How does friction between wind and seawater create currents?

Wind creates ocean currents through the transfer of momentum via frictional forces at the sea surface, a process known as wind stress. When wind blows over the ocean, it exerts a shear stress on the surface water, setting it in motion in the direction of the wind.123

This interaction initiates a wind-driven circulation that extends into the upper layers of the ocean, specifically within the Ekman layer. Within this layer, the movement of water is influenced by the Coriolis effect, which causes the surface current to deflect at an angle—approximately 45° to the right of the wind in the Northern Hemisphere and to the left in the Southern Hemisphere.24

As momentum is transferred from the surface downward, frictional forces between water layers cause the current velocity to decrease with depth, while the direction of the flow rotates to form an Ekman spiral. This wind-induced motion is a primary driver of large-scale ocean circulation patterns, including the formation of gyres.425