The state-of-the-art measurement capabilities of ICESat-2 allow high spatiotemporal resolution of complex ice-dynamic processes that occur during a surge. Detailed and precise mapping of height changes on surging glaciers has previously escaped observations from space due to the limited resolution of space-borne altimeter data and the surface characteristics of glaciers during surge, such as heavy crevassing. This makes geophysical interpretation of deformation and assessment of mass transfer difficult. In this paper, we present an approach that facilitates analysis of the evolution of geophysical processes during a surge, including height changes, crevassing, mass transfer and roughness. We utilize all data from two years of ICESat-2 observations collected during the mature phase of the Negribreen Glacier System surge in 2019 and 2020. The progression of Negribreen's surge has resulted in large-scale elevation changes and wide-spread crevassing, making it an ideal case study to demonstrate ICESat-2 measurement capabilities, which are maximized when coupled with the Density Dimension Algorithm for ice surfaces (DDA-ice). Results show expansion of the surge in upper Negribreen which demonstrates the ability of ICESat-2/DDA-ice to measure a rapidly changing surging glacier and provide the best estimates for cryospheric changes and their contributions to sea-level rise.

Ice rises hold valuable records revealing the ice dynamics and climatic history of Antarctic coastal areas from the Last Glacial Maximum to today. This history is often reconstructed from isochrone radar stratigraphy and simulations focusing on Raymond arch evolution beneath the divides. However, this relies on complex ice-flow models where many parameters are unconstrained by observations. Our study explores quad-polarimetric, phase-coherent radar data to enhance understanding near ice divides and domes, using Hammarryggen Ice Rise (HIR) as a case study. Analysing a 5 km profile intersecting the dome, we derive vertical strain rates and ice-fabric properties. These align with ice core data near the summit, increasing confidence in tracing signatures from the dome to the flanks. The Raymond effect is evident, correlating with surface strain rates and radar stratigraphy. Stability is inferred over millennia for the saddle connecting HIR to the mainland, but dome ice-fabric appears relatively young compared to 2D model predictions. In a broader context, quad-polarimetric measurements provide valuable insights into ice-flow models, particularly for anisotropic rheology. Including quad-polarimetric data advances our ability to reconstruct past ice flow dynamics and climatic history in ice rises.

The processes governing iceberg calving from ice shelves remain poorly understood. Recent studies suggest that anomalous atmospheric moisture transport events – atmospheric rivers – can act as triggers for calving. These conclusions, however, were based on studies of case studies of individual icebergs or ice shelves, making it difficult to determine if this relationship remains apparent when considering a wider set of calving events and ice shelves. Here, we assemble an Antarctic-wide catalog of tabular iceberg calving events to evaluate whether a significant correlation exists between calving and enhancement of total and meridional integrated vapor transport (IVT), a measure of atmospheric moisture transport. We find that ~80% of the calving events in our study occur when metrics of IVT are less than the 90th percentile of their monthly climatologies. However, the remaining ~20% of calving events that occur during periods with short-term enhanced IVT exhibit a statistically significant correlation. The results, however, are regionally dependent, with a statistically significant correlation between enhanced IVT and calving in the Antarctic Peninsula and none in the Amundsen Sea Embayment. This suggests that, although enhanced IVT is not a primary control on the iceberg calving process, enhanced IVT may play a role in triggering calving events under certain conditions.

The ongoing deceleration of Whillans Ice Stream, West Antarctica, provides an opportunity to investigate the co-evolution of ice-shelf pinning points and ice-stream flux variability. Here, we construct and analyze a 20-year multi-mission satellite altimetry record of dynamic ice surface-elevation change (dh/dt) in the grounded region encompassing lower Whillans Ice Stream and Crary Ice Rise, a major pinning point of Ross Ice Shelf. We developed a new method for generating multi-mission time series that reduces spatial bias and implemented this method with altimetry data from the Ice, Cloud, and land Elevation Satellite (ICESat; 2003–09), CryoSat-2 (2010–present), and ICESat-2 (2018–present) altimetry missions. We then used the dh/dt time series to identify persistent patterns of surface-elevation change and evaluate regional mass balance. Our results suggest a persistent anomalous reduction in ice thickness and effective backstress in the peninsula connecting Whillans Ice Plain to Crary Ice Rise. The multi-decadal observational record of pinning-point mass redistribution and grounding zone retreat presented in this study highlights the on-going reorganization of the southern Ross Ice Shelf embayment buttressing regime in response to ice-stream deceleration.

The momentum conservation equation for glacier flow can be described through minimization of an action functional. Several software packages for glacier flow modeling use this action principle in the design of numerical solution procedures. We derive here an equivalent dual action principle for the shallow stream approximation and implement this model using the finite element method. The key feature of the dual action is that the flow law and friction law are both inverted, which changes the character of the non-linearities. This altered character makes it possible to implement numerical solvers for the dual form that work even when the ice thickness or strain rate are exactly equal to zero. Solvers for the primal form typically fail on such input data and require regularization of the problem. This robustness makes it possible to implement iceberg calving in a simple way: the modeler sets the ice thickness to zero in the desired area. We provide several demonstrations and a reference implementation.

