Seasonal variations of halite saturation in the Dead Sea

Abstract

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.

Seasonal dynamics of internal waves governed by stratification stability and wind: Analysis of high‐resolution observations from the Dead Sea

“…The samples were kept warm to avoid salt precipitation prior to laboratory analysis. Accurate density measurements were critical for this study and were performed in the laboratory (DMA 5000) at 30°C, with an accuracy of ±0.005 kg m −3 (Gertman et al ; Arnon et al ; Sirota et al ). The density difference between the epilimnion and hypolimnion is based on the difference of samples from 10 and 50 m. This difference is positive under holomictic conditions, as presented in this study.…”

“…Ignoring chemical composition variations is justified for short‐term simulations (days to weeks) that are needed for internal waves simulations. However, in longer simulations (months to years), it would be preferable to account for halite precipitation and dissolution (Arnon et al ; Sirota et al , ) and for double diffusive fluxes (Arnon et al ); both of these are beyond the scope of this article.…”

“…C,D) and diminishes toward the winter due to surface cooling (Gertman and Hecht ;Arnon et al ; Sirota et al ). The temperature, salinity, and density of the upper layer are governed by atmosphere–lake interactions, salt precipitation, and double diffusion diapycnal fluxes; Arnon et al () distinguish between these governing factors, showing that in mid‐summer and late summer, double diffusion plays a major role in reducing salinity from the epilimnion, whereas halite precipitation plays a major role in autumn and winter (Arnon et al ; Sirota et al ). Throughout the seasonal cycle, temperature plays the major role in controlling the density of the upper layer and thus on the density gradient (Fig.…”

Halite Precipitation From Double‐Diffusive Salt Fingers in the Dead Sea: Numerical Simulations

“…While these processes are small scale in nature, involving salt fingers that are millimeters to centimeters wide, we expect them to play an important role in the deposition of large‐scale halite layers at the bottom of basins that are tens to hundreds of kilometers wide and tens to hundreds of meters thick. Hence, these processes can influence the dynamics of stratified hypersaline bodies of water subjected to a hydrological crisis, such as the present‐day Dead Sea (Arnon et al, ; Sirota et al, , ) or the Mediterranean during the Messinian Salinity Crisis (Garcia‐Castellanos & Villaseñor, ). A fundamental property of such evaporitic basins is that the thickness of the rock layers increases toward the deep parts of the basins.…”

“…The setup for the numerical simulations of double‐diffusive salt fingers and precipitation of halite is guided by in situ observations from the Dead Sea (Arnon et al, ; Sirota et al, ) in terms of temperature, salinity, saturation, and halite crystallization rate (Figure d). The convective fluxes and saturation conditions are strongly affected by the low diffusivity and corresponding large gradients of salinity.…”