Kinetics of calcium carbonate in seawater

Berner, R.A. Morse, J.M. 1974. Dissolution kinetics of calcium carbonate in seawater. IV. Theory of calcite dissolution, American Journal of Science, 274,108-134. 

Morse J.W. (1978) Dissolution kinetics of calcium carbonate in seawater. VI The near-equilibrium dissolution kinetics of calcium carbonate-rich deep sea sediments. Amer. J. Sci. 278, 344-355. 

Calcium carbonate is accumulating in deep ocean sediments, in which the overlying water is undersaturated with respect to both aragonite and calcite, and sediment marker levels closely correspond to unique saturation states. This indicates that dissolution kinetics play an important role in determining the relation between seawater chemistry and calcium carbonate accumulation in deep ocean basins. It is, therefore, necessary to have knowledge of the dissolution kinetics of calcium carbonate in seawater if the accumulation of calcium carbonate is to be understood. 

Morse, J.W., de Kanel, J., and Harris, K. The dissolution kinetics of calcium carbonate in seawater VII. The dissolution kinetics of synthetic aragonite and pteropods, Amer. Jour. Sci. (in press). 

Keir R.S. (1980) The dissolution kinetics of biogenic calcium carbonates in seawater. Geochim. Cosmochim. Acta 44, 241-252. 

A major portion of the studies on calcium carbonate reaction kinetics has been done in seawater because of the many significant geochemical problems related to this system. Morse and Berner (1979) summarized the work on carbonate dissolution kinetics in seawater and their application to the oceanic carbonate system. The only major seawater component in addition to Mg2+ that has been identified as a dissolution inhibitor is SO42- (Sjoberg, 1978 Mucci et al., 1989). Sjoberg s studies of other major and minor components (Sr2+, H3BO3, F-) showed no measurable influence on dissolution rates. Morse and Berner (1979) and Sjoberg (1978) found that for near-equilibrium dissolution in phosphate-free seawater, the dissolution rate could be described as ... 

Two experimental approaches have been used to determine calcium carbonate dissolution kinetics in seawater. The first is suspension of different carbonates in the ocean at various depths. After a given period of time, the samples are recovered and the rate of dissolution determined by weight loss. The second experimental approach is the determination of dissolution kinetics in the laboratory at different undersaturations. A detailed discussion of the findings of these studies is presented in this section. 

The kinetics of the formation of the magnesium hydroxide and calcium carbonate are functions of the concentration of the bicarbonate ions, the temperature, and the rate of release of CO2 from the solution. At temperatures up to 82°C, CaCO predominates, but as the temperature exceeds 93 0, Mg(OH)2 becomes the principal scale. Thus, ia seawater, there is a considerable tendency for surfaces to scale with an increase in temperature. 

In most of recently published studies, the calcium carbonate dissolution in seawater and in pore water of surface sediments is assumed to follow a kinetic process that can be described by the eqnation (Morse 1978 Keir 1980) ... 

Dolomite is one of the most abundant sedimentary carbonate minerals. However, after years of intense study its mode of formation remains controversial, and its properties under Earth surface conditions are less well known than for most other carbonate minerals. The primary reason for this is that its formation is kinetically hindered by its well-ordered structure. Another problem in understanding dolomite may be as stated by Land (1985) there are dolomites and dolomites and dolomites. Most recently formed marine dolomites are classified as protodolomites. They are far from being perfectly ordered stmcturally and usually contain a few percent excess calcium. Attempts to measure their solubility have been frustrating, but it does appear that they can be one or two orders of magnitude more soluble than ideal dolomite. Thus, seawater may not be supersaturated with respect to protodolomites. 

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