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

Formation rates for various products of hydrogen sulfide oxidation by δ-MnO2 were studied as a function of pH, temperature, concentration of the reactants, and ionic strength at the environmentally-relevant conditions. The main goals of this work were studying the effects of these parameters on speciation of zero-valent sulfur, including individual polysulfides and revealing the mechanism of its formation. A reaction between hydrogen sulfide and manganese dioxide is the fastest environmentally-relevant abiotic process of polysulfides formation, reactive sulfur species, which participate in complexation of metals, pyrite formation, sulfurization of organic matter and may serve as a substrate for microorganisms. In the pH range of 7.0 to 10.5, zero-valent sulfur accounted for > 55% of the sulfur in the products of hydrogen sulfide oxidation, while at pH ≥ 7.5, the formation rates of polysulfide zero-valent sulfur were higher than those of particulate zero-valent sulfur formation. Speciation of polysulfides on the initial stage of the reaction shows significant shift toward the higher polysulfides compared to their speciation calculated under assumption of thermodynamic equilibrium in both H2S - Sn2− - S8(aq) - α-S8 and H2S - Sn2− - S8(aq) - S8(coll) systems. We suggest that the shift in the speciation of polysulfide system results from the presence of a short-living highly reactive sulfur atoms, which are formed on the first stage of the reaction: two-electron transfer from hydrogen sulfide to manganese dioxide. Results of this study provide constraints on the rates of polysulfide formation at the redox interfaces of the stratified aquatic systems, and allows quantitative assessment of their role in sulfur cycling.

Deep-sea hydrothermal vents are a significant source of dissolved metals to the global oceans, producing midwater plumes enriched in metals that are transported thousands of kilometers from the vent source. Particle precipitation upon emission of hydrothermal fluids controls metal speciation and the magnitude of metal export. Here, we document metal sulfide particles, including pyrite nanoparticles, within the first meter of buoyant plumes from three high-temperature vents at the East Pacific Rise. We observe a zone of particle settling 10–20 cm from the orifice, indicated by stable sulfur isotopes; however, we also demonstrate that nanoparticulate pyrite (FeS2) is not removed from the plume and can account for over half of the filtered Fe (≤0.2 µm) up to one meter from the vent orifice. The persistence of nanoparticulate pyrite demonstrates that it is an important mechanism for near-vent Fe stabilisation and highlights the potential role of nanoparticles in element transport., There has been much interest recently in the transport mechanisms of metals from hydrothermal vents. Here the authors found that nanoparticulate pyrite is not removed from the plume and can account for over 50% of filtered iron one metre from the vent mouth.

The early evolution of life on Earth was intimately coupled with the evolution of ocean chemical composition and redox conditions in Archean ocean. However, the measurements of chemical and isotopic compositions of Archean sedimentary rocks does not provide sufficient information for understanding the biogeochemical processes that characterized oceans during this period. In this research, the cycling of the redox-sensitive elements in the water column and sediments of the seasonally stratified Lake Sihailongwan, China, was studied. It was found that during the stratification, the concentrations of sulfate ions in the epilimnion were −1. The hypolimnion of the lake becomes anoxic and contains iron, manganese and low concentrations of hydrogen sulfide. These conditions are similar to those suggested to exist in the Archean ocean, and therefore the biogeochemical cycles in Lake Sihailongwan may be analogous to those in the Archean ocean. In Lake Sihailongwan, the chemocline is always deeper than the thermocline. The hypolimnion is supersaturated with respect to iron sulfide in August, while in May and October, this supersaturation is present only in the lower hypolimnion. The concentration profiles of the redox species in the water column and in the sediments show that dissolved iron(II) and manganese(II) diffuse from the sediments into the water column, while hydrogen sulfide and sulfate diffuse into the sediment. At the hypolimnion, the sulfur isotope fractionation values are consistent with microbial sulfate reduction, possibly combined, to a minor extent, with disproportionation of zero-valent sulfur. The absolute sulfur isotope fractionation factor increases between spring and autumn and decreases with water depth, possibly due to precipitation of iron sulfide in the lower hypolimnion. The fraction of highly reactive iron in the sediments is mainly composed of iron(II) carbonates and the most reactive iron(III) (hydr)oxide phases. Iron-based redox proxies are consistent with sediment deposition under ferruginous water column conditions. In the sediment, concentrations of sulfate and hydrogen sulfide are low, and sulfur isotope composition of sedimentary pyrite is equal to that of the epilimnetic sulfate. The obtained results demonstrated that despite a low sulfate concentration in the water column, sulfur isotope fractionation is high. However, due to the complete consumption of the sulfate reservoir, the large isotope fractionation is not preserved in the sedimentary record.

The high fluxes of iron minerals associated with aeolian dry deposition may result in an anomalously high reactive iron content and the rapid reoxidation of hydrogen sulfide in sediments. This will prevent the formation of pyrite and result in a ‘cryptic’ sulfur cycle. We studied the cycling of iron and sulfur in deep water (>800 m water depth) sediments of the Red Sea and its northern extension, the Gulf of Aqaba. We found that the reactive iron content in the surface sediments of the Gulf of Aqaba and the Red Sea is high, whereas the amount of sulfur-bound iron is very low and decreases with the water depth. The presence of trace amounts of pyrite and zero-valent sulfur, as well as the isotopic compositions of sulfate and pyrite, which are consistent with sulfate reduction under substrate-limiting conditions, suggest that cryptic sulfur cycling is likely to be a result of the rapid reoxidation of hydrogen sulfide rather than the suppression of microbial sulfate reduction. The low amount of reactive iron and high organic carbon content in the sediments of the Shaban Deep, which are overlain by hypersaline hydrothermal brines, result in a non-cryptic sulfur cycle characterized by the preservation of pyrite in the sediments. Supplementary material: Data for sulfur speciation, iron speciation and sulfur isotope composition are available at https://doi.org/10.6084/m9.figshare.c.5508155 Thematic collection: This article is part of the Sulfur in the Earth system collection available at: https://www.lyellcollection.org/cc/sulfur-in-the-earth-system

