This study involves examination of glaciological mass-balance time series, glacier and climatic descriptors, the application of machine learning methods for glaciological clustering, and computation of mass-balance time series based upon the clustering and statistical analyses relative to gridded air temperature datasets. Our analysis revealed an increasingly coherent mass-balance trend but a latitudinal bias of monitoring programs. The glacier classification scheme delivered three clusters, suggesting these correspond to climate-based first-order regimes, as glacier morphometric characteristics weighed little in our multivariate analysis. We combined all available surface mass-balance data from in situ monitoring programs to study temperature sensitivity for each cluster. These aggregated mass-balance time series delivered spatially different statistical relationships to temperature. Results also showed that surface mass balance tends to have a temporal self-correlation of ~20 years. Using this temporal window to analyze sensitivity since ~ 1950, we found that in all cases temperature sensitivity, while generally negative, tended to fluctuate through time, with the largest absolute magnitudes occurring in the 1980s and becoming less negative in recent years, revealing that glacier sensitivity is non-stationary. These findings point to a scenario of a coherent signal of change no matter the glacier regime. This work provides new insights into glacier–climate relationships that can guide observational and analytical strategies.

Khovsgol Lake, a seasonal ice-covered lake located in boreal Siberia, plays important economic, transportation and agricultural roles for local residents. On 11 January 2021, an Mw 6.7 earthquake struck the center of this lake, providing a unique opportunity to better understand lake ice movement, ridge distribution, and hydraulic and hydrodynamic processes, as a result of the mainshock. We use a pixel-tracking method on both Sentinel-1 synthetic aperture radar and Sentinel-2 optical remote-sensing data covering this lake before, during and after the mainshock to obtain lake-ice displacement. Combining these measurements with different viewing geometries, we determine the locations of pressure ridges in each period and derive their relative 3D displacement maps with a precision of <2.2 m. Our results indicate a large E-W displacement of up to 10.3 m and a vertical displacement of up to 4.6 m during the coseismic period, which has a distinctly different magnitude and pattern of displacement compared to the pre- and post-event periods. Given the ice motion pattern and magnitude, we speculate that the unique ice displacement of Khovsgol Lake may have been caused by a rare seismic seiche after the mainshock.

A 3-year record of weekly snow water equivalent (SWE) accumulation at Summit Camp, central Greenland ice sheet, obtained by direct sampling, is presented. While the overall SWE accumulation of 24.2 cm w.e. a−1 matches long-term ice core estimates, variability increases at shorter timescales. Half of the annual SWE accumulation occurs during a few large events, with the average accumulation rate decreasing 35% between the first and second halves of the record coinciding with exceptional anticyclonic conditions in the spring and summer of 2019. No seasonality in accumulation is detected. Rather, local accumulation rates appear to be significantly impacted by wind redistribution that obscures temporal patterns in snowfall. Surface snow density is consistent, on average, with previously measured values but does not correlate with near surface temperature or wind speed. Two surface mass balance reanalysis models significantly underestimate accumulation rates at Summit Camp. This is concerning because such models are often used to estimate ice-sheet mass loss.

We used Sentinel-2 satellite imagery at 10 m resolution to map the extent of Norway's glaciers and ice-marginal lakes over 2018–19. We applied a standardized semi-automated band ratio method to derive glacier outlines and ice-marginal lakes. To optimise the results, we manually edited the ice-lake interfaces, debris, snow and parts of the glaciers situated under shadow. We compared our Sentinel-2 derived outlines with very high-resolution aerial orthophotos and Pléiades satellite orthoimages. Glaciers larger than 0.3 km2 have area differences within 7%, whereas values are larger for smaller glaciers. The orthophotos and orthoimages provide more details and a higher mapping accuracy for individual glaciers, but require manual digitisation, have smaller spatial and temporal coverage and can have adverse snow conditions. We found a total glacier area of 2328 ± 70 km2 of which the ten largest glaciers accounted for 52%. The glacier area decreased 15% since the previous inventory (Landsat data from 1999 to 2006), the reduction being largest in northern Norway (22%) compared to southern Norway (10%). We detected more than 2000 previously undetected smaller glaciers and ice patches (covering 37 km2) and 360 new ice-marginal lakes.

