UC Berkeley

The authors regret that in the original article, the kinetic fractionation factors (KFFs) related to the CO2 hydroxylation reaction (CO2(aq) + OH– → HCO3–) were calculated using atmospheric δ18OCO2 values of 0.0 ± 0.5 ‰ (VPDB) while the correct values are 10.25 ± 0.5 ‰ (VPDB). We erroneously employed the atmospheric δ18OCO2 values from the NOAA CO2 global network (Trolier et al., 1996) by not converting atmospheric δ18OCO2 from the VPDB-CO2 scale to the VPDB scale through the following expression (e.g. Srivastava and Verkouteren, 2018): [Formula presented] This correction affects the reported oxygen isotope KFFs for CO2 hydroxylation to form HCO3– prior to CaCO3 precipitation. We have corrected Table 7 and Fig. 13 accordingly (see below). The composition of atmospheric CO2 was also incorrectly plotted on the VPDB scale in Figs. 1, 8 and 15 of our original manuscript based on previous works (Fig. 8 in Clark and Fontes, 1990; Fig. 2 in Clark et al., 1992). Importantly, the modelling outputs and main conclusions of the original article are not affected by these corrections. Nevertheless, the updated KFFs resolve an apparent discrepancy between the laboratory and field studies in our original article. Moreover, the oxygen isotope KFF for CO2 hydroxylation now displays a positive temperature dependence over the 4–28 °C range, which was not statistically significant in the original article (Fig. 13c, r2 = 0.86, n = 10, p-value <0.01): [Formula presented]where T is in °C, the uncertainty represents one standard error, and KFF* is the oxygen isotope kinetic fractionation factor between the HCO3– product and ‘CO2(aq) + H2O’ expressed as the per mil deviation from unity: [Formula presented] Here and in the original article, the KFF is expressed relative to the weighted sum ‘CO2(aq) + H2O’ rather than ‘CO2(aq) + OH–’ (i.e. the reactants) to avoid the uncertainty on the OH––H2O fractionation factor (Zeebe, 2020; Bajnai and Herwartz, 2021). δ18O and oxygen KFF values in bold have been corrected by converting atmospheric δ18OCO2 values from the VPDB-CO2 scale to the VPDB scale using Eq. (1). The authors apologize for any inconvenience caused.