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Recent studies of seawater compositions of some ‘non-traditional’ stable isotope systems, such as 26Mg/24Mg (reported as δ26Mg), have uncovered great potential to enhance our understanding of the past Earth. However, differences between existing oceanic records, and the scarcity of such record data, currently limit this approach. Thus, new archives for these isotope compositions, independent of the commonly-used carbonate archives, are required. Marine evaporites have been widely used to decipher the chemical and ‘traditional’ isotope compositions (such as 87Sr/86Sr, S isotopes, etc.) history of past oceans. In several studies [1, 2, 3], we investigate the Mg isotope composition of different evaporite minerals and brines, presenting two examples: an experimental study of marine Mg-K (potash) salts and an in-situ study of pore-water and sediment from a modern sabkha environment.The δ26Mg value of marine-derived brines and precipitating Mg-salts during the evaporation path of seawater were determined experimentally, up to a degree of evaporation (DE) of ca. 500. The sequence of Mg-salts included epsomite, kainite, carnallite, kieserite, and bischofite. We identify a mineral-dependent Mg isotope fractionation in both directions (i.e., some minerals are enriched in 26Mg relative to the brine, whereas others are depleted in 26Mg). Due to the precipitation of multi-mineral assemblages having opposite fractionations, the δ26Mg value of the brines changed only slightly throughout the evaporation path, despite considerable Mg removal.The Mg concentrations and δ26Mg values of all pore-water samples extracted from the sabkha sediments are elevated relative to modern seawater and the closest evaporitic lagoon. Evaporation (DE range between 6.5 and 11), mixing, and Mg loss into dolomite are the three processes that determine the Mg concentration. Dolomite formation and mixing with ‘fresh’ lagoon water determine the δ26Mg values of pore-water. This shows that, in such evaporitic environments, the evaporitic minerals may precipitate from an already altered solution (with δ26Mg different than seawater), leading to a somewhat more complicated interpretation of the ancient record.Based on these data, we suggest that by taking into account the complexity of evaporitic systems, the δ26Mg values of evaporites preserved in the geological record may be used to 1) quantify geochemical processes that fractionate Mg-isotopes within the basin, such as dolomite formation; and 2) complete the secular variations curve of the marine δ26Mg record using well-established evaporitic sequences. [1] Shalev N., Lazar B., Halicz L., and Gavrieli I. (2021), The Mg isotope signature of marine Mg-evaporites. Geochimica et Cosmochimica Acta, 301, 30-47, https://doi.org/10.1016/j.gca.2021.02.032.[2] Shalev N., Bontognali T.R.R. and Vance D. (2021), Sabkha Dolomite as an Archive for the Magnesium Isotope Composition of Seawater. Geology, 49 (3), 253–257, https://doi.org/10.1130/G47973.1.[3] Shalev N., Lazar B., Köbberich M., Halicz L., and Gavrieli I. (2018), The chemical evolution of brine and Mg-K-salts along the course of extreme evaporation of seawater - An experimental study. Geochimica et Cosmochimica Acta, 241, 164-179, https://doi.org/10.1016/j.gca.2018.09.003.

Hydrological restriction from the Atlantic Ocean and a negative freshwater balance transformed the Mediterranean Sea into a giant saline basin during the Messinian Salinity Crisis (MSC) (5.97 – 5.33 million years ago). After more than 50 years of research, it is still unclear if the deposition of nearly one million km3 of evaporite salts during this event was accompanied by a major (≥ 1.5 km) drawdown of Mediterranean sea level; and if halite deposition occurred only during this drawdown event, or also in a filled Mediterranean connected to the Atlantic.We present evidence based on the chlorine stable isotope composition of halite for a sea level drawdown of 2 km in the eastern Mediterranean during the final stages of deposition of the Mediterranean halite layer. This is the largest sea level drop ever reported from the geological record and implies a short (~20 kyr), but nearly complete hydrological disconnection of the Mediterranean from the Atlantic. About half of the halite volume in the eastern Mediterranean was deposited during this drawdown event. Scant chlorine isotope data from the western Mediterranean, together with new estimates of western basin halite volume, suggest that the complete western halite deposit accumulated during the drawdown event. This mode of halite deposition - termed “evaporative drawdown” - had been already proposed as an evolution of the “deep-basin, shallow-water” scenario for the MSC (Hsü et al., 1973).Chlorine isotopes indicate that the remaining half of the eastern Mediterranean halite volume accumulated prior to the drawdown, in a filled Mediterranean that received a continuous input of Atlantic waters. This halite accumulation phase lasted about 70 kyr and was driven by a restricted - but not fully blocked - outflow of deep western Mediterranean waters to the Atlantic. This model of halite deposition corresponds to the “deep-basin, deep-water” scenario for the MSC (Schmaltz, 1969). In summary, our results show that both the “deep-basin, deep-water” and the “deep-basin, shallow-water” modes of halite accumulation took place during the MSC, and that the complete deep-basin MSC halite deposit accumulated in less than 100 kyr. Hsu, K., Ryan, W. & Cita, M. Late Miocene Desiccation of Mediterranean. Nature 242, 240–244 (1973).Schmalz, R. F. Deep-water evaporite deposition, a genetic model. American Association of Petroleum Geologists Bulletin53, 798–823 (1969).

The rapid retreat of the Dead Sea during the past four decades led to the exposure of unique structures of massive gypsum along the shores. Many of these structures (having the shape of mounds) are associated with the activity of Ein Qedem-type saline springs that currently discharge Ca-chloride brine to the lake. Field observations, radiocarbon dating of aragonite (within the gypsum mounds) that yield ancient ages, and the narrow range of δ34S and δ18O values ( δ 34 S gyp : 14.1–16.9‰; δ 18 O gyp : 14.4–16.5‰) indicates that the formation of the gypsum structures is related to the mixing of brines: the Dead Sea brine and ancient (last glacial) Ein Qedem type brine. These are Ca-chloride brines having different salinities and sulfur concentrations that satisfy conditions of an outsalting process whereby supersaturation of gypsum is attained by the mixing of these two brines in the offshore shallow water environment. Thermodynamic calculations (using the PHREEQC software) show that gypsum outsalting occurred when both brines were enriched with sulfate as compared to the present. The Ein-Qedem brine had higher sulfate when subjected to less intensive bacterial sulfate reduction. The Dead Sea was characterized by higher sulfate concentrations during intervals of low lake stands. The conditions of higher sulfate concentrations and enhanced discharge of the saline springs occurred repeatedly in the Dead Sea between ∼6.6 to 0.6 ka and were intermittent with periods of enhanced supply of sulfate to the lake by freshwaters.

The sources and fate of radiocarbon (14C) in the Dead Sea hypersaline solution are evaluated with 14C measurements in organic debris and primary aragonite collected from exposures of the Holocene Ze’elim Formation. The reservoir age (RA) is defined as the difference between the radiocarbon age of the aragonite at time of its precipitation (representing lakeʼs dissolved inorganic carbon [DIC]) and the age of contemporaneous organic debris (representing atmospheric radiocarbon). Evaluation of the data for the past 6000 yr from Dead Sea sediments reveal that the lakeʼs RA decreased from 2890 yr at 6 cal kyr BP to 2300 yr at present. The RA lies at ~2400 yr during the past 3000 yr, when the lake was characterized by continuous deposition of primary aragonite, which implies a continuous supply of freshwater-bicarbonate into the lake. This process reflects the overall stability of the hydrological-climate conditions in the lakeʼs watershed during the late Holocene where bicarbonate originated from dissolution of the surface cover in the watershed that was transported to the Dead Sea by the freshwater runoff. An excellent correlation (R2=0.98) exists between aragonite ages and contemporaneous organic debris, allowing the estimation of ages of various primary deposits where organic debris are not available.