This study investigates how glacially delivered reactive iron (oxyhydr) oxide and manganese oxide phases influence the biogeochemical cycling of sulfur in sediments of three Arctic fjords and how the biogeochemical signatures of these processes are preserved. Results reveal differences in the concentrations of dissolved iron and manganese in pore-waters and the concentration of solid-phase sulfur species within individual fjords and amongst the three fjords, likely controlled by the varying input of reactive iron (oxyhydr) oxides to the sediment. Broadly, the stations can be divided into three categories based on their biogeochemical signals. Stations in the first category, located in Smeerenburgfjorden, are characterized by relatively low concentrations of (easily) reducible particulate iron phases, increasing concentrations of iron monosulfides, pyrite, and elemental sulfur with depth, and low pore-water dissolved iron and manganese concentrations. Biogeochemical processes at these stations are primarily driven by organoclastic sulfate reduction, sulfur disproportionation and the subsequent reaction and sequestration of sulfide in the sediment as iron monosulfide and pyrite. Sulfur and oxygen isotope values of sulfate display progressive enrichment in heavy isotopes with depth at these stations. In contrast, concentrations of (easily) reducible particulate iron phases and pore-water dissolved iron (up to 850 mu M) and manganese (up to 650 mu M) are very high at stations of the second and third category, located in Kongsfjorden and Van Mijenfjorden, while iron monosulfide and pyrite contents are extremely low. The amount of pyrite and its isotope values in conjunction with organic sulfur compounds provide evidence for a detrital origin of a fraction of these sulfur compounds. At the Kongsfjorden and Van Mijenfjorden stations, oxidative pathways of the sedimentary sulfur cycle, controlled by the high availability of reducible particulate iron phases, play an important role, leading to the effective recycling of sulfide to sulfate through sulfur intermediates and concomitant resupply of the sulfate reservoir with S-32. In both fjords, elemental sulfur was only detected at the outer fjord stations grouped into the third category. Our study provides a framework for interpreting the Fe-S-C geochemistry of similar continental shelf areas in modern settings and ultimately for identifying these environments in the rock record.

The accumulation of oxygen in Earth’s atmosphere and oceans in the late Archean had profound implications for the planet’s biogeochemical evolution. Oxygen impacts sulfur cycling through the oxidation of sulfide minerals and the production of sulfate for microbial sulfate reduction (MSR). The isotopic signature of sulfur species preserved in the geologic record is affected by the prevailing biological and chemical processes and can therefore be used to constrain past oxygen and sulfate concentrations. Here, in a study of a late Archean analogue, we find that the sulfur isotopic signature in the water column of a seasonally stratified lake in southern China is influenced by MSR, whereas model results indicate that the isotopic signature of the underlying sediments can be best explained by concurrent sulfate reduction and sulfide oxidation. These data demonstrate that small apparent sulfur isotope fractionations (δ34Ssulfate-AVS = 4.2‰–1.5‰; AVS—acid volatile sulfides) can be caused by dynamic sulfur cycling at millimolar sulfate concentrations. This is in contrast to current interpretations of the isotopic record and indicates that small fractionations do not necessarily indicate very low sulfate or oxygen.

In order to characterize biogeochemical sulfur cycling in the metalimnion of a thermally stratified freshwater lake, we followed changes in the concentrations and isotopic composition of sulfur species during a 24-h period, during which the chemocline oscillated at an amplitude of 5.3 m due to internal wave activity. Hourly sampling at a fixed depth (17.1 m) enabled study of redox changes during the transition from oxic to sulfidic conditions and vice versa. The oxidation–reduction potential, pH, conductivity and turbidity correlated linearly with the water temperature (a proxy for depth relative to the chemocline). The highest concentrations of thiosulfate and sulfite were detected approximately 2.5 m below the chemocline. Concentrations of zero-valent sulfur increased ~ 10 fold when the chemocline rose into the photic zone due to phototrophic sulfide oxidation. Triple isotopic composition of sulfur species indicates a shift with depth from values typical for sulfate reduction right below the chemocline to values which may be explained by either sulfate reduction alone or by a combination of microbial sulfate reduction and microbial sulfate disproportionation. We conclude that consumption of hydrogen sulfide at the chemocline of Lake Kinneret is controlled by the combination of its chemical and/or chemotrophic oxidation to sulfur oxoanions and predominantly phototrophic oxidation to zero-valent sulfur.

