Based on studies in the Antarctic Oceans, the contribution of the snow cover to sea-ice growth has become of major interest. Snow can result in upward ice growth in contrast with ordinary downward congelation growth at the bottom. A sea-ice study was conducted to verify the upward ice growth found in a previous study and to investigate the relation between sea-ice growth and radar backscattering signature. Sea-ice samples collected at four points in Lützow-Holm Bay, Antarctica, from 1998 to 2003 are analyzed. Analyses of snow-/ice-gauge measurements, snow depth and ice structure reveal an extremely large amount of upward ice growth of up to 1.0 m during one full year compared with a slight amount of downward growth. The upward growth was caused mostly by snow ice and to a lesser extent by superimposed ice. The salinity profile remained unchanged, although the ice survived the summer melt season. Characteristics of superimposed ice such as salinity, δ18O values and structure were obliterated during the summer, implying complete melting or dissolution of the superimposed layer. The ERS-2 backscatter showed a remarkable annual variation: It had a minimum value in midsummer and increased abruptly to a maximum value in late summer, then decreasing gradually in wintertime. The relation of the backscatter coefficient to the growth and properties of the snow cover and sea ice are discussed.

The word “lake” in the context of Antarctica has been used to describe both surface features (10–12 km in size) and areas of liquid water on the bedrock beneath the ice sheet (typically a few kilometres in size and at a depth of over 3000 m), There has been however only limited evidence for a relationship between the two phenomena.

This paper reports an analysis of Seasat altimeter observations of an extremely flat area on the surface of the East Antarctic ice sheet, approximately 30 km in extent, centred at 68.6°S 136.0°E and close to the edge of the sub-glacial Astrolabe Basin. It has a regional slope of between zero and 0.01° , and non-random variations in height along track of about ± 1m on the scale of a few kilometres. The average radar backscatter coefficient is 5±2 dB in the region of the Astrolabe Basin, compared to a more usual value of about 10 dB for other areas of the ice sheet. A computer enhanced Landsat image of the region clearly shows the rougher steeper terrain to the North, with the surface in and around the flat area appearing totally smooth and featureless.

NSF/SPRI/TUD radio echo-sounding data from the region, although limited in extent, shows a relatively strong signal (indicative of ice at the pressure melting point) over a large region. The signal under the flat area, however, is particularly strong and smooth, confirming the association between the surface feature and a bedrock lake 3800 m below.

Oceanographic data have been obtained from beneath the Ronne Ice Shelf at a site on the southeastern side of a sea-floor trough, the Ronne Depression. The data consist of 5 d of conductivity temperature depth (CTD) profiling and a long-term temperature record from a thermistor cable. The water column was found to be composed of two layers: a cold buoyant layer of lce Shelf Water (ISW) overlying a layer of unmodified Western Shelf Water (WSW).

A change in the water column was observed on the last day of profiling, the WSW layer thinning, a cold intrusion appearing directly above the WSW and the ISW becoming colder. In addition, on three profiles the ISW cooled further and increased in salinity, becoming apparently statically unstable. The temperature record from the thermistor cable confirms that the ISW layer occasionally becomes colder. with greater variation in temperature than seen on the CTD profiles. These low temperatures and high salinities arc interpreted as indicating that water containing ice crystals in suspension has been advected beneath the site.

This paper presents a small scale modelling of a snowdrift using activated clay particles.

Characteristic properties of activated clay particles, which are different from model snow particles proposed previously by other investigators, are fineness, high angle of repose and wide range of cohesion. Such properties may provide a similitude of a snowdrift and the phenomena caused by wet snow particles in a small scale model.

Experimental results presented in this paper show that activated clay particles are the most suitable substitute for natural snow particles in modelling, and indicate also the possibility of using them to model wet snow particles.

Twelve years of observation at Austre Okstindbreen, Norway, have demonstrated that the drainage systems of glaciers change with time, both between and within seasons. Random events indicative of instability have been recorded, and disruption of the glacier systems has preceded some outbursts from Kalvtjørna, the glacier-dammed lake. The results of dye-tracer tests suggest that, although discrete systems exist within the glacier, these vary between years. They also demonstrate that some of the water entering the glacier is stored temporarily as the capacities of the systems change. The chemical composition of river water emerging from Austre Okstindbreen differs from year to year, and it is found that both systematic patterns of variation and random deviations from them occur. Although waters of different origin mix within drainage systems, not all systematic patterns of isotopie composition are eliminated by this mixture; diurnal variations are superimposed on longer-term trends, which sheds light on drainage conditions. Between-year differences of within-season trends probably reflect changing spatial patterns of drainage. The general level of oxygen-isotope (δ18O) values of bulk glacier river water in a particular summer is much lower than the values of δ18O for old snow and glacier ice, and indicates the relative contribution of the base-flow component, which may be sustained either by accumulation-area sources or by water release from storage.

