Ice-shelf thickness is an important boundary condition for ice-sheet and sub-ice-shelf cavity modelling. It is required near the grounding line to calculate the ice flux used to determine ice-sheet mass balance by comparison with the upstream accumulation. In this mass budget approach, the accuracy of the ice thickness is one of the limiting factors in the calculation. We present a satellite retrieval of the ice thickness for all Antarctic ice shelves using satellite radar altimeter data from the geodetic phases of the European Remote-sensing Satellite (ERS-1) during 1994–95 supplemented by ICESat data for regions south of the ERS-1 latitudinal limit. Surface elevations derived from these instruments are interpolated on to regular grids using kriging, and converted to ice thicknesses using a modelled firn-density correction. The availability of a new spatial variable firn-density correction significantly reduces the error in ice thickness as this was previously the dominant error source. Comparison to airborne data shows good agreement, particularly when compared to SOAR CASERTZ data on the largest ice shelves. Biases range from −13.0 m for areas where the assumption of hydrostatic equilibrium breaks down, to 53.4 m in regions where marine ice may be present.

The geometry of the ice sheets during the Pliocene to early Pleistocene is not well constrained. Here we apply an ice-flow model in the study of the Greenland ice sheet (GIS) during three extreme intervals of this period constrained by geological observations and climate reconstructions. We study the extent of the GIS during the Mid-Pliocene Warmth (3.3–3.0 Ma), its advance across the continental shelf during the late Pliocene to early Pleistocene glaciations (3.0–2.4 Ma) as implied by offshore geological studies, and the transition from glacial to interglacial conditions around 2.4 Ma as deduced from the deposits of the Kap København Formation, North Greenland. Our experiments show that no coherent ice sheet is likely to have existed in Greenland during the Mid-Pliocene Warmth and that only local ice caps may have been present in the coastal mountains of East Greenland. Our results illustrate the variability of the GIS during the Pliocene to early Pleistocene and underline the importance of including independent estimates of the GIS in studies of climate during this period. We conclude that the GIS did not exist throughout the Pliocene to early Pleistocene, and that it melted during interglacials even during the late Pliocene climate deterioration.

Subglacial lakes beneath Antarctica’s fast-moving ice streams are known to undergo ∼1 km3 volume changes on annual timescales. Focusing on the MacAyeal Ice Stream (MacIS) lake system, we create a simple model for the response of subglacial water distribution to lake discharge events through assimilation of lake volume changes estimated from Ice, Cloud and land Elevation Satellite (ICESat) laser altimetry. We construct a steady-state water transport model in which known subglacial lakes are treated as either sinks or sources depending on the ICESat-derived filling or draining rates. The modeled volume change rates of five large subglacial lakes in the downstream portion of MacIS are shown to be consistent with observed filling rates if the dynamics of all upstream lakes are considered. However, the variable filling rate of the northernmost lake suggests the presence of an undetected lake of similar size upstream. Overall, we show that, for this fast-flowing ice stream, most subglacial lakes receive >90% of their water from distant distributed sources throughout the catchment, and we confirm that water is transported from regions of net basal melt to regions of net basal freezing. Our study provides a geophysically based means of validating subglacial water models in Antarctica and is a potential way to parameterize subglacial lake discharge events in large-scale ice-sheet models where adequate data are available.

A low-cost, compact, short-pulse ice-penetrating radar (IPR) system with a center frequency of 50 MHz for sounding glacier topography is presented. The radar was developed to measure ice thickness and to image internal structures and basal conditions of glaciers and ice sheets with a maximum range of ∼16000 ns and a depth resolution better than 2.5 m. The receiver of the IPR system employs asynchronous operation mode, avoiding the need for a cable between the transmitter and receiver. A new sampling technology using a high-speed field programmable gate array, which implements a 256-trace stacking algorithm to realize the analog-to-digital conversion, both simplifies the structure of the receiver and increases the sampling efficiency. The power consumption of the whole receiver is <1.5 W, which can be supplied by a laptop computer. Test measurements were made during the 5th China Expedition to the Grove Mountains in East Antarctica. Field tests show the capability of this system to measure ice thickness up to 650 m and to define internal layers within the ice body.

