depths is driven by density differences rather than by wind energy. The whole ocean is involved in slow thermohaline circulation, a process responsible for the large-scale vertical movement of ocean water and the circulation of the global ocean as a whole.

18. What is the general pattern of thermohaline circulation?

Water sinks relatively rapidly in a small area where the ocean is very cold, but it rises much more gradually across a very large area in the warmer temperate and tropical zones. The continual diffuse upwelling of deep water maintains the existence of the permanent thermocline found everywhere at low and mid-latitudes.

19. What are water masses? What determines their relative position in the ocean?

A water mass has distinct temperature and salinity characteristics. The relative positions of water masses depend on their densities. Water masses don’t often mix easily when they meet due to their differing densities; instead, they usually flow above or beneath each other.

20. Where are distinct water masses formed?

The characteristics of each water mass are usually determined by the conditions of heating, cooling, evaporation, and dilution that occurred at the ocean surface when the mass was formed.

21. How does thermohaline circulation force the thermocline toward the ocean’s surface?

Water sinks relatively rapidly in a small area where the ocean is very cold, but it rises much more gradually across a very large area in the warmer temperate and tropical zones. The continual diffuse upwelling of deep water maintains the existence of the permanent thermocline found everywhere at low and mid-latitudes.

22. Compare the length of time required for completion of a circuit of surface circulation to that

40 | P a g e


needed for thermohaline circulation.

The circulation time of most deep water about 200 to 300 years. In contrast, a bit of surface water in the North Atlantic gyre may take only a little more than a year to complete a circuit.

23. Using common objects, could you conduct research on ocean currents?

Because they’re biodegradable and float with nearly even with the water surface (and are therefore not unduly influenced by winds), citrus fruits make great current trackers is enclosed harbors and bays. Farther afield, the dependable message-in-a-bottle works well. Just be sure to provide any reward you promise to the sender!

24. Traditional methods of studying currents are being replaced with high-tech devices. How do some of these work?

Modern research on currents is being carried out by devices that measure current speed by sensing the electromagnetic force generated by seawater as it moves in Earth’s magnetic field, Doppler current profilers that project beams of sonic pulses (“pings”) into the water each second, autonomous gliders like the Slocums, and other promising technologies.

25. How can chlorofluorocarbons (CFCs) be used as such tracers? Would CFC-based methods be equally suitable for analysis of surface currents and thermohaline circulation?

Because they dissolve easily in seawater, chlorofluorocarbons (CFCs) can be used as current tracers. A totally artificial chemical first produced in the 1930s for use as refrigerants, aerosol propellants, and blowing agents for foam, CFCs spread through the ocean like a dye, following oceanic circulation. The speed of thermohaline currents has been measured by careful analysis of their CFC content.

Chapter 9: WAVES1. I wrote that an ocean wave is, in a sense, an illusion. What’s actually moving in an ocean wave?

You can point to a wave crest and follow its progress, but only energy is moving long distances in ocean waves, not water mass.

2. Draw an ocean wave, and label its parts. Include a definition of wave period.

41 | P a g e


Draw the anatomy of a wind wave, and then check Figure 9.2.

3. Make a list of ocean waves, arranged by disturbing force and wavelength.

In wavelength order (shortest to longest): capillary waves, wind waves, seiches, tsunami, tides.

4. What is a gravity wave?

A wave with wavelength greater than 1.73 centimeters (0.68 inch) whose restoring forces are gravity and momentum.

5. What is restoring force?

Restoring force is the dominant force that returns the water surface to flatness after a wave has formed in it.

6. What defines a deep-water wave? Are there any waves that can never be in deep water, no matter how distant the seabed above which they are moving?

Deep-water waves move through water deeper than half their wavelength. Only capillary waves and wind waves can be in “deep” water.

7. What is the mathematical relationship between celerity (speed), wavelength, and wave period for deep-water waves? For shallow-water waves?

For deep-water waves, celerity (speed) may be expressed as: C= L

T

For shallow-water waves, celerity may be expressed as: C=√ gd

8. How are wind waves formed? What’s a fetch?

Wind waves form when a water surface irregularity deflects wind upward, slows it, and causes some of the wind’s energy to be transferred into the water to drive the wave crest forward. Fetch is the distance wind blows across the ocean to generate sets of wind waves.

42 | P a g e


9. How does the wavelength of a wind wave affect its speed?

Wavelength and wave speed are proportional in deep-water waves – the longer the wavelength, the greater the wave speed (C).

10. What is a fully developed sea?

In a fully developed sea the maximum wave size theoretically possible for a wind of a specific strength, duration, and fetch is reached.

11. How is group velocity different from the velocity of an individual wave within the group?

Though each individual wave moves forward with a speed proportional to its wavelength in deep water (C), the group velocity is only half that speed.

12. Can constructive or destructive interference ever be seen on a casual visit to the beach?

Constructive and destructive interference is often seen at wave-swept beaches. Do you notice that every 9th wave is the largest (or 12th, or 5th)? The cause is shown in Figure 9.13.

13. What’s a rogue wave? Are rogue waves potentially dangerous?

A rare confluence of crests at sea can form a rogue wave which would be much larger than any noticed before or after, and would be higher than the theoretical maximum wave capable of being sustained in a fully developed sea. Rogue waves have broken many large ships.

14. When does a wind wave become a shallow-water wave as it approaches shore?

A wave ceases to be in “deep” water when it moves over a seabed shallower than half the wave’s wavelength.

15. What factors influence the breaking of a wind wave?

A wave break is influenced by wavelength, bottom depth, bottom contour, bottom texture, wind conditions, and shore steepness.

43 | P a g e


16. What might cause waves approaching a shore at an angle to bend to break nearly parallel with the shore?

A wave approaching shore at an angle does not break simultaneously along its length because different parts of it are in different depths of water. The part of the wave line in shallow water slows down, but the attached segment still in deeper water continues at its original speed; so the wave line bends, or refracts.

17. Are the wave speed and period of an internal wave comparable to those of a wind wave? A tsunami?

Because the density difference between the joined media in internal waves is very small, their speed and period are very slow. They are not comparable to wind waves or tsunami.

18. Are internal waves dangerous?

Internal waves are not dangerous at the ocean surface, and pose a threat only to delicate oceanographic sensing equipment or (rarely) submariners.

19. Is there really any such thing as a true “tidal wave?”

True “tidal waves” cause the tides. You’ll learn about these largest of all waves in the next chapter.

20. What causes a storm surge? Why is a storm surge so dangerous?

The low atmospheric pressure associated with a great storm will draw the ocean surface into a broad dome which accompanies the storm to shore, becoming much higher as the water gets shallower at the coast. They are dangerous because of their height and sudden onslaught.

21. Can a storm surge be predicted?

Storm surge can be predicted from a tropical cyclone’s wind speed, probable path, and atmospheric pressure.

22. Lake Michigan is long and narrow and trends north-south. Could a seiche develop in this lake? Do seiches tend to be dangerous?

44 | P a g e


Seiches form in Lake Michigan as persistent north winds drive water toward the southern shore. When the wind ceases, parts of the Lake rocks rhythmically for a day or two. Seiches are generally not dangerous, but there are exceptions. A rare confluence of high wind and low atmospheric pressure generated a seiche in Lake Michigan in 1954 that drowned eight fishermen.

23. What would a standing wave look like in a rectangular swimming pool?

As any active kid knows, swimming pools can easily be seiched. Stand in the middle with a kick-board (surfboard, etc.) and make waves by pushing the board away from you and pulling it back. Find the natural resonance of the pool and reinforce it (that is, time your pushes as you would push a child on a swing). Soon the center of the pool will be high when the edges are low, and vice versa. Add more energy and watch the fun!

24. What causes tsunami? Do all geological displacements cause tsunami?

Tsunami are caused by the rapid displacement of ocean water.

25. How fast does a tsunami move?

Tsunami move at high speeds – 750 kilometers (470 miles) per hour is typical.

26. Is a tsunami a shallow-water wave or a deep-water wave?

Tsunami are shallow-water waves. Half their wavelength would be 100 kilometers (62 miles), and even the deepest ocean trenches do not exceed 11 kilometers (7 miles) in depth.

27. What is the wave height of a typical tsunami away from land? Are tsunami dangerous in the open sea?

A ship on the open ocean that encounters a tsunami with a 16-minute period would rise to a crest only 0.3 to 0.6 meter (1 or 2 feet) above average sea level. Tsunami are not dangerous in the open ocean.

28. Does a tsunami come ashore as a single wave? A series of waves? Does a tsunami wave break like a surfing wave?

Unless the location is very close to the causal epicenter, tsunami typically come ashore as a series of wave at regular intervals.

