DOI: 10.21963/13187
title: Detailed dissolved organic matter composition for different permafrost types across the western Canadian Arctic

description: 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 that reflects a particular deposit type. Importantly, diversity in permafrost history of formation and thaw modification processes have led to spatial and stratigraphic variability, but our understanding of variation in the composition of DOM derived from differing permafrost types (end-members) is poor. Here, we use Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) 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 processed mixed material), lacustrine (previously thawed lake basin sediments), 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 deposits were predominantly aliphatic, while compounds unique to peat, lacustrine, and diamicton deposits spanned saturation and oxygenation. All permafrost leachates were generally higher in aliphatics, lower in aromatics, and were less oxygenated than active layer leachates. Compositional differences appear to reflect not only variation in permafrost parent materials, but also a strong effect from thaw-driven modification processes. Constraining DOM composition and assessing its stratigraphic variability will become more pressing as the spatial and stratigraphic extent of thaw increases with future warming.
description: Borehole sites were initially selected by the Government of Northwest Territories to assess ground conditions prior to building a road, the Inuvik-Tuktoyaktuk Highway (ITH). The borehole samples presented the opportunity to quantify the geochemical and geotechnical characteristics and variability of the substrate, which could then be entered into the Northwest Territories Geotechnical Database. In collaboration with scientists at the Northwest Territories Geological Survey, and other scientists at the University of Alberta, we sought to further expand the geochemical characterization by completing a detailed compositional analysis for leachates derived from different permafrost types. The compositional analyses of the leachates were completed using a combination of ITH borehole sample material, collected in the winter of 2017, as well as more shallow samples from the same sites, collected in the summer of 2018. Additionally, samples were collected from one site in the Klondike region, Yukon. The specific objectives of the leachate compositional analyses were to assess (1) how DOM composition may vary across permafrost end-members that have contrasting formational histories and have been subject to varying degrees of thaw modification, and (2) how contemporary active layer samples from multiple terrain types compares to those from permafrost end-members. We used a highly detailed technique to characterize dissolved organic matter composition for the water-extractable fraction leached from diverse permafrost end-member types, including tills, diamicton, lacustrine, peat, and Yedoma deposits, as well as from contemporary active layer samples from multiple landscape types (peatland, riparian and hilltop). These data accompany a manuscript that will soon be submitted for consideration at Environmental Research Letters (citation forthcoming). Further geotechnical characterization of the borehole samples can be found in Ensom et al. (2020). Ensom, T., Morse, P.D., Kokelj, S.V., MacDonald, E., Young, J., Tank, S., Subedi, R., Grozic, E., and Castagner, A., 2020. Permafrost Geotechnical Borehole Data Synthesis: 2013 ̶ 2017 Inuvik-Tuktoyaktuk region, Northwest Territories; Northwest Territories Geological Survey, NWT Open Report 2019-012; Geological Survey of Canada, Open File 8652, 78 pages, geotechnical data, and appendices. https://doi.org/10.4095/321869