For accurate ice-sheet flow modelling, the anisotropic behaviour of ice must be taken fully into account. However, physically based micro-macro (μ-M) models for the behaviour of an anisotropic ice polycrystal are too complex to be implemented easily in large-scale ice-sheet flow models. An easy and efficient method to remedy this is presented. Polar ice is assumed to behave as a linearly viscous orthotropic material whose general flow law (GOLF) depends on six parameters, and its orthotropic fabric is described by an ‘orientation distribution function’ (ODF) depending on two parameters. A method to pass from the ODF to a discrete description of the fabric, and vice versa, is presented. Considering any available μ-M model, the parameters of the GOLF that fit the response obtained by running this μ-M model are calculated for any set of ODF parameters. It is thus possible to tabulate the GOLF over a grid in the space of the ODF parameters. This step is performed once and for all. Ice-sheet flow models need the general form of the GOLF to be implemented in the available code (once), then, during each individual run, to retrieve the GOLF parameters from the table by interpolation. As an application example, the GOLF is tabulated using three different μ-M models and used to derive the rheological properties of ice along the Greenland Icecore Project (GRIP) ice core.

Dye-tracer experiments undertaken over two summer melt seasons at polythermal John Evans Glacier, Ellesmere Island, Canada, were designed to investigate the character of the subglacial drainage system and its evolution over a melt season. In both summers, dye injections were conducted at several moulins and traced to a single subglacial outflow. Tracer breakthrough curves suggest that supraglacial meltwater initially encounters a distributed subglacial drainage system in late June. The subsequent development and maintenance of a channelled subglacial network are dependent upon sustained high rates of surface melting maintaining high supraglacial inputs. In a consistently warm summer (2000), subglacial drainage became rapidly and persistently channelled. In a cooler summer (2001), distributed subglacial drainage predominated. These observations confirm that supraglacial meltwater can access the bed of a High Arctic glacier in summer, and induce significant structural evolution of the subglacial drainage system. They do not support the view that subglacial drainage systems beneath polythermal glaciers are always poorly developed. They do suggest that the effects on ice flow of surface water penetration to the bed of predominantly cold glaciers may be short-lived.

A grid-based surface energy-balance mass-balance model has been developed to simulate snow- and ice melt in mountainous regions with an hourly resolution. The model is applied to Storglaciären, a valley glacier in Sweden, using a 30 m resolution digital elevation model. Emphasis is directed towards computing the radiation components. These are modelled individually, considering the effects of slope angle, aspect and effective horizon. A new parameterization for snow albedo is suggested, modifying the albedo of the preceding hour as a function of time after snowfall, air temperature and cloudiness. The model is used to provide the meltwater input for discharge modelling and to assess the influence of the individual components on melt. Results are validated by means of observed melt rates, patterns of snow-line retreat and proglacial discharge. In general, simulations are in good agreement with observations. In particular, the diurnal and seasonal fluctuations of discharge are simulated remarkably well.

We describe the validation of surface albedos of snow and glacier ice as derived from Advanced Very High Resolution Radiometer (AVHRR) and MOderate Resolution Imaging Spectrometer (MODIS) satellite data. For this purpose we measured surface albedos from a helicopter over Vatnajokull, Iceland, and the Kangerlussuaq transect (western part of the Greenland ice sheet) in Thematic Mapper (TM) bands 2 and 4 and AVHRR bands 1 and 2, and converted these values to ‘measured albedos’ in three MODIS bands. Relative to other validation methods, our helicopter measurements have the advantages of larger spatial coverage and of (almost) direct measurements in satellite-sensor spectral bands. We found the smallest differences between the satellite-derived and helicopter albedos for the Kangerlussuaq transect: for AVHRR data a mean difference of 0.01 in both bands (with the satellite in near-nadir position) and for two MODIS images a mean difference of 0. 00-0.02 for bands 2 and 4, and 0.03 for band 1. For two AVHRR images of Vatnajokull, we found mean differences of up to 0.06. Differences are primarily due to errors in the satellite-derived albedos, which, in turn, are mainly caused by errors in the calibration coefficients of the satellite sensors and insufficient knowledge of the angular distribution of the radiation reflected by snow and ice. Satellite data obtained from view zenith angles larger than ~50-55° appeared to be unsuitable.

