Uniaxial compression tests were carried out with specimens cut from several deep ice cores obtained at Dye 3, Greenland, in 1980 and 1981. The power law relationship of = Αση was obtained between the uniaxial strain-rate and the uniaxial stress σ. In a range of strain-rates between 10−8 and 10−7 s−1, the value of the power n for samples with strong single maximum fabric was approximately 4, significantly larger than the value of 3 which has been generally accepted from experiments using artificial polycrystalline ice. A work-hardening effect was found in the ice-core samples taken from a depth of 1900 m, which had a smaller grain size than the others. Recrystallization occurred when the temperature of the specimen was raised during the test and this ultimately caused the formation of the so-called diamond pattern ice fabric.

Various types of sea-ice and snow-cover data are required for operational purposes in real time, for engineering assessments of associated hazards and for regional to global-scale modeling of the climate system. Data on the primary characteristics of ice and snow (extent, depth or thickness, and ice concentration) are becoming available to meet many present types of modeling requirement but secondary properties such as snow-water content, ridging intensity, open-water fraction and ice drift are less readily available.

Data for these major variables of snow and ice cover are considered with respect to problems encountered in obtaining and using digital information necessary for modern computer analyses. Such problems include the limitations of the basic observations (observational or sensor accuracy), the spatial and temporal resolution of different data sets, varying national practices of observing and reporting, and the problems of meshing data collected by different means and having spatial differences and temporal changes of observation time, site location, sensor system and resolution, etc. The relative reliability and climatic “information content” of some historical data sets are briefly examined and available digital data sets on modern global ice- and snow-cover conditions are described.

In order to study in some detail the variability of the 10Be concentration and its correlation with climatic parameters such as δ18O we have investigated 28 samples of the deep ice core from Dye 3, Greenland, covering the depth interval from 1 860 to 1 890 m which corresponds to the period 30 to 40 ka BP. The results show that the mean 10Be concentration during this period is higher by a factor of 1.7 than during the twentieth century and that there is a correlation between 10Be results and δ18O values. A possible explanation is that during cold periods (low δ18O values) precipitation rates are lower and therefore the number of 10Be atoms per gram of ice is higher. However, processes strongly related to δ18O values alone cannot explain the entire variability of the 10Be results.

Modelling temperature distribution in non-temperate mountain glaciers presents problems not normally encountered when modelling ice sheets or ice shelves. These problems are mainly concerned with numerical instabilities caused by the high, nonuniform gradients of various input parameters (geometry, mass balance, surface temperature, and flow velocity). Steady-state solutions must be used to check and complete data sets, before using models of greater complexity to calculate temperature fields in a more realistic way. Test runs with a computer model, which allows for true two-dimensional solutions and realistic velocity fields, are described for two examples from the Swiss Alps. These steady-state calculations illustrate, in a semi-quantitative way, that advection of cold ice by glacier flow strongly influences the temperature distribution in both an existing large valley glacier with a cold accumulation zone (Grenzgletscher), and a large piedmont glacier of the last ice age, around 18 ka BP (Rheingletscher). Non-steady-state models are being prepared and tested for future calculations.

The aim of the paper is (1) to develop theory to describe sea ice as a collection of finite-sized floes and (2) to construct a rheology based on this description.

Successful sea-ice models have considered the ice to be a two-dimensional continuum with a nonlinear plastic rheology, a two-dimensional yield curve being used to determine the internal ice stresses as functions of the strain-rate (Hibler 1979). In this paper, the shape but not the size of such a yield curve is derived from an idealized picture of floes as moving discs, randomly distributed in a plane. The expected collision rate, which determines the energy loss, is calculated in terms of the average floe size, the areal floe-number density, and the strain-rate. For the case in which the ice strength is low, the dependence of the energy loss upon the strain-rate implies a lens-shaped yield curve, the curved portions being parts of a sine wave. This compares with circular, tear drop-shaped and elliptical yield curves that have been used in sea-ice models to date (Coon 1974, Colony 1976, Hibler 1979). The applicability of the derived yield curve to cases where the ice strength is not low and significant ridging takes place, such as in a continuous ice cover is discussed.

