A joint global carbon inversion system using both CO<sub>2</sub> and <sup>13</sup>CO<sub>2</sub> atmospheric concentration data Academic Article uri icon

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abstract

  • <p><strong>Abstract.</strong> Observations of <sup>13</sup>CO<sub>2</sub> at 73 sites compiled in the GLOBALVIEW database are used for an additional constraint in a global atmospheric inversion of the surface CO<sub>2</sub> flux using CO<sub>2</sub> observations at 210 sites (62 collocated with <sup>13</sup>CO<sub>2</sub> sites) for the 2002–2004 period for 39 land regions and 11 ocean regions. This constraint is implemented using prior CO<sub>2</sub> fluxes estimated with a terrestrial ecosystem model and an ocean model. These models simulate <sup>13</sup>CO<sub>2</sub> discrimination rates of terrestrial photosynthesis and ocean–atmosphere diffusion processes. In both models, the <sup>13</sup>CO<sub>2</sub> disequilibrium between fluxes to and from the atmosphere is considered due to the historical change in atmospheric <sup>13</sup>CO<sub>2</sub> concentration. This joint inversion system using both<sup>13</sup>CO<sub>2</sub> and CO<sub>2</sub> observations is effectively a double deconvolution system with consideration of the spatial variations of isotopic discrimination and disequilibrium. Compared to the CO<sub>2</sub>-only inversion, this <sup>13</sup>CO<sub>2</sub> constraint on the inversion considerably reduces the total land carbon sink from 3.40<span class="thinspace"></span>±<span class="thinspace"></span>0.84 to 2.53<span class="thinspace"></span>±<span class="thinspace"></span>0.93<span class="thinspace"></span>Pg C<span class="thinspace"></span>year<sup>−1</sup> but increases the total oceanic carbon sink from 1.48<span class="thinspace"></span>±<span class="thinspace"></span>0.40 to 2.36<span class="thinspace"></span>±<span class="thinspace"></span>0.49<span class="thinspace"></span>Pg C<span class="thinspace"></span>year<sup>−1</sup>. This constraint also changes the spatial distribution of the carbon sink. The largest sink increase occurs in the Amazon, while the largest source increases are in southern Africa, and Asia, where CO<sub>2</sub> data are sparse. Through a case study, in which the spatial distribution of the annual <sup>13</sup>CO<sub>2</sub> discrimination rate over land is ignored by treating it as a constant at the global average of −14. 1<span class="thinspace"></span>‰, the spatial distribution of the inverted CO<sub>2</sub> flux over land was found to be significantly modified (up to 15<span class="thinspace"></span>% for some regions). The uncertainties in our disequilibrium flux estimation are 8.0 and 12.7<span class="thinspace"></span>Pg C<span class="thinspace"></span>year<sup>−1</sup><span class="thinspace"></span>‰ for land and ocean, respectively. These uncertainties induced the unpredictability of 0.47 and 0.54<span class="thinspace"></span>Pg C<span class="thinspace"></span>year<sup>−1</sup> in the inverted CO<sub>2</sub> fluxes for land and ocean, respectively. Our joint inversion system is therefore useful for improving the partitioning between ocean and land sinks and the spatial distribution of the inverted carbon flux.</p>

publication date

  • March 16, 2017