Carbon isotopic fractionation and precipitation kinetics of synthetic aragonite and calcite grown in dilute solutions

An open system chemo-stat technique was used to study the carbon isotope fractionation and kinetics associated with the heterogeneous growth of aragonite and calcite in dilute solutions. Pure aragonite or calcite seed material was used as the substrate for crystal growth. Aragonite and calcite overgrowths were precipitated at 10;Precipitation rate is shown to be strongly a function of saturation state at each temperature. Empirical reaction orders calculated from the saturation state-precipitation rate relation for aragonite are independent of temperature while rate constants covary with temperature. Calcite reaction orders and rate constants are highly variable and show no relation to temperature. This variability may be explained in terms of the relationship of precipitation rate to solution Pco;Temperature and precipitation rate effects on carbon isotopic fractionation during the precipitation process were characterized from these same experimental runs. Calcite-bicarbonate enrichment factors ;Aragonite-bicarbonate enrichment factors...