HR: 1340h
AN: B23A-0926    [Abstracts]
TI: Boundary-layer measurements of CO$_{2}$ concentration, carbon and oxygen isotopes of atmospheric CO$_{2}$ over montane forest regions in Colorado, USA
AU: * Hu, J
EM: jia.hu@colorado.edu
AF: University of Colorado, Dept of Ecology and Evolutionary Biology Campus Box 334, Boulder, CO 80309
AU: Lai, C
EM: lai@biology.utah.edu
AF: University of Utah, Department of Biology 257S, 1400E , Salt Lake City, UT 84112-0840
AU: Stephens, B
EM: stephens@ucar.edu
AF: National Center for Atmospheric Research, PO Box 3000 1850 Table Mesa Drive , Boulder, CO 80307-3000
AU: Ehleringer, J
EM: ehleringer@biology.utah.edu
AF: University of Utah, Department of Biology 257S, 1400E , Salt Lake City, UT 84112-0840
AU: Monson, R
EM: russell.monson@colorado.edu
AF: University of Colorado, Dept of Ecology and Evolutionary Biology Campus Box 334, Boulder, CO 80309
AU: Schimel, D
EM: schimel@cgd.ucar.edu
AF: National Center for Atmospheric Researach, Climate and Global Dynamics Division P.O. Box 3000 , Boulder, CO 80307-3000
AB: Air samples were collected with 100ml flasks in the atmospheric and canopy boundary layers using aircraft and ground-based samplers as an integral part of the Airborne Carbon in the Mountains Experiment (ACME) in May and July 2004. A total number of 524 flasks were collected during the two study periods for the analyses of concentration, carbon (\delta$^{13}$C) and oxygen (\delta$^{18}$O) isotopes of atmospheric CO$_{2}$. Air samples were collected in the early morning (beginning ~ 7:00 am) using a C-130 airplane to characterize regional-scale isotopic signals of respiration (\delta$^{13}$C$_{R}$) in the residual boundary layer. As the ground heated after sunrise and the convective boundary layer (CBL) increased, flasks were collected again to estimate isotope ratios of net CO$_{2}$ exchange between the atmosphere and the biosphere. In addition, vertical profiles of atmospheric CO$_{2}$, \delta$^{13}$C and \delta$^{18}$O in the CBL were measured with the aircraft. Two automated sampling systems conducted the ground-based sampling. The first sampled at 15-min intervals the night before a flight (9:00 pm to 12:30 am). These measurements were conducted within forest canopies and were used to capture \delta$^{13}$C ratios of nighttime respiration at the ecosystem scale. The second was programmed to sample every 45 minutes and started approximately two hours before the airborne flights (4:30 am to 3:00 pm). These measurements overlapped aircraft observations, providing information about daytime CO$_{2}$ exchange in the atmosphere-forest interface. Preliminary results showed that a CO$_{2}$ gradient of 27.9 ppm with a corresponding \delta$^{13}$C difference of 1.16 \permil was captured in the residual boundary layer on a July morning. Using a two-source mixing line approach, the regional-scale \delta$^{13}$CR was estimated to be -24.5 \pm 0.4 (S.E.) \permil, which was significantly (p < 0.05) more positive compared to measured nighttime /delta$^{13}$C$_{R}$ values within the forest canopy (-25.7 \pm 0.1 \permil). This difference partially reflects the disparity in sampling footprints represented by the two different methods for measuring CO$_{2}$. Similar results were found on several days, which could perhaps contribute to a better understanding of the CO$_{2}$ flux exchanged between montane forests and the atmosphere.
DE: 0315 Biosphere/atmosphere interactions
DE: 0394 Instruments and techniques
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting