Strong geologic methane emissions from discontinuous terrestrial permafrost in the Mackenzie Delta, Canada

Arctic permafrost caps vast amounts of old, geologic methane (CH₄) in subsurface reservoirs. Thawing permafrost opens pathways for this CH₄ to migrate to the surface. However, the occurrence of geologic emissions and their contribution to the CH₄ budget in addition to recent, biogenic CH₄ is uncertain. Here we present a high-resolution (100 m × 100 m) regional (10,000 km²) CH₄ flux map of the Mackenzie Delta, Canada, based on airborne CH₄ flux data from July 2012 and 2013. We identify strong, likely geologic emissions solely where the permafrost is discontinuous. These peaks are 13 times larger than typical biogenic emissions. Whereas microbial CH₄ production largely depends on recent air and soil temperature, geologic CH₄ was produced over millions of years and can be released year-round provided open pathways exist. Therefore, even though they only occur on about 1% of the area, geologic hotspots contribute 17% to the annual CH₄ emission estimate of our study area. We suggest that this share may increase if ongoing permafrost thaw opens new pathways. We conclude that, due to permafrost thaw, hydrocarbon-rich areas, prevalent in the Arctic, may see increased emission of geologic CH₄ in the future, in addition to enhanced microbial CH₄ production.