Upwelling - (n.)

Upwelling is a process whereby cold water from below the warm surface layer comes to the sunlit zone, where the cold nutrient-rich water causes much growth of microscopic plankton, which feeds zooplankton, which in turn feeds fish. Upwelling regions, therefore, are favorite fishing areas. Most of the upwelling in the ocean occurs in two settings: along the shores bathed by eastern boundary currents (the eastern portions of the great central gyres) and along the equator. Normally, the upwelling water derives from depths between 100 and 300 m, a factor that depends on the strength of the upwelling motion. Upwelling is driven by winds and both the coastal upwelling along the eastern boundary currents and equatorial upwelling rely on the trade winds. See also “Coastal Upwelling.”