Snow grain size is a primary control on albedo and snowmelt. Compact imaging spectrometers and lidars mounted on uncrewed aerial systems (UAS) now offer flexible, high-resolution observations, but their relative performance for optical snow property retrievals has not been assessed. We compared grain size retrievals from two UAS-mounted imaging spectrometers (925–1700 nm and 900–2500 nm) and two lidars (905 nm and 1550 nm) against field spectroscopy over snow covered terrain (Mores Creek Summit, ID in March 2024). The compact imagers and 905 nm lidar retrieved grain sizes within ∼10% of field reference values, with little sensitivity to flight altitude (40–120 m). The 1550 nm lidar showed large negative bias (>90% error) due to strong shortwave-infrared absorption by ice. Results demonstrate that affordable, lightweight UAS sensors can accurately map grain size, with 905 nm lidar offering flexibility, notably in conditions unsuitable for passive optical measurements.

NASA’s ICESat-2 mission was launched in 2018, carrying a photon-counting laser altimeter, with a primary objective of measuring height changes across Earth’s surface. ICESat-2 has provided measurements of ice surface height between 88º N and S, repeated four times per year, with high vertical accuracy and along-track spatial resolution. Its accuracy and coverage has enabled near-complete recovery of height changes across the ice sheets, capturing subtle changes in the interior, and rapid changes along the dynamic margins with steep slopes and the floating peripheral ice shelves. The ICESat-2 Science Team has developed a suite of algorithms that produce along-track and gridded land ice height products at various levels of processing, all freely available at the National Snow and Ice Data Center. Here, we describe three higher-level land-ice data products derived from ATL06 and their underlying algorithms: along-track height change (ATL11), digital elevation model (ATL14) and gridded surface height change (ATL15). We demonstrate the suitability of each data product for studying different ice sheet regions. We then show height changes for Greenland and Antarctica from ATL15 during the first 6 years of the ICESat-2 mission (October 2018–December 2024), illustrating how ICESat-2 measurements can distinguish the multi-year trends from seasonal fluctuations.

Regional-scale glacier mass-balance (MB) estimates are essential for understanding the impacts of climate change on alpine hydrology but remain challenging to obtain. Remotely sensed phenology metrics, such as the cumulative melting index (CMI) derived from Moderate Resolution Imaging Spectroradiometer (MODIS) data, are increasingly used for MB estimation; however, the strength of this relationship varies across glaciers. This study analyzes the relationship between the MODIS-derived CMI and glacier annual MB across 88 alpine glaciers globally and investigates sources of variability. By standardizing CMI values, we reduce interglacier variability in CMI–MB relationship. Principal component analysis (PCA) and Gaussian mixture model are employed to classify glaciers into six climate-based clusters. Cluster-specific linear regression models improve MB estimation accuracy. When glacier predictions from the cluster-specific models are combined across all 88 glaciers worldwide, the overall root-mean-square error is 511.0 mm w.e., compared with 571.4 mm w.e. using a single regression model. Applied to 616 glaciers in the European Alps, the model estimates a 20 year (2002–21) annual average mass loss of −981.9 ± 11 mm w.e. a−1. These findings highlight the potential of MODIS-derived phenology metrics for scalable glacier MB estimation and emphasize the influence of regional climatic controls on glacier sensitivity to climate variability.

The Canadian Arctic Archipelago constitutes a primary source of contemporary sea-level rise from glaciers and ice caps, yet glacier-scale, multi-decadal records on Baffin and Bylot Islands remain limited. This study reconstructs long-term elevation and volume change for seven glaciers, six in Auyuittuq National Park and one in Sirmilik National Park, using 1958/59 imagery from the Canadian National Air Photo Library. Historical digital elevation models were reconstructed using TanDEM-X for vertical ground control and PlanetScope imagery for horizontal ground control, with ArcticDEM supporting final co-registration and on-ice elevation-change analysis. Uncertainty was quantified from stable-terrain residuals, with normalized median absolute deviation values of $2.08$–$4.07$ m. Specific geodetic mass balances for the Auyuittuq glaciers ranged from $-0.22$ to $-0.35$ m w.e. a$^{-1}$ for 1959–2021/22, while Fountain Glacier averaged $-0.35$ m w.e. a$^{-1}$ for 1958–2022. Cumulative ice-volume change totalled $-4.76 \times 10^{9}$ m$^{3}$, equivalent to $-4.05 \pm 0.29$ Gt. Auyuittuq glaciers shortened by $7$–$16\%$ and lost $9$–$28\%$ of their area. Spatial variability reflects glacier hypsometry, with lower-elevation glacier areas showing greater sensitivity to atmospheric warming. These results provide new glacier-scale geodetic mass-balance estimates for the Canadian Arctic Archipelago based on archival photogrammetry, although density assumptions that omit firn evolution require further refinement when estimating mass change.

