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Physical mechanisms which control water budget and sea level in the Dead Sea |
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Before the 20 century, the Dead Sea (DS) level underwent natural fluctuations from about 380 m to 420 m below Mediterranean Sea level (bmsl). These fluctuations were associated with inter-annual variability of precipitation in the Levant region (Kushnir and Stein, 2010). Since the early 1960’s, the anthropogenic reduction in the Dead Sea runoff outweighed its natural variability because Israel, Jordan and Syria (Fig. 1) increased the water consumption intensively. Moreover, Israel and Jordan use the Dead Sea water for the production of minerals, contributing to the water deficit. Until 1978 the Dead Sea consisted of a large and deep northern basin and a smaller and shallower southern basin (Neev and Emery, 1967). Following the recession of the water level, the entire southern basin would have dried up. However, dikes were erected to transform the southern basin into evaporation ponds for mineral production (Anati 1997). In the northern basin after the extremely rainy winters 1992-1993 the sea level dropped with rate approximately 1 m/year (Gertman and Hecht, 2002). It brought dramatic degradation of the coast regions including intensive development of sinkholes (Frumkin et al., 2011). During the dried years after 1996 evaporation rates was 1.1-1.2 m/year (Lensky et al., 2005). While the evaporation rate in the saline Dead Sea is very high, it is still lower than in the neighboring fresh Sea of Galilee, 1.4-1.5 m/year (Rimmer et al., 2009). The relatively low evaporation rate of DS is due to its high salinity (Krumgalz et al., 2000). There are several projections of equilibrium of the sea level, which can be achieved in about 500 years in case of fixation of water budget on the current level (Yechieli et al., 1998; Krumgalz et al., 2000; Asmar and Ergenzinger, 2002). The basis of these projection is reverse proportion of evaporation rate and salinity (Asmar and Ergenzinger, 2002). Therefore, an accurate simulation of vertical mixing, which defines salinity of upper mixed layer (UML) hence sea surface salinity modulating the evaporation rate, is crucial for the Dead Sea. However, research carried out in the Atlantic indicated, that the vertical flux of salinity, its surface value, and hence the rate of evaporation could depend on the structure of the underlying water column. The main characteristics of the water column in this respect is the existence or non-existence of the step-like structures (SLS). The aim of this project is to test the hypothesis that the observed SLS in the DS (Arnon et al. ,2016 ) has a significant effect on the rate of evaporation and hence the drop of the sea level. The methodology is based on the use of 2 contrasting numerical ocean models: one including and one excluding the development of the SLS. The outcome of the simulation would assess the necessity of the inclusion of the SLS into predictive models of the DS, despite the increased computational cost. In order to achieve this, a numerical modelling will be carried out to address the following objectives: 1. Collation of historical observational data in the region in order to prepare initial and boundary conditions for modelling. 2. Numerical simulation of the changes in the Dead Sea level using a model capable of representing the step-like structures. 3. Numerical simulations of the changes in the Dead Sea level by a model without step-like structures. 4. Scientific analysis of results in order to determine the effect of step-like structures on the rate of sea level drop. |
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The major results so far:
Poster and Abstract presented on the General Assembly of European Geoscienes Union (Vienna, 2018). |
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