Pine Island Glacier is one of the major ice streams draining West Antarctica. We calculated average velocities for both its grounded and floating parts by tracking crevasses and other patterns moving with the ice on two sequential images acquired in February and December 1992 by ERS-1 SAR (European Remote-Sensing Satellite, Synthetic Aperture Radar). Velocities in the fast-moving central parts of the glacier range from about 1.3 km a−1 on the grounded part to about 2.6 km a−1 on the floating part. Velocity increases rapidly just below the grounding line. For the floating part, velocities are approximately 0.3 km a−1 faster than previously established from Landsat images by other workers. This observation suggests that the discharge is larger and, therefore, the mass balance less positive than previously thought; however, our study also shows that current information is insufficient to allow for precise mass-balance calculations. Images of the glacier front show that a calving event released an iceberg about 5 km wide between February and December 1992. The position of the glacier front has not changed substantially between 1973 (Landsat image) and 1992 (ERS-1 images).

We present a model for wave propagation in the marginal ice zone (MIZ). The model is based on a two-dimensional linear water wave floating-elastic-plate solution in the frequency domain using a matched eigenfunction expansion. The model is fully coherent so the results are dependent on exact geometry, and we show firstly that this dependence can be effectively removed by averaging over random floe lengths. We present a range of predictions from the model which show various curves of transmitted energy as a function of the floe thickness, number of floes and wave period. These curves show that it is possible with this simple model to make predictions about wave intensity with distance into the MIZ. The results predict that the MIZ acts as a low-pass filter and and that the filtering is strongly dependent on floe thickness and number but that it is independent of floe length.

Central to an understanding of evolution in sea-ice characteristics in response to climate change is an understanding of sea-ice dynamics. In this study, we investigate regional differences in ice dynamics in the Beaufort Sea and High Arctic using high-frequency ice buoy (beacon) data deployed during the SEDNA and IPY-CFL field campaigns from spring 2007 to winter 2008. Examined in particular are scaling laws determined from absolute dispersion statistics. We create temporal scaling maps to determine whether distinct dynamical regimes can be identified with differing scaling properties. The results from this analysis provide an alternative characterization to changes in sea ice based on dynamics rather than concentration and thickness, and thus insight into, and improved understanding of, the connections between sea-ice drift and morphology.

We present, analyse and discuss air-pressure data from finite-volume chute flows of dry fine snow in air. These experiments have the correct similarity criteria to model powder-snow avalanches and demonstrate the transition from a dense to a suspended flow. We measured the dynamic air pressure at the base of the flow, which features a marked negative pressure peak immediately behind the front. This feature is also seen in observations of natural powder-snow avalanches measured in Russia, Japan and Switzerland in direct numerical simulations of non-Boussinesq suspension flows and in ping-pong ball avalanches. This is evidence for large internal motions and suggests that there is a coherent vortex in the avalanche front. This can result in impact pressures many times larger than those expected from the mean flow velocity. We analyse the external air pressures using three models and show how the geometry and velocity of the flow can be found from this single air-pressure measurement. We also measured flow heights and speeds using image analysis and show that the speed is roughly independent of the slope angle and scales with the release size raised to the power 1/4, as predicted by similarity analysis for pseudo two-dimensional (2-D) flows.

In winter 2002/03 and 2003/04, thermistors were installed in the ice on two shallow ponds in central Alaska, USA, in order to obtain data on ice temperatures and their response to increasing and decreasing air temperatures, and flooding and snow-ice formation. Snow depth and density, and ice thickness were also measured in order to understand how they affected and were affected by ice temperature variability. The lowest ice temperature (–15.5˚C) and steepest temperature gradient (–39.8˚Cm–1) occurred during a 9week period in autumn 2002/03 when there was no snow on the ice. With snow on the ice, temperature gradients were more typically in the range –20 to –5˚Cm–1. Average ice temperatures were lower during the warmer, first winter, and higher during the cooler, second winter because of differences in the depth and duration of the snow cover. Isothermal ice near the freezing point resulted from flooding and snow-ice formation, and brief episodes of warm weather with freezing rain. Under these circumstances, congelation-ice growth at the bottom of the ice cover was interrupted, even reversed. It is suggested that the patterns in temperatures brought about by the snow-ice formation and rain events may become more prevalent due to the increase in frequency of these events in central Alaska if temperature and precipitation change as predicted by Arctic climate models.

