Advancement in Permafrost Modeling: The Role of Adsorption-Aware Thermodynamics in Fine-Grained Soils

Permafrost and seasonally frozen ground are critical components of the Arctic cryosphere, playing a fundamental role in regulating hydrological processes. Permafrost underlies approximately 13-18% of the Northern Hemisphere’s exposed land surface and stores vast quantities of organic carbon. Its thermal stability has profound implications for infrastructure, carbon cycle, and hydrological processes under changing climate. Modeling permafrost dynamics is critical, yet standard cryo-hydrological models often struggle to capture the complex phase changes in fine-grained soils, particularly in clayey soils where liquid water persists at temperatures well below the classical freezing point.

To overcome this challenge, we propose an advanced thermodynamic framework that moves beyond the classical soil freezing characteristic curves (SFCC). By incorporating adsorption potential (μ_ads), this framework accounts for the exponential energy decay near mineral surfaces, physically explaining the persistence of liquid water in clay nanopores down to −80℃. While the theoretical foundation for this approach is established in the enthalpy-based solver WHETGEO-1D (Tubini & Rigon, 2022), we evaluate its significance through a comparative study using field forcing and hypothetical experiments.

We conducted this analysis in two stages. First, the 1D GEOtop model was applied to two sites along the Inuvik-Tuktoyaktuk Highway (Canada) using ERA5 and JRA-3QG reanalysis data (1950–2023). At this stage, the model performance was evaluated against ground temperature observations (2017–2022) to ensure realistic surface fluxes and ground temperatures. Second, using these validated forcing conditions, we performed hypothetical experiments to compare the classical and adsorption-aware frameworks across different soil types.

Our initial analysis indicates that the classical and adsorption-aware frameworks yield divergent results in the timing of latent heat exchange and moisture redistribution. By bridging the gap between pore-scale thermodynamics and Darcy-scale modeling, this study provides a robust roadmap for implementing next-generation physics into permafrost models.