Table of Contents

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

We quasi-instantaneously precipitated BaCO3 by bubbling CO2 gas that was in full isotopic equilibrium with NaHCO3 solution through highly concentrated BaCl2 solutions buffered at alkaline pH. As the CO2 gas entered the BaCl2 solution through a fritted disk, a small fraction of it was transformed into HCO3− via diffusion and hydration across the thin-film of the bubbles. The resultant HCO3− immediately reacted with Ba2+ in the solution and precipitated as BaCO3. By measuring δ13C and δ18O values of the BaCO3 samples and experimental NaHCO3 and H2O and applying oxygen mass-balance, we constrained kinetic C and O isotope effect associated with the hydration of CO2.

All carbonate samples (BaCO3 and NaHCO3) were analyzed at the University of California Santa Cruz for δ13C and δ18O, using a Thermo Finnigan MAT-253 dual-inlet isotope ratio monitoring mass spectrometer (irm-MS) coupled to a Kiel IV carbonate device. The samples were reacted with orthophosphoric acid and the resultant CO2 gas was analyzed by the irm-MS. Note that all samples were treated as if they are calcite, which means that we did not apply the corrections to account for BaCO3-specific and NaHCO3-specific acid fractionation factor.

All H2O samples were analyzed for δ18O at the University of Hawaii on a PICARRO L2130-i isotope and gas concentration analyzer.

BCO-DMO Processing:
- renamed fields to comply with BCO-DMO naming conventions;
- created separate columns for standard deviations.

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.