Fossil diatoms and the paleolimnology of Lake Rukwa, Tanzania

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Abstract
SUMMARY. 1. A 23.1 m sediment core from Lake Rukwa, southwest Tanzania, records 13,000 years of climatic change in five diatom assemblage zones. Zone E (13,000–12,7000 bp) reflects the transition from the waning late glacial arid phase to pluvial conditions, as indicated by the co‐occurrence of diatoms associated with fresh and relatively saline conditions. Zone D (12,700–4400 bp) represents a moist period with frequent stratification, indicated by the halophobic genera Melosira and Stephanodiscus, whieh also represent alternating silica‐rich and silica‐dcpleled waters. Beginning with Zone C (4400–3900 bp) the lake became much more saline with Thalassiosira predominating. This drying trend was reversed slightly in Zone B (3900–3300 bp). During the last three millennia (Zone A), lake salinity was further reduced, while transitory moist phases were occurring in more northerly lakes such as Victoria and Kivu.2. Lake Rukwa was relatively stable over a time scale of centuries, but on an annual basis is quite variable in salinity depending on the local rainy season.3. These results agree well with the generalized paleoclimatie chronology of East Africa and suggest that the Holocene climatic regime of East Africa extended at least to 8°S.

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