We apply a novel one-dimensional glacier hydrology model that calculates hydraulic head to the tidewater-terminating Sermeq Avannarleq flowline of the Greenland ice sheet. Within a plausible parameter space, the model achieves a quasi-steady-state annual cycle in which hydraulic head oscillates close to flotation throughout the ablation zone. Flotation is briefly achieved during the summer melt season along a ∼17 km stretch of the ∼50 km of flowline within the ablation zone. Beneath the majority of the flowline, subglacial conduit storage ‘closes’ (i.e. obtains minimum radius) during the winter and ‘opens’ (i.e. obtains maximum radius) during the summer. Along certain stretches of the flowline, the model predicts that subglacial conduit storage remains open throughout the year. A calculated mean glacier water residence time of ∼2.2 years implies that significant amounts of water are stored in the glacier throughout the year. We interpret this residence time as being indicative of the timescale over which the glacier hydrologic system is capable of adjusting to external surface meltwater forcings. Based on in situ ice velocity observations, we suggest that the summer speed-up event generally corresponds to conditions of increasing hydraulic head during inefficient subglacial drainage. Conversely, the slowdown during fall generally corresponds to conditions of decreasing hydraulic head during efficient subglacial drainage.

Ice in polar ice sheets undergoes deformation during its flow towards the coast. Deformation and recrystallization microstructures such as subgrain boundaries can be observed and recorded using high-resolution light microscopy of sublimation-edged sample surfaces (microstructure mapping). Subgrain boundaries observed by microstructure mapping reveal characteristic shapes and arrangements. As these arrangements are related to the basal plane orientation, full crystallographic orientation measurements are needed for further characterization and interpretation of the subgrain boundary types. X-ray Laue diffraction measurements validate the sensitivity of different boundary types with sublimation used by microstructure mapping for the classification. X-ray Laue diffraction provides misorientation values of all four crystal axes. Line scans across a subgrain boundary pre-located by microstructure mapping can determine the rotation axis and angle. Together with the orientation of the subgrain boundary this yields information on the dislocation types. Tilt and twist boundaries composed of dislocations lying in the basal plane, and tilt boundaries composed of nonbasal dislocations were found. A statistical analysis shows that nonbasal dislocations play a significant role in the formation of all subgrain boundaries.

We describe a compact lightweight impulse radar for radio-echo sounding of subsurface structures designed specifically for glaciological applications. The radar operates at frequencies between 10 and 75 MHz. Its main advantages are that it has a high signal-to-noise ratio and a corresponding wide dynamic range of 132 dB due mainly to its ability to perform real-time stacking (up to 4096 traces) as well as to the high transmitted power (peak voltage 2800 V). The maximum recording time window, 40 μs at 100 MHz sampling frequency, results in possible radar returns from as deep as 3300 m. It is a versatile radar, suitable for different geophysical measurements (common-offset profiling, common midpoint, transillumination, etc.) and for different profiling set-ups, such as a snowmobile and sledge convoy or carried in a backpack and operated by a single person. Its low power consumption (6.6 W for the transmitter and 7.5 W for the receiver) allows the system to operate under battery power for >7 hours with a total weight of <9 kg for all equipment, antennas and batteries.

We investigated the morphological evolution of laboratory snow under isothermal conditions at −3,−9 and −19°C, using X-ray tomography. We employed a two-point density correlation function to measure spatial fluctuations of the density of the bicontinuous ice/vapor system at different length scales. Length scales were derived from the correlation function to distinguish between interfacial coarsening due to the minimization of surface energy on the smallest scales and anisotropic structural rearrangements due to gravity on larger scales. On the smallest scales our data suggest a crossover between T = −9 and −19°C from evaporation/condensation to surface diffusion as the dominant transport mechanism. Anomalous growth was found for the slope of the correlation function at the origin, and it was similar to those reported for the coarsening of fractal clusters. This is consistent with the observed persistence of dendritic structures throughout an entire year. The dynamics of large-scale morphology was characterized by the first zero-crossing of the correlation function which displays a nonmonotonic evolution with a pronounced anisotropy between the direction of gravity and horizontal directions. Since the correlation function naturally emerges in problems of scattering of radiation in snow, our results appear to be important for optical and remote-sensing methods.