Fast ice flow on the Antarctic continent constitutes much of the mass loss from the ice sheet. However, geophysical methods struggle to constrain ice flow history at depth, or separate the signatures of topography, ice dynamics and basal conditions on layer structure. We develop and demonstrate a methodology to compare layer signatures in multiple airborne radar transects in order to characterize ice flow at depth, or improve coverage of existing radar surveys. We apply this technique to generate synthetic, along-flow radargrams and compare different deformation regimes to observed radargram structure. Specifically, we investigate flow around the central sticky spot of Whillans Ice Stream, West Antarctica. Our study suggests that present-day velocity flowlines are insufficient to characterize flow at depth as expressed in layer geometry, and streaklines provide a better characterization of flow around a basal sticky spot. For Whillans Ice Stream, this suggests that ice flow wraps around the central sticky spot, supported by idealized flow simulations. While tracking isochrone translation and rotation across survey lines is complex, we demonstrate that our approach to combine radargram interpretation and modeling can reveal critical details of past ice flow.

To exploit the high accuracy potential of laser ranging, suitable laser-altimeter calibration procedures combining laboratory and in-flight calibration steps are needed. Previous calibration schemes have limited the calibration process to flying over planar surfaces, and systematic errors remained in the system. In this paper we present a laser calibration algorithm that utilizes natural surfaces as calibration sites. This is especially important for calibrating systems in the interior of ice sheets. The proposed approach is demonstrated in calibrating the U.S. National Science Foundation Support Office for Aerogeophysical Research laser altimetry system. The results show a significant improvement in accuracy.

In this work, we study the size of the particles involved in a powder-snow avalanche. To determine this value, we study all the phenomena encountered by the particles before they arrive in the “body” of the avalanche. We study the boundary layer which is at the bottom of the avalanche. We determine, with the help of experimental data, the range of sizes of particles that can be entrained by the avalanche. We then examine the possibility of these particles reaching the top of the boundary layer and thus taking part in the avalanche. Our final result is that the typical size of particles suspended in a powder-snow avalanche is < 200 μm.

In the evening of 24 December 1789, 2100 km southeast of Cape Town and after encountering three icebergs, the HMS Guardian under Captain Edward Riou collided with the submerged foot of a large iceberg. Despite severe damage to the ship and its abandonment by many of its crew and passengers, Riou sailed the hulk back to Cape Town, arriving on 22 February 1790. From present-day research and field studies, the formation of the foot in the collision is consistent with the above-freezing seawater temperatures inferred from Riou's commentary. Further, the observed 60 m iceberg height suggests that it calved from the Filchner Ice Shelf in the Weddell Sea. Comparison of the positions of Riou's icebergs with historic sightings, satellite observations and iceberg drift and fracture models also shows that they originated in the Weddell Sea and that their likelihood of occurrence in the collision region is small.

Investigations into glacial changes, including understanding variations in the rates of glacial volume and surface-elevation changes, have increased over the past decade. This study uses historical glacier elevation data in the form of topographic maps from 1970 and a digital elevation model from the mid-1980s to calculate surface-elevation and volume changes for Ha-Iltzuk Icefield, southwest British Columbia, Canada. Results indicate that the icefield thinned at an average rate of 0.76±0.25 ma–1 during this period. A previous study of Ha-Iltzuk Icefield also using the geodetic method found a thinning rate of 1.0±0.20ma–1 between the mid-1980s and 1999, indicating a slight increase in the amount of icefield thinning. Within the ablation zone, thinning increased with decreasing elevation at a rate of 1.9±0.68 ma–1 km–1 between these two periods (1970 to mid-1980s versus mid-1980s to 1999). Analysis of meteorological data suggests that increases in both temperature and rainfall, as well as decreases in snowfall, likely contributed to the increased thinning rate.

