In recent decades, Greenland’s marine-terminating glaciers have retreated and accelerated, contributing significantly to sea level rise. The presence of an ice mélange and its associated buttressing force on a glacier terminus has a significant impact on glacier advance and retreat. The buttressing force is modulated by mélange thickness, which is influenced by mélange melt rate, but our understanding of mélange melting remains limited. We model the melting of ice mélange by the ocean using MITgcm, focusing on the relationship between melt rate and mélange thickness. Melt rates generally increase with mélange thickness (thicker mélange reaches further into deep warm water) and are particularly sensitive at thicknesses shallower than 100 metres. We test three ways of incorporating the mélange thickness into a parameterisation of mélange melt rates with additional inputs of subglacial discharge and oceanic thermal forcing. We apply the most general parameterisation to 27 instances of ice mélange around Greenland, estimating summertime melt rates of 0.01–0.62 m/d. Melt rates are primarily controlled by oceanic thermal forcing, followed by mélange thickness. The development of these parameterisations represents a key step in advancing our understanding of ice mélange dynamics and enabling a representation of mélange in climate and ice sheet models.

The retreat and acceleration of Greenland’s marine-terminating glaciers are linked to enhanced submarine melting driven by ocean warming. Despite the significance of these ice-ocean interactions, observations of ice-front proximal waters remain limited due to logistical challenges. Buoyant subglacial meltwater plumes entrain deep, warm Atlantic waters during their ascent. Using a plume model, we demonstrate that when these plumes reach the surface in deep fjords (>400 m), their surface temperatures can serve as a proxy for subsurface ocean temperature variability. Here, we optimise and validate a Landsat sea surface temperature algorithm for Arctic waters using in situ measurements, with an accuracy of ∼0.4°C for Landsat 5, 7, 8 and 9. Applying this method, we analyse plume surface temperatures at Sermeq Kujalleq (Store Glacier) from 1985 to 2024 and compare Landsat-derived plume surface temperatures with plume model simulations forced by in situ measurements and four ocean reanalysis products. The Landsat-derived plume surface temperatures are of the correct magnitude and reveal trends consistent with expected interannual ocean variability. While large seasonal variability and confounding physical processes still make it difficult to isolate the subsurface signal, our 40 year record suggests that plume surface temperatures could become a useful proxy for subsurface ocean change.

Basal melting is a major component of Antarctic ice mass loss. It is mainly driven by the circulation of water in ice shelf cavities. One approximation of this circulation is by models of buoyant plumes rising along the ice shelf base. For large-scale ice sheet models, a local melt parameterization of plume models that can be applied at an ice shelf-wide scale is desirable, and such a parameterization has recently been proposed and shown to perform well compared to a spatially resolved plume model when the ice shelf profile is fixed. In this study, we test the local parameterization for a dynamically evolving ice shelf, which allows for feedbacks between basal slope and melt rate. We find that these feedbacks enhance melt for steep basal slopes and reduce melt for small slopes. This decreases the parameterization performance, and under certain conditions the parameterization introduces an unphysical melt discontinuity. This can lead to large differences in the predicted melt rate and ice shelf length compared to the nonlocal plume model. More generally, our findings suggest that i) local parameterizations should be applied with caution in coupled ice–ocean frameworks, and ii) melt parameterizations should be evaluated in coupled settings to avoid unwanted behavior.

Sea ice develops a porous structure as impurities from sea water are rejected during freezing. This study revisits factors regulating noble gas inclusion in sea ice and, for the first time, parameterizes the bulk sea ice–sea water partition coefficient (kiw)—the ratio of concentrations in sea ice to sea water—as a function of ice properties. Ten sea-water freezing experiments were conducted in a gas-tight chamber to quantify gas partitioning. Experimental kiw spanned kiw, helium = 1.31–1.90, kiw, neon = 0.29–1.34, kiw, krypton = 0.12–0.67, kiw, xenon = 0.12–0.66 and kiw, salt = 0.15–0.49, reflecting variations in ice growth rates and properties. Partitioning trends were analyzed against ice temperature, salinity and growth rate (n = 10) and brine porosity (n = 8). Bulk sea-ice salinity was the statistically strongest indicator of kiw and predicted >70% of variability in kiw, krypton and kiw, xenon. Doubling ice salinity (e.g. from 5 to 10) increased kiw by 140–150% for krypton and xenon. Neon did not exhibit statistically significant trends in kiw with ice properties, likely due to its small size and low solubility facilitating bubble nucleation and/or crystal lattice inclusion. Gases larger than the ice-Ih cavity radius showed nearly identical kiw, consistent with firn diffusion models.