Ice cores (∼4 m long) obtained from areas of different surface velocities near the terminus of Sørsdal Glacier, East Antarctica, have been investigated using two versions of a fabric analyser (G50). In sections parallel to the flow plane, the microstructure is typically interlocking with elongate grains that parallel air-bubble elongation, X, reflecting their development in an earlier ductile regime. The c-axis fabric patterns vary with respect to X and vary from single–double maxima to asymmetric small-circle girdles oblique to the planar foliation, which can be attributed to a simple shear regime. The siteto-site variations in the c-axis patterns can be related to areas of different surface velocities, the asymmetry of fabrics correlating with localized strain variations and differences in the deformation path, but not to the current strain pattern recorded by the near-surface deformation conditions. Overprinting fractures have little effect on microstructure except for local dissolution and precipitation along stylolitic surfaces. Comparison of results from the two different fabric analysers reveals that with a higher pixel resolution the incorporation of additional monochromatic light-emitting diodes and repositioning of a retarder plate produce more reliable c-axis measurements.

We apply a point-scale energy-balance model to a small polythermal glacier in the St Elias Mountains of Canada in order to investigate the applicability and limitations of different treatments of the glacier surface temperature and subsurface heat flux. These treatments range in complexity from a multilayer subsurface model that simulates snowpack evolution, to the assumption of a constant glacier surface temperature equal to 0°C. The most sophisticated model includes dry densification of the snowpack, penetration of shortwave radiation into the subsurface, internal melting, refreezing of percolating meltwater and generation of slush layers. Measurements of subsurface temperature and surface lowering are used for model validation, and highlight the importance of including subsurface penetration of shortwave radiation in the model. Using an iterative scheme to solve for the subsurface heat flux as the residual of the energy-balance equation results in an overestimation of total ablation by 18%, while the multilayer subsurface model underestimates ablation by 6%. By comparison, the 0°C surface assumption leads to an overestimation of ablation of 29% in this study where the mean annual air temperature is about −8°C.

Models are proposed for channelized and distributed flow of meltwater at the base of an ice sheet. The volumes of both channel and distributed systems evolve according to a competition between processes that open drainage space (e.g. sliding over bedrock, melting of the ice) and processes that close it (e.g. viscous creep of the ice due to a positive effective pressure). Channels are generally predicted to have lower water pressure and therefore capture water from the surrounding regions of distributed flow. There is a natural length scale associated with the distributed system that determines the width of the bed from which water can be drawn into a channel. It is suggested that this determines the spacing between major channels and that this may be reflected in the spacing of eskers. A more permeable distributed system results in more widely spaced, and therefore larger, channels. Calculations of the flow into the head of a channel reveal that there is a critical discharge necessary for it to form, and provide a criterion for where channels can exist.

Dispersed facies basal ice – massive (i.e. structureless) ice with dispersed debris aggregates – is present at the margins of many glaciers and, as a product of internal glacial processes, has the potential to provide important information about the mechanisms of glacier flow and the nature of the subglacial environment. The origin of dispersed facies is poorly understood, with several hypotheses having been advanced for its formation, and there is disagreement as to whether it is largely a sedimentary or a tectonic feature. We test these established hypotheses at the temperate glacier Svínafellsjökull, Iceland, and find that none fully account for dispersed facies characteristics at this location. Instead, dispersed facies physical, sedimentological and stable-isotope (δ18O, δD) characteristics favour a predominantly tectonic origin that we suggest comprises the regelation and strain-induced metamorphism of debris-rich basal ice that has been entrained into an englacial position by tectonic processes operating at the base of an icefall. Further thickening of the resultant dispersed facies may also occur tectonically as a result of ice flow against the reverse bed slope of a terminal overdeepening. Lack of efficient subglacial drainage in the region of the overdeepening may limit basal melting and thus favour basal ice preservation, including the preservation of dispersed facies. Despite the relatively low sediment content of dispersed facies ( ∼1.6% by volume), its thickness (up to 25 m) and ubiquity at Svínafellsjökull results in a significant contribution to annual sediment discharge (1635–3270 m3 a−1) that is ∼6.5 times that contributed by debris-rich stratified facies basal ice.

