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2005 Salt Lake City Annual Meeting (October 16–19, 2005)

Paper No. 3
Presentation Time: 2:00 PM

ORBITAL AND NON-ORBITAL FORCING OF HYDROLOGIC AND VEGETATION CHANGE IN WEST AFRICA SINCE THE LGM AS REVEALED BY GEOCHEMICAL RECORDS AND HYDROLOGIC MODELING OF LAKE BOSUMTWI, GHANA


SHANAHAN, Timothy M.1, OVERPECK, Jonathan T.2, HUGHEN, Konrad3, DRENZEK, Nick3, BECK, J. Warren4, PECK, John A.5, KING, John6, SCHOLZ, Chris7 and WHEELER, C. Winston8, (1)Geosciences, University of Arizona, 1040 East Fourth St, Tucson, AZ 85721, (2)Dept. Geosciences and Institute for the Study of Planetary Earth, University of Arizona, 1040 East Fourth St, Tucson, AZ 85721, (3)Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Mailstop 25, Woods Hole, MA 02543, (4)Arizona AMS Laboratory and Department of Physics, University of Arizona, Tucson, AZ 85721, (5)Department of Geology, University of Akron, 126 Crouse Hall, Akron, OH 44325-4101, (6)Marine Geology & Geophysics, Univ of Rhode Island Graduate School of Oceanography, Narragansett Bay Campus, Narragansett, RI 02882, (7)Department of Earth Sciences, Syracuse University, 204 Heroy Geology Laboratory, Syracuse, NY 13244-1070, (8)Geological & Environmental Sciences Department, Stanford University, Braun Hall (Geo Corner) #118, 450 Serra Mall, Building 320, Stanford, CA 94305, shanahan@geo.arizona.edu

Hydrologic and vegetation changes in tropical Africa and South America are believed to have played an important role in the global climate changes during glacial to interglacial climate transitions, particularly through their influence on variations in atmospheric methane and the global hydrologic cycle. Here we present a multiproxy record of hydrologic and vegetation change in West Africa, which is based on a combination of isotopic and geochemical measurements on lake sediments and hydrologic modeling of well-dated paleo-beaches from Lake Bosumtwi, Ghana. Modeling results suggest that lake level changes since the LGM reflect the combined influence of precipitation, temperature, windiness and cloud cover, resulting from insolation-induced changes in the West African monsoon. Geochemical records support the dominant influence of low-latitude insolation forcing of the monsoon on hydrologic changes in West Africa, but also suggest that higher frequency changes related to tropical sea surface temperature variations played a key role in controlling glacial and Holocene climate changes. Molecular fossil indicators of terrestrial and aquatic organic matter suggest a complex biological response to hydrologic changes, but one that is consistent with both a direct vegetation response to changes in the monsoon and a West African source of atmospheric methane variations.

Session No. 239

Paleoclimatology/Paleoceanography II
Wednesday, 19 October 2005: 1:30 PM-5:30 PM
Geological Society of America Abstracts with Programs. Vol. 37, No. 7, p.524
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