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Concept
Courant de Benguela
Résumé
The Benguela Current bɛŋˈɡɛlə is the broad, northward flowing ocean current that forms the eastern portion of the South Atlantic Ocean gyre. The current extends from roughly Cape Point in the south, to the position of the Angola-Benguela front in the north, at around 16°S. The current is driven by the prevailing south easterly trade winds. Inshore of the Benguela Current proper, the south easterly winds drive coastal upwelling, forming the Benguela Upwelling System. The cold, nutrient rich waters that upwell from around depth in turn fuel high rates of phytoplankton growth, and sustain the productive Benguela ecosystem.
Source waters for the Benguela include cold upwelled waters from the depths of the Atlantic Ocean close inshore, joined further off-shore by nutrient poor water that has crossed the Southern Atlantic from South America as part of South Atlantic Gyre. Eddies from the warm South Indian Ocean Agulhas current along South Africa's east coast come round the Cape of Good Hope from time to time to join the Benguela current. The Benguela current is 200 to 300 km wide and widens further as it flows north and northwest. Its western, seaward edge is well-defined, with many temporary and seasonal eddies and meanders. There is however a well-defined thermal front between the waters associated with the Benguela Upwelling System and those of the eastward flowing Atlantic currents which are not deflected northward by the African continent.
The icy Benguela and the warm, south-flowing Agulhas current do not meet off the Cape of Good Hope (see diagram on the right, above), but there is a body of water off the South African south coast, east and particularly west of Cape Agulhas that consists of eddies from both currents, so that offshore water temperatures along the south coast of Africa vary chaotically.
Northward winds along the coast result in Ekman transport offshore and upwelling of nutrient-rich deep water to the euphotic zone. The intensity of the upwelling event is determined by wind strength.
Source officielle
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