Environmental context The quality of drinking water can be greatly compromised by the presence of dimethyl polysulfides. We studied the rate and mechanism of decomposition of dimethyl polysulfides in aqueous solution under solar irradiation, and found that they decompose photochemically in seconds to minutes, i.e. much faster than under dark conditions. These results suggest that photochemical pathways of dimethyl polysulfide decomposition may prevail in euphotic zones of natural aquatic systems. Abstract The presence of malodorous dimethyl polysulfides (DMPSs) has been documented in marine and limnic systems as well as in tap water distribution systems. These compounds compromise the quality of drinking water. Under oxic conditions and in the absence of radiation, DMPSs with n ≥ 3 sulfur atoms disproportionate into DMPSs with n + 1 and n − 1 sulfur atoms, and, finally, to dimethyl disulfide (DMDS) and S8. DMDS, in turn, decomposes to methyl mercaptan (MT) and methanesulfinic acid. Under these conditions, the half-lives of DMPSs vary from months for dimethyl pentasulfide (DM5S) to hundreds of thousands of years for DMDS. In this work, we studied the kinetics and mechanisms of the decomposition reactions of DMPSs with 2–5 sulfur atoms in aqueous solutions in the presence of oxygen and under exposure to solar radiation. The quantum yields of decomposition of DMPSs with 2, 3, 4 and 5 sulfur atoms do not depend on either the concentration of DMPSs or pH, and are 40 ± 10, 2.0 ± 0.2, 35 ± 10 and 10 ± 4 respectively. The quantum yields, which are higher than unity, suggest that under exposure to solar radiation the photochemical decomposition of DMPSs proceeds by a radical chain reaction mechanism. Half-lives of DMPSs in oxic aquatic solutions exposed to solar radiation under a very clear atmosphere and a solar elevation angle of 90 ° were calculated from the quantum yields and were found to be as low as 43 ± 13 s for DMDS, 40 ± 4 s for dimethyl trisulfide (DMTS), 2.1 ± 0.6 s for dimethyl tetrasulfide (DM4S) and 4.2 ± 1.7 s for DM5S.

The microbial reduction of sulfate to sulfide coupled to organic matter oxidation followed by the transformation of sulfide back to sulfate drives a dynamic sulfur cycle in a variety of environments. The oxidative part of the sulfur cycle in particular is difficult to constrain because the eight electron oxidation of sulfide to sulfate occurs stepwise via a suite of biological and chemical pathways and produces a wide variety of intermediates (Sx2-, S0, S2O32-, S4O62-, and SO32-), which may in turn be oxidized, reduced or disproportionated. Although the potential processes affecting these intermediates are well-known from microbial culture and geochemical studies, their significance and rates in the environment are not well constrained. In the study presented here, time-course concentration measurements of intermediate sulfur species were made in amended freshwater water column and sediment incubation experiments in order to constrain consumption rates and processes. In sediment incubations, consumption rates were Scolloidal0>Sx2->SO32-≈ S4O62-> S2O32-, which is consistent with previous measurements of SO32-, S4O62-, and S2O32- consumption rates in marine sediments. In water column incubations, however, the relative reactivity was Scolloidal0>SO32->Sx2-> S2O32-> S4O62-. Consumption of thiosulfate, tetrathionate and sulfite was primarily biological, whereas it was not possible to distinguish between abiotic and biological polysulfide consumption in either aqueous or sediment incubations. Scolloidal0 consumption in water column experiments was biologically mediated, however, rapid sedimentary consumption was likely due to reactions with iron minerals. These experiments provide important constraints on the biogeochemical reactivity of intermediate sulfur species and give further insight into the diversity of biological and geochemical processes that comprise (cryptic) environmental sulfur cycling.

The Gulf of Aqaba is an oligotrophic marine system with oxygen-rich water column and organic carbon-poor sediments (≤0.6% at sites that are not influenced by anthropogenic impact). Aeolian dust deposition from the Arabian, Sinai, and Sahara Deserts is an important source of sediment, especially at the deep-water sites of the Gulf, which are less affected by sediment transport from the Arava Desert during seasonal flash floods. Microbial sulfate reduction in sediments is inferred from the presence of pyrite (although at relatively low concentrations), the presence of sulfide oxidation intermediates, and by the sulfur isotopic composition of sulfate and solid-phase sulfides. Saharan dust is characterized by high amounts of iron minerals such as hematite and goethite. We demonstrated, that the resulting high sedimentary content of reactive iron(III) (hydr)oxides, originating from this aeolian dry deposition of desert dust, leads to fast re-oxidation of hydrogen sulfide produced during microbial sulfate reduction and limits preservation of reduced sulfur in the form of pyrite. We conclude that at these sites the sedimentary sulfur cycle may be defined as cryptic.

Zero-valence sulfur (S°) is a central intermediate in the marine sulfur cycle and forms conspicuous accumulations at sediment surfaces, hydrothermal vents and in oxygen minimum zones. Diverse microorganisms can utilize S°, but those consuming S° in the environment are largely unknown. We identified possible key players in S° turnover on native or introduced S° in benthic coastal and deep-sea habitats using the 16S ribosomal RNA approach, (in situ) growth experiments and activity measurements. In all habitats, the epsilonproteobacterial Sulfurimonas/Sulfurovum group accounted for a substantial fraction of the microbial community. Deltaproteobacterial Desulfobulbaceae and Desulfuromonadales were also frequently detected, indicating S° disproportionation and S° respiration under anoxic conditions. Sulfate production from S° particles colonized in situ with Sulfurimonas/Sulfurovum suggested that this group oxidized S°. We also show that the type strain Sulfurimonas denitrificans is able to access cyclooctasulfur (S₈), a metabolic feature not yet demonstrated for sulfur oxidizers. The ability to oxidize S°, in particular S8 , likely facilitates niche partitioning among sulfur oxidizers in habitats with intense microbial sulfur cycling such as sulfidic sediment surfaces. Our results underscore the previously overlooked but central role of Sulfurimonas/Sulfurovum group for conversion of free S° at the seafloor surface.

