Cl Isotope Research Articles

Studies on Isotope Ratio Measurement of Cl by Inductively Coupled Plasma Triple-quad Mass Spectrometry.

Fundamental studies on isotope ratio measurement of Cl were carried out using inductively coupled plasma triple-quad mass spectrometry (ICP-MS/MS) and the analytical performance obtained was compared to that obtained by ICP sector field mass spectrometer (ICP-SFMS). Though the polyatomic ion interferences of 16O18O1H and 36Ar1H with respect to 35Cl and 37Cl, respectively, made a negative effect on the accuracy and the precision for isotope ratio measurements of Cl, the ICP-SFMS could eliminate these interferences by medium mass resolution mode (m/Δm = 4000) and achieved the isotope ratio measurements with 0.2 - 0.5% of relative standard deviation (RSD) at the concentrations of Cl from 1 to 10 mg kg-1. In the case of ICP-MS/MS, both the single-MS mode without collision reaction gas and the MS/MS mode with collision reaction gases such as oxygen (O2) and hydrogen (H2) were examined and compared their analytical sensitivities as well as the precisions of isotope ratio measurement of Cl. The precisions of Cl isotope ratio measurements were 3 - 14% of RSD at the concentrations of Cl from 5 to 100 mg kg-1, when single-MS mode was carried out, even though the similar isotope ratios of 35Cl/37Cl could be obtained. In the case of O2 gas for MS/MS mode with mass-shift method, precisions of 0.3 - 2% of RSD were obtained at the concentration range of 1 - 100 mg kg-1. In the case of H2 gas, similar sensitivities as those obtained by ICP-SFMS and the precisions of 0.2 - 0.5% of RSD at the concentration range of 1 - 10 mg kg-1 were obtained. From these results, it was evaluated that the ICP-MS/MS in MS/MS mode with collision reaction gas could be used for Cl isotope ratio measurements for such studies as stable isotope tracers, isotope abundance measurements in nuclear chemistry and accurate determinations by isotope dilution mass spectrometry.

Chlorine isotope composition of volcanic rocks and gases at Stromboli volcano (Aeolian Islands, Italy): Inferences on magmatic degassing prior to 2014 eruption

Among the magmatic volatiles, chlorine (Cl) is degassed at shallow depths offering the opportunity to investigate the behavior of magmatic degassing close to the surface, and the possible occurrence of chemical and isotopic fractionation related to gas/melt partitioning. However, it is still unclear if the isotopic composition of Cl (δ37Cl) can be used as a proxy of magmatic degassing. In this work, we investigate the concentrations of chlorine and sulfur, and the Cl isotope composition of rocks and plume gases collected at Stromboli volcano, Aeolian Islands, Italy. This volcano was chosen because it is characterized by persistent eruptive activity (i.e., Strombolian explosions) and by the presence of magma at very shallow levels in the conduits. Rocks belonging to the different magmatic series erupted throughout the formation of the volcano have δ37Cl values ranging between −1.0 and +0.7‰. The isotopic composition seems independent of the Cl concentration of the rocks, but shows a negative correlation with SiO2 content. Plume gases have a greater isotopic compositional variability than the rocks (−2.2‰≤δ37Cl≤+1.5‰) and the composition seems related to the level of volcanic activity at Stromboli. Gases collected in 2011–2013 during days of ordinary eruptive activity are characterized by δ37Cl values ranging from +0.3 to +1.5‰ and S/Cl molar ratios between 1.4 and 2.2, similar to previous S/Cl measurements performed at Stromboli with other techniques. Plume gases collected in July 2014, in days of high-level eruptive activity preceding the onset of the 2014 effusive eruption, have negative δ37Cl values (−2.2‰≤δ37Cl≤−0.1‰) and S/Cl between 0.9 and 1.2, which are among the lowest S/Cl values measured at this volcano. The amplitude of the volcanic tremor and the variation in the inclination of very long period (VLP) seismic signal polarization clearly indicate that in July 2014 the intensity and frequency of Strombolian explosions, as well as the level of magma in the conduits, were higher than normal. This suggests that when magmatic degassing occurs at very shallow depths (magma residing at few tens of meters below the craters), isotopic fractionation between gaseous and dissolved chlorine (lnαgas-melt>0) can occur, resulting in a depletion of 37Cl in the melt. Finally, we argue that the range of δ37Cl values measured in rocks and gases at Stromboli overlaps most of the known mantle reservoirs (i.e., DMM, HIMU and EM-EM1), indicating that the transfer of chlorine from the mantle to the surface occurs without significant isotopic fractionation. This work opens new perspectives for better constraining the isotope signature of chlorine of different magmatic systems and mantle reservoirs on the Earth.

