A 2,258-YEAR DIATOM HISTORY FROM THE CENTRAL BASIN OF LAKE TANGANYIKA (TANZANIA)

We collected a laminated sediment core LT14 7A (~1 m in length) from a water depth of ~354 m in central Lake Tanganyika, one of the deepest, oldest, and largest freshwater lakes in the world. The core was subsampled into 1-cm intervals and analyzed for diatoms. Our preliminary age model estimates the bottom age for the core at ~2260 years before present. Diatom assemblages prior to ~2,200 years before present were dominated by Nitzschia species with smaller abundace of Aulacoseria species. Between ~2,163 to 1,752 years before present, Nitzschia species were dominant. Alucoseria species were dominant from ~1,725 to 1,550 years before present. After ~1550 years before present, Nitzschia species became dominant again. We interpret the changes in the diatom assemblages to reflect differences in nutrient concentrations in the water column, potentially related to stratification and convective mixing patterns or changes in the influx of nutrients to the lake system related to hydroclimate variability. This record is part of a larger project that includes analyses of other biological indicators, such as fossil phytoliths, which should help us create a more robust interpretation of the observed changes during this interval. Because diatoms are a critical component of the base of the lacustrine food web, identifying long-term changes in the patterns of these algae can provide us with important information about natural variability in the trophic system.