High‐Frequency Correlations Between Winds and p CO 2 Change the California Coastal Upwelling System From a CO 2 Sink to a Source

Net sea‐air CO 2 flux can be calculated from observations of seawater and atmosphere partial pressure of CO 2 ( p CO 2 ) and estimates of the gas transfer velocity. Typically, these quantities are calculated at a monthly resolution, which misses potentially important high‐frequency temporal variability. Here, we calculated sea‐air CO 2 flux at a 3‐hourly resolution using a 10‐year mooring data set (2011–2020) from the central California coastal upwelling region. We identified a significant flux of CO 2 from the ocean to the atmosphere due to a positive correlation between seawater p CO 2 and wind speed at timescales of hours to days, particularly during the late spring and early summer upwelling season. Accounting for this variability changes the region from a net sink to a net source of CO 2 to the atmosphere. These findings imply that CO 2 fluxes computed from monthly‐resolution data may miss important shorter‐term variability that contributes to a net outgassing of CO 2 from the ocean.