Thawed soil portions during deep winter in permafrost regions (Eight Mile Lake, Alaska): studying talik connectivity with silicon isotopes
(2025) ELI-Day 2025 — Location: Louvain-la-Neuve (27.May.2025)
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- Authors
Henrion, Maud 
- Abstract
- In permafrost regions from the Arctic, soils are composed of permafrost (i.e., perennially frozen ground) located below an active layer (i.e., seasonally frozen ground). In deep winter, portions of soil remain unfrozen in the active layer, leading to talik formation. These portions of unfrozen soils can be surrounded by frozen soil (closed talik), or connected to each other (open talik) which drives lateral water pathways. Maintaining lateral water flow during deep winter has potential implications for soil biogeochemical connectivity, but the extent of talik connectivity remains poorly quantified and difficult to assess. Here, we use silicon (Si) isotope measurements in soil pore water to identify open and closed taliks. Silicon isotopes are analyzed on soil pore water collected in February-March 2024 at Eight Mile Lake, Alaska, USA in soils from water tracks where taliks were identified. Our hypothesis to use Si isotopes to distinguish the two systems is the following : in a closed talik, silicic acid concentration is increasing upon freezing, leading to amorphous silica precipitation that induces Si isotope fractionation with 28Si preferentially incorporated into the colloidal amorphous silica, leaving the residual solution enriched in 30Si. In an open talik, the saturation for amorphous silica precipitation is not reached, which does not lead to Si isotope fractionation. Soil pore waters are therefore expected to present different δ30Si values whether the talik is open or closed. These data will allow us to better understand the biogeochemical connectivity in arctic soils during deep winter, which notably influences the release of permafrost carbon into the atmosphere.
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Citations
Villani, M., Roux, P., Henrion, M., Denis, G., Schuur, E., & Opfergelt, S. (2025). Thawed soil portions during deep winter in permafrost regions (Eight Mile Lake, Alaska): studying talik connectivity with silicon isotopes. ELI-Day 2025, Louvain-la-Neuve. https://hdl.handle.net/2078.5/269629