Subsurface gas transport is critical for containment performance following underground nuclear detonations or high-explosive tests. Such gases can provide fingerprinting needed to identify whether detected seismic signals have a nuclear or chemical source, provided that their subsurface transport can be accurately interpreted. In this study, we examine carbon dioxide (CO2) diffusion through dry core samples taken from representative lithologies at the Nevada National Security Site (NNSS) and compare laboratory-measured transport with field observations after a subsurface high-explosive experiment. Controlled laboratory breakthrough tests quantified CO2 migration across lithologies with varying zeolite content. Results show pronounced lithologic dependence, with zeolite-rich samples exhibiting marked retardation of CO2 attributed to adsorption within the zeolite frameworks. Field measurements of post-detonation gas composition and concentration gradients similarly revealed delayed CO2 migration within more zeolitized horizons, which were distinct from dissolution into pore water. This corresponding behavior across laboratory and field scales indicates that zeolite content exerts a dominant control on CO2 subsurface mobility and retention at the NNSS. These findings highlight the need to account for mineralogically controlled sorptive processes when modeling gas transport in zeolitized formations and underscore the value of linking laboratory diffusion data with field-scale observations to improve predictions of post-detonation gas behavior at the NNSS and similar sites.

Abstract. Measurements of methane (CH4) molecules containing two rare isotopes (13CH3D and 12CH2D2), also termed doubly substituted or ‘clumped’ isotopologues, have the potential to provide two additional isotopic dimensions to help investigating mechanisms producing the recent global trends and CH4 budget over decadal timescale. In this work, we summarise the current state of research on doubly substituted CH4 isotopologues, with an emphasis on compiling results of all relevant work. The database comprises 1475 records compiled from the literature published until April 2025 (https://dx.doi.org/10.5285/51ae627da5fb41b8a767ee6c653f83e6). For field samples, 40 % of records were sourced from natural gas reservoirs, while microbial terrestrial (e.g., agriculture, lake, wetland) samples account only for 12.5 %. Lakes samples contribute 75 % to collected microbial terrestrial samples. There is limited or no representation of samples coming from significant microbial CH4 sources to the atmosphere, like wetlands, agriculture and landfill. To date, laboratory experiments were mostly focused on microbial (28 % of samples from laboratory experiments) and pyrogenic (15 %) methanogenesis or anaerobic (16 %), and aerobic (8 %) CH4 oxidation, and only a single contribution to studies of photochemical oxidation via OH and Cl (5 %). The distinct ranges of Δ13CH3D and Δ12CH2D2 values measured in these studies suggests their potential to improve our understanding of atmospheric CH4. This work provides an overview of the major gaps in measurements and identifies where further studies should be focussed to enable the highest immediate impact on understanding global CH4.

Measurements of methane (CH4) molecules containing two rare isotopes (13CH3D and 12CH2D2), also termed doubly substituted or "clumped" isotopologues, have the potential to provide two additional isotopic dimensions to help investigate the mechanisms underlying global atmospheric trends in CH4. In this work, we summarise the current state of research on doubly substituted CH4 isotopologues, with an emphasis on compiling results of all relevant work. The database comprises 1475 records compiled from the literature published until April 2025 (10.5285/51ae627da5fb41b8a767ee6c653f83e6, Defratyka et al., 2025). For field samples, 40% of records were sourced from natural gas reservoirs, while microbial terrestrial (e.g., agriculture, lake, wetland) samples account only for 12.5 %. Lakes samples contribute 75 % to collected microbial terrestrial samples. There is limited or no representation of samples coming from significant microbial CH4 sources to the atmosphere, like wetlands, agricultural practices and landfills. To date, laboratory experiments were mostly focused on microbial (28 % of samples from laboratory experiments) and pyrogenic (15 %) methanogenesis or anaerobic (16 %), and aerobic (8 %) CH4 oxidation, with only single study of photochemical oxidation via OH and Cl, which constitutes 5 % of the laboratory experiments entries. The distinct ranges of triangle(CH3D)-C-13 and triangle(CH2D2)-C-12 values measured in these studies suggests their potential to improve our understanding of atmospheric CH4. This work provides an overview of the major gaps in measurements and identifies where further studies should be focussed to enable the highest impact on understanding global CH4.

