81606 ch01 0001-revsamples.jbpub.com/9780763781606/81606_ch01_0001 … · · 2010-11-03thought to...

1ST REVISE

1.1 The Changing Marine

Environment

Charting the Deep

A Different View of the Ocean Floor

1.2 The World Ocean

Visualizing the World Ocean

Seeing in the Dark

1.3 Properties of Seawater

Pure Water

Seawater

1.4 The Ocean in Motion

Wind Waves

Surface Currents

Ocean Tides

Vertical Water Movements

1.5 Classification of the Marine

Environment

C H A P T E R

1

A synthetic view of our ocean planet.

C H A P T E R O U T L I N E

© Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION.

© Jones & Bartlett Learning, LLCNOT FOR SALE OR DISTRIBUTION




















Earth’s oceans are home to an extraordinary variety of liv-ing organisms adapted to the special conditions of thesea. The characteristics of these organisms and the vari-

ety of marine life itself are consequences of the many prop-erties of the ocean habitat. This chapter provides a survey ofthe developmental history and present structure of the oceanbasins and a general discussion of some properties of seawa-ter and of ocean circulation processes. Adaptations to theseproperties and processes have molded the character of theocean’s inhabitants through their very long history of evolu-tionary development.

As students of the Earth’s oceans, an appropriate perspec-tive is needed. We naturally tend to see the world from a hu-man point of view, with human scales of time and distance andwith land under our feet and air surrounding us. To begin tounderstand the marine environment of our home planet andhow it and its inhabitants evolved to their present forms, wemust broaden our perspective to include very different timeand distance scales. Terms such as “young” and “old” or “large”and “small” have limited meaning unless placed in some use-ful context. Figure 1.1 compares size and time scales for a fewcommon oceanic features and inhabitants. Throughout thisbook, these scales are revisited, and others are introduced tohelp you develop a practical sense of the time and space scalesexperienced by marine organisms.

The Ocean as a Habitat

2 CHAPTER 1 The Ocean as a Habitat

1ST REVISE© Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION.





















The Changing Marine Environment 3

1.1The Changing Marine EnvironmentOur solar system, including Earth, is

thought to have been formed about 5 billion yearsago. Modern concepts of the origin of our solar sys-tem indicate that the planets aggregated from a vastcloud of cold gas and dust particles into clusters ofsolid matter. These clumps continued to grow as grav-ity attracted them together. As Earth grew in thismanner, pressure from the outer layers compressedand heated the Earth’s center. Aided by heat from de-cay of radioactive elements, the planet’s interiormelted. Iron, nickel, and other heavy metals settledto the core, whereas the lighter materials floated tothe surface and cooled to form a density-layered planetwith a relatively thin and rigid crust (Fig. 1.2).

Early in Earth’s history, volcanic vents pokedthrough the crust and tapped the upper mantle forliquid material and gases that were then spewed outover the surface of the young Earth, and a primitiveatmosphere developed. Water vapor was certainlypresent. As it condensed, it fell as rain, accumulatedin low places on the Earth’s surface, and formed prim-itive oceans. Additional water may have arrived as“snowballs” from space in the form of comets collid-

ing with the young Earth. Atmospheric gases dis-solved into accumulating seawater, and other chem-icals, dissolved from rocks and carried to the seas byrivers, added to the mixture, eventually creating thatcomplex brew of water, ions, and molecules that wecall seawater.

Since their initial formation, ocean basins haveexperienced considerable change. New materialderived from the Earth’s mantle has extended thecontinents so that they are now larger and stand higherthan at any time in the past. The oceans have keptpace, getting deeper with accumulations of new wa-ter from volcanic gases and from the chemical break-down of rock. Earth’s early life forms (represented bybacterial fossils older than about 3.5 billion years)also had a significant impact on the character of theirphysical environment. Whether the earliest life formsoriginated at hot seeps on the deep-sea floor or inwarm pools at the sea’s edges is a matter of continu-ing speculation and research. What is clear, however,is that life on this planet requires water; in fact, liv-ing organisms are mostly water.

Early in life’s history on Earth, molecular oxygen(O2) began to be produced in increasing amounts bymicroscopic photosynthetic prokaryotes. The O2

phytoplankto

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humans

whales

current

gyres

Earth

oceanbasins

fishes

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ury

mill

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10–3 10 3 10 6 10 9 1012

Time scale, days

Siz

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ale,

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Time and size scales for a range of major marine features and inhabitants.

Figure 1.1























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content of the atmosphere 600 million years ago wasprobably about 1% of its present concentration. Itwas not much, but it was an important turning point,the time when organisms that could take advantageof O2 in aerobic respiration became dominant andorganisms not using O2 (anaerobes) became lessprevalent (more on this in Chapter 2).

The evolution of more complex life forms usingincreasingly efficient methods of energy utilizationset the stage for an explosion of marine species. By500 million years ago, most major groups of marineorganisms had made their appearance. Worms,sponges, corals, and the distant ancestors of terrestrialanimals and plants were abundant, but life at that timecould exist only in the sea, where a protective blanketof seawater shielded it from intense solar radiation.

As O2 became more abundant in the upper at-mosphere, some of it was converted to ozone (O3).The process of forming ozone absorbed much of thelethal ultraviolet radiation coming from the sun andprevented the radiation from reaching Earth’s sur-face. The O2 concentration of the atmosphere 400million years ago is estimated to have reached 10%of its present level and achieved its current concen-tration in the Mesozoic Era about 200 million yearsago. The additional ozone screened out enough ultra-violet radiation to permit a few life forms to abandon

their sheltered marine home and colonize the land.Only recently have we become aware that industrial-ized society’s increasing use of aerosols, refrigerants,and other atmospheric pollutants is gradually de-pleting this protective layer of ozone. Figure 1.3 pro-vides a general timeline for a few of the major eventsin the early development of life on Earth.

Charting the Deep

People must have explored their local coastal envi-ronments very early in their history, but few of theirdiscoveries were recorded. By 325 B.C., Pytheas, aGreek explorer, had sailed to northwestern Europeand developed a method for determining latitude(Fig. 1.4). About a century later, Eratosthenes ofAlexandria, Egypt provided the earliest recordedestimate of Earth’s size, its first dimension. His cal-culated circumference of 39,690 km was only about1% less than today’s accepted value of 40,008 km.During the Middle Ages, Vikings, Arabians, Chinese,and Polynesians sailed over major portions of Earth’soceans. By the 15th century, all the major inhabit-able land areas were occupied; only Antarctica re-mained unknown to and untouched by humans. Evenso, precise charting of the ocean basins had to awaitseveral more voyages of discovery.

Between 1768 and 1779, James Cook, an Englishnavigator, conducted three exploratory voyages, mostlyin the Southern Hemisphere. He was the first to crossthe Antarctic Circle and to understand and conquerscurvy (a disease caused by a deficiency of vitamin C).He is best remembered as the first global explorer tomake extensive use of the marine chronometer de-veloped by John Harrison, a British inventor. Thechronometer, a very accurate shipboard clock, wasnecessary to establish the longitude of any fixed pointon the Earth’s surface. Together with Pytheas’s 2000-year-old technique for fixing latitude, reasonablyaccurate positions of geographic features anywhereon the globe could be established for the first time,and our two-dimensional view of Earth’s surface wasessentially complete. Today, coastal Long Range Nav-igation (LORAN) stations and satellite-based globalpositioning systems (GPSs) enable individuals todetermine their position to within a few meters any-where on the Earth.

In 1872, one century after Cook’s voyages, thefirst truly interdisciplinary global voyage for scien-tific exploration of the seas departed from England.The H.M.S. Challenger was converted expressly for

6343 km2855 km

Hydrosphere(4 km)

Continental crust 0.1%35–50 km

Mantle 45.0%

Outer core 54.9%Inner core

Oceanic crust (3–10 km)

1278 km2210 km

A section through the Earth, showing its density-layered interior structureand the thickness of each layer.

Figure 1.2























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First fishes

Sharks abundantFirst reptiles

First dinosaurs

Mammals abundant

First mammalsDinosaurs extinct

Latest Ice Ages

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Time, in billions of years before present

A summary of some biological and physical milestones in the early development of life on Earth.The purple curve represents the relative diversity of life; the orangecurve represents the O2 concentration of the atmosphere. Several of the terms used here are defined in Chapter 2.

Figure 1.3

lines oflongitude

lines oflatitude

equator

An “orange peel”projection of the Earth’s surface, with latitude and longitude lines at 30-degree intervals.The red track traces the voyage of H.M.S. Challenger (inset).

Figure 1.4






















this voyage. The voyage lasted over 3 years, sailedalmost 69,000 nautical miles in a circumnavigationof the globe (Fig. 1.4), and returned with such a wealthof information that 10 years and 50 large volumeswere required to publish the findings. During thevoyage, 492 depth soundings were made. Thesesoundings traced the outlines of the Mid-AtlanticRidge under 2 km of ocean water, plumbed theMariana Trench to a depth of 8185 m, and filled inrough outlines of the third dimension of the worldocean, its depth.

A Different View of the Ocean Floor

Early in the 20th century, Alfred Wegener proposedthat the oceans were changing in other ways. Wegenerdeveloped a detailed hypothesis of continental drift toexplain several global geologic features, includingthe remarkable jigsaw-puzzle fit of some continents(especially the west coast of Africa and the east coast of South America). He proposed that our presentcontinental masses had drifted apart after the breakupof a single supercontinent, Pangaea. His evidence was


1ST REVISE

in progress

The rapid introduction of steam powerand the mass production of goods inmechanized factories in Britain in thelate 18th and 19th centuries is regardedas the Industrial Revolution. Althoughresponsible for the many luxuries of lifein western nations today, this Revolu-tion also initiated the greatest anthro-pogenic impact on Earth’s ecology todate. As long ago as 1824, French scientist Joseph Fourier warned thescientific community that the wasteproducts of industry could result in aglobal greenhouse effect. In 1859, labo-ratory experiments conducted by John Tyndall in Britain demonstrated that CO2

does trap infrared radiation (the funda-mental cause of global warming). Theimpact on Earth’s temperature thatwould be caused by a doubling of CO2

in our atmosphere was predicted, withchilling accuracy, in 1896 by chemistSvente Arrhenius in Sweden. Theory

began to give way to fact in 1938 whenG. S. Callendar stated that global cli-mate change already was occurring,and our modern acceptance of anthro-pogenic global warming and climatechange was launched in 1957 by RogerRevelle and Hans Suess via their semi-nal paper in the scientific journal Tellus.Since then, thanks to tireless efforts ofthe scientific community, a foolproofcase demonstrating the causal linksbetween increased accumulation ofCO2 and other greenhouse gases in ouratmosphere, the resultant warming ofour planet, and concomitant climatechange has been developed.

Objectively assessing the data pub-lished each year in peer-reviewed sci-entific journals is the IntergovernmentalPanel on Climate Change (IPCC), whichwas established in 1988 by the UnitedNations Environment Programme andthe World Meteorological Organization.The IPCC takes a three-pronged ap-proach when considering the pheno-menon of climate change via globalwarming by assessing the science ofclimate change, the socioeconomic andnatural effects of climate change, andour options for mitigating climatechange by limiting emission of CO2 andother greenhouse gases.

The IPCC publishes an AssessmentReport at regular intervals, the first ofwhich appeared in 1990 and helped

to establish the UN Framework Con-vention on Climate Change (UNFCCC),an important entity that provides theoverall policy framework for address-ing global issues of climate change.The IPCC’s second Assessment Report,Climate Change 1995, led to the adop-tion of the Kyoto Protocol to the UNFCCC in 1997, a multinational agree-ment that attempts to stabilize the con-centration of greenhouse gases in ouratmosphere by mandating a reductionof greenhouse gas emissions by signa-tory nations. As of this writing, althoughit has been signed by nearly 200 gov-ernment entities, the United States, theworld’s largest emitter of CO2 from thecombustion of fossil fuels, has yet toratify the Kyoto Protocol.

