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Although persistent drought in West Africa is well documented from the instrumental record and has been primarily attributed to changing Atlantic sea surface temperatures, little is known about the length, severity, and origin of drought before the 20th century. We combined geomorphic, isotopic, and geochemical evidence from the sediments of Lake Bosumtwi, Ghana, to reconstruct natural variability in the African monsoon over the past three millennia. We find that intervals of severe drought lasting for periods ranging from decades to centuries are characteristic of the monsoon and are linked to natural variations in Atlantic temperatures. Thus the severe drought of recent decades is not anomalous in the context of the past three millennia, indicating that the monsoon is capable of longer and more severe future droughts.

Lake Victoria is the largest lake in Africa and harbors more than 300 endemic species of haplochromine cichlid fish. Seismic reflection profiles and piston cores show that the lake not only was at a low stand but dried up completely during the Late Pleistocene, before 12,400 carbon-14 years before the present. These results imply that the rate of speciation of cichlid fish in this tropical lake has been extremely rapid.

Seismic data reveal that water level in Lake Malawi, East Africa, was 250 to 500 meters lower before about 25,000 years ago. Water levels in Lake Tanganyika at that time were more than 600 meters below the current lake level. A drier climate appears to have caused these low stands, but tectonic tilting may also have been a contributing factor in Lake Malawi. High-angle discordances associated with shallow sequence boundaries suggest that these low stands probably lasted many tens of thousands of years. Because of its basement topography, the Lake Tanganyika basin had three separate paleolakes, whereas the Lake Malawi basin had only one. The different geographies of these paleolakes may be responsible in part for the differences in the endemic fish populations in these lakes.