Characterization of atmospheric methane release at hotspots in the outer Mackenzie River Delta

Spatio-temporal patterns of methane (CH₄) and carbon dioxide (CO₂) release from natural sources needs to be better understood across the Arctic region. Climate change in the Arctic is occurring at a pace that may be 2 to 4 times the global average, and existing measurements derive from a limited number of field sites, and most originate during the growing season although important studies show that release continues during winter. The Mackenzie River Delta in the western Canadian Arctic holds thin and destabilizing permafrost, high organic content soils, a high proportion of wetlands, and vast natural gas occurrences at depth, all of which create high methane potential. In the present study, we conducted atmospheric CH₄ and CO₂ measurements using a mobile laboratory equipped with a greenhouse gas analyzer during the summer and winter. We also visited known aquatic and terrestrial CH₄ flux hotspots, including pingos, lakes, river channels and wetlands, where we measured concentration transects and stable carbon isotope (¹³C-CH₄) values to characterize CH₄source and spatial pattern. Source stable carbon isotope (δ¹³C-CH₄) signatures at hotspots ranged from -42 to -88 ‰ δ¹³C-CH₄. Active surface microbial production was responsible for at least 4 of the 8 hotspots investigated, indicating that microbial production may be responsible for a greater number of CH₄ hotspots than is indicated by previous studies in the region. Mobile surveys showed that shrubland, grassland and deep water were the most important ecosystems for CH₄ and CO₂ production during the wintertime and that low lying areas of the Delta had the highest atmospheric mixing ratios of CH₄.