The O-2 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 atmospher e by biomass burning and the combustion of fossil fuels. Some added CO2 rem ains in the atmosphere. However, substantial amounts are taken up by the oc eans and land biosphere, attenuating the atmospheric increase. Atmospheric O-2 measurements provide one constraint for partitioning uptake rates betwe en the ocean and the land biosphere. Here we review studies of atmospheric O-2 concentration variations and discuss their implications for CO2 uptake by the ocean and the land biosphere. We compare estimates of anthropogenic carbon fluxes from O-2 studies with estimates from other approaches and exa mine the contribution of natural ocean carbon fluxes to atmospheric O-2 var iations.