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Experimental results are presented showing the variation in the relationship between odd isotopes of tin (Sn) in mass-independent fractionation caused by the magnetic isotope effect (MIE), which has previously only been observed for mercury. These results are consistent with the trend predicted from the difference between the magnitudes of nuclear magnetic moments of odd isotopes with a nuclear spin. However, the correlation between odd isotopes in fractionation induced by the MIE for the reaction system used in this study (solvent extraction using a crown ether) was different from that reported for the photochemical reaction of methyltin. This difference between the two reaction systems is consistent with a theoretical prediction that the correlation between odd isotopes in fractionation induced by the MIE is controlled by the relationship between the spin conversion time and radical lifetime. The characteristic changes in the correlation between odd isotopes in fractionation induced by the MIE observed for Sn in this study provide a guideline for quantitatively determining fractionation patterns caused by the MIE for elements that have multiple isotopes with a nuclear spin. These results improve our understanding of the potential impact of the MIE on mass-independent fractionation observed in natural samples, such as meteorites, and analytical artifacts of high-precision isotope analysis for heavy elements. [ABSTRACT FROM AUTHOR]

Mercury (Hg) is a highly volatile metal exhibiting both isotope mass-dependent (MDF, defined as δ202Hg) and mass-independent (MIF, expressed as Δ199Hg) fractionation. Assessing the Hg isotopic composition of the upper continental crust is crucial for the use of this new geochemical tool for petrogenetic tracing, particularly for understanding crust-mantle interaction. Here, we report Hg isotopic compositions of granitic rocks with distinct source affinity (I-, A-, and S-type) and of metasedimentary enclaves from the South China Craton. The results of more than 100 rock samples show large δ202Hg variations of −2.03 to 0.47 ‰ and small Δ199Hg variations of −0.16 to 0.09 ‰. The S-type granites studied here exhibit higher δ202Hg values (−0.58 to 0.00 ‰; n = 57) than their sedimentary protoliths (metasedimentary enclaves; −2.03 to −0.91 ‰; n = 7), suggesting significant Hg-MDF during magmatic processes. The Δ199Hg values of S-type granites (−0.08 to 0.09 ‰) are indistinguishable from their sedimentary protoliths (−0.16 to 0.02 ‰), suggestive of the absence of Hg-MIF during crustal anatexis and subsequent magmatic differentiation. The I- and A-type granites studied have smaller Δ199Hg variations of −0.11 to 0.04 ‰ (n = 28) and −0.07 to 0.04 ‰ (n = 15), respectively, but are within the range of the S-type granites. The compositional range of all granite variants may be explained by the variable intensity of large-scale MASH (melting-assimilation-storage-homogenization) processes. Our new data combined with previously published data of igneous, sedimentary, and metamorphic rocks allow us to estimate that the upper continental crust (UCC) has a Hg abundance of 13.5 ppb and a weighted average δ202Hg of −1.15 ± 1.01 ‰ (2SD), both of which are higher than the corresponding values of the primitive mantle. However, the weighted average Δ199Hg value of the UCC (0.03 ± 0.15 ‰; 2SD) is nondistinguished from the primitive mantle, suggesting no obvious Hg-MIF during the formation and differentiation of the continental crust. [ABSTRACT FROM AUTHOR]

Mercury is a ubiquitous contaminant known to accumulate in wildlife, particularly bird species at higher trophic levels. Knowledge of tissue-specific Hg distributions aids our understanding of Hg bioaccumulation in organisms. In this study, one adult and three juvenile Collared Scops Owls (Otus lettia) were studied to elucidate the bioaccumulation of Hg in body tissues. Six tissues and organs (feathers, nails, heart, liver, gizzard, and muscle), as well as gastric contents, were examined for total Hg (THg) and methylmercury (MeHg) contents, Hg isotopic compositions including mass-dependent fractionation (MDF; δ202Hg) and mass-independent fractionation (MIF; Δ199Hg and Δ201Hg), and C (δ13C) and N (δ15N) isotopic compositions. Tissue-specific THg and MeHg concentrations in the adult were in the ranges of 150–1360 ng/g and 17–1060 ng/g, and lower in the juveniles at 91–419 ng/g and 67–350 ng/g, respectively. The δ202Hg values in the adult were strongly negative at −1.75‰ ± 0.17‰ compared with the juveniles at −0.99‰ ± 0.25‰. The adult exhibited lower MIF values than the juveniles, at 0.23‰ ± 0.07‰ for Δ199Hg and 0.2‰ ± 0.11‰ for Δ201Hg, compared with 0.81‰ ± 0.09‰ and 0.66‰ ± 0.07‰, respectively. The lower adult MDF and MIF values suggest that the adult tended to accumulate negative Hg isotopes but the juvenile's positive Hg isotopes. Differences between adult and juvenile tissue Hg concentrations indicate that metabolic processes play an important role in Hg accumulation. [ABSTRACT FROM AUTHOR]

Chemical physics plays a large role in determining the isotopic compositions of gases in Earth's atmosphere, which in turn provide fundamental insights into the sources, sinks, and transformations of atmospheric gases and particulates and their influence on climate. This review focuses on the kinetic and photolysis isotope effects relevant to understanding the isotope compositions of atmospheric ozone, carbon dioxide, methane, nitrous oxide, and other gases and their historical context. The discussion includes non-mass-dependent isotope compositions of oxygen-containing species and a brief overview of the recent growth of clumped isotope measurements at natural isotopic abundances, that is, of molecules containing more than one rare isotope. The intention is to introduce chemistry researchers to the field of using isotope compositions as tracers of atmospheric chemistry and climate both today and back in time through ice and rock records and to highlight the outstanding research questions to which experimental and theoretical physical chemists can contribute. [ABSTRACT FROM AUTHOR]

Mass-independent fractionation of stable sulfur isotopes (MIF-S) is believed to be a unique tracer of modern stratospheric eruptions as well as the Archean Earth's reducing atmosphere. The Δ36S/Δ33S ratio has been suggested as a strong constraint to the photochemical origin(s) of MIF-S data, because the variation of Δ36S/Δ33S ratio is commonly thought insignificant when mass-independent fractionated sulfur species (i.e., non-zero Δ33S or Δ36S values) are mixed with mass-dependent fractionated sulfur species (i.e., Δ33S = Δ36S = 0‰). Given the assumption that mixing makes a straight line in Δ33S versus Δ36S space, mixing would spread Δ33S and Δ36S values of geological or atmospheric samples along a line starting from the initial composition of 0 and the original Δ36S/Δ33S slope could be preserved. The Δ36S/Δ33S ratio, however, does not always remain constant during mixing, for the equations that define Δ33S and Δ36S, which by definition represent deviations from mass-dependent behavior, are not linear. Several different definitions (linear, exponential, and logarithmic expressions) have been widely applied for Δ33S and Δ36S, which make the Δ36S/Δ33S ratio a definition-dependent value. Given that each definition has advantages and disadvantages, attention should be paid to the robustness of the Δ36S/Δ33S ratio they predict. To examine the robustness of Δ36S/Δ33S ratio, we performed numerical and analytical analyses of its definition dependence and the behavior during two-component mixing. Our results suggest that the calculated Δ33S and Δ36S derived from different definitions vary with absolute values of δ34S (|δ34S|): at larger |δ34S|, the deviations become more prominent, and when |δ34S| is larger than ∼34‰, the discrepancy of Δ36S values determined by different definitions is over 1‰, which leads to significant definition-dependent variation in Δ36S/Δ33S at identical δ33S, δ34S, and δ36S values. This definition-dependence of Δ36S/Δ33S is negligible for most natural samples that show small 34S/32S fractionation. However, particular attention should be paid when dealing with processes that yield not only significant MIF-S but also large 34S isotopic fractionations, such as SO 2 photolysis and elemental sulfur polymerization. Among the tested expressions, the linear definitions are the most convenient to model two-component mixing when the δ34S difference between the end members is large, because Δ33S and Δ36S values of the mixture can strictly fall on the linear arrays in Δ33S versus Δ36S spaces. By applying the linear expression, the Δ36S−Δ33S distributions observed in the modern stratospheric records can be reproduced by SO 2 photolysis experiments. This agreement has been previously overlooked because the laboratory-produced Δ36S/Δ33S ratios by exponential and logarithm definitions did not match the values for the modern stratospheric records. • We study relationships among different definitions of sulfur mass-independent fractionation (Δ33S and Δ36S). • Δ33S and Δ36S variations due to the different definitions are approximately a function of |δ34S|. • Δ36S values differ >1‰ with the definitions at |δ34S| over ∼34‰. • With the linear expression, modern stratospheric and Archean Δ36S/Δ33S can be reproduced by SO 2 photolysis experiments. • Most natural Δ36S/Δ33S can be modeled by SO 2 photolysis, dilution, and differential overprinting by mass-dependent processes. [ABSTRACT FROM AUTHOR]

