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A new assessment is made of the possible range of responses of the Antarctic ice sheet to future global warming by performing a series of sensitivity tests to prescribed climatic forcing with an ice-sheet model. The model includes thermodynamics; it is three-dimensional, with 20 km horizontal grid spacing and 30 points in the vertical, and it treats the ice shelves explicitly. To obtain an appropriate initial present state for the ice sheet, it has been necessary to perform a series of simulations through the last glacial cycle with prescribed forcing including accumulation, sea level are less importantly climatic temperature. For the future climatic forcing, General Circulation Model simulations have been used with particular concern for the changes in the sea-ice cover and ocean warming. Effects of progressive changes have been examined with increases of basal-melt rates up to 10 m a1, surface annual mean temperatures by up to 7°C and surface-accumulation rates to double the present values. Without additional accumulation, the increased basal melt of 10 m a-1 would greatly reduce the ice shelves and contribute to sea-level rise of 0.3 m in 100 years and over 0.6 m by 500 years. The additional accumulation counteracts this to dive about zero change by 100 years and -1.2 m by 500 years.

A global energy balance model has been developed which includes an interactive mixed layer ocean, sea ice, and snow and ice cover on the land. A full annual cycle is included and the model provides a close simulation to the variation of surface temperature through the year over land and over ocean as a function of latitude. The present annual variations of sea ice and snow on the ground are also well simulated. The model has been used for a wide range of sensitivity tests which include variations of the solar constant, surface albedos, and the effects of feed-back, or absence of feed-back, in the reponse of the snow and ice cover. Studies have been made of the model’s response to the long term variations in the Earth’s Orbital characteristics such as changes in the perihelion, the obliquity and the eccentricity as well as various combined changes. Independent sensitivity studies of the response of the model to the presence of the large ice sheets in the northern hemisphere have also been carried out. A series of model runs have been performed to study climatic changes around the globe from 160 000 years Β.P. (Before Present) to the present. An examination is made of the impacts of the orbital changes alone, as well as with the feed-back from the large ice sheets.

Ice core and borehole studies along flowlines in ice sheets show that the ice crystal structure and flow properties evolve together with strain and rotation along the particle paths. Laboratory studies of initially isotropic polycrystalline ice show that the changes in crystal structure and flow properties of the ice sheets can be simulated by subjecting the ice to the same history of deformation, rotation and stress configuration undergone by the ice in situ. For isotropic ice the minimum creep rate dependence of stress and temperature is given for stresses 0.2–10 bars and temperatures −0.05 to −50°C. Tertiary and anisotropic flow rates are dependent on stress configuration, strain and rotation. Results for uniaxial compression and simple shear are presented. Other factors examined include crystal size, ice density, and the solid and chemical impurity content. Near the base of ice sheets large variations in stress and strain rate can occur. The formation of basal ice crystal structure is discussed, incuding the large crystal multi-maxima fabric ice and its flow properties. Shear rates from boreholes can be complicated by the complex local stress regime caused by bedrock variations. In the interior of ice sheets the relatively cold, stiff upper layers and warmer softer basal layers result in surface velocities which reflect the large scale average of the basal layer shear stress and temperature. An exception occurs approaching the grounding line where basal shear stress and normal stress decrease and sliding becomes dominant over internal deformation.

By 1969 considerable data had been collected over Law Dome from surface measurements. These included surface elevation, ice thickness, accumulation rates, ice movement and strain-rates, surface mean temperatures, and several temperature-depth gradients. Since then core drilling up to 380 m in depth has been carried out from the summit to the coast where the cores reached close to the bed. The bore holes have been concentrated on two main flow lines: one to Cape Folger and the other to Cape Poinsett. The bore-hole temperatures give a clear indication of the temperature distribution throughout the ice cap.Numerical modelling shows that the measured deep temperatures closely match the steady-state temperature distribution calculated from the present regime. The variations in the temperature profiles over the dome are primarily associated with the flow regime.The Cape Folger line has low accumulation rates and low velocities which results in positive surface temperature-depth gradients increasing towards the coast. By contrast the Cape Poinsett line has high accumulation rates and high velocities which result in a large negative temperature-depth gradient there. The profile at the Dome summit is close to isothermal primarily due to the high accumulation rates and lack of horizontal motion.

