Stable isotope signatures in N2O and CH4: linking microbial processes to atmospheric chemistry

The stable isotope content (15N, 18O, 13C, D/H) of atmospheric nitrous oxide (N2O) and methane (CH4) reflects the overall balance of isotopic fractionation associated with its formation, transport and destruction. Knowledge of process-specific isotope eff ects has become a powerful tool in clarifying source-sink relationships for these important greenhouse gases and helps to constrain the global budgets for N2O and CH4. Recent analytical developments in continuous flow isotope ratio mass spectrometry (CF-I RMS) now also allow determination of the site-specific 15N abundance within the linear N2O molecule. This opens for an additional, independent signal to further confine N2O sources and sinks. Substantial knowledge exists to date about the kinetic isotope effects (KIE) of the major atmospheric sink processes, UV-photolysis, O(1D)-oxidation and hydroxyl-reaction. The isotopic imprints of the dominant biogenic source processes, nitrification, denitrification and methanogenesis, in contra Norway and at the Institute for Energy Technology Kjeller, to perform in-depth studies on the kinetic fractionations associated with the production, consumption and emission of N2O and CH4, including the site-preference of 15N in N2O. This work draws heav ily on in-house expertise in the ecophysiology of microbial C- and N-transformation and on instrumentation to measure and control the kinetics of such transformations. The project, and its strong international dimension, will enable us to participate in m odern studies of biosphere-atmosphere interactions and to make theses rapidly developing techniques available for other groups within Norwegian climate research.