The Solubility Of Calcite And Aragonite And The Composition Of Calcite Overgrowths In Seawater And Related Solutions

Date of Award




Degree Name

Doctor of Philosophy (Ph.D.)


Marine and Atmospheric Chemistry


The apparent solubility constants of calcite and aragonite in seawater were determined over a wide range of salinity (5-44('o)/oo) and temperature (5-40(DEGREES)C). Factors not generally carefully considered in previous studies, such as the source of the material, solid to solution ratio, equilibration time and cross-phase contamination, were examined for their influences on the observed solubilities. The effect of solution composition, especially magnesium concentration, on the solubility of calcite and aragonite in seawater related solutions was also investigated. Recently measured thermodynamic solubility products of calcite and aragonite in conjunction with the most recent methods of estimating total ion activity coefficients in complex electrolyte solutions were used to analyze the experimental results. The findings of this study indicate that, within the present precision (approximately 5%) of the K(,c)' and K(,a)' measurements, the influence of coprecipitates in the equilibrium or solubility controlling phases on the solubility behavior of calcium carbonate cannot be discerned.The compositions of calcite overgrowths precipitated from seawater and related solutions were determined at 25(DEGREES)C. The amount of magnesium and strontium incorporated within the calcite crystal lattice was independent of the precipitation rate over the range investigated. Precipitation rates were varied by approximately an order of magnitude, while the saturation state varied from 3 to 17 depending on the solution composition. However, the overgrowth composition did vary with the magnesium to calcium concentration ratio in solution. The amount of magnesium incorporated in the overgrowth is not directly proportional to the magnesium to calcium concentration ratio in solution over the whole range studied (1-20). Below a ratio of 7.5, the composition of the overgrowth is enriched in magnesium carbonate relative to what is predicted by the constant distribution coefficient measured above a ratio of 7.5. The increased magnesium in the overgrowths precipitated from solutions with a ratio below 7.5 correlates with the relative enrichment of magnesium ions in the surface or adsorbed layers. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of school.) UMI



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