Glacier ice melt, a key driver of sea level rise, depends on how the ocean currents interact with ice. The roughness and shape of the ice on scales smaller than 10 m are important and remain poorly understood due to a lack of observations. We investigate submarine ice roughness using fine-resolution multibeam sonar measurements from 13 grounded icebergs and a drone survey of a recently capsized floating iceberg in the temperate tidewater glacial fjord Xeitl Geeyi’ (LeConte Bay), Alaska. From these 14 icebergs, 55 gridded iceberg surfaces (20–40 cm resolution) were derived. We apply a spectral, scale-resolved approach to quantify iceberg roughness. Spectral analysis shows that 40 of these surfaces were dominated by vertically oriented channels with wavelengths ranging from 0.9 m to 3.7 m, likely shaped by buoyancy-driven meltwater plumes. Statistical analyses reveal a mean peak wavelength of 1.9 m, RMS height of 0.3 m, skewness of -0.3 and kurtosis of 4.3. Roughness at medium- to small-scales $\mathcal{O}$(0.5-5 m) can nearly double the ice–ocean boundary surface area and, when combined with iceberg-scale morphology $\mathcal{O}$(10 m), underscores the need to integrate realistic roughness and morphology parameters into melt models, which may improve melt predictions.

Glaciers that terminate in the ocean or lakes exhibit unique dynamics that can drive rapid change. These dynamics, governed by many complex and interacting processes, challenge calibration and validation of physics-based models. We take a data-driven approach to quantify the imprint of glacier–ocean interactions on global non-ice sheet glacier ice volumes. Using curated datasets, we build a hierarchy of models that capture the influence of ice shelves and grounded marine termini. We find that tidewater and lake-terminating glaciers are systematically thicker than glaciers ending on land. Summed globally, this effect accounts for about 20% of non–ice-sheet glacier volume. Thicker ice is observed both for glaciers with ice shelves, where buttressing supports upstream ice, and for water-terminating glaciers without shelves. We interpret this result in terms of a simple mechanical model whereby water pressure permits thicker termini than possible in air, consistent with theoretical limits on ice cliff height. Our results highlight how ice–ocean interactions shape the equilibrium geometry of glaciers, offering a large-scale complement to process-based studies of calving and frontal melt. While most global glacier models omit these interactions, our analysis motivates their inclusion in forecasts of glacier change and sea level rise.

Sequential photographic records of glacier termini go back to the mid-20th century, revealing climate-driven retreat. More recently, time-lapse imagery has enabled detailed analysis of glacier dynamics, including calving. Here, we use long-term, high-frequency (15 min) time-lapse images from May–October 2016 to manually investigate calving activity at Hansbreen, a marine-terminating glacier in Hornsund Fjord, Svalbard. We explore the spatio-temporal variability in calving frequency and styles along the glacier terminus and its relationship to environmental drivers. Average calving frequency was found to be 30 events d−1, and peaking at 60 d−1. The calving activity aligns well with air and ocean temperature at a seasonal scales, while some peaks in calving correspond to increased modeled meltwater runoff and rainfall. These links are inconsistent and reflect high complexity. Calving at Hansbreen varies greatly in time and across five delineated terminus zones. In two of the zones, over 60% of waterline events occur during ebb tide; these segments also experience regular ice cave formation. However, further efforts are needed to explore the high-frequency evolution of terminus morphology and its link to calving. Our dataset can also be used to train automated algorithms for calving detection from time-lapse imagery.