The hypersaline Dead Sea and its sediments are natural laboratories for studying extremophile microorganism habitat response to environmental change. In modern times, increased freshwater runoff to the lake surface waters resulted in stratification and dilution of the upper water column followed by microbial blooms. However, whether these events facilitated a microbial response in the deep lake and sediments is obscure. Here we investigate archived evidence of microbial processes and changing regional hydroclimate conditions by reconstructing deep Dead Sea chemical compositions from pore fluid major ion concentration and stable S, O, and C isotopes, together with lipid biomarkers preserved in the hypersaline deep Dead Sea ICDP-drilled core sediments dating to the early Holocene (ca. 10,000 years BP). Following a significant negative lake water balance resulting in salt layer deposits at the start of the Holocene, there was a general period of positive net water balance at 9500-8300 years BP. The pore fluid isotopic composition of sulfate exhibit evidence of intensified microbial sulfate reduction, where both δ34S and δ18O of sulfate show a sharp increase from estimated base values of 15.0‰ and 13.9‰ to 40.2‰ and 20.4‰, respectively, and a δ34S vs. δ18O slope of 0.26. The presence of the n-C17 alkane biomarker in the sediments suggests an increase of cyanobacteria or phytoplankton contribution to the bulk organic matter that reached the deepest parts of the Dead Sea. Although hydrologically disconnected, both the Mediterranean Sea and the Dead Sea microbial ecosystems responded to increased freshwater runoff during the early Holocene, with the former depositing the organic-rich sapropel 1 layer due to anoxic water column conditions. In the Dead Sea prolonged positive net water balance facilitated primary production and algal blooms in the upper waters and intensified microbial sulfate reduction in the hypolimnion and/or at the sediment-brine interface.

Morphology and crystal size distribution of gypsum precipitated from a wide range of hypersaline compositions (ionic strength = 5.5–10 m) were studied in batch experiments containing mixtures of Ca...

Marine Mg-evaporites are a small oceanic sink of magnesium, precipitating only from extremely evaporated brines. The isotopic composition of Mg in seawater, δ26Mgseawater, has recently been shown to be an effective tool for reconstructing the Mg budget of the modern and past oceans. However, estimations of the Mg isotope fractionation between the Mg-evaporites and their precipitating solution are required for full quantification of the isotope effect of the evaporitic sink on δ26Mgseawater, as well as for utilizing ancient evaporitic sequences as an archive for past δ26Mgseawater. Here, we estimate the Mg isotope fractionation between Mg-evaporites and modern marine-derived brine along the course of seawater evaporation, up to degree evaporation of >200. The sequence of Mg-salts included epsomite (MgSO4·7H2O), kainite (KMgClSO4·3H2O), carnallite (KMgCl3·6H2O), kieserite (MgSO4·H2O) and bischofite (MgCl2·6H2O). The following isotope fractionation values, either negative or positive, were calculated from the isotope difference between the salt and its precipitating brine, and from the evolution of δ26Mg in the brine throughout the evaporation: Δcarnallite-brine = +1.1‰, Δepsomite-brine = +0.59‰, Δbischofite-brine = +0.33‰, Δkieserite-brine = −0.2‰ and Δkainite-brine = −1.3‰. Magnesium isotopic compositions determined on minerals from different ages in the geological record corroborate well these results. Due to precipitation of multi-mineral assemblages having isotope fractionation values of opposing signs, the δ26Mg value of the brine changes only slightly (50%). The isotope fractionations are shown to correlate with the number of water molecules coordinated to the Mg2+ and with Mg-O bond length in the mineral lattice. Given these isotope fractionations, it is calculated that a volume of 0.4 · 106–0.8 · 106 Km3 of a mono-mineral assemblage of kainite or carnallite needs to precipitate in order to change seawater δ26Mg by only 0.1‰. This huge volume is by far larger than the volume of these minerals known to date in the global geological record. Therefore, it is concluded that the impact of Mg-evaporites formation on δ26Mgseawater has been insignificant since the Proterozoic. The results of this study suggest that the Mg isotopic composition of Mg-evaporites preserved in the geological record of evaporitic basins may be used to: 1) quantify geochemical processes that fractionate Mg-isotopes within these basins, such as dolomitization; and 2) complete the secular variations curve of the marine δ26Mg record using basins with well-established evaporitic sequences., Geochimica et Cosmochimica Acta, 301, ISSN:0016-7037, ISSN:1872-9533

The geochemistry of groundwater surrounding the Dead Sea reflects mixing between different water bodies that occupied the Dead Sea basin and fresh groundwater flowing from the highlands to the basin. The distribution of various geochemical parameters is affected by changes in the lake level, including natural fluctuations and the present lake level drop. This chapter deals with different aspects of groundwater flow mechanisms in the coastal aquifer of the Dead Sea and their relationship with the groundwater geochemistry. Dead Sea water circulation in the coastal aquifer occurs during a steady-state lake level but also persists during lake level drop. This interaction between the Dead Sea water and the sediments removes Ba, U, and 226Ra and contributes Fe, Mn, and short-lived Ra isotopes to the Dead Sea. 14C and tritium values in the Dead Sea groundwaters are affected by mixing with fresh water and between brines that occupied the Dead Sea Rift during different times. In addition to the inorganic water–rock interaction between the Dead Sea groundwater and the sediments, DIC δ13C, and S and O isotopes in dissolved SO4 suggest that methane oxidation coupled with bacterial sulfate reduction is taking place. On longer time-scales (glacial-interglacial), lake water penetrates the aquifer sediments during high stands and discharge back to the Dead Sea during low stands. The Ein-Qedem thermal springs composition suggests that the brine penetrated to the aquifer during the last glacial when the lake level was high and is discharging now back into the Dead Sea from a depth of about 1000 m.

The Messinian salinity crisis (MSC) is an extreme event in Earth history during which a salt giant (>1×106 km3) accumulated on the Mediterranean seafloor within ~640 kyrs. The Messinian salt giant was formed about 6 million years ago when the restriction of water exchanges between the Atlantic Ocean and the Mediterranean Sea turned the Mediterranean into an enormous saline basin. After more than 40 years of research, the timing and the depositional environments of shallow ( The Levant Basin is the only deep Mediterranean basin where the entire Messinian section has been penetrated by wells tied to high resolution 3D seismic surveys. Here we present two studies challenging the desiccation paradigm dominating the MSC scientific literature for more than 40 years. The first study focuses on the nearly flat top erosion surface (TES) that truncates a basinward-tilted Messinian evaporitic succession. This truncation is commonly interpreted to be the result of subaerial erosion at the end of the MSC. However, based on high resolution seismic surveys and wireline logs, we show that (1) the TES is actually an intra-Messinian truncation surface (IMTS) located ~100 m below the Messinian-Zanclean boundary; (2) the topmost, post-truncation, Messinian unit is very different from the underlying salt deposits and consists mostly of shale, sand, and anhydrite showing typical 87Sr/86Sr values and fauna assemblages from stage 3; and (3) the flat IMTS is a dissolution surface related to significant dilution and stratification of the water column during the transition from stage 2 to stage 3. We suggest that dissolution occurred upslope where salt rocks at the seabed were exposed to the upper diluted brine, while downslope the salt rocks were preserved because submerged in the deeper halite-saturated layer. The model, which requires a stratified water column, is inconsistent with a complete desiccation of the eastern Mediterranean Sea. The second study focuses on the onset of the Messinian salinity crisis in the deep Eastern Mediterranean basin. Biostratigraphy and astronomical tuning of the Messinian pre-salt succession in the Levant Basin allows for the first time the reconstruction of a detailed chronology of the MSC events in deep setting and their correlation with marginal records that supports the CIESM (2008) 3-stage model. Our main conclusions are (1) MSC events were synchronous across marginal and deep basins, (2) MSC onset in deep basins occurred at 5.97 Ma, (3) only foraminifera-barren, evaporite-free shales accumulated in deep settings between 5.97 and 5.60 Ma, (4) deep evaporites (sulfate and halite) deposition started later, at 5.60 Ma. The wide synchrony of events implies inter-sub-basin connection during the whole salinity crisis and is not compatible with large sea-level fall that would have separated the eastern and western basins producing diachronic processes.

A novel quantitative assessment of late Holocene precipitation in the Levant is presented, including mean and variance of annual precipitation and their trends. A stochastic framework was utilized and allowed, possibly for the first time, linking high-quality, reconstructed rises/declines in Dead Sea levels with precipitation trends in its watershed. We determined the change in mean annual precipitation for 12 specific intervals over the past 4500 yr, concluding that: (1) the twentieth century was substantially wetter than most of the late Holocene; (2) a representative reference value of mean annual precipitation is 75% of the present-day parameter; (3) during the late Holocene, mean annual precipitation ranged between −17 and +66% of the reference value (−37 to +25% of present-day conditions); (4) the driest intervals were 1500–1200 BC and AD 755–890, and the wettest intervals were 2500–2460 BC, 130–40 BC, AD 350–490, and AD 1770–1940; (5) lake-level rises and declines probably occurred in response to trends in precipitation means and are less likely to occur when precipitation mean is constant; (6) average trends in mean annual precipitation during intervals of ≥200 yr did not exceed 15mm per decade. The precipitation trends probably reflect shifts in eastern Mediterranean cyclone tracks.

