Hypersaline lakes and seas were common in the past, precipitating thick evaporitic salt deposits. The only modern analogue for the paleolimnology of deep salt‐saturated aquatic environments exists in the Dead Sea. In this study, we present new insights from the Dead Sea on the role of seasonal thermohaline stratification and water balance on the seasonal and depth variations of the degree of saturation of halite (salt) and the rate of halite growth along the water column. We developed methodologies to accurately determine the empirical degree of halite saturation of the lake based on high accuracy densitometry, and to quantify halite growth rate along the water column. During summer, the epilimnion is undersaturated and halite is dissolved, whereas during winter the entire water column is supersaturated and crystallizes halite. This result is not trivial because the variations in the water balance suggest the opposite; summer is associated with higher loss of water by evaporation from the lake compared to the winter. Hence, the thermal effect overcomes the hydrological balance effect and thus governs the seasonal saturation cycle. The hypolimnion is supersaturated with respect to halite and crystallizes throughout the year, with higher super saturation and higher crystallization rates during winter. During summer, simultaneous opposing environments coexist—an undersaturated epilimnion that dissolves halite and a supersaturated hypolimnion that crystallizes halite, which results in focusing of halite deposits in the deep hypolimnetic parts of the evaporitic basins and thinning the shallow epilimnetic deposits.

The 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.

The thermal stratification of the Dead Sea was observed in high spatial and temporal resolution by means of fiber-optics temperature sensing. The aim of the research was to employ the novel highresolution profiler in studying the dynamics of the thermal structure of the Dead Sea and the related processes including the investigation of the metalimnion fluctuations. The 18 cm resolution profiling system was placed vertically through the water column supported by a buoy 450 m from shore, from 2 m above to 53 m below the water surface (just above the local seafloor), covering the entire seasonal upper layer (the metalimnion had an average depth of $20 m). Temperature profiles were recorded every 5 min. The May to July 2012 data set allowed quantitative investigation of the thermal morphology dynamics, including objective definitions of key locations within the metalimnion based on the temperature depth profile and its first and second depth derivatives. Analysis of the fluctuation of the defined metalimnion locations showed strong anticorrelation to measured sea level fluctuations. The slope of the sea level versus metalimnion depth was found to be related to the density ratio of the upper layer and the underlying main water body, according to the prediction of a two-layer model. The heat content of the entire water column was calculated by integrating the temperature profiles. The vertically integrated apparent heat content was seen to vary by 50% in a few hours. These fluctuations were not correlated to the atmospheric heat fluxes, nor to the momentum transfer, but were highly correlated to the metalimnion and the sea level fluctuations (r 5 0.84). The instantaneous apparent heat flux was 3 orders of magnitude larger than that delivered by radiation, with no direct correlation to the frequency of radiation and wind in the lake. This suggests that the source of the momentary heat flux is lateral advection due to internal waves (with no direct relation to the diurnal cycle). In practice, it is shown that snap-shot profiles of the Dead Sea as obtained with standard thermal profilers will not represent the seasonal typical status in terms of heat content of the upper layer.