The presence of cave ice is documented in many karst regions but very little is known about the age range of this potential paleoclimate archive. This case study from the Monlesi ice cave, Swiss Jura Mountains, demonstrates that dating of cave ice is possible using a multi-parameter approach. Ice petrography, debris content and oxygen isotope composition have the potential for identification of annual growth layers, but require a continuous core from the ice deposits, limiting application of this approach. Furthermore, complete melting of ice accumulations from individual years may occur, causing amalgamation of several annual bands. Use of 3H content of the ice and 14C dating of organic debris present in the ice proved to be of limited utility, providing rather broad bounds for the actual age. Initial estimates based on 210Pb analyses from clear ice samples gave results comparable to those from other methods. The most reliable techniques applied were the determination of ice turnover rates, and the dating of anthropogenic inclusions (a roof tile) in the ice. These suggest, respectively, that the base of the cave ice was a minimum of 120 and a maximum of 158 years old. Therefore, our data support the idea that mid-latitude and low-altitude subsurface ice accumulations result from modern deposition processes rather than from presence of Pleistocene relict ice.

We describe exact solutions to the thermomechanically coupled shallow-ice approximation in three spatial dimensions. Although artificially constructed, these solutions are very useful for testing numerical methods. In fact, they allow us to verify a finite-difference scheme, that is, to show that the results of our numerical scheme converge to the correct continuum values as the grid is refined in three dimensions. Comparison of numerical results with exact solutions has helped us to precisely quantify and understand some of the numerical errors we are making. Our verified numerical scheme shows the basal temperature spokes which arose in the EISMINT (European Ice Sheet Modelling INiTiative) II intercomparison (Payne and others, 2000). A careful analysis describes these warm spokes as numerical errors which occur when the derivative of the strain-heating term with respect to the temperature is large. On the other hand, the appearance of basal temperature spokes in a verified numerical scheme strongly suggests that they are a feature of the EISMINT II experiment F continuum problem. In fact, they are clear evidence of an unstable equilibrium point of the continuum problem. This paper is a sequel to Bueler and others (2005) which addresses exact solutions and verification in the isothermal case.

Analyses of confined and unconfined compression combined with shear, and of biaxial stress laterally confined or unconfined, are presented for a general deviatoric viscous relation describing the response of an incompressible material. At present, numerical models for ice-sheet flow commonly adopt a very simple viscous law throughout the ice sheet, in which the deviatoric stress is coaxial with the strain rate, and the single response function depends on only one invariant, and is determined by single stress component tests which cannot verify the validity of the simplification. The analysis presented here is concerned with two-stress-component experimental configurations which could determine the general quadratic form of a viscous relation, with two response functions depending on two invariants. It is shown that the two combined compression and shear tests can also check the consistency of a viscous fluid assumption, but not so the biaxial stress tests. Each test allows a direct assessment of the significance of the quadratic term. It is then shown that a significant quadratic term changes the relative stress magnitudes in the commonly adopted reduced model for ice-sheet flow, and that the crucial simplifications are not achieved.

Colinear-polarized 5 MHz radar profiling data were obtained on Mýrdalsjökull, a temperate glacier in Iceland. Radar transects, and therefore polarization planes, were aligned approximately parallel, transverse and oblique to the ice flow direction. Echoes from the shallower half to two-thirds of the ice were 10–20dB stronger on the oblique and longitudinal transects than those on the transverse transects. Anisotropy as a function of depth is clearly seen at the sites where the transects cross. Strong scattering on longitudinal transects apparently caused extinction of a radar-reflecting layer that was continuously profiled on the transverse transects. A radio-wave scattering model shows that scattering from a longitudinal water-filled conduit parallel to the glacier surface can explain the observed azimuthal variations of the echo. We conclude that low-frequency (~MHz) radio waves can help to characterize englacial water regimes.