Extreme evaporation experiments of modern seawater, up to a degree of evaporation (DE) of 870 on Li scale and brine density of 1.40 g·ml−1 were conducted under controlled semi-natural conditions. This DE is well within the bischofite facies and, to the best of our knowledge, is the highest experimental DE ever reported. During the experiments, brine temperature varied between ∼20 °C and ∼40 °C with few excursions to higher temperatures, thereby demonstrating the effect of temperature on the precipitating mineral assemblages. Results were compared to a thermodynamic simulation of the evaporation experiment at 25 °C, based on the Harvie-Moller-Weare activity coefficients correction. The relative amounts of the precipitated minerals were evaluated from the bulk chemical composition of the collected precipitates, applying a Li-based methodology for subtracting the contribution of the brine adsorbed on the precipitated salts. The following minerals were identified during the evaporation experiments: halite (NaCl), epsomite (MgSO4∙7H2O), kainite (KMgClSO4∙3H2O), carnallite (MgKCl3∙6H2O), kieserite (MgSO4∙H2O) and bischofite (MgCl2∙6H2O). The precipitation of the Mg-salts was accompanied by continuous halite precipitation up to DE of ∼170. The experimental results are in good agreement with literature experimental data, available up to DE = 98, and generally follow the thermodynamic calculations, thereby supporting both the established methodology of the experiments and the simulation parameters and assumptions. Minor differences between the experiments and the thermodynamic calculation are mainly due to temperature variations. The experiments suggest that, at warmer temperatures (∼50 °C), kainite and bischofite precipitate instead of kieserite, which precipitates to a greater extent at lower temperatures (25–30 °C). The presence of organic matter (OM) in the brine was found to reduce the evaporation rate and the final DE at which evaporation ceased, but not to significantly affect the chemical evolution of the brine. The detailed systematic data-set presented here is useful for both geochemical and applied purposes. For example, it can be used as a reference for reconstructing the evolution of ancient marine-derived brines, using evaporitic sequences far beyond the halite facies. Hence, this study provides new insights on the formation of such evaporitic minerals and opens the way for further studies on these highly soluble evaporitic sequences as clues to the chemical composition of the ancient oceans.

Ca-chloride brines have circulated between the lakes and the adjacent aquifers throughout the history of the Dead Sea lacustrine-hydrology system. The Ein-Qedem (EQ) hydrothermal saline springs system discharging at the western shores of the modern Dead Sea is the modern manifestation of this essential and continuous process. The EQ springs comprise the most significant source of Ca-chloride brine that currently discharges into the lake. The chemical composition of EQ brine has remained virtually uniform during the past ca. 40 yr, indicating that the brine represents a large groundwater reservoir. The EQ brine evolved from ancient Ca-chloride brine that occupied the tectonic depression of the Dead Sea Basin during the Quaternary. During this period, the composition of lake's brine was affected by mixing with freshwater and formation of primary minerals. Based on chronological and geochemical data, we argue that the EQ brine comprises the epilimnetic solution of last glacial Lake Lisan that penetrated and circulated through the adjacent Judea Group aquifer. 14C and 81Kr dating indicates recharge ages spanning the time interval of ∼40–20 ka, coinciding with the period when the lake reached its highest stand (of ∼ 200 ± 30 m below msl, at ∼31–17.4 ka) and maintained a stable layered (stratified) configuration for a period of several ten thousand years. The presented evidence suggests that the circulation of the Ca-chloride brine involves penetration into the aquifer during high stands (EQ brine recharge) and its discharge back into the lake during the modern low stands (∼400 to 430 m below msl). Accordingly, the mechanism of brine circulation between the lake and the marginal aquifers is related to the long-term hydro-climate history of the Dead Sea basin and its vicinity.

"Man-made" or unconventional freshwater, like desalinated seawater or reclaimed effluents, is increasingly introduced into regional water cycles in arid or semi-arid countries. We show that the breakthrough of reverse osmosis-derived freshwater in the largely engineered water cycle of the greater Tel Aviv region (Dan Region) has profoundly changed previous isotope fingerprints. This new component can be traced throughout the system, from the drinking water supply, through sewage, treated effluents, and artificially recharged groundwater at the largest Soil-Aquifer Treatment system in the Middle East (Shafdan) collecting all the Dan region sewage. The arrival of the new water type (desalinated seawater) in 2007 and its predominance since 2010 constitutes an unplanned, large-scale, long-term tracer test and the monitoring of the breakthrough of desalination-specific fingerprints in the aquifer system of Shafdan allowed to get new insights on the water and solute flow and behavior in engineered groundwater systems. Our approach provides an investigation tool for the urban water cycle, allowing estimating the contribution of diverse freshwater sources, and an environmental tracing method for better constraining the long-term behavior and confinement of aquifer systems with managed recharge.

The chemical composition and δ 37 Cl of pore fluids from the ICDP core drilled in the deepest floor of the terminal and hypersaline Dead Sea, and halites from the adjacent Mount Sedom salt diapir, are used to establish the dynamics of halite precipitation and dissolution during the last interglacial and glacial periods. Between ∼132 and 116 thousand years ago (ka) halites precipitated in the lake resulting in the expulsion of Na+ and Cl− from the residual solution. Over 50% of the Cl− reservoir was removed, resulting in a decrease in the Na/Cl ratio from 0.57 to 0.19. This process was accompanied by a decrease in δ 37 Cl values in the precipitating halites and the associated residual Cl− in the lake. The observed decrease fits a Rayleigh distillation curve with a fractionation factor of Δ(NaCl–Dead Sea solution) = +0.32‰ (±0.12) determined in the present study. This behavior implies negligible contribution of external sources of Cl− to the lake during the main peak of the last interglacial, MIS5e. Subsequently, during the last glacial (ca. 117 to 17 ka) dissolution of halite took place, the Na+ and Cl− inventory were replenished, accompanied by an increase in Na/Cl from 0.21 to 0.55 and in the δ 37 Cl values from −0.46‰ to −0.12‰. While the lake underwent significant dilution during that time, the decrease in salinity was somewhat suppressed by the dissolution of the halite which was mostly derived from Mount Sedom salt diapir.

The main obstacle in the formulation of a quantitative rate-model for mineral precipitation is the absence of a rigorous method for coupling nucleation and growth processes. In order to link both processes, we conducted a series of batch experiments in which gypsum nucleation was followed by crystal growth. Experiments were carried out using various stirring methods in several batch vessels made of different materials. In the experiments, the initial degree of supersaturation of the solution with respect to gypsum (Ωgyp) was set between 1.58 and 1.82. Under these conditions, heterogeneous nucleation is the dominant nucleation mode. Based on changes in SO42− concentration with time, the induction time of gypsum nucleation and the following rate of crystal growth were calculated for each experiment. The induction time (6–104 h) was found to be a function of the vessel material, while the rates of crystal growth, which varied over three orders of magnitude, were strongly affected by the stirring speed and its mode (i.e. rocking, shaking, magnetic stirrer, and magnetic impeller). The SO42− concentration data were then used to formulate a forward model that couples the simple rate laws for nucleation and crystal growth of gypsum into a single kinetic model. Accordingly, the obtained rate law is based on classical nucleation theory and heterogeneous crystal growth.

National exercises are an excellent opportunity to practice earthquake preparedness. Such exercises can greatly benefit from productive communication between the civil protection agencies (CPs) and the earth sciences community (SC). The challenge of the scientists in this interaction is to properly formulate their message and convey their perspective in a manner understandable to the responsible emergency agencies. On October 2012, Israel held its first national earthquake emergency exercise (TP6) that examined the response of the country’s systems at large to an Mw ~ 7 earthquake. The exercise greatly benefited from brain storming meetings between the CPs and researchers from the Geological Survey of Israel (GSI) that were held prior to the drill. These helped in choosing the earthquake scenario and establish the concept of the exercise. Geological hazards and damage maps, including numerous discrete events, were prepared in advance with the HAZUS Multi-Hazard Loss Estimation software and were conveyed to the drilled authorities during the exercise. The exercise also benefitted from close collaboration between researchers of FEMA and the GSI. During the drill, the GSI and its relevant scientists practiced the preparation and transfer of the relevant material to the decision makers in “real time.” The drill provided the following lessons: (1) In real time, the damage maps should be delivered by earthquake researchers, thereby helping the CP agencies to grasp the information. (2) Damage maps should be prepared in advance and accessibly stored by the CP agencies for a range of probable scenarios. (3) Damage maps based on dot density that represent number of buildings damaged, number of casualties and weight of debris were found to be the most comprehensible when presenting the scope of the damage. The lessons learned from the collaboration between the CP and SC in TP6 provide an excellent example for optimal planning of national earthquake exercises, thereby helping in minimizing the anticipated impact of destructive earthquakes.

