Sea-ice extent and concentration are routinely measured using satellite sensors. However, regional estimates of sea-ice thickness cannot be measured directly from space, and largely depend on field observations with in the pack ice. One difficulty is estimating the amount of ice contained in pressure ridges. These ridges can contribute substantially to the total ice volume, yet are highly variable both spatially and temporally. Here we provide estimates of sea-ice ridge height and frequency in the East Antarctic region around 65° S, 140° E. We calculate ridge height distributions using high-resolution (< 1 m) digital aerial photography collected in August 1995. Wc examine the ridge height distribution and ridge concentration from near the coast of Antarctica northwards to the marginal ice zone. The area-averaged volume of ice in ridges contributes 0.06-1.35 m to the undeformed ice thickness in winter. There is a band of less deformed ice centred around 65° S, with more highly deformed ice to the south. Similar features are identified in satellite synthetic aperture radar data collected over the same region in August 1995 and 1996, and in observations of sea-ice characteristics collected during field experiments.

Detailed surface topography is presented for two dome features of the West Antarctic ice sheet, Siple Dome and Roosevelt Island. Both these domes show linear topographic features, or “scars”, on [heir flanks. Topography is determined from a combination of existing digital elevation models (DEMs; based on satellite radar altimctry), photoclinomctry (using advanced very high-resolution radiometer images to quantitatively infer topographic details) and, in the case of Siple Dome, surface global positioning system topographic profiles. The enhanced DEMs provide heights and shapes for a variety of surface features in the vicinity of the domes, such as scars, surface undulations, ice rises and the domes themselves.

The DEMs indicate that the scar features on both domes are high relative to adjacent rapid-ice-llow areas. Scars and other related morphologic features on the flanks of both domes can be interpreted as former active ice streams and stream margins. For Siple Dome, this interpretation is confirmed by radar profiling. The evolution of the topographic height of the scars is a combination of two processes: initial elevation rise due to a positive mass balance at the shear margin in the immediate aftermath of shut-down of the ice stream; and later downslope flow as the scars become part of the dome and the dome surface velocity field. Superimposed on these events is accumulation, which buries the original shear margin but elevates the scar surface expression. Depending upon the timing of shut-flown, and the relative magnitude of these processes, the height of the scars above the current rapidly flowing surfaces may be indicative of ice-sheet thinning since shut-down, or dome expansion across former ice-stream trunks in a more or less steady-state ice sheet.

Glaciological and related observations from 1961 to 2005 at the summit of Mt Wrangell (62.00° N, 144.02°W; 4317m a.s.l.), a massive glacier-covered shield volcano in south-central Alaska, show marked changes that appear to have been initiated by the Great Alaska Earthquake (Mw = 9.2) of 27 March 1964. The 4×6 km diameter, ice-filled Summit Caldera with several post-caldera craters on its rim, comprises the summit region where annual snow accumulation is 1–2m of water equivalent and the mean annual temperature, measured 10 m below the snow surface, is –20°C. Precision surveying, aerial photogrammetry and measurements of temperature and snow accumulation were used to measure the loss of glacier ice equivalent to about 0.03 km3 of water from the North Crater in a decade. Glacier calorimetry was used to calculate the associated heat flux, which varied within the range 20–140Wm–2; total heat flow was in the range 20–100MW. Seismicity data from the crater’s rim show two distinct responses to large earthquakes at time scales from minutes to months. Chemistry of water and gas from fumaroles indicates a shallow magma heat source and seismicity data are consistent with this interpretation.

The performance of a regional atmospheric climate model (RACMO) with a horizontal resolution of 55 km X 55 km is evaluated using measured temperature and humidity profiles. Parameterisations of the physical processes are taken from the EC-HAM4 general circulation model (GCM). Sea-surface temperatures and sea-ice mask in the model are prescribed from observations. The model is forced by re-analyses of the European Centre for Medium-range Weather Forecasts (ECMWF) at the lateral boundaries.

