From Glossary of Meteorology
The rising of water from between 200 and 400 m to the surface along coastlines where an alongshore blowing wind has the coast on its left in the Northern Hemisphere or on its right in the Southern Hemisphere.
Because the surface currents of the Ekman spiral are deflected offshore in these situations, the surface water is drawn away from the coast, causing the colder water from deeper layers to upwell. The associated lowering of the sea surface temperature results in atmospheric heat loss and modifies the local climate. The upwelled water is also rich in nutrients, and coastal upwelling regions are among the most important fishing regions of the World Ocean. The most important coastal upwelling regions are found in the eastern boundary currents of the subtropical gyres, that is, in the Peru/Chile, California, Benguela, and Canary Currents. The Somali, East Arabian, and South Java Currents develop upwelling on a seasonal basis.