Accurate modeling of firn densification is necessary for ice core interpretation and assessing the mass balance of glaciers and ice sheets. In this paper, we revisit the nonlinear-viscous firn rheology introduced by Gagliardini and Meyssonnier (1997) that allows multidimensional firn densification problems to be posed, subject to arbitrary stress and temperature fields. First, we extend the calibration of the coefficient functions that control firn compressibility and viscosity to five additional Greenlandic sites, showing that the original calibration is not universally valid. Next, we demonstrate that the transient collapse of a Greenlandic firn tunnel can be reproduced in a cross-section model, but that anomalous warm summer temperatures during 2012–14 reduce confidence in attempts to independently validate the rheology. Finally, we show that the rheology can explain the increased densification rate and varying bubble close-off depth observed across the shear margins of the Northeast Greenland Ice Stream. Although we suggest more work is needed to constrain the near-surface compressibility and viscosity functions of the rheology, our results strengthen the empirical grounding of the rheology for future use, such as modeling horizontal firn density variations over ice sheets for mass-loss estimates or estimating ice-gas age differences in ice cores subject to complex strain histories.

The proposed Thermal Sidewall Ice Corer (TSIC) is designed to accurately sample horizontal ice layers of scientific interest, such as tephra layers, basal ice and shear zones, and retrieve ice cores back to the surface. The system features a bending core barrel with a thermal coring head, which bends as it extends from the drill body, enabling it to penetrate horizontal interlayers while maintaining a horizontal position until the ice core is extracted. The bending core barrel is driven by screw pairs, powered by a motor, to apply drilling load and pulling force. As the barrel bends, the ice cores are broken inside and transported to the surface along with the drill via a winch. A camera system has been incorporated into the TSIC to precisely locate the target layer. The corer is suitable for ice boreholes with diameters ranging from 135 to 170 mm, capable of retrieving ice cores with a diameter of 20–30 mm, and achieving a maximum penetration rate of 2 m h−1. The maximum length of ice samples that can be retrieved in a single drilling run is 500 mm. The coring performance for horizontal sampling has been validated through the development and testing of a prototype in the laboratory.

In many technical and geomechanics applications, for example tire and ski design or avalanche prediction, the capability to model the mechanical behaviour of snow is of high importance. To this end, we propose in the present study to extend the 3-D H-model, a multi-scale constitutive law originally developed for granular materials, to densely packed snow. In the model, single ice grains are described by spherical particles bonded by brittle elasto-viscoplastic bridges. Snow is thus described explicitly through its ice skeleton microstructure. As a validation, confined compression test results from the litterature are used to assess the suitability of the model to correctly describe snow behaviour. Multiple parameter studies were conducted to demonstrate the capability of the model to capture the behaviour of different snow types over a significant range of temperatures and loading rates at small deformations. Notably, the initial bond radius emerges as an effective proxy for snow aging under isothermal conditions, with stress levels increasing directly with the initial bond radius. Additionally, low strain rates and elevated temperatures are shown to influence the viscous response of ice bonds, their failure rates and the overall stress within the snow material.

Regional climate models (RCMs) are fundamental tools in understanding and quantifying the contribution of the Greenland ice sheet to sea-level rise. We perform an extensive evaluation of the daily air temperature simulated by two RCMs, MARv3.12 and RACMO$2.3\text{p}2$, and a global atmospheric reanalysis, ERA5, at 35 locations across the ice sheet over the period 1995–2020. We compare model results to weather station data from two climate networks, focusing on the spatial and temporal variability in mean biases (MBs). All three models perform well at low elevations (<1500 m a.s.l.) with an MB of 0.16∘C (MAR), $0.36^{\circ}\mathrm{C}$ (RACMO) and $0.41^{\circ}\mathrm{C}$ (ERA5), while warm biases (>1.70$^{\circ}\mathrm{C}$) are found at high elevations (>1500 m a.s.l.). Temperature biases exhibit a strong seasonality, being more pronounced during winter and much smaller during summer ranging from $0.11^{\circ}\mathrm{C}$ to $0.59^{\circ}\mathrm{C}$. No interannual variability is found in the biases of all three datasets. Daily variability within each month is captured well by both climate models and the reanalysis at most locations. Finally, all three models perform overall better in the ablation zone during summer, i.e. where and when considerable melt production occurs.

