PFEL Coastal Upwelling Indices

What is an Upwelling Index?

The frictional stress of equatorward wind on the ocean's surface, in concert with the effect of the earth's rotation, causes water in the surface layer to move away from the western coast of continental land masses. This offshore moving water is replaced by water which upwells, or flows toward the surface from depths of 50 to 100 meters and more. Upwelled water is cooler and saltier than the original surface water, and typically has much greater concentrations of nutrients such as nitrates, phosphates and silicates that are key to sustaining biological production. It is for this reason that marine ecosystems in the ocean's eastern boundary currents are highly productive, and capable of maintaining large standing crops of plankton, massive fish stocks such as sardines and anchovies, and major populations of marine mammals and sea birds. The major eastern boundary currents include the Canary off the Iberian peninsula and northwestern Africa, the Benguela off southwestern Africa, the Peru off western South America, and the California Current System off western North America. Moreover variations in upwelling over seasonal to interannual periods, due to large-scale shifts in wind patterns and atmospheric systems, are linked to variability in fish populations and other biological components in coastal ocean ecosystems.

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