CLIMATE CONTROLS ON LAST GLACIAL MAXIMUM TO EARLY HOLOCENE GLACIER EXTENTS IN THE RWENZORI MOUNTAINS, UGANDA-DEMOCRATIC REPUBLIC OF CONGO

Understanding the climatic controls on tropical glaciers is crucial to predicting the response of these glaciers to future warming. However, whereas temperature controls the mass balance of glaciers in the midlatitudes, the primary drivers of tropical glacier extent are unclear. The Rwenzori Mountains (~1ºN, 30ºE) host the most extensive glacial system in Africa and are composed of quartz-rich bedrock lithologies, enabling ¹⁰Be dating of boulders embedded in moraine crests. Here we present a chronology of past glacial extents in the Rwenzori and compare this with local and regional paleoclimate records to infer the climate controls on glaciation. In the lower Mubuku Valley, samples from large (~50-100 m relief) lateral moraines that extend down to ~2000 m asl indicate that deposition occurred at ~23.4 ka and ~20.1 ka, during the global Last Glacial Maximum (LGM; ~24-19 ka) and coincident with a period of dry, cool conditions in East Africa. To the south in the Moulyambouli Valley, ¹⁰Be ages of boulders on a lateral moraine (~50 m relief, 2880-2780 m asl) indicate deposition at ~17.2 ka, during Heinrich Stadial 1 (H1, ~18-15 ka). Although the reasons for the difference in moraine ages in these two valleys are not clear, we suggest that temperature decrease, rather than precipitation increase, was the primary influence on glacier extents during the LGM and H1. In the upper Mubuku Valley, smaller moraines between 3450 and 3720 m asl document stillstands or readvances of glacier ice at ~13.8 ka, ~13.4 ka, and ~11.1 ka. In the nearby Nyagumasani Valley, moraines at similar elevations (3870-4020 m asl) indicate stillstands or readvance at ~11.5 ka, ~10.6 ka, and ~10.5 ka. Paleoclimate records document dry conditions during Younger Dryas (YD; ~12.9-11.6 ka) time with no significant late-glacial temperature reversal, leaving the primary drivers of glacier advance uncertain. Increasing temperatures and wetter conditions following the YD may suggest glacier retreat due to precipitation falling as rain rather than snow. We are continuing to develop the Rwenzori moraine chronology in order to improve interpretations of climate control on glacier fluctuations during late-glacial to early Holocene time.