Controls on Hydroclimate and Hydrogen Isotopes in High-Elevation Regions of Eastern Equatorial Africa Since the Last Glacial Maximum

Tropical African hydroclimate underwent significant changes since the Last Glacial Maximum (LGM). However, the atmospheric and oceanic processes that control precipitation in eastern Africa during this time period are not well-understood. We produced a new record of leaf wax hydrogen isotopes (δD_wax) from sediment cores from the high-elevation Lake Rutundu, on the eastern slope of Mount Kenya (3078 m), which we compared to a synthesis of existing δD_wax records from lower elevation sites throughout Africa. Most of the sites in our synthesis exhibit coherent changes in hydroclimate characterized by a more enriched δD_wax during a drier LGM, and a more depleted δD_wax during a wetter late Holocene. However, our new δD_wax record from Lake Rutundu shows an LGM that was ~15‰ more depleted relative to the late Holocene. Although this could suggest a wetter LGM climate, consistent with the hypothesis that Sunda Shelf exposure caused wet conditions in easternmost Africa during the LGM, spatiotemporal changes in the east African δD_wax records, and comparison to other environmental indicators of moisture balance, suggest that the δD_wax at Lake Rutundu was controlled by processes other than the amount effect. D-depletion during the LGM may have alternatively resulted from increased isotopic distillation of ascending air masses during a colder LGM climate with a steeper temperature lapse rate, resulting in a steeper isotopic lapse rate. Current work to generate a δD_wax record from another high-elevation lake further west in eastern Africa, Lake Mahoma, Rwenzori Mountains, Uganda (2990 m), will provide a test of the relative impacts of geography and elevation to clarify the factors controlling δD_wax and hydroclimate in high-elevation environments in eastern Africa since the LGM.