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

Abstract

The Benguela Current, located o 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 e ect 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 e ect 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.

Post-Gondwana Africa and the vertebrate history of the Angolan Atlantic Coast

“…As alluded to above, the position of a continent below a high pressure descending limb of an atmospheric Hadley Cell is a first order predictor of continental aridity and coastal upwelling between 15° and 30° latitude, notwithstanding significant but regional, transient, or smaller scale perturbations and trends (Etourneau et al, 2009;Heyman et al, 2004;Jung et al, 2014;Rommerskirchen et al, 2011;Shuster, 2006;Zhang, 2014). Africa currently straddles the descending limbs of both the northern and southern hemisphere Hadley cells, it has done so since it became defined as a continent, and it is the only continent with that distinction.…”

Mantle superplumes induce geomagnetic superchrons

“…The situation is different for the African superplume, where extensive portions of the African continent have been located above the African LLSVP since the Mesozoic. Much effort has gone into documenting the uplift history of Africa, particularly in the second half of the Cenozoic, because of its implications for paleoclimate change and primate evolution (Jung et al, 2014), but also earlier in the Mesozoic because of its implications for the behavior of continental crust in response to supercontinent breakup. There is evidence from thermochronometry and geodynamical considerations for two main uplift phases.…”

Influence of topography on tropical African vegetation coverage

“…The experiments were branched off from the control run at year 301 and run for another 300 years. It was demonstrated by Jung et al (2014) (Supplementary Information) that the spinup period was sufficient to get the upper ocean into equilibrium. A spinup period long enough to get the deep ocean into equilibrium was not envisaged due to the comparably high resolution used for this set of experiments.…”

“…The strongly reduced forest coverage of South-East Africa that can be observed with lower African topography is connected to a year-round persistent rainfall deficit. Just in a small coastal strip of Namibia and South Africa, rainfall is larger with lower African topography which might be associated with the decreased Benguela upwelling intensity and the warmer tropical Atlantic Ocean (Jung et al 2014). The impact of African uplift on West African rainfall distribution is not strong enough to affect the regional biogeography.…”

“…A control simulation (CTRL), as described in detail further below, was run using present-day topography. Two sensitivity studies were performed that are identical to CTRL, except that topography was lowered to half of the present-day altitude in one experiment for Eastern and Southern Africa (AF) as in Jung et al (2014) and for the Himalaya and the Tibetan Plateau (HT) in the other simulation (Fig. 1).…”