We measured the surface velocity field during the summers of 1999 and 2000 on the 7 km long, 185 m thick Bench Glacier, Alaska, USA. In the spring of both years, a short-lived pulse of surface velocity, 2-4 times the annual mean velocity, propagated up-glacier from the terminus at a rate of ~200-250md-1. Displacement attributable to rapid sliding is ~5-10% of the annual surface motion, while the high-velocity event comprised 60-95% of annual basal motion. Sliding during the propagating speed-up event peaked at 6-14 cm d-1, with the highest rates in mid-glacier. Continuous horizontal and vertical GPS measurements at one stake showed divergence and then convergence of the ice surface with the bed as the velocity wave passed, with maximum surface uplift of 8-16 cm. High divergence rates coincided with high horizontal velocities, suggesting rapid sliding on the up-glacier side of bedrock steps. Initiation of the annual speed-up event occurred during the peak in englacial water storage, while the glacier was entirely snow-covered. Basal motion during the propagating speed-up event enlarges cavities and connections among them, driving a transition from a poorly connected hydrologic system to a well-connected linked-cavity system. Sliding is probably halted by the development of a conduit system.

A deep ice core has been drilled on Akademii Nauk ice cap, Severnaya Zemlya, Eurasian Arctic. High-resolution chemical analysis has been carried out for the upper 53 m of this ice core to study its potential as an atmospheric aerosol archive, despite strong meltwater percolation. These records show that a seasonal atmospheric signal cannot be deduced. However, strong year-to-year variations have allowed the core to be dated, and a mean annual net mass balance of 0.46 m w.e. a-1 was deduced. The chemical signature of an extraordinarily high peak in electrical conductivity at 26 m depth pointed clearly to the eruption of Bezymianny, Kamchatka, in 1956. However, in general, peaks in the electrical conductivity are not necessarily related to deposition of volcanogenic sulphur aerosol. In contrast, maximum sulphate and nitrate concentrations in the ice could be related to maximum SO2 and NOx anthropogenic emissions in the 1970s, probably caused by the nickel- and copper-producing industries in Norilsk and on the Kola peninsula or by industrial combustion processes occurring in the Siberian Arctic. In addition, during recent decades sulphate and nitrate concentrations declined by 80% and 60%, respectively, reflecting a decrease in anthropogenic pollution of the Arctic basin.

A real-time video camera probe was deployed in a hot-water drilled borehole through the Amery Ice Shelf, East Antarctica, where a total ice thickness of 480 m included at least 200 m of basal marine ice. Down-looking and side-looking digital video footage showed a striking transition from white bubbly meteoric ice above to dark marine ice below, but the transition was neither microscopically sharp nor flat, indicating the uneven nature (at centimetre scale) of the ice-shelf base upstream where the marine ice first started to accrete. Marine ice features were imaged including platelet structures, cell inclusions, entrained particles, and the interface with sea water at the base. The cells are assumed to be entrained sea water, and were present throughout the lower 100-150 m of the marine ice column, becoming larger and more prevalent as the lower surface was approached until, near the base, they became channels large enough that the camera field of view could not contain them. Platelets in the marine ice at depth appeared to be as large as 1-2 cm in diameter. Particles were visible in the borehole meltwater; probably marine and mineral particles liberated by the drill, but their distribution varied with depth.