In the initial online version of the article, the sampling station location “F” was missing in Fig. 1. The original article has been corrected.

Environmental context Dimethyl polysulfides are malodorous compounds formed from decomposing algal matter. The decomposition of dimethylpolysulfides with 3–5 sulfur atoms was studied in aqueous solution under dark, oxygenated conditions and compared with observations of natural systems. The half-lives of dimethyl tri- and tetrasulfides are very long (176–100 000 years), while the half-life of dimethyl pentasulfide (

We have quantified the major forms of volatile organic sulfur compounds (VOSCs) distributed in the water column ofstratified freshwater Fayetteville Green Lake (FGL), to evaluate the biogeochemical pathways involved in their production.The lake’s anoxic deep waters contain high concentrations of sulfate (12–16 mmol L 1 ) and sulfide (0.12 lmol L 1 to1.5 mmol L 1 ) with relatively low VOSC concentrations, ranging from 0.1 nmol L to 2.8 lmol L 1 . Sulfur isotope measure-ments of combined volatile organic sulfur compounds demonstrate that VOSC species are formed primarily from reducedsulfur (H 2 S/HS ) and zero-valent sulfur (ZVS), with little input from sulfate. Thedata support a role of a combination ofbiological and abiotic processes in formation of carbon–sulfur bonds between reactive sulfur species and methyl groups oflignin components. These processes are responsible for very fast turnover of VOSC species, maintaining their low levels inFGL. No dimethylsulfoniopropionate (DMSP) was detected by Electrospray Ionization Mass Spectrometry (ESI-MS) inthe lake water column or in planktonic extracts. These observations indicate a pathway distinct from oceanic and coastal mar-ine environments, where dimethylsulfide (DMS) and other VOSC species are principally produced via the breakdown ofDMSP by plankton species. 2013 Elsevier Ltd. All rights reserved.1. INTRODUCTIONThe use of stable isotopes to understand the biogeo-chemical cycling of sulfur in oceanic (Rees et al., 1978;Jorgensen et al., 2004; Bo¨ttcher et al., 2006), freshwater(Fry, 1986; Canfield et al., 2010; Zerkle et al., 2010), andterrestrial systems (Goldhaber and Kaplan, 1980; Habichtand Canfield, 2001) has focused mostly on the dynamicsof inorganic sulfate, sulfide and their intermediate species.Few studies (e.g., Amrani et al., 2009; Oduro et al., 2011)have examined organic sulfur compounds, such as dimeth-ylsulfide (DMS; CH

The deep Black Sea is known to be depleted in electron-acceptors for sulfide oxidation. This study on depth distributions of sulfur species (S(II), S(0), S n 2 - , S 2 O 3 2 - , SO 3 2 - , SO 4 2 - ) in the Dvurechenskii mud volcano, a cold seep situated in the permanently anoxic eastern Black Sea basin (Sorokin Trough, 2060 m water depth), showed remarkable concentrations of sulfide oxidation products. Sulfite concentrations of up to 11 μmol L−1, thiosulfate concentrations of up to 22 μmol L−1, zero-valent sulfur concentrations of up to 150 μmol L−1 and up to five polysulfide species were measured in the upper 20 cm of the sediment. Electron-acceptors found to be available in the Dvurechenskii mud volcano (DMV) for the oxidation of hydrogen sulfide to sulfide oxidation intermediates are iron-minerals, and probably also reactive manganese phases. Up to 60 μmol g−1 of reactive iron-minerals and up to 170 μmol L−1 dissolved iron was present in the central summit with the highest fluid upflow and fresh mud outflow. Thus, the source for the oxidative power in the DMV are reactive iron phases extruded with the mud from an ancient source in the deeply buried sediments, leading to the formation of various sulfur intermediates in comparably high concentrations. Another possible source of sulfide oxidation intermediates in DMV sediments could be the formation of zero-valent sulfur by sulfate dependent anaerobic microbial oxidation of methane followed by disproportionation of zero-valent sulfur. Sulfide oxidation intermediates, which are produced by these processes, do not reach thermodynamic equilibrium with rhombic sulfur, especially close to the active center of the DMV due to a short equilibration time. Thus, mud volcano sediments, such as in the DMV, can provide oxidizing niches even in a highly reduced environment like the abyssal part of the Black Sea.

Concentrations of sulfate, sulfide and intermediate sulfur species as well as quadruple sulfur isotope compositions of sulfate, sulfide and zero-valent sulfur (ZVS) were analyzed in the water column of Lake Rogoznica (Croatia), a stratified marine euxinic lake. The chemocline in the lake, which was located at 8.5–9.5 m depth, supports a dense population of purple phototrophic sulfide oxidizing bacteria from the genus Chromatium. The highest ZVS (5.42 μmol L−1) and sulfite (1.13 μmol L−1) concentrations were detected at the chemocline. Thiocyanate concentrations up to 288 nmol L−1 were detected near the bottom of the lake. The thiocyanate profile suggests that it diffuses up from the sediment, where it may be produced by the reaction of cyanide with sulfide oxidation intermediates. Multiple sulfur isotope fractionations between sulfate and sulfide were consistent with a model finding that disproportionation is not a dominant process below the chemocline. Microbial sulfide oxidation was found to be the dominant process of the reoxidative part of the sulfur cycle. Despite the absence of a clear signal for sulfur disproportionation in multiple sulfur isotope values, δ34S fractionations between sulfate and sulfide were in the range of 43.8–45.2‰, is relatively large in comparison to most laboratory culturing studies. Our results suggest that such fractionation is achieved by microbial sulfate reduction alone, which is in agreement with metabolic models and recent laboratory studies.

