A 3-D microphotographic method was developed to measure densities of snowflakes accurately. Microscopic observations and photographs were taken in the field. The volume of a snowflake which is an aggregate of snow crystals was estimated from the 3-D photo by polyhedron approximation. The weight of the snowflake was measured with an electro-balance. The density values obtained were compared with the degree of riming and the size of each snowflake. The results clearly show that riming is a prime factor in increasing the density of the snowflake. The density of a snowflake is not sensitive to the change of size of the flake itself, but depends slightly on the size of its constituent snow crystals. The technique developed here will be applied in the future to study of the density of falling snowflakes.

A dark layer (∼1 cm thick, 93.41 m deep) was identified in an ice core (116 m deep, covering the period -1350-1995) drilled at Styx Glacier plateau, northern Victoria Land, Antarctica. The ice-core section was dated around AD 1500 ± 20 by a firn-densification model. A chemical characterisation was performed on ten subsamples (resolution 3 cm) located around the dark layer by ion chromatography. The concentration/depth profiles of anions (Cl-, Br-, NC3-, H2PO4-, SO42-), cations (Na+, NH4+, K+, Mg*+, Ga2^) and some organic anions (acetate, formate, propionate and methanesulphonate (MSA)) indicate very high concentration peaks for all the components. However, non-sea-salt sulphate (nssSo/-) and F- show the greatest increase with respect to background values (370 and 860 times, respectively). A crustal contribution is attributed to Ga2+ and MSA. The profiles of gas-phase emitted substances (HF, HBr, HNOs and carboxylic acid) suggest gas emission just before the volcanic eruption. Chloride depletion is evident in the dark layer with respect to Na+/Cl- sea-water ratio. At present, it is not possible to attribute an unambiguous source to the volcanic event, but several pieces of evidence lead us to believe that this may be a time-limited local event.

The spatial pattern of glacier surface melt was measured with a resolution of 20–100m within a region extending 1 km up-glacier from the terminus of Rhonegletscher, Switzerland. The melt rate was monitored from 6 July to 6 September 2009 using 44 ablation stakes. We also measured the surface albedo near the stakes to investigate the importance of this parameter for the melt-rate distribution. The melt rate varied from 32.8 to 71.9 mm w.e. d–1 in the study area. Our measurements suggest that the spatial variation of the melt rate can be explained by (1) shading of the ice surface by neighbouring mountains, (2) surface albedo and (3) effects of microclimate (e.g. radiation from sidewalls) on the surface energy balance. The observed melt-rate distribution was compared to the results of a temperature-index melt model, which takes into account shading of direct solar illumination but not the other two effects. The model reproduces some important features of the field data, but its spatial variations are generally less than the measured values. Our study shows the importance of albedo and other local conditions in the accurate estimation of the small-scale melt-rate distribution.

An important component of models of the cryosphere is the calculation of accumulation rates over polar ice sheets. As a first-order approximation, many models rely on the assumption that temperature is the main controlling factor for precipitation. However, compilation of available ice-core data, including a new core from Taylor Dome, East Antarctica, suggests that precipitation is significantly decoupled from temperature for a large proportion of both the Greenland and Antarctic ice sheets. While the estimated glacial-to-interglacial change in temperature does not differ greatly among ice cores from each ice sheet, the estimated change in accumulation rate varies by more than a factor of 2. A simple vapor-pressure parameterization gives reasonable estimates of accumulation in the ice-sheet interior, but this is not necessarily the case close to the ice-sheet margin, where synoptic weather systems are important.

Snow and ice played important roles in determining the occurrence and timing of pH depressions in the shallow (∼1 m) nearshore waters of a small lake of the Canadian Shield. The influences of the terrestrial snowpack and lake-surface snow on the chemical composition of under-ice water were distinctly different. On land, acidic meltwater from snow was enriched with lithological elements in the soil/litter layer during lateral movement to the lake shoreline. The resulting run-off water was of relatively high ionic strength (X conductivity 55 μS cm−1), low pH (X 4.1) and contained high concentrations of Al (X 1786 μg 1−1), an element potentially toxic to aquatic biota. Snow cover on the ice surface controlled thermal conditions in the underlying water, dictating the depth to which run-off water penetrated. Uniformly cold conditions (<2°C) allowed penetration of run-off water to the substrate while under-ice warming to 4°C resulted in surface layering of less dense run-off water. flooding of the ice with lake water and melting of the ice and snow-surface cover served to counteract the effects of the run-off water through dilution.

