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Carbon-nitrogen interactions regulate climate-carbon cycle feedbacks: results from an atmosphere-ocean general circulation model
1Climate and Ecosystem Processes, Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6335, USA
2Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA 02543-1543, USA
3Climate and Global Dynamics Division, National Center for Atmospheric Research, Boulder, CO 80307-3000, USA
4Department of Earth System Science, University of California, Irvine, CA 92697-3100, USA
5Department of Earth and Atmospheric Sciences, Cornell University, Ithaca, NY 14850, USA
6Department of Earth and Planetary Science, University of California, Berkeley, CA 94720-4767, USA
7NOAA Earth System Research Laboratory, Chemical Sciences Division, 325 Broadway, Boulder, CO 80305-3337, USA
8Atmospheric Chemistry Division, National Center for Atmospheric Research, Boulder, CO 80307-3000, USA
9Department of Geography, University of Kansas, Lawrence, KS 66045-7613, USA
Abstract. Inclusion of fundamental ecological interactions between the terrestrial carbon and nitrogen cycles in the land component of an atmosphere-ocean general circulation model (AOGCM) leads to increased carbon storage on land under radiatively-forced anthropogenic climate change, and an overall negative climate-carbon cycle feedback. The primary mechanism responsible for increased land carbon storage is shown to be fertilization of plant growth by increased mineralization of nitrogen directly associated with increased decomposition of soil organic matter under a warming climate. Results from the fully-coupled AOGCM also confirm a previously reported pattern of significantly reduced CO2-fertilization of terrestrial carbon uptake compared to simulations without an explicit nitrogen cycle. Our results show a significant growth in the airborne fraction of anthropogenic CO2 emissions over the coming century, attributable in part to a steady decline in the ocean sink fraction. Comparison to experimental studies on the fate of radio-labeled nitrogen tracers in temperate forests indicates that the model representation of competition between plants and microbes for new mineral nitrogen resources is reasonable. Our results suggest a weaker dependence of net land carbon flux on soil moisture changes in tropical regions, and a stronger positive growth response to warming in those regions, than predicted by a similar AOGCM implemented without land carbon-nitrogen interactions. We expect that the between-model uncertainty in predictions of future atmospheric CO2 concentration and associated anthropogenic climate change will be reduced as additional climate models introduce carbon-nitrogen cycle interactions in their land components.
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Citation: Thornton, P. E., Doney, S. C., Lindsay, K., Moore, J. K., Mahowald, N., Randerson, J. T., Fung, I., Lamarque, J.-F., Feddema, J. J., and Lee, Y.-H.: Carbon-nitrogen interactions regulate climate-carbon cycle feedbacks: results from an atmosphere-ocean general circulation model, Biogeosciences Discuss., 6, 3303-3354, 2009. Bibtex EndNote Reference Manager
