Three different approaches to ice-core age dating are employed to develop a depth–age relationship at Vostok, Antarctica: (1) correlating the ice-core isotope record to the geophysical metronome (Milankovich surface temperature cycles) inferred from the borehole temperature profile, (2) importing a known chronology from another (Devils Hole, Nevada, USA) paleoclimatic signal, and (3) direct ice-sheet flow modeling. Inverse Monte Carlo sampling is used to constrain the accumulation-rate reconstruction and ice-flow simulations in order to find the best-fit glaciological time-scale matched with the two other chronologies. The general uncertainty of the different age estimates varies from 2 to 6 kyr on average and reaches 6–15 kyr at maximum. Whatever the causes of this discrepancy might be, they are thought to be of different origins, and the age errors are assumed statistically independent. Thus, the average time-scale for the Vostok ice core down to 3350m depth is deduced consistent with all three dating procedures within the standard deviation limits of ±3.6 kyr, and its accuracy is estimated as 2.2 kyr on average. The constrained ice-sheet flow model allows, at least theoretically, extrapolation of the ice age–depth curve further to the boundary with the accreted lake ice where (at 3530m depth) the glacier-ice age may reach ∼2000 kyr.

Field studies at Mueller and Tasman Glaciers in New Zealand and in Iceland have revealed extensive ice-marginal moraine sequences fed by a series of debris bands containing characteristic rounded debris. We interpret these debris bands as meltwater deposits from relict conduits. The process of sediment accumulation described requires that debris undergoing basal or high-level ice transport is entrained by running water, becoming comminuted and rounded before being returned to high-level ice transport and eventual deposition in marginal moraines. Tins sequence of events suggests a link between glacier hydrology and ice-marginal sedimentation, possible mechanisms for which are explored. Pronounced moraines with rounded debris can be expected if (a) large quantity of debris is carried within the englacial drainage network; (b) there is a tendency for this debris to be abandoned within the ice; and (c) ice-flow trajectories and ablation ensure that this debris congregates at the ice surface. Streams which flow at high level within the ice can intercept and entrain englacial debris derived from rock fall. However, debris sources at Gigjökull and Steinholtsjökull in Iceland are restricted to the glacier bed, suggesting that, in certain cases, the presence of a basal overdeepening acts as a key factor controlling the accumulation of these moraines. Water pressure rises as channels encounter an overdeepening, forcing debris-laden streams to leave the bed and take an englacial route. That debris may pass from ice to water and back into ice before deposition has gone largely unrecognised in accounts of glacial process systems, yet it provides an explanation of how temperate alpine glaciers can include water-worked debris in their marginal depositional facies.

A study of the spatial and temporal distribution of methane sulphonic aeid (MSA) and nssSO42- concentrations in snow-pit samples was performed to determine the main and secondary sources, transport effects and seasonal pattern of biogenic sulphur compounds. Four snow pits, about 3 m deep, excavated at the same time at different altitudes (870-2960 m a.s.1.) in northern Victoria Land, Antarctica, gave coherent information about the effect of altitude and seasonality on the snow chemical composition. A progressive, well-defined decreasing concentration trend is shown as altitude increases, with the biggest effect in the first 1000 m a.s.1. At higher altitudes, biogenic sources make the most important contribution to the tola! sulphate balance with respect to sea-mray input. Particular attention was paid to the relationship between MSA and nssSO42- by using MSA as a univoca] biogenic marker. The nssSO42- /MSA ratio was evaluated with respect to altitude and seasonality to determine the effect of transport mechanisms (such as long-range transport and fractionation) or non-dimethyl sulphide sources on nssSO42- snow content.

A two-dimensional convective transport model has been been developed to investigate the phase and compositional evolution of a flooded slush layer overlying sea ice. The processes governing the solutal and compositional evolution of the flooded layer are investigated in an attempt to explain field observations of salinity and oxygen isotope ratios. Simulations indicate fairly vigorous convective transport in the slush layer, which may lead to the formation of porous channels, depending on permeability. It is found that the salinity and δ18O composition of the freezing slush layer is determined primarily by the sea-ice permeability. Simulated salinity and δ18O profiles produce varied results, though consistent with observations. The influence of the slush on the salinity and δ18O composition of the underlying ice was found to be minimal.

