The equation describing the surface evolution of a large ice sheet is examined on the basis of a scale analysis applied to Antarctic conditions. Changes in the surface elevation are mainly driven by mass-balance fluctuations which approximately follow global atmospheric temperature variations. The essential spatial non-uniformity of the accumulation rate and the resultant difference between central and coastal regions in reaction time-scales are taken into account. The dynamic interaction of the time-lagging interior with the quasi-stationary margin is described. As a result, a simplified model is deduced to simulate the surface-elevation variations in the central parts of the Antarctic ice sheet caused by mass-balance perturbations corresponding to the main Milankovich cycles with the periods of 19–100 kyears. Special computational tests are performed to validate the model through intercomparison with the predictions obtained with a two-dimensional thermomechanical model. The sensitivity of the model to physical factors (represented by dimensionless tuning parameters) is discussed. Climatically controlled variations of the ice-sheet thickness in the vicinity of Vostok Station during the past 200 kyears are estimated.

Using significant technological breakthroughs and unconventional approaches, the goal of the in situ probing of glacier ice for a better understanding of the orbital response of climate (SUBGLACIOR) project is to advance ice core research by inventing, constructing and testing an in situ probe to evaluate if a target site is suitable for recovering ice as old as 1.5 million years. Embedding a laser spectrometer, the probe is intended to make its own way down into the ice and to measure, in real time and down to the bedrock, the depth profiles of the ice δD water isotopes as well as the trapped CH4 gas concentration and dust concentration. The probe descent is achieved through electromechanical drilling combined with continuous meltwater sample production using a central melting finger in the drill head. A key aspect of the project lies in the design and implementation of an efficient method to continuously transfer to the surface the ice chips being produced by the drill head and from the refreezed water expulsed downstream from the melting finger, into the borehole. This paper presents a detailed calculation and analysis of the flow rates and pressure conditions required to overcome friction losses of the drilling fluid and to effectively transport ice chips to the surface.

D 57 station in Terre Adélie lies between the coast and the central Antarctic plateau. A 200 m ice core was recovered in summer 1980–81 at this location and analyzed by an electroconductometric method to detect exceptional acid levels linked to fallout from major volcanic eruptions. Several signals were indeed found. The corresponding ice-core sections were then analyzed for mineral acids (H2SO4 and HNO3). We detected several large volcanic events, in particular two eruptions identified as Tarabora (1815) and Galunggung (1822). The background concentration of sulphate was found to be relatively low (about 0.5 μeq 1−1). On the other hand nitrate values were higher than at coastal or central Antarctic locations (except for the Sauth Pole). Two spikes were found in the nitrate profile at depths of 140 and 148 m. It is thought that they could be either linked to the 1604 and 1572 supernovae Kepler and Tycho or correspond to epochs of particularly high solar activities. With the aid of these sulphate and nitrate exceptional events, a dating of the D 57 ice core can now be proposed which corresponds to a mean snow accumulation rate of 22 cm of ice equivalent per year over the last four centuries.

Variation of the microparticle concentration in an ice core from Mizuho station, East Antarctica, does not show the annual cycle that has been demonstrated for ice cores from Antarctica and Greenland by other authors. Possible reasons for the lack of a annual cycle are considered and two causes are suggested. (1) Semi-annual variation of microparticle concentration as observed in drift-snow. The low particle concentration in March and in August to October is not due to minor particle transport, but to the dilution of microparticles transported mainly from arid regions in the southern hemisphere through the troposphere by falling snow. (2) Discontinuous surface-layer formation. A seasonal or an annual sequence of the variation in microparticle concentration in surface snow layers may be interrupted by the absence of surface snow-layer formation.

Small quantities of liquid water lining triple junctions in polycrystalline glacier ice form connected vein networks that enable material exchange with underlying basal environments. Diffuse debris concentrations commonly observed in ice marginal regions might be attributed to this mechanism. Following recent cryogenic ring-shear experiments, we observed emplacement along grain boundaries of loess particles several tens of microns in size. Here, we describe an idealized model of vein liquid flow to elucidate conditions favoring such particle transport. Gradients in liquid potential drive flow toward colder temperatures and lower solute concentrations, while deviations of the ice stress state from hydrostatic balance produce additional suction toward anomalously low ice pressures. Our model predicts particle entrainment following both modest warming along the basal interface resulting from anticipated natural changes in effective stress, and the interior relaxation of temperature and solute concentration imposed by our experimental protocols. Comparisons with experimental observations are encouraging, but suggest that liquid flow rates are somewhat higher and/or more effective at dragging larger particles than predicted by our idealized model with nominal parameter choices. Diffuse debris entrainment extending several meters above the glacier bed likely requires a more sophisticated treatment that incorporates effects of ice deformation or other processes.

