Thermohaline stratification and double diffusion diapycnal fluxes in the hypersaline Dead Sea

Abstract

AbstractThe Dead Sea is a hypersaline terminal lake, experiencing negative water balance, increasing salinity, and NaCl (halite) crystallization. We observed atypical evolution of the thermohaline stratification in comparison to most lakes due to the role of salt crystallization and diapycnal fluxes across lake layers. We characterized the dynamics of the thermohaline properties of the lake strata through high‐resolution continuous measurements of temperature profiles, novel water sampling methods, and observation of vertical profiles of salt crystallization. The diapycnal fluxes across the metalimnion were explained by Double Diffusion (DD) salt fingering driven by instability between warmer saltier water above cooler less salty water. The DD flux is associated with: (1) sharpening of the metalimnion from a 20 m wide transition in early summer, to staircase, ultimately merging to a single sharp sub‐meter step, (2) salinity decline from the epilimnion starting from mid‐summer synchronous with increasing salinity and temperature of the hypolimnion, and (3) active halite crystallization in the hypolimnion. We hypnotize that the salt fingering mechanism in saturated brines reveals a unique asymmetry; i.e., the descending cooling fingers become supersaturated and crystallize halite, whereas the ascending warming fingers becomes undersaturated. The DD flux in the Dead Sea is shown to be fundamental in the dynamics of stratification, providing a framework for general understanding DD flux in hypersaline environments. The finding that the epilimnion experiences seasonal halite undersaturation whereas the hypolimnion continuously precipitates salt by DD flux, has wide implications on the understanding of the dynamics of deposition of evaporitic rocks.