Minor elements ocean

Edmond, J., Measures, C., Mcduff, E. et al. (1979) Ridge crest hydrothermal activity and the balances of major and minor elements in the ocean The Galapagos data. Earth Planet. Sci. Lett., 46, 1-18. 

OCEAN WATER. An electrolyte solution containing minor amounts of nonelectrolytes and composed predominantly of dissolved chemical species of fourteen elements O, H, Cl, Na. Mg, S, Ca, K, Bl, C, Sr, B, Si, and F (Table 1). The minor elements, those that occur in concentrations of less than 1 ppm by v/eight. although unimportant quantitatively in determining the physical properties of sea water, are reactive and are important in organic and biochemical reactions in the oceans. 

We know the analytical concentrations of the major and many of the minor elements in the ocean, but we do not know their activities with respect to the normal aqueous standard state. In particular, for the hydrogen ion we do not know, strictly speaking, either the activity or the concentration. (The acidity of the sea is reported in terms of pH values whose thermodynamic meaning in this particular medium is not well understood.) The temperature of the sea varies between 0° and 30°C., and the pressure varies between 1 and 2000 atm. 

Eased on two main lines of evidence, Niu et al. (1997) concluded that abyssal peridotites are the end products of melt extraction followed by variable amounts of olivine crystallization. First, in their set of reconstructed compositions they found that model fractional and batch melt extraction trends could not reproduce major and minor element variations in their data set. Most importantly, they found that melt extraction models failed to account for the strong positive correlation between FeO and MgO, as well as incompatible minor-element concentrations. Specifically, at a given Na20 or Ti02 content, abyssal peridotites are enriched in MgO relative to model melt extraction residues. Niu et al. (1997) showed that these compositional anomalies can be reconciled by a model of melt extraction followed by olivine crystallization, with more MgO-enriched samples having more accumulated olivine. If correct, this model has important implications for understanding melt extraction at oceanic ridges, and it has recently been the focus of re-evaluation. 

Izuka S. K. (1988) Relationships of magnesium and other minor elements in tests of Cassidulina Subglo-bosa and C. Oriangulata to physical oceanic properties. J. Foraminiferal Res. 18(2), 151—157. 

The activities of humans have had some impacts on both the major and minor element chemistry of the modem oceans. For example, seawater major ion budgets mostly assume the estimated riverwater input to seawater is that of the pristine (pre-human) system. However, anthropogenic processes have altered some of these fluxes. For example, the riverine CF flux may have increased by more than 40% as a result of human activity and the SOj flux may have doubled, due mainly to fossil fuel combustion and oxidation of pollution-derived H2S. 

Human effects on total ocean minor element budgets... 

Since iodine in these processes is present in various chemical forms, the chemical speciation of iodine is important for understanding its geochemistry in oceans. Further, iodine is redox sensitive and the most abundant biophilic minor element in the oceans. Here, the behaviors of various iodine species in seawater will be described in regard to biological and abiological processes. 

Mukasa S.B. and Henry D.S., 1990, The San Nicolas bathoUdi of coastal Pnu early Palaeozoic continental arc or continental rift magmatism Ceol Soc. Land., 147, 27-39. Mullen E.D., 1983, Mn0/Ti02/P20s a minor element discriminant for basaltic rocks of oceanic environments and its Implications for petrogenesis. Earth Planet. Set, Lett., 62, 53-62., , ... 

Tables I and II clearly show some of the major chemical differences between basalt and granite. A rock consisting chiefly of quartz and feldspar, granite shows high Si, Na and K values basalt, which is made up chiefly of Fe-Mg silicates and Ca-Na feldspar, is rich in Fe, Mg, and Ca. (Since the oceanic crast is largely basalt, its inclusion in the average analysis would result in largervalues for these latter three elements.) Minor elements in the two rocks tend to follow major elements of similar chemical properties thus Ba, Rb, and La are more abundant in granite, while V, Cr, and Ni predominate in basalt. Some elements, for example, Al, Ga, and Nb, show little difference from one rock to the other and are also the same in the cmstal average.

In Chapter 4, we saw how conservative chemicals are used to trace the pathway and rates of water motion in the ocean. True conservative behavior is exhibited by a relatively small number of chemicals, such as the major ions and, hence, salinity. In contrast, most of the minor and trace elements display nonconservative behavior because they readily undergo chemical reactions under the environmental conditions found in seawater. The rates of these reactions are enhanced by the involvement of marine organisms, particularly microorganisms, as their enzymes serve as catalysts. Rates are also enhanced at particle interfaces for several reasons. First, microbes tend to have higher growth rates on particle surfaces. Second, the solution in direct contact with the particles tends to be highly enriched in reactants, thereby increasing reaction probabilities. Third, adsorption of solutes onto particle surfaces can create fevorable spatial orientations between reactants that also increases reaction probabilities. 

---