448 Chapter 16

16.1 Ocean Circulation

Reading StrategyIdentifying Main Ideas Copy and expandthe table below. As you read, write the mainidea of each topic.

Key ConceptsHow do surface currentsdevelop?

How do ocean currentsaffect climate?

Why is upwellingimportant?

How are density currentsformed?

Vocabulary◆ ocean current◆ surface current◆ gyre◆ Coriolis effect◆ upwelling◆ density current

Ocean water is constantly in motion, powered by many differentforces. Winds, for example, generate surface currents, which influencecoastal climate. Winds also produce waves like the ones shown inFigure 1. Some waves carry energy from powerful storms to distantshores, where their impact erodes the land. In some areas, density dif-ferences create deep-ocean circulation. This circulation is importantfor ocean mixing and recycling nutrients.

Surface CirculationOcean currents are masses of ocean water that flow from one place toanother. The amount of water can be large or small. Ocean currentscan be at the surface or deep below. The creation of these currents canbe simple or complex. In all cases, however, the currents that are gen-erated involve water masses in motion.

Surface Currents Surface currents are movements of water thatflow horizontally in the upper part of the ocean’s surface.

Surface currents develop from friction between the ocean andthe wind that blows across its surface. Some of these currents do notlast long, and they affect only small areas. Such water movements areresponses to local or seasonal influences. Other surface currents aremore permanent and extend over large portions of the oceans. Thesemajor horizontal movements of surface waters are closely related tothe general circulation pattern of the atmosphere.

Figure 1 Wind not only createswaves, but it also provides theforce that drives the ocean’ssurface circulation.

Topic Main Idea

Surface currents a.

Gyres b.

Ocean currents and climate c.

Upwelling d. ?

?

?

?

448 Chapter 16

FOCUS

Section Objectives16.1 Explain how surface currents

develop.16.2 Describe how ocean currents

affect climate.16.3 State the importance of

upwelling.16.4 Describe the formation of

density currents.

Build VocabularyParaphrase Have students define thewords in this section using their ownwords. For example, students maydefine gyre as “flow of water in a largecircle.”

Reading StrategyPossible responses are as follows:a. caused by windb. circular movement of waterc. Currents transfer heat from hotterregions to cooler regions and modifyclimate.d. cold water exposed at the surfacee. vertical currents caused by densitydifferences; denser water sinksf. Cold surface water sinks at the polesbecause it is dense.g. causes increased salinity andincreased densityh. Ocean water moves around Earthbecause of density differences.

L2

L2

Reading Focus

1

Section 16.1

HSES_1eTE_C16.qxd 5/16/04 12:38 PM Page 448

S. Equatorial C.

California C.

N. Pacific C.

West Wind Drift

Gul

f Stream

Warm

Cold60˚

40˚

20˚

0˚

20˚

40˚

60˚East Wind Drift

80˚

80˚

120°60°0°30˚150° 120°

60˚

40˚

20˚

0˚

20˚

40˚

60˚

80˚

80˚

30˚60°90° 90° 150°

120°60°0°30˚150° 120° 30˚60°90° 90° 150°

East Wind Drift

West Wind

N. Equatorial C.

N. Equatorial C.

Alaskan

C.

W. A

ustr

alia

nC

.

S. Equatorial C.

N. Equatorial C.

S. Equatorial C.

Benguela

C.

Peru

C.

Bra

zil C

.

N. Atlantic C.

Labrador C. E. Gree

nland C.

Norwegian

C.

CanaryC

.

Somali

C.

Agulh

asC

.

Leeu

win

C.

E.A

ustr

alia

nC.

Kuroshio C.Oya

shio

C.

NorthPacific Gyre

SouthPacific Gyre South

AtlanticGyre

NorthAtlantic

Gyre

IndianOcean Gyre

The Dynamic Ocean 449

Gyres Huge circular-moving current systems dominate the surfacesof the oceans. These large whirls of water within an ocean basin arecalled gyres (gyros � a circle). There are five main ocean gyres: theNorth Pacific Gyre, the South Pacific Gyre, the North Atlantic Gyre,the South Atlantic Gyre, and the Indian Ocean Gyre. Find these gyresin Figure 2.