Very few studies have emphasized the effects of high-pressure sintering on snow density evolution, even though snow as a type of engineering material is widely used in construction engineering in cold regions for snow pavement, snow runway and polar infrastructure. This study presents new experimental results of snow densification under high pressures of up to 100 MPa for a temperature range from −3.5 to −17.3°C and uniaxial compression at the temperature of −10°C and constant strain rates from 5 × 10−4 to 10−1 s−1. Results reveal that density evolution of snow to ice under high-pressure sintering can be achieved in a wide temperature range within a duration as short as 5 min. The compressive strength of snow-sintered ice was ~1.2–2.2 times as large as that of water-frozen ice reported by previous work. The orthogonal experiment showed that pressure is a more significant factor affecting the final density in comparison with sintering temperature and time. The increased rates of ice fabrication, low limitations on temperature and reliable sintered snow strength indicate that snow-ice engineering, such as airport construction in Greenland and Antarctica, can be improved by high-pressure sintering of snow to overcome the harsh environment.

Tidewater glaciers have been observed to experience instantaneous, stepwise increases in velocity during iceberg-calving events due to a loss of resistive stresses. These changes in stress can potentially impact tidewater glacier stability by promoting additional calving and affecting the viscous delivery of ice to the terminus. Using flow models and perturbation theory, we demonstrate that calving events and subsequent terminus readvance produce quasi-periodic, sawtooth oscillations in stress that originate at the terminus and propagate upstream. The stress perturbations travel at speeds much greater than the glacier velocities and, for laterally resisted glaciers, rapidly decay within a few ice thickness of the terminus. Consequently, because terminus fluctuations due to individual calving events tend to be much higher frequency than climate variations, individual calving events have little direct impact on the viscous delivery of ice to the terminus. This suggests that the primary mechanism by which calving events can trigger instability is by causing fluctuations in stress that weaken the ice and lead to additional calving and sustained terminus retreat. Our results further demonstrate a stronger response to calving events in simulations that include the full stress tensor, highlighting the importance of accounting for higher order stresses when developing calving parameterizations.

An end of summer snowline (EOSS) photographic dataset for Aotearoa New Zealand contains over four decades of equilibrium line altitude (ELA) observations for more than 50 index glaciers. This dataset provides an opportunity to create a climatological ELA reference series that has several applications. Our work screened out EOSS sites that had low temporal coverage and also removed limited observations when the official survey did not take place. Snowline data from 41 of 50 glaciers in the EOSS dataset were retained and included in a normalised master snowline series that spans 1977–2020. Application of the regionally representative normalised master snowline series in monthly and seasonally resolved climate response function analyses showed consistently strong relationships with austral warm-season temperatures for land-based stations west of the Southern Alps and the central Tasman Sea. There is a trend towards higher regional snowlines since the 1990s that has been steepening in recent decades. If contemporary decadal normalised master snowline series trends are maintained, the average Southern Alps snowline elevation will be displaced at least 200 m higher than normal by the 2025–2034 decade. More frequent extremely high snowlines are expected to drive more extreme cumulative mass-balance losses that will reduce the glacierised area of Aotearoa New Zealand.

The vast Greenland and Antarctic Ice Sheets are covered by many tens of meters of polar firn, which is snow that is years to centuries old and has experienced significant metamorphism. Both ice-sheet modeling and decoding satellite data require knowledge of the thermal conductivity of polar firn with depth, yet direct measurements are not available for depths below the top several meters. We present the first direct measurements of the effective thermal conductivity of polar firn over depths down to 48 m. A custom guarded hot plate has been designed and constructed, and validation of this device using materials of known thermal conductivity is presented. Using the validated device, measurements were made on firn core samples spanning depths from 4 to 48 m from an undisturbed site near the South Pole, Antarctica. Results show that the thermal conductivity of polar firn at South Pole increases with depth and with density. The thermal conductivity of polar firn from the surface to 48 m depth is well-explained as a function of density by the relationship kfirn(ρ) = 0.144 e0.00308·ρ and as a function of depth by the relationship kfirn(z) = 0.536 e0.0144·z. The associated thermal diffusivities range from 19.0 to 28.5 m2 a-1.