Evidence of multiple halogen sources in scapolites from iron oxide-copper-gold (IOCG) deposits and regional Na[sbnd]Cl metasomatic alteration, Norrbotten County, Sweden

Scapolites from barren regional NaCl metasomatic assemblages (RM), iron oxide-copper-gold deposits (IOCG), scapolite altered metabasic rocks (IOCG-M), and from IOCG-proximal alteration/Na-Skarns (IOCG-PS) from Norrbotten County in Northern Sweden have been analysed for halogen content and Cl stable isotope composition. The aim of the study was to constrain the source of halogens within alteration assemblages, and to investigate the possible fractionation of Cl isotopes between scapolite and the hydrothermal fluid. Scapolite separates were analysed for Cl, Br, and major oxide concentrations using electron probe micro-analysis (EPMA) and micro-X-ray fluorescence (XRFM) spectrometry. Chlorine was extracted from the scapolite separates via pyrohydrolysis and then analysed for their stable Cl isotope compositions by isotope ratio mass spectrometry (IRMS).All samples of scapolite investigated in this study are marialitic in composition. One of the scapolites from the Gruvberget deposit (IOCG-PS) had a Cl/Br molar ratio of 2363, which is the highest amongst all scapolites reported in the literature to date. Cl/Br molar ratios lower than seawater (650), were identified in two IOCG-PS scapolite samples (Cl/Br=554 and 271), as well as in two IOCG-M scapolites (Cl/Br=393 and 565). Three RM scapolites had Cl/Br molar ratios very close to, or slightly higher than, seawater values (639 to 770). Samples with Cl/Br molar ratios less than seawater are inferred to have halogens derived from evaporative residual brines; whereas samples with molar ratios higher than seawater may have halogens derived from fluids that have dissolved halite and/or are from magmatic systems. Considering the wide variation of the Cl/Br molar ratios in the IOCG-PS and IOCG-M scapolites compared to the restricted composition of the regional alteration (RM), it is proposed that the hydrothermal fluids interacted with several different protoliths to generate the IOCG alteration.RM alteration scapolites had δ37Cl values from −0.1‰ to +0.3‰, two IOCG-M scapolites had values of 0.2‰ and IOCG-PS scapolites had δ37Cl values from −0.1‰ to +1.0‰. Using a previously published δ37Cl value from fluid inclusion leachates (−1.7‰) from the IOCG-M mineralisation at Pahtohavare and the δ37Cl value of co-existing scapolite measured in this study (0.2‰), an empirical fluid-scapolite fractionation factor was calculated to be +1.9‰. This large fractionation factor is not supported by previous predictions for monovalent chlorides and, assuming equilibrium, indicates that 37Cl was preferentially accommodated in the A site of the scapolite structure. This indicates that either the stable Cl isotope partitioning between the CaCl2-rich brine and the scapolite may differ from currently available estimates for NaCl brines in equilibrium with silicate minerals, or that the scapolite and brine are not in isotopic equilibrium.Overall, the data in this study suggest that halogens in early scapolites were derived from residual brines and halite, during metamorphism of evaporites linked to the RM alteration. Later in the history of the Norrbotten district components of the RM alteration were recycled and mixed during magmatic and local metasomatic events to varying extents, resulting in the brines associated with IOCG alteration.