45 | P a g e


29. What caused the most destructive tsunami in recent history? Where was the loss of life and property concentrated?

The 2004 Indonesian event was the most lethal earthquake in five centuries. The numbers of dead exceeded 176,000 with another 67,000 missing.

30. How might one detect and warn against tsunami?

Tsunami warning systems depend on seabed seismometers, and submerged devices and satellites that watch the shape of the sea surface.

Chapter 10: TIDES1. How is a forced wave different from a free wave?

Tide waves are called forced waves because they are never free of the forces that cause them. In contrast, after they are formed, wind waves, seiches, and tsunami are free waves -- they are no longer being acted upon by the force that created them and they do not require a maintaining force to keep them in motion.

2. What celestial bodies are most important in determining tides?

The position and proximity of the moon makes the most important contribution to tidal patterns. The sun’s influence on the tides is only 46% that of the moon’s.

3. In general terms, how is the pull of gravity between two bodies related to their distance?

The pull of gravity between two bodies is proportional to the masses of the bodies but inversely proportional to the square of the distance between them.

4. What is a tractive force? How is it generated?

The combined outward-flinging force of inertia and inward-pulling force of gravity are called tractive forces. Gravity and inertia don’t always act in exactly the same balanced way on each particle of Earth and moon; the tractives forces are the net strength and direction that result when the two forces are combined (Figure 10.5). The key to understanding tides is to imagine Earth turning beneath bulges of water formed by tractive forces (as in Figure 10.7).

46 | P a g e


5. What body generates the strongest tractive forces?

Because of its proximity to Earth, the moon generates the strongest tractive forces.

6. What is a spring tide? A neap tide?

Spring tides occur when Earth, moon, and sun are aligned (Figure 10.11a). Neap tides occur when Earth, moon, and sun form a right angle (Figure 10.11b).

7. How does the equilibrium theory of tides differ from the dynamic theory?

The dynamic theory correctly treats tide waves as shallow-water waves. As Earth turns, landmasses divert, slow, and otherwise complicate the movements of tidal crests. This interference produces different patterns in the arrival of tidal crests at different places.

8. Are tides always shallow-water waves? Are they ever in “deep” water?

Because of their immense wavelength, tides can never be in “deep” water (that is, water deeper than half the wavelength), even though their crests may traverse abyssal depths.

9. What tidal patterns are observed on the world’s coasts?

Some coastlines experience semidiurnal (twice daily) tides: two high tides and two low tides of nearly equal level each lunar day. Others have diurnal (daily) tides: one high and one low. Coastlines with mixed (or semidiurnal mixed) tides have successive high tides or low tides of significantly different heights, caused by blending of diurnal and semidiurnal tides. Figure 10.13 shows an example of each tidal pattern.

10. Are there tides in the open ocean?

Tidal crests rotate around amphidromic points – “no tide” points in the open ocean (Figure 10.15). Because of the shape and placement of land masses around ocean basins, the tidal crests and troughs cancel each other at these points.

11. How does basin shape influence tidal activity?

The largest tidal ranges occur at the edges of the largest ocean basins, especially in bays or inlets that concentrate tidal energy because of their shape. If the basin is narrow and

47 | P a g e


restricted, the tide wave crest cannot rotate around an amphidromic point and simply moves into and out of the bay. In other cases, arriving tide crests stimulate natural oscillation periods of around 12 or 24 hours, resulting in extreme tides.

12. What’s a tidal bore?

A tidal bore is a steep wave moving upstream generated by the action of the tide crest in the enclosed area of a river mouth.

13. What is a meteorological tide?

Meteorological tides are weather-related alterations to predicted tidal cycles, such as those associated with the storm surge of tropical cyclones.

14. Can astronomical and meteorological tides interact?

Arrival of a storm surge on top of a high tide can be especially devastating to coastal regions. Some of the astonishing destructiveness of Hurricane Katrina in 2005 can be attributed to the arrival of the surge (and wind-driven masses of water) coincidentally with a high tide.

15. Distinct zones of marine organisms can usually be seen along rocky shores. How might tidal patterns result in this sort of differential growth?

Within the intertidal zone, organisms are exposed to varying amounts of emergence and submergence. The animals and plants sort themselves into horizontal bands based on the amount of exposure they can tolerate. Each distinct zone is an aggregation of animals and plants best adapted to the conditions within a particular narrow habitat.

16. Where is electrical power being generated from tidal movement?

There are major tidal power stations in France on the estuary of the river Rance and on the Annapolis River in Nova Scotia. The system in Strangford Lough, Northern Ireland, is also on line.

17. Why isn’t tidal power being developed more aggressively?

Tidal power plants can be damaged by storms and corroded by seawater. Computer simulations have suggested that installing a dam would change the resonance modes of a bay or

48 | P a g e


estuary—and therefore the height of the tide wave. Studies also suggest that sensitive planktonic and benthic marine life would be disrupted.

Chapter 11: COASTS1. How is a shore different from a coast?

The place where ocean meets land is usually called the shore. Coast refers to the larger zone affected by the processes that occur at this boundary.

2. What factors affect sea level and the location of a coast?

Sea level depends on the amount of water in the world ocean, the volume of the ocean’s “container,” and the temperature of the water (water expands as it warms). Tectonic forces of uplift and subsidence (along with isostatic equilibrium) determine the position of the shore.

3. How is an erosional coast different from a depositional coast?

Erosional coasts are new coasts in which the dominant processes are those that remove coastal material. Depositional coasts are usually older coasts that are steady or growing because of their rate of sediment accumulation.

4. What wears down erosional coasts?

Erosional coasts are shaped and attacked from the land by stream erosion, abrasion by wind-driven grit, glacial activity, rainfall, dissolution by acids from soil, and slumping. From the sea, large storm surf routinely generates tremendous pressures. Tiny pieces of sand, bits of gravel, or stones hurled by the waves are effective at eroding the shore.

5. What are some features common to erosional coasts?

Common features include sea cliffs, sea caves, and wave-cut platforms just offshore. Much of the debris removed from cliffs during the formation of these structures is deposited in the quieter water farther offshore, but some can rest at the bottom of the cliffs as exposed beaches.

6. Over time, coastal erosion tends to produce a straight shoreline. Why?

49 | P a g e


Because of wave refraction, wave energy is focused onto headlands and away from bays by wave refraction .Over time, coastal erosion tends to produce a straight shoreline.

7. How might volcanic activity shape a coast?

As we saw in Chapter 4, most islands that rise from the deep ocean are of volcanic origin. If the volcanism has been recent, the coasts of a volcanic island will consist of lobed lava flows extending seaward, common features in the Hawaiian Islands. Craters at the coast may fill with seawater after volcanic activity has slowed.

8. Do erosional coasts tend to evolve into depositional coasts, or is it the other way around?

Over time, erosional shorelines can evolve into depositional ones.

9. What is the most common feature of a depositional coast?

The most familiar feature of a depositional coast is the beach.

10. What two marine factors are most important in shaping beaches?

Tidal range, pattern, and height – coupled with wave action – are the most important factors determining beach profile.

11. How does sand move on a beach?

The movement of sediment along the coast, driven by wave action, is referred to as longshore drift. Longshore drift occurs in two ways: the wave-driven movement of sand along the exposed beach, and the current-driven movement of sand in the surf zone just offshore.

12. Distinguish between sand spits and bay mouth bars.

A bay mouth bar forms when a sand spit closes off a bay by attaching to a headland adjacent to the bay.

13. What is the difference between sea islands and barrier islands?

50 | P a g e


Barrier islands are narrow, exposed sandbars that are parallel to but separated from land. Unlike barrier islands, sea islands contain a firm central core that was part of the mainland when sea level was lower.

14. Why don’t deltas form at every river mouth?

A broad continental shelf must be present to provide a platform on which sediment can accumulate to form a delta. Tidal range must be low, and waves and currents generally mild. Deltas are most common on the low-energy shores of enclosed seas (where the tidal range is not extreme) and along the tectonically stable trailing edges of some continents.

15. What organisms can affect coastal configuration?

Coral animals, some forms of cyanobacteria, and mangroves are all effective at modifying coastlines. The greatest of all biologically modified coasts is the Great Queensland Barrier Reef in Australia.

16. What is an estuary?

An estuary is a body of water partially surrounded by land, where fresh water from a river mixes with ocean water.

17. Estuaries are classified by their origins. What types of estuaries exist?

By origin, estuary types are drowned river mouths, fjords, bar-built, or tectonic.

18. Estuaries are also classified by the type of water they contain and the flow characteristics of that water. How are estuaries classified by water circulation patterns?

By water circulation patterns, estuaries are classified as salt-wedge, well-mixed, partially mixed, and reverse estuaries.

