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Understanding paleo-ice flow chronology is essential for reconstructing past ice mass dynamics, interpreting the current landscape, and identifying the sources of Quaternary sediments in deglaciated regions. A recent systematic mapping of striated bedrock and streamlined landforms south of Lake Mistassini in Canada reveals a complex sequence of five ice flows. The earliest flow was directed to the southeast (SE) and originated from a NE-SW ice divide located northwest of Lake Mistassini at the Last Glacial Maximum. A progressive clockwise rotation of this ice divide, likely triggered during the early deglaciation, appears to have generated ice flows toward the south–southeast (SSE) and then toward the south (S). During the later stages of deglaciation, the flow originated from the Québec–Labrador Dome, initially toward the south–southwest (SSW) and then toward the southwest (SW). This study presents new data on ice flows south of Lake Mistassini and shows that the southward and south–southeastward ice events occurred before the late stage of deglaciation. This interpretation contradicts some previous studies and will contribute to the discussion on the dynamics of the Laurentide Ice Sheet in the Mistassini area and support mineral exploration efforts in the region. [ABSTRACT FROM AUTHOR]

Seismology is increasingly used to infer the magnitude and direction of glacial ice flow. However, the effects of interstitial meltwater on seismic properties remain poorly constrained. Here, we extend previous studies on seismic anisotropy in temperate ices to consider the role of melt preferred orientation (MPO). We used the ELLE numerical toolbox to simulate microstructural shear deformation of temperate ice with variable MPO strength and orientation, and calculated the effective seismic properties of these numerical ice‐melt aggregates. Our models demonstrate that even 3.5% melt volume is sufficient to rotate fast directions by up to 90°, to increase Vp anisotropy by up to +110%, and to modify Vs anisotropy by −9 to +36%. These effects are especially prominent at strain rates ≥3.17 × 10−12 s−1. MPO may thus obscure the geophysical signatures of temperate ice flow in regions of rapid ice discharge, and is therefore pivotal for understanding ice mass loss. Plain Language Summary: Ice on Earth is pulled toward the sea by gravity, contributing to global mean sea level rise. To better understand the flow, or movement, of ice at the continent scale, geophysical surveys are increasingly being used to measure the microscopic alignment ("fabric") of ice crystals, since ice with a strong fabric flows more readily. However, in temperate regions close to the ice melting point, melt pockets may also become aligned, creating additional macroscopic geophysical signatures. Here, we use numerical simulations to examine the combined effects of ice crystal fabric and melt alignment on the geophysical (seismic) properties of ice containing small amounts of melt. We show that melt can change the seismic fast direction (related to the inferred flow direction) of ice by up to 90°, particularly as the volume of melt exceeds 3.5%, and that different melt orientations can either enhance or diminish the anisotropy‐based estimates of flow that some studies use to predict ice mass loss. These effects are especially prominent in faster‐flowing ice, highly relevant to ice mass loss in warming regions. Geophysical studies that do not account for melt orientation may therefore produce incorrect estimates of flow, leading to inaccuracies in future climate models. Key Points: We used simulations of deforming temperate ice to show that the alignment of interstitial meltwater changes bulk seismic propertiesThe amount of melt required to significantly modify seismic properties is at least 50% lower than previously reportedMelt should be considered when using seismic and radar anisotropy to interpret viscous ice deformation and enhancement [ABSTRACT FROM AUTHOR]

The topography of bedrock beneath an ice sheet is one of the several factors that influence the flow of ice. It has the potential to change the direction of ice movement, which can lead to confusion when interpreting glacial striae and landforms. In the Mistassini area in Canada, formerly glaciated by the Laurentide Ice Sheet during several phases of the Quaternary, we used a high-resolution digital elevation model to calculate hillshade, slope gradient, and slope aspect. These derived topographic parameters were then combined with mapped glacial indicators to investigate how the underlying bedrock topography potentially influenced the direction of ice flow. The results show that during the older southeastward (SE) event, there was a notable deflection of the ice towards the south in the southern part of the study area. During the southward (S) event, and to a lesser extent south–southeastward (SSE) event, the impact of bedrock topography on ice movement appears to be less pronounced than during the previous southeastward phase (SE). As the ice gradually thinned during the final south–southwestward flow (SSW), the ice sheet became increasingly sensitive to the local bedrock topography. This sensitivity was particularly pronounced in the southern part of the area, where a dominant north-south topographic pattern constrained the ice to flow towards the south. This study demonstrates the feasibility of conducting a quick assessment of the influence of bedrock topography on paleo-ice flows through morphometric analysis of current topography and glacial evidence preserved on bedrock surfaces. [ABSTRACT FROM AUTHOR]

Streamlined subglacial bedforms observed in deglaciated landscapes provide the opportunity to assess the sensitivity of glacier dynamics to bed characteristics across broader spatiotemporal scales than is possible for contemporary glacial systems. While many studies of streamlined subglacial bedforms rely on manual mapping and qualitative (i.e., visual) assessment, we semi‐automatically identify 11,628 sedimentary and bedrock bedforms, created during and following the Last Glacial Maximum across nine geologically and topographically diverse deglaciated sites in the Northern Hemisphere. Using this large dataset of landforms and associated morphometrics, we empirically test the importance of subglacial terrain on bedform morphology and ice‐flow behavior. A minimum bedform length–width ratio threshold provides a constraint on minimum morphometrics needed for streamlined bedforms to develop. Similarities in bedform metric distribution regardless of bed properties indicate that all bed types may support similar distributions of warm‐based ice flow conditions. Ice flow within valleys with easily erodible beds host the most elongate bedforms yet the widest range in bedform elongation and bedform surface relief. The presence of these highly elongate bedforms suggest high ice‐flow velocities occur within valley settings despite spatially heterogeneous landform‐generating processes. In contrast, lithified sedimentary beds within regions not constrained by topography on the scale of 1–102 km contain bedforms with high density and packing, low change in surface relief and low elongation, indicating spatially uniform and organized interactions at the ice–bed interface and consistency in ice‐flow velocity. Regardless of genesis, we find a sensitivity of bedform elongation (i.e., used to interpret ice‐flow speed or persistence) to topographic conditions on the scale of 1–102 km, while bedform density is sensitive to bed lithology. The findings presented in this study provide analogues for processes of subglacial erosion and deposition, ice–bed interactions and warm‐based ice flow within contemporary glacial systems. [ABSTRACT FROM AUTHOR]

The morphology of glacier is a key factor impacting the glacier mass redistributions. High-resolution digital elevation models (DEMs) provide a reliable method to explore the vertical characteristics of glacier surface elevation changes in different types. Using topographic maps from 1969 and Shuttle Radar Topography Mission (SRTM) data acquired in 2000, we calculated the surface elevation changes for 18 glaciers to generate vertical profiles of elevation difference (VPED) in the Dongkemadi region, central Tibetan Plateau. The results showed that the VPEDs vary highly among different glacier types. For valley glaciers, surface thinning at middle elevations is less than that at higher and lower elevations; for cirque glaciers, however, the maximum surface decline occurred in the middle section; whereas hanging glaciers experienced progressively less surface lowering with increasing elevation. Glacier geometry directly affects ice dynamics, which in turn dictates the VPEDs of specific glaciers. This regulation of glacier evolution can be applied to project how valley glaciers might eventually assume the VPEDs of cirque and hanging glaciers due to ongoing warming.

