Sulfur Isotope Fractionation Research Articles

Natural and anthropogenic factors controlling hydrogeochemical processes in a fractured granite bedrock aquifer, Korea

Contamination of groundwater has become a critical environmental concern, prompting international inquiries. In this study, the impacts of natural and anthropogenic factors in the granite bedrock groundwater system were identified based on the hydrogeochemical compositions including environmental isotopes (δ18O, δ2H, 222Rn, δ34SSO4, δ18OSO4) using multivariate statistical methods. Hierarchical clustering analysis classified the groundwater samples into three groups for both dry and wet seasons. The first group, observed in both seasons, represents groundwater influenced by water–rock interactions in low flow and also demonstrates anthropogenic contamination near densely populated residential areas. The second group corresponds to higher flow groundwater, where surface water interaction affects with minimal anthropogenic impact. The third group characterizes relatively radon-contaminated groundwater, representing the predominant groundwater type in the study area. The isotope mixing model based on δ34SSO4 and δ18OSO4 identified proportional contributions of precipitation (~ 14%), sewage (~ 22%), soil (~ 78%), and sulfide oxidation (~ 27%) sources. The redox processes of bacterial sulfate reduction and sulfide oxidation were determined to have a minimal influence on sulfur isotope fractionation within the system. By integrating hydrogeochemical analysis, sulfur isotopes, and the MixSIAR model to trace sulfate sources, uncertainties are able be accounted in source contributions. The groundwater system was mainly influenced by natural factors through infiltration, particularly via the unsaturated soil layer during the wet season. This also indicates enhanced mixing of multiple factors during the recharge or discharge processes triggered by rainfall events. In contrast, anthropogenic contributions declined indicating strong seasonal influences, especially from sewage which decreased from 22 to 6% in groundwater most affected by human activity. This highlights the role of rainfall in diluting human-induced contaminants from the groundwater system. To understand the fractured granite groundwater system, a conceptual model was developed, detailing groundwater types and identifying sulfur sources.

The Evolution of Atmospheric Composition: Why Earth is a Habitable Planet

The long term evolution of Earth’s atmosphere and climate has been an active topic of investigation for at least the last 60 years. My own participation in this investigation goes back more than 45 years, and this monograph relates that story from my personal perspective. One major thread concerns the rise of atmospheric O2 from near-zero levels initially to the 21 percent mixing ratio that we observe today. Photochemical models developed by me and my students, along with some close colleagues, have helped to better constrain the prebiotic O2 concentration and to interpret the constraints imposed by the record of mass independent fractionation of sulfur isotopes. Most geochemists now agree that a so called Great Oxidation Event (GOE) occurred between 2.4 and 2.2 Ga and that the atmosphere has been O2-rich since that time. However, the exact level of O2 during the ensuing Proterozoic Era remains controversial, as do the timing and magnitude of subsequent O2 increases. The corresponding development of the ozone layer is also of interest because of its moderating influence on surface solar UV fluxes and their effect on biological evolution. This can also be studied with photochemical models. A second thread concerns the gradual decline in atmospheric CO2 in response to slowly increasing solar luminosity. The early Earth would have been frozen had the atmosphere not contained high concentrations of greenhouse gases, most importantly CO2. A negative feedback in the carbonate-silicate cycle that controls CO2 over long time scales has ensured that Earth’s surface has remained habitable during most of Earth’s history, despite occasional forays into Snowball Earth conditions. Evidence from palaeosols provides support for this hypothesis. CH4 is an additional greenhouse gas that may have supplemented surface warming prior to the GOE. The increase in O2 at that time may have caused CH4 to decrease, possibly triggering the Huronian glaciations. The same feedback mechanism that controls long term CO2 evolution on Earth could operate on Earth-like planets orbiting other stars, increasing the probability that some of them may harbour life. Large direct imaging space telescopes currently under development may eventually allow us to test this hypothesis and to learn whether we have company in this part of our galaxy.

