Explain what is meant by Ekman transport and what role it plays in producing oceanic gyres in the surface waters of the subtropical oceans

Question

What will be an ideal response?

Answer 1

The surface Ekman layer, which extends to about 100 to 300 meters depth, is a boundary layer feature in which the direct stresses of the wind are felt. The transport within the Ekman layer is 90° towards the right of the wind in the northern hemisphere, and 90° to the left of the wind in the southern hemisphere. The Ekman transport is proportional to the wind stress, which is proportional to the square of the wind speed. In a clockwise gyre in the Northern Hemisphere, the effect of Ekman transport is to push water into the center of the gyre. Note that the counterclockwise gyres in the Southern Hemisphere will produce exactly the same result, because the Coriolis Effect deflects the water to the left.
The subtropical gyres are formed by geostrophic currents that occur when Ekman transport from the wind-driven currents causes water to pile up in the center of the gyre. There is a force due to gravity, acting down the gradient of the surface slope that is opposed by the Coriolis Effect. The net effect is a flow of water at approximately 90° to the slope. The result is a geostrophic current that flows approximately perpendicular to the slope of the sea surface around the gyre.