Distant glacial areas are interconnected by a complex system of fractures and water channels which run in the glacier interior and characterize the englacial realm. Water can slowly freeze in these channels where the slow freezing excludes air bubbles giving the ice a clear aspect. This ice is uplifted to the surface ablation zone by glacial movements and can therefore be observed in the form of clear surface ice bands. We employed an indirect method to sample englacial water by coring these ice bands. We were able, for the first time, to compare microbial communities sampled from clear (i.e. frozen englacial water bands) and cloudy ice (i.e. meteoric ice) through 16S rRNA gene sequencing. Although microbial communities were primarily shaped and structured by their spatial distribution on the glacier, ice type was a clear secondary factor. One area of the glacier, in particular, presented significant microbial community clear/cloudy ice differences. Although the clear ice and supraglacial communities showed typical cold-adapted glacial communities, the cloudy ice had a less defined glacial community and ubiquitous environmental organisms. These results highlight the role of englacial channels in the microbial dispersion within the glacier and, possibly, in the shaping of glacial microbial communities.

Ice stream discharge responds to a balance between gravity, basal friction and lateral drag. Appreciable viscous heating occurs in shear margins between ice streams and adjacent slow-moving ice ridges, altering the temperature-dependent viscosity distribution that connects lateral drag to marginal strain rates and ice stream velocity. Warmer ice deforms more easily and accommodates faster flow, whereas cold ice supplied from ice ridges drives advective cooling that counteracts viscous heating. Here, we present a two-dimensional (three velocity component), steady-state model designed to explore the thermal controls on ice stream shear margins. We validate our treatment through comparison with observed velocities for Bindschadler Ice Stream and verify that calculated temperatures are consistent with results from previous studies. Sweeping through a parameter range that encompasses conditions representative of ice streams in Antarctica, we show that modeled steady-state velocity has a modest response to different choices in forcing up until temperate zones develop in the shear margins. When temperate zones are present, velocity is much more sensitive to changes in forcing. We identify key scalings for the emergence of temperate conditions in our idealized treatment that can be used to identify where thermo-mechanical feedbacks influence the evolution of the ice sheet.

In this study, our goal is to track internal ice layers on the Snow Radar data collected by NASA Operation IceBridge. We examine the application of deep learning methods on radar data gathered from polar regions. Artificial intelligence techniques have displayed impressive success in many practical fields. Deep neural networks owe their success to the availability of massive labeled data. However, in many real-world problems, even when a large dataset is available, deep learning methods have shown less success, due to causes such as lack of a large labeled dataset, presence of noise in the data or missing data. In our radar data, the presence of noise is one of the main obstacles in utilizing popular deep learning methods such as transfer learning. Our experiments show that if the neural network is trained to detect contours of objects in electro-optical imagery, it can only track a low percentage of contours in radar data. Fine-tuning and further training do not provide any better results. However, we show that selecting the right model and training it on the radar imagery from the start yields far better results.

Drag at the bed and along the lateral margins are the primary forces resisting flow in outlet glaciers. Simultaneously inferring these parameters is challenging since basal drag and ice viscosity are coupled in the momentum balance, which governs ice flow. We test the ability of adjoint-based inverse methods to infer the slipperiness coefficient in a power-law sliding law and the flow-rate parameter in the constitutive relation for ice using a regularization scheme that includes coefficients weighted by surface strain rates. Using synthetic data with spatial variations in basal drag and ice rheology comparable to those in West Antarctic Ice Streams, we show that this approach allows for more accurate inferences. We apply this method to Bindschadler and MacAyeal Ice Streams in West Antarctica. Our results show relatively soft ice in the shear margins and spatially varying basal drag, with an increase in drag with distance upstream of the grounding line punctuated by localized areas of relatively high drag. We interpret soft ice to reflect a combination of heating through viscous dissipation and changes in the crystalline structure. These results suggest that adjoint-based inverse methods can provide inferences of basal drag and ice rheology when regularization is informed by strain rates.