The firn layer in the upper part of the Antarctic ice sheet represents a crucial transitional zone during the transformation from snow to glacial ice, and its structural characteristics play an essential role in evaluating the surface mass balance of the ice sheet. Surface-wave inversion offers strong constraints on shallow subsurface stratification, and compared with conventional ambient noise, traffic-induced seismic vibrations provide higher-frequency signals that can significantly enhance near-surface imaging resolution. In this study, we identified traffic noise signatures within ambient seismic data recorded during the 40th Chinese National Antarctic Research Expedition in the Larsemann Hills, East Antarctica. Using these data, we performed high-resolution shear-wave velocity imaging of the firn layer through surface-wave inversion based on seismic interferometry and one-dimensional Monte Carlo inversion. The retrieved virtual shot gathers revealed clear surface-wave energy, and the inverted shear-wave velocity profiles were in good agreement with borehole data obtained at the center of the survey line. Vibrations generated by vehicles such as PB300 can serve as an effective, low-cost and environmentally friendly seismic source. This traffic-source-based approach provides a practical pathway for high-resolution firn imaging and offers valuable potential for future large-scale, long-term monitoring of ice-sheet structure and mass balance.

Formation and sudden drainage of glacial lakes pose increasing hazards in high-mountain regions, threatening downstream communities, infrastructure and ecosystems. Accurate bathymetric reconstruction and lake volume estimation are crucial for flood modeling, hazard assessment, and monitoring climate-driven glacial lake dynamics. This study uses a recently drained lake at the margin of Gornergletscher, Monte Rosa Massif, Western Alps, to reconstruct its bathymetry and estimate its volume by combining a high-resolution digital elevation model (DEM) from low-cost uncrewed aerial vehicle (UAV) imagery with multispectral Sentinel-2 data. The UAV data were used to generate an orthomosaic and a high-resolution DEM of the empty lake basin. Lake extents corresponding to five filling stages, together with the DEM, enabled pixelwise depth estimation, yielding a mean lake depth for maximal filling of 21.94 m and an estimated corresponding water volume of 0.298 ± 0.11 × 10⁶ m3. Field observations indicated direct glacier contact and subglacial drainage through vertical conduits. Sentinel-2 also revealed smaller lakes in 2017 and 2018. Comparative analysis of climate variables from lake (2017, 2018 and 2022) and no-lake (2019–21) years highlighted higher April–June temperatures as the dominant factor controlling lake formation. This study demonstrates the value of integrating UAV three-dimensional (3-D) terrain modeling with satellite remote sensing for high-resolution glacial lake monitoring.

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.

If crevasse fields deliver meltwater to the bed of the Greenland ice sheet, it would affect seasonal ice flow speeds and total mass balance. The best current automated tool to map crevasse fields extends only a few dozen kilometers inland. To address this gap, we develop MimiNet, a neural-network-based tool that identifies surface crevasse fields. We train MimiNet on Sentinel-1 scenes across a 629 km2 area in Pâkitsoq, central-western Greenland, and use it to locate crevasse fields annually over 2015–24. We find that the crevassed area varied from a minimum of 106 ± 5 km2 in 2019 to a maximum of 144 ± 6 km2 in 2016, with no overall trend over the 10 year study period. We find some evidence that seasonal ice velocity anomalies in crevasse fields are higher than those in moulin-drained areas in the late melt season. This may suggest that the subglacial drainage system under crevasse fields remains inefficient all summer, and thus that at least some Pâkitsoq crevasse fields deliver meltwater to the bed. Interannual variability in ice dynamics may drive the observed variability in crevassed areas; we expect crevasse extent to become more variable in time as ice flow speeds and their variations, amplify under climate change.

The export of fresh water (solid and liquid) from glaciers and ice sheets plays an important role in the global climate system. Icebergs influence ocean salinity and circulation patterns and pose a growing hazard to Arctic navigation as sea ice cover declines. Therefore, quantifying the volume of icebergs calved from the Greenland ice sheet is essential. Here, we present iceberg size and volume distributions derived from high-resolution Satellite Pour l’Observation de la Terre (SPOT) images for Upernavik Isfjord, Northwest Greenland, during the 2020 open water season. The iceberg area–volume conversion is constrained by a 3D photogrammetric survey of icebergs within the fjord. By integrating glacier discharge over estimated iceberg residence times, we link remotely sensed iceberg volumes to calving rates at the primary outlet glaciers. We detected 343 769 icebergs with a total volume of 4.7 km$^3$. This corresponds to 88.7% of the estimated solid ice discharge and falls within the derived discharge range of 3.4–12.2 km$^3$. Uncertainties are primarily controlled by variability in residence time, extrapolation of the area–volume relationship beyond its calibration domain and assumptions regarding ice density.

