Temporal decomposition of near-surface air temperature in Maritime Antarctica: seasonality, trend and residual variability across Livingston and Deception islands

Abstract The Antarctic Peninsula region is one of the most climatically dynamic sectors of Antarctica, yet most temperature studies in the area have focused on mean values, linear trends or thermal extremes without explicitly separating the seasonal, long-term and irregular components of the signal. Here, we analyse near-surface air temperature series from eight stations of the PERMATHERMAL network on Livingston and Deception islands for the period 2000–2022 using additive seasonal-trend decomposition based on locally estimated scatterplot smoothing (LOESS). Hourly observations were aggregated to daily and monthly series and decomposed into seasonal, trend and remainder components to evaluate how thermal variability is structured in time and how it differs among stations. The results show that the temperature signal is dominated by a strong annual cycle, especially at the monthly scale, confirming that recent atmospheric change in the South Shetland Islands is superimposed on a still strongly recurrent polar thermal regime. The trend component is positive at most stations, but its magnitude is spatially heterogeneous and does not follow a simple altitudinal pattern. The strongest background evolution is observed at Crater Lake, Juan Carlos I and Sofía stations, whereas weaker changes occur at other sites, particularly Incinerador station. The remainder is also substantial, particularly at the daily scale, and reveals a marked spatial and seasonal structure, with larger residual variability in winter and at stations such as Sofía and Crater Lake. Event analysis based on the residual component shows that warm and cold residual departures can be coherent across the network while differing strongly in local intensity, as illustrated by years of widespread residual event activity such as that which occurred in 2011 and 2015. These results show that additive decomposition provides a useful framework for understanding how recent atmospheric change is organized in time in Maritime Antarctica and for identifying the combined roles of seasonal structure, low-frequency evolution and short-term thermal residual departures in environments close to the climatic threshold of frozen-ground stability.