A 6,000 Year Record of Holocene Hydroclimate and Lake Water Balance from Lake Edward (Uganda - D.R. Congo)

Despite projected precipitation increases over East Africa, climate models suggest that water-availability in this already water-stressed region will decline further in the future due to changes in the intensity of rainfall events and increased evaporation, highlighting the importance of controls on terrestrial water-availability beyond changes in precipitation amount. Existing late Quaternary African paleoclimate records indicate that temperatures increased by ~2 °C during a wetter mid-Holocene 5-6 thousand years ago, although proxy records have rarely been used to disentangle changes in precipitation amount from surface water balance. As such, high-resolution Holocene paleolimnological climate records may serve as informative natural experiments through which the combined impacts of warm/cold and wet/dry climate states on East African surface hydrology can be assessed. This project will use the stable isotopic composition of precipitation and surface paleo-waters from lacustrine sedimentary archives in a hydrologic mass-balance model to assess changes in atmospheric evaporative demand and its influence on terrestrial water-availability. In particular, we leverage the distinct dD vs. d18O slopes of meteoric water lines from those of surface waters subjected to kinetic fractionation effects during evaporative enrichment to investigate surface water balance. This analysis will employ a new ~6 kyr organic geochemical record of the hydrogen isotopic composition of terrestrial plant leaf waxes (n-alkane dD), a proxy for precipitation isotopic composition, together with data on the oxygen isotopic composition (d18O) of authigenic carbonates (mainly recording variation in evaporated lakewater compositions) from Lake Edward in the Western Rift of Equatorial East Africa to constrain millennial-scale fluctuations in evaporation, and to better elucidate the evolution of Holocene moisture regimes in the region. Evaporative enrichment of surface waters may increase the amplitude of the isotopic offset between the Lake Edward dDwax and carbonate d18O records, indicating a trend of declining water balance from the mid to late Holocene, in agreement with independently-derived lake level records and other geochemical indices of water balance.