Cl-37 in the Dead Sea system - preliminary results

摘要

This study presents the first set of delta(37)Cl measurements in the Dead Sea 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 parts per thousand SMOC for the UWM (Upper Water Mass) and +0.55 parts per thousand 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 evolution of the Dead Sea during the last few centuries and require corroboration by more measurements. The 1979 overturn wiped out almost completely the isotopic differences between the UWM and LWM. Even so, Cl isotope data could be used to decipher physical processes related to the overturn such as incomplete homogenization of the deep water mass. Inputs into the lake, comprising 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 freshwater 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 ponds) and of recent Dead Sea halite, the Cl isotopic composition of the originating 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 post-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 indicating its formation at the last stages of halite deposition from evaporating sea water. The hypersaline En Ashlag spring gave a depleted delta(37)Cl value of -0.32 parts per thousand, corresponding to a residual brine formed in the very latest stages (including bishofite deposition) of seawater evaporation. (C) 1998 Elsevier Science Ltd. All rights reserved. [References: 31]