19. Of what value are estuaries?

Estuaries often support a tremendous number of living organisms. The easy availability of nutrients and sunlight, protection from wave shock, and the presence of many habitats permit the growth of many species and individuals. Estuaries are frequently nurseries for marine animals; several species of perch, anchovy. Unfortunately for their inhabitants, the high demand for development is incompatible with a healthy estuarine ecosystem.

51 | P a g e


20. Briefly compare the U.S. Pacific, Atlantic, and Gulf coasts. What are the most important forces influencing these coasts?

The Pacific coast is an actively rising margin on which volcanoes, earthquakes, and other indications of recent tectonic activity are easily observed. Most of the sediments on the Pacific coast originated from erosion of relatively young granitic or volcanic rocks of nearby mountains. The Atlantic coast is a passive margin, tectonically calm and subsiding because of its trailing position on the North American Plate. Subsidence along the coast has been considerable—3,000 meters (10,000 feet) over the last 150 million years. A deep layer of sediment has built up offshore, material that helped produce today’s barrier islands. The Gulf coast experiences a smaller tidal range and—hurricanes excepted—a smaller average wave size than either the Pacific or Atlantic coasts. Reduced longshore drift and an absence of interrupting submarine canyons allow the great volume of accumulated sediments from the Mississippi and other rivers to form large deltas, barrier islands, and a long raised “super berm” that prevents the ocean from inundating much of this sinking coast.

21. Generally speaking, would you say human intervention in coastal processes has been largely successful in achieving long-term goals of stabilization?

Steps taken to preserve or “improve” a stretch of coast may have the opposite effect, and coastal residents do not always learn by example. Intervention in coastal processes is almost always costly and temporary.

22. Again, generally speaking, would you say beaches on U.S. coasts are growing, shrinking, or staying about the same size?

Because sediment flow into coastal cells has lessened due to dams and sediment diversion, United States beaches are generally shrinking.

Chapter 12: LIFE IN THE OCEAN1. What do I mean when I write “all life in Earth is fundamentally the same?” A shark and a seaweed don’t seem similar.

A shark and a seaweed are certainly superficially dissimilar, but the physical and biochemical organization of the cells that comprise both is startling in its similarity. On the molecular level, there are surprisingly few differences.

52 | P a g e


2. Is evolution by natural selection a random process?

Although mutations occur randomly, evolution by natural selection is anything but random. The natural environment winnows favorable mutations from unfavorable ones—hence the origin of the term natural selection.

3. How is evolution by natural selection thought to operate?

Write a summary of the steps, and then check the list in the chapter.

4. How are new species thought to originate?

Species can arise by physical isolation. Because the number of breeding animals within an isolated species may be small, evolutionary change may be rapid. Generation after generation, the species will change relatively rapidly to suit its new habitat.

5. What’s convergent evolution?

Since physical conditions in the open ocean are relatively uniform, large marine animals with similar life-styles but different evolutionary heritages eventually tend to look much the same. That is, similar conditions may result in coincidentally similar organisms.

6. How is a natural system of classification different from an artificial system?

A natural system of classification for living organisms relies on organism's evolutionary history and developmental characteristics. Any system dependent on other schemes is artificial – that is, it does not reflect the underlying biological relationships between categorized organisms.

7. What are the three domains of living things?

Bacteria, Archaea, and Eukarya

8. How are organisms named?

Linnaeus's system of classification was decidedly natural. Though Darwin's insights into evolutionary relationships were nearly a century in the future, Linnaeus's understanding of the relationships between organisms, and his ability to arrange organisms into like categories, was remarkable. His was a system of classification based on hierarchy, a grouping of objects by degrees of complexity, grade, or class. In this boxes-within-boxes approach, sets of small

53 | P a g e


categories are nested within larger categories. Linnaeus devised names for the categories, starting with kingdom (the largest category) and passing down through phylum, class, order, family, and genus, to species (the smallest category).

9. How does an atom of iron in steel differ from an atom of iron in your blood?

An atom of iron is an atom of iron wherever it is found. There are no differences in the structure of an iron atom incorporated into a hemoglobin molecule and an atom or iron holding up a bridge. The definition of life depends on the manipulation of energy, not the physical composition of the objects themselves.

10. What are the starting products for photosynthesis? The end products?

Photosynthesis requires carbon dioxide, water, and light energy. The carbohydrate glucose and oxygen are end products.

11. How is chemosynthesis different from photosynthesis?

Chemosyntheis does not require light, but instead releases the energy held in chemical bonds in molecules of simple hydrogen- and sulfur-containing compounds to construct glucose from carbon dioxide.

12. What do primary producers produce? How is productivity expressed?

The immediate organic material produced is the carbohydrate glucose. Primary productivity is expressed in grams of carbon bound into organic material per square meter of ocean surface area per year (gC/m2/yr).

13. What is a trophic pyramid? What is the relationship of organisms in a trophic pyramid? Does this have anything to do with food webs? How?

A trophic pyramid is a representation of mass flow through a system of producers and consumers . A food web a more accurate representation of what actually happens: a group of organisms interlinked by complex feeding relationships in which the flow of energy can be followed from primary producers through consumers.

A trophic pyramid implies an oversimplistic view of a marine community. Real communities are more accurately described as food webs, an example of which is provided as Figure 12.15. A food web is a group of organisms linked by complex feeding relationships in which the flow of energy can be followed from primary producers through consumers. Organisms in a food web almost always have some choices of food species.

54 | P a g e


14. What is an extremophile?

Extremophiles are capable of life under extreme conditions of temperature, salinity, pressure, or chemical stress.

15. What is an autotroph? A heterotroph? How are they similar? How are they different?

Autotrophs make their own food. The bodies of autotrophs are rich sources of chemical energy for any organisms capable of consuming them. Heterotrophs are organisms (such as animals) that must consume food from other organisms because they are unable to synthesize their own food molecules.

16. What’s a limiting factor? Can you provide an example?

Often too much or too little of a single physical factor can adversely affect the function of an organism. Lack of light would be limiting to a photosynthetic organism.

17. How characterizes the photic, euphotic, and disphotic zones?

Light illuminates the entire photic zone (during the day). The euphotic zone is the upper segment of the photic zone in which illumination is sufficient for photosynthesis to occur. The disphotic zone, while still lit, is too dark to support photosynthesis.

18. How does metabolic rate vary with temperature?

An organism's metabolic rate increases with temperature. Clearly there is an upper limit – too much heat and the organism cooks.

19. How do dissolved gas concentrations vary with temperature? Now look at your answer to the last question. Do you see a problem for marine organisms?

Colder water contains more gas at saturation. Metabolic rates rise with rising temperature. As temperature rises, metabolic demand for oxygen will exceed supply which may lead to the death of the plants and animals in the area.

20. Does the great hydrostatic pressure of the seabed crush organisms?

55 | P a g e


Land animals live in air pressurized by the weight of the atmosphere above them. Pressures inside and outside an organism are virtually the same, both in the ocean and at the bottom of the atmosphere. Nobody gets mashed.

21. How is diffusion different from osmosis?

Liquids and gases diffuse through water from zones of high concentration to zones of low concentration. Osmosis is more specialized -- it is diffusion of water through a membrane.

22. Can you think of any way to prevent a cataclysmic asteroid or comet impact once the object’s path has been shown to be on a certain collision course?

The near-space environment is being scanned for Earth-crossing comets and asteroids (bodies whose orbits intersect that of the Earth). The resources dedicated to this task are meager, however, and it will be decades before most of the potential threats are catalogued. Congress has not supported a significant increase in funds for this purpose, and the attention of the public waxes and wanes with Hollywood’s interest in the topic.

Some indication of public response can be gleaned from the same Hollywood movies. Among the earliest and best of these is a 1950s George Pal production titled “When Worlds Collide” that greatly influenced me to study science when I was a small and impressionable boy. In that memorable film, a select few folks left Earth in large transport ships moments before the collision to settle on another world. A better solution (or so it seems to me) would be to identify and then deflect any incoming asteroids. How might that deflection be accomplished? With the NASA budget being cut, one wonders.

23. Do you think all life on Earth would be wiped out by a huge impactor?

Life is tenacious. Unless surface temperatures rose everywhere to high temperatures, some extremophiles might survive. Given another few hundreds of millions of years, evolutionary processes would again produce some interesting organisms.

24. Why do we see relatively few impact craters on Earth?

Because, unlike the Moon or Mars, our active atmosphere supplies erosive water to scour the surface, erasing the images of impacts more than a few million years old. And don’t forget about the recycling of Earth’s surface by tectonic processes (Chapter 3).

