High‐resolution temperature sensing in the Dead Sea using fiber optics

The thermal stratification of the Dead Sea was observed in high spatial and temporal resolutionby means of fiber-optics temperature sensing. The aim of the research was to employ the novel high-resolution profiler in studying the dynamics of the thermal structure of the Dead Sea and the related proc-esses including the investigation of the metalimnion fluctuations. The 18 cm resolution profiling systemwas placed vertically through the water column supported by a buoy 450 m from shore, from 2 m above to53 m below the water surface (just above the local seafloor), covering the entire seasonal upper layer (themetalimnion had an average depth of 20 m). Temperature profiles were recorded every 5 min. The May toJuly 2012 data set allowed quantitative investigation of the thermal morphology dynamics, including objec-tive definitions of key locations within the metalimnion based on the temperature depth profile and its firstand 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 metalimniondepth 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 calcu-lated by integrating the temperature profiles. The vertically integrated apparent heat content was seen tovary by 50% in a few hours. These fluctuations were not correlated to the atmospheric heat fluxes, nor tothe 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 byradiation, with no direct correlation to the frequency of radiation and wind in the lake. This suggests thatthe source of the momentary heat flux is lateral advection due to internal waves (with no direct relation tothe diurnal cycle). In practice, it is shown that snap-shot profiles of the Dead Sea as obtained with standardthermal profilers will not represent the seasonal typical status in terms of heat content of the upper layer.

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