Recent work has shown that surface-to-bed drainage systems re-form annually on parts of the Greenland ice sheet and some High Arctic glaciers, leading to speed-up events soon after the onset of summer melt. Surface observations and geophysical data indicate that such systems form by hydrologically driven fracture propagation (herein referred to as ‘hydrofracturing’), although little is known about their characteristics. Using speleological techniques, we have explored and surveyed englacial drainage systems formed by hydrofracturing in glaciers in Svalbard, Nepal and Alaska. In Hansbreen, Svalbard, vertical shafts were followed through ∼60 m of cold ice and ∼10 m of temperate basal ice to a subglacial conduit. Deep hydrofracturing occurred at this site due to a combination of extensional ice flow and abundant surface meltwater at a glacier confluence. The englacial drainage systems in Khumbu Glacier, Nepal, and Matanuska Glacier, Alaska, USA, formed in areas of longitudinal compression and transverse extension and consist of vertical slots that plunge down-glacier at angles of 55° or less. The occurrence of englacial drainages initiated by hydrofracturing in diverse glaciological regimes suggests that it is a very widespread process, and that surface-to-bed drainage can occur wherever high meltwater supply coincides with ice subjected to sufficiently large tensile stresses.

A gamma-ray density gauge can provide high-resolution and high-precision density measurements of firn and ice cores. This study describes the design, gamma-ray energy optimization and mass attenuation coefficient calibration of the Maine Automated Density Gauge Experiment (MADGE), a portable, field-operable gamma-ray density gauge used on overland traverses in East Antarctica. The MADGE instrument uses a 241Am gamma-ray source, a pulse-mode counting system and electronic core diameter calipers to collect high-precision (±0.004 g cm−3) density data from 3–8 cm diameter firn and ice cores. The data are collected at a 3.3 mm spatial resolution and an average throughput of 1.5 m h−1 for 5 cm diameter cores.

The volume distribution of atmospheric dust particles (microparticles) of 1–30 μm diameter in Muztagata, Dunde, Dasuopu and Everest ice cores from the Tibetan Plateau was measured and fitted as a log-normal function in order to characterize their basic size properties. Our results reveal that whether the volume distribution fits the log-normal function or not largely depends on the dust concentration and the specific dust-storm event but is independent of physiographical location and season. Our results show only high-concentration samples obey the log-normal distribution in volume, with mode sizes ranging from 3 to 161 μm. The log-normal distribution was largely attributed to the mid-sized particles between 3 and 15 μm, which contribute most (>70%) of the total volume. The volume size distribution characteristics for mineral dust particles from ice cores reveal that the coarse particles might be common in the upper-level troposphere over the Tibetan Plateau. These dust size features are useful to advance our understanding of dust effects on climate, and provide clues to better characterize atmospheric dynamics over the Tibetan Plateau that will help to improve the current models.

The Amery Ice Shelf, East Antarctica, undergoes high basal melt rates near the southern limit of its grounding line where 80% of the ice melts within 240 km of becoming afloat. A considerable portion of this later refreezes downstream as marine ice. This produces a marine ice layer up to 200 m thick in the northwest sector of the ice shelf concentrated in a pair of longitudinal bands that extend some 200 km all the way to the calving front. We drilled through the eastern marine ice band at two locations 70 km apart on the same flowline. We determine an average accretion rate of marine ice of 1.1 ± 0.2 m a−1, at a reference density of 920 kg m−3 between borehole sites, and infer a similar average rate of 1.3 ± 0.2 m a−1 upstream. The deeper marine ice was permeable enough that a hydraulic connection was made whilst the drill was still 70–100 m above the ice-shelf base. Below this marine close-off depth, borehole video imagery showed permeable ice with water-filled cavities and individual ice platelets fused together, while the upper marine ice was impermeable with small brine-cell inclusions. We infer that the uppermost portion of the permeable ice becomes impermeable with the passage of time and as more marine ice is accreted on the base of the shelf. We estimate an average closure rate of 0.3 m a−1 between the borehole sites; upstream the average closure rate is faster at 0.9 m a−1. We estimate an average porosity of the total marine ice layer of 14–20%, such that the deeper ice must have even higher values. High permeability implies that sea water can move relatively freely through the material, and we propose that where such marine ice exists this renders deep parts of the ice shelf particularly vulnerable to changes in ocean properties.

