PALEOLIMNOLOGICAL EVIDENCE OF A GRADUAL RESPONSE TO THE END OF THE AFRICAN HUMID PERIOD IN CENTRAL LAKE TANGANYIKA, EAST AFRICA

Middle and Early-Late Holocene sediments have not been extensively sampled at Lake Tanganyika, one of the most important sedimentary archives of tropical environmental change in sub-Saharan Africa. Therefore, proxy records capturing the termination of the African Humid Period (AHP), a period of orbitally enhanced monsoon precipitation that resulted in a "Green Sahara", are rare from Lake Tanganyika. Here, we present the sedimentology and geochemistry of a radiocarbon-dated sediment core from the Kavala Island Ridge, central Lake Tanganyika (Tanzania), revealing paleolimnological and hydroclimate variability since ~ 5880 cal yr BP. Sediments dating to the AHP are represented by massive blue-grey clayey silts. Carbon concentrations and light stable isotopes (C, N) suggest an influx of river-borne soil organic matter and weathered clay minerals to the lake during this time, likely due to enhanced weathering and erosion under a wetter climate. Following what appears to be a gradual termination to the AHP (concluding at ~ 4640 cal yr BP), laminated and organic carbon-rich sediments accumulated at the study site; δ¹⁵N, C/N, and hydrogen index data suggest a mix of algae and cyanobacteria prevailed at this time, likely due to strong seasonal winds that promoted upwelling and higher primary production under a drier hydroclimate that prevailed from ca. 4640 cal BP to 1820 cal BP. The transition to the Common Era is marked a change to considerable variability in sediment properties and geochemistry, which could represent the influence of high frequency hydroclimate change as well as anthropogenic disturbance in the landscape following the migration of Bantu-speaking people to the Tanganyika shore at this time.