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

Continental drilling extending from the East African Rift into western Asia has yielded transformative discoveries, altering our understanding of paleoenvironments, paleoclimatology, paleoecology, and paleoanthropology. This session, in honor of Andrew Cohen, will celebrate these successes and define new directions.

Sunday, 19 October 2025
1:30 PM - 5:30 PM
HBGCC, 214A

Branched GMGTs Capture Mid- to Late-Pleistocene Temperature Change in the Lake Malawi Drill Core

Paper number: 42-4
Program: Technical Sessions
Time: 2:30 PM – 2:45 PM

Authors

Abstract

Branched glycerol monoalkyl glycerol tetraethers (brGMGTs, or “H-shaped” GDGTs) are archaeal membrane-spanning lipids produced throughout the water column and anoxic sediments of lakes and marine environments, similar in structure to glycerol dialkyl glycerol tetraethers (GDGTs) that are widely used for organic geochemical paleoclimate reconstructions. The production and structural distribution of both GDGTs and GMGTs are variably affected by a range of environmental factors, including growth temperature. Modern surveys of branched and isoprenoid GDGT distributions in terrestrial, lacustrine, and marine environments have formed the basis for numerous well-studied paleotemperature proxies, including the MBT′5ME and TEX86 indices. Although brGMGTs have similarly been investigated for potential applications to paleothermometry in tropical lakes, the mechanisms governing brGMGT distributions are challenging to disentangle in both ancient sediments and modern environments, complicated by variable sourcing within the lake and possible sensitivities to other environmental conditions. To better understand the controls on brGMGT production in sedimentary archives, we analyze brGMGTs from a section of the ICDP Lake Malawi Drill Core (MAL05-1) spanning several glacial-interglacial cycles from approximately 20,000 to 600,000 years ago. We compare these brGMGT distributions with brGDGT-derived MBT′5ME paleotemperature measurements at Malawi. We find that many major brGMGTs display a significant correlation with temperature, and we capture this relationship at Lake Malawi through a novel proxy: the Archaeal Lake indeX of brGMGTs (ALX). Furthermore, we find that applying ALX to other East African lake surface sediments yields a similarly strong correlation with modern temperature while addressing some of the complications known to compromise previously published brGMGT paleothermometers. These findings ultimately highlight the viability of brGMGTs and the ALX as an additional paleothermometer at Lake Malawi with the potential for application to other tropical lacustrine sedimentary archives.

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

doi: 10.1130/abs/2025AM-412365

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