Snowpack changes during the melt season are often not incorporated in modelling studies of the surface mass balance of the Greenland ice sheet. Densification of snow accelerates when meltwater is present, due to percolation and subsequent refreezing, and needs to be incorporated in ice-sheet models for ablation calculations. In this study, simple parameterizations to calculate surface melt, snow densification and meltwater retention are included as surface boundary conditions in a large-scale ice-sheet model of Greenland. Coupling the snow densification and meltwater-retention processes achieves a separation of volume and mass changes of the surface layer, in order to determine the surface melt contribution to runoff. Experiments for present-day conditions show that snow depth at the onset of melt, mean annual near-surface air temperature and the mean density of the annual snow layer are key factors controlling the quantity and spatial distribution of meltwater runoff above the equilibrium line on the Greenland ice sheet.

Ice streams are a fact of ice-sheet dynamics, draining up to 90% of the ice. Thermal convection in ice below the density inversion is a speculation. An attempt is made to meld the two in such a way that the speculation becomes an explanation for the fact.

We investigate the dynamics of a small surge-type valley glacier as part of a study to characterize glacier response to climate in the Donjek Range, southwest Yukon, Canada. Pole displacements were measured using kinematic GPS techniques during three consecutive summer field seasons. Measured surface velocities range from <10 m a−1 over the lower 1500 m of the 5 km long glacier to a maximum of ∼25–35 m a−1 over the upper 3500 m. Basal velocities along an approximate flowline are reconstructed from the measured surface velocities using inverse methods. Control tests are used to validate the inversion scheme, and sensitivity tests are performed to evaluate the influence of the flow-law coefficient, shape factor and longitudinal averaging length. Inversion of the real data shows that basal motion accounts for 50–100% of the total surface motion along the flowline. Based on these results, and several other lines of evidence, we suggest this glacier may be undergoing a slow surge.

Glacier runoff from the Yangtze River source region (YRSR), China, is estimated for the period 1961–2000 using a degree-day approach. In the investigation area, glacier runoff accounts for 11.0% of the total river runoff during the period 1961–2000. In the 1990s its contribution to river runoff rises to 17.0%. Due to the current rate of glacier decline, the impact of glacier runoff on river runoff has recently increased in the source region. Based on two different climate-change scenarios derived from ECHAM5/MPI-OM, future glacier runoff is assessed for the period 2001–50. In all climate-change scenarios, annual glacier runoff shows a significant increase due to intensified ice melting. There is an increase in glacier runoff during spring and early summer, yet a significant decrease in late summer. This study highlights the current and future impact of glacier runoff on river runoff in the YRSR.

An investigation was made to estimate the variance, measurement errors and sampling error in currently accepted practices for manual snow density measurement carried out as part of snow profile observations using the available variety of density cutters. A field experiment in dry snow conditions was conducted using a randomized block design to account for layer spatial variability. Cutter types included a 500 cm3 aluminium tube, 200 and 100 cm3 stainless-steel box types, 200 cm3 stainless-steel wedge types and a 100 cm3 stainless-steel tube. Without accounting for variation due to weighing devices, the range of values for ‘accepted practice’ determined in this study included variation within individual cutters of 0.8–6.2%, variation between cutters of 3–12%, variation between cutter means and layer means of 2–7%, and under-sampling errors of 0–2%. The results of a statistical analysis suggest that snow density measurements taken using various density cutters are significantly different from each other. Without adjustment for under-sampling, and given that the mean of all measurements is the accepted true value of the layer density, variation exclusively between cutter types provides ‘accepted practice’ measurements that are within 11% of the true density.

The automatic weather station (AWS) on the snout of the Vadret da Morteratsch, Switzerland, has delivered a unique 12 year meteorological dataset from the ablation zone of a temperate glacier. This dataset can be used to study multi-annual trends in the character of the surface energy budget. Since 2003 there has been a substantial darkening of the glacier tongue due to the accumulation of mineral and biogenic dust. The typical surface albedo in summer has dropped from 0.32 to 0.15. We have analysed the implications of the lowered albedo for the energy balance and the annual ablation. For the 4 year period 2003–06, the decreased albedo caused an additional removal of about 3.5 m of ice. Calculations with an energy-balance model show that the same increase in ablation is obtained by keeping the ice albedo fixed to 0.32 and increasing the air temperature by 1.7 K. Our analysis confirms that for retreating glaciers the deposition of dust from exposed side moraines on the glacier surface constitutes an important feedback mechanism. The mineral dust stimulates the growth of algae, lowers the surface albedo, enhances the melt rates, and thereby facilitates the further retreat of the glacier snout.

