HR: 13:55h
AN: PP13C-02    [Abstracts]
TI: The Lake Bosumtwi Drilling Project: A 1 Ma West African Paleoclimate Record
AU: * Peck, J A
EM: jpeck@uakron.edu
AF: Dept. of Geology, Univ. of Akron, Akron, OH 44325-4101 United States
AU: Heil, C
PP13C-02 AF: Grad. School of Oceanography, Univ. of RI, Narragansett, RI 02882 United States
AU: King, J W
PP13C-02 AF: Grad. School of Oceanography, Univ. of RI, Narragansett, RI 02882 United States
AU: Scholz, C A
PP13C-02 AF: Dept. of Earth and Environmental Sciences, Syracuse Univ., Syracuse, NY 13244-1070 United States
AU: Shanahan, T M
PP13C-02 AF: Dept. of Geological Sciences, Univ. of Arizona, Tucson, AZ 85721 United States
AU: Overpeck, J T
PP13C-02 AF: Dept. of Geological Sciences, Univ. of Arizona, Tucson, AZ 85721 United States
AU: Fox, P A
PP13C-02 AF: Dept. of Geology, Univ. of Akron, Akron, OH 44325-4101 United States
AU: Amoako, P Y
PP13C-02 AF: Ghana Geological Survey Department, Ministry Branch Post Office, Accra, M80 Ghana
AU: Forman, S L
PP13C-02 AF: Dept. of Earth and Envir. Sci., Univ. of Ill at Chicago, Chicago, IL 80607-7059 United States
AU: Koeberl, C
PP13C-02 AF: Dept. of Geological Sciences, Univ. of Vienna, Vienna, A-1090 Austria
AU: Milkereit, B
PP13C-02 AF: Dept. of Physics, Univ. of Toronto, Toronto, ON M5S 1A7 Canada
AB: Lake Bosumtwi occupies a 1.07 Ma impact crater located in Ghana, West Africa centered at 06*32'N and 01*25'W. This 78 m deep, hydrologically-closed lake has a water budget extremely sensitive to the precipitation/evapotranspiration balance and is located in the path of the seasonal migration of the ITCZ. Therefore, Lake Bosumtwi is ideally situated to provide a long record of change in North African monsoon strength. In addition, the stratified water column allows for the preservation of finely-laminated sediments and the potential for high-resolution (annual) paleoclimate reconstruction. Using the GLAD800 lake drilling system, five drill sites were occupied along a water-depth transect in order to facilitate the reconstruction of the lake level history. At these five sites, a total of 14 separate holes were drilled yielding a total sediment recovery of 1,833 m. The shallow water drill sites consist of alternating laminated lacustrine mud (deepwater environment), moderately-sorted sand (nearshore beach environment) and sandy gravel (fluvial or lake marginal environments). These sediment cores and seismic reflection profiles are being used to construct a basin-wide stratigraphic framework, in order to extend further back in time the present Bosumtwi lake level histories obtained from highstand terraces and short piston cores. At a deep water site, the complete 1 Ma lacustrine stratigraphic section was recovered in 294 m deep holes that ended in impact-glass bearing, accretionary lapilli fallout representing the initial days of sedimentation. The lowermost lacustrine sediment is a bioturbated, light-gray mud with abundant gastropod shells indicating that a shallow-water oxic lake environment was established in the crater. Much of the overlying 294 m of mud is laminated thus these sediment cores will provide a unique 1 million year record of tropical African climate change. Two contrasting litholgies identified in the dated, upper part of the deep water drill hole, were deposited over the last glacial cycle. Increased insolation forcing and the resulting intensified summer monsoon produce a positive moisture balance and high lake levels. Organic-rich sediment with a low-coercivity magnetic mineralogy accumulated during these wet intervals. However, at times of decreased summer insolation and the accompanying weaker summer monsoon, lake levels fell and a mineral rich sediment with lower organic content accumulated. During these dry periods aerosol dust export from North Africa increased greatly contributing to a high-coercivity magnetic mineral assemblage in Bosumtwi. On precessional time scales, the Bosumtwi profiles of organic carbon and rock magnetic parameters are readily correlated with the Vostok methane record thus reflecting an important role for equatorial African wetlands on regulating methane variability. Ongoing work will utilize the varved sediment record to address the abruptness of environmental change in West Africa as well as connections between high and low-latitude climate change.
DE: 1637 Regional climate change
DE: 1807 Climate impacts
DE: 1845 Limnology (0458, 4239, 4942)
DE: 3344 Paleoclimatology (0473, 4900)
DE: 9305 Africa
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005