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Subglacial Antarctic aquatic environments are important targets for scientific exploration due to the unique ecosystems they support and their sediments containing palaeoenvironmental records. Directly accessing these environments while preventing forward contamination and demonstrating that it has not been introduced is logistically challenging. The Whillans Ice Stream Subglacial Access Research Drilling (WISSARD) project designed, tested and implemented a microbiologically and chemically clean method of hot-water drilling that was subsequently used to access subglacial aquatic environments. We report microbiological and biogeochemical data collected from the drilling system and underlying water columns during sub-ice explorations beneath the McMurdo and Ross ice shelves and Whillans Ice Stream. Our method reduced microbial concentrations in the drill water to values three orders of magnitude lower than those observed in Whillans Subglacial Lake. Furthermore, the water chemistry and composition of microorganisms in the drill water were distinct from those in the subglacial water cavities. The submicron filtration and ultraviolet irradiation of the water provided drilling conditions that satisfied environmental recommendations made for such activities by national and international committees. Our approach to minimizing forward chemical and microbiological contamination serves as a prototype for future efforts to access subglacial aquatic environments beneath glaciers and ice sheets.

Seismic studies of glaciers yield insights into spatio-temporal processes within and beneath glaciers on scales relevant to flow and deformation of the ice. These methods enable direct monitoring of the bed in ways that complement other geophysical techniques, such as geodetic or ground penetrating radar observations. In this work, we report on the analysis of passive seismic data collected from the interior of the North East Greenland Ice Stream, the Greenland ice sheet's largest outlet glacier. We record thousands of basal earthquakes, many of which repeat with nearly identical waveforms. We also record many long-duration glacial tremor episodes that migrate across the seismic network with slow velocities (e.g. ~4–12 m s−1). Analysis of the basal earthquakes indicates a transition between times of individual event activity and times of tremor activity. We suggest that both processes are produced by shear slip at localized asperities along the bed. The transition between discrete and quasi-continuous slipping modes may be driven by pore-water pressure transients or heterogeneous strain accumulation in the ice due to strength contrasts of the underlying till.

The uncertain response of marine terminating outlet glaciers to climate change at time scales beyond short-term observation limits models of future sea level rise. At temperate tidewater margins, abundant subglacial meltwater forms morainal banks (marine shoals) or ice-contact deltas that reduce water depth, stabilizing grounding lines and slowing or reversing glacial retreat. Here we present a radiocarbon-dated record from Integrated Ocean Drilling Program (IODP) Site U1421 that tracks the terminus of the largest Alaskan Cordilleran Ice Sheet outlet glacier during Last Glacial Maximum climate transitions. Sedimentation rates, ice-rafted debris, and microfossil and biogeochemical proxies, show repeated abrupt collapses and slow advances typical of the tidewater glacier cycle observed in modern systems. When global sea level rise exceeded the local rate of bank building, the cycle of readvances stopped leading to irreversible retreat. These results support theory that suggests sediment dynamics can control tidewater terminus position on an open shelf under temperate conditions delaying climate-driven retreat., Tidewater glaciers in fjords can advance/retreat independent of climate due to stabilization by sediments at their termini. We show that an Alaskan paleo-ice stream behaved similarly on an open shelf, suggesting that increased sediment flux may delay catastrophic retreat of outlet glaciers in a warming world.

The central sector of the British-Irish Ice Sheet during the last glaciation was characterised by complex ice-flow reflecting interacting ice streams and changing dominance of different ice dispersal centres. At Tunstall, east Yorkshire, two subglacial till units have been traditionally identified as the Late Devensian Skipsea and Withernsea tills, and thought to record two separate ice advances onto the Holderness coast, from divergent ice flow directions. Our study presents the first quantitative lithological, sedimentological and structural evaluation of glacial sediments at the site. The lithological composition of both till units suggests that ice extended southwards from southern Scotland, incorporating material from north-east England and the western margin of the North Sea Basin. Notably, the bulk lithological properties of both the Skipsea and Withernsea tills are very similar. Subtle variations in colour, texture and lithology that do occur simply appear to reflect spatial and temporal variability in subglacial entrainment along the flow path of the North Sea Lobe. The relative arrangements of the units plus the fracture sets also indicates phases of intra-till thrust-stacking and unloading (F2), consolidation and shrinkage (F1, F3) suggestive of cycles of ice re-advance (thrusting) and ice-marginal retreat (unloading and shrinkage) possibly relating to active recession. The findings from this study reveal a sedimentary and structural complexity that is not recognised by the current Late Devensian till stratigraphy of east Yorkshire.

Basal units – visibly distinct englacial structures near the ice-bed interface – warrant investigation for a number of reasons. Many are of unknown composition and origin, characteristics that could provide substantial insight into subglacial processes and ice-sheet history. Their significance, moreover, is not limited to near-bed depths; these units appear to dramatically influence the flow of surrounding ice. In order to enable improved characterization of these features, we develop and apply an algorithm that allows for the automatic detection of basal units. We use a tunable layer-optimized SAR processor to distinguish these structures from the bed, isochronous englacial layers and the ice-sheet surface, presenting a conceptual framework for the use of radio-echo character in the identification of ice-sheet features. We also outline a method by which our processor could be used to place observational constraints on basal units’ configuration, composition and provenance.

Antarctica contains most of Earth’s fresh water stored in two large ice sheets. The more stable East Antarctic Ice Sheet is larger and older, rests on higher topography, and hides entire mountain ranges and ancient lakes. The less stable West Antarctic Ice Sheet is smaller and younger and was formed on what was once a shallow sea. Recent observations made with several independent satellite measurements demonstrate that several regions of Antarctica are losing mass, flowing faster, and retreating where ice is exposed to warm ocean waters. The Antarctic contribution to sea level rise has reached ~8 millimeters since 1992. In the future, if warming ocean waters and increased surface meltwater trigger faster ice flow, sea level rise will accelerate.

The response of very-high-elevation glaciated areas on Mont Blanc to climate change has been analysed using observations and numerical modelling over the last 2 decades. Unlike the changes at low elevations, we observe very low glacier thickness changes, of about −2.6 m on average since 1993. The slight changes in horizontal ice flow velocities and submergence velocities suggest a decrease of about 10 % in ice flux and surface mass balance. This is due to less snow accumulation and is consistent with the precipitation decrease observed in meteorological data. Conversely, measurements performed in deep boreholes since 1994 reveal strong changes in englacial temperature reaching a 1.5 ∘C increase at a depth of 50 m. We conclude that at such very high elevations, current changes in climate do not lead to visible changes in glacier thickness but cause invisible changes within the glacier in terms of englacial temperatures. Our analysis from numerical modelling shows that glacier near-surface temperature warming is enhanced by increasing melt frequency at high elevations although the impact on surface mass balance is low. This results in a non-linear response of englacial temperature to currently rising air temperatures. In addition, borehole temperature inversion including a new dataset confirms previous findings of similar air temperature changes at high and low elevations in the Alps.