Jutulstraumen is a major outlet glacier in East Antarctica that drains into the Fimbulisen, Dronning Maud Land (DML). Here, we present the first long-term (∼60 years) record of its behavior using optical satellite imagery. Our analysis reveals that the ice front has been steadily advancing since its last major calving event in 1967, with a steady ice flow velocity of ∼720 ± 66 m yr−1 (2000–2021), accompanied by spatially variable thickening of the grounded ice at +0.14 ± 0.04 m yr−1 (2003–2020). We also find evidence to suggest a minor grounding line advance of ∼200 m between 1990 and 2022, albeit with large uncertainties. Mapping of the major rifts on Jutulstraumen’s ice tongue (2003–2022) reveals an overall increase in their length, accompanied by some minor calving events along its lateral margins. Given the present-day ice front advance rates (∼740 m yr−1), the ice tongue would reach its most recent maximum extent (attained in the mid-1960s), in ∼40 years, but extrapolation of rift lengthening suggests that a major calving event may occur sooner, possibly in the late 2050s. Overall, there is no evidence of any dynamic imbalance, mirroring other major glaciers in DML.

Globally, glaciers are changing in response to climate warming, with those that terminate in water often undergoing the most rapid change. In Alaska and northwest Canada, proglacial lakes have grown in number and size but their influence on glacier mass loss is unclear. We characterized the rates of retreat and mass loss through frontal ablation of 55 lake-terminating glaciers (>14 000 km2) in the region using annual Landsat imagery from 1984 to 2021. We find a median retreat rate of 60 m a−1 (interquartile range = 35–89 m a−1) over 1984–2018 and a median loss of 0.04 Gt a−1 (0.01–0.15 Gt a−1) mass through frontal ablation over 2009–18. Summed over 2009–18, our study glaciers lost 6.1 Gt a−1 to frontal ablation. Analysis of bed profiles suggest that glaciers terminating in larger lakes and deeper water lose more mass to frontal ablation, and that the glaciers will remain lake-terminating for an average of 74 years (38–177 a). This work suggests that as more proglacial lakes form and as lakes become larger, enhanced frontal ablation could cause higher mass losses, which should be considered when projecting the future of lake-terminating glaciers.

SnowModel-LG reconstructs snow depth and density over sea ice, explicitly resolving important snow sinks like blowing snow sublimation, static surface sublimation and melt, but not snow-ice formation. To examine snow sinks on level sea ice, we coupled SnowModel-LG with HIGHTSI, a 1-D thermodynamic sea-ice model, to create SMLG_HS. SMLG_HS simulations of snow depth and level ice thickness were evaluated against high-resolution airborne observations from the western Arctic, highlighting the importance of snow mass redistribution processes, i.e. snow’s tendency to leave level ice and accumulate over deformed ice due to wind-induced redistribution. Not accounting for snow mass redistribution, SMLG_HS overestimates snow depth on level ice, resulting in underestimation of level ice thickness and overestimation of snow-ice thickness. Our case study shows that snow depth on level ice needs to be reduced by 40% to simulate both snow depth and level ice thickness realistically in the western Arctic in April 2017. An independent analysis of snow volume distribution between level and deformed sea ice using airborne radar observations supported the model results and revealed a linear relationship that enables estimating the amount of snow remaining on level ice at the end of winter based on the amount of ice deformation.

The Antarctic Peninsula (AP) and James Ross Island (JRI) region have experienced exceptionally warm spells in recent decades, leading to substantial glacier mass loss. This study investigates a sequence of three massive heat waves between November 2022 and January 2023, leading to extreme surface ablation. Their impact was examined through a wide range of in-situ atmospheric and glaciological observations on two JRI glaciers: the cirque-based Triangular Glacier and the dome-shaped Davies Dome. Furthermore, the Weather Research and Forecasting model was used with a very-high horizontal resolution of 300 m to provide insights into surface–atmosphere interactions and the synoptic- and meso-scale drivers of the exceptionally high near-surface air temperatures. The three investigated events generated total surface ablation of 1237 mm w.e. on Triangular Glacier and 271 mm w.e. on Davies Dome contributing to annual ablation ≥4 times higher than a recent mean on Triangular Glacier. A striking local variability in atmosphere–glacier energy exchange was found in the complicated topography of the northeastern AP region. A complex foehn mechanism analysis revealed that isentropic drawdown with a small contribution of latent heat release played a crucial role in enhancing leeward warming and surface melt.

Despite the increased awareness and action towards Equality, Diversity and Inclusion (EDI), the glaciological community still experiences and perpetuates examples of exclusionary and discriminatory behavior. We here discuss the challenges and visions from a group predominantly composed of early-career researchers from the 2023 edition of the Karthaus Summer School on Ice Sheets and Glaciers in the Climate System. This paper presents the results of an EDI-focused workshop that the 36 students and 12 lecturers who attended the summer school actively participated in. We identify common threads from participant responses and distill them into collective visions for the future of the glaciological research community, built on actionable steps toward change. In this paper, we address the following questions that guided the workshop: What do we see as current EDI challenges in the glaciology research community and which improvements would we like to see in the next fifty years? Contributions have been sorted into three main challenges we want and need to face: making glaciology (1) more accessible, (2) more equitable and (3) more responsible.

