A High-Resolution Late Holocene Record of Rainfall From Lake Edward, Equatorial Africa: Linkages Between the African and Indian Monsoons

High-resolution analyses of the chemical composition of calcite and the biogenic silica content of sediments from piston cores spanning the past 3,500 years from Lake Edward, Uganda-Congo, document multidecadal to millennial-scale climate variability in the heart of equatorial Africa. Major drought events in the Lake Edward record occur at about 500, 850, 1500, ~2000, and 2700 cal yr BP, in addition to numerous other events of lesser magnitude/duration. Comparison of our record to other Holocene records of African lake levels suggests that most of these intervals of drought affected most of equatorial East Africa. However, wet conditions at about 500 cal yrs BP at sites to the east of Lake Edward could indicate spatial heterogeneity within the African continent during the "Little Ice Age", which could have resulted from complex interactions between the African (Atlantic) and Indian Ocean monsoons. Spectral analysis of our drought record, sampled at a 3-year step, shows evidence for numerous multidecadal to century-scale drought periods in the region. The periodicities observed do not appear linked to solar forcing; rather, periods of ~125, ~70, ~28, and ~18 years apparent in our record as well as other records from the Indian Ocean basin may arise from climate variability internal to the tropical oceans, in particular the Indo-Pacific. Lastly, the Lake Edward record suggests that the climate of equatorial Africa has been unusually stable and generally wet for the past ca. 100 years. This stability appears unusual in light of the considerable climate variability suggested by our record for the past several millennia, a finding with clear implications for East African societies.