The Drygalski Ice Tongue in East Antarctica stretches 90 km into the Ross Sea and influences the local ocean circulation, and persistence of the Terra Nova Bay Polynya. We examine the controls on the size of this floating ice body by comparing the propagation of six large fractures on the ice tongue's northern side using 21 years of Landsat imagery with hydrostatic ice thickness maps and strain rate calculations. We also apply a subglacial hydrology model to estimate the location and discharge from subglacial channels over the grounding line and compare these with basal channels identified along the ice tongue using remote sensing and airborne radar data. Our results suggest that large fractures are inhibited from full-width propagation by thicker ice between basal channels. We hypothesize that only once the ice tongue thins towards the terminus, can fractures propagate and cause large calving events. This suggests an important relationship between the melting of floating ice from subglacial and ocean sources and the expansion of fractures that lead to ice tongue calving.

Effective snow grain radius (re) is mapped at high resolution using near-infrared hyperspectral imaging (NIR-HSI). The NIR-HSI method can be used to quantify re spatial variability, change in re due to metamorphism, and visualize water percolation in the snowpack. Results are presented for three different laboratory-prepared snow samples (homogeneous, ice lens, fine grains over coarse grains), the sidewalls of which were imaged before and after melt induced by a solar lamp. The spectral reflectance in each ~3 mm pixel was inverted for re using the scaled band area of the ice absorption feature centered at 1030 nm, producing re maps consisting of 54 740 pixels. All snow samples exhibited grain coarsening post-melt as the result of wet snow metamorphism, which is quantified by the change in re distributions from pre- and post-melt images. The NIR-HSI method was compared to re retrievals from a field spectrometer and X-ray computed microtomography (micro-CT), resulting in the spectrometer having the same mean re and micro-CT having 23.9% higher mean re than the hyperspectral imager. As compact hyperspectral imagers become more widely available, this method may be a valuable tool for assessing re spatial variability and snow metamorphism in field and laboratory settings.

Subglacial hydrological systems require innovative technological solutions to access and observe. Wireless sensor platforms can be used to collect and return data, but their performance in deep and fast-moving ice requires quantification. We report experimental results from Cryoegg: a spherical probe that can be deployed into a borehole or moulin and transit through the subglacial hydrological system. The probe measures temperature, pressure and electrical conductivity in situ and returns all data wirelessly via a radio link. We demonstrate Cryoegg's utility in studying englacial channels and moulins, including in situ salt dilution gauging. Cryoegg uses VHF radio to transmit data to a surface receiving array. We demonstrate transmission through up to 1.3 km of cold ice – a significant improvement on the previous design. The wireless transmission uses Wireless M-Bus on 169 MHz; we present a simple radio link budget model for its performance in cold ice and experimentally confirm its validity. Cryoegg has also been tested successfully in temperate ice. The battery capacity should allow measurements to be made every 2 h for more than a year. Future iterations of the radio system will enable Cryoegg to transmit data through up to 2.5 km of ice.

Lemon Creek Glacier, a temperate valley glacier in the Juneau Icefield of Southeast Alaska, is the site of long running (>60 years) glaciological studies. However, the most recent published estimates of its thickness and subglacial topography come from two ~50 years old sources that are not in agreement and do not account for the effects of years of negative mass balance. We collected a 1-km long active-source seismic line on the upper section of the glacier parallel and near to the centerline of the glacier, roughly straddling the equilibrium-line altitude. We used these data to perform joint reflection-refraction velocity modeling and reflection imaging of the glacier bed. We find that this upper section of Lemon Creek Glacier is as much as 150 m (~65%) thicker than previously suggested with a large overdeepening in an area previously believed to have a uniform thickness. Our results lead us to reinterpret the impact of basal motion on ice flow and have a significant impact on expectations of subglacial hydrology. We suggest that further efforts to develop a whole-glacier model of subglacial topography are necessary to support studies that require accurate models of ice thickness and subglacial topography.

