HR: 14:40h
AN: PP13D-03    [Abstracts]
TI: West African monsoon variability along the Guinea coast during the Holocene
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: Beck, J W
EM: wbeck@physics.arizona.edu
AF: Department of Physics, University of Arizona, NSF-AMS Facility Bldg., Tucson, AZ 85721, United States
AU: Cole, J E
EM: jecole@email.arizona.edu
AF: Department of Geosciences, University of Arizona, Gould Simpson Bldg, Tucson, AZ 85721, United States
AU: Anchukaitis, K J
EM: kja@ldo.columbia.edu
AF: Tree Ring Laboratory, Lamont-Doherty Earth Observatory, Columbia University, 61 Route 9W, Palisades, NY 10964, United States
AU: Peck, J A
EM: jpeck@uakron.edu
AF: Department of Geology and Environmental Science, 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: Variations in major element concentrations of anoxic sediments from Lake Bosumtwi, Ghana, are used to reconstruct changes in the West African monsoon during the Holocene with subdecadal to annual resolution. Low elemental concentrations occur during the early- to mid-Holocene, when lake level was high and the exposed catchment area contributing sediments to the lake basin was small. Late Holocene increases in elemental concentrations are consistent with enriched oxygen isotope values of authigenic carbonates, indicating decreasing lake level and enhanced erosional transport of terrigenous material to the basin following the onset of dry conditions. The highest elemental concentrations and the most enriched isotopic values are synchonous with paleolake lowstands in seismic data, supporting our interpretation of the proxy data as indicators of past hydrologic changes. The mid- to late-Holocene decline in West African monsoon strength commenced abruptly between 3.5 and 2.6 kyr, after which it continued to decrease gradually until ca. 0.8 kyr. This contrasts with dust records from North Africa, which indicate a single abrupt shift from wet to dry conditions at ca. 5.5 kyr, and with other monsoon systems (e.g. Indian, Asian), which indicate a gradual decline in monsoon strength throughout this period. This suggests that during the late Holocene, the West African monsoon underwent at least 2 abrupt reorganizations in response to gradually changing summer insolation. Superimposed on these low-frequency hydrologic changes is significant centennial-scale variability. Cross spectral correlation with the record of atmospheric carbon-14 indicates that at least some of this variability may be linked to changes in solar irradiance, as also suggested in records from the Asian and Indian monsoon systems.
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