Chapter 13: PELAGIC COMMUNITIES

56 | P a g e


1. How is a community different than a population?

A community is comprised of the many populations of organisms that interact with one another at a particular location. A population is a group of organisms of the same species occupying a specific area. The location of a community, and the populations that comprise it, depend on the physical and biological characteristics of that living space.

2. How are benthic communities different from pelagic communities?

Benthic organisms live on or in the bottom; pelagic organisms live suspended in the water column.

3. How is a niche different from a habitat?

There are many different places to live and many different "jobs" for organisms within even a simple community. Those “jobs” are called niches. A habitat is an organism's "address" within its community, its physical location. Each habitat has a degree of environmental uniformity. An organism's niche is its "occupation" within that habitat, its relationship to food and enemies, an expression of what the organism is doing. For example, the small fishes living among the coral heads in a coral reef community share the same habitat, but each species has a slightly different niche. Each population in the community has a different "job" for which its shape, size, color, behavior, feeding habits, and other characteristics particularly suit it.

4. Distinguish between the pelagic and neritic zones.

Pelagic denotes the open ocean. The neritic division of the pelagic realm is the open ocean found relatively close to land – over the continental shelves, for example.

5. Where would you look for a benthic organism?

On (or in) the ocean floor.

6. What distinguishes pelagic communities from benthic communities?

Pelagic organisms live suspended in seawater, while benthic organisms (which you will meet in the next chapter) live on or in the ocean bottom

7. How are plankton different from nekton? Into which category would most fishes fit?

57 | P a g e


The pelagic organisms that constitute plankton are as important as they are inconspicuous. The word is derived from the Greek word planktos, meaning “wandering.” . The plankton drift or swim weakly, going where the ocean goes, unable to move consistently against waves or current flow. The nekton are pelagic organisms that actively swim. Most fishes are nektonic as adults.

8. Why did I write that plankton is an “artificial category” of organisms?

The plankton contains many different plant-like species and virtually every major group of animals. Thus, the term plankton is not a collective natural category like mollusks or algae, which would imply an ancestral relationship between the organisms; instead it describes a basic ecological connection.

9. Are all plankters plants?3 All animals?

The plankton contains many different plant-like species and virtually every major group of animals. Members of the plankton community, informally referred to as plankters, can and do interact with one another: There is grazing, predation, parasitism, and competition among members of this dynamic group.

10. Are all members of the plankton community capable of being collected using nets?

Very small plankton can slip through a plankton net. Their capture and study requires concentration by centrifuge, or entrapment by a fine plankton filter through which water is drawn. The filter is later disassembled and the plankton studied in place. The smallest of plankton is trapped by specially made unglazed porcelain filters through which water is forced under very high pressure.

11. What is a “photosynthetic autotroph?” Can you give a non-marine example?

Photosynthetic autotrophs construct food molecules (usually the carbohydrate glucose) from water and carbon dioxide using light energy (the sun). Autotrophic plankton are generally called phytoplankton, a term derived from the Greek word phyton, meaning “plant.” A huge, nearly invisible mass of phytoplankton drifts within the sunlit surface layer of the world ocean.

The roses blooming in your garden are also photosynthetic autotrophs.

12. How are phytoplankton different from zooplankton? Which category represents autotrophs?

3 Members of the plankton community, informally referred to as plankters, can and do interact with one another

58 | P a g e


Phytoplanktonic organisms are photosynthetic autotrophs. Zooplankton are heterotrophic – that is, they consume autotrophic organisms (or organisms that consumed autotrophs).

13. Why was the activity of picoplankton overlooked until quite recently?

These organisms are often too small to be resolved by light microscopes and slip undetected through all but the finest filters. Their size, typically about 0.2 to 2 micrometers (4 to 40 millionths of an inch) across, is made up for by their abundance: an astonishing 100 million in every liter of seawater, at all depths and latitudes!

14. I wrote of an “black-market economy” in the microbial loop. Why isn’t this “economy” available to the typical consumers of phytoplankton?

The microbial loop is a complete microecosystem—a community operating on the smallest possible scale—that manufactures and consumes particulate and dissolved carbon in amounts almost beyond comprehension. They function as a sort of ecological black market below the “official economy” of the relatively huge diatoms and dinoflagellates. As if they weren’t busy enough, these heterotrophic bacteria also decompose organic material spilled into the water when phytoplankton are eaten by zooplankton, turn soluble organic materials released by zooplankton back into inorganic nutrients, and break down particulate organic matter into a dissolved form they can consume for their own growth. Biological oceanographers now believe that the greatest fraction of organic particles in the water column of the open ocean is composed of these metabolically active heterotrophic bacterial cells operating in this microbial loop (Figure 13.7). This “black market economy” is almost certainly as productive as the “official economy.” It is not available to fishes and other larger consumers because the small animals on which they prey are unable to separate these exceedingly small organisms from the surrounding water. Microconsumers simply utilize the carbon and shuttle the metabolic products back to the small cyanobacterial producers.

15. Which group of relatively large single-celled autotrophs dominates the phytoplankton ? Why are they important?

Apart from cyanobacteria, the most productive photosynthetic organisms in the plankton are the diatoms. Diatoms evolved comparatively recently, and began to dominate phytoplanktonic productivity in the Cretaceous period about 100 million years ago. Their abundance and photosynthetic efficiency increased the proportion of free oxygen in Earth’s atmosphere. More than 5,600 species of diatoms are known to exist. The larger species are barely visible to the unaided eye.

59 | P a g e


16. How is the covering (shell, or test) of a diatom different from that of a dinoflagellate?

A diatom’s consists of silica (SiO2), giving this heavy but beautiful covering the optical, physical, and chemical characteristics of glass—clearly an ideal protective window for a photosynthesizer. A dinoflagellate’s covering is often of a cellulose-like compound, neither completely transparent nor completely rigid.

17. Which planktonic organisms are usually responsible for HABs? Can a HAB event be harmful to people?

Some species of dinoflagellates can become so numerous that the water turns a rusty red as light reflects from the accessory pigments within each cell. These species are responsible for harmful algal blooms -- HABs (Figure 13.6b). During times of such rapid growth (usually in springtime), concentration of these microscopic organisms may briefly reach 6 million per liter (23 million per gallon)! At night, the huge numbers of dinoflagellates in a HAB (also called a “red tide”) can cause breaking waves to glow a bright blue, a phenomenon known as bioluminscence.

HABs can be dangerous because some dinoflagellate species synthesize potent toxins as byproducts of metabolism. Among the most effective poisons known, these toxins may affect nearby marine life or even humans. Some of the toxins are similar in chemical structure to the muscle relaxant curare, but are tens of times more powerful. Humans should avoid eating certain species of clams, mussels, and other filter feeders during summer months when toxin-producing dinoflagellates are abundant in the plankton. If shellfish from a particular area are unsafe, a state governmental agency will issue an advisory which may remain in effect for six weeks or more until the danger is past.

18. Why are the open tropical oceans essentially oceanic deserts?

The open tropical oceans have abundant sunlight and CO2 but are generally low in surface nutrients because the strong thermocline discourages the vertical mixing necessary to bring nutrients from the lower depths. The tropical oceans away from land are therefore oceanic deserts nearly devoid of visible (that is, non-cyanobacterial) plankton. The typical clarity of tropical water underscores this point. In most of the tropics productivity rarely exceeds 30 g C/m2/yr, and seasonal fluctuation in productivity is low.

19. If the polar oceans are lighted 24-hours a day in the local summer, why isn’t total annual productivity high?

At very high latitudes the low sun angle, reduced light penetration due to ice cover, and weeks or months of darkness in winter severely limit productivity. At the height of summer, however, 24-hour daylight, a lack of surface ice, and the presence of upwelled nutrients can lead

60 | P a g e


to spectacular plankton blooms. The surface of some sheltered bays can look like tomato or split-pea soup because dinoflagellates and other plankton are so abundant. This bloom cannot last because nutrients are not quickly recycled and because the sun is above the critical angle for a few weeks at best. The short-lived summer peak does not compensate for the long, unproductive winter months.

20. Choosing between the polar, tropical, and temperate zones, which part of the ocean are the most productive over a year’s time?

With the tropics generally out of the running for reasons of nutrient deficiency and the north polar ocean suffering from slow nutrient turnover and low illumination, the overall productivity prize is left to the temperate and southern subpolar zones. Thanks to the dependable light and the moderate nutrient supply, annual production over temperate continental shelves and in southern subpolar ocean areas is the greatest of any open ocean area.

21. How are zooplankton different from phytoplankton?

Heterotrophic plankton—the planktonic organisms that eat the primary producers—are collectively called zooplankton. Phytoplankton are autotrophic (primary producers).

22. How are holoplankton different from meroplankton?

Most zooplankton spend their whole lives in the plankton community, so we call them holoplankton. But some planktonic animals are the juvenile stages of crabs, barnacles, clams, sea stars, and other organisms that will later adopt a benthic or nektonic lifestyle. These temporary visitors are meroplankton (Figure 13.13). Most animal groups are represented in the meroplankton; even the powerful tuna serves a brief planktonic apprenticeship. These useful categories can be applied to phytoplankton as well as zooplankton. Holoplanktonic organisms are by far the most numerous forms of both phytoplankton and zooplankton.

23. Why are krill important?

One of the ocean’s most important zooplankters is the pelagic arthropod known as krill (genus Euphausia), the keystone of the Antarctic ecosystem. This thumb-sized shrimplike crustacean mostly grazes on the abundant diatoms of the southern polar ocean. In turn, krill are eaten in tremendous numbers by seabirds, squids, fishes, and whales. Some 500 to 750 million metric tons (550 to 825 million tons) of krill inhabit the Antarctic Ocean, with the greatest concentrations in the productive upwelling currents of the Weddell Sea. Krill travel in great schools that can extend over several square miles, and collectively exceed the biomass of Earth’s entire human population! They behave more like schooling fish than planktonic crustaceans.

61 | P a g e


24. How is nekton different from plankton?

The pelagic organisms that constitute plankton are as important as they are inconspicuous. The word is derived from the Greek word planktos, meaning “wandering.” . The plankton drift or swim weakly, going where the ocean goes, unable to move consistently against waves or current flow. The nekton are pelagic organisms that actively swim. Most fishes are nektonic as adults.

25. How is an invertebrate different from a vertebrate?

Most nektonic animals are vertebrates (animals with backbones, such as fishes, reptiles, marine birds, and marine mammals), but a few representatives are invertebrates (animals without backbones, such as squid and nautiluses, and some species of shrimp-like arthropods).

26. Which organisms are the most abundant and successful nektonic invertebrates? Vertebrates?

Arthropoda, the animal category that includes the copepods (Figure 13.12), krill (Figure 13.14) lobsters, shrimp, crabs, and barnacles is the most successful animal group on Earth.

Fishes are the most abundant and successful vertebrates. There are more species of fishes, and more individuals, than species and individuals of all other vertebrates combined.

27. What adaptations contribute to the success of fishes?

Seawater may seem to be an ideal habitat, but living in it does present difficulties. These most successful vertebrates have structures and behaviors to cope. Among them are adaptations of movement, shape, and propulsion. Active fish usually have streamlined shapes that make their propulsive efforts more effective. A fish's resistance to movement, or drag, is determined by frontal area, body contour, and surface texture. A fish's forward thrust comes from the combined effort of body and fins. Muscles within slender flexible fish (such as eels) cause the body to undulate in S-shaped waves that pass down the body from head to tail in a snake-like motion. Advanced fishes have a relatively inflexible body, which undulates rapidly through a shorter distance, and a hinged scythe-like tail to couple muscular energy to the water. Maintenance of level is crucial to any swimming animal. The density of fish tissue is typically greater than that of the surrounding water, so fishes will sink unless their weight is offset by propulsive forces or by buoyant gas- or fat-filled bladders. Cartilaginous fishes have no swim bladders and must swim continuously to maintain their position in the water column. Bony fishes that appear to hover motionless in the water usually have well-developed swim bladders just below their spinal columns. The volume of gas in these structures provides enough buoyancy to offset the animal's weight. Gas exchange is also important: How can fish breathe underwater? Gas exchange, the process of bringing oxygen into the body and eliminating carbon

62 | P a g e


dioxide (CO2), is essential to all animals. Fish take in water containing dissolved oxygen at the mouth, pump it past fine gill membranes, and exhaust it through rear-facing slots. The higher concentration of free oxygen dissolved in the water causes oxygen to diffuse through the gill membranes into the animal; the higher concentration of CO2 dissolved in the blood causes CO2 to diffuse through the gill membranes to the outside. The gill membranes themselves are arranged in thin filaments and plates efficiently packaged into a very small space. Feeding and defense is also critical to success. Competitive pressure among the large number of fish species has caused a wonderful variety of feeding and defense tactics to evolve. Sight is very important to most fishes, enabling them to see their prey or avoid being eaten. Even some deep-water fishes that live below the photic zone have excellent eyesight for seeing luminous cues from potential mates or meals. Hearing is also well developed, as is the ability to detect low-frequency vibrations with the lateral-line system. More subtle means of offense or defense depend on trickery -- looking like something you're not, or changing color to blend with the background. These kinds of cryptic coloration or camouflage may be active or passive. Schooling behavior is also useful -- about a quarter of all bony fish species exhibit schooling behavior at some time during their life cycle. I can personally attest to the effectiveness of schooling as a means of defense. On a few diving trips I've noticed a large moving mass just beyond the limit of clear visibility. Is it a fish school, or is it a single large animal? Many predators might not stay around long enough to find out!

28. What are the largest animals ever to have lived on Earth? From what are they thought to have evolved?

The 79 living species of cetaceans (whales) are thought to have evolved from an early line of ungulates -- hooved land mammals related to today's horses and sheep -- whose descendants spent more and more time in productive shallow waters searching for food.

Chapter 14: BENTHIC COMMUNITIES

1. Where would you expect to find a benthic organism?

Benthic organisms live on or in the ocean bottom. Some benthic creatures spend their lives buried in sediment, others rarely touch the solid seabed; most attach to, crawl over, swim next to, or otherwise interact with the ocean bottom continuously throughout their lives.

2. What is implied in a random distribution of objects?

A random distribution implies that the position of one organism in a bottom community in no way influences the position of other organisms in the same community. A truly random

63 | P a g e


distribution indicates that conditions are precisely the same throughout the habitat, an extremely unlikely situation except possibly in the unvarying benthic communities of abyssal plains.

3. What is the rarest natural pattern of organisms?

Uniform distribution with equal space between individuals, such as the arrangement of trees we see in orchards, is the rarest natural pattern of all.

4. How can seaweeds (multicellular algae) survive without vessels to transport fluid and nutrients?

Algae is a collective term for autotrophs possessing chlorophyll and capable of photosynthesis but – unlike plants – lacking vessels to conduct sap. All parts of a seaweed are productive, so material is cycled (used) where it is made and needed. Land plants, by contrast, must conduct water and nutrients from roots to leaves, and then pay the roots for their efforts by transferring carbohydrates back down to the roots.

5. How are seaweeds classified?

Seaweeds are classified by the presence of accessory pigments, colored compounds in their tissues. These accessory pigments (or masking pigments) are light absorbing compounds closely associated with chlorophyll molecules. Accessory pigments may be brown, tan, olive green, or red; they are what give most marine autotrophs, especially seaweeds, their characteristic color. Multicellular marine algae are segregated into three divisions based on their observable color. The green algae, with their unmasked chlorophyll, are the Chlorophyta, the brown algae Phaeophyta, and the red algae Rhodophyta. Phaeophytes are most familiar to beachcombers, and rhodophytes the most numerous.

6. How can seaweeds photosynthesize below the depth to which red light penetrates?

Rhodophytes can live in surprisingly deep water. They excel in dim light because their sophisticated accessory pigments absorb and transfer enough light energy to power photosynthetic activity at depths where human eyes cannot see light. The record depth for a photosynthesizer is held by a small rhodophyte discovered in 1984 at a depth of 268 meters (879 feet) on a previously undiscovered seamount in the clear tropical Caribbean.

7. Give some examples of marine vascular plants. How are they different from seaweeds? Similar?

Seaweeds may look like plants, but they are actually a form of multicellular algae. The single-celled diatoms and dinoflagellates discussed in the last chapter are unicellular algae. As

64 | P a g e


we have seen, algae lack the vessels and other structural and chemical features of true plants. Nearly all large land plants are vascular plants. A few species of vascular plants have recolonized the ocean. All have descended from land ancestors, and all live in shallow coastal water. The most conspicuous marine vascular plants are the sea grasses and the mangroves.

Perhaps the most beautiful sea grass is the vivid, emerald-green surf grass, genus Phyllospadix, with its seasonal flowers and fuzzy fruit. These hardy plants survive in the turbulent, wave-swept intertidal and subtidal zones of temperate East Asia and western North America (Figure 14.6).

8. What makes estuaries so productive and high in biomass?

Primary productivity in estuaries is often extraordinarily high because of the availability of nutrients, the great variety of organisms present, strong sunlight, and the large number of niches. The mass of living matter per unit area in a typical estuary is among the highest per unit of surface area of any marine community.

9. Few habitats are as rigorous as rocky shores, yet a great many organisms have become adapted to these places. What advantages do rocky shores provide?

