Comment on egusphere-2022-549

Abstract

The Mackenzie River Delta is the second largest Arctic river delta in the world. Thin and destabilizing permafrost coupled with vast natural gas reserves at depth, high organic content soils, and a high proportion of wetlands create a unique ecosystem conducive to high rates of methane production from biogenic and thermogenic sources. Hotspots are known to have a significant contribution to summertime CH4 emissions in the region, but little research has been done to determine how often geologic or biogenic methane contributes to CH4 hotspots in the Mackenzie River Delta. In the present study, stable carbon isotope analysis was used to identify the source of CH4 at several aquatic and terrestrial sites thought to be hotspots of CH4 flux to the atmosphere. Source stable carbon isotope (δ13C-CH4) signatures were derived from keeling plots of point samples and ranged from -42 to -88 ‰ δ13C-CH4, identifying both biogenic and thermogenic and mixed biogenic/thermogenic sources. A CH4 source was determined for eight hotspots, two were thermogenic in origin, four were biogenic in origin, and two were from mixed biogenic/thermogenic sources, as evidenced by δ13C-CH4 signatures. This indicates that the largest hotspots of CH4 production in the Mackenzie River Delta are caused by a variety of sources. In addition to biogenic production at the surface we have identified CH4 migration to the surface from the Taglu gas field over an area of approximately 20 km from north to south and two different sites of mixed biogenic/thermogenic CH4 that were approximately 30 km apart.