HR: 08:55h
AN: B41F-04    [Abstracts]
TI: Carbon Fluxes in the Underobserved Tropics
AU: * Jacobson, A R
EM: andy.jacobson@noaa.gov
AF: University of Colorado and NOAA Earth System Research Laboratory, Global Monitoring Division 325 Broadway, Boulder, CO 80305, United States
AU: Baker, D F
EM: dfb@cgd.ucar.edu
AF: National Center for Atmospheric Research, PO Box 3000, Boulder, CO 80307, United States
AU: Sarmiento, J L
EM: jls@princeton.edu
AF: Princeton University, 300 Forrestal Road, Sayre Hall, Princeton, NJ 08544,
AU: Gloor, M
EM: E.Gloor@leeds.ac.uk
AF: Earth and Biosphere Institute and School of Geography, University of Leeds, Woodhouse Lane, Leeds, LS2 9JT, United Kingdom
AU: Gruber, N
EM: nicolas.gruber@env.ethz.ch
AF: Institute of Biogeochemistry and Pollutant Dynamics, ETH, Universitätstrasse 16, Zurich, 8092, Switzerland
AB: Two papers appearing in 2007 introduced new constraints to the perpetually-underdetermined atmospheric carbon dioxide surface flux inversion problem, but came to significantly different conclusions about the magnitude of tropical land fluxes. Stephens et al. (Science 316, 2007) used a new compilation of aircraft profiles to argue that most atmospheric transport models have unrealistic vertical transport, and that those models which agree with vertical CO₂ profiles yield very small "flux polarity": a modest northern land uptake of carbon and effectively neutral net tropical land exchange. In contrast, the joint ocean-atmosphere inversion of Jacobson et al. (GBC 21, 2007) uses JGOFS ocean interior data to tightly constrain long-term average air-sea exchange of CO₂. This strong constraint on oceanic fluxes allows atmospheric CO₂ gradients to inform us more directly about terrestrial fluxes. We find relatively high flux polarity, with a tropical land source that is consistent with estimates of flux due to deforestation and land-use change. The discrepancy between these two papers for tropical and southern land flux is over 2 PgC yr^-1. To resolve these radically different perspectives on surface fluxes of carbon dioxide, we have explored the use of model subsets as suggested by Stephens et al., and we have created a new joint inversion using a more advanced time-dependent atmospheric analysis. Preliminary results suggest that both groups are in part right: while flux polarity is indeed diminished by considering vertical CO₂ gradients in the atmosphere, the tropical terrestrial biosphere remains a significant source of carbon to the atmosphere.
DE: 1615 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 4805, 4912)
DE: 1631 Land/atmosphere interactions (1218, 1843, 3322)
DE: 4806 Carbon cycling (0428)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting