152 Integrating 20 Years of Scientific Drilling in the East African-Syrian Rift: A Session In Honor of Andrew Cohen (Posters)

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.

Monday, 20 October 2025
8:00 AM - 5:30 PM
HBGCC, Hall 1

Unveiling Eastern African Climate Variability Through Multi-species Single Ostracod Isotope Analysis in the Turkana Basin, Kenya

Paper number: 152-0
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM

Authors

Abstract

Understanding environmental and climatic variability is essential for reconstructing ecosystem changes through time. In the Turkana Basin (Kenya), the third largest arid basin lake in the world, these variabilities take on added significance as this is a key fossil locality for hominin evolution. In particular, the effect of global climatic forcing on modern and paleo-lakes is an important line of inquiry from the annual to millennial time scale. As ostracods live in the water column, their fossil valves provide an important proxy archive with the potential to quantify hydroclimate. Because different species live in different ecological niches, their abundances, and isotopic composition are expected to vary among genera and species. This study combines ostracod taxonomy with single-valve isotope analysis to better constrain interspecies specific variability and isotopic fractionation, and ultimately the short-term variability in the runoff and evaporation in the Turkana Basin. Isotopic analysis was conducted using isotope ratio mass spectrometry on multiple (n > 10) ostracod valves of six different genera from stratigraphically constrained sediment samples from both the Late Pleistocene and Holocene. While different genera display distinct δ13C values (clusters), the δ18O values do not show statistically significant differences from each other. The δ18O values cover a large range from ~2-4.5 ‰. Using the ostracod Limnocythere minor from the Holocene Galana Boi Formation, we also investigated the δ18O changes through an interval during the African Humid Period (~15-5 ka). These results show a significant decrease in δ18O values over time. The variance as measured by standard deviation of the δ18O values of single ostracod valves (n > 10) shows a temporal pattern characterized by an increase through time before subsequently decreasing. We interpret these trends as a progressive freshening of lake water during the AHP, coupled with an increase in seasonal rainfall, before maintaining a fresh lake even as the strength of the seasonal signal declined.

 

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

doi: 10.1130/abs/2025AM-413657

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