Saline Deep Water Research Articles

Origin of groundwater salinity (current seawater vs. saline deep water) in a coastal karst aquifer based on Sr and Cl isotopes. Case study of the La Clape massif (southern France)

In this study a typical coastal karst aquifer, developed in lower Cretaceous limestones, on the western Mediterranean seashore (La Clape massif, southern France) was investigated. A combination of geochemical and isotopic approaches was used to investigate the origin of salinity in the aquifer. Water samples were collected between 2009 and 2011. Three groundwater groups (A, B and C) were identified based on the hydrogeological setting and on the Cl− concentrations. Average and maximum Cl− concentrations in the recharge waters were calculated (ClRef. and ClRef.Max) to be 0.51 and 2.85mmol/L, respectively). Group A includes spring waters with Cl− concentrations that are within the same order of magnitude as the ClRef concentration. Group B includes groundwater with Cl− concentrations that range between the ClRef and ClRef.Max concentrations. Group C includes brackish groundwater with Cl− concentrations that are significantly greater than the ClRef.Max concentration. Overall, the chemistry of the La Clape groundwater evolves from dominantly Ca–HCO3 to NaCl type. On binary diagrams of the major ions vs. Cl, most of the La Clape waters plot along mixing lines. The mixing end-members include spring waters and a saline component (current seawater or fossil saline water). Based on the Br/Clmolar ratio, the hypothesis of halite dissolution from Triassic evaporites is rejected to explain the origin of salinity in the brackish groundwater.Groundwaters display 87Sr/86Sr ratios intermediate between those of the limestone aquifer matrix and current Mediterranean seawater. On a Sr mixing diagram, most of the La Clape waters plot on a mixing line. The end-members include the La Clape spring waters and saline waters, which are similar to the deep geothermal waters that were identified at the nearby Balaruc site. The 36Cl/Cl ratios of a few groundwater samples from group C are in agreement with the mixing hypothesis of local recharge water with deep saline water at secular equilibrium within a carbonate matrix. Finally, PHREEQC modelling was run based on calcite dissolution in an open system prior to mixing with the Balaruc type saline waters. Modelled data are consistent with the observed data that were obtained from the group C groundwater. Based on several tracers (i.e. concentrations and isotopic compositions of Cl and Sr), calculated ratios of deep saline water in the mixture are coherent and range from 3% to 16% and 0% to 3% for groundwater of groups C and B, respectively.With regard to the La Clape karst aquifer, the extension of a lithospheric fault in the study area may favour the rise of deep saline water. Such rises occur at the nearby geothermal Balaruc site along another lithospheric fault. At the regional scale, several coastal karst aquifers are located along the Gulf of Lion and occur in Mezosoic limestones of similar ages. The 87Sr/86Sr ratios of these aquifers tend toward values of 0.708557, which suggests a general mixing process of shallow karst waters with deep saline fossil waters. The occurrence of these fossil saline waters may be related to the introduction of seawater during and after the Flandrian transgression, when the highly karstified massifs invaded by seawater, formed islands and peninsulas along the Mediterranean coast.