Increased anthropogenic-induced aerosol concentrations over the Himalayas and Tibetan Plateau have affected regional climate, accelerated snow/glacier melting, and influenced water supply and quality in Asia. Although sulfate is a predominant chemical component in aerosols and the hydrosphere, the contributions from different sources remain contentious. Here, we report multiple sulfur isotope composition of sedimentary sulfates from a remote freshwater alpine lake near Mount Everest to reconstruct a two-century record of the atmospheric sulfur cycle. The sulfur isotopic anomaly is utilized as a probe for sulfur source apportionment and chemical transformation history. The nineteenth-century record displays a distinct sulfur isotopic signature compared with the twentieth-century record when sulfate concentrations increased. Along with other elemental measurements, the isotopic proxy suggests that the increased trend of sulfate is mainly attributed to enhancements of dust-associated sulfate aerosols and climate-induced weathering/erosion, which overprinted sulfur isotopic anomalies originating from other sources (e.g., sulfates produced in the stratosphere by photolytic oxidation processes and/or emitted from combustion) as observed in most modern tropospheric aerosols. The changes in sulfur cycling reported in this study have implications for better quantification of radiative forcing and snow/glacier melting at this climatically sensitive region and potentially other temperate glacial hydrological systems. Additionally, the unique Δ33S-δ34S pattern in the nineteenth century, a period with extensive global biomass burning, is similar to the Paleoarchean (3.6-3.2 Ga) barite record, potentially providing a deeper insight into sulfur photochemical/thermal reactions and possible volcanic influences on the Earth's earliest sulfur cycle.

Understanding the sources of mercury (Hg) in coal is crucial for understanding the natural Hg cycle in the Earth's system, as coal is a natural Hg reservoir. We conducted analyses on the mass-dependent fractionation (MDF), reported as δ 202 Hg, and mass-independent fractionation (MIF), reported as Δ 199 Hg, of Hg isotopes among individual Hg species and total Hg (THg) in Chinese coal samples. This data, supplemented by a review of prior research, allowed us to discern the varying trend of THg isotope fractionation with coal THg content. The Hg isotopic composition among identified Hg species in coal manifests notable disparities, with species exhibiting higher thermal stability tending to have heavier δ 202 Hg values, whereas HgS species typically display the most negative Δ 199 Hg values. The sources of Hg in coal are predominantly attributed to Hg accumulation from the original plant material and subsequent input from hydrothermal activity. Hg infiltrates peat swamps via vegetation debris, thus acquiring a negative Δ 199 Hg isotopic signature. Large-scale lithospheric Hg recycling via plate tectonics facilitates the transfer of Hg with a positive Δ 199 Hg from marine reservoirs to the deep crust. The later-stage hydrothermal input of Hg with a positive Δ 199 Hg enhances coal Hg content. This process has resulted in an upward trend of Δ 199 Hg values corresponding with the increase in coal THg content, ultimately leading to near-zero Δ 199 Hg in high-Hg coals. Coal Hg reservoirs are affected by large-scale natural Hg cycling, which involves the exchange of Hg between continents and seas., Competing Interests: Declaration of competing interest The authors declare no conflicts of interest relevant to this study., (Copyright © 2024 Elsevier B.V. All rights reserved.)

[Display omitted] • Distinct Δ199Hg values of several tuff layers suggest that their magma sources can be different. • Volcanisms triggered the Late Ordovician and end-Guadalupian mass extinctions. • Hg isotopes as a useful proxy in revealing the type of volcanism in geological history. Mercury (Hg) anomalies in sedimentary records are a newly developed proxy of large volcanism in the geological past. Tuff layers host abundant volcanic ash and record key information on the type of volcanic emission (e.g., arc volcanism and large igneous province eruptions). Here, we measured the Hg isotopic compositions of several tuff layers in South China. Tuff samples in the Late Ordovician Wufeng Formation and the Middle Triassic Guanling Formation mostly show positive Δ199Hg values of – 0.01 to 0.10‰ and – 0.06 to 0.16‰, respectively, suggesting arc volcanism occurred during these two periods. Tuff samples in the Middle Permian Dachang Layer mostly show near-zero Δ199Hg values (– 0.08 to 0.00‰), suggesting volcanism was driven by the Emeishan large igneous province eruption. Results of this study verify Hg isotopes as a useful proxy in revealing the type of volcanism in geological history. [ABSTRACT FROM AUTHOR]

Mercury (Hg) is a volatile, bioaccumulative, and toxic heavy metal, and its global distribution is controlled by the Hg biogeochemical cycle in the atmosphere-land-ocean systems and the deep Hg cycle in interior reservoirs (e.g., mantle and crust). The biogeochemical cycle has been relatively well studied, but the deep Hg cycle remains relatively poorly constrained. Mercury isotopes undergo mass-dependent fractionation (MDF) and unique mass-independent fractionation (MIF) which can provide good constraints on large-scale Hg cycling. In this review, we provide a summary of available results on Hg abundance and isotopic composition in the atmosphere-land-ocean systems and interior reservoirs, with a focus on linking the Hg biogeochemical cycle to the deep Hg cycle. Through this effort, a few key points can be pointed out: (1) Natural and anthropogenic activities release large amounts of Hg into the atmosphere, which is transported on a global scale and deposited in terrestrial and marine systems; (2) Major constituents of the mantle and crust, e.g., mid-ocean ridge basalts (MORBs) and granites, show much lower Hg abundance than the atmosphere-land-ocean systems due to volcanic Hg(0) degassing and the formation of Hg-bearing ore deposits; (3) Mercury isotopes, especially Δ199Hg values, are useful in tracing surface Hg recycling into mantle and crust; (4) Hg(II) photo-reduction in the atmosphere yields negative Δ199Hg values in gaseous Hg(0) and positive Δ199Hg values in Hg(II) species, which results in negative Δ199Hg values in terrestrial systems (dominant deposition of Hg(0)) and positive Δ199Hg values in marine systems (dominant deposition of Hg(II); (5) MORBs and arc-related basalts (IABs) show positive Δ199Hg values, suggesting marine Hg recycling into the oceanic crust and upper mantle via plate subduction. Oceanic island basalts (OIBs) and continental flood basalts (CFBs) mostly display near-zero Δ199Hg values, suggesting limited surface Hg recycling into the lower mantle. Granites show positive to negative Δ199Hg values, suggesting the continental crust receives Hg from the metasomatized mantle and remelted terrestrial material. Opposing Δ199Hg values in arc-related and intracontinental hydrothermal systems highlights the great potential of using Hg isotopes for metallogenic tracing. [ABSTRACT FROM AUTHOR]

