An ice sheet with fixed boundary conditions may have two steady configurations, as shown by a new one-dimensional model including the physics and continuity of ice, water, and deforming subglacial till. In one steady state, a steep surface slope causes rapid internal ice shearing but forces basal water through subglacial aquifers, suppressing basal velocity; in the other steady state, a gentle surface slope causes only slow ice shearing but allows water to lubricate the ice-bed interface and cause rapid basal velocities. Small climatic forcing may cause large ice-sheet response during a switch between steady states.

Recent warming has occurred in near-surface firn in central Greenland, as shown by analysis of a 217 m temperature profile from the GISP2 site. However, this warming falls within the range of natural variability and provides no clear evidence of a greenhouse signal.

With an airborne lidar, we have observed massive plumes of condensate particles rising from wintertime leads in the Arctic Ocean. Some of these plumes reached an altitude of 4 km; some extended over 200 km down-wind from their surface source. Here we invert the lidar equation and use lidar backscatter data to infer particle concentrations within two such plumes. Assuming that the plumes consist of supercooled water droplets of radius 5 μm, we estimate typical concentrations of 3–6 × 105 droplets m-3 just above the leads. Concentrations within the plumes can still be as high as 104 droplets m-3 at an altitude of 3 km and 200 km down-wind from some leads. Had we assumed that the plume particles are ice spheres of radius 40 μm, concentrations would be just 100 times less than these.

Temperature-depth measurements from two sites on Crary Ice Rise, Antarctica are analyzed to deduce the time the ice first grounded at each location. At the thicker site (480 m), the best estimate of the time since grounding is 1100 years. At the shallower site (369 m) the grounding is more recent, 580 years ago, and there is evidence that basal cooling was delayed for 450 years while water at the base was freezing. This analysis leads to the conclusion that Crary Ice Rise was formed by at least two separate grounding events and is not a remnant of a more extensive grounded ice sheet which occupied the present position of the Ross Ice Shelf.

We present a simplified numerical three-dimensional ice-sheet/ice-shelf model with a coarse horizontal resolution (100 km), designed for simulations of ice-volume changes on ice-age time scales (100 000 years and longer). The ice-sheet part uses the shallow-ice approximation to determine the flow, and includes a three-dimensional temperature calculation. The ice shelf is described in a quasi-stationary way. Ice-shelf thickness depends only on the thicknesses at the grounding line and the distances to the grounding line. The effect of the transition zone between ice sheet and ice shelf (assuming a width ≪100 km) is parameterized in terms of the ice thicknesses defined on the coarse grid. The characteristics at the base of the transition zone formally enter through a friction coefficient μ. We performed a series of sensitivity experiments with the coupled system, by integrating over 10 000 model years, starting from the present (modelled) state of the Antarctic and forcing the model by currently-observed accumulation rates. The position of the grounding line of the ice-sheet/ice-shelf model is quite sensitive to the choice of the friction parameter μ (in the range 0.025 > μ > 0.01). With μ = 0.05, the grounding line was maintained at the currently-observed position in the model.

Increased ablation under a greenhouse-effect climate is calculated by an energy-balance model for two sites at the margin of the Greenland ice sheet: Nordbogletscher, south Greenland, and Qamanârssûp sermia, West Greenland. The change in summer ablation is nearly linear with change in summer temperature, with gradients of 0.43 and 0.57 m water a−1 deg−1 for Nordbogletscher and Qamanârssûp sermia, respectively. However, the increase in ablation rate must be less in the higher parts of the ice sheet. A future climatic warming will therefore cause a rapid retreat of the ice-sheet margin and a steeper ice-sheet profile.

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.

Air-ice-ocean feedback mechanisms, which are not conventionally incorporated within either climate or glacial models, are investigated to illustrate their potential role in generating ice advance/retreat on the time scale of 103–104 years; i.e. for examining the internal causes for the ice oscillation.

Three main feedback loops are found from a coupled air-ice-ocean model developed in this paper: (a) ice advance → lower air temperature → ice freezing → ice advance; and (b) ice advance → higher ocean temperature → ice melting → ice retreat; (c) ice advance/retreat → modification of evaporation rate → change of ice accumulation rate and sea-level height → ice advance/retreat. The relative strength of the three feedback mechanisms determines the characteristics of the modes: growing or decaying, oscillatory or non-oscillatory. The solutions show the generation of growing oscillatory modes with the time scale of 103–104 years in certain parameter ranges.

This paper discusses some modeling results that indicate how the atmospheric response to the topography of the continental ice of the Last Glacial Maximum (LGM) may be related to the cold North Atlantic Ocean of that time. Broccoli and Manabe (1987) used a three-dimensional general circulation model (GCM) of the atmosphere coupled with a fixed-depth, static ocean mixed-layer model with ice-age boundary conditions to investigate the individual influences of the CLIMAP ice sheets, snow-free land albedos, and reduced atmospheric CO2 concentrations. They found that the ice sheets are the most influential of the ice-age boundary conditions in modifying the northern hemisphere climate, and that the presence of continental ice sheets alone leads to cooling over the North Atlantic Ocean.

One approach for extending these GCM results is to consider the stationary waves generated by the ice sheets. Cook and Held (1988) showed that a linearized, steady-state, primitive equation model can give a reasonable simulation of the GCM’s stationary waves forced by the Laurentide ice sheet. The linear model analysis suggests that the mechanical effect of the changed slope of the surface, and not changes in the diabatic heating (e.g. the high surface albedos) or time-dependent transports that necessarily accompany the ice sheet in the GCM, is largely responsible for the ice sheet’s influence. To obtain the ice-age stationary-wave simulation, the linear model must be linearized about the zonal mean fields from the GCM’s ice-age climate. This is the case because the proximity of the cold polar air to the region of adiabatic heating on the downslope of the Laurentide ice sheet is an important factor in determining the stationary waves. During the ice age, cold air can be transported southward to balance this downslope heating by small perturbations in the meridional wind, consistent with linear theory. Since the meridional temperature gradient is more closely related to the surface albedo (ice extent) than to the ice volume, this suggests a mechanism by which changes in the stationary waves and, therefore, their cooling influence at low levels over the North Atlantic Ocean, can occur on time scales faster than those associated with large changes in continental ice volume.

Numerous studies have shown that climate has varied between ice-free and glaciated states, with transitions often marked by abrupt steps. We summarize some modeling studies that have attempted to explain elements of the long-term trend and discuss a particular model for abrupt transitions that involves instabilities due to albedo discontinuities at the snow/ice edge.

The sensitivity of Arctic sea-ice thickness to the optical properties of clouds is investigated. Pollution aerosol has the potential to modify cloud optical properties significantly, which in turn could perturb the radiation balance at the surface of the pack ice. A one-dimensional thermodynamic model of sea ice is employed in this study. Radiative fluxes are parameterized in terms of integrated liquid (ice) water path and the particle effective radius. Results from these calculations show that, for a constant liquid (ice) water path, increasing cloud droplet concentration and the associated reduction in drop size results in a significantly altered surface radiation balance, contributing to an increase in sea-ice thickness. Considerable sensitivity has also been shown of the surface radiation balance to the frequency of occurrence and optical depth of lower tropospheric ice crystals that are present during the cold part of the year.

A one-dimensional time-dependent ice-sheet model is employed to simulate ice-volume variations throughout the Pleistocene epoch of Earth history. The model is based upon the explicitly-described physics of ice-sheet accumulation and flow and the physics of the viscoeleastic relaxation of the Earth under the weight of the ice load. The model of the viscoelastic relaxation of the Earth incorporates the vertical variation of density and viscosity of its interior in great detail. An abrupt variation of some of the parameters that govern the height of the ice-sheet equilibrium line, and a gradual increase in the strength of a generalized feedback mechanism that is turned on after mid-Pleistocene time, lead to simulation of ice volume that has the general features of observed δ18O records, in particular the new high-resolution oxygen-isotope record from site ODP 677 (Peltier and others, 1989).