Origin of Salinity in a Coastal Karst System: La Clape Massif, SE France

Recent increases in groundwater salinity, exceeding the guidelines for irrigation, prompted this investigation on the origin of mineralisation in the La Clape karst aquifer (SE France). The La Clape massif (Aude) is a typical Jurassic and Cretaceous carbonate aquifer that was deeply karstified during the Messinian crisis. The massif is affected by the vicinity of the Cevennes lithospheric fault, and numerous normal faults related to the Oligocene distension event. Potential sources of salinity are seawater intrusion, upward migration of deep saline waters, as well as dissolution of Triassic evaporites. A contribution from halite can be ruled out on the basis of the measured Br/Cl ratios that are similar to that of seawater and deep saline waters. Sr concentrations suggest mixing with an end member slightly more enriched in Sr than current seawater. Ranging from 0.707852 to 0.708875, 87Sr/86Sr ratios of groundwaters are lower than that of modern Mediterranean seawater (0.709163), and higher than that of the carbonate matrix, ranging from 0.707276 to 0.707477. Those ratios tend towards that of deep saline groundwaters observed at the nearby site of Balaruc. 36Cl/Cl ratios measured on a few samples agree with a mixing hypothesis of superficial karst waters with deep saline water at secular equilibrium with the carbonate matrix. Including dissolution of carbonate and mixing with a saline end member, PHREEQ C modelling confirms that Balaruc-type waters are a likely end member. Calculated parts of mixing range from 0 to 16% of deep saline water. This suggests that seawater intrusion in the karst system is prevented by thick off-shore sedimentary deposits. The deeply faulted and karstified La Clape system is likely to favor the upward movement of deep saline waters. At the regional scale, saline groundwaters of three coastal karst aquifers located along the Gulf of Lion show 87Sr/86Sr ratios tending towards a Sr isotopic ratio of 0.70847. This may suggest a similar origin for the observed salinities in these coastal karst systems, by upward movement of deep saline waters.

Feasibility of the Combination of CO2 Geological storage and Saline Water Development in Sedimentary Basins of China

Utilization plays a key role in the deployment of CCS in China. CO2 geological storage and utilization (CGSU) shows most charming potential for carbon mitigation in China according to the technology roadmap study of carbon capture, utilization, and storage (CCUS) in China. After a general review and a thorough investigation, the partition of China mainland into three CCUS zones is figured out mainly according to the different types of aquifer systems. Focusing on coal chemical enterprises in the western China (Zone I), a novel CGSU method is proposed in this paper. By CO2 enhanced recovery of deep saline water, a tripartite win system is charming promotion of China western development. The cross point of the developed system is to attract investment on coal chemical industry to use local rich coal resources, to meet great water demand of coal chemical industry in the water shortage of China western region, and to maximum optimize of pressure buildup of CO2 geological storage.

Aerobic methanotrophy within the pelagic redox-zone of the Gotland Deep (central Baltic Sea)

Abstract. Water column samples taken in summer 2008 from the stratified Gotland Deep (central Baltic Sea) showed a strong gradient in dissolved methane concentrations from high values in the saline deep water (max. 504 nM) to low concentrations in the less dense, brackish surface water (about 4 nM). The steep methane-gradient (between 115 and 135 m water depth) within the redox-zone, which separates the anoxic deep part from the oxygenated surface water (oxygen concentration 0–0.8 mL L−1), implies a methane consumption rate of 0.28 nM d−1. The process of microbial methane oxidation within this zone was evident by a shift of the stable carbon isotope ratio of methane between the bottom water (δ13C CH4 = −82.4‰ and the redox-zone (δ13C CH4 = −38.7‰. Water column samples between 80 and 119 m were studied to identify the microorganisms responsible for the methane turnover in that depth interval. Notably, methane monooxygenase gene expression analyses for water depths covering the whole redox-zone demonstrated that accordant methanotrophic activity was probably due to only one phylotype of the aerobic type I methanotrophic bacteria. An imprint of these organisms on the particular organic matter was revealed by distinctive lipid biomarkers showing bacteriohopanepolyols and lipid fatty acids characteristic for aerobic type I methanotrophs (e.g., 35-aminobacteriohopane-30,31,32,33,34-pentol), corroborating their role in aerobic methane oxidation in the redox-zone of the central Baltic Sea.

Estimation of seasonal and long-term variability of oceanological conditions in the Bering Strait

Carried out is analysis of variations of temperature, salinity, and currents in the Bering Strait area based on the data of American and Russian-American studies of the Bering Strait during the period from 1992 to 2010. Major attention is paid to the analysis of the long-term variability of water dynamics using the data of observations at the autonomous buoy stations in the Russian and American parts of the Bering Strait. Revealed are the trends towards the increase in the velocity of the Pacific water transport to the Chukchi Sea and Arctic Ocean, as well as the absence of the significant trend towards the changes in the temperature and salinity of deep waters in the Bering Strait. Estimated is the seasonal variability of hydrophysical conditions.