Climate Change 2001, IPCC’s thirdAssessment Report, may be viewed asthe turning point during which globalawareness and acceptance of the factof climate change via anthropogenicglobal warming was achieved. TheSummary for Policy Makers in thisthird assessment stated that data indi-cate that the world is warming andthat changes in the climate system areoccurring, that human activities areresponsible for these changes, thatanthropogenic greenhouse gases andaerosols continue to change our at-mosphere and climate, that the IPCC’sconfidence in climate prediction mod-

Global Warming andClimate Change:It Is Time to Act






















ambiguous, though, and most scientists at the time re-mained unconvinced. It was not until the early 1960sthat new evidence compelled two geophysicists to in-dependently, and almost simultaneously, propose theclosely related concepts of seafloor spreading and platetectonics. In hindsight, these related concepts seemcompletely obvious—that the Earth’s crust is dividedinto giant irregular plates (Fig. 1.5). These rigid crustalplates float on the denser and slightly more plasticmantle material. Each plate edge is defined byoceanic trench or ridge systems, and some plates

include both oceanic and continental crusts. Newoceanic crustal material is formed continually alongthe axes of oceanic ridges and rises. As crustal platesgrow on either side of the ridge, they move awayfrom the ridge axis in opposite directions, carryingbottom sediments and attached continental masseswith them (Fig. 1.6).

In 1968, a new and unusual ship, the GlomarChallenger, was launched to probe Earth’s historyas recorded in sediments and rocks beneath theoceans. Equipped with a deck-mounted drilling rig,


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in progress

els has increased, and that humanswill continue to change atmosphericcomposition throughout this century.

In early February 2007, the IPCCpublished their fourth Assessment Report, an irrefutable summary of the fact of warming-induced climatechange coupled with chilling predic-tions for the health of our planet ifemissions are not decreased. This As-sessment’s frightening Summary forPolicy Makers states that warming ofthe Earth’s climate system is unequiv-ocal, that they are greater than 90%confident that the recorded increasein global temperatures during the last50 years is very likely due to human activities, that higher temperaturesand elevations in sea level would continue for centuries even if gasemissions are stabilized, that worldtemperatures may rise between 1.1°Cand 6.4°C during this century, that sealevels could rise between 18 cm and59 cm, that heat waves and heavyrainfall will almost certainly increasein frequency, that they have a confi-dence level above 66% that droughts,hurricanes, and extreme high tidesalso will become more frequent, and that current concentrations ofCO2, methane, and nitrous oxide in our atmosphere have increased dramatically since the start of the Industrial Revolution and now are

greater than at any point during thepast 650,000 years.

This horrifying assessment of thestate of Earth’s atmospheric healthsuggests consequences so cata-strophic that they are nearly incon-ceivable. These dire predictionsinclude the extinction of one millionspecies by 2050, deaths from globalwarming reaching 300,000 people per year in the next 25 years, and a six-meter rise in sea level as a result of the loss of shelf ice inGreenland and Antarctica and anice-free Arctic Ocean by 2050.Clearly, Prince Albert II of Monacowas correct when he said, “The houris no longer for skepticism. It is timeto act, and act urgently.”

In response to these dreadful pre-dictions, the International Polar Yearwas launched in March of 2007. Thisscientific initiative, which unites re-searchers from 63 countries, includes228 studies of the health of polar re-gions, including a quantification of the volume of freshwater leaking fromAntarctica’s ice sheets, the installationof an early-warming climate monitor-ing system in the Arctic Ocean, a cen-sus of Antarctica’s deep-sea fauna,sonic sounding of Antarctica’s sub-icesheet lakes and mountains, an investi-gation of plasma and magnetic fields,and a study of the culture and politics

of some of the Arctic’s 4 million resi-dent humans.

You also can take action today todecrease your contribution of green-house gases to our atmosphere. Replace traditional light bulbs withfluorescent bulbs, avoid single-passenger cars by car pooling, usingmass transit, or even walking or bik-ing to your destination, recycle asmuch as possible, maintain proper airpressure in your car’s tires, plant atree, change your thermostat’s opti-mal setting by just two degrees, anduse less hot water by installing low-flow showerheads and launderingclothing in cold or warm water. It istime to act.

biology.jbpub.com/marine/For more information on this topic,go to this book’s Web site at http://biology.jbpub.com/marine/.

Global Warming andClimate Change:It Is Time to Act























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the Glomar Challenger was capable of drilling into theseafloor in water over 7000 m deep (Fig. 1.7). Within2 years, the Glomar Challenger recovered vertical sed-iment core samples from enough sites on both sidesof the Mid-Atlantic Ridge to finally and firmly con-firm the hypothesis of seafloor spreading and conti-nental drift. Before being decommissioned in 1983,the Glomar Challenger traveled almost 700,000 kmand drilled 318,461 m of seafloor in 1092 drill holesat 624 sites in all ocean basins. Subsequent analysesof microscopic marine fossils recovered from thistremendous store of marine sediment samples haveled to refined estimates of the ages and patterns of evo-lution of all the major ocean basins.

Pacific Plate

Nazca Plate

North American Plate

South American Plate

Antarctic Plate

African Plate

Eurasian Plate

Indian-Australian Plate

The major plates of the Earth’s crust. Compare the features of this map with those of Figure 1.11.

Figure 1.5

0

Continentalcrust

100

200

Dep

th (

km)

300

400

0

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Depth (km

)300

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Volcanic islandarc

Oceanwater

Spreading oceanridge

Oceancrust

Frictional drag

ASTHENOSPHERE(ductile, low strength)

Deep-seatrench

“Pull”

LITHOSPHERE

Cold

Hot

Cross-section of a spreading ocean floor, illustrating the relative motions of oceanic and continental crusts. New crust is created at the ridge axis, and old crust is lostin trenches.

Figure 1.6

The ocean drill ship, Glomar Challenger.

Figure 1.7























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Scientists working in the deep-diving researchsubmersible Alvin in 1977 made a remarkable dis-covery of previously unknown marine animal com-munities associated with seafloor hot water ventsin the eastern equatorial Pacific Ocean. Several othervents and their associated animal communitiesfound elsewhere during the past quarter centuryassociated with ridge or rise axes are discussed inChapter 12.

The changes that seafloor spreading and platetectonics have wrought on the shapes and sizes ofthe oceans have been impressive. Currently, theAfrican continent is drifting northward on a collisioncourse with Europe, relentlessly closing the Mediter-ranean Sea. The Atlantic Ocean is becoming wider atthe expense of the Pacific Ocean. Australia and In-dia continue to creep northward, slowly changingthe shapes of the ocean basins they border. Occa-sional violent earthquakes are only incidental tremorsin this monumental collision of crustal plates. Therates of seafloor spreading have been determined forsome oceans, and they vary widely. The South At-lantic is widening about 3 cm each year (or approx-imately your height in your lifetime). The PacificOcean is shrinking somewhat faster. The fastestseafloor spreading known, 17.2 cm/yr, was measuredalong the East Pacific Rise.

The breakup of the megacontinent, Pangaea, pro-duced ocean basins where none existed before. Theseas that existed 200 million years ago have changedsize or have disappeared altogether. Some of the pastpositions of the continents and ocean basins, basedon our present understanding of the processes in-volved, are reconstructed in Figure 1.8. Excess crustproduced by seafloor spreading folds into mountainranges (the Himalayas are a dramatic example) orslips down into the mantle and remelts (Fig. 1.6).Consequently, most marine fossils older than about200 million years can never be studied; they too havebeen carried to destruction by the “conveyor belt” ofsubduction, the sinking of seafloor crust at trenchlocations to be remelted in the mantle. Ironically, theonly fossil evidence we can find for the first 90% ofthe evolutionary history of marine life is found inlandforms that were once ancient seabeds.

On much shorter time scales, other processeshave been at work to alter the shapes and sizes ofocean basins. During the past 200,000 years, ourplanet has experienced two major episodes of globalcooling associated with extensive continental glacia-tion. Just 18,000 years ago, northern reaches ofEurope, Asia, and North America were frozen under

the grip of the most recent ice age, or the last glacialmaximum. The massive amount of water containedin those glaciers lowered the sea level about 150 mbelow its present (and also its preglacial) level.Between 18,000 and 10,000 years ago, melting and shrinking of these continental glaciers wereaccompanied by a 150-m rise in global sea level andthe flooding of land exposed during the last glacialmaximum. Coral reefs, estuaries, and other shallowcoastal habitats were modified extensively during thisflooding; these topics are discussed in Chapters 8and 10. Currently, warmer summer temperaturesaround Antarctica are creating some concern aboutthe potential for melting glaciers to cause another risein global sea levels of a few meters.

180 millionyears ago

65 millionyears ago

Today

L A U R A S I A

G O N D W A N A

About 200 million years ago, the megacontinent, Pangaea, separated intotwo large continental blocks, Laurasia and Gondwana. Since then, theyhave fragmented into smaller continents and continue to drift apart.These maps outline the changing past positions of the continents andocean basins. (Adapted from Dietz and Holden 1970.)

Figure 1.8























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in Figure 1.9. The Antarctic continent is surroundedby a “Southern Ocean,” which has three large embay-ments extending northward. These three oceanic ex-tensions, partially separated by continental barriers,are the Atlantic, Pacific, and Indian Oceans. Othersmaller oceans and seas, such as the Arctic Ocean andthe Mediterranean Sea, project from the margins of thelarger ocean basins. These broad connections betweenmajor ocean basins permit exchange of both seawaterand the organisms living in it, reducing and smooth-ing out differences between adjacent ocean basins.

Figure 1.10 represents a more conventional view ofthe world ocean, with the world ocean separated intofour major ocean basins, the Atlantic, Pacific, Indian,and Arctic, and without the emphasis on the extensivesouthern connections apparent in Figure 1.9. The for-mat of Figure 1.10 is often more useful because ourinterest in the marine environment has been focusedon the temperate and tropical regions of Earth.

The equator also is a very real physical bound-ary extending across the tropical center of the largeocean basins. The curvature of the Earth’s surfacecauses areas near the equator to receive more radi-ant energy from the sun than equal-sized areas in po-lar regions. The resultant heat gradient from warmtropical to cold polar regions establishes the basicpatterns of atmospheric and oceanic circulation. Sur-face ocean current patterns display a nearly mirror-image symmetry in the northern and southern halvesof the Pacific and Atlantic Oceans. This symmetryestablishes it as a natural, although intangible, focusfor the graphic representation of these features andof the life zones they define.

Nearly two thirds of our planet’s land area is lo-cated in the Northern Hemisphere. The SouthernHemisphere is an oceanic hemisphere, with 80% ofits surface covered by water. The Pacific Ocean aloneaccounts for nearly one half of the total ocean area.A few descriptive measurements for features of thesix largest marine basins are listed in Table 1.1.

Maximum oceanic depths extend to over 11,000 m, but most of the ocean floor lies between3000 and 6000 m below the sea surface. A syntheticimage of the northern and central parts of the AtlanticOcean (Fig. 1.11) illustrates some of the larger-scale fea-tures of the ocean floor. The continental shelf, whichextends seaward from the shoreline and is actually astructural part of the continental landmass, would notbe considered an oceanic feature if sea level were low-ered by as little as 5% of its present average depth. Thewidth of continental shelves varies, from being nearlyabsent off southern Florida to over 800 km wide in

SUMMARY POINTSThe Changing Marine Environment

• True understanding of the sea requires a shiftin perspective, from human-centric conceptsof time and distance to full appreciation of theancient age and enormous volume of the world’socean.

• Terrestrial habitats often are described in termsof two-dimensional surface area. The sea mustbe viewed as a 3D environment wherein verti-cal changes in biological, physical, and chemi-cal factors are as important as horizontal changesdue to differences in latitude or longitude.

• Earth’s surface is dominated by our world ocean,a single interconnected volume of seawaterpartially separated by land masses into a num-ber of ocean basins and coastal seas.

• The sizes and shapes of ocean basins, as wellas the chemistry of seawater itself, is continu-ally changing due to various geological phenom-ena (e.g., volcanism, seafloor spreading, erosion,glaciation, and plate tectonics).