Drumlin shape has been hypothesized to correlate with ice‐flow duration and slip speed, but modern‐day analogues and the Coulomb nature of till render the basis of these correlations in question. The evolution of flow‐parallel subglacial landforms is of importance for ice flow because the form drag they provide may be a dominant factor in regulating glacier slip speeds. Here we examine the relationship between drumlin shape and cumulative slip displacement (i.e. time‐integrated slip speed) as a dominant glaciological control on drumlin shape. First, a new method is developed that allows slip speed to be estimated for deformable bedded glaciers along a flow line from an ice surface profile. Then, reconstructed surface profiles for ice margin chronologies of the Green Bay Lobe (GBL) are used to construct and estimate the spatially varying cumulative slip displacement for use in comparison with drumlin elongation ratios. We focus on a sector of the GBL near the central flow line where the geology is simple and glaciological controls are likely to dominate bedform development. Using Bayesian statistical analysis, a positive and statistically robust relationship between cumulative slip displacement and drumlin elongation ratio is found. Our analysis indicates that drumlin shape could be used to infer palaeo glacier slip speeds if time under the ice can be well constrained and geologic influences are minimal. These findings also suggest that drumlin‐supplied drag could decrease with increased cumulative slip displacement in the absence of rigid geologic features that fix drumlin positions. [ABSTRACT FROM AUTHOR]

In order to understand ice sheet response to climate change, it is critical to examine errors associated with ice flow model boundary conditions and forcing. It is also important to understand how these errors propagate through numerical ice sheet models and contribute to uncertainty in model output. Using established uncertainty quantification methods within the Ice Sheet System Model (ISSM), we investigate the sensitivity of ice flow within the Northeast Greenland Ice Stream (NEGIS) to key fields, including ice viscosity and basal drag, and compare them with model sensitivity to climate forcing. In addition, we examine how errors in model input manifest as mass flux uncertainties during a forward simulation of the NEGIS from 1989 to 2010. Overall, we find that mass flux is most uncertain in the main outlets, Nioghalvfjerdsbræ and Zachariæ Isstrøm, and that mass flux is most sensitive to basal drag, though errors associated with basal drag are poorly constrained and difficult to quantify. Given our knowledge of errors associated with the thermal properties of ice, we estimate that in the ablation area, the effects of cryohydrologic warming contribute over 4 times more mass flux uncertainty that do errors in geothermal heat flux. We find that NEGIS total ice discharge is associated with a 0.7 Gt/yr (2.6%) uncertainty due to errors in geothermal heat flux and a 3.3 Gt/yr (11.6%) uncertainty due to the added effects of cryohydrologic warming. In comparison, errors in surface mass balance contribute 4.5 Gt/yr to NEGIS total discharge uncertainty. Key Points Mass flux is most sensitive to basal drag Mass flux is the most uncertain at the 79North outlet Geothermal heat flux uncertainty is less than that from cryohydrologic warming.

The behavior of the Greenland Ice Sheet, which is considered a major contributor to sea level changes, is best understood on century and longer time scales. However, on decadal time scales, its response is less predictable due to the difficulty of modeling surface climate, as well as incomplete understanding of the dynamic processes responsible for ice flow. Therefore, it is imperative to understand how modeling advancements, such as increased spatial resolution or more comprehensive ice flow equations, might improve projections of ice sheet response to climatic trends. Here we examine how a finely resolved climate forcing influences a high-resolution ice stream model that considers longitudinal stresses. We simulate ice flow using a two-dimensional Shelfy-Stream Approximation implemented within the Ice Sheet System Model (ISSM) and use uncertainty quantification tools embedded within the model to calculate the sensitivity of ice flow within the Northeast Greenland Ice Stream to errors in surface mass balance (SMB) forcing. Our results suggest that the model tends to smooth ice velocities even when forced with extreme errors in SMB. Indeed, errors propagate linearly through the model, resulting in discharge uncertainty of 16% or 1.9 Gt/yr. We find that mass flux is most sensitive to local errors but is also affected by errors hundreds of kilometers away; thus, an accurate SMB map of the entire basin is critical for realistic simulation. Furthermore, sensitivity analyses indicate that SMB forcing needs to be provided at a resolution of at least 40 km.

Neptune's moon Triton is among the Solar System's most geologically active bodies, allowing for study of its internal dynamics through surface features. Here, I consider whether the unusually great extent of its nitrogen ice cap constrains its geothermal heat. I find that viscous spreading alone can result in a hemispheric‐scale ice sheet, which only yields a loose constraint on geothermal heat flow ≥2 mW/m2. However, if the ice cap's great extent is additionally aided by basal melting, heat flow would be constrained between 5 and 18 mW/m2. This latter range would require a significant heat source beyond radiogenic heating and be sufficient to drive vigorous geological activity, providing an explanation for the moon's youthful surface and strengthening the case for Triton as an ocean world. High‐resolution images and topographic data from a new spacecraft mission at Triton would allow for testing of these possibilities and constraints on the moon's internal heat. Plain Language Summary: Triton is the largest moon of Neptune and one of the objects in the Solar System thought to be an "ocean world," but relatively little is known about it because the only spacecraft to visit Triton was Voyager 2 in 1989. One way to learn about a world's interior is through its surface features. Here, I use computer models to test whether Triton's internal heat controls the size of its largest surface feature: a huge polar ice cap of solid nitrogen ice. I find that the polar ice cap could have attained its great extent either from ice flowing outward and/or from ice melting at its bottom. Both processes could prevent the ice from growing vertically, forcing it to grow laterally instead. Only a small amount of heat sourced from Triton's interior is required for ice flow, but more heat is required for basal melting and would likely power other recent geological activity. This internal heat would be most easily explained if Triton has a subsurface ocean and experiences significant heating as a result of its orbit around Neptune. A new spacecraft mission to the Neptune system would be needed to test these ideas convincingly and estimate Triton's internal heat. Key Points: Viscous flow of solid nitrogen on Triton can explain its unusually large ice cap, which would imply a geothermal heat flux ≥2 mW/m2Basal melting of nitrogen ice is plausible, which would imply a geothermal heat flux of 5–18 mW/m2, sufficient to drive endogenic activityNew image and topography data at Triton would allow for precise estimates of its internal heat through study of its surface features [ABSTRACT FROM AUTHOR]

We present a 1:42,000 scale map of Isunguata Sermia, a land-terminating outlet glacier draining the western-sector of the Greenland Ice Sheet. Structure-from-Motion software applied to ∼3,600 aerial images collected by a fixed-wing unmanned aerial vehicle in July 2015 allowed us to produce a high resolution (0.3 m ground sampling distance (GSD)) orthomosaic and digital elevation model (DEM; 1.5 m GSD).These products were used to map and describe the structural, geomorphological and hydrological features of the lower 16 km terminus of Isunguata Sermia and include many thousands of crevasses, crevasse traces and supraglacial channels. Additionally, several geomorphological features and pro-glacial hydrological features were identified, including debris-covered ice, lateral moraines and ice-marginal lakes. The map has potential for informing and reconstructing the long-term dynamic history of the glacier, including its response to variable environmental forcing.

