The Impact of Freeze-Thaw Cycles to the Physical and Biogeochemical Properties of Alaskan Permafrost Soils

• Main Author: Rooney, Erin C.
• Other Authors: Kleber, Markus, Lybrand, Rebecca A., Bailey, Vanessa L., Hatten, Jeffery, Dragila, Maria, Bachelet, Dominique, Kennedy, Robert, Crop and Soil Science
• Format: Doctoral or Postdoctoral Thesis
• Language: English; unknown
• Published: Oregon State University
• Subjects: Arctic; permafrost
• Online Access: https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/2n49t887p

Arctic warming is exposing thawing permafrost to repeated freeze-thaw, a disruptive process that can alter soil biogeochemistry and physical structure. To investigate the impact of permafrost exposure to freeze-thaw, soil response was tested across three scales: 2.5 cm³ aggregates, a forested hillslope, and two sites at contrasting latitudes. XCT imaging was employed to investigate pore deformation while FT-ICR-MS informed comparisons of carbon chemistry at the soil horizon, hillslope, and site levels. The initial stages of pore-scale freeze-thaw deformation following permafrost thaw resulted in decreasing connectivity and both expansion and collapse of pore throats with potential ramifications for spatial access to carbon and water holding capacity. At the hillslope scale, canopy-driven differences in soil temperature and carbon decomposition were more prevalent in conditions with lower moisture and thinner organic mats compared with high-moisture downslope soils. Across sites with differing freeze-thaw histories, there was greater oxidation of carbon molecules and loss of aliphatics following experimental freeze-thaw at the lower latitude site. Our findings indicate that factors such as freeze-thaw history, moisture, and organic mat thickness may influence carbon response to warming in permafrost soils, resulting in a heterogeneous response to freeze-thaw at both the site and hillslope scale.