This paper describes the design and experimental validation of a novel flow-through reactor system conceived for experimental studies to determine the kinetics and thermodynamics of mineral precipitation and dissolution in environmental conditions relevant to CO2 geological storage. The experimental system was designed to work under a confining pressure of up to 150 bar, temperature up to 150 °C and corrosive conditions. The unique design allows the injection of precise amounts of liquid CO2 into the reactor while avoiding the formation of multiple CO2 phases. The modular design enables the in-situ measurement of pH using a pressure resistant in-line probe and electronic gauges which record pressure and temperature at multiple points. The system enables the user to withdraw liquid samples without disturbing the experimental conditions in the reactor. Customized computer software was developed and connected to the system to provide automatic data-logging capabilities, remote process control and the ability to partially shut-down the system in case of safety issues.

We present a basin-wide correlation of the pre-evaporitic succession across the deep Levant basin, based on integrated bio- and cyclostratigraphy. The onset of Messinian salinity crisis (MSC) can be placed in all studied wells where foraminifers suddenly disappear and normal marine calcareous nannofossils are replaced by opportunistic assemblages. These changes mark the base of the Foraminifers Barren Interval (FBI), a 10s-of-m-thick (below seismic resolution), evaporite-free, shale unit that records the entire duration of the first stage. Moving towards the basin margin the FBI is progressively truncated on top by the Messinian erosional surface (MES), a regional-scale discontinuity sealed by a thin clastic evaporite units overlain by thick halite deposits. Our results confirm previous hypothesis suggesting that the crisis started in deep- as well as in shallow-water settings at 5.97 Ma and pointing to a synchronous onset of the MSC but diachronous deposition of evaporites. During stage 1 of the crisis, coeval with gypsum deposition in marginal basins, the salinity in deep basins progressively increased (with possible oxygen reduction) hindering the life of marine organisms. Then, at 5.60 Ma, when salinity in deep basins exceeded halite saturation, massive halite precipitation started, and a nearly 2-km-thick salt sequence accumulated in deep basins within a short period of 60 kyr. At that time (stage 2), sedimentation rate jumped by an order of magnitude reaching a few cm/yr. Similar sedimentation rates are inferred for the Realmonte salt mine (Sicily) and observed in the modern Dead Sea and artificial salinas.

The response of hypersaline terminal lakes to negative water balance was investigated by studying brines evaporating to extreme salinities in sinkholes along the western coast of the Dead Sea and during on-site evaporation experiments of the Dead Sea brine. Density and temperature were determined in the field and all samples were analyzed for their major and a few minor solutes. The activity of H 2 O ( a H2O ) in the brines was calculated, and the degree of evaporation (DE) was established using Sr 2+ as a conservative solute. The relations between density and water activity were obtained by polynomial regression, and the relation between the lake’s volume and level was established using Hall’s (1996) hypsographic model for the Dead Sea basin. Relating the results to the modern, long-term relative humidity (RH) over the basin shows that (a) The lowermost attainable level of a terminal lake undergoing evaporation with no inflow is dictated by the median RH; this level represents equilibrium between the brine's a H2O and RH; (b) Small, saline water bodies with high surface to volume ratios (A/V), such as the hypersaline brines in the sinkholes, are very sensitive to short term changes in RH; in these, the brines' a H2O closely follows the seasonal changes; (c) the level decline of the Dead Sea due to evaporation under present climatic conditions and assuming no inflow to the lake may continue down to 516–537 m below mean sea level (bmsl), corresponding to a water activity range of 0.46–0.39 in its brine, in equilibrium with the overlying relative air humidity; this suggests that the lake level cannot drop more than ∼100 m from its present level; and (d) The maximum RH values that existed over the precursor lake of the Dead Sea (Lake Lisan) during geologically reconstructed minima levels can be similarly calculated.

Chemical precipitation of CaCO 3 occurs in diverse marine and lacustrine environments. In the hypersaline Ca-chloride lakes that have been occupying the Dead Sea basin since the late Pleistocene, CaCO 3 precipitated, mostly as aragonite. The aragonite sediments precipitated mainly during periods of high lake level stands as a result of mixing of bicarbonate-rich freshwater runoff with Dead Sea brine, that is Ca-rich and have high Mg/Ca ratio. During periods of arid conditions with limited freshwater inflow, water level declined, salinity increased and gypsum and halite became the dominant evaporitic minerals to precipitate. The present study investigates the carbon cycle of the Dead Sea under the current limited water and bicarbonate supply to the brine, representing periods of extremely arid conditions. The decrease of inflows to the Dead Sea in recent years stems mainly from diversion of freshwater from the drainage basin and results in dramatic water level decline and massive halite precipitation. During 2013–2014, bi-monthly depth profiles of total alkalinity, dissolved inorganic carbon (DIC) and its isotopic composition (δ 13 C) were conducted in the Dead Sea, from surface down to the bottom of the lake (290 m). Mass balance calculations conducted for the period 1993–2013 show that while inventories of conservative ions such as Mg 2+ remained constant, the net DIC inventory of the lake decreased by ∼10%. DIC supply to the lake during this period, however, amounted to ∼10% of lake’s inventory indicating that during 20 years, the lake lost ∼20% of its 1993s inventory. Compilation of historical data with our data shows that during the past two decades the lake's low DIC (∼1 mmol kg −1 ) and very high PCO 2 (1800 ppm V) remained relatively constant, suggesting that a quasi-steady-state situation prevails. In spite of the surprisingly stable DIC and CO 2 concentrations, during this 20 year period δ 13 C DIC increased significantly, from 1.4‰ to 2.7‰. An isotopic mass balance calculation together with the high PCO 2 of the brine show that during that period the lake lost about 3.7 · 10 10 moles of DIC, of which ∼60% by CO 2 degassing and ∼40% by aragonite precipitation. The deviation from the common 1:1 CO 2 :CaCO 3 ratio in most aqueous systems is facilitated by the dominance of the borate alkalinity of the Dead Sea. Nucleation and crystal growth experiments suggest that throughout this time the Dead Sea remained supersaturated with respect to aragonite, a situation facilitated by combination of slow nucleation rates and absence of growth surfaces. The very high PCO 2 of the Dead Sea is maintained by the low CO 2 piston velocity of the brine, calculated to be only ∼4.5 m yr −1 , more than an order of magnitude slower than seawater value.

Pore fluids extracted from a 456 m sediment core, recovered within the framework of a multinational and International Continental Scientific Drilling Program (ICDP) co-sponsored effort at the bottom of the terminal Dead Sea, recorded the chemical variations in the deep lake over the past 220 k.y. Mg 2+ and Br – were shown to be conservative in the pore fluids, increasing in concentration during interglacial periods, diluting during glacials, and providing excellent proxies for deep lake net water balance changes. Furthermore, the Na/Cl ratio recorded the process of halite precipitation and dissolution induced by these hydrological changes. Mg 2+ and Br – records follow a glacial-interglacial pattern, such as observed in atmospheric CO 2 concentrations and global sea-surface temperatures, albeit with a phase offset. At the end of the last interglacial (ca. 116 ka), there is a delay in onset of dilution of the deep lake, most likely due to the limnological transition from holomictic to meromictic conditions. The increase in deep lake concentrations at Last Glacial Termination I is delayed as a result of freshwater input into the deep lake during the cooler Younger Dryas period. There is a persistent relationship between precipitation in the watershed and North Atlantic sea-surface temperatures, similar to conditions observed over the past instrumental record. Deviations from the long-term trends occurred during interglacial periods, Marine Isotope Stages MIS 5e and MIS 1, when the deep Dead Sea was significantly diluted, and coincided with Mediterranean sapropel layers S5 and S1.