Current underground nuclear explosion (UNE) detection strategies rely heavily on atmospheric noble gas sampling of radioxenon. However, discriminating nuclear weapons testing programs from civilian sources is difficult due to highly variable atmospheric radioxenon backgrounds and processes affecting subsurface transport of parent radionuclides. We aim to study the transport of gases produced by subsurface explosions as novel stable signatures for underground nuclear explosion (UNE) monitoring. These gases may be produced in large quantities with distinct molecular ratios, which will be impacted by subsurface transport processes. To demonstrate how ratios of gases produced by explosions can change during transport in geomaterials, we conducted laboratory benchtop experiments on the transport of carbon dioxide (CO2) and hydrogen (H2) gases through variably saturated zeolitic tuff, which is abundant at the historic US testing site. We observed that zeolitic tuff sorbs substantial quantities of CO2 while allowing H2 to transport more freely, leading to changes in the molecular ratios of the two gases along the transport pathway. Gas uptake in the dry zeolitic tuff core was 72.3

Naturally occurring bedded salt deposits are considered robust for the permanent disposal of heat-generating nuclear waste due to their unique physical and geological properties. The Brine Availability Test in Salt (BATS) is a US-DOE Office of Nuclear Energy funded project that uses heated borehole experiments underground (∼655 meters depth) at the Waste Isolation Pilot Plant (WIPP) in the bedded salt deposits of the Salado Formation to investigate the capacity for safe disposal of high-level, heat generating nuclear waste in salt. Uncertainties associated with brine mobility near heat-generating waste motivates the need to characterize the processes and sources of brine in salt deposits. Intragranular halite fluid inclusions are a potential source of brine that can migrate under temperature gradients toward heat sources. We developed a methodology to measure the stable isotopic compositions of water (δD VSMOW, δ18 O VSMOW) in brine from halite fluid inclusions using Cavity Ring-Down Spectroscopy that accounts for memory effects using a unique reference-sample-reference bracketing approach and that minimizes sample size requirements. We applied this approach to halite samples obtained from WIPP and compare these data to seeped brines collected from horizontal boreholes at WIPP after drilling at ambient conditions. The stable isotope compositions that we obtain for halite fluid inclusions (δ18 O VSMOW = +3.24 ± 0.53‰, δD VSMOW = -25.3 ± 5.1‰, ±1σ, n = 5) generally agree with previous measurements and likely reflect a combination of syn-depositional and/or postdepositional processes. The seep brines are isotopically distinct (δ18 O VSMOW = +3.46 ± 0.84‰, δD VSMOW = +7.3 ± 3.5‰, ±1σ, n = 35) and instead resemble evaporated seawater. We discuss our results in the context of prior WIPP-proximal waters and lay the groundwork for using stable isotopes of water in brine as a tool to assess the heat-induced mobilization of halite fluid inclusions in ongoing heating experiments that comprise the Brine Availability Test in Salt.

to national authorities to aid in resolving ambiguities and to serve as the basis for appropriate action. To collect this evidence, one must develop technologies that can detect and identify the signals from a nuclear test against a background of hundreds of thousands of benign events. The monitoring system must have high sensitivity to detect the events of interest and, to minimize false alarms, it must identify those events with a high level of confidence.

Abstract Signatures of mass‐independent fractionation (MIF) of sulfur in Archean sulfide and sulfate minerals are widely thought to record an anoxic early Earth’s atmosphere. While experiments of ultraviolet irradiation of SO2 produce significant sulfur mass‐independent fractionation (S‐MIF) in reaction products (elemental sulfur and residual sulfur dioxide), they have not been able to reproduce the isotope patterns, in particular Δ36S/Δ33S ratios, observed in the geologic rock record. Studies that focused on organic sulfur gases and hazes in Archean did not report organosulfur aerosol photoproducts as major contributors to Archean S‐MIF chemistry. Here we show, for the first time, that photochemical reactions of SO2 in the presence of gaseous hydrocarbons (CH4, C2H2, and C2H4) produce haze‐like organosulfur aerosols bearing S‐MIF with variable Δ36S/Δ33S ratios. The isotope trends for the organosulfur photoproducts produced in our experiments suggest that in addition to elemental sulfur, organosulfur compounds—in particular methanesulfonic acid—are a key component of S‐MIF signals from the atmosphere to the ocean and sediments with possible links to Archean atmosphere warmed by a methane greenhouse.

