Oxygen isotopes of calcite precipitated at high ionic strength: CaCO3-DIC fractionation and carbonic anhydrase inhibition
Oxygen isotopes of calcite precipitated at high ionic strength: CaCO3-DIC fractionation and carbonic anhydrase inhibition
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DOI：
10.1016/j.gca.2022.01.028
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发表时间：
2022-02
影响因子：
5
通讯作者：
E. Olsen;J. Watkins;L. Devriendt
中科院分区：
文献类型：
--
作者：
E. Olsen;J. Watkins;L. Devriendt
背景电解质影响方解石的沉淀和溶解速度，因此有可能影响方解石和溶解的无机碳(DIC)物种之间的动力学同位素分馏。我们从氯化钠-氯化钙溶液中生长了无机方解石(T=0.25℃，pH=0.8.3，晶体生长速度−=10.10−6.3±0.3molm−2s−1)，以测试潜在的离子强度对方解石和同位素平衡的无机碳库(αc/eIC)之间氧同位素分馏的影响。方解石是在来自牛红细胞的碳酸氢酶(Bca)的存在下生长的，以促进DIC池的同位素平衡。当NaC l浓度达到0.35时，没有发现离子强度对αc/EIC有影响的证据(1000lnαc/w=228.0±100.1；n=17.7)。对于用0.35微米的[氯化钠]进行的实验，由于氯化钠对生物碱的抑制作用，DIC池不能与水保持同位素平衡。在离子强度接近或高于海水离子强度的溶液中，可能需要使用其他类型的CA来维持DIC的同位素平衡。氧同位素结果被成功地用跟踪每种DIC物种和CaCO3同位素组成的CO2供给溶液的同位素盒模型模拟。实验和模拟结果表明，BCA的有效性随着[NaC l]的增加呈指数下降。我们量化了盐对催化CO2水合速率常数kcat/Km的影响，它与BCA的浓度有关。盐效应可以在生物矿化模型中实现，有可能扩大我们对海洋生物中氧同位素重要作用的了解。
Background electrolytes affect calcite precipitation and dissolution rates and hence have the potential to impact kinetic isotope fractionation between calcite and the dissolved inorganic carbon (DIC) species. We grew inorganic calcite from NaCl-CaCl2solutions (T= 25 °C, pH = 8.3, and crystal growth rate = 10−6.3 ± 0.3mol m−2s−1) to test for potential ionic strength effects on the oxygen isotope fractionation between calcite and an isotopically equilibrated inorganic carbon pool (αc/EIC). Calcite was grown in the presence of the enzyme carbonic anhydrase from bovine erythrocytes (bCA) to promote isotopic equilibration of the DIC pool.No evidence of an ionic strength effect on αc/EICwas found for NaCl concentrations up to 0.35 M (1000lnαc/w= 28.0 ± 0.1;n= 7). For experiments conducted with [NaCl] > 0.35 M, the DIC pool could not be maintained in isotopic equilibrium with water due to the inhibitory effect of NaCl on bCA. The use of other types of CA may be required to maintain isotopic equilibration of DIC in solution with ionic strength close to or above that of seawater.The oxygen isotope results were modeled successfully with an isotopic box model for a CO2-fed solution that tracks the isotopic composition of each DIC species and CaCO3. The experimental and modeling results suggest that the efficacy of bCA decreases exponentially with increasing [NaCl]. We quantify the salt effect on the quantitykcat/KM, which relates the catalyzed rate constant for CO2hydration to the concentration of bCA. The salt effect can be implemented in models of biomineralization with potential to extend our knowledge of oxygen isotope vital effects in marine organisms.