We present polar ice core organic matter (OM) fluorescence signatures to reconstruct ancient and modern atmospheric compositions and relate OM signals to past ecological changes. OM composition from three Arctic ice cores (Canada and Greenland) was characterized by fluorescence spectroscopy and compared to an Antarctic OM record. Diverse OM was measured in ancient and modern ice in both hemispheres and similarities existed across vast spatiotemporal scales. We determined three OM markers, indicating paleoclimate and modern carbon trends: (i) ‘humic-like’, detected in Holocene ice of more complex and aromatic character, supporting trends of higher plant influences in warmer climates, (ii) monolignol- and non-amino acid-like, describing simple, lignin-like OM precursors ubiquitous in the environment and the microbial degradation products of more complex materials from plants/soils, and (iii) amino acid- and tannin-like, indicating microbial degradation of simple OM chemical species, compared to the other markers. Concentration trends were inferred from fluorescence intensities of individual OM types and related to warmer temperatures. No indicators of freshly produced OM by microbes were detected; signals were interpreted as materials externally produced from the ice and transported to polar regions. This marks the first global comparison of atmospheric reconstructions from OM across vast spatiotemporal scales.

Advances in analytical methods have made it possible to obtain high-resolution water isotopic data from ice cores. Their spectral signature contains information on the diffusion process that attenuated the isotopic signal during the firn densification process. Here, we provide a tool for estimating firn-diffusion rates that builds on the Community Firn Model. Our model requires two main inputs, temperature and accumulation, and it calculates the diffusion lengths for δ17O, δ18O and δD. Prior information on the isotopic signal of the precipitation is not a requirement. In combination with deconvolution techniques, diffusion lengths can be used in order reconstruct the pre-diffusion isotopic signal. Furthermore, the temperature dependence of the isotope diffusion and firn densification makes the diffusion length an interesting candidate as a temperature proxy. We test the model under steady state and transient scenarios and compare four densification models. Comparisons with ice core data provide an evaluation of the four models and indicate that there are differences in their performance. Combining data-based diffusion length estimates with information on past accumulation rates and ice flow thinning, we reconstruct absolute temperatures from three Antarctic ice core sites.

Crary Ice Rise formed after the Ross Ice Shelf re-grounded ~1 kyr BP. We present new ice-penetrating radar data from two systems operating at center frequencies of 7 and 750 MHz that confirm the ice rise is composed of a former ice shelf buried by subsequent accumulation. Stacks of englacial diffraction hyperbolas are present almost everywhere across the central ice rise and extend up to ~350 m above the bed. In many cases, bed reflections beneath the diffraction hyperbolas are obscured for distances up to 1 km. Waveform modeling indicates that the diffraction hyperbolas are likely caused by marine ice deposits in former basal crevasses and rifts. The in-filling of rifts and basal crevasses may have strengthened the connection between the ice rise and the surrounding ice shelf, which could have influenced local and regional ice dynamics. Three internal reflection horizons mark the upper limit of disturbed ice and diffraction hyperbolas in different sections of the ice rise, indicating at least three stages of flow stabilization across the ice rise. A surface lineation visible in MODIS imagery corresponds spatially to deepening and strong deformation of these layers, consistent with the characteristics of former grounding lines observed elsewhere in Antarctica.

Observations of teleseismic earthquakes using broadband seismometers on the Ross Ice Shelf (RIS) must contend with environmental and structural processes that do not exist for land-sited seismometers. Important considerations are: (1) a broadband, multi-mode ambient wavefield excited by ocean gravity wave interactions with the ice shelf; (2) body wave reverberations produced by seismic impedance contrasts at the ice/water and water/seafloor interfaces and (3) decoupling of the solid Earth horizontal wavefield by the sub-shelf water column. We analyze seasonal and geographic variations in signal-to-noise ratios for teleseismic P-wave (0.5–2.0 s), S-wave (10–15 s) and surface wave (13–25 s) arrivals relative to the RIS noise field. We use ice and water layer reverberations generated by teleseismic P-waves to accurately estimate the sub-station thicknesses of these layers. We present observations consistent with the theoretically predicted transition of the water column from compressible to incompressible mechanics, relevant for vertically incident solid Earth waves with periods longer than 3 s. Finally, we observe symmetric-mode Lamb waves generated by teleseismic S-waves incident on the grounding zones. Despite their complexity, we conclude that teleseismic coda can be utilized for passive imaging of sub-shelf Earth structure, although longer deployments relative to conventional land-sited seismometers will be necessary to acquire adequate data.