Abstract The region of Recovery Glacier, Slessor Glacier, and Bailey Ice Stream, East Antarctica, has remained poorly explored, despite representing the largest potential contributor to future global sea level rise on a centennial to millennial time scale. Here we use new airborne radar data to improve knowledge about the bed topography and investigate controls of fast ice flow. Recovery Glacier is underlain by an 800 km long trough. Its fast flow is controlled by subglacial water in its upstream and topography in its downstream region. Fast flow of Slessor Glacier is controlled by the presence of subglacial water on a rough crystalline bed. Past ice flow of adjacent Recovery and Slessor Glaciers was likely connected via the newly discovered Recovery‐Slessor Gate. Changes in direction and speed of past fast flow likely occurred for upstream parts of Recovery Glacier and between Slessor Glacier and Bailey Ice Stream. Similar changes could also reoccur here in the future.

We use remotely sensed ice velocities in combination with observations of surface elevation and glacier area change to investigate the dynamics of Hagen Bræ, North Greenland in high detail over the last 35 years. From our data, we can establish for the first time that Hagen Bræ is a surge‐type glacier with characteristics of both Alaskan‐ and Svalbard‐type surging glaciers. We argue that the observed surge was preconditioned by the glacier geometry and triggered by englacially stored meltwater. At present, the glacier is in a transitional state between active and quiescence phases and is not building up to its pre‐surge geometry. We suggest that the glacier is adjusting to the loss of its floating section, general thinning, and changes in fjord conditions that occurred over the study period which are unrelated to the surge behavior. The high temporal resolution of the ice velocity data gives insight to the sub‐annual glacier flow. Key Points: Thirty‐five years of remotely sensed data document the recent dynamics and surge cycle of Hagen Bræ in high detailWe argue that the surge was preconditioned by geometry but triggered by englacially stored meltwaterThe onset of the observed surge was abrupt while its termination was gradual [ABSTRACT FROM AUTHOR]

In this study we used a modeling approach to reconstruct the space-time trajectory of the Dakota airplane which crashed on the Gauligletscher in 1946 and was subsequently buried by snow accumulation. Our aim was to localize its present position and predict when and where it would re-appear at the surface. As a first step we modeled the ice flow field and the evolution of Gauligletscher from 1946 using a combined Stokes ice flow and surface mass balance model, which was calibrated with surface elevation and velocity observations. In a second step the modeled ice velocity fields were integrated forward-in-time, starting from the crash location. Our results suggest that the main body of the damaged aircraft will be released approximately between 2027 and 2035, 1 km upstream of the parts that emerged between 2012 and 2018. Our modeling results indicate that the recently found pieces of the Dakota might have been removed from the original aircraft location and moved down-glacier before being abandoned in the late 40s.

Ice rises are regions of grounded ice embedded within floating ice shelves. The deformation of ice past them increases the back stress generated by the ice shelf, slowing the flow of the ice sheet. We present ground‐based ice‐penetrating radar data from Henry Ice Rise in the Ronne Ice Shelf, West Antarctica, that indicates regrounding during the Holocene. Relic crevasses and melt synclines are observed upstream of the present‐day grounding line. We conclude that these features formed during a previous flow configuration, from which the grounding line has since advanced to its current position. In agreement with previous work, our observations can be explained if initial grounding of the ice shelf occurred on a bathymetric high, forming an ice rumple that migrated upstream and temporarily ungrounded over the topographic high. The grounding line then advanced, preserving relic basal crevasses in the newly grounded ice. Using a simple ice‐flow model, we simulate the burial of these crevasses. While accounting for uncertainty in accumulation, firn density, radar‐derived depth, ice‐thickening history, initial crevasse height, and glacial isostatic adjustment, we estimate a burial time of 6 ± 2 kyr before present for the oldest relic crevasses, indicating that the ice rise formed at approximately this time. This potentially increased the buttressing generated by the Ronne Ice Shelf, causing thickening and advance of the ice sheet. By dating the formation and providing details of ice‐rise formation, these new results can provide useful constraints on both large‐scale ice‐sheet models and models of ice‐rumple and ice‐rise formation. Plain Language Summary: We present results from an ice‐penetrating radar survey on a grounded section of ice (Henry Ice Rise) within the floating Ronne Ice Shelf in West Antarctica. The radar reveals preserved crevasses at the base of the ice that are now inactive and signs of melting from contact with the ocean, both in areas that are grounded today. This implies that these areas were part of the floating ice shelf in the past. Using the distribution and size of relic crevasses within the ice, we date the formation of this grounded area to approximately 6 kyr before present. Our date has an associated uncertainty of ±2 kyr, primarily due to uncertainty in the rate of snowfall and the size of the crevasses when they first formed. The grounding of this area most likely allowed the West Antarctic Ice Sheet to grow to its present‐day configuration. Key Points: Ice‐penetrating radar data from Henry Ice Rise reveal englacial structures indicative of regrounding and grounding line advanceWe present a conceptual model, constrained by data, for the formation of HIR and date formation to approximately 6 kyr before presentGrounding of HIR likely increased buttressing from the Ronne Ice Shelf and was a precursor to ice‐sheet advance in the Weddell Sea sector [ABSTRACT FROM AUTHOR]