Although wind is the force that generates surface currents, otherfactors also influence the movement of ocean waters. The most signif-icant of these is the Coriolis effect. The Coriolis effect is the deflectionof currents away from their original course as a result of Earth’s rota-tion. Because of Earth’s rotation, currents are deflected to theright in the Northern Hemisphere and to the left in the SouthernHemisphere. As a consequence, gyres flow in opposite directions inthe two different hemispheres.

Four main currents generally exist within each gyre. For example,the North Pacific Gyre consists of the North Equatorial Current, theKuroshio Current, the North Pacific Current, and the CaliforniaCurrent. The tracking of floating objects that are released into theocean reveals that it takes about six years for the objects to go all theway around the loop.

Why do gyres in the Northern Hemisphere flow inthe opposite direction of gyres in the SouthernHemisphere?

Ocean Surface Currents

Figure 2The ocean’s circulation isorganized into five majorgyres, or circular currentsystems. The West Wind Driftflows around the continentof Antarctica.

MovementLocate Which currents makeup the North Atlantic Gyre?Locate Find the West WindDrift on the map. Explainwhy the West Wind Drift isthe only current thatcompletely encircles Earth. Drawing ConclusionsWhy is there not anothercomparable current thatencircles Earth at the samelatitude in the NorthernHemisphere?

INSTRUCT

Surface Circulation

Locate North Atlantic Gyre consists ofthe North Equatorial Current, the GulfStream, the North Atlantic Current, theCanary Current.

Locate The West Wind Drift can encircleEarth because there are no land masses/continents obstructing its path.

Drawing Conclusions In the NorthernHemisphere at the same latitude, there arelandmasses and continents that block thepath of a circumpolar current.

Use VisualsFigure 2 This diagram shows oceansurface currents all over the world. Ask:What happens to ocean currentswhen they hit a landmass? (They aredeflected parallel to the shore.) Why dogyres in the northern Atlantic andPacific oceans mostly rotateclockwise? (The Coriolis effect causescurrents to be deflected to the right inthe Northern Hemisphere.) Why dogyres in the southern Atlantic andPacific oceans mostly rotatecounterclockwise? (The Coriolis effectcauses currents to be deflected to the leftin the Southern Hemisphere.)Visual

L1

2

The Dynamic Ocean 449

Customize for English Language Learners

Teach students that gyre comes from the wordgyros, which means “circle.” List several otherwords containing this root, and have studentslook up their definitions. Have students explainwhat all the words have in common. Forexample: gyre, gyroscope, gyrate, gyration,

and gyroscopic all have to do with moving ina circle. Also introduce students to the Greekfood, the gyro, which is meat that rotates on aspit and is served in a pita. Show students apicture of a gyro, and if possible let themtaste one.

Answer to . . .

because currents aredeflected to the right in

the Northern Hemisphere and to theleft in the Southern Hemisphere dueto Earth’s rotation

HSES_1eTE_C16.qxd 5/16/04 12:38 PM Page 449

450 Chapter 16

Ocean Currents and Climate Ocean cur-rents have an important effect on climates. Whencurrents from low-latitude regions move intohigher latitudes, they transfer heat from warmer tocooler areas on Earth. The Gulf Stream, a warmwater current shown in Figure 3, is an excellent exam-ple of this phenomenon. The Gulf Stream bringswarm water from the equator up to the NorthAtlantic Current, which is an extension of the GulfStream. This current allows Great Britain and muchof northwestern Europe to be warmer during thewinter than one would expect for their latitudes,

which are similar to the latitudes of Alaska and Newfoundland. Theprevailing westerly winds carry this warming effect far inland. Forexample, Berlin, Germany (52 degrees north latitude), has an averageJanuary temperature similar to that experienced at New York City,which lies 12 degrees latitude farther south.

