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>

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<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>