The area of West Antarctica which drains into the Ross Ice Shelf is examined for the purpose of understanding its dynamics and developing a numerical model to study its reaction to environmental changes. A high resolution 20 km grid is used to compile a database for surface and bedrock elevation, accumulation, and surface temperatures. Balance velocities Vb are computed and found to approximate observed velocities. These balance velocities are used with basal shear stress and ice thickness above buoyancy Z* to derive parameters k2, p and q for a sliddinq relation of the form

Reasonable matching is obtained for p = 1, q = 2 and k2= 5 × 106 m3 bar−1 a−1. This sliding relation is then used in a first complete dynamic and thermodynamic velocity calculation for West Antarctica and for an improved simulation of the whole Antarctic ice sheet.

A discussion is presented of the elements of the sea-ice seasonal cycle which are significant in climatic description, and an annual cycle of measured microwave radiance is shown and discussed. Areas are defined where interpretation of spacecraft data could improve the seasonal picture of sea ice including snow cover, surface albedo, and ice production.

The isotope composition of ocean sediments is the chief data source for Pleistocene climatic changes. It is generally believed that the 18O/16O ratio of a sample indicates the global total of glacial ice at the time the sample was deposited. This is roughly correct, but numerous complicating factors limit the accuracy of the isotope proxies.

A 40 km line across George VI Ice Shelf was sounded in January 1981 by both radio echo and seismic reflection methods. Because the velocities of radio and seismic waves vary with ice density in different ways, an accurate comparison of travel times from the two methods allowed the average density of the ice shelf to be calculated.

A distinguishable echo from the base of the ice shelf was recorded at 22 out of 23 seismic stations. Continuous radio echo profiling was achieved in ice varying in thickness from about 200 to 350 m. The calculated mean densities fell into two groups, In an area where summer meltwater frequently floods the surface the average densities were around 0.915 Mg m−3, while in the drier areas the average densities were around 0.884 Mg m−3. Apart from this division, there was no apparent systematic variation of average density with position. The sounding was carried out approximately along a flowline on the ice shelf.

The variation of ice density with depth and position is difficult to allow for when modelling the deformation of ice shelves. Measured values of surface strain-rate, for example, may in some circumstances need to be corrected for effects due to the compressibility of snow.

Seven Magnavox MX1502 satellite receivers were used during the summers of 1980 and 1981 to obtain the coordinates of 22 stations in three locations on the Greenland ice sheet. Two of the receivers were located at stationary sites on the west coast of Greenland for both seasons. This allowed the short-arc method to be used to obtain relative coordinates with high precision. The stations were located at about 65° N, and positions on the ice sheet were obtained with formal accuracies of better than 0.20 m. From the coordinates, the station velocities, ice-sheet slopes, baseline lengths (between the stations) and strain-rates were calculated. Our results show that the two stations just to the east of the ice crest are not moving in the expected direction (north-east) but are moving in a direction slightly west of north. Hence, the positions of the ice crest and the ice divide do not coincide. The other stations are moving approximately as expected. No major velocity differences between, neighboring flow lines are apparent. The magnitudes of the maximum strain and the velocities increase away from the ice divide and with increasing slope.

Quaternary surface temperature and ice conditions have lowered today’s temperatures in the uppermost 1 to 2 km of the Earth’s crust in the Swiss plateau by about 5 to 6°C in regions of formerly temperate glacier beds, and these effects were even greater on temperatures in formerly periglacial regions. Effects of latent heat exchange during the formation and thawing of ice-rich permafrost in high-porosity sediments enhance the effects of heat diffusion in low-porosity rock. The influence of underground ice formation, however, seems to be limited. This is due both to the limited thickness of high-porosity sediments and to the fact that high post-glacial surface temperatures in the Swiss plateau shortened the thaw time of ice-rich permafrost which formed at the time of maximum glaciation (18 ka BP). The greatest effects of ice conditions in 18 ka BP may therefore be expected outside the plateau in Alpine valleys. Here, advection of cold ice through glacier flow may have cooled high-porosity sediments of considerable thickness well below 0°C.

