Salt precipitation and dissolution in the late Quaternary Dead Sea: Evidence from chemical and δ³⁷Cl composition of pore fluids and halites

The chemical composition and δ³⁷Cl of pore fluids from the ICDP core drilled in the deepest floor of the terminal and hypersaline Dead Sea, and halites from the adjacent Mount Sedom salt diapir, are used to establish the dynamics of halite precipitation and dissolution during the last interglacial and glacial periods. Between ∼132 and 116 thousand years ago (ka) halites precipitated in the lake resulting in the expulsion of Na⁺ and Cl⁻ from the residual solution. Over 50% of the Cl⁻ reservoir was removed, resulting in a decrease in the Na/Cl ratio from 0.57 to 0.19. This process was accompanied by a decrease in δ³⁷Cl values in the precipitating halites and the associated residual Cl⁻ in the lake. The observed decrease fits a Rayleigh distillation curve with a fractionation factor of Δ_{(NaCl–Dead Sea solution)} = +0.32‰ (±0.12) determined in the present study. This behavior implies negligible contribution of external sources of Cl⁻ to the lake during the main peak of the last interglacial, MIS5e. Subsequently, during the last glacial (ca. 117 to 17 ka) dissolution of halite took place, the Na⁺ and Cl⁻ inventory were replenished, accompanied by an increase in Na/Cl from 0.21 to 0.55 and in the δ³⁷Cl values from −0.46‰ to −0.12‰. While the lake underwent significant dilution during that time, the decrease in salinity was somewhat suppressed by the dissolution of the halite which was mostly derived from Mount Sedom salt diapir.