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The origin, evolution, and cycling of volatiles on the Moon are established by processes such as the giant moon forming impact, degassing of the lunar magma ocean, degassing during surface eruptions, and lunar surface gardening events. These processes typically induce mass‐dependent stable isotope fractionations. Mass‐independent fractionation of stable isotopes has yet to be demonstrated during events that release large volumes of gas on the moon and establish transient lunar atmospheres. We present quadruple sulfur isotope compositions of orange and black glass beads from drive tube 74002/1. The sulfur isotope and concentration data collected on the orange and black glasses confirm a role for magmatic sulfur loss during eruption. The Δ33S value of the orange glasses is homogenous (Δ33S = −0.029‰ ± 0.004‰, 2SE) and different from the isotopic composition of lunar basalts (Δ33S = 0.002‰ ± 0.004‰, 2SE). We link the negative Δ33S composition of the orange glasses to an anomalous sulfur source in the lunar mantle. The nature of this anomalous sulfur source remains unknown and is either linked to (a) an impactor that delivered anomalous sulfur after late accretion, (b) sulfur that was photochemically processed early during lunar evolution and was transported to the lunar mantle, or (c) a primitive sulfur component that survived mantle mixing. The examined black glass preserves a mass‐dependent Δ33S composition (−0.008‰ ± 0.006‰, 2SE). The orange and black glasses are considered genetically related, but the discrepancy in Δ33S composition among the two samples calls their relationship into question. Plain Language Summary: Using isotopic compositions measured in volatile elements, we can identify the processes linked to isotopic fractionations and ultimately understand processes involved in a planets' evolution. We present sulfur isotope compositions of lunar glass beads from drive tube 74002/1 and demonstrate that an anomalous sulfur source was erupted from the lunar mantle with the orange glass beads. The observed isotopic anomaly has an unknown origin, but it requires a source of sulfur that was photochemically processed prior to its delivery to the lunar mantle and eruption at ∼3.6 Ga. Our results suggest that the lunar mantle is not well mixed with respect to sulfur sources and requires future multi‐disciplinary investigations to reconcile these important observations. Key Points: Orange glass 74002 preserves negative Δ33S valuesThe negative Δ33S associated with orange glass is linked to photochemically processed sulfur in the erupted sourceOrange and black glass preserve different S isotope compositions that calls into question their genetic relationship [ABSTRACT FROM AUTHOR]

Particle-bound mercury (PBM) records the oxidation of elemental mercury, of which the main oxidation pathways (Br∙/Cl∙/OH∙/O3) remain unclear, especially in the Southern Hemisphere. Here, we present latitudinal covariations of Hg and S-isotopic anomalies in cross-hemispheric marine aerosols that evidence an equator-to-poleward transition of Hg oxidants from OH∙/O3 in tropics to Br∙/Cl∙ in polar regions highlighting thus the presence of distinct oxidation processes producing PBM. The correlations between Hg, S and O-isotopic compositions measured in PBM, sulfates and nitrates respectively within the aerosols highlight the implication of common oxidants in their formations at different latitudes. Our results open a new window to better quantify the present-day atmospheric Hg, S and N budgets and to evaluate the influences of aerosols on climate and ecosystems once the isotopic fractionations associated with each process have been determined.

[Display omitted] • Large variations in δ202Hg and Δ199Hg were observed in an epithermal Ag-Pb-Zn deposit. • Distinct Δ199Hg signals were observed among bulk ore, hydrothermal minerals and wall rocks. • Hg-MIF signals discriminate two metal sources in the evolution of the ore system. • Hg isotopic data can illustrate the tectonic setting of epithermal ore deposits. Epithermal metal deposits along convergent plate margins are of large economic value, however, the origin of the typical metal spectrum (Au, Ag, Sb, As, Hg) in these deposits remains debated. Here, we study the Hg isotope geochemistry of the vein-style Erdaokan Ag-Pb-Zn deposit of epithermal type in the eastern part of the Central Asian Orogenic Belt in NE China, to provide direct constraints on its metal source. Bulk ore samples and early-stage hydrothermal minerals (magnetite, pyrite, and quartz) show negative δ202Hg (−1.52 to −0.18‰) and positive Δ199Hg (−0.03 to 0.17‰) values similar to those of previously reported epithermal Au deposits in NE China, and also of marine systems in general. However, late-stage calcite shows weak negative to positive δ202Hg (-0.61 to 0.90‰) and significant negative Δ199Hg (−0.18 to −0.02‰), similar to the Late Paleozoic sandstone country rocks (δ202Hg, −1.09 to 0.76‰; Δ199Hg, −0.09 to 0.04‰). Hydrothermally altered gabbro and diorite show large variations in δ202Hg (−1.83 to 0.50‰) and Δ199Hg (−0.14 to 0.15‰) which overlap with those of the ore and country rocks, indicating a mixed source. The Δ199Hg signature in the bulk ore and early-stage hydrothermal minerals likely derives from dehydration of the subducted oceanic slab, whereas Hg in late-stage calcite is likely derived from the sedimentary country rocks. Hydrothermal deposits in different tectonic settings have distinct Δ199Hg signals, and our study suggests that Hg isotopes are a robust tool to distinguish metal sources of hydrothermal ore deposits. [ABSTRACT FROM AUTHOR]

