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EncyclopedicEntry
oceangyre
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http://education.nationalgeographic.com/encyclopedia/ocean-gyre/
AnoceangyreisalargesystemofcircularoceancurrentsformedbyglobalwindpatternsandforcescreatedbyEarth’s
rotation.
Themovementoftheworld’smajoroceangyreshelpsdrivethe“oceanconveyorbelt.”Theoceanconveyorbeltcirculates
oceanwateraroundtheentireplanet.Alsoknownasthermohalinecirculation,theoceanconveyorbeltisessentialfor
regulatingtemperature,salinityandnutrientflowthroughouttheocean.
HowaGyreForms
Threeforcescausethecirculationofagyre:globalwindpatterns,Earth’srotation,andEarth’slandmasses.Winddragson
theoceansurface,causingwatertomoveinthedirectionthewindisblowing.
TheEarth’srotationdeflects,orchangesthedirectionof,thesewind-drivencurrents.ThisdeflectionisapartoftheCoriolis
effect.TheCorioliseffectshiftssurfacecurrentsbyanglesofabout45degrees.IntheNorthernHemisphere,oceancurrents
aredeflectedtotheright,inaclockwisemotion.IntheSouthernHemisphere,oceancurrentsarepushedtotheleft,ina
counterclockwisemotion.
Beneathsurfacecurrentsofthegyre,theCorioliseffectresultsinwhatiscalledanEkmanspiral.Whilesurfacecurrentsare
deflectedbyabout45degrees,eachdeeperlayerinthewatercolumnisdeflectedslightlyless.Thisresultsinaspiralpattern
descendingabout100meters(330feet).
Earth’scontinentsandotherlandmasses(suchasislands)alsoinfluencethecreationofoceangyres.ThemassiveSouth
PacificGyre,forinstance,includeshundredsofkilometersofopenocean.ItisboundedonlybythecontinentsofAustralia
andSouthAmerica,aswellastheEquatorandpowerfulAntarcticCircumpolarCurrent(ACC).
Incontrast,thenorthernIndianOceanGyreisamuchsmalleroceangyre.UnliketheSouthPacificGyre,itsextentis
determinedlargelybylandmasses.TheEquatorformsitssouthernboundary,butitisboundedelsewherebytheHornof
Africa,SriLankaandtheIndiansubcontinent,andtheIndonesianarchipelago.
TypesofGyres
Therearethreemajortypesofoceangyres:tropical,subtropical,andsubpolar.
Subpolargyresforminthepolarregionsoftheplanet.Theysitbeneathanareaoflowatmosphericpressure.Winddrivesthe
currentsinsubpolargyresawayfromcoastalareas.Thesesurfacecurrentsarereplacedbycold,nutrient-richwaterina
processcalledupwelling.TheNorthernHemispherehasseveralsubpolargyres,boundedbyislandssuchasIceland,
Greenland,andtheAleutians;andthenorthernreachesofScandinavia,Asia,andNorthAmerica.
TropicalgyresformneartheEquator.TheCorioliseffectisnotpresentattheEquator,andwindsaretheprimarycreatorsof
currents.Forthisreason,tropicalgyrestendtoflowinamoreeast-west(insteadofcircular)pattern.TheIndianOceanGyre
isactuallytwodistincttropicalgyres—thenorthernandsouthernIndianOceanGyres.
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Mostoftheworld’smajorgyresaresubtropicalgyres.TheseformbetweenthepolarandequatorialregionsofEarth.
Subtropicalgyrescircleareasbeneathregionsofhighatmosphericpressure.Theseareplacidoceanareasthousandsof
kilometersindiameter.Unlikecoastalzones,thesecentralregionsarerelativelystable.Theoceanwatergenerallystaysin
oneplacewhilethecurrentsofthegyrecirculatearoundit.
MovementofGyres
GyresarecomprisedofoceancurrentsthatlinkupastheyfollowthecoastlinesoftheEarth’scontinents.Eachgyrehasa
powerfulwesternboundarycurrentandaweakereasternboundarycurrent.
TheNorthAtlanticGyrebeginswiththenorthwardflowoftheGulfStreamalongtheEastCoastoftheUnitedStates.The
GulfStreamisthewesternboundarycurrentofthegyre.ThegyrethenbecomestheNorthAtlanticCurrent,whichflows
acrosstheNorthAtlantictoEurope.Stillflowinginacircularpattern,thecurrentflowssouthasfarasthenorthwesterncoast
ofAfrica,whereitisknownastheCanaryCurrent—thegyre’seasternboundarycurrent.ThegyreiscompletedastheNorth
AtlanticEquatorialCurrentcrossestheAtlanticOceantotheCaribbeanSea.Thisentirecircleandthewaterwithinitisthe
NorthAtlanticGyre.
