Regional Uncertainty Analysis in the Air–Sea CO2 Flux

Accurate quantification of the ocean carbon sink and its associated uncertainty is critical for guiding international policy efforts and the accurate monitoring, reporting, and verification of marine carbon dioxide removal interventions. Here we use error propagation to break down the uncertainty in air–sea ${\text{CO}}_2$ flux into three primary sources: the gas transfer velocity $\left(k_w\right)$, the solubility $\left(K_0\right)$, and the difference in partial pressure of ${\text{CO}}_2$ $\left(\Delta {\text{pCO}}_2\right)$ between the ocean and atmosphere. These are further decomposed into uncertainties from the underlying variables (e.g., temperature and salinity used to calculate $K_0$). We find gas transfer velocity is the dominant term driving uncertainty in the air–sea ${\text{CO}}_2$ flux. $K_0$ and $\Delta {\text{pCO}}_2$ drive uncertainty near river mouths and eastern boundary upwelling zones, respectively. This methodology provides a foundation for a comprehensive quantification of uncertainty and its underlying drivers. The software used in this study is publicly available (Gloege, 2024, https://doi.org/10.5281/zenodo.13851044).