To investigate glacier mass loss and ice dynamics in northwestern Greenland, we measured surface mass balance (SMB), ice velocity and surface elevation from 2012 to 2025 on Qaanaaq Glacier, an outlet glacier of Qaanaaq Ice Cap. Stake measurements at six locations along the central flowline suggested an ice-cap-wide mass loss of −8.01 ± 0.22 m w.e. over the 13-year period. Horizontal ice velocities decreased by 8–64% in the ablation area, whereas the change was insignificant in the upper reaches. The emergence velocity varied from −0.35 ± 0.10 m a−1 above the equilibrium line altitude to 0.94 ± 0.12 m a−1 near the terminus. Along the flowline, the glacier surface elevation decreased by 8.7 m on average. Ice thinning accelerated from 2012–2019 to 2019–2025 in the lower reaches (<500 m a.s.l.). Approximately 50% of this change was due to a decrease in the emergence velocity, and the remainder was attributed to a more negative SMB. In contrast, the thinning rate showed little change in the upper reaches (>800 m a.s.l.), where an increase in the emergence velocity compensated for the increasingly negative SMB. This study highlights the essential role of ice dynamics in surface elevation change.

Despite advances in global glacier modeling, notable uncertainties remain in part due to model overparameterization. We develop a novel Bayesian inference framework to calibrate the Python Glacier Evolution Model (PyGEM) against spatially distributed surface elevation change data. The utility of this framework is demonstrated using a 1994–2021 airborne laser altimetry record for 185 glaciers in Alaska, which altogether represent over half of the region’s glacier area. Calibration against these data reduces parameter uncertainty by 5–18% and lowers the mean absolute error in hindcast surface elevation change by 0.18 m a−1 (15% compared to prior models). Model projections for these 185 glaciers estimate mass loss ranging from 43 $ \pm $ 17% to 67 $ \pm $ 27% depending on the emissions scenario. The projections highlight considerable subregional variability ranging from a median glacier mass loss of 57–99% by the end of the century for Lake Clark, Denali, Kenai Fjords, and Glacier Bay national parks, compared to 28–51% lost for Wrangell–St. Elias National Park and Preserve. As additional spatially distributed elevation change datasets become available in Alaska and elsewhere, the framework presented here is well suited to further refine model calibration and improve projections, while remaining flexible to incorporate additional glacier change observations as they become available.

Subglacial water flow is critical to basal sliding and ice dynamics. Modelling the coupled evolution of subglacial drainage and ice flow remains challenging, however. This study investigates the evolution of the basal ice–water interface by analysing heat and fluid flow in idealised englacial channels. We extend the classical Röthlisberger model for circular channels to elliptical channel geometries. A hybrid laminar–turbulent melt scheme captures heat generation and melting from both viscous and turbulent dissipation, while a viscous flow law models the creep closure of the surrounding ice. Whilst the flow of ice tends to increase the eccentricity of the channel, we find that elliptical channels tend towards a circular shape when laminar melting dominates due to differential melting between the roof and walls of the channel. Our hybrid melt model predicts the existence of stable, non-circular cross-sections. Unlike circular channels, these channels obey pressure-flux relationships that, beyond a critical volume flux threshold, suggest a preference for flux sharing, a behaviour characteristic of distributed drainage networks. This contrasts with circular channels, which undergo channelisation towards fewer, larger conduits. These idealised channels suggest potential simplifications to modelling subglacial drainage networks and the dynamics of evolving subglacial hydrological networks.

One of the current limitations of reproducing the past evolution of the Greenland ice sheet with numerical models is the lack of a digital elevation model (DEM) prior to the year 2000 that can provide an initial state based on historical observations. Here we combine historical DEMs from aerial photography of the margins with laser altimetry data from the interior to reconstruct a complete DEM at 600 m grid resolution that represents the state of the Greenland ice sheet in the 1980s. To this end, we apply two methods: First, we use Gaussian process regression constrained by empirically derived spatial covariance functions. We find that after standardization, the signal is stationary and correlated over more than 100 km, allowing for interpolation over large data gaps. In a second, more novel approach, we use the singular value decomposition to extract spatial patterns from a series of model-generated DEMs. The Gaussian process regression shows smaller cross-validation errors and yields robust uncertainties; for the second method, we expect it could reduce nonphysical transient behavior in the historical simulations. With these reconstructions, we provide initial states that predate the earliest high-resolution ($ \lt 1~\mathrm{km}$) DEM of the Greenland ice sheet by around 20 years.

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.