1.2 The World OceanCurrently, Earth is the only planet in our

solar system that has liquid water at its surface. Un-like the faces of any planet we can see from Earth,from space our Blue Planet stands apart from allothers in our solar system because 70% of our planet’ssolid face is hidden by water too deep for light topenetrate. Our world ocean has an average depth ofabout 3800 m (3.8 km). This may seem like a lot ofwater, but when compared with Earth’s diameter of12,756 km, the world ocean is actually a relativelythin film of water filling the low places of Earth’scrustal surface. On the scale of the view of Earth fromspace shown on page 1, the average ocean water depthis represented by a distance of about 0.04 mm (aboutone one-thousandth of an inch). Although shallowon a planetary scale, these water depths of severalthousand meters easily dwarf the largest of the plantsor animals living there.

Visualizing the World Ocean

One can visualize the Earth’s marine environment asa single large interconnected ocean system as shown






















The World Ocean 11

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SouthAmerica

NorthAmerica

Asia

AfricaAfrica

Antarctica

Australia

PACIFIC OCEAN

ATLANTIC OCEAN

INDIANOCEAN

Greenwichmeridian Equator

Internationaldateline

A modified polar view of the world ocean, emphasizing the extensive oceanic connections between major ocean basins in the Southern Hemisphere.

Figure 1.9

Arctic Ocean

ArabianSea

Bay ofBengal

RossSea

WeddellSea

INDIAN

OCEAN

PACIFICATLANTIC

BeringSea

SouthChinaSea

CaribbeanSea

Gulf ofMexico

MediterraneanSea

OCEANOCEAN

NorthSea

equator

An equatorial view of the world ocean.

Figure 1.10























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North America

South America

Continental slope

Midoceanicridge

Islands

Africa

Europe

Continental shelf

Abyssal plain

Island arc

Trench

Some large-scale features of the North Atlantic seafloor.

Figure 1.11

the Arctic Ocean north of Siberia. Continental shelvesaccount for 8% of the ocean’s surface area; this is equiv-alent to about one sixth of the Earth’s total land area.

Most continental shelves are relatively smoothand slope gently seaward. The outer edge of theshelf, called the shelf break, is a vaguely definedfeature that usually occurs at depths between 120and 200 m. Beyond the shelf break, the bottomsteepens slightly to become the continental slope.

Continental slopes reach depths of 3000 to 4000 mand form the boundaries between continental massesand the deep ocean basins.

A large portion of deep ocean basins consists offlat sediment-covered areas called abyssal plains.These plains have almost imperceptible slopes, muchlike that of eastern Colorado. The sediment blanketover abyssal plains often completely buries smallercrustal elevations, called abyssal hills. Most abyssal

Some Comparative Features of the Major Ocean Basins

Ocean or Sea Area � 106 km2 Volume � 106 km3 Average depth (m) Maximum depth (m)

Pacific 165.2 707.6 4282 11,033Atlantic 82.4 323.6 3926 9200Indian 73.4 291.0 3963 7460Arctic 14.1 17.0 1205 4300Caribbean 4.3 9.6 2216 7200Mediterranean 3.0 4.2 1429 4600Other 18.7 17.3Totals (average) 361.1 1370.3 (3795)

Tabl

e 1.1






















The World Ocean 13

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plains are situated near the margins of the ocean basinsat depths between 3000 and 5000 m.

Oceanic ridge and rise systems, such as the Mid-Atlantic Ridge and East Pacific Rise, occupy over 30%of the ocean basin area. The ridge and rise systemsare rugged, more or less linear features that form acontinuous underwater mountain chain encirclingthe Earth. The Mid-Atlantic Ridge actually resemblesa 20- to 30-km-wide canyon like the East African RiftValley, sitting atop a broadly elevated seafloor aligneddown the center of the Atlantic Ocean. The top ofthe Mid-Atlantic Ridge may extend 4 km above thesurrounding abyssal hills, and isolated peaks occa-sionally extend above sea level to form islands suchas Iceland and Ascension Island. The East Pacific Riseis much lower and broader, with a barely perceptiblerift about 2 km wide.

Trenches are distinctive ocean-floor features, withdepths usually extending deeper than 6000 m. Mosttrenches, including the seven deepest, are located alongthe margins of the Pacific Ocean. The bottom of theChallenger Deep, in the Mariana Trench of the west-ern North Pacific, is 11,033 m deep, the greatest oceandepth found anywhere. (This is as far below sea levelas commercial jets typically fly above the sea surface.)The enormous depths of trenches impose extreme con-ditions of high water pressure and low temperatureon their inhabitants. Although trenches account forless than 2% of the ocean bottom area, they are inte-gral parts in the processes of seafloor spreading andplate tectonics, acting as sites where crustal plates tensor hundreds of millions of years old are finally sub-ducted back into the mantle to be remelted.

Most oceanic islands, seamounts, and abyssalhills have been formed by volcanic action. Oceanicislands are volcanic mountains that extend above sealevel; seamounts are volcanic mountains whose topsremain below the sea surface. Most of these featuresare located in the Pacific Ocean. Islands in tropicalareas are often submerged and capped by coral atollsor fringed by coral reefs. These reefs, examined inChapter 10, form some of the most beautiful and com-plex animal communities found anywhere.

Seeing in the Dark

Humans are visual beings; we continually examine oursurroundings through the clarity of air. In the oceans,however, the opacity of seawater has long thwartedour ability to examine its depths in detail. Fortunately,the opacity of seawater to light is compensated by itstransparency to sound. The early ancestors of dolphinscapitalized on this feature of water about 20 million

years ago by evolving sophisticated biosonar systemscapable of high-resolution target discrimination.Biosonar is based on the production of sharp sounds,detecting the echo as it bounces off a target and mea-suring the time delay between sound production andecho return (more details on dolphin biosonar can befound in Chapter 6). In a technologic sense, we arecatching up with dolphins with the development ofvarious types of electronic sonar (sound navigatingranging) systems. Without going into the history ofthe development of sonar, it is sufficient to indicatethat several different types of sonar systems with dif-ferent resolutions have been central to obtaining de-tailed pictures of the deep ocean floor.

The most widespread and familiar type of sonaris operated from surface ships. You may be famil-iar with commercial versions of these as fish findersor depth finders on personal boats. At sea, surfacesonar systems operate from a single ship-based trans-mitter to produce a single line or track of sequentialdepth measurements below the ship as it is under-way. This system provides an acoustic view of theseafloor in two dimensions, with poor resolution ofsmall structures or fine detail.

Multiple-beam sonar systems also are operatedfrom surface vessels, but with an array of severalsound transmitters and receivers arranged from bowto stern. The numerous overlapping sound beams re-turn much more information about the seafloor, in-formation that would be a useless jumble of datawithout computers to decipher it. Multiple-beamsonar can map a swath of ocean bottom several kilo-meters wide in a single pass and with much higherresolution than single transmitter systems. The re-sult is the acoustic equivalent of a continuous stripof aerial photographs of the ocean floor (Fig. 1.12).

A multiple-beam sonar image of the coastal margin of southern California.

Figure 1.12























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Sidescan sonar systems are variants of the multiple-beam technique. As its name implies, sidescan sonardirects sound beams to the sides of the ship’s track.Images obtained with sidescan sonar show in richdetail the fine texture of the seafloor, equivalent toclose-up photographs of the ocean floor.

1.3 Properties of SeawaterSeveral common properties of seawater are

crucial to the survival and well-being of the ocean’s in-habitants. Water accounts for 80–90% of the volumeof most marine organisms. It provides buoyancy andbody support for swimming and floating organismsand reduces the need for heavy skeletal structures.Water is also the medium for most chemical reactionsneeded to sustain life. The life processes of marine or-ganisms in turn alter many fundamental physical andchemical properties of seawater, including its trans-parency and chemical makeup, making organisms anintegral part of the total marine environment. Under-

standing the interactions between organisms and theirmarine environment requires a brief examination ofsome of the more important physical and chemical at-tributes of seawater. The characteristics of pure waterand seawater differ in some respects and, thus, weconsider first the basic properties of pure water andthen examine how those properties differ in seawater.

Pure Water

Water is a common yet very remarkable substance.It is the only substance on Earth that is abundant asa liquid (mostly in oceans), with substantial quanti-ties left over as a gas in the atmosphere and as a solidin the form of ice and snow. Individual water mole-cules have a simple structure, represented by its mo-lecular formula, H2O. Yet the collective properties ofmany water molecules interacting with each other ina liquid are quite complex. Each water molecule hasone atom of oxygen (O) and two atoms of hydrogen(H), which together form water (H2O). Some char-acteristics of these and other biologically importantmolecules and ions are described in this chapter.

The many unusual properties of water stem fromits molecular shape: a four-cornered tetrahedronwith the two hydrogen atoms forming angles of about105 degrees with the oxygen atom. This molecularshape is simplified to two dimensions in Figure 1.13.This atomic configuration creates an asymmetricwater molecule, with the oxygen atom dominatingone end of the molecule and the hydrogen atoms dom-inating the other end. The covalent bond between eachhydrogen and the oxygen atom is formed by the shar-ing of two negatively charged electrons. The oxygenatom attracts the electron pair of each bond, causingthe oxygen end of each water molecule to assume aslight negative charge. The hydrogen end of the mol-ecule, by giving up part of its electron complement, is

SUMMARY POINTSThe World Ocean

• About 70% of our planet’s surface is covered byseawater to an average depth of 3800 meters.

• Antarctica is surrounded by a “Southern Ocean”that has three large embayments extendingnorthward, the Atlantic, Indian, and PacificOceans.

• Nearly two thirds of our planet’s land area islocated in the Northern Hemisphere, with edgesof continental masses being characterized bya shallow continental shelf that extends sea-ward to meet the shelf break at a depth of120–200 meters.

• Beyond the shelf break, the continental marginslopes sharply and descends as the continen-tal slope which meets the deep sea floor atdepths of 3000–4000 meters.

• The deep sea floor, or abyssal plain, extend sea-ward, ending at mid-oceanic ridge and rise sys-tems which are the geological source of newoceanic crust.

• Because light does not travel far through sea-water, topographic details of ocean basins areacquired via the use of sonar systems whichrely on detection of echoes of transmitted soundbouncing off the sea floor.

H

O

–

+

105˚

H

The arrangement of H and O atoms in a molecule of water (H2O).The oxygenend has a slight net negative charge, whereas the hydrogen end has a slightnet positive charge.

Figure 1.13






















Properties of Seawater 15

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Hydrogen bonding between adjacent molecules of liquid water.The blackdashed lines represent hydrogen bonds.

Figure 1.14

Some Biologically Important Physical Properties of Water

Property Comparison with other substances Importance in biological processes

Boiling point High (100°C) for molecular size Causes most water to exist as a liquid at Earth surface temperatures

Freezing point High (0°C) for molecular size Causes most water to exist as a liquid at Earth surface temperatures

Surface tension Highest of all liquids Crucial to position maintenance of sea-surface organismsDensity of solid Unique among common natural Causes ice to float and inhibits complete freezing of

substances large bodies of waterLatent heat of vaporization Highest of all common natural Moderates sea-surface temperatures by transferring

substances (540 cal/g) large quantities of heat to the atmosphere through evaporation

Inhibits large-scale freezing of the oceansLatent heat of fusion Highest of all common natural Moderates daily and seasonal temperature changes

substances (80 cal/g)Solvent power Dissolves more substances in greater Maintains a large variety of substances in solution,

amounts than any other liquid enhancing a variety of chemical reactionsHeat capacity High (1 cal/g/°C) for molecular size Stabilizes body temperatures of organisms

Tabl

e 1.2

with similar molecular sizes, such as O2 or CO2.Water’s high freezing point of 0°C and boiling pointat 100°C causes most water at the Earth’s surface toexist as a liquid, making life as we know it possible.Hydrogen bonding also accounts for several otherunique and important properties of water. Some ofthese properties are listed in Table 1.2 and are dis-cussed in the following paragraphs.

Viscosity and Surface TensionHydrogen bonding between adjacent water mole-cules within a mass of liquid water creates a slight“stickiness” between these molecules. This property,known as viscosity, has a marked effect on all ma-rine organisms. The viscosity of water reduces thesinking tendency of some organisms by increasingthe frictional resistance between themselves andnearby water molecules. At the same time, viscositymagnifies problems of frictional drag that activelyswimming animals must overcome.