We compared simulations for January 1993 with boundary-layer profiles measured at the Swedish research station Svca (Dronning Maud Land, Antarctica) and with radiosonde measurements made at the Georg von Neumayer (GvN) and South Polar stations for the same period. This comparison was performed in order to study some model characteristics before the model is used for mass-balance calculations. The vertical temperature gradient at Svea during the night is overestimated by RACMO, but corresponds much more closely to the observations than do the ECMWF re-analyses. in the re-analyses a decoupling of the lowest model layer from the higher atmosphere occurs. The differences between the absolute temperatures at the GvN and SP stations and the absolute temperatures at the model gridpoints corresponding most closely to these sites are less than 5°C. The humidity profiles indicate that the model generally underestimates the turbulent transport of moisture from the surface to higher levels.

During the 16th Italian Antarctic Expedition (2000/01) a geomorphological survey of permafrost-related polygons was carried out in the Mesa Range area, upper Rennick Glacier. The investigated site is located in the uppermost reaches of Pain Mesa, which forms the northern sector of the Mesa Range. An ice wedge was found in a volcanic regolith at about 2200ma.s.l. This altitude is below a well-defined erosional trimline, located at about 2380ma.s.l. in this sector of Pain Mesa. The ice was sampled by inserting an ice screw, with an internal diameter of 14 mm, into the ice wedge in vertical sequences. Oriented block samples for thin sections were taken. A co-isotopic study was performed, measuring both oxygen (δ18O) and hydrogen (δD) isotope compositions. Tritium activity was measured, and major cations and anions were determined. The δ18O and δD obtained showed a strong divergence from the snowfalls expected to occur at this elevation, with extremely negative d excess values. Sublimation processes were taken into account to define the origin of the ice forming the wedge. The tritium data obtained suggest that the growth process of the ice wedge might still be active today.

The granular nature of the Arctic pack ice, and the plastic nature of the deformation of the pack due to ridging, has long been recognised. However, because of a lack of experimental data, assumptions must be made to define the shape of the yield curve and the associated flow rule which characterize the aggregate rheology of the ice pack. In this work, the results of numerical experiments with a simulated granular viscous-plastic material are presented. The experiments model the granular texture of the ice pack as a dense assembly of non-uniform diameter disks in a rectangular control area. Deformation of the control area is driven by constant strain rates. In the experiments, the ratio of the principal strain rates is varied from isotropic convergence through uniaxial divergence. The stresses computed in the experiments, at the various strain-rate ratios, define a yield curve in principal-stress space. The effects of different coefficients of friction and viscous damping on the shape of the yield curve are explored.

Experimental investigations on the formation and growth processes of air-hydrate crystals were carried out to determine the transformation process of air bubbles into air-hydrate crystals in deep ice sheets. The microscopic observations revealed that the transformation began at the boundary between a bubble and ice. Faster transformation occurred along the boundary and, subsequently, the transformation progressed towards the center of the bubble at a lower rate. Each transformation rate increased with pressure and also with temperature. The activation energy of the transformation was about 0.52 eV for the primary transformation process and about 0.90 eV for subsequent processes. These results indicate that the rate determining the process of transformation is mainly supplementation of water molecules to the transformation site. An estimation of the transformation period of an air bubble into an air-hydrate crystal in a deep ice sheet reveals that it is about one thousandth of the time period of the transition zone, where both air-hydrates and air bubbles exist

Measurements of electrical conductivity (EC) and deuterium isotopes in glacier run-off provide the basis for the application of simple mixing models that separate hydrographs into four constitutive components: subglacial, englacial, melt and rainfall-derived waters. Volumes of these components are determined from the models in two adjacent drainage basins within the glacier. Peak arrival times of both EC and isotopes during discharge events on short-term time-scales (days to weeks) differ in each terminus stream by as much as a factor of 5. Englacial water storage determined from the model varied greatly (98%) between neighboring basins within the glacier. Estimates of basal water volumes expressed as a layer thickness at the bed of the glacier differed by 50% (5 and 10mm each). Other results suggest that a greater percentage of water is stored at the glacier bed during rainfall events, and exceeds the storage capacity found within the seasonal snow and englacial zones combined.