Chlorine Isotope Geochemistry

Chlorine played a prominent role in the discovery of isotopes. The famous Cavendish Laboratory scientists were fascinated with the atomic mass of Cl. Most elements have a mass that is a close approximation of the multiple of hydrogen (e.g., Aston 1927). By 1920, it was recognized that the atomic weight of Cl was ~35.5, which appeared to violate Francis Aston’s whole number rule. Sir Joseph J. Thomson started the famous “Discussion on Isotopes” (Thomson et al. 1921) with the following: “I will plunge at once into the most dramatic case of the isotopes—the case of chlorine”. The discussion that followed between three Nobel Prize winners pitted Thomson against Aston and Frederick Soddy, the latter two in defense of multiple isotopes of a single element. And so the game began. Aston (1919, 1920) argued that the mass spectra of Cl-bearing compounds (e.g., HCl, COCl) supported the existence of at least two isotopes of Cl, 35Cl and 37Cl. However, Thomson contended that the spectra may be the result of different compounds of Cl and not necessarily different isotopes of Cl (Thomson et al. 1921). Ultimately, Aston was proven correct (e.g., Harkins and Hayes 1921; Harkins and Liggett 1923) and is now credited with the discovery of the two stable isotopes of Cl, which is notable for the unusually large abundance of its “rare” isotope. The relative abundances of 35Cl and 37Cl are currently accepted to be 75.76% and 24.24%, respectively (Berglund and Wieser 2011). It was not until ~75 years after the discovery of the stable isotopes of Cl that they become more “routinely” analyzed and the chlorine isotope compositions of various chlorine reservoirs were beginning to be determined. Here we summarize the current state of chlorine isotope standards, analytical methods, and fractionation, as well …

Estimating groundwater age in the Cambrian–Ordovician aquifer in Iowa: implications for biofuel production and other water uses

Deep confined water from the Cambrian–Ordovician (C–O) aquifer is being increasingly used for ethanol production in Iowa. In this study, we used isotopic age dating to estimate the age of groundwater in the aquifer and assess how groundwater use for all purposes, including ethanol production, may be affecting the long-term sustainability of the aquifer. Eight municipal wells located across the extent of the aquifer in Iowa were sampled for major and minor ions, stable isotopes (δ18O and δD) and the radioactive isotope 36Cl. Multiple lines of evidence from this study suggest that groundwater in the C–O aquifer is older than 10,000 years, with results from 36Cl analyses suggesting groundwater travel times in the aquifer ranging from approximately 70,000 to nearly 180,000 years old from northern to central Iowa. Our study suggests that pumping from the C–O aquifer for all uses, including ethanol production, is extracting old groundwater from the aquifer. To mitigate long-term impacts, we recommend that expansion of new ethanol production should be based on accessibility of sustainable groundwater resources, rather than siting facilities where deep groundwater reserves are needed for production.

Stable isotope analyses of oxygen (18 O:17 O:16 O) and chlorine (37 Cl:35 Cl) in perchlorate: reference materials, calibrations, methods, and interferences.

Perchlorate (ClO4- ) is a common trace constituent of water, soils, and plants; it has both natural and synthetic sources and is subject to biodegradation. The stable isotope ratios of Cl and O provide three independent quantities for ClO4- source attribution and natural attenuation studies: δ37 Cl, δ18 O, and δ17 O (or Δ17 O or 17 Δ) values. Documented reference materials, calibration schemes, methods, and interferences will improve the reliability of such studies. Three large batches of KClO4 with contrasting isotopic compositions were synthesized and analyzed against VSMOW-SLAP, atmospheric O2 , and international nitrate and chloride reference materials. Three analytical methods were tested for O isotopes: conversion of ClO4- to CO for continuous-flow IRMS (CO-CFIRMS), decomposition to O2 for dual-inlet IRMS (O2-DIIRMS), and decomposition to O2 with molecular-sieve trap (O2-DIIRMS+T). For Cl isotopes, KCl produced by thermal decomposition of KClO4 was reprecipitated as AgCl and converted into CH3 Cl for DIIRMS. KClO4 isotopic reference materials (USGS37, USGS38, USGS39) represent a wide range of Cl and O isotopic compositions, including non-mass-dependent O isotopic variation. Isotopic fractionation and exchange can affect O isotope analyses of ClO4- depending on the decomposition method. Routine analyses can be adjusted for such effects by normalization, using reference materials prepared and analyzed as samples. Analytical errors caused by SO42- , NO3- , ReO42- , and C-bearing contaminants include isotope mixing and fractionation effects on CO and O2 , plus direct interference from CO2 in the mass spectrometer. The results highlight the importance of effective purification of ClO4- from environmental samples. KClO4 reference materials are available for testing methods and calibrating isotopic data for ClO4- and other substances with widely varying Cl or O isotopic compositions. Current ClO4- extraction, purification, and analysis techniques provide relative isotope-ratio measurements with uncertainties much smaller than the range of values in environmental ClO4- , permitting isotopic evaluation of environmental ClO4- sources and natural attenuation. Copyright © 2016 John Wiley & Sons, Ltd.

