Distribution of Recent nannofossils beneath the Benguela system: Southwest African continental margin

Abstract

One hundred and forty eight surface samples recovered from the southwest African continental margin (35°-17°S) have been examined for their nannofossil content. Coccolith abundance is high in sediments from the deep water areas, but declines toward the coast under the main areas of upwelling. Five distinct bathymetric/oceanographic assemblages can be characterized by their nannofossil content: coastal upwelling, Orange Bank, intermediate, southern deep water, and northern deep water-Angola Current. These distinctions are based on the distribution of eight ecologically significant taxa. In order of decreasing abundance they are Gephyrocapsa oceanica, Helicopontosphaera kamptneri, Cyclococcolithina leptopora, Coccolithus pelagicus, Syracosphaera div. sp., Thoracosphaera div. sp., Rhabdosphaera div. sp. and Umbilicosphaera sibogae. Sea-surface temperature and salinity variations, which correlate with the extent and intensity of the main upwelling cells, are thought to be the most important controls on coccolith distribution, although nutrient availability and reduction of surface water transparency may be of local importance. The exclusion of three stratigraphical index species for the Quaternary ( Emiliania huxleyi, Gephyrocapsa caribbeanica, and G. ericsonii) from the quantitative analysis will permit the future application of these results to paleoceanographic reconstructions of the Benguela system in Pleistocene core sections.