Soil moisture as a key control on active layer thickness prediction on James Ross Island, Antarctica

Thermal properties of permafrost-affected soils play a key role in determining their response to ongoing climate warming. These properties influence the rate of active layer thickening and govern whether permafrost degradation is amplified or inhibited. Soil thermal characteristics are closely linked to other physical soil factors, with moisture often considered the most critical due to its potentially high interannual variability. In the eastern Antarctic Peninsula, projections indicate precipitation changes between −5 and +10%. However, it remains unclear whether these changes will have a noticeable effect on soil moisture, as the area is generally classified as polar-arid, with very low effective precipitation throughout the year. We therefore hypothesize that drying mechanisms will prevail, namely (a) increasing surface evapotranspiration driven by surface warming and (b) enhanced infiltration into the ground due to thickening of the active layer.

In this study, we present potential trajectories of active layer thickness (ALT) evolution on James Ross Island, Antarctic Peninsula, for the period 2010–2050 and different soil moisture scenarios. ALT was predicted using the Stefan model parameterized by: (a) climate outputs from the WRF model forced by SSP2-4.5 at a 2 km spatial resolution and (b) laboratory analysis of the relationship between soil thermal conductivity and soil moisture. Experiments were conducted using an ISOMET 2114 soil thermal properties analyzer on samples collected from three sites. Soil thermal properties were measured on samples with a fixed bulk density across several moisture states, ranging from fully saturated to completely dry.

The Stefan model was run for four soil moisture scenarios (5%, 15%, 25%, and 35%). Predicted ALT under the driest scenarios (5% and 15%) was approximately 40 cm deeper than under the wettest scenario (35%). Overall, the results indicate an increase in ALT under SSP2-4.5 conditions by 2050.