Snow cover in the Tibetan Plateau is highly variable in space and time and plays a key role in ecological processes of this cold-desert ecosystem. Resolution of passive microwave data is too low for regional-scale estimates of snow cover on the Tibetan Plateau, requiring an alternate data source. Optically derived snow indices allow for more accurate quantification of snow cover using higher-resolution datasets subject to the constraint of cloud cover. This paper introduces a new optical snow index and assesses four optically derived MODIS snow indices using Landsat-based validation scenes: MODIS Snow-Covered Area and Grain Size (MODSCAG), Relative Multiple Endmember Spectral Mixture Analysis (RMESMA), Relative Spectral Mixture Analysis (RSMA) and the normalized-difference snow index (NDSI). Pearson correlation coefficients were positively correlated with the validation datasets for all four optical snow indices, suggesting each provides a good measure of total snow extent. At the 95% confidence level, linear least-squares regression showed that MODSCAG and RMESMA had accuracy comparable to validation scenes. Fusion of optical snow indices with passive microwave products, which provide snow depth and snow water equivalent, has the potential to contribute to hydrologic and energy-balance modeling in the Tibetan Plateau.

The current generation of continental-scale ice-sheet models cannot successfully reproduce the complex ice/water/sediment interactions of the West Antarctic ice sheet (WAIS) in a physically meaningful manner. The potential of a thin-film-based subglacial water-flow model for incorporation into a continental-scale coupled ice/water flow model of the WAIS is evaluated in this paper. The subglacial water-flow model is applied to the Ross Sea sector of the WAIS, in both a steady-state and time-dependent form, to derive the equilibrium water depth for the present-day configuration. The potential for coupling the model to an ice-flow model is then demonstrated, using a variable sliding parameter that is a function of the subglacial water depth. A coupled ice/water flow model, using the parameterization tested in this paper, could have the potential for reproducing the surface elevation, velocity and thermal regime of the WAIS successfully. These requirements are crucial in modelling the evolution of the WAIS, and must be addressed before reliable continental-scale predictive models can be utilized.

This paper aims to interpret the temporal variations of microwave brightness temperature (at 19 and 37GHz and at vertical and horizontal polarizations) in Antarctica using a physically based snow dynamic and emission model (SDEM). SDEM predicts time series of top-of-atmosphere brightness temperature from widely available surface meteorological data (ERA-40 re-analysis). To do so, it successively computes the heat flux incoming the snowpack, the snow temperature profile, the microwaves emitted by the snow and, finally, the propagation of the microwaves through the atmosphere up to the satellite. Since the model contains several parameters whose value is variable and uncertain across the continent, the parameter values are optimized for every 50 km × 50 km pixel. Simulation results show that the model is inadequate in the melt zone (where surface melting occurs on at least a few days a year) because the snowpack structure and its temporal variations are too complex. In contrast, the accuracy is reasonably good in the dry zone and varies between 2 and 4 K depending on the frequency and polarization of observations and on the location. At the Antarctic scale, the error is larger where wind is usually stronger, suggesting either that meteorological data are less accurate in windy regions or that some neglected processes (e.g. windpumping, surface scouring) are important. At Dome C, in calm conditions, a detailed analysis shows that most of the error is due to inaccuracy of the ERA-40 air temperature (∼2 K). Finally, the paper discusses the values of the optimized parameters and their spatial variations across the Antarctic.

As an ice sheet evolves, there are ice elements near the surface only recently subjected to stress following deposition, and others that have been subjected to stress over many ranges of time. The constant stress and constant strain-rate responses of ice in uniaxial compressive stress exhibit non-viscous behaviour, that is, the strain rate is not fixed by the stress (and conversely) but both vary with time. At constant stress the initial primary strain rate decreases with time to a minimum, described as secondary creep. It then increases and approaches an asymptotic limit, described as tertiary creep. Analogously, at constant strain rate the initial stress increases to a maximum then decreases to an asymptotic limit. These responses are used to construct a simple viscoelastic fluid constitutive law of differential type. Such a time-dependent law, with timescales changing widely with temperature, can be expected to yield a flow field in an ice sheet that is very different from that obtained from the viscous law. Only comparison solutions for both constitutive laws can determine the differences and significance of the non-viscous behaviour, and the simple law constructed would be a candidate for such comparisons.

