Experimental Constraints on Clumped Isotope Fractionation During BaCO3 Precipitation
Experimental Constraints on Clumped Isotope Fractionation During BaCO3 Precipitation
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DOI：
10.1029/2021gc010249
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发表时间：
2022-03
期刊：
影响因子：
3.7
通讯作者：
Yangrui Guo;W. Deng;G. Wei
中科院分区：
文献类型：
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作者：
Yangrui Guo;W. Deng;G. Wei
通过碳酸盐簇同位素 (Δ47) 测温法进行可靠的温度重建需要碳酸盐生长过程中的同位素平衡。然而，许多碳酸盐矿物生长速度很快，并且表现出不平衡的同位素状态。由碳酸盐生长特有的动力学同位素效应 (KIE) 引起的碳酸盐 Δ47 不平衡仍不清楚，需要实验限制。在这里，我们提出了一系列快速毒重石 (BaCO3) 沉淀实验，旨在在各种 pH 和温度条件下从溶解的无机碳溶液中单向沉淀 BaCO3 过程中限制大量碳、氧和团块同位素分馏。我们发现，BaCO3 的快速生长会导致 HCO3 主导溶液中的 δ13C、δ18O 和 Δ47 值降低，尤其是在低温下。我们的实验提供了与碳酸盐快速生长及其温度依赖性相关的动力学分馏因子（KFF）的约束。 δ13C 和 δ18O 的 KFF 与之前的实验估计大致一致，尽管 HCO3-主导溶液中 BaCO3 沉淀的 Δ47 KFF 与早期的理论估计不一致，因此需要重新评估与碳酸盐生长相关的当前 KIE 模型。我们的结果清楚地验证了碳酸盐沉淀过程中对 CO32− 途径的偏好，对天然碳酸盐的新同位素分馏模型具有重要意义。本研究中发现的 Δ47 和 δ18O 之间的分馏关系可以更精确地识别与碳酸盐快速生长相关的 KIE。
Reliable temperature reconstruction by carbonate clumped isotope (Δ47) thermometry requires isotopic equilibrium during carbonate growth. However, many carbonate minerals grow at high rates and exhibit disequilibrium isotopic states. Carbonate Δ47 disequilibrium arising from kinetic isotope effects (KIEs) specific to carbonate growth still remains unclear, and requires experimental constraints. Here we present a series of rapid witherite (BaCO3) precipitation experiments intended to constrain bulk carbon, oxygen and clumped isotopic fractionation during unidirectional precipitation of BaCO3 from dissolved inorganic carbon solutions under various pH and temperature conditions. We found that rapid BaCO3 growth can lead to lower δ13C, δ18O, and Δ47 values in HCO3−‐dominated solutions, especially at low temperatures. Our experiments provide constraints on kinetic fractionation factors (KFFs) associated with the rapid carbonate growth and their temperature dependence. KFFs for δ13C and δ18O are broadly consistent with previous experimental estimates, although the Δ47 KFF for BaCO3 precipitation from HCO3−‐dominated solution is not consistent with an earlier theoretical estimate, necessitating a re‐evaluation of the current model of the KIE associated with carbonate growth. Our results clearly verify a preference for the CO32− pathway during carbonate precipitation, with important implications for new isotope fractionation models for natural carbonates. The fractionation relationship between Δ47 and δ18O found in this study allows more precise identification of KIEs associated with rapid carbonate growth.