Mass loss from ice shelves is a strong control on grounding-line dynamics. Here we investigate how calving and submarine melt parameterizations affect steady-state grounding-line positions and their stability. Our results indicate that different calving laws with the same melt parameterization result in more diverse steady-state ice-sheet configurations than different melt parameterizations with the same calving law. We show that the backstress at the grounding line depends on the integrated ice-shelf mass flux. Consequently, ice shelves are most sensitive to high melt rates in the vicinity of their grounding lines. For the same shelf-averaged melt rates, different melt parameterizations can lead to very different ice-shelf configurations and grounding-line positions. If the melt rate depends on the slope of the ice-shelf draft, then the positive feedback between increased melting and steepening of the slope can lead to singular melt rates at the ice-shelf front, producing an apparent lower limit of the shelf front thickness as the ice thickness vanishes over a small boundary layer. Our results illustrate that the evolution of marine ice sheets is highly dependent on ice-shelf mass loss mechanisms, and that existing parameterizations can lead to a wide range of modelled grounding-line behaviours.

Under global warming, many glaciers worldwide are receding. However, recent studies have suggested the extension of the Karakoram Anomaly, a region of anomalous glacier mass gain, into the western Kunlun and eastern Pamir mountains. However, the eastern limit of this anomaly in the Kunlun Mountains is unclear. This study, using changes in glacier area and surface elevation, estimates the eastern limit of the Kunlun-Pamir-Karakoram anomaly at ~85°E. Over the past 50 years, glaciers west of 85°E in the Kunlun Mountains decreased in area from 8401 to 7945 km2 at a rate of −0.12 ± 0.07% a−1, showed a reduction in the rate of retreat through time and have recently gained mass, with surface elevation changes of 0.15 ± 0.35 m a−1 over the period of 2000–2013. Glaciers east of 85°E have experienced greater rates of area change (−61 ± 12 km2 and −0.43 ± 0.13% a−1) over the past 50 years, accelerated area loss in recent years and elevation change rate of −0.51 ± 0.18 m a−1 between 2000 and 2013. These patterns of elevation and area change are consistent with regional increases in summer temperature in the eastern Kunlun Mountains and slight cooling in the western Kunlun Mountains.

Increasing ice flux from glaciers retreating over deepening (retrograde) bed topography has been implicated in the recent acceleration of mass loss from the Greenland and Antarctic ice sheets. We show in observations that some glaciers have remained at peaks in bed topography without retreating despite enduring significant changes in climate. Observations also indicate that some glaciers which persist at bed peaks undergo sudden retreat years or decades after the onset of local ocean or atmospheric warming. Using model simulations, we show that persistence of a glacier at a bed peak is caused by ice slowing as it flows up a reverse-sloping bed to the peak. Persistence at bed peaks may lead to two very different future behaviors for a glacier: one where it persists at a bed peak indefinitely, and another where it retreats from the bed peak after potentially long delays following climate forcing. However, it is nearly impossible to distinguish which of these two future behaviors will occur from current observations. We conclude that inferring glacier stability from observations of persistence obscures our true commitment to future sea-level rise under climate change. We recommend that further research is needed on seemingly stable glaciers to determine their likely future.

Iceberg calving is one of the major mechanisms of ice loss from tidewater glaciers and ice sheets, but obtaining accurate estimates of ice discharge that are both continuous and accurate is a challenging task. Recent results have demonstrated the effective application of passive cryoacoustics – the use of naturally generated sounds to study the cryosphere – to quantify subaerial calving fluxes. However, little is known about the acoustic signatures of submarine calving. This study investigates the underwater noise from 656 subaerial and 162 submarine calving events observed at Hansbreen, Svalbard in the summers of 2016 and 2017. Statistical analysis of the acoustic signal shows that the normalized power of the calving noise is log-normally distributed regardless of the calving mode. However, submarine events can be distinguished from subaerial events by using the shape parameter of the log-normal distribution paired with the calving signal duration. The newly developed classification model may potentially be used for two purposes: (1) to study potential causal relationships between these two calving modes and (2) to separate calving fluxes into subaerial and submarine components. The latter will also require knowledge of the relationship between ice mass and sound spectral level for submarine calving events.

The Desert Andes contain >4500 ice masses, but only a handful are currently being monitored. We present the mass changes of the small mountain glacier Agua Negra (1 km2) and of the rest of glaciers in the Jáchal river basin. Remote-sensing data show Agua Negra glacier lost 23% of its area during 1959–2019. Glaciological measurements during 2014–2021 indicate an average annual mass balance of −0.52 m w.e. a−1, with mean winter and summer balances of 0.80 and −1.33 m w.e. a−1, respectively. The Equilibrium Line Altitude (ELA) is estimated to be 5100 ± 100 m a.s.l., which corresponds to an Accumulation Area Ratio (AAR) of 0.28 ± 0.21. Geodetic data from SRTM X and Pléiades show a doubling of the loss rate from −0.32 ± 0.03 m w.e. a−1 in 2000–2013, to −0.66 ± 0.06 m w.e. a−1 in 2013–2019. Comparatively, the ice losses for the entire Jáchal river basin (25 500 km2) derived from ASTER show less negative values, −0.11 ± 16 m w.e. a−1 for 2000–2012 and −0.23 ± 14 m w.e. a−1 for 2012–2018. The regional warming trend since 1979 and a recent decline in snow accumulation are probably driving the observed glacier mass balance.

