Experimental Determination of Equilibrium and Kinetic Fractionation of Boron, Carbon, and Oxygen Isotopes during Carbonate Precipitation

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Istopic fractionation of boron, carbon and oxygen will be evaluated under controlled conditions. Accurate equilibrium fractionation factors from these inorganic calcification experiments will provide a common yardstick against which to evaluate the potential magnitude of biogenic disequilibrium calcification. Simutaneous experimental analysis of 8 11 B, 8 13 C, and 8 18 O fractionation during inorganic calcificaiton is attractive because a recent theory of biogenic calcification proposes correlated kinetic dissequilibria in 8 13 C and 8 18 O as a function of calcification rate. According to this model, isotopic disequilibrium arises from rate dependent inorganic hydration and hydroxylation reactions during calcification. Because calcification rate is controlled to some extent by solute pH at the site of calcification, 8 11 B fractionation, which is pH sensitive, should be correlated with 8 13 C, and 8 18 O kinetic disequilibrium. A pH controlled, continuously stirred tank reactor (CSTR) will be used to evaluate the effects of temperature and precipitaiton rate (solute chemistry) on the isotopic composition of seeded inorganic calcite precipitation. Carefully selected reagent grade calcite seed material with XRD confirmed mineralogy and known isotopic composition will be employed during these experiments to control for fractionation effects due to minerological differences (e.g. aragonite vs. calcite).