Sulfate aerosols have long been implicated as a primary forcing agent of climate change and mass extinction in the aftermath of the end-Cretaceous Chicxulub bolide impact. However, uncertainty remains regarding the quantity, residence time, and degree to which impact-derived sulfur transited the stratosphere, where its climatic impact would have been maximized. Here, we present evidence of mass-independent fractionation of sulfur isotopes (S-MIF) preserved in Chicxulub impact ejecta materials deposited in a marine environment in the Gulf Coastal Plain of North America. The mass anomalous sulfur is present in Cretaceous-Paleogene event deposits but also extends into Early Paleogene sediments. These measurements cannot be explained by mass conservation effects or thermochemical sulfate reduction and therefore require sulfur-bearing gases in an atmosphere substantially different from the modern. Our data cannot discriminate between potential source reaction(s) that produced the S-MIF, but stratospheric photolysis of SO2 derived from the target rock or carbonyl sulfide produced by biomass burning are the most parsimonious explanations. Given that the ultimate fate of both of these gases is oxidation to sulfate aerosols, our data provide direct evidence for a long hypothesized primary role for sulfate aerosols in the postimpact winter and global mass extinction. [ABSTRACT FROM AUTHOR]

The late Mesozoic antimony (Sb) mineralization belt in South China hosts a large portion of the world's Sb reserves. However, the source and mineralization processes of these Sb deposits remain controversial. Here, we measured mercury (Hg) concentrations and isotopic compositions of stibnite in the Banpo Sb-only and Woxi Sb-polymetallic ore deposits, as well as associated rocks in the Yangtze Block in order to constrain the metal sources and ore formation processes in the South China Sb mineralization belt. Stibnite samples from both deposits exhibit significant enrichment in Hg (4.23–50.6 ppm) and have higher δ202Hg values (−0.47‰ to 2.03‰) than the studied Precambrian basement rocks (−1.42‰ to 0.59‰), Paleozoic sedimentary rocks (−2.40‰ to −0.32‰), and other natural Hg reserves (e.g., marine and continental systems). This indicates that significant mass-dependent fractionation of Hg isotopes occurred during hydrothermal processes. Negative to slightly positive Δ199Hg values of −0.17‰ to 0.02‰ were obtained for stibnite from the studied deposits, similar to values for the Precambrian basement rocks, but different from those of the Paleozoic sedimentary rocks and data previously reported for mantle materials. This suggests that Precambrian basement rocks were the source of Hg and associated metals. Our data and the tectonic evolution of South China indicate that late Mesozoic asthenospheric upwelling, in response to the Paleo-Pacific oceanic slab foundering, generated heat that drove the circulation of fluids in the basement and crustal basinal rocks. These fluids leached Sb, Hg, and other metals from the Precambrian basement rocks and formed the world-class Sb mineralization belt in South China. [ABSTRACT FROM AUTHOR]

A series of investigations have been conducted concerning the study of traditional stable isotopes and rare gas stable isotopes in natural gas. However, little is known regarding non-traditional stable isotopes of mercury in natural gas, especially in the development and utilization of shale gas in recent years. In fact, the presence of mercury in natural gas (including shale gas) provides a basis for research on mercury isotopes. Mercury was extracted from shale gas at the Wufeng-Longmaxi Formation in the YS108 block of the Zhaotong National shale gas demonstration area in the Sichuan Basin by using an acid potassium permanganate solution, followed by the analysis of mercury content and stable isotope composition. The mercury content in the marine shale gas at the Wufeng-Longmaxi Formation ranged from 171 to 2,906 ng/m3, with an average of 1,551.08 ± 787.08 ng/m3 (n = 37, 1 SD). The Δ199Hg values of mercury stable isotopes range from 02‰ to 0.39‰, with an average of 22‰ ± 0.08‰ (n = 37, 1 SD); the δ202Hg values range from −1.68‰ to −0.04‰, with an average of −0.87‰ ± 0.31‰ (n = 37, 1 SD), which are significantly different from the Δ199Hg and δ202Hg information of coalbed gas, but similar to the Δ199Hg and δ202Hg information of terrestrial oil-type gas and the Δ199Hg in the main hydrocarbon-forming organic matter of lower organisms such as algae (t-test, p > 0.05). This indicates that terrestrial target strata with abundant algae or strata with positive Δ199Hg are the target strata for the exploration of terrestrial oil and gas.

[Display omitted] • S ulfide minerals from Hongtoushan Cu-Zn-Au deposit have slightly various δ34S Δ33S values. • The slightly negative mass-independent fractionation indicates a dominant igneous source of sulfur with ∼2.5–3.5 % seawater sulfate contribution. • Multiple sulfur isotope analyses may be used to predict the size, the grade of Cu, and the grade of Au for the Archean VMS deposits. In-situ multiple sulfur isotope analyses of pyrite, pyrrhotite, and chalcopyrite from the ∼2.55 Ga Hongtoushan Cu-Zn-Au VMS deposit are reported. Three sulfide minerals (pyrite, pyrrhotite, chalcopyrite) display slightly different mean δ34S values of +0.94 ‰, +0.60 ‰, and +0.57 ‰ and mean Δ33S values of –0.07 ‰, –0.02 ‰, and –0.05 ‰, respectively. The sulfide minerals show obvious signatures of slightly negative mass-independent fractionation for sulfur isotopes, indicating a dominant igneous source of sulfur with ∼2.5–3.5 % seawater sulfate contribution during the formation of this deposit. According to the suggestion by Chen et al. (2015) that the ore tonnages of Archean VMS deposits are linked to the Δ33S values, the Hongtoushan deposit may have greater prospecting potential. This study also proposes that not only do high Au-grade Archean VMS deposits have relatively high Δ33S values (near-zero) as suggested by Sharman et al. (2015), but low Au-grade Archean VMS deposits might also have high Δ33S values (near-zero). The Cu grades may also be directly linked to the Δ33S values for the Archean VMS deposits, as a greater seawater contribution (rapid temperature decrease; more negative Δ33S values) would be linked to higher Cu grades. These new findings may have great implications for our understanding of Archean VMS deposit genesis, and multiple sulfur isotope analyses may be used to predict the size, grade of Cu, and grade of Au for Archean VMS deposits. [ABSTRACT FROM AUTHOR]

Abstract The isotopic enhancement of atmospheric ozone (O3) is mainly determined by two processes of formation and photolytic decomposition. The formation is known to be associated with isotopic fractionation which can be as high as 120‰ relative to the parent oxygen. Photolysis‐induced isotopic fractionation in O3, however, is not known accurately. Absorption cross sections of various ozone species have been calculated by Zero Point Energy‐based model and quantum mechanical wave packet model. But their predictions pertaining to isotopic fractionations have not been verified experimentally. In the present work, we performed irradiation experiments of O3 at several wavelengths in the Hartley and Chappuis bands and determined the dissociative isotopic fractionation factors by a Rayleigh distillation model. In laboratory conditions, photolysis of ozone produces reactive atomic and/or molecular oxygen which influence the dissociative process through secondary chemistry. The complex interplay of primary photolysis and secondary chemistry was tracked by a kinetic model, and isotopic fractionation factors associated with photolysis alone were derived within a range of uncertainties. The fractionations are found to depend on the photon wavelength and deviate significantly at some wavelengths from the predicted values. For example, at 254 nm the zero point energy‐based models predict lower photolysis rate coefficients for the lighter isotopic species; the present data show about 50‰ higher values.

