Prevalence of strong vertical CO2 and O2 variability in the top meters of the ocean

The gradient in the partial pressure of carbon dioxide (pCO(2)) across the air-sea boundary layer is the main driving force for the air-sea CO2 flux. Global data bases for surface seawater pCO(2) are actually based on pCO(2) measurements from several meters below the sea surface, assuming a homogeneous distribution between the diffusive boundary layer and the upper top meters of the ocean. Compiling vertical profiles of pCO(2), temperature, and dissolved oxygen in the upper 5-8 m of the ocean from different biogeographical areas, we detected a mean difference between the boundary layer and 5 m pCO(2) of 131 mu atm. Temperature gradients accounted for only 11% of this pCO(2) gradient in the top meters of the ocean; thus, pointing to a heterogeneous biological activity underneath the air-sea boundary layer as the main factor controlling the top meters pCO(2) variability. Observations of pCO(2) just beneath the air-sea boundary layer should be further investigated in order to estimate possible biases in calculating global air-sea CO2 fluxes.