Interpretation of ice-core records requires accurate knowledge of the past and present surface topography and stress–strain fields. The European Project for Ice Coring in Antarctica (EPICA) drilling site (75.0025° S, 0.0684° E; 2891.7 m) in Dronning Maud Land, Antarctica, is located in the immediate vicinity of a transient and forking ice divide. A digital elevation model is determined from the combination of kinematic GPS measurements with the GLAS12 datasets from the ICESat. Based on a network of stakes, surveyed with static GPS, the velocity field around the drilling site is calculated. The annual mean velocity magnitude of 12 survey points amounts to 0.74 m a–1. Flow directions mainly vary according to their distance from the ice divide. Surface strain rates are determined from a pentagonshaped stake network with one center point close to the drilling site. The strain field is characterized by along-flow compression, lateral dilatation and vertical layer thinning.

Uniqueness of the transition zone solution is discussed. It is argued that when it is assumed that the stresses are continuous at the grounding line, the ice-shelf solution at the grounding line should possess a zero slope. In order to avoid issues caused by the mathematical singularity of the solution, the same technique as that used to study the transition zone is applied to a similar problem of lifting an elastic sheet from a rigid substrate, which allows a better physical understanding. This exemplifies the effect of the bottom boundary condition of no vertical motion imposed up to a fixed grounding line position, while the forcing parameters, such as the flow rate, vary. Its effect is to produce multiple solutions due to suppression of the separation mechanism.

Knowledge of ice flow and strain rate in the vicinity of the Taylor Dome (East Antarctica) ice-core site enhances interpretation of the paleoclimate information from the ice core. We measured surface ice motion by repeated optical and GPS surveys of a network of 253 markers. We developed a robust data reduction method that uses least squares based on singular value decomposition, to simultaneously calculate positions and velocities of these markers in a geocentric coordinate system. Constrained by these surface velocities, we used a finite-element model to compute the modern ice velocity field at depth. As the geometry of Taylor Dome appears to have been steady through the Holocene, we used particle paths from a steady-state model to track ice particles to the ice core from their points of origin on the surface. By removing the effects of path-dependent vertical strain, we derived past accumulation rates at the origin points of those particle paths from measured layer thicknesses in the ice core. Comparison with accumulation rates estimated from concentrations of 10Be and SO4 in the core suggests that significant amounts of snow were lost by wind scouring during the Last Glacial Maximum and at ~50kyr BP.

We present preliminary results on the occurrence of Pb, Cd, Zn, Al and Fe in dated samples collected from snow–firn packs at an altitude of 4130 m on Ürűmqi glacier No. 1, eastern Tien Shan. Extreme precautions for avoiding contamination were taken throughout the sampling, processing, transportation and analysis procedures. The concentrations of trace metals were determined by a double-focusing inductively coupled plasma mass spectrometer in an ultra-clean room. The average concentrations for these metals in surface snow are (in ng g–1): Pb, 2.4; Cd, 0.05; Zn, 10.0; Al, 100.0; and Fe, 130.0. These are higher concentrations (especially for Pb and Zn) than those in the polar and/or low-latitude remote areas. The data show that the input of trace metals to the snow has a clear seasonal change. Lower concentrations in surface snow can be found in July through September and higher concentrations from October to March, with an exception for January. The mean concentrations of the elements in the snow–firn pack also indicate seasonal variations and show a marked inverse relationship with temperature, possibly a result of meltwater percolation in the snow–firn pack.

To avoid some of the limitations of studying soft-bed processes through boreholes, a prism of simulated till (1.8 m × 1.6 m × 0.45 m) with extensive instrumentation was constructed in a trough blasted in the rock bed of Engabreen, a temperate glacier in Norway. Tunnels there provide access to the bed beneath 213 m of ice. Pore-water pressure was regulated in the prism by pumping water to it. During experiments lasting 7–12 days, the glacier regelated downward into the prism to depths of 50–80 mm, accreting ice-infiltrated till at rates predicted by theory. During periods of sustained high pore-water pressure (70–100% of overburden), ice commonly slipped over the prism, due to a water layer at the prism surface. Deformation of the prism was activated when this layer thinned to a sub-millimeter thickness. Shear strain in the till was pervasive and decreased with depth. A model of slip by ploughing of ice-infiltrated till across the prism surface accounts for the slip that occurred when effective pressure was sufficiently low or high. Slip at low effective pressures resulted from water-layer thickening that increased non-linearly with decreasing effective pressure. If sufficiently widespread, such slip over soft glacier beds, which involves no viscous deformation resistance, may instigate abrupt increases in glacier velocity.