One reason for the great diversity and success of organisms in the rocky intertidal zone is the large quantity of food available. The junction between land and ocean is a natural sink for living and once-living material. The crashing of surf and strong tidal currents keep nutrients stirred and ensure a high concentration of dissolved gases to support a rich population of autotrophs. Minerals dissolved in water running off the land serve as nutrients for the inhabitants of the intertidal zone as well as for plankton in the area. Many of the larval forms and adult organisms of the intertidal community depend on plankton as their primary food source.

10. What specific defenses do organisms deploy to succeed in the rocky intertidal environment?

For intertidal areas exposed to the open sea, wave shock is a challenging physical factor. Motile animals, like crabs, move to protective overhangs and crevices where they cower during intense wave activity. Attached, or sessile, animals hang on tightly, often gaining assistance from rounded or very low profile shells, which deflect the violent forces of rushing water around their bodies. Some sessile animals have a flexible foot that wedges into small cracks to provide a good hold; others, like mussels, form shock-absorbing cables that attach to something solid.

11. What problems confront dwellers on sand beaches? What adaptations have evolved to allow success?

A beach is a forbidding place. Sand itself is the key problem. Many sand grains have

65 | P a g e


sharp pointed edges, so rushing water turns the beach surface into a blizzard of abrasive particles. Jagged grit works its way into soft tissues and wears away protective shells. A small organism's only real protection is to burrow below the surface, but burrowing is difficult without a firm footing. When the grain size of the beach is small, capillary forces can pin down small animals and prevent them from moving at all. If these organisms are trapped near the sand surface, they may be exposed to predation, to overheating or freezing, to osmotic shock from rain, or to crushing as heavy animals walk or slide on the beach.

12. Are sand or cobble beaches generally highly populated habitats?

No. Only a few specialized species can live in these places. Occasionally, when conditions are good, a population explosion of one of these species will occur, but such events are few and far between.

13. I have written (in Chapter 6 and 13) that the tropics are generally devoid of nutrients and support very little life. Why do tropical coral reefs support such huge numbers of life forms?

The key to the difference between the open tropical ocean and the tropical reefs lies in the productivity of the reefs themselves, wave-resistant structures dominated by strong and rigid masses of living (or once-living) organisms. Not all reefs are built of coral -- other reef builders include red and green algae, cyanobacteria, worms, even oysters -- but we think first of coral reefs when the words reef and tropics are mentioned together.

14. How is hermatypic coral different from ahermatypic coral?

Tropical reef-building corals are hermatypic, a term derived from the Greek word for mound-builder. Their bodies contain masses of tiny symbiotic dinoflagellates. Coral's success in the nutrient-poor water of the tropics depends upon its intimate biological partnership with specialized dinoflagellates. The microscopic dinoflagellates carry on photosynthesis, absorb waste products, grow, and divide within their coral host. The coral animals provide a safe and stable environment and a source of carbon dioxide and nutrients; the dinoflagellates reciprocate by providing oxygen, carbohydrates, and the alkaline pH necessary to enhance the rate of calcium carbonate deposition. The coral occasionally absorbs a cell, "harvesting" the organic compounds for its own use. The dinoflagellates are captive within the coral, so none of their nutrients are lost as they would be if the dinoflagellates were planktonic organisms that could drift away from the reef. Instead nutrients are used directly by the coral for its own needs. The cycling of materials is short, direct, quick, and very efficient.

Deepwater corals, know as ahermatypic corals, build smooth banks on the cold, dark, outer edges of temperate continental shelves from Norway to the Cape Verde Islands, and off New Zealand and Japan.

66 | P a g e


15. What is coral bleaching? What is thought to cause coral bleaching?

Marine biologists have been baffled by recent incidents of coral bleaching—corals expelling their symbiotic dinoflagellates (zooxanthellae)—in the Caribbean and tropical Pacific. As noted above, hermatypic corals depend on these dinoflagellates for a portion of their carbohydrate and oxygen requirements. For reasons that are not well understood, when water temperature exceeds a normal summer high by 1°C (1.8°F) or more for a few weeks, coral polyps eject their dinoflagellates, turn pale, and begin to starve. If the water temperature returns to normal in few weeks the coral can regain their algae populations and survive the bleaching event. If not, filamentous algae or other decomposers overtake the polyps. A coral reef’s ability to survive bleaching depends on the level of stress that it endures before and during such events. The warm El Niño year of 1998 saw the death of about 16% of living corals worldwide. As the ocean warms, bleaching events will probably be more widespread.

16. How are coral reefs classified?

As their name implies, fringing reefs cling to the margin of land. As can be seen in Figure 14.15a, a fringing reef connects to shore near the water surface. Fringing reefs form in areas of low rainfall runoff primarily on the lee (downwind side) of tropical islands. The greatest concentration of living material will be at the reef's seaward edge where plankton and clear water of normal salinity are dependably available. Most new islands anywhere in the tropics have fringing reefs as their first reef form. Permanent fringing reefs are common in the Hawaiian Islands and in similar areas near the boundaries of the tropics.

Barrier reefs are separated from land by a lagoon (Figure 14.15b). They tend to occur at lower latitudes than fringing reefs, and can form around islands or in lines parallel to continental shores. The outer edge -- the barrier -- is raised because the seaward part of the reef is supplied with more food and is able to grow more rapidly than the shore side. The lagoon may be from a few meters to 60 meters (200 feet) deep, and may separate the barrier from shore by only tens of meters, or by 300 kilometers (190 miles) in the case of northeastern Australia's Great Barrier Reef. Coral grows slowly within the lagoon because fewer nutrients are available and because sediments and fresh water run off from shore. As you would expect, conditions and species within the lagoon are much different from those of the wave-swept barrier. The calm lagoon is often littered with eroded coral debris moved from the barrier by storms. The Australian Barrier Reef is the largest biological construction on the planet.

An atoll (Figure 14.15c and d) is a ring-shaped island of coral reefs and coral debris enclosing, or almost enclosing, a shallow lagoon from which no land protrudes. Coral debris may be driven onto the reef by waves and wind to form an emergent arc on which coconut palms and other land plants can take root. These plants stabilize the sand and lead to colonization by birds and other species. Here is the tropical island of the travel posters.

17. How are atolls thought to have been formed?

67 | P a g e


A quick review of Figure 14.15 will remind you that coral grows upward as an island’s fringing reef sinks. In this case, the island does not sink at a rate faster than coral organisms can build upward.

18. What is the most striking feature of the deep-sea floor?

The relative richness of species diversity, in my opinion (see next answer). Also, the adaptations to this habitat (which include gigantism, chemosynthesis, and extremely long lifespans, to name a few).

19. Which generally contains more organisms per unit area – an intertidal sandy beach or a typical sedimentary deep bottom habitat?

Most of the deep-ocean floor is an area of endless sameness. It is eternally dark, almost always very cold, slightly hypersaline (to 36‰), and highly pressurized. Scientists once thought that such rigors would limit the extent of communities there. Not so. In the 1980s researchers investigating bottoms at depths between 1,500 and 2,500 meters (5,000 to 8,000 feet) found an average of nearly 4,500 organisms per square meter. There were 798 species recorded in 21 1m2 samples, 46 of which were new to science!

20. What unique features are shared by organisms in deep rock communities?

These chemosynthetic organisms have a very slow metabolism, are able to tolerate extremes of temperature and pH and pressure, and are exceedingly small. Conditions on Earth at the time of the origin of life were hot and oxygen-free, and the genetic make-up of these bacteria and archaeans suggests they’ve evolved more slowly and in different directions than other forms of life here.

21. Why do deep vent communities depend on chemosynthesis to produce carbohydrates? Isn’t photosynthesis more efficient?

Photosynthesis is very efficient if light is available. Other less-efficient energy-binding pathways evolved in its absence.

22. Could deep vent organisms colonize ocean surface environments – tidal pools, for example?

Very unlikely. The slow growing pogonophorans and other vent invertebrates would be subject to rapid predation, their enzymes would be unsuited to surface conditions, and they’d roast in the sun. Their symbiotic bacteria would be especially displeased, one should think.

68 | P a g e


23. How do you suppose organisms sense the presence of a whale fall?

As sulfide produced by these bacteria diffuses out of the bone, planktonic larvae of vent organisms might sense its presence—perhaps by smell or another chemical signal -- settle, grow, and reproduce. With luck, their offspring might drift to another whale fall and repeat the process.

