Responses of thermokarst pond dynamics to climate change on Inexpressible Island, Antarctica (1987–2023)

Inexpressible Island is an ice-free island located in Antarctica, characterized by a distribution of numerous thermokarst ponds, which serve as warning indicators of permafrost degradation, and their evolution can indirectly reveal local climate change. In this study, we explored changes in thermokarst ponds on Inexpressible Island over the period 1987–2023 using Landsat series dataset and Sentinel-2 data. Over the study period, the total pond area exhibited an 11.3% increase, with the lowest value recorded in 1990 and the highest in 2019. Cumulatively, 54 ponds were monitored during the period with their count rising from 37 in 1987 to 39 in 2023. Ponds were classified as either persistent or transient, the latter not continuously existing throughout the study period. Among the 22 persistent ponds, an overall increasing trend in their total area was observed, with most experiencing area augmentation. However, a few persistent ponds, situated in the higher elevations of the northwestern part of the island, exhibited a slight shrinkage. The number of transient ponds displayed considerable fluctuations, reaching its peak at 30 in 2018 and 2019, contrasting with only 5 transient ponds recorded in 1999. The occurrences of transient lake ponds varied, ranging from 2 to a maximum of 26. This study highlights the dominant influence of temperature on the monthly, seasonal, and long-term dynamics of these ponds, while precipitation significantly affected the short-term variations. Additionally, the melting of ice wedges and the subsequent seepage into thawed permafrost formations were identified as potential processes that may affect pond persistence and drainage.