Computer Science
Scientific paper
Jul 1985
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1985gecoa..49.1503w&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 49, Issue 7, pp.1503-1513
Computer Science
16
Scientific paper
The dissolution kinetics of shallow water marine carbonates (low-Mg calcite, aragonite and Mg-calcites) were investigated in seawater ( S = 35) at 25°C and a P CO 2 of 10 -2.5 atm. using the pH-stat method. Carbonate dissoluton rates ( moles g -1 hr -1 ) fit the empirical kinetic expression, R = k (1 - ) n , where R = dissolution rate, k = rate constant, = saturation state, and n = order of reaction. Reaction orders were near 2.9 for low-Mg calcites, 2.5 for aragonites and 3.4 for Mg-calcites. The rate constant, k , expressed as moles g -1 hr -1 , varied by nearly a factor of ten for the different samples, reflecting differences in amount of reactive surface area. Reactive surface area of the biogenic phases ranged from 0.3% to 66% of the total surface area determined by the BET gas adsorption method. The discrepancy between reactive and total surface area was greatest for samples with high BET surface areas (> 1 m 2 g -1 ) and delicate microstructures. Relative dissolution rates of the various biogenic carbonates as a function of seawater calcium carbonate ion molal product (IMP) were related to both mineral stability and grain microstructure. In seawater undersaturated with respect to aragonite, finely crystalline aragonites dissolved more rapidly than thermodynamically less stable high Mg-calcites (15-18 mole% MgCO 3 ) with lower reactive surface areas. Therefore, under certain conditions, differences in grain microstructural complexity can override thermodynamic constraints and lead to selective dissolution of a thermodynamically more stable mineral phase.
Morse John W.
Walter Lynn M.
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