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At least 19 recordsLinked to original sources
PubMed2004

Assessment of sulfate sources in high-elevation Asian precipitation using stable sulfur isotopes.

Stable sulfur isotope measurements (delta34S) made on samples collected from a 2 m snowpit on the Inilchek Glacier, Tien Shan Mountains (42.16 degrees N, 80.25 degrees E, 5100 m) are used to estimate sources of sulfate (SO4(2-)) in high-elevation Central Asian precipitation. Comparison of snowpit oxygen isotope (delta18O) data with previous work constrains the age of the snowpit samples to the summer season during which they were retrieved (1999). Delta34S measurements were made at 10 cm resolution (20 samples total), with delta34S values ranging from 0.4/1000 during background ([SO4(2-)] < 1 microequiv L(-1)) periods to 19.4/1000 during a single high [SO4(2-)] event. On the basis of the significant correlation (r = 0.87) between [SO4(2-)] and delta34S values, coupled with major ion concentration time series and concentration ratios, we suggest a two-component mixing system consisting of evaporite dust and anthropogenic SO4(2-) to explain the observed delta34S values. Using a regression model, we estimate that during the 1999 summer season 60% of the deposited SO4(2-) was from an evaporite dust source, while 40% of the SO4(2-) was from anthropogenic sources. Due to the potentially large and unconstrained range of delta34S values for both evaporite and anthropogenic SO4(2-) sources in Asia, the error in our estimates is difficult to assess. However, the delta34S data from the 1999 Tien Shan snowpit provide the first unambiguous identification of evaporite and anthropogenic SO4(2-) in high-elevation Asian precipitation, and future ice core studies using improved analysis techniques and source delta34S values can provide detailed information on sulfur biogeochemistry and anthropogenic impacts in Asian alpine regions.

Air Pollutants↗
PubMedDate not supplied

[Fractionation of sulfur isotopes by phototrophic sulfur bacterium Ectothiorhodospira shaposhnikovii].

Two processes of sulphur isotope fractionation have been found in experiments with the sulphur purple bacterium Ectothiorhodospira shaposhnikovii. As a result, a light isotope, 32S, is concentrated in residual hydrogen sulphide, and a heavy isotope, 34S, in elementary suphur which is deposited outside the cell. The sulphate produced is lighter than elementary sulphur. Fractionation of sulphur isotopes is observed in natural conditions and is confined to places of mass growth of photosynthetic sulphur bacteria.

Chemical Fractionation↗
PubMed1981

Stable isotope fractionation by Clostridium pasteurianum. 4. Sulfur isotope fractionation during enzymatic S3O6(2-), S2O3(2-), and SO3(2-) reductions.

Cell-free extracts from Clostridium pasteurianum grown on SO3(2-) utilize H2 to reduce S3O6(2-), S2O3(2-), SO3(2-) to H2S at a much faster rate than extracts from SO4(2-)-grown cells. This further supports the concept of an inducible dissimilatory type SO3(2-) reductive pathway in this organism. 35S dilution experiments further support the concept that S3O6(2-) and S2O3(2-) are pathway intermediates. The inducible SO3(2-) reductase is ferredoxin linked and the kinetics of the reduction and the sulfur isotope fractionation of the product can be altered by altering the growth conditions. The attending sulfur isotope fractionations are similar to those observed during the chemical decomposition of these compounds. In the case of S2O3(2-), 35S labelling experiments verified the conclusions derived from the stable isotope fractionation data concerning the relative reduction rates of the sulfane and sulfonate sulfurs. The reduction rates were also affected by enzyme concentration. The integrity of the whole cell is a necessary requirement for the large inverse isotope effects previously reported.

Clostridium↗
PubMed1976

The use of stable sulfur isotope labelling to elucidate sulfur metabolism by Clostridium pasteurianum.

An unique isotope labelling experiment was conducted whereby mixtures of sulfate and sulfite of different isotopic compositions were metabolized by Clostridium pasteurianum. The results showed during reduction of 1 mM SO3= plus 1 mM SO4=, essentially all evolved H2S arose from the sulfite whereas in the case of cellular sulfur, 85% was derived from sulfite and the remainder from sulfate.

Clostridium↗
PubMed2004

Seawater sulfur isotope fluctuations in the Cretaceous.

The exogenic sulfur cycle is tightly coupled with the carbon and oxygen cycles, and therefore a central component of Earth's biogeochemistry. Here we present a high-resolution record of the sulfur isotopic composition of seawater sulfate for the Cretaceous. The general enrichment of isotopically light sulfur that prevailed during the Cretaceous may have been due to increased volcanic and hydrothermal activity. Two excursions toward isotopically lighter sulfur represent periods of lower rates of pyrite burial, implying a shift in the location of organic carbon burial to terrestrial or open-ocean settings. The concurrent changes in seawater sulfur and inorganic carbon isotopic compositions imply short-term variability in atmospheric oxygen partial pressure.

Journal Article↗
PubMed1980

Are sulfur isotope ratios sufficient to determine the antiquity of sulfate reduction?

Sulfur isotope fractionation values have been measured in sedimentary sulfides of varying ages, The 'Antiquity and evolutionary status of bacterial sulfate reduction...' has been inferred from these measurements by Schidlowski (1979). However, under experimental conditions, the isotope values vary widely due to inadequately controlled variables. Thus the direct extrapolation of sulfur isotope fractionation values measured in the laboratory to those measured in sedimentary rocks is unwarranted. New sulfur transforming microbes have been described and recent measurements indicate that inorganic processes affect sulfur isotope fractionation values. This information is summarized here; at present sulfur isotope fractionation values are insufficient to determine the antiquity of sulfate reduction.

Desulfovibrio↗
PubMed1979

Antiquity and evolutionary status of bacterial sulfate reduction: sulfur isotope evidence.

The presently available sedimentary sulfur isotope record for the Precambrian seems to allow the following conclusions: (1) In the Early Archaean, sedimentary delta 34S patterns attributable to bacteriogenic sulfate reduction are generally absent. In particular, the delta 34S spread observed in the Isua banded iron formation (3.7 x 10(9) yr) is extremely narrow and coincides completely with the respective spreads yielded by contemporaneous rocks of assumed mantle derivation. Incipient minor differentiation of the isotope pattersn notably of Archaean sulfates may be accounted for by photosynthetic sulfur bacteria rather than by sulfate reducers. (2) Isotopic evidence of dissimilatory sulfate reduction is first observed in the upper Archaean of the Aldan Shield, Siberia (approximately 3.0 x 10(9) yr) and in the Michipicoten and Woman River banded iron formations of Canada (2.75 x 10(9) yr). This narrows down the possible time of appearance of sulfate respirers to the interval 2.8--3.1 x 10(9) yr. (3) Various lines of evidence indicate that photosynthesis is older than sulfate respiration, the SO4(2-) Utilized by the first sulfate reducers deriving most probably from oxidation of reduced sulfur compounds by photosynthetic sulfur bacteria. Sulfate respiration must, in turn, have antedated oxygen respiration as O2-respiring multicellular eucaryotes appear late in the Precambrian. (4) With the bulk of sulfate in the Archaean oceans probably produced by photosynthetic sulfur bacteria, the accumulation of SO4(2-) in the ancient seas must have preceded the buildup of appreciable steady state levels of free oxygen. Hence, the occurrence of sulfate evaporites in Archaean sediments does not necessarily provide testimony of oxidation weathering on the ancient continents and, consequently, of the existence of an atmospheric oxygen reservoir.

Bacteria↗
PubMed2002

Survey of stable sulfur isotope ratios (34S/32S) of sulfite and sulfate in foods.

A study was conducted to determine the natural abundance sulfur isotope ratios in foods containing sulphite preservatives. This involved determining (1) the accuracy and repeatability of sulfur isotope ratios measured using an elemental analyser (EA) coupled to an isotope ratio mass spectrometer (IRMS); and (2) the isotope ratios of 21 samples of commercially available S(IV) oxo-anion compounds, nine samples of S(VI) sulfate salts and the isotope ratios of the sulfate obtained by modified Monier-Williams distillation of SO(2) from 33 retail foods containing sulfite preservatives. The sulfur isotope ratio data for SO(2) recovered from foodstuffs showed a large spread of results, which suggested that the SO(2) derived from sulfite preservatives does not have a distinctive sulfur signature ratio. The range of results (3.1-52.1) overlapped with that found for a range of commercially available sulfite and sulfate reagents commonly used to preserve food (sulfites 2.5-13.7, sulfates 10.0-16.9). Whilst the variability in isotope ratios originated from the food samples themselves, evidence from the analysis of SO(2) gas suggested that isotope fractionation during dissolution, reaction and recovery was also a confounding factor.

Barium Sulfate↗
PubMed2001

In situ assessment of microbial sulfate reduction in a petroleum-contaminated aquifer using push-pull tests and stable sulfur isotope analyses.

Anaerobic microbial activities such as sulfate reduction are important for the degradation of petroleum hydrocarbons (PHC) in contaminated aquifers. The objective of this study was to evaluate the feasibility of single-well push-pull tests in combination with stable sulfur isotope analyses for the in situ quantification of microbial sulfate reduction. A series of push-pull tests was performed in an existing monitoring well of a PHC-contaminated aquifer in Studen (Switzerland). Sulfate transport behavior was evaluated in a first test. In three subsequent tests, we injected anoxic test solutions (up to 1000 l), which contained 0.5 mM bromide (Br-) as conservative tracer and 1 mM sulfate (SO4(2-)) as reactant. After an initial incubation period of 42.5 to 67.9 h, up to 1100 l of test solution/groundwater mixture was extracted in each test from the same location. During the extraction phases, we measured concentrations of relevant species including Br-, SO4(2-) and sulfide (S(-II)), as well as stable sulfur isotope ratios (delta 34S) of extracted, unconsumed SO4(2-) and extracted S(-II). Results indicated sulfate reduction activity in the vicinity of the test well. Computed first-order rate coefficients for sulfate reduction ranged from 0.043 +/- 0.013 to 0.130 +/- 0.015 day-1. Isotope enrichment factors (epsilon) computed from sulfur isotope fractionation of extracted, unconsumed SO4(2-) ranged from 20.2 +/- 5.5@1000 to 22.8 +/- 3.4@1000. Together with observed fractionation in extracted S(-II), isotope enrichment factors provided strong evidence for microbially mediated sulfate reduction. Thus, push-pull tests combined with stable sulfur isotope analyses proved useful for the in situ quantification of microbial sulfate reduction in a PHC-contaminated aquifer.

Biodegradation, Environmental↗
PubMed1998

Sulfur isotopic composition of cenozoic seawater sulfate

A continuous seawater sulfate sulfur isotope curve for the Cenozoic with a resolution of approximately 1 million years was generated using marine barite. The sulfur isotopic composition decreased from 19 to 17 per mil between 65 and 55 million years ago, increased abruptly from 17 to 22 per mil between 55 and 45 million years ago, remained nearly constant from 35 to approximately 2 million years ago, and has decreased by 0.8 per mil during the past 2 million years. A comparison between seawater sulfate and marine carbonate carbon isotope records reveals no clear systematic coupling between the sulfur and carbon cycles over one to several millions of years, indicating that changes in the burial rate of pyrite sulfur and organic carbon did not singularly control the atmospheric oxygen content over short time intervals in the Cenozoic. This finding has implications for the modeling of controls on atmospheric oxygen concentration.

Journal Article↗
PubMed2001

Diversity of sulfur isotope fractionations by sulfate-reducing prokaryotes.

