14-6 Extreme Warming and Hydroclimate Instability in Tropical Southeast Africa: Three Superinterglacials at Lake Malawi

Session: Lake Sedimentary Records of Past Climate and Environment

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The hydroclimatic sensitivity of Tropical Southeast Africa to globally warm extremes remains uncertain, as this region is variably sensitive to a wide range of local, pan-tropical, and global dynamics, including monsoonal variability, migration of tropical convergence zones, and high latitude teleconnections. As the communities living in this region are highly vulnerable to climate change, resolving the mechanisms governing Tropical Southeast African hydroclimate under future extreme warmth remains critical. These mechanisms, however, are particularly difficult to parse on long timescales due to a lack of long-term instrumental observations and because the region displays a complex, spatially variable pattern of Late Pleistocene hydroclimatic change captured in lacustrine paleoclimate reconstructions. The Lake Malawi drill core (MAL-05) spans the past 1.4 million years, making it the longest continuous record of paleoclimatic change in continental East Africa. As Lake Malawi is currently situated at the southernmost annual extent of the Tropical Rain Belt, this site represents an ideal sedimentary archive for understanding regional hydroclimatic sensitivities to extreme global warmth in Tropical Southeast Africa. Here we present a multiproxy biomarker record of temperature and hydroclimate during three Pleistocene superinterglacials: Marine Isotope Stages 5e (120-100 ka), 11c (410-396 ka), and 33-31 (1114-1050 ka). These intervals each represent periods of global warmth similar to or exceeding that of the pre-industrial Holocene, making them robust analogues for successive future warming scenarios under anthropogenic forcing. Importantly, MIS 31 coincides with the last known collapse of the West Antarctic Ice Sheet, a likely consequence of modern anthropogenic warming within the coming century. Our paleotemperature record derived from branched glycerol dialkyl glycerol tetraethers (brGDGTs) reveals extreme warmth during each of these warm intervals at Malawi, and stable hydrogen isotope analyses on plant wax n-alkanes and cyanobacterial hopanes, both proxies for hydroclimatic change, reveal a pattern of progressive, profound aridity during these superinterglacials. Through these analyses, we constrain the relationship between global warmth and regional hydroclimate, ultimately contextualizing the likelihood of rapid aridification and hydroclimatic instability in Tropical Southeast Africa under imminent future warming scenarios.

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