chapter07 ocean currents.ppt - Geology Guypowerpoints.geology-guy.com › trujillo › chapter07_ocean_currents.pdf · Oceanography 101 Oceanography 101 – – Phil FarquharsonPhil

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CHAPTER 7CHAPTER 7Ocean CirculationOcean Circulation

Words…Words…

Ocean currentsOcean currents

Moving seawaterMoving seawaterSurface ocean currentsSurface ocean currents–– Transfer heat from warmer to cooler Transfer heat from warmer to cooler

areasareas

Oceanography 101 Oceanography 101 –– Phil FarquharsonPhil Farquharson

–– Similar to pattern of major wind beltsSimilar to pattern of major wind belts–– Affect coastal climatesAffect coastal climates

Deep ocean currentsDeep ocean currents–– Provide oxygen to deep seaProvide oxygen to deep sea

Affect marine lifeAffect marine life

Types of ocean currentsTypes of ocean currents

Surface currentsSurface currents–– WindWind--drivendriven–– Primarily horizontal motionPrimarily horizontal motion

Deep currentsDeep currents


pp–– Driven by differences in density caused by Driven by differences in density caused by

differences in temperature and salinitydifferences in temperature and salinity–– Vertical and horizontal motionsVertical and horizontal motions

Measuring surface currentsMeasuring surface currents

Direct methodsDirect methods–– Floating device Floating device

tracked through timetracked through time–– Fixed current meterFixed current meter

Oceanography Oceanography 101 101 –– Phil FarquharsonPhil Farquharson

Indirect methodsIndirect methods–– Pressure gradientsPressure gradients–– Radar altimetersRadar altimeters–– Doppler flow meterDoppler flow meter

Fixed current meterFixed current meter


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Measuring surface currents (accidentally)Measuring surface currents (accidentally)


Curt EbbesmeyerCurt Ebbesmeyer




Measuring deep currentsMeasuring deep currents

Floating devices tracked through timeFloating devices tracked through timeChemical tracersChemical tracers–– TritiumTritium

Oceanography Oceanography –– Phil FarquharsonPhil Farquharson

–– ChlorofluorocarbonsChlorofluorocarbonsCharacteristic temperature and Characteristic temperature and salinitysalinity

Measuring Deep CurrentsMeasuring Deep CurrentsArgoArgo–– Global array of freeGlobal array of free--

drifting profiling floatsdrifting profiling floats–– Floating device Floating device

tracked through timetracked through timegg

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Measuring Deep CurrentsMeasuring Deep CurrentsArgoArgo

Surface CurrentsSurface CurrentsOccur above pycnoclineOccur above pycnocline–– Affect only 10% of ocean water on EarthAffect only 10% of ocean water on Earth

Friction between wind and ocean surfaceFriction between wind and ocean surface–– 2% of wind energy transferred to ocean 2% of wind energy transferred to ocean

surfacesurface–– Surface currents slower speed than Surface currents slower speed than

corresponding windscorresponding windsGenerally follow Earth’s wind belt patternGenerally follow Earth’s wind belt pattern

Surface currentsSurface currentsFrictional drag between wind and oceanFrictional drag between wind and oceanWind plus other factors such asWind plus other factors such as–– Distribution of continentsDistribution of continents–– GravityGravity–– FrictionFriction


–– FrictionFriction–– Coriolis effectCoriolis effect

GyresGyres or large circular loops of moving or large circular loops of moving waterwater

Ocean gyresOcean gyresSubtropical gyresSubtropical gyres

Centered about Centered about 3030oo

N or SN or SEquatorial currentEquatorial currentWestern Boundary Western Boundary


currentscurrentsNorthern or Southern Northern or Southern Boundary currentsBoundary currentsEastern Boundary Eastern Boundary currentscurrents

Other surface currentsOther surface currentsEquatorial CountercurrentsEquatorial CountercurrentsSubpolar gyresSubpolar gyres


