Dataset: Experimental data on kinetic C and O isotope fractionation of CO2 hydration

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.