δ88/86Sr data published over the last few years suggest that continental waters are enriched with 88Sr as compared to the rocks in their drainage basins. In an attempt to understand this phenomenon, this study established the fractionation in the 88Sr/86Sr ratio during precipitation of continental carbonates (i.e., carbonates precipitated on land from surface, pedogenic, or ground waters), and evaluated the contribution of this process to the 88Sr-enrichment in rivers. For this, stable and radiogenic Sr isotopes (88Sr, 87Sr and 86Sr) were measured in calcite samples and their precipitating waters collected in various continental environments, such as soil, cave, streams and groundwater. The results indicate that continental carbonates are 88Sr-depleted relative to their precipitating waters, placing them as one of the most 88Sr-depleted reservoirs on earth. The average difference in δ88/86Sr values between waters and solid CaCO3 (tufas or speleothems) that they precipitate is Δ carb-water = − 0.218 ± 0.014 ‰ (1SD). An even larger fractionation ( e carb-water = − 0.285 ± 0.02 ‰ ) was measured in groundwater with particularly high carbonate-alkalinity and high carbonate precipitation rate that depleted ∼65% of the Sr in the groundwater, resulting in substantial 88Sr-enrichment in the residual dissolved Sr ( δ Sr 88 / 86 = 0.656 ‰ ). Results also suggest that pedogenic carbonate precipitation in soil profile removes 50–85% of the Sr from the recharging soil–water, thereby increasing the δ88/86Sr value of the soil-water from ∼ 0.18 ‰ to 0.3 ‰ – 0.6 ‰ . Similar 88Sr-enrichment was observed in drip water from a karst cave. A maximum removal flux of Sr into continental carbonates of about 20 Gmol(Sr)⋅y−1 is required to yield the reported 88Sr-enrichment in global rivers ( δ Sr 88 / 86 = 0.32 ‰ ) relative to their rock sources when using the fractionation factor derived in this study, Δ carb-water = − 0.218 ‰ , and the published δ88/86Sr composition of marine carbonates of 0.16‰. This surprisingly large flux requires that ∼40% of the originally weathered Sr should co-precipitate with continental carbonates. This calculation may suggest that CaCO3 precipitation is a significant mechanism in the continental Sr cycle. It is possible however that other mechanisms such as Sr uptake by plants or incongruent weathering of silicates, could also contribute to the riverine 88Sr-enrichment. Alternatively, the average δ88/86Sr value of marine carbonate rock sections undergoing weathering is higher than suggested in current literature. It is concluded that additional δ88/86Sr data on marine carbonate rock sections should be collected to resolve the enigma of the high value of riverine δ88/86Sr.

Solutions of different chemical compositions will precipitate gypsum crystals with different morphology. The dependence of gypsum morphology on the chemical composition can therefore be a tool for interpreting the paleo-chemistry and environments of solutions from which gypsum in the geological record precipitated. In addition, the morphology of the gypsum that will precipitate in the Dead Sea once the Red Sea-Dead Sea conduit is built will determine if the crystals will remain in suspension in the surface brine, thereby leading to “whitening” of the lake. Despite its importance, little is known about the impact of the different parameters on the morphology of gypsum precipitated from natural brines. In the present study we conducted single point batch experiments with mixtures of Dead Sea - Red Sea brines and utilized image processing techniques to study the morphology of the gypsum that precipitated from different solution compositions at different degrees of oversaturation. The results from the first data set towards the understanding of what controls the morphology of gypsum while providing a preliminary tool for the forecast of the future of the Dead Sea are presented here.

The rate of salt dissolution is an important factor in many natural processes including the formation of sinkholes along the western shores of the Dead Sea (DS). The formation of these sinkholes which appear during the last 20 years in ever increasing numbers (~ 7000), is attributed to salt dissolution in the subsurface, by saline groundwater. However the rate of salt dissolution in the subsurface, by DS brines diluted with groundwater, is not known and is the main purpose of this study. Whereas most previous experimental studies on halite dissolution rates were performed in pure NaCl solutions and in fresh water, this study focuses on natural DS brines. The chemical composition of the DS is complex and besides NaCl includes high concentrations of Br and of Mg, Ca, and K chlorides. The present study is a laboratory attempt to assess the dissolution rates of natural halite in dilutions of DS brines, 10% to 90% by volume, under stirring and under no stirring conditions. The dissolution rates have been estimated by first order kinetics in the stirred runs and by derivatives of power best fits in the unstirred runs. In quiescent conditions, at 10 min the dissolution rates exhibit a very close to linear, inverse relationship to the degree of dilution and ranged between 12.2 mg/cm2 min in 10% DS and 1.4 mg/cm2 min in 90% DS. With stirring, in dilutions of 50% DS, the dissolution rates were about twice larger than without stirring: at 10 min they were 13 mg/cm2 min vs. 5.8 mg/cm2 min, respectively. The dissolution rates in stirred runs of DS dilutions appear to be about threefold slower than those reported in pure NaCl solutions of similar salinity and in a quite similar experimental setup. This divergence emphasizes the importance of measuring halite dissolution rates in natural solutions. The measured dissolution rates, in both stirred and non stirred solutions, decrease exponentially as the degree of saturation vs. halite, DSH, becomes larger, i.e. as saturation is approached. The exponential decrease in non stirred solutions is much faster. The results of this study will enable future studies to determine the rate of sinkhole formation in the Dead Sea area and other locations where halite salt is dissolved.

Deep saline aquifers are among the preferred potential repositories for carbon dioxide Geological Storage (CGS). Modeling the interaction of the injected CO2 with the brine is essential for proper planning of CGS, including avoidance of local precipitation of minerals such as sulfates which may clog the injection borehole and decrease the injectivity of the surrounding rock mass. In the present study gypsum solubility at various molal concentrations of dissolved CO2 at pressures of up to 100 bar was investigated. A series of semi-batch experiments was performed in a novel flow-through reactor system, designed to withstand high pressures, temperatures and corrosion. Solubilities attained in the experiments match (within a 3% uncertainty) the new PHREEQC v.3′s predictions (Appelo et al., 2014) in which pressure and dissolved CO2 concentrations are two of the new variables. Accordingly, gypsum solubility was found to increase as pressure rises and to decrease as CO2 concentration ascends.

An ancient, brackish, anoxic, and relatively hot water body exists within the Yarqon-Tanninim Aquifer in southern Israel. A hydrogeological-geochemical conceptual model is presented, whereby the low water quality is the outcome of three conditions that are met simultaneously: (1) Presence of an organic-rich unit with low permeability that overlies and confines the aquifer; the confining unit contains perched horizons with relatively saline water. (2) Local phreatic/roofed conditions within the aquifer that enable seepage of the organic-rich brackish water from above. The oxidation of the dissolved organic matter in the seeping water consumes the dissolved oxygen and continues through bacterial sulfate reduction, with H2S as a product. These exothermic reactions result in some heating. (3) The seeping water comprises a relatively large portion of the water volume. In the presented case study, the latter condition first developed in the Late Pleistocene following climate change, which led to a dramatic decline in recharge. Consequently, water flow in the local basin has nearly ceased, as evident by old water ages, specific isotopic composition, and nearly equipotential water levels. The continuous seepage from above into the almost stagnant water body has resulted in degraded water quality. Seepages of organic-rich brackish water exist at other sites throughout the aquifer but have limited impact on the salinity and redox conditions due to the dynamic water flow, which flushes the seeping water, that is, the third condition is not met. The coexistence of the above three conditions may explain the development of anoxic and saline groundwater in other aquifers worldwide.

Gypsum (CaSO4·2H2O) is the most common sulfate mineral on Earth and is also found on Mars. It is an evaporitic mineral that predominantly precipitates from brines. In addition to its precipitation in natural environments, gypsum also forms an undesired scale in many industrial processes that utilize or produce brines. Thus, better insights into gypsum formation can contribute to the understanding of natural processes, as well as improving industrial practices. Subsequently, the thermodynamics, nucleation and crystal growth mechanisms and kinetics, and how these factors shape the morphology of gypsum have been widely studied. Over the last decade, the precipitation of gypsum under saline and hypersaline conditions has been the focus of several studies. However, to date, most of the thermodynamic data are derived from experiments with artificial solutions that have limited background electrolytes and have Ca2+/SO42− ratios that are similar to the 1:1 ratio in the mineral. Moreover, direct observations of the nucleation and growth processes of gypsum are still derived from experimental settings that can be described as having low ionic strength. Thus, the mechanisms of gypsum precipitation under conditions from which the mineral precipitates in many natural environments and industrial processes are still less well known. The present review focuses on the precipitation of gypsum from a range of aspects. Special attention is given to brines. The effects of ionic strength, brine composition, and temperature on the thermodynamic settings are broadly discussed. The mechanisms and rates of gypsum nucleation and growth, and the effect the thermodynamic properties of the brine have on these processes is demonstrated by recent microscopic and macroscopic observations. The morphology and size distribution of gypsum crystals precipitation is examined in the light of the precipitation processes that shape these properties. Finally, the present review highlights discrepancies between microscopic and macroscopic observations, and studies carried out under low and high ionic strengths. The special challenges posed by experiments with brines are also discussed. Thus, while this review covers contemporary literature, it also outlines further research that is required in order to improve our understanding of gypsum precipitation in natural environments and industrial settings.