Detailed 210Pb profiles were determined for four “Chernobyl dated” snowpits sampled during a wide-ranging survey of the Greenland ice sheet during the 1988 season. The profiles from widely separated pits show little or no coherence; even for two pits only 40 km apart the profiles differ in detail. There does not appear to have been any seasonality in the deposition of 210Pb onto the ice sheet in the two years since the Chernobyl accident. The total deposition of 210Pb during this period (10-20 bq m-2) was about 20 times less than has been observed at mid-latitude sites in the eastern United States. The three pits west of the ice-sheet divide recorded very similar depositional fluxes, while the one eastern pit had only two-thirds the average of the others, suggesting a west-to-east gradient in the deposition of 210Pb, and perhaps other continentally-derived submicron aerosols, onto the Greenland ice sheet.

We present a two-dimensional climate model to be used for basic dynamic studies on ice-age time scales (103 to 106 years). The model contains an ice sheet, where flow and temperature are calculated in a vertical plane, oriented in the north-south direction. The model ice sheet is forced by a zonally-averaged atmospheric energy-balance model, including a seasonal cycle and a simplified hydrological cycle, which specifies ice temperature and the mass balance at the ice-sheet surface. At the bottom of the ice sheet, the geothermal heat flux is prescribed. In addition, delayed bedrock sinking (or bedrock rising) is assumed.

A stationary state is achieved after 200 000 model years. This long time scale is introduced by the slow evolution of the temperature field within the ice sheet. Using reasonable parameter values and presently observed precipitation patterns, modified by ice-sheet orography, the observed thickness to length ratio (4 km/3300 km) of the Laurentide ice sheet can be simulated within a realistic build-up time (40 000 years). Near the ice bottom, temperate regions developed. They may have had an important effect on ice-sheet build-up and ice-sheet decay.

Over a distance of 150 km inland across British Columbia, glaciation level (altitudinal threshold for glacier generation) rises north-eastward from 1800 m near Jervis Inlet, to 2800m near Lillooet on Fraser River. The methods of Østrem (1966b) are revised for more detailed work from air photographs; inclusion of small but active glaciers gives a glaciation level some 200 m below Østrem’s from 1:250 000 maps, or 110 m below that from 1:50 000 maps.

Mountains which rise slightly above the altitudinal threshold invariably support glaciers only on their northerly slopes. Mountain crests need to be some 300 m higher before they support glaciers on most slopes: this defines an “all-sided” glaciation level. Since summit heights vary from 2500 to 2900 m through most of the transect considered here, east- and west-facing glacier sources are found mainly in the coastal half; south-facing sources are rare outside icefields.

For particular mountain ranges bounded by valleys and low passes, the aspects (azimuths) of glacier sources can be summarised by vector analysis. The higher the range rises above glaciation level, the more widespread the aspects represented and the weaker the resultant vector strength. Strengths as high as 90% are observed on landward ranges with a relatively sunny, continental climate, while 20-60% is found for coastal ranges where cloudiness reduces slope variations in incident solar radiation. Vector mean aspects throughout are close to north.

Perennial lee drifts on icefields show that wind directions during and immediately after snowfalls are from the south or from south-south-west. Together with orographic details of the glaciation level, this suggests that snow-bearing winds come from the south rather than the west. These winds reinforce radiation contrasts, giving north-south asymmetry of glacier aspect even near the coast.

A global model is presented that simulates zonal averages of stable isotopes δ(18O), δ(D) and precipitation rates at sea level. The model is empirical and uses as input zonal averages of evaporation, meridional water-vapour flux, air temperature, sea temperature, wind speed, relative humidity, sea-ice cover, and supersaturation in clouds as a function of temperature. The global model provides input to high-latitude regional solutions that are found integrating up assumed vapour trajectories, which need not be at sea level. Model precipitation rates, δ(18O) and δ(D), compare well to measured values on an annual and seasonal basis. The stable-isotope-temperature relation poleward of about 35° latitude as well as the isotope-precipitation relation in the tropics is simulated by the zonal global model. The Queen Elizabeth Islands stable-isotope pattern is given as an example of a regional solution of the model. Zonal moisture contributions for high-elevation sites are found to be different between northern hemisphere (Crête, Greenland) and southern hemisphere (Vostok, East Antarctica) with the southern high-latitude cold oceans making a larger relative contribution.