We performed X-ray diffraction measurements on eight ice samples taken between 3200 and 3611 m depth of the Vostok (Antarctica) ice core to observe lattice distortions of ice crystals. Selected samples represent three distinct sections of the core: (i) glacier (meteoric) ice with well-preserved climatic record (down to 3310 m), (ii) ‘shear zone’ at the base of the glacier ice (3450– 3537 m) within which the climatic record is disturbed by ice deformation, and (iii) accretion ice formed by freezing of subglacial Vostok lake waters at the base of the ice sheet (from about 3537 m depth to the bottom of the core). The dislocation density decreases from 1012 to 108m–2 with increasing depth. In the accretion ice, lattice distortion tends to decrease with depth. However, the dislocation density does not reach a level typical for laboratory-grown columnar ice even at 3610 m. This reflects plastic deformation which accretion ice has undergone after its formation.

Measurements of a sample from ~580 m depth in the WAIS Divide (WDC06A) ice core reveal that bubbles are preferentially elongated in the basal plane of their parent grain, as expected if bubble shape preserves the record of dominant basal glide. This suggests that a method using bubbles as strain gauges could provide insights to grain-scale ice deformation. We introduce a technique using fabric and image analyses of paired thin and thick sections. Comparison of the crystallographic orientations of 148 grains and the shape orientations of 2377 intragrain bubbles reveals a strongly preferred elongation of bubbles in the grain basal planes (R2 = 0.96). Elongation magnitudes are consistent with a balance between ice flow deformation and diffusive restoration, with larger bubbles more elongated. Assuming bubbles record ice strain, grains with greater resolved stress on their basal planes from the far-field ice flow stresses show greater deformation, but with large variability suggesting that heterogeneity of the local stress field causes deformation even in unfavorably oriented grains. A correlation is also observed among bubble elongation, grain size, and bubble size, explaining a small but significant fraction of the variance ( P< 0.05), with implications for controls on ice deformation, as discussed here.

The spatial pattern of accumulation rate for eastern Kemp Land in the elevation range 1850-2700 m is presented together with observations of the physical parameters of snow temperature, average microwave emissivity (19 GHz, H polarization), distribution of depth hoar and firn-crystal diameter. The broad accumulation pattern in the region was found to be significantly low when compared to other coastal areas of East Antarctica such as Wilkes Land. The low accumulation regime is attributed to low atmospheric moisture transport and low penetration of synoptic cyclonic systems on to the coastal slopes. In the absence of high coastal precipitation, the accumulation rate is determined predominantly by surface snow redistribution processes. Attempts to determine accumulation-rate time series using visible layer, δ18O isotope and electrical conductivity stratigraphies were unsuccessful due to the relatively low coastal accumulation rates (less than 280 kg m-2a-1) and the complex modification of precipitation by redistribution processes.δ18O variations of seemingly cyclic nature observed throughout the cores were interpreted as a product of the snow-dune building and erosion processes, together with general redistribution of snows by the surface wind field, under the influence of mesoscale topographic roughness

The Tianger area in the Tien Shan preserves many glacial landforms to which several methods of estimating ancient equilibrium-line altitudes (ELAs) can be applied. Thus it provides the opportunity to compare different methods and evaluate the correlation between the methods and their errors. This comparison provides guidance in the application of these methods in other mid-latitude alpine glaciated areas. In this paper we calculate characteristic ratios relating to the ELAs, including accumulation–area ratio (AAR), toe–headwall altitude ratio (THAR), terminus–summit altitude method (TSAM) and Höfer value, and their correlations with each other and the geomorphological characteristics. The AAR of a glacier is small when the slope of the bedrock beneath it is small and the area is large, and the AAR of a glacier with such characteristics is better correlated with its THAR, TSAM and Höfer value. Paleoclimate information derived from these characteristic ratios relating to ELAs is discussed. The glaciers and the glacial climate of the early and middle stage of the last glacial are more continental than those of the Last Glacial Maximum (LGM). Compared with those of the LGM on the Qinghai–Tibetan Plateau and surrounding mountains, the ELA characteristics of the early and middle stage of the last glacial in the Tianger area show more continental features.

Ice sheets consist of several disjoint regions, each with physically distinct behavior. Parts are cold; others are temperate and either partly or completely saturated. Varying dust content, impurities, debris content, etc., may affect the ice flow. Usually, these regions are separated by material or non-material surfaces or boundaries. We use mixture concepts, involving the balances of mass, momentum, energy and entropy. When applied to regular domain points these concepts and appropriate constitutive postulates yield the field equations for the evolution of the constituents. When formulated in terms of singular surfaces, boundary and transition conditions emerge. Our presentation takes the form of an extended abstract of work that is presently under consideration (Hutter and Engelhardt 1988; Hutter and Engelhardt, in preparation).

