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
([email protected])

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