HR: 15:10h
AN: B33F-07    [Abstracts]
TI: Fundamental influence of carbon-nitrogen cycle coupling on climate-carbon cycle feedbacks
AU: * Thornton, P
EM: thornton@ucar.edu
AF: National Center for Atmospheric Research, P.O. Box 3000, Boulder, CO 80307, United States
AU: Lindsay, K
EM: lindsay@ucar.edu
AF: National Center for Atmospheric Research, P.O. Box 3000, Boulder, CO 80307, United States
AU: Doney, S
EM: sdoney@whoi.edu
AF: Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA 02543-1543, United States
AU: Moore, J K
EM: jkmoore@uci.edu
AF: University of California, Irvine, 3214 Croul Hall, Irvine, CA 92697-3100, United States
AU: Mahowald, N
EM: nmm63@cornell.edu
AF: Department of Earth and Atmospheric Science, Cornell University, Ithaca, NY 14853, United States
AB: A long history of ecological and biogeochemical research demonstrates the critical role of nutrients in general, and nitrogen in particular, in the dynamics of the terrestrial carbon cycle. The current generation of global coupled climate-carbon cycle models has not included an explicit (prognostic) representation of the nitrogen cycle over land. Recent development of the NCAR Community Climate System Model (CCSM) includes the introduction of coupled carbon and nitrogen cycles in the Community Land Model component (CLM-CN). The most important new mechanism captured in the model is the two-way coupling between net primary production (NPP) and heterotrophic respiration (HR) through carbon and nitrogen pathways. Previous models have represented the dependence of HR on NPP as the source of carbon to the decomposition pathways, but CLM-CN introduces the dependence of NPP on HR as the primary source of mineral (plant-available) nitrogen for new growth. Introduction of carbon-nitrogen cycle dynamics in a fully-coupled global simulation fundamentally alters the nature of the predicted climate-carbon cycle feedbacks: the land biosphere response to CO2 fertilization is reduced by about a factor of three, and the sign of the climate-carbon cycle gain is switched from positive to negative feedback, compared to previous carbon-only model predictions. So, with prognostic nitrogen cycle included, the land biosphere takes up substantially less of the fossil fuel emissions than previously predicted, but the global warming (and wetting) associated with greenhouse gas radiative forcing results in a modest additional uptake of carbon, as opposed to the release of carbon due to climate change predicted by all previous coupled climate- carbon cycle models.
DE: 0315 Biosphere/atmosphere interactions (0426, 1610)
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0428 Carbon cycling (4806)
DE: 0469 Nitrogen cycling
SC: Biogeosciences [B]
MN: 2007 Fall Meeting