Abdou A. Abouelmagd

Doctoral Dissertation Announcement

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Candidate: Abdou A. Abouelmagd

Degree of: Doctor of Philosophy

Department: Geosciences

Title: Paleoclimatic Regimes of the African Sahara Desert During Pleistocene and the Origin of Groundwater in the Nubian Sandstone Aquifer System

Committee:
Dr. Alan E. Kehew, Chair
Dr. Mohamed Sultan
Dr. R. V. Krishnamurthy
Dr. Neil Sturchio

Date: Thursday, May 10, 2012 1:00 p.m. to 3:00 p.m.
1122 Rood Hall

Abstract:
This study involves an integrated three-fold approach to better understand the paleoclimatic regimes over the North African Sahara Desert with emphasis on the origin of groundwater in the Nubian Sandstone Aquifer System. Specifically, the nature and origin of the paleo-wind regimes that produced the precipitation that recharged the fossil aquifers in North Africa in the previous wet climatic periods are deciphered using inferences from stable isotope data, noble gases, remote sensing and GIS.
In the first phase, the progressive depletion trend of stable isotopic composition in the fossil groundwaters under influence of paleowesterlies across North Africa Sahara Desert is simulated using a Raleigh Distillation Model. Then, the precipitation events that gave rise to precipitation with isotopic signatures similar to those of the fossil groundwater in North African Aquifers are identified. In the second phase, the temporal satellite data (METEOSAT First Generation) are used to identify the directions of the modern wind regimes that influencing those precipitation events.
To substantiate the findings from the first two phases, groundwater samples were collected from the Nubian Aquifer underlying Sinai Peninsula, Egypt to extract the recharge temperatures using dissolved noble gas concentrations in the samples and to determine their ages. The following observations and findings support recharge of the Saharan fossil (over) aquifers by intensification of paleowesterlies during wet cool glacial periods: (1) rare west to east propagation clouds produce precipitation that is progressively depleted in its isotopic composition (O, H) with distance traveled across the Sahara; the observed isotopic compositions and patterns for modern precipitation are similar to those reported for the North African fossil aquifers, and (2) groundwater samples from the fossil aquifers are depleted in their isotopic composition and their ages are found to be consistent with the deposition during cool glacial periods. The average recharge temperatures (from dissolved noble gases concentration) are lower than current mean annual air temperatures by approximately 4.0 °C and the groundwater ages for the Nubian Sandstone Aquifer are ranging from 14C: 32 x 10 raised to the power of 3 yrs B.P. to 26 x 10 raised to the power of 3 yrs B.P.