Ocean Currents and Global Climate · currents. Locate some of the major ocean currents on a map and a globe. Analyze the effects of ocean currents on global climate. In the second

80 STC/MS™ CATA S T R O P H I C EV E N T S

INTRODUCTIONUsing temperature sensors and buoys that floatat fixed depths, scientists have found thatwater in the oceans is on the move, even in thedeepest trenches. The sun powers deep oceancurrents. Wind guides surface currents. Oceancurrents are essential to life in the sea. Theydissolve oxygen from the atmosphere and bringminerals up to the surface, where tiny floatingplants can use them. And like the air in theearth’s atmosphere, ocean currents help moveheat around the globe.

You now know that temperature differenceson the earth occur because the sun heats theearth unevenly. The sun is a major force thatcauses convection currents in the air and cur-rents in the oceans. Temperature and wind aremajor forces that drive ocean currents. Otherfactors also affect ocean currents. These includethe earth’s rotation and the water’s density. Forexample, salt dissolved in ocean water will causethe water to be heavy and to sink.

In this lesson, you will investigate the effectsof temperature and wind on ocean currents. Youwill also investigate how these currents affectthe climate throughout the entire world.

7Ocean Currents and GlobalClimate

LESSON

OBJECTIVES FOR THIS LESSON

Analyze why the temperatures at theequator and poles differ.

Investigate the effect of watertemperature on the way water moves.

Investigate the effect of wind on surfacecurrents.

Locate some of the major oceancurrents on a map and a globe.

Analyze the effects of ocean currents onglobal climate.

In the second half of the 18th century, American statesman

and scientist Benjamin Franklin made some of the earliest

studies of ocean surface currents.

NO

AA/D

EPAR

TMEN

T O

F C

OM

MER

CE

STC/MS™ CATA S T R O P H I C EV E N T S 81

Getting Started

1. Discuss the results from your homework,Student Sheet 6.2: Tracking HurricaneAndrew, with your teacher. Review youranswers to the following questions, whichare also listed on your student sheet:

A. Where did Tropical Storm Andrewstart? Why do you think it started there?

B. At what point (longitude and latitude)did the tropical storm become a hurricane?

C. In what direction did the storm move?

D. Look back to the reading selection“Why Does the Wind Blow?” in Lesson 5.What do you think caused HurricaneAndrew to move along this path?

E. Where did Hurricane Andrew lose itsenergy and turn back into a tropicalstorm? Why do you think it happened inthat location?

F. If you had been working at the NationalHurricane Center when HurricaneAndrew struck, which cities or areaswould you have evacuated? What daywould you have requested the evacua-tion? Why?

MATERIALS FORGETTING STARTED

For you1 completed copy of

Student Sheet 6.2:Tracking HurricaneAndrew


LESSON 7 OC E A N CU R R E N T S A N D GL O B A L CL I M AT E

4. One student will go to the class globe torecord the final temperatures at the equa-tor, middle latitudes, and poles. What dothe results tell you about global heating ofthe earth? On the basis of this activity,how do you think the sun’s energy causesconvection currents in both the atmos-phere and the oceans on the earth?

5. Brainstorm what you know and want toknow about ocean currents. Then answerthese questions:

A. You know what causes convectioncurrents in the air. What do you thinkcauses currents in the ocean?

B. How do you think ocean currentsaffect global weather?

2. Look at the class globe and the clamplamp. Make a prediction: How do youthink the light from the lamp will affectthe temperatures of different parts of theglobe? Discuss your predictions with theclass. Then watch as one student recordsthe starting temperatures.

3. While the light shines on the globe for afew minutes, look at Figure 7.1. In a classdiscussion, answer the following questions:

A. Examine the equator and the poles.How are they alike? How are they different?

B. How do you think these factors affectthe temperature of air and water at theequator? How do you think they affecttemperatures at the poles?

