This study presents a simple and inexpensive method for deriving a high-resolution density proxy record for the firn part of an ice core using digital images. The image data have better resolution and are less sensitive to core quality than is density derived through dielectric profiling (DEP). Simple image analysis is thus suitable to derive a density proxy record in the firn section of ice cores drilled in the percolation or wet snow zone, and to better interpret the results of a DEP record. The images may be used as a permanent record when evaluating other types of ice-core data. Suggestions are provided to improve data quality and decrease post-processing time of the image analysis in future studies.

Snow pits sampled during two consecutive years (2001, 2002) at the summit of Lomonosovfonna ice cap in central Spitsbergen, Svalbard, showed that ion concentrations were spatially homogeneous. The snowpack on Lomonosovfonna shows no evidence of aerosol deposition from Arctic haze, in contrast to Holtedahlfonna (a glacier at a similar altitude in northern Spitsbergen) where there is a clear signature. In common with many other ice caps in the Arctic, Lomonosovfonna experiences periodic melting, and the deepest of the snow pits contained a record of one exceptionally warm (2001) and one long summer (2000). The most easily eluted species are nitrate and the divalent ions. Very low ion concentrations and high values of a melt indicator log([Na+]/[Mg2+]) were a result of either deep percolation or runoff of ions during melting. Comparing the snow-pit record with the ion record of more than 800 years from an ice core drilled on Lomonosovfonna in 1997 reveals some layers with similar composition to those that suffered significant melting in the snowpack: a few years in the 20th century and around AD 1750, and all of the core from before AD 1200 show unusually heavy melting.

Existing snow-climate classifications are primarily based on meteorological parameters that describe the average weather during the main winter months. However, field experience and measurements show that the characteristics of weak snowpack layers, including type, structure and details of formation, are primary indicators of avalanches that form. Despite its importance in the characteristics of local avalanche activity, weak-layer information is currently not a formal part of any snow-climate classification scheme. The focus of this study is the analysis of persistent snowpack weak layers in southwestern Canada. Observations from the industrial information exchange (InfoEx) of the Canadian Avalanche Association are used to examine the frequency, sequence and distribution of the most common types of snowpack weakness and their related avalanche activity. The results show significant temporal and spatial variations in areas with the same snow-climate characteristics. The weak-layer patterns observed in transitional snow-climate areas are clearly more complex than a simple combination of maritime and continental influences. ‘Avalanche winter regime’ is suggested as a new classification term that describes the snowpack structures relevant for local avalanche activity and complements the existing snow-climate classification system. Three preliminary avalanche winter regimes are identified for southwestern Canada.

The suitability of secondary ion mass spectrometry (SIMS) for the analysis of polar ice is assessed. A magnetic sector SIMS instrument, modified to permit analysis of cryogenically prepared specimens, was used to analyze a sample of naled ice from in front of midre Lovénbreen, Svalbard. The ion-induced secondary electron imaging capability of the instrument permitted identification of features such as grain boundaries, triple junctions, filaments, pore spaces and cracks. Secondary ion maps were acquired with sub-micron resolution, permitting the characterization of chemical impurities at grain boundaries. Two regions of interest were analyzed and are described in detail. In the first, discrete particles of impurity (possibly precipitates) containing Na, Mg, K and Cl were identified along a grain boundary. Additionally, Mg was found to be present along the full length of the boundary. In the second analysis, impurity containing Na, Mg, K and Cl was found at a triple junction and some evidence for segregation of impurity to grain boundaries was gained. In both regions of analysis, Na, K and Cl were more apparent in grain interiors than Mg, despite the presence of the latter element at the boundaries. Results corroborate previous scanning electron microscopy with energy-dispersive X-ray spectrometry (SEM-EDS) observations.

Length records of two pairs of glaciers are used to reconstruct the equilibrium-line altitude (ELA) and to estimate glacier response times. The method is based on the assumption that neighbouring glaciers should be subject to the same climatic forcing, and that differences in the length records are thus caused by differences in response times and climate sensitivities. By means of a control method, in which the difference between the reconstructed histories of the ELA is minimized, realistic response times are found. The pairs of glaciers studied are: (i) Vadret da Morteratsch and Vadret da Palü in the Swiss Alps and (ii) Briksdalsbreen and Nigardsbreen in southern Norway. In both cases the reconstructed ELA histories of the individual glaciers are very similar, in spite of the large differences in the length records. Short e-folding response times are found for the steep glaciers: 4.4 years for Vadret da Palii, 5.0 years for Briksdalsbreen. For the larger glaciers with a more gentle slope the response times are substantially larger: 33.0 years for Vadret da Morteratsch, 34.8 years for Nigardsbreen.

