An ice-flow model has been developed and applied to Law Dome, East Antarctica, at the location of the Dome Summit South deep borehole. The results are used to reconstruct an ice-sheet history of accumulation rate, ice thickness and the rate of change in ice thickness. The focus of this study is on the effect of the variation in anisotropic flow properties on the ice-sheet surface elevation change. The enhancement factor, defined as the ratio of the strain rate for anisotropic ice to the strain rate for isotropic ice, is used in the ice-flow relations to account for the anisotropic properties of the ice with fabric development. The model is run with the various ice rheologies which represent anisotropic or isotropic ice-flow properties. The results show that the model incorporating anisotropic flow properties of the ice is more sensitive to the climate-change history.

An expression for force balance is derived for the general case of gradients in longitudinal and lateral normal stresses and lateral shear stress. In order to consider horizontal glacial mechanics in Newton’s style of actions and reactions, the full stresses are partitioned into lithostatic and resistive, Rij, components. The lithostatic stress is the weight of ice above, and the horizontal gradient in lithostatic force on a vertical column is the familiar driving stress, which accounts for the horizontal effect of body or action forces. The horizontal resistive-stress components describe the reactions to this horizontal action of gravity. Force balance is

with horizontal coordinates x1, x2 and vertical z. The upper and bottom elevations are h and b, and τdi and τbi are driving stress and basal drag respectively. This describes net reaction due to normal resistance, lateral shear resistance, and basal drag resistance, and finally the action or driving stress. This equation is exact. Resistive stresses are simply linked to deviatoric stresses, and hence to strain-rates, through the flow law.

Satellite-borne, radar altimeters have already demonstrated an ability to produce high-precision, topographic maps of the ice sheets. Seasat operated in a tracking mode, designed for use over oceans, but successfully tracked much of the flatter regions of the ice sheet to ± 72° latitude. ERS-1 will extend coverage to ± 82° latitude and will be equipped with an ocean mode similar to that of Seasat and an ice mode designed to permit tracking of the steeper, peripheral regions. The ocean mode will be used over the flatter regions, because of its greater precision.

Altimeter performance over the ice sheets has been investigated through a study of Seasat tracking behaviour and the use of an altimeter performance simulator, with a view to assessing the likely performance of ERS-1 and the design of improved tracking systems. Analysis of Seasat data shows that lock was frequently lost, as a result of possessing a non-linear height error signal over the width of the range window. Having lost lock, the tracker frequently failed to transfer rapidly and effectively to track mode. Use of the altimeter performance simulator confirms many of the findings from Seasat data and it is being used to facilitate data interpretation and mapping, through the modelling of waveform sequence.

Long-term maintenance of camp constructions on snow and ice surfaces involves repeated adjustments of the vertical position of buildings due to snow accumulation or ice ablation. The principle of a low-effort vertical-adjustment station structure is presented. The basic idea is to construct a floatable spherical-shaped building that can be lifted by adding water underneath, which will then refreeze, or can be lowered by melting ice away from the base. Under cold polar conditions, the power requirement for melting the base free is approximately 100 Wm–2 and is usually available as waste heat from the electric power generator of the station.

Drifting snow creates problems which have practical effects in France in two situations. The first situation is when the result of wind action on snow is to cause accumulation of this snow on mountains, leeward of crests, and consequently to create the potential hazard of avalanche. The second is when the result is to pile up snow in flat regions wherever there are obstacles such as road cuttings and vegetation. This paper focuses on the second type of problem, which affects large areas of central and north-eastern France. We explain how we have chosen our test site, which initial experiments we have conducted in order to assess the general geometrical features which a snow fence must possess in order to function most effectively in collecting snow, and how subsequently we have assessed the properties and costs of different fencing systems.

As part of a long-term mass-balance program run by SWEDARP since 1988, a detailed study on Plogbreen, Dronning Maud Land, Antarctica, was undertaken during the austral summer of 2003 to investigate the long-term mass balance. We compare ice outflux, φout, through a cross-sectional gate with ice influx, φin, from the upstream catchment area. The φin is based on calculations of snow accumulation upstream of the gate using data available from published ice-core records. The φout is based on Glen’s flow law aided by thermodynamic modeling and force-budget calculations. Input data from the field consist of measurements of ice surface velocity and ice geometry. The ice surface velocity was measured using repeated differential global positioning system surveying of 40 stakes over a period of 25 days. The ice geometry was determined by 174 km of ground-penetrating radar profiling using ground-based 8MHz dipole antennas. This study presents the collected velocity and geometry data as well as the calculated ice flux of Plogbreen. The results show a negatively balanced system within the uncertainty limits; φout = 0.55 ± 0.05 km3 a–1 and φin = 0.4 ± 0.1 km3 a–1. We speculate that the negative balance can be explained by recent eustatic increase reducing resistive stresses and inducing accelerated flow.

