Reconstructing the recent carbon cycle from atmospheric CO2, δ13C and O2/N2 observations*

This paper presents an attempt to recover the space–time structure of fluxes of CO₂ to the atmosphere over the period 1980–1995 from atmospheric concentration and isotopic composition measurements. The technique used is Bayesian synthesis inversion in which sources are aggregated into large regions and their strengths adjusted to match observed concentrations. The sources are constrained by prior estimates based on a priori knowledge. The input data are atmospheric CO₂ concentration measurements from the NOAA/CMDL network, 13CO₂ composition and O²/N² ratios measured at Cape Grim, Tasmania by CSIRO Atmospheric Research. The primary findings are a relatively large long-term mean ocean uptake of CO₂, and seasonal fluxes over land with similar integrated magnitude, but smaller peak amplitude, compared with those derived by Fung and co-workers. Predicted interannual variability is smaller than reported in previous studies. The largest contributor is the oceanic tropics where fluxes vary on the time scale of the southern oscillation. There is evidence of longer time-scale variation in land uptake. Increases in ocean uptake and northern land uptake in the early 1990s are consistent with a response to the Mt. Pinatubo eruption.