Cl-37 in the Dead Sea system - preliminary results

This study presents the first set of delta(37)Cl measurements in the Dead S ea environment. delta(37)Cl values for the meromictic (long term stratified ) Dead Sea water column prior to its complete overturn in 1979 were -0.47 p arts per thousand SMOC for the UWM (Upper Water Mass) and +0.55 parts per t housand SMOC for the LWM (Lower Water Mass). The delta(37)Cl values for the pre-overturn Dead Sea cannot be explained by the prevailing model on the e volution of the Dead Sea during the last few centuries and require corrobor ation by more measurements. The 1979 overturn wiped out almost completely t he isotopic differences between the UWM and LWM. Even so, Cl isotope data c ould be used to decipher physical processes related to the overturn such as incomplete homogenization of the deep water mass. Inputs into the lake, co mprising freshwaters (springs and the Jordan River) and saline springs gave a range of -0.37 parts per thousand to +1.0 parts per thousand with the fr eshwater sources being more enriched in delta(37)Cl. Based on the delta(37) Cl measurements of the End-Brine (the effluent from Dead Sea evaporation po nds) and of recent Dead Sea halite, the Cl isotopic composition of the orig inating brines have been estimated. They gave a narrow isotopic spread, +0. 01 parts per thousand and +0.07 parts per thousand and fall within the same range with Dead Sea pore water (+0.13 parts per thousand) and with the pos t-overturn Dead Sea (-0.03 parts per thousand and +0.16 parts per thousand) . Rock salt from Mount Sdom gave a value of -0.59 parts per thousand indica ting its formation at the last stages of halite deposition from evaporating sea water. The hypersaline En Ashlag spring gave a depleted delta(37)Cl va lue of -0.32 parts per thousand, corresponding to a residual brine formed i n the very latest stages (including bishofite deposition) of seawater evapo ration. (C) 1998 Elsevier Science Ltd. All rights reserved.