Iceberg calving at glacier termini results in mass loss from ice sheets, but the associated fracture mechanics is often poorly represented using simplistic (empirical or elementary mechanics-based) failure criteria. Here, we propose an advanced Mohr–Coulomb failure criterion that drives cracking based on the visco-elastic stress state in ice. This criterion is implemented in a phase field fracture framework, and finite element simulations are conducted to determine the critical conditions that can trigger ice cliff collapse. Results demonstrate that fast-moving glaciers with negligible basal friction are prone to tensile failure causing crevasse propagation far away from the ice front, while slow-moving glaciers with significant basal friction are likely to exhibit shear failure near the ice front. Results also indicate that seawater pressure plays a major role in modulating cliff failure. For land terminating glaciers, full thickness cliff failure is observed if the glacier exceeds a critical height, dependent on cohesive strength $\tau_\mathrm{c}$ ($H \approx 120\;\text{m}$ for $\tau_\mathrm{c}=0.5\;\text{MPa}$). For marine-terminating glaciers, ice cliff failure occurs if a critical glacier free-board ($H-h_\mathrm{w}$) is exceeded, with ice slumping only observed above the ocean-water height; for $\tau_\mathrm{c} = 0.5\;\text{MPa}$, the model-predicted critical free-board is $H-h_\mathrm{w} \approx 215\;\text{m}$, which is in good agreement with field observations. While the critical free-board height is larger than that predicted by some previous models, we cannot conclude that marine ice cliff instability is less likely because we do not include other failure processes such as hydrofracture of basal crevasses and plastic necking.

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.

Understanding firn densification is essential for interpreting ice core records, predicting ice sheet mass balance, elevation changes and future sea-level rise. Current models of firn densification on the Antarctic ice sheet (AIS), such as the Herron and Langway (1980) model are either simple semi-empirical models that rely on sparse climatic data and surface density observations or complex physics-based models that rely on poorly understood physics. In this work, we introduce a deep learning technique to study firn densification on the AIS. Our model, FirnLearn, evaluated on 225 cores, shows an average root-mean-square error of 31 kg m−3 and explained variance of 91%. We use the model to generate surface density and the depths to the $550\,\mathrm{kg\,m}^{-3}$ and $830\,\mathrm{kg\,m}^{-3}$ density horizons across the AIS to assess spatial variability. Comparisons with the Herron and Langway (1980) model at ten locations with different climate conditions demonstrate that FirnLearn more accurately predicts density profiles in the second stage of densification and complete density profiles without direct surface density observations. This work establishes deep learning as a promising tool for understanding firn processes and advancing towards a universally applicable firn model.

Basal sliding and other processes affecting ice flow are challenging to constrain due to limited direct observations. Inversion methods, which typically fit an ice-flow model to observed surface velocities, enable the reconstruction of basal properties from readily available data. We present a numerical inversion framework for reconstructing the glacier basal sliding coefficient, applied to both synthetic and real-world alpine glacier scenarios. The framework employs automatic differentiation (AD) to generate adjoint code and runs in parallel on graphics processing units. We explore two inversion workflows using the shallow ice approximation as the forward model: a time-independent approach fitting to a single snapshot of annual ice velocity and a time-dependent inversion accounting for both ice velocity and changes in geometry. We find that the time-dependent inversion yields more robust and accurate velocity fields than the snapshot inversion. However, it does not significantly improve the problematic initial transients often encountered in forward model runs that employ sliding fields from snapshot inversions. This is likely due to the limitations of the forward model. This methodology is transferable to more complex forward models and can be readily implemented in languages supporting AD.

Glacier collapse features, linked to subglacial cavities, are increasingly common on retreating Alpine glaciers. These features are hypothesized to result from glacier downwasting and subsurface ablation processes but the understanding regarding their distribution, formation and contribution to glacier mass loss remains limited. We present a Swiss-wide inventory of 223 collapse features observed over the past 50 years, revealing a sharp increase in their occurrence since the early 2000s. Using high-resolution digital elevation models, we derive a relationship between collapse feature area and ice ablation and estimate the Swiss-wide contribution of collapse features to glacier mass loss to be $19.8\times 10^6\,\text{m}^3$ of ice between 1971 and 2023. Based on extensive observations at Rhonegletscher, including surface displacement, ground-penetrating radar and drone-based elevation models, we quantify subsurface ablation rates of up to 27 cm d−1 and provide a detailed description of the collapse processes. We propose that glacier downwasting, enhanced energy supply through subglacial conduits and locally increased basal melt are key components to subglacial cavity growth. Our results highlight the importance of collapse features in the ongoing retreat of Alpine glaciers, stressing the need for further research to understand their formation and long-term implications for glacier dynamics under climate change.