Supraglacial debris strongly modifies melt rates on debris-covered glaciers, yet simulating this effect remains challenging because modelling the full surface energy balance (SEB) and the vertical conduction of heat through the debris layer requires many (unknown) parameters, which are often poorly constrained and highly site-specific. Here, we develop a physically based parameterization and calibration procedure for sub-debris melt rates, which links a simplified formulation of the SEB to heat conduction through the debris. The model is tuned using mass-balance measurements and debris surface temperatures from the debris-covered region of the Djankuat Glacier (Caucasus) and uses a minimal number of input data to reproduce the observed debris-related melt-modification effects. An optional relative melt enhancement for thin debris extends the procedure into a regime where the model physics are not valid, and sub-debris melt is governed by other processes than heat conduction alone. This allows the model to be applied in (large-scale and long-term) debris-covered glacier evolution frameworks where the full range of debris thicknesses could occur. As hard-to-constrain inputs have been replaced with simplified and tunable parameters, the approach balances the trade-off between model complexity and physical realism and can be transferred to other debris-covered glaciers, provided that sufficient observations for model calibration are available.

Supraglacial lake drainages create spatially finite regions of reduced basal friction, slippery patches, at the ice-bed interface that perturb local stresses in the overlying ice, potentially sufficiently to trigger cascading hydrofracture-driven lake drainage events. We derive analytical solutions for the perturbed stress response to such slippery patches using the shallow-shelf approximation and validate these solutions against two-dimensional full-Stokes numerical simulations for Newtonian and non-Newtonian (Glen) rheologies, spanning a range of flow parameters. The stress perturbation magnitude scales linearly with patch length and surface slope and decays exponentially into the ice away from the patch over a decay lengthscale dependent on ice thickness, rheology and basal sliding coefficient outside the patch. The stress decay lengthscale increases with larger ice thickness and smaller basal traction. Combining stress magnitude and decay lengthscale, we define an absolute coupling length as the distance over which the perturbed stress remains above a given threshold, which is largest in the Greenland ablation zone. We discuss implications of these results for the magnitude and spatial reach of stress communication among lake drainage events, especially under a warming climate.

The Milne Ice Shelf was, until recently, a relatively stable ice shelf on the north coast of Ellesmere Island. In summer 2020, it underwent a major calving event, losing 43% of its surface area from its northern, ocean edge. A mass balance network across the ice shelf indicates that this calving was preceded by a mean annual surface mass balance of −0.40 ± 0.13 m water equivalent from 2008 to 2019, but with large inland-to-ocean variability. Individual stake measurements indicate that ablation is highest at the rear of the ice shelf, furthest from the ocean, while summer air temperature and shortwave radiation are lower towards the front of the ice shelf, where snow accumulation is greatest. The ice shelf shifts to a state of strongly negative mass balance in years with >200 cumulative positive degree-days, which occurred half the time over the study period. The mass balance gradient may help explain the 2020 calving pattern, as sustained thinning and fracture near the rear of the ice shelf may have reduced structural integrity, weakening the mechanical connection to the seaward section prior to its detachment.

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.

Glacier snowline altitudes (SLAs) are indicators of glacier mass balance and are useful to understand the response of a glacier to climatic changes. In situ measurements of SLAs are challenging in rugged, difficult-to-access areas of the Himalaya, and optical remote-sensing methods suffer from limitations due to shadows, crevasses and cloud cover. The SLA at the end of the ablation season (SLAmax) is generally considered to represent the glacier equilibrium line altitude (ELA). While this relationship is fairly well established in mid-latitude and temperate regions, it remains underexplored in monsoon-dominated areas such as the central and eastern Himalaya. Here, we tested this assumption using sub-monthly SLAs for the Dudh Koshi basin over the period 2015–23. We improved a semiautomated SLA method to extract 6330 sub-monthly SLAs for Sentinel-2/Landsat 8 over 2015–23 in the Dudh Koshi basin, and we validate these with Planet/VENμS imagery. Our results show good agreement between Sentinel-2/Landsat 8 SLAs and Planet/VENμS (R2 = ∼0.8, vertical root-mean-square error = ∼61 m). However, when we compared the remote-sensing SLAmax with the field-based ELAs on Mera Glacier, we found that these were systematically lower, challenging the assumption that remote-sensing SLAmax represents the true ELA. We offer potential hypotheses to explain these differences based on field measurements and conclude that the SLA-ELA relationship should be used with caution when estimating ELA and glacier mass balance in monsoon-dominated regions.

Exact solutions for surface elevation profiles of idealised glaciers and ice sheets provide valuable insights into the geometry and flow of their real-world counterparts. These solutions are also useful in testing numerical glacier models. Here, we present an exact solution for the elevation profile of glaciers on erodible bedrock, assuming a steady competition between subglacial erosion and a uniform, time-independent rock uplift rate. The subglacial erosion rate is assumed to be proportional to the product of the local ice flux and the surface slope. Given a mass-balance profile that is linear in surface elevation and a Gaussian dependence of the glacier width on the surface elevation, the exact solution for the steady surface elevation profile has an inverse error-function form. This idealised solution provides insights into the steady-state shape and interannual variability of the mass balance of real-world glaciers.