Ocean CirculationOcean Circulation

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surface currentssurface currentsFrom Curt Ebbesmeyer:From Curt Ebbesmeyer:Five Subtropical GyresFive Subtropical Gyres

North Atlantic North Atlantic –– Columbus GyreColumbus GyreSouth Atlantic South Atlantic –– Navigator GyreNavigator GyreNorth Pacific North Pacific –– Turtle GyreTurtle GyreSouth Pacific South Pacific –– Heyerdahl GyreHeyerdahl GyreIndian Ocean Indian Ocean –– MajidMajid GyreGyre

Subtropical Gyres and CurrentsSubtropical Gyres and Currents Gyres and Boundary CurrentsGyres and Boundary Currents

Subtropical Gyre CurrentsSubtropical Gyre CurrentsEquatorial Currents Equatorial Currents –– North or southNorth or south–– Travel westward along equatorTravel westward along equator

Western Boundary Currents Western Boundary Currents W t f t i l iW t f t i l i–– Warm waters from equatorial regionsWarm waters from equatorial regions

–– Western edge of ocean basinsWestern edge of ocean basins

Subtropical Gyre CurrentsSubtropical Gyre CurrentsNorthernNorthern or or Southern Boundary Currents Southern Boundary Currents –– Easterly water flow across ocean basinEasterly water flow across ocean basin–– Northern boundary currents in Northern Northern boundary currents in Northern

HemisphereHemisphere–– Southern boundary currents in SouthernSouthern boundary currents in Southern–– Southern boundary currents in Southern Southern boundary currents in Southern

HemisphereHemisphereEastern Boundary Currents Eastern Boundary Currents –– Cool watersCool waters–– Eastern edge of ocean basinsEastern edge of ocean basins

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Other Surface CurrentsOther Surface CurrentsEquatorial Countercurrents Equatorial Countercurrents –– Eastward flow between North and South Eastward flow between North and South

Equatorial CurrentsEquatorial Currents–– Due to minimal Coriolis effect at equatorDue to minimal Coriolis effect at equator

Subpolar GyresSubpolar GyresSubpolar Gyres Subpolar Gyres –– Rotate opposite subtropical gyresRotate opposite subtropical gyres–– Smaller and fewer than subtropical gyresSmaller and fewer than subtropical gyres

Ekman Spiral and Ekman TransportEkman Spiral and Ekman Transport

Observation that Arctic Ocean ice moved at a Observation that Arctic Ocean ice moved at a 2020-- to 40to 40--degree angle to the right of the winddegree angle to the right of the windSouthern Hemisphere movement to the left of Southern Hemisphere movement to the left of the windthe windthe windthe wind

Ekman SpiralEkman Spiral

V. Walfrid Ekman V. Walfrid Ekman –– Developed circulation model in 1905Developed circulation model in 1905

Ekman spiral Ekman spiral –– Explains balance between friction andExplains balance between friction andExplains balance between friction and Explains balance between friction and

Coriolis effectCoriolis effect–– Describes direction and flow of Describes direction and flow of

surface waters at different depthssurface waters at different depths

Ekman spiralEkman spiralSurface currents move at angle to windSurface currents move at angle to windEkman spiral describes speed and direction of Ekman spiral describes speed and direction of seawater flow at different depthsseawater flow at different depthsEach successive layer moves increasingly to right Each successive layer moves increasingly to right (N hemisphere)(N hemisphere)


Ekman transportEkman transportAverage movement of seawater under influence of Average movement of seawater under influence of windwind9090oo to right of wind in Northern hemisphereto right of wind in Northern hemisphere9090oo to left of wind in Southern hemisphereto left of wind in Southern hemisphere


Ekman SpiralEkman Spiral

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Geostrophic flowGeostrophic flowEkman transport Ekman transport piles up water piles up water within subtropical within subtropical gyresgyresSurface water Surface water flows downhill flows downhill (gravity) and(gravity) and


Also to the right Also to the right (Coriolis effect)(Coriolis effect)Balance of Balance of downhill and to downhill and to the right causes the right causes geostrophic flow geostrophic flow around the “hill”around the “hill”

Western IntensificationWestern IntensificationTop of hill of water displaced toward west Top of hill of water displaced toward west due to Earth’s rotation.due to Earth’s rotation.Western boundary currents intensified in Western boundary currents intensified in both hemispheres.both hemispheres.–– FasterFaster–– NarrowerNarrower–– DeeperDeeper–– WarmerWarmer

Coriolis effect contributes to western Coriolis effect contributes to western intensification.intensification.