Petermann Fjord is a deep (>1000 m) fjord that incises the coastline of north-west Greenland and was carved by an expanded Petermann Glacier, one of the six largest outlet glaciers draining the modern Greenland Ice Sheet (GrIS). Between 5 and 70 m of unconsolidated glacigenic material infills in the fjord and adjacent Nares Strait, deposited as the Petermann and Nares Strait ice streams retreated through the area after the Last Glacial Maximum. We have investigated the deglacial deposits using seismic stratigraphic techniques and have correlated our results with high-resolution bathymetric data and core lithofacies. We identify six seismo-acoustic facies in more than 3500 line kilometres of sub-bottom and seismic-reflection profiles throughout the fjord, Hall Basin and Kennedy Channel. Seismo-acoustic facies relate to bedrock or till surfaces (Facies I), subglacial deposition (Facies II), deposition from meltwater plumes and icebergs in quiescent glacimarine conditions (Facies III, IV), deposition at grounded ice margins during stillstands in retreat (grounding-zone wedges; Facies V) and the redeposition of material downslope (Facies IV). These sediment units represent the total volume of glacial sediment delivered to the mapped marine environment during retreat. We calculate a glacial sediment flux for the former Petermann ice stream as 1080–1420 m3 a−1 per metre of ice stream width and an average deglacial erosion rate for the basin of 0.29–0.34 mm a−1. Our deglacial erosion rates are consistent with results from Antarctic Peninsula fjord systems but are several times lower than values for other modern GrIS catchments. This difference is attributed to fact that large volumes of surface water do not access the bed in the Petermann system, and we conclude that glacial erosion is limited to areas overridden by streaming ice in this large outlet glacier setting. Erosion rates are also presented for two phases of ice retreat and confirm that there is significant variation in rates over a glacial–deglacial transition. Our new glacial sediment fluxes and erosion rates show that the Petermann ice stream was approximately as efficient as the palaeo-Jakobshavn Isbræ at eroding, transporting and delivering sediment to its margin during early deglaciation.

An extensive network of GPS sites on the Filchner–Ronne Ice Shelf and adjoining ice streams shows strong tidal modulation of horizontal ice flow at a range of frequencies. A particularly strong (horizontal) response is found at the fortnightly (Msf) frequency. Since this tidal constituent is absent in the (vertical) tidal forcing, this observation implies the action of some non-linear mechanism. Another striking aspect is the strong amplitude of the flow perturbation, causing a periodic reversal in the direction of ice shelf flow in some areas and a 10 %–20 % change in speed at grounding lines. No model has yet been able to reproduce the quantitative aspects of the observed tidal modulation across the entire Filchner–Ronne Ice Shelf. The cause of the tidal ice flow response has, therefore, remained an enigma, indicating a serious limitation in our current understanding of the mechanics of large-scale ice flow. A further limitation of previous studies is that they have all focused on isolated regions and interactions between different areas have, therefore, not been fully accounted for. Here, we conduct the first large-scale ice flow modelling study to explore these processes using a viscoelastic rheology and realistic geometry of the entire Filchner–Ronne Ice Shelf, where the best observations of tidal response are available. We evaluate all relevant mechanisms that have hitherto been put forward to explain how tides might affect ice shelf flow and compare our results with observational data. We conclude that, while some are able to generate the correct general qualitative aspects of the tidally induced perturbations in ice flow, most of these mechanisms must be ruled out as being the primary cause of the observed long-period response. We find that only tidally induced lateral migration of grounding lines can generate a sufficiently strong long-period Msf response on the ice shelf to match observations. Furthermore, we show that the observed horizontal short-period semidiurnal tidal motion, causing twice-daily flow reversals at the ice front, can be generated through a purely elastic response to basin-wide tidal perturbations in the ice shelf slope. This model also allows us to quantify the effect of tides on mean ice flow and we find that the Filchner–Ronne Ice Shelf flows, on average, ∼ 21 % faster than it would in the absence of large ocean tides.

Fast ice flow on the Antarctic continent constitutes much of the mass loss from the ice sheet. However, geophysical methods struggle to constrain ice flow history at depth, or separate the signatures of topography, ice dynamics and basal conditions on layer structure. We develop and demonstrate a methodology to compare layer signatures in multiple airborne radar transects in order to characterize ice flow at depth, or improve coverage of existing radar surveys. We apply this technique to generate synthetic, along-flow radargrams and compare different deformation regimes to observed radargram structure. Specifically, we investigate flow around the central sticky spot of Whillans Ice Stream, West Antarctica. Our study suggests that present-day velocity flowlines are insufficient to characterize flow at depth as expressed in layer geometry, and streaklines provide a better characterization of flow around a basal sticky spot. For Whillans Ice Stream, this suggests that ice flow wraps around the central sticky spot, supported by idealized flow simulations. While tracking isochrone translation and rotation across survey lines is complex, we demonstrate that our approach to combine radargram interpretation and modeling can reveal critical details of past ice flow.

Submarine landslides are common at glaciated continental margins. The onset of large-scale landslides coincides with the initiation of Northern Hemisphere glaciations in the Quaternary. This implies that processes related to glacial cycling provide favourable conditions for submarine landslides at high-latitude margins. Potential processes include glacial deposition patterns and enhanced seismicity. It is also possible that advances and retreats of ice sheets, a highly dynamic process in geologic terms, makes slopes discernible to failure by modifying the stress regime. Here, we quantify this effect using 2D Finite Element modelling of a glaciated continental margin. Different model runs investigate the pore pressure development in homogeneous as well as layered slopes during glaciation when loaded by an ice stream with one or multiple ice advances. Ice streams cause significant variations in excess pore pressure in the very shallow sediment sequences at the continental shelf. However, lateral fluid flow is not efficient enough to increase pore pressures significantly at the slope, where large-scale submarine slides are observed. Hence, while ice sheet dynamics appear to favour the occurrence of shallow slides close to the shelf edge, ice sheets seem to be irrelevant for the generation of large-scale submarine landslides at the continental slope.

Accurate estimations of ice thickness and volume are indispensable for ice flow modelling, hydrological forecasts and sea-level rise projections. We present a new ice thickness estimation model based on a mass-conserving forward model and a Bayesian inversion scheme. The forward model calculates flux in an elevation-band flow-line model, and translates this into ice thickness and surface ice speed using a shallow ice formulation. Both ice thickness and speed are then extrapolated to the map plane. The model assimilates observations of ice thickness and speed using a Bayesian scheme implemented with a Markov chain Monte Carlo method, which calculates estimates of ice thickness and their error. We illustrate the model's capabilities by applying it to a mountain glacier, validate the model using 733 glaciers from four regions with ice thickness measurements, and demonstrate that the model can be used for large-scale studies by fitting it to over 30 000 glaciers from five regions. The results show that the model performs best when a few thickness observations are available; that the proposed scheme by which parameter-knowledge from a set of glaciers is transferred to others works but has room for improvements; and that the inferred regional ice volumes are consistent with recent estimates.

