Table of Contents

• Dataset Description
  • Methods & Sampling
  • Data Processing Description
• Data Files
• Supplemental Files
• Related Publications
• Parameters
• Instruments
• Project Information
• Funding

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.

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.

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.

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

* 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.

* 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.

* 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.

* Data_Entry.m: 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.

* 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.

* TS2_CAmn.dat: 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.

* 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.

* 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.

* 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.

All of the .dat files are organized as follows:

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

Related publications:

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

Carbonate samples (BaCO3 and experimental NaHCO3) were digested with 104% phosphoric acid at 90 °C in a common acid bath. After purification, the CO2 gases liberated from acid digestion of the samples were analyzed by a Thermo Finnigan MAT253 dual-inlet isotope ratio monitoring mass spectrometer for δ13C, δ18O and Δ47 at the California Institute of Technology.

The codes for the ExClump38 model are developed in the Matlab computational software.

BCO-DMO processing notes:

* added model code and datafiles as supplemental documentation
* added NACHO3 file as data file
* BaCO3 file is added as main data file and viewable in the dataviewer.
* adjusted data parameter names to comply with database requirements.

NSF Award Abstract:
The chemical reaction of carbon dioxide (CO2) with water in the marine environment is a fundamental process that creates carbonic acid (H2CO3) and all of the associated chemical ions (carbonate (CO3); hydrogen ions (H+), and bicarbonate (HCO3-)) that serve as the dominant buffer for pH in the ocean. Dehydration refers to the opposite reaction that releases CO2 gas. By entering into important reactions and serving to control pH, these species govern a wide variety of chemical and biological processes in the ocean. Surprisingly, while the important reactions that involve CO2 hydration and its resulting products have been extensively studied in the ocean, some of the fundamental mechanisms remain poorly understood and datasets are sparse. In particular, almost nothing is known about how the natural isotopes of the carbon and oxygen atoms are involved and this is critically needed to explain observed changes in chemical species and solid calcium carbonate such as that created by coral reefs. This research aims to carefully produce novel experimental data that includes critical measurements of carbon and oxygen isotopes before and after the hydration of CO2 in the ocean. Because these resulting carbonate species are used widely in many studies in the ocean sciences, particularly those examining past climates, this research will have far-reaching influences. Additionally, the results will provide new fundamental insight on exactly how the ocean will take up and respond to changing concentrations of atmospheric CO2 in a changing climate. The research will fund an early-career scientist who is dedicated to graduate and undergraduate education as well as scientific outreach to the community.

While hydration/dehydration of CO2 in the ocean critically influences a variety of marine chemical and biological processes, there are certain aspects of the reaction that are poorly understood. The molecular mechanism is not yet clear, as there are two possible pathways that have been proposed. Additionally, kinetic isotope effects during CO2 have not been well studied, and the data regarding this topic is inconsistent. This research aims to study the carbon and oxygen isotope fractionation, which will not only clarify the molecular mechanism of the reaction but also will add a consistent dataset on kinetic isotope effects. The main challenge in this study is separating the product, HCO3-, from CO2 before re-equilibration, but the researcher will resolve this by rapidly precipitating dissolved carbon as carbonate. Since carbonates formed from the process of hydration are considered critical indicators of water chemistry, biological processes, and the inorganic carbon cycle as a whole and are used in a wide variety of oceanographic research, particularly as paleo-proxies, this research will provide fundamental mechanistic data that will greatly advance studies reaching beyond the physical chemical measurements that will be made here.