Methane clumped isotope compositions signify the relative natural abundances of rare, doubly substituted isotopic species of methane (13CH3D and 12CH2D2) and have emerged as a new isotopic tool to trace the sources, sinks, and lifecycles of methane in the environment. Such measurements can identify equilibration (or reequilibration) temperatures if found to be in isotopic equilibrium or non-equilibrium processes (e.g., kinetically controlled reactions or mixing) if not in isotopic equilibrium. Naturally occurring thermogenic methane-formed by the thermally activated breakdown of larger organic molecules-has been found to have clumped isotope compositions consistent with equilibrium at reasonable gas formation temperatures in some settings and non-equilibrium processes occurring during either formation, migration, storage, or extraction in others. To explore the potential controls on the isotopic composition of thermogenic methane, we conducted isothermal time-series ethane pyrolysis experiments at 550 and 600 & DEG;C to measure methane and ethane 13C/12C and D/H fractionations and methane clumped isotope compositions (resolved 13CH3D and 12CH2D2). We explore the effects of modifying the initial clumped isotope composition of ethane and the addition of water vapor to pyrolysis experiments. We observe that ethane and methane 13C/12C are controlled by kinetic isotope effects and Rayleigh distillation processes. In contrast, ethane and methane D/H and methane clumped isotope compositions appear to be controlled by a combination of these processes and hydrogen isotope exchange. The hydrogen isotope exchange processes lead to isotopic equilibrium as reaction completion is approached for both D/H (ethane/methane) and methane clumped isotope compositions. We develop a chemical model based on a mass balance approach that accounts for inheritance vs. hydrogen-abstraction formation pathways for singly and doubly substituted isotopologues of ethane and methane that is compared to the experimental data. The model allows the determination of carbon and hydrogen kinetic isotope effects associated with ethane cracking and hydrogen abstraction reactions that, where applicable, we compare to prior theoretical constraints. From the comparison of the model to the experimental data, we infer that the kinetically controlled ethane and methane bulk isotope compositions and methane clumped isotope compositions are controlled by kinetic isotope effects (both primary and secondary) associated with both C-C bond and C-H bond cleavage reactions. Specifically, the methane clumped isotope compositions likely result from a combination of clumped isotope effects associated with ethane breakdown and/or assembly of methane isotopologues (expressed in terms of & gamma;-factor parameters =/ 1) and combinatorial effects that arise probabilistically. We discuss our experimental results in the context of recent pyrolysis experiments and observations of naturally occurring thermogenic methane. We consider a proposal consistent with observations from nature that the hydrogen isotope exchange reactions that promote equilibration of methane isotopic molecules at or near formation temperature may be facilitated by free radicals generated by pyrolysis reactions. In this framework, isotope exchange effectively ceases when pyrolysis effectively ceases locking in compositions that can be consistent with peak formation temperatures.