Recent observations show that the rate at which the Antarctic Ice Sheet (AIS) is contributing to sea level rise is increasing. Increasing ice-ocean heat exchange has the potential to induce substantial mass loss through the melting of its ice shelves. Lack of data and limitations in modelling, however, have made it challenging to quantify the importance of ocean-induced changes in ice-shelf thickness as a driver for ongoing mass loss. Here, we use a numerical ice-sheet model in combination with satellite observations of ice-shelf thinning from 1994 to 2017 to quantify instantaneous changes in ice flow across all AIS grounding lines, resulting from changes in ice-shelf buttressing alone. Our process-based predictions are in good agreement with observed spatial patterns of ice loss, providing support for the notion that a significant portion of the current ice loss of the AIS is ocean driven and caused by a reduction in ice-shelf buttressing.

An edited version of this paper was published by AGU. Copyright 2019 American Geophysical Union.

We describe elongate, wet, subglacial bedforms in the shear margins of the NE Greenland Ice Stream and place some constraints on their formation. Lateral shear margin moraines have been observed across the previously glaciated landscape, but little is known about the ice-flow conditions necessary to form these bedforms. Here we describe in situ sediment bedforms under the NE Greenland Ice Stream shear margins that are observed in active-source seismic and ground-penetrating radar surveys. We find bedforms in the shear margins that are ~500 m wide, ~50 m tall, and elongated nearly parallel to ice-flow, including what we believe to be the first subglacial observation of a shear margin moraine. Acoustic impedance analysis of the bedforms shows that they are composed of unconsolidated, deformable, water-saturated till. We use these geophysical observations to place constraints on the possible formation mechanism of these subglacial features.

Ramparted depressions (doughnut-shaped debris-cored ridges with peat- and/or sediment-filled central basins) are commonly perceived to represent the relict collapsed forms of permafrost ground-ice mounds (i.e. pingos or lithalsas). In Wales, UK, ramparted depressions of Late Pleistocene age have been widely attributed to permafrost-related processes. However, a variety of alternative glacial origins for these enigmatic landforms are also consistent with the available geological and geomorphological evidence, although previous studies have barely considered such alternative processes of formation. From detailed geophysical, sedimentological and remote-sensing studies at two field sites, we demonstrate that: (i) the wastage of stagnating glacier ice is a viable alternative explanation for the formation of ramparted depressions in Wales; (ii) the glacial geomorphology and geology of these landforms is analogous to supraglacial and subglacial landforms from the last Laurentide and Fennoscandian ice sheets; (iii) these landforms have significant potential for characterising the nature of deglaciation around the margins of the Irish Sea during the last glacial cycle, and may record evidence for the overextension and stagnation of the south-eastern margin of the Irish Sea Ice Stream; and (iv) investigations of ramparted depressions within formerly glaciated terrains must consider both glacial and periglacial mechanisms of formation.

Late Holocene sediment deposits in Pine Island Bay, West Antarctica, are hypothesized to be linked to intensive meltwater drainage during the retreat of the paleo-Pine Island Ice Stream after the Last Glacial Maximum. The uppermost sediment units show an abrupt transition from ice-proximal debris to a draped silt during the late Holocene, which is interpreted to coincide with rapid deglaciation. The small scale and fine sorting of the upper unit could be attributed to origins in subglacial meltwater; however the thickness and deposition rate for this unit imply punctuated- rather than continuous-deposition. This, combined with the deposit's location seaward of large, bedrock basins, has led to the interpretation of this unit as the result of subglacial lake outbursts in these basins. However, the fine-scale sorting of the silt unit is problematic for this energetic interpretation, which should mobilize and deposit a wider range of sediment sizes. To resolve this discrepancy, we present an alternative mechanism in which the silt was sorted by a distributed subglacial water system, stored in bedrock basins far inland of the grounding line, and subsequently eroded at higher flow speeds during retreat. We demonstrate that this mechanism is physically plausible given the subglacial conditions during the late Holocene. We hypothesize that similar silt units observed elsewhere in Antarctica downstream of bedrock basins could be the result of the same mechanism.

Numerical ice-sheet models are commonly matched to surface ice velocities from InSAR measurements by modifying basal drag, allowing the flow and form of the ice sheet to be simulated. Geophysical measurements of the bed are rarely used to examine if this modification is realistic, however. Here, we examine radio-echo sounding (RES) data from the Weddell Sea sector of West Antarctica to investigate how the output from a well-established ice-sheet model compares with measurements of the basal environment. We know the Weddell Sea sector contains the Institute, Möller and Foundation ice streams, each with distinct basal characteristics: Institute Ice Stream lies partly over wet unconsolidated sediments, where basal drag is very low; Möller Ice Stream lies on relatively rough bed, where basal drag is likely larger; and Foundation Ice Stream is controlled by a deep subglacial trough with flow-aligned bedrock landforms and smooth unconsolidated sediments. In general, the ice-sheet model represents each ice-stream system well. We also find that ice velocities do not match perfectly in some locations, and that adjustment of the boundaries of low basal drag, to reflect RES evidence, should improve model performance. Our work showcases the usefulness of RES in calibrating ice-sheet model results with observations of the bed.

The previously presented Multidimensional Small Baseline Subset (MSBAS-2D) technique computes two-dimensional (2D), east and vertical, ground deformation time series from two or more ascending and descending Differential Interferometric Synthetic Aperture Radar (DInSAR) data sets by assuming that the contribution of the north deformation component is negligible. DInSAR data sets can be acquired with different temporal and spatial resolutions, viewing geometries and wavelengths. The MSBAS-2D technique has previously been used for mapping deformation due to mining, urban development, carbon sequestration, permafrost aggradation and pingo growth, and volcanic activities. In the case of glacier ice flow, the north deformation component is often too large to be negligible. Historically, the surface-parallel flow (SPF) constraint was used to compute the static three-dimensional (3D) velocity field at various glaciers. A novel MSBAS-3D technique has been developed for computing 3D deformation time series where the SPF constraint is utilized. This technique is used for mapping 3D deformation at the Barnes Ice Cap, Baffin Island, Nunavut, Canada, during January–March 2015, and the MSBAS-2D and MSBAS-3D solutions are compared. The MSBAS-3D technique can be used for studying glacier ice flow at other glaciers and other surface deformation processes with large north deformation component, such as landslides. The software implementation of MSBAS-3D technique can be downloaded from http://insar.ca/.

