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 resolution by means of fiber optics temperature sensing. The aim of the research was to explore the dynamics of the metalimnion, including: i) short period fluctuations of the depth of thermocline, i.e. - seich, and ii) seasonal sharpening of the metalimnion and the role to double diffusion flux. A 55 m long profiling system was placed vertically through the water column supported by a buoy with spatial resolution of 18 cm. The profiler covered the entire seasonal upper layer, including the upper mixed layer (upper ~20 m), the metalimnion and the hypolimnion. Temperature profiles were recorded every 5 min along the stratification period from MAY to DEC 2012. The analysis of the temperature profiles was based on defining objective key locations within the metalimnion based on the temperature depth profile and its first and second depth derivatives and then analyzing of the time series. We present thermal stratification dynamics in the scale of i) a few hours, which is related to internal waves at the water surface and along the metalimnion interface, i.e. - seich,  and ii) in the seasonal scale, where we observed  metalimnion sharpening associated with double diffusion. The thermocline depth fluctuations reach 10 m offsets within a few hours. Synchronous level measurements reveal ~ 1 cm offsets of the sea level within the same time period. We found strong anti-correlation of the defined metalimnion locations to measured sea level fluctuations with amplitudes that match the density ratio of the water layers (e.g. – a level rise of 1 cm is correlated with deepening of the thermocline by ~5 m). In the seasonal scale, the temperature depth profile is sharpening, starting from a gradual round temperature profile, to distinct staircases, through the merging of the staircases until a single sharp step was achieved in late summer. This sharpening process occurred synchronously with heat and salt fluxes between the strata, and pointed a typical double diffusion diapycnal flux in the lake.

PhD research under the supervision of: Brenner Steve Geography and environment department