CIRCULATION OF CIRCULATION OF OCEANSOCEANS
OCEAN & ATMOSPHEREOCEAN & ATMOSPHERESIMILARITIESSIMILARITIES
Circulation of Atmosphere & Oceans both Circulation of Atmosphere & Oceans both driven by convection currentsdriven by convection currents
Coriolis force rotates ocean currents in the Coriolis force rotates ocean currents in the same way as wind currentssame way as wind currents
IMPORTANT DIFFERENCESIMPORTANT DIFFERENCES
Density controlled by SALINITY as well asDensity controlled by SALINITY as well as
temperaturetemperature Ocean heated from top rather than bottomOcean heated from top rather than bottom Wind shear importantWind shear important Landmasses interrupt flowLandmasses interrupt flow Velocity of flow much slowerVelocity of flow much slower
TWO TYPES OF CURRENTTWO TYPES OF CURRENT
DENSITY DRIVENDENSITY DRIVEN
Cold, saline water sinks, Cold, saline water sinks, warmer water of lower warmer water of lower
salinity rises salinity rises producing producing
VERTICAL CURRENTSVERTICAL CURRENTS
(Downwelling & (Downwelling & Upwelling)Upwelling)
WIND DRIVENWIND DRIVEN
Wind shear over the Wind shear over the surface produces surface produces
HORIZONTAL HORIZONTAL CURRENTSCURRENTS
andand
VERTICALVERTICAL
UPWELLING UPWELLING
Voyage of the Fram 1893-6Voyage of the Fram 1893-6
WIND DRIVEN CURRENTSWIND DRIVEN CURRENTS
THE EKMAN SPIRAL discovered as a THE EKMAN SPIRAL discovered as a result of Nansen’s observations on the result of Nansen’s observations on the Fram 1893-6Fram 1893-6
Coriolis force not only rotates winds but Coriolis force not only rotates winds but also ocean currents driven by windalso ocean currents driven by wind
Result is huge rotating current gyres Result is huge rotating current gyres
EKMAN SPIRALEKMAN SPIRAL
90o
45o
Ekman Transport(Average of all vectors)
Surface Current< 3% Wind Speed
WESTERLY WINDS
Effect dies outBelow 100 m
Water layers of increasing depth
CURRENT GYRESCURRENT GYRES
AN EXAMPLE AN EXAMPLE
THE NORTH ATLANTIC GYRETHE NORTH ATLANTIC GYRE
First studied by Franklin & FolgerFirst studied by Franklin & Folger
Wind BeltsWind Belts
SUBTROPICAL HIGH
A M
E R
I C
A S
E U
R O
P E
A F
R I C
A
W E S T E R L I E S
N E T R A D E S
North Atlantic Current GyreNorth Atlantic Current GyreA
M E
R I
C A
SE
U R
O P
E A
F R
I C A
North Atlantic Current
North Equatorial Current
GulfStream
CanaryCurrentCanaryCurrent
North Atlantic Gyre
South Atlantic Gyre
Subpolar Gyre
Not Developed(Antarctica)
Equatorial Counter Current
N. Equatorial Current
S. Equatorial Current
West Wind Drift
North Atlantic Current
Polar Current
EKMAN TRANSPORTEKMAN TRANSPORTA
M E
R I
C A
SE
U R
O P
E A
F R
I C A
2m 1m
Effects of Ekman TransportEffects of Ekman Transport
1. Surface water piled into center of gyres1. Surface water piled into center of gyres
Effects of Ekman TransportEffects of Ekman Transport
1. Surface water piled into center of gyres1. Surface water piled into center of gyres 2. Water also pushed to west end of gyres 2. Water also pushed to west end of gyres
because Coriolis force increases with latitudebecause Coriolis force increases with latitude
Effects of Ekman TransportEffects of Ekman Transport
1. Surface water piled into center of gyres1. Surface water piled into center of gyres 2. Water also pushed to west end of gyres 2. Water also pushed to west end of gyres
because Coriolis force increases with latitudebecause Coriolis force increases with latitude 3. Piling of water at west end leads to a 3. Piling of water at west end leads to a
GEOSTROPHIC effect which accelerates GEOSTROPHIC effect which accelerates current at west end of gyre (w intensification)current at west end of gyre (w intensification)
