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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 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.

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.

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 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.

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]

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]

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]

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]

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 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]

In this paper, remote sensing data of Amery ice shelf was used to study Antarctica ice motion and flux problem by a hierarchical image matching method. It combines feature points and grid points to provide a dense, precise and reliable matching result. First, seed points are extracted at the top level of image pyramid using the SIFT algorithm with RANSAC approach to remove mismatches and enhance robustness. These points are used to construct an initial triangulation. Then, feature point and grid point matching are conducted based on the triangle constraint. In the process of hierarchical image matching, the parallaxes from upper levels are transferred to levels beneath with triangle constraint. At last, outliers are detected and removed based on local smooth constraint of parallax. Also, bidirectional image matching method is adopted to verify the matching results and increase the number of matched points. Experiments with Landsat7 images show that the proposed method has the capacity to generate reliable and dense matching results for surface velocity estimation from stereo satellite imagery. Global warming will lead to Amery shelf and glaciers melt and flow rate increase, which can be confirmed by on-site GPS and remote sensing data. Through research the ice shelf flow velocity field, the bottom can calculate the ice flux of this area, and result confirm that the impact of climate for glacier and ice shelf. [ABSTRACT FROM AUTHOR]

Abstract: We applied an image correlation method to Japanese Earth Resources Satellite-1 (JERS-1) synthetic aperture radar (SAR) data obtained from 1996 to 1998 to examine flow velocity within Shirase Glacier, Antarctica. From the grounding line to the downstream region of the glacier, the obtained ice-flow velocity was systematically higher on the western streamline than the eastern. The differences between the two streamlines were 0.31km/a in 1996 and 0.37km/a in 1998, significantly larger than the error estimate of 0.03km/a. The direction of ice flow was about 312° at the grounding line and changed to 327° at 10km, 346° at 20km and 2° at 30km downstream from the grounding line. The total accumulated deflection is 50° to the east. Under the assumption of the conservation of ice mass across the glacier, the observed eastward change in flow direction can be explained by an asymmetric deepening of bedrock topography, that is, across the 8km width of the glacier, the eastern side is 50m (10%) deeper than the western side. This eastward turning of flow direction appears to be accelerated by tributary inlets, that flow to the north and northeast at 60–75% of the velocity of inlets on the western streamline. [Copyright &y& Elsevier]

Abstract: This paper presents estimates of detailed seasonal variations in ice-flow velocity for Shirase Glacier calculated using data obtained by Japanese Earth Resources Satellite-1 (JERS-1) synthetic aperture radar (SAR). We used 12 pairs of images (44-day repeat cycle) over the interval from 30 April 1996 to 1 July 1998 to estimate ice-flow fields using an image correlation method. Geometric registration was performed with reference to the RADARSAT Antarctic Mapping Project (RAMP) image dataset. Error analysis based on feature mismatch indicated an absolute error of ±0.30km/a and relative error of ±0.04km/a in the estimated flow velocity. The obtained ice-flow velocity increases rapidly from the upstream region (1.18km/a) to the grounding line, where it becomes stagnant (2.32km/a), before accelerating gradually to 2.62–2.82km/a in the downstream region and then increasing to 3.05–3.50km/a at the terminus of the floating ice tongue. The ice-flow velocities in the downstream region are highly variable, depending on both the distance from the grounding line and the observed epoch (season). Most of the obtained seasonal variations in ice-flow velocity at the floating ice tongue are within the range of the associated error estimate, but the annual difference between 1997 (3.11km/a) and 1998 (3.50km/a) is significant, reflecting a possible acceleration in the ice-flow velocity in association with the disappearance of the floating ice tongue between April and May of 1998. In terms of the summer–winter difference in averaged air temperature, the large difference recorded in 1997 (17.0°C) relative to 1996 (13.9°C) corresponds to a reduced ice-flow velocity in 1997 (approximately 0.20km/a) relative to that in 1996 (approximately 0.30km/a), indicating interactions between air, sea ice, and glacier flow in Lützow-Holm Bay. [Copyright &y& Elsevier]