Volatile methylated sulfur compounds emitted from terrestrial and aquatic ecosystems play a significant role in the global sulfur cycle, yet no satisfactory methods are available to trace their source and transformation in natural systems. Here we present a method for quantification and multiple sulfur isotopic analysis of a variety of volatile sulfur species as well as their natural precursors via hydrodesulfurization with a Raney nickel catalyst. The detection limit of this method for methanethiol (MT), dimethylsulfide (DMS), dimethyldisulfide (DMDS), and carbon disulfide (CS2) is 0.2 mg of sulfur per sample. Average recovery of ~ 95% was attained for samples containing more than 1.3 mg of these sulfur compounds. Triplicate to quadruplicate sulfur isotopic analyses of reduced standard materials yield average standard deviations of 0.3‰, 0.02‰, and 0.1‰, respectively, for δ34S, ∆33S, and ∆36S. The method developed here was used for determination of sulfur isotopic compositions of volatile organic sulfur compounds (VOSCs) and their precursor dimethylsulfoniopropionoate (DMSP) in sediment cores and a C4 plant Spartina alterniflora collected from the Delaware Great Marsh. Application of the method to these natural samples indicates that the S-isotope compositions of VOSCs and DMSP-S are similar to, but slightly 34S-depleted (~0.6–0.9), relative to porewater sulfide. These compounds are 34S-enriched (~ 1.7–2.0‰) relative to the compositions of the coexisting sulfide. Both suggest a relationship between source sulfide and these organic sulfur compounds.

We present a 3-year study of concentrations and sulfur isotope values (δ34S, Δ33S, and Δ36S) of sulfur compounds in the water column of Fayetteville Green Lake (NY, USA), a stratified (meromictic) euxinic lake with moderately high sulfate concentrations (12–16 mM). We utilize our results along with numerical models (including transport within the lake) to identify and quantify the major biological and abiotic processes contributing to sulfur cycling in the system. The isotope values of sulfide and zero-valent sulfur across the redox-interface (chemocline) change seasonally in response to changes in sulfide oxidation processes. In the fall, sulfide oxidation occurs primarily via abiotic reaction with oxygen, as reflected by an increase in sulfide δ34S at the redox interface. Interestingly, S isotope values for zero-valent sulfur sampled at this time still reflect production and recycling by phototrophic S-oxidation. In the spring, sulfide S isotope values suggest an increased input from phototrophic oxidation, consistent with a more pronounced phototroph population at the chemocline. This trend is associated with smaller fractionations between sulfide and zero-valent sulfur, suggesting a metabolic rate control on fractionation similar to that for sulfate reduction. Comparison of our data with previous studies indicates that the S isotope values of sulfate and sulfide in the deep waters are remarkably stable over long periods of time, with consistently large fractionations of up to 58‰ in δ34S. Models of the δ34S and Δ33S trends in the deep waters (considering mass transport via diffusion and advection along with biological processes) require that these fractionations are a consequence of sulfur compound disproportionation at and below the redox interface in addition to large fractionations during sulfate reduction. The large fractionations during sulfate reduction appear to be a consequence of the high sulfate concentrations and the distribution of organic matter in the water column. The occurrence of disproportionation in the lake is supported by profiles of intermediate sulfur compounds and by lake microbiology, but is not evident from the δ34S trends alone. These results illustrate the utility of including minor S isotopes in sulfur isotope studies to unravel complex sulfur cycling in natural systems.

Zero-valent sulfur species dynamics in tidal flat pools of Wadden Sea (North Sea) were studied. Concentrations of solid sulfur, colloidal sulfur of different particle sizes and distribution of inorganic polysulfide species were detected near the bottom of different pools as a function of time after detachment of the pool from sea. Concentrations of these species were detected also in the incubated sediment cores taken from the same site with the pumping of anoxic seawater, anoxic seawater spiked with sulfide and anoxic seawater spiked with lactate. Sulfide concentration in the pool increased during the first 2 h of pool detachment from the sea to a maximum of 273 µM. Polysulfides were present at the beginning of the detachment of the pool and higher concentrations of elemental sulfur and polysulfides lead to more rapid coagulation and precipitation of dispersed solid sulfur. The process of the formation of zero-valent sulfur began with the formation of polysulfides and colloidal sulfur with a particle size less than 5 μm. Further coagulation led to an increase in the amount of colloidal sulfur with the particle size more than 5 μm followed by crystallization of solid sulfur particles. Maximum concentration of colloidal sulfur detected in the pools was 73 µM and that of solid sulfur was 25 µM. Maximum concentration of the sum of all polysulfide species measured was 5.9 µM, which corresponded to 23.1 µM of detected polysulfide sulfur or to 27.7 µM of polysulfide sulfur taking into account the calculated concentrations of species with concentration under detection limit. Polythionates were not detected. Levels of total zero-valent sulfur usually reached the value of 40 µM, but can be even higher than 100 µM. This depended on the overall concentration of sulfide. In the tidal pools, polysulfide chain lengths were short and the polysulfide system was found not to be in equilibrium with solid or colloidal sulfur at any time of pool detachment from sea. Flow-through incubation experiments, however, exhibited polysulfide in equilibrium with respect to rhombic sulfur. No difference in the polysulfide speciation was observed in experiments where sulfide was artificially added and sulfide was produced through enhanced bacterial sulfate reduction. The differences were attributed to the kinetics and to competing oxidation processes present in the exposed Wadden Sea tidal pools as compared to the longer running and more restricted incubation experiments.

