1. CIRCULATION OF OCEANS

2. OCEAN & ATMOSPHERE SIMILARITIES
Circulation of Atmosphere & Oceans both driven by convection currents
Coriolis force rotates ocean currents in the same way as wind currents

3. IMPORTANT DIFFERENCES
Density controlled by SALINITY as well as
temperature
Ocean heated from top rather than bottom
Wind shear important
Landmasses interrupt flow
Velocity of flow much slower

4. TWO TYPES OF CURRENT DENSITY DRIVEN
Cold, saline water sinks, warmer water of lower salinity rises producing
VERTICAL CURRENTS
(Downwelling & Upwelling)
WIND DRIVEN
Wind shear over the surface produces HORIZONTAL CURRENTS
and
VERTICAL
UPWELLING

5. Voyage of the Fram

6. WIND DRIVEN CURRENTS
THE EKMAN SPIRAL discovered as a result of Nansen’s observations on the Fram
Coriolis force not only rotates winds but also ocean currents driven by wind
Result is huge rotating current gyres

7. EKMAN SPIRAL WESTERLY WINDS Surface Current Effect dies out
Ekman Transport
(Average of all vectors)
WESTERLY WINDS
Effect dies out
Below 100 m
Surface Current
< 3% Wind Speed
Water layers of increasing depth

8. CURRENT GYRES AN EXAMPLE THE NORTH ATLANTIC GYRE
First studied by Franklin & Folger

9. Wind Belts W E S T E R L I E S E U R O P E A F R I C A A M E R I C A S
SUBTROPICAL HIGH
A M E R I C A S
E U R O P E A F R I C A
N E T R A D E S

10. North Atlantic Current Gyre
A M E R I C A S
Gulf
Stream
E U R O P E A F R I C A
Canary
Current
North Equatorial Current

11. North Atlantic Gyre
South Atlantic Gyre
Subpolar Gyre
Not Developed
(Antarctica)
Polar Current
North Atlantic Current
N. Equatorial Current
Equatorial Counter Current
S. Equatorial Current
West Wind Drift

13. EKMAN TRANSPORT
A M E R I C A S
E U R O P E A F R I C A 2m 1m

14. Effects of Ekman Transport
1. Surface water piled into center of gyres

15. Effects of Ekman Transport
1. Surface water piled into center of gyres
2. Water also pushed to west end of gyres because Coriolis force increases with latitude

16. Effects of Ekman Transport
1. Surface water piled into center of gyres
2. Water also pushed to west end of gyres because Coriolis force increases with latitude
3. Piling of water at west end leads to a GEOSTROPHIC effect which accelerates current at west end of gyre (w intensification)

17. Geostrophic Effect North Atlantic Current E U R O P E A F R I C A
A M E R I C A S
Gulf
Stream
(9km/hr)
Canary
Current
(0.9 km/hr)
E U R O P E A F R I C A 2m 1m
North Equatorial Current

18. Final Current Vector accelerates
Geostrophic Effect
Effect of
Ekman Transport
Gravity
Effect of Coriolis
Force
Final Current Vector accelerates
Wind-driven current

19. Effects of Ekman Transport
1. Surface water piled into center of gyres
2. Water also pushed to west end of gyres because Coriolis force increases with latitude
3. Piling of water at west end leads to a GEOSTROPHIC effect which accelerates current at west end of gyre (w intensification)
4. Loss of surface water to west end of gyre is made good by coastal upwelling at east end.

20. Coastal Upwelling North Atlantic Current Gulf Stream 9km/hr Canary
Warm Surface Water
UPWELLING 1m
North Equatorial Current

21. COASTAL UPWELLING
Result of migration of surface water to west end of current gyres
Allows nutrient-rich deep water to upwell at east end
Upwelling nutrients encourage plankton
Rich fishing grounds

23. EL NINO & LA NINA
Coastal Upwelling at east end of S Pacific gyre provides rich fishing off Peru
Anchovy of great economic importance
Periodically upwelling fails and Anchovy industry collapses (El Nino)
Part of larger phenomenon –Southern Ocean Oscillation with world-wide effects ( floods & droughts)

24. La Nina
Strong Trades
Warm Surface Water
UPWELLING
Strong Westerlies

25. El Nino
Weak Trades
Warm Surface Water
Strong Westerlies

26. LA NINA
EL NINO

27. EL NINO & LA NINA
Coastal Upwelling at east end of S Pacific gyre provides rich fishing off Peru
Anchovy of great economic importance
Periodically upwelling fails and Anchovy industry collapses (El Nino)
Part of larger phenomenon –Southern Ocean Oscillation with world-wide effects ( floods & droughts)

28. TWO TYPES OF CURRENT DENSITY DRIVEN
Cold, saline water sinks, warmer water of lower salinity rises producing
VERTICAL CURRENTS
(Downwelling & Upwelling)
WIND DRIVEN
Wind shear over the surface produces HORIZONTAL CURRENTS
and
VERTICAL
UPWELLING

29. THERMOHALINE CIRCULATION
VERTICAL circulation driven by DENSITY
Recall that density of sea water controlled by temperature, salinity and pressure
Of these factors temperature is most important
Since warm water has low density and oceans are heated from the top vertical circulation is problematic

30. IMPORTANCE OF VERTICAL CIRCULATION
DOWNWELLING
Carries oxygen to the deep ocean
UPWELLING
Carries carbon dioxide and nutrients to the surface

31. THERMOCLINE Warm water heated by sun rests on colder unheated water
Steep temperature gradient is called the thermocline
Thermocline at right is stable
Stable
Thermocline
Depth
Temperature

32. HALOCLINE
Depending on climate and precipitation surface water is usually less saline than deep water.
Salinity of surface water is increased by evaporation and ice formation
Steep gradient is called the halocline
Stable
Halocline
Depth
Saliinity

33. PYCNOCLINE
Even when surface water is saline it is nearly always less dense than deep water because of temperature
There is a steep, stable density gradient (pycnocline) between surface and deep water
Stable
Pycnocline
Depth
Density

34. Effect of Latitude Thermoclines Haloclines P T E P E T Depth
Temperature
Salinity

35. DOWNWELLING
Since stratification of oceans is so stable how and where is downwelling possible? E T P
Only possible
close to poles especially when
ice freezes
and expels salt
Depth
Pycnocline
Density

36. High
Salinity
Density
Temperature
Low 90 60 30 30 60 90
Latitude

37. Labrador Sea
Norwegian Sea
E Greenland
Weddell Sea

38. Areas of Downwelling
North Atlantic Deep Water due to freezing in Norwegian, Labrador & E Greenland Seas
Antarctic Bottom Water due to freezing & salt expulsion in Weddell Sea
Intermediate Waters due to Arctic and Antarctic Convergences

39. SHALLOW & DEEP CIRCULATION

40. SUMMARY SURFACE CIRCULATION Current gyres driven by wind UPWELLING
Driven by wind, important for nutrients
DOWNWELLING & DEEP CIRCULATION
Driven by density, important for oxygenation of deep

43. Westward Intensification
North Atlantic Current
A M E R I C A S
Gulf
Stream
E U R O P E A F R I C A
Canary
Current 2m 1m
North Equatorial Current