Variability of terrestrial CO2 fluxes after volcanic eruptions

Recent analyses report that terrestrial biospheric processes play a large role in the interannual variability in atmospheric CO2 concentrations, 13C/12C ratios and O2 concentrations. We use a biogeochemical model (CASA) to study the sensitivity of biospheric processes and net biospheric CO2 fluxes at the global scale to observations of interannual variability in climate (solar irradiance, temperature and precipitation), in vegetation amount (FPAR), and in volcanic aerosols during the period 1982 to 1998. The variability in terrestrial carbon fluxes during the two decades is dominated by ENSO cycles and the eruption Mt Pinatubo in 1991. Variability in the CO2 fluxes are mostly driven by changes in FPAR and by increases in diffuse irradiance caused by volcanic aerosols. The year following the Mt. Pinatubo eruption (1992) was marked by low growing season temperatures, low FPAR, increased diffuse irradiance and a reportedly large terrestrial carbon sink at the global scale. Low temperature inhibition of heterotrophic respiration was modest and only stimulation of production by increased diffuse irradiance could offset the influence of lower FPAR and could produce a terrestrial carbon sink for this period.