A stratified air mass enriched in methane (CH$_{4}$) was sampled at ~600 m to ~2000 m altitude, between the north coast of Norway and Svalbard as part of the Methane in the Arctic: Measurements and Modelling campaign on board the UK's BAe-146-301 Atmospheric Research Aircraft. The approach used here, which combines interpretation of multiple tracers with transport modeling, enables better understanding of the emission sources that contribute to the background mixing ratios of CH$_{4}$ in the Arctic. Importantly, it allows constraints to be placed on the location and isotopic bulk signature of the emission source(s). Measurements of δ$^{13}$C in CH$_{4}$ in whole air samples taken while traversing the air mass identified that the source(s) had a strongly depleted bulk δ$^{13}$C CH$_{4}$isotopic signature of −70 (±2.1)‰. Combined Numerical Atmospheric-dispersion Modeling Environment and inventory analysis indicates that the air mass was recently in the planetary boundary layer over northwest Russia and the Barents Sea, with the likely dominant source of methane being from wetlands in that region. ; Other ; The MAMM project was funded by the UK Natural Environment Research Council (grant NE/I029293/1). S.J. O'Shea is in receipt of a NERC studentship, and G. Allen is a NERC Fellow (NE/I021276/1). Airborne data were obtained using the Facility for Airborne Atmospheric Measurements (FAAM) BAe-146 Atmospheric Research Aircraft (ARA) operated by Directflight Ltd. and managed by the Facility for Airborne Atmospheric Measurements (FAAM), which is a joint entity of the Natural Environment Research Council (NERC) and the UK Meteorological Office. This work was supported by the Norwegian Research Council through project 207587 entitled “GAME: Causes and effects of global and Arctic changes in the methane budget.” J.A.P. also acknowledges support through the ERC ACCI project 267760.