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

硼、碳和氧的同位素分馏将在受控条件下进行评价。从这些无机钙化实验中精确的平衡分馏因子将提供一个共同的尺度来评估生物不平衡钙化的潜在程度。无机钙化过程中8 - 11b、8 - 13c和8 - 18o分选的同时实验分析是有吸引力的，因为最近的生物源钙化理论提出8 - 13c和8 - 18o的相关动力学不平衡是钙化速率的函数。根据该模型，在钙化过程中，同位素不平衡是由速率依赖的无机水化和羟基化反应引起的。由于钙化速率在一定程度上受钙化部位溶质pH的控制，因此对pH敏感的811b分馏应与813c和818o的动力学不平衡有关。采用pH控制连续搅拌槽式反应器（CSTR）评价温度和沉淀速率（溶质化学）对种子无机方解石沉淀同位素组成的影响。在这些实验中，将使用经过XRD确认的矿物学和已知同位素组成的精心挑选的试剂级方解石种子材料来控制由于矿物学差异（例如文石和方解石）而产生的分选效果。

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).