Measurements of δ13C in CH4 and using particle dispersion modeling to characterize sources of Arctic methane within an air mass.

Michelle Cain ,J A Pyle ,Charles George ,N J Warwick ,Jurek Müller ,Axel Welpott ,Stéphane Bauguitte ,Keith Bower ,Grant Allen ,Martin Gallagher ,Garry Hayman ,Sam Illingworth ,Cathrine Lund Myhre ,Carl J Percival ,Benjamin Jones ,Michael Le Breton ,David Lowry ,Sebastian O’shea ,Mathias Lanoisellé ,Alistair J Manning ,Rebecca E Fisher ,E G Nisbet

doi:10.1002/2016jd026006

Abstract

A stratified air mass enriched in methane (CH4) 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 CH4 in the Arctic. Importantly, it allows constraints to be placed on the location and isotopic bulk signature of the emission source(s). Measurements of δ13C in CH4 in whole air samples taken while traversing the air mass identified that the source(s) had a strongly depleted bulk δ13C CH4 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.

Highlights

Methane (CH4) is well known to be a powerful greenhouse gas, with approximately 28 times the global warming potential of carbon dioxide over a 100 year period, and is the second most important anthropogenic greenhouse gas in terms of radiative forcing [Denman et al, 2007; Myhre et al, 2013]
A maximum mixing ratio of CH4 of ~1920 ppb was observed in the core of the air mass with enhanced methane
The Numerical Atmospheric-dispersion Modeling Environment (NAME) modeling indicates that a large fraction of the back trajectories at the heart of the enhanced CH4 air mass pass through the boundary layer over an area of northwest Russia, which is up to 20% wetland according to MODIS land use [Friedl et al, 2010]

Summary

Introduction

Methane (CH4) is well known to be a powerful greenhouse gas, with approximately 28 times the global warming potential of carbon dioxide over a 100 year period, and is the second most important anthropogenic greenhouse gas in terms of radiative forcing [Denman et al, 2007; Myhre et al, 2013]. Other sources of CH4 within the Arctic include the tundra permafrost melt [Wille et al, 2008], subsea permafrost and hydrate degradation [Shakhova et al, 2014; Vonk et al, 2012; Westbrook et al, 2009], Arctic ocean surface waters [Kort et al, 2012], natural geological CH4 seepage [Walter et al, 2012], and anthropogenic emissions such as fugitive emissions from oil and gas platforms. Sources such as CH4 hydrates are not as yet thought to be contributing significantly to the FRANCE ET AL

Methods

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Discussion

Conclusion