upwellings

Upwellings are oceanographic processes in which deeper, nutrient-rich water rises toward the surface, bringing with it nutrients that fuel marine ecosystems. The resulting vertical exchange supports high biological productivity and forms the basis for major fisheries in many regions. Upwelling occurs in several settings, most notably along western continental margins and at the equator.

Coastal upwelling is driven by winds that blow parallel to the coastline. In the Northern Hemisphere, winds along western coasts create Ekman transport away from the shore, causing surface water to diverge and deeper water to replace it. Equatorial upwelling occurs where surface currents diverge near the equator due to the combined action of trade winds and the Coriolis effect, which is weaker at low latitudes, allowing deep water to rise. Bathymetry, coastal geometry, and mesoscale eddies modulate the strength and location of upwelling.

Ecologically, upwelling zones exhibit high phytoplankton productivity, supporting rich fisheries and diverse ecosystems. Seasonal cycles and climate variability, including El Niño-Southern Oscillation, strongly influence upwelling intensity; El Niño often weakens or suppresses it, while La Niña can intensify it.

Measurement and study rely on satellite observations of sea surface temperature and chlorophyll, as well as in situ instruments such as ocean color sensors, acoustic Doppler current profilers, and Argo floats. Globally, major upwelling systems include the Humboldt (Peru-Chile) and California Currents, the Canary Current, and the Benguela Current.