Interannual variability of air‐sea O₂ fluxes and the determination of CO₂ sinks using atmospheric O₂/N₂

Motivated by the use of atmospheric O 2 /N 2 to determine CO 2 sinks under the assumption of negligible interannual variability in air‐sea O 2 fluxes, we examine interannual fluctuations of the global air‐sea flux of O 2 during the period 1980–1998 using a global ocean circulation and biogeochemistry model along with an atmospheric transport model. It is found that both the El Niño/Southern Oscillation (ENSO) cycle and wintertime convection in the North Atlantic are primary drivers of global air‐sea oxygen flux interannual variability. Model estimated extremes of O 2 flux variability are −70/+100 × 10 12 mol/yr (Tmol/yr), where positive fluxes are to the atmosphere. O 2 /N 2 variability could cause an up to ±1.0 PgC/yr error in estimates of interannual variability in land and ocean CO 2 sinks derived from atmospheric O 2 /N 2 observations.