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Ocean Circulation II Ekman transport & Geostrophic currents

Ocean Circulation II Ekman transport & Geostrophic currents. Ocean Circulation. 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)

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Ocean Circulation II Ekman transport & Geostrophic currents

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  1. Ocean Circulation II Ekman transport & Geostrophic currents

  2. Ocean Circulation • 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) • 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

  5. Ekman Motion

  6. Ekman Spiral

  7. Ekman Spiral • 45o surface transport offset • 90o 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 CurrentsEkman surface transport

  14. Open Ocean Geostrophic currents

  15. Geostrophic currents andcontinents

  16. Geostrophic currents andcontinents

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

  18. Global Surface Currents

  19. 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) Oceanic Gyres 1 Sverdrup = 100000 m3/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 150 Sv 30 Sv

  23. Gulf Stream

  24. Cold and Warm Water Eddies

  25. SST – Gulf Stream

  26. SST – Gulf Stream

  27. California Seasonal Reversal

  28. The End

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