Supraglacial lakes (SGLs) are widespread across the Greenland ice sheet and cause transient changes in ice flow. Here, we produce the first annual ice-sheet wide database of maximum summer SGL extents spanning 1985 to 2023 using all July and August Landsat images. Lake visibility percentages were calculated to estimate the uncertainty induced by variable image data coverage. SGLs were mainly distributed between 1000 and 1600 m elevation, with large lake area observed in northwestern, northeastern and southwestern basins. Lake area increased at a rate of 50.5 km2 a−1 across the entire Greenland, and lakes advanced to higher elevations at an average rate of 10.2 m a−1 during 1985–2023. We leveraged spatiotemporally matched ICESat-2 and Landsat 8 reflectance data to develop a deep learning model for lake depth inversion for the period 2014–23. This model demonstrates the highest accuracy among all image-based methods, albeit with an underestimation of ~15% when compared to ICESat-2 data. A significant positive correlation between lake volume and area is used to up-scale the approach to the entire time period, indicating a lake volume increase of 221.9 ± 63.6 × 106 m3 a−1. Increasing air/land surface temperature, surface pressure and decreasing snowfall were the most important contributing factors in driving lake variability.

The Ice-sheet and Sea-level System Model (ISSM) provides numerical solutions for ice sheet dynamics using finite element and fine mesh adaption. However, considering ISSM is compatible only with central processing units (CPUs), it has limitations in economizing computational time to explore the linkage between climate forcings and ice dynamics. Although several deep learning emulators using graphic processing units (GPUs) have been proposed to accelerate ice sheet modeling, most of them rely on convolutional neural networks (CNNs) designed for regular grids. Since they are not appropriate for the irregular meshes of ISSM, we use a graph convolutional network (GCN) to replicate the adapted mesh structures of the ISSM. When applied to transient simulations of the Pine Island Glacier (PIG), Antarctica, the GCN successfully reproduces ice thickness and velocity with a correlation coefficient of approximately 0.997, outperforming non-graph models, including fully convolutional network (FCN) and multi-layer perceptron (MLP). Compared to the fixed-resolution approach of the FCN, the flexible-resolution structure of the GCN accurately captures detailed ice dynamics in fast-ice regions. By leveraging 60–100 times faster computational time of the GPU-based GCN emulator, we efficiently examine the impacts of basal melting rates on the ice sheet dynamics in the PIG.

Diffuse optical spectroscopy (DOS) techniques characterize scattering media by examining their optical response to laser illumination. Time-domain DOS methods involve illuminating the medium with a laser pulse and using a fast photodetector to measure the time-dependent intensity of light that exits the medium after multiple scattering events. While DOS research traditionally focused on characterizing biological tissues, we demonstrate that time-domain diffuse optical measurements can also be used to characterize snow. We introduce a model that predicts the time-dependent reflectance of a dry snowpack as a function of its density, grain size, and black carbon content. We develop an algorithm that retrieves these properties from measurements at two wavelengths. To validate our approach, we assembled a two-wavelength lidar system to measure the time-dependent reflectance of snow samples with varying properties. Rather than measuring direct surface returns, our system captures photons that enter and exit the snow at different points, separated by a small distance (4–10 cm). We observe clear, linear correlations between our retrievals of density and black carbon concentration, and ground truth. For black carbon concentration the correlation is nearly one-to-one. We also find that our method is capable of distinguishing between small and large grain sizes.

Surface meltwater can influence subglacial hydrology and ice dynamics if it reaches ice sheet's base. Firn aquifers store meltwater and drain into wide crevasses marking the aquifer's downstream boundary, indicating water from firn aquifers can drive hydrofracture to establish surface-to-bed hydraulic connections at inland locations. Yet, sparse observations limit our understanding of the physical processes controlling firn aquifer drainage. We assess the potential for future inland firn aquifer drainage migration with field observations and linear elastic fracture mechanics (LEFMs) modeling to determine the conditions needed to initiate and sustain hydrofracture on Helheim Glacier, Greenland. We find that local stress conditions alone can drive crevasse tips into the firn aquifer, allowing hydrofracture initiation year-round. We infer inland expansion of crevasses over the firn aquifer from crevasse-nucleated whaleback dune formation and Global Navigation Satellite System-station detected crevasse opening extending 14 and 4 km, respectively, inland from the current, farthest-upstream drainage point. Using our LEFM model, we identify three vulnerable regions with coincidence between dry crevasse depth and water table variability, indicating potential future inland firn aquifer drainage sites. These results suggest the downstream boundary of firn aquifers can migrate inland under future warming scenarios and may already be underway.