At the surface of a water mass (such as the air–seaboundary), the mutual attraction of water moleculescreates a flexible molecular “skin” over the water sur-face. This, the surface tension of water, is sufficientlystrong to support the full weight of a water strider(Fig. 1.15). Both surface tension and viscosity are tem-perature dependent, increasing as the temperaturedecreases.

Density–Temperature RelationshipsMost liquids contract and become more dense as theycool. The solid form of these substances is denser than

left with a small positive charge. The resulting electri-cal polarization of water molecules, one end with a pos-itive charge and the other end with a negative charge,has profound consequences for liquid water. When water is in its liquid form, each end of one water mol-ecule attracts the oppositely charged end of other water molecules. This attractive force creates a weakbond, a hydrogen bond or H-bond, between adjacentwater molecules (Fig. 1.14). These bonds are muchweaker and less stable than the covalent bonds withina single water molecule and are continually breakingand reforming as they change partners with other water molecules millions of times per second.

The H-bonds between water molecules requirethat water must be warmed to a much higher tem-perature to boil than that needed for other substances























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the sea, some of the sun’s radiant energy is convertedto heat energy that is then transferred from place toplace primarily by convection (mixing) and secondar-ily by conduction (the exchange of heat energy be-tween adjacent molecules). Heat energy is measuredin calories.2

Water has the ability to absorb or give up heatwithout experiencing much of a temperature change.To illustrate the high heat capacity of water, imag-ine a 1-g block of ice at –20°C on a heater thatprovides heat at a constant rate. Heating the ice from–20°C to 0°C requires 10 calories, or 0.5 calories perdegree of temperature increase (the heat capacity ofice); however, converting 1 g of ice at 0°C to liquidat 0°C requires 80 calories. Conversely, 80 caloriesof heat must be removed from 1 g of liquid waterat 0°C to freeze it to ice at the same temperature.(This is referred to as water’s latent heat of fusion.)Continued heating of the 1-g water sample from0°C requires 1 calorie of heat energy for each 1°change in temperature (the heat capacity of liquidwater) until the boiling point (100°C) is reached.At this point, further temperature increase stopsuntil all of the water is converted to water vapor.For this conversion, 540 calories of heat energy arenecessary (water’s latent heat of vaporization). Fig-ure 1.16 summarizes the energy requirements forthese changes in water temperature. The high heatcapacity and the large amount of heat required forevaporation enable large bodies of water to resistextreme temperature fluctuations. Heat energy is

1The maximum density of pure water is used to define thefundamental metric measure of mass, the gram, which isdefined as the mass of pure water at 4°C contained in thevolume of 1 cubic centimeter. Thus, the density, the ratio of mass to volume, of pure water is 1.000 g/cm3.

2A calorie is a unit of heat energy, defined as the quantity of heatneeded to elevate the temperature of 1 g of pure water 1°C.

0 200 400 600 800

0

20

40

60

80

100

120VAPOR PHASE

LIQUID PHASE

SOLID PHASE

range of ocean temperatures

Calories of heat energy added

Tem

pera

ture

, °C

A water strider (Halobates),one of the few completely marine insects,is supported by the surface tension of seawater.

Figure 1.15

The heat energy necessary to cause temperature and phase changes in water.

Figure 1.16

the liquid form. Over most of the temperature rangeat which pure water is liquid, it behaves like otherliquids. At 4°C or above, the density decreases withincreasing temperature. Below 4°C, however, waterbehaves differently: The density–temperature pat-tern of pure water reverses so that the density beginsto decrease as temperatures fall below 4°C. One modelused to explain this unique behavior of water pro-poses that, at near-freezing temperatures, less-denseicelike clusters consisting of several water moleculesform and disintegrate very rapidly within the bodyof liquid water. As liquid water continues to cool,more clusters form, and the clusters survive longer.Eventually, at 0°C, all the water molecules becomelocked into a rigid, solid crystal lattice of ice. Thewater ice formed is about 8% less dense than liquidwater at the same temperature, and thus, ice alwaysfloats on liquid water. This is an unusual, but veryfortunate, property of water. Without this uniquedensity–temperature relationship, ice would sinkas it formed, and lakes, oceans, and other bodies ofwater would freeze solid from the bottom up. Wintersurvival for organisms living in such an environmentwould be much more difficult.1

Heat CapacityHeat is a form of energy, the energy of molecular mo-tion. The sun is the source of almost all energy enter-ing the Earth’s surface heat budget. At the surface of























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H O2

Cl

+Na

–

–

Cl

+Na

NaCl crystal

A salt crystal (above) and the action of charged water molecules in dissolvingthe crystal to dissociated sodium (Na+) and chloride (Cl–) ions.

Figure 1.17

absorbed slowly by water when the air above is warmerand is gradually given up when the air is colder, pro-viding a crucial global-scale temperature-moderatingmechanism for marine environments and adjacentland areas.

Solvent ActionThe small size and polar charges of each water mol-ecule enable it to interact with and dissolve most nat-urally occurring substances, especially salts, whichare composed of atoms or simple molecules, calledions, that carry an electrical charge. Salts held to-gether by ionic bonds (bonds between oppositelycharged adjacent ions) are particularly susceptible tothe solvent action of water. Figure 1.17 illustrates theprocess of a salt crystal dissolving in water. Initially,several water molecules form weak H-bonds witheach sodium (Na+) and chloride (Cl–) ion, and theyeventually overcome the mutual attraction of thoseions that previously bound them together in the crystal-line structure. As more Na+ and Cl– ions are removedin this way, the solid crystal structure disintegrates,and the salt dissolves.

Water is not a good universal solvent, however,for some large organic molecules such as waxes andoils or for small molecules that lack electrical charges.

A notable and biologically crucial example of the sec-ond category is O2, for water can only dissolve a fewparts per million of O2.

Seawater

Seawater is the accumulated product of several bil-lion years of water condensing as rain from theatmosphere, eroding rocks and soil, and washing itall to the sea. About 3.5% of seawater is composed ofdissolved compounds from these sources. The other96.5% is pure water. Traces of all naturally occurringsubstances probably exist in the ocean and can be sep-arated into three general categories: (1) inorganic sub-stances, usually referred to as salts, including nutrientsnecessary for plant growth; (2) dissolved gases suchas N2, O2, and CO2; and (3) organic compounds de-rived from living organisms. Organic compounds dis-solved in seawater include fats, oils, carbohydrates,vitamins, amino acids, proteins, and other substances.Some compounds are valuable sources of nutritionfor marine bacteria and some other organisms. Cur-rent research indicates that other organic compounds,especially synthetically created ones such as poly-chlorinated biphenyls (PCBs) and other chlorinatedhydrocarbons, have accumulated in marine foodchains and have had serious negative impacts on thedevelopment and reproduction of some forms ofmarine life (see Chapter 8).

Dissolved SaltsSalts account for most dissolved substances in seawa-ter. The total amount of dissolved salts in seawater isreferred to as its salinity and is measured in parts perthousand (‰) rather than in parts per hundred (%).Salinity values range from nearly zero at river mouthsto greater than 40‰ in arid areas, such as the Red Sea.Yet, in open-ocean areas away from coastal influences,salinity averages approximately 35‰ and varies onlyslightly over large distances (Fig. 1.18).

Salinity is altered by processes that add or removesalts or water from the sea. The primary mechanismsof salt and water addition or removal are evaporation,precipitation, river runoff, and the freezing and thaw-ing of sea ice. When evaporation exceeds precipita-tion, it removes water from the sea surface, therebyconcentrating the remaining salts and increasing thesalinity. Excess precipitation decreases salinity by di-luting the sea salts. Freshwater runoff from rivers hasthe same effect. Figure 1.19 illustrates the average an-nual north–south variation of sea-surface evapora-tion and precipitation. Areas with more evaporation























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Excess precipitation

Excess evaporation

Evaporation

Precipitation

Evaporation and precipitation, cm/year

Sou

th

Lat

itude

, °

Nor

th

150100500

60

30

0

30

60

Average north–south variation of sea surface evaporation and precipitation.(Redrawn by permission of G. Dietrich, 1963. General Oceanography. New York:Interscience Publishers.)

Figure 1.19

than precipitation (Fig. 1.19, gray-shaded areas)generally correspond to the high surface salinity regions shown in Figure 1.18 and to the latitudeswith most of the great land deserts of the world. Inpolar regions where seawater can freeze, only the water molecules are incorporated into the devel-oping freshwater ice crystal. The dissolved ions are excluded from the growing ice crystal, causingthe salinity of the remaining liquid seawater to increase. The process is reversed when ice melts.Freezing and thawing of seawater are usually sea-sonal phenomena, resulting in little long-term salin-ity differences.

When salts dissolve in water, they release bothpositively and negatively charged ions. The morecommon ions found in seawater are listed in Table 1.3and are grouped as major or minor constituents ac-cording to their abundance. The major ions accountfor greater than 99% of the total salt concentrationin seawater. In relation to each other, concentra-tions of these major ions remain remarkably con-stant even though their total abundance may differfrom place to place. Most of the more abundant ionsenumerated in Table 1.3 are important componentsof marine organisms. Magnesium, calcium, bicar-bonate, and silica are important components of thehard skeletal parts of marine organisms. Plants neednitrate and phosphate for the synthesis of organicmaterial.

3233

33

33

34

34

34

34

3434

34

34

34

35

35

35

3535

35

35

35

3535

36

36

36

36

36

36

37

37

Geographic variations of surface ocean salinities, expressed in parts per thousand (‰).

Figure 1.18























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Salt and Water BalanceThe well-being of living organisms requires that theymaintain relatively constant internal environmentalconditions, within physiological limits. Homeosta-sis is the term used to describe the tendency of liv-ing organisms to control or regulate fluctuations oftheir internal environment. Homeostasis is the re-sult of coordinated biological processes that regu-late conditions such as body temperature or bloodion concentrations. When working properly, theseprocesses result in a dynamic regulation of condi-tions that vary within definite and tolerable limits.This section describes those processes that affect thehomeostasis of salt and water exchange between thebody fluids of an organism and its seawater environ-ment. Other homeostatic processes are presented inlater chapters.

The body fluids of marine organisms are sepa-rated from seawater by boundary membranes thatparticipate in several vital exchange processes, in-cluding absorption of oxygen and nutrients and ex-cretion of waste materials. Small molecules, such aswater, easily pass through some of these membranes,but the passage of larger molecules and the ions abun-dant in seawater is blocked. Such membranes are se-lectively permeable; they allow only small moleculesand ions to pass through while blocking the passageof larger molecules and ions. When substances arefree to move, as they are when dissolved in seawater,they move along a gradient from regions where theyexist in high concentrations to regions of lower con-

centrations. This type of molecular or ionic motionis known as diffusion. Diffusion causes both watermolecules and dissolved substances to move alongconcentration gradients within living organisms andsometimes across selectively permeable membranesbetween organisms and their surrounding seawater.

Light and Temperature in the SeaMost marine organisms living in the upper portionsof the sea use light energy from the sun for one oftwo functions, vision or photosynthesis. The amountof energy reaching the sea surface through the at-mosphere depends on the presence of dust, clouds, andgases that absorb or scatter a portion of the incom-ing solar radiation (Fig. 1.20). On an average day, about65% of the sun’s radiation arriving at the outer edgeof our atmosphere reaches the Earth’s surface. Theintensity of incoming solar radiation is reduced whenthe angle of the sun is low, as it is in winter or at highlatitudes, and a portion of the light that does makeit through the atmosphere is reflected back into spaceby the sea surface.

Of the broad spectrum of the sun’s electromag-netic radiation (Fig. 1.21, top), most marine animalscan visually detect only a very narrow band near thecenter of the spectrum. Our eyes visually respond onlyto the portion labeled visible light in Figure 1.21 (vi-olet through red), and most other animals with eyes,whether they see in color or not, respond visually toapproximately the same portion of the electromag-netic radiation spectrum.