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.

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.

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 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.

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.

We use a global coupled ocean-sea ice model to test the hypothesis that the disintegration of the West Antarctic ice sheet (WAIS), or just its ice shelves, may modify ocean circulation and sea-ice conditions in the Southern Ocean. We compare the results of three model runs: (1) a control run with a standard (modern) configuration of landmask in West Antarctica, (2) a no-shelves run with West Antarctic ice shelves removed and (3) a no-WAIS run. In the latter two runs, up to a few million square kilometres of new sea surface area opens to sea-ice formation, causing the volume and extent of Antarctic sea-ice cover to increase compared with the control run. In general, near-surface waters are cooler around Antarctica in the no-shelves and no-WAIS model runs than in the control run, while warm intermediate and deep waters penetrate further south, increasing poleward heat transport. Varying regional responses to the imposed changes in landmask configuration are determined by the fact that Antarctic polynyas and fast ice develop in different parts of the model domain in each run. Model results suggest that changes in the extent of WAIS may modify oceanographic conditions in the Southern Ocean.

Results of laboratory uniaxial compression tests over the stress range 0.18–0.52 MPa and the strain range 0.5–8.6% at approximately –5 and –20°C are presented. Grain-size analysis and comparisons with annealing tests confirm that grain-growth reducing processes are active during deformation. Microstructural observations reveal that subgrain-rotation recrystallization and grain-shape changes due to strain-induced grain-boundary migration are the causes of the grain-growth deceleration. Further results from microstructural observations show that obstacle formation by dislocation walls and subgrain boundaries is the reason for isotropic hardening during creep. Subgrainboundary types that are likely to be relevant for studies on the activity of different dislocation types are described.

We show that it is possible to extract a high-resolution (annual) paleoclimate record from the surface of a blue-ice area (BIA). The variability of the surface stable-isotope values suggests that almost all the surface ice in Scharffenbergbotnen BIA, East Antarctica, is of Holocene age. The isotopic changes across the BIA show that the modern climate there is warmer than the climate in the early-Holocene optimum (11 kyr BP). A volume-conserving ice flow model for the BIA constrained by isotopic variability and layer thicknesses, and a series of 14C ages indicate both that the BIA has been smaller than now, and that the surface velocities were considerably smaller during the Last Glacial Maximum. Changes in ice-sheet thickness drive the BIA towards present-day conditions. The relatively young age of the majority of the BIA also explains the lack of meteorite finds in this area, and may be typical for many BIAs in low-elevation nunatak areas.

The Australian Antarctic Program’s iceberg dataset (from ship-based observations), including information from the austral summer seasons 1984/85 to 1999/2000, is examined and used to extend earlier studies. Using ‘snapshots’ of the iceberg population to provide an idea of the iceberg life cycle, the distribution of icebergs between 60 and 150° E is discussed in terms of calving regions and ocean currents. Temporal changes are also examined. The discussion leads us to the point where we can define an area, bounded to the north by the maximum sea-ice limit and to the south by the Antarctic Divergence, in which icebergs are confined as they drift eastward. This allows estimation of total dissolution, in terms of iceberg numbers and volume, within 10° longitudinal sectors and, with knowledge of drift speeds, iceberg movement rates and freshwater input across the sector. Iceberg dissolution rates are found to be ~0.03–0.05 m d–1 and the total mass contribution of fresh water to the ocean as the icebergs traverse our 30° of longitude study sector is ~32 Gt. This amounts to a contribution equivalent to precipitation of ~15.5 cm a–1, accounting for ~2% of the total iceberg discharge from the Antarctic ice sheet.