New experimental constraints on the magnitude of kinetic C and O isotope fractionation for CO2 hydration

Website: https://www.bco-dmo.org/dataset/865161
Data Type: experimental
Version: 1
Version Date: 2021-11-17

Project
» Experimental study of CO2 hydration in seawater: Mechanism and kinetic isotope effects (CO2 Hydration Mechanism and KIEs)
ContributorsAffiliationRole
Zeebe, RichardUniversity of HawaiiPrincipal Investigator
Uchikawa, JojiUniversity of HawaiiCo-Principal Investigator
Rauch, ShannonWoods Hole Oceanographic Institution (WHOI BCO-DMO)BCO-DMO Data Manager

Abstract
These are experimental data on kinetic C and O isotope fractionation of CO2 hydration. These data were published in Yumol et al., 2020 (doi: 10.1016/j.gca.2020.03.041).


Coverage

Temporal Extent: 2017 - 2019

Methods & Sampling

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.


Data Processing Description

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


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Data Files

File
kinetic_C_and_O_isotope_fract.csv
(Comma Separated Values (.csv), 935 bytes)
MD5:1449d437600f04a9675adeea093a8591
Primary data file for dataset ID 865161

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Related Publications

Yumol, L. M., Uchikawa, J., & Zeebe, R. E. (2020). Kinetic isotope effects during CO2 hydration: Experimental results for carbon and oxygen fractionation. In Geochimica et Cosmochimica Acta (Vol. 279, pp. 189–203). Elsevier BV. https://doi.org/10.1016/j.gca.2020.03.041
Results

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Parameters

ParameterDescriptionUnits
Samplesample number unitless
Ttemperature degrees Celsius
pHpH (NBS) unitless
d13Cdelta 13C, VPDB per mil (‰)
d13C_stdevstandard deviation of d13C per mil (‰)
d18Odelta 18O, VSMOW per mil (‰)
d18O_stdevstandard deviation of d18O per mil (‰)
KIF13_CO2g_BaCO313KIFCO2(g)-BaCO3 refers to the 13C/12C fractionation between CO2(g) and BaCO3, where the d13C values of CO2(g) were calculated using known equilibrium fractionation factors per mil (‰)
KIF13_CO2g_BaCO3_stdevstandard deviation of KIF13_CO2g_BaCO3 per mil (‰)
KIF18_CO2g_BaCO318KIFCO2(g)-BaCO3 refers to the 18O/16O fractionation between CO2(g) and BaCO3, where the d18O values of CO2(g) were calculated using known equilibrium fractionation factors per mil (‰)
KIF18_CO2g_BaCO3_stdevstandard deviation of KIF18_CO2g_BaCO3 per mil (‰)
KIF18_Instkinetic isotope fractionation (KIF)between instantaneously formed HCO3 (inst) and BaCO3 per mil (‰)
KIF18_Inst_stdevstandard deviation of KIF18_Inst per mil (‰)


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Instruments

Dataset-specific Instrument Name
Thermo Finnigan MAT-253 dual-inlet isotope ratio monitoring mass spectrometer (irm-MS)
Generic Instrument Name
Isotope-ratio Mass Spectrometer
Dataset-specific Description
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.
Generic Instrument Description
The Isotope-ratio Mass Spectrometer is a particular type of mass spectrometer used to measure the relative abundance of isotopes in a given sample (e.g. VG Prism II Isotope Ratio Mass-Spectrometer).

Dataset-specific Instrument Name
PICARRO L2130-i isotope and gas concentration analyzer
Generic Instrument Name
Picarro L2130-I deltaD/delta18O Isotopic Water Analyzer
Dataset-specific Description
All H2O samples were analyzed for δ18O at the University of Hawaii on a PICARRO L2130-i isotope and gas concentration analyzer.
Generic Instrument Description
A portable analyser designed for laboratories or field based isotope analysis. It uses Cavity Ring-Down Spectroscopy (CRDS) to measure the spectral signature of the molecule of interest. The instrument includes a closed-loop temperature and pressure control. The L2130-i can be used in all aspects of the water cycle: water vapor, liquid water, or water trapped in solids. It has a typical precision of 0.25 per mil for d18O and 1.20 per mil for dD in solid samples. Corresponding typical values for liquid samples are 0.011 per mil for d18O and 0.038 per mil for dD.


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Project Information

Experimental study of CO2 hydration in seawater: Mechanism and kinetic isotope effects (CO2 Hydration Mechanism and KIEs)

Coverage: University of Hawaii at Manoa


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.



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Funding

Funding SourceAward
NSF Division of Ocean Sciences (NSF OCE)

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