Pore size heterogeneity and groundwater flow as key factors contributing to subsea permafrost change in the Beaufort Sea

Recent observations indicate that Arctic permafrost is warming and degrading rapidly. While the processes disrupting terrestrial permafrost are now relatively well documented, the dynamics of subsea permafrost on Arctic continental shelves remain poorly constrained. In particular, the combined influence of sedimentary heterogeneities and groundwater circulation remains largely underrepresented in current models. 
 
We present a multiphysical numerical modelling approach to better constrain the thermo-hydrological evolution of subsea permafrost in the Beaufort Sea. The model explicitly incorporates thermal conduction and advection, salinity transport, water-ice phase changes, and realistic sediment stratification (sand, silt, and clay) resulting from marine transgression and regression cycles during previous glacial-interglacial cycles. Our results show that lithology exerts a major control on the distribution of submarine permafrost. Clay-rich units, characterised by low permeability, have a drop in melting temperature depending on pore size (Gibbs–Thomson equation), leading to high spatial heterogeneity in the ice fraction, consistent with observations from recent seismic data. Conversely, sandy units, which are more permeable, can promote upward groundwater flows. Under conditions of negative seabed temperatures, these flows induce local desalination near the surface and the formation of new ice, consistent with recent field observations.
 
Our simulations include the last glacial–interglacial cycle (approximately 125 ka) and future warming scenarios, allowing us to evaluate both the glacial heritage and the transient response of the system to climate forcings. Comparing modelling results with drilling and seismic survey data, we provide a theoretical basis for interpreting field data. This study highlights the need to explicitly integrate sedimentary stratification and hydrogeological processes to reduce uncertainties about the future evolution of subsea permafrost and associated geological risks.