CHLORINE ABUNDANCES IN COOL STARS

Chlorine abundances are reported in 15 evolved giants and one M dwarf in the solar neighborhood. The Cl abundance was measured using the vibration-rotation 1-0 P8 line of H$^{35}$Cl at 3.69851 $\mu$m. The high resolution L-band spectra were observed using the Phoenix infrared spectrometer on the Kitt Peak Mayall 4m telescope. The average [$^{35}$Cl/Fe] abundance in stars with --0.72$<$[Fe/H]$<$0.20 is [$^{35}$Cl/Fe]=(--0.10$\pm$0.15) dex. The mean difference between the [$^{35}$Cl/Fe] ratios measured in our stars and chemical evolution model values is (0.16$\pm$0.15) dex. The [$^{35}$Cl/Ca] ratio has an offset of $\sim$0.35 dex above model predictions suggesting chemical evolution models are under producing Cl at the high metallicity range. Abundances of C, N, O, Si, and Ca were also measured in our spectral region and are consistent with F and G dwarfs. The Cl versus O abundances from our sample match Cl abundances measured in planetary nebula and \ion{H}{2} regions. In one star where both H$^{35}$Cl and H$^{37}$Cl could be measured, a $^{35}$Cl/$^{37}$Cl isotope ratio of 2.2$\pm$0.4 was found, consistent with values found in the Galactic ISM and predicted chemical evolution models.

Halogen and Cl isotopic systematics in Martian phosphates: Implications for the Cl cycle and surface halogen reservoirs on Mars

The Cl isotopic compositions and halogen (Cl, F, Br, and I) abundances in phosphates from eight Martian meteorites, spanning most rock types and ages currently available, have been measured in situ by Secondary Ion Mass Spectrometry (SIMS). Likewise, the distribution of halogens has been documented by x-ray mapping. Halogen concentrations range over several orders of magnitude up to some of the largest concentrations yet measured in Martian samples or on the Martian surface, and the inter-element ratios are highly variable. Similarly, Cl isotope compositions exhibit a larger range than all pristine terrestrial igneous rocks. Phosphates in ancient (>4 Ga) meteorites (orthopyroxenite ALH 84001 and breccia NWA 7533) have positive δ37Cl anomalies (+1.1 to +2.5‰). These samples also exhibit explicit whole rock and grain scale evidence for hydrothermal or aqueous activity. In contrast, the phosphates in the younger basaltic Shergottite meteorites (<600 Ma) have negative δ37Cl anomalies (−0.2 to −5.6‰). Phosphates with the largest negative δ37Cl anomalies display zonation in which the rims of the grains are enriched in all halogens and have significantly more negative δ37Cl anomalies suggestive of interaction with the surface of Mars during the latest stages of basalt crystallization. The phosphates with no textural, major element, or halogen enrichment evidence for mixing with this surface reservoir have an average δ37Cl of −0.6‰, supporting a similar initial Cl isotope composition for Mars, the Earth, and the Moon. Oxidation and reduction of chlorine are the only processes known to strongly fractionate Cl isotopes, both positively and negatively, and perchlorate has been detected in weight percent concentrations on the Martian surface. The age range and obvious mixing history of the phosphates studied here suggest perchlorate formation and halogen cycling via brines, which have been documented on the Martian surface, has been active throughout Martian history.

