In this paper we explore simulated responses of electromagnetic (EM) signals relative to in situ field surveys and quantify the effects that different values of conductivity in sea ice have on the EM fields. We compute EM responses of ice types with a three-dimensional (3-D) finite-volume discretization of Maxwell’s equations and present 2-D sliced visualizations of their associated EM fields at discrete frequencies. Several interesting observations result: First, since the simulator computes the fields everywhere, each gridcell acts as a receiver within the model volume, and captures the complete, coupled interactions between air, snow, sea ice and sea water as a function of their conductivity; second, visualizations demonstrate how 1-D approximations near deformed ice features are violated. But the most important new finding is that changes in conductivity affect EM field response by modifying the magnitude and spatial patterns (i.e. footprint size and shape) of current density and magnetic fields. These effects are demonstrated through a visual feature we define as ‘null lines’. Null line shape is affected by changes in conductivity near material boundaries as well as transmitter location. Our results encourage the use of null lines as a planning tool for better ground-truth field measurements near deformed ice types.

A three-dimensional dynamic, thermodynamic ice-sheet model has been developed to simulate the past, present, and future behaviour of the Antarctic ice sheet. The present ice velocities depend on the deep ice temperatures which in turn depend on the past changes of the ice sheet, including surface temperature, accumulation rate, and ice thickness. The basal temperatures are also strongly dependent on the geothermal heat flux. The model has therefore been used to study the effect on the basal temperatures, of changes to the geothermal heat flux, as well as the past changes of surface temperature and accumulation rate based on results obtained from the Vostok deep ice core. The model is also used to compute the distribution of surface velocity required to balance the present accumulation rate and the dynamics velocity based on the stress, temperature, and flow properties of ice, for the internal deformation, plus a component due to ice sliding. These velocities are compared to observed surface velocities in East Antarctica to assess the state of balance and the performance of the dynamics formulation.

A 2.2 m deep pit and the top 42.5 m of an ice core recovered at Snøfjellafonna, northwestern Spitsbergen, were continuously analyzed for Na+, Cl−, NO3−, SO42− and pH. Seasonal variations in ionic concentrations seem to have remained in the pit and the core, in spite of the relatively severe summer melting. We dated the core by counting annual peaks of Na+ and made an adjustment with the use of a tritium peak in 1963 as a reference horizon. It turned out that the depth of 42.5 m went back to the early 1930s or late 1920s. The 60–70 year record of snow chemistry showed that the concentrations of both NO3− and SO42− had increased in the 1950s and had decreased in the late 1970s and the 1980s. The increase would be explained in terms of anthropogenic inputs from the industrial areas. The later decrease of the same ions may have been caused by a combination of the reduction of the atmospheric precursors due to pollution controls and the meltwater-associated processes.

Summer profiles of sea-water temperature, salinity and flow were obtained on George VI Ice Shelf near its northern ice front. At each depth, temperature salinity and density show little variation between sites. Their respective variation to 250 m depth confirms a linear temperature-salinity dependence. This is the first place in the world where observations confirm precisely the form of the T-S diagram predicted for fresh ice melting in sea-water. Both tidal and residual flow are small, except at the western margin of the ice front, where a strong outflow is concentrated immediately beneath the ice shelf. The observations lead to a simple circulation model for the ice-shelf regime. Warm Deep Water flows southwards into George VI Sound, replacing the colder water that spreads northwards in the surface outflow. Thermohaline exchanges beneath the ice shelf determine the salinity profile, which itself provides evidence of upwelling. Estimates can be made of the basal melt rate of the ice shelf. The rates vary from around 10 m a−1 at the ice front to an average value for the ice shelf of order 1 m a−1. The average value is consistent with earlier estimates from surveys of ice-shelf strain.

A series of boreholes were drilled with high-pressure hot water across a section of Haut Glacier d’Arolla, Switzerland, in summer 1995. Twenty-three of the boreholes were profiled with a digital inclinometer soon aller drilling, and 14 were re-profiled up to 6 weeks later to determine changes in the longitudinal shape of boreholes with time. In addition to the main surveys, three boreholes were surveyed 14 times each to assess the accuracy and reproducibility of inclinometry measurements. These repeat surveys suggest that caution is needed in the interpretation of short-term borehole displacement measurements, and that the reoccupation of boreholes from one year to the next may be a better way to determine patterns of internal deformation and basal sliding. The annual scale may also have advantages in providing more long-term insight into glaciological processes than short term (single season) measurements.