Contribution of the oldest Paleoproterozoic marine sulfate evaporites to Bushveld Complex Lower Zone mineralization

Abstract In the past two decades, multiple-sulfur isotope systematics has become increasingly used as a tool to differentiate sulfur sources with implications for exploration targeting. The involvement of crustal sulfur in triggering the Bushveld Complex (South Africa) Cu-Ni-PGE (PGE—platinum group element) mineralization of the Platreef intrusion is widely recognized; however, the extent and source of contamination are still debated. High-Mg magma of the Uitloop Lower Zone intrusion contained insufficient amounts of mantle-derived sulfur to reach the sulfide saturation required for mineralization. Sulfide saturation was reached when magma assimilated sulfur as it ascended through sedimentary strata deposited before and during the Great Oxidation Episode (GOE). Magmatic sulfides on Uitloop are 34S-enriched and either lack, or show small, mass-independent sulfur isotope fractionation, whereas sulfides from the Archean sedimentary footwall rocks exhibit the Archean-style multiple sulfur isotope covariations. We suggest that assimilation of the early Paleoproterozoic upper Duitschland Formation sulfate evaporites, corresponding to an ingrowth of a mass-dependently fractionated seawater sulfate reservoir at the early stage of the GOE, led to sulfide saturation and formation of Cu-Ni-PGE Platreef-style sulfide deposits. The GOE thus not only changed the oxidation state of the atmosphere and oceans, and the style of sediment-hosted mineral deposits, but also generated the sedimentary sulfate reservoir that since then served as a prolific sulfur source for magmatic ore deposits.

Origin of the Miaoling Gold Deposit, Xiong’ershan District, China: Findings Based on the Trace Element Characteristics and Sulfur Isotope Compositions of Pyrite

The Xiong’ershan district is situated on the southern margin of the North China Craton (NCC) and located within the Qinling–Dabieshan Orogen’s orogenic zone. It is adjacent to the XiaoQinling mining district and exhibits very favorable geological conditions for mineralization, as the district contains numerous gold deposits, positioning it as one of the key gold-producing areas of China. The Miaoling gold deposit is a hydrothermal deposit and is controlled by the Mesozoic nearly NS-trending fault. The ore bodies are hosted in the Mesoproterozoic Xiong’er Group of the Changcheng System of volcanic rocks, with reserves reaching large-scale levels. Pyrite is the main gold-bearing mineral and can be classified into four generations: early-stage fine- to medium-grained euhedral to subhedral cubic pyrite (Py1); medium- to coarse-grained euhedral to subhedral cubic granular pyrite in quartz veins (Py2a); fine-grained subhedral to anhedral disseminated pyrite in altered rocks (Py2b); and late-stage anhedral granular and fine-veinlet pyrite in later quartz veins (Py3). Through in situ trace element analysis of the pyrite using LA-ICP-MS, a positive correlation between Au and As was observed during the main mineralization stage; gold mainly exists as a solid solution within the pyrite lattice, and the ablation signal curve reflecting the intensity of trace element signals showed that gold also occurs as micron-scale mineral inclusions. The trace element content suggested a gradual increase in oxygen fugacity from Stage 1 to Stage 2, followed by a decrease from Stage 2 to Stage 3. The Co/Ni values in the pyrite (0.56 to 62.02, with an average of 12.34) exhibited characteristics of magmatic hydrothermal pyrite. The in situ sulfur isotope analysis of the pyrite using LA-MC-ICP-MS showed δ34S values of 4.24‰ for Stage 1, −6.63‰ to −13.79‰ for Stage 2, and −4.31‰ to −5.15‰ for Stage 3. Considering sulfur isotope fractionation, the δ34S value of the hydrothermal fluid during the main mineralization stage was calculated to be between 0.31‰ and 2.68‰.

Sulfur isotope anomalies in coal combustion: Applications to the present and early Earth environments

The observation of mass-independent sulfur isotope fractionations (S-MIF) in Archean-Paleoproterozoic rocks has been instrumental in constraining oxygen levels on early Earth. The S-MIF effect, experimentally demonstrated to result from photochemical reactions, has now been observed in coal combustion, expanding our understanding of this phenomenon. Our study reveals that the negative Δ33S anomalies produced by coal combustion are consistent with similar anomalies observed in present-day sulfate aerosols in Beijing, China, and the black crust sulfates formed on building stones, monument walls, and sculptures in Europe that contribute to carbonate stone deterioration and cultural heritage damage. This finding provides independent evidence for a critical role of atmospheric sulfate from coal combustion in maintaining isotopic balance and offers an effective method for tracing sulfate aerosol sources. These insights are vital for developing more effective regulatory policies to control air pollution and protect public health. Given that coal energy production remains a significant issue in climate science, accurately mapping the global distribution of its by-products is imperative.