Hydrogen sulfide (nH2S) and sulfur oxide (SOn; n = 1, 2, 3) gases in early Earth's globally anoxic atmosphere were subjected to gas-phase chemical transformations by UV light. A principal photolysis pathway at that time produced elemental sulfur aerosols with mass-independently fractionated (MIF) isotopic values carrying variable minor isotope (33S, 36S) compositions. These rained into the sulfate-deficient Archean (ca. 3.85–2.5 Ga) oceans to react with [Fe2+]aq and form sedimentary sulfides. The MIF-bearing sulfides were incorporated into Archean sediments, including banded iron formations (BIF). Such aerosols may also have fueled microbial sulfur metabolisms, and thus are traceable by the MIF sulfur isotopes. Yet, data show that before ∼3.5 Ga mass-dependent34S/32S values in Early Archean sediments tend to fall within a narrow (±0.1%) range even as they carry mass-independent values. By about 3.5 Ga, 34S/32S values show much greater changes (>1%) in range congruent with microbial metabolic processing. Here, we trace probable pathways of elemental sulfur aerosols into Archean sediments, and couple our study with analysis of the evolutionary relationships of enzymes involved in sulfur metabolism to explain the observed trends. Our model explains why elemental sulfur aerosols were apparently not utilized by the Eoarchean (pre-3.65 Ga) biosphere even though an immediate precursor to the required enzyme may have already been present. Evolution of microbial sulfur metabolisms is tracked by multiple sulfur isotopes Alkaline hydrothermal vents were an abode for early microbial life Sulfite detoxification prompted anaerobic respiration Reversal of respiratory electron transport chain (ETC) stimulated photothiotrophy Surplus e- acceptors permitted the emergence of elemental sulfur reduction [ABSTRACT FROM AUTHOR]

Experimental results are presented showing the variation in the relationship between odd isotopes of tin (Sn) in mass-independent fractionation caused by the magnetic isotope effect (MIE), which has previously only been observed for mercury. These results are consistent with the trend predicted from the difference between the magnitudes of nuclear magnetic moments of odd isotopes with a nuclear spin. However, the correlation between odd isotopes in fractionation induced by the MIE for the reaction system used in this study (solvent extraction using a crown ether) was different from that reported for the photochemical reaction of methyltin. This difference between the two reaction systems is consistent with a theoretical prediction that the correlation between odd isotopes in fractionation induced by the MIE is controlled by the relationship between the spin conversion time and radical lifetime. The characteristic changes in the correlation between odd isotopes in fractionation induced by the MIE observed for Sn in this study provide a guideline for quantitatively determining fractionation patterns caused by the MIE for elements that have multiple isotopes with a nuclear spin. These results improve our understanding of the potential impact of the MIE on mass-independent fractionation observed in natural samples, such as meteorites, and analytical artifacts of high-precision isotope analysis for heavy elements., Competing Interests: Competing interests statement:The authors declare no competing interest.

Abstract Recent insights into fundamental mechanisms underlying quadruple stable sulfur isotope (32S, 33S, 34S, and 36S) mass‐independent fractionation (S‐MIF) chemistry and potential implications for planetary processes highlight the urgent need of conducting laboratory experiments to delineate the chemical physics of S‐MIF. Elemental sulfur (S0), a ubiquitous component in the atmospheres of early Earth and Mars, is a major product or reactant in most experiments. Developing different chemical protocols for isotopic analysis is consequently of utility. The reduction of S0 to hydrogen sulfide (H2S) is the first step of the fluorination method for isotopic analysis, but existing S0 reduction methods require relatively long chemical reagent preparation time. Here we present an operationally simple and rapid method for reducing S0 to H2S directly by “Thode solution.” External uncertainties of our method for δ34S, Δ33S, and Δ36S measurements (associated with reduction, fluorination, purification, and mass spectrometer analysis) are 0.3‰, 0.01‰, and 0.2‰, respectively, comparable with traditional methods. This new technique was used to determine quadruple stable sulfur isotope compositions of product S0 in a set of pilot experiments designed to investigate possible symmetry‐dependent isotope effects in planetary‐relevant elemental sulfur recombination reactions. Differences in Δ33S and Δ36S between initial and produced S0 are slightly larger than analytical errors, shedding new light into the role of sulfur recombination reactions in S‐MIF. Our study offers a practical approach for measuring multiple isotopic compositions of S0 in laboratory and natural samples and creates new opportunities for deepening understanding of S‐MIF signatures in Archean rocks and Martian meteorites.

A series of photochemical experiments with sulfur dioxide were carried out using a xenon lamp (λ > 200 nm), a low-pressure mercury lamp (λ = 184.9 and 253.7 nm), and an UP-213 laser system (λ = 213 nm) as light sources. Based on the isotope data obtained for elemental sulfur (the end product of SO2 photolysis), we revealed specifics in correlations between δ34S, ∆33S, and ∆36S values depending on the spectral characteristics of the incident radiation. Our studies showed that the Archean Δ33S/δ34S and Δ36S/Δ33S ratios could be reproduced in the SO2 photolysis experiments by combining spectral composition of the radiation, the intensity of the spectral components, and the partial pressure of SO2. The results of the experiments suggest that the UV radiation with wavelengths less than 200 nm was a determining factor in the production of sulfur isotopic anomalies in the Archean atmosphere. [ABSTRACT FROM AUTHOR]

The Himalayas and Tibetan Plateau, identified as the Third Pole (TP), is a unique region because of its insertion into global environmental and climatic changes. Deposition of atmospheric nitrate in this region is one of the most important sources of reactive nitrogen to glacial‐hydrologic system and ecosystems. The isotopic composition of atmospherically deposited nitrate preserved in ice bodies plays a central role in delineating environmental and climatic changes, present, and past. Here, we provide an overview of the complete isotopic compositions (δ15N, δ18O, and Δ17O) of nitrate in aerosol, snow, ice, and water samples (n = 46) collected across the Southern, Southeastern, Central, and Northern TP to constrain complex nitrogen cycles of the atmosphere, cryosphere, hydrosphere, and, potentially, the biosphere. A large variability of snow nitrate isotopic compositions is observed across the TP at different spatial scales (from a single glacier to the entire plateau), likely due to the complex landscape and relevant physical and chemical processes across the TP. Large nitrate Δ17O values are observed in water samples collected from the Mt. Everest region, highlighting the considerable fraction (up to 45%) of atmospheric nitrate to the nitrate load in this Himalayan hydrologic system. Our work reveals the complex chemical, depositional, and postdepositional processes over the TP that are greater than previously thought and identifies further comprehensive investigations, which entail using nitrate isotopic compositions as an identifier for nitrate source apportionment in various ecosystems and understanding past atmospheric and climatic conditions in this region. Key Points: Complete isotopic compositions of nitrate in aerosol, snow, ice, and water samples collected across the Tibetan Plateau were measuredNitrate isotopic compositions in the cryosphere over the Tibetan Plateau is spatially highly heterogeneousContribution of atmospheric nitrates to the hydrologic system is high at Himalayas [ABSTRACT FROM AUTHOR]

Isotope fractionation due to photochemical self-shielding is believed to be responsible for the enrichment of inner solar system planetary materials in the rare isotopes of carbon, nitrogen, and oxygen relative to the Sun. Self-shielding may also contribute to sulfur isotope mass-independent fractionation in modern atmospheric sulfates, although its role in the early Earth atmosphere has not yet been convincingly established. Here, I present an analytical formulation of isotopic photodissociation rate coefficients that describe self-shielding isotope signatures for 3 and 4-isotope systems broadly representative of O and S isotopes. The analytic equations are derived for idealized molecular spectra, making an analytic formulation tractable. The idealized spectra characterize key features of actual isotopologue spectra, particularly for CO and SO 2 , but are applicable to many small molecules and their isotopologues. The analytic expressions are convenient for evaluating the magnitude of isotope effects without having to pursue involved numerical solutions. More importantly, the analytic expressions illustrate the origin of particular isotope signatures, such as the previously unexplained large mass-dependent fractionation associated with photodissociation of optically-thick SO 2. The formulation presented here elucidates the origin of some of these important isotopic fractionation processes. [ABSTRACT FROM AUTHOR]

