Refreezing is a critical component of the mass balance of glaciers in Svalbard, yet the processes and changes under a warming climate are not fully understood. Here, we investigate changes in firn properties of the Austfonna ice cap, Svalbard, using a combination of observations and model simulations. We analyze firn stratigraphy and density from five newly retrieved and 11 previously retrieved firn cores, collected at elevations ranging from 506 m a.s.l. to 791 m a.s.l. between 1958 and 2022. All cores exhibit frequent ice layers that indicate persistent refreezing of meltwater; however, no ice slabs (layers exceeding 1 m) were observed. A 13-year-long firn temperature time series from a site near the summit (773 m a.s.l.) shows that annual water percolation reaches depths of 7 m to over 13 m. A notable transition in the firn thermal regime occurred in 2013, transitioning from cold to temperate conditions above the firn-ice interface despite the seasonal cooling occurring in the upper firn layers. Simulations using the CryoGrid community model from 2009 to 2022 corroborate this thermal shift and suggest the development of a firn aquifer multiple times since 2013, with increasing duration and thickness over time.

Accelerated glacier mass loss across the Antarctic Peninsula has consequences for sea level rise and local ecology. However, there are few direct glaciological observations available from this region. Here, we reveal glacier changes on the James Ross Archipelago between 2010 and 2023. The median rate of glacier area loss (remote-sensing derived) increased over the study period, with the most significant changes observed in smaller glaciers. In situ measurements show that ablation has prevailed since 2019/20 with the most negative point surface mass balance change measured as −1.39 ± 0.12 m water equivalent at Davies Dome and Lookalike Glacier in 2022/23 (200–300 m a.s.l.). We identified a tripling of the frontal velocity of Kotick Glacier in 2015, which, combined with terminus surface elevation gains (bulging), suggests that this is the first surge-type glacier identified in Antarctica from velocity and surface elevation change observations. We contend that the glacier recession rate has increased due to increased air temperatures (0.24 ± 0.08°C yr−1, 2010–23), decreased albedo and glacier elevation change feedbacks. These processes could decrease glacier longevity on the archipelago. Future research should prioritise monitoring albedo and rising equilibrium-line altitudes and identify glaciers most vulnerable to rapid future mass loss.

The climatic conditions, particularly the sources of precipitation that enabled extensive glacial growth during the Last Glacial Maximum (LGM) in the European Alps, remain poorly constrained. Here, we apply an inversion method to reconstruct equilibrium line altitude (ELA) fields using glacier footprints, such as the moraines deposited by Alpine glaciers during the LGM. By employing a machine-learning emulator trained on outputs from a glacier-evolution model, we predict glacier maximal thickness. The emulator is integrated into a gradient-based inversion scheme to derive ELA fields consistent with LGM footprints. The results show that the reconstructed ELA fields align with those from previous studies, validating the robustness of our approach. Unlike existing inversion methods, our approach is more general and avoids restrictive assumptions. Notably, by incorporating the transient response of glaciers to climate variability (we do not assume steady state), we show that the cold spell period is crucial for interpreting the reconstructed climate patterns—an aspect previously overlooked. Our findings provide new insights into climatic variability during the LGM, particularly concerning the interaction between precipitation patterns and the cold spell period. Furthermore, the computational efficiency of our method makes it applicable to large-scale paleoclimate reconstructions based on glacier footprints.