Characterization of atmospheric methane release in the outer Mackenzie River Delta from biogenic and thermogenic sources

• Main Authors: Wesley, Daniel, Dallimore, Scott, MacLeod, Roger, Sachs, Torsten, Risk, David
• Format: Text
• Language: English
• Published: 2023
• Subjects: Arctic; Mackenzie River; Mackenzie river; permafrost
• Online Access: https://doi.org/10.5194/egusphere-2022-549; https://egusphere.copernicus.org/preprints/2022/egusphere-2022-549/

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 (CH 4 ) emission from biogenic and thermogenic sources. Hotspots are known to have a significant contribution to summertime CH 4 emissions in the region. Still, little research has been done to determine how often geologic or biogenic CH 4 contributes to hotspots in the Mackenzie River delta. In the present study, stable carbon isotope analysis was used to identify the source of CH 4 at several aquatic and terrestrial sites thought to be hotspots of CH 4 flux to the atmosphere. Walking transects and point samples of atmospheric CH 4 and CO 2 concentrations were measured. Source stable carbon isotope ( δ 13 C-CH 4 ) signatures were derived from keeling plots of point samples and ranged from −42 ‰ to −88 ‰ δ 13 C-CH 4 , identifying both biogenic and thermogenic sources. A CH 4 source was determined for eight hotspots, two of which were thermogenic in origin ( −42.5 ‰ , −44.7 ‰ ), four of which were biogenic in origin ( −71.9 ‰ to −88.3 ‰ ), and two of which may have been produced by the oxidation of biogenic CH 4 ( −53.0 ‰ , −63.6 ‰ ), as evidenced by δ 13 C-CH 4 signatures. This indicates that the largest hotspots of CH 4 production in the Mackenzie River delta are caused by a variety of sources.