Eastern Boundary CurrentsEastern Boundary CurrentsEastern side of ocean basinsEastern side of ocean basinsTend to have the opposite properties of Tend to have the opposite properties of Western Boundary CurrentsWestern Boundary Currents–– ColdCold–– SlowSlow–– ShallowShallow–– WideWide

Eastern and Western Boundary CurrentsEastern and Western Boundary Currents

Ocean currents and climateOcean currents and climate

Warm ocean currents warm air at Warm ocean currents warm air at coastcoast–– Warm, humid airWarm, humid air


–– Humid climate on adjoining landmassHumid climate on adjoining landmassCool ocean currents cool air at coastCool ocean currents cool air at coast–– Cool, dry airCool, dry air–– Dry climate on adjoining landmassDry climate on adjoining landmass

Ocean currents and climateOcean currents and climate

Oceanography 112 Oceanography 112 –– Phil FarquharsonPhil FarquharsonAverage AugustTemperatures

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Ocean currents and climateOcean currents and climateAverage February

Temperatures


Upwelling and DownwellingUpwelling and Downwelling

UpwellingUpwelling –– Vertical movement of cold, Vertical movement of cold, nutrientnutrient--rich water to surfacerich water to surface–– High biological High biological productivity productivity –– an abundance of an abundance of

l t th b f th f d bl t th b f th f d balgae at the base of the food webalgae at the base of the food webDownwellingDownwelling –– Vertical movement of Vertical movement of surface water downward in water columnsurface water downward in water column

Diverging surface seawaterDiverging surface seawaterSurface Surface seawater seawater moves away moves away Deeper Deeper seawater seawater (cooler, (cooler, nutrientnutrient--rich) rich) replacesreplacesreplaces replaces surface watersurface waterUpwellingUpwellingHigh High biological biological productivityproductivity Fig. 7.9

Converging surface seawaterConverging surface seawaterSurface seawater Surface seawater moves towards moves towards an areaan areaSurface seawater Surface seawater piles uppiles up


Seawater moves Seawater moves downwarddownwardDownwellingDownwellingLow biological Low biological productivityproductivity

Coastal upwelling and downwellingCoastal upwelling and downwelling

Ekman transport Ekman transport moves surface moves surface seawater seawater onshore onshore (downwelling) or(downwelling) or


Offshore Offshore (upwelling)(upwelling)

Coastal upwelling and downwellingCoastal upwelling and downwelling

Ekman transport Ekman transport moves surface moves surface seawater seawater onshore onshore (downwelling) or(downwelling) or


Offshore Offshore (upwelling)(upwelling)

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Other Causes of UpwellingOther Causes of Upwelling

Offshore windsOffshore windsSeafloor Seafloor obstruction obstruction Coastal Coastal

t ht hgeometry changegeometry changeLack of Lack of pycnoclinepycnocline–– High latitude High latitude

oceansoceans

Antarctic CirculationAntarctic Circulation

Antarctic Circumpolar Antarctic Circumpolar CurrentCurrent–– Also called Also called West Wind West Wind

DriftDrift and and Penguin GyrePenguin Gyre–– Only current toOnly current toOnly current to Only current to

completely encircle completely encircle EarthEarth

–– Moves more water Moves more water than any other currentthan any other current

Antarctic CirculationAntarctic CirculationAntarctic ConvergenceAntarctic Convergence–– Cold, dense Antarctic waters converge with Cold, dense Antarctic waters converge with

warmer, less dense subwarmer, less dense sub--Antarctic waters.Antarctic waters.–– Northernmost boundary of Antarctic OceanNorthernmost boundary of Antarctic Ocean

