Dr. Ittai Gavrieli
Geological Survey of Israel

Topic: The Dead Sea: Past present and future

Academic host: Catherine Fontana

Abstract: The Dead Sea (DS), the lowest place on the continental Earth (currently at ~ 438 m below sea level), is a hyper-saline terminal lake with a unique composition that evolved from evaporation of seawater which transgressed into the Dead Sea Rift Valley in the early Pliocene, followed by precipitation of evaporites and intensive water rock interactions. Since then, the DS basin has been occupied by a series of water bodies of different characteristics and areal extents. The sediments deposited from these lakes are excellent archives of the climatic history of the Levant region as well as their limnological evolution. Pore water extracted from sediments recovered by the ICDP Dead Sea Deep Drilling Project show that even during high stands and positive water balance (mostly glacial periods), the lakes were stratified but remained hypersaline. During prolonged periods of negative water balance (inter-glacial) and lake level drops the water column underwent overturn and the meromictic regime changed to a monomictic one.  Thick halite intervals recovered by the cores show evidence for severe arid conditions in the eastern Mediterranean during the last three inter-glacials. These halite layers as well as the dominant alternating aragonite and detrital laminae and gypsum and mud layers have been correlated to global and local climatic events. 
Modern diversion of freshwater from the drainage basin of the DS, mostly by Israel and Jordan, as well as evaporation of the brine in ponds of the DS chemical industries, has resulted in water level drop of more than 40 m since the 1960s. Currently water level continues to drop at an unprecedented rate of over 1 m/yr, representing annual water deficient of ~750·106 m3. The massive anthropogenic intervention in the water balance of the lake has resulted in the onset in 1980s of halite precipitation from the brine, which continues to date. Groundwater level of the coastal aquifer, and the elevation of the fresh/saline groundwater interface within it, decline in response to the falling level of the lake. This has led to wide-spread dissolution of a 10,000 year old halite layer in the subsurface, resulting in the development of thousands of sinkholes along the shores of the lake, in effect making them unsafe and the shorelines un-accessible. Incisions of deep canyons in the newly exposed mud flats and alluvial sediments enhance erosion and jeopardize and damage the highway that runs along the lake. 
The desiccation of the DS and the associated environmental impacts has led to outcry to “save the Dead Sea”, which culminated in the proposed Red Sea - Dead Sea project to convey reject brine from desalination to the DS, agreed upon by Israel and Jordan. The aim of this project would be 2-fold: 1) Provide badly needed potable water to Jordan 2) Slow down, stabilize or even raise the water level by discharging the reject brine to the DS. However, our studies indicate that mixing of the reject brine with the DS brine will have its own environmental impacts, including: 1) Dilution and change in composition of the surface water if discharge volume exceeds 400·106 m3 per year. 2) Potential “whitening” of the lake due to spontaneous precipitation of gypsum upon mixing. 3) Massive blooming of endemic dunaliella and archaea in the diluted epilimnion, enabled by the dilution of the brine and supply of phosphate derived from anstiscalants in the reject brine. This blooming will color the lake red and change its appearance. The pro and cons of the environmental impacts as well as the political and social significance of the said project are at the center of the discussion of the future of the Dead Sea.