Late Pleistocene paleohydrography and diatom paleoecology of the central basin of Lake Malawi, Africa

Analysis of sedimentary diatom assemblages (10 to 144ka) form the basis for a detailed reconstruction of the paleohydrography and diatom paleoecology of Lake Malawi. Lake-level fluctuations on the order of hundreds of meters were inferred from dramatic changes in the fossil and sedimentary archives. Many of the fossil diatom assemblages we observed have no analog in modern Lake Malawi. Cyclotelloid diatom species are a major component of fossil assemblages prior to 35ka, but are not found in significant abundances in the modern diatom communities in Lake Malawi. Salinity- and alkalinity-tolerant plankton has not been reported in the modern lake system, but frequently dominant fossil diatom assemblages prior to 85ka. Large stephanodiscoid species that often dominate the plankton today are rarely present in the fossil record prior to 31ka. Similarly, prior to 31ka, common central-basin aulacoseiroid species are replaced by species found in the shallow, well-mixed southern basin. Surprisingly, tychoplankton and periphyton were not common throughout prolonged lowstands, but tended to increase in relative abundance during periods of inferred deeper-lake environments.