The mixture of icebergs and sea ice in tidewater glacier fjords, known as ice mélange, is postulated to impact iceberg calving directly through physical buttressing and indirectly through freshwater fluxes altering fjord circulation. In this contribution, we assess the textural characteristics of ice mélange in summer and winter at the terminus of Helheim Glacier, Greenland, using high resolution (1-3 m) X-band Synthetic Aperture Radar (SAR) imagery from the ICEYE small satellite constellation. The Grey Level Co-occurrence Matrix (GLCM) and statistical variations in pixel intensity downfjord reveal structural zoning within the mélange matrix in both summer and winter. The boundary between these zones represents the transition between ice concentrations, demonstrating structural weaknesses in the mélange that may persist throughout the year. Furthermore, we compare two iceberg segmentation methods, texture-based vs the Segment Anything Model (SAM). Both techniques detect large (> 0. 1 km2) icebergs in summer when pixel variations are larger, but SAM has high iceberg detection accuracy in both seasons. The detected icebergs stabilise near concentration boundaries in the mélange, suggesting they act as the nucleus of mélange zones and control matrix stability. Our study demonstrates the potential for using high-resolution ICEYE SAR imagery for studying dynamic processes in glaciology and beyond.

Basal channels are incised troughs formed by elevated melt beneath ice shelves. Channels often coincide with shear margins, suggesting feedbacks between channel formation and shear. However, the effect of channel position and shape on ice-shelf flow has not been systematically explored. We use a model to show that, as expected, channels concentrate deformation and increase ice-shelf flow speeds, in some cases by over 100% at the ice-shelf center and over 80% at the grounding line. The resulting increase in shear can cause stresses around the channels to exceed the threshold for failure, suggesting that rifting, calving and retreat might result. However, channels have different effects depending on their width, depth and position on an ice shelf. Channels in areas where ice shelves are spreading freely have little effect on ice flow, and even channels in confined regions of the shelf do not necessarily alter flow significantly. Nevertheless, if located in areas of vulnerability, particularly in the shear margins near the grounding line, melt channels may alter flow in a way that could lead to catastrophic ice-shelf breakup by mechanically separating shelves from their embayments.

We present a 1000 km transect of phase-sensitive radar measurements of ice thickness, basal reflection strength, basal melting and ice-column deformation across the Ross Ice Shelf (RIS). Measurements were gathered at varying intervals in austral summer between 2015 and 2020, connecting the grounding line with the distant ice shelf front. We identified changing basal reflection strengths revealing a variety of basal conditions influenced by ice flow and by ice–ocean interaction at the ice base. Reflection strength is lower across the central RIS, while strong reflections in the near-front and near-grounding line regions correspond with higher basal melt rates, up to 0.47 ± 0.02 m a−1 in the north. Melting from atmospherically warmed surface water extends 150–170 km south of the RIS front. Melt rates up to 0.29 ± 0.03 m a−1 and 0.15 ± 0.03 m a−1 are observed near the grounding lines of the Whillans and Kamb Ice Stream, respectively. Although troublesome to compare directly, our surface-based observations generally agree with the basal melt pattern provided by satellite-based methods but provide a distinctly smoother pattern. Our work delivers a precise measurement of basal melt rates across the RIS, a rare insight that also provides an early 21st-century baseline.

We present the first simulations of Jakobshavn Isbrae (Sermeq Kujalleq), west Greenland, using a 3D Stokes calving model that permits unrestricted advance and retreat. Using the position-based crevasse-depth calving law, the model is applied to simulate the calving dynamics of 2016–2017 season when Jakobshavn Isbrae is assumed to be stable because of the presence of a strong proglacial ice mélange. The calving law needs to be adjusted to avoid an underestimation of calving, but once adjusted the calving model simulates seasonal calving dynamics that reflect observed calving-driven retreat very well. We find that a crevasse penetration threshold of 94.5% best matches observations from satellite imagery. Additional, 2-year transient simulations show that although ice mélange is essential to the glacier's winter readvance, when removed, the glacier only retreats a couple of kilometres before reaching a stable position. While the backstress provided by the ice mélange allows the glacier to advance beyond this point, the retreated terminus position is determined by a combination of bed geometry and glacier dynamics. Ultimately, while the ice mélange allows winter readvance, cessation of the well-documented rapid retreat of Jakobshavn Isbrae will be influenced by the bed geometry.

