Estimating regional terrestrial carbon fluxes for the Australian continent using a multiple-constraint approach: II. The Atmospheric constraint

Bayesian synthesis inversion was applied to in-situ hourly CO₂ concentrations measured at Cape Grim, Australia to refine the estimates of monthly mean gross photosynthesis, total ecosystem respiration and net ecosystem production by the CSIRO Biospheric Model (CBM) for eight regions in Australia for the period 1990–1998. It was found that in-situ measurements of hourly CO₂ concentrations at Cape Grim could provide significant information about the carbon fluxes from Tasmania, central-south and south-east Australia only. The process-based model, CBM, overestimates the ecosystem respiration during summer in south-east Australia, but underestimates ecosystem respiration in Tasmania and central-south Australia. It was concluded that the respiration submodel of CBM should be improved to account for the seasonal variation in the plant and soil respiration parameters in south-east Australia. For the whole period of 1990 to 1998, the mean net ecosystem productions of terrestrial ecosystems in Tasmania, central-south Australia and south-east Australia were estimated to be, respectively, 6 ± 10, 7 ± 27 and −64 ± 18 Mt C yr⁻¹. The yearly uptake rate (being negative) of the terrestrial ecosystems in south-east Australia was smallest (−42 ± 55 Mt C yr⁻¹) in 1998 and largest (−91 ± 52 Mt C yr⁻¹) in 1992.