Profiles of the ice cover in the North Water area were obtained in the winter of 1980/81 by using low-level infrared thermometry. The flight measurements were carried out from December to March. The statistical analysis of the sea ice surface temperature was carried out to yield distributions, frequencies and widths of fractures. Ice-free as well as ice-covered fractures with a maximum ice thickness of 0.4 m were analysed. Typical fracture frequencies were 0.25 per km for Lancaster Sound and 0.14 per km for Baffin Bay and the North Water area, with 90% of fractures being less than 0.6 km wide. From December to March, the fractures occupied 8.8% of the Ice cover in the North Water area, 8.7% along the Baffin Bay profile and 10% in the Lancaster Sound. In the North Water area the distance (y) between fractures for different fracture widths (x) is an exponential function of the form y=Aexp(ax) (A,a are constants), for fractures between 50 and 800 m wide. In the North Water area during winter, fractures of all widths occur 5 times more frequently than in M’Clure Strait and about 7 times more frequently than in southern Beaufort Sea. The heat loss in Lancaster Sound at the ice-air interface was found to be 40 to 100% larger due to the fractures compared to a fast ice situation in the same winter.

This paper presents a model of snow structure (model of regular grain packing) that is based on experimental determination of various geometrical characteristics of fine-, medium- and large-grained granular snow. Data analysis supports the possibility of approximating the ice-matrix configuration as a regular lattice of nearly spherical ice grains connected by rigid ice bonds. The model was successfully used for relating microstructural parameters of snow to snow density, compaction behavior and evolution of mechanical properties.

Experiments were performed on columnar saline ice prepared in the laboratory. Specifically, using a true multiaxial loading system, relatively large cubes (159 mm on edge) were proportionally loaded along three orthogonal directions; viz. perpendicular to (σ13 and σ22) and parallel to (σ33), the long axis of the columnar grains. The ice was strained at 10−2 s at −10°C where it behaved in a brittle mariner. Four sets of experiments were performed by setting the ratio σ22/σ11 to 0, 0.25, 0.5 or 1, and varying the ratio σ22/σ11 and σ22/σ11. Sections through the failure surface were then constructed. For loading along σ22 = 0, the confining stress did not significantly affect the maximum principal stress at failure. For loading along σ22 =0.25σ11, σ22 = 0.5 σ11 and σ22 = 0.5 σ11, the application of a moderate confining stress resulted in a large increase in failure stress. However, further increase in the level of the confining stress did not have a significant effect on the failure stress. The observations are presented in terms of a failure surface and are discussed in terms of the possible failure mechanisms.

Extensive internal melting (puddle formation) was observed on the sheet of fast sea ice near Ongle Island, East Antarctica in 1980. In late November that year, when surface melting was not seen, puddles did not form beneath snow cover with a hig albedo (0.7 to 0.8) but were present in bare sea ice with low albedo (0.2 to 0.3). Electro-conductivities of puddle water ranged from 3.3-6.6 mS/cm; these were higher than for drinking water from an iceberg or snow drift (below 0.9 mS/cm), but lower than for sea water (30-42 mS/cm). Puddle water is therefore considered to originate from the internal melting of sea ice, as a result of the internal absorption of solar radiation from the surface down to a certain depth. The mechanism of puddle formation is explained by numerical analysis of a differential equation of heat conduction, which includes the amount of heat evolved by the absorbed solar radiation.

Precipitation predictions from globai-climate models (GCMs) for the ice-covered Arctic Ocean and the ice sheets of Antarctica are among the most important aspects of the inferred response of the polar areas to climate change. It is generally recognized that the atmospheric hydrologic cycle, which includes precipitation as a key part, is one of the components of the climate system that GCMs do not handle particularly well.

The present-day atmospheric-moisture budget poleward of 70° latitude in both hemispheres, as represented by two versions of the NCAR (U.S. National Center for Atmospheric Research) community climate model (CCM1 and CCM2), is compared with observational analyses. The quantities examined on the seasonal and annual timescales are precipitation, evaporation/sublimation and atmospheric poleward moisture transport. The results are discussed in terms of the physiographic and climatic characteristics of both polar regions and how the particular models handle moisture transport: CCM1 uses the positive-moisture fixer and CCM2 the semi- Lagrangian transport. A particularly important test both for models and for observations is the degree to which the independently determined moisture-budget quantities actually balance. Deficiencies of both observations and models are discussed.