The effects of these warm ocean currents are felt mostly in themiddle latitudes in winter. In contrast, the influence of cold currentsis most felt in the tropics or during summer months in the middle lat-itudes. Cold currents begin in cold high-latitude regions. As coldwater currents travel toward the equator, they help moderate thewarm temperatures of adjacent land areas. Such is the case for theBenguela Current along western Africa, the Peru Current along thewest coast of South America, and the California Current. These cur-rents are shown in Figure 2.

Ocean currents also play a major role in maintaining Earth’s heatbalance. They do this by transferring heat from the tropics, where thereis an excess of heat, to the polar regions, where less heat exists. Oceanwater movement accounts for about a quarter of this heat transport.Winds transport the remaining three-quarters.

Upwelling In addition to producing surface currents, winds canalso cause vertical water movements. Upwelling is the rising of coldwater from deeper layers to replace warmer surface water. Upwelling isa common wind-induced vertical movement. One type of upwelling,called coastal upwelling, is most characteristic along the west coasts ofcontinents, most notably along California, western South America, andWest Africa.

Coastal upwelling occurs in these areas when winds blow towardthe equator and parallel to the coast. Coastal winds combined with theCoriolis effect cause surface water to move away from shore. As thesurface layer moves away from the coast, it is replaced by water that“upwells” from below the surface. This slow upward movement ofwater from depths of 50 to 300 meters brings water that is cooler than

Figure 3 Gulf Stream This false-color satellite image of seasurface temperatures shows thecourse of the Gulf Stream. Thewarm waters of the Gulf Streamare shown in red and orangealong the east coast of Floridaand the Carolinas. Thesurrounding colder waters areshown in green, blue, and purple.Compare this image to the mapof the Gulf Stream in Figure 2.

For: Links on ocean currents

Visit: www.SciLinks.org

Web Code: cjn-5161

450 Chapter 16

IntegrateSocial StudiesEarly Settlers Early settlers of the 13original colonies were quite surprisedby, and unprepared for, the bitter coldwinters they encountered in the NewWorld. Since America was farther souththan England, they assumed the climatehere would be warmer. However, theydid not know that the powerful, warmGulf Stream current kept England at awarmer temperature than would beexpected based on latitude alone. Directstudents to use Figure 2, the reading,and their own knowledge to answer thefollowing questions. Ask: What partsof North America are at the samelatitude as England? (Alaska, northernCanada) Why is northeastern Canadaso much colder than England? (Englandis warmed by the Gulf Stream Current,while northeastern Canada is cooled bythe Labrador Current.) If the Englishknew America was colder thanEngland, how might this have changedtheir expeditions? (Sample answers:They would have brought warmer clothesor more food, or they might not havesettled in the northern colonies.)Visual, Logical

L2

Section 16.1 (continued)

During upwelling, cold water is exposed at thesurface when the warm surface layer of wateris removed by strong winds. Upwelling ofnutrient rich cold water is critical to fishingindustries all over the world, but it is especially

important off the coast of Peru. Unfortunately,El Niño events often disrupt upwelling byreducing surface wind speeds, which causesterrible consequences for fishes.

Facts and Figures

Download a worksheet on oceancurrents for students to complete,and find additional teacher supportfrom NSTA SciLinks.

HSES_1eTE_C16.qxd 5/16/04 12:38 PM Page 450

The Dynamic Ocean 451

the original surface water and results in lower surface water tempera-tures near the shore.

Upwelling brings greater concentrations of dissolved nutri-ents, such as nitrates and phosphates, to the ocean surface. Thesenutrient-enriched waters from below promote the growth of micro-scopic plankton, which in turn support extensive populations of fish andother marine organisms. Figure 4 is a satellite image that shows highproductivity due to coastal upwelling off the southwest coast of Africa.