River ice jams are a common occurrence on northern rivers, and their formation can present a severe flood risk to nearby communities. As more and more river regulation projects are developed to provide an alternative to fossil fuels for electrical power-generating capacity, our need to understand the mechanisms associated with ice jam formation under variable flow conditions becomes more vital. This is because, at present, hydropeaking operations are often severely curtailed during the ice-affected seasons due to concerns that sudden flow fluctuations might instigate ice jams and associated flooding. Here, an experimental investigation explores the effects of rapid increases in discharge on ice jam formation and evolution. It is found that the thickness of ice jams formed under highly dynamic flow conditions tend to be slightly thinner than those formed during steady carrier flows for comparable discharges. Also, despite the highly dynamic nature of these consolidation events, the resulting ice thicknesses appear reasonably well approximated by steady flow theory. [ABSTRACT FROM AUTHOR]

A major problem for understanding the dynamics of ice streams has been a lack of precise data on ice streaming longevity and sediment-transport efficacy. Here we present the first well-constrained data on sediment flux from a paleo-ice stream. This has been achieved by computing the volume of sediment deposited as debris flows on the fan located at the outlet of the Norwegian Channel ice stream, and converting to a flux measurement by accounting for the duration of streaming in this episode (between 20 and 19 ka during the last glacial stage). In this period the ice stream delivered an average 1.1 Gt of sediment per year, equivalent to 8000 m³yr-1 per meter width of ice stream front. The calculated flux is an order of magnitude higher than most previous estimates for other paleo-ice streams and is comparable to the present sediment flux from the world's largest rivers. The short period of debris-flow deposition suggests that the Norwegian Channel ice stream underwent rapid on-off switching, with punctuated iceberg delivery to the North Atlantic as a consequence. [ABSTRACT FROM AUTHOR]

Abstract: Glacier de Taconnaz is a hanging glacier in the Mont-Blanc area with an upper accumulation area stretching from Dôme du Goûter (4300 m a.s.l.) down to a wide ice cliff at an altitude of about 3300 m a.s.l., over which flows most of the ice accumulated upstream. During winter, ice blocks breaking off the cliff often trigger off large avalanches constituted of a mixture of snow and ice which can be devastating for the downward inhabited areas in the Chamonix valley as was the case in 1988 and 1999. The approach proposed here is twofold. It first consists of quantifying the flow regime over the accumulation area and consequently the yearly amount of ice falling off the cliff. For this purpose, a network of large stakes was first installed in June 2001 and regularly updated since. From the measured height above surface corrected with time series mass balance of two nearby glaciers, a yearly net mass balance map over the accumulation area has been established and converted into a mean discharge of 1.2±0.3×106 m3 year−1 at the cliff. Moreover, monthly remote topographic surveys of the same stakes provided annual surface velocities, which after some assumptions led to a similar independent amount of discharge. The second part consists of trying to assess the frequency at which the collapses occur from similar monthly topographic measurements of the cliff edge position. Although the time series are still short, a single period of about 180 days seems to control the major ice falls. These data also allow for estimation of ice volumes breaking off which, associated with flow values, could help constraining the frequency of falling events. [Copyright &y& Elsevier]

Physical and numerical models were used to assess ice passage at navigation locks, focusing on key factors such as the design of the lock filling and emptying system and the intakes to the lock filling culverts. Unconventional ice passage techniques such as manifolds in the miter gates were also evaluated. Physical model results were compared to field observations and to a parallel series of tests using the DynaRICE ice-hydraulic numerical model. The study focused on three general ice processes at locks: (1) ice accumulating near culvert intakes during lock filling; (2) drawing ice into the lock chamber; and (3) flushing ice out of the lock. Ice accumulation thickness in the upper lock approach was found to be the most important parameter affecting ice passage into the lock chamber. Physical and numerical model results compared reasonably well, proving DynaRICE to be a useful tool for assessing ice passage for new lock designs. [ABSTRACT FROM AUTHOR]

Some GPS points were set up and occupied and reocupied along the traverse route from Zhongshan Station to Dome-A The result analysis for the GPS data processed by GAMIT/GLOBK package was presented in this paper. It was indicated that the ice along the traverse route flowed with an 8–25 m/a velocity to the northwest in the last three years, which was the direction of the edge of the ice sheet. The maximum horizontal flow velocity is about 100 m/a. Moreover, due to the ice flow, a 0.2-1 m/a sedimentation rate is achieved. Finally, a 1–5 m/a2 horizontal acceleration is achieved from the GPS data of the three different stages. [ABSTRACT FROM AUTHOR]