The inability to resolve the exact temporal relationship between two pivotal events in Earth history, the Paleoproterozoic Great Oxidation Event (GOE) and the first "snowball Earth" global glaciation, has precluded assessing causality between changing atmospheric composition and ancient climate change. Here we present temporally resolved quadruple sulfur isotope measurements (δ34S, Δ33S, and Δ36S) from the Paleoproterozoic Seidorechka and Polisarka Sedimentary Formations on the Fennoscandian Shield, northwest Russia, that address this issue. Sulfides in the former preserve evidence of mass-independent fractionation of sulfur isotopes (S-MIF) falling within uncertainty of the Archean reference array with a Δ36S/Δ33S slope of -1.8 and have small negative Δ33S values, whereas in the latter mass-dependent fractionation of sulfur isotopes (S-MDF) is evident, with a Δ36S/Δ33S slope of -8.8. These trends, combined with geochronological constraints, place the S-MIF/S-MDF transition, the key indicator of the GOE, between 2,501.5 ± 1.7 Ma and 2,434 ± 6.6 Ma. These are the tightest temporal and stratigraphic constraints yet for the S-MIF/S-MDF transition and show that its timing in Fennoscandia is consistent with the S-MIF/S-MDF transition in North America and South Africa. Further, the glacigenic part of the Polisarka Formation occurs 60 m above the sedimentary succession containing S-MDF signals. Hence, our findings confirm unambiguously that the S-MIF/S-MDF transition preceded the Paleoproterozoic snowball Earth. Resolution of this temporal relationship constrains cause-and-effect drivers of Earth's oxygenation, specifically ruling out conceptual models in which global glaciation precedes or causes the evolution of oxygenic photosynthesis. [ABSTRACT FROM AUTHOR]

The Golden Mile and Mount Charlotte deposits in the Kalgoorlie Terrane, Western Australia, display three main mineralization styles: Fimiston, comprised of interconnected shear zones associated with ankerite-pyrite ± hematite- ± magnetite-gold-telluride alteration; Oroya, made up of breccia bodies with V-muscovite-ankerite-pyrite ± pyrrhotite-gold-telluride alteration; and Mount Charlotte, which consists of vein arrays with symmetrical ankerite-sericite-albite-pyrite ± pyrrhotite ± gold alteration. Pyrite is in equilibrium with gold in all three mineralization styles and has been selected as a proxy to record the sulfur source of the mineralizing fluids as well as the nature of the hydrothermal processes. The δ34S, Δ33S, and Δ36S analyses on pyrite grains from the different mineralization styles, including oxidized and reduced sulfide-oxide assemblages, reveal (1) a large variation in δ34S (from − 12.6 to + 23.5‰), and (2) a previously unrecognized occurrence of anomalous Δ33S and Δ36S signatures (from − 1.0 to + 1.1‰ and from − 2.3 to + 0.9‰, respectively). It is argued that the mineralizing fluids that formed the Golden Mile and Mount Charlotte deposits record mixing among three components: mantle sulfur, oxidized seawater sulfur (e.g., SO4), and reduced elemental sulfur (e.g., S8). Petrographic evidence in conjunction with Δ33S and Δ36S data suggest that MIF-S was acquired during the deposition of shales and basalts present in the Kalgoorlie Terrane and later mixed with mantle-derived sulfur during the mineralization events. The negative δ34S values that predominate in Fimiston style mineralization are consistent with a prevalence of oxidized fluids during the ore-forming process, as reflected by the presence of hematite-pyrite-magnetite-gold assemblages. Conversely, the positive δ34S values that dominate in the Mt Charlotte and Oroya mineralization styles reflect a reducing environment, as reflected by the presence of pyrite-pyrrhotite-gold assemblages. [ABSTRACT FROM AUTHOR]

Artisanal and small-scale gold mining (ASGM) is currently one of the largest anthropogenic sources of mercury (Hg) to the atmosphere and a significant source to downstream terrestrial aquatic systems. Given the potential toxicity of Hg when it is released to aquatic ecosystems, both scientific and regulatory communities have interest in the development of tools and methods for understanding the fate and transport of Hg in the environment. Although Hg isotopes are applied extensively to trace other anthropogenic point sources of Hg in aquatic ecosystems, few studies have used isotopic analyses to investigate the downstream impacts of ASGM. Furthermore, these studies are currently limited by relatively sparse Hg isotopic analyses on ASGM materials. In this study, ASGM samples from Portovelo-Zaruma (Ecuador), representing various stages of the processing of low-grade gold-bearing ores, were analyzed for Hg concentrations and stable isotope ratios. These data were used to assess the isotopic variability of the ASGM endmember and confirm the results of prior isotopic analyses of ASGM materials and downstream sediments from Portovelo-Zaruma. While the Hg concentrations of the ASGM samples varied significantly, isotopic analyses revealed a limited range of signatures that was characterized by relatively heavy mass-dependent fractionation (MDF) with little to no significant mass-independent fractionation (MIF). The signatures of ASGM samples analyzed in this study matched well with previously reported ASGM samples from Portovelo-Zaruma as well as downstream sediments (for up to 120 km). Furthermore, the overall Hg isotopic compositions of potential ASGM endmembers are distinct from typical compositions observed in freshwater ecosystems (e.g., from soil erosion, atmospheric deposition), allowing Hg isotopes to be a powerful tool in tracing downstream Hg contamination from ASGM. Unlabelled Image • Hg isotopes were used to understand input of Hg from ASGM to adjacent water bodies. • Hg concentrations varied significantly in ASGM materials depending on processing. • Isotope ratios of ASGM endmember had relatively positive MDF with little to no MIF. • Isotopic signatures of ASGM samples were distinct from typical background sources. • Hg isotopes are a powerful tool to trace ASGM Hg in freshwater ecosystems. [ABSTRACT FROM AUTHOR]

