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

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 ) emiss...

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Bibliographic Details
Published in:The Cryosphere
Main Authors: D. Wesley, S. Dallimore, R. MacLeod, T. Sachs, D. Risk
Format: Article in Journal/Newspaper
Language:English
Published: Copernicus Publications 2023
Subjects:
Environmental sciences
GE1-350
Geology
QE1-996.5
Arctic
Mackenzie River
Mackenzie river
permafrost
The Cryosphere
Online Access:https://doi.org/10.5194/tc-17-5283-2023
https://doaj.org/article/e30a8c4c13054025a5272f88f2bb2b0a
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Summary: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.

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