The measurement of atmospheric O 2 concentrations and related oxygen budget have been used to estimate terrestrial and oceanic carbon uptake. However, a discrepancy remains in assessments of O 2 exchange between ocean and atmosphere (i.e. air-sea O 2 flux), which is one of the major contributors to uncertainties in the O 2 -based estimations of the carbon uptake. Here, we explore the variability of air-sea O 2 flux with the us...