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Open Access Publications from the University of California

Exchanges of Atmospheric CO2 and 13CO2 with the Terrestrial Biosphere and Oceans from 1978 to 2000. IV. Critical Overview


CO2 are inferred by a three-dimensional tracer inversion model from simultaneous measurements of the concentration and 13C/12C isotopic ratio of atmospheric CO2. Terrestrial exchange of CO2 with the atmosphere range from −0.9 to +1.6 PgC yr−1 in the northern polar zone, −3.1 to +0.2 PgC yr−1 in the north temperate zone, −2.3 to +6.7 PgC yr−1 in the tropics, and −2.1 to +0.8 PgC yr−1 in the southern temperate zone. Oceanic exchange shows relatively little interannual variability, except in the tropics where a weak sink, up to −0.6 PgC yr−1 during El Nin˜o events in 1983, 1987, and 1998, alternated with a source, as great as 1.7 PgC yr−1. If isotopic data are disregarded as an indicator of interannual variability, inferred fluxes are altered only slightly in the polar and temperate zones, but substantially reduced in the tropical zone to a minimum sink of − 0.2 PgC yr−1 and a maximum source of 4.1 PgC yr−1. For three broader zones, divided at 30° N and S, average fluxes that we deduce from 1980-1989 and 1990-1996 agree within about 1 PgC yr−1 with decadal averages of 7 other inversion studies, except in the tropics where we find a larger source of CO2 than most other studies in the 1980’s and all other studies from 1990-1996. The interannual variability that we find exceeds that of most other studies.

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