A high-resolution geochemical record from Lake Edward, Uganda Congo and the timing and causes of tropical African drought during the late Holocene

High-resolution analyses of the elemental composition of calcite and biogenic silica (BSi) content in piston cores from Lake Edward, equatorial Africa, document complex interactions between climate variability and lacustrine geochemistry over the past 5400 years. Correlation of these records from Lake Edward to other climatically-forced geochemical and lake level records from Lakes Naivasha, Tanganyika, and Turkana allows us to develop a chronology of drought events in equatorial East Africa during the late Holocene. Major drought events of at least century-scale duration are recorded in lacustrine records at about 850, 1500, ∼2000, and 4100 cal year BP. Of these, the most severe event occurred between about 2050 and 1850 cal year BP, during which time Lake Edward stood about 15 m below its present level. Numerous additional droughts of less intensity and/or duration are present in the Lake Edward record, some of which may be correlated to other lacustrine climate records from equatorial East Africa. These events are superimposed on a long-term trend of increasingly arid conditions from 5400 to about 2000 cal year BP, followed by a shift toward wetter climates that may have resulted from an intensification of the winter Indian monsoon. Although the causes of decade- to century-scale climate variability in the East African tropics remain obscure, time-series spectral analysis suggests no direct linkage between solar output and regional rainfall. Rather, significant periods of ∼725, ∼125, 63-72, 31-25, and 19-16 years suggest a tight linkage between the Indian Ocean and African rainfall, and could result from coupled ocean-atmosphere variability inherent to the tropical monsoon system.