Sulfur oceanic sources

Lovelock et al. (2) made the first quantitative measurement of DMS in the surface ocean and suggested that it, rather than H S, made up the principle oceanic sulfur source. Since that time, a number of measurements have been made of both water column and atmospheric DMS and flux calculations support the view that the emissions of this organic sulfur compound constitute a major global flux. However, the relative importance of the fluxes of DMS and H2S as... 

The first report of DMS in the ocean appeared in 1972 (22.)- The authors suggested that DMS might be more important than H2S as a biogenic sulfur source for balancing the global sulfur budgets. Preliminary estimates of DMS sea-to-air flux based on the limited data were made by Liss and Slater (741. 

Other processes which may explain changes in DMS concentration with depth, on a short time scale, are those related to bacteria. Studies conducted in sediments (31-39.62) have shown that DMS can be consumed by microorganisms. Based on sulfur requirements of microorganisms, the availability of sulfur from sulfate in these environments far exceeds that of DMS. However, as a carbon source, the concentration of DMS is similar to other compounds of low molecular weight and may be cycled by microorganisms to serve as both a carbon ana sulfur source. Although the utilization of DMS aerobically has been reported (63.64). the extent to which similar processes exist in oceanic environments is not known. For futher discussions of the microbial processes related to DMS the reader is referred to another Chapter of this book (65). 

The data from remote marine air are of particular interest because both the sulfur sources and the atmospheric oxidant fields should be fairly homogeneous. Andreae and Raemdonck (141 presented the first data showing the diurnal variations of DMS over the open ocean, from the equatorial Pacific ocean. They obtained a mean concentration of 128 ppt with a standard deviation of S3 ppt. By averaging the data into 4 hour intervals they showed a daytime minimum and nighttime maximum with a diurnal range of 90 to 149 ppt. Dividing the maximum by the minimum gives a factor of 1.65 diurnal variation for this data set. 

Hydrogen Sulfide. There have been several studies of the concentration of H2S in marine air using variations of the Natusch technique described earlier 126-29.6). The results of the earlier studies, summarized in Table II, indicated that H S concentrations over the oceans were substantial, suggesting that the flux of H2S from the surface ocean is significant relative to other sulfur sources. Anomalous diurnal behavior of hydrogen sulfide was noted by Delmas and Servant 127) in which a midday maxima and nighttime minima were observed. As discussed earlier, both the elevated H2S levels and the diurnal variations are likely to be the result of artifact sulfide production from atmospheric OCS collected on the filters. 

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. 

The third sulfur source is provided by the formation of sea salt particles at the surface of the ocean (see Section 4.2). According to Eriksson (1960) the sulfur mass in sea salt particles produced yearly is 44 x 106 1. This figure seems to be rather well established, and for this reason, we shall not discuss it in more detail. 

Thallium occurs in crooksite, lorandite, and hutchinsonite. It is also present in pyrites and is recovered from the roasting of this ore in connection with the production of sulfuric acid. It is also obtained from the smelting of lead and zinc ores. Extraction is somewhat complex and depends on the source of the thallium. Manganese nodules, found on the ocean floor, contain thallium. 

Sulfur dioxide occurs in industrial and urban atmospheres at 1 ppb—1 ppm and in remote areas of the earth at 50—120 ppt (27). Plants and animals have a natural tolerance to low levels of sulfur dioxide. Natural sources include volcanoes and volcanic vents, decaying organic matter, and solar action on seawater (28,290,291). Sulfur dioxide is beHeved to be the main sulfur species produced by oxidation of dimethyl sulfide that is emitted from the ocean. 

Under low-dose conditions, forest ecosystems act as sinks for atmospheric pollutants and in some instances as sources. As indicated in Chapter 7, the atmosphere, lithosphere, and oceans are involved in cycling carbon, nitrogen, oxygen, sulfur, and other elements through each subsystem with different time scales. Under low-dose conditions, forest and other biomass systems have been utilizing chemical compounds present in the atmosphere and releasing others to the atmosphere for thousands of years. Industrialization has increased the concentrations of NO2, SO2, and CO2 in the "clean background" atmosphere, and certain types of interactions with forest systems can be defined. 

