42-4 Eight Glacial Cycles from a Tropical African Lake Core

Session: Integrating 20 Years of Scientific Drilling in the East African-Syrian Rift: A Session In Honor of Andrew Cohen, Part II

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Studies of low-latitude continental climates frequently focus on hydroclimate variability because tropical (paleo)climate is characterized by large and abrupt changes in rainfall. The history of tropical continental temperature variability, however, is not well constrained, especially prior to the Last Glacial Maximum (23–19 ka). Extreme temperatures over landmasses have increased significantly in recent decades, a trend that is expected to amplify in the future, especially in the tropics. Here we present a temperature reconstruction from Lake Malawi drill core MAL05-1B, located in the southeastern African tropics, based on the methylation of branched tetraethers (MBT′_5ME), membrane lipids produced by bacteria. Our MBT′_5ME record spans the past 800,000 years and reveals that Mid-Pleistocene glacial terminations were characterized by larger temperature changes compared to the Termination I deglacial warming (the transition from the LGM to the Holocene), which is marked by a warming of 4-5˚C at numerous sites in eastern Africa. A prominent climatic event occurred during Glacial Termination V (430-400 ka), when a rapid warming of ~7˚C was accompanied by a shift to extreme aridity. This shift from unusually cool conditions during Marine Isotope Stage (MIS) 12, when Malawi experienced high lake levels, to warm conditions and a massive drop in lake level of around -400 m during MIS 11, attests to both a major hydroclimate and temperature shift at this time. Climate variability associated with Termination V may have contributed to a major extinction of large-bodied East African mammals that occurred around this time, noted at sites in Kenya.  Our finding that Mid-Pleistocene interglacials at Lake Malawi were both warm and arid contrasts with previous studies that have reported warm and wet climate associations at numerous sites throughout eastern Africa during the Holocene. Our Lake Malawi MBT′_5ME record for the first time provides a continuous and quantitative temperature reconstruction from the continental tropics spanning multiple glacial-interglacial cycles. Results of this study demonstrate that tropical temperature variability is an important factor that warrants further consideration in climate models, necessary for improved predictions of future warming, rainfall and drought on the African continent.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-6503

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