NATURE AND TIMING OF THE QUATERNARY WET CLIMATIC PERIODS IN NORTH AFRICA AND ARABIA: ISOTOPIC, CHRONOLOGIC, AND REMOTE SENSING CONSTRAINTS

The Quaternary wet climatic periods in north Africa and Arabia have been traditionally attributed to intensification monsoons and progressive south to north migration of the monsoonal front during interglacial periods. The intensification of the paleo-westerlies during glacial periods, not the monsoons, can account for the following observations: (1) progressive west to east depletion in isotopic composition (δ²H: Morocco: -20 to -40‰; Algeria: -30 to -70 ‰; Libya: -70 to -80‰; Egypt: -80 to -83‰) of fossil groundwater; (2) observed high lake levels during glacial periods for Lake Lisan (maximum extension during glacial marine isotopic satge 2 [MIS-2]) (160 mbsl: 26 to 23 ka); (3) Speleothem U series ages from two caves in eastern Israel suggest episodic moist climate during glacial (MIS) 6, 4, and 2; (4) depleted isotopic compositions of groundwater compared to modern precipitation (δ²H: Morocco: -25.8; Algeria: -21.3; Libya: -17.7; Egypt: -11.7‰); (5) analysis of noble gas concentration in groundwater yield low recharge temperatures (2-6 °C below average annual temperatures); (6) analysis of cloud propagation trajectories indicate that only clouds travelling from west to east produce precipitation with isotopic compositions similar to those of Saharan fossil aquifers; (7) uranium series dating of flood deposits in southern Tunisia yielded glacial (MIS-6) ages (150 ka) and substage MIS-5b ages (90ka) ; and (8) OSL dating of thick (up to 50 m) wetland deposits in Wadi Feiran watershed in Sinai yield glacial MIS-2 ages (27 to 11 ka). Similar observation in the Arabian Peninsula suggest that wet periods in northern and central Arabia were also glacial periods: (1) a progressive north to south depletion in groundwater composition (north & center: δ²H: -26.6 to -2.5‰; south: δ²H: -76.6 to -26.9‰); (2) OSL ages (88 to 147 ka) of sediments in paleo-lakes (e.g., lake Mundafan) yield largely glacial MIS 6 ages; (3) depleted isotopic compositions of the groundwater (δ²H: -76.6 to -26.9‰) compared to modern precipitation (δ²H: -22 to -45‰); (4) well documented records of monsoon-related wet events in Oman are not well developed northwards in the Empty Quarter; and (5) well-developed paleo-channels and theater-headed valleys in north and central Arabia compared to southern Arabia.