Figure 7.1 Modeling uneven global heating

(A) Light to the equator

(B) Light to the poleNorth Pole

MiddleLatitudes

Equator



MATERIALS FORINQUIRY 7.1

For you1 copy of Student

Sheet 7.1a:Investigating theEffect of Temper-ature on OceanCurrents

1 copy of StudentSheet 7.1b:Storms Review

1 pair of safetygoggles

For your group1 tote tray2 metal digital

thermometers2 beakers of room-

temperature water1 dropper bottle of

chilled water (withpurple dye)

1 dropper bottle ofheated water (withpurple dye)

2 index cards 1 flexible straw

Inquiry 7.1Investigating the Effect ofTemperature on OceanCurrentsPROCEDURE

1. Read “Ocean Currents,” on page 84. Howwould you define a current? In this lab,you will investigate the effect of tempera-ture on how water moves, and you willapply your observations to ocean currents.

2. Collect one copy of Student Sheet 7.1a:Investigating the Effect of Temperature onOcean Currents. Read the question in thefirst box: How does the temperature ofwater affect the way water moves? Lookat one set of materials. Share with yourgroup and the class any ideas you mighthave for using the materials to investigatethe question. Then discuss ProcedureSteps 7 through 14. (You may have tocomplete all but the last box of StudentSheet 7.1a for homework.)

3. Look at Figure 7.2 and at the tote tray ofwater your teacher has set up for thisinquiry. This is a model of a deep oceancurrent. The crystals will show how the

Cold waterand ice

Potassiumpermanganatecrystals

Hot water

Figure 7.2 Deep ocean

current model. Do not dis-

turb the water. View the

model from the sides.



water in the pan moves. Make some pre-dictions: How do you think the crystalswill move near the cold water? How doyou think they will move near the hotwater?

4. If you haven’t already, complete all boxeson the student sheet except the last one.You will describe the materials and proce-dures you will use, how you will controlall variables except the one you are test-ing, and what you will look out for andmeasure. As you work, your teacher mayselect one or more groups to observe themovement of the crystals in the tote trayof water.

5. Review the Safety Tips on page 85 withyour class.

6. Pick up your materials.

7. Use the metal digital thermometers tomeasure the temperature of the water inboth beakers. Record these data onStudent Sheet 7.1a. To make this a fairtest, the temperatures should be aboutthe same.

8. Collect one hot dropper bottle and onecold dropper bottle from the water baths.Record the temperature of each bottle’ssolution.

OCEAN CURRENTSThe waters of the ocean move in streamscalled currents. A current results when a fluid,either gas or a liquid, moves in a definite direc-tion. Ocean currents form in response to manyfactors: heat from the sun, wind, salinity (salti-ness), land masses acting as barriers, and therotation of the earth. Some currents are strongenough to affect the speed and direction ofships. Others bring drastic weather changes tofaraway lands.

In the 18th century, Benjamin Franklin madesome of the earliest studies of ocean currents.From first-hand experience, he knew that shipscrossing the North Atlantic from America wereeither helped or hindered by a current flowingin a northeasterly direction toward Europe.Franklin investigated the temperature of thecurrent. He found that it was warmer than thewater around it. Instead of mixing with the sur-rounding water, the current moved along like ariver within the ocean. The boundary betweenthe warm and the cold water was sharp. Frank-lin discovered how sailors could use thermo-meters to guide their ships into the current orout of it.

Why do you think the warm water moved ina northeasterly direction? What might havecaused the sharp boundary between the warmwater and cold water? Think back to earlierlessons on how air moves. Try to apply someof the things you have learned about air cur-rents to what you will learn in this lessonabout ocean currents.



SAFETY TIPS

Be careful whenyou are handlingthe hot dropperbottle. The waterbath and thewater in the bot-tle are hot.

Wear your safetygoggles whenyou are filling oremptying thedroppers.

Do not get thepurple solutionon your skin orclothing; it willcause stains.

Only one memberof your groupshould use thestraw. Do notshare it.

9. Set up your investigation. As an option,you can place the cold bottle in a beakerof ice water and the hot bottle in a beakerof hot water, as shown in Figure 7.3.

10. Label one index card “Hot” and the otherone “Cold.” Have a group member holdthe index cards behind the beakers. Thiswill make it easier to observe the results.

11. Fill the dropper from each bottle, onecold and one hot. Have one group mem-ber slowly release 10 drops of water, 1drop at a time, from each dropper, into itsbeaker of water. Drop cold purple solutioninto the beaker labeled “Cold” and hotpurple solution into the beaker labeled“Hot.” To ensure a fair test, have thesame person do both droppers because heor she will squeeze the droppers with thesame force and at the same time. What doyou observe? Discuss your observationswith your group.