A record of accumulation and ablation from a network of 47 stakes at a coastal blue-ice area in Terre Adélie, Antarctica, is presented and analyzed. The record covers early 2004 to early 2006, from 25 field surveys including some in austral winter. The two years are very different, with a virtually null surface mass balance during the 2004 winter but large accumulation during the 2005 winter. A snow/ice energy- and mass-balance model is used to reproduce the accumulation and ablation record. A parameterization for snow erosion by wind is included. Input meteorology is from the European Centre for Medium-Range Weather Forecasts (ECMWF) analyses and forecasts, corrected using 1 year of local meteorological observations from an automatic weather station. Model results agree reasonably well with the observations. Wind erosion is the largest contributor to ablation, removing much of the precipitation. Sublimation and, to a lesser extent, melt/runoff together account for >60 cm w.e. of ablation in 2 years, mainly in summer. Although the record is short, it confirms high interannual variability and thus high sensitivity to meteorology and climate. Monitoring and understanding the mass balance of such coastal blue-ice areas may help monitor and detect climate change in the Antarctic coastal regions.

Polycrystalline ice near an ice divide typically shows a crystal fabric (crystal preferred orientation) with c axes clustered vertically. We explore the effect of this fabric on the large-scale flow pattern near an ice divide. We incorporate an analytical formulation for anisotropy into a non-linear flow law within a finite-element ice-sheet flow model. With four different depth profiles of crystal fabric, we find that the effect of fabric is significant only when a profile has a minimum cone angle of less than ~25º. For a steady-state divide, the shape and size of the isochrone arch can depend as much on the crystal fabric as it does on the non-linearity of ice flow. A vertically oriented fabric tends to increase the size of the isochrone arch, never to reduce it. Also, non-random fabric has little effect on the ice-divide-flow pattern when ice is modeled as a linear (Newtonian) fluid. Finally, when we use a crystal-fabric profile that closely approximates the measured profile for Siple Dome, West Antarctica, the model predicts concentrated bed-parallel shearing 300 m above the bed.

The University of Maine Ice Sheet Model was used to study basal conditions during retreat of the Laurentide ice sheet in Maine. Within 150 km of the margin, basal melt rates average ∼5 mm a−1 during retreat. They decline over the next 100 km, so areas of frozen bed develop in northern Maine during retreat. By integrating the melt rate over the drainage area typically subtended by an esker, we obtained a discharge at the margin of ~1.2 m3 s-1. While such a discharge could have moved the material in the Katahdin esker, it was likely too low to build the esker in the time available. Additional water from the glacier surface was required. Temperature gradients in the basal ice increase rapidly with distance from the margin. By conducting upward into the ice all of the additional viscous heat produced by any perturbation that increases the depth of flow in a flat conduit in a distributed drainage system, these gradients inhibit the formation of sharply arched conduits in which an esker can form. This may explain why eskers commonly seem to form near the margin and are typically segmented, with later segments overlapping onto earlier ones.

During the summer field seasons of 1987–91, studies of central East Antarctica by airborne radio-echo sounding commenced. This scientific work continued in the 1990s in the Vostok Subglacial Lake area and along the traverse route from Mirny, and led to the discovery of 16 new subglacial water cavities in the areas of Domes Fuji and Argus and the Prince Charles Mountains. Twenty-nine subglacial water cavities were revealed in the area near Vostok, along with a feature we believe to be a subglacial river. Two subglacial lakes were discovered along the Mirny–Vostok traverse route. These are located 50 km north of Komsomolskaya station and under Pionerskaya station. We find high geothermal heat flux in the vicinity of the largest of the subglacial lakes, and suggest this may be due to their location over deep faults where additional mantle heat is available.

