HR: 1340h
AN: B43B-0165    [Abstracts]
TI: Constraining the Methane Budget: The use of $\delta$$^{13}$C-CH$_{4}$ data as a constraint for methane source estimates
AU: * MacClune, K A
EM: Kenneth.Mack@colorado.edu
AF: INSTAAR - University of Colorado, Campus Box 450, Boulder, CO 80309 United States
AU: Miller, J B
EM: John.B.Miller@noaa.gov
AF: NOAA Climate Monitoring & Diagnostics Laboratory, 325 Broadway R/CMDL1, Boulder, CO 80305 United States
AU: White, J W
EM: jwhite@colorado.edu
AF: INSTAAR - University of Colorado, Campus Box 450, Boulder, CO 80309 United States
AU: Tans, P
EM: Pieter.Tans@noaa.gov
AF: NOAA Climate Monitoring & Diagnostics Laboratory, 325 Broadway R/CMDL1, Boulder, CO 80305 United States
AU: Dlugokencky, E
EM: Ed.Dlugokencky@noaa.gov
AF: NOAA Climate Monitoring & Diagnostics Laboratory, 325 Broadway R/CMDL1, Boulder, CO 80305 United States
AU: Dreier, M
EM: dreier@stripe.colorado.edu
AF: INSTAAR - University of Colorado, Campus Box 450, Boulder, CO 80309 United States
AU: Claymore, V
EM: morrisv@mail.colorado.edu
AF: INSTAAR - University of Colorado, Campus Box 450, Boulder, CO 80309 United States
AB: Methane is the second most potent greenhouse gas and is responsible for nearly 20% of the enhanced greenhouse effect. The most common means of estimating the source budget are through inverse modeling techniques using variations of the atmospheric concentration in space and time and by extrapolation of localized source flux measurements to a global scale. Yet, due to the wide array of methane sources and a relative paucity of measurements, its budget is not well constrained. Carbon-13 measurements offer a means to help clarify the methane budget because different groups of methane sources have distinct isotopic signatures. For example, the isotopic ratio of microbially produced methane is around -60 per mil, while that originating from biomass burning is around -25 per mil. Since 1998, in co-operation with NOAA/CMDL, $\delta$$^{13}$C-CH$_{4}$ has been measured at the University of Colorado's Stable Isotope Lab from samples drawn on a weekly basis from select sites of the NOAA/CMDL Cooperative Air Sampling Network. We use a box model to simulate the effect that different methane source estimates would have on atmospheric CH$_{4}$ and $\delta$$^{13}$C-CH$_{4}$ values at our measurement sites. We then compare the modeled $\delta$$^{13}$C-CH$_{4}$ values with $\delta$$^{13}$C-CH$_{4}$ data to evaluate those source estimates. We focus our analysis on comparison of seasonal variations in methane concentration and $\delta$$^{13}$C-CH$_{4}$ to better understand seasonal source dynamics and how they might be changing over our study timeframe. In addition we compare model and observed latitudinal gradients from 1998 to the present to evaluate changes in source strength and distribution.
DE: 1610 Atmosphere (0315, 0325)
DE: 1615 Biogeochemical processes (4805)
DE: 0315 Biosphere/atmosphere interactions
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting