Permafrost-derived dissolved organic matter composition varies across permafrost end-members in the western Canadian Arctic

Abstract

Organic matter, upon dissolution into the aqueous state as dissolved organic matter (DOM), can undergo mineralization by microbes. There has been increasing effort to characterize DOM released from thawing permafrost because it may perpetuate a permafrost carbon feedback. Permafrost-derived DOM often has a composition that can be highly susceptible to mineralization by microbes, but most studies to date that characterize permafrost-derived DOM have been limited to select regions, and tend to focus on a single type of permafrost (sometimes unspecified) that reflects a particular deposit type. Importantly, diversity in the nature of the deposit, formation of permafrost, and thaw modification processes leads to spatial and stratigraphic variability in its properties, but our understanding of variation in the composition of DOM derived from differing permafrost types (end-members) is poor. Here, we used ultrahigh-resolution mass spectrometry to characterize DOM composition derived from a series of permafrost end-member types that are commonly found within the thaw-vulnerable western Canadian Arctic, including: tills (glacially deposited), diamicton (thawed and remobilized material of mixed origin), lacustrine (lake basin sediments into which permafrost has aggraded), peat (partially decomposed organic material), and Yedoma (syngenetic silty loess) deposits. We identified marked variation in DOM composition among permafrost end-member types. Tills were compositionally dissimilar to all other permafrost end-members. Compounds unique to Yedoma were predominantly aliphatic, while compounds unique to peat, lacustrine, and diamicton spanned saturation and oxygenation gradients. All permafrost leachates were generally higher in aliphatics, lower in aromatics, and less oxygenated than active layer leachates. Compositional differences appear to reflect variation in permafrost parent materials, and particularly strong effects from past modification processes while in the unfrozen or thawed state. Constraining DOM composition and assessing its stratigraphic variability will become more pressing as the spatial and stratigraphic extent of thaw increases with future warming.

Terrestrial Dissolved Organic Matter Mobilized From Eroding Permafrost Controls Microbial Community Composition and Growth in Arctic Coastal Zones

“…Our results show that the composition and biodegradability of DOM differs between post-glacial landscape units and that these differences are related to the glacial processes. In agreement with our results, a recent study also found a coupling between permafrost soil formation and DOM character for different permafrost end-member types (tills, diamicton, lacustrine, peat, and Yedoma deposits) (MacDonald et al, 2021). In addition, different soil-forming factors such as ice content, permafrost extent and parent material (epigenetic vs. syngenetic formation) shape the biogeochemical response to permafrost thaw in aquatic systems (Tank et al, 2020).…”

Pan‐Arctic Riverine Dissolved Organic Matter: Synchronous Molecular Stability, Shifting Sources and Subsidies

“…In Sweden (Hodgkins et al., 2016), Russia (Gandois et al., 2019), and the Canadian Arctic (Fouché et al., 2017), waters draining permafrost thaw (i.e., thermokarst) features have shown greater contributions of heteroatom‐containing formulae and/or microbial DOM than waters draining less degraded permafrost landscapes, suggesting the increasing importance of microbial DOM sources with increasing water residence time and flow depth in soils due to thaw. Fundamentally, differences in type and extent of permafrost impact hydrology and DOM chemistry (MacDonald et al., 2021; O'Donnell, Aiken, Swanson, et al., 2016). The six watersheds in this study encompass a continuum of types of surface‐groundwater connectivity.…”

Limited Presence of Permafrost Dissolved Organic Matter in the Kolyma River, Siberia Revealed by Ramped Oxidation

“…Through the use of FT‐ICR MS, we saw a large number of the aliphatic compounds present in the undegraded permafrost (t0) but absent in the Kolyma River (t0) (Figure ). Recent studies have noted the relative enrichment of aliphatic assigned formula in yedoma permafrost derived DOM (Drake et al., 2018; MacDonald et al., 2021; Spencer et al., 2015). This aliphatic rich signature (high H/C) is a distinctive characteristic of permafrost‐influenced waters and is not reported in either the mainstem of Arctic rivers or other riverine DOM (Drake et al., 2018; Spencer et al., 2015; Stubbins et al., 2010).…”

“…Ultimately, the fate of permafrost DOM is tied to its composition which is linked to how the permafrost formed as well as past thaw modification, with different permafrost endmembers showing marked DOM compositional variability (MacDonald et al., 2021; Spencer et al., 2015; Ward & Cory, 2016). DOC in streams thawing from yedoma permafrost in the Kolyma Basin is 14 C depleted (∼20,000 14 C yBP old) and exhibits an exceedingly aliphatic (high H/C) dissolved organic matter (DOM) compositional signature (Spencer et al., 2015; Stubbins et al., 2017).…”