A 24,000 yr Diatom Record from the Northern Basin of Lake Malawi

Abstract

Diatom analysis of core M98-2P from the northern basin of Lake Malawi shows changes in lake level and mixing during the last 24,000 calendar years. Fluctuations between the major planktonic diatoms (Aulacoseira nyassensis, Stephanodiscus spp. and Cyc/ostephanos spp.) are interpreted as reflecting different degrees of nutrient upwelling whereas the percentages, concentrations and influxes of periphytic diatoms are primarily related to variations in water level. Total diatom biovolume is used to give a firstorder approximation of relati ve diatom productivity at the core site. The diatom results suggest periods of low lake level at the LGM and for much of the Late Holocene period. Short-lived regressions are also suggested during the YD, at 10,600 and 8500-8200 years BP. Conversely the lake was high and probably overflowing 15,700-13,000 and 7500-6600 years BP. A low lake level during the LGM contradicts the interpretation of this period made by previous studies from Lake Malawi. However, intermediate lake levels in the Early Holocene support earlier work that suggested that Lake Malawi was lower than northern East African lakes at this time.