Icequakes radiating from an ice-stream base provide insights into otherwise difficult to observe sub-kilometer-scale basal heterogeneity. We detect basal icequakes beneath an ∼3-km-wide seismic sensor network installed on the Whillans Ice Plain (WIP) in West Antarctica, and we use S-wave back-projection to detect and locate thousands of basal icequakes occurring over 14 and 21 days in January 2014 and 2015, respectively. We find flow-parallel streaks of basal icequakes beneath the WIP, which we conjecture are related to the presence of mega-scale glacial lineations (MSGLs) indicated by ice-penetrating radar, with at least one streak originating in a local trough adjacent to a MSGL. Patterned basal seismicity can be caused by systematic spatial variation in basal pore pressure, bed-material frictional properties, or both. We interpret these flow-parallel icequake streaks as being due to frictionally heterogeneous bed materials in the presence of a streamlined ice-stream bed: bedform ridges correspond to aseismic, high-porosity deforming till, and some troughs to ephemeral exposures of deeper, seismogenic material such as lodged till or older sediments or rocks. Our results are consistent with MSGL formation by either erosion in troughs to expose deeper seismogenic material, or deposition of aseismic high-porosity till in bedform highs. Our results also suggest that evolving subglacial geomorphology can impact basal traction by reorganizing the spatial distribution of basal materials with varying mechanical properties.

The rapid warming observed in the western Antarctic Peninsula gives rise to a fast disintegration of ice shelves and thinning and retreat of marine-terminating continental glaciers, which is likely to raise global sea levels in the near future. In order to understand the contemporary changes in context and to provide constraints for hindcasting models, it is important to understand the Late Quaternary history of the region. Here, we build on previous work on the deglacial history of the western Antarctic Peninsula and we present four new cosmogenic 10Be exposure ages from Horseshoe Island in Marguerite Bay, which has been suggested as a former location of very fast ice stream retreat. Four samples collected from erratic pink granite boulders at an altitude of ~80 m above sea level yielded ages that range between 12.9 ± 1.1 ka and 9.4 ± 0.8 ka. As in other studies on Antarctic erratics, we have chosen to report the youngest erratic age (9.4 ± 0.8 ka) as the true age of deglaciation, which confirms a rapid thinning of the Marguerite Trough Ice Stream at the onset of Holocene. This result is consistent with other cosmogenic age data and other proxies (marine and lacustrine 14C and optically stimulated luminescence) reported from nearby areas.

We developed a tilt sensor for studying ice deformation and installed our tilt sensor systems in two boreholes drilled close to the shear margin of Jarvis Glacier, Alaska to obtain kinematic measurements of streaming ice. We used the collected tilt data to calculate borehole deformation by tracking the orientation of the sensors over time. The sensors' tilts generally trended down-glacier, with an element of cross-glacier flow in the borehole closer to the shear margin. We also evaluated our results against flow dynamic parameters derived from Glen's exponential flow law and explored the parameter space of the stress exponentnand enhancement factorE. Comparison with values from ice deformation experiments shows that the ice on Jarvis is characterized by highernvalues than that is expected in regions of low stress, particularly at the shear margin (~3.4). The highernvalues could be attributed to the observed high total strains coupled with potential dynamic recrystallization, causing anisotropic development and consequently sped up ice flow. Jarvis'nvalues place the creep regime of the ice between basal slip and dislocation creep. TuningEtowards a theoretical upper limit of 10 for anisotropic ice with single-maximum fabric reduces thenvalues by 0.2.

Bathymetric and seismic data from the Southwest Greenland margin have been used to provide an integrated shelf-to-basin overview of the margin architecture between 57° N and 64° N. A variety of glacially formed morphologic features, contour current-related erosion and sedimentary deposits, and evidence of downslope sediment transport via canyons, channels and gullies is found here. The study area is characterized by two major canyons bordering Fylla Bank in the northern part and a narrow shelf and steep slope to the south, where erosion due to strong boundary currents occur down to c. 3000 m water depth. The narrow shelf area appears to be an intra-ice stream area, and numerous channels and gullies on the upper slope point to hyperpycnal melt water release from a stable or retreating wide ice front. Further southward, the shelf is widening and the morphology indicates dominance of former ice stream activity. This difference in glaciation style may reflect the different bedrock types. Sedimentary and morphologic characteristics of the Fylla Bank canyons and some of the slope gullies and channels point to actual cascading of dense winter water or hyperpycnal melt water flow from the shelf. Deep-water channels at the base of the slope evidence transport of Greenland-derived sediment to the central Labrador Sea basin and buried channels further west indicate a former contribution to the Northwest Atlantic Mid-Ocean Channel (NAMOC) system. However, in contrast to widespread turbidite channels on the present seabed bordering NAMOC to the west, east of NAMOC contourite deposits have largely covered the deep-water tributary turbidite channels originating from the Greenland margin.

Englacial layers in Antarctica and Greenland are indicators of the dynamic, rheological and subglacial configuration of the ice sheets. Airborne radar sounder data is the primary remote sensing solution for directly observing englacial layers and structures at the glacier-catchment to ice-sheet scale. However, when traditional along-track synthetic aperture radar (SAR) processing is applied, steep layers can disappear, limiting the detectability and interpretability of englacial layer geometry. This study provides a reconstruction algorithm to address the problem of destructive phase interference during the radargram formation. We develop and apply a novel SAR processor optimized for layer detection that enhances the Signal-to-Noise ratio (SNR) of specular reflectors. The algorithm also enables the automatic estimation of layer slope. We demonstrate the algorithm using data acquired at the Institute Ice Stream, West Antarctica.

Despite the potentially detrimental impact of large-scale calving events on the geometry and ice flow of the Antarctic Ice Sheet, little is known about the processes that drive rift formation prior to calving, or what controls the timing of these events. The Brunt Ice Shelf in East Antarctica presents a rare natural laboratory to study these processes, following the recent formation of two rifts, each now exceeding 50 km in length. Here we use a unique 50-years' time series of in-situ and remote sensing observations, together with numerical modelling, to reveal how slow changes in ice shelf geometry over time caused build-up of mechanical tension far upstream of the ice front, and culminated in rift formation and a significant speed-up of the ice shelf. These internal feedbacks, whereby ice shelves generate the very conditions that lead to their own (partial) disintegration are currently missing from ice flow models, which severely limits their ability to accurately predict future sea level rise.

Three sediment cores recovered on the lower slope of the continental shelf in western Baffin Bay (Arctic Canada) as well as swath bathymetry and subbottom profiler data collected on the shelf and slope of the region were analysed to investigate whether the Laurentide Ice Sheet (LIS) reached the shelf edge offshore Home Bay during the Last Glacial Maximum (LGM). Physical, sedimentological and palaeomagnetic analyses of the cores were also used to constrain the chronostratigraphy of upper sedimentary facies of the Home Bay trough‐mouth fan (TMF). Seven lithofacies were identified in the cores and reveal that the sediments recorded a genuine geomagnetic signal and that the cores span the last 40 ka. In the Home Bay Trough, sets of elongated ridges are discernible on swath bathymetry imagery and are interpreted as mega‐scale glacial lineations (MSGLs) resulting from an ice stream eroding the trough and delivering glacigenic sediments to the TMF. The geomorphology of the TMF, combined with the sedimentary records and the chronostratigraphy, indicates that a series of debris flows and turbidity currents were generated between 35 and 15 ka BP. These results indicate that the LIS margin extended near the shelf edge during the LGM and allow us to propose a new maximum extent of the LIS during the Last Glacial episode.

