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

将在受控条件下评估硼、碳和氧的同位素分馏。从这些无机钙化实验中得到的准确的平衡分馏系数将为评估生物成因不平衡钙化的潜在程度提供一个通用的标准。无机钙化过程中811B、813C和818O分馏的同时实验分析很有吸引力，因为最近的生物成因钙化理论提出了813C和818O的相关动力学平衡作为钙化速率的函数。根据这个模型，在钙化过程中，同位素不平衡是由速度依赖的无机水化和羟化反应引起的。由于钙化速率在一定程度上受控于钙化部位的溶质pH，因此对pH敏感的811B分馏应与813C和818O动力学不平衡相关联。利用pH控制的连续搅拌釜式反应器(CSTR)研究了温度和沉淀速率(溶质化学)对晶种无机方解石沉淀的同位素组成的影响。在这些实验中，将使用经过精心挑选的试剂级方解石种子材料，其矿物学得到确认，并具有已知的同位素组成，以控制由于矿物学差异(例如文石与方解石)而产生的分馏效应。

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).