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CIRCULATION OF OCEANS.

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Presentation on theme: "CIRCULATION OF OCEANS."— Presentation transcript:

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

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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

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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

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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

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