EAST AFRICAN CLIMATE DURING A MAJOR TURNOVER IN MAMMAL SPECIES BETWEEN 400 AND 500 THOUSAND YEARS AGO

Roughly 85% of mammalian herbivore species in southern Kenya were replaced by smaller, more adaptable species at some time between 400,000 years ago (400ka) and 500 ka. While this major taxonomic turnover has been attributed to a shift to more a more arid and variable climate and tectonic activity, we wondered if a particularly abrupt shift, a “tipping point,” in climate at some time between 400 and 500 ka was the cause. We analyzed the highest resolution paleoclimate record available in East Africa, Lake Malawi drill core MAL05-1B, for organic geochemical proxies, including branched glycerol dialkyl glycerol tetraethers (GDGTs) and leaf wax deuterium isotopic records to develop the temperature and precipitation history, respectively, between 600 and 200 ka. Results show an abrupt temperature increase of ~6°C occurring in less than 3000 years during Glacial Termination V, which is the Marine Isotope Stage (MIS) 12 to MIS 11 transition at ~430 ka. Surprisingly, even more intense warming occurred during Glacial Termination VI around 510 ka. Notably, these deglacial warmings coincide with enriched leaf wax deuterium isotopic values suggesting a shift to more arid conditions in interglacials MIS 13 and 11 than in glacials MIS 14 and 12, respectively. These changes from cold/wet glacials to warm/dry interglacials contrast with the cool/dry pattern of the Last Glacial Maximum (LGM) in East Africa that transitioned to a warm/wet Holocene. We propose that the major warming and drying during Termination V in the Malawi basin represents a significant abrupt change that impacted much of eastern Africa around 430 ka and was a likely driver of the major faunal turnover noted in the region.