The forces snow avalanches are able to exert on protection dams or buildings are of crucial interest in order to improve avalanche mitigation measures and to quantify the mechanical vulnerability of structures likely to be damaged by snow avalanches. This paper presents an analytical model that is able to calculate these forces taking into account dead-zone mechanisms. First, we present a 2-D analytical hydrodynamic model describing the forces on a wall overflown by gravity-driven flows down an inclined plane. Second, the 2-D model is successfully validated on discrete simulations of granular flows. Third, we provide ingredients to extend the 2-D model to flows of dry and cold snow. Fourth, we propose a simplified 3-D analytical model taking into account lateral fluxes. Finally, the predictions from the simplified 3-D analytical model are successfully compared to recent measurements on two full-scale snow avalanches released at the Lautaret site in France.

Antarctic radio-echo sounding (RES) data at 60 MHz have been used to determine an independent stratigraphy for the ice core at Vostok station, based on internal radio-echo layering. A-scope RES data allow the amplitude of reflected electromagnetic (e/m) waves to be measured and, by accounting fur geometric spreading and absorption losses of the e/m wave, power reflection coefficients (PRCs) to be calculated. This information is compared with time-continuous Z-scope RES data in order to trace continuous e/m reflectors across the ice sheet. Internal ice-sheet horizons deeper than 800 m are caused by layers of ice that possess distinctly different dielectric properties (i.e. acidic layers) compared with ice above and/or below. Comparison of four PRC samples, located ~ 5 km from Vostok station, revealed five distinct internal reflections between 1000 and 2200 m. Z-scope data from directly over the Vostok station site show the same five prominent internal radio-echo layers. The depth-related radio-echo signals were then compared with chemical records from the Vostok ice core, including the H2SO4 signal, a major component of which is derived from volcanic events. From this procedure, internal radio-echo reflectors and Vostok ice-core acid measurements were correlated. Avery good match was made between Z-scope and ice-core data. However, vertical offsets observed between A-scope-derived RES layers and peaks in the chemical signal of up to 100 m are probably due to the general Inkling of the ice-sheet layering between the core site and the RES flight-line. We conclude that 60 MHz RES layering may be regarded as a stratigraphy independent of palaeoclimate, and may be used to correlate other deep Southern Hemisphere ice cores.

An X-ray transmission method has been developed to obtain a continuous profile of bulk densities of ice cores. Intensities of X-rays transmitted through an ice-core sample were continuously measured by an X-ray detector during translation of the sample across the X-ray beam. A thick section of an ice core with a constant thickness was prepared by band-sawing followed by microtome planing. The X-ray intensity profile obtained was converted to a density profile using a calibration curve for X-ray absorption vs ice thickness. Using this method, spatial resolution of the density profile was down to 1 mm. X-ray radiographs were also taken on a two-dimensional detector imaging plate, in order to observe layer structures of the ice cores.

The method was applied to Dome Fuji (Antarctica) ice cores from the surface to 110 m depth. From the density profile obtained we calculated the power spectrum of the density variation by the discrete Fourier transform, and obtained several peaks at different frequencies. The center period in the spectrum was close to the annual accumulation thickness at the drill site.

