Changes in Gross and Net CO2 Fluxes Over the Last two Decades Deduced from CO2, 13C, and 18O Atmospheric Measurements

Year-to-year fluctuations in the growth rate of atmospheric CO2 are largely contributed by the effects of climate variability on terrestrial CO2 fluxes. High precision atmospheric 13C time series can be used in so called "double deconvolutions" to separate land from oceans fluxes. But 13C data alone provide almost no information on the interannual variability of the gross fluxes (Photosynthesis, Ecosystem Respiration, Combustion) controlling the carbon balance of terrestrial ecosystems. We used records of 18O in CO2 in addition to 13C and CO2 from the CMDL and CSIRO global air sampling networks, which span over the past two decades into a bayesian 'triple deconvolution". This method allows to infer year-to-year variations in photosynthesis and respiration at the hemispheric level, given additional a priori knowledge of the variability in isotopic fractionations and disequilibrium terms. The magnitude of the changes in gross CO2 fluxes that are required to explain the variability of the 18O signal will be compared to the magnitude of changes in the net fluxes.