Fortunat Joos, and Thomas F. Stocker, Climate and Environmental
Physics, Physics Insitute, University of Bern, Bern, Switzerland
1Now at Institute of Geophysics and Planetary Physics, University of California, Los Angeles, Los Angeles, California, USA
Carbon budgets inferred from measurements of the atmospheric oxygen to nitrogen ratio (O2/N2) are revised considering sea-to-air fluxes of O2 and N2 in response to global warming and volcanic eruptions. Observational estimates of changes in ocean heat content are combined with a model-derived relationship between changes in atmospheric (O2/N2) due to oceanic outgassing and heat fluxes to estimate ocean O2 outgassing. The inferred terrestrial carbon sink for the 1990s is reduced by a factor of two compared with the most recent estimate by the Intergovernmental Panel on Climate Change (IPCC). This also improves the agreement between calculated ocean carbon uptake rates and estimates from global carbon cycle models, which indicate a higher ocean carbon uptake during the 1990s than the 1980s. The simulated decrease in oceanic O2 concentrations is in qualitative agreement with observed trends in oceanic O2 concentrations.