Chlorine and hydrogen degassing in Vesta's magma ocean

The hydrophilic nature of halogens makes these elements ideal for probing potential hydrous geologic processes. Generally, in magmatic settings the stable isotopes of Cl may fractionate when H is in low concentrations and little fractionation occurs when the H concentration is high. We determined the Cl isotope composition and halogen content (F, Cl, Br, and I) of apatite and merrillite in seven basaltic eucrites, which are meteorites linked to the asteroid 4-Vesta, by using secondary ion mass spectrometry. We compare our halogen results with H isotope data, existing bulk rock concentrations, and petrologic models. The inferred Cl isotope composition of eucrites from this study, expressed in standard δ37Cl notation, which ranges from −3.8 to 7.7‰, correlates with the bulk major- and trace-element content, e.g., the Cl isotope composition positively correlates with Mg and Sc, while Cl isotope composition negatively correlates with K, V, and Cr. Here we suggest that eucrites preserve evidence of a degassing magma ocean as evidenced by the decreasing bulk rock K content with increasing δ37Cl. If the eucrite parent body, 4-Vesta, accreted with a negative δ37Cl of −3.8±1.1‰, at least some parts of the solar nebula would have been isotopically light compared to most estimates of the Earth, which on average is close to 0‰.

Band-Selective 2D HSQMBC: A Universal Technique for Detection and Measurement of 35,37Cl Isotope Effects for 13C Nuclei.

A novel technique that allows efficient measurement of the 35,37Cl isotope pattern for any 13C resonance has been developed. The band-selective CLIP-HSQMBC experiment is reliable and universally applicable for the indirect measurement of the 35,37Cl isotope shift of 13C resonances. The experiment provides advantages over conventional 1D 13C NMR and the recently developed bs-HSQC experiments. The utility and performance of the bs-CLIP-HSQMBC experiment is demonstrated for polyhalogenated synthons in a synthetic route and for a polyhalogenated marine natural product.

Subducted lithosphere controls halogen enrichments in the Iceland mantle plume source

Abstract The chlorine isotope composition of Earth’s interior can place strong constraints on deep-Earth cycling of halogens and the origin of mantle chemical heterogeneity. However, all mantle-derived volcanic samples studied for Cl isotopes thus far originate from submarine volcanic systems, where the influence of seawater-derived Cl is pervasive. Here, we present Cl isotope data from subglacial volcanic glasses from Iceland, where the mid-ocean ridge system emerges above sea level and is free of seawater influence. The Iceland data display significant variability in δ37Cl values, from −1.8‰ to +1.4‰, and are devoid of regional controls. The absence of correlations between Cl and O isotope ratios and the lack of evidence for seawater-derived enrichments in Cl indicate that the variation in δ37Cl values in Icelandic basalts can be solely attributed to mantle heterogeneity. Indeed, positive correlations are evident between δ37Cl values and incompatible trace element ratios (e.g., La/Y), and long-lived radiogenic Pb isotope ratios. The data are consistent with the incorporation of altered lithosphere, including the uppermost sedimentary package, subducted into the Iceland mantle plume source, resulting in notable halogen enrichments in Icelandic basalts relative to lavas from adjacent mid-ocean ridges.

Chlorine isotopic constraint on contrastive genesis of representative coastal and inland shallow brine in China

There are great scientific interests to reveal the shallow brine genesis in different geologic environments and also practical significance for resource production and environmental protection, which have not yet gained much attention, however. This study took shallow Quaternary brine in the coastal plain of Laizhou Bay and salt lake brine/intercrystalline brine in arid inland Qaidam Basin in China as two kinds of representative shallow brines, and comparatively analyzed the Cl stable isotopic signatures, coupled with hydrochemistry and water isotopes, aiming at finding out the salinity origin of shallow brines in the coast and inland basin, and further discussing Cl stable isotopic behavior in actual hydrogeological systems. The results indicated that shallow brine in the coastal zone originated from evaporation and precipitation formerly, and halite dissolution by tidewater or rainwater later, as a result of which, most of shallow brine exhibited enriched Cl isotopic signatures. As a contrast in arid inland basin, superficial brine originated from the dissolution of precipitated salt minerals by river water formerly, and intensive evaporation with subsequent precipitation in basin center later, for which all the brines finally exhibited the depleted Cl isotopic signatures. In addition, diffusion and ion filtration in the coast zone, and inflow of deep oilfield water in inland basin, were proposed as potential processes contributing to respective Cl isotopic signatures. In the coast, 37Cl are enriched and 81Br are depleted in most of shallow brines, while all the superficial brine (saline water) samples in arid inland basin exhibit negative δ37Cl and positive δ81Br values. Precipitation and dissolution of salt minerals were believed to contribute primarily to the contrary isotopic signatures, which would not change the Br isotopic compositions a lot for the solution in which the original Br concentration has been relatively high, which is not the case for Cl isotope, however.