The determination of basal properties on ice streams from surface data is formulated as a Bayesian statistical inference problem. The theory is applied to a flowline on Rutford Ice Stream, West Antarctica. Estimates of bed topography and basal slipperiness are updated using measurements of surface topography and the horizontal and vertical components of the surface velocity. The surface topography is allowed to vary within measurement errors. We calculate the transient evolution of the surface until rates of surface elevation change are within limits given by measurements. For our final estimation of basal properties, modelled rates of elevation change are in full agreement with estimates of surface elevation changes. Results are discarded from a section of the flowline where the distribution of surface residuals is not consistent with error estimates. Apart from a general increase in basal slipperiness toward the grounding line, we find no evidence for any spatial variations in basal slipperiness. In particular, we find that short-scale variability (<10 × ice thickness) in surface topography and surface velocities can be reproduced by the model by variations in basal topography only. Assuming steady-state conditions, an almost perfect agreement is found between modelled and measured surface geometry, suggesting that Rutford Ice Stream is currently close to a steady state.

Using a snow/atmosphere coupled model, the evolution of the surface and near-surface snow temperature is modeled at Dome C, Antarctica, during the period 20–30 January 2010. Firstly, the detailed multilayer snow model Crocus is run in stand-alone mode, with meteorological input forcing data provided by local meteorological observations. The snow model is able to simulate the evolution of surface temperature with good accuracy. It reproduces the observed downward propagation of the diurnal heatwave into the upper 50 cm of the snowpack reasonably well. Secondly, a fully coupled 3-D snow/atmosphere simulation is performed with the AROME regional meteorological model, for which the standard single-layer snow parameterization is replaced by Crocus. In spite of a poor simulation of clouds, the surface and near-surface snow temperatures are correctly simulated, showing neither significant bias nor drifts during the simulation period. The model reproduces particularly well the average decrease of the diurnal amplitude of air temperature from the surface to the top of the 45 m instrumented tower. This study highlights the potential of snow/atmosphere coupled models over the Antarctic plateau and the need to improve cloud microphysics and data assimilation over polar regions.

Temporal trends related to recent climatic fluctuations are extracted from the longest glacier-wide winter and summer mass-balance series recorded in the Alps, at Glacier de Sarennes, France. For this, all point balances measured at the glacier surface are used, and different statistical models are developed and tested. First, Lliboutry’s linear variance analysis model is extended to the two seasonal components of the balance. The explicit modelling of variability sources and correlations is proved useful for appropriately quantifying uncertainties in the different components of the balance and estimating missing data. Next, a non-exchangeable structure is added to model the winter and summer balance time series. Two change points separating different underlying trends are thus detected. The first change was in 1976, with a shift of +23% in the winter balance. The second was in 1982 for the summer balance series. These systematic changes explain 20–30% of the variability of the different components of the balance, the rest being made up of random interannual fluctuations. Simplified and/or less physically based models are less efficient in capturing data variability. As a result, the cumulative glacier-wide balance shows systematic parabolic trends, which result in an accelerated mass loss for Glacier de Sarennes over the last 25 years.

Radar studies of firn on the ice sheets have revealed complex folds on its internal layering that form from the interplay of snow accumulation and ice flow. A mathematical theory for these fold structures is presented, for the case where the radar cross section lies along the ice-flow direction and where the accumulation rate and ice-flow velocity are time-invariant. Our model, which accounts for firn densification, shows how ‘information’ (the depth and slope of isochrones) propagates on the radargram to govern its layer undulations. This leads us to discover universal rules behind the pattern of layer slopes on a distance–age domain and understand why the loci of layer-fold hinges curve, emerge and combine on the radargram to form closed loops that delineate areas of rising and plunging isochrones. We also develop a way of retrieving the accumulation rate distribution and layer ages from steady isochrone patterns. Analysis of a radargram from the onset zone of Bindschadler Ice Stream, West Antarctica, indicates that ice flow and accumulation rates have been steady there for the past ∼400 years, and that spatial anomalies in the latter are coupled to surface topography induced by ice flow over the undulating ice-stream bed. The theory provides new concepts for the morphological interpretation of radargrams.