Late Wisconsinan glacial sediments, exposed on Whidbey Island and Camano Island, Puget Sound (Washington State, USA), were deposited in a proglacial shallow marine/outwash environment during northward retreat of the Puget Lobe of the Cordilleran ice sheet. Sediments mainly comprise massive and cross-bedded sand and gravels, and rhythmically-bedded clay and silt/fine sand couplets, interbedded with diamictons that were deposited by a range of mass flows of different viscosities. Although sediment stratigraphy and ice advance–retreat patterns are well established for the Puget Lobe, brittle and ductile deformation structures within, and separating, these sediment units are less well understood. These structures record the nature of ice–bed interactions taking place in subglacial and proglacial environments. This study examines evidence for these processes and environments. Key deformation structures identified include open to overturned folds, normal and reverse faults, clastic dikes and hydrofractures and passive-loading structures. Evidence for coeval development of ductile and brittle deformation structures shows the close relationship between porewater changes, sediment rheology and sediment system responses to changes in strain caused by ice–bed interactions.

The mechanisms of strong winds associated with snow clouds, and the relationship between strong winds and blowing/drifting snow, were investigated. A snowstorm occurred with a typical L-mode snow band which was generated and organized longitudinally during a continental cold-air outbreak over the Sea of Japan. Doppler radar observations revealed that the snow band consisted of small echo cells arranged along the direction of the snow band. When one of the echo cells passed, blowing/drifting snow was generated and intensified by a snow cloud-induced gust, and the horizontal visibility near the ground surface was significantly decreased. Doppler radar and radiosonde data showed that the gust was due to the cold air outflow (CAO) from the snow clouds. The leading edge of the CAO was about 9 km ahead of the center of the snow cloud and the depth of the CAO was about 600 m near the forward flank of the snow cloud. The CAO was caused by a downdraft at the center of the snow cloud, which was initiated at a height of about 1.3 km and with a velocity in excess of 1 ms−1. The observed CAO speed was explained by the theory of the gravity current.

A theory based on classical fluid mechanics for an incompressible, chemically non-reacting, atmospheric mixture of air and entrained snow particles is derived. These continuum equations of motion are then expanded to include turbulent flow. The reduced, one-dimensional equations of this theory are further refined by order-of-magnitude analysis and correlation of the turbulent terms to mean flou parameters. The resulting one-dimensional, turbulent equations of motion for the snow contain apparent turbulent forces which enhance entrainment of snow where gradients of the air flow are high. These turbulent equations of motion are then solved numerically for snow particle velocity and concentration as a function of height above the surface. The results are similar to observed profiles of snow concentration and the superposition of the solution of this turbulent mixture theory for snow entrainment with an appropriate solution for the saltation layer will eventually lead to a working continuum theory for blowing snow.

Dry-snow metamorphism was the focus of extensive investigations in Russia over several decades. Large amounts of data were collected and used to construct a conceptual model based on crystallographic laws. The difference in terminology compared with the conventional model made these results less accessible to the wider international snow science community. This paper attempts to explain this terminology and its background so that the reported findings are not overlooked in ongoing investigations of the driving forces and consequences of snow metamorphism.

A simple model tests the effect on ice-core impurity concentrations of climate-induced changes in the physical conditions of the atmosphere influencing transport and deposition processes, while keeping source areas and production rates constant. The model results show that the increased glacial concentrations observed for most impurities can be explained entirely by changes in transport and deposition. No increase in source emission is necessary, however possible, to explain the ten-fold increase in impurity concentrations during the Last Glacial Maximum. This shows that the effect of dynamic changes in the atmosphere can be large and has to be taken into account before translating deposition records into emission records. The total impurity content in the global atmosphere during the glacial period was higher if dynamic changes in the atmosphere rather than source-emission changes were responsible for the variations observed in polar areas. This implies that a climate-forcing mechanism is to be found in the dynamics of the atmosphere, since the radiative properties of the atmosphere depend on the total content of impurities in the atmosphere. The effect on the climate can probably be compared with, although opposite in sign to, the present-day anthropogenic greenhouse forcing.

