42-3 New Insights on Millennial-scale Climate Variability Recorded in Sediments of Northern Lake Malawi Over the Past 100 Kyr

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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Sediments of the North Basin of Lake Malawi (southern East Africa) are sensitive recorders of changing regional conditions. Previous work has demonstrated that the chemical composition of sediments responds to biological productivity, sediment provenance (in turn impacted by wind direction), and hydrologic balance. Proxies representing these processes can be evaluated at the mm-scale using bulk elemental composition determined by x-ray fluorescence core scanning. New chronological controls (radiocarbon, presence of Toba Ash, OSL-based dates for onset and termination of closed-basin conditions) provide a basis for re-examination of how millennial scale variability in Lake Malawi over the past 100 kyr reflects regional and global processes.  Proxies for runoff (Ti) and chemical weathering (K:Ti) show little relationship to broader global processes, whereas proxies for for primary productivity (Si:Ti for biogenic silica and incoherent:coherent scatter for organic matter), and for weathered volcanic ash (enrichment in Zr:Ti, without the accompanying enrichment in K:Ti characteristic of regional tephras) appear to have teleconnections to global processes.  These are enriched at times that generally coincide with Dansgaard-Oeschgar stadials; this is interpreted as a response to northerly winds, which induce primary productivity through upwelling in the North Basin and delivery aeolian material sourced from the Rungwe Volcanic Field, the most substantial active volcanism in the lake’s airshed.  Northerlies may be associated with southward excursions of the intertropical convergence zone, and this behavior will be examined in the context of regional records.  Prior to 75 ka Lake Malawi experienced closed basin conditions (high Ca, due to calcite preservation) during which the coring location would have been considerably shallower, impacting the sensitivity of these proxies to global forcing.

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

doi: 10.1130/abs/2025AM-10860

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