Ekmantransportin

Ekmantransportin, commonly referred to as the Ekman transport, is the net movement of ocean water in the upper, wind-driven layer known as the Ekman layer. It results from the balance among wind stress, the Coriolis force due to the Earth's rotation, and friction within a rotating fluid. In the classical model of a homogeneous, constant-density ocean, the depth-integrated Ekman transport Te is approximately equal to the surface wind stress τ divided by the Coriolis parameter f and seawater density ρ: Te ≈ τ / (ρ f). The transport is perpendicular to the wind: in the Northern Hemisphere it points to the right of the wind direction, and in the Southern Hemisphere to the left.

The Ekman layer exhibits a velocity that decays with depth in what is known as the Ekman spiral, and its net transport is the integrated effect of this shear. Real oceans depart from the simple model due to stratification, variable viscosity, and complex coastline geometry, which can modify both the magnitude and direction of transport.

Geophysical implications include the generation of vertical motions when Ekman transport converges or diverges. Offshore Ekman transport near coastlines promotes upwelling of nutrient-rich deeper waters, while onshore transport promotes downwelling. Ekman transport also participates in larger-scale ocean circulation when combined with pressure gradients and geostrophic flow, notably in the context of Sverdrup transport in basin-scale dynamics.

The concept was introduced by Vagn Walfrid Ekman in 1905 and remains a foundational element in physical oceanography, linking atmospheric forcing to coastal and open-ocean circulation patterns.