2007 GSA Denver Annual Meeting (28–31 October 2007)

Paper No. 8
Presentation Time: 10:15 AM


STONE, Jeffery Robert, Dept. of Geosciences, Univ of Arizona, 214 Bessey Hall, Dept. of Geosciences, University of Nebraska, Lincoln, NE 68588, COHEN, Andrew S., Department of Geosciences, University of Arizona, Tucson, AZ 85721, BEUNING, Kristina R.M., Department of Biology, University of Wisconsin-Eau Claire, Department of Biology, University of Wisconsin, Eau Claire, WI 44325, SCHOLZ, C.a., Department of Earth Sciences, Syracuse University, 204 Heroy Geology Laboratory, Syracuse, NY 13244, JOHNSON, Thomas C., Large Lakes Observatory and Department of Geological Sciences, University of Minnesota Duluth, Duluth, MN 55812 and KING, John, Marine Geology & Geophysics, Univ of Rhode Island Graduate School of Oceanography, Narragansett Bay Campus, Narragansett, RI 02882, jstone@unlserve.unl.edu

Evidence of changes to extremely arid climate is present in both the early and late Pleistocene sediment history of Lake Malawi. Lake response to climate change is expressed clearly in the late Pleistocene record by the repeated introduction of paleoecological indicator species sensitive to changes in lake depth and water chemistry. Striking changes occur in fossil diatom assemblages throughout the sediment record; despite the highly-dilute nature of modern Lake Malawi, fossil assemblages commonly include groups that prefer environments with rapid salinity fluctuations and elevated alkalinity levels. Simultaneous changes in ostracode faunal assemblages suggest periods of drastically-lowered lake levels, including at least one multi-millennial episode where lake levels were approximately 600 meters below modern lake elevations. The presence of a late Pleistocene "mega-drought" is corroborated by several other lines of evidence, including changes in the pollen assemblages, substantial shifts in the record of charcoal fragments, variations in sedimentary chemistry, and seismic data detailing several stages of basin-wide sediment truncation.

Preliminary results of the fossil diatom and ostracode records of the early Pleistocene (approximately 1 million years before present) indicate that Lake Malawi responded to several stages of severe climate change, producing shifts in the diatom flora and ostracode faunal similar to those observed in the late Pleistocene. Here, we utilize multivariate and time series analyses to compare the lake response to climate change inferred from paleoecological proxies; our results focus primarily upon the timing and nature of lake dynamics affected by changing lake levels, including variations in ionic concentration, turbidity, nutrient cycling, and vertical mixing. We highlight the differences in lake response to climate change between these two periods, each spanning more than 100,000 years, from the early and late Pleistocene.