Geostrophic EffectGeostrophic EffectA
M E
R I
C A
SE
U R
O P
E A
F R
I C A
2m
1m
North Atlantic Current
North Equatorial Current
GulfStream(9km/hr)
CanaryCurrent
(0.9 km/hr)
Effect of Ekman Transport
Effect ofGravity
Effect of CoriolisForce
Final Current Vector acceleratesWind-driven current
Geostrophic EffectGeostrophic Effect
Effects of Ekman TransportEffects of Ekman Transport
1. Surface water piled into center of gyres1. Surface water piled into center of gyres 2. Water also pushed to west end of gyres 2. Water also pushed to west end of gyres
because Coriolis force increases with latitudebecause Coriolis force increases with latitude 3. Piling of water at west end leads to a 3. Piling of water at west end leads to a
GEOSTROPHIC effect which accelerates GEOSTROPHIC effect which accelerates current at west end of gyre (w intensification)current at west end of gyre (w intensification)
4. Loss of surface water to west end of gyre is 4. Loss of surface water to west end of gyre is made good by coastal upwelling at east end.made good by coastal upwelling at east end.
Coastal UpwellingCoastal Upwelling
1m
North Atlantic Current
North Equatorial Current
GulfStream9km/hr
CanaryCurrent0.9 km/hr
CanaryCurrent0.9 km/hr
UPWELLING
Warm Surface Water
COASTAL UPWELLINGCOASTAL UPWELLING
Result of migration of surface water to Result of migration of surface water to west end of current gyreswest end of current gyres
Allows nutrient-rich deep water to upwell Allows nutrient-rich deep water to upwell at east endat east end
Upwelling nutrients encourage plankton Upwelling nutrients encourage plankton Rich fishing grounds Rich fishing grounds
EL NINO & LA NINAEL NINO & LA NINA
Coastal Upwelling at east end of S Pacific Coastal Upwelling at east end of S Pacific gyre provides rich fishing off Peru gyre provides rich fishing off Peru
Anchovy of great economic importanceAnchovy of great economic importance Periodically upwelling fails and Anchovy Periodically upwelling fails and Anchovy
industry collapses (El Nino)industry collapses (El Nino) Part of larger phenomenon –Southern Ocean Part of larger phenomenon –Southern Ocean
Oscillation with world-wide effects ( floods & Oscillation with world-wide effects ( floods & droughts)droughts)
La NinaLa Nina
UP
WE
LLING
Warm Surface Water
Strong Trades
Strong Westerlies
El NinoEl Nino
Warm Surface Water
Strong Westerlies
Weak Trades
LA NINA
EL NINO
EL NINO & LA NINAEL NINO & LA NINA
Coastal Upwelling at east end of S Pacific Coastal Upwelling at east end of S Pacific gyre provides rich fishing off Peru gyre provides rich fishing off Peru
Anchovy of great economic importanceAnchovy of great economic importance Periodically upwelling fails and Anchovy Periodically upwelling fails and Anchovy
industry collapses (El Nino)industry collapses (El Nino) Part of larger phenomenon –Southern Ocean Part of larger phenomenon –Southern Ocean
Oscillation with world-wide effects ( floods & Oscillation with world-wide effects ( floods & droughts)droughts)
TWO TYPES OF CURRENTTWO TYPES OF CURRENT
DENSITY DRIVENDENSITY DRIVEN
Cold, saline water sinks, Cold, saline water sinks, warmer water of lower warmer water of lower
salinity rises salinity rises producing producing
VERTICAL CURRENTSVERTICAL CURRENTS
(Downwelling & (Downwelling & Upwelling)Upwelling)
WIND DRIVENWIND DRIVEN
Wind shear over the Wind shear over the surface produces surface produces
HORIZONTAL HORIZONTAL CURRENTSCURRENTS
andand
VERTICALVERTICAL
UPWELLING UPWELLING
THERMOHALINE THERMOHALINE CIRCULATIONCIRCULATION