Effect of Cd2+ and Cu2+ on Desulfovibrio vulgaris strain ATCC 7757: Insights from sulfur isotope fractionation

Effect of Cd2+ and Cu2+ on Desulfovibrio vulgaris strain ATCC 7757: Insights from sulfur isotope fractionation

Sulfur isotopic fractionation during hydrolysis of carbonyl sulfide

Sulfur isotopic fractionation during hydrolysis of carbonyl sulfide

A new Re-Os age constraint informs the dynamics of the Great Oxidation Event

Abstract The early Paleoproterozoic (ca. 2.5–2.2 Ga) represents a critical juncture in Earth history, marking the inception of an oxygenated atmosphere while bearing witness to potentially multiple widespread and severe glaciations. Deciphering the nature of this glacial epoch and its connection with atmospheric oxygenation has, however, proven difficult, hindered by a reliance on disputed stratigraphic correlations given the paucity of direct radiometric age constraints. Nowhere is this more acute than within the South African Transvaal Supergroup: Here, while the loss of oxygen-sensitive mass-independent sulfur isotope fractionation (S-MIF) has been reported from both the Duitschland and Rooihoogte formations, divided opinion surrounding the time-equivalence of these units has prompted authors to argue for vastly different oxygenation trajectories. Addressing this debate, we present a depositional Re-Os age (2443 ± 33 Ma) from diamictite samples preserved in drillcore of the upper Duitschland Formation. The 100-million-year separation between the Duitschland Formation and its previously presumed equivalent reveals at least two isolated disappearances of S-MIF, requiring that the Great Oxidation Event was dynamic and proceeded via discrete oxygenation episodes whose structure remains incompletely understood. Importantly, our revised framework aligns the lower Duitschland diamictite with the low-latitude glacigenic Makganyene Formation, supporting hypotheses of widespread regional, and potentially global, early Paleoproterozoic glaciation.

Oceanic and Sedimentary Microbial Sulfur Cycling Controlled by Local Organic Matter Flux During the Ediacaran Shuram Excursion in the Three Gorges Area, South China.

The increased difference in the sulfur isotopic compositions of sedimentary sulfate (carbonate-associated sulfate: CAS) and sulfide (chromium-reducible sulfur: CRS) during the Ediacaran Shuram excursion is attributed to increased oceanic sulfate concentration in association with the oxidation of the global ocean and atmosphere. However, recent studies on the isotopic composition of pyrites have revealed that CRS in sediments has diverse origins of pyrites. These pyrites are formed either in the water column/shallow sediments, where the system is open with respect to sulfate, or in deep sediments, where the system is closed with respect to sulfate. The δ34S value of sulfate in the open system is equal to that of seawater; on the contrary, the δ34S value of sulfate in the closed system is higher than that of seawater. Therefore, obtaining the isotopic composition of pyrites formed in an open system, which most likely retain microbial sulfur isotope fractionation, is essential to reconstruct the paleo-oceanic sulfur cycle. In this study, we carried out multiple sulfur isotope analyses of CRS and mechanically separated pyrite grains (>100 μm) using a fluorination method, in addition to secondary ion mass spectrometry (SIMS) analyses of insitu δ34S values of pyrite grains in drill core samples of Member 3 of the Ediacaran Doushantuo Formation in the Three Gorges area, South China. The isotope fractionation of microbial sulfate reduction (MSR) in the limestone layers of the upper part of Member 3 was calculated to be 34ε = 55.7‰ and 33λ = 0.5129 from the δ34S and Δ33S' values of medium-sized pyrite grains ranging from 100 to 300 μm and the average δ34S and Δ33S' values of CAS. Model calculations revealed that the influence of sulfur disproportionation on the δ34S values of these medium-sized pyrite grains was insignificant. In contrast, within the dolostone layers of the middle part of Member 3, isotope fractionation was determined to be 34ε = 47.5‰. The 34ε value in the middle part of Member 3 was calculated from the average δ34S values of the rim of medium-sized pyrite grains and the average δ34S values of CAS. This observation revealed an increase in microbial sulfur isotope fractionation during the Shuram excursion at the drill core site. Furthermore, our investigation revealed correlations between δ34SCRS values and CRS concentrations and between CRS and TOC concentrations, implying that organic matter load to sediments controlled the δ34SCRS values rather than oceanic sulfate concentrations. However, these CRS and TOC concentrations are local parameters that can change only at the kilometer scale with local redox conditions and the intensity of primary production. Therefore, the decreasing δ34SCRS values likely resulted from local redox conditions and not from a global increase in the oceanic sulfate concentration.