Deep-Ocean CirculationIn contrast to the largely horizontal movements of surface currents,deep-ocean circulation has a significant vertical component. Itaccounts for the thorough mixing of deep-water masses.

Density Currents Density currents are vertical cur-rents of ocean water that result from density differencesamong water masses. Denser water sinks and slowlyspreads out beneath the surface. An increase in sea-water density can be caused by a decrease in temperatureor an increase in salinity. Processes that increase the salin-ity of water include evaporation and the formation of seaice. Processes that decrease the salinity of water includeprecipitation, runoff from land, icebergs melting, and seaice melting. Density changes due to salinity variations areimportant in very high latitudes, where water temperatureremains low and relatively constant.

High Latitudes Most water involved in deep-oceandensity currents begins in high latitudes at the surface. Inthese regions, surface water becomes cold, and its salinityincreases as sea ice forms. When this water becomes denseenough, it sinks, initiating deep-ocean density currents.Once this water sinks, it is removed from the physicalprocesses that increased its density in the first place. Its tem-perature and salinity remain largely unchanged during thetime it is in the deep ocean. Because of this, oceanographerscan track the movements of density currents in the deepocean. By knowing the temperature, salinity, and densityof a water mass, scientists are able to map the slow circula-tion of the water mass through the ocean.

What is upwelling?Figure 4 Effects of UpwellingThis image from the SeaStarsatellite shows chlorophyllconcentration along thesouthwest coast of Africa. Highchlorophyll concentrations, in red, indicate high amounts ofphotosynthesis, which is linked to upwelling nutrients.

Winds

Surfacecurrent

Deep-OceanCirculation

Many students think that salinity has noeffect on the density of water. Duringthe Teacher Demo described below,students will see that saltwater sinksbeneath fresh water. Therefore,saltwater is denser than fresh water.Visual

Creating DensityCurrentsPurpose Students will see howtemperature and salinity create densitycurrents.

Materials 2 deep and clear containers,ice water, salt, tap water, food coloring,2 smaller and clear containers

Procedure Partly fill each deepcontainer with tap water, and add redfood coloring. Add blue food coloring toice water in a small container. Add saltand green food coloring to tap water inanother small container. Slowly pour theblue ice water into one deep containerthat is already partly filled with red tapwater. Slowly pour the green saltwaterinto the other deep container that ispartly filled with red tap water.

Safety Food coloring may stain skinor clothing.

Expected Outcomes Students willsee that both cold water and saltwatersink to the bottom and spread out inthe warmer fresh water. Repeat thisdemonstration as needed until studentsare convinced that saltwater and coldwater are denser than warmer, freshwater. Students may ask you to tryputting the cold or salty water in first, orthey may ask you to try heating the tapwater before adding the cold or saltywater. You can also allow students totry this activity themselves or in smallgroups.Visual, Kinesthetic

L2

L2

The Dynamic Ocean 451

Before large ocean currents like the Gulf Streamwere understood, people wondered why aboat trip west across the Atlantic Ocean tooknearly two weeks longer than the trip backeast. Ben Franklin’s cousin, Timothy Folger,advised Franklin that this was because thecaptains of many ships were not aware of the

Gulf Stream Current that flowed west to eastacross the Atlantic. Franklin then shared thisinformation with the mariners by creating amap showing the Gulf Stream. This mapallowed sailors attempting to go from eastto west to avoid being slowed down by thispowerful current.

Facts and Figures

Answer to . . .

Upwelling is the rising ofcold water from deeper

layers to replace warmer surface water.

HSES_1eTE_C16.qxd 5/16/04 12:38 PM Page 451

452 Chapter 16

Near Antarctica, surface conditions create the highest density waterin the world. This cold, salty water slowly sinks to the sea floor, whereit moves throughout the ocean basins in slow currents. After sinkingfrom the surface of the ocean, deep waters will not reappear at the sur-face for an average of 500 to 2000 years.