VERTICAL circulation driven by DENSITYVERTICAL circulation driven by DENSITY Recall that density of sea water controlled Recall that density of sea water controlled
by temperature, salinity and pressureby temperature, salinity and pressure Of these factors temperature is most Of these factors temperature is most
importantimportant Since warm water has low density and Since warm water has low density and
oceans are heated from the top vertical oceans are heated from the top vertical circulation is problematiccirculation is problematic
IMPORTANCE OF VERTICAL IMPORTANCE OF VERTICAL CIRCULATIONCIRCULATION
DOWNWELLINGDOWNWELLING
Carries oxygen to the Carries oxygen to the deep oceandeep ocean
UPWELLINGUPWELLING
Carries carbon dioxide Carries carbon dioxide and nutrients to the and nutrients to the
surfacesurface
THERMOCLINETHERMOCLINE
Warm water heated Warm water heated by sun rests on colder by sun rests on colder unheated water unheated water
Steep temperature Steep temperature gradient is called the gradient is called the thermoclinethermocline
Thermocline at right is Thermocline at right is stablestable
Depth
Temperature
StableThermocline
HALOCLINEHALOCLINE
Depending on climate Depending on climate and precipitation and precipitation surface water is surface water is usually less saline usually less saline than deep water.than deep water.
Salinity of surface Salinity of surface water is increased by water is increased by evaporation and ice evaporation and ice formationformation
Steep gradient is Steep gradient is called the haloclinecalled the halocline
Depth
Saliinity
StableHalocline
PYCNOCLINEPYCNOCLINE
Even when surface Even when surface water is saline it is water is saline it is nearly always less nearly always less dense than deep dense than deep water because of water because of temperaturetemperature
There is a steep, There is a steep, stable density stable density gradient (pycnocline) gradient (pycnocline) between surface and between surface and deep waterdeep water
Depth
Density
StablePycnocline
Effect of LatitudeEffect of LatitudeThermoclinesThermoclines HaloclinesHaloclines
Depth
TemperatureSalinity
P T E P E T
DOWNWELLINGDOWNWELLING Since stratification of oceans is so stable Since stratification of oceans is so stable
how and where is downwelling possible?how and where is downwelling possible?
Depth
Pycnocline
E T P
Only possibleclose to poles especially whenice freezes and expels salt
Density
030 3060 6090 90
Salinity
Temperature
Density
Latitude
Low
High
Norwegian SeaLabrador Sea
E Greenland
Weddell Sea
Areas of DownwellingAreas of Downwelling
North Atlantic Deep Water due to freezing in North Atlantic Deep Water due to freezing in Norwegian, Labrador & E Greenland SeasNorwegian, Labrador & E Greenland Seas
Antarctic Bottom Water due to freezing & Antarctic Bottom Water due to freezing & salt expulsion in Weddell Seasalt expulsion in Weddell Sea
Intermediate Waters due to Arctic and Intermediate Waters due to Arctic and Antarctic ConvergencesAntarctic Convergences
SHALLOW & DEEP SHALLOW & DEEP CIRCULATIONCIRCULATION
SUMMARYSUMMARY
SURFACE CIRCULATIONSURFACE CIRCULATIONCurrent gyres driven by windCurrent gyres driven by wind
UPWELLINGUPWELLINGDriven by wind, important for nutrientsDriven by wind, important for nutrients
DOWNWELLING & DEEP CIRCULATION DOWNWELLING & DEEP CIRCULATION Driven by density, important for oxygenation of Driven by density, important for oxygenation of
deepdeep
Westward IntensificationWestward IntensificationA
M E
R I
C A
SE
U R
O P
E A
F R
I C A
2m
1m
North Atlantic Current
North Equatorial Current
GulfStream
CanaryCurrent