CirculationoftheOceanSurfacecurrentsCausesofformationDistributionBoundarycurrentsUpwellinganddownwellingElNinoandLaNina2.Deep-seacirculationWhatisacurrent?SurfaceCurrentsDuetotheforcesofpressuregradient,theCorioliseffect,topography,andsurfacewinds,wateroftenmovesinacircularpatterncalledagyre.SurfaceCurrentsAreDrivenbytheWindsThewesterliesandthetradewindsaretwoprimemoversoftheocean’ssurfacecurrents.Acombinationoffourforces–surfacewinds,thesun’sheat,theCorioliseffect,andgravity–circulatestheoceansurfaceclockwiseintheNorthernHemisphereandcounterclockwiseintheSouthernHemisphere,forminggyres.SurfaceCurrentsFlowaroundthePeripheryofOceanBasinsEkmanspiralandEkmantransportTheeffectofEkmanspiralingandtheCorioliseffectcausethewaterwithinagyretomoveinacircularpattern.ThemovementofwaterawayfrompointBisinfluencedbytherightwardtendencyoftheCorioliseffectandthegravity-poweredmovementofwaterdownthepressuregradient.ThesurfaceisraisedthroughwindmotionandEkmantransporttoformalowhill.Thewestward-movingwateratB‘feels’abalancedpullfromtwoforces:theoneduetoCorioliseffect(whichwouldturnthewatertotheright)andtheoneduetothepressuregradient,drivenbygravity(whichwouldturnittotheleft).Geostrophicflow（地转流）OceansurfacetopographySeasurfacewaterFlowsNotetheboundarycurrentsinthismap.Westernboundarycurrents–Thesearewarm,narrow,deep,fastcurrentsfoundatthewesternboundariesofoceanbasins.GulfStreamBrazilCurrentKuroshioCurrentEasternAustralianCurrentAgulhasCurrentEasternboundarycurrents–Thesecurrentsarecold,shallowandbroad,andtheirboundariesarenotwelldefined.CanaryCurrentBenguelaCurrentCaliforniaCurrentPeruCurrentWesternAustralianCurrentThegeneralsurfacecirculationoftheNorthAtlantic.EddyformationThewesternboundaryoftheGulfStreamisusuallydistinct,markedbyabruptchangesinwatertemperature,speed,anddirection.(a)Meanders(eddies)formatthisboundaryastheGulfStreamleavestheU.S.coastatCapeHatteras.Themeanderscanpinchoff(b)andeventuallybecomeisolatedcellsofwarmwaterbetweentheGulfStreamandtheco