Air Temperature and Thermal Regime Evolution in Livingston and Deception Islands, Maritime Antarctica (2000–2022)

Near-surface air temperature is the main atmospheric forcing of frozen-ground systems in maritime Antarctica, yet most studies have emphasized mean annual or seasonal trends rather than thermal-regime evolution. This study analyzes hourly air-temperature records from eight PERMATHERMAL monitoring stations on Livingston and Deception Islands (South Shetland Islands, Antarctica) for 2000–2022 to evaluate changes in mean conditions, daily thermal regimes, degree-day forcing, and their implications for frozen ground. Hourly data were aggregated to daily, monthly, annual, and thermal-year scales, and valid days were classified into six thermal regimes (F1, F2, IS, FT, T2, and T1). FDD, TDD, annual degree-day balance (BDD), and freezing and thawing season duration were also calculated. Recent warming is expressed not only as higher mean annual air temperature, but also as a reorganization of the annual thermal regime, with fewer cold days, more thaw-related conditions, and less negative BDD values at most stations. These changes are consistent with previously reported GST evolution and indicate a shift in atmospheric forcing toward weaker freezing dominance and more thaw-favorable conditions. However, their implications for active-layer thickness and permafrost stability should be interpreted as climatic indications rather than as the direct evidence of ground thermal change.