The hydrography of the Mozambique Channel from six years of continuous temperature, salinity, and velocity observations

Temperature, salinity and velocity data are presented, along with the estimated volume transport, from seven full-length deep sea moorings placed across the narrowest part of the Mozambique Channel, southwest Indian Ocean, during the period November 2003 to December 2009. The dominant water mass in the upper layer is Sub-Tropical Surface Water (STSW) which overlies South Indian Central Water (SICW), and is normally capped by fresher Tropical Surface Water (TSW). Upper ocean salinity increased through 2005 as a result of saline STSW taking up a relatively larger part of the upper layer, at the expense of TSW. Upper waters are on average warmer and lighter in the central Channel than on the sides. Throughout the upper 1.5km of the water column there is large hydrographic variability, short-term as well as interannual, and in particular at frequencies (four to seven cycles per year) associated with the southward passage of anticyclonic Mozambique Channel eddies. The eddies have a strong T–S signal, in the upper and central waters as well as on the intermediate level, as the eddies usually carry saline Red Sea Water (RSW) in their core. While the interannual frequency band displays an east–west gradient with higher temperature variance on the western side, the eddy frequency band shows highest variance in the centre of the Channel, where the eddy band contains about 40% of the total isopycnal hydrographic variability. Throughout the >6 years of measurements, the frequency and characteristics of eddies vary between periods, both in terms of strength and vertical structure of eddy T–S signals. These changes contribute to the interannual variability of water mass properties: an increase in central water salinity to a maximum in late 2007 coincided with a period of unusually frequent eddies with strong salinity signals. The warmest and most saline deep water is found within the northward flowing Mozambique Undercurrent, on the western side of the Channel. The Undercurrent has two cores: an intermediate one mainly containing diluted Antarctic Intermediate Water (AAIW), and a deep one consisting of North Atlantic Deep Water (NADW). In the intermediate core, T–S properties are strongly correlated with current velocity, probably because of the strong salinity gradient at the interface between Red Sea Water (RSW) and AAIW. In the deep core, velocity and hydrographic time series do not correlate on a daily basis, but they do at longer time scales.

Hydrogeological characterization of seawater intrusion in tidally-forced coastal fractured bedrock aquifer

Summary Hydrogeological investigation was carried out to characterize seawater intrusion in a tidally-forced coastal fractured bedrock aquifer in the west coast of Korea peninsular, which was also subject to heavy groundwater extraction. Times series analysis, using the data of electrical conductivity (EC), groundwater level and tidal oscillation, showed that intensive groundwater extraction from the wells near the shore caused a severe seawater intrusion. The geophysical loggings and hydraulic tests indicated that the tidally-forced coastal fractured aquifer in the study area was characterized by the shallow fresh groundwater, transition zone, and deep high saline water zone. The extent of seawater intrusion highly depended on conductive fractures and their hydraulic connectivity. In the deep saline water layer, progressive seawater intrusion took place mainly by persistent intensive pumping and in part by tidal activity. The conductive fractures acted as a pathway for saline water flow from the deep saline water zone to the transition zone, when groundwater was extracted. The extent of transition zone depended on the change of groundwater level by groundwater pumping or recharge. This study indicated that a persistent intensive extraction of groundwater would intensify seawater intrusion in tidally-forced coastal fractured aquifer and proper measures would be required to prevent it.

The study of the hydrogeological setting of the Chamshir Dam site with special emphasis on the cause of water salinity in the Zohreh River downstream from the Chamshir Dam (southwest of Iran)