Values Of Effective thermal conductivities of snow and firn were obtained at Filchner Ice Shelf (Antarctica). We employed a transient line source method (a needle probe with a diameter of 1.6 mm) for conductivity determination, which allows quick measurements with high spatial resolution. Our data yield a linear relationship between effective thermal conductivity (lg keff) and density (p) of snow which implies a strong dependence of thermal conductivity on density for 0.24≤p≤0.42, Comparison of thermal conductivities and other snow pit data suggests that density alone is a poor measure of effective thermal conductivities of snow and firn. We propose that grain structure is probably the governing parameter in determining heat transport in the upper firn layers.

In order to investigate the deposition of radioactive fission nuclides in the high-altitude snow and firn of the Swiss Alps after the Chernobyl accident, core samples from nine mountain peaks were analyzed. The observed radiological signal is described, together with the characteristics of the snow in which it is embedded. Total activity is of the same order of magnitude (around 10 kBq/m2) as deposition rates measured at lower altitudes, and shows a comparable regional distribution. A clear altitudinal trend only exists with respect to snow conditions: above about 4000 m a.s.l., erosion, mixing and resedimentation of cold snow by wind could have occurred during or shortly after the deposition, whereas at lower altitudes formation and percolation of melt water had already started — probably selectively — to redistribute the nuclides within temperate firn layers.

Many of the ice-coring objectives in the Ice Drilling Program Office (IDPO) Long Range Science Plan, such as those in the International Partnerships in Ice Core Sciences (IPICS) 2k array and 40k network, are attainable in many locations with an intermediate depth drill (IDD) that can collect core from a fluid-filled hole down to 1500 m depth. The Ice Drilling Design and Operations (IDDO) group has designed and is in the process of building an agile IDD to meet this objective. The drill tent, power distribution and core-processing systems are an integral part of the IDD, which can be deployed by small aircraft and assembled by hand to minimize logistic requirements. The new drill system will be ready for testing in Greenland beginning in late spring 2014. The first production drilling is scheduled for the 2014/15 field season at the South Pole.

A 40.9 m ice core was recovered from Far East Rongbuk Glacier (FER), Qomolangma (Mount Everest), Himalaya, and an 80.4 m core from neighboring East Rongbuk Glacier (ER). Both are dated by seasonal variations of δ18O and major-ionic profiles, together with references of β-activity peaks. In this paper we compare the chemical records of these two cores to show post-depositional modification processes. The smoothed β18O profiles of the two cores show a similar trend. However, the mean β18O value of the FER core for the period 1954—96 is 3.12%o less than that of the corresponding part of the ER core, and the major-ionic profiles of the two cores differ considerably. We suggest that melting-away of the snow layer deposited during the pre-monsoon season may account for lower β18O values of the FER than of the ER core, and higher terrestrial ion concentrations in the FER core for the period 1957-63 may contribute to changes by chemical reactions in the presence of snowmelting. The significantly decreased NH4 and, to a lesser degree, SO42 concentrations in the FER core could be caused by the ion elution process that moved most chemicals away with runoff.

As previously reported, repeat-pass airborne laser altimetry measurements made in May 1996 and May 2002 show a large positive ice-surface elevation change rate over parts of the accumulation area of Austfonna, eastern Svalbard. The maximum growth rate is estimated to be equivalent to a 35–40% increase in snowfall over the area of thickening. Thinning is observed at lower elevations. Here we discuss in detail the possible causes of these elevation changes, including ice-cap dynamics and/or firn density changes, and conclude that sea-ice loss producing a localized increase in precipitation over Austfonna remains the most convincing explanation. This study highlights the problems of interpreting relatively short-term altimetry measurements where auxiliary data are limited in both spatial and temporal extent.

We show that two different types of dry-snow slab avalanches may result from a tensile failure of the slab crown triggered by either a quasi-static or an unstable shear propagation of a basal crack at the slab/substrate interface The triggering conditions for both modes are derived analytically. The latter only takes place if the depth of the top layer is above a critical value, and in a “window” centred around a critical slope of 35.3°, if residual friction on the basal crack surfaces is neglected. The width of this window increases with snow thickness. The introduction of a residual friction on the basal crack surfaces increases the critical slope.

