Sulfur reservoirs

The vast majority of sulfur at any given time is in the lithosphere. The atmosphere, hydrosphere, and biosphere, on the other hand, are where most transfer of sulfur takes place. The role of the biosphere often involves reactions that result in the movement of sulfur from one reservoir to another. The burning of coal by humans (which oxidizes fossilized sulfur to SO2 gas) and the reduction of seawater sulfate by phytoplankton which can lead to the creation of another gas, dimethyl sulfide (CH3SCH3), are examples of such processes. 

The remainder of this chapter, which discusses the cycling of sulfur, is divided into an 

The remainder of this chapter, which discusses the cycling of sulfur, is divided into an atmospheric part and an oceanic/solid earth part. The amount of sulfur in the atmosphere at any given time is small, even though the fluxes are large, because the lifetime of most sulfur compounds in air is relatively short (e.g. days). Sulfur in the ocean as SOj is cycled much more slowly, and the primary interactions in that cycle are with the solid earth. 

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Accepting these relative proportions from evaporites (2/3) and sulfides (1/3), the characteristic times, T of cycling of the evaporite sulfur and sulfide sulfur reservoirs can be estimated from the reservoir sizes (R,) in Table 13-3, and the river flux of sulfur. For evaporites ... 

Fig. 2.20 5 S-values of some geologically important sulfur reservoirs...

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. 

Table 4.1. Sulfur reservoirs and sulfur recovery factor.

Sulfur reservoir Sulfur storage Lifetime of sulfur in the reservoir... 

Table 4.3. Some estimates of the sulfur reservoirs that can be used as initial data.

Reservoir Identifier in Equations (4.1)-(4.18) Quantitative estimate of the sulfur reservoir (mg/m2)... 

The surface part of the sulfur cycle is connected with the functioning of the atmosphere-vegetation-soil system. Plants adsorb sulfur from the atmosphere in the form of S02 (fluxes C7 and C22) and assimilate sulfur from the soil in the form of SO4 (flux C15). In the hierarchy of soil processes, two levels can be selected defining the sulfur reservoirs as dead organics and S04 in soil . The transitions between them are described by flux C16 = b2STL, where the coefficient b2 = b2, b2 2 reflects the rate b2 of transition of sulfur contained in dead organics into the form assimilated by vegetation The coefficient b2>2 indicates the content of sulfur in dead plants. 

In its fully oxidized state, sulfur exists as sulfate. Sulfate is the second most abundant anion in seawater, and the SO4- in marine environments represents a large, slowly cycled sulfur reservoir. 

Living and dead organic matter compose a smaller, more rapidly cycled sulfur reservoir. Largely inert sulfur reservoirs include metal sulfides in rocks, elemental sulfur deposits, and fossil fuels. 

Estimated sulfur reservoirs (After Holser and Kaplan, 1966, Ref. 1, and Ericksson, 1963, Ref. 2.)... 

In comparison to other spheres, the sulfur content of the atmosphere is small, about 1.8 Tg compared with 1.3 X 10 Tg for hydrosphere (Table 6.4.1). However, in terms of the global cycle of sulfur, the atmosphere plays a complex and critical role (Fig. 6.4.1). The residence time for sulfur in the atmosphere is considered to be a few days with wide variations dependent upon meteorological and other factors (Kellogg et al., 1972). This contrasts with the case of the lithosphere, for example, which although by far the largest sulfur reservoir, has a turnover time in the order of millions of years (Holser and Kaplan, 1966). The atmosphere is also the recipient of the majority of anthropogenic sulfur. 

Table 24. Sulfur reservoirs in biosphere (After Dobrovoslky, 1994).

Hence the Archaean sulfur cycle (Fig. 5.5) would comprise inputs into the atmosphere and oceans from volcanic gases and into the oceans from hydrothermal activity but not river-borne sulfate. In addition, in the anoxic oceans, the oxidative alteration of the ocean floor would not take place. Thus the surface sulfur reservoir would have been small and most sulfur recycled back into the mantle as sulfide minerals. The sulfate part of the sulfur cycle is unlikely to have been fully operational until the late Proterozoic (Canfield, 2004). 

Sulfate anions are retained only weakly by soils, but the retention increases with soil acidity. Sulfate anions are absorbed readily by plants and incorporated into biomass. Hence, biomass and SOM constitute large sulfur reservoirs at the earth s surface. The C/S mass ratio in soil organic matter is typically about 100/1. The sulfate content of soils increases with aridity and with salt accumulation. 

List the major sulfur reservoirs and the forms found in wetland and aquatic environment. 

In an open system some isotopic discrimination between the rubber-like polymer (PCLM) and the H2S formed is expected. This is due to two stages (1) attack to form the C-Sx bonds and (2) the extraction of hydrogens to form the H2S leading to the aromatic stable thiophenes structure. This discrimination for the open systems was lately demonstrated by us also for the reaction of elemental sulfur with unsaturated hydrocarbons (unpublished results). Nevertheless, since the system described above is totally closed (hydrocarbons and elemental sulfur in ampoule), remixing of the sulfur reservoir and its isotope ratio occurs. The above results support the suggested high temperature re-reaction of previously released reduced sulfur with no isotopic discrimination under closed vessel reactions. 

This reasoning constrains the closure of cycle with the smaller reservoir, sulfur. The total sedimentary plus ocean sulfur reservoir is 350 x 10 mol of S [14]. For example, Wolery and Sleep [16] assumed that the crustal residence... 

Calvert, J. G., K. Theurer, G. T. Rankin and W. M. MacNevin (1954) A study of the mechanisms of the photochemical synthesis of hydrogen peroxide at zinc oxide surfaces. Journal of the American Chemical Society 76, 2575-2578 Canfield, D. E. (2004) The evolution of the earth surface sulfur reservoir. American Journal of Science 304, 839-861... 

Sulfur has four stable isotopes , gS, j S, which are -95.02%, -0.75%, -4.21% and 0.02% abundant, respectively. Sulfur is ubiquitous in the global environment and major sulfur reservoirs include sulfate in the oceans, evaporites, sulfide ore deposits, and organic sulfur compounds. Sulfur isotope abundance variations are shown in Figure 11. 

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