Paleoclimatic Regimes of the African Sahara Desert during Pleistocene and the Origin of Groundwater in the Nubian Sandstone Aquifer System
Though this dissertation is available electronically only on the WMU campus, a print copy can be found in Waldo Library at call number GB9999.2.A268 and can be requested through Interlibrary Loan.
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 African Sahara Desert is simulated using a Rayleigh 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 (e.g., Nubian Sandstone Aquifer System) are identified. In the second phase, the temporal satellite data (METEOSAT First Generation) are used to identify the directions of the modern wind regimes influencing those precipitation events.
To substantiate the findings from the first two phases, groundwater samples are collected from the Nubian Aquifer underlying Egyptian Sinai Peninsula 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 Sahara fossil aquifers by intensification of paleowesterlies during wet cool glacial periods: (1) modern rare west to east propagation clouds produce precipitation that is progressively depleted in its isotopic composition (0, 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 gas concentrations) are lower than current mean annual air temperatures by approximately 4.0 °C and the groundwater ages for the Nubian Sandstone Aquifer range from 14 C: 32 x 103 yrs B.P. to 26 x 10 3 yrs B.P.