Dissolution of evaporite formations, emergence of salty water springs, and intrusion of deep saline waters are important causes in changing the quality of surface water. The study area is part of the reservoir and downstream of Chamshir Dam, which is located in watershed of the Zohreh River 20 km southeast of Gachsaran City (southwest Iran). To construct powerhouse and related structures for supplying water to agricultural lands located in downstream of dam, water quality of Zohreh River was studied by eight sampling stations in the study area. Early studies showed that water quality of the Zohreh River decreases severely downstream of the Chamshir Dam. Spatial variations diagram of major ions, Piper and composition diagrams of water samples in selected stations mark the presence of two slight and major contaminating zones at sampling station R4 and R5. In these zones, concentration of Ca, SO4 and Na, Cl ions increase suddenly. Results of hydrogeological, hydrochemical, lithological and tectonics studies showed that even though there are several low discharges springs in the contaminated zone they cannot be related to surface dissolution of evaporate layers by Zohreh River. There is an important fault zone including Chamshir faults I and II in the contamination zones through which intrusion of sulfate brackish and chloride brine waters occur along the fault zone and then enter Zohreh River below its base level. In the absence of any surface evidence, the fault zone is the main cause of salinity. Evaluation of water balance salinity in contaminated zones shows that the discharge rate of saline waters to the river is not low and cannot be separated. These findings show that there are serious restrictions upon the purposes of the project.

The formation and dynamics of the cold-dome off northeastern Taiwan

The cold-dome off northeastern Taiwan is commonly observed by remote-sensing of Sea Surface Temperature (SST) and in-situ observation. The recent remote-sensing SST and subsurface Argo profiles were analyzed to investigate possible formation mechanisms and dynamics. The observed time series of SST anomaly suggested that the surface cold-dome occurred more frequently in summer, including an unusual contribution due to the cold water residual associated with typhoon events. Subsurface hydrographic features from Argo float data indicated that the near-shore thermocline can be lifted up about 85 m by Kuroshio dynamics, and the cold saline deep water (100 m deep off northeastern Taiwan) can only result from subsurface Kuroshio. We examined the possible formation mechanisms using a duo-grids North Pacific Ocean model (DUPOM) with a horizontal resolution of 1/8° for the East Asian Seas and 1/4° for the remaining North Pacific. The model reproduced several cold-dome formation events and displayed typical cold-dome features. Further analysis shows that the geostrophic component of Kuroshio transport is the main contributor to the cold-dome formation (57.4% of the total isotherm uplift) and dominates seasonal occurrence of the cold-dome. The contribution resulting from the associated cyclonic eddy is only 3.3% of the total isotherm uplift. Additional sensitivity tests suggested that the remaining contribution (39.6% of the total isotherm uplift) is mainly due to the topographically controlled upwelling in this region. Moreover, the local boundary Ekman transport may enhance the surface appearance of the cold-dome, but plays only a minor role.

CO2 plume modeling in deep saline reservoirs by 2D ERT in boreholes

The need to manage [Formula: see text] emissions for mitigating the greenhouse effect has led to worldwide research to reduce atmospheric [Formula: see text]. Techniques of carbon capture and storage (CCS) must (1) be effective and cost-competitive, (2) provide stable, long-term storage, and (3) be environmentally benign. Potential terrestrial media for [Formula: see text] storage include depleted oil and gas reservoirs, coal seams that cannot be mined, and deep saline water reservoirs capped by impermeable rock to prevent upward leakage.

Coastal aquifers of Europe: an overview

Europe has a long coastline along which many human activities are concentrated. Coastal aquifer development is often intensive and subject to salinity problems as a result of seawater intrusion, upconing of deep saline water, and residual salinity in aquitards. Studies have been carried out since the end of the nineteenth century, and have set the basic principles of freshwater/marine-water relations. Some aquifers are carefully studied, monitored and managed; examples can be found in The Netherlands, Belgium, southern Italy and northeastern Spain. Often important coastal aquifers are of relatively small size but crucial to supply human needs, which vary from mostly urban and industrial in mid to high latitudes, to dominantly seasonal for irrigation in the Mediterranean area and the archipelagos. The different situations can be grouped into: recent deltas, other coastal detritic formations, carbonate formations, and the special situations in small islands. Comments on these situations are provided and some examples are introduced, just for illustration.

