The northernmost greenhouse gas flux measurement stations of Finnish Meteorological Institute were part of the study in which the isotopic signatures of the methane emissions in the Fennoscandian Arctic were determined.
Measurements were conducted in chambers over wetland, in the air 0.3 to 3m above the wetland surface and by aircraft sampling from 100m above wetlands up to the stratosphere. Overall, the methane flux to atmosphere showed a coherent δ13C isotopic signature of –71 ± 1‰, measured in situ on the ground in wetlands. This is in close agreement with δ13C isotopic signatures of local and regional methane increments measured by aircraft campaigns flying through air masses containing elevated methane mole fractions. In contrast, results from wetlands in Canadian boreal forest farther south gave isotopic signatures of –67 ± 1‰.
Wetland emissions dominated the local methane source measured over the European Arctic in summer. Chamber measurements demonstrated a highly variable methane flux and isotopic signature, but the results from air sampling within wetland areas showed that emissions mix rapidly immediately above the wetland surface and methane emissions reaching the wider atmosphere do indeed have strongly coherent C isotope signatures.
Isotopic data provide powerful constraints on regional and global methane emissions and their source profiles. However, inverse modeling of spatially resolved methane flux is currently constrained by a lack of information on the variability of source isotopic signatures. The study suggests that for boreal wetlands (>60°N) global and regional modeling can use an isotopic signature of –71‰ to apportion sources more accurately, but there is much need for further measurements over other wetlands regions to verify this.
Researcher Annalea Lohila, tel. +358 50 366 3242
Fischer R.E., France J.L., Lowry D., Lanoisellé M., Brownlow R., Pyle J.A., Cain M., Warwick N., Skiba U.M., Drewer J., Dinsmore K.J., Leeson S.R., Bauguitte S.J.-B., Wellpott A., O'Shea S.J., Allen G., Gallagher M.W., Pitt J., Percival C.J., Bower K., George C., Hayman G.D., Aalto T., Lohila A., Aurela M., Laurila T., Crill P.M., McCalley C.K., and E.G. Nisbet. 2017. Measurement of the 13C isotopic signature of methane emissions from Northern European wetlands. Global Biogeochemical Cycles, in press, doi:10.1002/2016GB005504.
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