Sulfur isotopes biogenic

Figure 7.4 shows the reduction in sulfates and the corresponding growth of both the parent carbonates and the offspring methane with subbottom depth. The methane production is parallel but lower in isotope production than the carbonates. In Figure 7.4 the sulfur isotope (< 34S) content is defined in an identical manner to Equation 7.2 with the replacement of the fraction 13C/12C by 34S/32S in both the numerator and the denominator, using Canon Diablo meteoritic troilite as a standard. The < 34S value increases from 20-60%c before substantial biogenic methane is produced. 

Summary of Non-Marine Sulfur Emissions. S S values for continental sources of atmospheric sulfur dioxide vary, ranging between -32 and +10 0/00. This makes it difficult to use sulfur isotope ratios to distinguish sulfate from these individual sources. It appears that the f S value for marine biogenic sulfur is much more enriched in the heavier isotope than sulfur from continental origins. Therfore, it should be possible to isotopically distinguish between marine biogenic and continentally-derived sulfur. 

These examples convincingly demonstrate that specific OSC are formed during the early stages of diagenesis by reactions of reduced sulfur species with specific biogenic substrates. The reactive substrates are proposed to contain either carbon-carbon double bonds or other reactive functional groups that react with either hydrogen sulfide or polysulfides to form the OSC (88). These views are consistent with evidence from sulfur isotopes that H2S produced by microbial sulfate reduction is the major source of reduced sulfur in sediments... 

Ohmoto H., Kakegawa T., and Lowe D. R. (1993) 3.4-billion-year-old biogenic pyrites from Barberton, South Africa sulfur isotope evidence. Science 262, 555—557. 

Kohn M. J., Riciputi L. R., Stakes D., and Orange D. L. (1998) Sulfur isotope variability in biogenic pyrite reflections of heterogeneous bacterial colonization Am. Mineral 83(11-12 (Part 2)), 1454-1468. 

On the basis of the experimental trends outlined on p. 327, sulfur isotope data have been used in unravelling the sulfur biogeochemistry of springs. The relationships between finely divided iron sulfides in the beds of springs and biogenic sulfide have been determined on isotopic evidence. 

Calhoun, J.A. Bates, T.S. (1989) Sulfur isotope ratios. Tracers of nonsea-salt sulfur in the remote atmosphere. In Saltzman E.S. Cooper W.J. (Eds) Biogenic Sulphur in the Environment. Washington, DC American Chemical Society, pp. 369-379. 

The biogenic reduction of sulfate follows two biosynthetic pathways (1) assimilatory incorporation of sulfur into the amino acids e.g. cysteine) with very small sulfur isotope fractionation (2) dissimilatory production of sulfide coupled to oxidation of OM to CO2 (see Scheme 1). If we take, for example, methane as the electron donor, the reaction is... 

The early studies of biogenically reduced sulfur isotope SRB signature were performed on the chemically stable pyrite (Goldhaber and Kaplan, 1974). Since the formation of iron... 

Summary of Biogenic Sulfur Emissions from the Ocean. To summarize the source fractionation patterns for biogenic sulfur emissions from the oceam a simple isotopic model has been constructed (Figure 1). From this, the S S value of sulfate from a marine biogenic source of atmospheric sulfur can be estimated. 

Non-Marine Sulfur Sources. Non-marine sources of atmospheric sulfur to the remote atmosphere require long distance transport from continental areas. The following section summarizes the isotopic data from anthropogenic, volcanic, and terrestrial biogenic sulfur sources. 

Calhoun, J. C. Zoller, W. H. Charlson, R. J. Kelly, W. R. Isotope Analysis for Understanding the Importance of DMS in the Production of Excess Sulfate over the Remote Oceans. Solid Source Mass Spectrometry The Technique and its Application. 194th National Meeting of the American Chemical Society Biogenic Sulfur in the Environment Symposium, New Orleans 1987,261-2. 

Starting Materials. Pyrite isolated from the two kerogens constitutes approximately 2 wt % and has S S vaiues Qf +8.7 per mil. These values are enriched by 20-30 per mil compared to pyrite formed from near-surface biogenically reduced sulfate in porewaters of "normal" near-surface marine sediments (5). Bitumens extracted from the two samples contain 8.0 and 8.7 wt % organic sulfur with 5 4 vaiues 0f + 17.3 and +18.5 per mil respectively. Both pyrite free kerogens contained 10.3 wt % organic sulfur with isotope values of +15.9 per mil and +17.0 per mil respectively. 

Solid and gaseous biogenous sulfur products are enriched in the light isotope. For instance, the content of S isotope is increasing in the reduced HtS whereas... 

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