Evaporation Density currents can also result from increased salin-ity of ocean water due to evaporation. In the Mediterranean Seaconditions exist that lead to the formation of a dense water mass atthe surface that sinks and eventually flows into the Atlantic Ocean.Climate conditions in the eastern Mediterranean include a dry north-west wind and sunny days. These conditions lead to an annual excessof evaporation compared to the amount of precipitation. When sea-water evaporates, salt is left behind, and the salinity of the remainingwater increases. The surface waters of the eastern Mediterranean Seahave a salinity of about 38‰ (parts per thousand). In the wintermonths, this water flows out of the Mediterranean Sea into the Atlantic

Figure 5 Sea Ice in the ArcticOcean When seawater freezes,sea salts do not become part ofthe ice, leading to an increase inthe salinity of the surroundingwater. Drawing Conclusions Howdoes this process lead to theformation of a density current?

Figure 6 This cross section of theAtlantic Ocean shows the deep-water circulation of water massesformed by density currents.

Dep

th (k

ilom

eter

s)

1

2

3

4

5

6

South Equator North

60° 40° 20° 0°

Warm water

AIWMW

NADW

ABW

ABW

60°40°20°Latitude

Key

AIW: Antarctic Intermediate Water MW: Mediterranean Water NADW: North Atlantic Deep Water ABW: Antarctic Bottom Water

452 Chapter 16

Build Reading LiteracyRefer to page 246D in Chapter 9, whichprovides guidelines for relating causeand effect.

Relate Cause and Effect Oncestudents have read this section, ask:What are the possible causes foran increase in density? (temperaturedecrease and salinity increase) How doestemperature affect density? (Highertemperatures result in lower density,while colder temperatures result in higherdensity.) How does salinity affectdensity? (Higher salinity results in higherdensity.) How does evaporation affectdensity? (Evaporation leads to highersalinity and thus higher density.)Verbal, Logical

Use VisualsFigure 6 Be sure students understandthe orientation of this cross section bycomparing it geographically to the mapin Figure 2. The cross section would berepresented by a north-south linethrough the Atlantic Ocean. Ask: Whydon’t the arrows on the two figuresmatch? (Figure 2 shows surface currents;Figure 6 shows density currents.)Describe the probable temperatureand salinity characteristics andgeneral movements of the AntarcticBottom Water. (cold and highly saline;forms in the Antarctic, sinks, and flowsnorthward along the ocean floor as far as20oN latitude) Describe the probabletemperature and salinity character-istics and general movements of thewater from the Mediterranean. (warmand highly saline; flows westward into theAtlantic, cools, and sinks slightly as mostof it heads toward the equator)

L1

L1

Section 16.1 (continued)

HSES_1eTE_C16.qxd 5/16/04 12:39 PM Page 452

Section 16.1 Assessment

Reviewing Concepts1. How do surface currents develop?

2. What is the Coriolis effect? How does itinfluence the direction of surface currentsflowing in the ocean?

3. How do ocean currents affect climate?

4. Why is upwelling important?

5. How are density currents formed?

Thinking Critically6. Applying Concepts The average surface

water temperature off of the coast of Ecuadoris 21ºC. The average surface watertemperature off of the coast of Brazil at thesame latitude is about 27ºC. Explain why thereis such a difference in water temperaturebetween these areas at the same latitude.

7. Inferring During an El Niño event, theupwelling of cold, nutrient-rich water stops inareas off the coast of Peru. How might thisaffect the food web in this area?

Ocean. At 38‰, this water ismore dense than the AtlanticOcean surface water at 35‰, soit sinks. This Mediterraneanwater mass can be tracked as farsouth as Antarctica. Figure 6shows some of the differentwater masses created by densitycurrents in the Atlantic Ocean.

