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Coastal upwelling is the best known type of upwelling, and the most closely related to human activities as it supports some of the most productive fisheries in the world. Coastal upwelling will occur if the wind direction is parallel to the coastline and generates wind-driven currents.
Ekman suction occurs both along coastlines and in the open ocean, but also occurs along the equator. Along the Pacific coastline of California, Central America, and Peru, as well as along the Atlantic coastline of Africa there are areas of upwelling due to Ekman suction, as the currents move equatorwards. [ 1 ]
The Great South Australian Coastal Upwelling System is a seasonal upwelling system in the eastern Great Australian Bight, extending from Ceduna, South Australia, to Portland, Victoria, over a distance of about 800 kilometres (500 mi). Upwelling events occur in the austral summer (from November to May) when seasonal winds blow from the southeast.
Therefore, wind stress impacts biological activity around the globe. Two important forms of wind-driven upwelling are coastal upwelling and equatorial upwelling. Coastal upwelling occurs when the wind stress is directed with the coast on its left (right) in the Northern (Southern) Hemisphere.
While upwelling promotes abundant primary and secondary production in the upper parts of the water column and near the coast, deeper waters with limited oxygen exchange create hypoxic areas called oxygen minimum zones at the coastal shelf and upper coastal slope. The Benguela oxygen minimum zone starts around a depth of 100 m and is a few ...
The coastal upwelling in the south-eastern Arabian Sea occurs seasonally. It begins in the mid Spring (Mid May) along the southern tip of India and as the season advances it spreads northward. It is not a uniform wind-driven upwelling system, [1] but is driven by various factors.
In addition to coastal upwelling, strong upwelling also occurs along the equator. In this case, the Coriolis force is small near the equator as it changes sign between the hemispheres. The westward trade winds then lead to an Ekman transport that moves the surface waters away from the equator in both hemispheres.
These wind patterns result in a wind stress curl that drives Ekman pumping in the subtropics (resulting in downwelling) and Ekman suction in subpolar regions (resulting in upwelling). [3] Ekman pumping results in an increased sea surface height at the center of the gyre and anticyclonic geostrophic currents in subtropical gyres. [3]