An Ekman spiral (A) is a rotating column of water that forms when water moves at an angle to the wind direction due to the Coriolis Effect. The net effect of the rotating water (B) is movement at right angle to the wind direction. The example shown above is for the Northern Hemisphere. The water turns to the left instead of right in the Southern Hemisphere.
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How the Ocean Surface Moves
As Arctic explorer Fridtjof Nansen tried to get to the North Pole in 1893, he noticed that the sea ice in the Arctic Ocean was not moving in the same direction as the wind. It was always moving to the right of the wind direction. Nansen didn’t know why this was happening. Today we do. It is called Ekman transport.
As wind blows across the ocean, it moves water at the surface. Because the Earth rotates, water moves to the right of the wind in the Northern Hemisphere and to the left of the wind in the Southern Hemisphere.
The water deeper down changes direction. The water underneath the surface turns a bit more, and the water below that turns even more. This makes a spiral of moving water 100 to 150 meters (330 to 500 ft) deep. The average direction of all this turning water is about a right angle (90°) from the wind direction. This average is Ekman transport.
Ekman transport is named for Swedish scientist V. Walfrid Ekman who first described the spiral of water in 1905. To help him make a model of these movements, Ekman used the observations that Nansen made while he was in the Arctic.
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