The solubility of cyclooctasulfur in water and sea water at various temperatures in the range between 4 and 80 °C was determined. Cyclooctasulfur in equilibrium with rhombic sulfur reacted with hot acidic aqueous potassium cyanide to form thiocyanate anion which was measured by anion chromatography. Sulfur solubility in pure water was found to increase with temperature by more than 78 times: from 6.1 nM S 8 at 4 °C to 478 nM S 8 at 80 °C. The following thermodynamic values for solubilisation of S 8 in water were calculated from the experimental data: K° = 3.01 ± 1.04 × 10 −8 , Δ G r ° = 42.93 ± 0.73 kJ mol −1 , Δ H r ° = 47.4 ± 3.6 kJmol −1 , Δ S r ° = 15.0 ± 11.7 J mol −1 K −1 ). Solubility of cyclooctasulfur in sea water was found to be 61 ± 13% of the solubility in pure water regardless of the temperature.

A HPLC-based protocol has been developed for the determination of zero-valent sulfur (ZVS) speciation, including solid, colloidal elemental sulfur and individual inorganic polysulfides in natural aquatic samples. The protocol includes four experimental procedures: (1) determination of polysulfide speciation by rapid single-phase derivatisation with methyl trifluoromethanesulfonate; (2) determination of the sum of polysulfide and colloidal sulfur by reaction with hydrogen cyanide (cyanolysis); (3) determination of total zero-valent sulfur by treatment with zinc chloride followed by extraction with chloroform; and (4) chromatographic determination of polythionates without sample pre-treatment. With proper sampling and preservation techniques in the field or on board ship, this combination of methods allowed the quantitative determination of: (a) individual polysulfide species; (b) dispersed colloidal sulfur; (c) dispersed solid elemental sulfur; and (d) tetra-, penta- and hexathionates. With minor modification, the method could be expanded to include other polythionates. Sixteen various wet chemical and liquid chromatographic methods were tested on nine synthetic reference samples (including solid elemental sulfur, colloidal elemental sulfur, inorganic polysulfides and polythionates) to establish the optimal protocol. The protocol was further evaluated by analysing the zero-valent sulfur content in microbially-produced sulfur and in sulfur from two natural samples of sulfide-rich seawater from tidal flats pools of the Wadden Sea (Germany).

We propose a novel protocol for detection of reactive zero-valent sulfur (ZVS) in natural aquatic samples including seawater. Reaction with hot potassium cyanide at slightly acidic conditions recovers ZVS from col- loidal fraction of particulate elemental sulfur, polysulfides (S n 2- ), and their protonated forms. Preconcentration by partial evaporation of the sample and separation of thiocyanate anions by high-performance liquid chro- matography on the C30 reverse phase column modified with poly(ethylene glycol) followed by spectrophoto- metric detection at 220 nm wavelength allows us to detect reactive ZVS with detection limit of 3 nmol L -1 for fresh water samples and 6 nmol L -1 for seawater samples. Storage at 4°C for 6 weeks does not change the con- centration of thiocyanate in the sample by more than 10%.

Polysulfides are abundant form of reduced sulfur compounds whose distribution in aquatic systems continues to pose environmental challenge. The Gibbs free-energy of formation, enthalpy of formation, and standard entropy of inorganic polysulfides were derived based on measurements of the temperature-dependent distribution of inorganic polysulfides in supersaturated aqueous polysulfide solutions. The data complements the relevant Gibbs free-energy data that were derived in our recent publication. The thermodynamic data show that the average polysulfide length is increased and polysulfides dissolve better at elevated temperatures, though the extent of this increase is pH dependent. At high pH (pH10) increasing the temperature from 25 to 80 degrees C results in a 5.6% increase in the concentration of polysulfide bound sulfur (i.e., dissolved zerovalent sulfur) and increases the average chain length (n) by 0.2 sulfur atoms, whereas at pH 8.2 the n increases by 0.25, and the dissolved polysulfide sulfur increases threefold.

Inorganic polysulfides are important intermediates in the formation of dimethylpolysulfides and possibly other volatile sulfur compounds of environmental significance. Currently, direct determination of these ions in the concentration range of natural systems is practically impossible, particularly under oxic conditions. Polysulfide quantification by derivatization with methyl iodide or d6-methyl iodide is emerging as a valuable alternative method for studies of polysulfide formation in natural systems. This manuscript presents detailed studies aimed at the evaluation of this method. We determined the conversion of the inorganic polysulfides to dimethylpolysulfides by methylation with methyl iodide. Close to 100 per cent of the molar concentration of polysulfide salts were converted to organic polysulfides for very low concentrations of dissolved polysulfide solutions, but only a small recovery was obtained for high concentrations of polysulfide precursors or when the solubility limit was exceeded. The recovery of polysulfides based on the calculated dissolved polysulfide concentration exceeds 1,000 per cent for very low dissolved concentrations of polysulfides. This unexpected dependence is attributed to continuous inorganic polysulfide formation from hydrogen sulfide and sulfur precipitate concurrent with, and in fact driven by, the methylation process.