Applications of the azimuthal electromagnetic (EM) method that establish the internal structure of landforms consisting of sediment are sparse. In the Kiskatinaw streamlined landform field of northeastern British Columbia, ice-flow parallel till ridges formed beneath the Cordilleran Ice Sheet during the late Wisconsinan. EM anisotropy data from the Kiskatinaw field are systematically related to ridge elongation and orientation and, in part, to clast fabrics. However, in contrast to previous studies, we find that resistivity measurements do not necessarily record the orientation of ice flow, and electrical anisotropy in till may not be a simple indicator of ice-flow direction. For highly elongate ridges (l/w > 3), the long axes of resistivity ellipses are at high angles to the long axes of the landforms. Tills in these elongate ridges are matrix rich (>85%) and display strong unimodal ice-flow parallel clast fabrics. For more equant ridges (l/w < 3), the long axes of resistivity ellipses are at low angles to the long axes of the landforms. Tills in these ridges are clast rich (up to 60%) and display polymodal clast fabrics with both ice-flow parallel and ice-flow transverse modes. Because clast fabrics in the more equant ridges are so variable, despite unimodal resistivity patterns, and because groundwater well data indicate relatively fresh pore waters and the till matrix contains clay (average 12%), we speculate that the resistivity/conductivity anisotropy we observed may record aligned matrix clays rather than clast fabrics alone. We interpret that the highly elongate ridges indicate subglacial shear along a non-cohesive easily deformed bed, whereas the more equant ridges mark 'sticky spots' where high clast concentrations produced local areas that resisted subglacial shear and induced local ice-flow parallel shortening, which limited landform elongation and clast alignment. • Resistivity ellipse orientation does not necessarily record ice flow direction. • Major axes of resistivity ellipses are at high angles to landforms with l/w > 3. • Major axes of resistivity ellipses are at low angles to landforms with l/w < 3. • Electrical anisotropy from till may be valuable for evaluating subglacial rheology. [ABSTRACT FROM AUTHOR]

The Recovery subglacial basin, with its largest glacier Recovery Glacier, has been identified as potentially the biggest contributor to future sea level rise from East Antarctica. Subglacial lakes along the main trunk have been detected from satellite data, with four giant lakes (Recovery Lakes A, B, C, and D) located at the onset of the fast ice flow (≥15 m/yr) and multiple smaller lakes along the glacier. The presence of subglacial water potentially plays a key role in the control of fast ice flow of Recovery Glacier. We present new insights on the Recovery Lakes from airborne radar data collected in 2013 and 2015. Using an adjusted classification scheme, we show that a single large area consisting of smaller lakes connected by likely saturated sediment, referred to as Lake AB, exists in the originally proposed area of the Recovery Lakes A and B. We estimate that the current size of Lake AB is ∼4,320 km2. Water likely leaks from the western shore of Lake AB lubricating the bed initiating fast ice flow at this location. The difference in the outlines of Lake AB and the Lakes A and B previously derived from surface features suggested that a larger paleolake existed here in the past. From our data, we find Recovery Lake C to be dry; we attribute fast ice flow originating from this area to be due to a topographic step and thus an increase in ice thickness rather than enhanced lubrication at the bed. Plain Language Summary: Lakes of liquid water exist under the Antarctic ice sheet. The lake surface is very smooth, and the ice can easily slide over it. This is reflected in a very smooth ice surface, which can be detected in satellite images. To gain more detailed information about subglacial lakes, we need to look below the ice. This is possible with radar waves that travel through the ice where they are reflected at the interface between ice and bedrock or ice and water. Analyzing the reflected signal strength, we derive information about the conditions at the bed and can detect water. Four giant lakes (Recovery Lakes A–D) were identified from satellite data at the onset of fast ice flow of Recovery Glacier. Analyzing a 10‐km grid of radar data over these lakes, we now show that Lakes C and D are dry and only one lake exists in the area of the proposed Lakes A and B. This one lake likely regulates the fast ice flow of Recovery Glacier by water leakage from the lake shore. Key Points: Automatic classification reveals patchy lake area at onset of Recovery GlacierThe main ice flow branch of Recovery Glacier is likely initiated through leakage of water from the lake areaFast ice flow originating at the dry Lakes C and D is triggered by a topographic step [ABSTRACT FROM AUTHOR]

The paper describes procedures of verification and subsequent correction by means of mathematical modeling of a field of geothermal heat flux aimed at the following application of the field in numerical experiments with the Earth system model. The main component of the system is the Greenland ice sheet which is investigated here. The corrected field of the geothermal heat flux is tested for a case when the field is reconstructed from data of measured atmospheric precipitation sums as well as for a field generated by means of simple model of the water-heat balance. This simple model is used as a buffer between the general atmosphere circulation model and the ice sheet model.

One of the main sources of our knowledge about past air temperature variations is the isotopic composition of the ice cores obtained during deep drilling of the ice sheets. During 2001–2006 deep drilling was carried out at Kohnen station in Dronning Maud Land, Antarcticawithin the frameworks of the European Project for Ice Coring in Antarctica (EPICA). As a result, an ice core of 2774 mlength was obtained. Variations of air temperature are linearly dependent on isotopic composition of an ice core, but the reconstructed temperature series contains besides the climatic signal, a topographic bias. Appearance of this bias is explained by the upstream advection from the elevated sites where the ice particles were originally deposited, and by the local vertical movements of the surface of the ice sheet through time. In order to calculate this non-climatic (topographic) bias in the isotopic and reconstructed air temperature record, we applied a methodology based on mathematical ice-flow modeling. In the lower part of the ice sheet ice chronology and non-climatic biases are strongly affected by unknown value of the geothermal heat flux (G). Melt water, which was found close to the bedrock suggests that that assumed G = 54.6 mWm-2 (the average value for Antarctica) was very likely underestimated in the surroundings of Kohnen. In order to estimate the range of possible values of ice age and of non-climatic bias in the lower part of the core we carried out a series of numerical experiment with G increased by 5–30%.

Considered in the paper, three-dimentsional mathematical model of dynamics of Marukh Glacier, Western Caucasus. Block structure of the model and interaction between blocs is described. Key model parameters are calibrated using field radio-echo-sounding, topographic and gravimetrical measurements, as well as observations on surface air temperature and precipitation amount at Klukhorsky Pereval meteostation, closest to the glacier. We determine meanings of parameters favourable to minimum deviations between calculated and observed flow velocities and normalized surface mass balance. The model is supposed to be used in future for prognostic calculations of Caucasus glacier evolution in changing climatic conditions.

Contemporary thinning of the marine-based areas of ice sheets is believed to be the consequence of the grounding line retreat caused mainly by ocean gradual warming beneath the ice shelves. In order to estimate potential contribution of ice sheets into the future sea-level rise grounding line migration must be accurately described in the mathematical models. We incorporated an algorithm based on application of the boundary condition on the mass flux across the grounding line into a two-dimensional ice flow model. In the numerical experiments, externally forced ice sheet returns to its initial equilibrium state after termination of the external forcing (either accumulation rate or sea-level change anomalies). In future, the model will be modified to incorporate buttressing effect.