Recent insights into fundamental mechanisms underlying quadruple stable sulfur isotope (32S, 33S, 34S, and 36S) mass‐independent fractionation (S‐MIF) chemistry and potential implications for planetary processes highlight the urgent need of conducting laboratory experiments to delineate the chemical physics of S‐MIF. Elemental sulfur (S0), a ubiquitous component in the atmospheres of early Earth and Mars, is a major product or reactant in most experiments. Developing different chemical protocols for isotopic analysis is consequently of utility. The reduction of S0 to hydrogen sulfide (H2S) is the first step of the fluorination method for isotopic analysis, but existing S0 reduction methods require relatively long chemical reagent preparation time. Here we present an operationally simple and rapid method for reducing S0 to H2S directly by "Thode solution." External uncertainties of our method for δ34S, Δ33S, and Δ36S measurements (associated with reduction, fluorination, purification, and mass spectrometer analysis) are 0.3‰, 0.01‰, and 0.2‰, respectively, comparable with traditional methods. This new technique was used to determine quadruple stable sulfur isotope compositions of product S0 in a set of pilot experiments designed to investigate possible symmetry‐dependent isotope effects in planetary‐relevant elemental sulfur recombination reactions. Differences in Δ33S and Δ36S between initial and produced S0 are slightly larger than analytical errors, shedding new light into the role of sulfur recombination reactions in S‐MIF. Our study offers a practical approach for measuring multiple isotopic compositions of S0 in laboratory and natural samples and creates new opportunities for deepening understanding of S‐MIF signatures in Archean rocks and Martian meteorites. Plain Language Summary: Quadruple stable sulfur isotope analysis (32S, 33S, 34S, and 36S) of elemental sulfur (S0) using the fluorination method and isotope ratio mass spectrometer is useful for deepening understanding of biogeochemical and cosmochemical processes. We outline a new protocol for the chemical pretreatment of S0 using a mixture of hydriodic acid, hypophosphorous acid, and hydrochloric acid. The new protocol eliminates time‐consuming works of preparing or purifying chemical reagents and offers a new avenue for rapid isotope analysis of S0 produced from laboratory experiments and extracted from natural samples. We examined the applicability of our new method on S0 produced in a set of pilot chemical physics experiments relevant to planetary processes such as impact events and volcanoes. The results highlight the applicability of this new technique and an urgent need of understanding fundamental mechanisms of sulfur isotope effects in various planetary processes. Key Points: A simple elemental sulfur reduction method was developed for quadruple sulfur isotopic analysisThe external uncertainties of the new method are comparable with traditional methodsPilot experimental tests of isotope effects in sulfur recombination reactions were carried out as an application example of the new method [ABSTRACT FROM AUTHOR]

All of the Big Five mass extinctions (BFMEs) of the Phanerozoic are postulated to have been associated with eruptions of large igneous provinces (LIPs), although the role of LIP magmatism in some of these biocrises remains contentious. Mercury (Hg)-system proxies are now widely used to identify volcanic fluxes to stratigraphic successions. Here, we review Hg proxies and isotopic records for the BFMEs as well as seven non-BFME LIP events in the Phanerozoic to evaluate the extent to which Hg-system data support a link with LIP magmatism. LIP influence is assessed based on Hg/TOC EF of >3 (i.e., enrichment factors of Hg normalized to total organic carbon for the event interval relative to the pre- and/or post-event background) and on characteristic Δ199Hg shifts. The relationships of Hg-system anomalies to eruption volume, distance from the putative LIP source, depositional water depth, and average sedimentation rates were evaluated by multiple regression analysis (MRA). No LIP is universally registered by sedimentary Hg deposits: positive "hits" are recorded variably by 15-71% of the sections contemporaneous with individual major LIPs. Because Hg anomalies can have multiple origins, Hg-isotope data are crucial to recognition of the source of LIP-associated Hg anomalies. For the end-Permian and end-Triassic mass extinctions, average Hg/TOC EF values for all sections are respectively 4.7 and 4.2 (with 71% and 67% of sections yielding values >3) and Δ199Hg shifts are >±0.10‰, providing evidence of LIP influence. For seven non-BFME LIP events, average Hg/TOC EF ranges from 1.8 to 4.2, with 15% to 67% of the sections exhibiting anomalous Hg enrichment and isotopic shifts (−0.15‰ to +0.08‰). In contrast, the Late Ordovician and Late Devonian mass extinctions exhibit less common Hg enrichment (<30% of sections with Hg/TOC EF >3) and Δ199Hg shifts mostly <±0.04‰, indicating no fundamental change in Hg sources during these events and, thus, providing no support for an LIP trigger of these biocrises. Rather, the Hg anomalies associated with these events were likely due to localized Hg uptake related to depositional water depth and/or watermass redox conditions (i.e., euxinia). The end-Cretaceous mass extinction yields negative Δ199Hg shifts (−0.16‰ to −0.01‰) associated with local volcanism, suggesting limited influence by LIP magmatism. Among the variables examined by MRA, the LIP source (i.e., subaerial vs. submarine), distance from LIP source, and sedimentation rates show by far the strongest relationships to Hg anomalies. In summary, our results indicate that (1) Hg-concentration data must be supplemented by Hg-isotope data to accurately evaluate LIP influences in sedimentary systems, and (2) the extant Hg-system data support the dominant role of LIPs in the end-Permian and end-Triassic mass extinctions but not in the Late Ordovician and Late Devonian biocrises. • Mercury (Hg) volcanic proxy data for Phanerozoic Big Five mass extinctions (BFMEs). • Multiple regression analysis to evaluate key factors influencing Hg records. • End-Permian and end-Triassic extinctions marked by abundant LIP-related Hg inputs. • End-Cretaceous extinction modestly Hg enriched; volcanism was background factor. • Late Ordovician and Devonian extinctions show limited Hg anomaly or isotope shift. [ABSTRACT FROM AUTHOR]

The 17O-excess (Δ17O) of sulfate (SO 4 2−) in Antarctic ice cores is a potential tool for assessing past oxidant chemistry. However, a significant gap between atmospheric and ice core Δ17O(SO 4 2−) has been reported in Antarctica. Here, we report Δ17O(SO 4 2−) of surface snow at sites with different snow accumulation rates along a latitudinal traverse route in East Antarctica. While the Δ17O(nss-SO 4 2−) values for the coastal region showed an average of 1.0 ± 0.5‰ (n = 8) that can be explained by atmospheric Δ17O(SO 4 2−) variations, Δ17O(nss-SO 4 2−) in the katabatic (2.7 ± 0.2‰, n = 5) and inland (3.5 ± 0.3‰, n = 6) regions showed relatively high values that cannot be explained only by atmospheric deposition. Lower methanesulfonate (MSA) fluxes and lower mass ratios of MSA to SO 4 2−, along with higher Δ17O(nss-SO 4 2−) values, were observed in the katabatic and inland regions, suggesting the production of SO 4 2− with a high Δ17O value through MSA oxidation via OH radicals. The influence of this chemical post-depositional effect on MSA and Δ17O(SO 4 2−) is more pronounced in the inland compared to the katabatic region. The Δ17O(SO 4 2−) records in Antarctic ice cores with low accumulation rates may be impacted by elevated Δ17O(SO 4 2−) values originating from MSA oxidation, necessitating careful interpretation. In particular, the shift in Δ17O(SO 4 2−) from glacial to interglacial periods, previously interpreted as a change in atmospheric sulfate formation, requires reconsideration. • Antarctica has a discrepancy of atmospheric and ice core Δ17O(SO 4 2−). • Δ17O(nss-SO 4 2−) in snow differs latitudinally from coastal to inland regions. • Interpretation of ice core Δ17O(SO 4 2−) needs caution with considering the post-depositional change. [ABSTRACT FROM AUTHOR]

• The Hiroshima glasses are condensates produced by the Hiroshima nuclear explosion. • The wide silicon kinetic fractionations in the Hiroshima glasses can only be explained by condensation. • In Hiroshima glasses, oxygen mass-independent fractionations resulted from chemical reactions during condensation. • A scenario was established to describe the formation of the Hiroshima fallout. • The Hiroshima glasses can be considered an analog of the first condensates of the solar system. A new kind of Hiroshima nuclear fallout, the Hiroshima glasses, was discovered around the Hiroshima Bay. Here, the chemical compositions and the silicon and oxygen triple isotope compositions were analyzed to understand the formation process of these new fallouts. The chemical analysis shows four different families of glasses: the melilitic glasses, the anorthositic glasses, the soda-lime glasses, and the silica glass. The silicon isotopic compositions show wide variations in the glasses, with δ30Si varying between -23.0 ± 1.8 ‰ and -1.5 ± 1.1 ‰. The oxygen isotopic compositions indicate the presence of mass-independent fractionation on ≈38 % of the analyses, reaching a Δ17O of -3.1 ± 0.6 ‰. The chemical and silicon isotopic compositions of the Hiroshima glasses show that these glasses were formed by condensation within the nuclear fireball. Our scenario for the Hiroshima glasses formation, tested by modeling (GGchem code), considers a rapid condensation (1.7–5.5 s) in the nuclear fireball (3200–1000 K) at atmospheric pressure with a gas resulting from a mixing between air, and vaporized water and city materials. Chemical reactions during the Hiroshima glasses condensation are the most probable source for the oxygen mass-independent fractionation. The formation of the Hiroshima glasses by condensation implies that they may be an analog to the first condensates in the solar system: Calcium-Aluminum-rich Inclusions (CAIs), which are found in chondrites. The Hiroshima glasses exhibit similarities with CAIs in their chemical and isotopic compositions (Si and O). [ABSTRACT FROM AUTHOR]