Screening halogenated environmental contaminants in biota based on isotopic pattern and mass defect provided by high resolution mass spectrometry profiling

In the present work, we addressed the question of global seeking/screening organohalogenated compounds in a large panel of complex biological matrices, with a particular focus on unknown chemicals that may be considered as potential emerging hazards. A fishing strategy was developed based on untargeted profiling among full scan acquisition datasets provided by high resolution mass spectrometry. Since large datasets arise from such profiling, filtering useful information stands as a central question. In this way, we took advantage of the exact mass differences between Cl and Br isotopes. Indeed, our workflow involved an innovative Visual Basic for Applications script aiming at pairing features according to this mass difference, in order to point out potential organohalogenated clusters, preceded by an automated peak picking step based on the centWave function (xcms package of open access R programming environment). Then, H/Cl-scale mass defect plots were used to visualize the datasets before and after filtering. The filtering script was successfully applied to a dataset generated upon liquid chromatography coupled to ESI(−)-HRMS measurement from one eel muscle extract, allowing for realistic manual investigations of filtered clusters. Starting from 9789 initial obtained features, 1994 features were paired in 589 clusters. Hexabromocyclododecane, chlorinated paraffin series and various other compounds have been identified or tentatively identified, allowing thus broad screening of organohalogenated compounds in this extract. Although realistic, manual review of paired clusters remains time consuming and much effort should be devoted to automation.

CHARACTERIZATION OF THE LATE APTIAN TOP‐DARIYAN DISCONFORMITY SURFACE OFFSHORE SW IRAN: A MULTI‐PROXY APPROACH

The late Aptian disconformity at the top of the carbonate‐dominated Dariyan Formation is a regional‐scale surface recognised throughout SW Iran and adjacent areas to the south. This study investigates the disconformity using wireline logs, petrographic analyses, SEM observations, and CL and stable isotope data from an oilfield offshore SW Iran. The top‐Dariyan surface in the studied field is characterised by erosional incisions and clastic‐filled fissures which, together with secondary porosity in the underlying carbonates, uranium enrichment and meteoric infill cements, are interpreted as subaerial exposure‐related features. The clastic‐filled fissures were identified from gamma‐ray logs in horizontal wells, and infill material is composed of argillaceous carbonates, clays, quartz and iron‐bearing minerals. The correlation of GR logs in 19 vertical wells resulted in the recognition of erosional incisions (up to about 16 m deep) on the top‐Dariyan surface, together with thickening of siliciclastic sediments in the overlying basal part of the Kazhdumi Formation. Back‐filled sediments in erosional incisions may form potential exploration targets. Secondary porosity in the uppermost 20 m of the Dariyan Formation was created by meteoric processes during subaerial exposure. Cathodoluminescence microscopy of diagenetic cements, carbon and oxygen isotope data and elemental analyses were used to reconstruct the diagenetic history of the carbonates in the Upper Dariyan interval.