An analysis of snow compaction and hardness has been carried out to assess the prospects for preparation of a compacted snow runway for wheeled aircraft on Law Dome near Casey, Antarctica. Snow which successfully duplicates the in situ surface snow on the Law Dome has been made in the laboratory. Compaction, unconfined compression and California Bearing Ratio (CBR) tests have been performed on this laboratory-made snow. The CBR value of compacted snow depends strongly on its density. A pavement CBR value of not less than 10 is required by a wheeled C130 aircraft and this was achieved at a snow density of 0.6 Mg m −3 . If allowance is made for the scatter in the experimental data, then this requirement corresponds to an average CBR of about 15, and initially this can be achieved at a snow density of about 0.63 Mg m −3 for temperatures around −5°C to −10°C. The CBR strength of compressed snow increased with time after compaction. The temperature of the compacted snow did not influence the CBR strength of the snow as strongly as the density. However, snow is more easily compacted to high densities at higher temperatures. The pavement thickness required for C130 operation depends on the pavement CBR, the subgrade CBR and the acceptable wheel settlement. Calculations indicate that for a wheel settlement of 20 mm, a pavement CBR of 10 and a subgrade CBR of 3, a minimum pavement thickness of about 0.5 m is required.

Systematic knowledge of the mechanical properties of ice is a fundamental requirement for the solution of a wide range of problems in the earth sciences and engineering. Past research has been characterized by specialized studies, involving a variety of motivations and scientific disciplines, without much overall coordination. When the results of this research are synthesized, a reasonably coherent picture emerges, but there are major gaps in knowledge. From the deduced behavior of ice, and from informed speculation where data are lacking, a coherent plan for future research can be developed. This report summarizes existing knowledge and proposes experiments and test programs for a new research thrust. The studies that are proposed can be expected to yield significant benefits in glacier studies, ice engineering, and the mechanics of frozen ground.

A flow relation for the minimum strain-rates for isotropic ice is presented. This flow relation has been compiled from laboratory tests in shear and compression, and covers the temperature and stress ranges typical of natural ice masses. However, the ice in natural ice masses is mostly anistropic. Three cores drilled at Law Dome, Antarctica, are used as examples to illustrate some of the different anisotropies that develop in ice masses in relation to the stress configurations and accumulated strains. For the shear- or compression-stress configurations, anistropic flow rates can be derived as enhancements of the minimum isotropic flow rates for the particular stress, temperature, and stress configuration. For compression, this enhancement asymptotically approaches 3. For shear, the enhancement may be as high as 8. For combinations of shear and compression, further tests are required.

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.

The fundamental equation for the longitudinal stress and strain-rate gradient For ice masses with small slope (Budd, (1968)) has been derived exactly for any slope by Nye (1969) who shows that by using a variable longitudinal axis inclination, parallel to the surface, this equation takes on its simplest form. However for the integration of this equation along the ice mass to obtain stress and strain-rates it is necessary to use a fixed axis direction. Here the equation is derived generally for a longitudinal axis of arbitrary inclination, from which the relation between the expressions for the fundamental equation with respect to any longitudinal axis inclination such as parallel to the surface, parallel to the base or horizontal is readily discerned.An expression for the longitudinal strain-rate is derived to obtain the flow law from longitudinal stress and strain-rate measurements. A single “generalized viscosity function” is introduced to avoid the complication of both the power flow-law parameters varying with stress.

