Geomorphic indicators of holocene winds in Egypt's Western Desert

Geomorphic mapping of Egypt's Western Desert from LANDSAT-MSS images reveals oriented aeolian landforms that record, in part, Holocene winds. Wind directions reconstructed from these landforms indicate the dominance of N-S airflow from 30degreesN to 20degreesN, turning clockwise southward to NE-SW, conformable with modern circulation. A second direction appears over western Egypt, W between 30degreesN and 26degreesN, NW between 26degreesN and 20degreesN. Cross-cutting aeolian landforms show that W/ NW winds are older than the N/NE winds. Geomorphic evidence, abundant south to 26degreesN and less abundant to 20degreesN, also indicates that W and NW winds were early Holocene `palaeowesterlies'. Some evidence also indicates that they extended eastward to at least 30degreesE, perhaps to the Red Sea. These winds steered moist Atlantic/Mediterranean air masses to Egypt, sustaining early Holocene lakes and playas north of the limit of tropical monsoonal rainfall at 20degreesN. Upon aridification, beginning after 5 kyr BP, yardangs oriented west to east were eroded in early Holocene basinal sediments in western Egypt, indicating that these winds continued there for 1-2 kyr, until 3-4 kyr BP. Optically stimulated luminescence (OSL) ages of surface sand sheet in southern Egypt indicate that the present north-south winds were established ca. 3-4 kyr BP, at the same time as the northern savanna boundary was stabilized at its present position. (C) 2003 Elsevier Science B.V. All rights reserved.