East Wind Drift East Wind Drift –– Polar EasterliesPolar Easterlies–– Creates surface divergence with opposite Creates surface divergence with opposite

flowing Antarctic Circumpolar Currentflowing Antarctic Circumpolar CurrentAntarctic DivergenceAntarctic Divergence–– Abundant marine lifeAbundant marine life

Atlantic Ocean CirculationAtlantic Ocean Circulation

North Atlantic Subtropical North Atlantic Subtropical GyreGyre

–– North Equatorial CurrentNorth Equatorial Current–– Gulf StreamGulf Stream

North Atlantic CurrentNorth Atlantic Current–– North Atlantic CurrentNorth Atlantic Current–– Canary CurrentCanary Current–– South Equatorial CurrentSouth Equatorial Current–– Atlantic Equatorial Counter Atlantic Equatorial Counter CurrentCurrent


Atlantic Ocean Atlantic Ocean circulationcirculation

South Atlantic South Atlantic Subtropical GyreSubtropical GyreBrazil CurrentBrazil Current


Antarctic Circumpolar Antarctic Circumpolar CurrentCurrentBenguela CurrentBenguela CurrentSouth Equatorial South Equatorial CurrentCurrent

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Gulf StreamGulf StreamBest studied of all ocean currentsBest studied of all ocean currentsMeanders and loopsMeanders and loopsMerges with Merges with Sargasso SeaSargasso Sea–– Circulates around center of North Atlantic GyreCirculates around center of North Atlantic Gyre–– Unique biology Unique biology –– Sargassum Sargassum

Gulf StreamGulf Stream

Meanders or loops may cause loss of water Meanders or loops may cause loss of water volume and generate:volume and generate:

–– WarmWarm--core ringscore rings –– warmer Sargasso Sea water warmer Sargasso Sea water trapped in loop surrounded by cool watertrapped in loop surrounded by cool waterColdCold core ringscore rings cold water trapped in loopcold water trapped in loop–– ColdCold--core rings core rings –– cold water trapped in loop cold water trapped in loop surrounded by warmer watersurrounded by warmer water

Unique biological Unique biological populationspopulations

Gulf StreamGulf Stream


Other North Atlantic currentsOther North Atlantic currents

Labrador CurrentLabrador CurrentIrminger CurrentIrminger CurrentNorwegian CurrentNorwegian CurrentNorth Atlantic CurrentNorth Atlantic Current


North Atlantic CurrentNorth Atlantic Current

Climate effects of North Atlantic currentsClimate effects of North Atlantic currents

Gulf Stream warms East coast of U.S. and Gulf Stream warms East coast of U.S. and Northern EuropeNorthern EuropeNorth Atlantic and Norwegian Currents North Atlantic and Norwegian Currents warm northwestern Europewarm northwestern Europe


ppLabrador Current cools eastern CanadaLabrador Current cools eastern CanadaCanary Current cools North Africa coastCanary Current cools North Africa coast

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Indian Ocean CirculationIndian Ocean Circulation

MonsoonsMonsoons –– seasonal reversal of winds seasonal reversal of winds over northern Indian Oceanover northern Indian OceanHeat Capacity DifferentialHeat Capacity DifferentialNortheast monsoon Northeast monsoon –– winterwinterSouthwest monsoon Southwest monsoon –– summer summer


Indian Ocean MonsoonIndian Ocean MonsoonAffects seasonal Affects seasonal land land weather weather Affects seasonal Affects seasonal Indian Indian Ocean current Ocean current circulationcirculationAffects phytoplankton productivityAffects phytoplankton productivity


Indian Ocean Subtropical GyreIndian Ocean Subtropical Gyre–– Agulhas CurrentAgulhas Current

Australian CurrentAustralian Current–– Australian CurrentAustralian Current–– LeeuwinLeeuwin CurrentCurrent