A numerical ice-shelf model is employed to observe the inception of the West Antarctic ice sheet (WAIS) from a thin (20 m thick) floating ice cover under the following conditions: (i) a lower sea-level than at present, due to ice-sheet formation in the Northern Hemisphere, (ii) surface and basal temperature and accumulation rates approximately equal to those of present Antarctic ice shelves, and (iii) ice flow from East Antarctica into West Antarctica is neglected. The model determines the flow and thickness of floating ice and assumes that grounded ice is stagnant. Under these constraints, all regions except the Ross Sea, the Filchner region (east of Berkner Island), and up-stream of Thwaites Glacier ground within 4000 years. Ice readily grounds in the Ronne region (west of Berkner Island), forcing ice from Ellsworth Land to flow east toward the Filchner region. It is suggested that grounding over the Ross Sea, the Filchner region, and up-stream of Thwaites Glacier occurs only after grounded-ice flow is established. Grounded-ice flow is also a prerequisite of bed erosion and sediment deposition, which leave historical records of the actual ice-sheet formation. It is suggested that erosion and sediment deposition is minimal over the Ronne region and considerable along the path from Ellsworth Land to the Filchner region, because more ice flows toward the Filchner region than the Ronne region. It is probably difficult for ice to ground over the Ross region, so this region should have a high proportion of glacial marine sediments.

Cryogenic brines are under-studied, despite the fact that they may contain information about past ice-sheet behavior. Cryogenic brines form through cryoconcentration of seawater, although the specific setting and mechanism of formation have been debated. Previous conceptual models of brine formation require seawater isolation from the ocean in a closed basin experiencing freezing. We propose instead that they may form in pore spaces of marine sediments subjected to repeat cycles of ice-sheet advance and retreat. During periods of basal freezing, cryoconcentration produces hypersaline brines which experience downward flow driven by unstable density stratification. Our advection-diffusion model of porewater chemistry evolution successfully recreates the porewater chemistry of two deep Antarctic cores containing cryogenic brines (AND-1B and AND-2A), suggesting that cryogenic brines can be formed through the repeated isolation and cryoconcentration of marine waters within subglacial sediment pore spaces of modern and past ice sheets.

With the development of coupled atmosphere–ocean models for the polar seas, there will be a great need of surface radiation budget data over partially ice-covered sea surfaces of the marginal ice zones. This paper presents an attempt to retrieve the surface radiation budget components over the Fram Strait area from operational satellite data, i.e. AVHRR visible and infrared radiances and SSM/I passive microwave brightness temperatures. The cloud optical thickness, which is the main modulator for the incoming solar flux, is retrieved from AVHRR visible radiances through a radiative transfer model, assuming surface conditions deduced from the SSM/I ice concentrations. The cloud base emissivity, required for the downwelling infrared flux computation, is linked to the optical thickness through the liquid water path. The results presented show a good agreement with field measurements and little sensitivity to the cloud and aerosol properties extracted from the literature rather than from the satellite data. Infrared fluxes retrievals would however require a better knowledge of the atmosphere temperature profile and cloud base altitude.

The present paper gives the preliminary results of the analyses on microparticle concentration and electrical conductivity of a 700.56 m ice core from Mizuho Station, Antarctica. Concentration of microparticles coarser than 0.63 μm in diameter increases more than twofold at the 240-440 m depth interval compared with that below 440 m in depth. The higher particle concentration is well associated with higher electrical conductivity and lower δ18O. Periods of high particle concentration are estimated to be 3000-6000 years B.P. A visible volcanic dirt band was found at 500.7 m below the surface. This dirt band may be isochronous with the shallowest ash band of the Byrd Station core, found at 799 m depth. The present study indicates that large-scale environmental changes possibly occurred in the Southern Hemisphere in the middle of the Holocene.

Mapping of areas exposed to avalanche hazard for the Norwegian Army was started by the Norwegian Geotechnical Institute in 1986. The background to this mapping is that large-scale military exercises are held annually in northern Norway, in terrain where there is a high danger of avalanche activity. Avalanche areas are divided into two zones: potential starting zones, and potential run-out zones. All potential avalanche areas are indicated on maps, and mapping is carried out by computer using a terrain model and digital maps. An interactive graphic work station is used to outline danger areas. Starting and run-out zones are identified by using terrain parameters which may be extracted from digital maps. The usual scale of the avalanche maps is 1 : 50 000, with 20 m contour intervals.

To confirm radio-echo layering due to changes in density variations and in specific conductivity in the amount of acid impurities, radio-echo sounding surveys with impulse radar technique were carried out. The continuous and strong internal layers of the snow covers were found to give good correlation with strong peaks of specific conductivity of melted samples from ice cores, rather than the differences in density fluctuations between depositional layers. Measured high conductivity due to acidity variations in ice cores may be correlated with recent volcanic eruptions in the northern hemisphere, and in the Scotia Arc and the South Sandwich Islands.