Global transport and inter-reservoir exchange of carbon dioxide with particular reference to stable isotopic distributions |
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| Authors: | G I Pearman P Hyson |
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| Institution: | (1) CSIRO Division of Atmospheric Research, Private Bag No. 1, 3195 Mordialloc, Victoria, Australia |
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| Abstract: | A two-dimensional model of global atmospheric transport is used to relate estimated air-to-surface exchanges of carbon dioxide (CO2) to spatial and temporal variations of atmospheric CO2 concentrations and isotopic composition. The atmospheric model coupled with models of the biosphere and mixed layer of the ocean describes the gross features of the global carbon cycle. In particular this paper considers the change in isotopic composition due to interreservoir exchanges and thus the potential application and measurement requirements of new isotopic observational programs.A comparison is made between the model-generated CO2 concentration variation and those observed on secular, interannual and seasonal time scales and spatially through the depth of the troposphere and meridionally from pole-to-pole.The relationship between isotopic and concentration variation on a seasonal time-scale is discussed and it is shown how this can be used to quantitatively estimate relative contributions of biospheric and oceanic CO2 exchange. Further, it is shown that the interhemispheric gradient of concentration and isotopic ratio results primarily from the redistribution of fossil fuel CO2. Both isotopic and concentration data indicate that tropical deforestation contributes less than 2 Gt yr-1 of carbon to the atmosphere.The study suggests that changes in the rate of change of the ratio of 13C to 12C in the atmosphere of less than 0.03 yr-1 might be expected if net exchanges with the biosphere are the cause of interannual variations of CO2 concentrations. |
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| Keywords: | Carbon cycle stable carbon isotopes carbon dioxide atmospheric transport model biosphere isotopic fractionation |
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