A sudden increase in salinity about 7000 years ago caused a shift in the deposited sediments of the Black Sea from limnic to brackish-marine. Due to the development of an anoxic deep water basin and a relatively high sulfate concentration, organic matter is mineralized primarily through sulfate reduction in modern Black Sea sediments. Earlier studies showed that sulfate-reducing bacteria are abundant within the limnic sub-surface sediment in spite of extremely low concentrations of sulfate and organic carbon. A main objective of the present study was therefore to understand the depth distribution of sulfate reduction across the different sediment units, even deep below the sulfate–methane transition. Our study combined experimental measurements of sulfate reduction using 35 S radiotracer with analyses of sulfur and iron geochemistry in pore water and sediment. Potential sulfate reduction rates were measured with 35 S in sediment samples that were amended with sulfate and organic substrates and incubated in time-series up to 48 h. Sulfate reduction could thereby be detected and quantified at depths where concentrations of sulfate were otherwise too low to enable calculation of the rates. The results demonstrate that sulfate-reducing bacteria are active several meters below the sulfate–methane transition in Black Sea sediments. The cryptic sulfate reduction below the sulfate–methane transition may be driven by sulfate produced from re-oxidation of reduced sulfur species with oxidized iron minerals buried in the deep limnic sediment.

The rate of the reversible homogeneous disproportionation of polysulfides was studied by following the optical absorbance of polysulfide solutions in a continuous plug flow reactor equipped with an on-line photometric detector. In order to avoid heterogeneous slow reactions involving sulfur colloids or precipitate, the reaction was initiated by an abrupt pH change from an undersaturated solution containing predominantly tetrasulfide species to a pH where pentasulfide is the dominant species. The disproportionation was found to follow first order reversible reaction dynamics. At environmentally relevant conditions the characteristic time of the disproportionation reaction is of the order of 10 s. This characteristic time implies that necessary conditions for speciation of the different polysulfide species by chromatography or another separation and subsequent quantification scheme should be of the order of 1 s.

Background: The paper presents a quantification of main (hydrogen sulfide and sulfate), as well as of intermediate sulfur species (zero-valent sulfur (ZVS), thiosulfate, sulfite, thiocyanate) in the Yellowstone National Park (YNP) hydrothermal springs and pools. We combined these measurements with the measurements of quadruple sulfur isotope composition of sulfate, hydrogen sulfide and zero-valent sulfur. The main goal of this research is to understand multiple sulfur isotope fractionation in the system, which is dominated by complex, mostly abiotic, sulfur cycling. Results: Water samples from six springs and pools in the Yellowstone National Park were characterized by pH, chloride to sulfate ratios, sulfide and intermediate sulfur species concentrations. Concentrations of sulfate in pools indicate either oxidation of sulfide by mixing of deep parent water with shallow oxic water, or surface oxidation of sulfide with atmospheric oxygen. Thiosulfate concentrations are low (

Background Pyrite is one of the most abundant and widespread of the sulfide minerals with a central role in biogeochemical cycles of iron and sulfur. Due to its diverse roles in the natural and anthropogenic sulfur cycle, pyrite has been extensively studied in various experimental investigations of the kinetics of its dissolution and oxidation, the isotopic fractionations associated with these reactions, the microbiological processes involved, and the effects of pyrite on human health. Elemental sulfur (S0) is a common product of incomplete pyrite oxidation. Preexisting S0 impurities as unaccounted reaction products are a source of experimental uncertainty, as are adhered fine grains of pyrite and its oxidation products. Removal of these impurities is, therefore, desirable. A robust standardized pretreatment protocol for removal of fine particles and oxidation impurities from pyrite is lacking. Here we describe a protocol for S0 and fine particle removal from the surface of pyrite by rinsing in acid followed by repeated ultrasonication with warm acetone. Results Our data demonstrate the presence of large fractions of S0 on untreated pyrite particle surfaces, of which only up to 60% was removed by a commonly used pretreatment method described by Moses et al. (GCA 51:1561-1571, 1987). In comparison, after pretreatment by the protocol proposed here, approximately 98% S0 removal efficiency was achieved. Additionally, the new procedure was more efficient at removal of fine particles of adhered pyrite and its oxidation products and did not appear to affect the particle size distribution, the specific surface area, or the properties of grain surfaces. Conclusions The suggested pyrite pretreatment protocol is more efficient in removal of impurities from pyrite grains, and provides multiple advantages for both kinetic and isotopic investigations of pyrite transformations under various environmental conditions. Graphical Abstract Pyrite pretreatment by a commonly used technique (Method I) and a novel protocol (Method II)

We present the first observations on the occurrence of inorganic polysulfides in an oxygen rich aquatic system. Inorganic polysulfides were found both in the hypolimnion and the epilimnion of a freshwater lakeLake Kinneret. The presence of these compounds in oxic systems resolves the enigma concerning the mechanism of formation of dimethyl disulfide, dimethyltrisulfide, and dimethyltetrasulfide in oxygen rich aquatic systems and marine water. The abundance of low molecular weight organic and inorganic polysulfides relative to the a priori postulated dominance of the pentasulfide family is explained by the low level of polysulfides in oxygen-rich aquatic systems. Thermodynamic calculations show that for trace levels of reduced sulfur compounds, dimethyl disulfide becomes the dominant polysulfide form.

Methylation of polysulfides [(NH4)2Sn)] by reaction with CF3SO3CH3 followed by separation of the produced dimethylpolysulfides by liquid chromatography and subsequent highly accurate stable isotope analysis by a continuous-flow isotope ratio mass spectrometer shows that polysulfide anions in an aqueous solution exchange isotopes with the other sulfur species in the system. It demonstrates for the first time that polysulfide anions are 34S-enriched in equilibrium relative to total sulfur as a function of their sulfur chain length.