Inorganic polysulfur compounds (polysulfides, Sx2-; polysulfur radical ions, Sx·-; thiosulfate, S2O32-; polythionate, SxO62-; elemental sulfur, e.g. S8) participate in numerous geochemical processes related to the sulfur cycle. These include authigenic pyrite formation in sediments undergoing early stages of diagenesis, reactions associated with magmatic-hydrothermal processes, and numerous other aquatic sulfur redox processes (e.g., pyrite and sulfide oxidation). Sulfur isotope fractionations among many of these and associated compounds (e.g., H2S, HSO4-) are either unknown or unconstrained over wide ranges of temperatures. We present theoretical estimates of equilibrium sulfur isotope fractionation factors among aqueous polysulfur compounds (including select polysulfides, polysulfur radical anions, and polythionates) and select aqueous sulfide and sulfate compounds that correspond to all three stable isotope ratios of sulfur (33S/32S, 34S/32S, 36S/32S). Our estimates are based on electronic structure calculations performed at the B3LYP/6–31+G(d,p) level of theory and basis set implemented in concert with an explicit solvation model whereby molecules are encapsulated in water clusters of varying size (30–52 H2O) to simulate the aqueous solvation environment. These calculations yield relatively small magnitude fractionation factors between aqueous polysulfides, polysulfur radicals, and reduced sulfur moieties in polythionates relative to the aqueous sulfide compounds but reveal numerous crossovers that result in non-intuitive temperature dependencies. Our predictions of 34S/32S-based fractionation factors among aqueous sulfur compounds generally agree with previous experimental constraints where available within estimated uncertainties (e.g., HSO4-/H2S(aq), H2S(aq)/HS-, HSO4-/S0, H2S(aq)/S0). We use our calculations to explore equilibrium isotope fractionations among polysulfur and sulfide compounds that are precursors to authigenic pyrite in the framework of established mechanisms (e.g., the polysulfide mechanism). We examine possible explanations for why pyrite formation may be associated with relatively small isotope fractionation with respect to precursor aqueous sulfur compounds. We additionally use our theoretical calculations to constrain multiple sulfur isotope (33S/32S, 34S/32S, 36S/32S) mass balance models associated with the abiotic hydrolytic disproportionation of intermediate sulfur compounds (SO2, S8, S3·-) relevant to hydrothermal-magmatic-volcanic systems in order to illustrate the potential for subtle but potentially resolvable effects expressed in values of Δ33S and Δ36S associated with these processes. We apply a SO2 disproportionation mass balance model based on previous work but newly constrained by our theoretical calculations to (hyper-) acid crater lakes associated with active volcanoes, and newly highlight the potential for the utility of multiple sulfur isotope analyses in volcanic gas monitoring and constraining sulfur cycling processes in such systems.

The stable isotopic composition of methane (CH4) is commonly used to fingerprint natural gas origins. Over the past 50 years, there have been numerous proposals that both microbial and thermogenic CH4 can form in or later attain hydrogen isotopic equilibrium with water (H2O) and carbon isotopic equilibrium with carbon dioxide (CO2). Evaluation of such proposals requires knowledge of the equilibrium fractionation factors between CH4 and H2O or CO2 at the temperatures where microbial and thermogenic CH4 form in or are found in the environment, which is generally less than 200 degrees C. Experimental determinations of these fractionation factors are only available above 200 degrees C, requiring extrapolation of these results beyond the calibrated range or the use of theoretical calculations at lower temperatures. Here, we provide a calibration of the equilibrium hydrogen isotopic fractionation factor for CH4 and hydrogen gas (H-2) ((D)alpha(CH4( g)-H2(g))) based on experiments using gamma-Al2O3 and Ni catalysts from 3 to 200 degrees C. Results were regressed as a 2nd order polynomial of 1000 x ln(D) alpha(CH4(g)-H2(g)) vs. 1/T (K-1) yielding: 1000 x ln D alpha(CH4(g)-H2(g)) = 3.5317x10(7)/T-2 + 2.7749x10(5)/T - 179.48 We combine this calibration with previous experimental determinations of hydrogen isotope equilibrium between H-2, H2O(g), and H2O(l) and we provide an interpolatable experimental calibration of 1000 x ln(D) alpha(CH4( g)-H2O(l)) from 3 to 200 degrees C. Our resulting 4th order polynomial is the following equation: 1000 x ln(D) alpha(CH4(g)-H2O(l)) = -7.9443x10(12)/T-4 + 8.7772x10(10)/T-3 + 3.4973x08/T-2 + 5.4398x10(5)/T - 382.05 At 3 degrees C, the value from our calibration differs by 93% relative to what would be calculated based on the extrapolation of the only experimental calibration currently available to temperatures below its calibrated range (lowest temperature of 200 degrees C; Horibe and Craig, 1995). We additionally provide new theoretical estimates of hydrogen isotopic equilibrium between CH4(g), H-2(g), and H2O(g) and carbon isotopic equilibrium between CH4(g) and CO2(g) using Path Integral Monte Carlo (PIMC) calculations. Our PIMC calculations for hydrogen isotopic equilibrium between CH4 and H-2 agree 1:1 with our experiments. Finally, we compile carbon and hydrogen isotopic measurements of CH4, CO2, and H2O from various environmental systems and compare observed differences between carbon and hydrogen isotopes to those expected based on isotopic equilibrium. We find that isotopic compositions of some microbial gases from marine sedimentary, coalbed, and shale environments are consistent with those expected for CH(4)AH(2)O(l) hydrogen and CH(4)ACO(2) carbon isotopic equilibrium. In contrast, microbial terrestrial and pure culture gases are not consistent with both CH(4)AH(2)O(l) hydrogen and CH(4)ACO(2) carbon isotopic equilibrium. These results are explained qualitatively using previously developed conceptual models that link free energy gradients available to microorganisms to the degree that their enzymes can promote isotope-exchange reactions between CH4, CO2, and H2O. (C) 2021 Published by Elsevier Ltd.

