HR: 1330h
AN: A52A-0763    [PDF]
TI: Disturbance-Induced Changes in the Oxygen Isotopic Composition of Atmospheric CO$_{2}$ at High Northern Latitudes
AU: * Welp, L R
EM: welp@caltech.edu
AF: California Institute of Technology, Environmental Science and Engineering, 1200 E. California Boulevard, Pasadena, CA 91125 United States
AU: Randerson, J T
EM: jranders@uci.edu
AF: University of California, Irvine, Department of Earth System Science, 3212 Croul Hall, Irvine, CA 92697 United States
AB: At high northern latitudes, interannual variation in the seasonal cycle of atmospheric C$^{18}$OO exceeds that observed for $^{13}$CO$_{2}$ or CO$_{2}$. Shifts in species composition or climate may contribute to this variability in C$^{18}$OO by influencing the timing of photosynthesis and respiration and the cycling of meteoric water. We hypothesized that increased forest fire frequency contributes to variability in C$^{18}$OO by changing surface energy partitioning, fluxes of water and CO$_{2}$, and vegetation structure and function. We measured the $\delta^{18}$O of ecosystem water pools (leaf, stem, soil, water vapor, and precipitation) in an 80 year old Picea mariana stand and a 15 year old Populus tremuloides stand in the Alaskan interior. The two forests displayed similar $\delta^{18}$O values for precipitation, soil, and stem water, however mid-day leaf water in P. mariana was consistently more enriched in $^{18}$O than that of P. tremuloides on the order of 2 $\permil$. We predicted differences in diurnal and seasonal C$^{18}$OO fluxes between sites by incorporating net CO$_{2}$ eddy flux and micrometeorological measurements with oxygen isotopic signatures of ecosystem water pools, local background atmospheric CO$_{2}$, and nighttime ecosystem respiration. We then used a simple age-distribution model of boreal forests to predict changes in the shape of the seasonal cycle of C$^{18}$OO that would accompany shifts in the disturbance regime.
DE: 0315 Biosphere/atmosphere interactions
SC: Atmospheric Sciences [A]
MN: 2003 Fall Meeting