CLIMATE AND VEGETATION CHANGE IN SOUTH AFRICA AND NAMIBIA IN RELATION TO THE BENGUELA UPWELLING SYSTEM

Upwelling is a significant part of the ocean circulation controlling largely the transport of cold waters to the surface and, therefore, influences ocean productivity and global climate. Major upwelling regions are found along the eastern boundary currents. They are characterized by cold and nutrient-rich waters favoring high primary production. One of the more important upwelling regions is the Benguela Upwelling system (BUS) along the south-western coast of Africa. The BUS is supposed to have initiated in the early Late Miocene (~10-15 Ma) during a phase of global cooling. This cooling is part of the transition from a warm and humid variable climate to cooler and drier conditions of the late Neogene driven by changes of the Antarctic ice sheets. However, uplift of eastern and southern Africa in relation to the development of the African Rift system also played a role. The impact of the upwelling on terrestrial ecosystems is profound. High marine productivity conveys carbon-rich material to the marine sediments and thus reduces atmospheric CO₂. Low sea surface temperatures directly affect the aridity on the adjacent continent. The latter had strong influence on the vegetation and flora of southern Africa. Using palynological and organic geochemical records from marine sediments, I’ll discuss important developments since the Late Miocene concerning precipitation sources, succulent vegetation, and C₄ savannahs in south-western Africa.