Circulation and Transport in the Western Boundary Currents at Cape Farewell, Greenland

Abstract The circulation and volume transports in the western boundary currents around Cape Farewell, Greenland, are derived from full-depth hydrographic and velocity measurements from August–September 2005. The western boundary currents from surface to seafloor transport 40.5 ± 8.1 Sv (Sv ≡ 106 m3 s−1) southward in the Irminger Sea, and 53.8 ± 10.8 Sv northward in the Labrador Sea. The Deep Western Boundary Current (DWBC, defined as water with potential density greater than 27.80 kg m−3) transports 12.3 ± 2.5 Sv southward in the Irminger Sea. The deep water transport is reduced south of Cape Farewell, where it changes flow direction from southward to northward (the south corner). At a section over the Eirik Ridge, a bathymetric feature extending southwest of Cape Farewell, the DWBC transports 8.7 ± 1.7 Sv westward. The reduction in transport at the south corner is associated with decreased velocities within the deepest layers and the volumetric loss of the most saline deep water types. The observations suggest that the paths of the shallow and deep western boundary currents diverge at the south corner. Downstream in the eastern Labrador Sea the deep water transport is increased to 19.7 ± 3.9 Sv northward, with the addition of recirculating denser deep waters. The representativeness of the results from the semisynoptic survey is discussed with reference to companion current meter measurements of the DWBC.

Iodine-rich waters involved in supergene enrichment of the Mantos de la Luna argentiferous copper deposit, Atacama Desert, Chile

Recent studies have suggested the involvement of highly saline deep formation waters that modified preexisting Cu assemblages to form atacamite during supergene oxidation of Cu deposits in the Atacama region. In this report, we document the occurrence of (Ag-I) inclusions hosted by supergene chalcocite from Mantos de la Luna, an argentiferous Upper Jurassic stratabound Cu deposit in the Coastal Range of northern Chile. The presence of this unusual mineral assemblage indicates that iodargyrite precipitated from reducing iodine-rich waters, suggesting that the fluids involved in supergene enrichment of Cu deposits in the Coastal Range were more complex than previously thought. This suggests the prevalence of hyperarid conditions during the latest stages of supergene enrichment of the Mantos de la Luna Cu deposit in the Atacama region, supporting the notion that supergene enrichment processes in hyperarid areas are dynamic in nature and do not exclusively require the presence of meteoric water.

Atacamite formation by deep saline waters in copper deposits from the Atacama Desert, Chile: evidence from fluid inclusions, groundwater geochemistry, TEM, and 36Cl data

The presence of large amounts of atacamite in oxide zones from ore deposits in the Atacama Desert of northern Chile requires saline solutions for its formation and hyperarid climate conditions for its preservation. We investigated the nature and origin of atacamite-forming solutions by means of coupling groundwater geochemical analyses with fluid inclusion data, high-resolution mineralogical observations, and chlorine-36 (36Cl) data in atacamite from the Mantos Blancos and Spence Cu deposits. In both deposits, the salinities of fluid inclusions in atacamite are comparable to those measured in saline groundwaters sampled from drill holes. The average salinity of fluid inclusions in atacamite for the Mantos Blancos and Spence deposits (~7–9 and 2–3 wt.% NaCleq, respectively) are strongly correlated to the salinities at which gypsum supersaturates from groundwaters in both deposits (total dissolved solids ~5–9 and 1–3 wt.% NaCleq, respectively). This correlation is confirmed by transmission electron microscopy observations of atacamite-bearing samples, revealing an intimate association between atacamite and gypsum that can be traced down to the nanometer scale. 36Cl data in atacamite provide new lines of evidence concerning the origin and age of the saline waters that formed atacamite in various stratabound and porphyry Cu deposits from the Atacama Desert. All atacamite samples show very low 36Cl-to-Cl ratios (11 × 10−15 to 28 × 10−15 at at−1), comparable to previously reported 36Cl-to-Cl ratios of deep formation waters and old groundwaters. In addition, 36Cl-to-Cl ratios in atacamite correlate with U and Th concentration in the host rocks but are independent from distance to the ocean. This trend supports an interpretation of the low 36Cl-to-Cl ratios in atacamite as representing subsurface production of fissiogenic 36Cl in secular equilibrium with the solutions involved in atacamite formation. Therefore, 36Cl in atacamite strongly suggest that the chlorine in saline waters related to atacamite formation is old (>1.5 Ma) but that atacamite formation occurred more recently (<1.5 Ma) than suggested in previous interpretations. Our data provide new constraints on the origin of atacamite in Cu deposits from the Atacama Desert and support the recent notion that the formation of atacamite in hyperarid climates such as the Atacama Desert is an ongoing process that has occurred intermittently since the onset of hyperaridity.