Englacial cave systems were mapped using speleological techniques in three debris-covered glaciers in the Khumbu Himal, Nepal. Detailed three-dimensional mapping of the cave systems and observations of relationships with structures in the surrounding ice show conduits formed by a mechanism directly analogous to speleogenesis in limestone karst. The highest, oldest parts of all passages developed along debris-filled crevasse traces with hydraulic conductivity in the range 10–4 to 10–5ms–1. Conduits form when these hydraulically efficient pathways bridge between areas with different hydraulic potential. They then evolve by grading (through head-ward migration of nick points and vertical incision) to local base level, often the surface of supraglacial lakes. Most supraglacial lakes on Himalayan glaciers are perched above the elevation of the terminal stream, and exist for a few years before draining through englacial conduits. As a result, near-surface drainage evolution is frequently interrupted by base-level fall, and conduits may record multiple phases of incision. Conduits commonly migrate laterally during incision, undermining higher levels of the ice and encouraging collapse. Voids can be created by fluvial processes and collapse of crevassed ice. The oft-noted resemblance of the surface morphology of debris-covered glaciers to karst landscapes thus extends to the subsurface, and karst hydrology provides a framework for understanding englacial drainage.

The mechanisms controlling the spatial distribution and temporal fluctuations of the thermal structure in polythermal glaciers have, to date, been poorly investigated and are not fully understood. We have investigated the sensitivity of the cold surface layer thickness to different forcing parameters and the causes for an observed thinning of the cold surface layer on Storglaciären, northern Sweden, between 1989 and 2001 using a one-dimensional thermomechanical model and measurements of ice surface temperature, vertical velocity and net mass balance. Similarities between the spatial patterns of the cold surface layer, net mass balance and emergence velocity together with modelled high sensitivity to variations in emergence velocities suggest that the net ablation and vertical ice advection are the dominant forcing parameters. Results from transient model experiments suggest that the cold surface layer reaches a new equilibrium after a perturbation in the forcing within a few decades. No significant change in ice flow or mass balance has been observed at Storglaciären in recent decades. Instead, an increase of 1°C in winter air temperature since the mid-1980s is probably the cause of the observed thinning of the cold surface layer. Increased winter temperatures at the ice surface result in a reduced formation rate of cold ice at the base of the cold surface layer and lead to a larger imbalance between net loss of ice at the surface and freezing of temperate ice at the cold–temperate transition surface. Model results indicate that the cold surface layer is more sensitive to changes in ice surface temperature in areas with lower emergence velocity, which explains the observed complex thinning pattern of the cold surface layer.

The road along the Óshlíð hillside in the West Fjords region of Iceland is one of the most hazardous roads in Iceland due to avalanches, rockfalls and debris flows. The road has little traffic, but nevertheless traffic accidents caused by the severe conditions at the site are common. A number of avalanche tracks are found on the hillside. In some of these tracks, avalanches occur more frequently than in others. When there is an avalanche threat, avalanches generally flow over many tracks in a short time. Monitoring vibrations in the tracks with the highest avalanche frequency can indicate when avalanches start flowing down the hillside in a snowstorm, and avalanche hazard can then be declared with the specific site indicated. The same methodology can be used for rockfalls and debris flows, which are strongly affected by weather conditions and typically occur in clusters. Based on this knowledge, a research project was initiated in February 1996 with the objective of developing an automatic system based on seismic measurements to detect and analyze avalanches on the Óshlíð hillside and to instantly send a warning to a control station.

High-frequency (diurnal) temperature variations occur simultaneously at multiple depths separated by meters of snow in at least several and probably many Arctic and Antarctic thermocouple datasets. These temperature variations cannot be caused by heat conduction from the surface because their amplitudes are too large and there is no phase lag with depth, and they cannot be caused by heat advection because the air flux required is greater than is available. Rather, the simultaneous temperature variations (STVs) appear to originate within the box that houses the data logger as thermocouple-like offset voltages, wire heating or thermistor error. The STVs can be corrected by requiring that the temperatures vary smoothly with time at the greatest depth at which temperature is measured. The correction voltage determined in this fashion, when applied to the thermocouples at other depths, corrects the entire dataset. The method successfully removes STVs with 24 hour period that are up to 3.8°C in amplitude, and is superior to the averaging techniques commonly used to correct thermocouple data because it introduces no spurious (non-physical) temperature variations. The correction method described can be applied to all thermocouple data where temperature measurements have been made at depths > ~0.5 m into the snowpack. The corrections should allow more physical process and parameter information to be extracted more confidently from existing firn temperature data. Identification of the STVs and their probable cause also suggests how better data might be collected in the future.