The new ice core obtained from the NEEM site in the north-western Greenland (77.449˚N, 51.056˚W, 2447 m a.s.l) in 2008–2012 was expected to improve our knowledge about the Last interglacial (also known as the Eemian, ca. 115 to 130 kyr before present). A numerical modeling, the overview of which is given in this paper, aims at assistance in interpretation of the NEEM ice core. For this purpose, an area of 400 × 400 km was delineated in northwestern Greenland as the domain for the fine-scale model at 2.5 km resolution. Modeled present-day surface velocity was in good agreement with satellite and GPS measurements. The nested ice-sheet model was run over the last two glacial cycles to reconstruct the flow history relevant for interpreting the NEEM ice core. A Lagrangian backtracing procedure was applied to determine the particle trajectories of the ice drilled at the NEEM site. This provides the places of origin at the time of deposition of NEEM ice, from which the ice chronology and non-climatic biases of the records are determined. The latter biases arise from elevation changes of the ice sheet, advection of higher upstream ice, and from latitudinal contrasts in isotopical composition of the ice. These need to be separated from the isotope records to retrieve the climatic signal. In spite of initial expectations, the segment in the NEEM ice core between 2206 m and 2435 m turned out to be heavily disturbed. The presence of high isotope values below 2206 m depth however reveals that there is ice from the previous warm interglacial. Our model locates the EMBED Equation.DSMT4 maximum of the warmest Eemian ice at the right depth (2400 m). On this basis we suggest that the measured contrast between the present and the Eemian EMBED Equation.DSMT4 must be increased by about 1.5 ‰. Most of this non-climatic bias results from upstream advection over an estimated distance of ~175 km. Except for the disturbed section, we are still confident to be able to provide accurate model-based estimates of the ice chronology and non-climatic biases for the core down to ~87% of relative depth. This requires revision the palaeo-accumulation parameterization to better match thinner annual layer thicknesses observed in the ice core for the last glacial period.

Highlights • Analysis of circa 12,000 micrographs of Antarctic ice from 8 depths and covering the range 94–853 m revealed two contrasting evolution regimes for the orientation of slip bands. • Unexpected behavior of slip bands in shallow bubbly ice reveals the inheritance of certain mechanical and microstructural features from ancient firn, probably related to former force chains within the firn skeleton. • Such inherited features gradually fade away in shallow bubbly ice, through the action of dynamic recovery and recrystallization, and the redistribution of internal stresses. This evanescence is explained through the postulation of a new hypothesis of microstructural fading memory. • The hypothesis of microstructural fading memory is compatible with a number of observations of microstructure evolution in firn and ice, and it lays the foundations for a new experimental and theoretical framework to study the elusive process of dynamic recovery in polar ice. Abstract The Antarctic Ice Sheet is a continental ice mass with circa 23 million gigatons of ice, which represent roughly 67 % of world's freshwater supply. This colossal mass of ice is by no means static, as the old ice slowly creeps under its own weight towards the ocean, while new ice is continually formed through the sintering of snow deposited on the ice sheet surface. A crucial role in this metamorphism is played by firn, which is the porous material in an intermediate state between the granular snow and the solid polycrystalline ice. Understanding the snow–firn–ice metamorphism is essential not only for a precise determination of the mechanical (creep) properties of polar ice, but also for comprehending the formation and decay of climate proxies widely used in ice-core studies. This work investigates the transition from firn to ice through the spatial and directional distributions of slip bands in bubbly ice. The analysis of high-resolution micrographs of ice sections extracted from the EPICA-DML Deep Ice Core allows us to identify a clear influence of strain-induced anisotropy (viz. c -axis preferred orientations) on the evolution of slip-band inclinations in deep bubbly ice. In contrast, we discover an unanticipated behaviour of slip bands in shallow bubbly ice, which prompts the introduction of the hypothesis of microstructural fading memory and the definition of a stabilization zone that may penetrate hundreds of metres into the bubbly ice. Within this stabilization zone, highly localized concentrations of strain energy and internal stresses once generated by force chains in the ancient firn are gradually redistributed by the newly formed bubbly-ice microstructure. We show that this hypothesis is compatible with the localized dynamic recrystallization episodes observed in polar firn (even at temperatures close to − 45 ∘ C), and it may also explain the sluggish rotation of c -axes observed in the upper hundreds of metres of polar ice sheets. [ABSTRACT FROM AUTHOR]

We present a 1:42,000 scale map of Isunguata Sermia, a land-terminating outlet glacier draining the western-sector of the Greenland Ice Sheet. Structure-from-Motion software applied to ∼3,600 aerial images collected by a fixed-wing unmanned aerial vehicle in July 2015 allowed us to produce a high resolution (0.3 m ground sampling distance (GSD)) orthomosaic and digital elevation model (DEM; 1.5 m GSD).These products were used to map and describe the structural, geomorphological and hydrological features of the lower 16 km terminus of Isunguata Sermia and include many thousands of crevasses, crevasse traces and supraglacial channels. Additionally, several geomorphological features and pro-glacial hydrological features were identified, including debris-covered ice, lateral moraines and ice-marginal lakes. The map has potential for informing and reconstructing the long-term dynamic history of the glacier, including its response to variable environmental forcing. [ABSTRACT FROM AUTHOR]

Abstract The subglacial hydrology of tidewater glaciers is a key but poorly understood component of the complex ice-ocean system, which affects sea level rise. As it is extremely difficult to access the interior of a glacier, our knowledge relies mostly on the observation of input variables such as air temperature, and output variables such as the ice flow velocities reflecting the englacial water pressure, and the dynamics of plumes reflecting the discharge of meltwater into the ocean. In this study we use a cost-effective Vertical Take-Off and Landing (VTOL) Unmanned Aerial Vehicle (UAV) to monitor the daily movements of Bowdoin Glacier, north-west Greenland, and the dynamics of its main plume. Using Structure-from-Motion photogrammetry and feature-tracking techniques, we obtained 22 high-resolution ortho-images and 19 velocity fields at the calving front for 12 days in July 2016. Our results show a two-day-long speed-up event (up to 170%) – caused by an increase in buoyant subglacial forces – with a strong spatial variability revealing that enhanced acceleration is an indication of shallow bedrock. Further, we used the Particle Image Velocimetry (PIV) method to analyze water flow from successive UAV images taken while flying over the main plume of the glacier. We found that PIV successfully captures the area of radially diverging flow of the plume, and provides information on spatial and time variability as no other remote sensing technique can. Most interestingly, the active part of the plume features pulsating water jets at the time scale of seconds, and is 1 to 5 times smaller than its visual footprint defined by the iceberg-free area. Combined with an ice flow model or a non-steady plume model, our approach has the potential to generate a novel set of input data to gather information about the depth of the bedrock, the discharge of meltwater, or the subglacial melting rate of tidewater glaciers. Highlights • First use of a VTOL UAV for glacier monitoring • First use of Particle Image Velocimetry (PIV) to infer meltwater plume flow • A major short-lived ice speed-up event of a calving glacier is captured. • PIV results evidence of the unsteady nature of the plume dynamics. • Ice and plume flows give insights into subglacial hydrological system. [ABSTRACT FROM AUTHOR]