Dust particles in an ice core from East Rongbuk Glacier on the northern slope of Qomolangma (Mount Everest; 28°01′ N, 86°58′ E; 6518 m a.s.l.), central Himalaya, have been identified as mica using a combination of scanning electron microscope-based techniques and energy-dispersive X-ray spectroscopy to identify the elements present, and electron backscatter diffraction to identify the crystal type. This technique for identifying individual crystalline dust particles in samples of glacial ice could be especially useful in the future for identifying water-soluble crystals in ice, for studying the strain history (glaciotectonics) of basal ice or in studies of ice–mica composites used as analogs of quartz-mica rocks.

Recent topographical and ground-penetrating radar (GPR) surveys of Kårsaglaciären, which is a small (<1 km2) and thin (<56 m) mountain glacier in Arctic Sweden, show that there are small areas of temperate ice in the lowermost part of the glacier. This is curious because we would expect such a small and thin glacier to have a fully cold ablation zone. Specifically, with our analyses of present glacier geometry and thickness and of the prevailing climate, we are unable to explain the presence of temperate ice within the snout of Kårsaglaciären using prevailing models of glacier thermal structure. This leads us to suggest that the presence of temperate ice within Kårsaglaciären is a remnant of a previous polythermal state that existed when the glacier was larger and thicker. Kårsaglaciären is thus out of synch with current geometry and climate and is exhibiting a ‘thermal lag’. We propose that, with time, Kårsaglaciären’s ablation zone and perhaps the entire glacier may well become fully cold as the temperate zone shrinks further. We anticipate that such a thermal lag is likely to be present within other Arctic glaciers. A thermal lag and an evolution to a fully cold thermal state have significant implications for the dynamic behaviour of small Arctic glaciers and for meltwater production from them.

We investigate the elevation and mass-balance response of tributary glaciers following the loss of the Larsen A and B ice shelves, Antarctic Peninsula (in 1995 and 2002 respectively). Our study uses MODIS imagery to track ice extent, and ASTER and SPOT5 digital elevation models (DEMs) plus ATM and ICESat laser altimetry to track elevation changes, spanning the period 2001–09. The measured Larsen B tributary glaciers (Hektoria, Green, Evans, Punchbowl, Jorum and Crane) lost up to 160 m in elevation during 2001–06, and thinning continued into 2009. Elevation changes were small for the more southerly Flask and Leppard Glaciers, which are still constrained by a Larsen B ice shelf remnant. In the northern embayment, continued thinning of >3 m a−1 on Drygalski Glacier, 14 years after the Larsen A ice shelf disintegrated, suggests that mass losses for the exposed Larsen B tributaries will continue for years into the future. Grounded ice volume losses exceed 13 km3 for Crane Glacier and 30 km3 for the Hektoria–Green–Evans glaciers. The combined mean loss rate for 2001–06 is at least 11.2 Gt a−1. Our values differ significantly from published mass-budget-based estimates for these embayments, but are a reasonable fraction of GRACE-derived rates for the region (∼40 Gt a−1).

Recent surface elevation changes of Kaskawulsh Glacier, Yukon, Canada, are quantified by comparing an air-photo derived DEM from 1977 and airborne lidar measurements from 1995, 2000 and 2007. Surface-area changes are assessed using historical aerial photography from 1956 and satellite imagery from 1977 to 2007. Combined, these measurements provide some of the first detailed records of volume change of a large Yukon glacier. Between 1977 and 2007, Kaskawulsh Glacier underwent a decrease in area of 1.53% and a decrease in volume of 3.27–5.94 km3 w.e.). The terminus also retreated by 655 m over the period 1956–2007. There was relatively minor volume change over the period 1977–95 (<+0.01 km3 w.e.a−1), while over the periods 1995–2000 and 2000–07 volume losses occurred at a relatively constant rate of −0.51 and −0.50 km3 a−1 w.e., respectively. Since 1995, thinning has been prominent throughout the ablation zone, while relative stability and even slight thickening has occurred in the accumulation zone. These findings are similar to those recently observed at other nearby Alaskan glaciers.