Toward a better understanding of palaeoclimatic regimes that recharged the fossil aquifers in North Africa: Inferences from stable isotope and remote sensing data

The isotopic composition of modern precipitation collected monthly from the International Atomic Energy Agency (IAEA) stations over North Africa is enriched (average delta D: Morocco: -25.8 parts per thousand; Algeria: -21.3 parts per thousand; Tunisia: -20.6 parts per thousand; Libya: -17.7 parts per thousand; Egypt: -11.7 parts per thousand) compared to fossil groundwater across North Africa, which shows progressive west-to-east depletion; this indicates that precipitation from paleowind regimes was different from those prevailing in the present day (late Holocene). However, a few monthly records (March 1982, December 1987, December 1991, March 2002, and April 2002) collected from IAEA stations (Sidi Barrani, Cairo. Rafah, and El-Arish) showed isotopic depletions (delta D = -56 parts per thousand to -43.7 parts per thousand) approaching those of the fossil groundwater in Egypt. For each of the five events, we investigated the direction of cloud propagation in relation to the isotopic composition of precipitation as it travels over the African continent and surroundings. Cloud propagation directions and air parcel flow paths were extracted from temporal (every 30 min) Meteosat image products: (1) Infra-red EUMETSAT, (2) Cloud Motion Winds (CMW), and (3) Back Trajectory Models (BTM). The inferred wind regimes for each of these events were then compared to those for the remaining Egyptian records (160) that produced precipitation with enriched to intermediate isotopic compositions (delta D: -39.7 parts per thousand to +34.6 parts per thousand). The extracted cloud propagation directions and the observed spatial variation in the isotopic compositions of the precipitating rain support a model that attributes previous wet climatic periods over North Africa to the intensification of palaeowesterlies during glacial periods. Published by Elsevier B.V.