We characterize the basal mass balance of the Ekström Ice Shelf, Dronning Maud Land, Antarctica, using interferometrically derived surface velocities and ice thickness measurements from radio-echo sounding (RES). The surface velocities are based on data from European Remote-sensing Satellites-1 and -2 (ERS-1/2) during 1994–97. The ice thickness grid consists of 136 RES profiles acquired between 1996 and 2006. Mass fluxes are calculated along selected RES profiles where possible, to reduce uncertainties from ice thickness interpolation. Elsewhere large-scale mass fluxes are calculated using interpolated ice thickness data. Themass flux into the Ekström Ice Shelf from the main grounded drainage basins is estimated to be 3.19±0.4Gt a–1. The mass flux near the ice shelf front is 2.67±0.3Gt a–1. Assuming steady state, and based on the equation of continuity, we interpret the residual mass flux as a combined effect of snow accumulation and subglacial melting/refreezing. Using net snow accumulation rates from previous studies, we link the mass flux divergence in irregular-shaped polygons to processes beneath the ice shelf. The highest subglacial melt rates of ~1.1ma–1 are found near the grounding zone of two main inflow glaciers, and around the German station Neumayer III. The detection of unlikely refreezing in a small area ~15 km west of Neumayer III is attributed to both dataset inaccuracies and a (possibly past) violation of the steady-state assumption. In general, the method and input data allow mapping of the spatial distribution of basal melting and the results are in good agreement with several previous studies.

The temperature of the snow-ice interface was measured every 2.4 h throughout winter 1997/98 at 30 locations near the Surface Heat Budget of the Arctic Ocean (SHEBA) camp in the Beaufort Sea. Measurements were obtained from young ice, ridges, refrozen melt ponds and ice hummocks. Average snow depths at these locations were 567 cm, while mean interface temperatures ranged from −8° to −25°C, with minimums varying from −12° to −39°C. Interface temperatures were linearly related to snow depth, with increasing scatter at greater depths. The conductive heat flux during the winter, Fc, was estimated for each location using air and interface temperatures, snow depths and measured snow thermal conductivities. Fc was integrated to determine total heat loss for the winter at each site. Losses varied by a factor of four, with variations over short distances (10 m) as large as the variations between ice floes. Spot measurements along traverse lines confirm that large variations in interface temperature are common, and imply that small-scale spatial variability in the conductive flux is widespread. A comparison of the dependence of Fc on snow depth and ice thickness based on our observations with the dependence predicted by a one-dimensional theoretical model suggests that spatial heterogeneity may be an important issue to consider when estimating the heat flux over large aggregate areas. We suggest that the small-scale variability in the conductive flux arises because the combined snow and ice geometry can produce significant horizontal conduction of heat.

A glacier system is regarded as the ensemble of many glaciers sharing the same region, influenced by a similar climate and organized by certain intrinsic laws. It can be either ‘sensitive’ or ‘steady’. On the basis of the structure of the glacier system and the nature of the equilibrium-line altitudes at the steady state, functional models of a glacier system responding to climate warming were established, using the Kotlyakov–Krenke equation relating annual glacier ablation and mean summer temperature and the glacier system’s median size. The modeling results under the climatic scenarios with a rate of temperature increase of 0.01, 0.03 and 0.05 K a-1 indicate that by the end of this century the glacial area of China will be reduced by –14%, –40%and –60% respectively. However, model results show distinct differences between the sensitive glacier system and the steady glacier system.

The porosity and water saturation of the firn of South Cascade Glacier were measured in order to determine both the volume of water stored in it and the significance of this water content for the water volume stored in the glacier. The distance to water below the firn surface was found never to be greater than 4 m, and the average thickness of the water-saturated layer was estimated to be 1.25 m. The average firn porosity was 0.15, the water saturation was 0.61, and the total volume of water stored in the firn was approximately 1.78 × 105 m3 representing about 12% of the total spring storage. The water table was found to exhibit a pattern of diurnal fluctuation which starts in late June or early July, indicating that melt water from the accumulation zone may pressurize the bed at diurnal frequencies. The depth-averaged permeability was found to be 1.5 × 10−5 m/s, a value which compares favorably with those from other studies.