Sea-ice motion and dynamic thickness build-up play an important role in the transfer of heat between the ocean and the atmosphere and so must be included in large-scale climate studies. A “cavitating-fluid” approximation allows these dynamic processes to be parameterized in a simple way by ignoring shear and tensile strength yet retaining compressive strength. A simple procedure for approximating a cavitating fluid is presented here and is compared to the more complete viscous-plastic sea-ice model by performing several three year simulations with daily varying and monthly average wind forcing. Although differences exist on a monthly basis, the two models compare favourably over a seasonal cycle, particularly when compared to a thermodynamics only model in which ice motion is ignored. The lack of shear strength in a cavitating-fluid approximation makes it less sensitive to smoothing of the wind fields (as demonstrated by the monthly average wind simulations); however it also changes the detailed circulation and thickness build-up patterns somewhat. Overall, the cavitating-fluid approximation shows considerable promise for including sea-ice dynamics in large-scale climate models, especially where averaged wind fields are employed.

This study entails the parameterization, by means of a linear multiple-regression analysis, of the annual surface temperature and mass balance of Antarctica. The analysis was performed for the entire ice cap as well as for three separate regions: ice shelves (elevation less than 200 m), the interior (elevation above 1500 m), and the escarpment region in between. It was found that temperature can be parameterized very well in terms of elevation and latitude. The latitudinal gradient on the ice shelves can be explained by the super-adiabatic lapse rate along the surface and latitudinal temperature gradient in the interior, assuming adiabatic descent of air in the inversion layer from the interior region towards the coast and an axisymmetric spreading over the ice shelves. The surface mass balance can be parameterized reliably only in the interior, where it has a strong positive correlation with the saturation vapour pressure of the free atmosphere, and a significant correlation with the shape of the dome. The convex shape of the dome contributes to the mass balance by inducing subsidence of the relatively moist air of the free atmosphere into the inversion layer. This results in precipitation, as radiative cooling in the inversion exceeds adiabatic warming. An estimate is made of the annual horizontal and vertical advective velocities in the free atmosphere above the interior, based on regression results and a physical analysis of the precipitation processes in this region.

A temperature sensitivity analysis was performed for the current mass-balance distribution. For a 1 K. rise in surface temperature, the regression estimate of the increase in accumulation on the grounded ice sheet is equivalent to a rate of sea-level lowering of 0.2 mm a−1. This is about 30% less than estimates based on the current mass balance perturbated by the increase in saturation vapour pressure of the free atmosphere.

In 1987 an ice core to the bedrock at a depth of 85.6 m was drilled at the top of Høghetta ice dome in northern Spitsbergen. Chronology of the ice core was examined by tritium and 14C methods showing time gap at about 50 m depth. The age of three bottom ice samples was determined as 4150–5670 year B.P. by 14C method done for frozen bacteria colonies and a frozen petal. This chronology and negative bottom temperature of −9.4°C suggest that glaciers in Spitsbergen shrank considerably during the hypsithermal. The pH of melt-water samples lower than 5.0 corresponds well to large northern hemispheric volcanic eruptions during the last 300 years. Increase of acidity from 30 m depth to the surface may reflect the spread of air pollution to the Arctic during the past 200 years. On the basis of ice-core analyses on electrical conductivity, pH, chemical composition and air bubble pattern, climate and environment in Spitsbergen during the last 6000 years are discussed.

Evidence for climatic changes during the last 520 years was inferred from 18O content of a 100 m ice core from the Ronne Ice Shelf, Antarctica. The core was stratigraphically dated using seasonal variations of l8O content. The mean 18O content of the annual layers calculated on the basis of this dating decreases with depth z according to δ18O (‰) = −27.3 - 0.049z (m) and reflects first of all the decrease of the 18O content of the near-surface layers in the catchment area of the core from the drilling site 250 km to the south. This effect was corrected by assuming a linear decrease of the 18O content of the near-surface layers with increasing distance from the drilling site. Corrected δ18O values show a large scatter from year-to-year due to the local variability. The smoothed isotopic record displays variations in different time scales, which are caused most probably by climatological induced temperature variations. The gradient of 18O content with the 10 m firn temperature of 1.15‰/K found in the middle part of the Filchner-Ronne Ice Shelf was used to transfer the 18O series to a temperature record.