Connie Harpur

Ice-marginal lakes are increasingly widespread around the Greenland Ice Sheet (GrIS), but their influence on ice dynamics remains poorly constrained. Elsewhere, recent work has shown that ice-contact lakes are more thermally complex than previously thought, with potential implications for rates of melt undercutting and calving losses. Here, we assess the relationship between lake thermal regime and calving frequency at a lake-terminating outlet glacier in west Greenland using in situ observations collected during the summers of 2024 and 2025. Lake water temperature varied across the summer season, exhibiting a distinct warm phase during August characterised by a positive thermal gradient and brief period of stratification. Calving activity was dominated by waterline and collapse events, with event frequency peaking during the warm lake phase. Statistical modelling indicates that this was also the period when lake water temperature and calving frequency were most strongly associated. These findings suggest that intraseasonal changes in lake thermal structure may modulate calving behaviour, likely through enhanced melt undercutting. Overall, we highlight the potential for thermally driven calving to become an increasingly important mechanism of ice-loss at lake-contact margins of the GrIS with continued climate warming, and thus lake warming.

Ice-marginal lakes are increasingly widespread around the Greenland Ice Sheet (GrIS), but their influence on ice dynamics remains poorly constrained. Elsewhere, recent work has shown that ice-contact lakes are more thermally complex than previously thought, with potential implications for rates of melt undercutting and calving losses. Here, we assess the relationship between lake thermal regime and calving frequency at a lake-terminating outlet glacier in west Greenland using in situ observations collected during the summers of 2024 and 2025. Lake water temperature varied across the summer season, exhibiting a distinct warm phase during August characterised by a positive thermal gradient and brief period of stratification. Calving activity was dominated by waterline and collapse events, with event frequency peaking during the warm lake phase. Statistical modelling indicates that this was also the period when lake water temperature and calving frequency were most strongly associated. These findings suggest that intraseasonal changes in lake thermal structure may modulate calving behaviour, likely through enhanced melt undercutting. Overall, we highlight the potential for thermally driven calving to become an increasingly important mechanism of ice-loss at lake-contact margins of the GrIS with continued climate warming, and thus lake warming.

Ice-marginal lakes can alter glacier dynamics, typically accelerating mass loss. The number and size of lakes bordering the Greenland Ice Sheet have increased over recent decades, but their influence on the velocity of outlet glaciers remains largely unquantified. Here, we compare the longitudinal velocity profiles of 102 lake- and land-terminating glaciers across the Greenland Ice Sheet. We find that lake-terminating glaciers are 231% faster at the terminus and exhibit enhanced ice speeds up to ~3.5 km inland. Furthermore, ~44% of lake-terminating glaciers accelerate towards their termini, compared to only ~4% of land-terminating glaciers. The relationship between lake size and glacier behaviour is complex, but glaciers terminating in the largest lakes generally exhibit greater rates of down-ice acceleration than those terminating in the smallest lakes. Together, these results demonstrate that outlet glaciers respond dynamically to lakes at their termini, which should be accounted for in models of ice sheet evolution.

At present, 10% of the Greenland Ice Sheet (GrIS) margin terminates in a lake, but this is forecast to increase significantly over coming decades with ongoing retreat and thinning of the ice margin. This is important because the existence of more and larger lakes implies greater mass loss at the margin as well as an increase in dynamic thinning up-ice. At the same time, non-glacial lake surface waters worldwide have been shown to be warming yet the record of temperature change in ice-marginal lakes is extremely sparse. These ice-marginal lakes are likely to become increasingly important drivers of mass loss, and so there is an urgent need to investigate more closely the connection between their evolution and changes in the ice sheet. Therefore, a key objective is to explore the thermal properties of these lakes.The majority of Greenland’s ice marginal lakes are small (

Large parts of the Greenland Ice Sheet are fringed by ice-marginal (or ice-contact) lakes. These lakes have increased in number and size as a result of enhanced ice melt and the retreat of the ice sheet margin over recent decades. It has historically been assumed that Greenlandic ice-marginal lakes exist at a relatively uniform temperature of around 1°C year-round, thus having minimal influence on ice dynamics and subaqueous melt rates at the ice-water interface. However, there are almost no in-situ temperature measurements to test this hypothesis, meaning their influence on future ice sheet behaviour remains unclear. Here, we present continuous time series of lake water temperatures collected between July 2024 and August 2025, within three lakes on the western margin of the Greenland Ice Sheet. The results show that lake surface temperatures reached highs exceeding 10°C, with water temperatures above 4°C throughout the entire water column of one study lake during summer months. Summer stratification often persisted for several weeks, whilst inverse stratification was observed when water temperatures fell below 4°C. During winter months, surface ice cover maintained stable inverse stratifications, with lake temperatures ranging between 0 and 4 °C. Although lake temperatures remained largely stable during winter, one lake exhibited a cooling trend and significantly higher variability, potentially indicative of continued subglacial meltwater input.We combine our sub-hourly lake temperature measurements with meteorological, lake turbidity and ice front calving data, enabling us to investigate sub-diurnal to seasonal controls on lake temperature variability. These analyses show how neighbouring lakes can have markedly differing thermal characteristics, likely due to differences in size, localised topography and variable subglacial and supraglacial meltwater inputs. Our results highlight how uniformly cold temperature values are likely unsuitable when modelling ice-lake dynamics, and that lake terminating sectors of the ice sheet may be experiencing greater rates of frontal ablation than previously realised.

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.

Glaciers terminating in lakes typically flow, thin and lose mass more rapidly than those that terminate on land. This is due to a range of thermomechanical processes exerted at the lake-ice interface, where lake waters drive melt-induced undercutting, enable flotation and facilitate calving. In Greenland, ice marginal lakes (IMLs) have increased in size and number over recent decades and now occupy more than 10% of the ice sheet margin. Despite this, very few observations of their effects on ice dynamics exist, meaning they remain largely unaccounted for in models of ice sheet change.Here, we use ITS_LIVE ice surface velocity data and the How et al. (2021) IML inventory to compare the flow characteristics of 102 lake-terminating outlet glaciers and 102 neighboring land-terminating outlet glaciers across the Greenland Ice Sheet (GrIS) during 2017. We find that along-flow decelerations are much less pronounced at lake- versus land-terminating glaciers, and that some lake-terminating glaciers (n = 33) even speed up towards the ice margin. In turn, lake-terminating glaciers are on average 4.6 times faster than their land-terminating counterparts within the terminus region. Moreover, the fastest flowing glaciers are found to terminate in the largest lakes, suggesting that lake influence evolves with lake development. Ultimately, these observations demonstrate the capacity of IMLs to enhance the surface velocity of Greenlandic outlet glaciers, highlighting their potential to accelerate future mass loss from the GrIS.