Despite widespread use of radio-echo sounding (RES) in glaciology and broad distribution of processed radar products, the glaciological community has no standard software for processing impulse RES data. Dependable, fast and collection-system/platform-independent processing flows could facilitate comparison between datasets and allow full utilization of large impulse RES data archives and new data. Here, we present ImpDAR, an open-source, cross-platform, impulse radar processor and interpreter, written primarily in Python. The utility of this software lies in its collection of established tools into a single, open-source framework. ImpDAR aims to provide a versatile standard that is accessible to radar-processing novices and useful to specialists. It can read data from common commercial ground-penetrating radars (GPRs) and some custom-built RES systems. It performs all the standard processing steps, including bandpass and horizontal filtering, time correction for antenna spacing, geolocation and migration. After processing data, ImpDAR's interpreter includes several plotting functions, digitization of reflecting horizons, calculation of reflector strength and export of interpreted layers. We demonstrate these capabilities on two datasets: deep (~3000 m depth) data collected with a custom (3 MHz) system in northeast Greenland and shallow (<100 m depth, 500 MHz) data collected with a commercial GPR on South Cascade Glacier in Washington.

We discuss a decameter-wavelength airborne radar sounder, the Warm Ice Sounding Explorer (WISE), that provides ice thickness in areas where radar signal penetration at higher frequencies is expected to be limited. Here we report results for three campaigns conducted in Greenland (2008, 2009, 2010) and two in Antarctica (2009, 2010). Comparisons with higher-frequency radar data indicate an accuracy of ±55 m for ice-thickness measurements in Greenland and ±25 m in Antarctica. We also estimate ice thickness of the Qassimiut lobe in southwest Greenland, where few ice-thickness measurements have been made, demonstrating that WISE penetrates in strongly scattering environments.

A narrow bridge of floating ice that connected the Wilkins Ice Shelf, Antarctica, to two confining islands eventually collapsed in early April 2009. In the month preceding the collapse, we observed deformation of the ice bridge by means of satellite imagery and from an in situ GPS station. TerraSAR-X images (acquired in stripmap mode) were used to compile a time series. The ice bridge bent most strongly in its narrowest part (westerly), while the northern end (near Charcot Island) shifted in a northeasterly direction. In the south, the ice bridge experienced compressive strain parallel to its long axis. GPS position data were acquired a little south of the narrowest part of the ice bridge from 19 January 2009. Analysis of these data showed both cyclic and monotonic components of motion. Meteorological data and re-analysis of the output of weather-prediction models indicated that easterly winds were responsible for the cyclic motion component. In particular, wind stress on the rough ice melange that occupied the area to the east exerted significant pressure on the ice bridge. The collapse of the ice bridge began with crack formation in the southern section parallel to the long axis of the ice bridge and led to shattering of the southern part. Ultimately, the narrowest part, only 900 m wide, ruptured. The formation of many small icebergs released energy of >125 ×106 J.

The Patagonia icefields constitute a unique location in the Southern Hemisphere for obtaining non-polar paleo-records from ice cores south of 45°S. Nevertheless, no ice-core record with meaningful paleoclimate information has yet been obtained from Patagonia. This deficiency is due to extremely harsh field conditions, and to the fact that the main plateaus of both Hielo Patagónico Norte (HPN; northern Patagonia icefield) and Hielo Patagónico Sur (HPS; southern Patagonia icefield) are strongly affected by meltwater percolation. In order to explore the suitability of high-elevation glacier sites at HPS as paleoclimate archives, three shallow firn cores were retrieved covering the altitude range 1543−2300 ma.s.l. The glaciochemical records from the two lower sites confirm the presence of superimposed ice, a clear sign of meltwater formation and percolation. In the core from 2300 m, the glaciochemical signature appears to be preserved, indicating that no significant melting occurred. Although there might be problems associated with wind erosion and extreme melt events, there is good potential for well-preserved paleo-records within glaciers in the Patagonia icefields located higher than 2300 m.