In lieu of direct glacier surface mass-balance measurements, equilibrium-line altitudes (ELAs) have been measured over a 28 year period at 50 selected glaciers distributed along the glacierized length of New Zealand’s Southern Alps. Analysis of the data shows that ELAs are a useful measurement of glacier response to annual climate fluctuations, although there is much variability in the degree of response between glaciers in any given year. Comparisons of individual glacier annual ELA with the mean for all annual ELAs of the Southern Alps show a large variation of individual glacier response, with coefficients of variation (r2) ranging from 0.53 to 0.90. The ELA data show detailed, but qualitative, annual mass-balance variations on both regional and individual glacier scales. The ELA record closely predicts glacier termini responses that follow after appropriate response time delays. The recorded variability in climate response for the Southern Alps suggests no single glacier is truly representative for detailed studies of glacier-climate relationships, and that a large number of ELA measurements may be as good an indicator of climate as a few mass-balance measurements. Given the appropriate mass-balance gradient, mass-balance values may be calculated for any of the monitored glaciers.

We present evidence for melting at the base of the ice that overlies Lake Concordia, an 800 km2 subglacial lake near Dome Concordia, East Antarctica, via a combination of glaciohydraulic melting (associated with the tilted ice ceiling and its influence on lake circulation/melting temperature) and melting by extreme strain heating (where the ice sheet is grounded). An influx of water is necessary to provide nutrients, material and biota to support subglacial lake ecosystems but has not been detected previously. Freezing is the dominant observed basal process at over 60% of the surface area above the lake. The total volume of accreted ice above the lake surface is estimated as 50-60 km3, roughly 25-30% of the 200 ± 40 km3 estimated lake volume. Estimated rates of melting and freezing are very similar, ±2-6 mm a-1. The apparent net freezing may reflect the present-day response of Lake Concordia to cooling associated with the Last Glacial Maximum, or a large influx of water either via a subglacial hydrological system or from additional melting of the ice sheet. Lake Concordia is an excellent candidate for subglacial exploration given active basal processes, proximity to the Dome Concordia ice core and traverse resupply route.

Hielo Patagónico Sur (HPS; southern Patagonia icefield) is the largest temperate ice mass at mid-latitudes in the Southern Hemisphere. With few exceptions, the glaciers in this region have been retreating during the last 50 years. Based on field data, vertical aerial photographs and satellite images, ice-elevation changes since 1975 on Glaciar Chico, one of the main tongues of HPS, are presented. A maximum ice thinning of 5.4 ± 0.55 m a-1 was observed at the glacier front between 1975 and 1997. Global positioning system (GPS) data were used in the accumulation area of the glacier to infer a thinning rate of 1.9 ± 0.14 m a-1 between 1998 and 2001. This thinning rate is three times higher than the snow accumulation rate estimated for that part of the glacier. A mean net glacier mass balance of -0.29 ± 0.097 km3 w.e. a-1 was estimated between 1975 and 2001. Climate data suggest an increase in temperature and a reduction in precipitation during most of the 20th century in the vicinity of HPS. Although these climate changes are the primary explanation for the observed ice-elevation changes of the glacier, ice-dynamics effects are also believed to play an important role.

Recent snow accumulation rate is a key quantity for ice-core and mass-balance studies. Several accumulation measurement methods (stake farm, fin core, snow-radar profiling, surface morphology, remote sensing) were used, compared and integrated at eight sites along a transect from Terra Nova Bay to Dome C, East Antarctica, to provide information about the spatial and temporal variability of snow accumulation. Thirty-nine cores were dated by identifying tritium/b marker levels (1965_66) and non-sea-salt (nss) SO42_ spikes of the Tambora (Indonesia) volcanic event (1816) in order to provide information on temporal variability. Cores were linked by snow radar and global positioning system surveys to provide detailed information on spatial variability in snow accumulation. Stake-farm and ice-core accumulation rates are observed to differ significantly, but isochrones (snow radar) correlate well with ice-core derived accumulation. The accumulation/ablation pattern from stake measurements suggests that the annual local noise (metre scale) in snow accumulation can approach 2 years of ablation and more than four times the average annual accumulation, with no accumulation or ablation for a 5 year period in up to 40% of cases. The spatial variability of snow accumulation at the kilometre scale is one order of magnitude higher than temporal variability at the multi-decadal/secular scale. Stake measurements and firn cores at Dome C confirm an approximate 30% increase in accumulation over the last two centuries, with respect to the average over the last 5000 years

