Paper No. 3
Presentation Time: 2:15 PM
A MID-HOLOCENE THERMAL MAXIMUM AT THE END OF THE AFRICAN HUMID PERIOD
BERKE, Melissa A., Large Lakes Observatory, Department of Geological Sciences, University of Minnesota Duluth, Duluth, MN 55812, JOHNSON, Thomas C., Large Lakes Observatory and Department of Geological Sciences, University of Minnesota Duluth, Duluth, MN 55812, WERNE, Josef P., Department of Geology & Planetary Science, University of Pittsburgh, Pittsburgh, PA 15260, SCHOUTEN, Stefan, Marine Biogeochemistry and Toxicology, Netherlands Institute for Sea Research, PO BOX 59, Den Burg, 1790 AB, Netherlands and SINNINGHE DAMSTÉ, Jaap S., Marine Organic Biogeochemistry, NIOZ Royal Netherlands Institute for Sea Research, P.O. Box 59, Den Burg, 1790AB, Netherlands, berk0135@umn.edu
The termination of the African Humid Period (AHP) ~5.5 thousand years ago (ka) was the most dramatic climate shift in Africa since the end of the Pleistocene. Much of northern and equatorial Africa went from a wet, verdant landscape, with a lake-filled “green Sahara” and high lake levels as far south as Lake Rukwa (~8ºS latitude) to expansive desert, diminished lake levels, and the replacement of mesic taxa with drought-tolerant flora. Understanding the environmental shift has been confounded by responses captured in paleorecords, with evidence for both an abrupt shift towards aridity, completed over decades to centuries, and more gradual response over several millennia. The AHP lasted from ~14.5 to 5 ka, and is attributed to a non-linear response to Northern Hemisphere summer insolation forcing that strengthened, then weakened the African Monsoon system, amplified by atmosphere-vegetation feedbacks.
Here we report an important excursion in temperature that accompanied the AHP termination, based on high resolution (<90 year time step) TEX86 paleotemperature records from Lake Turkana, Kenya. Our results indicate that a temperature shift of 2-3ºC occurred over the two millennia spanning the end of the AHP (~6-4 ka), achieving a Holocene temperature maximum at about 5 ka that was warmer than the present. This thermal history is also recorded in the sediments of Lakes Malawi and Tanganyika, as well as in the ice cores of Mt. Kilimanjaro, and thus extends over a broad expanse of tropical East Africa. This important element of East African climate history is not yet captured by climate models, yet it undoubtedly influenced the distribution of flora and fauna, and the consequent migration of our human ancestors in the region.
