Biodegradability of Thermokarst Carbon in a Till‐Associated, Glacial Margin Landscape: The Case of the Peel Plateau, NWT, Canada

Abstract

AbstractThe Peel Plateau is a characteristic glacial margin landscape, with permafrost comprised of thick, ice‐rich glacial tills deposited at the end of the Last Glacial Maximum. Unmodified tills at depth are overlain by a paleo‐active layer, created when early Holocene warming deepened regional active layers, enabling organic matter incorporation into now‐frozen soils. Ice‐rich permafrost encourages retrogressive thaw slumps, which mobilize variable proportions of modern active layer, paleo‐active layer, and Pleistocene tills to downstream systems. Here we investigate the biolability of thaw‐released dissolved organic carbon (DOC) on the Peel Plateau and compare our results to previous studies from nontill‐dominated landscapes. Similar to other Arctic regions, biolability was significantly greater for slump‐derived DOC (retrogressive thaw slump runoff) than for DOC from paired, unimpacted locations. However, runoff source was an important control on biolability. Lability was greater for slumps releasing water with a Holocene‐like δ18O signature than for slumps with a more Pleistocene‐like signature, while a small slump, with runoff δ18O similar to the modern active layer, showed no biolability increase. Similar to other Arctic regions, biolability was strongly related to DOC aromaticity and molecular weight. However, lability also increased significantly with increasing nutrients, which has not been shown universally. Previous work has shown that DOC concentration dynamics differ sharply on the Peel Plateau when compared to other permafrost thaw landscapes. This work indicates that the lability of permafrost DOC may be relatively uniform across variable Arctic regions, although some factors—such as the importance of nutrient status—may need further exploration.