Calibrated pollen-based reconstruction of East African vegetation and landscape change throughout the entire existence of anatomically modern humans from the ~ 250,000 yr Lake Challa sediment record

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Long, continuous records of Quaternary palaeoecological change in Africa are rare, despite their importance for addressing palaeoclimatic, biogeographic, and evolutionary controversies in the tropics. This proposed project is part of an international project called DeepCHALLA which was granted funding for drilling operations by DFG Priority Program 1006 International Continental Drilling Program (ICDP). The overarching scientific aim of DeepCHALLA is to improve our understanding of the temporal distribution and causes of climate variability (e.g. extreme drought) and the impact on vegetation in equatorial East Africa at inter-annual to millennial time. The ~215m long sediment core already drilled from Lake Challa, Tanzania/Kenya, preserves a ~250,000 years palaeoenvironmtal record, thus encompassing two complete glacial-interglacial cycles and the entire existence of anatomically modern humans.While the ICDP DeepCHALLA project will produce a climate reconstruction, this proposed DFG project will focus on long-term vegetation dynamics in response to this climate change, to elucidate which combination of climate factors most thoroughly influence temporal vegetation dynamics and thus spatial distribution during particular time windows. The principal objective is therefore to acquire a calibrated pollen record of continental ecosystem dynamics near the equator. The calibration (1) of palaeoenvironmental data contained in the Lake Challa pollen record will be achieved by the establishment of quantitative modern pollen–vegetation and pollen-climate relationships in different savanna vegetation, the establishment of the quantitative relationship between the composition of actual pollen rain recorded by the sediment trap in Lake Challa and the actual proportion of vegetation and the development of transfer functions relating modern pollen assemblages from the Kilimanjaro and Challa area directly to the climate. Further, the calibrated pollen-based reconstruction (2) of past vegetation dynamics for equatorial Africa over the past 250,000 years will allow the investigation of long-term biodiversity patterns and ecological dynamics of a tropical savanna (grassland-woodland) ecosystem in response to changes in atmospheric CO2, temperature, moisture balance, and fire.The results of this project will show exactly how often, when, and how much the East African landscape has changed throughout the entire existence of anatomically modern humans. Specifically, documentation of the magnitude and geographical distribution of severe drought episodes across tropical Africa is critical to reconstruct why our ancestors decided - or felt forced - to expand from their African homeland into the Middle East and Eurasia ~100,000 years ago.