Methyl groups are found in numerous biogenic and synthetic materials including geologically preserved materials such as wood. The carbon and hydrogen isotope compositions of methyl groups are used as tracers in biogeochemical cycles, as pale-othermometers, and to determine the hydrogen isotopic composition of ancient rain. Here we present analyses of resolved C-13-D ((CH2D)-C-13) and D-D ((CHD2)-C-12) clumped isotope compositions of methyl groups as new variables for the study of methyl groups in the present and past. We first present chemical methods to extract, purify, and derivatize methyl groups from methoxyl (R-O-CH3) groups as CH3F and CH3Cl, and high-resolution mass spectrometric techniques to determine the clumped isotope compositions of these species. We achieve precisions for C-13-D clumping of +/- 0.25 parts per thousand and D-D clumping of +/- 2.5 parts per thousand. We anchor our clumped isotopic measurements to a thermodynamic reference frame by first calculating the theoretical temperature dependences of C-13-D and D-D clumping in CH3Cl, then placing our measurements onto this reference frame through experimental internal isotopic equilibration of CH3Cl at 200 degrees C. Finally, we provide and analyze an initial dataset of clumped 13C-D and D-D compositions of methyl groups from various commercial/synthetic monomers and environmental woods. We observe ranges in clumped isotope compositions of similar to 11 parts per thousand in C-13-D and similar to 48 parts per thousand in D-D, and systematic differences within these ranges between methyl groups from commercial monomers and wood. Specifically, commercial clumped 13C-D compositions are between 0 and 3 parts per thousand, which correspond to apparent equilibrium temperatures between 170 degrees C and the infinite temperature limit. In contrast, the clumped 13C-D compositions of wood methoxyl groups are distinctively high (9.50-11.25 parts per thousand) and 3-6 parts per thousand higher than would be expected if formed in internal isotopic equilibrium at Earth-surface temperatures. Commercial/synthetic methyl and wood methoxyl clumped D-D compositions are also distinct: -5 to +13 parts per thousand in commercial monomers vs. -35 to -8 parts per thousand in wood-such negative values cannot result from formation in isotopic equilibrium and require kinetic processes to have occurred. These results indicate that wood methoxyl groups are formed out of isotopic equilibrium and that clumped isotope compositions of methyl groups may be useful tracers of methyl group sources and sinks in the environment. For instance, isotopic clumping in methyl groups may be useful for understanding controls on isotopic clumping in methane produced by methylotrophic methanogens. (C) 2020 Elsevier Ltd. All rights reserved.