24. Why would “stepping stones” be needed between vent communities? How could a whale fall act as a “stepping stone?”

Even though humans have greatly diminished the numbers of living whales, researchers estimate that whale carcasses may be spaced at roughly 25 kilometer (16 mile) intervals across areas like the North Pacific. If a vent community were to “go quiet” (that is, if the vents ceased to be geologically active), the larvae of the residents might be capable of drifting toward a (relatively) nearby whale fall, but not all the way to a new and distant vent. Repeat the process a few times, and a new vent system could be colonized.

Chapter 15: USES AND ABUSES OF THE OCEAN

1. Human population grew explosively in the last century. Is the number of humans itself the main driver of resource demand?

The human population grew by 400% during the twentieth century. This growth, coupled with a 4.5-fold increase in economic activity per person, resulted in accelerating exploitation of Earth’s resources. By most calculations we have used more natural resources since 1955 than in all of recorded human history up to that time.

2. Distinguish between physical and biological resources.

Physical resources result from the deposition, precipitation, or accumulation of useful substances in the ocean or seabed. Most physical resources are mineral deposits, but petroleum and natural gas, mostly remnants of once-living organisms, are included in this category. Fresh water obtained from the ocean is also a physical resource. Biological resources are living animals and plants collected for human use.

3. Distinguish between renewable and nonrenewable resources.

Renewable resources are naturally replaced on a seasonal basis by the growth of marine organisms or by other natural processes. Non-renewable resources such as oil, gas, and solid mineral deposits are present in the ocean in fixed amounts and cannot be replenished over time spans as short as human lifetimes.

69 | P a g e


4. What are the three most valuable physical resources? How does the contribution of each to the world economy compare to the contribution of that resource derived from land?

The three most valuable physical resources are petroleum and natural gas, sand and gravel, and fresh water.

About 34% of the crude oil and 30% of the natural gas produced in 2005 (the last year for which I have reliable data) came from the seabed. More than 1.4 billion metric tons (1.5 billion tons) of sand and gravel valued at about three-quarters of a billion dollars were mined offshore in 2005. Only about 1.5% of the world's total sand and gravel production is scraped and dredged from continental shelves each year, but the seafloor supplies about 20% of the sand and gravel used in the island nations of Japan and the United Kingdom. Potable water derived from the ocean makes an insignificant contribution to the total amount of fresh water available to the world's human population. Still, desalination is becoming a big business. More than 15,000 desalination plants are presently operating worldwide, producing a total of about 32.4 million cubic meters (8.5 billion gallons) of fresh water per day.

5. Is the discovery of new sources of oil keeping up with oil use? Is oil being made (by natural processes) as fast as it is being extracted?

There is a growing deficit between consumption and the discovery of new reserves – in 2005, about 32 billion barrels of oil were consumed worldwide, while only eight billion barrels of new oil reserves were discovered. Huge, easily exploitable oil fields are almost certainly a thing of the past. It takes millions of years to turn organic material into oil and natural gas – we’re depleting our supplies much more rapidly than they’re being synthesized.

6. Is recovery of freshwater from seawater economically viable?

Yes and no, depending on where one is located. Where I live (southern California), conservation much more cost-effective than desalination. In the Middle East, central West Africa, and other exceedingly dry places, desalination may be the only choice.

7. What renewable marine energy source is presently making a contribution to the world economy?

Shown in Figure 10.21, the first successful commercial marine tidal power plant began operation in Northern Ireland’s Strangford Lough in August, 2007. Its 1.2 megawatt generator provides clean electricity for about 1,000 homes. Also, France’s River Rance estuary is spanned by the largest tidal power generator yet operating.

70 | P a g e


8. What’s the most valuable biological resource?

Fish, crustaceans, and mollusks are the most valuable living marine resources.

9. Fishing effort has increased greatly over the last decade. Has the per capita harvest also increased?

The cost to obtain each unit of seafood has risen dramatically in spite of all this high-tech assistance. The increasing expense of fuel for the fishing fleets and processing plants, the rising cost of wages for the crews, and the greater distances that boats must cover to catch each ton of fish have all helped drive up the cost of seafood. In spite of greater efforts, the total marine catch leveled off in about 1970 and remained surprisingly stable until 1980, when greater demand and increasing prices began to drive the tonnage upward again. Harvests are now declining in spite of increasingly desperate attempts to increase yields. Since 1970 the world human population has grown; so the average per capita world fish catch has fallen significantly.

10. What is meant by “overfishing?” Are most of the world’s marine fishes overfished?

Overfishing occurs when a species is taken more rapidly than the breeding stock of that species can generate replacements. Even when faced with evidence that it is depleting a stock and disrupting the equilibrium of a fragile ecosystem, the fishing industry's response is usually to increase the number of boats and develop more efficient techniques for capturing animals in order to maintain profits. The result is commercial extinction, depletion of a resource species to a point where it is no longer profitable to harvest. Most of the world’s marine fishes are overfished.

11. What is “bycatch?”

In some fisheries, bycatch—animals unintentionally killed while collecting desirable organisms—sometimes greatly exceeds target catch.

12. Does anyone still kill whales? Why?

Under intense pressure from its major fishing industry, Norway resumed whaling in 1993. Japan never stopped. Their prime target, the minke whale, is the smallest and most numerous of the great whale species (see Figure 13.25). The meat and blubber of this whale is prized in Japan as an expensive delicacy to be eaten on special occasions.

13. Can mariculture make a significant contribution to marine economics?

71 | P a g e


Worldwide mariculture production is thought to be about one-eighth that of freshwater aquaculture. Several species of fish, including plaice and salmon, have been grown commercially, and marine and brackish-water fish account for to thirds of the total production. Shrimp mariculture is the fastest growing and most profitable segment, with an annual global value exceeding US$15 billion in 2005.

14. Are any drugs derived from the ocean presently approved for use by humans?

Yes. A compound derived from cyanobacteria stimulated the immune system of test animals by 225% and cells in culture by 2,000%; the drug may be useful in treating AIDS. Vidabarine, another antiviral drug developed from sponges, may attack the AIDS virus directly. Cone shell toxins show great promise for the relief of pain and treatment of neurological disorders such as epilepsy and Alzheimer’s disease -- a new drug (Prialt) derived from cone shells was approved for clinical use in 2007. Cystic fibrosis may soon be treated with a mucus-clearing drug (Brevenal) derived from the toxic dinoflagellate Karenia.

15. What use of the ocean in place (a non-extractive resource) is most valuable?

Non-extractive resources are uses of the ocean in place -- transportation of people and commodities by sea, recreation, and waste disposal are examples. Transportation and recreation are the most valuble nonextractive resources the oceans provide.

16. How has the advent of containerized shipping changed world economics?

Modern harbors are essential to transportation. Cargoes are no longer loaded and off-loaded piece by piece by teams of longshoremen. Today’s harbors bristle with automated bulk terminals, high-volume tanker terminals (both offshore and dockside), containership facilities (see Figures 15.25), roll-on–roll-off ports for automobiles and trucks, and passenger facilities required by the growing popularity of cruising. Most of this specialized construction has occurred since 1960. New Orleans is now the greatest North American port; nearly 204 million tons of cargo—most of it grain—passed through its docks in 2004. The world’s busiest container terminal is in Hong Kong, China. In 1995, it was the first facility to move more than 1 million containers in a single month; its present capacity is more than three times that number!

17. Which is the largest U.S. Port. What is its main export?

New Orleans is now the greatest North American port; nearly 204 million tons of cargo—most of it grain—passed through its docks in 2004. The world’s busiest container terminal is in Hong Kong, China. In 1995, it was the first facility to move more than 1 million containers in a single month; its present capacity is more than three times that number!

72 | P a g e


18a. What is the world’s largest industry? Is it ocean-related?4

Tourism is now the world’s largest industry. In the last decade, the cruise industry has experienced spectacular growth. Passengers on luxurious ocean liners and cruise ships can enjoy a few relaxing days on the ocean crossing the North Atlantic, visiting tropical islands, or touring places accessible to the public only by ship.

18b. What is pollution? What factors determine how dangerous a pollutant is?

We define marine pollution as the introduction into the ocean by humans of substances or energy that change the quality of the water or affect the physical and biological environment.

A pollutant causes damage by interfering directly or indirectly with the biochemical processes of an organism. In most cases, an organism's response to a particular pollutant will depend on its sensitivity to the combination of quantity and toxicity of that pollutant. Some pollutants are toxic to organisms in tiny concentrations. For example, the photosynthetic ability of some species of diatoms is diminished when chlorinated hydrocarbon compounds are present in parts-per-trillion quantities. Other pollutants seem harmless, as when fertilizers flowing from agricultural land stimulate plant growth in estuaries. Still other pollutants may be hazardous to some organisms but not to others. For example, crude oil interferes with the delicate feeding structures of zooplankton and coats the feathers of birds but simultaneously serves as a feast for certain bacteria.

