Ground surface temperature variability in rock glaciers from a marginal periglacial environment: Evidence from the southern Carpathians

Long-term observations of ground thermal conditions remain scarce in marginal mountain permafrost environments, where permafrost occurs in isolated patches strongly influenced by local conditions. This study presents one of the most extensive ground surface temperature (GST) datasets from southeastern Europe, comprising up to 15 years of observations (2009–2024) from 17 sensors installed on 13 rock glaciers in the Southern Carpathians, Romania. We examine the ground thermal regime, assess the influence of atmospheric forcing and site-specific conditions, evaluate implications for permafrost occurrence, and investigate recent thermal changes. Mean annual ground surface temperatures at sites located above 2050 m generally ranged from about −1 to 1.5 °C while winter equilibrium temperatures (WEQT) were commonly below −2 °C and often below −3 °C, indicating conditions compatible with permafrost persistence. Despite broadly coherent interannual fluctuations across the monitoring network, substantial and persistent thermal differences occur among sites. Mixed-effects modelling showed that atmospheric forcing explained only part of the thermal variability, whereas including local topographic complexity substantially increased the variance explained by the fixed effects. This indicates that a common regional climatic signal is strongly modulated by local topographic conditions. The longest continuous record, at D1, shows a positive tendency in MAGST and a significant warming trend in WEQT over 2009–2024, although the statistical significance of the WEQT trend is sensitive to individual years. In contrast, spring GST shows a significant warming trend that remains significant after correction for multiple testing. The predominantly cold GST conditions, together with previous geophysical evidence and regional permafrost modelling, support the persistence of isolated permafrost at several monitored rock glaciers. Overall, the results reveal strong local modulation of regional climatic forcing and demonstrate the importance of long monitoring records for detecting thermal changes in marginal mountain permafrost environments.