Rift propagation, rather than basal melt, drives the destabilization and disintegration of the Thwaites Eastern Ice Shelf. Since 2016, rifts have episodically advanced throughout the central ice-shelf area, with rapid propagation events occurring during austral spring. The ice shelf's speed has increased by ~70% during this period, transitioning from a rate of 1.65 m d−1 in 2019 to 2.85 m d−1 by early 2023 in the central area. The increase in longitudinal strain rates near the grounding zone has led to full-thickness rifts and melange-filled gaps since 2020. A recent sea-ice break out has accelerated retreat at the western calving front, effectively separating the ice shelf from what remained of its northwestern pinning point. Meanwhile, a distributed set of phase-sensitive radar measurements indicates that the basal melting rate is generally small, likely due to a widespread robust ocean stratification beneath the ice–ocean interface that suppresses basal melt despite the presence of substantial oceanic heat at depth. These observations in combination with damage modeling show that, while ocean forcing is responsible for triggering the current West Antarctic ice retreat, the Thwaites Eastern Ice Shelf is experiencing dynamic feedbacks over decadal timescales that are driving ice-shelf disintegration, now independent of basal melt.

Greenland's marine- and land-terminating glaciers are retreating inland due to climate warming, reconfiguring the way the ice sheet interacts with its proglacial environment. Here we use three decades of satellite imagery to determine whether the ice-sheet margin is becoming more or less exposed to marine and lacustrine processes. During our 1990–2019 study period, we find that the length of ice-sheet perimeter in contact with the ocean shrank by 12.3 ± 3.8% (196.2 ± 10.4 km), due to the retreat of marine-terminating glaciers into narrower fjords. On the other hand, we find that the length of the ice-sheet perimeter in contact with freshwater lakes exhibited more divergent trends that is better explored at regional scales. The length of ice–lake boundaries increased in southwest, north and northwest Greenland but declined in southeast and central east Greenland. The magnitude of change we document during our study period leads us to conclude that the ice sheet is poised for further, substantial reconfiguration in the coming decades with consequences for the flux of fresh water, nutrients and primary productivity in Greenland's terrestrial and oceanic environment.

Basal channels, which are troughs carved into the undersides of ice shelves by buoyant plumes of water, are modulators of ice-shelf basal melt and structural stability. In this study, we track the evolution of 12 large basal channels beneath ice shelves of the Amundsen and Bellingshausen seas region in West Antarctica using the Landsat record since its start in the 1970s through 2020. We observe examples of channel growth, interactions with ice-shelf features, and systematic changes in sinuosity that give insight into the life cycles of basal channels. We use the last two decades of the record, combined with contemporary ice-flow velocity datasets, to separate channel-path evolution into components related to advection by ice flow and those controlled by other forcings, such as ocean melt or surface accumulation. Our results show that ice-flow-independent lateral channel migration is overwhelmingly to the left when viewed down-flow, suggesting that it is dominated by Coriolis-influenced ocean melt. By applying a model of channel-path evolution dominantly controlled by ice flow and ocean melt, we show that the majority of channels surveyed exhibit non-steady behavior that serves as a novel proxy for increased ocean forcing in West Antarctica starting at least in the early 1970s.

Ice tongues are unconfined by land on their lateral margins and are sensitive to external forcing from the ocean. They are found sporadically around the Antarctic coast but are common in the western Ross Sea. Lateral flexure creates bending stresses within these ice tongues which is likely to contribute to their fragility and may restrict their spatial distribution. A three-year time series (2017–2020) of synthetic aperture radar interferometry (InSAR) and differential interferometry (DInSAR) is used to observe the lateral flexure of the 10 km long Erebus Ice Tongue as a result of ocean currents. The fast ice area around the ice tongue was mapped during the same period. It was found that when fast ice was absent (34.7% of the time), the average lateral movement of the ice tongue was twice as high (0.44 m) as when it was embedded in fast ice (0.19 m). A significant correlation (0.45) between flexure and tidal currents was found when fast ice was absent. An analytical model tuned to observations suggests that even without sea ice for stabilisation, the lateral bending stresses induced by the ocean are insufficient to cause calving without additional amplifying factors.