The flux of grounded ice from the Antarctic Ice Sheet (AIS) primarily occurs through narrow, fast-flowing outlet glaciers and ice streams. Shearing generates heat in the lateral glacier margins, where there is a transition from fast-flow to near-stagnant ice or rock. This heat warms the ice and can form zones of water-saturated porous ice at the melting temperature, known as temperate ice. Here we derive a one-dimensional thermomechanical model to infer which AIS shear margins may contain temperate ice. Our model provides expressions for the critical shear strain rate at which a zone of temperate ice initiates and the thickness of the temperate zone. Both of these quantities are described by two nondimensional numbers—the Brinkman and Péclet numbers—that are functions of observable parameters such as shear strain rate, surface temperature, surface accumulation rate, and ice thickness. The development of temperate zones is incited by shear strain rates (Brinkman number) and suppressed by the advection of cold ice from the surface (Péclet number), which scales with surface accumulation rate. We also include a parametrization for lateral advection, which can suppress the formation of temperate ice. Applying recent observations and outputs from a regional climate model, we show that many active glacier shear margins could contain temperate ice. The spatial distribution and thickness of temperate zones are controlled largely by shear strain rates and surface accumulation rates. [ABSTRACT FROM AUTHOR]

The polar layered deposits (PLDs) provide a wealth of information about the past climate evolution of Mars. Surface mass fluxes and ice flow mainly governed topography and layering of the PLD. China’s Mars probe including an orbiter and a landing rover will be launched by 2020. A new type satellite-borne Mars penetrating radar instrument has been selected to be a part of the payloads on the orbiter. Its main scientific objectives are to map the distribution of water, water–ice and to detect the soil characteristics at global scale on the Martian crust. Compared with Mars Advanced Radar for Subsurface and Ionospheric Sounding and Shallow Radar, the biggest difference is that the antenna system of this Mars penetrating radar consists of two dipole antennas mutually perpendicular. This special configuration enables the investigation of the ice flow of PLD by detecting and analyzing the features of anisotropic crystal-orientation fabric (COF). Thus, relying on the fact that the radio waves are depolarized while passing through an anisotropic COF layer, in this paper, a method for anisotropic COF detection based on this radar system is proposed. The radar echo formulation of anisotropic COF is derived and the ratio of the signals measured by the two perpendicular antennas is used to analyze the anisotropy of COF. We demonstrate that the ratio is an ideal criterion for the detection and analysis of COF, since it contains all parameters about the anisotropy feature of COF and it is independent of the attenuation in the propagation path and the reflection coefficient. In order to verify the validity of the derived analytical expression of the ratio for the detection of COF, finite-different time-domain simulations are carried out based on a simple model of the subsurface of PLD which contains an anisotropic COF layer. The advantages of this method, the potential application scenarios, and the effects of the Martian environment are also discussed. [ABSTRACT FROM AUTHOR]

One of the largest sources of uncertainty in sea level rise prediction is glacial acceleration, of which the surge phenomenon is the least understood type. The surge of the Bering Bagley Glacier System (BBGS), Alaska, in 2011–2013 has provided a rare opportunity to study the surge phenomenon in a large and complex glacier system. A surge results in widespread crevassing throughout the glacier system complicating many traditional techniques used to study glacier dynamics. In this paper, we utilize crevassing as a means to investigate the recent BBGS surge through numerical modeling and geostatistical data analysis. Following the principles of structural glaciology, image‐based crevasse characterizations are obtained through geostatistical methods applied to Landsat‐7 data, supplemented by airborne field observations. On the modeling side, a 3‐D full‐Stokes finite element model of the BBGS is developed and applied to investigate ice dynamics and surface structures during the recent surge. A von Mises criterion is adopted to simulate crevassing at the glacier surface, oriented along the axes of maximum principal tensile stress. To facilitate evaluation of model‐ and data‐derived crevasse characteristics, three different comparison methods are introduced. General agreement in the model‐data comparisons indicates that the model has the ability to represent the BBGS system during peak acceleration. The crevasse‐based approach is also employed to optimize the basal sliding parameter and the von Mises stress threshold in the model. Results further indicate that bed topography is an important constraint in modeling the surge process. [ABSTRACT FROM AUTHOR]

Abstract: In times of warming in polar regions, the prediction of ice sheet discharge is of utmost importance to society, because of its impact on sea level rise. In simulations the flow rate of ice is usually implemented as proportional to the differential stress to the power of the exponent n = 3. This exponent influences the softness of the modeled ice, as higher values would produce faster flow under equal stress. We show that the stress exponent, which best fits the observed state of the Greenland Ice Sheet, equals n = 4. Our results, which are not dependent on a possible basal sliding component of flow, indicate that most of the interior northern ice sheet is currently frozen to bedrock, except for the large ice streams and marginal ice. [ABSTRACT FROM AUTHOR]

There has been recent progress in the understanding of the evolution of Quaternary climate. Simultaneously, there have been improvements in the understanding of glacial erosion processes, with better parameter constraints. Despite this, there remains much debate about whether or not the observed cooling over the Quaternary has driven an increase in glacial erosion rates. Most studies agree that the erosional response to climate change must be transient; therefore, the time scale of the climatic change and the response time of glacial erosion must be accounted for. Here we analyze the equations governing glacial erosion in a steadily uplifting landscape with variable climatic forcing and derive expressions for two fundamental response time scales. The first time scale describes the response of the glacier and the second one the glacial erosion response. We find that glaciers have characteristic time scales of the order of 10 to 10,000 years, while the characteristic time scale for glacial erosion is of the order of a few tens of thousands to a few million years. We then use a numerical model to validate the approximations made to derive the analytical solutions. The solutions show that short period forcing is dampened by the glacier response time, and long period forcing (>1 Myr) may be dampened by erosional response of glaciers when the rock uplift rates are high. In most tectonic and climatic conditions, we expect to see the strongest response of glacial erosion to periodic climatic forcing corresponding to Plio‐Pleistocene climatic cycles. Finally, we use the numerical model to predict the response of glacial systems to the observed climatic forcing of the Quaternary, including, but not limited to, the Milankovich periods and the long‐term secular cooling trend. We conclude that an increase of glacial erosion in response to Quaternary cooling is physically plausible, and we show that the magnitude of the increase depends on rock uplift and ice accumulation rates. [ABSTRACT FROM AUTHOR]

Abstract: The region of Recovery Glacier, Slessor Glacier, and Bailey Ice Stream, East Antarctica, has remained poorly explored, despite representing the largest potential contributor to future global sea level rise on a centennial to millennial time scale. Here we use new airborne radar data to improve knowledge about the bed topography and investigate controls of fast ice flow. Recovery Glacier is underlain by an 800 km long trough. Its fast flow is controlled by subglacial water in its upstream and topography in its downstream region. Fast flow of Slessor Glacier is controlled by the presence of subglacial water on a rough crystalline bed. Past ice flow of adjacent Recovery and Slessor Glaciers was likely connected via the newly discovered Recovery‐Slessor Gate. Changes in direction and speed of past fast flow likely occurred for upstream parts of Recovery Glacier and between Slessor Glacier and Bailey Ice Stream. Similar changes could also reoccur here in the future. [ABSTRACT FROM AUTHOR]