A Conveyor Belt A simpli-fied model of ocean circulationis similar to a conveyor belt thattravels from the Atlantic Oceanthrough the Indian and Pacific oceans and back again. Figure 7 showsthis conveyor belt model. In this model, warm water in the ocean’supper layers flows toward the poles. When the water reaches the poles,its temperature drops and salinity increases, making it more dense.Because the water is dense, it sinks and moves toward the equator. Itreturns to the equator as cold, deep water that eventually upwells tocomplete the circuit. As this “conveyor belt” moves around the globe,it influences global climate by converting warm water to cold waterand releasing heat to the atmosphere.

The Dynamic Ocean 453

Figure 7 This “conveyor belt”model of ocean circulation showsa warm surface current with anunderlying cool current.

AtlanticOcean

PacificOceanIndian

OceanAfrica

SouthAmerica

Australia

AsiaNorth

AmericaEurope

NorthAmerica

Warmsurfa

ce flow

Cool subsurface flow

Arctic Ocean

Antarctica

Explanatory Paragraph During the1700s, mail ships sailed back and forthbetween England and America. It wasnoted that it took the ships two weekslonger to go from England to America thanto travel the same route from America toEngland. It was determined that the GulfStream was delaying the ships. Write aparagraph explaining why this is true. UseFigure 2 to explain how sailors could avoidthe Gulf Stream when sailing to America.

Build Reading LiteracyRefer to p. 446D, which providesguidelines for sequencing.

Sequence As students read the sectionA Conveyor Belt, ask them to create aflowchart showing the movement ofwater starting with the phrase “warmwater flows toward poles” and endingwith the phrase “the cycle repeats.”(For example: warm water flows towardpoles → temperature drops and salinityincreases → density increases → densewater moves toward equator → cold,deep water upwells → upwelled waterwarms → the cycle repeats)Visual, Verbal

ASSESSEvaluateUnderstandingAsk students to use Figure 2 to predictthe movement of an abandoned boatleft adrift in the Atlantic Ocean off thecoast of Florida (the Bermuda Triangle).

ReteachHave students write a short storydescribing the voyage of a droplet ofwater through the ocean. The dropletshould start and end near the north pole.

Sample answer: When ships traveledfrom England to America they had tomove against the direction of the GulfStream, thus delaying their arrival.Ships could cross the Gulf Stream at itsnorthern end and travel near the coastbetween the current and land to avoidhaving to move against the current.

L1

L2

3

L1

The Dynamic Ocean 453

Answer to . . .

Figure 5 As salinity increases, thedensity of water increases. As surfacewater becomes denser than underlyingwater, it sinks, forming a density current.

areas of Earth; for example, the Gulf Streamand North Atlantic currents warm northwest-ern Europe in the winter months. Cold watercurrents from the poles moderate warmtemperatures of adjacent land areas.4. Upwelling brings dissolved nutrients to theocean surface, providing the necessary nutri-ents for phytoplankton to undergo photosyn-thesis. This productivity supports extensivepopulations of fish and other organisms.5. They are formed when the density ofwater changes due to a change in salinityor temperature.

Section 16.1 Assessment

1. Surface currents develop from frictionbetween the ocean and the wind that blowsacross its surface.2. The deflection of currents away from theiroriginal course as a result of Earth’s rotationis the Coriolis effect. It causes currents in theNorthern Hemisphere to turn to the rightand currents in the Southern Hemisphere toturn to the left.3. Warm water currents that come fromequatorial regions transfer heat to cooler

6. The current off of the coast of Ecuador is acold-water current that comes from high lati-tudes. The current off of the coast of Brazil isa warm-water current that comes from theequator.7. The food web in this area is dependentupon the high levels of productivity thatresult from it having nutrient-rich water.Without the nutrients, productivity signifi-cantly declines, leaving many organisms withtoo little food or no food source. Organismswill either starve or must seek out anotherfood source.

