Bi‐annual intrusion of tropical water in the northern Benguela upwelling

Abstract

The Benguela Current is one of the most productive marine ecosystems in the world. A difference from other eastern boundary currents is a thermal front at its northern border, the Angola Benguela Front (ABF) separating warm tropical water from cold upwelled water. There is an annual net modelled transport of 0.45 Sverdrup of near surface tropical water flowing poleward across the ABF into the northern Benguela Current upwelling system. This transport follows a bi‐annual harmonic quasi‐synchronized to the annual cycle of sea level anomaly in the eastern tropical Atlantic with maxima in October and February and minima in June and December. The bi‐annual advection of warm Angolan water in the Northern Benguela across the ABF is a key element in the development of Benguela Niños, warmer than normal oceanic events that have an impact on fisheries, hypoxia and rainfall of the region.