The interannual change of atmospheric CO2: contribution of subtropical ecosystems?

The global terrestrial carbon cycle model CARAIB (CARbon Assimilation In th e Biosphere) is used to study the response of the terrestrial ecosystems to the large scale climate variations over the period 1980-1993. The global n et carbon exchange flux with the atmosphere is calculated and compared with the terrestrial contribution derived from the deconvolution of the atmosph eric CO2 and delta(13)C measurements. A fairly large CO2 biospheric source is predicted during the strong El Nino events of 1982-83 and 1986-87 as a c onsequence of the induced global warming. The direct and indirect temperatu re controls of the primacy production and respiration dominate the CO2 anom aly. An analysis of the relative contribution by latitudinal bands and ecos ystems shows that low-latitude vegetation dominates the variability at the El Nino time scale. In savannas, the model indicates that the interannual c hanges result, to a large extent, from the control of soil water content on gross primary production (GPP). In the tropical cain forests, both respira tion and GPP contribute to the response of the net biospheric flux.