We report the isotope shifts of the rotational constants and vibrational band progressions of the sulfur dioxide molecule (SO), for all four stable sulfur isotopes32S,33S,34S, and36S. These are extracted from exact quantum theoretical calculations of the SO rovibrational energy levels, as reported in Chem. Phys.450–451, 59 (2015) and Chem. Phys.461, 34 (2015) and by fitting these levels to a J-shifting (JS)-type scheme, applied to a representative set of total angular momentum (J) values. The approach used to obtain the rotational constants is unusual in that it is derived directly from the quantum theoretical framework used for the earlier calculation, which gives rise to a flexible (i.e., vibrational- and rotational-state-dependent) but symmetric rotor description. The usual rotational quantum numbers are thus replaced with a single body-fixed azimuthal rotation quantum number, K, with various strategies introduced a posteriori to address rotor asymmetry. The new model fits the numerically computed rovibrational levels well, over a fairly broad range of vibrational (v) and rotational (J) excitations. The computed rotational constants agree well with previously reported experimental values [J. Chem. Phys.58, 265 (1973)]. The explicitly v- and J-dependent approach used here should thus prove valuable in broader contexts—e.g., for an analysis of self-shielding in sulfur mass-independent fractionation, even though the rovibrational levels themselves exhibit mass-dependent fractionation. [ABSTRACT FROM AUTHOR]

• High resolution S isotopes measured over volcanic events in ice cores by MC-ICP-MS. • S isotopes in ice fingerprint stratospheric tropical and extra-tropical eruptions. • Isotope mass balance constrains proportion of stratospheric sulfate deposited in ice. • Method can be used to improve reconstructions of volcanic forcing of climate. The record of volcanic forcing of climate over the past 2500 years is based primarily on sulfate concentrations in ice cores. Of particular interest are large volcanic eruptions with plumes that reached high altitudes in the stratosphere, as these afford sulfate aerosols the longest residence time in the atmosphere, and thus have the greatest impact on radiative forcing. Sulfur isotopes measured in ice cores can be used to identify these large eruptions because stratospheric sulfur is exposed to UV radiation, which imparts a time-evolving mass independent fractionation (MIF) that is preserved in the ice. However, sample size requirements of traditional measurement techniques mean that the MIF signal may be obscured, leading to an inconclusive result. Here we present a new method of measuring sulfur isotopes in ice cores by multi-collector inductively coupled plasma mass spectrometry, which reduces sample size requirements by three orders of magnitude. Our method allows us to measure samples containing as little as 10 nmol of sulfur, with a precision of 0.11‰ for δ 34 S and 0.10‰ for Δ 33 S, enabling a high-temporal resolution over ice core sulfate peaks. We tested this method on known tropical (Tambora 1815 and Samalas 1257) and extra-tropical (Katmai/Novarupta 1912) stratospheric eruptions from the Tunu2013 ice core in Greenland and the B40 ice core from Antarctica. These high-resolution sulfur isotope records suggest a distinct difference between the signatures of tropical versus extra-tropical eruptions. Furthermore, isotope mass balance on sulfate from extra-tropical eruptions provides a means to estimate the fraction of sulfate deposited that was derived from the stratosphere. This technique applied to unidentified eruptions in ice cores may thus improve the record of explosive volcanism and its forcing of climate. [ABSTRACT FROM AUTHOR]

We present results of study of sulfide ore occurrence in highly metamorphosed (granulite facies) Archean rocks of the Siberian craton basement. The host rocks and ore minerals are briefly described, and new data on the multiple sulfur isotope (δ33S, δ34S, Δ33S) composition of sulfides are presented. Application of high-resolution analytical methods enabling the assessment of the sulfur isotope behavior in situ made it possible to reveal mass-independent fractionation of sulfur isotopes in the rock samples. The isotopic composition of sulfur in the sulfides indicates its inflow from several sources, including the ancient Archean atmosphere, where primary sulfur has passed through a cycle of fractionation. Despite the high-gradient metamorphism, the subsequent ultrametamorphic and post-ultrametamorphic transformations accompanied by a change in the primary mineral composition of rocks and by chemogenic fractionation of sulfur, the signature of the sedimentary source of sulfur in sulfide ores has been well preserved. Analysis of the chemical composition of rocks and ore minerals and of sulfur isotopes has led to the conclusion that the studied rocks are metamorphosed Late Archean analogs of black shales and the sulfide mineralization is of stratiform pyrite type. [ABSTRACT FROM AUTHOR]

Abstract–This paper presents the results of experimental studies of the behavior of mass-independent isotope effects of sulfur Δ33S and Δ36S during photochemical processes initiated by a broadband ultraviolet radiation. Experiments were performed in a flow photochemical reactor using a high-pressure mercury lamp, which is a source of radiation of a wide range with maximum radiation intensity in the wavelength range of 270−330 nm and weaker intensity in the range of 190−250 nm. The temperature and SO2 pressure dependences of the sulfur isotope ratios in the elemental sulfur products are revealed. Based on a comparative analysis of our isotope data with data from previous experimental studies with xenon and hydrogen lamps, it was shown that the correlation between the values of δ34S, Δ33S and Δ36S in elemental sulfur depends on the relative spectral distribution of the radiation intensity. Based on a comparison of our isotope data with data from previous experimental studies with xenon and hydrogen lamps, it was shown that the correlation between the values of δ34S, Δ33S and Δ36S in elemental sulfur depends on the relative spectral distribution of the radiation intensity. Our experiments suggest that photochemical processes in the range of 250−330 nm could play a significant role in the production of an isotope sulfur anomaly in the Archean atmosphere. The conditions in which 250− 330 nm radiation prevails over the 190−220 nm radiation are consistent with the assumption that the level of solar radiation reaching the Earth's surface in Archean was several orders of magnitude higher in the wavelength range 200−300 nm compared with the current level of radiation in this range. [ABSTRACT FROM AUTHOR]

The isotopic enhancement of atmospheric ozone (O3) is mainly determined by two processes of formation and photolytic decomposition. The formation is known to be associated with isotopic fractionation which can be as high as 120‰ relative to the parent oxygen. Photolysis‐induced isotopic fractionation in O3, however, is not known accurately. Absorption cross sections of various ozone species have been calculated by Zero Point Energy‐based model and quantum mechanical wave packet model. But their predictions pertaining to isotopic fractionations have not been verified experimentally. In the present work, we performed irradiation experiments of O3 at several wavelengths in the Hartley and Chappuis bands and determined the dissociative isotopic fractionation factors by a Rayleigh distillation model. In laboratory conditions, photolysis of ozone produces reactive atomic and/or molecular oxygen which influence the dissociative process through secondary chemistry. The complex interplay of primary photolysis and secondary chemistry was tracked by a kinetic model, and isotopic fractionation factors associated with photolysis alone were derived within a range of uncertainties. The fractionations are found to depend on the photon wavelength and deviate significantly at some wavelengths from the predicted values. For example, at 254 nm the zero point energy‐based models predict lower photolysis rate coefficients for the lighter isotopic species; the present data show about 50‰ higher values. Key Points: Laser‐based new ozone photolysis experiments at several wavelengths at Hartley and Chappuis bands are presented to provide new insightsAlong with box modeling, the photolysis‐induced fractionation factors are derived and show distinctive values from model predictionsThe results call for urgent needs for a systematic exploration of photolysis‐induced fractionation and revisit of atmospheric applications [ABSTRACT FROM AUTHOR]

