QUATERNARY RESEARCH 48, 29–37 (1997) ARTICLE NO. QR971907 Precipitation Source Inferred from Stable Isotopic Composition of Pleistocene Groundwater and Carbonate Deposits in the Western Desert of Egypt Mohamed Sultan and Neil Sturchio Environmental Research Division, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439 Fekri A. Hassan Institute of Archaeology, University College London, 31-34 Gordon Square, London WC1H0PY, United Kingdom Mohamed Abdel Rahman Hamdan Department of Geology, Faculty of Science, Cairo University, Cairo, Egypt Abdel Moneim Mahmood Ain Shams University, Cairo, Egypt Zeinhom El Alfy Egyptian Geological Survey and Mining Authority, 3 Salah Salem St., Abbassia, Cairo, Egypt and Tom Stein Department of Earth and Planetary Sciences, Washington University, St. Louis, Missouri 63130 Received February 14, 1996 per year (Petit-Maire, 1986). Geologic evidence shows that An Atlantic source of precipitation can be inferred from stable arid and wet periods alternated throughout the Quaternary, isotopic data (H and O) for fossil groundwaters and uranium- with the last of the major wet periods occurring in the Holo- series-dated carbonate spring deposits from oases in the Western cene between 9500 and 4500 yr ago. Holocene climatic vari- Desert of Egypt. In the context of available stable isotopic data ations in North Africa are generally attributed to northward for fossil groundwaters throughout North Africa, the observed expansion of the summer monsoon during the wet periods isotopic depletions (dD 072 to 081‰; d 18 O 010.6 to 011.5‰) of and a southward shift of the westerly system during the fossil (§32,000 yr B.P.) groundwaters from the Nubian aquifer glaciations (Ritchie and Haynes, 1987; Petit-Maire, 1989). are best explained by progressive condensation of water vapor Similarly, earlier wet (up to 150,000 yr ago) periods were from paleowesterly wet oceanic air masses that traveled across attributed to intensification of the monsoons (e.g., Prell and North Africa and operated at least as far back as 450,000 yr before the present. The values of d 18 O (17.1 to 25.9‰) for 45,000- to Kutzbach, 1987; Yan and Petit-Maire, 1994), as suggested ú450,000-yr-old tufas and vein-filling calcite deposits from the by the sapropels (black organic-rich layers) resulting from Kharga and Farafra Oases are consistent with deposition from River Nile discharge into the east Mediterranean (Rossignol- groundwaters having oxygen isotopic compositions similar to those Strick, 1983). For the past 450,000 yr, the African monsoons of fossil groundwaters sampled recently at these locations.  1997 were heaviest when the northern summer monsoon index University of Washington. attained maximum values; the timing of heavy African mon- soons was obtained by dating the sapropels, and the monsoon index was computed from the orbital variation of insolation INTRODUCTION (Rossignol-Strick, 1983). Additional support for this hypoth- esis comes from: (1) an apparent correspondence between At present, the Sahara of North Africa is one of the most arid deserts in the world, receiving less than 20 mm of rain periods of high lake levels in southern Egypt and northern 29 0033-5894/97 $25.00 Copyright  1997 by the University of Washington. All rights of reproduction in any form reserved. AID QR 1907 / a60c$$$$81 07-09-97 13:06:29 qral AP: QR