PRELIMINARY DIATOM STRATIGRAPHY OF CORE MAL05-1C, LAKE MALAWI, AFRICA

Core MAL05-1C is a long, continuous sediment record recovered from one of two scientific drilling sites at Lake Malawi (East African Rift Valley) in 2005. The core was collected in very deep water (592m) from a site in the Central Basin. The sediments extend back roughly 150,000 years and has been initially sampled at an intermediate resolution of approximately 300 years. Lake Malawi is an ideal candidate for long-term paleoclimate reconstructions, because of its excellent preservation of microfossils, continuous sedimentation, and high sensitivity to changes in effective moisture (precipitation-evaporation).

Preliminary diatom analyses of sediment spanning the last 75,000 years indicates the predominance of assemblages typical of deep-water sites from large lakes, which are characterized by low-diversity and dominated by centric planktonic genera. Variation in the diatom assemblages appears to primarily reflect fluctuations in the abundance of major planktonic species and probably represents changes in nutrient availability. Prior to 75,000 years BP, diatom assemblages characterized by poor preservation and increased abundance of periphyton are more prevalent. These assemblages are typically found in conjunction with other proxy indicators of low lake-level stands, such as abundant littoral fossil ostracode and prominent lithological changes, and probably represent a substantial departure from modern Lake Malawi, with lake-level elevations at least 590 meters below modern levels.