ENVIRONMENTAL RESPONSES TO CLIMATE CHANGES IN THE EASTERN SAHARA SINCE THE PENULTIMATE GLACIAL

The chronology, style and extent of environmental changes as manifested in lacustrine sequences and offshore dust flux records is well established in West Africa for the period since c. 20 ka. This record is dominated by a significant transition from desert conditions to a more verdant landscape during the early Holocene insolation maximum. Evidence for significant increases in moisture during this period has also been described from the Eastern Sahara. Evidence of environmental changes during previous insolation maxima, during either glacial or interglacial stages is less well known throughout the Sahara.

Here we describe our attempts to extend the recorded evidence of environmental changes for the Eastern Sahara back to M.I.S 6. By optically dating a series of variously pedogenetically altered aeolian sand sheets, lacustrine and fluvial sediments, we have generated a regional model of inferred shifts in moisture regime over this period. Evidence from Bir Tafawi indicates the occurrence of superimposed and unconformity-bounded lake basins that relate to the three precessional maxima that occurred during M.I.S. 5. The analysis of so-called 'radar river'-like fluvial sediments confirms that during at least some periods of M.I.S. 5, there was a significant and interconnected surface drainage network present in the vicinity of southwestern Egypt and Northwest Sudan. Deposition during the last glacial period was dominated by sand sheets, which are well known from the Selima region of southern Egypt. These deposits have been variably reworked and pedogenically altered during periods of ameliorated (i.e. humid) climate. Periods of climatic amelioration correspond closely with insolation maxima during the glacial period, suggesting that intensification of the monsoon occurred during this time, though probably not of sufficient intensity to result in the generation of extensive surface waters. Likewise, during the last glacial, insolation minima correspond to phases of widespread aeolian deposition. Some evidence of abrupt climatic transitions, including a possible Younger Dryas age aeolian reactivation, is apparent. We present details of the preserved and dated sedimentary record, along with inferences relating to the geographical extent of the palaeomonsoon in the Eastern Sahara.