The Thermal History of the East African Rift Lakes Region Since the Last Glacial Maximum Reconstructed Using TEX86
Melissa A. Berke
Large Lakes Observatory & Department of Geological Sciences, University of Minnesota Duluth, Duluth, MN 55812, USA
The molecular proxy called TEX86 (tetraether index of tetraethers with 86 carbon atoms) uses membrane lipids from the aquatic Crenarchaeota that have been shown to have a positive correlation between the number of cyclopentane rings and growth temperature. These lipids act as a paleothermometer, recording mean annual surface temperatures. TEX86 serves as a proxy for air temperature because mean annual lake surface temperatures closely track mean annual air temperature. This study uses the TEX86 temperature records generated from lacustrine sediments of East African Rift Lakes (including Lakes Turkana, Albert, Victoria, and Malawi) to reconstruct the thermal history of tropical Africa for the last ~20,000 years.
Temperature records from Lake Malawi fall within modern surface lake temperatures and show a gradual cooling of ~3ºC during the late Holocene. Lake Albert shows an intriguing two-step cooling during the Younger Dryas, reaching temperatures ~2.5ºC lower than temperatures preceding or following this interval. The temperature record of Lake Turkana shows an interesting ~500 year cyclicity of low temperatures punctuated by abrupt warming events. Lakes Turkana and Albert show TEX86 paleotemperatures considerably lower than modern surface water temperatures (~8ºC cooler in Lake Albert and <4ºC cooler in Lake Turkana). Although these records appear to be valid in terms of the range of temporal variability, the temperature departures from a global lake TEX86 calibration curve may indicate varying Crenarchaeota populations among lakes or other environmental factors are influencing the temperatures recorded by the TEX86.
AAPG Search and Discovery Article #90094 © 2009 AAPG Foundation Grants in Aid