Mostoceangyresareverystableandpredictable.TheNorthAtlanticOceanGyrealwaysflowsinasteady,clockwisepath
aroundtheNorthAtlanticOcean.Somegyresexperienceseasonalvariation,however.
TheIndianOceanGyreisacomplexsystemofmanycurrentsextendingfromtheeasterncoastofAfricatothewestern
coastofAustralia.ThenorthernpartofthesystemcirculatesbetweentheHornofAfricaandtheIndonesianarchipelago.Itis
sometimescalledtheIndianmonsooncurrent.
TheIndianmonsooncurrenttakesitsnamefromthewind—themonsoon—thatdrivesit.Itisoneoftheveryfewcurrentsin
anoceangyrethatchangedirection.Inthesummer,thecurrentflowsclockwise,asthemonsoonblowsinfromthe
southwesternIndianOcean.Inthewinter,thecurrentflowscounterclockwise,asthewindblowsinfromtheTibetanplateau
inthenortheast.
Thetemperatureinanoceangyredependsonmanyfactors,includingthecurrent.TheGulfStreamandsummermonsoon
currentarewarmcurrents.TheyareheatedbythewarmtropicalwatersoftheCaribbeanSea(GulfStream)andequatorial
IndianOcean(summermonsooncurrent).TheNorthAtlanticCurrentandwintermonsooncurrentarecoolcurrents.Theyare
cooledbyArcticwindsandoceancurrents(NorthAtlantic)andthewintermonsoonblowingfromtheicyHimalayas(winter
monsooncurrent).
GarbagePatches
Oceangyrescirclelargeareasofstationary,calmwater.Debrisdriftsintotheseareasand,duetotheregion’slackof
movement,canaccumulateforyears.Theseregionsarecalledgarbagepatches.TheIndianOcean,NorthAtlanticOcean,
andNorthPacificOceanallhavesignificantgarbagepatches.ThegarbagepatchintheNorthPacificOceanissometimes
calledthePacifictrashvortexortheGreatPacificGarbagePatch.
Garbagepatchesarecreatedslowly.MarinedebrismakesitswayintotheGreatPacificGarbagePatch,forinstance,from
currentsflowingalongthewestcoastofNorthAmericaandtheeastcoastofAsia.Someofthedebrisisalsodumpedfrom
oceanvessels.
Thecircularmotionofthegyredrawsinthedebris,mostlysmallparticlesofplastic.Eventually,thedebrismakesitswayto
thecenterofthegyre,whereitbecomestrappedandbreaksdownintoakindofplasticsoup.
Oceanographersandecologistsareconcernedaboutgarbagepatches.Inparticular,theyarestudyingthedegradation,or
breakingdown,ofplastics.Unlikenaturalsubstances,suchaswoodormetal,plasticdoesnotdisintegrateintoorganic
substances.Itsimplybreaksdownintosmallerandsmallerpiecesofplastic.Thesetinyplasticparticlesareassmallasthe
algaeandplanktonthatformthebasisoftheentireoceanfoodweb.Speciessuchasshrimp,birds,andfishconsumethese
micro-plastics,whichoftentimeskillthem.Theplasticchemicalscanalsobeabsorbedbypredatorsofthesespecies.The
concentrationofthesechemicalsincreasesthrougheachtrophiclevelofthefoodchain,aprocessknownas
biomagnification.
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Garbagepatchesgenerallyaccumulatefarfromanycountry’scoastline,anditisnearlyimpossibletotracktheoriginof
marinedebris.Thetinyplasticparticlesthatmakeupmostofthepatchesarealsoverydifficultandexpensivetodetectand
remove.Fewnationshaveacceptedtheresponsibilityofcleaninguptheocean’sgarbagepatches.
LifeinaGyre
Scientistsareonlybeginningtounderstandthebiodiversityofoceangyres.Theircalmcentershavetraditionallybeen
regardedasoligotrophic,ornutrient-poor,becausetheyhavefewconcentrationsoftheorganicchemicalsthatsupport
producers,suchasalgaeandplankton,intheoceanfoodweb.
