Comment on egusphere-2022-549

Abstract

<strong class="journal-contentHeaderColor">Abstract.</strong> 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 (&delta;¹³C-CH₄) signatures were derived from keeling plots of point samples and ranged from -42 to -88 &permil; &delta;¹³C-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 &delta;¹³C-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.