Soviet plans to divert water from rivers flowing into the Arctic Ocean have led to research into the impact of a reduction in discharge on Arctic sea ice. We consider the mechanisms by which discharge reductions might affect sea-ice cover and then test various hypotheses related to these mechanisms. We find several large areas over which sea-ice concentration correlates significantly with variations in river discharge, supporting two particular hypotheses. The first hypothesis concerns the area where the initial impacts are likely to which is the Kara Sea. Reduced riverflow is associated occur, with decreased sea-ice concentration in October, at the time of ice formation. This is believed to be the result of decreased freshening of the surface layer. The second hypothesis concerns possible effects on the large-scale current system of the Arctic Ocean and, in particular, on the inflow of Atlantic and Pacific water. These effects occur as a result of changes in the strength of northward-flowing gradient currents associated with variations in river discharge. Although it is still not certain that substantial transfers of riverflow will take place, it is concluded that the possibility of significant cryospheric effects and, hence, large-scale climate impact should not be neglected.

A relatively simple, three-parameter model is used to simulate the annual precipitation (accumulation) distribution for the Greenland ice sheet and surrounding regions. The three parameters are (1) the flux of relative vorticity at the 500 mbar level (a measure of cyclonic activity), (2) atmospheric moisture content, and (3) surface terrain. The climatological (1946–79) precipitation distribution predicted by the model displays major features of the observed distribution derived from pit studies. However, the model suggests that, due to changes in storm tracks during this period of 33 a, accumulation distribution maps based on pit studies for varying periods of record may not be representative of a true mean for a uniform period of record. The model is then applied to reconstructed ice-age conditions. Compared to present conditions, accumulation reductions of 60¾ or more are indicated for much of the southern half of Greenland; only slight reductions are noted for northern Greenland.

The dynamic-thermodynamic model of sea ice due to Hibler (1979) has been adapted for simulations of the Baffin Bay pack. The simulations were carried out for wind fields characteristic of the more common synoptic situations for July, the ice conditions of July 1969 being taken as typical of this month to initialize the model. Average long-term currents were also used. The modelled ice characteristics were consistent with expected results for the forcing fields and rheology of the ice. A comparison of advectional ice losses through Davis Strait with the melt in situ shows the melt to be an order of magnitude larger. However, the melt alone cannot clear the ice out of Baffin Bay. It seems that the mechanism for this process involves a slow consistent melt coupled with a short period of northwesterly winds.

An important new sea-ice database is presently being created at the National Climatic Data Center in Asheville, North Carolina, USA. The data are digitized from weekly charts prepared at the US Navy/National Oceanic and Atmospheric Administration (NOAA) Joint Polar Ice Center and converted into a digital format prescribed by the World Meteorological Organization. The data cover both the Arctic and Antarctic for a ten-year period of record. The grid points are identified by earth coordinates and have a resolution of 15 nm or better.

This paper is intended to inform potential users of sea-ice data about the availability of the new data set. Topics covered are (1) data source, (2) brief description of the processing procedures, (3) the SIGRID output format, and (4) future plans.

Sensitivity experiments can be used to illustrate the response of the general circulation to prescribed changes in lower boundary conditions (such as ocean temperature) or external forcing conditions (such as solar radiation). The climatic record from the late-glacial and the Holocene provides examples for both types of prescribed change experiments. A number of general circulation model experiments have been carried out. These are reviewed.

At 18 ka 8P, orbital parameter values were very much like those of today, but the lower boundary conditions (ocean temperature, ice-sheet extent, etc.) were very different. The change in ocean temperature, and ice-sheet extent and thickness, were prescribed from the results of the Climate: Long-range Investigation Mapping and Prediction (CLIMAP) project.

At 9 ka BP, orbital parameter values were very different from present, leading to increased radiation in July and decreased radiation in January (compared to present). The North American ice sheet still covered a significant area, so that lower boundary conditions also differed from the present ones. The combined and individual effects of these prescribed changes on the general circulation are reviewed, particularly in the context of changes of the monsoon circulation.

At 6 ka BP, the solar radiation distribution differed from that of today in much the same fashion as at 9 ka BP, although the magnitude of the change was reduced. Lower boundary conditions were probably very similar to those of today.