Glaciers located in western High Mountain Asia (HMA) have shown mass gain or limited mass losses compared to other mountain regions since ~2000. Increases in accumulation may be responsible. Although no contemporary measurements exist to explore this hypothesis, extensive historic measurements including firn density, stratigraphy and accumulation rates at ~4400 m a.s.l. on Abramov Glacier, Pamir Alay, provide valuable indications of accumulation changes. Abramov Glacier is located at the northern margin of western HMA. In this study, we assess unique historical firn data of Abramov Glacier from the 1970s to evaluate past firn conditions in this data sparse region. The current firn state is investigated based on a series of in situ measurements including firn cores and ground-penetrating radar measurements performed in 2018. We compare the legacy data with contemporary firn characteristics. Our results indicate a high year-to-year variability, but generally increasing net accumulation during the last 60 years on Abramov Glacier, with 0.84 ± 0.22 m w.e. for 2011–18 compared to 0.68 ± 0.32 m w.e. for 1965–72 and 0.59 ± 0.22 m w.e. for 1970–97. These results from in situ data provide ground truth for the data-sparse western HMA.

During the last few decades, the lake-terminating glaciers in the Himalaya have receded faster than the land-terminating glaciers as proglacial lakes have exacerbated the mass loss of their host glaciers. Monitoring the impacts of glacier recession and dynamics on lake extent and water volume provides an approach to assess the mass interplay between glaciers and proglacial lakes. We describe the recession of Longbasaba Glacier and estimate the mass wastage and its contribution to the water volume of its proglacial lake. The results show that the glacier area has decreased by 3% during 1988–2018, with a more variable recession prior to 2008 than in the last decade. Longbasaba Lake has expanded by 164% in area and 237% in water volume, primarily as a result of meltwater inflow produced from surface lowering of the glacier. Over the periods 1988–2000 and 2000–18, the mass loss contributed by glacier thinning has decreased from 81 to 61% of the total mass loss, accompanied by a nearly doubled contribution from terminus retreat. With the current rate of retreat, Longbasaba glacier is expected to terminate in its proglacial lake for another four decades. The hazard risk of this lake is expected to continue to increase in the near future because of the projected continued glacier mass loss and related lake expansion.

A variation in the α−β model which is a regression model that allows a deterministic prediction of the extreme runout to be expected in a given path, was applied for calculating avalanche runout in the Catalan Pyrenees. Present knowledge of major avalanche activity in this region and current mapping tools were used. The model was derived using a dataset of 97 ‘extreme’ avalanches that occurred from the end of 19th century to the beginning of 21st century. A multiple linear regression model was obtained using three independent variables: inclination of the avalanche path, horizontal length and area of the starting zone, with a good fit of the function (R2 = 0.81). A larger starting zone increases the runout and a larger length of the path reduces the runout. The new updated equation predicts avalanche runout for a return period of ~100 years. To study which terrain variables explain the extreme values of the avalanche dataset, a comparative analysis of variables that influence a longer or shorter runout was performed. The most extreme avalanches were treated. The size of the avalanche path and the aspect of the starting zone showed certain association between avalanches with longer or shorter runouts.

Greenland's future contribution to sea-level rise is strongly dependent on the extent to which dynamic perturbations, originating at the margin, can drive increased ice flow within the ice-sheet interior. However, reported observations of ice dynamical change at distances >~50 km from the margin have a very low spatial and temporal resolution. Consequently, the likely response of the ice-sheet's interior to future oceanic and atmospheric warming is poorly constrained. Through combining GPS and satellite-image-derived ice velocity measurements, we measure multi-decadal (1993–1997 to 2014–2018) velocity change at 45 inland sites, encompassing all regions of the ice sheet. We observe an almost ubiquitous acceleration inland of tidewater glaciers in west Greenland, consistent with acceleration and retreat at glacier termini, suggesting that terminus perturbations have propagated considerable distances (>100 km) inland. In contrast, outside of Kangerlussuaq, we observe no acceleration inland of tidewater glaciers in east Greenland despite terminus retreat and near-terminus acceleration, and suggest propagation may be limited by the influence of basal topography and ice geometry. This pattern of inland dynamical change indicates that Greenland's future contribution to sea-level will be spatially complex and will depend on the capacity for dynamic changes at individual outlet glacier termini to propagate inland.