Chlorine isotope geochemistry of Icelandic thermal fluids: Implications for geothermal system behavior at divergent plate boundaries

The chlorine isotope composition of thermal fluids from Iceland were measured in order to evaluate the source of chlorine and possible chlorine isotope fractionation in geothermal systems at divergent plate boundaries. The geothermal systems studied have a wide range of reservoir temperatures from 40 to 437 °C and in-situ pH of 6.15 to 7.15. Chlorine concentrations range from 5.2 to 171 ppm and δ37Cl values are −0.3 to +2.1‰ (n=38). The δ37Cl values of the thermal fluids are interpreted to reflect the source of the chlorine in the fluids. Geothermal processes such as secondary mineral formation, aqueous and vapor speciation and boiling were found to have minimal effects on the δ37Cl values. However, further work is needed on incorporation of Cl into secondary minerals and its effect on Cl isotope fractionation. Results of isotope geochemical modeling demonstrate that the range of δ37Cl values documented in the natural thermal fluids can be explained by leaching of the basaltic rocks by meteoric source water under geothermal conditions. Magmatic gas partitioning may also contribute to the source of Cl in some cases. The range of δ37Cl values of the fluids result mainly from the large range of δ37Cl values observed for Icelandic basalts, which range from −0.6 to +1.2‰.

Chlorine isotope and Cl–Br fractionation in fluids of Poás volcano (Costa Rica): Insight into an active volcanic–hydrothermal system

Halogen-rich volcanic fluids issued at the surface carry information on properties and processes operating in shallow hydrothermal systems. This paper reports a long-term record of Cl–Br concentrations and δ37Cl signatures of lake water and fumaroles from the active crater of Poás volcano (Costa Rica), where surface expressions of magmatic-hydrothermal activity have shown substantial periodic changes over the last decades. Both the hyperacid water of its crater lake (Laguna Caliente) and subaerial fumaroles show significant temporal variability in Cl–Br concentrations, Br/Cl ratios and δ37Cl, reflecting variations in the mode and magnitude of volatile transfer. The δ37Cl signatures of the lake, covering the period 1985–2012, show fluctuations between +0.02±0.06‰ and +1.15±0.09‰. Condensate samples from adjacent fumaroles on the southern shore, collected during the interval (2010–2012) with strong changes in gas temperature (107–763°C), display a much larger range from −0.43±0.09‰ to +14.09±0.08‰. Most of the variations in Cl isotope, Br/Cl and concentration signals can be attributed to interaction between magma-derived gas and liquid water in the volcanic–hydrothermal system below the crater. The δ37Cl were lowest and closest to magmatic values in (1) fumarolic gas that experienced little or no interaction with subsurface water and followed a relatively dry pathway, and (2) water that captured the bulk of magmatic halogen output so that no phase separation could induce fractionation. In contrast, elevated δ37Cl can be explained by partial scavenging and fractionation during subsurface gas–liquid interaction. Hence, strong Cl isotope fractionation leading to very high δ37Cl in Poás’ fumaroles indicates that they followed a wet pathway. Highest δ37Cl values in the lake water were found mostly in periods when it received a significant input from subaqueous fumaroles or when high temperatures and low pH caused HCl evaporation. It is concluded that combined monitoring of δ37Cl and Br/Cl in Laguna Caliente and adjacent fumaroles provides valuable information on activity in the subsurface hydrothermal system with significant relevance for volcanic surveillance of Poás.

Using environmental isotopes and dissolved methane concentrations to constrain hydrochemical processes and inter-aquifer mixing in the Galilee and Eromanga Basins, Great Artesian Basin, Australia

Summary Groundwater recharge processes, water–rock interaction and the hydraulic connectivity between aquifers of the Galilee and Eromanga Basins in central Queensland, Australia, were investigated using stable (δ 2 H, δ 18 O, δ 13 C and 87 Sr/ 86 Sr) and radiogenic ( 36 Cl) isotopes and dissolved methane concentrations, complemented by major ion chemistry. The central Eromanga and the upper sequence of the Galilee basins are both sub-basins of the Great Artesian Basin (GAB), and the coal seams of the Galilee Basin are currently explored for their potential as commercial coal seam gas deposits. In order to understand the potential influence of depressurisation of coal seams required to release the gas on adjacent aquifers, a detailed understanding of recharge processes and groundwater hydraulics of these basins prior to any development is required. Each of the different isotope systems were used in this study to provide different information on specific processes. For example, the assessment of δ 13 C and 87 Sr/ 86 Sr ratios suggested that carbonate dissolution is one of the major processes controlling the water chemistry within some aquifers. In addition, the combined assessment of δ 2 H, δ 18 O and major ion chemistry indicates that transpiration is the primary process controlling the solute concentration in the GAB recharge area, whereas evaporation appears to be less significant. Groundwaters in the Galilee Basin recharge area (outside the limits of the GAB) are different to any groundwater within the GAB units. This difference is attributed to the dissolution of potassium-bearing micas, which are absent in the GAB. Groundwater age estimates based on 36 Cl/Cl ratios suggest that there is a steady increase along the flow paths, and this lack of anomalous age estimates from the recharge areas to the deeper parts of the basin indicates that there is no evidence for regional inter-aquifer mixing based in isotopes only. However, dissolved methane concentrations and groundwater chemistry near faults indicates the potential mix of gas and/or water from the coal seams into the GAB groundwaters, suggesting that there may be local influence of faults as gas/water conduits.