The ice discharge from the grounded parts of marine ice sheets into the ocean is modulated by their floating extensions – ice shelves. The ice-shelf impact on the grounded ice is typically described as ‘backpressure’ or ‘buttressing’. Theoretical analyses of their effects have been restricted to one horizontal dimension. This study revisits the concepts of ‘backpressure’ introduced by Thomas (1977) and ‘buttressing’ numbers and ratios introduced by Gudmundsson (2013) and extends their theoretical analysis to two horizontal dimensions. Using the integral form of the momentum-balance formulation suitable for fast-flowing ice streams and ice shelves, our analysis provides a natural definition for the total backpressure force exerted by an ice shelf to the grounded ice upstream of its grounding line. The results of numerical analyses suggest that ice shelves whose second principal stress component is compressional over larger areas may provide more buttressing compared to ice shelves with smaller areas of compressional stresses or to ice shelves with both principal stresses being tensile.

Climate change is causing Himalayan glaciers to shrink rapidly and natural hazards to increase, while downstream exposure is growing. Glacier shrinkage promotes the formation of glacial lakes, which can suddenly drain and produce glacier lake outburst floods (GLOFs). Bhutan is one of the most vulnerable countries globally to these hazards. Here we use remotely sensed imagery to quantify changes in supraglacial water storage on Tshojo Glacier, Bhutan, where previous supraglacial pond drainage events have necessitated downstream evacuation. Results showed a doubling of both total ponded area (104 529 m2 to 213 943 m2) and its std dev. (64 808 m2 to 158 550 m2) between the periods 1987–2003 and 2007–2020, which was predominantly driven by increases in the areas of the biggest ponds. These ponds drained regularly and have occupied the same location since at least 1967. Tshojo Glacier has remained in the first stage of proglacial lake development for 53 years, which we attribute to its moderate slopes and ice velocities. Numerical modelling shows that pond outbursts can reach between ~6 and 47 km downstream, impacting the remote settlement of Lunana. Our results highlight the need to better quantify variability in supraglacial water storage and its potential to generate GLOFs, as climate warms.

Glacier surges can create ice-dammed lakes when the advancing terminus blocks drainage. Such lakes are inherently unstable and can drain abruptly as glacial lake outburst floods (GLOFs), presenting a hazard to downstream populations and infrastructure in high mountain environments. We present satellite image analysis of the evolution of an ice-dammed lake formed by the 2018–20 surge of Shisper Glacier, western Karakoram. Our analysis identifies six phases of lake evolution. A large lake of up to 33.7 ± 9% million m3 formed in 2018–19, 2019–20, 2020–21 and 2021–22. In each case, the lake began to fill late in the year, reached a maximum size in May, and had completely drained between May and July, typically over 1–2 days. This analysis provides further evidence that GLOF hazards associated with lakes dammed by glacier surges can persist for several years after surge termination.

Plateau icefields are large stores of fresh water, preconditioned to enhanced mass loss due to their gently sloping accumulation areas. Accurate modelling of their mass balance is therefore crucial for sea-level rise projections. Here, we use the COupled Snowpack and Ice surface energy and mass-balance model in PYthon (COSIPY) to simulate historical and future mass balance of the Juneau Icefield, Alaska – a high elevation (>1200 m) plateau icefield. We force the model with dynamically downscaled climate simulations, for both past and future (RCP 8.5) conditions. The icefield's mass balance decreased from a mean of −0.22 ± 0.38 m w.e. a−1 (1981–2019) to −1.52 ± 0.27 m w.e. a−1 (2031–2060), with many glaciers shifting from positive to negative mass balances at the start of the 21st century. This mass loss is attributed to projected rising air temperatures and reduced snowfall, causing the equilibrium line altitude to rise and triggering albedo and melt-elevation feedbacks. These processes exacerbate melt, potentially leading to increased glacier disconnections at icefalls.

Ridge B is one of the least studied areas in Antarctica but has been considered to be a potential location for the oldest ice on Earth. Among important parameters for calculating where very old ice may exist, geothermal heat flux (GHF) is critical but poorly understood. Here, GHF is determined by quantifying the transitions between dry and wet basal conditions using a radioglaciological method applied to airborne radio-echo sounding data. GHF is then constrained by a thermodynamic model matched to the transitions. The results show that GHF in Ridge B varies locally and ranges from 48.5 to 65.1 mW m−2, with an average value of 58.0 mW m−2, which is consistent with the current known GHF constrained by subglacial lakes and derived from Vostok ice core temperature measurements. Our work highlights the value of considering local GHF when locating the oldest ice in this potential region or other regions.

Taku Glacier recently began retreating for the first time since the late 19th century but limited observations of its bed leaves uncertainties on how this retreat will proceed. In this study, we use ground-based gravity measurements to improve the extent of bed-elevation estimates on the Taku by modelling the glacier in 3D. We find the across-flow geometry of the middle to upper reach of the Taku and the Matthes branch has a step-like feature near the edge and a wide, flat bottom. We constrain the ice thickness along flow within uncertainty limits and provide a range of expected values. Along the centre line of our model, we find a maximum ice thickness of 1556 ± 143 m and the deepest bed at 445 ± 166 m below sea level. The along-flow results also delineate two bedrock bumps, which could help stabilise the retreat of the Taku when its terminus is submerged in water. We model the bed to be below sea level until at least 35 km upstream of the terminus where the Matthes branch joins the main branch, improving constraints on how far upstream the Taku would be vulnerable to marine retreat.