HR: 11:20h
AN: PP52B-05    [Abstracts]
TI: Abrupt changes in hydrology and vegetation in the West African monsoon region since the Last Glacial Maximum
AU: * Hughen, K A
EM: khughen@whoi.edu
AF: Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, MS#4, Woods Hole, MA 02540, United States
AU: Shanahan, T M
EM: tshanahan@whoi.edu
AF: Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, MS#4, Woods Hole, MA 02540, United States
AU: Overpeck, J T
EM: jto@u.arizona.edu
AF: Institute for the Study of Planet Earth and Department of Geosciences, University of Arizona, 715 North Park Avenue, Tucson, AZ 85721, United States
AU: Drenzek, N J
EM: ndrenzek@whoi.edu
AF: Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, MS#4, Woods Hole, MA 02540, United States
AU: Pigati, J
EM: jpigati@usgs.gov
AF: United States Geological Survey, 520 N. Park Avenue, Tucson, AZ 85721, United States
AU: Peck, J A
EM: jpeck@uakron.edu
AF: Department of Geology and Environmental Sciences, University of Akron, University of Akron, Akron, OH 44325, United States
AU: Scholz, C A
EM: cascholz@syracuse.edu
AF: Department of Earth Sciences, Syracuse University, 204 Heroy Geology Laboratory, Syracuse, NY 13244, United States
AU: King, J
EM: jking@gso.uri.edu
AF: Graduate School of Oceanography, University of Rhode Island, Bay Campus, Narragansett, RI 02882, United States
AB: The West African monsoon is a complex dynamical system that depends on feedbacks between land surface, including vegetation, and the ocean. Modeling and existing paleoclimatic data suggest that the coupling between these system components makes it particularly susceptible to abrupt change. Characterization of each of these components is therefore crucial in understanding their role in West African monsoon variability during different climate regimes. Here we utilize organic geochemical and molecular isotopic approaches to reconstruct vegetation, hydrological and paleoenvironmental changes spanning the last ~30 kyr from the sediments of Lake Bosumtwi, an anoxic lake located in the heart of the West African monsoon region. Prior to 16 kyr, carbon isotopic values of long-chain n-alkanes, synthesized as terrestrial leaf waxes, were as much as 10 per mil higher than during the Holocene, suggesting a dramatic shift from C4 grasslands to tropical forests at that time. The transition between these two states is characterized by abrupt isotopic reversals of up to 3-5 permil, consistent with model predictions of unstable vegetation regimes during periods of changing monsoon strength. Concentrations of levoglucosan, a proxy for fire intensity and frequency, show a complex relationship with vegetation and climate, but appear to be elevated during these abrupt transitions, perhaps as a result of the competing influences of changing fuel loads and aridity. During the glacial period, leaf wax carbon isotopic values are relatively invariant and lack the large-scale shifts evident in isotopic measurements of aquatic compounds and bulk organic matter. These results highlight the importance of a compound-specific approach in reconstructing past environmental changes from carbon isotopic variations in sediment records.
DE: 0458 Limnology (1845, 4239, 4942)
DE: 1605 Abrupt/rapid climate change (4901, 8408)
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
DE: 1631 Land/atmosphere interactions (1218, 1843, 3322)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting