Sulfur elemental isotope effects

The biochemical reduction of sulfate to sulfide by bacteria of the genus Desulfovibrio in anoxic waters is a significant process in terms of the chemistry of natural waters since sulfide participates in precipitation and redox reactions with other elements. Examples of these reactions are discussed later in this paper. It is appropriate now, however, to mention the enrichment of heavy isotopes of sulfur in lakes. Deevey and Nakai (13) observed a dramatic demonstration of the isotope effect in Green Lake, a meromictic lake near Syracuse, N. Y. Because the sulfur cycle in such a lake cannot be completed, depletion of 32S04, with respect to 34S04, continues without interruption, and 32S sulfide is never returned to the sulfate reservoir in the monimolimnion. Deevey and Nakai compared the lake to a reflux system. H2S-enriched 32S diffuses to the surface waters and is washed out of the lake, leaving a sulfur reservoir depleted in 32S. The result is an 34S value of +57.5% in the monimolimnion. 

Metastable Iron Sulfides Organic Sulfur Elemental Sulfur MECHANISM OF PYRITE FORMATION. 4.1 Evidence from Experimental Studies. 4.2 Isotope Effects during Experimental Pyrite Formation. 4.3 Origin of Morphological Variations in Pyrite SULFUR DIAGENETIC PROCESSES IN MARINE SEDIMENTS. 5.1 Depth Distribution of Diagenetic Sulfur Products. 5.2 Rates of Sulfate Reduction... 

Kusakabe M., Komoda Y., Takano B., and Abiko T. (2000) Sulfur isotopic effects in the disproportionation reaction of sulfur dioxide in hydrothermal fluids implications for the delta S-34 variations of dissolved bisulfate and elemental sulfur from active crater lakes. J. Volcanol. Geotherm. Res. 97(1-4), 287-307. 

The lighter the element, the larger is the ratio of the heavy and the light isotope masses. Thus, the ratio of deuterium and hydrogen masses is 2/1, and that of sulfur-34 and sulfur-32 is 34/32 = 1.0625. This is why the primary kinetic isotope effect of deuterium is relatively high compared to that of sul-fur-34. Consequently, the lowering of the zero-point energies is... 

There is considerable evidence that, in nature, bacterial sulfate reduction plays an important role in the formation of some deposits of elemental sulfur. Free sulfur is not, however, produced by sulfate-reducers per se and its formation depends, therefore, on chemical or biological oxidation of sulfide. Microorganisms capable of effecting the latter reaction are discussed in Chapters 6.1 and 6.3 while isotopic selectivities associated with this conversion are summarised in Table 6.4.2 (see p. 406). As discussed in Chapters 6.1 and 6.3 colourless sulfide-oxidising bacteria, e.g. Beggiatoa, and Thio-bacillus, inhabit aerobic zones of ponds, etc. while in the underlying anaerobic zones, where light can penetrate, photosynthetic oxidisers, such as Chro-matium and Chlorobium, are active. 

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