Researchershaverecentlydiscoveredanexpansionofoligotrophicregionsinoceangyres.Theyhavecorrelatedthis
expansionwithincreasesinsea-surfacetemperatures—warmwatersgenerallyhavefarfewernutrientsthancoldwater.
TheUniversityofHawaiiistakingadvantageofitspositionintheNorthPacificGyretofurtherstudythegyreandfactorsthat
impactit.Scientistsregularlystudy“thethermohalinestructure,watercolumnchemistry,currents,opticalproperties,primary
production,planktoncommunitystructure,andratesofparticleexport”inthisoceangyre.
VOCABULARY
Term
PartofSpeech
Definition
absorb
verb
tosoakup.
accumulate
verb
togatherorcollect.
algae
pluralnoun
(singular:alga)diversegroupofaquaticorganisms,thelargestofwhichare
seaweeds.
Antarctic
Circumpolar
Current(ACC)
noun
mostpowerfulsurfaceoceancurrentintheworld,whichrotatesclockwisearound
thecontinentofAntarctica.AlsocalledtheWestWindDrift.
archipelago
noun
agroupofcloselyscatteredislandsinalargebodyofwater.
Arctic
noun
regionatEarth'sextremenorth,encompassedbytheArcticCircle.
atmospheric
pressure
noun
forceperunitareaexertedbythemassoftheatmosphereasgravitypullsitto
Earth.
biodiversity
noun
allthedifferentkindsoflivingorganismswithinagivenarea.
biomagnification
noun
processinwhichtheconcentrationofasubstanceincreasesasitpassesupthe
foodchain.
bound
verb
tolimitorconfine.
boundary
noun
lineseparatinggeographicalareas.
circulate
verb
tomovearound,ofteninapattern.
coast
noun
edgeoflandalongtheseaorotherlargebodyofwater.
complex
adjective
complicated.
comprise
verb
tocontainorbemadeupof.
concentration
noun
measureoftheamountofasubstanceorgroupinginaspecificplace.
consume
verb
touseup.
continent
noun
oneofthesevenmainlandmassesonEarth.
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Corioliseffect
noun
theresultofEarth'srotationonweatherpatternsandoceancurrents.TheCoriolis
effectmakesstormsswirlclockwiseintheSouthernhemisphereand
counterclockwiseintheNorthernHemisphere.
correlate
verb
tobringdifferentsetsofdataintoorder,orestablisharelationshiporconnection
betweenthem.
current
noun
steady,predictableflowoffluidwithinalargerbodyofthatfluid.
debris
noun
remainsofsomethingbrokenordestroyed;waste,orgarbage.
deflect
verb
toalterfromastraightline.
degradation
noun
breakingdown.
detect
verb
tonotice.
determine
verb
todecide.
disintegrate
verb
tofallapartanddisappear.
EastCoast
noun
AtlanticcoastoftheUnitedStates.
ecologist
noun
scientistwhostudiestherelationshipsbetweenorganismsandtheirenvironments.
Ekmanspiral
noun
rotatingcolumnofwaterformedasoceansurfacecurrentsaredeflectedbythe
Corioliseffect,wind,andfrictionforces.
Equator
noun
imaginarylinearoundtheEarth,anotherplanet,orstarrunningeast-west,0
degreeslatitude.
essential
adjective
needed.
expensive
adjective
verycostly.
extent
noun
degreeorspacetowhichathingextends.
factor
noun
elementcontributingtoaneventoroutcome.
foodchain
noun
groupoforganismslinkedinorderofthefoodtheyeat,fromproducersto
consumers,andfromprey,predators,scavengers,anddecomposers.
foodweb
noun
allrelatedfoodchainsinanecosystem.Alsocalledafoodcycle.
fund
verb
togivemoneytoaprogramorproject.
GreatPacific
GarbagePatch
noun
areaoftheNorthPacificOceanwherecurrentshavetrappedhugeamountsof
debris,mostlyplastics.
GulfStream
noun
warmcurrentthatstartsintheGulfofMexicoandtravelsalongtheeasterncoastof
theU.S.andCanadabeforecrossingtheNorthAtlanticOcean.
island
noun
bodyoflandsurroundedbywater.
landmass
noun
largeareaofland.
marine
adjective
havingtodowiththeocean.
massive
adjective
verylargeorheavy.
monsoon
noun
seasonalchangeinthedirectionoftheprevailingwindsofaregion.Monsoon
usuallyreferstothewindsoftheIndianOceanandSouthAsia,whichoftenbring
heavyrains.
nation
noun
politicalunitmadeofpeoplewhoshareacommonterritory.
