2011 GSA Annual Meeting in Minneapolis (912 October 2011)
Paper No. 58-3
Presentation Time: 2:05 PM-2:20 PM

PALEOCLIMATIC INSIGHT INTO THE DEPLETED ISOTOPIC RATIOS OF FOSSIL AQUIFER WATERS, NORTHERN AFRICA, BASED ON A RALEIGH DISTILLATION MODEL

ABOUELMAGD, Abdou, Environmental Sciences and Engineering Division, Water Desalination and Reuse Center, King Abdullah University of Science and Technology, Thuwal, 23955-6900, Saudi Arabia, abdou_aly@hotmail.com, KRISHNAMURTHY, R.V., Geosciences, Western Michigan University, Kalamazoo, MI 49008, SULTAN, Mohamed, Geosciences, Western Michigan University, 1903 W. Michigan Avenue, Kalamazoo, MI 49008, KEHEW, Alan, Dept. of Geoscience, Western Michigan University, 1187 Rood Hall, Kalamazoo, MI 49008, and MILEWSKI, Adam, Geology, University of Georgia, Geography-Geology Building, 210 Field Street, Athens, GA 30602

The stable oxygen and hydrogen isotopic composition of fossil groundwater (>30k yrs B.P.) over North Africa is progressively depleted from west to east (e.g., average δ18O: Morocco: –6.4‰; Algeria: –8.01‰; Tunisia: –8.38‰; Libya: –8.56‰; and Egypt: –10.98‰) compared to the modern precipitation (e.g., average δ18O ± 1δ: Morocco: –5.46‰ ± 1.22‰; Algeria: –3.9‰ ± 1.19‰; Tunisia: –4.67‰ ± 0.54‰; Libya: –3.8‰ ± 0.44‰; and Egypt: –3.96‰ ± 0.54‰) suggesting that the precipitation during the previous wet climatic periods (450,000 yr B.P to 10,000 yr B.P) resulted from wind regimes different from those prevailing today. The isotopic composition of fossil ground water can be used as a proxy for the isotopic composition of the paleo-precipitation recharging those ground waters with the Atlantic Ocean providing the source of moisture for recharging waters over Northern Africa. Based on this premise, a simple box model can be considered to model the paleo-precipitation to follow a simple Rayleigh distillation. Such a model shows that the reduction vapor factor was up to 30% by the time the moisture bearing air masses reached what is modern day Egypt. This model will be compared with available precipitation data for present day North African sites to constrain atmospheric processes that operated during the Pleistocene over Northern Africa that were responsible for the formation of the fossil aquifers (e.g. Nubian Aquifer) with depleted isotopic ratios.

2011 GSA Annual Meeting in Minneapolis (912 October 2011)
General Information for this Meeting
Session No. 58
Advances in Terrestrial Paleoclimatology and Paleoecology: Geochemical Techniques and Examples Using Inorganic and Organic Molecules in Fossil Soils, Plants, Invertebrates, and Vertebrates I
Minneapolis Convention Center: Room 200FG
1:30 PM-5:30 PM, Sunday, 9 October 2011

Geological Society of America Abstracts with Programs, Vol. 43, No. 5, p. 162

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