Despite the importance of glacial lake development in ice dynamics and glacier thinning, in situ and satellite-based measurements from lake-terminating glaciers are sparse in the Bhutanese Himalaya, where a number of proglacial lakes exist. We acquired in situ and satellite-based observations across lake- and land-terminating debris-covered glaciers in the Lunana region, Bhutanese Himalaya. A repeated differential global positioning system survey reveals that thickness change of the debris-covered ablation area of the lake-terminating Lugge Glacier (-4.67±0.07 m a−1) is more than 3 times more negative than that of the land-terminating Thorthormi Glacier (-1.40±0.07 m a−1) for the 2004–2011 period. The surface flow velocities decrease down-glacier along Thorthormi Glacier, whereas they increase from the upper part of the ablation area to the terminus of Lugge Glacier. Numerical experiments using a two-dimensional ice flow model demonstrate that the rapid thinning of Lugge Glacier is driven by both a negative surface mass balance and dynamically induced ice thinning. However, the thinning of Thorthormi Glacier is minimised by a longitudinally compressive flow regime. Multiple supraglacial ponds on Thorthormi Glacier have been expanding since 2000 and have merged into a single proglacial lake, with the glacier terminus detaching from its terminal moraine in 2011. Numerical experiments suggest that the thinning of Thorthormi Glacier will accelerate with continued proglacial lake development.

The Greenland Ice Sheet is losing mass at a significant rate, driven in part by increasing surface-melt-induced runoff. Because the ice sheet's surface melt is closely connected to changes in the surface albedo, studying multidecadal changes in the ice sheet's albedo offers insight into surface melt and associated changes in its surface mass balance. Here, we first analyse the CM SAF Cloud, Albedo and Surface Radiation dataset from AVHRR data second edition (CLARA-A2) Surface Albedo (SAL), covering 1982–2015, to obtain decadal albedo trends for each summer month. We also examine the rates of albedo change during the early summer, supported with atmospheric reanalysis data from MERRA-2 (Modern-Era Retrospective analysis for Research and Applications, version 2), to discern changes in the intensity of early summer melt, and their likely drivers. We find that rates of albedo decrease during summer melt have accelerated during the 2000s relative to the early 1980s and that the surface albedos now often decrease to values typical of bare ice at elevations 50–100 m higher on the ice sheet. The southern margins exhibit the opposite behaviour, though, and we suggest this is due to increasing snowfall over the area. We then subtract ice discharge from the mass balance estimates observed by the Gravity Recovery and Climate Experiment (GRACE) satellite mission to estimate surface mass balance. The CLARA-A2 albedo changes are regressed with these data to obtain a summer-aggregated proxy surface mass balance time series for the summer periods 1982–2015. This proxy time series is compared with latest regional climate model estimates from the MAR model to perform an observation-based test on the dominance of surface runoff in the magnitude and variability of the summer surface mass balance. We show that the proxy time series agrees with MAR through the analysed period within the associated uncertainties of the data and methods, demonstrating and confirming that surface runoff has dominated the rapid surface mass loss period between the 1990s and 2010s. Finally, we extend the analysis to the drainage basin scale to examine discharge–albedo relationships. We find little evidence of surface-melt-induced ice flow acceleration at annual timescales.

Basal thermal conditions play an important role in ice sheet dynamics, and they are sensitive to geothermal heat flux (GHF). Here we estimate the basal thermal conditions, including basal temperature, basal melt rate, and friction heat underneath the Lambert-Amery glacier system in east Antarctica, using a combination of a forward model and an inversion from a 3D ice flow model. We assess the sensitivity and uncertainty of basal thermal conditions using six different GHFs. We evaluate the modelled results using all available observed subglacial lakes. There are very large differences in modelled spatial pattern of temperate basal conditions using the different GHFs. The two most-recent GHF fields inverted from aerial geomagnetic observations have higher values of GHF in the region, produce a larger warm-based area, and match the observed subglacial lakes better than the other GHFs. The fast flowing glacier region has a lower modelled basal friction coefficient, faster basal velocity, with higher basal frictional heating in the range of 50–2000 mW m−2 than the base under slower flowing glaciated areas. The modelled basal melt rate reaches ten to hundreds of mm per year locally in Lambert, Lepekhin and Kronshtadtskiy glaciers feeding the Amery ice shelf, and ranges from 0–5 mm yr−1 on the temperate base of the vast inland region.

Basal properties beneath ice streams and glaciers are known to be a control for ice flow dynamics, hence knowledge of them is crucial for predicting sea level due to changes in glacial dynamics. Ba...

Basal conditions directly control the glacier sliding rate and the dynamic discharge of ice. Recent glacier destabilization events indicate that some marine-terminating glaciers quickly respond to lubricated beds with increased flow speed, but the underlying physics, especially how this vulnerability relates to glacier geometry and flow characteristics, remains unclear. This paper presents a 1D physical framework for glacier dynamic vulnerability assuming sudden basal lubrication as an initial perturbation. In this new model, two quantities determine the scale and the areal extent of the subsequent thinning and acceleration after the bed is lubricated: Péclet number (Pe) and the product of glacier speed and thickness gradient (dubbed J0 in this study). To validate the model, this paper calculates Pe and J0 using multi-sourced data from 1996 to 1998 for outlet glaciers in the Greenland ice sheet and Austfonna ice cap, Svalbard, and compares the results with the glacier speed change during 1996/1998–2018. Glaciers with lower Pe and J0 are more likely to accelerate during this 20-year span than those with higher Pe and J0, which matches the model prediction. A combined factor of ice thickness, surface slope, and initial flow speed physically determines how much and how fast glaciers respond to lubricated beds in terms of speed, elevation, and terminus change.

Future projections of global mean sea level change are uncertain, partly because of our limited understanding of the dynamics of Greenland's outlet glaciers. Here we study Nioghalvfjerdsbr AE, an outlet glacier of the Northeast Greenland Ice Stream that holds 1.1 m sea-level equivalent of ice. We use GPS observations and numerical modelling to investigate the role of tides as well as the elastic contribution to glacier flow. We find that ocean tides alter the basal lubrication of the glacier up to 10 km inland of the grounding line, and that their influence is best described by a viscoelastic rather than a viscous model. Further inland, sliding is the dominant mechanism of fast glacier motion, and the ice flow induces persistent elastic strain. We conclude that elastic deformation plays a role in glacier flow, particularly in areas of steep topographic changes and fast ice velocities. Ice flow dynamics in Greenland's outlet glaciers are influenced by elastic deformation, both in the area of tidal influence up to 14 km inland from the grounding line and further upstream, suggest analyses of GPS observations and numerical simulations.