The thermohaline circulation below a regularly shaped ice shelf comparable in dimensions to the Ronne Ice Shelf, Antarctica, is investigated by means of a three-dimensional primitive-equation model. To handle the strongly inclined ocean surface as well as the bottom topography, we use scaled coordinates in the vertical direction. Preliminary results of two model versions containing open and closed open-ocean boundaries, respectively, prove the internal circulation is almost independent of the hydrography outside the ice shelf.

Merely driven by the pressure-dependence of the sea-water freezing point (-0.000753 K dbar-1), a stationary circulation pattern evolves, forced by the buoyancy flux due to melting and freezing. The redistribution of ice from deep to shallow ice-shelf drafts resembles the ice-pump mechanism. Its strength depends on the ice-thickness gradients, namely, the differences of the freezing point at the ice-shelf base. As simulated melting and accumulation rates convincingly reproduce the interactions observed at the base of the Ronne Ice Shelf, the present model can act as a tool coupling ice-ocean dynamics.

Spring snow melt over the Beaufort and East Siberian seas is examined using visible-band DMSP imagery, SMMR brightness temperatures, and surface air temperatures for the years 1979, 1980 and 1984–86. Regional melt onset, as identified from the SMMR data, typically begins in early June, but can vary by up to two weeks between years. The subsequent pace of melt, estimated from the difference in days between the SMMR signal and visual identification of melt features in the DMSP data, exhibits a similar range. Interannual differences in snow melt are examined with respect to variations in cloud cover and geostrophic meridional winds. While over the Beaufort Sea, early melt onset and rapid melt progression may be favored by a combination of limited cloud cover and, as inferred from the wind data, strong northward air advection, no firm conclusions can be drawn from the available data. Presumably, potential relationships between melt and atmospheric forcings tend to be masked by additional factors, such as variations in initial snow depth and uncertainties in the data sets.

We produced four independent temperature time series derived from different sensors for the Siple Dome region of West Antarctica to investigate seasonal to interannual temperature variability over the last 20 years. We use data from automatic weather station air-temperature records (1997–99), European Centre for Medium-range Weather Forecasts surface temperature from the 15 year re-analyses (ERA-15, 1979–93), and emissivity-corrected brightness temperatures from the Special Sensor Microwave/Imager (1987–99) and the Scanning Multichannel Microwave Radiometer (1978–87). Each technique has limitations and errors, but all respond to temperature, and all agree in the large patterns of temperature variability over time. Our results show that there is high seasonal to interannual variability in both mean temperature and variance in the Siple Dome region during the study period. In particular, fluctuations in seasonal to interannual temperature variance occur on an approximately 5 year cycle and correlate with variations in the Southern Oscillation Index.

A new plano-altimetric map of the Dome Concordia (Dome C) area was drawn up from 1995/96 kinematic double-frequency global-positioning-system (GPS) data of two different projects, as well as static GPS data from a geodetic net for deformation analysis and ice-flow velocity measurements covering an area of about 2000 km2.

The GPS surveys were carried out for EPICA during the 10th and 11th Italian Expeditions to choose the optimal location for deep ice-core drilling at Dome C. The accuracy of the kinematic survey was tested by analysing the height-value differences at intersections between different profiles; values ranged from 50–150 mm.

The new map was compared with the 1993 kinematic interferential GPS data and residuals between the 1993 and 1995 data were calculated. The surface topographic values were used to calculate the elevation of the Dome C area bedrock, obtained from the reference ground-based and airborne radio-echo-sounding surveys.

During the ninth Italian Antarctic Expedition, a 22 m deep firn core was drilled on the Hercules Névé (ΗΝ) in the Transantarctic Mountains, northern Victoria Land, Antarctica, The continuous dust record from HN, spanning 70 years from 1927 to 1994, displays sharp differences between the upper 15.5 m and the bottom part. The background of dust concentration in the upper part is quite homogeneous, with values around 6.5 x 103 particles g −1 of water, and some peaks reaching maximum values of 1.0-1.5 x 104 particles g−1 of water. in this part the volume-size distribution of particles shows a relative maximum around 0.9 μm while a second maximum occurs for particles larger than 12 μm . The larger particles are likely to have a local origin, while the small-size component may be representative of long-range transport dust. Below 15.5 m the record shows higher values in both background and peak concentration, with mean values of 1.6 x 104 particles g−1. The volume-size distribution changes from 0.9 to 1.5μm in parallel with the increase of dust concentration. The dust record suggests significant increases in concentration for the periods 1932-42 and 1951-64. It suggests some correlations with precipitation anomalies over South America and indirectly supports the hypothesis that small-sized dust at HN may originate from South America.