Methane is produced and consumed via numerous microbial and chemical reactions in atmospheric, hydrothermal, and magmatic reactions. The stable isotopic composition of methane has been used extensively for decades to constrain the source of methane in the environment. A recently introduced isotopic parameter used to study the formation temperature and formational conditions of methane is the measurement of molecules of methane with multiple rare, heavy isotopes ("clumped") such as (CH3D)-C-13 and (CH2D2)-C-12. In order to place methane clumped isotope measurements into a thermodynamic reference frame that allows calculations of clumped isotope-based temperatures (geothermometry) and comparison between laboratories, all past studies have calibrated their measurements using a combination of experiment and theory based on the temperature dependence of clumped isotopologue distributions for isotopically equilibrated systems. These have previously been performed at relatively high temperatures (>150 degrees C). Given that many natural occurrences of methane form below these temperatures, previous calibrations require extrapolation when calculating clumped isotope-based temperatures outside of this calibration range. We provide a new experimental calibration of the relative equilibrium abundances of (CH3D)-C-13 and (CH2D2)-C-12 from 1 to 500 degrees C using a combination of gamma-Al2O3- and Ni-based catalysts and compare them to new theoretical computations using Path Integral Monte Carlo (PIMC) methods and find 1:1 agreement (within +/- 1 standard error) for the observed temperature dependence of clumping between experiment and theory over this range. This demonstrates that measurements, experiments, and theory agree from 1 to 500 degrees C, providing confidence in the overall approaches. Polynomial fits to PIMC computations, which are considered the most rigorous theoretical approach available, are given as follows (valid T >= 270 K): Delta(CH3D)-C-13 congruent to 1000 X ln((KCH3D)-C-13) = (1.47348 X 10(19))/T-7 - (2.08648 x 10(17))/T-6 + (1.19810 x 10(15))/T-5 (3.54757 x 10(12))/T-4 + (5.54476 X 10(9))/T-3 (3.49294 x 10(6))/T-2 + (8.89370 x 10(2))/T and Delta(CH2D2)-C-12 congruent to 1000 X ln(8/3K(12)CH(2)D(2)) = (9.67634 X 10(15))/T-6 + (1.71917 X 10(14))/T-5 (1.24819 X 10(12))/T-4 (4.30283 X 10(9))/T-3 (4.48660 X 10(6))/T-2 + (1.86258 X 10(3))/T. We additionally compare PIMC computations to those performed utilizing traditional approaches that are the basis of most previous calibrations (Bigeleisen, Mayer, and Urey model, BMU) and discuss the potential sources of error in the BMU model relative to PIMC computations.

Sulfide oxidation is a major component of the global sulfur cycle that requires consideration in isotope-based models of aquatic and sedimentary systems, but the isotope fractionations based on analyses of all three isotope ratios of sulfur (S-33/S-32, S-34/S-32, S-36/S-32) have yet to be documented for abiological sulfide oxidation processes. We present experimental determinations of the reaction rates and sulfur isotope fractionations associated with the oxidation of aqueous sulfide (principally HS-) by molecular oxygen ('autoxidation') in high pH (approximate to 9.8), low ionic strength carbonate/bicarbonate buffered solutions as a function of temperature (5-45 degrees C) and trace metal catalysis (ferrous iron, added [Fe2+]similar to 50-150 nM). Rates and isotope fractionations are quantified via the analysis of sulfide as a function of reaction progress over relatively low extents of reaction (ca.33-47 parts per thousand). The oxidation of sulfide at pH = 9.8 and 25 degrees C without any catalyst added is associated with a computed second order rate constant (k) of lnk = 3.49 +/- 0.38 (k in M-1 hr(-1); 2 s.d.,quadruple experiments) and major sulfur isotope discrimination of (34)epsilon(P-R) = -5.85 +/- 0.43 parts per thousand (2 s.d., duplicate experiments) that are both consistent with previous studies, and a corresponding minor sulfur isotope fractionation relationship of (33/34)theta = 0.509 +/- 0.004 that translates to Delta S-33(P-R) = 0.033 +/- 0.018 parts per thousand (2 s.d.). The dependence of (34)epsilon(P-R) on reaction rate due to either temperature or ferrous iron catalysis over the ranges we have studied is small (<similar to 1 parts per thousand in (34)epsilon(P-R)) and similar values for (33/34)theta and Delta S-33(P-R) are obtained for all conditions studied (e.g., mean of all 7 experiments: (33/34)theta = 0.5082 +/- 0.0031 and Delta S-33(P-R) = 0.037 +/- 0.014 parts per thousand; 2 s.d.). These results indicate that the process of sulfide autoxidation has a mass dependence that is resolvable from the expectations of typical equilibrium isotope exchange. Values for (36/34)theta and Delta S-36(P-R) may also exhibit deviations from typical equilibrium isotope exchange but are not resolved under all conditions studied. The shift in values of (33/34)theta and Delta S-33 (and potentially (36/34)theta and Delta S-36) is consistent with the hypotheses that kinetic isotope effects can be associated with different mass laws than equilibrium processes or with reversibility occurring in the initial parts of the reaction network leading to oxidation products, but both hypotheses will likely require further investigation. We provide an example of how our experimentally calibrated 'signature' for sulfide autoxidation may be identified in natural data using the previously published Delta S-34 and Delta S-33 values of dissolved sulfide in proximity to the oxic-sulfidic interface in the water column of the Cariaco Basin. The observation that the autoxidation of aqueous sulfide in high pH media is associated with a non-zero Delta S-33(P-R) will influence how chemical oxidation processes are treated in environmental and global scale models of the sulfur cycle based on multiple sulfur isotopes. (C) 2018 Elsevier Ltd. All rights reserved.

