Modelling the evolution of permafrost temperatures and active layer thickness in King George Island, Antarctica, since 1950

Abstract. The dynamics of permafrost and the active layer is crucial for ecosystem processes in the ice-free areas of the Antarctic Peninsula, where a strong long-term warming trend, with an increase of 3.4 °C in the mean annual air temperature since 1950 has been recorded. The consequences of this warming on past and future permafrost degradation are still not fully understood, mainly due to the sparse spatial coverage and limited time span of borehole data, which have only been available since the mid to late 2000’s. This motivated the application of the CryoGrid Community Model for modelling ground temperatures at the bedrock drilled King Sejong Station borehole (KSS) in Barton Peninsula, King George Island. The objective was to assess the model's quality and potential for applicability in other ice-free areas of the Antarctic Peninsula, aiming to improve understanding of the recent evolution of permafrost temperature and active layer thickness and reconstitute the past evolution since 1950. ERA5 reanalysis data underestimated air temperature, strongly impacting the ground warming velocity and intensity in the shoulder seasons. Linear regression using in situ observations was used to correct the ERA5 forcing. The results of a short-term simulation from 2020–2022 evaluated against observations show that the model successfully represents the conditions at the KSS borehole. Down to 6 m depth correlations above 0.9 were obtained, while below 6 m, the correlations were above 0.8. Mean Absolute Error ranged from 0.1 to 0.7 °C. Active layer depths of 2.9 to 3.1 m showed an overestimation of c. 0.4 m. The long-term simulation of permafrost and active layer temperatures from 1950 to 2022 using ERA5 data showed a ground warming trend at 20 m of 0.25 °C/decade, accompanied by an increase of the active layer thickness of 2.0 m, from 1.5 m in 1950 to 3.5 m in 2022. The warming rate intensified significantly since 2015 to 0.9 °C/ decade.