Batch culture experiments were performed with 32 different sulfate-reducing prokaryotes to explore the diversity in sulfur isotope fractionation during dissimilatory sulfate reduction by pure cultures. The selected strains reflect the phylogenetic and physiologic diversity of presently known sulfate reducers and cover a broad range of natural marine and freshwater habitats. Experimental conditions were designed to achieve optimum growth conditions with respect to electron donors, salinity, temperature, and pH. Under these optimized conditions, experimental fractionation factors ranged from 2.0 to 42.0 per thousand. Salinity, incubation temperature, pH, and phylogeny had no systematic effect on the sulfur isotope fractionation. There was no correlation between isotope fractionation and sulfate reduction rate. The type of dissimilatory bisulfite reductase also had no effect on fractionation. Sulfate reducers that oxidized the carbon source completely to CO2 showed greater fractionations than sulfate reducers that released acetate as the final product of carbon oxidation. Different metabolic pathways and variable regulation of sulfate transport across the cell membrane all potentially affect isotope fractionation. Previous models that explained fractionation only in terms of sulfate reduction rates appear to be oversimplified. The species-specific physiology of each sulfate reducer thus needs to be taken into account to understand the regulation of sulfur isotope fractionation during dissimilatory sulfate reduction.

Culture Media↗
PubMed1988

Sulfur isotope effects associated with oxidation of sulfide by O2 in aqueous solution.

Normal sulfur isotope effects averaging epsilon = -5.2 +/- 1.4% (s.d.) were consistently observed for the oxidation of sulfide in aqueous solution. Reaction products were sulfate, thiosulfate and sulfite at pH 10.8-11 in distilled water; S0 was formed in two experiments with synthetic seawater at pH 8-9.5. Because the -5.2% normal isotope effect differs significantly from the previously measured +2% inverse effect associated with anaerobic oxidation of sulfide by photosynthetic bacteria, stable sulfur isotopic measurements are potentially useful for distinguishing aerobic vs. anaerobic sulfide oxidation in marine and freshwater sulfureta.

Bacteria, Anaerobic↗
PubMed2002

Anomalous fractionation of sulfur isotopes during sputtering.

Secondary ion mass spectrometric (SIMS) measurements of sulfur isotope ratios obtained during sputtering with a Cs(+) beam and detection of negative secondary ions show a strong dependence of isotope fractionation on secondary ion energy for ions with approximately 2-10 eV excess kinetic energy (approximately 9 per thousand/eV), and a weak dependence for ions with approximately 10-approximately 350 eV (0.05 per thousand/eV). Variable collection of the low-energy ions could thus result in variable measured sulfur isotope ratios. Being aware of this behavior should allow the analyst to avoid such a problem. The fractionation of the isotopes does not appear to follow theoretical or measured behavior for positive ions, and suggests that, at least for sulfur, the process of negative secondary ion emission is incompletely understood and may require different theoretical models.

Journal Article↗
PubMed1993

3.4-Billion-year-old biogenic pyrites from Barberton, South Africa: sulfur isotope evidence.

Laser ablation mass spectroscopy analyses of sulfur isotopic compositions of microscopic-sized grains of pyrite that formed about 3.4 billion years ago in the Barberton Greenstone Belt, South Africa, show that the pyrite formed by bacterial reduction of seawater sulfate. These data imply that by about 3.4 billion years ago sulfate-reducing bacteria had become active, the oceans were rich in sulfate, and the atmosphere contained appreciable amounts (>>10(-13) of the present atmospheric level) of free oxygen.

Geologic Sediments↗
PubMed2002

Mass-independent fractionation of sulfur isotopes in Archean sediments: strong evidence for an anoxic Archean atmosphere.

Mass-independent fractionation (MIF) of sulfur isotopes has been reported in sediments of Archean and Early Proterozoic Age (> 2.3 Ga) but not in younger rocks. The only fractionation mechanism that is consistent with the data on all four sulfur isotopes involves atmospheric photochemical reactions such as SO2 photolysis. We have used a one-dimensional photochemical model to investigate how the isotopic fractionation produced during SO2 photolysis would have been transferred to other gaseous and particulate sulfur-bearing species in both low-O2 and high-O2 atmospheres. We show that in atmospheres with O2 concentrations < 10(-5) times the present atmospheric level (PAL), sulfur would have been removed from the atmosphere in a variety of different oxidation states, each of which would have had its own distinct isotopic signature. By contrast, in atmospheres with O2 concentrations > or = 10(-5) PAL, all sulfur-bearing species would have passed through the oceanic sulfate reservoir before being incorporated into sediments, so any signature of MIF would have been lost. We conclude that the atmospheric O2 concentration must have been < 10(-5) PAL prior to 2.3 Ga.

Archaea↗