We derive work dissipation functionals for granular snow avalanches flowing in simple shear. Our intent is to apply constructive theorems of non-equilibrium thermodynamics to the snow avalanche problem. Snow chute experiments show that a bi-layer system consisting of a non-yielded flow plug overriding a sheared fluidized layer can be used to model avalanche flow. We show that for this type of constitutive behaviour the dissipation functionals are minimum at steady state with respect to variations in internal velocity; however, the functionals must be constrained by subsidiary mass- continuity integrals before the equivalence of momentum balance and minimal work dissipation can be established. Constitutive models that do not satisfy this equivalence are henceforth excluded from our consideration. Fluctuations in plug and slip velocity depend on the roughness of the flow surface and viscosity of the granular system. We speculate that this property explains the transition from flowing avalanches to powder avalanches. Because the temperature can safely be assumed constant, we demonstrate within the context of non-equilibrium thermodynamics that granular snow avalanches are irreversible, dissipative systems, minimizing – in space – entropy production. Furthermore, entropy production is linear both near and far from steady-state non-equilibrium because of the mass-continuity constraint. Finally, we derive thermodynamic forces and conjugate fluxes as well as expressing the corresponding phenomenological Onsager coefficients in terms of the constitutive parameters.

This paper considers the role of structural glaciology in debris entrainment, transport and deposition at Haut Glacier d’Arolla, a temperate valley glacier in Valais, Switzerland. Sedimentological descriptions and cIast anaIysis have been used to identify reIationships between ice structure and debris transport. Relationships identified are (1) debris associated with crevasse traces, (2) the folding of rockfall material incorporated within primary stratification to form medial moraines and (3) dirt cones and engIaciaI debris Iayers associated with reactivated crevasse traces. A conceptuaI modeI is introduced to summarize the manner in which ice structures at Haut Glacier d’Arolla control entrainment and deposition of debris.

We investigate velocity changes occurring along Whillans Ice Stream (WIS) by comparing velocities derived from repeat aerial photographs acquired in 1985-89 (average date of 1987) to interferometric satellite radar (InSAR) velocities collected in 1997. Three different analysis methods are applied to the velocity data. First, temporal and spatial changes in velocities are correlated to identifiable features (flowlines, shear margins, bed features) visible on the 1997 RADARSAT Antarctic Mapping Project mosaic. Second, we relate velocity gradients to stresses via the flow law and, along with surface topography and ice-thickness data, apply the force-budget technique to determine the relative importance of driving stress, side drag and basal drag over time. Finally, the mass balance of the main part of WIS is determined for 1987 and 1997. Our results are consistent with previous studies that show an overall deceleration resulting in downstream thickening of the ice stream (Whillans and others, 2001; Joughin and others, 2002).

We describe an instrument developed to make in situ measurements of salinity and solid- fraction profiles in growing sea ice. The vertical resolution of the measurements is up to a few millimeters, with a temporal resolution of up to fractions of a second. The technique is based on impedance measurements between platinum wires around which sea ice grows. Data obtained using this instrument in laboratory experiments are in good agreement with theoretical predictions. In a field test in the Arctic, the bulk salinity of growing sea ice has been measured in situ throughout the whole depth of the ice layer. The data are compared with bulk salinities obtained from ice cores, and confirm the general understanding that the bulk salinity in ice-core studies is significantly underestimated in the lower parts of the cores. The approach can also be used in other glaciological applications and for general studies of two-phase, two-component porous media.