HR: 0800h
AN: B11A-1002    [Abstracts]
TI: Spatial and temporal variations in terrestrial carbon isotope disequilibria simulated in coupled runs of the Community Climate System Model
AU: * Suits, N S
EM: nsuits@atmos.colostate.edu;
AF: Department of Atmospheric Science, Colorado State University, Fort Collins, CO 80523 United States
AU: Denning, A S
EM: denning@cea.fr
AF: Department of Atmospheric Science, Colorado State University, Fort Collins, CO 80523 United States
AU: Thornton, P E
EM: thornton@ucar.edu
AF: National Center for Atmospheric Research, 1850 Table Mesa Dr., Boulder, CO 80305 United States
AU: Baker, I T
EM: baker@atmos.colostate.edu
AF: Department of Atmospheric Science, Colorado State University, Fort Collins, CO 80523 United States
AU: Lee, J
EM: jeff@ucar.edu
AF: National Center for Atmospheric Research, 1850 Table Mesa Dr., Boulder, CO 80305 United States
AB: We introduce carbon isotope discrimination to the Community Climate System Model (CCSM) in order to simulate temporal and spatial variations in terrestrial fluxes of 12CO2 and 13CO2 and their impact on atmospheric CO2 and the seasonal and interannual isotope disequilibria, i.e., the differences between the isotopic ratios of photosynthetic and respiration. CCSM is initially spun up under preindustrial atmospheric CO2 concentrations and carbon isotope ratios to reach steady state sizes and carbon isotope ratios for soil and plant biomass. It is then run forward in coupled mode from 1900 using observed changes in atmospheric CO2 concentrations and isotope ratios. Initial results show that large seasonal and interannual isotope disequilibria associated with ENSO and associated root-zone soil-water drought stress in the tropics may be useful in determining whether observed changes in net CO2 fluxes are the result of decreases in photosynthesis or increases in respiration. In addition, we show that interannual variations in the relative contributions of C4 plants to total photosynthesis are important drivers of terrestrial disequilibria. And finally, recent rapid decreases in d13C of atmospheric CO2 due to the increasing rate of fossil fuel combustion make the use of isotope disequilibria in double deconvolutions an increasingly powerful tool in determining locations and timing of CO2 sources and sinks.
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: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0545 Modeling (4255)
SC: Biogeosciences [B]
MN: Fall Meeting 2005