HR: 11:50h
AN: PP31D-07    [PDF]
TI: Synchronous high lake levels in East Africa at 135 kyr BP
AU: * Bergner, A G
EM: bergner@geo.uni-potsdam.de
AF: Institute of Geosciences, University of Potsdam, Postfach 601553, Potsdam, 14415 Germany
AU: Duehnforth, M
EM: miriam.duehnforth@erdw.ethz.ch
AF: Institute of Geology, ETH Zuerich, ETH Zentrum, NOH 48, Zuerich, 8092 Switzerland
AU: Trauth, M H
EM: trauth@geo.uni-potsdam.de
AF: Institute of Geosciences, University of Potsdam, Postfach 601553, Potsdam, 14415 Germany
AB: Variations in the temporal and spatial distribution of solar radiation caused by orbital changes provide a partial explanation for the observed long-term fluctuations in African lake levels. The understanding of such relationships is essential for designing climate-prediction models for the tropics. Our assessment of the nature and timing of East African climate change is based on lake-level fluctuations of the Central-Kenyan- Rift Lakes Naivasha and Nakuru-Elmenteita, as they were inferred from sediment characteristics, diatoms, authigenic mineral assemblages and single-crystal 40Ar/39Ar age determinations on intercalated tuff layers. Using a simple lake-balance modeling approach, potential precipitation-evaporation changes in the lake basins were estimated. Our results show that the hydrologic and hence the climate conditions in East Africa at ~135 kyr BP were significantly different from today. The main difference is a ~15% higher value in precipitation compared to the present. An adaptation and migration of vegetation in the cause of climate changes would result in a ~30% increase in precipitation. Assuming that these fluctuations reflect orbitally-induced climate changes, the lake records demonstrate that periods of increased humidity in East Africa mainly followed maximum equatorial solar radiation in March or September. Interestingly, the reconstructed high lake levels are consistent with other well-dated low-latitude climate records, but do not correspond to peaks in Northern Hemisphere summer insolation as the trigger for the ice-age cycles. Our East African lake records therefore provide evidence for low-latitude forcing of the ice-age climate cycles.
DE: 1620 Climate dynamics (3309)
DE: 1833 Hydroclimatology
DE: 3344 Paleoclimatology
DE: 9604 Cenozoic
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2003 Fall Meeting