12. In the last box of your student sheet,record what happened in the beakers.Remember to explain why you think thishappened and give evidence to supportyour answer.

Figure 7.3 Setting up the temperature lab

Cold dropper bottle Hot dropper bottle



C. Pour the water in the beakers into a sink(or bucket).

D. Fill the beakers with 200 mL of cleanroom temperature water.

E. Place a thermometer next to each beaker.Turn off the thermometers.

F. Throw away the straw. Set out a new onefor the next group.

13. Have a member of your group use thestraw to gently blow across both beakers ofwater, as shown in Figure 7.4. The othermembers should watch the purple solutionvery carefully. What happened to the solu-tion when air blew across the water’s sur-face? Discuss your observations.

14. Clean up by following these steps:

A. Prepare for the next class by setting upthe materials exactly as they were whenyou started.

B. Return the hot and cold dropper bottlesto their water baths.

Figure 7.4 Blow across the water’s surface using a straw.



HOW TRADE WINDS CAUSE UPWELLING When you blew across the surface of thewater in the beaker in Inquiry 7.1, your breathpushed the surface water to one side. Thecold, purple water at the bottom rose to thetop. This is how the strong winds that blownear the equator work. These winds, known astrade winds, usually blow from east to westacross the tropical Pacific Ocean. Just as yourbreath blew water to one side in the experi-ment, trade winds push warmer water towardthe west, where it accumulates aroundIndonesia. Then cold water rises from deepareas of the ocean along North and SouthAmerica. The rising water brings with it richnutrients from the ocean bottom that feed fishand other marine life. This rising of cold, deepwater is known as upwelling.

Sometimes the trade winds weaken, and anEl Niño warming takes place. El Niño is anunusually warm flow of surface water. Duringan El Niño warming, there is no wind to pushthe warm water westward, and the cold waternear the Americas cannot rise to the surface.The nutrients from the bottom of the oceanstay at the bottom. Sea organisms thatdepend on those nutrients die.

How surface winds cause upwelling

Surfacewatermovement

Wind

Movement of cold, deep,nutrient-rich water

REFLECTING ON WHAT YOU’VE DONE

1. Answer the following questions. Then talkwith your class about how temperatureaffects the density and movement ofwater.

A. How does temperature affect the waywater moves? Which is more dense: hotwater or cold water? What evidence doyou have to support your answer?

B. Think of your globe and how lightreached it. How might the uneven heat-ing of the earth cause ocean currents?

C. What happened to the cold water(with purple dye) when you blewacross the beaker? Why do you thinkthis happened?

2. Read “How Trade Winds Cause Upwelling.”

3. Analyze your observations of the tote trayof water. How do you think it models deepocean currents on the earth?

4. Pick up one copy of Student Sheet 7.1b.You will use this to prepare for the Stormsassessment in Lesson 8.



MATERIALS FORINQUIRY 7.2

For your group1 tote tray1 petri dish base 1 small cup, with

lid, containingtalcum powder

1 beaker containingroom-temperaturewater

4 flexible straws5 removable yellow

dots2 erasable

transparencymarkers (blue andred)CatastrophicEvents World Map

Inquiry 7.2Investigating SurfaceCurrents

PROCEDURE

1. Read “Surface Currents,” on page 89. Youwill investigate how wind creates surfacecurrents. Then you will apply your obser-vations to ocean currents on the earth.

2. Consider the following question: How dowinds affect ocean waters? Discuss yourideas with the class.

3. Review Procedure Steps 4 through 8 withyour teacher. With your teacher’s permis-sion, adapt the procedures to match yourgroup’s ideas as needed. Then pick upyour materials.

4. Pour water into your petri dish until it ishalf full.

5. Use the tip of your finger to place a pinchof talcum powder on the surface of thewater in your petri dish. Use only apinch. More will interfere with yourresults.



SURFACE CURRENTSThe atmosphere and oceans on the earth are closely linked. Wind blow-ing over the oceans produces surface ocean currents. These currents,along with the wind, transfer heat from tropical areas near the equator,where there is a lot of heat energy, to polar regions, where it is colder.Because ocean currents move heat from one region to another, theyhave a strong effect on global climate.

