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Plot-scale (660 square centimeters (cm2) measurements of methane (CH4) were made using a portable chamber system at North Star Yedoma (NSY), a grassland field in interior Alaska characterized by thermokarst (thaw) mounds forming due to degradation of ice-rich Yedoma, polygonal-ground permafrost soil and at 25 other extensive thermokarst-mound study sites in Alaskan tundra, boreal forest and grassland ecosystems. Measurements were made during summer, winter, and thaw seasons from March 2020 through March 2023. Soil temperature and moisture were measured in-situ with handheld probes on unfrozen soils. Thermokarst mounds are regularly spaced conical hills (≤15 meters (m) diameter, ≤5 m height) separated by trenches (≤3 m width) that form in degrading ice-rich Yedoma permafrost environments. Their formation and morphology are based on the melting of large syngenetic ice wedges in polygonal patterned ground, where the polygon margins (trenches) underlain by ice wedges subside faster and deeper than the less ice-rich polygon centers (mound tops), leaving behind distinct conical-mound features in regularly-spaced patterns. Thermokarst mounds are known to emit nitrous oxide [Marushchak et al. 2021, doi.org/10.1038/s41467-021-27386-2], but their carbon fluxes have until now remained largely uncharacterized. This data set characterizes thermokarst-mound methane fluxes in Alaska.
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The Biophysical Role of Water and Ice Within Permafrost Nearing Collapse: Insights From Novel Geophysical Observations
Abstract The impact of permafrost thaw on hydrologic, thermal, and biotic processes remains uncertain, in part due to limitations in subsurface measurement capabilities. To better understand subsurface processes in thermokarst environments, we collocated geophysical and biogeochemical instruments along a thaw gradient between forested permafrost and collapse‐scar bogs at the Alaska Peatland Experiment site near Fairbanks, Alaska. Ambient seismic noise monitoring provided continuous high‐temporal resolution measurements of water and ice saturation changes. Maps of seismic velocity change identified areas of large summertime velocity reductions nearest the youngest bog, indicating potential thaw and expansion at the bog margin. These results corresponded well with complementary borehole nuclear magnetic resonance measurements of unfrozen water content with depth, which showed permafrost soils nearest the bog edges contained the largest amount of unfrozen water along the study transect, up to 25% by volume. In situ measurements of methane within permafrost soils revealed high concentrations at these bog‐edge locations, up to 30% soil gas. Supra‐permafrost talik zones were observed at the bog margins, indicating talik formation and perennial liquid water may drive lateral bog expansion and enhanced permafrost carbon losses preceding thaw. Comparison of seismic monitoring with wintertime surface carbon dioxide fluxes revealed differential responses depending on time and proximity to the bogs, capturing the controlling influence of subsurface water and ice on microbial activity and surficial emissions. This study demonstrates a multidisciplinary approach for gaining new understanding of how subsurface physical properties influence greenhouse gas production, emissions, and thermokarst development.
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- Award ID(s):
- 1636476
- PAR ID:
- 10447330
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Earth Surface
- Volume:
- 126
- Issue:
- 6
- ISSN:
- 2169-9003
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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