A georesistivity survey was made on part of George VI Ice Shelf (71°55'S, 67°20'W). The principal objectives were to determine the electrical structure of the 1ce shelf, in particular how refrozen melt water differs in electrical behaviour from dry firn, and to Investigate the environment beneath the ice shelf.

Apparent resistivity profiles using a Schlumberger electrode configuration have been interpreted using Ghosh's convolution method for vertical electrical sounding (VES), adapted for use where extreme resistivity contrasts are present.

Warm, wet surface conditions tend to reduce the gross resistivity of shallow permeable layers. The electrical results indicate that the refrozen free water has affected the resistivity only indirectly; the mean density of firn is raised to about 0.915 Mg m−3 within the uppermost 10 m of the ice shelf at which point the resistivity is comparable to that of Ice of the same density but formed by compaction of firn. The apparent resistivities in the top 100 m reflect the variation of density with depth; a small range of resistivities implies that the range of density 1s narrow and that densification is affected by the percolation and refreezing of melt water.

The bulk of the ice behaves as if resistivity either Is independent of temperature or has only a slight dependence (activation energy ~0.15 eV) with a basal melting rate in excess of 1 to 2 m a−1. The principal resistivities determined for two sites on George VI Ice Shelf were within 10% of those at station BC on the Ross Ice Shelf, allowing for differences in temperature. This Indicates that polar ice, I.e. non-temperate ice, has a very narrow range of resistivity. The apparent resistivity profiles are consistent with there being sea-water of oceanic salinity under the Ice shelf.

Continuous profiles of deuterium excess, d = δD − 8δ18O, in the snow-pack have been measured at continental, high-elevation stations: Dye 3/4B (2480 m a.s.l.) in southern Greenland, and Site G (3110 m a.s.l.; 70 km south-east of Crête) in central Greenland.

Figure 1 shows the δ18O and the d profiles along the upper 4.3 m of firn at Site G. These profiles represent the snow accumulation from late 1974 to mid-1985, judging from the clear seasonality in the δ18O record. There is also a seasonality in the d values, which generally range from +5 to +12 ‰. In contrast to the findings at low-elevation stations, the two seasonal cycles are not in antiphase; the d curve lags the δ18O curve by only approximately 90°. These same features appear when plotting similar data from Dye 3.

Modelling of the data proceeds in three steps. First, the isotopic composition of vapour evaporating from an oceanic source area is calculated on the basis of Merlivat and Jouzel’s (1979) model, which takes kinetic effects into account. Secondly, the vapour is advected to the ice sheet, without mixing with vapour from other sources. Any liquid precipitation is assumed to be formed by a Rayleigh condensation process down to −5°C. Thirdly, the snow formation at lower temperatures is modelled, taking account of kinetic effects due to supersaturation of vapour with respect to ice (Jouzel and Merlivat 1984).

The result of this modelling is that the initial mixing ratio (wso; g H2O/kg dry air; data from IAEA/WMO) largely determines the change of d in the precipitate as δ18O decreases during cooling. Furthermore, the absolute magnitude of the deuterium excess is mainly determined by the sea-surface temperature (Ts) in the source area.

The combined result of these effects is shown in Figure 2, the upper part of which applies to a high-latitude source region (Weathership A at 62 °N, 34 °W), and the lower part to a mid-latitude source region (Weathership E at 35 ° N, 48 ° W). dvo is the deuterium excess of the parent vapour as it leaves the source area; dpo is that of first-stage precipitation predicted by the model, and dp is the predicted deuterium excess in the precipitate at Site G.