The choice of the best protection system against avalanches on a particular path requires an accurate description, or image, of these avalanches. In order to get this image, avalanche consultants can use several numerical models which are often difficult to handle. Moreover, these models deal only with a part of the phenomena involved in avalanches and ignore the others. As a result, the consultants must use their experience and knowledge to imagine the avalanches on any particular path.

This paper presents ELSA (Etude et Limites de Sites Avalancheux), a computer system dedicated to the modelling of the knowledge of avalanche experts and to the integration of the new symbolic computer models with the classical numerical models. The basic aim of integration is to build a unique computer system incorporating all these models.

After a description of the terrain representation, we present the different scenarios that ELSA takes into account. Then, the methods which deal with some phenomena occurring in avalanches are described. The problems involved in the integration of these methods close this paper.

Field experiments were carried out to investigate a change in salinity of the snow cover on sea ice and of the snow ice. Snow which covered thin sea ice was flooded with the brine that was pushed out onto the sea ice surface, resulting in a rise in salinity to more than 32‰, which was higher than that of sea water. On the day after the salination of the snow, the flooded snow was found to have been either frozen into snow ice or kept unfrozen. In either case the brine was excluded in turn from the flooded snow. As a result, the wet snow or snow ice had a salinity somewhat above 20‰. It is suggested that subsequently the wet snow keeps the salinity at more than 20‰, while the salinity of the snow ice decreases gradually with time.

Uniaxial compression tests were carried out on fresh-water, isotropic, granular ice at a strain rate of 6 × 10−4 s−1. We investigated the effect of temperature (between −2 and −39°C) and grain-size (1 mm–8 mm) on the critical stress and strain at the initial crack nucleation. The amount of non-elastic strain at this event was estimated. The critical stress for initial crack nucleation increased strongly with decreasing temperature, following an Arrhenius law. It also exhibited a linear increase with dg−1/2 (where dg is the average grain-size). It is shown that the results cannot be explained by the purely brittle model of Sunder and Wu (1990). The results are interpreted in terms of grain-boundary sliding, controlled by the intrinsic viscosity of the boundary.

Deciphering the localisation of solid and dissolved impurities on the micron-scale in glacial ice remains a challenge, but is critical to understand the integrity of ice core records and internal deformation. Here we report on the state-of-the-art in microstructural impurity research by highlighting recent progress in bringing together cryo-Raman spectroscopy and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). We show the potential of both methods and discuss possibilities to improve inter-method approaches aiming for a more holistic understanding of the evolution of impurity localisation throughout the ice column, including post-depositional processes. In this framework, we elaborate on future research priorities such as LA-ICP-MS imaging on firn samples and integrating a large cryo-cell with imaging capabilities.

The surface of the Greenland Ice Sheet is darkening, which accelerates its surface melt. The role of glacier ice algae in reducing surface albedo is widely recognised but not well quantified and the feedbacks between the algae and the weathering crust remain poorly understood. In this letter, we summarise recent advances in the study of the biological darkening of the Greenland Ice Sheet and highlight three key research priorities that are required to better understand and forecast algal-driven melt: (i) identifying the controls on glacier ice algal growth and mortality, (ii) quantifying the spatio-temporal variability in glacier ice algal biomass and processes involved in cell redistribution and (iii) determining the albedo feedbacks between algal biomass and weathering crust characteristics. Addressing these key research priorities will allow us to better understand the supraglacial ice-algal system and to develop an integrated model incorporating the algal and physical controls on ice surface albedo.

Ice motion in the Weddell Sea is examined for the period 19 August (Day 232) to 12 October (Day 286) 1986 using the tracks of four Argos buoys deployed during the Winter Weddell Sea Project 1986 (WWSP 86). Two were SPRI/BAS buoys, launched in December 1985 and March 1986 in the south-east and north-west Weddell Sea. The others were part of a mesoscale array deployed in the Maud Rise area by H. Hoeber of the Meteorologisches Institut der Universität Hamburg, during the WWSP 86 cruise of FS Polarstern. The four buoys operated together for 44 d, comprising a basin-scale quadrilateral from which the differential kinematic parameters of divergence, vorticity, shear, and stretch were extracted, as well as the large-scale pattern of motion. It is found that most deformation episodes were associated with atmospheric forcing events.