The effect of phosphonate-based antiscalant on the precipitation kinetics of gypsum under the hyper-saline solutions relevant to the Red Sea-Dead Sea desalination project was studied. Batch experiments were carried out to determine the effect on the induction times and rates of nucleation and gypsum crystal growth. A wide range of ionic strength (5.5–9 m), pH (6.33–6.91) and oversaturation with respect to the mineral (1.69 ≤ Ωgypsum ≤ 2.11) were covered in the experiments. Induction times in solutions that contained the antiscalant were longer by about 20–500% compared to solutions with a similar composition that did not contain the antiscalant. In the presence of the antiscalant fewer crystals precipitated that were larger in size. The specific surface area of the crystals that precipitated in solutions that contained the antiscalant were smaller in about 20–500% than those that precipitated in solutions that did not contain the antiscalant, and the relative specific surface area was in agreement with the induction time. We conclude that increased interfacial tension in the presence of the antiscalant, retards nucleation and reduces the surface area available for growth. Subsequent rates of crystal growth were impervious to the presence of the antiscalant.

The freshwater of the Judea Group aquifer that recharges on the crest of the Judea and Samria Mountain ridge flows east and west, defining two groundwater basins. At the foothills of both basins the freshwater encounters ancient saline or brackish water. The mode of interaction between the two water bodies within each basin is different, although both eventually discharge as brackish spring system. We describe these systems and identify the source of the higher salinity end members.

The main comment by Charrach (2019) on the Levy et al. (2019) paper is that the Sedom salt diapir could not have been a source for sulfate to Lake Lisan (last glacial Dead Sea), arguing that the dissolution of the salt diapir started following the onset of the Holocene Dead Sea. We refute the comment for the following reasons: (1) The nature of the unconformity between the salt diapir and the overlying sediments indicates that it emerged from the surface prior to the last glacial and was submerged in Lake Lisan; (2) The formation of a ∼40 m thick layer of dissolution residue (caprock) sitting on an almost flat dissolution unconformity surface (salt mirror) suggests that 600 m-to-800 m thick layer of Sedom Fm. was dissolved under phreatic settings. During most of the Holocene, the diapir has been subjected to vadose type dissolution which formed karst cutting through the caprock, salt mirror and rock-salt below; (3) Based on the Charrach (2019) hypothesis, estimated diapir uplift rates during the early Holocene would have required to be an order of magnitude higher than the measured and calculated rates for the present and Holocene, respectively, provided by other studies; (4) Na/Ca ratios from primary aragonite in the Lisan Fm. found at the vicinity of Mt. Sedom, as well as Na/Cl ratios, saturation state of halite and isotopic composition of chloride in the pore fluids from the deep Dead Sea Deep Drilling Project (DSDDP) core 5017-1-A, suggests significant dissolution of halite from Mt. Sedom into Lake Lisan. In addition to halite, dissolution of the next abundant evaporite mineral, anhydrite, resulted in mobilization of sulfate to the lake.

We document and analyze the rapid development of a real-time karst system within the subsurface salt layers of the Ze'elim Fan, Dead Sea, Israel by a multidisciplinary study that combines interferometric synthetic aperture radar and light detection and ranging measurements, sinkhole mapping, time-lapse camera monitoring, groundwater level measurements and chemical and isotopic analyses of surface runoff and groundwater. The >1 m/yr drop of Dead Sea water level and the subsequent change in the adjacent groundwater system since the 1960s resulted in flushing of the coastal aquifer by fresh groundwater, subsurface salt dissolution, gradual land subsidence and formation of sinkholes. Since 2010 this process accelerated dramatically as flash floods at the Ze'elim Fan were drained by newly formed sinkholes. During and immediately after these flood events the dissolution rates of the subsurface salt layer increased dramatically, the overlying ground surface subsided, a large number of sinkholes developed over short time periods (hours to days), and salt-saturated water resurged downstream. Groundwater flow velocities increased by more than 2 orders of magnitudes compared to previously measured velocities along the Dead Sea. The process is self-accelerating as salt dissolution enhances subsidence and sinkhole formation, which in turn increase the ponding areas of flood water and generate additional draining conduits to the subsurface. The rapid terrain response is predominantly due to the highly soluble salt. It is enhanced by the shallow depth of the salt layer, the low competence of the newly exposed unconsolidated overburden and the moderate topographic gradients of the Ze'elim Fan.

The pH of aqueous environments is determined by the dominant buffer systems of the water, defined operationally as total alkalinity (TA). The major buffer systems in the modern ocean are carbonic and boric acids of which the species bicarbonate, carbonate and borate make up about 77%, 19% and 4% of the TA, respectively. During the course of seawater evaporation (e.g. lagoons) the residual brine loses considerable portion of the dissolved inorganic carbon (DIC) and carbonate alkalinity (CA) already at the early stages of evaporation. DIC and CA decrease due to massive precipitation of CaCO3, while total boron (TB) increases conservatively, turning borate to the dominant alkalinity species in marine derived brines. In the present work we assess the apparent dissociation constant value of boric acid ( K B ′ ) in saline and hypersaline waters, using the Dead Sea (DS) as a case study. We explain the DS low pH (∼6.3) and the effect of the boric and carbonic acid p K ′ -s on the behavior of the brine's buffer system, including the pH increase that results from brine dilution. The K B ′ in DS was estimated from TB, TA, DIC and pH data measured in this study and early empirical data on artificial DS brines containing just carbonic acid. The K B ′ value was corroborated by Pitzer ion interaction model calculations using PHREEQC thermodynamic code applied to the chemical composition of the DS. Our results show that K B ′ increases considerably with the brine's ionic strength, reaching in the DS to a factor of 100 higher than in “mean” seawater. Based on theoretical calculations and analyses of other natural brines it is suggested that brines' composition is a major factor in determining the K B ′ value and in turn the pH of such brines. We show that the higher the proportion of divalent cations in the brine the higher the dissociation constants of the weak acids (presumably due to formation of complexes). The low pH of the Dead Sea is accordingly explained by its extremely high ionic strength (TDS = 348 g/L) and the dominance of the divalent cation, Mg2+. Other natural hyper-saline brines with high concentration of divalent cations such as Kunteyi Lake in China and Don-Juan Pond in Antarctica follow the same general pattern. In contrast, the high pH of soda lakes results not only from their high TA but also by the dominance of the monovalent cation, Na+. Our study emphasizes the strong control of brine composition on p K B ′ and pH. These factors should be taken into consideration when reconstructing past and present environmental evaporitic environments.

Nitrate contamination of shallow aquifers poses a major challenge in the development of sustainable agriculture, particularly in (semi-)arid regions, where groundwater is also used as potable water. In this study we estimate the relative contribution of the various nitrate sources contaminating the shallow aquifers underlying agricultural fields in the extremely arid region of the Central Arava Valley (CAV), southern Israel. The estimates are based on a chemical and isotopic mixing-reaction model describing the evolution of the δ18ONO3 and δ15NNO3 isotopic compositions from the sources to the aquifer. The model indicates that all fertilizers used in the agricultural fields: synthetic NO 3 − , synthetic NH 4 + and manure, contaminate the CAV groundwater with nitrate. In most of CAV groundwaters, the contribution of each fertilizer to the groundwater contamination is relative to its proportion in the fertilization scheme of the cultivated fields. Two exceptions of this general observation were found: 1. One field showed a direct nitrate contamination from a “leaking” sewage reservoir, as indicated by its exceptionally high δ15NNO3 value that reached 9.2‰; and 2. A very shallow alluvial aquifer, recharged by winter floods and not by the irrigation water, showed no nitrate isotopic “fingerprint” of manure, which is applied to the cultivated fields only during summer. Groundwater nitrate contamination is actuated by infiltration of irrigation water, which in addition underwent salinization as a result of evapo-transpiration in the cultivated fields. Based on the relatively uniform and depleted groundwater δ18OH2O compositions and the depleted δ18ONO3 values, within the possible range of fertilizers-derived nitrate as deduced by the model, the water-loss in the cultivated fields is transpiration-controlled. The isotope mixing-reaction model used here to identify the major nitrate contamination sources maybe used to help design a sustainable cultivation management strategy in similar arid regions. It can also be used to assess the fertilization efficiency and the relative impact of each fertilizer type. Such models may be particularly useful in evaluating highly heterogeneous and complicated aquifer systems, for which the formulation of absolute water and nitrate mass balances are impossible.

pH in natural waters is commonly measured with a pH glass combination electrode. This method, however, yields accurate results only in low ionic strength solutions whereas its application to high ionic strength solutions "suffers" from bias introduced mainly by liquid junction potential. The determination of pH in high ionic strength solutions was conducted with dual ion selective electrodes systems that are liquid-junction-free. In the present work, we provide a method for determining the pH over a very wide range of ionic strengths using a conventional glass pH electrode. The method is based on calibrating the signal of the conventional combination glass electrode against the signal of a liquid-junction-free H+|Cl- electrode pair. The calibration was conducted on the Dead Sea brine and its dilutions with deionized water. It yielded a pH correction function of ionic strength, ΔpH(I), that allows evaluating the pH of Dead Sea brines and other brines of similar compositions using a regular glass combination pH electrode, over an ionic strength range of ~1-10 m. A pH measurement of the Dead Sea brine with a conventional combination glass electrode yielded a value of 6.26 ± 0.04 after applying the ΔpH(I) correction function, identical to the 6.27 ± 0.03 value obtained by the liquid-junction-free H+|Cl- electrode pair.

