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Employing synthetic soil environments to test the impact of freeze-thaw and pore geometry on iron, phosphorus, and carbon interactions in permafrost-affected soil

EMSL Project ID


Arctic warming is accelerating permafrost thaw, exposing previously frozen soil to repeated freeze-thaw disturbance. Freeze-thaw cycles can alter the physical and geochemical environment with implications for carbon stabilization and nutrient availability in arctic tundra soils. While physical impacts to soil pores have been documented following freeze-thaw, the role of soil pore morphology and geometry in freeze-thaw driven chemical transformations remains understudied. Understanding how freeze-thaw alters the distribution of redox conditions and elemental associations (iron, carbon, and phosphorus) across pore networks and within individual pores is necessary for predicting mechanisms of carbon destabilization in warming permafrost-affected soils. Our proposed project employs synthetic soil environments and X-ray Photoelectron Spectroscopy (XPS) to assess the role of pore geometry on geochemical transformations following 1, 2, and 5 freeze-thaw cycles. Micromodels will be designed based on previous XCT-resolved pore networks in permafrost aggregates from Toolik, Alaska. Synthetic soil micromodels will be constructed with and without embedded iron minerals. Micromodels with embedded iron minerals will be used to target the impact of freeze-thaw cycles and pore morphology on iron associations with added carbon and phosphorus. Synthetic soil micromodels without embedded iron oxides will undergo flooding with oxygen-free, iron-rich water followed by an addition of oxygenated water to investigate the distribution of redox conditions and iron oxidation across the pore network under repeated freeze-thaw. Our micromodel experiments will be complemented by bulk soil characterization and mineral grain imaging from permafrost-affected soils in Toolik, Alaska, allowing for upscaling of pore-level findings. Buried mineral bags will contain ferrihydrite-coated quartz, manganese oxide-coated quartz, and quartz, and undergo imaging analysis via XPS. Bulk soil will undergo a freeze-thaw incubation (1, 2, and 5 freeze-thaw cycles) and analysis via Fourier transform ion cyclotron mass spectrometry (FTICR-MS), X-ray diffraction (XRD), and Mössbauer. Results of this research will be used to determine how the pore-scale effects of freeze-thaw may alter redox chemistry, nutrient availability, and carbon loss in a warming Arctic.

Project Details

Project type
Exploratory Research
Start Date
End Date


Principal Investigator

Erin Rooney
University of Tennessee


Elizabeth Herndon
Oak Ridge National Laboratory

Team Members

Matthew Berens
Oak Ridge National Laboratory

Kristen Butler
University of Tennessee