Oceanic metallic species

The coordination chemistry of sea water represents a new and useful approach to understanding the chemical properties of sea water. The coordination chemistry of sea water differs from contemporary coordination chemistry in the following respects most complexes involve pretransition metals, most complexes are labile, the ligands are simpler (water, hydroxide, chloride, carbonate, sulfate), and time and space are important parameters. Principles of coordination chemistry are applied to contemporary research in marine science in four areas analysis of constituents of natural waters, the nature of metallic species in the oceans, the Red Tide problem, and carbonate geochemistry. 

From Mc2Hg data in surface sea water samples and in the corresponding marine atmosphere, a first estimation of the transfer of this compound from the Southern Ocean, the Arctic Ocean and the Atlantic Ocean was carried out by equation (1) (see Table 7.7) (45). This estimate was calculated under the questionable assumptions that the measured data were representative for the whole area and that no seasonal variation occurs. The great uncertainty in such calculations can also be inferred by the great variability in the data for the total biogenic Hg emission from all oceans, which range from 0.6 10 to 7700 10 g yr (66, 67). However, the calculated input of more than 0.2 10 g yr of Hg as Mc2Hg from each of the polar oceans is more than 10% of the total emission of this heavy metal species from the Atlantic Ocean. In addition, more recent data from Lindqvist et al. and... 

The reduced species Fe2+ and Mn2+ have been detected electrochemically in anoxic waters (De Vitre et al., 1988). Vanadyl (V02 + ) is known to be incorporated in geoporphyrins in organic-rich sediments (Eckstrom et al., 1983). Moffett and Zika (1988) measured reduced Cu(I) photometrically in surface waters of the open ocean. The oxidation of these four metal species involves a simple one-electron transfer step. Haber and Weiss (1934) proposed a kinetic mechanism for the oxygenation of the ferrous ion, in which the first step in the four-electron reduction of the dioxygen molecule determines the rate. The redox potentials for the corresponding oxygen couples support this view they are plotted ill... 

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. 

No documented report of fatal copper deficiency is available for any species of aquatic organism, and no correlation is evident in aquatic biota for the presumed nutritional copper requirements of a species and its sensitivity to dissolved copper (Neff and Anderson 1977). Extremely low copper concentrations (5.5 and 6.7 mg/kg DW) in whole bodies of 2 of 17 species of crustaceans from the Antarctic Ocean support the hypothesis that certain Antarctic species may show copper deficiencies or reduced metal requirements (Petri and Zauke 1993). 

The systematic removal of elements by runoff and the reimmobilization from solution by organic matter are continuously counterbalanced by the new input of chemical species, which maintain both biological and biogeochemical cycles. The main sources of water-soluble elements are oceanic aerosols deposited on the land surface and the weathering of rocks. The airborne input of the trace metals may be ranked as follows for the Spitzbergen island ecosystems (Table 4). 

The geochemical fate of most reactive substances (trace metals, pollutants) is controlled by the reaction of solutes with solid surfaces. Simple chemical models for the residence time of reactive elements in oceans, lakes, sediment, and soil systems are based on the partitioning of chemical species between the aqueous solution and the particle surface. The rates of processes involved in precipitation (heterogeneous nucleation, crystal growth) and dissolution of mineral phases, of importance in the weathering of rocks, in the formation of soils, and sediment diagenesis, are critically dependent on surface species and their structural identity. 

In contrast to their rather low dissolved concentrations in seawater, some of the trace metals, e g., iron and aluminum, along with oxygen and silicon, comprise the bulk of Earth s crust. Some trace elements are micronutrients and, hence, have the potential to control plankton species composition and productivity. This provides a connection in the crustal-ocean-atmosphere fectory to the carbon cycle and global climate. 

Trace metals are introduced to the ocean by atmospheric feUout, river runoff, and hydrothermal activity. The latter two are sources of soluble metals, which are primarily reduced species. Upon introduction into seawater, these metals react with O2 and are converted to insoluble oxides. Some of these precipitates settle to the seafloor to become part of the sediments others adsorb onto surfaces of sinking and sedimentary particles to form crusts, nodules, and thin coatings. Since reaction rates are slow, the metals can be transported considerable distances before becoming part of the sediments. In the case of the metals carried into the ocean by river runoff, a significant fraction is deposited on the outer continental shelf and slope. Hydrothermal emissions constitute most of the somce of the metals in the hydrogenous precipitates that form in the open ocean. 

The adsorption of ions on iron oxides regulates the mobility of species in various parts of the ecosystem (biota, soils, rivers, lakes, oceans) and thereby their transport betv een these parts. Examples are the uptake of plant nutrients from soil and the movement of pesticides and other pollutants from soils into aquatic systems. In such environments various ions often compete with each other for adsorption sites. Adsorption is the essential precursor of metal substitution (see Chap. 3), dissolution reactions (see Chap. 12) and many interconversions (see Chap. 14). It also has a role in the synthesis of iron oxides and in crystal growth. In industry, adsorption on iron oxides is of relevance to flotation processes, water pollution control and waste and anticorrosion treatments. 

Aluminum Solute Species and Solubility. The qualitative importance of metal-ion hydrolysis in determining the solution chemistry of aluminum is generally recognized. Considerable practical and theoretical interest in the behavior of aqueous aluminum in the oceans (where it is one of the highly reactive elements), in geochemical studies of aluminosilicates and related systems, and in water treatment technology (coagulation and... 

Recent reviews on chemical speciation are published by e.g. Stumm and Brauner (1975), Florence and Batley (1980) and Leppard (1983) sometimes, with special reference to metal-organic interactions (Mantoura, 1982) or complexation in natural waters (Kramer and Duinker, 1984b). Bruland (1983) summarized the distribution and behaviour of trace elements in ocean waters. The occurrence of certain species is largely dependent on the environmental conditions. There exists a strong competition of trace metals with H+ or major cations like Ca2+ and Mg2+ in seawater, but also with other trace metals which might form more stable complexes with the ligand in question on the other side, many potential ligands or chelators compete for one trace element. 

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