Measurements at Wolverine Glacier, Alaska, from 1968 to 1988 indicate unsteady increases of air temperature and precipitation since the early 1970s. These increases were due almost entirely to changes in winter. Variations in annual temperature and precipitation at Wolverine Glacier and at Seward, a nearby climatological station at sea level, correlate positively with global temperature variations and are in general agreement with the changes at high latitudes predicted by five recent general atmospheric circulation models forced by anticipated rises of CO2.

A consequence of the air temperature and precipitation increases at Wolverine Glacier was a change to a generally positive mass balance after 1976. Although these observations in the coastal maritime climate of Alaska run against the common, oversimplified notion that in a warming climate glaciers will melt, causing sea level to rise, they are logical and easily understood when the sensitivity of the glacier to the seasonal distribution of the changes is considered. The observed seasonal changes at Wolverine Glacier also are in agreement with global climate models. Snow precipitation and glacier accumulation increased, but at the same time warming affected only these those temperatures below about −5°C, and melting was not altered. The extent of this response is not well known, but the process may be taking place in other important glacierized regions.

The stochastic relationships between terrestrial snow water equivalent (SWE) and measures of the atmospheric circulation were investigated for the Canadian Prairies and the American Great Plains for the winter of 1988. Snow-cover extent, derived from EASE-grid SSM/I satellite data, and griddcd atmospheric data from the National Meteorological Center were averaged at five day intervals. Principal components analysis (PCA) were performed for the time series of SSM/I snow-cover imagery as well as for 700 mb geopotential height and temperature, 500 mb height and 700–500 mb thickness. Canonical correlation analysis of the derived principal component weights was used to identify relationships between atmospheric variables and SWE. Results of the PCA indicate that a high degree of variance in upper air variables (>75%) can be explained by the first three principal components, while the first three SWE components account for over 90% of the variance in the original data. Results of the canonical correlation analysis show positive relationships between snow-cover accumulation and a meridional pressure distribution pattern, while snow ablation is linked to a zonal atmospheric pressure pattern.

The available experimental data on acoustic parameters and dynamic elastic moduli of dry coherent snow-ice formations in their whole density range are analysed and generalized in this paper. A set of critical densities at which there are sufficiently sharp changes in the laws of these property variations have been discovered and are discussed. The empirical equations describing the elastic-wave propagation velocities (Vp and Vs), acoustic resistivities and elastic moduli as functions of the porosity factor of the medium are obtained for five sub-ranges in the density range from light snow to massive ice.

Austdalsvatn in western Norway was regulated in 1988 as a reservoir for a hydropower development. From a pre-1988 water level of 1157 m a.s.l. the new water level will vary more or less annually from 1170 to 1200 m a.s.l. The outlet glacier Austdalsbreen calves into this reservoir. About 1600 m up-valley from its terminus the glacier flows over a bedrock riegel that is, at its lowest point, ∼ 15 m above the projected maximum lake level of 1200 m. As a result of the increase in water level, the surface velocity near the front has increased from about 0.07 to 0.13 m d−1.

Calculations suggest that the glacier terminus will retreat about 750 m in 50 years. The measured response of the glacier terminus for the first three years is in good agreement with the simulations.

A data collection platform was placed near the centre of a 950 m x 800 m near-rectangular iceberg in the Weddell Sea on 4 February 1979. Meteorological conditions and the dynamic behaviour of the iceberg were recorded for every three hours over a one-year period. The following parameters were measured: barometric pressure, wind speed and direction, air and snow temperatures, and iceberg heading, tilt, and strain. Platform elevation was 35 m a.s.l. corresponding to an iceberg thickness of about 210 m. The platform was deployed at lat. 70°5'S., long. 20°3'W, Figure 1 shows the iceberg drift and sea-ice conditions between 4 February and 4 May 1979.

Fig. 1.

Drift track of the iceberg for the period 4 February to 4 May 1979. The berg was surrounded by pack ice from about 6 March.

