INTERANNUAL VARIATION OF CARBON EXCHANGE FLUXES IN TERRESTRIAL ECOSYSTEMS

A global prognostic physiologically based model of the carbon budget i n terrestrial ecosystems, the Frankfurt Biosphere Model (FBM), is appl ied to simulate the interannual variation of carbon exchange fluxes be tween the atmosphere and the terrestrial biosphere. The data on climat ic forcing are based on Cramer and Leemans climate maps; the interannu al variation is introduced according to records of temperature anomali es and precipitation anomalies for the period 1980 to 1993. The calcul ated net exchange flux between the atmosphere and the terrestrial bios phere is compared to the biospheric signal deduced from C-13 measureme nts. Some intermediate results are presented as well: the contribution s of the most important global ecosystems to the biospheric signal, th e contributions of different latitudinal belts to the biospheric signa l, and the responses of net primary production (NPP) and heterotrophic respiration (R(h)) From the simulation results it can be inferred tha t the complex temperature and precipitation responses of NPP and R(h) in different latitudes and different ecosystem types add up to a globa l CO2 signal contributing substantially to the atmospheric CO2 anomaly on the interannual timescale. The temperature response of NPP was fou nd to be the most important factor determining this signal.