Pollutants also vary in their persistence; some reside in the environment for thousands of years while others last only a few minutes. Some pollutants break down into harmless substances spontaneously or through physical processes (like the shattering of large molecules by sunlight). Sometimes pollutants are removed from the environment through biological activity. For example, some marine organisms escape permanent damage by metabolizing hazardous substances to harmless ones. Indeed, many pollutants are ultimately biodegradable, that is, able to be broken down by natural processes into simpler compounds. Most pollutants resist attack by water, air, sunlight, or living organisms, however, because the synthetic compounds of which they are composed resemble nothing in nature.

19. How does oil enter the marine environment? Which source accounts for the greatest amount of introduced oil?

Oil is a natural part of the marine environment. Oil seeps have been leaking large quantities of oil into the sea for millions of years. The amount of oil entering the ocean has increased in recent years, however, because of our growing dependence on marine transportation for petroleum products, offshore drilling, nearshore refining, and street runoff carrying waste oil from automobiles (Table 15.2).

4 A typographical error in early printings of the text resulted in a Question #18 on page 365, and another Question #18 on page 378. I have separated these here as 18a and 18b.

73 | P a g e


20. What is biomagnification? Why is it dangerous?

The level of synthetic organic chemicals in seawater is usually very low, but some organisms at higher levels in the food chain can concentrate these toxic substances in their flesh. This biomagnification is especially hazardous to top carnivores in a food web.

21. How do heavy metals enter the food chain? What can be the results?

Among the most dangerous heavy metals being introduced into the ocean are mercury and lead. Human activity releases about five times as much mercury and 17 times as much lead as is derived from natural sources, and incidents of mercury and lead poisoning, major causes of brain damage and behavioral disturbances in children, have increased dramatically over the last two decades.

Lead particles from industrial wastes, landfills, and gasoline residue reach the ocean through runoff from land during rains, and the lead concentration in some shallow water bottom feeding species is increasing at an alarming rate. Consumers should be wary of seafood taken near shore in industrialized regions.

22. Why is plastic so dangerous to marine organisms?

The attributes that make plastic items useful to consumers, their durability and stability, also makes them a problem in marine environments. Scientists estimate that some kinds of synthetic materials—plastic six-pack holders, for example—will not decompose for about 400 years! While oil spills get more attention as a potential environmental threat, plastic is a far more serious danger. Oil is harmful but, unlike plastic, it eventually biodegrades.

23. What benefits to estuaries provide? What are some threats to marine estuaries?

The hardest hit habitats are estuaries, the hugely productive coastal areas at the mouths of rivers where fresh water and seawater meet. Pollutants washing down rivers enter the ocean at estuaries, and estuaries often contain harbors, with their potentials for oil spills. As little as 1 part of oil for every 10 million parts of water is enough to seriously affect the reproduction and growth of the most sensitive bay and estuarine species. Some of the estuaries along Alaska’s Prince William Sound, site of the 1989 Exxon Valdez accident, were covered with oil to a depth of 1 meter (3.3 feet) in places. The spill’s effects on the $150-million-a-year salmon, herring, and shrimp fishery will be felt for years to come.

24. What dangers threaten coral reef communities?

74 | P a g e


Some coral reefs are in jeopardy from intentional chemical pollution. Especially damaging to tropical reefs has been the practice of using cyanide to collect tropical fish. Fishermen squirt a solution of sodium cyanide over the reef to stun valuable species. Many fish die; those that survive are sent to collectors all over the world. At the same time the invertebrate populations of the sensitive coral reef communities are decimated.

25. The ocean is becoming more acidic as it absorbs more carbon dioxide. What effects could this increasing acidity have on marine organisms?

Average oceanic pH has fallen by 0.025 units since the early 1990s and is expected to drop to pH 7.7 by 2100, lower than any time in the last 420,000 years (Figure 15.43). Fewer carbonate ions will be available for shell-building organisms. Eventually, corals, plankton, and other organisms will fail to form strong skeletons.

26. Have areas set aside for marine conservation areas and sanctuaries grown in overall size or become smaller in the last decade?

Beginning in 1972, the U.S. federal government has established a dozen national marine sanctuaries. These areas are intended as safe havens for marine life. They vary in size, but now cover about 410,000 square kilometers (158,000 square miles) of coral reefs, whale migration corridors, undersea archaeological sites, deep canyons, and zones of extraordinary beauty and biodiversity (Figure 15.37).

27. What is “greenhouse effect?” What gases are most responsible for it?

The surface temperature of Earth varies slowly over time. The global temperature trend has been generally upward in the 18,000 years since the last ice age, but the rate of increase has recently accelerated. This rapid warming is probably the result of an enhanced greenhouse effect, the trapping of heat by the atmosphere.

Glass in a greenhouse is transparent to light but not to heat. The light is absorbed by objects inside the greenhouse, and its energy is converted into heat. The temperature inside a greenhouse rises because the heat is unable to escape. On Earth greenhouse gases—carbon dioxide, water vapor, methane, CFCs, and others—take the place of glass. Heat that would otherwise radiate away from the planet is absorbed and trapped by these gases, causing a surface temperature to rise. Figure 15.40 shows this mechanism.

28. Is greenhouse effect always bad?

The greenhouse effect is necessary for life; without it, Earth’s average atmospheric temperature would be about -18°C (0°F). Earth has been kept warm by natural greenhouse gases. The sources of these gases are volcanic and geothermal processes, the decay and burning of

75 | P a g e


organic matter, and respiration and other biological sources. The removal of these gases by photosynthesis and absorption by seawater appears to prevent the planet from overheating.

29. What causes global warming?

Earth is now absorbing about 0.85 watts per square meter more energy from the Sun than it is emitting into space. There has been a 5°C (9°F) rise in global temperature from the end of the last ice age until today. Carbon dioxide and other human-generated greenhouse gases produced since 1880 are thought to be responsible for some or most of that increase.

30. What effects might be caused by global warming?

Among the more serious are:

Warming may shift the strength and position of ocean surface currents. What would happen to the agricultural economy of Europe if the warming Gulf Stream were to alter course?

The ocean is becoming more acidic. As you may recall from Chapter 6, seawater becomes slightly more acidic when CO2 dissolves in it to form carbonic acid. Average oceanic pH has fallen by 0.025 units since the early 1990s and is expected to drop to pH 7.7 by 2100, lower (that is, more acidic) than any time in the last 420,000 years. Because an acidic environment tends to dissolve calcium carbonate, shell- and bone-forming species are being affected, with coral reefs at greatest risk.

Phytoplankton productivity in the last 20 years has dropped by about 9% in the North Pacific and nearly 7% in the North Atlantic. This may be due in part to warmer ocean water and diminished winds to provide the light dusting of terrestrial iron needed for their metabolism. Deeper penetration of ultraviolet radiation may also play a role. Less phytoplankton means less carbon dioxide uptake and significant changes in oceanic ecosystems.

Diseases may spread more rapidly. Mosquito-borne infections may become more troublesome because a warmer climate prolongs their breeding and feeding seasons.

Ecosystems and crop production could be damaged beyond repair. For example, North American farmers have already noticed a northward “migration” of fields suitable for winter wheat.

Financial effects could be severe. Though a link between an increased rate of warming and the severity of tropical cyclones has not been demonstrated, the economic losses from severe storms in 2005 were the worst on record. Will rising sea level require us to

76 | P a g e


relocate the world’s vast port infrastructure? How many billions of dollars of real estate will be devastated by erosion?

31. What alternatives exist for burning hydrocarbon fuels for energy?

The leading alternatives are wind and solar power, energy from tidal flow and currents, and nuclear energy.

32. What was the “tragedy” implicit in Hardin’s “The Tragedy of the Commons?”

Garrett Hardin suggests that absolute freedom in a commons brings ruin to all. If each of us continues to keep the benefit of environmental use for ourselves, but shares his and her discards with all the world, our species will not survive. The imbalance is unsustainable. No economy can be based on perpetual growth.

33. Is there is a solution to the difficult environmental solutions in which we presently find ourselves? What form might that solution take? What are the alternatives?

Each of us can make a difference. A moment's careful reflection on the environmental consequences of what to purchase, how to traveling to work or class, to what degree to use air conditioning and heating, and how to recycle materials can make a large difference if enough of us are willing to make changes. Given our present political and educational situation, the chances for long-term survival don’t look particularly good. We have entered a time of inadvertent global experimentation, and the trials ahead will be interesting, indeed.

As I wrote in the book's Afterword: There is much good in the world. Go and add to it.

77 | P a g e

college.cengage.comcollege.cengage.com/coursemate/earth_science/... · web viewtraditionally, we...

Documents