Bisulfite (HSO3-) and sulfite (SO32-) compounds play key roles in numerous geochemical and biochemical processes extending from the atmosphere to the subseafloor biosphere. Despite decades of spectroscopic investigations, the molecular composition of HSO3-in solution remains uncertain and, thus, the role of bisulfite in (bio) chemical and isotope fractionation processes is unclear. We report new experimental estimates for the bisulfite isomer quotient (Q(i) = [(HO)SO2-]/[(HS)O-3(-)]; [] = concentration) as a function of temperature from the interpretation of Raman spectra collected from aqueous NaHSO3 solutions contained in fused silica capsules. In pure NaHSO3 solutions (1Na(+): 1HSO(3)(-), stoichiometric) over [NaHSO3] = 0.2-0.4 m (moles/kg H2O), the following relationship is obtained: ln (Q(i)) -878.59(+/- 32: 98)/T -1: 9642(+/- 0: 1081), where T = 278-358 K (5-85 degrees C) (based on 50 determinations; additional significant figures are provided to avoid rounding errors). This relationship suggests that the minor isomer, (HS)O-3(-), may comprise 23-38% (+/- 3%) of the mole fraction of HSO3- over 5-85 degrees C, respectively, which is higher in relative abundance than has generally been understood previously. We additionally provide estimates for Q(i) in NaHSO3 solutions containing a total ionic strength of mu = 1.0 m (0.2 m NaHSO3 + 0.8 m NaCl) and different pH (3.3-4.5), but do not appear to resolve any significant differences in Q(i) as a function of these additional variables. These new values of Q(i) are employed to re-assess the bulk sulfur isotope fractionations among bisulfite and other S (IV) compounds as a function of temperature, which appear to be highly dependent on the amount of (HS)O-3 present. Our new constraints on the bisulfite isomer quotient may allow for a detailed assessment of the molecular composition and isotope mass balance of S(IV) solutions containing HSO3-, and may be useful in the further investigation of the mechanisms and isotope fractionations associated with a number of processes that involve bisulfite compounds. These may include the intracellular enzymatic transformations of sulfite and bisulfite compounds that occur as part of dissimilatory sulfate reduction, which is a major and geologically important form of anaerobic respiration. (C) 2017 Elsevier Ltd. All rights reserved.