Reliable projections of sea‐level rise depend on accurate representations of how fast‐flowing glaciers slip along their beds. The mechanics of slip are often parameterized as a constitutive relation (or “sliding law”) whose proper form remains uncertain. Here, we present a novel deep learning‐based framework for learning the time evolution of drag at glacier beds from time‐dependent ice velocity and elevation observations. We use a feedforward neural network, informed by the governing equations of ice flow, to infer spatially and temporally varying basal drag and associated uncertainties from data. We test the framework on 1D and 2D ice flow simulation outputs and demonstrate the recovery of the underlying basal mechanics under various levels of observational and modeling uncertainties. We apply this framework to time‐dependent velocity data for Rutford Ice Stream, Antarctica, and present evidence that ocean‐tide‐driven changes in subglacial water pressure drive changes in ice flow over the tidal cycle.

Glaciers and ice sheets are experiencing dramatic changes in response to recent climate change. This is true in both mountain and polar regions, where the extreme sensitivity of the cryosphere to warming temperatures may be exacerbated by amplification of global climate change. For glaciers and ice sheets, this sensitivity is due to a number of non-linear and threshold processes within glacier mass balance and glacier dynamics. Some of this is simply tied to the freezing point of water; snow and ice are no longer viable above 0°C, so a gradual warming that crosses this threshold triggers the onset of melting or gives rise to an abrupt regime shift between snowfall and rainfall. Other non-linear, temperature-dependent processes are more subtle, such as the evolution from polythermal to temperate ice, which supports faster ice flow, a shift from meltwater retention to runoff in temperate or ice-rich (i.e., heavily melt-affected) firn, and transitions from sublimation to melting under warmer and more humid atmospheric conditions. As melt seasons lengthen, there is also a longer snow-free season and an expansion of glacier ablation area, with the increased exposure of low-albedo ice non-linearly increasing melt rates and meltwater runoff. This can be accentuated by increased concentration of particulate matter associated with algal activity, dust loading from adjacent deglaciated terrain, and deposition of impurities from industrial and wildfire activity. The loss of ice and darkening of glaciers represent an effective transition from white to grey in the world's mountain regions. This article discusses these transitions and regime shifts in the context of challenges to model and project glacier and ice sheet response to climate change.

The predicted Antarctic contribution to global-mean sea-level rise is one of the most uncertain among all major sources. Partly this is because of instability mechanisms of the ice flow over deep b...

We present an ice-penetrating radar data set which consists of 26 internal reflecting horizons (IRHs) that cover the entire Dome C area of the East Antarctic plateau, the most extensive to date in the region. This data set uses radar surveys collected over the space of 10 years, starting with an airborne international collaboration in 2008 to explore the region, up to the detailed ground-based surveys in support of the Beyond EPICA – Oldest Ice (BE-OI) European Consortium. Through direct correlation with the EPICA-DC ice core, we date 19 IRHs that span the past four glacial cycles, from 10 ka, beginning of the Holocene, to over 350 ka, ranging from 10 % to 83 % of the ice thickness at the EPICA-DC ice core site. We indirectly date and provide stratigraphic information for seven older IRHs using a 1D ice flow inverse model, going back to an estimated 700 ka. Depth and age uncertainties are quantified for all IRHs and provided as part of the data set. The IRH data set presented in this study is available at the US Antarctic Program Data Center (USAP-DC) (https://doi.org/10.15784/601411, Cavitte et al., 2020) and represents a contribution to the SCAR AntArchitecture action group (AntArchitecture, 2017).

Basal ice-shelf melting is the key driver of Antarctica's increasing sea-level contribution. In diminishing the buttressing force of the ice shelves that fringe the ice sheet the melting increases the solid-ice discharge into the ocean. Here we contrast the influence of basal melting in two different ice-shelf regions on the time-dependent response of an idealized, inherently buttressed ice-sheet-shelf system. Carrying out three-dimensional numerical simulations, the basal-melt perturbations are applied close to the grounding line in the ice-shelf's 1) ice-stream region, where the ice shelf is fed by the fastest ice masses that stream through the upstream bed trough and 2) shear margins, where the ice flow is slower. The results show that melting below one or both of the shear margins can cause a decadal to centennial increase in ice discharge that is more than twice as large compared to a similar perturbation in the ice-stream region. We attribute this to the fact that melt-induced ice-shelf thinning in the central grounding-line region is attenuated very effectively by the fast flow of the central ice stream. In contrast, the much slower ice dynamics in the lateral shear margins of the ice shelf facilitate sustained ice-shelf thinning and thereby foster buttressing reduction. Regardless of the melt location, a higher melt concentration toward the grounding line generally goes along with a stronger response. Our results highlight the vulnerability of outlet glaciers to basal melting in stagnant, buttressing-relevant ice-shelf regions, a mechanism that may gain importance under future global warming.

The discovery of the deepest subglacial trough beneath the Denman Glacier, combined with high rates of basal melt at the grounding line, have caused significant concern over its vulnerability to retreat. Recent attention has therefore been focusing on understanding the governing dynamic controls, although knowledge of the wider regional context and timescales over which the future responses may occur remains poor. Here we consider the whole Shackleton system, comprising of the Shackleton ice shelf, Denman Glacier and adjacent Scott, Northcliffe, Roscoe and Apfel glaciers, about which almost nothing is known. We widen the context of previously observed dynamic changes in the Denman Glacier into the wider region of the Queen Mary and Knox coasts; with a multi-decadal timeframe and an improved biannual temporal frequency of observations in the last seven years (2014–21). We integrate new satellite observations of ice structure, changes in ice front position and ice-flow velocities to investigate changes in the system. We furthermore use the BISICLES ice sheet model to assess the sensitivity and simulate the response times of the Queen Mary and Knox coasts to hypothetical disintegration of its floating ice areas, in response to coupled ocean and atmospheric forcing. Over the 60-year period of observation, the Queen Mary and Knox coasts do not appear to have changed significantly and higher frequency observations have not revealed any significant annual or sub-annual variations in ice flow. A previously observed increase in the ice flow speed of the Denman Glacier has not continued beyond 2008, and we cannot identify any related change in the surface structure of the system since then. We do, however, observe more significant change in the Scott Glacier, with an acceleration in ice flow associated with calving and progressing from the ice front along the floating tongue since early 2020. No changes in surface structure or ice flow speed are observed closer to the grounded ice. Our upper limit numerical simulations for a 400-year period are consistent with noticeable grounding line retreat in the Denman Glacier in the next two centuries if all floating ice were lost, before stabilising again in the third century from now. This equates to around 6 cm of sea level rise, a small contribution when compared to other areas of East Antarctica expected to change over the same time frame. It is clear that current knowledge is insufficient to explain the observed spatial and temporal changes in the dynamic behaviour of the grounded and floating sections in the Shackleton system. Given the potential vulnerability of the system to accelerating retreat better data recording the glaciological, oceanographic, and geological conditions in the Queen Mary and Knox coasts are required to improve the certainty of numerical model predictions. With access to these remote coastal regions a major challenge, coordinated internationally collaborative efforts are required to quantify how much the Queen Mary and Knox coastal region is likely contribute to sea level rise in the coming centuries.