Geochemical Tracers to Evaluate Hydrogeologic Controls on River Salinization

The salinization of rivers, as indicated by salinity increases in the downstream direction, is characteristic of arid and semiarid regions throughout the world. Historically, salinity increases have been attributed to various mechanisms, including (1) evaporation and concentration during reservoir storage, irrigation, and subsequent reuse; (2) displacement of shallow saline ground water during irrigation; (3) erosion and dissolution of natural deposits; and/or (4) inflow of deep saline and/or geothermal ground water (ground water with elevated water temperature). In this study, investigation of salinity issues focused on identification of relative salinity contributions from anthropogenic and natural sources in the Lower Rio Grande in the New Mexico-Texas border region. Based on the conceptual model of the system, the various sources of water and, therefore, salinity to the Lower Rio Grande were identified, and a sampling plan was designed to characterize these sources. Analysis results for boron (delta(11)B), sulfur (delta(34)S), oxygen (delta(18)O), hydrogen (delta(2)H), and strontium ((87)Sr/(86)Sr) isotopes, as well as basic chemical data, confirmed the hypothesis that the dominant salinity contributions are from deep ground water inflow to the Rio Grande. The stable isotopic ratios identified the deep ground water inflow as distinctive, with characteristic isotopic signatures. These analyses indicate that it is not possible to reproduce the observed salinization by evapotranspiration and agricultural processes alone. This investigation further confirms that proper application of multiple isotopic and geochemical tracers can be used to identify and constrain multiple sources of solutes in complex river systems.

High resolution seafloor images in the Gulf of Cadiz, Iberian margin

In the Gulf of Cadiz, the hydrodynamic process acting on particle transport and deposition is a strong density-driven bottom current caused by the outflow of the saline deep Mediterranean water at the Strait of Gibraltar: the Mediterranean Outflow Water (MOW). New high resolution acoustic data including EM300 multibeam echo-sounder, deep-towed acoustic system SAR and very high resolution seismic, completed by piston cores collected during the CADISAR cruise allow to improve the understanding of the hydrodynamics of the MOW in the eastern part of the Gulf of Cadiz. Interpretation of data corrects the previous model established in this area and allows, for the first time, the accurate characterization of various bedforms and erosive structures along the MOW pathway and the precise identification of numerous gravity instabilities. The interaction between the MOW, the seafloor morphology and the Coriolis force is presently the driving force of the sedimentary distribution pattern observed on the Gulf of Cadiz continental slope.

Rebound at Pb-Zn Mines Hosted in Carbonate Aquifers: Influence on the Chemistry of Ground Water

Closure of Pb-Zn mines in the Iglesiente district (SW Sardinia, Italy) caused the cessation of pumping in 1997 at Monteponi, and in 1998 at San Giovanni. Consequent flooding of underground workings occurred in the district and also involved Campo Pisano. In June 1998, as the water table rose from 160 to 20 m below sea level, the deep saline water mixed with the shallow ground water at Monteponi and nearby mines. In the same period, an increase in dissolved metals (especially Zn, Cd, and Pb) was observed under near-neutral pH conditions. Following peak concentrations, a marked decrease of Zn, Cd, and Hg occurred. Dissolved Pb showed fluctuating concentrations over the monitoring period (1996-2005). In January 2000, when the water table rose to 20 m above sea level, the salinity of ground water decreased significantly at all of the mines. Stratification caused the more saline water at depth to settle three years after rebound started. Depth profiles carried out in 2005 at Monteponi, San Giovanni, and Campo Pisano showed an increase in conductivity and dissolved metals in ground water at deeper levels, especially at depths below sea level.After eight years of rebound, a marine component was still present at depth in ground water at San Giovanni (about 2%), and to a lesser extent at Monteponi (about 0.4%).

