One million year old groundwater in the Sahara revealed by krypton-81 and chlorine-36 -: art. no. L05503

Measurements of Kr-81/Kr in deep groundwater from the Nubian Aquifer (Egypt) were performed by a new laser-based atom-counting method. Kr-81 ages range from similar to2 x 10(5) to similar to1 x 10(6) yr, correlate with Cl-36/Cl ratios, and are consistent with lateral flow of groundwater from a recharge area near the Uweinat Uplift in SW Egypt. Low delta(2)H values of the Kr-81-dated groundwater reveal a recurrent Atlantic moisture source during Pleistocene pluvial periods. These results indicate that the Kr-81 method for dating old groundwater is robust and such measurements can now be applied to a wide range of hydrologic problems.