Isotope fractionation effect during soil uptake of methane, carbon monoxide and hydrogen This proposal was submitted in response to the Environmental Geochemistry and Biogeochemistry (EGB) solicitation, NSF 06-152. It is being jointly funded by the Divisions of Ocean Sciences and Atmospheric Science. The objective of this proposal is to measure isotope fractionation during soil uptake of carbon monoxide (CO), methane (CH4) and hydrogen (H2). These fractionation effects are important to quantify so that continued atmospheric measurements of these greenhouse gases can take full advantage of isotopic data to fingerprint specific sources and sinks. This will allow for a significant advancement in our understanding of the global cycles of these radiatively important trace gases. The PI's propose to empirically measure the isotopic fractionation effect using soil enclosures and measuring air samples collected as a time-series in the headspace. The site specific data will be extrapolated to regional and global scales using soil characteristics (e.g. temperature, moisture, porosity, composition, etc.). Overall, the proposed measurements, when coupled with on-going time series measurements of the isotopic composition of CH4, CO and anticipated measurements of H2, will provide the framework needed to determine the influence of soil uptake on the seasonal changes in the concentration and isotopic composition of these gases in temperate northern latitudes and on the interhemispheric asymmetry of their isotopic composition.