Ozone exhibits large and mass independent isotopic fractionations (MIF) in oxygen isotope ratios relative to molecular di-oxygen (O 2) from which it is formed. An interpretation of this effect was proposed based on the behavior of the indistinguishable isotopes 16O in scattering processes. We report here an experiment aimed at testing one of the predictions of this model. O 3 was formed by high frequency discharge in O 2 with pressures ranging between 1.6 and 38 Torr. The isotopic evolution of the closed O 2 reservoir was monitored during its distillation taking place during the continuous removal of ozone by condensation. Its composition evolves from a mass independent to a mass dependent fractionation along with the decrease in pressure. The isotopic pathways defined by this evolution in the 3 isotopes diagram are in quantitative agreement with the theoretical prediction of the disappearance of MIF with the increase of the complex lifetime stabilized as ozone. [ABSTRACT FROM AUTHOR]

Mercury (Hg) stable isotope is a useful tool to understand the transformation of atmospheric Hg. The observation on the enrichment of heavier isotopes in gaseous elemental Hg (GEM) relative to oxidized HgII species in atmosphere cannot be convincingly explained by isotope fractionation of Hg redox processes. This review shows that the large Hg isotope mass dependent fractionation (MDF) in coal-fired boilers is one of the underlying reasons. The reported Hg isotope data of feed coals and their combustion products are first summarized to give a general overview of how Hg isotopes fractionate before Hg discharge from coal-fired boilers. Then, predictive MDF models are discussed to simulate δ202Hg values of different Hg species in coal combustion flue gases. The discharged GEM is predicted to have the highest δ202Hg followed by gaseous HgII and particulate-bound HgII, which is in consistent with the observed MDF pattern of atmospheric Hg species. [ABSTRACT FROM AUTHOR]

The anomalous abundances of sulfur isotopes in ancient sediments provide the strongest evidence for an anoxic atmosphere prior to ∼2.45 Ga, but the mechanism for producing this ‘mass-independent’ fractionation pattern remains in question. The prevailing hypothesis has been that it is created by differences in the UV photolysis rates of different SO 2 isotopologues. We investigate here a recently proposed additional source of fractionation during gas-phase formation of elemental sulfur (S 4 and S 8 ). Because two minor S isotopes rarely occur in the same chain, the longer S 4 and S 8 chains should be strongly, and roughly equally, depleted in all minor isotopes. This gives rise to negative Δ 33 S values and positive Δ 36 S values in elemental sulfur—just the opposite of (and much larger than) what is predicted from SO 2 photolysis itself. Back-reactions during chain formation, specifically photolysis of S 2 and S 3 , pass sulfur having the opposite fractionation back to atomic S, and thence to other sulfur species, causing H 2 S, SO 2 , sulfate, and short-chain elemental sulfur to have positive Δ 33 S and negative Δ 36 S. Positive Δ 33 S values in elemental sulfur produced in laboratory SO 2 photolysis experiments could be caused by the initial fractionation during photolysis, combined with rapid condensation of short-chain sulfur species on the walls of the reaction chamber, along with a scarcity of back-reactions. The simulated fractionations produced by the chain formation mechanism do not directly match fractionations from the rock record. The mismatch might be explained if the isotopic signals leaving the atmosphere were significantly modulated by life, by uncertainties in the rates of reactions of both major and minor isotopic sulfur species, or by the relatively large potential range of atmospheric parameters. Further work is needed to better constrain these uncertainties, but this novel mechanism suggests new avenues to explore in our search for a explanation for the S-MIF record. [ABSTRACT FROM AUTHOR]

Abstract The particle bound mercury (PBM) in urban-industrial areas is mainly of anthropogenic origin, and is derived from two principal sources: Hg bound to particulate matter directly emitted by industries and power generation plants, and adsorption of gaseous elemental mercury (GEM) and gaseous oxidized mercury (GOM) on air particulates from gas or aqueous phases. Here, we measured the Hg isotope composition of PBM in PM10 samples collected from three locations, a traffic junction, a waste incineration site and an industrial site in Kolkata, the largest metropolis in Eastern India. Sampling was carried out in winter and monsoon seasons between 2013–2015. The objective was to understand whether the isotope composition of the PBM represents source composition. The PBM collected from the waste burning site showed little mass independent fractionation (MIF) (Δ199Hg = +0.12 to -0.11‰), similar to the signature in liquid Hg and Hg ores around the world with no seasonal variations. Samples from the industrial site showed mostly negative MDF and MIF (δ202Hg = -1.34 to -3.48 ‰ and Δ199Hg = +0.01 to -0.31‰). The MDF is consistent with PBM generated by coal combustion however, the MIF is 0.15‰ more negative compared to the Hg isotope ratios in Indian coals. The traffic junction PBM is probably not produced in situ, but has travelled some distances from nearby industrial sources. The longer residence time of this PBM in the atmosphere has resulted in-aerosol aqueous photoreduction. Thus, the MIF displays a larger range (Δ199Hg = +0.33 to -0.30‰) compared to the signature from the other sites and with more positive values in the humid monsoon season. Different Hg isotopic signature of PBM in the three different sampling locations within the same city indicates that both source and post emission atmospheric transformations play important roles in determining isotopic signature of PBM.

Variations in the composition of stable isotopes of mercury contained in tissues (root, stem, leaf, and hypocotyl or flower) of three typical mangrove plants ( Kandelia candel, Aegiceras corniculata, and Bruguiera gymnorhiza), collected from the mangrove wetland of Jiulong estuary, SE China, were used to investigate the sources and transformation of mercury in the mangrove plants. Tissue samples from the plants were digested and mercury in the solution was pre-concentrated with purge-trap method and then analyzed by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). The results showed that the mass dependent fractionation (MDF) of mercury ranged from −2.67 to −0.87 ‰ for δ Hg while the mass independent fractionation (MIF) of mercury isotopes ranged from −0.16 to 0.09 and −0.19 to 0.05 ‰ for ΔHg and ΔHg, respectively, relative to the standard NIST SRM 3133. The ratio of ΔHg/ΔHg was 0.991, indicating that the mercury had been photo-reduced before being accumulated in mangrove plants. Analyses of the data from MIF studies revealed that the major portion of the mercury measured in leaves (∼90 %) originated from the atmosphere while the source of over half of the mercury present in roots was the surficial sediment. This study, the first of its kind investigating the variations in isotopic composition of mercury in the tissues of mangrove plants, could be helpful to identify the source of mercury contamination in mangroves and understand the biogeochemical cycle of mercury in the estuarine mangrove wetlands. [ABSTRACT FROM AUTHOR]

Photochemical mechanisms of Sulfur Mass-Independent Fractionation (S-MIF) are still poorly understood. Previous laboratory experiments have indicated that the S-MIF depends largely on the spectrum of the incident light source and the partial pressure of SO 2 , though the basic character of the Archean S-MIF ( Δ S 36 / Δ S 33 = ∼ − 1 ) has never been reproduced. We have conducted new photochemical experiments at low pSO 2 (1–10 Pa) conditions under the presence of CO and found a reasonable mechanism to reproduce the Δ 36 S/Δ 33 S slope about −1. As previously suggested ( Ono et al., 2013 ), the low pSO 2 is key to studying the self-shielding effect within a range of realistic atmospheric conditions. Also, reducing conditions are critical for simulating the O 2 -poor atmosphere, whereas photolysis of pure SO 2 provides excess O atoms that significantly change the overall chemistry. Our experimental results confirmed that significant S-MIF ( Δ S 36 / Δ S 33 = − 2.4 ) can be produced by self-shielding in the SO 2 photolysis band (185–220 nm), even if the SO 2 column density is as low as 10 16 molecules cm −2 . Thus, photolysis within a volcanic plume of ∼0.1 ppm SO 2 is capable of producing a large S-MIF signature. The isotopic fractionations originating from the different absorption cross sections of SO 2 isotopologues (i.e. wavelength dependent effect; without self-shielding) are only minor (potentially up to +4‰ for Δ 33 S). Under reducing conditions, however, another S-MIF signal with Δ 36 S/Δ 33 S ratio of ∼+0.7 is produced due to collision-induced intersystem crossing (ISC) from singlet to triplet states of SO 2 ( Whitehill et al., 2013 ), and should also be transferred into the final product that is responsible for changing the Δ 36 S/Δ 33 S slope. Based on a photochemical model of the S–O–C system with the two S-MIF-yielding reactions, the largest S-MIF observed in the late Archean Mt. McRae Fm. ( Δ S 33 = + 9.4 ‰ , Δ S 36 = − 7.5 ‰ ) can be reproduced by solar UV irradiation of a SO 2 column of ∼ 6.4 × 10 16 molecules cm −2 with a sufficiently high concentration of reducing gasses (∼2% CO or CH 4 ) where the ISC-derived MIF contributes ∼3% through the photoexcitation channel initiated in the 240–340 nm region. Our work shows that a photochemical model considering the two major S-MIF-yielding reactions ( SO 2 + h ν → SO + O and SO 2 1 + M → SO 2 3 + M ) can explain the behavior of the S-MIF observed in laboratory experiments. The combination of the two effects is more important under reducing condition and should be considered to interpret the geological record. [ABSTRACT FROM AUTHOR]

Stable sulfur isotope ratio has been useful for tracing a wide range of biogeochemical processes. The conventional SF 6 method allows us to make high-precision analyses of all four of the stable isotopes ( 32 S/ 33 S/ 34 S/ 36 S), though the fluorination step is time consuming and requires the hazardous elemental fluorine (F 2 ). Here we show a novel flash-fluorination technique for instantaneous preparation of SF 6 from sulfide samples by reaction with cobalt fluoride (CoF 3 ) instead of F 2 . Flash heating by using a Curie-point pyrolyzer dramatically simplifies the fluorination procedure. A series of experiments demonstrated that silver sulfide (Ag 2 S) can be converted into SF 6 at 590 °C within 3 s with sufficient reproducibilities for δ 34 S (± 0.4‰), Δ 33 S (± 0.01‰) and Δ 36 S (± 0.1‰). Instrumental fractionation is negligible for δ 34 S and Δ 33 S, but should be corrected for Δ 36 S, when fluorinating small samples less than 150 nmol. Further, application of the method to various other sulfur compounds shows that pyrite and several organic sulfur species can be directly converted into SF 6 , though more work is necessary for improving the accuracy of isotopic analysis comparable to that of Ag 2 S. Nevertheless, the new CoF 3 -flash-fluorination technique provides fast, convenient and safe procedure for high-precision analysis of quadruple sulfur isotopes. [ABSTRACT FROM AUTHOR]

The isotopic anomaly of stable sulfur isotope could be a useful new tracer for decoding atmospheric chemistry of early Earth from ancient rock samples. Here, we summarize current status of the experimental works and discuss what the isotopic anomaly tells about early Earth's atmosphere. [ABSTRACT FROM AUTHOR]

We report in situ quadruple sulfur isotope analysis ( 32 S, 33 S, 34 S and 36 S) of a pyritized microbial mat from the ∼3480 Ma Dresser Formation, Pilbara Craton, Western Australia. These data yield positive δ 34 S and Δ 33 S, indicative of sulfur sourced from a pool with similar character as the putative atmospheric elemental sulfur channel of Pavlov and Kasting (2002). Contrary to previous data from the Dresser Formation, however, this pyrite is heavily depleted in 36 S with a Δ 36 S/Δ 33 S slope of c. −3.6, much steeper than slopes typically seen in other early Archean rock successions (Δ 36 S/Δ 33 S ≈ −1) which suggests either a different atmospheric signature for deposited S or a different pool altogether. Significant micro-scale isotopic heterogeneity is observed within the microbial mat (δ 34 S = +1.6‰ to +6.7‰; Δ 33 S = +0.4‰ to +2.6‰; Δ 36 S = −3.1‰ to −8.1‰), implying a role for microbial S metabolism. While metabolic S cycling has been shown to shift Δ 36 S to lower values, microbial metabolization of S does not appear sufficient to account for the full range of Δ 36 S. We conclude that the isotopic composition of the pyrite was controlled by the relative proportions of mass independently fractionated (MIF) S 0 and sulfate-derived sulfur incorporated into polysulfide pyrite precursors during reactions in the microbial mat. The dominance of the MIF-S 0 isotopic signature (+δ 34 S, +Δ 33 S, −Δ 36 S) indicates that contributions from the sulfate-derived sulfur pool were relatively small, consistent with low concentrations of sulfate in Archean seawater, and that contributions from a non-sulfate pool were significant. Micro-scale isotopic heterogeneity in the pyrite points to mixing between the two sulfur pools in selected micro-environments within the microbial mat. The particularly negative Δ 36 S observed here reveals a 3480 Ma sulfur reservoir with novel Δ 36 S/Δ 33 S chemistry whose significance now requires further investigation. [ABSTRACT FROM AUTHOR]

Many aspects of Earth's early sulfur cycle, from the origin of mass-anomalous fractionations to the degree of biological participation, remain poorly understood—in part due to complications from postdepositional diagenetic and metamorphic processes. Using a combination of scanning high-resolution magnetic superconducting quantum interference device (SQUID) microscopy and secondary ion mass spectrometry (SIMS) of sulfur isotopes (32S, 33S, and 34S), we examined drill core samples from slope and basinal environments adjacent to a major Late Archean (~2.6-2.5 Ga) marine carbonate platform from South Africa. Coupled with petrography, these techniques can untangle the complex history of mineralization in samples containing diverse sulfur-bearing phases. We focused on pyrite nodules, precipitated in shallow sediments. These textures record systematic spatial differences in both mass-dependent and mass-anomalous sulfur-isotopic composition over length scales of even a few hundred microns. Petrography and magnetic imaging demonstrate that mass-anomalous fractionations were acquired before burial and compaction, but also show evidence of postdepositional alteration 500 million y after deposition. Using magnetic imaging to screen for primary phases, we observed large spatial gradients in Δ33S (>4‰) in nodules, pointing to substantial environmental heterogeneity and dynamic mixing of sulfur pools on geologically rapid timescales. In other nodules, large systematic radial δ34S gradients (>20‰) were observed, from low values near their centers increasing to high values near their rims. These fractionations support hypotheses that microbial sulfate reduction was an important metabolism in organic-rich Archean environments-even in an Archean ocean basin dominated by iron chemistry. [ABSTRACT FROM AUTHOR]

Mass-independent isotope fractionations driven by differences in volumes and shapes of nuclei (the field shift effect) are known in several elements and are likely to be found in more. All-electron relativistic electronic structure calculations can predict this effect but at present are computationally intensive and limited to modeling small gas phase molecules and clusters. Density functional theory, using the projector augmented wave method (DFT-PAW), has advantages in greater speed and compatibility with a three-dimensional periodic boundary condition while preserving information about the effects of chemistry on electron densities within nuclei. These electron density variations determine the volume component of the field shift effect. In this study, DFT-PAW calculations are calibrated against all-electron, relativistic Dirac-Hartree-Fock, and coupled-cluster with single, double (triple) excitation methods for estimating nuclear volume isotope effects. DFT-PAW calculations accurately reproduce changes in electron densities within nuclei in typical molecules, when PAW datasets constructed with finite nuclei are used. Nuclear volume contributions to vapor-crystal isotope fractionation are calculated for elemental cadmium and mercury, showing good agreement with experiments. The nuclear-volume component of mercury and cadmium isotope fractionations between atomic vapor and montroydite (HgO), cinnabar (HgS), calomel (Hg2Cl2), monteponite (CdO), and the CdS polymorphs hawleyite and greenockite are calculated, indicating preferential incorporation of neutron-rich isotopes in more oxidized, ionically bonded phases. Finally, field shift energies are related to Mössbauer isomer shifts, and equilibrium mass-independent fractionations for several tin-bearing crystals are calculated from 119Sn spectra. Isomer shift data should simplify calculations of mass-independent isotope fractionations in other elements with Mössbauer isotopes, such as platinum and uranium. [ABSTRACT FROM AUTHOR]