Gravity measurements were made with a very sensitive gravimeter in permafrost terrain containing massive ground ice and other segregated ice. Measurements were first taken along a line over undisturbed terrain where a road cut was to be made; a second gravity profile parallel to the first profile but laterally displaced from it by about 36 m was subsequently made along the edge of the roadbed after road construction. Data from pre-construction borings and a profile of subsurface soil and ice conditions, synthesized from information obtained during cutting, were used for ground-truth information and compared with the gravity measurements. The horizontal dimensions and locations of the deposits of ground ice embedded in the soil layer correlated reasonably well with the dimensions and locations of the lows in the gravity profile. However, the second profile, taken along the roadbed, also showed significant variation even after the usual types of gravity corrections were applied, suggesting that there are significant horizontal variations in the density of the topmost layers of the underlying bedrock (schist) through which the cut was made.

The density contrast of the undisturbed ice-rich soil as a function of distance along the first pro-file was estimated assuming the contrast was produced by infinitely long, transverse, rectangular blocks of given dimensions but unknown density. A set of equations dependent (to a first approximation) only on the unknown block densities was constructed from the corrected gravity data and solved by the Gauss-Seidel method. The maximum contrast for one block was found to be about 0.4 Mg m3 which gives a volumetric ice content of about 80% for the block, if the mean den-sity for all the blocks is taken to be 1.45 Mgg m3

A third gravity profile was made over an artificially-constructed ice mass with dimensions of 34 × 0.69 × 3.2 m buried at a depth of 1.2 m. This profile did not show conclusively the presence of the ice mass, partly because the anomaly it produces is close to the nominal limit of detection of the gravimeter.

It is concluded that large massive ground ice can be detected by means of its gravitational field using sensitive commercially-available gravimeters in conjunction with some ground-truth data. However, the application of such gravimeters to routine pre-construction investigations and terrain reconnaissance for ground ice is limited by their sensitivity and by the requirement for a stable measuring platform. At present, the gravity method and possibly impulse radar are the only non-contacting remote methods for obtaining an estimate of the excess ice in permafrost.

A mathematical model makes it possible to estimate the stability of soils in permafrost, the origin of different forms of underground ice, and pingo formation in several parts of the surface in the permafrost. The cryogenic formation of pingos, which is very widespread in permafrost areas, is investigated in the paper. The velocity and height of pingo growth depend on the total moisture content in soil, the type of soil, the initial salinity and the climate conditions. This problem is addressed using equations of Stefan’s heat problem, filtration and salt diffusion and equations for water pressure, with water moving to the phase boundary under different hydrostatic and osmotic pressures.

A method of determining the temporally varying “state” of the ice cover (the concentrations of three surface types: open water, first-year ice, and multi-year ice) is presented. The methodology is that of Kalman smoothing: a physical model and a measurement model are used to blend satellite passive microwave data and buoy data to give an optimal estimate of the ice state. The estimates are optimal only to the degree that model parameter values are known and assumptions about variances are met. Uncertainty about these values and assumptions, and lack of independent data with which to compare results,leaves self-consistency as the most important test of results. A four-year record (1979-82) of the estimated Arctic Ocean ice balance is presented and shown to be self-consistent. Results are discussed in terms of the Arctic multi-year ice balance, which may be an important factor in the interaction ofocean, sea ice and climate because of its relationship to the minimum summer ice extent. The estimated area of multi-year ice decreases each year, but the decrease is small and insignificant based on four years of results. Furthermore, the observed decrease may be due to instrument drift or changes in the multi-year ice signature.

In the 1979–80 field season, a site survey was carried out in the southern Weddell Sea for the construction of a wintering station. The survey comprised glaciological investigations on the Filchner and Ronne ice shelves, such as ice movement, deformation, ice thickness, calving, accumulation, and snow temperature measurements which are relevant to mass-balance studies. Along with the investigations on the ice, oceanographical and bathymetrical observations were carried out along the ice front. The field data and observations lead to assumptions about the advance of the ice shelf as well as about the mass loss at the frontal zone due to calving and bottom melting. The ice-front velocity at 50°W is about 1 070 m a−1 and the bottom melting is estimated to be 3.2 m a−1 at 20 km south-west of the ice front.

The behavior of Griesgletscher, Switzerland, is studied by application of a numerical model of temperate glacier flow. The analysis addresses the possible danger posed to a hydroelectric dam which is 600 m from the calving terminus of the glacier. Model parameters are adjusted to fit data collected over eleven years. A calving law relating the calving flux to the water depth at the front provides a good fit of the data. Assuming a continuation of the present climate, the terminus is predicted to retreat 200 m over the next forty years, followed by an advance of 150 m lasting several centuries. Numerous experimental climate alterations show that the dam will not be threatened by short-term climatic changes. A long-term mass-balance increase of 0.12 m of ice per year (or a drop of 0.2°C in mean annual air temperature) would be sufficient to fill the reservoir with ice. With an additional increase of 0.07 m of ice per year the terminus would reach the dam. Data from the 1923 and 1850 moraines are used to suggest lower-bound estimates of temperature changes (-0.4 and -0.6°C respectively) during these periods of glacial maxima.