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