Abstract: Over the last decade, the use of multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) has significantly lowered the detection limit of sulfur isotope analyses, albeit typically with decreased precision. Moreover, the presence of isobaric interferences for sulfur prevented accurate analysis of the minor isotopes 33S and 36S. In the present study, we report improved techniques for measuring sulfur isotopes on the MC-ICP-MS Neptune Plus (Thermo Fischer Scientific) using a heated spray chamber coupled to a desolvating membrane (Aridus, Cetac). Working at high mass resolution, we measured δ34S values of natural samples with a typical reproducibility of 0.08–0.15‰ (2sd) on 5 to 40nmol sulfur introduced into the instrument. We applied this method to two seawater profiles, using 25μl of sample (700nmol of sulfate). The average δ34SVCDT value is 20.97±0.10‰ (2sd, n=25). We show that the amount of sulfate required for an analysis can be decreased to 5nmol. Because the plasma is sustained by Ar, measurement of 36S is impossible at the current mass resolution due to the presence of 36Ar+, but a reproducibility of 0.1–0.3‰ (2sd) is achieved on the measurement of mass independent fractionations (Δ33S). This is the first time such precision has been achieved on samples of this size. [Copyright &y& Elsevier]

Abstract: Salt marshes can be a significant source of MeHg in coastal marine organisms, however the sources and cycling of Hg in salt marsh sediments, and in coastal environments in general, remain unclear. We analyzed surface and cored sediments from a salt marsh and adjacent upland sand dune in Cabretta Island, Georgia, USA, for total mercury (HgT), Hg isotopes and trace metal concentrations to better constrain the sources of Hg in this coastal environment. HgT concentrations are lower in the upland sands (1–6ng/g) than in the marsh sediments (6–16ng/g). HgT shows a positive correlation with total organic content (TOC) and increasing proportion of fines in the sediments. Trace metal concentrations also show a positive correlation with HgT in the marsh sediments regardless of chemical affinity (i.e. chalcophile, siderophile or lithophile). All these data are consistent with surface adsorption (either directly on to sediments or on to organic matter) as a dominant mechanism of Hg and metals accumulation in the marsh sediments. The surface sediments show significant mass independent fractionation (MIF) of odd Hg isotopes: the upland dune sands have zero to slightly negative Δ199Hg (−0.07‰ to −0.14‰) and the marsh surface sediments have positive Δ199Hg (0.48‰ to 0.79‰). As in the surface samples, well-sorted sand layers in the cored sediments have low Hg concentrations and zero to slightly negative Δ199Hg, whereas fine particle-rich layers have higher Hg concentrations and positive Δ199Hg values. In the absence of any evidence for MIF of Hg isotopes by bacteria mediated methylation–demethylation reactions, the observed Hg isotope differences between marsh and upland sands can be explained by different sources of Hg. We suggest that local atmospheric Hg deposition dominates the Hg budget in the ombrotrophic upland sand, while the positive MIF in the marsh sediments are consistent with Hg dominantly of seawater origin. While in situ processes, like photoreduction and evasion can overprint the Hg depositional isotope signature, their effect on the sediments is currently unconstrained. Nevertheless, our data show that Hg isotopes can delineate different sources of Hg in a pristine coastal environment and at small spatial scales. Thus natural background isotope variability should be assessed as a baseline when Hg isotopes are used as tracers of Hg in anthropogenically-influenced sites. [Copyright &y& Elsevier]

Abstract: To confirm theoretical predictions of the isotopic signature of the nuclear volume effect (NVE) for Hg, liquid–vapor Hg isotope fractionation was investigated under equilibrium conditions in the dark at room temperature. Since the other mass independent fractionation (MIF) mechanism proposed for Hg is a kinetic phenomenon only, equilibrium experiments are the best approach to isolate the NVE. Because of the small magnitude of NVE MIF, previous equilibrium experimental results have had relatively large error. The equilibrium evaporation experiment resulted both in mass dependent fractionation (represented by δ202Hg) and MIF (Δ199Hg and Δ201Hg). The average liquid–vapor δ202Hg difference was 1.34±0.18‰ (2SE) and 1.08±0.07‰ (2SE) for two sets of experiments with the vapor phase isotopically lighter than the liquid. A positive MIF of the odd isotopes in the vapor phase was observed with an average Δ199Hg of 0.14±0.01‰ (2SE) and an average Δ201Hg of 0.09±0.01‰ (2SE). For the 6 experiments, the average ratio of NVE MIF of the two odd isotopes (Δ199Hg/Δ201Hg) in the vapor phase was 1.59±0.05 (2SE) confirming a recent estimation of the NVE Δ199Hg/Δ201Hg ratio of ~1.65. A conceptual model applying first principles was used to explain the fractionation observed between Hg liquid and Hg vapor under equilibrium conditions. [Copyright &y& Elsevier]

Abstract: The search for early Earth biological activity is hindered by the scarcity of the rock record. The very few exposed sedimentary rocks have all been affected by secondary processes such as metamorphism and weathering, which might have distorted morphological microfossils and biogenic minerals beyond recognition and have altered organic matter to kerogen. The search for biological activity in such rocks therefore relies entirely on chemical, molecular or isotopic indicators. A powerful tool used for this purpose is the stable isotope signature of elements related to life (C, N, S, Fe). It provides key informations not only on the metabolic pathways operating at the time of the sediment deposition, but more globally on the biogeochemical cycling of these elements and thus on the Earth''s surface evolution. Here, we review the basis of stable isotope biogeochemistry for these isotopic systems. Rather than an exhaustive approach, we address some examples to illustrate how they can be used as biosignatures of early life and as proxies for its environment, while keeping in mind what their limitations are. We then focus on the covariations among these isotopic systems during the Archean time period to show that they convey important information both on the evolution of the redox state of the terrestrial surface reservoirs and on co-occurring ecosystems in the Archean. [Copyright &y& Elsevier]