Blue ice areas (BIAs) allow for the collection of large-sized old ice samples in a cost-effective way because deep ice outcrops and make old ice samples available close to the surface. However, most chronostratigraphy studies on blue ice are complicated due to fold and fault structures. Here, we report a simple stratigraphy of ice from the Larsen BIA, Antarctica, making the area valuable for paleoclimate studies. Ice layers defined by dust bands and ground penetration radar (GPR) surveys indicate a monotonic increase in age along the ice flow direction on the downstream side, while the upstream ice exhibits a potential repetition of ages on scales of tens of meters, as shown in the complicated fold structure. Stable water isotopes (δ18Oice and δ2Hice) and components of the occluded air (i.e., CO2, N2O, CH4, δ15N-N2, δ18Oatm (= δ18O-O2), δO2/N2, δAr/N2, 81Kr and 85Kr) were analyzed for surface ice and shallow ice core samples. Correlating δ18Oice, δ18Oatm, and CH4 records of Larsen ice with existing ice core records indicates that the gas age at shallow coring sites ranges between 9.2–23.4 ka BP and ice age for entire surface sampling sites between 5.6–24.7 ka BP. Absolute radiometric 81Kr dating for the two cores confirms the ages within acceptable levels of analytical uncertainty. Our study demonstrates that BIA in northern Victoria Land may help researchers obtain high-quality records for paleoclimate and atmospheric greenhouse gas compositions through the last deglaciation.

The weakening and/or removal of floating ice shelves in Antarctica can induce inland ice flow acceleration. Numerical modelling suggests these processes will play an important role in Antarctica's future sea-level contribution, but our understanding of the mechanisms that lead to ice tongue/shelf collapse is incomplete and largely based on observations from the Antarctic Peninsula and West Antarctica. Here, we use remote sensing of structural glaciology and ice velocity from 2001 to 2020 and analyse potential ocean-climate forcings to identify mechanisms that triggered the rapid disintegration of ~2445 km2of ice mélange and part of the Voyeykov Ice Shelf in Wilkes Land, East Antarctica between 27 March and 28 May 2007. Results show disaggregation was pre-conditioned by weakening of the ice tongue's structural integrity and was triggered by mélange removal driven by a regional atmospheric circulation anomaly and a less extensive latent-heat polynya. Disaggregation did not induce inland ice flow acceleration, but our observations highlight an important mechanism through which floating termini can be removed, whereby the break-out of mélange and multiyear landfast sea ice triggers disaggregation of a structurally-weak ice shelf. These observations highlight the need for numerical ice-sheet models to account for interactions between sea-ice, mélange and ice shelves.

Here we present a comprehensive dataset of glacial geomorphological features covering an area of 65 000 km2 in central west Poland, located along the southern sector of the last Scandinavian Ice Sheet, within the limits of the Baltic Ice Stream Complex. The GIS dataset is based on mapping from a 0.4 m high-resolution digital elevation model derived from airborne light detection and ranging data. Ten landform types have been mapped: mega-scale glacial lineations, drumlins, marginal features (moraine chains, abrupt margins, edges of ice-contact fans), ribbed moraines, tunnel valleys, eskers, geometrical ridge networks, and hill–hole pairs. The map comprises 5461 individual landforms or landform parts, which are available as vector layers in GeoPackage format at https://doi.org/10.5281/zenodo.4570570 (Szuman et al., 2021a). These features constitute a valuable data source for reconstructing and modelling the last Scandinavian Ice Sheet extent and dynamics from the Middle Weichselian Scandinavian Ice Sheet advance, 50–30 ka, through the Last Glacial Maximum, 25–21 ka, and Young Baltic advances, 18–15 ka. The presented data are particularly useful for modellers, geomorphologists, and glaciologists.

The large ice sheets on Earth respond to changes in the global climate. Ice mass loss increases with rising global mean temperature and thus is a major contributor to sea-level rise. In order to reduce the uncertainty to predict the contributions to sea-level rise of ice sheets, it is crucial to study how the ice sheets‘ fast-flowing drainage pathways (so-called ice streams) have evolved over the last thousand to millions of years. In this thesis, a contribution to the understanding of the flow characteristics of large ice streams in Greenland and Antarctica is performed by an analysis of (ice-penetrating) radar reflections within the ice column and at the ice base. My focus lies on the question how these data can be used to obtain information about present and paleo ice flow regimes. I concentrate on radar data acquired in Northeast Greenland in the upstream regions of the North East Greenland Ice Stream (NEGIS) and in the upstream catchment of the Nioghalvfjerdsbrae (79°N Glacier) as well as on data recorded at the onset of the Jutulstraumen Glacier in Antarctica. In my studies, I show that the NEGIS in its present form is a relatively young feature and that its geometry and flow characteristics are intertwined with the subglacial topography. I also found indications for a re-organization of ice stream activity in the NEGIS catchment during the Holocene. This suggests that ice streams are probably are less persistent than previously thought and adapt in their entire length to the changing geometry of the ice sheet on short time scales. In Antarctica, I investigate past ice flow patterns over a period of millions of years, as in the example of the Jutulstraumen Glacier basin in Antarctica. Many of the glacial and fluvial landscapes, which developed since the glaciation of Antarctica, have been mostly preserved under the contemporary thick ice sheet, and some even serve as basins for active subglacial lakes today.

Although many convincing, diverse, and sometimes competing models of glacier surging have been proposed, the observed behavior of surging glaciers does not fit into distinct categories, and suggests the presence of a universal mechanism driving all surges. On the one hand, recent simulations of oscillatory flow behavior through the description of transient basal drag hint at a fundamental underlying process. On the other hand, the proposition of a unified model of oscillatory flow through the concept of enthalpy adopts a systems based view, in an attempt to rather unify different mechanisms through a single universal measure. While these two general approaches differ in perspective, they are not mutually exclusive, and seem likely to complement each other. A framework incorporating both approaches would see the mechanics of basal drag describing ice flow velocity and surge propagation as a function of forcing by conditions at the glacier bed, in turn modulated through the unified measure of enthalpy.

The crystal structure within an ice sheet evolves in response to deformation; hence ice-crystal fabric records ice-flow history. However, the complexity of crystal-fabric evolution, and the lack of model results with which to compare data, limit the usefulness of fabric measurements, particularly in areas with complex ice dynamics. Here, we use an ice-flow model to identify characteristic fabrics associated with ice-stream onset, with the goal of aiding interpretation of fabric measurements. Using time-dependent model simulations, we identify how crystal fabric may be used to diagnose changes in an ice stream's speed or lateral position. Consistent with previous work, we find that fabric within an ice stream is generally a vertical girdle, though horizontal shear can lead to a horizontal single maximum. Transient simulations demonstrate that effects from changes in flow may be recorded in the crystal fabric for thousands of years after an ice stream activates and more than ten thousand years after an ice stream stagnates. Both transient and steady effects on fabric are sufficiently large as to be measurable in ice cores or with polarized radar, suggesting that in certain scenarios fabric could be used to identify past flow changes. These results could be used to design radar surveys in areas where ice streams are known to deactivate, such as the Siple Coast in Antarctica, or where they may migrate laterally or widen, such as in Northeast Greenland.

