Assessing the Hydroclimate History and Climate Dynamics of Eastern Equatorial Africa since the Last Glacial Maximum

Understanding the hydroclimate history of eastern Africa provides insight into the atmospheric processes that control rainfall and drought in this region, as well as larger-scale tropical climate dynamics in the past and present. Although many records indicate drier conditions during the Last Glacial Maximum (LGM, 21 ka) in this region, recent work has suggested that easternmost-equatorial Africa may have been wetter than present. Addressing this discrepancy, records of the hydrogen isotopic composition of terrestrial leaf waxes (δD_wax) have emerged as a powerful proxy to trace atmospheric circulation and regional hydroclimate changes in Africa, and there are now many records of δD_wax that document isotope hydrology from the LGM to present. Here we provide a new record of δD_wax from Lake Rutundu, Mt. Kenya, as well as empirical orthogonal function (EOF) analyses of existing δD_wax records to evaluate continental-scale changes in the isotopic composition of meteoric waters since the LGM. Our new δD_wax reconstruction provides a unique record of African hydroclimate: its location, on the eastern slope of Mt. Kenya in easternmost-equatorial Africa, traces the moisture source and atmospheric circulation changes over easternmost-Africa (i.e., the dynamics of the Indian Ocean Walker Circulation), rather than western Africa (i.e., the Atlantic Ocean). Initial results of δD_wax analyses from Lake Rutundu indicate that eastern Africa was drier during the LGM relative to the present. This is in agreement with our EOF analyses of the African records of δD_wax, which primarily document a drier LGM. We compare these analyses to available isotope-enabled model simulations from iCAM5 spanning the LGM to further diagnose changes in circulation accompanying the observed drying signal. This work harbors important implications for our understanding of how Indian monsoons and zonal circulation over the Indian Ocean may be altered in a different mean climate state. We aim to help clarify how and why hydroclimate in eastern Africa and more remote tropical regions has changed since the LGM, and how it may change in the future.