A diagnostic, dynamic/thermodynamic ice-shelf model is applied to the George VI Ice Shelf, situated in the Bellinghausen Sea, Antarctica. The George VI Ice Shelf has a peculiar flow geometry which sets it apart from other ice shelves. Inflow occurs along the two longest, and almost parallel, sides, whereas outflow occurs on the two ice fronts that are relatively short and situated at opposite ends of the ice shelf. Two data sources were used to derive the ice thickness distribution: conventional radioecho sounding from the British Antarctic Survey was combined with thickness inferred from surface elevation obtained by the NASA GLAS satellite system assuming hydrostatic equilibrium. We simulate the present ice flow over the ice shelf that results from the ice thickness distribution, the inflow at the grounding line and the flow rate factor. The high spatial resolution of the ice thickness distribution leads to very detailed simulations. The flow field has some extraordinary elements (e.g. the stagnation point characteristics resulting from the unusual ice-shelf geometry).

Mass balance and climate sensitivity of Glaciar Perito Moreno (GPM), one of the main outlet glaciers of Hielo Patagónico Sur (southern Patagonia icefield), were investigated. Field measurements were carried out from 1995 to 2003, including ice ablation and velocity at stakes, seismic profiling, bathymetry of the lake near the calving fronts and meteorological data. The database was complemented by satellite observations, to derive the motion field by interferometric data, map glacier boundaries and snowlines from multi-year time series of radar images, and obtain glacier topography from the Shuttle Radar Topography Mission. In September 2003, GPM started to dam the southern arm of Lago Argentino, resulting in a maximum rise of the lake level of 9.35 m before the dam burst in March 2004. The ice dam formed again in August 2005, bursting in March 2006. Analysis of mass fluxes indicates no long-term trend in mass balance. This behaviour, contrasting with most retreating glaciers in the vicinity, can be attributed to a particular glacier geometry. Monthly climate sensitivity characteristics for glacier mass balance were derived using a degree-day model, showing similar importance of both temperature and precipitation. Also, the reconstruction of the mass balance for the last 50 years from local climate data shows a near-steady-state condition for GPM, with some small fluctuations, such as a slightly positive balance after 1998, that may have triggered the minor advance leading to damming events in 2003 and 2005.

As a result of intensive field activities carried out by several nations over the past 15 years, a set of accumulation measurements for western Dronning Maud Land, Antarctica, was collected, based on firn-core drilling and snow-pit sampling. This new information was supplemented by earlier data taken from the literature, resulting in 111 accumulation values. Using Geographical Information Systems software, a first region-wide mean annual snow-accumulation field was derived. In order to define suitable interpolation criteria, the accumulation records were analyzed with respect to their spatial autocorrelation and statistical properties. The resulting accumulation pattern resembles well- known characteristics such as a relatively wet coastal area with a sharp transition to the dry interior, but also reveals complex topographic effects. Furthermore, this work identifies new high-return shallowdrilling sites by uncovering areas of insufficient sampling density.

Compressive experiments were performed on square (160 mm × 160 mm) prismatic specimens of columnar-grained, S2 freshwater ice, biaxially loaded across the columns at −10°C. The work focused on brittle behavior, achieved by deforming the specimens at an applied strain rate of 4.5 ± 1.2 × 10 3s 1 in the direction of shortening. The results show that the specimen thickness (25–150 mm) has no detectable effect on the terminal failure strength of the ice. Likewise, the strength of the ice when loaded under proportional loading, where the minor stress varies during the test, was similar to that when loaded under a constant minor stress, implying that terminal failure depends only on the stress state and not on the path taken.

We present seismic and radar data from the onset region of Rutford Ice Stream, West Antarctica, which show the form and internal structure of a variety of bed forms beneath an active ice stream. The ice flow in the area of our survey accelerates from 72 to >200 m a–1, the ice is 2200–3200 m thick, and the bed of the ice stream lies up to 2000 m below present sea level. We have imaged the internal structure of the bed forms with seismic reflection techniques and also observed radar reflections from below the bed in some circumstances. We observed a transverse moraine 2 km wide and 1.5 km long beneath the slower-flowing part of the ice stream, which we interpret to be composed of unconsolidated sediment undergoing active deformation near the ice–sediment interface. We observed drumlins of classical form with elongation ratios of between 1:1.5 and 1:4.0 where the surface flow speed exceeded 95 m a–1. The conformity of the internal structure of the bed forms with the ice base suggests that the bed forms are active depositional features in congruence with the observation of a contemporary drumlin-forming episode in the distal part of the same ice stream. These observations provide the first direct evidence of the association between ice-stream flow speed and bed-form shape.