The band of light energy used by animals for vi-sion broadly overlaps that used in photosynthesis.Photosynthetic organisms must remain in the upperregion of the ocean (the photic zone) where solar en-ergy is sufficient to support rates of photosynthesisthat at least match their own respiratory needs. Thedepth of the photic zone is determined by how rapidlyseawater absorbs light and converts it to heat energy.Dissolved substances, suspended sediments, and evenplankton populations diminish the amount of lightavailable for photosynthetic activity and cause thedepth of light penetration to differ dramatically be-tween coastal and oceanic water (Fig. 1.20).

As sunlight travels through our atmosphere andinto the sea, its color characteristics are altered as sea-water rapidly absorbs or scatters the violet and theorange-red portions of the visible spectrum, leavingthe green and blue wavelengths to penetrate deeper.Even in the clearest tropical waters, almost all red lightis absorbed in the upper 11 m. Clear seawater ismost transparent to the blue and green portions of

Major and Minor Ions in Seawater of 35‰ Salinity

Chemical Concentration Ion formula (‰)

Chloride Cl– 19.3Sodium Na+ 10.6Sulfate SO4

2– 2.7Magnesium Mg2+ 1.3Calcium Ca2+ 0.4Potassium K+ 0.4Bicarbonate HCO3

– 0.1Bromide Br – 0.066Borate B(OH)4

– 0.027Strontium Sr2+ 0.013Fluoride F– 0.001Silicate SiO4

4– 0.001

Plus traces of other naturally occurring elements

⎫⎪⎪⎬⎪⎪⎭⎫⎪⎬⎪⎭

Major

Minor

Tabl

e 1.3























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the spectrum (450–550 nm); 10% of the blue lightpenetrates to depths of 100 m or more. However, eventhis light is eventually absorbed or scattered (Fig. 1.22).The deeper penetration and eventual back-scatteringof blue light account for the characteristic blue colorof clear tropical seawater. Coastal waters are com-monly more turbid, with a greater load of suspendedsediments and dissolved substances derived from landrunoff. Here, there is a shift in the relative penetra-tion of light energy, with green light penetrating deep-est. In many coastal regions, green light is reduced to1% of its surface intensity in less than 30 m. Adapta-tions to these different light regimes by photosyntheticorganisms are described in Chapter 3.

Temperature EffectsWhen sunlight is absorbed by water molecules, it isconverted to heat energy, and the motion of the watermolecules increases. Temperature, commonly reported

in almost all countries of the world as degrees Celsius(°C), is the way we measure and describe that changein molecular motion. Temperature is a universal fac-tor governing the existence and behavior of living organisms. Life processes cease to function above theboiling point of water, when protein structures are irreversibly altered (as when you cook an egg), or atsubfreezing temperatures, when the formation of icecrystals damages cellular structures, but between theseabsolute temperature limits, life flourishes.

The high heat capacity of water limits marinetemperatures to a much narrower range than airtemperatures over land (Fig. 1.23). Some marine or-ganisms survive in coastal tropical lagoons at tem-peratures as high as 40°C. Bacteria associated withdeep-sea hydrothermal vents sometimes experiencewater temperatures above 60°C. Other deep-sea an-imals spend their lives in water perpetually withinone or two degrees of 0°C. Penguins and a few other

Sunlight

S c a t t e r i n g a n d r e f l e c t i o n

Depth at which lightis reduced to 1% ofsurface intensity, in m

100

50

25

75

- Coastal seawater -

- Temperate oceanic seawater -

- Clearest tropical seawater -

Fate of sunlight as it enters seawater.The violet and red ends of the visible spectrum are absorbed first.

Figure 1.20























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birds and mammals adapted to extreme cold andcommonly tolerate air temperatures far below 0°Cin polar regions. Emperor penguins even manageto incubate and hatch eggs under these conditions(Fig. 1.24), but these are exceptions; most marinespecies typically experience water temperaturesbetween 5°C and 30°C.

Individual activity, cell growth, oxygen consump-tion, and other physiological functions, collectively

termed metabolism, proceed at temperature-regulatedrates. Most animals lack mechanisms for body tem-perature regulation. These are poikilotherms (ofteninappropriately described as cold-blooded). These or-ganisms are also referred to as ectotherms; their bodytemperatures vary with and are largely controlled byoutside environmental temperatures. The terms poi-kilotherm and ectotherm, often used interchangeably,refer to distinct aspects of body-temperature control.Poikilotherms experience varying body temperaturesin a 24-hour day and do not regulate their body tem-peratures physiologically; external conditions gov-ern the body temperatures of ectotherms. In the sea,the temperature-moderating properties of water re-strict fluctuations of temperatures experienced bymarine ectotherms. Most marine organisms are si-multaneously ectothermic and poikilothermic.

For marine ectotherms, water temperature is aprincipal factor controlling metabolic rates. Marineectotherms generally have fairly narrow optimal tem-perature ranges, bracketed on either side by widerand less optimal, but still tolerable, ranges. Withinthese tolerable temperature limits, the metabolic rateof many poikilotherms is roughly doubled by a 10°Ctemperature increase. This, however, is only a gen-eral rule of thumb; some processes may acceleratesixfold with a 10°C temperature increase, whereasother processes may change very little. The actualeffect of water temperature on the feeding rate of a

Cos

mic

ray

s

P

R

I

S

M

380 760500 600Wavelength, nm

Wavelength

1 km1 m1 mm1 nm 1 µm

Sunburn Infrared (IR) light

X-ra

y t

hera

py

Ultr

avio

let

(UV)

ligh

t

Hea

t coo

king

Mic

row

ave

coo

king

IR a

stro

nom

y

Rad

ar

Tele

visi

on

FM ra

dio

AM ra

dio

visi

ble

lig

ht

The electromagnetic radiation spectrum.The small portion known as visible light is passed through a prism to separate the light into its component colors.

Figure 1.21

400 700500 600Wavelength, nm

0

30

10

20

Dep

th, m

1

2

3

Penetration of various wavelengths of light in three different water types:(1) very turbid coastal water, (2) moderately turbid coastal water, and (3) clear tropical water. Note the shift to shorter wavelengths (bluer light) in clearer water.

Figure 1.22























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typical marine ectotherm, a submerged barnacle, isshown in Figure 1.25.

Only birds and mammals use physiological mech-anisms to maintain nearly constant body tempera-tures throughout a 24-hour day. They are known ashomeotherms. Their normal core body temperaturesare maintained between 37°C and 40°C by the pro-duction of heat by internal tissues and organs. Thus,they are also endotherms. Endothermic homeothermsare less restricted by environmental temperaturesthan are their poikilothermic neighbors. As a result,they range widely to exploit resources over all thermalregimes available in the sea.

A few large tunas, billfishes, and sharks exhibit athermoregulatory condition intermediate to the twojust discussed. These fishes are poikilothermic, andthus, their body temperatures fluctuate with that ofthe surrounding seawater. Even so, they are unlikemost other poikilotherms because they retain someof the heat produced by their swimming muscles.These animals are endothermic, yet they lack theconstant body temperatures characteristic of birdsand mammals. The special mechanisms used for thisheat retention are described in Chapter 6.

The distribution of various forms of marine lifeis closely associated with geographic differences in

°F °C85 Highest natural temperature

occurrence of any form of life (cyanobacteria in hot springs)

186

58

50

40

30

20

10

0–2

–10

–62

–89.2

Highest recorded air temperature (Libya, 1922)

Maximum surface temperature in shallow tropical lagoons

Surface temperature in tropical lagoons

Surface temperature in subtropical regions

Surface temperature in temperate regions

Surface temperature in subpolar regions

Surface temperature in polar regions

Lowest temperature in seawater (deepest parts of Antarctic basins)

Lowest observed limit for breeding of the Emperor penguin (Antarctica)

Lowest recorded air temperature (Antarctica, 1983)

136130

120

110

100

90

80

70

60

50

40

30

20

–80

–128.56

60140

The range of biologically important temperatures at the Earth’s surface.The temperature ranges of marine climatic regions in Figure 1.26 areincluded.

Figure 1.23

Emperor penguins are the only penguins to lay eggs and rear their young onice during the Antarctic winter.

Figure 1.24

range of tolerabletemperatures

5 10 15 20 25 30 35

Water temperature, °C

60

48

36

24

12

00

Filt

erin

g ra

te, b

eats

/min

Filtering rate of an intertidal barnacle as a function of water temperature.Only within the range of tolerable temperatures is the filtering rateproportional to the water temperature. (Adapted from Southward, A. J.Helgol. wiss. Meersuntersuch 10 (1964): 391–401.)

Figure 1.25























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seawater temperatures. Surface ocean temperaturesare highest near the equator and decrease toward bothpoles. This temperature gradient establishes severaleast–west-trending marine climatic zones (Fig. 1.26).The approximate temperature range of each zone isincluded in Figure 1.23. These marine climatic zonesserve as an important framework for organizing theremainder of this book.

Our Planetary GreenhouseThe average temperature of Earth’s surface is main-tained at its present temperature by a finely tunedglobal heat engine. About half of the solar energyhitting our upper atmosphere penetrates to Earth’ssurface, where it is converted to heat energy as it isabsorbed by water, vegetation, soil, and human-made structures. If the average temperature of Earth’ssurface is to remain stable, an equal amount of heatenergy must be re-radiated back into space. Heatenergy, however, radiates at longer wavelengths thandoes incoming visible light, and some atmosphericgases are more transparent to visible light than theyare to radiated heat. These atmospheric greenhousegases (especially water vapor, carbon dioxide, methane,and ozone) serve as a natural part of the global heatbudget system by trapping heat near the Earth’s sur-face and keeping most of our solar-powered planetwell above the freezing temperature of water.

We have, since the beginning of the IndustrialRevolution, enhanced the greenhouse effect by sub-stantially increasing the concentrations of naturalgreenhouse gases such as CO2 in our atmosphere(Fig. 1.27). Burning of fossil fuels and devegetationof land surfaces (especially burning of tropical rainforests, clear-cutting of temperate forests, and urbandevelopment) appear to be the main sources of theexcess CO2; combustion of fossil fuels adds CO2 to

Tropical

Subpolar

Polar

Subtropical

Subtropical

Temperate

Temperate

Subpolar

Polar

Earth’s sea-surface temperatures obtained from 2 weeks of satellite infrared observations during July 1984.Temperatures are color coded, with red being warmestand decreasing through oranges, yellows, greens, blues, and black.The temperature ranges of the labeled marine climatic zones are listed in Figure 1.23 and areshifted slightly northward during the Northern Hemisphere summer.

Figure 1.26

Pattern of atmospheric CO2 increase over five decades.The slight annualvariations are due to seasonal CO2 uptake and release by land plants.Reprinted courtesy of Global Warming Art, by Robert A. Rohde.

Figure 1.27























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our atmosphere, and devegetation removes plantsthat would have removed CO2 from our atmosphereif left undisturbed. A complete summary of thisgreenhouse effect is presented in Research in Progress,pages 6–7.

Salinity–Temperature–Density RelationshipsSeawater density is a function of both temperature andsalinity, increasing with either a temperature decreaseor a salinity increase. Under typical oceanic condi-tions, temperature fluctuations exert a greater influ-ence on seawater density because the range of marinetemperatures is much greater (–2°C to 30°C) thanthe range of open-ocean salinities. Figure 1.28 graph-ically demonstrates the relationships between thetemperature, salinity, and density of water.

Seawater sinks when its density increases. Thus,the densest seawater is naturally found near the seabottom; however, the physical processes that cre-ate this dense water (evaporation, freezing, cool-ing) occur only at the ocean surface. Consequently,dense water on the sea bottom originally must havesunk from the ocean surface. This sinking processis the only mechanism available to drive circula-tion of water in the deep portions of ocean basins.An obvious feature in most oceans is a thermocline,a subsurface zone of rapid temperature decreasewith depth (about 1°C/m). The temperature dropthat exists across the thermocline creates a zone ofcomparable density increase known as a pycnocline(Fig. 1.29). The large density differences on eitherside of the thermocline effectively separate the

oceans into a two-layered system: a thin well-mixedsurface layer above the thermocline overlying aheavier, cold, thick, stable zone below. The ther-mocline and resulting pycnocline inhibit mixingand the exchange of gases, nutrients, and some-times even organisms between the two layers. Intemperate and polar regions, the thermocline is aseasonal feature. During the winter, the surface wateris cooled to the same low temperature as the deeperwater. This cooling causes the thermocline to dis-appear and results in wintertime mixing between thetwo layers. Warmer marine climates of the tropicsand subtropics are more often characterized by well-developed permanent thermoclines and their asso-ciated pycnoclines (see Fig. 3.35).