Measurements of the concentration and size distribution of dust particles found in the EPICA (European Project for Ice Coring in Antarctica) Dome C ice core, East Antarctica, provide records covering the last 27000 years. the total concentration decreased drastically by a factor of 55 from the Last Glacial Maximum (LGM) (800 ppb) to the Holocene (15 ppb), with a well-marked absolute minimum around 11500–11600 years ago. This latter almost corresponds to the end of the Younger Dryas in Greenland, which was marked by a methane peak related to the expansion of tropical wetlands. Assuming that the source region forAntarctic dust is the southern part of South America, the Antarctic dust minimum suggests a larger geographical extent for this wet period. the volume (mass)-size distribution of the particles displays a mode which is close to 2 μm in diameter, shifting from 1.9 μm in the glacial period to 2.07 μm in the Holocene. As opposed to previous results from old Dome C, EPICA suggests a greater proportion of large particles in Holocene samples than in LGM samples. In addition, for the period 13 000–2000BP, structured millennial-scale oscillations of the dust mode appear. These are especially well marked before 5000 years ago, with higher frequencies also present. the difference between LGM and Holocene particle distributions may be related to changes in the pattern of dust transport to East Antarctica. At Dome C the greater proportion of coarse particles observed during the Holocene suggests greater direct meridional transport. During the LGM, atmospheric circulation was likely more zonal, causing a greater amount of large dust particles to be removed from the atmosphere before reaching Antarctica. Changes in atmospheric circulation could also be the cause of the millennial-scale dust-mode oscillations during the Holocene.

Variations in the chemical composition of subsurface runoff within Canada Glacier, Antarctica, are used to identify the main source waters, which are vertical surfaces, and melt from solar-heated debris within channels, cryoconite holes and pools. The main flow paths are subsurface connections between cryoconite holes, pools and riffles. The latter may become partially disconnected during hard freeze. The chemical composition of runoff at the outlet of Canada Glacier during January 2000 was dominated by Ca2+, HCO3– and sea salt (Na+ and Cl–), and became depleted in sea-salt and non-sea-salt (*) SO42– as the subsurface drainage system in a frozen pool-and-riffle system was flushed and the melting ice surface became depleted of overwinter dry deposited salts. Only during 2 days of hard freeze did sea salt and *SO42– increase in concentration together. Otherwise, sea salt and *SO42– declined while *Ca2+ and HCO3– increased. The latter ions are derived from the chemical weathering of sediment in frozen-topped pools, channels and cryoconite holes. It is inferred that the hydrochemical processes which occur in the vestigial, subsurface drainage system are the elution of ions from ice melt, dilution of these ions downstream by ice melt from vertical surfaces and the dissolution of dust, in subsurface pools, channels and/or cryoconite holes.

A constitutive theory of snow is developed to describe the mechanical properties of snow in terms of the properties of the ice grains and the necks that interconnect them. The principle of virtual work is used to calculate the stresses in the particles and necks. A number of different deformation mechanisms are investigated and, depending upon the deformation mechanism which is dominant for given load conditions, different equations are used to calculate the strains in the grains and necks. These strains around a representative ice grain are then averaged and scaled to obtain the global strains in the snow. The theory is then compared with experimental data to determine if the mechanical properties of snow can be adequately represented. Results show that the constitutive theory does work, but that it is cumbersome to implement, and that for practical use substantial computational capability is needed.

To develop avalanche runout models for short slopes, field measurements were made at 48 short-slope avalanche paths located in the Coast, Columbia and Rocky Mountains of western Canada, and at several paths in eastern Canada. Field studies included detailed topographic surveys and estimation of the extreme runout position in each path. A statistical runout model was developed using the runout ratio method, for which runout ratios from the four mountain ranges are well fit by an extreme-value type I (Gumbel) distribution when the β point is defined at the uppermost point where the slope is 24°. A second model was developed by regressing the α angle for the extreme runout position on numerous terrain variables. This regression model uses three predictor variables that can be easily measured in the field or on topographic maps. Length-scale effects were noted in both models, but are more pronounced in the runout ratio model. A comparison of models developed using the two methods shows that the runout ratio model estimates more conservative (longer) runout distances than the regression model for most threshold probabilities. Data from 13 additional paths from Switzerland and Québec, Canada, are used to test the models.