In the high-latitude case, dvo and dpo have pronounced summer minima and winter maxima. As the cooling proceeds (until the observed δ18O values at Site G are reached), this cycle is inverted so that at Site G the model predicts maximum dp in August and minimum dp in January, and deuterium excesses on the ice sheet which are far too low (cf. Fig. 1). This is true regardless of the choice of parameters for the model.

In contrast, starting with vapour from a mid-latitude source (such as the Weathership E area), the model predicts for Site G a maximum in September and a minimum in March, with values of 14 and 4‰ respectively.

The latter results are in good agreement with the observations at Site G (Fig. 1), and also with those at Site 4B, in respect of the annual mean as well as the seasonal amplitude and the phase.

We conclude that, in contrast to polar low-elevation stations, the ice sheet receives precipitation from moisture which originates predominantly from much lower latitudes. The moisture has probably been carried northward at considerable altitudes by the cyclonic conveyer belts, and is thus more or less separated from the ocean surface at an early stage.

A more complete description of the model will be submitted to Tellus in the near future.

Results from deep Greenland ice cores show rapid changes in several parameters in the deepest part. The most probable explanation for these variations is a fast-changing climate during part of the last glaciation. The question arises, however, of whether the observed changes in the ice cores could also be due to, or at least be influenced by, discontinuities in the stratigraphy. We present new CO2 and δ18O data from the Camp Century and Dye 3 deep ice cores. The data show rapid changes in CO2 and δ18O in both cores. One transition which was investigated in detail seems to be more rapid in the ice core from Dye 3 than in the Camp Century core. The broadening of a sharp δ18O transition due to molecular diffusion is discussed. Since this broadening is larger than the observed width of the transition, we discuss the possibility of a mechanism that can produce stratigraphic disturbances on a small scale. This mechanism is based on a calculation of the compression of horizontal layers which have equal density but different viscosities.

North Water is situated in the high Arctic between Greenland and Canada (74°-79°N, 70°-78°W) The sea surface of this region has no homogeneous ice cover during the winter and spring months, due to the occurrence of polynyas

The results of the heat balance and the airborne remote sensing over North Water during winter are reported The heat balance investigation was concerned with the identification of heat sources and their magnitudes The remote sensing was aimed at determining the sea surface temperature and clarifying the exact nature of the surface of North Water in winter

North Water was found to be mostly covered with new and young ice and probably devoid of first year ice until March The surface was about 20 °C warmer than that of the surrounding fast ice The warmest areas were frequently located in Smith Sound, Lady Ann Strait and around the Carey Islands Open water patches above freezing point, ranging from -1 5°C to -0 1 °C were often found along the west coast of Greenland

The surface of North Water receives heat from the sea water during winter between October and March at the rate of 15 MJm^d”1 of which 80% and 20% are from enthalpy contained in sea water and latent heat of fusion released as the surface water freezes, respectively. The basic difference in winter heat balance between North Water and other ice covered arctic seas is the magnitude of the enthalpy supplied by the seawater which is 9 MJn-2d-1 larger for the North Water This is the main heat source, which keeps the surface from becoming solidly frozen

The interannual to interdecadal variability and space–time statistics (including radius of decorrelation) of the Antarctic surface mass balance (SMB) are evaluated from climate models and meteorological analyses. At model resolution scales (>100 km), the interannual relative standard deviation of precipitation ranges from ∼5% (remotest interior) to ∼40% and possibly more. Time variability is spatially coherent at distances of ∼500km on average, less than 300 km in the interior near ridges, but in excess of 700 km in some regions. As far as spatial distributions are concerned, interannual statistics can be broadly transposed to interdecadal time-scales. The amplitude of variability may also be extrapolated across time-scales, using a ‘white’ spectrum hypothesis according to one coupled ocean– atmosphere model, but a significantly ‘red’ spectrum hypothesis according to another. Surface sublimation and blowing-snow processes are estimated to have limited contributions to the statistics of the SMB at model-resolved scales. Precipitation statistics can thus largely be transposed to SMB. The information reported here is expected to be useful for defining the details of field programmes such as the International Trans-Antarctic Scientific Expedition (ITASE), for extrapolating the spatial significance of field SMB data and for better interpreting Antarctic ice-sheet surface elevation changes from satellite altimetry.