The tilt sensor was a Singer-Kearfott bubble-type two-axis electrolytic vertical sensing element mounted on a levelling platform. This was fixed on a 2.2 m long, 0.16 m diameter white-painted tube, which was tightly placed in a vertical drill hole in the firn, and frozen in by the addition of water (firn temperature was -5°C). The tilt sensor was level with the snow surface, and aligned so that tilt was measured along and across the main axis of the iceberg. The range of the tilt sensor was ±4.4 x 10-3 rad with a resolution of 3.7 x 10-5 rad (Bø and others 1979). The strain-meter consisted of a 1 m invar rod fixed at the passive end of the instrument to a mounting block and plate, and at the active end to the core of a linear variable differential transformer (LVDT), The LVDT body was mounted in a cage connected to a rezeroing system. The strainmeter was placed in a 1.1 m deep pit and fixed to vertical wooden posts placed 2 m deeper and frozen in. The range of the strainmeter was 1.2 x 10-3 and the resolution 10-7 (Bø and others 1979).

Tilt and strain were sampled 20 times at intervals of 6 sec. This measuring sequence was repeated every three hours. The data were stored and transmitted over the TIROS-N/NOAA satellite, which provided approximately 13 passes per day for transmission of data. Eight of these gave the location of the iceberg. Analysis has been carried out of the tilt and strain data from the instrumented iceberg for the period 4 Fébruary to 4 May 1979.

The glacial geodetic contribution to the mass balance and dynamics of ice shelves includes repeated determinations of the absolute position (ϕ,λ,Η) of selected points (using satellite methods), the establishment of relative positions (y,x,Δh) in deformation figures, and height measurements. The results are used to establish ice-flow velocities and directions, strain and rotation rates, and changes in height. Modelling of deformation parameters at a few points over a large ice shelf is made possible by the collocation method. Results of these observations and analysis of Ekström Ice Shelf for the period 1979–87 are reported.

Geostatistical methods are applied in the analysis of radio-echo data from Scharffenbergbotnen, Dronning Maud Land, East Antarctica, in order to allow the following investigations: detailed and reliable cartography of subglacial bed topography and ice thickness, comparison of recent ice flow patterns and ice flow during earlier glacial maxima, and mass balance studies in relation to climatic changes.

In experimental snowdrifting mass-flux measurements many different instruments have been tested (Takeuchi, CEMAGREE Mases, etc.). Very often the results obtained are a function of the gauge used. However, in order to compare data from different instruments, orders of magnitude have to be similar.

Since 1992, snowdrifting has been studied at an experimental plot at La Molina ski resort (eastern Spanish Pyrenees). The alpine site, characterized by a plateau topography, is located at 2250 m.

In this paper, different gauges used to measure snowdrifting mass flux at this site are presented: one snow-collector column and two types of snow traps. Snow-collector columns (prismatic boxes) are permanent installations and are used to measure the mass-flux episode. Snow traps (Takeuchi, 1980: modified) are lighter and more mobile, and they are used for short experiments during a wind episode during which mass-flux data are obtained.

The three different gauges are compared and the rate of trapping efficiency is suggested from a comparison of the field data with estimated mass-flux data deduced from empirical formulae (Mellor and Fellers, 1986; Naaim-Bouvet and others, 1996). The mass-flux values obtained at the experimental site are lower than the estimated values.

The surface radiation budget was continuously measured in the sea-ice zone between 140° E (Terre Adélie) and 180° (McMurdo Sound) close to mid-summer, when the sea ice is disintegrating. These measurements were carried out during a cruise of the USCGC Polar Sea from Hobart, Tasmania, to McMurdo station, Antarctica, in 1998/99. Some of the findings are: the solar radiation is the major atmospheric energy source for the melting of ice. The sun was above the horizon for 24 h for most of the cruise. Due to a high amount of fractional cloudiness, the global radiation was somewhat reduced when compared to areas with lesser cloud cover Mean noon values were around 400 W m−2, while at midnight a value of 30 W m−2 was measured. Daily mean values of the net shortwave radiation varied widely, a function of the reflectivity of the surface, which is strongly dependent not only on the ice concentration, but also on the ice type (e.g. whether it is covered with snow, flooded, melting or dry). Detailed ice observations were carried out. Hourly values of the albedo varied from 6% (open water) to 84% (10/10 sea ice with a dry snow cover). The mean net longwave radiation was only modestly negative. The high amount of fractional cloud cover increased the longwave incoming radiation from the atmosphere. A mean value of −40 W m−2 was measured, which displayed only a very weak diurnal course. The sum of the short- and longwave radiation, the total radiation budget, showed the expected diurnal variation, with slightly negative values at night (for 6 h), and a mean maximum at solar noon of around 220 W m−2. A mean daily value of 98 W m−2 was calculated.