Tracing sulfate sources in a tropical agricultural catchment with a stable isotope Bayesian mixing model

Tracing sulfate sources in a tropical agricultural catchment with a stable isotope Bayesian mixing model

Evidence of both molecular cloud and fluid chemistry in Ryugu regolith.

The sulfur chemistry of (162173) Ryugu particles can be a powerful tracer of molecular cloud chemistry and small body processes, but it has not been well explored. We report identification of organosulfurs and a sulfate grain in two Ryugu particles, A0070 and A0093. The sulfate grain shows oxygen isotope ratios (δ17O = -11.0 ± 4.3 per mil, δ18O = -7.8 ± 2.3 per mil) that are akin to silicates in Ryugu but exhibit mass-independent sulfur isotopic fractionation (Δ33S = +5 ± 2 per mil). A methionine-like coating on the sulfate grain is isotopically anomalous (δ15N = +62 ± 2 per mil). Both the sulfate and organosulfurs can simultaneously form and survive during aqueous alteration within Ryugu's parent body, under reduced conditions, low temperature, and a pH >7 in the presence of N-rich organic molecules. This work extends the heliocentric zone where anomalous sulfur, formed by selective photodissociation of H2S gas in the molecular cloud, is found.

Mass-independent fractionation of oxygen and sulfur isotopes

Mass-independent fractionation of oxygen and sulfur isotopes

Oxidized Sulfur Species in Slab Fluids as a Source of Enriched Sulfur Isotope Signatures in Arcs

AbstractRecycling of oxidized sulfur from subducting slabs to the mantle wedge provides simultaneous explanations for the elevated oxygen fugacity (fO2) in subduction zones, their high hydrothermal and magmatic sulfur outputs, and the enriched sulfur isotopic signatures (i.e., δ34S > 0‰) of these outputs. However, a quantitative understanding of the abundance and speciation of sulfur in slab fluids consistent with high pressure experiments is lacking. Here we analyze published experimental data for anhydrite solubility in H2O‐NaCl solutions to calibrate a high‐pressure aqueous speciation model of sulfur within the framework of the deep earth water model. We characterize aqueous complexes, required to account for the high experimental anhydrite solubilities. We then use this framework to predict the speciation and solubility of sulfur in chemically complex fluids in equilibrium with model subducting mafic and ultramafic lithologies, from 2 to 3 GPa and 400 to 800°C at log fO2 from FMQ‐2 to FMQ+4. We show that sulfate complexes of calcium and sodium markedly enhance the stability of sulfate in moderately oxidized fluids in equilibrium with pyrite at fO2 conditions of FMQ+1 to +2, causing large sulfur isotope fractionations up to 10‰ in the fluid relative to the slab. Such fluids could impart oxidized, sulfur‐rich and high δ34S signatures to the mantle wedge that are ultimately transferred to arc magmas, without the need to invoke 34S‐rich subducted lithologies.

High-accuracy measurement of 36SF5 + signal using an ultrahigh-resolution isotope ratio mass spectrometer.

The Δ36S standard deviation measured in a conventional isotope ratio mass spectrometer such as MAT 253 is ca 0.1‰ to 0.3‰. At this precision, it is difficult to resolve the origin of non-mass-dependent sulfur isotope fractionation in tropospheric sulfate aerosol and in Martian meteorites or small deviations from the canonical mass-dependent fractionation laws. Interfering ions with m/z at 131 of 36SF5 + are suggested by the community as the cause of the poor precision, but the exact ion species has not been identified or confirmed. Here we examined the potential interfering ions by using a Thermo Scientific ultrahigh-resolution isotope ratio mass spectrometer to measure SF6 working gas and SF6 gases converted from IAEA-S1/2/3 Ag2S reference materials. We found that there are two resolvable peaks to the right of the 36SF5 + peak when a new filament was installed, which are 186WF4 2+ followed by 12C3F5 +. However, only the 12C3F5 + interference peak was observed after more than three days of filament use. 12C3F5 + is generated inside the instrument during the ionization process. Avoiding the interfering signals, we were able to achieve a Δ36S standard deviation of 0.046‰ (n = 8) for SF6 zero-enrichment and 0.069‰ (n = 8) for overall measurement start from silver sulfide IAEA-S1. Aging the filament with SF6 gas can avoid the interference of 186WF4 2+. Minimizing the presence of carbon-bearing compounds and avoiding the interfering signals of 12C3F5 + from 36SF5 +, we can improve Δ36S measurement accuracy and precision, which helps to open new territories for research using quadruple sulfur isotope composition.