Seasonal dynamics and decadal changes of benthic foraminiferal assemblages in the western Baltic Sea (NW Europe)

Abstract. Living benthic foraminiferal assemblages were monitored between January and July 2004 in the Kiel Bight, Baltic Sea. Phytoplankton blooms and the deposition of organic detritus were depicted by fluorometer hydro casts and pigment concentrations in surface sediments. Three depositional pulses of organic matter were identified by high phytoplankton concentrations above the sea floor and elevated pigment concentrations in the surface sediment. The foraminiferal assemblage composition remained rather constant but the population density of Elphidium excavatum clavatum showed a two- to six-fold increase within a few days after organic detritus deposition. The foraminiferal assemblage composition was compared to earlier studies in this area. Elphidium excavatum, Ammotium cassis and E. incertum dominated the living fauna in the 1960s and 1970s. The recent survey revealed a predominance of E. excavatum subspecies (more than 90% of the living assemblage). The average population densities were six times higher than in the 1970s. Data structure and model calculations suggested that E. excavatum clavatum is able to reproduce rapidly, with high offspring numbers at elevated food supply. The diminution of A. cassis has occurred in Kiel Bight during the last ten years and was most likely induced by a period of low deep-water salinities in the early 1990s.

Characteristics of deep groundwater flow in a basin marginal setting at Sellafield, Northwest England: 36Cl and halide evidence

A number of chemical and physical processes inside and outside a sedimentary basin (e.g. evaporite dissolution and topographic drive, respectively) affect groundwater flow near the basin’s margin. Contrasting formations at the margin, typically basinal sedimentary rocks and basement, are host to the interplay between these processes so that groundwater flows and compositions change within a relatively small volume. To interpret how groundwater flow and geochemistry have evolved, interactions between these processes must be understood. Such interactions were investigated near the margin of the East Irish Sea Basin in NW England, by sampling deep groundwaters (to 1500 m below sea level) from Ordovician volcanic basement rocks and Carboniferous to Triassic sedimentary cover rocks. Variable Br/Cl ratios and Cl concentrations in deep saline waters and brines indicate mixing patterns. Variations in 36Cl/Cl constrain the timing of mixing. Relatively low Br/Cl ratios (ca. 1 × 10 −3 by mass) characterise brine from the western sedimentary cover and reflect halite dissolution further west. Saline water with relatively high Br/Cl ratios (ca. 2 × 10 −3 by mass) of uncertain origin occupies the eastern basement. These two waters mix across the area. However, mixing alone cannot explain variable 36Cl/Cl ratios, which partly reflect differing in situ 36Cl production rates in different rock formations. Most 36Cl/Cl ratios in groundwater sampled from the eastern metavolcanic basement (mean = 25 × 10 −15) and western sedimentary cover (mean = 10 × 10 −15) are at or close to equilibrium with in situ 36Cl production. These variations in 36Cl/Cl across the site possibly took >1.5 Ma to be attained, implying that deep groundwater flow responded only slowly to the Quaternary glaciation of the site. Interplay between varied processes in basin marginal settings does not necessarily imply flow instability.

Long-term trends in the variability of deep-water thermohaline characteristics of the Black Sea

By using the archival hydrological data for 1955–1998, we analyze the trends of deep-water thermohaline characteristics of the Black Sea and their interannual and decadal variability. It was discovered that the level of salinity increased at depths greater than 1000 m in the west part of the sea from the mid-1950-s till the early 1980s and the opposite trend was observed for the next 15–20 yr. The average rate of increase in the deep-water salinity between 1960 and 1980 and its decrease after 1980 was equal to 0.05‰ per 20 yr. These facts demonstrate that the water exchange through Bosporus was intensified for the first 25 yr of the analyzed period and weakened for the next 20 yr. The interannual variability with a typical period of 6.5 yr and a quasi-20-yr periodicity are detected against the background of the parabolic trend.