Pacific Ocean CirculationPacific Ocean Circulation

North Pacific Subtropical GyreNorth Pacific Subtropical Gyre–– Kuroshio CurrentKuroshio Current–– North Pacific CurrentNorth Pacific Current–– California CurrentCalifornia Current–– North Equatorial CurrentNorth Equatorial Current–– Alaskan Alaskan CurrentCurrent

Pacific Ocean CirculationPacific Ocean Circulation

South Pacific Subtropical GyreSouth Pacific Subtropical Gyre–– East Australian CurrentEast Australian Current–– Antarctic Circumpolar CurrentAntarctic Circumpolar Current–– Peru CurrentPeru CurrentPeru CurrentPeru Current–– South Equatorial CurrentSouth Equatorial Current–– Equatorial Counter Equatorial Counter CurrentCurrent

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Pacific Ocean Pacific Ocean circulationcirculation


Atmospheric and oceanic disturbances Atmospheric and oceanic disturbances in Pacific Oceanin Pacific Ocean

Normal conditionsNormal conditions–– Air pressure across equatorial Pacific is higher Air pressure across equatorial Pacific is higher

in eastern Pacificin eastern PacificStrong southeast trade windsStrong southeast trade winds


–– Strong southeast trade windsStrong southeast trade winds–– Pacific warm pool on western sidePacific warm pool on western side–– Thermocline deeper on western sideThermocline deeper on western side–– Upwelling off the coast of PeruUpwelling off the coast of Peru

Normal conditionsNormal conditions


Atmospheric and oceanic disturbances Atmospheric and oceanic disturbances in Pacific Oceanin Pacific Ocean

El NiñoEl Niño--Southern Oscillation (ENSO)Southern Oscillation (ENSO)–– Warm (El Niño)Warm (El Niño) and and cold phases (La Niña)cold phases (La Niña)–– High pressure in eastern Pacific weakensHigh pressure in eastern Pacific weakens–– Weaker trade windsWeaker trade winds–– Warm pool migrates eastwardWarm pool migrates eastward–– Thermocline deeper in eastern PacificThermocline deeper in eastern Pacific–– DownwellingDownwelling–– Lower biological productivityLower biological productivity

Corals particularly sensitive to warmer seawaterCorals particularly sensitive to warmer seawater


El NiñoEl Niño--Southern Oscillation (ENSO):Southern Oscillation (ENSO):Warm phase (El Niño)Warm phase (El Niño)


ENSO Conditions in the Pacific OceanENSO Conditions in the Pacific Ocean

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El NiñoEl Niño--Southern Oscillation (ENSO): Southern Oscillation (ENSO): cool phase (La Niña)cool phase (La Niña)

Increased pressure difference across Increased pressure difference across equatorial Pacificequatorial PacificStronger trade windsStronger trade winds


Stronger upwelling in eastern PacificStronger upwelling in eastern PacificShallower thermoclineShallower thermoclineCooler than normal seawaterCooler than normal seawaterHigher biological productivityHigher biological productivity

El NiñoEl Niño--Southern Oscillation (ENSO)Southern Oscillation (ENSO)Cool phase (La Niña)Cool phase (La Niña)


La La NiñNiña Conditions a Conditions

El NiEl Niñño and La Nio and La Niññaa

ENSO eventsENSO events


ENSO Has Global ImpactsENSO Has Global Impacts

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Notable ENSO Notable ENSO EventsEvents

19821982––1983198319971997––1998 1998 Flooding droughtFlooding droughtFlooding, drought, Flooding, drought, erosion, fires, tropical erosion, fires, tropical storms, harmful storms, harmful effects on marine lifeeffects on marine lifeUnpredictableUnpredictable

Notable ENSO Notable ENSO EventsEvents

19821982––1983198319971997––1998 1998 Flooding droughtFlooding droughtFlooding, drought, Flooding, drought, erosion, fires, tropical erosion, fires, tropical storms, harmful storms, harmful effects on marine lifeeffects on marine lifeUnpredictableUnpredictable