Zero-valence sulfur (S°) is a central intermediate in the marine sulfur cycle and forms conspicuous accumulations at sediment surfaces, hydrothermal vents and in oxygen minimum zones. Diverse microorganisms can utilize S°, but those consuming S° in the environment are largely unknown. We identified possible key players in S° turnover on native or introduced S° in benthic coastal and deep-sea habitats using the 16S ribosomal RNA approach, (in situ) growth experiments and activity measurements. In all habitats, the epsilonproteobacterial Sulfurimonas/Sulfurovum group accounted for a substantial fraction of the microbial community. Deltaproteobacterial Desulfobulbaceae and Desulfuromonadales were also frequently detected, indicating S° disproportionation and S° respiration under anoxic conditions. Sulfate production from S° particles colonized in situ with Sulfurimonas/Sulfurovum suggested that this group oxidized S°. We also show that the type strain Sulfurimonas denitrificans is able to access cyclooctasulfur (S₈), a metabolic feature not yet demonstrated for sulfur oxidizers. The ability to oxidize S°, in particular S8 , likely facilitates niche partitioning among sulfur oxidizers in habitats with intense microbial sulfur cycling such as sulfidic sediment surfaces. Our results underscore the previously overlooked but central role of Sulfurimonas/Sulfurovum group for conversion of free S° at the seafloor surface.

It is generally thought that the sulfate reduction metabolism is ancient and would have been established well before the Neoarchean. It is puzzling, therefore, that the sulfur isotope record of the Neoarchean is characterized by a signal of atmospheric mass-independent chemistry rather than a strong overprint by sulfate reducers. Here, we present a study of the four sulfur isotopes obtained using secondary ion MS that seeks to reconcile a number of features seen in the Neoarchean sulfur isotope record. We suggest that Neoarchean ocean basins had two coexisting, significantly sized sulfur pools and that the pathways forming pyrite precursors played an important role in establishing how the isotopic characteristics of each of these pools was transferred to the sedimentary rock record. One of these pools is suggested to be a soluble (sulfate) pool, and the other pool (atmospherically derived elemental sulfur) is suggested to be largely insoluble and unreactive until it reacts with hydrogen sulfide. We suggest that the relative contributions of these pools to the formation of pyrite depend on both the accumulation of the insoluble pool and the rate of sulfide production in the pyrite-forming environments. We also suggest that the existence of a significant nonsulfate pool of reactive sulfur has masked isotopic evidence for the widespread activity of sulfate reducers in the rock record.

Inorganic polysulfides have significant technological importance, and their environmental role is gradually being unraveled. But despite their importance, there is still no method for quantification of the individual members of the polysulfide family in nonsynthetic samples. The method is based on fast, single-phase derivatization with methyl trifluoromethanesulfonate followed by one of three modes of sample treatment depending on polysulfide concentration. Under the most aggressive preconcentration treatment involving liquid-liquid extraction, solvent evaporation to dryness, dissolution in n-dodecane, and finally HPLC-UV analysis of the dimethylpolysulfane distribution, the minimum detection limits of the individual polysulfides are in the range 15-70 nM. The method was demonstrated for the analysis of synthetic solutions, natural groundwater, polysulfide fortified seawater, and surface water and for time tracing of the distribution of the individual polysulfides during the oxidation of hydrogen sulfide by hydrogen peroxide. The observed speciation was evaluated by comparison with the theoretical distribution of polysulfides at equilibrium with sulfur precipitate showing that the dominant polysulfides' (i.e., tetra- to hexasulfide) concentrations agree well with the predicted distribution (90% of the results fall within less than 30% deviation from the predicted values), whereas up to 3-fold deviation was observed for the less abundant trisulfide and octasulfide species.

Zerovalent sulfur and inorganic polysulfides were determined in nine sulfide-rich water wells in central and southern Israel. Although the two locations belong to the same aquifer, they are characterized by different pH and hydrogen sulfide levels. Hydrogen sulfide in the central Israel wells ranged between 19 and 32 μM, and the pH was 7.26 ± 0.07. The southern basin is characterized by lower water circulation, lower pH (around 6.8), and higher hydrogen sulfide levels (>470 μM). Polysulfides were determined by a rapid single-phase methylation using methyl trifluoromethanesulfonate (methyl triflate) reagent. The summary polysulfide concentration for S42−–S72− species was found to be around 0.14–0.75 μM in the central region of Israel and substantially higher, 2.3–4.6 μM in the southern region. The sum of polysulfide zerovalent sulfur and colloidal sulfur was quantitatively detected by cyanide derivatization and compared to polysulfide sulfur determined by methyl triflate derivatization and to the chloroform extraction of zerovalent sulfur. A method for the determination of sulfur undersaturation level—the ratio between dissolved elemental sulfur and its equilibrium concentration in the presence of solid sulfur—based on the observed levels of the major polysulfide species is described. The observed polysulfide speciation was compared with the predicted speciation under sulfur saturation conditions taking into account the water temperature, its ionic strength, and pH. Criteria for sulfur saturation versus unsaturated conditions were established based on (1) the chain length dependence of the ratio between the observed polysulfide concentrations and their predicted value under sulfur saturated conditions, and (2) the difference between the concentration of zerovalent sulfur, as determined by cyanolysis, and the total polysulfide sulfur. According to this dual criterion five of the water wells were classified as being undersaturated with respect to sulfur, though for all the examined water wells the majority of the zerovalent sulfur was in the form of polysulfide sulfur.