Accurate dating in ice sheets is required for a correct interpretation of palaeoclimatic records and for incorporation of material characteristics in the flow law which depend on ice age. In this paper, we make a comparison between a Lagrangian and Eulerian approach to the ice advection problem in numerical ice-sheet models. This comparison is first performed for a schematic two-dimensional ice sheet of Nye–Vialov type with a prescribed stationary velocity field. Severalcases are examined which incorporate basal melting, basal sliding and an undulating bed. A further comparison is made with an analytical solution for the ice divide. Both methods are also applied in a thermomechanical model of the Antarctic ice sheet for steady-state present-day conditions. Our main conclusion is that, for similar discretization parameters, the Lagrangian method produces less error than an Eulerian approach using a second-order upwinding finite-difference scheme, though the difference is small (<1%) for the largest part of the model domain. However, problems with the Lagrangian approach are introduced by the dispersion of tracers, necessitating the use of interpolation procedures that are a main source of additional error. It is also shown that a cubic-spline approximation of Lagrangian trajectories improves accuracy, but such a method is computationally hardly applicable in large-scale ice-sheet models.

Snow radar profiles were measured in Dronning Maud Land, East Antarctica, in the vicinity of the Finnish research station Aboa during austral summer 1999/2000. The aim was to study the annual layering in the upper 50 m of the snowpack and to compare the results obtained by three radar antenna frequencies (50, 100 and 800 MHz). Intercomparison of the radar profiles measured by the three frequencies shows that some individua linternal layers are visible with different antennas. Sparse accumulation-rate data from stake measurements and snow pits are compared with layer depths. The comparison reveals a great deal of scatter due to the large interannual variability in accumulation patterns. Using the radar layers as isochrones together with a model of depth–density–radar-wave velocity allows the individual accumulation data to be integrated, and a better estimate of accumulation patterns is obtained. Using the radar layering seems to be a much better method of estimating accumulation rate in this region than using a short series of stake measurements, even in the absence of deep ice cores to directly date the radar layering.

Systematic temperature observations were not undertaken in Norway until the early 19th century, and even then only sporadically. Climate-proxy data may be used to reconstruct temperatures before this period, but until now there have not been any climate proxies available for late winter. This situation has recently changed, as a diary containing historical ice break-up data from a farm near lake Randsfjord in southeastern Norway has been discovered. These data, together with observations from lake Mjøsa in the same region, make it possible to reconstruct temperature back to 1758. The reconstructed series, combined with instrumental series from the area near the lake, were merged into one composite time series covering the period 1758–2006. The lowest temperatures are seen during the Dalton sunspot minimum in the early 19th century. The 20th century was 1.3˚C warmer than the 19th century, whereas the 19th century was 0.4˚C warmer than the last 43 years of the 18th century. During the period 1758–1850, the mean temperature was 1.4˚C lower than the mean value of the 20th century. The warmth observed in the 1990s and at the start of the 21st century is unprecedented during the whole series.

Spaceborne data are becoming sufficiently extensive spatially and sufficiently lengthy over time to provide important gauges of global change. There is a potentially long record of microwave brightness temperature from NASA's Scanning Multichannel Microwave Radiometer (SMMR), followed by the Navy's Special Sensor Microwave Imager (SSM/I). Thus it is natural to combine data from successive satellite programs into a single, long record. To do this, we compare brightness temperature data collected during the brief overlap period (7 July-20 August 1987) of SMMR and SSM/I. Only data collected over the Antarctic ice sheet are used to limit spatial and temporal complications associated with the open ocean and sea ice. Linear regressions are computed from scatter plots of complementary pairs of channels from each sensor revealing highly correlated data sets, supporting the argument that there are important relative calibration differences between the two instruments. The calibration scheme was applied to a set of average monthly brightness temperatures for a sector of East Antarctica.

In order to facilitate the measurement of liquid-water content of snow in high mountains, a portable calorimeter named “Endo-type snow-water content meter” was developed. It is composed of a metal-coated container made of insulating materials and a lid of the container with a small-thermistor thermometer. Its strong points are its light weight, small size and easy fabrication with cheap materials. The total weight of the device is as light as 250 g, which is less than 10% of the snow-water content meter widely used in Japan (Akitaya-type snow-water content meter). The results of experiments have revealed that the device is capable of measuring the liquid-water content within 2 minutes with an accuracy of 2% by weight.