Creep due to ice flow is generally thought to be the main cause for the formation of crystallographic preferred orientations (CPOs) in polycrystalline anisotropic ice. However, linking the development of CPOs to the ice flow history requires a proper understanding of the ice aggregate's microstructural response to flow transitions. In this contribution the influence of ice deformation history on the CPO development is investigated by means of full-field numerical simulations at the microscale. We simulate the CPO evolution of polycrystalline ice under combinations of two consecutive deformation events up to high strain, using the code VPFFT/ELLE. A volume of ice is first deformed under co-axial boundary conditions, which results in a CPO. The sample is then subjected to different boundary conditions (co-axial or non-coaxial) in order to observe how the deformation regime switch impacts on the CPO. The model results indicate that the second flow event tends to destroy the first, inherited fabric, with a range of transitional fabrics. However, the transition is slow when crystallographic axes are critically oriented with respect to the second imposed regime. Therefore, interpretations of past deformation events from observed CPOs must be carried out with caution, particularly, in areas with complex deformation histories.

The Arctic's glacial history has classically been interpreted from marine records in terms of the fluctuations of the Eurasian and North American ice sheets. However, the existence, size, and timing of the East Siberian Ice Sheet (ESIS) remains highly uncertain. A recently discovered glacially scoured cross-shelf trough extending to the edge of the continental shelf north of the De Long Islands has provided additional evidence that glacial ice existed on parts of the East Siberian Sea (ESS) during previous glacial periods (MIS 6 and 4). This study concentrates on defining the mineralogical signature and dynamics of the ESIS. Sediment materials from the East Siberian shelf and slope were collected during the 2014 SWERUS-C3 expedition. The cores studied are 20-GC1 from the East Siberian shelf, 23-GC1 and 24-GC1 from the De Long Trough (DLT), and 29-GC1 from the southern Lomonosov Ridge (LR). Heavy mineral assemblages were used to identify prominent parent rocks in hinterland and other sediment source areas. The parent rocks areas include major eastern Siberian geological provinces such as the Omolon massif, the Chukotka Fold Belt, the Verkhoyansk Fold Belt, and possibly the Okhotsk–Chukotka Volcanic Belt. The primary riverine sources for the ESS sediments are the Indigirka and Kolyma rivers, which material then was glacially eroded and re-deposited in the DLT. The higher abundances of hornblendes in the heavy mineral assemblages may indicate ESS paleovalley of the Indigirka river as a major pathway of sediments, while the Kolyma river paleovalley pathway relates to a higher share of pyroxenes and epidote. Mineralogical signature in the DLT diamicts, consisting predominantly of amphiboles and pyroxenes with minor content of garnet and epidote, show clear delivery from the eastern sector of the ESIS. Although the physical properties of the DLT basal diamict closely resemble a pervasive diamict unit recovered across the southern LR, their source material is slightly different according to their heavy mineral content. Assemblages with elevated amphibole and garnet content, along with higher titanite and ilmenite content from core 29-GC1 from the southern LR emphasise the Verkhoyansk Fold Belt as a possible source. This suggests that glacial ice not only grew out from the East Siberian shelf, but also from the New Siberian Islands and westerly sources due to the dynamics in the ice flow and deposition. An increase in the iron oxides in the sediments overlying the diamicts relates to the deglaciation cycle of the ESIS when the central plateau, or at least the shoreline and river discharge region, were possibly free from ice, and the reworking as well as enrichment of iron oxides was possible. This indicates sea-ice rather than iceberg transport for the present distal shelf sediments.

The Amery Ice Shelf (AIS) dynamics and mass balance caused by iceberg calving and basal melting are significant in the ocean climate system. Using satellite imagery from Sentinel-1 SAR, we monitored the temporal and spatial variability of the frontal positions on the Amery Ice Shelf, Antarctica, from 2015 to 2021. In this paper, we propose an automatic algorithm based on the SO-CFAR strategy and a profile cumulative method for frontal line extraction. To improve the accuracy of the extracted frontal lines, we developed a framework combining the Constant False Alarm Rate (CFAR) and morphological image-processing strategies. A visual comparison between the proposed algorithm and state-of-the-art algorithm shows that our algorithm is effective in these cases including rifts, icebergs, and crevasses as well as ice-shelf surface structures. We present a detailed analysis of the temporal and spatial variability of fronts on AIS that we find, an advance of the AIS frontal line before the D28 calving event, and a continuous advance after the event. The study reveals that the AIS extent has been advanced at the rate of 1015 m/year. Studies have shown that the frontal location of AIS has continuously expanded. From March 2015 to May 2021, the frontal location of AIS expanded by 6.5 km; while the length of the AIS frontal line is relatively different after the D28 event, the length of the frontal line increased by about 7.5% during 2015 and 2021 (255.03 km increased to 273.5 km). We found a substantial increase in summer advance rates and a decrease in winter advance rates with the seasonal characteristics. We found this variability of the AIS frontal line to be in good agreement with the ice flow velocity.

Numerical simulations of ice sheets rely on the momentum balance to determine how ice velocities change as the geometry of the system evolves. Ice is generally assumed to follow a Stokes flow with a nonlinear viscosity. Several approximations have been proposed in order to lower the computational cost of a full-Stokes stress balance. A popular option is the Blatter-Pattyn or Higher-Order model (HO), which consists of a three-dimensional set of equations that solves the horizontal velocities only. However, it still remains computationally expensive for long transient simulations. Here we present a depth-integrated formulation of the HO model, which can be solved on a two-dimensional mesh in the horizontal plane. We employ a specific polynomial function to describe the vertical variation of the velocity, which allows us to integrate the vertical dimension using a semi-analytic integration. We assess the performance of this MOno-Layer Higher-Order model (MOLHO) to compute ice velocities and simulate grounding line dynamics on standard benchmarks (ISMIP-HOM and MISMIP3D). We compare MOLHO results to the ones obtained with the original three-dimensional HO model. We also compare the time performance of both models in time-dependent runs. Our results show that the ice velocities and grounding line positions obtained with MOLHO are in very good agreement with the ones from HO. In terms of computing time, MOLHO requires less than 10 % of the computational time of a typical HO model, for the same simulations. These results suggest that the MOno-Layer Higher-Order formulation provides improved computational time performance and a comparable accuracy compared to the HO formulation, which opens the door to Higher-Order paleo simulations.