The brine infiltration zone of Mc Murdo Ice Shelf, Antarctica, has been extensively studied by previous authors. Brine percolates inland laterally from the ice front, opposite to the direction of ice-shelf motion. Inland propagation of brine pulses following ice-shelf break-outs appears to be the primary brine-infiltration mechanism. During the 1992-93 field season, we used radio-echo sounding to resurvey the inland limit of the brine-infiltration zone. The boundary had been similarly mapped in 1977. We observed that since the earlier survey, one 7km section his retreated seaward by approximately 800 m while another 5 km section is unchanged. These displacements are consistent with the earlier hypothesis that brine infiltration occurs by the influx of brine pulses

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.

Tabular (massive) ground ice in periglacial areas of the Russian Arctic (Barents and Kara Sea coasts) is considered to be a remnant of past glacial epochs and is thus used as proof of the glacial extent. In this paper, we argue that the origin of these tabular ice bodies, which can be used as archives of specific climatic conditions and periglacial environments, is intra-sedimentary (migration/intrusion). The objective of this study is to establish geochemical benchmarks describing the ice formation from atmospheric moisture and compare them with geochemical data of tabular ground ice. Shokalsky glacier on Novaya Zemlya (NZ), on the east coast of the Barents Sea, was chosen as a possible moisture source for the formation of tabular ground ice at the key section ‘Shpindler’ on Yugorsky peninsula, on the south coast of the Kara Sea. Tabular ice in the Shpindler section was compared to the Shokalsky glacier ice in both isotope/geochemical and structural aspects. In general, the hydrochemical properties of glacier ice at NZ and ground ice from Shpindler are closely correlated, while stable-isotope, microelemental and microbiological properties are substantially different. It was concluded that glacier ice most likely participated in the formation of tabular ground ice, but only as a source of refrozen meltwater.

To investigate the environmental and climatic significance of the ice-core records from the Tien Shan, central Asia, the characteristics of ionic concentration and oxygen isotopic ratio (δ18O) as well as their variability are assessed from surface-snow samples as well as old-snow samples collected year-round at weekly intervals from November 2002 to October 2005 on Ürümqi glacier No. 1, eastern Tien Shan. The results indicate that the δ18O in surface-snow samples is reversely coincident with air temperature and insignificantly affected by post-depositional processes. Ionic concentrations in the wet-season (1 November to 31 March) snow are overall higher than those in dry-season (1 April to 31 October) snow, while the variability of relative ionic composition between dry seasons is slightly less than that between wet seasons. During dry seasons, surface-snow chemistry was mostly controlled by the chemical content entrained in some sporadic precipitations. When precipitation is absent, the effect of all post-depositional processes together elevated the ionic concentrations in surface snow. During wet seasons, the snow chemistry is determined mainly by the input of aerosols entrained in precipitation and the elution process from percolation of meltwater.

Observed and modeled sea-ice motions, combined via an optimal-interpolation assimilation method, are used to study two synoptic events in the Arctic. The first is a convergence event along the north Alaska coast in the Beaufort Sea during November 1992. Assimilation indicates stronger convergence than the stand-alone model, in agreement with Advanced Very High Resolution Radiometer-derived ice motions and Special Sensor Microwave/Imager-derived ice concentrations. The second event pertains to ice formation and advection in Fram Strait and the Barents and Greenland, Iceland and Norwegian Seas. Assimilation indicates export of thick, less saline ice out of the central Arctic into the East Greenland Sea. However, the model indicates little flow through Fram Strait, instead showing strong flow of thin, more saline first-year ice from the Barents Sea westward into the Greenland Sea. These results indicate that assimilation is a useful tool for investigating synoptic events in the Arctic and may be useful for both climate studies and operational analyses

Mapping the topography of the Antarctic ice sheet has confirmed that there is, typically, a decrease in the wavelength and increase in the amplitude of surface undulations with distance from ice divides. This pattern is distorted by converging ice flow in coastal regions and by other variations in subglacial relief, ice velocity, and viscosity. The near-symmetry of undulations indicates the extent of three-dimensional flow over bedrock peaks. Spectral analyses indicate the greater response of the ice sheet to bedrock features with longer wavelengths. This is affected, and in some cases dominated, by the inhomogeneous and non-isothermal nature of the ice sheet.