Projected climate warming and wettening will have a major impact on the state of glaciers and seasonal snow in High Arctic regions. Following up on a historical simulation (1957–2018) for Svalbard, we make future projections of glacier climatic mass balance (CMB), snow conditions on glaciers and land, and runoff, under Representative Concentration Pathways (RCP) 4.5 and 8.5 emission scenarios for 2019–60. We find that the average CMB for Svalbard glaciers, which was weakly positive during 1957–2018, becomes negative at an accelerating rate during 2019–60 for both RCP scenarios. Modelled mass loss is most pronounced in southern Svalbard, where the equilibrium line altitude is predicted to rise well above the hypsometry peak, leading to the first occurrences of zero accumulation-area ratio already by the 2030s. In parallel with firn line retreat, the total pore volume in snow and firn drops by as much as 70–80% in 2060, compared to 2018. Total refreezing remains largely unchanged, despite a marked change in the seasonal pattern towards increased refreezing in winter. Finally, we find pronounced shortening of the snow season, while combined runoff from glaciers and land more than doubles from 1957–2018 to 2019–60, for both scenarios.

Glaciers in the Tien Shan mountains contribute considerably to the fresh water used for irrigation, households and energy supply in the dry lowland areas of Kyrgyzstan and its neighbouring countries. To date, reconstructions of the current ice volume and ice thickness distribution remain scarce, and accurate data are largely lacking at the local scale. Here, we present a detailed ice thickness distribution of Ashu-Tor, Bordu, Golubin and Kara-Batkak glaciers derived from radio-echo sounding measurements and modelling. All the ice thickness measurements are used to calibrate three individual models to estimate the ice thickness in inaccessible areas. A cross-validation between modelled and measured ice thickness for a subset of the data is performed to attribute a weight to every model and to assemble a final composite ice thickness distribution for every glacier. Results reveal the thickest ice on Ashu-Tor glacier with values up to 201 ± 12 m. The ice thickness measurements and distributions are also compared with estimates composed without the use of in situ data. These estimates approach the total ice volume well, but local ice thicknesses vary substantially.

Subglacial topography is an important feature in numerous ice-sheet analyses and can drive the routing of water at the bed. Bed topography is primarily measured with ice-penetrating radar. Significant gaps, however, remain in data coverage that require interpolation. Topographic interpolations are typically made with kriging, as well as with mass conservation, where ice flow dynamics are used to constrain bed geometry. However, these techniques generate bed topography that is unrealistically smooth at small scales, which biases subglacial water flowpath models and makes it difficult to rigorously quantify uncertainty in subglacial drainage patterns. To address this challenge, we adapt a geostatistical simulation method with probabilistic modeling to stochastically simulate bed topography such that the interpolated topography retains the spatial statistics of the ice-penetrating radar data. We use this method to simulate subglacial topography using mass conservation topography as a secondary constraint. We apply a water routing model to each of these realizations. Our results show that many of the flowpaths significantly change with each topographic realization, demonstrating that geostatistical simulation can be useful for assessing confidence in subglacial flowpaths.

Casting snow is necessary to prevent metamorphism and deformation prior to X-ray micro-computed tomography (μCT) imaging. Current methods are insufficient for large-scale field sampling of snow due to safety considerations associated with the casting medium and/or lengthy sample preparation times. Here, a casting method using contrast-enhanced diethylphthalate (DEP) for μCT of snow is presented. The X-ray contrast of DEP is enhanced with barium titanate nanoparticles (BaTiO3) and iodine (I2). A partially unsupervised, three-phase segmentation method utilizing traditional Gaussian smoothing followed by a three-step process to address transition voxels is also presented. Synthetic images derived from real snow samples are used to evaluate the segmentation method with various configurations of trapped air bubbles. Real snow samples spanning a range of specific surface areas (SSAs) (8–28 m2 kg−1) and densities (135–463 kg m−3) are used to assess the performance of the segmentation method on real, cast samples. The method yields SSA, density and correlation length errors of less than 10% for synthetic images with air bubble surface areas less than 333 m−1 per sample volume for eight of the nine snow samples. For eight of the nine cast samples, the method yields errors of less than 10% for all three parameters.