Sulfur isotopes fractionations

R. W. FairbriiXjE, Encyclopedia of Geochemistry and Environmental Sciences, Van Nostrand, New York, 1972.. See sections on Geochemical Classification of the Elements Sulfates Sulfate Reduction-Microbial Sulfides Sulfosalts Sulfur Sulfur Cycle Sulfur Isotope Fractionation in Biological Processes, etc., pp. 1123 - 58. 

This lack of a concentration dependence contrasts with the sulfur isotope literature, which suggests that sulfur isotope fractionation induced by sulfate reduction decreases as the sulfate concentration decreases below 0.2 mmol/L (Canfield 2001 Habicht et al. 2002). This difference may reflect differences between S(VI) and Se(VI) reduction pathways or possible adaptations of bacteria to low Se concentrations, but at present no clear explanation has emerged. 

Bruchert V, Knoblauch C, Jorgensen BB (2001) Controls on stable sulfur isotope fractionation during bacterial sulfate reduction in Arctic sediments. Geochim Cosmochim Acta 65 763-776 Bryan BA, Shearer G, Skeeters JL, Kohl DH (1983) Variable expression of the nitrogen isotope effect associated with denitrification of nitrate. J Biol Chem 258 8613-8617 Canfield DE (2001) Biogeochemistry of sulfur isotopes. Rev Mineral Geochem 43 607-636 Chau YK, Riley JP (1965) The determination of selenium in sea water, silicates, and marine organisms. Anal Chim Acta 33 36-49... 

Habicht KS, Canfield DE (1997) Sulfur isotope fractionation during bacterial sulfate reduction in organic-rich sediments. Geochim CosmochimActa61(24) 5351-5361 Habicht KS, Gade M, Thamdrup B, Berg P, Canfield DE (2002) Calibration of sulfate levels in the Archean ocean. Science 298 2372-2374... 

The sulfur isotope fractionation in sulfide minerals and solute... 

Table 11.16 Slope coefficients relating sulfur isotopic fractionation factors between sulfides and aqueous H2S to temperature (K) (after Ohmoto and Rye, 1979).

In recent years additional informations on sulfur isotope fractionation mechanisms have been obtained from the analysis of the additional isotopes and (Farqnhar et al. 2003 Johnston et al. 2005 Ono et al. 2006, 2007). For long it was thonght and valnes carry no additional information, because sulfur isotope fractionations follow strictly mass-dependent fractionation laws. By studying all snlfnr isotopes with very high precision these authors could demonstrate that bacterial snlfate redaction follows a mass-dependent relationship that is slightly different from that expected by equilibrium fractionations. On plots vs mix-... 

Bottcher ME, Thamdrup B, Vennemann TW (2001) Oxygen and sulfur isotope fractionation during anaerobic bacterial disproportionation of elemental sulfur. Geochim Cosmochim Acta 65 ... 

Cypionka H, Smock A, BOttcher MA (1998) A combined pathway of sulfur compound disproportionation in Desulfovibrio desulfuricans. FEMS Microbiol Lett 166 181-186 Czamanske GK, Rye RO (1974) Experimentally determined sulfur isotope fractionations between sphalerite and galena in the temperature range 600°C to 275°C. Econ Geol 69 17-25 Dansgaard W (1964) Stable isotope in precipitation. Tellus 16 436 68... 

Wortmann UG, Bemasconi SM, Bdttcher ME (2001) Hypersulfldic deep biosphere indicates extreme sulfur isotope fractionation during single-step microbial sulfate reduction. Geology 29 647-650... 

Naturally occurring stable isotopes of C, N, and S have been used extensively for over a decade as direct tracers of element cycling in marine and terrestrial food webs (34-39). Carbon and sulfur isotopes fractionate very little between food and consumer thus their measurement indicates which primary producers or detrital pools are sources of C and S for consumers. For example, a study of plants and animals in Texas sand dunes showed that insect species had 813C values either like those of C3 plants or like those of C4 plants (-27 and -13%o, respectively). Rodent species had intermediate values near -20%o that indicated mixed diets of both C3 and C4 plants (40). The 13C measurements, used in simple linear mixing models, proved to be quick and reliable indicators of which plant sources provided the carbon assimilated by higher trophic levels. 

Detmers, J., Bruchert, V., Habicht, K.S., and Kuever, J. (2001) Diversity of sulfur isotope fractionations by sulfate-reducing Prokaryotes. Appl. Environ. Microbiol. 67, 888-894. 

Winner, W.E., Smith, C.L., Koch, G.W., Mooney, H.A., Bewley, J.D., and Krouse, H.R. (1981) Rates of emission of H2S from plants and patterns of stable sulfur isotope fractionation. Nature 289, 672-673. 

S.O. Danielache, et ah. Ab-initio study of sulfur isotope fractionation in the reaction of OCS with OH, Chem. Phys. Lett. 450 (2008) 214-220. 

Shanks W. C., Bischoff J. L., and Rosenbauer R. J. (1981) Seawater sulfate reduction and sulfur isotope fractionation in basaltic systems interaction of seawater with fayaUte and magnetite at 200-300°C. Geochim. Cosmochim. Acta 45, 1977-1995. 

Sulfur Isotopic Fractionation during Bacterial Reduction... 

Recent work has also addressed the impact of elevated temperature and decreased SO concentration on sulfur isotopic fractionation factors during sulfate reduction. Canfield et al. (2000) measured fractionation factors in marine sediment whose in situ temperature was up to 90 °C. Sediments maintained at temperatures up to 85 °C were found to reduce 804 with fractionation factors of 13-28%o. Habicht et al. (2002) studied isotopic fractionation factors as a function of S04 concentration. They found high fractionations of up to 32%o at sol concentrations of 200 p,M or greater, whereas fractionation dropped dramatically below this concentration. The low sol limit for large fractionation is less than 1 % of the modern seawater concentration of 28 mM. 

The mixing time of S04 in the ocean is short compared to its residence time. Thus, the isotopic composition of S04 in seawater is constant over geologically short time periods. One pathway for removal of this seawater sulfate is by precipitation of sulfate-bearing evaporite minerals. When marine evaporite minerals such as gypsum (CaS04 2H20) precipitate from seawater, the sulfur isotope fractionation between the aqueous and solid-phase sulfate is very small, about -b 1.7%o (Thode and Monster, 1965). The combination of these factors implies that contemporaneous marine evaporites have the same isotopic composition worldwide, and they are nearly identical isotopically to seawater SO of that age. When the sulfur isotopic composition of marine evaporite S04 is plotted as a function of... 

Bottcher M. E., Smock A. M., and Cypionka H. (1998) Sulfur isotope fractionation during experimental precipitation of iron(II) and manganese(II) sulfide at room temperature. Chem. Geol. 146, 127-134. 

Habicht K. S., Canfield D. E., and Rethmeier J. (1998) Sulfur isotope fractionation during bacterial reduction and disproportionation of thiosulfate and sulfite. Geochim. Cosmochim. Acta 62(15), 2585-2595. 

The reactions that involve sulfur oxidation states leave isotopically fractionated sulfur and hence sulfide, a target for investigation by the geologist. Though there is controversy about sulfur isotope fractionation (Farquhar et al, 2000), the strong fractionation of seen in... 

Kasting (2001) argues in support of the view of Farquhar et al (2000) (but see also Ohmoto et al, 2001) that sulfur isotope fractionation changed around 2.3 Ga. This opinion is based on the claim, from comparison of sulfur isotopes, that so-called mass independent fractionation occurred as a result of gas-phase photochemical reactions, particularly photolysis of SO2. Such fractionation would be much more likely to occur in a I0W-O2 atmosphere in which sulfur was present in a variety of oxidation states. Thus, the claim that fractionation changed around 2.3 Ga ago can be seen as supporting the notion that there was a substantial rise in O2 around this time. This, however, raises the question if cyanobacterial oxygen production had been sufficient to create the mbisco fingerprint in carbonates as early as 2.7-3.0Ga ago, why did the rise of free O2 only occur 400-700 Myr later ... 

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