This paper examines the basal ice sequence of Rhone Glacier, a cold-based glacier in the McMurdo Dry Valleys, Antarctica, using isotopic and solute chemistry data. Three different ice facies are identified: englacial, amber and stratified. The englacial facies is clean, bubbly ice of meteoric origin and is underlain by an amber facies. Amber ice is a characteristic of cold alpine glaciers in the McMurdo Dry Valleys and is distinctive for its high solute concentrations and much higher strain rates compared with the overlying englacial ice and the underlying stratified ice. Analysis of the stratified facies reveals an isotopic signature indicative of melt then refreeze processes and it is most likely associated with apron entrainment at the margin. By contrast, the amber facies has a co-isotopic slope of 8 and plots on a meteoric waterline. The inclusion of impurities in the amber ice reveals prolonged contact with the bed, and its depleted isotopic signature is consistent with ice formed during a cooler period. Comparison of the basal sequence of Rhone Glacier with other cold-based glaciers in the McMurdo Dry Valleys reveals strong similarities between valley-side glaciers (e.g. Meserve and Rhone Glaciers), whereas valley-floor glacier basal sequences (e.g. Suess Glacier) are characterized by structurally complex amalgamations of ice and debris.

We investigate the major sources of backscatter at 5.3 GHz, within the superimposed ice and firn areas of a polythermal glacier. Two ground-penetrating radar systems, an 800 MHz impulse system and a polarimetric 5.3 GHz frequency-modulated continuous-wave system, are used to acquire along-glacier profiles in the accumulation area of Kongsvegen, Svalbard. The 800 MHz response is used to map reflection horizons in the glacier. Using cores from the superimposed ice and firn areas, the causes of these reflection horizons, in terms of snow, firn and ice layers, are investigated. Superimposing the reflection horizons on the co-polarized and cross-polarized 5.3 GHz profile, we are able to determine how the 5.3 GHz frequency responds to the different media. Scattering at rough interfaces and volume scattering occur in the superimposed ice area and are apparently caused by air-bubble number, size and distribution. In the firn the strongest return originates from below the previous summer surface, consistent with previous findings. At approximately the same depth, strong incoherent scattering begins. The rapid decrease in coherent reflections indicates the significance of scattering in the firn.

In order to find environmental signals based on the dust and calcium-ion concentrations in ice cores, we determine the constituent elements of residue particles obtained after melting ice samples. We have designed a sublimating system that operates at −45°C, below the eutectic temperatures of major salts. This system permits us to obtain a great many non-volatile particles. After studying the non-volatile particles, we immersed them in water to remove soluble particles and compounds. We thereby analyzed a total of 1272 residue particles (from the melted sample), 2418 non-volatile particles (after sublimation) and 1463 insoluble particles taken from five sections of Last Glacial Maximum ice from the Dome Fuji (Antarctica) ice core. Their constituent elements were determined by scanning electron microscopy/energy-dispersive X-ray spectrometry (SEM-EDS) and compared to the dust, calcium-ion and sodium-ion concentrations measured by ion chromatography. Our results indicate that >99.9% of the insoluble particles contain silicon but no sulfur, nitrogen or chlorine. A significant number of the non-volatile particles, however, contain sulfur and chlorine. We conclude that insoluble dust consists mostly of silicate, that almost all calcium ions originate from calcium sulfate and that almost all sodium ions originate from sodium sulfate and sodium chloride.

Interest in crevasses and associated ice-fracture processes has recently increased due to recognition of the importance of calving glaciers to the mass balance of the cryosphere, as well as the importance of fractures in glacier hydrology. Recently developed calving criteria make use of models which predict crevasse depth from surface strain rates, but these models have rarely been tested against observations. In this study, we present data on crevasse depth and surface strain rates, and compare the measured values with results of two crevasse-depth models: a simple function proposed by Nye and a linear elastic fracture mechanics (LEFM) model developed by Van der Veen. Our results indicate that both models predict crevasse depths within the correct order of magnitude. The LEFM model, incorporating measured values of crevasse spacing and tuned for fracture toughness, performs better in predicting crevasse depths, but where lack of input data precludes such tuning, the results are similar to Nye’s model predictions. We conclude that both models may be used to calculate crevasse depths in calving models, although the Nye function is undoubtedly much simpler to implement within an ice-dynamics model.