The perennial ice concentration in the Beaufort Sea was examined using active- and passive-microwave observations. We compared the ice type and concentration estimates from SSM/I and ERS-1 SAR data over a seasonal cycle from January 1992 to January 1993. It was found the multi-year (MY) ice-concentration estimates from the SAR data were very stable and were nearly equivalent to the ice concentration estimated at the end of the previous summer. We contrast this with the variability of the MY ice-concentration and ice-fraction estimates obtained using the NASA Team algorithm. The passive- and active-microwave algorithms provide total ice concentrations that are comparable during the winter, hut the passive estimates are significantly lower during the summer. Passive-microwave estimates of multi-year-ice concentrations are consistently lower (up to 30%) than those from the SAR data. We discuss reasons for these discrepancies and the possible biases introduced by the active and passive algorithms.

We use a time-dependent ice-cap model to predict the pattern of growth and decay of the Patagonian ice cap during a simulated glacial cycle. The purpose is to illuminate the internal system dynamics and identity thresholds of stability related to the underlying topography. This is a necessary step if former ice-cap behaviour is to be linked to climatic change. The model, which is fully described elsewhere, portrays ice extent and surface altitude at intervals of 1000–5000 years. The modelling suggests that there are two stable ice-cap states largely influenced by topography, namely, the present distribution of upland ice fields and the long, linear ice cap along the Andes as represented by the Last Glacial Maximum. Both states can coexist in equilibrium with a climate similar to that of the present day. There is a third, larger variable state in which a more extensive ice cap extends into the adjacent plains, as occurred during early Quaternary glaciations. Warmer and/or drier conditions are required to remove all these ice caps. There are five ice centres during ice-cap growth.

Investigations of the stratigraphy and facies within a 2.69 m long gravity core (PS1423–2) from the southwestern Weddell Sea, Antarctica, indicate a significant change in the character of glaciomarine sedimentation since grounded ice withdrew from the continental shelf. Based on visual description, X-radiography, clast shape, particle-size analysis, physical properties and geochemical data, the core used in this analysis comprises five distinct units, from top to bottom: (i) massive diamicton, (ii) weakly to well-stratified diamicton, (iii) millimetre-scale laminated muds, with little or on coarse-clastic input, (iv) well- to weakly stratified diamicton, (v) massive diamicton. This succession is attributed to the variation in sedimentation associated with the recession of the grounding line of a previously advanced glacier. Grounded ice decoupled from the continental shelf to form an ice shelf, probably initiated by a rise in sea level in response to global climatic changes. Following disintegration of the ice shelf, sedimentation was influenced by marked variations in iceberg production. AMS-derived 14C ages from the upper 46 cm of the core indicate that the succession has been deposited since the end of the most recent glacial maximum (late Pleistocene), a conclusion supported by published data.

In 1978 two ice cores were drilled to depths of 46 and 92 m respectively at Camp 3, at the west margin of the Greenland ice sheet. Both core drillings reached bedrock. In addition, surface samples were collected in the marginal area along an estimated flow line.

The δl8O profiles of the two ice cores and of the surface samples show similar features. All three δ180 records reveal the characteristic shift (of 5–6 per mil for the Pleistocene-Holocene transition 11 000 years ago) observed in Greenland deep ice cores from Camp Century and Dye 3.

The δ18O results, as well as the measured temperature profiles in the bore holes, are used to provide more insight into the rheology of the ice sheet. The analyses of marginal ice samples is an important supplement to deep ice-core analyses.