Metabolism sedimentary

Oxygen 18o/16o 160 = 99.759 170 = 0.037 lsO = 0.204 Water, biomineralized carbonates and phosphates, sedimentary phosphates and carbonates, silicates, organic matter Climate, plant and animal water metabolism, ocean temperature, provenance (marble), chronostratigraphy... 

Deposition of elemental sulphur formed from sulphate Essential collaboration of at least two different microbial species occurs in the transformation of sulphate to S° in salt domes or similar sedimentary formations (see Ivanov, 1968). This transformation is dependent on the interaction of a sulphate reducer like Desulfovibrio desulfuricans, which transforms sulphate to H2S in its anaerobic respiratory metabolism, and an H2S oxidizer like Thiobacillus thioparus, which, under conditions of limited O2 availability, transforms H2S to S° in its respiratory metabolism (van den Ende van Gemerden, 1993). The collaboration of these two physiological types of bacteria is obligatory in forming S° from sulphate because sulphate reducers cannot form S° from sulphate, even as a metabolic intermediate. It should be noted, however, that the sulphate reducers and H2S oxidizers are able to live completely independent of each other as long as the overall formation of S° from sulphate is not a requirement. 

Heterotrophic respiration fueled by the rain of organic matter from the surface ocean is ubiquitous in marine sediments. Its rate determines one of the important characteristics of the sedimentary environment the depth of redox horizons below the sediment-water interface. Heterotrophic respiration is the process by which carbon and nutrients are returned to the water column it is important in the marine fixed nitrogen and sulfur cycles and the accumulation of metabolic products sets the conditions for the removal of phosphorus from the oceans in authigenic minerals. A great deal of effort has been directed toward quantifying the rates, pathways, and effects of metabolism in sediments. 

The pathways for sedimentary microbial metabolism are outlined in Table 2. They are presented in order of decreasing free energy yield for reaction of each oxidant (shown in bold type in the table) with sedimentary organic matter (Froelich et ai, 1979). Pore-water data support the assertion that the electron acceptors are used in this order of decreasing free energy yield. The order of the NO N2 and Mn02 Mn(II) reactions is uncertain, however, and examples exist in the literature for which Mn(IV) appears to be used before NO )" (Froelich et al., 1979 Klinkhammer, 1980) or for which NO appears to be used first (e.g., Shaw et al., 1990 Lohse et al., 1998). Thus, the order of electron acceptor use is O2, NO ... 

Plots of alkalinty versus Tqo2 and Ca " " versus alkalinity demonstrate conclusively the occurrence of metabolic dissolution. However, they do not show the ratio of the rates of dissolution and carbon oxidation well. The reason is that calcite dissolution is rapid relative to organic matter oxidation. Therefore, pore waters that have become undersaturated due to oxic metabolism re-equilibrate with sedimentary calcite very rapidly. The sedimentary layer in which the release of metabolic acids is not matched by dissolution is expected to be thin, so that the slope... 

The balance between dissolution and preservation of CaCOs in the oceans has important implications for the marine alkalinity balance and therefore for the atmospheric CO2 concentration. On the order of half the CaCOs dissolution in the oceans occurs in sediments. Studies of the sedimentary dissolution process are leading to a quantitative understanding of the role of sediments in the marine CaCOs cycle. Most importantly, they have highlighted the potential importance of the role of dissolution in sediments above the calcite lysocline, which is driven by neutralization of acids produced by oxic metabolism. Dissolution above the saturation horizon cannot be ignored in the marine CaCOs cycle, and possible temporal variations in its extent must be considered in interpreting the temporal record of sedimentary CaCOs accumulation. 

Nriagu, J., 1968. Sulfur metabolism and sedimentary environment Lake Mendota, Wisconsin. Limnol. Oceanogr., 13 430—439. 

Stromatolites and microbialites Stromatolites are "laminated lithified sedimentary growth structures that form by accretion, through the addition of new laminae away from the point or surface of accretion." They normally are made up of carbonate minerals and thought to have formed in a shallow water environment. Modern freshwater stromatolites are made up of algal and cyanobacte-rial filaments. In the marine environment they form microbial mats and columns. These comparisons led many scientists to believe that stromatolites found in the ancient record are biogenic in origin and that they are in fact microbialites. That is, they are sedimentary structures in which minerals are precipitated as either a by-product of microbial metabolisms or as a by-product of microbial decay. 

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