Upernavik Isstrøm, the largest contributor to sea-level rise in northwest Greenland, has experienced complex and contrasting ice-flow-speed changes across its five outlets over the last two decades. In this study, we present a detailed remote-sensing analysis of the ice dynamics at Upernavik's outlets from 2000 to 2021 to evaluate the details of these changes. Previous research suggested that the presence or absence of floating ice tongues strongly influences Upernavik's ice dynamics. We use several lines of evidence to document the presence of floating ice tongues, and find that, while several outlets experienced ice-tongue formation and/or loss during the study period, these changes do not explain observed fluctuations in ice-flow velocity. Further exploration of ice-dynamic forcings using a flowline model suggests that changes in basal slipperiness near the terminus have a strong impact on upstream ice dynamics and can explain the velocity variations. Our results suggest that speed fluctuations at Upernavik's outlets may be seasonally and interannually controlled by bed conditions near the terminus, and highlight the need for further research on the influence of basal conditions on complex tidewater glacier dynamics.

Both submarine melt and calving are important for the overall mass balance of marine-terminating glaciers, but uncertainty is rife with regards to the magnitude of the processes. Modelling allows for these processes to be investigated without the need to visit inaccessible ice marginal zones. This study looks at the impact of different submarine melt and sea-ice back pressure scenarios on modelled calving activity and dynamics at Kronebreen, Svalbard, by running separate summer and winter simulations with various submarine melt parameterisations and sea-ice characteristics. It is found that submarine melt is an important driver of seasonal variation in modelled glacier dynamics and calving activity, with the choice of sliding law also exerting a significant influence on results.

The hypothesis that ice-sheet evolution is only controlled by the long-term non-Newtonian viscous behavior of ice has been challenged by observations indicating that effects like brittle failure, stick-slip sliding, tides and wave action may affect ice-sheet evolution on sub-daily timescales. Over these timescales, the quasi-static-creep approximation is no longer appropriate and elastic effects become important. Simulating elastic effects in ice-sheet models over relevant timescales, however, remains challenging. Here, we show that by including a visco-elastic rheology and reintroducing the oft neglected acceleration term back into the ice-sheet stress balance, we can create a visco-elastic system where the velocity is locally determined and information propagates at the elastic wave speed. Crucially, the elastic wave speed can be treated like an adjustable parameter and set to any value to reproduce a range of phenomena, provided the wave speed is large compared to the viscous velocity. We illustrate the system using three examples. The first two examples demonstrate that the system converges to the steady-state viscous and elastic limits. The third example examines ice-shelf rifting and iceberg calving. This final example hints at the utility of the visco-elastic formulation in treating both long-term evolution and short-term environmental effects.

Progress in our understanding of wave–ice interactions is currently hindered by the lack of in situ observations and information of sea-ice properties, including the elastic modulus. Here, we estimate the effective elastic modulus of sea ice using observations of waves in ice through the deployment of three open-source geophone recorders on landfast sea ice. From observations of low-frequency dispersive waves, we obtain an estimate of the effective elastic modulus in the range of 0.4–0.7 GPa. This is lower than the purely elastic modulus of the ice estimated at 1 GPa as derived from in situ beam experiments. Importantly, our experimental observation is significantly lower than the default value currently in use in wave models. While our estimate is not representative for all sea ice, it does indicate that considerably more measurements are required to provide confidence in the development of parameterizations for this complex sea-ice property for wave models.

Changes in iceberg calving fluxes and oceanographic conditions around Antarctica have likely influenced the spatial and temporal distribution of iceberg fresh water fluxes to the surrounding ocean basins. However, Antarctic iceberg melt rate estimates have been limited to very large icebergs in the open ocean. Here we use a remote-sensing approach to estimate iceberg melt rates from 2011 to 2022 for 15 study sites around Antarctica. Melt rates generally increase with iceberg draft and follow large-scale variations in ocean temperature: maximum melt rates for the western peninsula, western ice sheet, eastern ice sheet and eastern peninsula are ~50, ~40, ~5 and ~5 m a−1, respectively. Iceberg melt sensitivity to thermal forcing varies widely, with a best-estimate increase in melting of ~24 m a−1°C−1 and range from near-zero to ~100 m a−1°C−1. Variations in water shear likely contribute to the apparent spread in thermal forcing sensitivity across sites. Although the sensitivity of iceberg melt rates to water shear prevents the use of melt rates as a proxy to infer coastal water mass temperature variability, additional coastal iceberg melt observations will likely improve models of Southern Ocean fresh water fluxes and have potential for subglacial discharge plume mapping.