HR: 13:40h
AN: PP13C-01    [Abstracts]
TI: Paleoenvironmental changes in West Africa since the Last Glacial Maximum from a geochemical and modeling study of Lake Bosumtwi, Ghana
AU: * Shanahan, T M
EM: shanahan@geo.arizona.edu
AF: Dept. Geosciences, University of Arizona, Tucson, AZ 85721 United States
AU: Overpeck, J T
PP13C-01 AF: Dept. Geosciences, University of Arizona, Tucson, AZ 85721 United States
AU: Peck, J
PP13C-01 AF: Dept. Geology, University of Akron, Akron, OH 44325 United States
AU: King, J
PP13C-01 AF: Grad. School of Oceanography, University of Rhode Island, Narragansett, RI 02882 United States
AU: Scholz, C
PP13C-01 AF: Dept. Earth Sciences, Syracuse University, Syracuse, NY 13244-1070 United States
AU: Hughen, K
PP13C-01 AF: Dept. Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA 02543 United States
AU: Drenzek, N
PP13C-01 AF: Dept. Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA 02543 United States
AU: Beck, J W
PP13C-01 AF: Dept. Physics, University of Arizona, Tucson, AZ 85721 United States
AB: Lake Bosumtwi is a 78 m deep, hydrologically isolated lake formed in a 1.07 Ma meteorite impact crater in southwestern Africa. Because of its location and hydrologic properties, it is extremely sensitive to changes in the precipitation/evaporation balance and the strength of the West African monsoon. In 2004, we recovered an extensive set of long (ca. 300 m) sediment cores extending from the surface to bedrock, offering the potential for reconstructing a million year long record of paleoenvironmental variability in West Africa. In the present study, we use a multiproxy approach to reconstruct the most recent, ca. 25 kyr portion of this record in order to understand the sensitivity of Lake Bosumtwi to global climate changes during glacial to interglacial transitions. Elemental variations in sediment cores provide evidence for large and abrupt shifts in the lake water balance, caused by changes in the strength of the monsoon and the position of the ITCZ, and are supported by evidence from paleoterrace reconstructions. Large scale changes in vegetation reconstructed from vascular plant biomarkers indicate that vegetation in West Africa responded directly to changes in the strength of the monsoon and could potentially provide a West African source for some late glacial changes in atmospheric methane production. Simulations of lake level fluctuations using a water balance model provide new constraints on the magnitude of these hydrologic changes. Our results suggest that a detailed record of both paleohydrologic and paleoenvironmental change are contained in the sediments from Lake Bosumtwi. Future work on deep drill cores using these and other proxies can provide additional insights into the nature of West African climate and environmental variability.
DE: 4901 Abrupt/rapid climate change (1605)
DE: 4914 Continental climate records
DE: 4942 Limnology (0458, 1845, 4239)
DE: 4950 Paleoecology
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005