Flowing northward along the East Coast of the United States is atremendous warm-water current called the Gulf Stream. The Gulf Streamcarries huge amounts of warm tropical water into areas farther north.Winds steer the Gulf Stream away from the coast of North America andmove it eastward toward Europe. Gradually, the Gulf Stream widens andslows as it merges with the broader North Atlantic Drift (see the illus-tration), another ocean current. The Gulf Stream then divides into twocurrents as it approaches Europe. Meanwhile, the Labrador Currentbrings cold water southward along the Atlantic coast of North America,as far south as Massachusetts in summer and North Carolina in winter.Where the Labrador and Gulf Stream currents flow side by side, there isa sharp temperature change between them. When warm Gulf Stream airblows over the cold Labrador Current water, fog forms. In this inquiry,you will discover where each of these currents is on the world map.

Surface ocean currents have a major effect on global climate. Warmcurrents carry heat from the tropics and spread it to cooler areas.Without the North Atlantic Drift, the sea around Scandinavia and north-ern Britain would freeze in the winter. Cold currents have the oppositeeffect. As they flow from the poles to the equator, they lower the tem-perature of regions that are typically warmer.

Surface currents, such as the North Atlantic Drift, affect global weather.

Greenland

NorthAtlanticDrift

WesterliesNorthAmerica

South America

Atlantic Ocean

Africa

Europe

Trade winds

Equator

GulfStream



8. Take out your group Catastrophic EventsWorld Map. Then do the following:

A. Read the descriptions in Table 7.1. Eachrow describes an ocean surface currentcaused by global winds in a certain regionof the world.

B. Using the transparency markers, draweach current on your group map. Use ared pen for warm currents and a blue penfor cold ones.

C. Label the currents with the appropriateletter (A, B, C, D, or E) from the table byfollowing these steps: Write the letter ona yellow dot. Stick the dot on the map.Use a political map in your classroom, ifneeded, to help you locate the regions.

6. Use a straw to blow gently across thewater’s surface. (See Figure 7.5.) Askother members of your group to watchthe water carefully. Using a new straweach time, allow each group member totry this. What do you observe? Discussyour observations with your group.

7. Clean up by doing the following:

• Put the lid on the talcum powder. Donot throw it away.

• Pour out the water in the petri dish andwipe the dish dry.

• Do not throw away the beaker of water.The next class will use it.

• Throw away your straws. Replace themwith four new straws.

• Return all equipment to the tote tray forthe next class.

Figure 7.5 Modeling surface currents



Table 7.1 Some Surface Currents on the Earth

Nearest Landmass TemperatureCurrent Hemisphere or Ocean Direction of Flow of Water

North American A. Gulf Stream Northern East Coast North; clockwise Warm

B. Humboldt Current South American(or Peru Current) Southern West Coast North; counterclockwise Cold

C. Antarctic Circumpolar Current Southern Antarctic Ocean West to east; straight Cold

D. California Current Northern U.S. West Coast South; clockwise Cold

Greenland and South; meetsE. Labrador Current Northern Eastern Canada Gulf Stream Cold

2. Look at the currents marked on yourworld map. Answer these questions:

A. What patterns do you notice in themovement of surface currents?

B. How are the paths of the ocean cur-rents you plotted on the map similar tothe paths of global winds (trade winds,westerlies, easterlies)?

C. How do you think ocean currentsaffect weather globally?

3. Watch as groups share the ocean currentsthey plotted on their world map.

REFLECTING ON WHAT YOU’VE DONE

1. Answer the following questions, and thendiscuss with your group what this inquirytells about surface currents.

A. What happened to the water when youblew across it?

B. How did the direction of the windaffect the direction of the surface cur-rent? How do you think this is similarto or different from the earth’s surfacecurrents?

C. Recall what you learned aboutupwelling during Inquiry 7.1. Howcan surface currents affect deep oceancurrents?



For the penguins living onthe Galapagos Islands offthe coast of Ecuador, life isusually good. Trade windscause a deep ocean current to rise to the surfaceof the Pacific Ocean at the edge of SouthAmerica. This current carries nutrients thatnourish tiny forms of life, which are eaten by fish.These fish, in turn, are a feast for the penguins.

