The Benguela Current Upwelling System
This chapter describes the Benguela upwelling system along the western coast of southern Africa and its interactions with the tropical ocean to the north and the Agulhas Current to the south. It covers the physics, chemistry and biology in the region, as
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The Benguela Current Upwelling System
Abstract This chapter describes the Benguela upwelling system along the western coast of southern Africa and its interactions with the tropical ocean to the north and the Agulhas Current to the south. It covers the physics, chemistry and biology in the region, as well as the fishery potential under the increasing pressure of climate change.
Keywords Upwelling Oceanography Benguela current Marine ecology Marine biogeochemistry Fisheries Fisk stock variations Climate-change impacts
The sea is the vast reservoir of nature The globe began with sea, so to speak and who knows if it will not end with it? Jules Verne (1828–1905) (Taken from Twenty Thousand Leagues Under the Sea, 1870)
7.1
Introduction
The Benguela Current upwelling system stretches along the southwest coast of Africa, essentially from the region north of Cape Frio, at about 15° S in Angola, to Cape Agulhas, the southern tip of the continent near 35° S. There is also intermittent upwelling at capes further east towards Port Elizabeth (Figs. 7.2 and 7.3), but these are not considered part of the Benguela system proper. At its southern end the system is bounded by the warm Agulhas Current, which sweeps down from Mozambique along the south coast of South Africa, while at the northern end, just north of the southern border of Angola, lies the Angola Front, a second boundary with warm water. Having warm water at both ends of the system makes the Benguela unique when compared with the other major upwelling areas. As with the
© Springer International Publishing Switzerland 2016 J. Kämpf and P. Chapman, Upwelling Systems of the World, DOI 10.1007/978-3-319-42524-5_7
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7 The Benguela Current Upwelling System
other three major eastern boundary current systems, the region supports important fisheries, and this has in the past led to over-exploitation, particularly in the period before 1982 when the concept of a 200 nautical mile exclusive economic zone was adopted as part of the UN Convention on the Law of the Sea (Fig. 7.1). Much of the west coast of South Africa and Namibia is either desert or semi-desert, with the only large riverine inputs being the Cunene, at the northern end of the region, and the Orange, at 29° N (Fig. 7.3). Two smaller rivers, the Berg and the Olifants, reach the sea just north of Cape Columbine and about 100 km north of this cape respectively. These rivers have strongly seasonal flows, which reach a maximum in winter (May–October) and are greatly reduced in summer. Maximum flows in the Orange and Cunene rivers, in contrast, are in summer (October–April and January–April respectively), but all four rivers tend to dam up
Fig. 7.1 The Benguela current upwelling region in the eastern South Atlantic. The inset shows ocean-colour-derived chlorophyll-a concentrations. Upwelling on the Agulhas Bank is also evident (see Sect. 9.5 for more details). Background image Google Earth with ETOPO 1 bathymetry layer. Insert MODIS-Aqua data from NASA’s Giovanni interface
7.1 Introduct
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