In January 2009, on its way from Cape Town to South America (at around 49.5∘S and 25∘W), the German research vessel Polarstern entered a region with a dense cover of icebergs and broken-off chunks of ice up to a few meters in size, largely hidden in a thick fog, a result of the microclimate created by the large agglomeration of icebergs and broken-off glacial ice. Melting of glacial ice led to a cooling (by up to 8∘C) and freshening (by up to 2.5 psu) of the surface ocean with perturbations reaching down to about 75 m depth. The observed surface ocean equilibrium fugacity of CO2, fCO2, dropped to values that were over 100 µatm lower than atmospheric fCO2 values. Given the similar concentrations in chlorophyll a and the macronutrients nitrate and phosphate inside and outside the perturbed areas, influences of potential iron input from disintegrating icebergs on phytoplankton productivity and fCO2 can be ruled out. The low fCO2 values, compared to adjacent regions, can be attributed to thermodynamic effects, i.e. mostly increase of CO2 solubility with decreasing temperature with a smaller contribution from the dilution due to freshwater inputs. Based on these observations, we consider the potential impact on atmospheric fCO2 by the release of an armada of icebergs during Heinrich events.

Ice shelves affect the stability of ice sheets by supporting the mass balance of ice upstream of the grounding line. Marine ice, formed from supercooled water freezing at the base of ice shelves, contributes to mass gain and affects ice dynamics. Direct measurements of marine ice thickness are rare due to the challenges of borehole drilling. Here we assume hydrostatic equilibrium to estimate marine ice distribution beneath the Amery Ice Shelf (AIS) using meteoric ice-thickness data obtained from radio-echo sounding collected during the Chinese National Antarctic Research Expedition between 2015 and 2019. This is the first mapping of marine ice beneath the AIS in nearly 20 years. Our new estimates of marine ice along two longitudinal bands beneath the northwest AIS are spatially consistent with earlier work but thicker. We also find a marine ice layer exceeding 30 m of thickness in the central ice shelf and patchy refreezing downstream of the grounding line. Thickness differences from prior results may indicate time-variation in basal melting and freezing patterns driven by polynya activity and coastal water intrusions masses under the ice shelf, highlighting that those changes in ice–ocean interaction are impacting ice-shelf stability.

In this paper, frontal variations and surface area changes for each of the years 2017–2023 are assessed for 277 Swedish glaciers, of which the majority is contained within the Randolph Glacier Inventory 7.0. Mapping of all Swedish glaciers became possible by combining Sentinel-2 imagery, semi-automated mapping procedures and the open-source Margin Change Quantification Tool (MaQiT). In addition, manual mapping was performed at a subset of 22 glaciers historically associated with the Swedish Front Variation Program. At four of those, mapping accuracy was assessed by contrasting Sentinel-2 mapped fronts to fronts mapped in situ using Global Navigation Satellite System (GNSS), a total station and an uncrewed aerial vehicle. Results show widespread retreat of all Swedish glaciers, with cumulative frontal variation amounting on average to −55.6 m during 2017–2023 or −9.3 m a−1. Swedish glaciers had a total area of ∼237 km2 in 2017 and of 210 km2 in 2023. The reduction by ∼27 km2 corresponds to a loss of 11% with respect to the areal extent in the year 2017 but varies across regions. It is also almost as large as the combined area loss of Swedish glaciers in the preceding 15 years (∼31 km2, 2002–2017).

Iceberg calving is a major source of ice loss from the Antarctic and Greenland ice sheets. However, it is still one of the most poorly understood aspects of ice sheet dynamics, in part due to its variability at a wide range of spatial and temporal scales. Despite this variability, most current large-scale ice sheet models assume that calving can be represented as a deterministic flux. In this study, we describe an approach to modeling calving as a stochastic process, using a one-dimensional depth-integrated marine-terminating glacier model as a demonstration. We show that for glaciers where calving occurs more frequently than the typical model time steps (days-months), stochastic calving schemes sampling a binomial distribution accurately simulate the probabilistic distribution of glacier state. We also find that incorporating stochastic calving into simulations of a glacier with a buttressing ice shelf changes the simulated mean glacier state, due to nonlinearities in ice shelf dynamics. Relatedly, we find that changes in calving frequency, without changes in the mean calving flux, can cause ice shelf retreat. This new stochastic approach can be implemented in large-scale ice sheet models, which should improve our capability to quantify uncertainty in predictions of future ice sheet change.