Sedimentary and stratigraphic architecture of the Duitschland and Rooihoogte formations (Palaeoproterozoic, South Africa): implications for tempo of the Great Oxidation Event

Abstract Determining the tempo and causality of key palaeoclimate events recorded in sedimentary strata depends on high-resolution numerical ages and well-constrained stratigraphic correlations at regional and global scale. This requirement is not necessarily met in Precambrian strata due to poorer age resolution, limited preservation, and secondary overprints. A good example includes the Palaeoproterozoic Rooihoogte and Duitschland formations in South Africa, which document the disappearance of mass-independent fractionation of sulphur isotopes (MIF-S) and contain glacial diamictites at their base. They are thus key records of Earth’s surface oxygenation during the Great Oxidation Event (GOE). However, previous studies have either correlated these units, resulting in a unidirectional oxidation trend; or have regarded them as successive strata, causing an interpretation of oscillating oxidation. This study uses extensive outcrop and new core material to investigate correlation between these two units, and to establish depositional models. Results show that key stratigraphic markers can be traced around the entire Kaapvaal craton both in outcrop and the subsurface. In particular, the basal Bevets breccia and the top Duitschland breccia are here re-interpreted as two separate units that are present at the base and top of both formations, supporting correlation of the formations. Consequently, the base of both formations records a major craton-wide event of uplift and karstification, leading to carbonate dissolution and chert brecciation. Erosion of older rocks from across the craton also delivered material for the basal glacial diamictite. The majority of mixed siliciclastic-carbonate sediments were deposited on a storm- and/or delta-influenced shelf. Depositional packages in both formations reflect post-glacial relative sea level rise, followed by progradation of a deltaic, storm or shoreline depositional system. There is a relatively short-lived depositional hiatus to overlying shales of the Timeball Hill Formation. Both Rooihoogte and Duitschland formations thus record only a single glacial event at their base, and a unidirectional trend of oxidation.

Atmospheric oxygenation at the onset of Earth’s Great Oxidation forced enhanced marine anoxia

Abstract Capturing the loss of mass-independent sulphur isotope fractionation (MIF-S), the correlative South African Duitschland and Rooihoogte formations are widely held to bear the isotopic fingerprint of the first atmospheric oxygenation at the onset of the so-called Great Oxidation Event (GOE). Surprisingly, however, while the multiple sulphur isotope systematics of these formations remain central to our understanding of the GOE, until now, comparatively little work has been done to elucidate the repercussions within the marine realm. Here we present chemostratigraphic records from four drill cores covering a large area of the Transvaal Basin, transcending these crucial units and continuing into the overlying Timeball Hill Formation (TBH), that document the immediate, yet counterintuitive, marine response to atmospheric oxygenation. Specifically, irrespective of the interpretative framework employed, our basin-wide redox-sensitive trace element data document an environmental change from oxic/suboxic conditions within the lower and middle parts of the Duitschland and Rooihoogte formations to suboxic/anoxic conditions within their upper reaches. Interestingly, in concert with a ~35‰ negative δ34S excursion that implicates increased sulphate availability and bacterial sulphate reduction, δ98/95Mo3134+0.25 values increase by ~1.0 to 1.5‰. Combining these observations with increased Fe/Mn ratios, elevated total sulphur and carbon contents and a trend towards lower δ13Corg values imply a shift toward less oxygenated conditions across the Transvaal Basin. The combined observations in the mentioned parameters expose a geobiological feedback-driven causality between the earliest oxygenation of the atmosphere and decreased redox potentials of medium to deep marine environments, at least within the Transvaal Basin.

