Ocean Circulation II Ekman transport & Geostrophic currents.

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Presentation transcript:

Ocean Circulation II Ekman transport & Geostrophic currents

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)

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

Ekman Motion

Ekman Spiral

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

Thermo, halo & Picnoclines

Coastal Ekman Transport

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)

Pressure Gradient and Coriolis equilibrium: Geostrophic currents

Geostrophic currents Geostrophic currents follow lines of equal pressure / height

Open Ocean Surface Currents Ekman surface transport

Open Ocean Geostrophic currents

Geostrophic currents and continents

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

Global Surface Currents

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 = m 3 /s

Western Boundary Current Intensification Stronger Coriolis force at higher latitudes

Western Boundary Current Intensification Subtropical Gyres displaced to the West

Gulf Stream 30 Sv 150 Sv

Gulf Stream

Cold and Warm Water Eddies

SST – Gulf Stream

California Seasonal Reversal

The End

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