Water PressureOrganisms living below the sea surface constantlyexperience the pressure created by the weight ofthe overlying water. At sea level, pressure from theweight of the Earth’s envelope of air is about 1 kg/cm2, or 15 lb/in2, or 1 atmosphere (atm). Pres-sure in the sea increases another 1 atm for every10-m increase in depth to more than 1100 atm inthe deepest trenches. Most marine organisms cantolerate the pressure changes that accompany mod-erate changes in depth, and some even thrive in theconstant high-pressure environment of the deepsea; however, fishes with swim bladders or whaleswith lungs that collapse and expand with depth(and pressure) changes have evolved some sophis-ticated solutions to the problems associated with

30 31 32 33 34 35 36 37 38 39 40

25

20

15

10

5

0

1.019

1.020

1.021

1.022

1.023

1.024

1.025

1.026

1.027

1.028

1.029

1.030

1.031Tem

pera

ture

, °C

Salinity,‰

Temperature–salinity–density diagram for seawater. Purple curved lines represent density values (in g/cm3) resulting from the combined effects of temperatureand salinity.Three fourths of the volume of the ocean is remarkably uniform, with salinity, temperature, and density characteristics defined by the dark blue area.

Figure 1.28























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large and rapid pressure changes. These adapta-tions are described in Chapter 10.

Dissolved Gases and Acid-Base BufferingThe solubility of gases in seawater is influenced bytemperature, with greater solubility occurring at lowertemperatures. Nitrogen, carbon dioxide, and oxygenare the most abundant gases dissolved in seawater.Although molecular nitrogen (N2) accounts for 78%of our atmosphere, it is comparatively nonreactiveand therefore is not used in the basic life processesof most organisms. (Notable exceptions are someN2-fixing bacteria and the occasional careless scubadiver who dives too deep for too long.) Carbon diox-ide and oxygen, on the other hand, are metabolicallyvery active. Carbon dioxide and water are used inphotosynthesis to produce oxygen and high-energyorganic compounds. Respiration reverses the resultsof the photosynthetic process by releasing the usableenergy incorporated in the carbohydrates and fats ofan organism’s food. In contrast to photosynthesis,oxygen is used in respiration, and carbon dioxide isgiven off.

Carbon dioxide is abundant in most regions ofthe sea, and concentrations too low to support plantgrowth seldom occur. Seawater has an unusually largecapacity to absorb CO2 because most dissolved CO2

does not remain as a gas. Rather, much of the CO2

combines with water to produce a weak acid, car-bonic acid (H2CO3). Typically, carbonic acid dissoci-ates to form a hydrogen ion (H+) and a bicarbonateion (HCO3

–) or two H+ ions and a carbonate ion(CO3

2–). These reactions are summarized in the following chemical equations:

CO2 + H2O ↔ H2CO3 (1)carbon water carbonic dioxide acid

H2CO3 ↔ H+ + HCO3– (2)

carbonic hydrogen bicarbonateacid ion ion

HCO3– ↔ H+ + CO3

2– (3)bicarbonate hydrogen carbonate

ion ion ion

The arrows pointing in both directions indicatethat each reaction is reversible, either producing orremoving H+ ions. The abundance of hydrogen ionsin water solutions controls the acidity or alkalinityof that solution and is measured on a scale of 0 to14 pH units (Fig. 1.30). The pH units are a measureof the hydrogen ion concentration. Water with a lowpH is very acidic because it has a high H+ ion con-centration. A pH of 14 is very basic (or alkaline) anddenotes low H+ ion concentrations. Neutral pH (thepH of pure water) is 7 on the pH scale. The carbonicacid–bicarbonate–carbonate system in seawaterfunctions to buffer or to limit changes in seawaterpH. If excess hydrogen ions are present, the reac-tions described previously here proceed to the left,and the excess hydrogen ions are removed from so-lution. Otherwise, the solution would become moreacidic. If too few hydrogen ions are present, moreare made available by the conversion of carbonic acidto bicarbonate and bicarbonate to carbonate (a shift-ing of the above reactions to the right). In open-ocean conditions, this buffering system is veryeffective, limiting ocean water pH fluctuations to anarrow range between 7.5 and 8.4. This buffering

Salinity, ppt34 35 36

1.026 1.027 1.0280 105 15 20Temperature, °C

Dep

th, m

1000

2000

3000

Density, g/cm3

P Y C N O C L I N E T H E R M O C L I N E

Variations in water temperature (orange curve) and salinity (blue curve) at a GEOSECS station in the western South Atlantic Ocean.The resulting density profile isshown at the right (black curve).

Figure 1.29























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system also functions as a crucial component of ourplanet’s ability to accommodate the increasing con-centrations of atmospheric CO2 resulting from ourindustrial and cultural practices on land. (See Re-search in Progress, pages 6–7, for a complete dis-cussion of the potential for CO2-induced globalwarming.)

Oxygen in the form of O2 is necessary for the sur-vival of most organisms. (The major exceptions aresome anaerobic microorganisms.) Water, however,is not a good solvent for O2. The concentration of O2

in seawater generally remains between 0 and 8 partsper million, not much for active oxygen-hungryanimals. Oxygen is used by organisms in all areas ofthe marine environment, including the deepesttrenches; however, the transfer of oxygen from theatmosphere to seawater and the production of excessoxygen by photosynthetic marine organisms are theonly global-scale processes available to introduce oxy-gen into seawater. Both of these processes occur onlyat or near the surface of the ocean. Oxygen consumednear the bottom can only be replaced by oxygen fromthe surface. If replenishment is not rapid enough,available oxygen supplies will be reduced or removedcompletely. Oxygen replenishment occurs by veryslow diffusion processes from the oxygen-rich sur-face layers downward and also by density-driven sink-ing that carries oxygen-enriched waters to deep-oceanbasins. At depths of about 1000 m, animal respira-

tion and bacterial decomposition use O2 as fast as itis replaced, creating an oxygen minimum zone. Fig-ure 1.31 illustrates a typical vertical profile of dis-solved oxygen concentration from the surface to thebottom of the sea.

Dissolved NutrientsNitrate (NO3

–) and phosphate (PO43–) dissolved in

seawater are crucial fertilizers of the sea. Nitrate isthe most common reactive form of nitrogen in sea-water. These and smaller amounts of other nutrients

1

2

3

4

5

6

7

8

9

10

11

12

13

14

Basi

c

Solu

tions

Aci

dic

Solu

tions

Neutral

pH

10–1

10–2

10–3

10–4

10–5

10–6

10–7

10–8

10–9

10–10

10–11

10–12

10–13

10–14

10–13

10–12

10–11

10–10

10–9

10–8

10–7

10–6

10–5

10–4

10–3

10–2

10–1

10–0

Hydrochloric acid

Example

Lime juice

Acetic acid

Tomato juice

Black coffee

Milk

Pure water

Seawater

Borax solution

Milk of magnesia

Household ammonia

Lye

Sodium hydroxide

[H+] [OH–]

The pH scale, showing the concentration of H+ ions at each pH value. Note that the concentration scale is exponential.

Figure 1.30

Dep

th, m

1000

2000

2500

1500

500

0 2 4 6

Dissolved O , ppm2

oxygen minimum zone}

Vertical distribution of dissolved O2 in the North Pacific (150° W, 47° N)during winter. (Data from Barkley, 1968.)

Figure 1.31






















The Ocean in Motion 27

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overlying a much thicker, cold, high-density, oxygen-poor, nutrient-rich layer below.

1.4 The Ocean in MotionOcean water is constantly in motion, mov-

ing and mixing nutrients, oxygen, and heat. Waveaction, tides, currents, and density-driven verticalwater movements enhance mixing and reduce vari-ations in salinity and temperature. Oceanic circula-tion processes also serve to disperse swimming andfloating organisms and their eggs, spores, and larvae.Toxic body wastes are carried away, and food, nutri-ents, and essential elements are replenished.

Wind Waves

The curvature of the sphere of the Earth causes thesun to warm latitudes of the Earth’s surface andoverlying air near the equator more than at thepoles. This differential warming of the atmosphereby the sun drives patterns of winds that blow acrossthe ocean surface, creating waves and surface cur-rents. Surface ocean waves are periodic vertical dis-turbances of the sea surface. They typically travelin a repeating series of alternating wave crests and

are used by photosynthetic organisms living in thenear-surface waters. These same nutrients eventu-ally are excreted back into the water at all depthsas waste products of the organisms that consumeand digest photosynthetic organisms. This once-living waste material sinks as part of a process thateventually removes nutrients from near-surface wa-ters and increases their concentrations in deeperwaters. (More details concerning these patterns ofnutrient distribution appear in Chapters 3 and 4.)

The vertical distribution of dissolved nutrientsis usually opposite that of dissolved oxygen. This op-posing pattern of vertical oxygen and nutrient dis-tribution reflect the contrasting biological processesthat influence their concentrations in seawater. Oxy-gen is normally produced by near-surface photosyn-thesizers and consumed by animals and bacteria atall depths, whereas nutrients are consumed by pho-tosynthesizers near the surface and are excreted byorganisms at all depths. These contrasting verticalpatterns of nutrient and oxygen abundance reinforcethe temperature and density-based stratification ofmuch of the ocean into a two-layer system (Fig. 1.32),a warm, low-density, oxygen-rich, nutrient-poor sur-face layer of ocean water a few tens of meters deep

PYCNOCLINE

high lighthigh temperaturelow density

low pressurelow nutrienthigh oxygen

SURFACE WATER

DEEP WATER

low lightlow temperaturehigh density

high pressurehigh nutrientlow oxygen

Contrasting features of shallow and deep ocean water resulting in a two-layer system separated by a pycnocline.

Figure 1.32

SUMMARY POINTSProperties of Seawater

• The unique characteristics of pure water deter-mine most of the basic properties of salt water.The differential affinity of oxygen and hydrogenfor electrons creates an electrical charge sepa-ration within water molecules that forms hydro-gen bonds between adjacent water molecules.Hydrogen bonding, in turn, affects water’s basicproperties, including viscosity, surface ten-sion, heat capacity, solvent capability, density–temperature relationships, and its stability asa liquid.

• Salt water contains a great variety of dissolvedsalts, gases, and other inorganic and organicsubstances. These dissolved molecules andcompounds affect many characteristics of sea-water, including its density, osmotic properties,buffering capacity, and other biologically sig-nificant features.























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ocean, the effective depth of mixing by wind-drivenwaves is generally no greater than 50 m.

Waves entering shallow water behave differentlythan open-ocean waves. When the water depth is lessthan one half the wavelength, bottom friction beginsto slow the forward speed of the waves. This slow-ing causes the waves to become higher and steeper.At the point where the wave height becomes greaterthan about one seventh of the wavelength, the wavetop becomes unstable as it outruns its base. It thenpitches forward and breaks. The energy released onshorelines (and on the organisms living there) bybreaking waves can be enormous and is a major forcein shaping the physical and biological character ofmost coastlines.

Surface Currents

Ocean surface currents occur when winds blowover the ocean with a constancy of direction andvelocity for a sufficient period of time to transfer

troughs. The size and energy of waves are depen-dent on the wind’s velocity, duration, and fetch (thedistance over which the wind blows in contact withthe sea surface). Ocean waves range in height fromvery small capillary waves a few millimeters highto monster storm waves surpassing 30 m in height(Fig. 1.33). Waves are commonly characterized bytheir height, wavelength (Fig. 1.34), and period (thetime required for two successive wave crests to passa fixed point). Regardless of their size, these gen-eral features of waves apply to all ocean waves.

