Deep desert aquifers as an archive for Mid- to Late Pleistocene hydroclimate: An example from the southeastern Mediterranean.

Many efforts have been made to illuminate the nature of past hydroclimates in semi-arid and arid regions, where current and future shifts in water availability have enormous consequences on human subsistence. Deep desert aquifers, where groundwater is stored for prolonged periods, might serve as a direct record of major paleo-recharge events. To date, groundwater-based paleoclimate reconstructions have mainly focused on a relatively narrow timescale (up to ∼40 kyr), limited by the relatively short half-life of the widely used radiocarbon (5.73 kyr). Here we demonstrate the usage of deep regional aquifers in the arid southeastern Mediterranean as a hydroclimate archive for earlier Mid-to-Late Pleistocene epochs. State-of-the-art dating tools, primarily the 81Kr radioisotope (t1/2 = 229 kyr), were combined with other atmosphere-derived tracers to illuminate the impact of four distinguishable wetter episodes over the past 400 kyr, with differences in climatic conditions and paleo-recharge locations. Variations in stable water isotope composition suggest moisture transport from more proximal (Mediterranean) and distal (Atlantic) sources to different parts of the region at distinct times. Large variability in the computed noble gas-based recharge temperature (NGT), ranging ~15-30 °C, cannot be explained by climate variations solely, and points to different recharge pathways, including geothermal heating in the deep unsaturated zone and recharge from high-elevation (colder) regions. The obtained groundwater record complements and enhances the interpretation of other terrestrial archives in the arid region, including a contribution of valuable information regarding the moisture source origin as reflected in the deuterium-excess values, which is unattainable from the common practice analysis of calcitic cave deposits. We conclude that similar applications in other deep (hundred-m-order) regional groundwater systems (e.g., the Sahara desert aquifers) can significantly advance our understanding of long-term (up to 1 Myr) paleo-hydroclimate in arid regions, including places where no terrestrial remnants, such as cave, lake, and spring sediments, are available.

Massive-Scale Dissolution, Conveyance, and Disposal of Dead Sea Potash Industry Halite Waste.

The Dead Sea (DS) potash industry halite waste accumulation rate is estimated at 0.2 m year-1, across 140 km2 of evaporation ponds in Israel and Jordan, totaling ∼28 million m3 year-1. As accommodation in the southern DS basin space is nearly exhausted, it is planned in Israel to dredge newly precipitated salt and convey it in a solid state to the northern DS basin by constructing a 30 km conveyor to the northern DS basin where the salt will be disposed. Concerns regarding the environmental impacts of such massive undertaking led to the examination of alternative solutions. The alternative discussed in the paper, which takes into account the estimated halite waste volumes in Jordan as well, examines the feasibility for dissolution of the dredged halite and its transport in a dissolved state and disposal in the DS by seawater (SW) or desalination reject brine (RB) from the Red Sea─Dead Sea Project (RSDSP), if constructed. Results show that the high halite solubility in SW/RB and rapid dissolution kinetics are sufficiently fast to dispose of the dredged halite with the discussed volumes of the RSDSP. Thermodynamic calculations are presented to show that precipitation dynamics following the mixing of the Na+-Cl--loaded SW/RB with the DS brine could be controlled to avoid outsalting at the mixing point in the DS.