The production of meltwater from glacier ice, which is exposed at the margins of land ice during the summer, is responsible for a large proportion of glacier mass loss. The rate of meltwater production from glacier ice is especially sensitive to its physical structure and chemical composition which combine to determine the albedo of glacier ice. However, the optical properties of near-surface glacier ice are not well known since most prior work has focused on laboratory-grown ice or deep cores. Here, we demonstrate a measurement technique based on diffuse propagation of nanosecond-duration laser pulses in near-surface glacier ice that enables the independent measurement of the scattering and absorption coefficients, allowing for a complete description of the processes governing radiative transfer. We employ a photon-counting detector to overcome the high losses associated with diffuse optics. The instrument is highly portable and rugged, making it optimally suited for deployment in remote regions. A set of measurements taken on Crook and Collier Glaciers, Oregon, serves as a demonstration of the technique. These measurements provide insight into both physical structure and composition of near-surface glacier ice and open new avenues for the analysis of light-absorbing impurities and remote sensing of the cryosphere.

The future contributions of the Antarctic Ice Sheet to sea level rise will depend on the evolution of its surface mass balance (SMB), which could amplify/dampen mass losses increasingly observed at the ice sheet's edge. In situ constraints of SMB over annual-to-decadal timescales consist mostly of firn/ice cores that have a surface footprint $\sim$cm$^{2}$. SMB constraints also come from climate models, which have a higher temporal resolution but a larger surface footprint of several km$^{2}$. We use ice-penetrating radar data to obtain an intermediate spatial and temporal resolution SMB record over three ice rises along the Princess Ragnhild Coast. The co-located ice cores allow us to obtain absolute radar-derived SMB rates at a multi-annual-to-decadal temporal resolution. By comparing the ice core SMB measurements and the radar-derived SMB records, we determine that pointwise measurements of SMB are representative of a small surface area, $\sim 200-500$ m radius extending from the ice core drill site for the ice rises studied here, and that the pointwise measurements are systematically 7–15 cm w.e. a$^{-1}$ lower than the mean SMB value calculated for the whole ice rises. However, ice core records are representative of an entire ice rise's temporal variability at the temporal resolution examined.

Over the last 25 years, radiowave detection of neutrino-generated signals, using cold polar ice as the neutrino target, has emerged as perhaps the most promising technique for detection of extragalactic ultra-high energy neutrinos (corresponding to neutrino energies in excess of 0.01 Joules, or 1017 electron volts). During the summer of 2021 and in tandem with the initial deployment of the Radio Neutrino Observatory in Greenland (RNO-G), we conducted radioglaciological measurements at Summit Station, Greenland to refine our understanding of the ice target. We report the result of one such measurement, the radio-frequency electric field attenuation length $L_\alpha$. We find an approximately linear dependence of $L_\alpha$ on frequency with the best fit of the average field attenuation for the upper 1500 m of ice: $\langle L_\alpha \rangle = ( ( 1154 \pm 121) - ( 0.81 \pm 0.14) \, ( \nu /{\rm MHz}) ) \,{\rm m}$ for frequencies ν ∈ [145 − 350] MHz.

We compare different ways the bulk flow nonlinearity of glacier ice can be captured in an orthotropic rheology. Specifically, we compare the unapproximated orthotropic rheology, derived from plastic potential theory, to existing approximations that assume either the nonlinear viscosity or fluidity is identical to that of Glen's isotropic flow law. We find, overall, a reasonable agreement between the three orthotropic rheologies, and with existing Dye 3 ice-core deformation tests, although assuming Glen's viscosity provides the best approximation to the unapproximated rheology. Our results therefore suggest that previous studies based on either approximation to the orthotropic rheology are on relatively safe ground in the sense that both approximations generally agree with the unapproximated rheology and experimental data. Finally, we provide the forward and inverse analytical forms of all three rheologies for use in future numerical ice-flow modelling.