An atmosphere–sea-ice model is used in combination with results from a coupled atmosphere–ocean–sea-ice model to examine the changes of the Antarctic sea-ice cover influenced by atmospheric circulation associated with the global sea-surface temperature (SST) changes alone over the past century. Using the current climatological SST of Reynolds for forcing, a reasonable seasonal simulation of the Antarctic sea-ice cover for the present climate (including ice concentration, thickness and coverage) is obtained. When global SST anomalies for the past century (derived from the coupled atmosphere–ocean–sea-ice model) are imposed, sea ice becomes more extensive, on the annual average, by 0.7-1.2° of latitude, more compact by about 5-7%, and thicker by 7-13 cm, than at present. These changes are similar to those simulated from changes in greenhouse gases using the coupled atmosphere–ocean–sea-ice model which gave corresponding changes of about 0.8° of latitude in extent, 6% in ice concentration and 12 cm in ice thickness. The simulated change in annual mean global surface temperature by the coupled atmosphere–ocean–sea-ice model was 0.7 Κ (0.6 Κ over the ocean including sea ice) which is similar to the observed change. Over the Antarctic the corresponding simulated change is 1.2 Κ which also appears compatible with observations.

In Antarctica, low-elevation (<1000 m) blue-ice areas (LEBIAs) may experience melt–freeze cycles due to absorbed solar radiation and the small heat conductivity in the ice. In some cases, LEBIAs can contain significant amounts of subsurface liquid water. Since the spatial extent of blue-ice areas depends on climatic conditions, they have been seen as good indicators of warming in Antarctica. A two-dimensional (x-z) model has been developed to simulate the formation and water circulation in the subsurface ponds. The model results show that for a reasonable parameter set, the formation of liquid water within the ice can be reproduced. Vertical convection and a weak overturning circulation is generated which acts to stratify the fluid and transport warmer water downward, thereby causing additional melting at the base of the pond. In a multi-year integration, a global warming scenario mimicked by a decadal-scale increase (3˚C per 100 years) in air temperature, leads to a general increase in subsurface water volume and changes in pond shape and depth. Even before melting at the surface is reached, heat that accumulates below a certain depth can no longer be removed during winter and leads to disintegration of the ice.

Accumulation rates in the eastern part of Ronne Ice Shelf were determined by isotopic stratigraphy (18O). The samples were taken from snow-pits dug during the Filchner I and II operations in 1984 and 1986. In general, the accumulation rate decreases towards the south; the greatest decrease, from 21.3 to 13.3 g cm−2 a−1, was observed between Filchner Station and measuring point 341, sited 270 km up-stream of the ice edge. The δ18O values of the near-surface layers vary between −25 and -29‰. The 18O content in the more southerly part is progressively depleted in the direction of Möllereisstrom, paralleling a decrease in the accumulation rate. Near the ice edge the 18O content decreases to the west. A 100 m ice core drilled in 1984 at point 340, 220 km from the ice edge, probably goes back to A.D. 1460; it has been dated by isotopic stratigraphy.

The accumulation rate up-stream of the drilling site was deduced from the sequence of annual layers, using a simple ice-flow model. The accumulation shows strong variations over the last 200 years, which may be caused in part by local variations in the accumulation on Ronne Ice Shelf.

All sources of cartographic, aerial photographic, satellite image, and related data, from the 18th century to the present, for the eight geographic groups of Iceland’s glaciers, were evaluated for use in preparing a preliminary inventory of Iceland’s glaciers, based on information requirements of the Temporary Technical Secretariat for World Glacier Inventory. On the basis of an evaluation of all sources of historic and modern data for the Langjökull Group, the 1:50 000 scale U.S. Army Map Service Series C762 maps of Iceland were determined to be the best maps from which to derive information for a preliminary inventory, as long as the limitations of these maps are considered and accommodated. The fluctuations of Langjökull’s principal outlet glaciers on maps and Landsat images were found to be consistent with field observations at the International Hydrological Decade monitoring stations. Accumulation area ratios were calculated from late summer snow lines on 1973 Landsat images of Vatnajökull (0.70), Langjökull (0.78), and Mýrdalsjökull (0.35), Measurements of the area of the now stagnant glacier on Ok showed a rapid reduction in area (68 per cent) between 1910 and 1960, but a decline in rate of wastage since 1960 (73 per cent between 1910 and 1978). From 1910 and 1945 topographic maps, the volume of the glacier on Ok was found to be reduced by 0.62 km3.

