THE O2 BALANCE OF THE ATMOSPHERE: A Tool for Studying the Fate of Fossil-Fuel CO2

Carbon dioxide is a radiatively active gas whose atmospheric concentration increase is likely to affect Earth's climate. CO2 is added to the atmosphere by biomass burning and the combustion of fossil fuels. Some added CO2 remains in the atmosphere. However, substantial amounts are taken up by the oceans and land biosphere, attenuating the atmospheric increase. Atmospheric O2 measurements provide one constraint for partitioning uptake rates between the ocean and the land biosphere. Here we review studies of atmospheric O2 concentration variations and discuss their implications for CO2 uptake by the ocean and the land biosphere. We compare estimates of anthropogenic carbon fluxes from O2 studies with estimates from other approaches and examine the contribution of natural ocean carbon fluxes to atmospheric O2 variations.