Variability in the sulfur isotopic composition in sediments can reflect atmospheric, geologic and biological processes. Evidence for ancient fluvio-lacustrine environments at Gale crater on Mars and a lack of efficient crustal recycling mechanisms on the planet suggests a surface environment that was once warm enough to allow the presence of liquid water, at least for discrete periods of time, and implies a greenhouse effect that may have been influenced by sulfur-bearing volcanic gases. Here we report in situ analyses of the sulfur isotopic compositions of SO2 volatilized from ten sediment samples acquired by NASA’s Curiosity rover along a 13 km traverse of Gale crater. We find large variations in sulfur isotopic composition that exceed those measured for Martian meteorites and show both depletion and enrichment in 34S. Measured values of δ34S range from −47 ± 14‰ to 28 ± 7‰, similar to the range typical of terrestrial environments. Although limited geochronological constraints on the stratigraphy traversed by Curiosity are available, we propose that the observed sulfur isotopic signatures at Gale crater can be explained by equilibrium fractionation between sulfate and sulfide in an impact-driven hydrothermal system and atmospheric processing of sulfur-bearing gases during transient warm periods. Ancient Mars may have had an active sulfur cycle. In situ analyses by the Curiosity rover reveal large variations in the current sulfur isotopic composition of Martian sediments that can be explained by geologic and atmospheric processes.

This study investigated whether the use of a gamified mobile learning app influenced students’ academic performance and boosted their engagement in the subject. Created to better engage students in lecture content, the app was used to deliver multiple-choice content-based quizzes directly to students’ personal mobile devices post-lecture and pre-tutorial. After measuring the relationships between students’ app usage and their engagement, retention and academic achievement in the subject, it is suggested that following the app’s introduction, student retention rates and academic performance increased, and there was a positive correlation between students’ scoring highly on the app and achieving higher academic grades. While the app’s affordances for learning are promising, the causal relationship between the app usage and improved student outcomes requires further investigation. Conclusions made in the context of the wider scholarship of mobile app enhanced learning and applied game principles in HE.

We have investigated the quadruple sulfur isotopic composition of inorganic sulfur-bearing phases from 13 carbonaceous chondrites of CM type. Our samples include 4 falls and 9 Antarctic finds. We extracted sulfur from sulfides, sulfates, and elemental sulfur (S0) from all samples. On average, we recover a bulk sulfur (S) content of 2.11±0.39wt.% S (1σ). The recovered sulfate, S0 and sulfide contents represent 25±12%, 10±7% and 65±15% of the bulk S, respectively (all 1σ). There is no evidence for differences in the bulk S content between falls and finds, and there is no correlation between the S speciation and the extent of aqueous alteration. We report ranges of Δ33S and Δ36S values in CMs that are significantly larger than previously observed. The largest variations are exhibited by S0, with Δ33S values ranging between −0.104±0.012‰ and +0.256±0.018‰ (2σ). The Δ36S/33S ratios of S0 are on average −3.1±1.0 (2σ). Two CMs show distinct Δ36S/33S ratios, of +1.3±0.1 and +0.9±0.1. We suggest that these mass independent S isotopic compositions record H2S photodissociation in the nebula. The varying Δ36S/Δ33S ratios are interpreted to reflect photodissociation that occurred at different UV wavelengths. The preservation of these isotopic features requires that the S-bearing phases were heterogeneously accreted to the CM parent body. Non-zero Δ33S values are also preserved in sulfide and sulfate, and are positively correlated with S0 values. This indicates a genetic relationship between the S-bearing phases: We argue that sulfates were produced by the direct oxidation of S0 (not sulfide) in the parent body. We describe two types of models that, although imperfect, can explain the major features of the CM S isotope compositions, and can be tested in future studies. Sulfide and S0 could both be condensates from the nebula, as the residue and product, respectively, of incomplete H2S photodissociation by UV light (wavelength <150nm). This idea requires that FeS formation and the S0 condensation co-occur. As an alternative, ice accretion to the CM parent body could allow the delivery of S-MIF in CMs. In that case, sulfides would have been the only S-bearing condensate in CM precursors, and S0 would have been derived from the oxidation of H2S trapped in ices, after its photodissociation at low temperature (<500K) in the nebula. In our models, the observations of H2S UV photodissociation is required to occur at the disk surface, and allowed in nebular environments with canonical C/O ratios. Vertical motions in the disk would redistribute phases that condensed at high altitude to the midplane, where they accreted in the phases that make up the chondritic matrix.