Ice-sheet modelling is an essential tool for estimating the effect of climate change on the Greenland ice sheet. The large spatial and long-term temporal scales of the ice-sheet model limits the amount of data which can be used to test model results. The geological record is useful because it provides test material on the time-scales typical for the memory of ice sheets (millennia). This paper compares modelled ice-margin positions with a geological scenario of ice-margin positions since the Last Glacial Maximum to the present in West Greenland. Morphological evidence of ice-margin positions is provided by moraines. Moraine systems are dated by 14C-dated marine shells and terrestrial peat. Three Greenland ice-sheet models are compared. There are distinct differences in modelled ice-margin positions between the models and between model results and the geological record. Disagreement between models and the geological record in the near-coastal area is explained by the inadequate treatment of marginal processes in a tide-water environment. A smaller than present ice sheet around the warm period in the Holocene (Holocene climatic optimum) only occurs if such a period appears in the forcing (ice-core record) or used temporal resolution. Smoothing of the GRIP record with a 2000 year average eliminates the climatic signal related to the Holocene climatic optimum. This underlines the importance of short-term and medium-term variations (decades, centuries) in climatic variables in determining ice-margin positions in the past but also in the future.

Summer melt is a primary source of mass loss on the Greenland ice sheet. An understanding of melt processes on the ice sheet, their connection with atmospheric processes, and the redistribution of meltwater is important for ascertaining the mass balance of the ice sheet. High-resolution radar measurements made in the percolation zone of the Greenland ice sheet reveal the evolving radar signature of summer surface melting and subsequent refreezing of meltwater. A traverse over the snow surface has resulted in the first radar map of snow stratigraphy over an extended distance. The dominant sources of back-scatter in the study area are the snow surface and effectively continuous annual ice layers. We suggest applications of our results to help define the extent of the percolation zone and to discriminate between regions where surface melt is lost to the sea and those where melt refreezes nearly in place.

A coupled atmosphere-sea-ice model is used to study the sensitivity of the Antarctic sea-ice distribution to oceanic heat flux (OHF). Remote sensing of sea ice from microwave radiometers provides data on ice extent and ice concentration. The ice-thickness data used are from ship-based observations. Our simulations suggest that OHF values of 0−5 W m−2 will cause sea ice to be too thick in the model. A value of 20−25 Wm−2 throughout the year causes sea ice to be too thin in the model. The model results indicate that a seasonally varying OHF is required to match the modelled thickness with observations. Values of 5−30 Wm with an annual mean of 10−15 Wm−2, give a reasonable distribution of sea-ice thickness. This agrees with the limited observations of OHF available for the Antarctic. The model results also indicate that the OHF should be varied spatially. When a seasonally and spatially variable OHF is applied to the coupled atmosphere-sea-ice model a still better simulation of the sea-ice distribution is obtained. Our results also suggest that the role of ice advection is very important in the determination of the sea-ice distribution, and it can be quantified by the model.

An integrated system for ice-fabric analysis on a Rigsby stage is described. The system consists of a regular Rigsby stage fitted with two opto-electronic sensors for assessment of azimuth and the tilt angle of each individual grain. Signals from the sensors are transmitted to a computer terminal via an interface box, which facilitates transformation of Gray-coded data to ASCII data records. The terminal is hooked up to a main-frame computer (VAX 750), where the digitized angles of the c-axis orientations of individual thin sections are stored in separate data files. These files are compatible with other already existing files containing additional ice-core data and thus become part of an extensive data bank. Appropriate software has been developed to produce, among other things, plots of c-axis orientations in a Schmidt net.

The impact of April sea-ice thickness (SIT) initialization on the predictability of September sea-ice extent (SIE) is investigated based on a series of perfect model ensemble experiments using the MIROC5.2 climate model. Ensembles with April SIT initialization can accurately predict the September SIE for greater lead times than in cases without the initialization – up to 2 years ahead. The persistence of SIT correctly initialized in April contributes to the skilful prediction of SIE in the first September. On the other hand, errors in the initialization of SIT in April cause errors in the predicted sea-ice concentration and thickness in the Pacific sector from July to September and consequently influence the predictive skill with respect to SIE in September. The present study suggests that initialization of the April SIT in the Pacific sector significantly improves the accuracy of the September SIE forecasts by decreasing the errors in sea-ice fields from July to September.

The continentality index is a good measure of the nature of the climate in a region, as it reflects not only the temperature but also the large-scale circulation. It correlates well with glacier mass-balance parameters. The climate along the west–east transect slightly north of the Arctic Circle across the Scandinavian Caledonides is governed by the prevailing westerlies; however, during winter the eastern part of the Caledonides is influenced by weather systems from the southeast. The differences in continentality meant by temperature and precipitation have a major impact on the response times of glaciers. The climatic change in this area has been dominated by increased summer mean temperatures (1910–20) and increased maritime influence since the 1980s. The slower-reacting glaciers on the Swedish side of the mountains are still adapting to the temperature increase at the beginning of the 20th century, and the increase in maritime influence gradually becomes less important towards the west. Thus, differences in the behaviour of glacier fronts along the west–east transect mirror differences in continentality.