Using sulfur isotopes to constrain the sources of sulfate in PM2.5 during the winter in Jiaozuo City

Using sulfur isotopes to constrain the sources of sulfate in PM2.5 during the winter in Jiaozuo City

Direct prediction of isotopic properties from molecular dynamics trajectories: Application to sulfide, sulfate and sulfur radical ions in hydrothermal fluids

In hydrothermal fluids, disulfur (S2•−) and trisulfur (S3•−) radical anions have been observed to coexist with the major hydrogen sulfide and sulfate species. These radical ions have potentially important effects on the solubility, transport and fractionation of metals and sulfur, with consequences for ore deposit formation and, more generally, for geochemical cycles of metals and volatiles. It is therefore essential to know the intrinsic isotopic properties of these important sulfur species in order to use sulfur isotopes for tracing different geological processes. Here, the theoretical equilibrium isotopic properties of the disulfur and trisulfur radical ions are computed and compared to the hydrogen sulfide (H2S) and sulfate ion (SO42−), using, for the first time, a first-principles molecular dynamics (MD) approach. The isotopic properties are calculated directly from molecular dynamics trajectories using the vibrational density of states and the atomic kinetic energy, and then compared to the more established method based on sampling of several snapshots. This comparison allowed us to validate the new modelling method and to assess its advantages and limitations. The predicted equilibrium isotope fractionation in terms of 34S/32S between S2•− and S3•− is small, i.e. <1‰, with a slight enrichment in the heavier isotope for S3•−, over the temperature range 200–500 °C. Both radical ions are slightly depleted in the heavier isotope, by 1 to 2‰, relative to aqueous H2S. Our results help tuning sulfur isotope fractionation models used for tracing the origin and evolution of hydrothermal fluids. Our method opens large perspectives for using the rapidly growing body of MD simulation data in geosciences on structure and stability of aqueous complexes to assess in parallel element isotope fractionations from MD-generated trajectories.

Sulfur Isotope Geochemistry of Ice‐Wedges in Yakutia, East Siberia

ABSTRACTSulfur, with its highly varying stable isotope ratio and involvement in numerous biogeochemical processes, is one of the most widely used elements as an isotopic paleoenvironmental proxy, yet the sulfur isotope ratios of ice‐wedges and their insoluble fraction remain unexplored. This study first presents the sulfur isotopic compositions of soluble sulfate, particulate organic matter (POM), and lithic particles recovered from East Siberian ice‐wedges. Soluble sulfate, primarily representing atmospheric sulfate deposition, shows comparable sulfur isotope ranges in Zyryanka and Batagay, while in Central Yakutia, ice‐wedge sulfate is more enriched in 34S, consistent with the orogenic and cratonic terranes in East Siberia. Given the wedge growth during the inland winter, it is likely that sulfate aerosols were derived mainly from erosion and weathering of regional basement rocks rather than from sea salt spray or biogenic emissions. Within individual ice‐wedges, however, the sulfur isotopic composition of soluble sulfate varies by as much as 7‰, possibly reflecting changes in the relative contributions of sulfur‐isotopically distinct source regions. Beyond the origin of sulfate, greater sulfur isotope fractionations between POM and sulfate during the last glaciation suggest that sulfate may have been anaerobically reduced to sulfide and vice versa in the adjacent root zone.

Energy flux couples sulfur isotope fractionation to proteomic and metabolite profiles in Desulfovibrio vulgaris.

Microbial sulfate reduction is central to the global carbon cycle and the redox evolution of Earth's surface. Tracking the activity of sulfate reducing microorganisms over space and time relies on a nuanced understanding of stable sulfur isotope fractionation in the context of the biochemical machinery of the metabolism. Here, we link the magnitude of stable sulfur isotopic fractionation to proteomic and metabolite profiles under different cellular energetic regimes. When energy availability is limited, cell-specific sulfate respiration rates and net sulfur isotope fractionation inversely covary. Beyond net S isotope fractionation values, we also quantified shifts in protein expression, abundances and isotopic composition of intracellular S metabolites, and lipid structures and lipid/water H isotope fractionation values. These coupled approaches reveal which protein abundances shift directly as a function of energy flux, those that vary minimally, and those that may vary independent of energy flux and likely do not contribute to shifts in S-isotope fractionation. By coupling the bulk S-isotope observations with quantitative proteomics, we provide novel constraints for metabolic isotope models. Together, these results lay the foundation for more predictive metabolic fractionation models, alongside interpretations of environmental sulfur and sulfate reducer lipid-H isotope data.