Abstract Mercury (Hg) stable isotopes are useful to understand Hg biogeochemical cycling because physical, chemical and biological processes cause characteristic Hg isotope mass-dependent (MDF) and mass-independent (MIF) fractionation. Here, source Hg isotope signatures and process-based isotope fractionation factors are integrated into a fully coupled, global atmospheric-terrestrial-oceanic box model of MDF (δ202Hg), odd-MIF (Δ199Hg) and even-MIF (Δ200Hg). Using this bottom-up approach, we find that the simulated Hg isotope compositions are inconsistent with the observations. We then fit the Hg isotope enrichment factors for MDF, odd-MIF and even-MIF to observational Hg isotope constraints. The MDF model suggests that atmospheric Hg0 photo-oxidation should enrich heavy Hg isotopes in the reactant Hg0, in contrast to the experimental observations of Hg0 photo-oxidation by Br. The fitted enrichment factor of terrestrial Hg0 emission in the odd-MIF model (5‰) is likely biased high, suggesting that the terrestrial Hg0 emission flux (160 Mg yr−1) used in our standard model is underestimated. In the even-MIF model, we find that a small positive atmospheric Hg0 photo-oxidation enrichment factor (0.22‰) along with enhanced atmospheric HgII photo-reduction and atmospheric Hg0 dry deposition (foliar uptake) fluxes to the terrestrial reservoir are needed to match Δ200Hg observations. Marine Hg isotope measurements are needed to further expand the use of Hg isotopes in understanding global Hg cycling. [ABSTRACT FROM AUTHOR]

Sulfur Mass‐Independent Fractionation (S‐MIF) may provide a clue to understanding Earth's early atmosphere. We examined total pressure dependence of the S‐MIF produced by SO2 photolysis. Isotopic self‐shielding is known to produce S‐MIF, which could be changed by both the partial pressure of SO2 (pSO2) and by the total pressure (pTotal). Our experimental results show that both Δ33S and Δ36S values are constant when total pressure is below 10 kPa at constant pSO2, whereas they decrease as total pressure increases. The result suggests that pressure broadening of the SO2 absorption line is responsible for the S‐MIF. The modeled high‐resolution isotopologue cross sections can reproduce our experimental results and its changes depending on both pSO2 and pTotal. Consequently, we conclude that the Archean Δ33S and Δ36S correlation can only be achieved when the total pressure of the Archean atmosphere was below 100 kPa, or it was produced in the upper atmosphere. Plain Language Summary: Sulfur Mass‐Independent Fractionation (S‐MIF) in Archean sedimentary rocks could be useful to constrain the chemical and physical states of Earth's early atmosphere. SO2 photolysis is known to produce large MIF. However, experimental results have yet to model the observed mechanisms of S‐MIF in SO2 photolysis. We examined the total pressure effect of S‐MIF by SO2 photolysis and succeeded in modeling the observed S‐MIF and its total pressure dependence. Comparing the results of this study with geological records, large Archean S‐MIF could only be achieved when total pressure is below 100 kPa, suggesting that the Archean atmosphere was not thicker than the modern atmosphere or that the S‐MIF‐yielding photolysis occurred mainly at a high altitude. Key Points: Total pressure effect of sulfur mass‐independent fractionation during SO2 photolysis was examinedThe observed total pressure dependence can be explained by self‐shielding with pressure broadening of the SO2 absorption lineBased on the results, the large Archean Δ36S/Δ33S fractionations can only be achieved when total pressure was lower than 100 kPa [ABSTRACT FROM AUTHOR]

Abstract Modern anthropogenic aerosols usually exhibit low but significant Δ33S signatures (−0.6 to 0.5‰) whose origin still remains unclear. While isotope fractionation factors associated with the oxidation of SO 2 by O 2 +TMI (Transition Metal Ion), H 2 O 2 or OH cannot lead to such extreme Δ33S-values, an increasing number of studies points to the significant role of NO 2 as a contributing oxidant, especially in the urban environment. To address the possible relation between atmospheric NO 2 and observed Δ33S-values in aerosols, we carried out laboratory experiments oxidizing SO 2 by NO 2 at temperatures ranging between −7 and 52 °C. Our results show that at temperatures ≥10 °C SO 2 oxidation by NO 2 is characterized by 1) a 34α-value whose temperature dependence (0.2437/T+0.0457) is distinct from those related to oxidation by O 2 +TMI, H 2 O 2 and OH oxidation pathways and 2) 33β (0.514 ± 0.0003) and 36β (1.90 ± 0.002) values that are closer to the mass dependent values (0.515 and 1.89 respectively) than those reported for the other oxidation pathways. This implies that the NO 2 oxidation pathway cannot explain the extreme Δ33S-values measured in urban aerosols. Our data show that if atmospheric SO 2 oxidation by NO 2 is neglected, both the O 2 +TMI and OH oxidation pathways would be overestimated in urban areas. Finally, we conclude that another oxidation reaction is responsible for the high Δ33S-values measured in urban aerosol samples. Graphical abstract Image 1 Highlights • Atmospheric SO 2 oxidation by NO 2 cannot explain mass-independent fractionation of sulfur isotopes measured in urban aerosols. • Neglecting the NO 2 oxidation pathway leads to overestimate SO 2 oxidation by O 2 +TMI and OH. • SO 2 oxidation by NO 2 presents a cross-over. [ABSTRACT FROM AUTHOR]

Photic zone euxinia (PZE) is a condition where anoxic, H2S-rich waters occur in the photic zone (PZ). PZE has been invoked as an impediment to the evolution of complex life on early Earth and as a kill mechanism for Phanerozoic mass extinctions. Here, we investigate the potential application of mercury (Hg) stable isotopes in marine sedimentary rocks as a proxy for PZE by measuring Hg isotope compositions in late Mesoproterozoic (∼1.1 Ga) shales that have independent evidence of PZE during discrete intervals. Strikingly, a significantly negative shift of Hg mass-independent isotope fractionation (MIF) was observed during euxinic intervals, suggesting changes in Hg sources or transformations in oceans coincident with the development of PZE. We propose that the negative shift of Hg MIF was most likely caused by (i) photoreduction of Hg(II) complexed by reduced sulfur ligands in a sulfide-rich PZ, and (ii) enhanced sequestration of atmospheric Hg(0) to the sediments by thiols and sulfide that were enriched in the surface ocean as a result of PZE. This study thus demonstrates that Hg isotope compositions in ancient marine sedimentary rocks can be a promising proxy for PZE and therefore may provide valuable insights into changes in ocean chemistry and its impact on the evolution of life. [ABSTRACT FROM AUTHOR]

Increased anthropogenic-induced aerosol concentrations over the Himalayas and Tibetan Plateau have affected regional climate, accelerated snow/glacier melting, and influenced water supply and quality in Asia. Although sulfate is a predominant chemical component in aerosols and the hydrosphere, the contributions from different sources remain contentious. Here, we report multiple sulfur isotope composition of sedimentary sulfates from a remote freshwater alpine lake near Mount Everest to reconstruct a two-century record of the atmospheric sulfur cycle. The sulfur isotopic anomaly is utilized as a probe for sulfur source apportionment and chemical transformation history. The nineteenth-century record displays a distinct sulfur isotopic signature compared with the twentieth-century record when sulfate concentrations increased. Along with other elemental measurements, the isotopic proxy suggests that the increased trend of sulfate is mainly attributed to enhancements of dust-associated sulfate aerosols and climate-induced weathering/erosion, which overprinted sulfur isotopic anomalies originating from other sources (e.g., sulfates produced in the stratosphere by photolytic oxidation processes and/or emitted from combustion) as observed in most modern tropospheric aerosols. The changes in sulfur cycling reported in this study have implications for better quantification of radiative forcing and snow/glacier melting at this climatically sensitive region and potentially other temperate glacial hydrological systems. Additionally, the unique Δ33S-δ34S pattern in the nineteenth century, a period with extensive global biomass burning, is similar to the Paleoarchean (3.6-3.2 Ga) barite record, potentially providing a deeper insight into sulfur photochemical/thermal reactions and possible volcanic influences on the Earth's earliest sulfur cycle. [ABSTRACT FROM AUTHOR]

