Marine sediments formation

The formation and dissolution of CaCOa in the ocean plays a significant role in all of these effects (34)- CaCOa is produced by marine organisms at a rate several times the supply rate of CaCOa to the sea from rivers. Thus, for the loss of CaCOa to sediments to match the supply from rivers, most of the CaCOa formed must be redissolved. The balance is maintained through changes in the [COa] content of the deep sea. A lowering of the CO2 concentration of the atmosphere and ocean, for example by increased new production, raises the [COa] ion content of sea water. This in turn creates a mismatch between CaCOa burial and CaCOa supply. CaCOa accumulates faster than it is supplied to the sea. This burial of excess CaCOa in marine sediments draws down the [COa] - concentration of sea water toward the value required for balance between CaCOa loss and gain. In this way, the ocean compensates for organic removal. As a consequence of this compensation process, the CO2 content of the atmosphere would rise back toward its initial value. 

As a starting point we can view the ocean as one large reservoir to which materials are continuously added and removed (Fig. 10-17). The major sources of material include rivers and winds, which carry dissolved and particulate materials from the continents to the sea. The major removal process is the formation of marine sediments both by settling of particles through the water column as well as by precipitation of insoluble solid phases. For many ele-... 

Radium, like most other group II metals, is soluble in seawater. Formation of Ra and Ra by decay of Th in marine sediments leads to release of these nuclides from the sediment into the deep ocean. Lead, in contrast, is insoluble. It is found as a carbonate or dichloride species in seawater (Byrne 1981) and adheres to settling particles to be removed to the seafloor. 

Surfactants such as LAS and NPEO have been found in compartments with low oxygen content, such as anaerobic sludge digesters or anaerobic continental and marine sediments [14,15,18-25]. One of the possible causes of this persistence is the inhibition of the anaerobic digestion [17,26,27]. Battersby and Wilson [27] observed inhibitory effects of NP at 50 mg CL-1 on methane formation in a survey of the anaerobic biodegradation potential of organic chemicals in digesting... 

Hagiwara (2000) completed a reconnaissance survey of Se isotope variation in marine sediments and sedimentary rocks (Table 4). The most important observation was a lack of strong enrichment in lighter isotopes in most shale samples and three Black Sea sediments. It appears that near-surface alteration has altered Se isotope ratios in some cases. All of the Phosphoria formation samples were probably altered by deep groundwater or hydrothermal... 

Karlin R, Lyle M, Heath CR (1987) Authigenic magnetite formation in suboxic marine sediments. Nature 326 490-493... 

Raiswell R, Canfield DE (1998) Sources of iron for pyrite formation in marine sediments. Am J Sci 298 219-245... 

Zheng Y, Anderson RF, van Geen A, Kuwabara J (2000a) Authigenic molybdenum formation in marine sediments A link to pore water sulfide in the Santa Barbara Basin. Geochim Cosmochim Acta 64 4165-4178... 

In the preceding sections, we have discussed the marine processes that control calcium carbonate s formation, dissolution, and delivery to the seafloor. Their combined effects determine the geographic distribution of calcium carbonate in marine sediments seen in Figure 15.5. As noted earlier, the global distribution of calcareous sediments does not seem to follow that of plankton production. This points to the overriding importance of the processes that control the dissolution and sedimentation of calcium carbonate. 

The sedimentary and metamorphic rocks uplifted onto land have become part of continents or oceanic islands. These rocks are now subject to chemical weathering. The dissolved and particulate weathering products are transported back to the ocean by river runoff. Once in the ocean, the weathering products are available for removal back into a marine sedimentary reservoir. At present, most mass flows on this planet involve transport of the secondary (recycled) materials rather than the chemical reworking of the primary (juvenile) minerals and gases. The natirre of these transport and sediment formation processes has been covered in Chapters 14 through 19 from the perspective of the secondary minerals formed. We now reconsider these processes from the perspective of impacts on elemental segregation between the reservoirs of the crustal-ocean-atmosphere factory and the mantle. 

In brief, the steps in the formation of pyrite in marine sediments are ... 

In addition, selected rare elements, such as precious metals, were extracted from matrix elements and preconcentrated to avoid isobaric interferences with polyatomic ions as demonstrated for platinum determination in the presence of a relatively high concentration of Hf, resulting in isobaric interferences at m/z = 194, 195 and 196 due to HfO+ diatomic ion formation.17 An improved method for extracting marine sediment fractions and its application for Sr and Nd isotopic analysis is described by Bayon et al.ls... 

Iron frequently has been postulated to be an important electron acceptor for oxidation of sulfide (58, 84,119, 142, 152). Experimental and theoretical studies have demonstrated that Fe(III) will oxidize pyrite (153-157). Reductive dissolution of iron oxides by sulfide also is well documented. Progressive depletion of iron oxides often is coincident with increases in iron sulfides in marine sediments (94, 158, 159). Low concentrations of sulfide even in zones of rapid sulfide formation were attributed to reactions with iron oxides (94). Pyzik and Sommer (160) and Rickard (161) studied the kinetics of goethite reduction by sulfide thiosulfate and elemental S were the oxidized S species identified. Recent investigations of reductive dissolution of hematite and lepidocrocite found polysulfides, thiosulfate, sulfite, and sulfate as end products (162, 163). 

Diagenesis the concurrent and consecutive chemical reactions which commence the alteration of organic matter (at temperatures up to 50°C (120°F) and ultimately result in the formation of petroleum from the marine sediment see also Catagenesis and Metagenesis. 

Mechanistic Studies of Organosulfur (Thiol) Formation in Coastal Marine Sediments... 

---