Quaternary paleoclimate of the north-eastern boundary of the Saharan Desert: reconstruction from speleothems of Negev Desert, Israel
Abstract
Carbonate cave deposits (speleothems) from caves of the Israeli deserts were used to reconstruct the paleoclimate conditions of the northern boundary of SaharanArabian Desert. The deserts studied in this work are of two types: the Negev Desert in southern Israel, which is part of the Saharan-Arabian desert belt; and the "rain shadow" desert located east of Central Mountain Ridge (CMR) in the rift valleys of the Jordan River and Dead-Sea (Judean Desert). The presence of speleothems in numerous caves in these present-day arid regions indicates that humid climatic conditions (i.e., periods with positive effective precipitation/infiltration index) occurred in the past. In this study, the timing of the speleothem growth, as an indicator of periods of increased effective precipitation, was obtained by precise U-Th dating; the origin of rainfall, its amounts and the types of vegetation were examined from studies of the speleothem δ18O and δ13C values and the δD values of their fluid inclusions, and the sources of dust were studied through the Sr isotopic composition of the speleothems. The minimum precipitation amounts necessary to deposit speleothems are estimated to be: 200-275 mm/year during glacial periods and 300-350 mm/year during interglacial periods. Speleothem deposition in the Jordan Valley mainly occurred during the three last glacial periods, with minor deposition occurring during Termination II (~135 ka) and MIS-7 interglacial (225-205 ka), and no speleothem deposition taking place during the Holocene, the peak of last glacial maximum (~19 ka), and for most of the previous interglacial MIS-5 (130-75 ka). The δ18O and δ13C profiles of speleothems deposited between 67 ka and 25 ka in the Jordan Valley match the general isotopic trends of previously studied speleothems from central and northern Israel; suggesting a similar Eastern Mediterranean (EM) Sea source for the precipitation and similar climatic conditions. Decrease in temperature and evaporation, and the consequent increase in effective precipitation,
