Shallow marine sediments

The case of bacterial reduction of sulfate to sulfide described by Berner (1984) provides a useful example. The dependence of sulfate reduction on sulfate concentration is shown in Fig. 5-4. Here we see that for [SO ] < 5 mM the rate is a linear function of sulfate concentration but for [SO4 ] > 10 itiM the rate is reasonably independent of sulfate concentration. The sulfate concentration in the ocean is about 28 mM and thus in shallow marine sediments the reduction rate does not depend on sulfate concentration. (The rate does depend on the concentration of organisms and the concentration of other necessary reactants - organic carbon in this case.) In freshwaters the sulfate concentration is... 

Although atmospheric methane concentrations appear to have stabilized over the past few decades, melting of gas hydrates in permafrost and shallow marine sediments have the potential to rapidly release large quantities of this potent greenhouse gas. As noted in... 

Hansen, K., and Kristensen, E. (1997). Impact of macrofaunal recolonization on benthic metabolism and nutrient fluxes in a shallow marine sediment previously overgrown with macroalgal mats. Estuar. Coast. Shelf. Sci. 45, 613—628. 

As far as one can tell from the data presented, verdine facies minerals are found on the surface of shallow marine sediments (Odin, 1988 Thamban and Rao, 2000 Kronen and Glenn, 2000). Berthierine in sedimentary rocks (Fritz and Toth, 1997 Moore and Hughes, 2000) formed at temperatures below 70 °C (Hornibrook and Long-staffe, 1996). It can apparently form from verdine facies minerals or by various mineral reactions during diagenesis (Fritz and Toth, 1997 Velde, 1989). Verdine facies minerals, mixed layered in nature, are therefore of low-temperature oceanic origin, while berthierine can possibly form as a pure phase under these conditions or under diagenetic conditions and temperatures up to 70 °C. 

Figure 8 The relationship between that rate at which S04 is consumed down-core in shallow marine sediments and the 8 The fit of the regression...

Alexandersson, E.T., 1972. Micritization of carbonate particles Processes of precipitation and dissolution in modern shallow-marine sediments Bull. Geol. Inst. Univ. Uppsala, N.S., 3 201-236. 

However, much of the methane produced in bottom sediments never reaches the atmosphere because it is oxidized to CO2 by microorganisms living in the surficial layers of the sediments and in the oxic, overlying waters. The oxidation of methane by sulfate reducers (or other organisms in the community) also has been examined and it is the principal removal mechanism of methane from shallow marine sediments (24, 25). Methane is also oxidized by certain chemoautotrophic bacteria in the presence of dissolved oxygen, although at much lower rates compared to those observed in sediments (27). 

Jannsen D., Voss J., Theilen F., 1985. Comparison of methods to determine Q in shallow marine sediments from vertical seismograms. Geophysical Prospecting 33 479-497... 

Gas hydrate formation involves the removal of water molecnles from the surrounding pore water, as they are seqnestered in the clathrate lattice. Removal of water, with the exclusion of the dissolved ions, leads to changes in the concentration of salts in the pore water. Becanse chloride is an abnndant and nsnally conservative ion in pore waters of shallow marine sediment, changes in dissolved chloride content are... 

The Cu concentration of crustal rocks (32 34 p,g g ) is approximately equivalent to that for average soils (25 4 p,g g ). However, as the earth material is weathered and transported to streams-lakes-shallow marine sediments there is a minimal enrichment in Cu concentration (39 = 34 = 43 p,gg ) (Table 4). And, as for Pb-Zn-Cd, riverine particulate matter is greatly enriched (100p,gg ) relative to the other sedimentary materials. While the Pb-Zn-Cd concentrations of deep-sea clay are enriched 1.5 times that of the continental sedimentary materials, Cu is enriched approximately five times. The substantial enrichment of Cu in oceanic pelagic clay relative to terrestrial earth materials is due to the presence of ubiquitous quantities of ferromanganese oxides in surficial ocean sediments (Drever, 1988). 

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