The nutrient-rich Benguela current which flows past the west coast supports a wide range of marine life. The cooling and upwelling of the Benguela current brings moisture-laden sea winds to the west coast which, together with the atmospheric factors, prevent rain from falling in the Namib. The affect of the cold, upwelling Benguela current and the persistent, strong South Atlantic high-pressure system (a stable anticyclone which lies above the Atlantic Ocean at 30° S) are two of the main causes for the present aridity along the south-western coast, the Namib and the dryness of the interior of the sub-continent.
Scientists believe that the present day flow paths of the Agulhas current, and the Benguela Upwelling System was already established during the Mio-Pliocene around 5 Million years ago, and may even have been in place as early as 10 million years ago. The introduction of a cold water current on the west coast accentuated the on-going trend of increased summer drought along the west coast, and strengthening high pressure systems brought drier conditions to the interior. The early development of a Mediterranean climate, which was essentially modern, would have prevented the spread of tropical C4
plants as these are favoured by a summer rainfall regime and is one of the reasons that research indicates that Langebaanweg was a C3
dominated environment around 5 million years ago. (See 'Plant photosynthesis and the paleoenvironment'
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