Seasonal and interannual influences of the terrestrial ecosystems on atmospheric CO2: a model study

The prognostic CARAIB (Carbon Assimilation
In the Biosphere) model has been used in conjunction
with the Max-Planck Institut TM2 atmospheric
transport model to calculate the atmospheric CO2 fluctuations
at the global scale. Two applications are briefly
described. In the first one, the seasonal CO2 variation is
calculated and a Fourier analysis is performed to determine
the relative contributions of the various vegetation
types. It is found that the seasonal signal is dominated
by the grasslands and needle leaf forests in the northern
boreal and temperate zones. In the southern hemisphere,
tropical deciduous forests and grasslands make
the primary contribution. In the second application, the
net primary productivity (NPP), soil heterotrophic respiration
(SHR) and net ecosystem productivity (NEP)
are calculated for years 1987 and 1988 with the model
driven by observed climatic variables. Preliminary results
indicate that the NEP variations between these
two years are strongly dominated by tropical ecosystems.
However, it is shown that the results are strongly
dependent on the dataset used for the 1987-88 temperature
record, raising the question of reliability of sudl
modelling studies of the interannual variability of the
biosphere. 01997 Elsevier Science Ltd