New sediment core data from a unique slow-sedimentation rate site in Lake Tanganyika contain a much longer and continuous record of limnological response to climate change than have been previously observed in equatorial regions of central Africa. The new core site was first located through an extensive seismic reflection survey over the Kavala Island Ridge (KIR), a sedimented basement high that separates the Kigoma and Kalemie Basins in Lake Tanganyika. Proxy analyses of paleoclimate response carried out on core T97-52V include paleomagnetic and index properties, TOC and isotopic analyses of organic carbon, and diatom and biogenic silica analyses. A robust age model based on 11 radiocarbon (AMS) dates indicates a linear, continuous sedimentation rate nearly an order of magnitude slower here compared to other core sites around the lake. This age model indicates continuous sedimentation over the past 79 k yr, and a basal age in excess of 100 k yr. The results of the proxy analyses for the past ∼ 20 k yr are comparable to previous studies focused on that interval in Lake Tanganyika, and show that the lake was about 350 m lower than present at the Last Glacial Maximum (LGM). Repetitive peaks in TOC and corresponding drops in δ13C over the past 79 k yr indicate periods of high productivity and mixing above the T97-52V core site, probably due to cooler and perhaps windier conditions. From ∼ 80 through ∼ 58 k yr the δ13C values are relatively negative (-26 to -28‰) suggesting predominance of algal contributions to bottom sediments at this site during this time. Following this interval there is a shift to higher values of δ13C, indicating a possible shift to C-4 pathway-dominated grassland-type vegetation in the catchment, and indicating cooler, dryer conditions from ∼ 55 k yr through the LGM. Two seismic sequence boundaries are observed at shallow stratigraphic levels in the seismic reflection data, and the upper boundary correlates to a major discontinuity near the base of T97-52V. We interpret these discontinuities to reflect major, prolonged drops in lake level below the core site (393 m), with the lower boundary correlating to marine oxygen isotope Stage 6. This suggests that the previous glacial period was considerably cooler and more arid in the equatorial tropics than was the last glacial period.
Bibliographical noteFunding Information:
We thank A.S. Cohen, M.R. Talbot, and J.-J. Tiercelin for reviewing earlier versions of this manuscript. We thank the crew of the R/V Explorer, and the Tanganyika-97 science team for their efforts during the field program. Numerous colleagues provided guidance and suggestions during the analytical phase of the project. The National Science Foundation supported this work. Seismic data processing and interpretation were carried out using software obtained on a grant to Syracuse University from Landmark Graphics Corporation.
Copyright 2008 Elsevier B.V., All rights reserved.
- East Africa
- Lake Tanganyika
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