Once created by surface winds, ocean waves travelaway from their area of formation. Only the wave shapeadvances, however, transmitting the energy forward.The water particles themselves do not advance in thedirection of the wave. Instead, their paths approximatevertical circles with little net forward motion (Fig. 1.34).Waves provide an important mechanism to mix thenear-surface layer of the sea. The depth to which wavesproduce noticeable motion is about one half the wave-length. As wavelengths seldom exceed 100 m in any

30

20

10

5 10 15

Wave period, s

Wav

e he

ight

, m

Rare, but

theoretically possible,

monster waves

0

(a) Range of ocean surface wave heights, determined over a 10-day period by the TOPEX/Poseidon satellite. (b) Wave periods and their corresponding range of heights.

Figure 1.33

(a)

(b)























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momentum to the water through friction. Unlikeocean waves, surface currents do represent the hor-izontal movement of water molecules. The momen-tum imparted to the sea by these winds drivesregular patterns of broad, slow, relatively shallowocean surface currents. Some currents transportmore than 100 times the volume of water carriedby all the Earth’s rivers combined. Currents of suchmagnitude greatly affect the distribution of marineorganisms and the rate of heat transport from trop-ical to polar regions.

These currents are driven by stable patterns ofwinds at the ocean surface. Three major wind beltsoccur in the Northern Hemisphere. The trade winds,near 15° N latitude, blow from northeast to south-west. The westerlies, in the middle latitudes, blowprimarily from the west–southwest. And the polar east-erlies, at very high latitudes, blow from east to west.Each of these wind belts has its mirror-image coun-terpart in the Southern Hemisphere. As the surfacelayer of water is moved horizontally by these broadbelts of surface winds, momentum is transferred firstto the sea surface and then downward. The speed ofthe deeper water steadily diminishes as momentumis lost to overcome the viscosity of the water. Even-tually, at depths generally less than 200 m, the speedof wind-driven currents becomes negligible.

The surface water moved by the wind does notflow parallel to the wind direction but experiencesan appreciable deflection, known as the Corioliseffect. The Coriolis effect influences moving air andwater masses by causing a deflection to the right inthe Northern Hemisphere and to the left in the South-ern Hemisphere. As successively deeper water layersare set into motion by the water above them, theyundergo a further Coriolis deflection away from the

direction of the water just above to produce a spiralof current directions from the surface downward ina pattern known as an Ekman spiral (Fig. 1.35). Themagnitude of the Coriolis deflection of wind-drivencurrents varies from about 15 degrees in shallowcoastal regions to nearly 45 degrees in the open ocean.The net Coriolis deflection from the wind headingscreates a pattern of wind-forced ocean-surface cur-rents that flows primarily in east to west or west toeast directions.

Except for the region just north of Antarctica,the continuous flow of these wind-driven east–westcurrents is obstructed by continents. This causes wa-ter transported by currents from one side of the oceanto pile up against continental margins on the otherside. The surface of the equatorial Pacific Ocean, forexample, is about 2 m higher on the west side thanit is on the east. The opposite is true in the middlelatitudes of both hemispheres, where the east side ishigher. Eventually, the water must flow away fromthese areas of accumulation. Either it flows directlyback against the established current, producing acountercurrent, or it flows as a continental bound-ary current parallel to a continental margin from ar-eas of accumulation to areas where water has beenremoved. Both these current patterns exist, but theyare particularly clear in the North Pacific Ocean(Fig. 1.36). An east-flowing Equatorial Countercur-rent divides the west-flowing North Pacific Equato-rial Current. The north–south-flowing continentalboundary currents merge into the east–west currentsto produce large circular current patterns, or gyres.Similar current patterns are found in the other majorocean basins (Fig. 1.37).

Maps similar to Figure 1.37 are useful for de-scribing long-term average patterns of surface ocean

Direction of wave travel

Wavelength (L)Height

Still water level

Wave crest

0.5 LWave trough

Wave form and pattern of water motion in a deep-water wave as it moves to the right toward a shoreline. Circles indicate orbits of water particles diminishing withdepth.There is little water motion below a depth equal to one half of the wavelength.

Figure 1.34























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circulation; however, they tend to hide the complex-ity and even the beauty that exist in these currentsat any moment in time. Current maps are analogousto the blurred images taken of a night freeway scenewhen the camera shutter is held open for hours. Thepattern of traffic flow is obvious, yet the details of ve-hicles’ slowing, accelerating, and changing lanes arecompletely lost. The continued development of satel-lite monitoring of ocean surface phenomena providesan improved approach for visualizing and understand-ing global-scale surface current patterns. Figure 1.38is a satellite image of a portion of the North Atlantic

Ocean, including the Gulf Stream. This image em-phasizes ocean-surface temperature differences andreveals remarkable meanders, constrictions, andnearly detached rings of Gulf Stream water as thecurrent flows north and east along the path shownin Figure 1.37.

Ocean Tides

Tides are ocean surface phenomena familiar to any-one who has spent time on a seashore. They areactually very-long-period waves that are usuallyimperceptible in the open ocean and only becomenoticeable near the shoreline, where they can be ob-served as a periodic rise and fall of the sea surface.The maximum elevation of the tide, known as hightide, is followed by a fall in sea level to a minimumelevation, or low tide. On most coastlines, two hightides and two low tides occur each day. The verticaldifference between consecutive high tides and lowtides is the tidal range, which varies from just a fewcentimeters in the Mediterranean Sea to more than15 m in the long narrow Bay of Fundy between NovaScotia and New Brunswick. The global tidal rangeaverages about 2 m.

In 1687, in his Principia Mathematica, Sir IsaacNewton explained ocean tides as the consequence ofthe gravitational attraction of the moon and sun on

Net watertransport

entscurrSpiraling

45°Surface current

No water motion

Win

d

EKMAN SPIRAL IN THE NORTHERN HEMISPHERE

A spiral of current directions, indicating greater deflection to the right (in the Northern Hemisphere), which increases with depth due to the Coriolis effect.The arrowlength indicates relative current speed.

Figure 1.35

wind-driven currents

continental boundary currents

Polar Easterlies

Westerlies

Trade Winds

Generalized surface-current flow in the North Pacific Ocean. Blue arrowsindicate general directions of ocean-surface winds.

Figure 1.36























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the oceans of the Earth. According to Newton’s lawof universal gravitation, our moon, because of itscloseness to the Earth, exerts about twice as muchtide-generating force as does the more distant butmuch larger sun. The constantly changing positionsof the Earth relative to the moon and sun nicelyaccount for the timing of ocean tides, yet Newton’sequilibrium model of ocean tides is seriously defi-cient in its ability to explain real tidal patterns in realoceans. Those of you interested in Newton’s modeland other models of ocean tides should consult a cur-rent oceanography text. For our purposes, a descrip-tion of the results of tide-producing forces, ratherthan their causes, will suffice.

The moon completes one orbit around the Eartheach lunar month (27.5 days). Hypothetically, if theEarth were completely covered with water, two bulgesof water, or lunar tides, would occur: one on the sideof the Earth facing the moon and the other on theopposite side of the globe (Fig. 1.39). As the Earthmakes a complete rotation every 24 hours, a pointon the Earth’s surface (indicated by the marker in

Fig. 1.39) would first experience a high tide (a), thena low tide (b), another high tide (c), another low tide(d), and finally another high tide (e). During that ro-tation, however, the moon advances in its own orbitso that an additional 50 minutes of the Earth’s rota-tion is required to bring our reference point directlyin line with the moon again. Thus, the referencepoint experiences only two equal high and twoequal low tides every 24 hours and 50 minutes (a lunar day).

In a similar manner, the sun–Earth system alsogenerates tide-producing forces that yield a solar tideabout one half as large as the lunar tide. The solartide is expressed as a variation on the basic lunar tidalpattern, not as a separate set of tides. When the sun,the moon, and the Earth are in approximate align-ment (at the time of the new moon and full moon,Fig. 1.40), the solar tide has an additive effect on thelunar tide, creating several days of extra-high hightides and very low low tides known as spring tides.One week later, when the sun and moon are at rightangles to each other relative to the Earth, the solar

* *

*

*

*

Antarctic

Circumpolar Current

*

1

1

1

1

1

1

22

2

34

65

7

8

9

10

1112

13

14

15

16

Major warm currents1 = Equatorial Currents2 = Equatorial Countercurrents3 = Kuroshio4 = Gulf Stream5 = East Australia6 = Brazil7 = Somali8 = Antilles9 = Alaska

Major cold currents10 = Peru11 = California12 = Canary13 = Benguela14 = Labrador15 = Oyashio16 = West Australia

= gyre centers

The major surface currents of the world ocean. (Adapted from Pickard, G. L. and W. J. Emory, eds. Descriptive Physical Oceanography. Pergamon Press, 1982.)

Figure 1.37























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tide partially cancels the effects of the lunar tide toproduce moderate tides known as neap tides. Dur-ing each lunar month, two sets of spring tides andtwo sets of neap tides occur.

So far, only the effects of tide-producing forcesin a not very realistic ocean covering a hypothetical

planet without continents have been considered.What happens when continental landmasses are takeninto consideration? The continents block the west-ward passage of the tidal bulges as the Earth rotatesunder them. Unable to move freely around the globe,these tidal impulses establish complex patterns withineach ocean basin that may differ markedly from thetidal patterns of adjacent ocean basins or even otherregions of the same ocean basin.

Figure 1.41 shows some regional variations in thedaily tidal configuration at three stations along theeast and west coasts of North America. Portland,Maine experiences two high tides and two low tideseach lunar day. The two high tides are quite similarto each other, as are the two low tides. Such tidal pat-terns, referred to as semidiurnal (semidaily) tides,are characteristic of much of the East Coast of theUnited States. The tidal pattern at Pensacola, Florida,on the Gulf Coast, consists of one high tide and onelow tide each lunar day. This is a diurnal, or daily,tide. Different yet is the daily tidal pattern at SanDiego, California. There, two high tides and two lowtides occur each day, but successive high tides arequite different from each other. This type of tidalpattern, characteristic of the West Coast of NorthAmerica, is a mixed semidiurnal tide. Figure 1.42 out-lines the geographical occurrence of diurnal, semi-diurnal, and mixed semidiurnal tides for coastal areas.

Tidal conditions for any day on a selected coast-line can be predicted because the periodic nature oftides is easily observed and recorded. For the most part,prediction of the timing and amplitude of future tidesis based on the astronomical positions of the sun andmoon relative to the Earth and on historical observa-tions of actual tidal occurrences at tide-recording

National Oceanic and Atmospheric Administration (NOAA) satellite image ofthe Gulf Stream off the U.S. East Coast during early April 1984.Water surfacetemperatures are represented by a range of colors, from cold (–2°C to 9°C,violet) through blue, green, yellow, orange, and red (very warm, 26°C to28°C).The Gulf Stream appears as a narrow band of warm water off theFlorida coast and then cools gradually as it moves northeast and releasesheat to the atmosphere. North of Cape Hatteras, the current begins tomeander and form isolated rings typical of strong surface ocean currents.

Figure 1.38

Elapsed time:

Tide height:

Stage of tide:

0 hr

(a)

High

6 hr

(b)

Low

12 hr

(c)

To Moon

High

18 hr

(d)

Low

24 hr

(e)

High

Each day as the Earth rotates, a point on its surface (in this case, Florida, as indicated by the yellow marker) experiences high tides when under tidal bulges (a, c, and eabove), and low tides when at right angles to tidal bulges (b and d above).

Figure 1.39























1ST REVISE

Day:

Phase:

Tideheight:

Tide:

1

Spring

Full

8

Neap

3rd quarter

15

Spring

New

22

Weekly inequality

Neap

1st quarter

29

Spring

Full

To Sun

Moon

Earth

Weekly tidal variations caused by changes in the relative positions of the Earth, moon, and sun.

Figure 1.40

Portland, Maine Pensacola, Florida San Diego, California

high tides

low tides

high tide

low tide

higherhightide

higherlowtidelower

lowtide

lowerhightide

-1

0

0 0 0 121212 24 24 24

SEMIDIURNAL DIURNAL MIXED SEMIDIURNAL

1

2

3

Tid

e he

ight

, m

Time, hr

Three common types of tides.

