East African Climate Variability Through a Major Faunal Transition at 550 to 250 ka: Preliminary Evidence from Organic Geochemical Proxies

Abstract:

During the Plio-Pleistocene, a critical time period for hominin evolution, warm climates gave way to cooler conditions. It has long been hypothesized that hominin speciation and extinction events are linked to climate variability, yet relatively few continuous Plio-Pleistocene East African climate reconstructions exist to test these ideas. In this study we generate high-resolution organic geochemical records from Lake Malawi focusing on the time interval between approximately 550 and 250 ka (spanning Marine Isotope Stages 9-13). We use sediments obtained by the Lake Malawi Drilling Project in 2005, which recovered the longest and highest-resolution climate archive currently available from continental Africa. The study interval marks the transition from Acheulean hand axe technology to the early Middle Stone Age and coincides with significant turnover in large mammalian fauna. We explore the use of the TEX₈₆ and MBT’_5Me proxies to reconstruct past lake temperature. Leaf wax carbon and deuterium isotopic analyses are underway to investigate past vegetation shifts and hydroclimate variability, respectively. Our initial results suggest that brGDGTs provide the more reliable temperature proxy in this part of the Malawi sedimentary record, with MBT’_5Me exhibiting pronounced glacial/interglacial cycles and especially rapid warming noted during glacial Termination 5. This study presents our initial paleoclimate reconstructions, which ultimately will provide an environmental context under which these major evolutionary events occurred.