The analysis of steady-state flow over bedrock perturbations of Budd(1970[a]) is extended to evaluate the stress variations associated with the flow. In particular the four separate terms of the fundamental one-dimensional (longitudinal) stress equation (Budd,1968) are examined to show explicitly how the longitudinal stress gradientG, the base stressτ, the surface slope stresss, and the integrated second derivative of the shear stressTall vary over-a given wave.The result shows an error of a factor of 2 in some earlier studies relating longitudinal stress variations to the slope. This error resulted from the erroneous assumption that remains constant at its regional value. In fact the basal stress varies over the undulations in a similar way to the longitudinal stress gradient, and this is the same as the surface slope stress for long waves, but for short wavesor less) requires the addition of the fourth termT, which then becomes dominant.

The general distribution and number density of icebergs in the Antarctic is known from the work of Shil'nikov (2) and Nazarov (7). More recent studies of iceberg size distributions by Romanov (3) and Dmitrash (10) allow the volume distributions to be calculated. Assuming a steady state the flux of ice into the ocean from the Antarctic ice sheet implies a melt rate of the coastal icebergs. Further from the coast recent results from the EOLE-iceberg programme (Tchernia (4))allows the northward drift rates of icebergs to be estimated which together with a steady state distribution enables the average melt rates to be calculated. The temperature data of the Antarctic waters from Gordon and Goldberg (5) allows the calculated iceberg melt rates to be interpreted in terms of the temperature, time and currents at various distances from the Antarctic coast. The implications regarding the expected melt-rates of icebergs under tow to lower latitudes is investigated.

We are interested in studying the processes of sliding of ice over a variety of rock surfaces with the object of determining an empirical relation for the basal shear stress appropriate for glaciers. The variables to be considered include: normal stress Ν, shear stress Ƭ, surface roughness r, sliding velocity V, temperature θ, water at the interface, and the presence of debris. The roughness is considered to be a function of two variables; the scale or wavelength λ, and the shape or slope of the roughness a / λ, where ais the amplitude of the variations of that scale.

A general two-dimensional numerical model for a typical flow line of a glacier or ice cap has been developed which results in periodical surging for certain ranges of the input parameters. The input includes the bedrock and surface-balance profiles along the flow line, some three-dimensional parameterization depending on the cross-section shape and the flow-line patterns, the flow properties of the ice, and a numerical basal lubrication factor. The movie shows how a number of different ice masses grow from zero thickness to either steady state or a periodically surging state depending on the input. Typical examples of real surging ice masses from the small to the large are closely matched by the model in many effects such as the period, duration, and speed of the surges, as well as the length and thickness changes. A preliminary study for the surging potential of a flow line in east Antarctica is also made even though the full temperature modelling is not included. The results indicate that periodic surging of the ice sheet can develop in spite of the expected high viscosity. The resultant surface profile is very similar to the measured profile. For much lower viscosities steady-state, fast-sliding, ice-stream flow develops.

Extensive glaciological studies on the Amery Ice Shell have been conducted since 1962 by the Australian National Antarctic Research Expeditions (ANARE). Deep core drilling to the depth of 310 m was carried out in 1968 at the site GI on the shell in order to obtain the vertical ice temperature distribution and to collect ice cores over the whole depth of the bore hole. General core analyses have been conducted since 1970 under an Australia- Japan Cooperative Project in order to clarify the structure of the ice shelf in connection with its flow. It was found through these analyses that the Amery Ice Shelf consists of three layers of different origin, which are denoted the top, middle, and bottom layers. The top layer is formed by the in situ accumulation of snow on the shelf, the middle layer is glacier ice flowing from the Lambert Glacier, originating far inland on the Antarctic ice sheet, and the bottom layer is developed by the freezing of sea-water at the bottom surface. Numerical calculations were made of the formation processes of the three-layered structure of the ice shelf, in which the accumulation and the densification of snow at the top surface, the straining of the shelf, and the freezing of sea-water at the bottom surface were taken into account. The thicknesses of the top and the bottom layers at site G1 obtained from the present calculations agree well with (hose obtained from the core analyses. The freezing rate of seawater at the bottom surface of the ice shelf estimated from the temperature profile is approximately 0.5 m a-1. This considerable growth of frozen sea-water at the base of the ice shelf results in water flowing out from under the ice shelf being more saline and warmer than that flowing in.