Kinetics of δ18O and Δ47 equilibration in the dissolved carbonate system revealed by time-series quantitative inorganic carbonate precipitation experiments and numerical modeling.

<p>We analyzed oxygen and clumped isotope values of inorganic BaCO₃ samples from Uchikawa and Zeebe (2012), which were quantitatively precipitated from NaHCO₃ solutions over the course of isotopic equilibration. These time-series quantitative inorganic BaCO₃ precipitation experiments were conducted under a normal condition at 25 °C and in the presence of varying amount of carbonic anhydrase enzyme that is known to catalyze CO₂ hydration and known to be possessed by a range of marine calcareous organisms.</p>

<p>Summary of new δ¹⁸O and Δ₄₇ values measured on BaCO₃ samples from Uchikawa and Zeebe (2012). These BaCO₃ samples were quantitatively precipitated from NaHCO₃ solutions at various times over the course of isotopic equilibration at 25 °C. Also included in the file are δ¹⁸O and Δ₄₇ values of the NaHCO₃ used in the experiments and original δ¹⁸O data by Uchikawa and Zeebe (2012) on the BaCO₃ samples and experimental NaHCO₃ and H₂O.</p>

<p>We also developed a fully open-sourced numerical codes (ExClump38 model) that can simulate the time-course of oxygen and clumped isotope equilibration in the dissolved carbonate system as a function of temperature, pH and carbonic anhydrase concentration by extending the work of Chen et al. (2018). By extending the framework of earlier work (Chen et al., 2018), this model tracks temporal change in the abundance of singly (i.e., δ¹³C and δ¹⁸O) and doubly-substituted (i.e., Δ₄₇) aqueous CO₂ and the sum of HCO₃- and CO₃^2- (referred to as the dissolved carbonate pool: DCP) from a given initial condition/state to the expected isotopic equilibrium in the dissolved carbonate system.</p>

<p><strong>Matlab codes for the ExClump38 model and accompanying experimental data.</strong> These data are attached to this datapackage as a supplemental file. The zipfile contains 9 different files. Descriptions of the files:</p>

<p>* ExClump38.m: A Matlab m-file for the ExClump38 model, which can simulate the progress of isotopic (δ¹⁸O and Δ₄₇) equilibration in the dissolved carbonate system as a function of temperature, pH and carbonic anhydrase activity.</p>

<p>* IsoEquilibration.m: A Matlab m-file containing a set of differential equations to be solved in the ExClump38 model. This file needs to be downloaded with ExClump.m and stored in the same folder.</p>

<p>* Model_Constants.m: A Matlab m-file containing a set of equilibrium and kinetic rate constants as well as isotope fractionation factors used in the ExClump38 model. This file needs to be downloaded with ExClump.m and stored in the same folder.</p>

<p>* Data_Entry.m:<u> </u>A supplementary Matlab m-file for the entry of our experimental data as well as the initial condition for each experimental series for the ExClump38 model.</p>

<p>* TS2.dat: A supplementary .dat file needed for the entry of isotope data from the “TS-2” experimental series. The TS-2 experiments were conducted at T = 25 °C, pH_NBS = 8.9 and in the absence of carbonic anhydrase enzyme.</p>

<p>* TS2_CAmn.dat:<u> </u>A supplementary .dat file needed for the entry of isotope data from the “TS-mnCA” experimental series. The TS-2 experiments were conducted at T = 25 °C and pH_NBS = 8.9, with the addition of carbonic anhydrase enzyme to a concentration of 3.7 nM.</p>

<p>* TS2_CA2.dat: A supplementary .dat file needed for the entry of isotope data from the “TS-2CA” experimental series. The TS-2 experiments were conducted T = 25 °C and pH_NBS = 8.9, with the addition of carbonic anhydrase enzyme to a concentration of 9.3 nM.</p>

<p>* TS2_CA3.dat: A supplementary .dat file needed for the entry of isotope data from the “TS-3CA” experimental series. The TS-2 experiments were conducted T = 25 °C and pH_NBS = 8.9, with the addition of carbonic anhydrase enzyme to a concentration of 19 nM.</p>

<p>* SS18.dat: A supplementary .dat file needed for the entry of isotope data from similar experiments done by Staudigel and Swart (2018) at T = 25 °C.</p>

<p>All of the .dat files are organized as follows:</p>

<p>* 1st column (far left): pH_NBS of the experimental NaHCO₃ solution.<br />
* 2nd column: Elapsed equilibration time (minutes)<br />
* 3rd column: δ¹³C of BaCO₃ samples (‰, VPDB)<br />
* 4th column: δ¹³C measurement uncertainty for BaCO₃ (1σ standard error, ‰ VPDB)<br />
* 5th column: δ¹⁸O of BaCO₃ samples (‰, VPDB)<br />
* 6th column: δ¹⁸O measurement uncertainty for BaCO₃ (1σ standard error, ‰ VSMOW)<br />
* 7th column: δ¹⁸O of experimental H₂O (‰, VSMOW) from Uchikawa &amp; Zeebe (2012)<br />
* 8th column: δ¹⁸O measurement uncertainty for H₂O (1σ standard error, ‰ VSMOW)<br />
* 9th column: Δ₄₇ of BaCO₃ samples (‰, ARF)<br />
* 10th column (far right): Δ₄₇ measurement uncertainty (1σ standard error, ‰ ARF)</p>