Distributions of sulfur isotopes in geological samples would provide a record of atmospheric composition if the mechanism producing the isotope effects could be described quantitatively. We determined the UV absorption spectra of 32SO2, 33SO2, and 34SO3 and use them to interpret the geological record. The calculated isotopic fractionation factors for SO2 photolysis give mass independent distributions that are highly sensitive to the atmospheric concentrations of O3, O3, CO2. H2O, CS2, NH3, N2O, H2S, OCS, and SO2 itself. Various UV-shielding scenarios are considered and we conclude that the negative Δ33S observed in the Archean sulfate deposits can only be explained by OCS shielding. Of relevant Archean gases, OCS has the unique ability to prevent SO2 photolysis by sunlight at λ >202 nm. Scenarios run using a photochemical box model show that ppm levels of OCS will accumulate in a CO-rich, reducing Archean atmosphere. The radiative forcing, due to this level of OCS, is able to resolve the faint young sun paradox. Further, the decline of atmospheric OCS may have caused the late Archean glaciation. [ABSTRACT FROM AUTHOR]

Abstract: Quadruple sulfur isotope ratios (32S/ 33S/34S/36S) were measured by a high precision SF6 method for early diagenetic pyrite in the 2.5Ga upper Prieska facies of the Griqualand West Basin from the Agouron drill core GKP01. Measured Δ33S (≈ δ33S–0.515δ34S) values range between −2.3 and +8.5‰ with no apparent meter-scale stratigraphic trend for 70m section. It was found that early diagenetic pyrites occur in two texturally and isotopically distinct populations such that bulk rock isotope data would reflect mixing of these two sulfur pools. Nodular and layered pyrite yield mostly negative (down to −2.3‰) and relatively constant Δ33S values over a few tens of cm scale. Disseminated pyrites, in contrast, yield positive (0.0–8.5‰) Δ33S values that are heterogeneous in sub-cm scales. The former pyrite sulfur was likely derived from seawater sulfate through microbial sulfate reduction, and the latter preferentially sampled aqueous H2S-S0 reservoirs in late Archean oceans. Relatively constant Δ33S values for layered pyrite suggest Archean sulfate reservoirs had residence times of a few million years. Most data yield a well-defined Δ36S/Δ33S ratios of −0.9, suggesting predominance of a single S-MIF source reaction. Four analyses of a two cm length sample (306.5m) yield Δ36S/Δ33S slope of −1.6. This slope is consistent with the relationship expected for a symmetry-breaking isotope effect during the S+S2 reaction, but deviations from the main Archean array (i.e., Δ36S/Δ33S=−0.9) may also result from various combinations of SO photolysis and SO2 oxidation. High spatial resolution-high precision SF6 measurements of Archean pyrite provide significant new insights into the origin of Archean sulfur mass-independent fractionation (S-MIF) and the late Archean sulfur cycle. [Copyright &y& Elsevier]

Few physical or chemical processes defy well-established laws of mass-dependent isotopic fractionation. A surprising example, discovered two decades ago, is that thermal decomposition of calcium and magnesium carbonate minerals (conducted in vacuo, to minimise back-reaction and isotopic exchange) causes the oxygen triple-isotope compositions of the resulting solid oxide and CO 2 to fit on parallel mass-dependent fractionation lines in ln(1 + δ17O) versus ln(1 + δ18O) space, with anomalous depletion of 17O in the solid and equivalent enrichment of 17O in the CO 2. By investigating the thermal decomposition of other natural divalent metal carbonates and one synthetic example, under similar conditions, we find that the unusual isotope effect occurs in all cases and that the magnitude of the anomaly (Δ′17O) seems to depend on the room temperature crystallographic structure of the carbonate. A lower cation coordination number (as associated with smaller cation radius) correlates with a Δ′17O value closer to zero. Local symmetry considerations may therefore be influential. Relative to a reference fractionation line of slope 0.524 and passing through VSMOW, solid oxides produced by thermal decomposition of orthorhombic carbonates were characterised by Δ′17O = −0.367 ± 0.004‰ (standard error). The comparable figure from rhombohedral examples was −0.317 ± 0.010‰, whereas from the sole monoclinic (synthesised) specimen it was −0.219 ± 0.011‰. The numerical values are, to some extent, dependent on details of the experimental procedure. We discuss potential origins of the isotopic anomaly, including the possibility of hyperfine coupling between 17O nuclei and unpaired electrons of transient radicals (the 'magnetic isotope effect'). A new mechanism based on the latter process is proposed. The associated transition state is compatible with that suggested by recent quantum chemical and kinetic studies of the thermal decompositions of calcite and magnesite. An earlier suggestion based on the magnetic isotope effect is shown to be incompatible with the generation of a 17O anomaly, regardless of the identity of the carbonate. We cannot exclude the possibility that a Fermi resonance between states leading to dissociation may additionally affect the magnitude of Δ′17O in some cases. Our findings have cosmochemical implications, with thermal processing of carbonates providing a potential mechanism for the mass-independent fractionation of oxygen isotopes in protoplanetary systems. [ABSTRACT FROM AUTHOR]

