HR: 11:35h
AN: U22B-06    [Abstracts]
TI: Orbital- versus glacial-mode forcing of tropical African climate: Results of scientific drilling in Lake Malawi, East Africa
AU: * Scholz, C A
EM: cascholz@syr.edu
AF: Department of Earth Sciences, Syracuse University, 204 Heroy Geology Laboratory, Syracuse, NY 13244, United States
AU: Cohen, A S
EM: cohen@email.arizona.edu
AF: Department of Geosciences, University of Arizona, Gould-Simpson Building #77, 1040 E 4th St, Tucson, AZ 85721, United States
AU: Johnson, T C
EM: tcj@d.umn.edu
AF: Large Lakes Observatory and Department of Geological Sciences, University of Minnesota Duluth, 10 University Drive, 204 RLB, Duluth, MN 55812, United States
AU: King, J W
EM: jking@gso.uri.edu
AF: Graduate School of Oceanography, University of Rhode Island, Bay Campus, South Ferry Road, Narragansett, RI 02882, United States
AU: Brown, E T
EM: etbrown@d.umn.edu
AF: Large Lakes Observatory and Department of Geological Sciences, University of Minnesota Duluth, 10 University Drive, 204 RLB, Duluth, MN 55812, United States
AU: Lyons, R P
EM: rplyons@syr.edu
AF: Department of Earth Sciences, Syracuse University, 204 Heroy Geology Laboratory, Syracuse, NY 13244, United States
AU: Stone, J R
EM: jstone@unlserve.unl.edu
AF: Department of Geosciences, University of Nebraska, 214 Bessey Hall, Lincoln, NE 68588, United States
AU: Beuning, K R
EM: beuninkr@uwec.edu
AF: Department of Biology, University of Wisconsin-Eau Claire, Phillips 330, Eau Claire, WI 54702, United States
AB: Lake Malawi extends from 9-14 degrees S within the East African Rift Valley, and at 700 m deep, contains more than 20 percent of the surface water on the African continent. In 2005 the Lake Malawi Scientific Drilling Project drilled 7 holes at two sites in the lake, recovering a continuous sediment record that samples much of the Quaternary. Detailed studies completed to date on sediments deposited during the past 145 ka indicate periods of severe aridity at precessional frequency between 135 and 75 ka, when the lake's water volume was periodically reduced by at least 95 percent. These dramatic drops in lake level (more than 550 m), signifying markedly arid conditions in the catchment, are documented in sediment lithology (decreased organic carbon content and increased authigenic carbonate content during severe lowstands), aquatic microfossils (appearance of a littoral ostracode fauna, and saline/alkaline lake diatom flora during extreme low lake stages), as well as in dramatic reductions in catchment pollen production. These intervals of pronounced tropical African aridity in the early late-Pleistocene were much more severe than the Last Glacial Maximum, and are consistent with sediment records from Lakes Tanganyika (East Africa) and Bosumtwi (West Africa). In all three lakes a major rise in water levels and a shift to more humid conditions is observed after ~70 ka. The transition to wetter, more stable conditions coincides with the relaxation of orbital eccentricity and a reduction in the amplitude of precession. The observed climate mode switch to decreased environmental variability is consistent with terrestrial and marine records from in and around tropical Africa, but these new drill cores provide evidence for dramatically drier conditions prior to 70 ka that have not as yet been detected in marine sediment records. Such climate change may have stimulated the expansion and migrations of early modern human populations.
UR: http://malawidrilling.syr.edu
DE: 4910 Astronomical forcing
DE: 4914 Continental climate records
DE: 4934 Insolation forcing
DE: 4942 Limnology (0458, 1845, 4239)
DE: 9305 Africa
SC: Union [U]
MN: 2007 Fall Meeting