<p>&nbsp;</p>

<p>Related publications:</p>

<p>* Data contained original data for d18O of H2O from&nbsp; Uchikawa, J., &amp; Zeebe, R. E. (2012)<br />
* The numerical model is adopted and modified from Chen et al. (2018)<br />
* The model is also applied to (their dataset is attached as SS18): Staudige &amp; Swart (2018)</p>

本研究分析了Uchikawa与Zeebe（2012）产出的无机碳酸钡（BaCO₃）样品的氧同位素与团簇同位素（clumped isotope）值。该批样品通过碳酸氢钠（NaHCO₃）溶液在同位素平衡过程中定量沉淀得到。本次时间序列定量无机碳酸钡沉淀实验于25℃标准条件下开展，实验体系中添加了不同梯度浓度的碳酸酐酶（carbonic anhydrase）——该酶可催化二氧化碳（CO₂）水合反应，且广泛存在于各类海洋钙化生物体内。

本数据集包含Uchikawa与Zeebe（2012）碳酸钡样品实测的全新δ¹⁸O与Δ₄₇值汇总。该批碳酸钡样品由碳酸氢钠溶液在25℃下的同位素平衡过程中，于不同时间点定量沉淀得到。数据集文件中同时收录了实验所用碳酸氢钠的δ¹⁸O与Δ₄₇值，以及Uchikawa与Zeebe（2012）原始发表的碳酸钡样品、实验用碳酸氢钠及水（H₂O）的δ¹⁸O数据。

本研究还开发了完全开源的数值代码（ExClump38模型），该模型基于Chen等人（2018）的研究拓展而来，可模拟溶解碳酸盐体系中氧同位素与团簇同位素平衡的时间演化过程，其演化过程受温度、pH值及碳酸酐酶浓度调控。本模型继承了Chen等人（2018）的研究框架，可追踪从指定初始状态出发，水溶液中单一取代（即δ¹³C与δ¹⁸O）与双重取代（即Δ₄₇）的二氧化碳（CO₂），以及碳酸氢根（HCO₃⁻）与碳酸根（CO₃²⁻）总和（定义为溶解碳酸盐库（dissolved carbonate pool, DCP））的丰度随时间的变化，直至体系达到理论同位素平衡状态。

**ExClump38模型配套Matlab代码与实验数据集**。本数据包以补充文件形式附入上述数据。压缩包中共包含9个文件，各文件说明如下：

* ExClump38.m：ExClump38模型的Matlab脚本文件，可模拟溶解碳酸盐体系中同位素（δ¹⁸O与Δ₄₇）平衡随温度、pH值及碳酸酐酶活性的演化进程。
* IsoEquilibration.m：ExClump38模型所需求解的微分方程组对应的Matlab脚本文件。该文件需与ExClump.m一同下载并置于同一文件夹内。
* Model_Constants.m：ExClump38模型中所用的平衡常数、动力学速率常数及同位素分馏系数对应的Matlab脚本文件。该文件需与ExClump.m一同下载并置于同一文件夹内。
* Data_Entry.m：用于录入本研究实验数据及ExClump38模型各实验序列初始条件的补充Matlab脚本文件。
* TS2.dat：用于录入“TS-2”实验序列同位素数据的补充.dat文件。TS-2实验于温度T=25℃、pH_NBS=8.9且无碳酸酐酶添加的条件下开展。
* TS2_CAmn.dat：用于录入“TS-mnCA”实验序列同位素数据的补充.dat文件。该实验于T=25℃、pH_NBS=8.9条件下开展，体系中添加了浓度为3.7 nM的碳酸酐酶。
* TS2_CA2.dat：用于录入“TS-2CA”实验序列同位素数据的补充.dat文件。该实验于T=25℃、pH_NBS=8.9条件下开展，体系中添加了浓度为9.3 nM的碳酸酐酶。
* TS2_CA3.dat：用于录入“TS-3CA”实验序列同位素数据的补充.dat文件。该实验于T=25℃、pH_NBS=8.9条件下开展，体系中添加了浓度为19 nM的碳酸酐酶。
* SS18.dat：用于录入Staudigel与Swart（2018）于25℃下开展的同类实验同位素数据的补充.dat文件。

所有.dat文件的格式均如下所示：
* 第1列（最左侧）：实验用碳酸氢钠溶液的pH_NBS值。
* 第2列：同位素平衡耗时（单位：分钟）
* 第3列：碳酸钡样品的δ¹³C值（单位：‰，VPDB标准）
* 第4列：碳酸钡样品δ¹³C的测量不确定度（1σ标准误，单位：‰，VPDB标准）
* 第5列：碳酸钡样品的δ¹⁸O值（单位：‰，VPDB标准）
* 第6列：碳酸钡样品δ¹⁸O的测量不确定度（1σ标准误，单位：‰，VSMOW标准）
* 第7列：Uchikawa与Zeebe（2012）实测的实验用水（H₂O）的δ¹⁸O值（单位：‰，VSMOW标准）
* 第8列：实验用水δ¹⁸O的测量不确定度（1σ标准误，单位：‰，VSMOW标准）
* 第9列：碳酸钡样品的Δ₄₇值（单位：‰，ARF标准）
* 第10列（最右侧）：碳酸钡样品Δ₄₇的测量不确定度（1σ标准误，单位：‰，ARF标准）

相关引用文献：
* 本数据集包含Uchikawa, J. 与 Zeebe, R. E.（2012）发表的实验用水δ¹⁸O原始数据
* 本数值模型基于Chen等人（2018）的研究改编而来
* 本模型同时应用于Staudigel与Swart（2018）的数据集（该数据集以SS18文件形式附入本数据包）