• Multiple sulfur isotopes from Cu-Au systems of the Carajás Mineral Province. • Sulfur experienced subtle, but detectable, MIF in these Cu-Au systems. • Neoarchean IOCG systems contain mantle sulfur and minor atmospheric-derived sulfur. • Paleoproterozoic IOCG systems show inherited Neoarchean sulfur with MIF signatures. • Sulfur from Paleoproterozoic Cu-Au-polymetallic deposit is diagenetic and magmatic. Multiple sulfur isotopes in sulfides were measured by in situ Secondary Ion Mass Spectrometry in order to constrain sulfur sources and pathways, as well as explore atmosphere–ore genesis implications on the metallogeny of the Neoarchean and Paleoproterozoic Cu-Au systems of the Carajás Domain, southeast Amazonian Craton, Brazil. All of the investigated Neoarchean (2.70–2.57 Ga; i.e., Salobo, Igarapé Bahia, Castanha and Sequeirinho) and Paleoproterozoic IOCG (ca 1.88 Ga; i.e., Alvo 118 and Sossego) deposits show Δ33S < 0‰ (-0.17‰ to + 0.02‰). The Paleoproterozoic Cu-Au(W-Sn-Bi) Breves deposit reveals Δ33S > 0‰ (+0.08‰ to + 0.27‰), implying that sulfur underwent mass-independent fractionation (MIF). In addition, three distinct δ34S ranges are defined: −3.07‰ to + 3.01‰ and + 2.17‰ to + 4.68‰ for the Neoarchean and Paleoproterozoic IOCG deposits, respectively, and −0.46‰ to + 3.81‰ for the Paleoproterozoic Breves deposit. In the Neoarchean IOCG deposits, sulfur is most likely of mantle/magmatic origin. However, a subtle but detectable MIF-S signature reflects the inheritance of a minor sulfur component transported to the atmosphere, experienced photolytic reactions and returned to the hydrosphere. The interaction between highly saline, hot, and deep-seated metalliferous fluids with the host rocks, including sulfate-bearing volcanic rocks that underwent seafloor alteration, may account for the small negative Δ33S values in the IOCG deposits. The similarity between the negative Δ33S signatures of the Neoarchean and the Paleoproterozoic IOCG deposits (i.e., Sossego and Alvo 118) suggest that the MIF signatures recorded by the latter most likely reflect inheritance of Neoarchean sulfur with MIF signatures acquired by large scale fluid-rock interaction triggered by the ca 1.88 Ga A-type granitic magmatism. The positive Δ33S values of sulfides from the Paleoproterozoic Breves deposit, in contrast, were probably generated by reduced sulfur species sourced from crustal sources (e.g., Archean pyrite-bearing sedimentary units) in addition to magmatic sulfur related to ca. 1.88 Ga A-type granite emplacement. [ABSTRACT FROM AUTHOR]

The existence of mass-independently fractionated sulfur in Archean rocks is almost universally accepted as evidence for low atmospheric O 2 and O 3 concentrations at that time. But the detailed patterns of the Δ 33 S values and of the ratios Δ 33 S / δ 34 S and Δ 36 S / Δ 33 S remain to be explained, and the mechanism for producing the mass-independent fractionation remains controversial. Here, we explore the hypothesis that the relatively low Δ 33 S values seen during the Mid-Archean, 2.7-3.5 Ga, were caused by the presence of organic haze produced from photolysis of methane. This haze helped shield SO 2 from photolysis, while at the same time providing surfaces on which unfractionated short-chain sulfur species could condense. The evolution of oxygenic photosynthesis, and the concomitant disappearance of organic haze towards the end of the Archean allowed more negatively fractionated S 4 and S 8 to form, thereby generating large positive fractionations in other sulfur species, including sulfate and H 2 S. Reduction of this sulfate to H 2 S by bacteria, followed by incorporation of H 2 S into pyrite, produced the large positive Δ 33 S values observed in the Neoarchean rock record, 2.5-2.7 Ga. • Organic haze can explain the relatively low (but non-zero) Δ 33 S values seen during the mid-Archean. • The disappearance of this haze at ∼2.7 Ga can explain the much higher Δ 33 S values seen then. • The disappearance of the haze may have been caused by the invention of oxygenic photosynthesis. • Combinatorial fractionation is likely the major contributor to the sulfur MIF signal seen in the Archean rock record. [ABSTRACT FROM AUTHOR]

High spatial resolution multiple sulfur isotope studies undertaken by multicollector secondary ion mass spectrometry (SIMS) commonly use well‐characterised sulfide reference materials that do not (or are assumed not to) exhibit mass independent fractionation in 33S and 36S, taking advantage of the three‐isotope plot to evaluate the extent of such fractionation in unknown targets. As a result, few studies to date have used a mass independently fractionated reference sulfide to demonstrate accuracy of measurement and/or data reduction procedures. This paper evaluates two mass independently fractionated sulfides, a pyrite from the 3.7 Ga Isua greenstone belt and a pyrrhotite from a 2.7 Ga gold deposit in Minas Gerais, Brazil which may be used to provide additional confidence in the obtained multiple sulfur isotope data. Additionally, the paper presents a method for measuring quadruple sulfur isotopes by SIMS at a comparable spatial and volume resolution to that typically employed for triple sulfur isotopes. This method has been applied to the Isua pyrite as well as to a sample of 2.5 Ga pyrite from the Campbellrand, Transvaal, South Africa previously investigated using SIMS for triple sulfur isotopes, illustrating its potential for quadruple sulfur investigations.©2012 The Authors. Geostandards and Geoanalytical Research ©2012 International Association of Geoanalysts [ABSTRACT FROM AUTHOR]