[Display omitted] • Three glacial events (1002 ± 190 CE, 1623 ± 149 CE, and 1874 ± 116 CE) were dated in the Drongtso Lungpa Co Valley. • Temperatures were 2.8–0.75 °C lower than today during these glacial events. • Precipitations were up to 70 % higher than today during these glacial events. • Glaciers of southeastern TP have experienced frequent variations over the last ∼ 1000 years, most marked during ∼ 950–1200 CE, ∼1200–1700 CE, and ∼ 1750–1900 CE. • Glacial events in the Drongtso Lungpa Co Valley occurred simultaneously with those in the SE Tibetan Plateau. The temperate glaciers of the southeastern Tibetan Plateau (TP) are highly sensitive to climate change. In this study, 11 exposure ages were obtained from the Drongtso Lungpa Co Valley in the southeastern TP to constrain the timing of glaciations during the late Holocene. The 10Be exposure dating method was employed to reconstruct the palaeoclimate during glaciations, using coupled mass balance and ice flow models. The results uncovered three typical glacial events, constrained at 1002 ± 190 CE, 1623 ± 149 CE, and 1874 ± 116 CE. The modelling results showed that the temperature during the glacial event at 1002 ± 190 CE was 2.8–1.8 °C lower than today, while the precipitation amounts were 20–70 % higher than the present-day level. The modelled temperature during the 1623 ± 149 CE event was 1.5–0.6 °C lower than today, while the modelled precipitation amounts were 10–50 % higher than today. The modelled temperature during the 1874 ± 116 CE event was 1.5–0.75 °C lower than today, while the modelled precipitation amounts were up to 30 % higher than the present-day level. A comparison with the ages of glacial events of the southern TP indicated that the timing of glacial variations in the Drongtso Lungpa Co Valley kept pace with other places in the southern TP. These other places experienced glacial events during ∼ 950–1200 CE, ∼1200–1700 CE, and ∼ 1750–1900 CE. [ABSTRACT FROM AUTHOR]

Wahlenbergfjorden is a fjord situated in the western part of Nordaustlandet in northern Svalbard. It leads into the 400 m deep Hinlopen Strait located between Nordaustlandet and Spitsbergen. High-resolution multibeam bathymetric and sub-bottom data, as well as sediment cores are used to study the past extent and dynamics of glaciers in Wahlenbergfjorden and western Nordaustlandet. The submarine landform assemblage in Wahlenbergfjorden consists of landforms characteristic of subglacial, ice marginal and proglacial conditions. Glacial lineations indicate that Wahlenbergfjorden was occupied by streaming ice during the LGM and most likely acted as an ice stream onset zone. Westward ice flow in the fjord merged with the ice stream in Hinlopen Strait. Absence of ice recessional landforms in outer Wahlenbergfjorden suggests relatively fast deglaciation, possibly by flotation of the glacier front in the deeper parts of the fjord. The inner part of Wahlenbergfjorden and Palanderbukta are characterized by De Geer moraines, indicating episodic retreat of a grounded glacier front. In Palanderbukta, longer still stands of the glacier terminus resulted in the formation of larger terminal moraine ridges. The inner part of Wahlenbergfjorden was deglaciated prior to 11.3 ± 55 Cal. ka BP. The submarine landform assemblages in front of Bodleybreen, Etonbreen, Idunbreen, Frazerbreen and Aldousbreen confirm that these glaciers have surged at least once during the Holocene. [ABSTRACT FROM AUTHOR]

About 16% of the Greenland Ice Sheet drains in the area of the Northeast Greenland shelf between 76°N and 80.5°N via marine terminating glaciers. Most of it is via the Northeast Greenland Ice Stream, the largest ice stream of Greenland. During ice ages, the ice sheet extended onto the continental shelf and modern-day cross-shelf troughs were filled by ice streams. In this study, high-resolution hydro-acoustic data acquired during three decades of research were jointly investigated to reveal the past glacial conditions. Our data shows that Westwind Trough and Norske Trough were filled by fast flowing ice streams that extended to the shelf edge during the last glacial maximum. In between the cross-shelf troughs, ice domes resided on shallow banks that may have contributed about a decimetre to global sea level. Most probably these ice domes initiated fast ice flow through sinks in the inter-trough area. In Westwind Trough, ice sheet retreat to the inner shelf after the last glacial maximum was intermittent. In contrast, in Norske Trough the ice sheet retreat appears relatively rapid with no evidences for phases of grounding line stabilization. Probably during the Younger Dryas, the ice sheet readvanced to a mid-shelf position in both troughs documented by grounding zone wedges. During this time, a thick ice shelf was present in Norske Trough releasing tabular icebergs. Ice sheet retreat from the mid-shelf to the coastline during Holocene deglaciation was rapid. [ABSTRACT FROM AUTHOR]

In spite of global warming, an unusual combination of hydrometeorological conditions can still produce serious frosts, and consequently ice floods on the Hungarian reach of the Danube river. Therefore a monitoring system was developed during the last 15 years in the region for a 130 km segment of the Danube. All together five cameras were installed at a 30-40 km interval to achieve optimal observational capabilities along the river. In January 2009 and later in February 2012 two ice events were successfully recorded at the monitoring locations. Primary analysis of the recorded events combined with ice depth measurements, morphological information and hydro-meteorological data showed great potential to derive space-time characteristics of the floating ice. These include ice formation, size composition, motion and rearrangement due to secondary currents and occasional packing or release at places. Repeated measurements have been done to quantify the space-time characteristics of the ice formation and to improve the , monitoring system. There have been several chances for utilization our gained experiences such as characterization of drifting floes, study of the hydrodynamic conditions during icy periods, verification of floe modelling, discharge estimation using LSPIV technique and additionally development of ice forecasting. Last but not least a new ice thickness staff was introduced for the easy and safe measurements of ice floes on rivers. [ABSTRACT FROM AUTHOR]

We report on the maturation of optical satellite-image-based ice velocity mapping over the ice sheets and large glacierized areas, enabled by the high radiometric resolution and internal geometric accuracy of Landsat 8's Operational Land Imager (OLI). Detailed large-area single-season mosaics and time-series maps of ice flow were created using data spanning June 2013 to June 2015. The 12-bit radiometric quantization and 15-m pixel scale resolution of OLI band 8 enable displacement tracking of subtle snow-drift patterns on ice sheet surfaces at ~ 1 m precision. Ice sheet and snowfield snow-drift features persist for typically 16 to 64 days, and up to 432 days, depending primarily on snow accumulation rates. This results in spatially continuous mapping of ice flow, extending the mapping capability beyond crevassed areas. Our method uses image chip cross-correlation and sub-pixel peak-fitting in matching Landsat path/row pairs. High-pass filtering is applied to the imagery to enhance local surface texture. The current high image acquisition rates of Landsat 8 (725 scenes per day globally) reduces the impact of high cloudiness in polar and mountain terrain and allows rapid compilation of large areas, or dense temporal coverage of seasonal ice flow variations. The results rival the coverage and accuracy of interferometric Synthetic Aperture Radar (InSAR) mapping. [ABSTRACT FROM AUTHOR]

