Uplift of Africa as a potential cause for Neogene intensification of the Benguela upwelling system

The Benguela Current, located off the west coast of southern Africa, is tied to a highly productive upwelling system(1). Over the past 12 million years, the current has cooled, and upwelling has intensified(2-4). These changes have been variously linked to atmospheric and oceanic changes associated with the glaciation of Antarctica and global cooling(5), the closure of the Central American Seaway(1,6) or the further restriction of the Indonesian Seaway(3). The upwelling intensification also occurred during a period of substantial uplift of the African continent(7,8). Here we use a coupled ocean-atmosphere general circulation model to test the effect of African uplift on Benguela upwelling. In our simulations, uplift in the East African Rift system and in southern and southwestern Africa induces an intensification of coastal low-level winds, which leads to increased oceanic upwelling of cool subsurface waters. We compare the effect of African uplift with the simulated impact of the Central American Seaway closure(9), Indonesian Throughflow restriction(10) and Antarctic glaciation(11), and find that African uplift has at least an equally strong influence as each of the three other factors. We therefore conclude that African uplift was an important factor in driving the cooling and strengthening of the Benguela Current and coastal upwelling during the late Miocene and Pliocene epochs.