1. Ocean Circulation II Ekman transport & Geostrophic currents

2. Ocean Circulation 1.Surface Circulation  Wind Driven –Ekman Transport and Geostrophic Currents –Surface layer and Picnocline zone –0 – 50,100m / 50,100m - ~1000m –Affects ~25% of total water mass –Fast (1-2 m/s) 2.Deep Circulation  Density Driven –Thermohaline Circulation –Below Picnocline zone (>~1000m) –Affects ~75% of total water mass –Slow (~ m/day)

3. Surface Ocean Circulation Ekman Spiral Geostrophic Currents Open Ocean Currents Global Surface Circulation

4. Ekman Motion

6. Ekman Spiral

7. 45 o surface transport offset 90 o net water transport Stronger winds cause deeper water movement –Wind 10 m/s  50 – 100 m watercolumn –Wind 20 m/s  100 – 200 m watercolumn

8. Thermo, halo & Picnoclines

9. Coastal Ekman Transport

10. Consequences of Ekman Transport Ekman affects picnocline layer Coastal Upwelling –Cold surface water, high nutrients –High phytoplankton productivity –Great fisheries (Sahara bank, Peru) Coastal Downwelling –Warm surface water, low nutrients –Low phytoplankton –Poor fisheries (Northern Brazil)

11. Pressure Gradient and Coriolis equilibrium: Geostrophic currents

12. Geostrophic currents Geostrophic currents follow lines of equal pressure / height

13. Open Ocean Surface Currents Ekman surface transport

14. Open Ocean Geostrophic currents

15. Geostrophic currents and continents

17. Upwelling and Downwelling Convergence and Divergence Downwelling – Convergence –Subtropical Gyres –Sargasso Sea example of Geostrophic current Upwelling – Divergence

18. Global Surface Currents

19. Oceanic Gyres Western Boundary Currents Gulf Stream, Kuroshio, Agulas currents Narrow (100 km) Deep (<2000 m) Swift (1.5 m/s) Warm High Volume (50-75 Sv) Eastern Boundary Currents California, Canary, Peru currents Broad (1000 km) Shallow (<500 m) Sluggish (0.3 m/s) Cool Low Volume (10-15 Sv) 1 Sverdrup = 100000 m 3 /s

20. Western Boundary Current Intensification Stronger Coriolis force at higher latitudes

21. Western Boundary Current Intensification Subtropical Gyres displaced to the West

22. Gulf Stream 30 Sv 150 Sv

23. Gulf Stream

24. Cold and Warm Water Eddies

25. SST – Gulf Stream

27. California Seasonal Reversal

28. The End