The Holocene paleolimnology and paleoclimatology of Lake Edward, Uganda-Congo

The objective of this research is to document the timing and magnitude of past variations in the precipitation-evaporation balance of tropical East Africa using sediment cores from Lake Edward, Uganda-Congo.; Lake Edward is one of the great rift lakes of East Africa, yet little is known of its physical hydrology. New data on the stable isotope hydrology of the lake that indicate that Lake Edward loses roughly 50% of its water via evaporation. This result allows a rigorous evaluation of previously published hydrologic budgets of Lake Edward, and highlights the sensitivity of the lake to changes in precipitation.; Biogeochemical analyses of piston cores from Lake Edward record hydroclimatic changes in the lake over the past 11,000 years. Palynologic, geochemical and fossil diatom analyses indicate that rainfall in the Lake Edward basin was about 50% higher than today between about 11,000 and 7000 cal yr BP, likely a response to precessional forcing of the African monsoon. Sedimentary sulfur data indicates considerable submillennial climate variability between about 9200 and 6700 cal yr BP, during which time fossil diatoms indicate Lake Edward's water column gradually became better mixed.; Authigenic calcite appears in piston cores from Lake Edward at 5400 cal yr BP, indicating enhanced aridity during the late Holocene. Elemental and stable isotopic analyses of inorganic calcite span the past 5400 years, and provide evidence for a series of droughts with a 725-year drought cycle that appears to be a harmonic of the high-latitude 1500-year cycle. The correlation of these two cycles could indicate a tropical source for this mode of climate variability during the Holocene. Analyses of the biogenic silica content of core E96-1P indicate numerous multi-decadal to century-scale climate periodicities that may be linked to coupled ocean-atmosphere variability in the Indian monsoon. Amongst these climate events, droughts at 900 and 2000 cal yr BP appear particularly severe and widespread in tropical East Africa.; These results show that climate in tropical East Africa has varied considerably at all time-scales, and highlights the importance of internally-driven variability in tropical sea surface temperatures to continental rainfall.