Early degassing of lunar urKREEP by crust-breaching impact(s)

Current models for the Moon's formation have yet to fully account for the thermal evolution of the Moon in the presence of H2O and other volatiles. Of particular importance is chlorine, since most lunar samples are characterised by unique heavy δ37Cl values, significantly deviating from those of other planetary materials, including Earth, for which δ37Cl values cluster around ∼0‰. In order to unravel the cause(s) of the Moon's unique chlorine isotope signature, we performed a comprehensive study of high-precision in situ Cl isotope measurements of apatite from a suite of Apollo samples with a range of geochemical characteristics and petrologic types. The Cl-isotopic compositions measured in lunar apatite in the studied samples display a wide range of δ37Cl values (reaching a maximum value of +36‰), which are positively correlated with the amount of potassium (K), Rare Earth Element (REE) and phosphorous (P) (KREEP) component in each sample. Using these new data, integrated with existing H-isotope data obtained for the same samples, we are able to place these findings in the context of the canonical lunar magma ocean (LMO) model. The results are consistent with the urKREEP reservoir being characterised by a δ37Cl ∼+30‰. Such a heavy Cl isotope signature requires metal-chloride degassing from a Cl-enriched urKREEP LMO residue, a process likely to have been triggered by at least one large crust-breaching impact event that facilitated the transport and exposure of urKREEP liquid to the lunar surface.

Ultra-high resolution band-selective HSQC for nanomole-scale identification of chlorine-substituted 13 C in natural products drug discovery.

Ultra-high resolution band-selective HSQC (bsHSQC) has been employed for detection of 35 Cl-37 Cl isotope shifted 13 C NMR signals for assignment of regioisomerism in bromo-chloro natural products. Optimum pulse sequence and instrumental parameters for maximization of detection of the isotope shifts were explored. The chlorine isotope shifts (Δδ) were detected within crosspeaks and were shown to vary with hybridization of 13 C, substitution of 13 C, presence of β-chloro substituents, and their relative configuration. Deconvolution of Cl-substituted CH bsHSQC crosspeaks may provide other useful information, including a potentially MS-independent method for quantitating 37 Cl/35 C isotopic fractionation during the biosynthesis of halogenated natural products. Copyright © 2016 John Wiley & Sons, Ltd.

Chlorine isotopes in sediments of the Qarhan Playa of China and their paleoclimatic significance

This study presents chlorine isotopic composition of salt deposits recovered in a core from the Qarhan Saline Lake in the Qinghai Province of China. The δ37Cl trend has three stages, and they correspond to the upper, middle, and lower salt-bearing groups of the entire evaporite system. The δ37Cl values are between −0.22‰ and 0.13‰ with an average value of −0.02‰ in the lower salt-bearing group. It ranges between 0.14‰ and 0.76‰ (x¯=0.36‰) in the middle salt-bearing group, and varies between −0.35‰ to 0.35‰ (x¯=−0.04‰) in the upper salt-bearing group. This work indicates that stratification of δ37Cl values is accompanied by stratigraphic variations in Mg/Cl and K/Cl in halite. We suggest a “evaporation cycles model” and it indicates the potential of Cl isotope as a geochemical tracer in order to understand paleoclimatic conditions during different stages of evaporite deposition.