The geological evolution of the unique Dead Sea Ca-chloride brine has been the focus of many research efforts for several decades. These studies relied on the information obtained from sedimentary exposures of the marginal terraces of the modern Dead Sea, mostly documenting the history of the surface lake brine during its high stands periods. The present study is the first attempt to establish the history of the deepest part of the lake by direct measurements of the chemical and isotopic composition of pore-fluids that were extracted from cores drilled during 2011 by ICDP in the deep basin of the Dead Sea at water depth of 300 m. The vertical profiles of chloride (Cl−) and oxygen isotopes ( δ O 18 ) in pore brines reveal a substantial decrease in the salinity of the hyper-saline lake during the last glacial and particularly during MIS2 ( ∼ 31 – 17 ka BP ). The Cl− concentration of the deep brine in the lake decreased gradually, reaching a minimum of less than 2/3 of its present value while the δ O 18 increased to maximum of ∼ 7 ‰ (3‰ higher than today). The low Cl− indicates significant dilution of the bottom water mass (hypolimnion) of Lake Lisan (the last glacial predecessor of the modern Dead Sea) during its highest stand period. Beforehand, during the interglacial and later during the post-glacial and the Holocene the Cl− concentrations and δ O 18 values were similar to those of the modern Dead Sea. The slow dilution of the deep Ca-chloride brine was caused probably by continuous turbulent mixing of the hypolimnion with the less saline high δ O 18 epilimnetic brine, across the epilimnion/hypolimnion interface (EHI). While the increase in δ O 18 during the salinity decrease of Lake Lisan is a result of “normal” evaporation of the less saline epilimnetic brine, the post-glacial δ O 18 decrease (contemporaneous with salinity increase) is attributed to the “reversed” behavior of δ O 18 during evaporation of high salinity brine. During the long freshening period the hypolimnion was enriched with dissolved sulfate supplied by the freshwater and transported by the turbulent mixing across the EHI until reaching gypsum saturation that commenced massive gypsum deposition at the end of this period, when full overturn took place.

Deep saline aquifers are among the preferred potential repositories for carbon dioxide geological storage (CGS). Modeling the interaction of the injected CO2 with the brine is essential for proper planning of CGS, including avoidance of local precipitation of minerals such as sulfates, which may clog the injection borehole and decrease the injectivity of the surrounding rock mass. In the present study gypsum crystal growth kinetics at the pressure range of 1–100 bar and with the addition of different molal concentrations of dissolved CO2 was investigated. A series of flow-through experiments were performed in a novel reactor system, designed to withstand high pressures, temperatures and corrosion. Gypsum growth rate was found to decrease with ascending pressure and increase with rising dissolved CO2 concentrations. Yet, separating the overall effect of these variables to their impact on the thermodynamics of the solution (i.e. super saturation) and on the reaction kinetics, reveal a very complex effect on the rate coefficient (khet). While due to the kinetic effect, the rate coefficient mostly decreases with rising dissolved CO2 concentrations, it has a second order polynomial behavior while pressure ascends. This implies that under the studied pressures and dissolved CO2 concentrations the thermodynamic is the main dominant parameter which governs the overall growth rate. It is suggested that both the thermodynamic and the kinetic effects arise from the respective dependence of the supersaturation of the solution and the rate coefficient (khet) on the solubility.

The stable isotope composition of strontium (the ratio 88 Sr/ 86 Sr expressed as δ 88/86 Sr) showed significant fractionation in mountain soils of the Judea Highland. In order to understand this phenomenon, we studied the elemental composition and the stable and radiogenic Sr isotopic composition in soil transects conducted from semi-arid (desert fringe) to wetter (Mediterranean) climate zones. These transects were selected because the degree of soil leaching depends on the amount of precipitation and the permeability of the underlying bedrock. These soils are the pedogenic products of leaching of the accumulated desert dust and the underlying carbonate bedrocks resulting in, among others, enrichment of the residual soils in Al-clays. A clear negative correlation was found between the δ 88/86 Sr and Al 2 O 3 (Al-clay content) values of the soils, the high δ 88/86 Sr-low Al 2 O 3 being the dust end-member. This preliminary study demonstrates the feasibility of using stable 88 Sr- 86 Sr isotopes as tracers of terrestrial weathering processes.

Manganese enrichment is common in various sedimentary environments, e.g. deep ocean floor, shallow sedimentary environments where the overlying water column is oxic and phreatic aquifers, in which the Mn aquatic geochemistry is controlled by redox conditions. In many cases, aquifers recharged by organic-rich waters contain high amounts of dissolved Mn 2+ that was mobilized from sedimentary Mn-oxides during microbial oxidation of the organic matter under low-oxygen conditions. Thus, the identification and quantification of the processes controlling Mn mobilization and speciation is of great practical importance as a geochemical tool for sustainable management of aquifers. This study uses column experiments to quantify the role of adsorption and precipitation in retarding Mn 2+ mobilization in sandy aquifers under low-oxygen conditions. Flow-through columns were packed with pristine sandy sediment and were recharged by low-oxygen artificial solutions containing different Mn 2+ concentrations. Outflow solutions from the column experiments were analyzed and simulated using a Mn 2+ transport-reaction model. The results were used to demonstrate the importance of adsorption on Mn mobilization in three different aquifers. The experimental data showed that adsorption of Mn 2+ on the column solids was the main control on the Mn 2+ breakthrough behavior. Nevertheless, up to 20% of the Mn that entered the experimental columns was precipitated as MnCO 3 . The rate of MnCO 3 precipitation ( k p = 0.04 h −1 ) was found to be ∼3 orders of magnitude slower than the rate of Mn 2+ adsorption ( k a = 10–200 h −1 ). Given the slow mineral-precipitation kinetics, the water flow rate is critical in determining the potential of MnCO 3 precipitation in immobilizing Mn within an aquifer. A scale-up of the Mn retardation time found in the column experiments to natural aquifer conditions, suggests that adsorption is responsible for the prolonged retardation of Mn 2+ observed in three different sandy aquifers. An important practical conclusion of this study is that the environmental response to perturbation in the hydro-geochemical regime of an aquifer might be delayed for several decades.

Gypsum nucleation kinetics from a wide range of chemical compositions (1.45 2+ / SO 4 2 - I = 2.5–10 m) and saturation state with respect to gypsum ( Ω gyp = 1.07–8.4) were examined in batch experiments containing mixtures of Ca 2+ -rich Dead Sea brine and SO 4 2 - -rich seawater with or without addition of extra Na 2 SO 4 and CaCl 2 ·2H 2 O. The induction times attained in the present study were compiled together with literature values from experiments carried out under significantly different conditions (synthetic NaCl solutions; I = 0.09–6.3 m; Ca 2+ / SO 4 2 - = 1; Ω gyp :1.59–7.76). Despite the variability in the experimental solutions, a single rate law based on classic nucleation theory was formulated to describe the induction times from more than 80 experiments: log T ind = log 1 3.17 · C s · exp - 7.08 ln 2 Ω + 0.072 · C s · exp - 1.426 ln 2 Ω where T ind is the induction time, C s is the solubility of gypsum and Ω is the saturation state with respect to gypsum. The rate law provides T ind for gypsum precipitation from aqueous solutions at 25 °C, containing no synthetic antiscalants or catalysts, within a 95% confidence interval within a factor of 5. Based on this rate law, we show that at present most of the precipitation of gypsum from the Dead Sea brine occurs following significant evaporation in the industrial evaporation ponds and not in the Dead Sea itself. Whereas T ind in Dead Sea brines is very long (on the order of 3 years), the evaporation of brine in the industrial ponds leads to increased Ω values, and thus to short T ind in the order of a few days. However, if seawater or reject brine from seawater desalinization will be introduced to the Dead Sea to restore its declining level, T ind will be significantly reduced and gypsum nucleation and precipitation will occur. For evaporated seawater, the proposed rate law predicts that even though saturation is obtained when seawater is evaporated by a factor of 2.8, gypsum will nucleate at reasonable times (few years) only when seawater are evaporated by a factor of ∼3.3.