Figure 1.41

stations along coastlines and in harbors around theworld. The National Ocean Survey of the U.S. Depart-ment of Commerce uses information from these recordsto compile and publish annual “Tide Tables of Highand Low Water Predictions” for principal ports alongmost coastlines of the world.

Vertical Water Movements

Vertical movements of ocean water are produced byupwelling and sinking processes. These processestend to break down the vertical stratification estab-lished by the pycnocline (Fig. 1.32). Localized areasof upwelling are created by several oceanic processesthat bring deeper nutrient-rich waters to the surface.These processes are described in Chapter 3. The

continuous availability of deep-water nutrients thatcan be used by photosynthetic organisms accountsfor the high productivity so characteristic of upwellingregions. Several of the world’s most important fish-eries are based in upwelling areas.

The physical processes that increase seawaterdensity are strictly surface features that affect watertemperature or salinity, and the resulting vertical cir-culation is referred to as thermohaline circulation.Seawater sinking from the surface is usually highlyoxygenated because it has been in contact with theatmosphere, and thus, it transports dissolved oxygento deep areas of the ocean basins that would other-wise be anoxic (lacking oxygen). The chief areas ofsinking are located in the colder latitudes, where seasurface temperatures are low. After sinking, this dense























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water continues to spread and flow horizontally asvery slow and ill-defined deep ocean currents. Timespans of a few hundred to a thousand years are re-quired for water that sinks in the North Atlantic toreach the surface again in the Southern Hemisphere.Figure 1.43 outlines the general patterns of large-scaledeep-ocean thermohaline circulation.

On a somewhat smaller scale, the Mediterraneanand Black Seas provide two contrasting examples ofdensity-driven thermohaline circulation. In the aridclimate of the Mediterranean Sea, particularly at itseastern end, evaporation from the sea surface greatlyexceeds precipitation and runoff. The resulting high-salinity and high-density water sinks and fills thedeeper parts of the Mediterranean basin. The sinkingof surface water provides substantial mixing and O2

replenishment for the deep water of the Mediterraneanand is similar to the deep circulation of the open ocean.Part of this deep dense water eventually flows out ofthe Mediterranean over a shallow sill at Gibraltar anddown into the Atlantic Ocean. To compensate for theoutflow and losses due to evaporation, nearly 2 mil-lion cubic meters of Atlantic surface water flow intothe Mediterranean each second. The currents at Gibral-tar can be compared with two large rivers flowing inopposite directions, one above the other (Fig. 1.44).

Like the Mediterranean, the Black Sea is isolatedby a shallow sill (at the Bosporus). In contrast to

the Mediterranean Sea, however, the Black Sea ischaracterized by a large excess of precipitation andriver runoff. In this sense, the circulation of the BlackSea resembles that of some semienclosed fjords of Scan-dinavia and the west coast of Canada. The dilute sur-face waters of the Black Sea form a shallow low-densitylayer that does not mix with the higher-salinity denserwater below. Instead, it flows into the MediterraneanSea through the Bosporus (Fig. 1.44). Low-salinityoxygen-rich surface water does not sink, and thus, themore common oxygen-dependent forms of marine lifeare restricted to the uppermost layer. Below 150 m,the Black Sea is stagnant and anoxic. Yet these anoxicdeep waters of the Black Sea (more than 80% of its vol-ume) are by no means lifeless. The rain of organic ma-terial from above accumulates and provides abundantnourishment for several types of anaerobic bacteria.

Semidiurnal tides Mixed semidiurnal tidesDiurnal tides

The geographic occurrence of the three types of tides described in Figure 1.41.

Figure 1.42

SUMMARY POINTSThe Ocean in Motion

• The sea is constantly moving, both horizontallyand vertically. Winds, waves, tides, currents,sinking water masses, and upwelling all con-tribute to the remarkable homogeneity of theworld ocean.






















Classification of the Marine Environment 35

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1.5Classification of the Marine EnvironmentThe large size and enormous complexity

of the marine environment make it a difficult sys-tem to classify. Many systems of classification havebeen proposed, each reflecting the interest and biasof the classifier. The system presented here is a slightlymodified version of a widely accepted scheme pro-posed by Hedgpeth over a half-century ago. Theterms used in Figure 1.45 designate particular zonesof the marine environment. These terms are easily

confused with the names of groups of organisms thatnormally inhabit these zones; these are introducedin the next chapter. The boundaries of these zonesare defined on the basis of physical characteristicssuch as water temperature, water depth, and avail-able light.

Working downward from the ocean surface, thelimits of intertidal zones are defined by tidal fluctua-tions of sea level along the shoreline. These zonesand their inhabitants are examined in detail in Chap-ter 9. The splash, intertidal, and inner shelf zones

ATLANTICOCEAN

MEDITERRANEANSEA

BLACKSEA

Evaporation

Precipitation Runoff

StagnantWell mixed

15

22

1630

39

3938

39

3837

36.5

Gib

ralta

r

Dep

th, k

m

Bosp

orus

A comparison of the deep-ocean circulation patterns of two marginal seas, the Mediterranean Sea and the Black Sea.The numbers represent salinity in ‰.

Figure 1.44

= areas of sinking surface water

The general pattern of deep-ocean circulation in the major ocean basins. Light blue represents flow at intermediate depths, whereas darker blue represents deeperflow. Sinking of cold surface water occurs at high latitudes indicated by ovals. (Adapted from Broecker,W. S., et al., Nature 315 (1985): XXX–XXX.)

Figure 1.43























occur in the photic (lighted) zone, where the lightintensity is great enough to accommodate photo-synthesis. The depth of the photic zone depends onconditions that affect light penetration in water, ex-tending much deeper (up to 200 m) in clear tropicalwaters than in murky coastal waters of temperate orpolar seas (sometimes less than 5 m). The rest of theocean volume is the perpetually dark aphotic (un-lighted) zone, where the absence of sunlight pro-hibits photosynthesis.

The benthic division refers to the environmentof the sea bottom. The inner shelf includes the seafloorfrom the low-tide line to the bottom of the photiczone. Beyond that, to the edge of the continental shelf,is the outer shelf. The bathyal zone is approximatelyequivalent to the continental slope areas. The abyssalzone refers to abyssal plains and other ocean-bottomareas between 3000 and 6000 m in depth. The up-per boundary of this zone is sometimes defined as theregion where the water temperature never exceeds4°C. The hadal zone is that part of the ocean bottombelow 6000 m, primarily the trench areas.

The pelagic division includes the entire watermass of the ocean. For our purposes, it is sufficientto separate the pelagic region into two provinces: theneritic province, which includes the water over the

continental shelves, and the oceanic province, thewater of the deep ocean basins. Each of these sub-divisions of the ocean environment is inhabitedby characteristic assemblages of marine organisms. Itis these benthic and pelagic organisms and their in-teractions with their immediate surroundings that arethe subject of the remaining chapters of this book.

SUMMARY POINTSClassification of the Marine Environment

• Energy from the sun warms the sea’s surfaceand creates winds that result in a two-layeredworld ocean, with a shallow, well-mixed, warm,sunlit layer overlaying a much deeper, cold,dark, high-pressure layer of slowly moving waterbelow.

• The three-dimensional marine environment canbe separated into two broad divisions, the ben-thic realm of the sea floor and the pelagic watercolumn. These, in turn, may be subdivided intosmaller categories based on water depth, lightavailability, and ambient temperature.

O C E A N I C P R O V I N C E

Photic zone

Aphotic zonePELAGIC DIVISION

Inte

rtida

l zon

e

Bathyal

Abyssal

Hadal

–0

–200

–4000

–6000

Dep

th, m

BENTHIC DIVISION

NERITICPROVINCE

Contin

ental

shelf

A system for classifying the marine environment. (Adapted from J.W. Hedgpeth, ed. Treatise on Marine Ecology and Paleoecology. 2 vols. Geological Society of America, 1966.)

Figure 1.45






















STUDY GUIDE

Topics for Discussion and Review

1. Volcanic activity, earthquakes, and the distribu-tion of continents on Earth today are all due toa single process. State what it is and describe howit is responsible for the above phenomena.

2. Label a diagrammatic cross-section of the NorthAtlantic Ocean with all benthic features (suchas trenches and shelf breaks) presented in thischapter. Then discuss whether this is the bestway to categorize the sea floor.

3. What is sonar, and why is it perhaps the best wayto determine the dimensions of ocean basins?

4. List three properties of pure water that are high-est of all common natural substances.

5. List and describe the major physical and chem-ical features of seawater that change markedlyfrom the sea surface downward. How do thesesame features change along the sea surface as oneproceeds from the equator north or south to either pole?

6. Compare and contrast the osmotic changes thata Portuguese man-of-war will experience whilebeing blown from the open sea into the mouthof a large river.

7. Why are the terms “cold blooded” and “warmblooded” often inappropriate when used to de-scribe the thermal strategies of marine animals?

8. Describe how the heating of the Earth is similarto the heating of a greenhouse.

9. Describe the buffering mechanism at work in thesea, and then compare it with the buffering ofyour own blood.

10. Define spring and neap tides, and then explainwhy both occur twice each month.

Suggestions for Further Reading

Broad, W. J. 1997. The Universe Below: Discoveringthe Secrets of the Deep Sea. Simon & Schuster,New York.

Clark, P. U., N. G. Pisins, T. F. Stocker, and A. J. Weaver.2002. The role of the thermohaline circulation inabrupt climate change. Nature 415:863–869.

Cloud, P. 1989. Oasis in Space: Earth History From theBeginning. W. W. Norton, New York.

Detrick, R. 2004. The engine that drives the earth.Oceanus 42(2):6–12.

Duxbury, A. C., and A. B. Duxbury. 1991. An Intro-duction to the World’s Oceans. Wm. C. BrownPublishing, Dubuque, Iowa.

Earle, S. 2001. National Geographic Atlas of theOcean: The Deep Frontier. National Geographic,Washington, D.C.

Ellis, R. 2000. Encyclopedia of the Sea. Knopf, New York.Geist, E. L., V. V. Titov, and C. E. Synolakis, 2006.

Tsunami: wave of change. Scientific American294:56–63.

Hogg, N. 1992. The Gulf Stream and its recircula-tion. Oceanus 35:28–37.

Jenkyns, H. C. 1994. Early history of the oceans.Oceanus 36:49–52.

Keleman, P. B. 2009. The origin of the land underthe sea. Scientific American 300(2):42–47.

Kunzig, R. 1999. The Restless Sea: Exploring the WorldBeneath the Waves. W. W. Norton, New York.

Leier, M. 2001. World Atlas of the Oceans: More than200 Maps and Charts of the Ocean Floor. FireflyBooks, Richmond Hill, Ontario.

Mann, M. E. 2007. Climate over the past two millen-nia. Annual Review of Earth and Planetary Sciences35:111–136.

McDonald, K. C., and P. J. Fox. 1990. The mid-oceanridge. Scientific American 262:72–79.

Melville, W. K., and P. Matusov. 2002. Distributionof breaking waves at the ocean surface. Nature417:58–63.

Satake, K. and A. F. Atwater. 2007. Long-term per-spectives on giant earthquakes and tsunamis atsubduction zones. Annual Review of Earth andPlanetary Sciences 35:349–374.

Tarduno, J. 2008. Hot spots unplugged. ScientificAmerican 298(1):87–93.

Weller, R. A., and D. M. Farmer. 1992. Dynamics ofthe ocean’s mixed layer. Oceanus 35:46–55.

Marine Biology Online

Connect to this book’s Companion Web Site athttp://biology.jbpub.com/marinelife/10e. Thesite provides an online review area, featuringchapter outlines, study quizzes, an interactiveglossary, crossword puzzles,animated flashcards, and Weblinks to help you explore theworld of marine biology onyour own.

Any copy of Introduction to the Biology ofMarine Life, Tenth Edition, that was purchasednew in North America should include a free,bound-in access code for the Companion WebSite. To redeem your code or to purchase accessseparately, please visit http://www.jblearning.com.

http

://biology.jbpub.com

/ma

rin

e/

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