HSES_1eTE_C16.qxd 5/16/04 12:39 PM Page 453

454 Chapter 16

Shoes and Toysas Drift Meters

Any floating object can serve as a makeshift driftmeter, as long as it is known where the objectentered the ocean and where it was retrieved. Thepath of the object can then be inferred, providinginformation about the movement of surface cur-rents. If the times of release and retrieval are known,the speed of currents can also be determined.Oceanographers have long used drift bottles—aradio-transmitting device set adrift in the ocean—totrack the movement of currents and, more recently,to refine computer models of ocean circulation.

Many objects have accidentally become drift meterswhen ships have lost some (or all) of their cargo atsea. In this way, athletic shoes have helped oceanog-raphers advance the understanding of surfacecirculation in the North Pacific Ocean. In May 1990,the container vessel Hansa Carrier was traveling fromKorea to Seattle, Washington, when it encountereda severe North Pacific storm. During the storm theship lost 21 deck containers overboard, includingfive that held athletic shoes. The shoes that werereleased from their containers floated and were car-ried east by the North Pacific Current. Within sixmonths, thousands of the shoes began to wash upalong the beaches of Alaska, Canada, Washington,and Oregon—over 2400 kilometers from the site ofthe spill. The inferred course of the shoes is shownin Figure 8. A few shoes were found on beaches innorthern California, and over two years later shoesfrom the spill were even recovered from the northend of the main island of Hawaii.

With help from the beachcombing public andremotely based lighthouse operators, information onthe location and number of shoes collected was com-piled during the months following the spill. Serialnumbers inside the shoes were traced to individualcontainers, which indicated that only four of the fivecontainers had released their shoes. Most likely, oneentire container sank without opening. A maximumof 30,910 pairs of shoes (61,820 individual shoes)were released. Before the shoe spill, the largestnumber of drift bottles purposefully released at onetime by oceanographers was about 30,000. Althoughonly 2.6 percent of the shoes were recovered, thiscompares favorably with the 2.4 percent recoveryrate of drift bottles released by oceanographers con-ducting research.

In January 1992, another cargo ship lost 12 con-tainers overboard during a storm to the north ofwhere the shoes had previously spilled. One of thesecontainers held 29,000 packages of small, floatable,colorful plastic bathtub toys in the shapes of blueturtles, yellow ducks, red beavers, and green frogs.Even though the toys were housed in plastic pack-aging glued to a cardboard backing, studies showedthat after 24 hours in seawater, the glue deterio-rated, thereby releasing over 100,000 individualfloating toys.

The floating bathtub toys began to come ashore insoutheast Alaska 10 months later, which verifiedcomputer models of North Pacific circulation. Themodels indicate that many of the bathtub toys will

continue to be carried by the Alaska Currentand will eventually disperse throughout theNorth Pacific Ocean.

Since 1992, oceanographers have contin-ued to study ocean currents by trackingother floating items spilled from cargoships, including 34,000 hockey gloves, 5million plastic Lego pieces, and an uniden-tified number of small plastic doll parts.

PACIFIC OCEAN

Shoes spilledMay 27, 1990

North Pacific Current

Alaska Current

California CurrentDrift of shoes

250 shoes

200 shoes

100 shoes200 shoes200 shoes

150shoes

200 shoes

55°

50°

45°

40°

35°

160° 150° 140° 130°

CANADA

UNITEDSTATES

CANADA

UNITEDSTATES

Figure 8 The map shows the path ofdrifting shoes and recovery locationsfrom a spill in 1990.

454 Chapter 16

Shoes and Toys asDrift MetersTeaching Tips• Have students read this feature in

groups and then share their feelingsabout what they read. Students maywonder about the environmentalimpact of ships spilling their cargo, orhow scientists were able to find outwhen and where cargo was lost andthen found.

• Discuss what this feature reveals aboutthe stories of people setting adrift amessage in a bottle. (The message couldtravel great distances as the bottle driftson ocean currents. Quite possibly thebottle will be washed onshore in a distantland.)

Interpersonal, Verbal

L2

HSES_1eTE_C16.qxd 5/16/04 12:39 PM Page 454