Finally, sulfur occurs in many localities as the sulfates of electropositive elements (see Chapters 4 and 5) and to a lesser extent as sulfates of Al, Fe, Cu and Pb, etc. Gypsum (CaS04.2H20) and anhydrite (CaSO ) are particularly notable but are little used as a source of sulfur because of high capital and operating costs. Similarly, by far the largest untapped source of sulfur is in the oceans as the dissolved sulfates of Mg, Ca and K. It has been estimated that there are some 1.5 x 10 cubic km of water in the oceans of the world and that 1 cubic km of sea-water contains approximately 1 million tonnes of sulfur combined as sulfate. 

Table 13-1 includes many of the key naturally occurring molecular species of sulfur, subdivided by oxidation state and reservoir. The most reduced forms, S( — II), are seen to exist in all except the aerosol form, in spite of presence of free O2 in the atmosphere, ocean and surface waters. With the exception of H2S in oxygenated water, these species are oxidized very slowly by O2. The exception is due to the dissociation in water of H2S into H + HS . Since HS reacts quickly with O2, aerobic waters may contain, and be a source to the atmosphere of, RSH, RSR etc. but not of H2S itself. Anaerobic waters, as in swamps or intertidal mudflats, can contain H2S and can, therefore, be sources of H2S to the air. 

Andreae, M. O. (1986). The ocean as a source of atmospheric sulfur compounds. In "The Role of Air-Sea Exchange in Geochemical Cycling" (P. Buat-Menard, ed.). Reidel, Dordrecht. 

Interest in the possible persistence of aliphatic sulfides has arisen since they are produced in marine anaerobic sediments, and dimethylsulfide may be implicated in climate alteration (Charlson et al. 1987). Dimethylsnlfoniopropionate is produced by marine algae as an osmolyte, and has aronsed attention for several reasons. It can be the source of climatically active dimethylsulfide (Yoch 2002), so the role of specific bacteria has been considered in limiting its flux from the ocean and deflecting the prodncts of its transformation into the microbial sulfur cycle (Howard et al. 2006). 

Acid rain is caused primarily by sulfur dioxide emissions from burning fossil fuels such as coal, oil, and natural gas. Sulfur is an impurity in these fuels for example, coal typically contains 2-3% by weight sulfur.1M Other sources of sulfur include the industrial smelting of metal sulfide ores to produce the elemental metal and, in some parts of the world, volcanic eruptions. When fossils fuels are burned, sulfur is oxidized to sulfur dioxide (SO2) and trace amounts of sulfur trioxide (SC>3)J21 The release of sulfur dioxide and sulfur trioxide emissions to the atmosphere is the major source of acid rain. These gases combine with oxygen and water vapor to form a fine mist of sulfuric acid that settles on land, on vegetation, and in the ocean. 

The major source of solutes and solids to the ocean is via river transport. The only major ion with a direct source associated with hydrothermal input seems to be calcium. The hydrothermal input of DSi is also significant. Volcanic gases are presently contributing a minor amount of HCl and sulfur gases (H2S and SO2). Each of these sources is discussed next with primary focus on how terrestrial chemical weathering provides most of the major ion input the oceans. 

Little snlfnr is re-emitted from wetlands into the atmosphere. Table 8.7 gives estimates of global emissions of volatile sulfur compounds from different sources. Total emissions are in the range 98 to 120 Tg (S) year 75 % is anthropogenic, mainly from fossil fnel combustion in the northern hemisphere. The main natural sources are the oceans and volcanoes. Wetlands and soils contribnte less than 3 % of the total emission. 

Another factor that is of great importance for the observed sulfur isotope variations of natural sulfides is whether sulfate reduction takes place in an open or closed system. An open system has an infinite reservoir of sulfate in which continuous removal from the source produces no detectable loss of material. Typical examples are the Black Sea and local oceanic deeps. In such cases, H2S is extremely depleted in " S while consumption and change in " S remain negligible for the sulfate. In a closed system, the preferential loss of the lighter isotope from the reservoir has a feedback on the isotopic composition of the unreacted source material. The changes in the " S-content of residual sulfate and of the H2S are modeled in Fig. 2.21, which shows that 5 S-values of the residual sulfate steadily increase with sulfate consumption (a linear relationship on the log-normal plot). The curve for the derivative H2S is parallel to the sulfate curve at a distance which depends on the magnitude of... 

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