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Northern
Hemisphere
noun
halfoftheEarthbetweentheNorthPoleandtheEquator.
nutrient
noun
substanceanorganismneedsforenergy,growth,andlife.
nutrient
noun
substanceanorganismneedsforenergy,growth,andlife.
oceanconveyor
belt
noun
systeminwhichwatermovesbetweenthecolddepthsandwarmsurfacein
oceansthroughouttheworld.Alsocalledthermohalinecirculation.
oceangyre
noun
anareaofoceanthatslowlyrotatesinanenormouscircle.
oceanographer
noun
personwhostudiestheocean.
oceanvessel
noun
ship,boat,submarine,orothervehicleabletotraveltheocean.
oligotrophic
adjective
havingfewnutrientsandsupportinglittlegrowth.
optical
adjective
havingtodowithvisionorsight.
organic
adjective
composedoflivingoronce-livingmaterial.
origin
noun
sourceorancestry.
particle
noun
smallpieceofmaterial.
placid
adjective
calm.
planet
noun
large,sphericalcelestialbodythatregularlyrotatesaroundastar.
plankton
pluralnoun
(singular:plankton)microscopicaquaticorganisms.
plastic
noun
chemicalmaterialthatcanbeeasilyshapedwhenheatedtoahightemperature.
plateau
noun
largeregionthatishigherthanthesurroundingareaandrelativelyflat.
polar
adjective
havingtodowiththeNorthand/orSouthPole.
predator
noun
animalthathuntsotheranimalsforfood.
predictable
adjective
regularorabletobeforecasted.
primary
adjective
firstormostimportant.
producer
noun
organismonthefoodchainthatcanproduceitsownenergyandnutrients.Also
calledanautotroph.
region
noun
anyareaontheEarthwithoneormorecommoncharacteristics.Regionsarethe
basicunitsofgeography.
responsibility
noun
beingaccountableandreliableforanactionorsituation.
rotation
noun
object'scompleteturnarounditsownaxis.
salinity
noun
saltiness.
Scandinavia
noun
regionandnameforsomecountriesinNorthernEurope:Iceland,Norway,
Sweden,Finland,andDenmark.
seasonal
adjective
likelytochangewiththeseasons.
significant
adjective
importantorimpressive.
Southern
Hemisphere
noun
halfoftheEarthbetweentheSouthPoleandtheEquator.
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stable
adjective
steadyandreliable.
stationary
adjective
unmoving.
subcontinent
noun
largesectionofacontinent.
subpolargyre
noun
circulatingoceancurrentthatformsathighlatitudesbeneathanareaoflow
atmosphericpressure,wherewinddrivescurrentsawayfromcoastalareas.
substance
noun
physicalmaterial.
subtropicalgyre
noun
circulatingoceancurrentthatformsbetweenEarth'spolarandequatorialregions,
beneathanareaofhighatmosphericpressure.
temperature
noun
degreeofhotnessorcoldnessmeasuredbyathermometerwithanumericalscale.
thermohaline
circulation
noun
oceanconveyorbeltsysteminwhichwatermovesbetweenthecolddepthsand
warmsurfaceinoceansthroughouttheworld.
trophiclevel
noun
oneofthreepositionsonthefoodchain:autotrophs(first),herbivores(second),
andcarnivoresandomnivores(third).
tropicalgyre
noun
circulatingoceancurrentthatformsinequatorialregionsandtendstoflowmostly
east-west.
upwelling
noun
processbywhichcurrentsbringcold,nutrient-richwatertotheoceansurface.
variation
noun
difference.
vortex
noun
columnofrotatingfluid,suchasair(wind)orwater.
watercolumn
noun
areareachingfromthesedimentofabodyofwatertoitssurface.
wind
noun
movementofair(fromahighpressurezonetoalowpressurezone)causedbythe
unevenheatingoftheEarthbythesun.
ForFurtherExploration
Articles&Profiles
WoodsHoleOceanographicInstitution:Currents,Gyres,andEddies
EarthSky:EmanueleDiLorenzoExplainsOceanGyres
InstructionalContent
COMETProgram:IntroductiontoTropicalMeteorology—GlobalUpperandDeepOceanCirculation
NationalGeographicEducation:TheGeographyofOceanCurrents
Websites
NASAOceanMotion:WindDrivenSurfaceCurrents
NOAAOceanServiceEducation:Currents
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