Every 3 to 7 years or so, the trade windsweaken. The Pacific Ocean becomes very warmthere. Cold water stays at the bottom of the

ocean. The fish near thesurface cannot live in thewarm water, and they leaveto search for food else-

where. The penguins go hungry!For centuries, Peruvian fishers have noticed

that their fish catch declined every 3 to 7 years.At the same time, the waters grew warmer.Christian monks named this warming “ElNiño,” for the boy Jesus, because the warmwater came at Christmastime and brought withit the gifts of abundant vegetation.

These six globes represent the appearance and disappearance of El Niño’s warm water in the eastern Pacific Ocean

in 1993.

El Niño Stirs Up the

WORLD’S WEATHER

NAS

A/G

OD

DAR

D S

PAC

E FL

IGH

T C

ENTE

R A

ND

SC

IEN

TIFI

C V

ISU

ALIZ

ATIO

N S

TUD

IO

El Niño affects far morethan penguins and fishersin South America. Thewarming causes rains andflooding on the west coasts of both North andSouth America. In other parts of the world, ElNiño causes dry weather. Southern Africa,Indonesia, and parts of Australia have severedroughts during these episodes.

Such big changes in the weather can be disas-trous. In 1982 and 1983, an unusually strong



El Niño caused 1000deaths and billions of dol-lars in damage around theglobe. In Eastern Australia,

the worst drought in history killed livestockand nearly caused a famine. Many people inIndonesia died of starvation. On the other sideof the globe, southern California had too muchrain, causing floods and mudslides. Five hurri-canes hit Tahiti in one year and left 25,000 peo-ple homeless.

Above: The 1983 El Niño caused drought in Australia. No rain meant little food for this cow and other animals.

Below: In 1998, this family was forced to leave their home north of Lima, Peru, to live in a refugee camp.

Heavy flooding caused by El Niño destroyed most of the area.

AP/W

IDE

WO

RLD

PH

OTO

S

© B

ILL

BAC

HM

AN/P

HO

TO R

ESEA

RC

HER

S,

INC

.



plentiful rains, Indonesian forests burned out ofcontrol. An airliner crashed in the thick smokefrom the fires, and hundreds of people werekilled.

The El Niño of 1997–1998 was also verystrong. Ocean temperatures climbed to severaldegrees above average. The waters were thewarmest they had been in 150 years. Without

© A

. R

AMEY

/WO

OD

FIN

CAM

P &

AS

SO

CIA

TES

AP/W

IDE

WO

RLD

PH

OTO

S

Top: Girls play in a dry riverbed near Kota, Bahru, which borders Thailand. Scientists believe El Niño caused drought in

this area. Bottom left: Excessive rains during El Niño caused landslides in the United States in 1998. Bottom right: The

Amazon forest burns in northern Brazil in 1998. A record drought caused by El Niño caused fires in more than 1.5 mil-

lion acres of forest.

AP/W

IDE

WO

RLD

PH

OTO

S



helped forecasters build computer models topredict how El Niño might change weatherpatterns. In 1997 and 1998, the predictionshelped farmers in Peru, Brazil, and Aus-tralia know what kind of weather wasahead. When they knew it would be wet,they planted grains that would grow well inrainy conditions. �

In the mid-1980s, scientists began theTropical Ocean and Global Atmosphere(TOGA) program to learn more about ElNiño. For nearly 10 years, TOGA scientistsmeasured air and ocean temperatures inthe tropical Pacific Ocean at 70 weatherbuoys. The readings were sent by satelliteto weather centers. This information

The impact of El Niño in 1997 was felt

worldwide. This map shows its effects

during the months of June through

September.

Something Has Changed

There may be good news forthose hungry penguins of theGalapagos Islands. In thespring of 1998, the temper-ature of a large area of thePacific Ocean along theequator dropped 9 ºC.

This cooling, called La Niña,follows some El Niño events.In La Niña years, some ElNiño weather patterns arereversed. The northwestUnited States experiences asevere, wet winter. Thesoutheastern United States

suffers through dry weatherand parched crops. Morehurricanes brew in theAtlantic. And, luckily for thepenguins, La Niña bringscold water and more fish tothe coast of South America.

Fewer storms than usual

Dryer than usual

Wetter and stormier than usual

Warmer than usual

Documents

Ocean Currents and Global Climate · currents. Locate some of the major ocean currents on a map and a globe. Analyze the effects of ocean currents on global climate. In the second