Dissolved Organic Carbon in Permafrost Soils: Where, When, and How Much Will be Released?

Abstract:

Terrestrial ecosystems across the northern permafrost region store large quantities of soil organic carbon (C). Lateral transport from this C pool as dissolved organic carbon (DOC) represents a significant source of organic C in circum-polar aquatic ecosystems, acting as a key substrate for microbial metabolism. As the permafrost region warms and soils thaw, this previous unavailable C pool becomes vulnerable to enhanced lateral transport and microbial decomposition. This will potentially have negative effects on a net C balance which is predominantly dependant on aquatic processing of terrestrially derived DOC. The quantity of permafrost-derived DOC exported laterally to aquatic ecosystems and its vulnerability to enhanced microbial decomposition remains uncertain. Yet, it is likely that both the quantity and lability of exported DOC will depend on characteristics of the terrestrial ecosystem the DOC is originally derived from and that ecosystems response to permafrost thaw. Here, we present a new circum-polar permafrost soil DOC dataset consisting of ~100 studies, including more than 1,500 values of DOC concentrations from pristine and disturbed permafrost soils across the circum-polar permafrost region. This meta-analysis uses studies published between 2000 – 2020 and includes a wide set of ecosystem properties such as geographical location, geomorphology, permafrost distribution and condition, soil type, and ecosystem type. This study highlights not only how concentrations of DOC differ between organic- or mineral-rich deposits across the circum-polar permafrost region, but also how the biodegradability and intrinsic controls on DOC decomposition vary with soil or ecosystem type. With this meta-analysis we aim to assess how future lateral transport of DOC will respond to the predicted increase of thaw in terrestrial permafrost ecosystems and highlight areas, in terms of geographical location and ecosystem classification, with a high potential for increased lateral transport of terrestrial permafrost DOC to freshwater and marine systems.