Gypsum precipitation kinetics were examined from a wide range of chemical compositions ( 11 Ca 2 + / SO 4 2 - 115 ) , ionic strengths (4.75–10 m) and saturation state with respect to gypsum (1.16–1.74) in seeded batch experiments of mixtures of Ca2+-rich Dead Sea brine and SO 4 2 - -rich seawater. Despite the variability in the experimental solutions, a single general rate law was formulated to describe the heterogeneous precipitation rate of gypsum from these mixtures: Rate het = k 1 · ( Ω 0.5 - 1 ) 10 + k 2 · ( Ω 0.5 - 1 ) 2 mol m - 2 s - 1 , where k1 and k2 are heterogeneous rate coefficients (mol s−1 m−2) that vary as a function of the solution compositions, and is the saturation state with respect to gypsum. It is suggested that two parallel mechanisms control the heterogeneous precipitation rate. Under closer-to-equilibrium conditions, the reaction is dominated by a mechanism best described as a 2nd order reaction with respect to Ω0.5 − 1, which fits to the predictions of both the Burton Cabrera and Frank (BCF) crystal growth theory ( Burton et al., 1951 ) and other layer-by-layer growth mechanisms ( Goto and Ridge, 1967 , Van Rosmalen et al., 1981 , Bosbach and Rammensee, 1994 ). Under further-away-from-equilibrium conditions, the reaction is dominated by an apparent 10th order reaction. A conceptual model for gypsum growth kinetics is presented. The model is based on the 2nd order kinetic coefficients determined in the present study and data from the literature and is valid under a wide range of ionic strengths and Ca 2 + / SO 4 2 - ratios. According to this model, the integration of SO 4 2 - to kinks on the surface of the growing crystals is the rate-limiting step in the precipitation reaction. At ionic strengths above 8.5 m the precipitation rate of gypsum is enhanced, possibly due to the formation of CaSO 4 ° ion pairs and/or a decrease in hydration frequencies.

Summary This research describes a field study and laboratory simulations of the geochemical evolution of groundwater following a recharge of effluent into aquifers. The study was conducted in the soil aquifer treatment (SAT) system of the Shafdan sewage reclamation plant, Israel. The SAT system recharges secondary effluent into the calcareous sandstone sediments of the Israeli Coastal Aquifer as a tertiary treatment. The reclaimed effluent is recovered ca. 500 m off the recharge basin and is used for unlimited irrigation. The laboratory simulations in which effluent was pumped through experimental columns packed with pristine Shafdan sediment showed that the chemical composition of the outflowing water was controlled mainly by cation exchange and CaCO3 dissolution. Na+, K+ and Mg2+ were adsorbed and Ca2+ was desorbed during the initial stage of recharge. The equilibrium distribution of the adsorbed cations was: Ca2+ ∼ 60%, Mg2+ ∼ 20%, and Na+ and K+ ∼ 10% each. The Ca2+ in the Shafdan production wells and in the experimental columns outflow (∼5 meq L−1) was always higher than the Ca2+ in the recharged effluent (∼3.5 meq L−1), indicating continuous CaCO3 dissolution. This study demonstrates that besides mixing, a suite of geochemical processes should be considered when assessing groundwater quality following artificial recharge of aquifers.

Abrupt arid events in the post-glacial (∼17.4–10 kyr BP) Dead Sea Basin (DSB) were recorded by significant lake level declines in Lake Lisan and massive deposition of gypsum and salt. Between 17.4 and 16 kyr cal BP, the lake level dropped from its late MIS2 stand of ∼260 m below mean sea level (m bmsl) to ∼330 m bmsl, depositing a thick sequence of gypsum. Between ∼16 and 15 kyr cal BP the lake level recovered but dropped abruptly again at ∼14 kyr cal BP to below 465 m bmsl, probably the lowest late Pleistocene stand. Then, between 13 and 11 kyr cal BP (the Younger Dryas time interval) the lake rose above 400 m bmsl and declined at 11–10 kyr cal BP depositing a thick sequence of salt. The abrupt lake level drops and salt deposition coincided with times of ice and meltwater discharges into the North Atlantic (NA): Heinrich event (H1) and Meltwater Pulse – MWP1a. Similar coincidence between ice and meltwater discharges in the NA (e.g., H-events) and arid episodes at the Levant was recorded during the colder last glacial period, demonstrating a persistent effect of the North Atlantic hydrology and sea ice advances on the Levant climate. The climatically “turmoil” post-glacial period was accompanied by significant developments in human culture: the collapse of the Natufian culture during the Bolling–Allerod and the rise of the Pre-Pottery Neolithic cultures, PPN A and B around the 11–10 kyr cal BP salt deposition interval marking the initiation of the “Neolithic revolution” in the region.

The Dead Sea brine is supersaturated with respect to gypsum ( Ω = 1.42). Laboratory experiments and evaluation of historical data show that gypsum nucleation and crystal growth kinetics from Dead Sea brine are both slower in comparison with solutions at a similar degree of supersaturation. The slow kinetics of gypsum precipitation in the Dead Sea brine is mainly attributed to the low solubility of gypsum which is due to the high Ca 2+ /SO 4 2− molar ratio (115), high salinity (∼280 g/kg) and to Na + inhibition. Experiments with various clay minerals (montmorillonite, kaolinite) indicate that these minerals do not serve as crystallization seeds. In contrast, calcite and aragonite which contain traces of gypsum impurities do prompt precipitation of gypsum but at a considerable slower rate than with pure gypsum. This implies that transportation inflow of clay minerals, calcite and local crystallization of minerals in the Dead Sea does not prompt significant heterogeneous precipitation of gypsum. Based on historical analyses of the Dead Sea, it is shown that over the last decades, as inflows to the lake decreased and its salinity increased, gypsum continuously precipitated from the brine. The increasing salinity and Ca 2+ /SO 4 2− ratio, which results from the precipitation of gypsum, lead to even slower kinetics of nucleation and crystal growth, which resulted in an increasing degree of supersaturation with respect to gypsum. Therefore, we predict that as the salinity of the Dead Sea brine continues to increase (accompanied by Dead Sea water level decline), although gypsum will continuously precipitate, the degree of supersaturation will increase furthermore due to progressively slower kinetics.

The chemical composition of groundwater in the Jordan Valley, along the section between the Sea of Galilee and the Dead Sea, is investigated in order to evaluate the origin of the groundwater resources and, in particular, to elucidate the role of deep brines on the chemical composition of the regional groundwater resources in the Jordan Valley. Samples were collected from shallow groundwater in research boreholes on two sites in the northern and southern parts of the Jordan Valley, adjacent to the Jordan River. Data is also compiled from previous published studies. Geochemical data (e.g., Br/Cl, Na/Cl and SO4/Cl ratios) and B, O, Sr and S isotopic compositions are used to define groundwater groups, to map their distribution in the Jordan valley, and to evaluate their origin. The combined geochemical tools enabled the delineation of three major sources of solutes that differentially affect the quality of groundwater in the Jordan Valley: (1) flow and mixing with hypersaline brines with high Br/Cl (>2 × 10−3) and low Na/Cl (

Recent geochemical and hydrological findings show that the water quality of the base flow of the Lower Jordan River, between the Sea of Galilee and the Dead Sea, is dependent upon the ratio between surface water flow and groundwater discharge. Using water quality data, mass-balance calculations, and actual flow-rate measurements, possible management scenarios for the Lower Jordan River and their potential affects on its salinity are investigated. The predicted scenarios reveal that implementation of some elements of the Israel–Jordan peace treaty will have negative effects on the Jordan River water salinity. It is predicted that removal of sewage effluents dumped into the river (∼13 MCM/a) will significantly reduce the river water’s flow and increase the relative proportion of the saline groundwater flux into the river. Under this scenario, the Cl content of the river at its southern point (Abdalla Bridge) will rise to almost 7000 mg/L during the summer. In contrast, removal of all the saline water (16.5 MCM/a) that is artificially discharged into the Lower Jordan River will significantly reduce its Cl concentration, to levels of 650–2600 and 3000–3500 mg/L in the northern and southern areas of the Lower Jordan River, respectively. However, because the removal of either the sewage effluents or the saline water will decrease the river’s discharge to a level that could potentially cause river desiccation during the summer months, other water sources must be allocated to preserve in-stream flow needs and hence the river’s ecosystem.