Air‐sea CO 2 fluxes in the near‐shore and intertidal zones influenced by the California Current

The study of air‐sea CO 2 fluxes ( F CO 2 ) in the coastal region is needed to better understand the processes that influence the direction and magnitude of F CO 2 and to constrain the global carbon budget. We implemented a 1 year (January through December 2009) paired study to measure F CO 2 in the intertidal zone (the coastline to 1.6 km offshore) and the near‐shore (∼3 km offshore) off the north‐western coast of Baja California (Mexico); a region influenced by year‐round upwelling. F CO 2 was determined in the intertidal zone via eddy covariance; while in the near‐shore using mooring buoy sensors then calculated with the bulk method. The near‐shore region was a weak annual net source of CO 2 to the atmosphere (0.043 mol CO 2 m −2 y −1 ); where 91% of the outgassed F CO 2 was contributed during the upwelling season. Sea surface temperature (SST) and Δ p CO 2 (from upwelling) showed the strongest relationship with F CO 2 in the near‐shore, suggesting the importance of meso‐scale processes (upwelling). F CO 2 in the intertidal zone were up to four orders of magnitude higher than F CO 2 in the near‐shore. Wind speed showed the strongest relationship with F CO 2 in the intertidal zone, suggesting the relevance of micro‐scale processes. Results show that there are substantial spatial and temporal differences in F CO 2 between the near‐shore and intertidal zone; likely a result of heterogeneity. We suggest that detailed spatial and temporal measurements are needed across the coastal oceans and continental margins to better understand the mechanisms which control F CO 2 , as well as reduce uncertainties and constrain regional and global ocean carbon balances.