ABSTRACT Landform mapping near the Athabasca valley was fundamental to determining whether the Late Wisconsinan Laurentide and Cordilleran Ice Sheets (LIS, CIS) coalesced. In this paper we examine the detailed landform record using new LiDAR digital elevation and hillshade models of the area of confluence and eventual desuturing of these ice sheets. This work reveals an earlier more extensive Cordilleran advance before coalescence with the LIS. When the ice sheets coalesced, the flow pattern was dominated by ice flow along the mountain front, with Cordilleran ice flowing out of major trunk valleys but Laurentide ice flowing into the Foothills up smaller valleys. This flow pattern implies that when the ice sheets coalesced the CIS was already waning, or at least was not at its maximum. Deglaciation was interrupted by several re-advances, probably related to the destabilizing effect of proglacial lakes along the ice margin. [ABSTRACT FROM AUTHOR]

We quantify the mass budget of the Shirase drainage basin (SHI), Antarctica, by separately estimating snow accumulation (surface mass balance; SMB) and glacier ice mass discharge (IMD). We estimated the SMB in the SHI, using a regional atmospheric climate model (RACMO2.1). The SMB of the mainstream A flow region was 12.1 ± 1.5 Gt a −1 for an area of 1.985 × 10 5 km 2 . Obvious overestimation of the model round the coast, ∼0.5 Gt a −1 , was corrected for. For calculating the IMD, we employed a 15-m resolution Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) with a digital elevation model (DEM) to determine the heights at the grounding line (GL), after comparison with the interpolated Bamber DEM grid heights; the results of this are referred to as the measured heights. Ice thickness data at the GL were inferred by using a free-board relationship between the measured height and the ice thickness, and considering the measured firn depth correction (4.2 m with the reference ice density of 910 kg m −3 ) for the nearby blue-ice area. The total IMD was estimated to be 14.0 ± 1.8 Gt a −1 . Semi-empirical firn densification model gives the estimate within 0.1–0.2 Gt a −1 difference. The estimated net mass balance, –1.9 Gt a −1 , has a two- σ uncertainty of ±3.3 Gt a −1 , and probable melt water discharge strongly suggests negative NMB, although the associated uncertainty is large. [ABSTRACT FROM AUTHOR]

Geomorphic, stratigraphic and geochronological evidence from northeast British Columbia (Canada) indicates that, during the late Wisconsinan (approximately equivalent to marine oxygen isotope stage [MIS] 2), a major lobe of western-sourced ice coalesced with the northeastern-sourced Laurentide Ice Sheet (LIS). High-resolution digital elevation models reveal a continuous 75 km-long field of streamlined landforms that indicate the ice flow direction of a major northeast-flowing lobe of the Cordilleran Ice Sheet (CIS) or a montane glacier (>200 km wide) was deflected to a north-northwest trajectory as it coalesced with the retreating LIS. The streamlined landforms are composed of till containing clasts of eastern provenance that imply that the LIS reached its maximum extent before the western-sourced ice flow crossed the area. Since the LIS only reached this region in the late Wisconsinan, the CIS/montane ice responsible for the streamlined landforms must have occupied the area after the LIS withdrew. Stratigraphy from the Murray and Pine river valleys supports a late Wisconsinan age for the surface landforms and records two glacial events separated by a non-glacial interval that was dated to be of middle Wisconsinan (MIS 3) age. [ABSTRACT FROM AUTHOR]

Abstract: The sudden breakup of ice shelves is expected to result in significant acceleration of inland glaciers, a process related to the removal of the buttressing effect exerted by the ice shelf on the tributary glaciers. In this paper, this process is analyzed by means of scaled analogue experiments reproducing the flow of a valley glacier draining an ice sheet grounded above sea level into an ice shelf, and analyzing the dynamic perturbations resulting from ice shelf disintegration and removal of buttressing effect. Models show a significant increase in glacier velocity close to its outlet following ice shelf breakup, a transient effect that does not significantly propagate upstream towards the ice sheet and rapidly decays with time. Basal lubrication and variations in ice thickness do not significantly influence the process that thus leaves the ice sheet almost unaffected by flow perturbations. [Copyright &y& Elsevier]

Abstract: Sea-floor landforms and acoustic-stratigraphic records allow interpretation of the past form and flow of a westward-draining ice stream of the Greenland Ice Sheet, Rink Isbrae. The Late Pliocene–Pleistocene glacial package is several hundred metres thick and down-laps onto an upper Miocene horizon. Several acoustic facies are mapped from sub-bottom profiler records of the 400 km-long Uummannaq fjord-shelf-slope system. An acoustically stratified facies covers much of the fjord and trough floor, interpreted as glacimarine sediment from rain-out of fine-grained debris in turbid meltwater. Beneath this facies is a semi-transparent deformation-till unit, which includes buried streamlined landforms. Landform distribution in the Uummannaq system is used to reconstruct past ice extent and flow directions. The presence of streamlined landforms (mega-scale glacial lineations, drumlins, crag-and-tails) shows that an ice stream advanced through the fjord system to fill Uummannaq Trough, reaching the shelf edge at the Last Glacial Maximum. Beyond the trough there is a major fan built mainly of glacigenic debris flows. Turbidity-current channels were not observed on Uummannaq Fan, contrasting with well-developed channels on Disko Fan, 300 km to the south. Ice retreat had begun by 14.8 cal. ka ago. Grounding-zone wedges (GZW) in Uummannaq Trough imply that retreat was episodic, punctuated by several still-stands. Ice retreat between GZWs may have been relatively rapid. There is little sedimentary evidence for still-stands in the inner fjords, except for a major moraine ridge marking a Little Ice Age maximum position. On the shallow banks either side of Uummannaq Trough, iceberg ploughing has reworked any morphological evidence of earlier ice-sheet activity. [Copyright &y& Elsevier]

Abstract: The behaviour of ice sheets and their geologic imprints in fjord regions are often multifaceted. Fjords, which were temporarily occupied by fast flowing ice-streams during major glaciations, and inter-fjord areas, which were covered by less active ice, show different signatures of past glaciations. The land and marine records of glaciations over the western Svalbard fjord region have been extensively studied during the last few decades. We have re-examined ice-flow records from stratigraphic and geomorphic settings, and propose a succession of ice-flow events that occurred repeatedly over glacial cycles: the maximum, the transitional, and the local flow style. The differently topographically constrained segments of the ice-sheet switched behaviour as glacial dynamics developed through each glacial cycle. These segments, as well as the different flow styles, are reflected differently in the offshore stratigraphic record. We propose that the glacial geomorphological signatures in the inter ice-stream areas mostly developed under warm-based conditions during a late phase of the glaciations, and that the overall glacial imprints in the landscape are strongly biased towards the youngest events. [Copyright &y& Elsevier]