A series of experimental results from 18, 9, and 6 ka BP are presented as “snapshot” estimates of the paleoclimate of those times. The results are based upon simulations with the community climate model of the National Center for Atmospheric Research.

A review of Byrd, Vostok and Dome C Antarctic ice-core records indicates significant changes in atmospheric characteristics between the late glacial maximum (LGM) and the Holocene. This data is relevant to general circulation model (GCM) boundary conditions and validation of output results. Reciprocally, GCM data could help to interpret ice-core results and to extend observed high-latitude changes to a larger scale.

During the LGM, low troposphere temperatures were colder by about 5 to 7°C and surface temperatures by 8 to 10°C over the Antarctic ice sheet. There are indications that snow accumulation was slightly lower and isotopic data suggests higher relative humidity over the ocean. A large increase in continental dust (up to a factor of 20) and marine aerosols (up to a factor of 5) is observed on the high Antarctic plateau, both explained by the increased (possibly up to 1.4 to 2 times) intensity of the large-scale atmospheric circulation modulated by desert and sea-ice area extension. Ice-core results show large changes in atmospheric CO2 concentrations with LGM values around 200 ppmv and “pre-industrial” values of about 260 ppmv. Finally, determinations of total gas content suggest that central West and East Antarctica were not thicker during the LGM, in contrast with higher surface elevations inferred from coastal-ice studies.

The dynamic state of the West Antarctic ice sheet has been termed the grand problem of glaciology. An attempt is presented to assess it by simulating the observed ice thickness and ice velocities along a cross-section from ice stream B (Ross Sea) to Pine Island Glacier (Pine Island Bay) with a numerical model developed from the one described by Budd and McInnes (1978). A kinematic analysis with topographical and regime data from various sources shows the mass fluxes observed near the grounding line of the Ross Ice Shelf to be of the order expected for steady-state balance. Deformation of the ice accounts for only a small fraction of the observed flow there. Simulations (to be described in detail elsewhere) with the Budd/McInnes surging mechanism can approximate the existing ice thickness as a post-surge feature but fail to reproduce the high balance velocities. Both these velocities and the existing ice-thickness profile are simulated successfully as a state of steady sliding, with parameterizations involving the ice thickness above that corresponding to buoyancy and realistically assumed longitudinal strain-rates. A range of results is presented to illustrate the sensitivity of the simulation to changes in various parameters.

The climatic influence of the land ice which existed 18 ka BP is investigated using a climate model developed at the Geophysical Fluid Dynamics Laboratory of the National Oceanic and Atmospheric Administration. The model consists of an atmospheric general circulation model coupled with a static mixed layer ocean model. Simulated climates are obtained from each of two versions of the model: one with the land-ice distribution of the present and the other with that of 18 ka BP.

In the northern hemisphere, the difference in the distribution of sea surface temperature (SST) between the two experiments resembles the difference between the SST at 18 ka BP and at present as estimated by CLIMAP Project Members (1981). In the northern hemisphere a substantial lowering of air temperature also occurs in winter, with a less pronounced cooling during summer. The mid-tropospheric flow field is influenced by the Laurentide ice sheet and features a split jet stream straddling the ice sheet and a long wave trough along the east coast of North America. In the southern hemisphere of 18 ka BP, the ice sheet has little influence on temperature. An examination of hemispheric heat balances indicates that this is because only a small change in interhemispheric heat transport exists, as the In situ radiative compensation in the northern hemisphere counterbalances the effective reflection of solar radiation by continental ice sheets.

Hydrologic changes in the model climate are also found, with statistically significant decreases in soil moisture occurring in a zone located to the south of the ice sheets in North America and Eurasia. These findings are consistent with some geological evidence of regionally drier climates from the last glacial maximum.

In the face of the faint young sun-climate paradox, the plausible effects of dynamical heat-flux feedbacks on global stability were examined using a coupled high- and low-latitude radiative-dynamical model. The global stability is found to depend very strongly on the vertical heat transport, which is also closely coupled to the meridional heat transport. This coupling and the associated dynamical heat-flux feedbacks, treated within the framework of the radiative-dynamical model, was found to produce a fairly strong negative feedback. Our results indicate that the dynamical heat-flux feedbacks inherent in the climate system may potentially enhance the global stability.