Millennial-scale climate change in southern East Africa since the LGM: implications for forcing factors
by
Philip Barker
Hysed, Department of Geography, Institute of Environmental and Natural Sciences, Lancaster University, Lancaster LA1 4YB, UK
Coauthors: Françoise Gasse (CEREGE, CNRS-Université d’Aix-Marseille III, BP. 80, 13545 Aix-en-Provence, Cedex 04, France

Milankovitch theory explains the millennial scale water balance fluctuations of East African lakes in the northern and equatorial latitudes and also predicts an anti-phase pattern of lake level change for the southern part of this region. The second component of the theory has been difficult to test because of a lack of data for the glacial period. In this poster we synthesise lake-level data for East Africa (0° and 30°S, East of 25°E) to evaluate the contribution of Milankovitch-driven insolation forcing of the southern equatorial region. We present recent records from three lakes in the data-poor southern part of East Africa, Lake Malawi (9 to 14°S), Lake Massoko (9°S), and Lake Rukwa (8°S). We also compare these sites to previously published lake level data for key regions and offshore SST records. Changes in lake-level are primarily inferred from diatoms. Our results show that in contrast to previous interpretations, the level of Lake Malawi was significantly lower than the present day at the LGM. This finding is consistent with interpretations from the more northerly lakes Massoko and Rukwa and published palaeoclimate records. However, the early Holocene climate of this region was more spatially heterogeneous since the diatom data suggest conditions intermediate between the LGM and the immediate post glacial period for Lake Malawi, whereas Lake Massoko, Lake Rukwa and most other tropical East African lakes were close to their maximum levels.

The recent PMIP synthesis shows that relative glacial aridity in East Africa is best simulated by GCMs using computed SSTs rather than the higher CLIMAP values. Moreover, these low SSTs must have been dominant over any precipitation rise caused by enhanced orbitally-induced insolation changes predicted by the Milankovitch mechanisms for the southern hemisphere. Nevertheless, Milankovitch processes may explain the relatively damped lake-level response inferred for Lake Malawi in the early Holocene.

Date received: March 26, 2001

Copyright © 2001 by the author(s). The author(s) of this document and the organizers of the conference have granted their consent to include this abstract in Atlas Conferences Inc. Document # cagc-28.