In the pre-oxygenated ancient Earth atmosphere, the lack of O 3 absorption allowed ultraviolet photodissociation of numerous molecules in the troposphere and lower stratosphere. For molecules with narrow line-type absorption spectra, optically thick columns would have produced isotope fractionation due to self-shielding of the most abundant isotopologues. In the lower atmosphere pressure broadening would modify, and in some cases, eliminate these isotope signatures. Shielding is particularly important for quantifying or constraining photolysis-derived isotope effects, such as those believed to explain the sulfur mass-independent fractionation in Archean sedimentary rocks. Here, we report pressure broadening coefficients for natural abundance SO 2 in the C ˜ 1 B 2 ← X ˜ 1 A 1 band system at 215 nm. For gas bath pressures up to 750 mbar, we find broadening coefficients of 0.30 ± 0.03 cm − 1 atm −1 and 0.40 ± 0.04 cm − 1 atm −1 for N 2 and CO 2 , respectively. These broadening coefficients are ∼30% larger than SO 2 broadening coefficients previously measured in the B ˜ − X ˜ bands at 308 nm. Because of the highly congested nature of the C ˜ − X ˜ bands, pressure broadening in the early Earth troposphere will cause line profile overlap that will diminish the self-shielding-derived mass-independent isotope fractionation for optically thick SO 2 columns. Thus, non-explosive volcanic eruptions may not have left a signature of SO 2 self-shielding in the ancient sedimentary rock record. [ABSTRACT FROM AUTHOR]

The presence of oxygen isotopic anomaly in hydrogen peroxide (H 2 O 2 ) has been established by measurements of three oxygen isotopes ( 16 O, 17 O, 18 O) in H 2 O 2 from experiments on H 2 O 2 formation using a water vapour discharge in presence of (O 2 , CO 2 , Ar) gases and using VUV photolysis of water vapour. The termolecular OH recombination reaction may be account for the source of MIF in H 2 O 2 due to a selective isotopic enrichment through the radical pair mechanism with non-equivalent nuclei. It was established that the magnitude of the observed MIF signals in H 2 O 2 depended on the presence of oxidising gases. [ABSTRACT FROM AUTHOR]

Archean sulfide and sulfate minerals commonly exhibit anomalous ratios among four stable sulfur isotopes, 32S, 33S, 34S, and 36S. These anomalous relationships, referred to as sulfur mass-independent fractionation (S-MIF), provide strong evidence for an early anoxic atmosphere. Correlated variations among three isotope ratios (δ33S, δ34S, and δ36S) can be observed in rocks throughout the Archean and are a key clue toward identifying the source reaction of S-MIF. Studies to investigate the origin of Archean S-MIF so far have primarily focused on the photochemistry of sulfur dioxide (SO2). Photolysis of SO2 at wavelengths <220 nm and photoexcitation at 240-340 nm both yield large-magnitude S-MIF. Proposed mechanisms of S-MIF include isotopologue-dependent self-shielding, cross-sectional amplitudes, and vibronic coupling during intersystem crossing. This review discusses the emerging picture of the physical origins of S-MIF and their implications for the chemistry of the early Earth's atmosphere. [ABSTRACT FROM AUTHOR]

We report mass-independent and mass-dependent Ca isotopic compositions for thirteen geological reference materials, including carbonates ( NIST SRM 915a and 915b), Atlantic seawater as well as ten rock reference materials ranging from peridotite to sandstone, using traditional ε and δ values relative to NIST SRM 915a, respectively. Isotope ratio determinations were conducted by independent unspiked and 43Ca-48Ca double-spiked measurements using a customised Triton Plus TIMS. The mean of twelve measurement results gave ε40/44Ca values within ± 1.1, except for GSP-2 that had ε40/44Ca = 4.04 ± 0.15 (2 SE). Significant radiogenic 40Ca enrichment was evident in some high K/Ca samples. At an uncertainty level of ± 0.6, all reference materials had the same ε43/44Ca and ε48/44Ca values. We suggest the use of δ44/42Ca to report mass-dependent Ca isotopic compositions. The precision under intermediate measurement conditions for δ44/42Ca over eight months in our laboratory was ± 0.03‰ (with n ≥ 8 repeat measurements). Measured igneous reference materials gave δ44/42Ca values ranging from 0.27‰ to 0.54‰. Significant Ca isotope fractionation may occur during magmatic and metasomatism processes. Studied reference materials with higher (Dyn/Ybn) tend to have lower δ44/42Ca, implying a potential role of garnet in producing magmas with low δ44/42Ca. Sandstone GBW07106 had a δ44/42Ca value of 0.22‰, lower than all igneous rocks studied so far. [ABSTRACT FROM AUTHOR]

Energy transfer mechanism for recombination of two sulfur atoms into a diatomic molecule, S 2 , is studied theoretically and computationally to determine whether the rate coefficient of this process can be significantly affected by isotopic substitutions, and whether the resultant isotope effect is expected to be mass-dependent or mass-independent. This is one of sulfur polymerization processes thought to be important in the anoxic atmosphere of the Archean Earth and, potentially, relevant to mass-independent fractionation of sulfur isotopes. A simplified theoretical approach is employed, in which all properties of S 2 molecule are characterized rather accurately, whereas the process of stabilization of metastable S 2 ∗ by bath gas collisions is described approximately. Properties of individual scattering resonances in S 2 are studied in detail, and it is found that most important contributions to the recombination process come from ro-vibrational states formed near the top of centrifugal barrier, and that the number of such states is about 50 (in 32 S 32 S). Absolute value of recombination rate coefficient is computed to be 1.22 × 10 −33 cm 6 /s (for 32 S 32 S at room temperature and atmospheric pressure), close to experimental result. Two distinct isotope effects are identified. One is a classical mass-dependent effect due to translational partition function, which leads to a weak, smooth, and negative mass-dependence of rate coefficient (4% decrease when the mass is raised from 32 S 32 S to 34 S 34 S). Second effect, due to quantized resonances, is two orders of magnitude stronger, but is local. In practice, due to presence of multiple individual resonances, this phenomenon leads to irregular mass-independent variations of rate coefficients in the ranges ±5%. It is also demonstrated that in real molecules this irregular behavior is expected to be somewhat smoother, and the isotope effect is somewhat smaller, due to dependence of stabilization cross section on properties of individual resonances (not described by present model). Thus, additional calculations of stabilization cross sections are needed in order to give quantitative prediction of this mass-independent isotope effect, and to determine its relevance to mass-independent fractionation of sulfur isotopes in the Archean rock record. [ABSTRACT FROM AUTHOR]

A hierarchy of isotopically substituted recombination reactions is formulated for production of sulfur allotropes in the anoxic atmosphere of Archean Earth. The corresponding system of kinetics equations is solved analytically to obtain concise expressions for isotopic enrichments, with focus on massindependent isotope effects due to symmetry, ignoring smaller mass-dependent effects. Proper inclusion of atom-exchange processes is shown to be important. This model predicts significant and equal depletions driven by reaction stoichiometry for all rare isotopes: 33S, 34S, and 36S. Interestingly, the ratio of capital △ values obtained within this model for 33S and 36S is -1.16, very close to the mass-independent fractionation line of the Archean rock record. This model may finally offer a mechanistic explanation for the striking mass-independent fractionation of sulfur isotopes that took place in the Archean atmosphere of Earth. [ABSTRACT FROM AUTHOR]