Occurrence of ENSO EventsOccurrence of ENSO EventsEl Niño warm phase about every El Niño warm phase about every 22––10 years10 yearsHighly irregularHighly irregularPhases usually last 12Phases usually last 12––18 months18 months10,00010,000--year sediment record of eventsyear sediment record of events10,00010,000 year sediment record of eventsyear sediment record of eventsENSO may be part of ENSO may be part of Pacific Decadal Pacific Decadal Oscillation (PDO) Oscillation (PDO) –– LongLong--term natural climate cycleterm natural climate cycle–– Lasts 20Lasts 20––30 years30 years

Predicting El Predicting El NiñNiño Events o Events

Tropical OceanTropical Ocean−−Global Atmosphere Global Atmosphere (TOGA) (TOGA) programprogram–– 19851985–– Monitors equatorial South PacificMonitors equatorial South Pacific–– System of buoysSystem of buoysy yy y

Tropical Atmosphere and Ocean (TOA) Tropical Atmosphere and Ocean (TOA) projectproject–– Continues monitoringContinues monitoring

ENSO still not fully ENSO still not fully understoodunderstood

DeepDeep--Ocean CurrentsOcean Currents

Thermohaline Circulation Thermohaline Circulation –– deep ocean deep ocean circulation driven by temperature and circulation driven by temperature and density differences in waterdensity differences in waterBelow the pycnoclineBelow the pycnocline9090% of all ocean water% of all ocean water9090% of all ocean water% of all ocean waterSlow velocitySlow velocity

Thermohaline circulationThermohaline circulation

Movement Movement caused by differences in caused by differences in density (temperature and salinity)density (temperature and salinity)–– Cooler seawater denserCooler seawater denser


–– Saltier seawater denserSaltier seawater denser

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Thermohaline CirculationThermohaline Circulation

Originates in high latitude surface oceanOriginates in high latitude surface oceanCooled, now dense surface water sinks Cooled, now dense surface water sinks and changes little.and changes little.DeepDeep water masses identified onwater masses identified onDeepDeep--water masses identified on water masses identified on temperaturetemperature––salinity (Tsalinity (T––S) diagram S) diagram –– Identifies deep water masses based on Identifies deep water masses based on

temperature, salinity, and resulting temperature, salinity, and resulting densitydensity

TT––S S DiagramDiagram


Selected deepSelected deep--water masseswater masses–– Antarctic Bottom WaterAntarctic Bottom Water–– North Atlantic Deep WaterNorth Atlantic Deep Water

Antarctic Intermediate WaterAntarctic Intermediate Water


–– Antarctic Intermediate WaterAntarctic Intermediate Water–– Oceanic Common WaterOceanic Common Water

Cold surface seawater sinks at polar regions Cold surface seawater sinks at polar regions and moves toward equatorand moves toward equator





ConveyorConveyor--belt circulationbelt circulationCombination deep ocean currents and surface currentsCombination deep ocean currents and surface currents


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Deep ocean currentsDeep ocean currents

Cold, oxygenCold, oxygen--rich surface water to deep rich surface water to deep oceanoceanDissolved ODissolved O22 important for life and mineral important for life and mineral processesprocesses


processesprocessesChanges in thermohaline circulation can Changes in thermohaline circulation can cause global climate changecause global climate change–– Example, warmer surface waters less dense, Example, warmer surface waters less dense,

not sink, less oxygen deep oceannot sink, less oxygen deep ocean

Power from CurrentsPower from Currents

Currents carry more Currents carry more energy than winds.energy than winds.FloridaFlorida––Gulf Stream Gulf Stream Current SystemCurrent SystemyyUnderwater turbinesUnderwater turbines–– ExpensiveExpensive–– Difficult to maintainDifficult to maintain–– Hazard to boating Hazard to boating

End of CHAPTER 7End of CHAPTER 7Ocean CirculationOcean Circulation


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chapter07 ocean currents.ppt - Geology Guypowerpoints.geology-guy.com › trujillo › chapter07_ocean_currents.pdf · Oceanography 101 Oceanography 101 – – Phil FarquharsonPhil