The interannual variations in atmospheric transport patterns to Summit, Greenland, are studied using twice-daily, three-dimensional, 10 day backward trajectory data corresponding to the summers (1 June–31 August) of 1989–98. While previous trajectory climatology studies have been prepared for Summit, the present work considers both the horizontal and vertical components of transport. A three-dimensional residence-time methodology is employed to account for both horizontal and vertical components of transport. the vertical transport component is quantified by passing all trajectories through a three-dimensional grid and tracking the time spent (i.e. the residence time) in each gridcell. This method also allows inspection of trajectory altitude distributions corresponding to transport from upwind regions of interest. the three-dimensional residence-time methodology is shown to be a valuable tool for diagnosing the details of long-range atmospheric transport to remote locations. for Summit, we find that the frequent transport from North America tends to occur at low altitudes, whereas transport from Europe is highly variable. Mean summertime flow patterns are described, as are anomalous patterns during 1990,1996 and 1998.

Ice sheets and smaller ice caps appear to behave in dynamically similar ways; both contain slow-moving ice that is probably frozen to the bed, interspersed with fast-flowing ice streams and outlet glaciers that terminate into the ocean. Academy of Sciences Ice Cap (Akademii Nauk ice cap; 5570 km2), Severnaya Zemlya, Russian High Arctic, provides a clear example of this varied flow regime. We have combined satellite measurements of elevation change and surface velocity to show that variable ice-stream dynamics dominate the mass balance of the ice cap. Since 1988, the ice cap has lost 58±16 Gt of ice, corresponding to ~3% of its mass or 0.16mm of sea-level rise. The climatic mass balance is estimated to be close to zero, and terminus positions have remained stable to within a few kilometers, implying that almost all mass loss has occurred through iceberg calving. The ice-cap calving rate increased from ~0.6 Gt a–1 in 1995 to ~3.0 Gt a–1 in 2000–02, but has recently decreased to ~1.4 Gt a–1 due to a likely slowdown of the largest ice stream. Such highly variable calving rates have not been reported before from High Arctic ice caps, suggesting that these ice masses may be less stable than previously thought.

A finite-element model for simulating multi-dimensional air flow with heat, mass and chemical species transport through firn is discussed. The model is applied to an investigation of near-surface layering effects on ventilation rates. Field measurements of permeability at Summit, Greenland, are presented that show that permeability varies by at least a factor of 10 over the top 3 m, with the surface windpack having much lower permeability, in general, than the underlying firn. The effect of a lower-permeability surface layer is to decrease the air flow in the underlying firn, yet there is still sufficient air flow in the top meters of the firn so that ventilation must be considered for species transport. Channeling, or increased air flow in a layer overlain by a less-permeable layer, can occur even if the microstructure of each layer is isotropic. Conventional estimates of chemical transport due to diffusion alone are likely to underestimate transport, while estimates of ventilation that consider the firn as a homogeneous half-space may overestimate ventilation effects at the near-surface. Effects of firn layering are important for ventilation and must be considered for accurate assessment of firn–air transport mechanisms.

Mass-balance measurements were initiated on Engabreen, an outlet glacier from the Svartisen ice cap, Norway, in 1970. The glacier boundary was defined based on where meltwater drained, as the interest in Engabreen was mainly hydrological. However, the apparent discrepancy between the calculated cumulative glacier mass balance since 1970 and changes in glacier geometry prompted a re-examination of the glacier boundary. The glaciological drainage boundary is defined by studying whether ice flow physically contributes to Engabreen tongue and corresponds to a glacier with an area of 27.2 km2, significantly smaller than that defined by the hydrological drainage boundary at 39.6 km2. This glaciological drainage boundary is here named the ice-flow perimeter. The area difference between this and the hydrological drainage boundary is largest for the altitudinal range 1300–1400ma.s.l. Generally, the ‘glaciological’ glacier is lower in mean altitude than the ‘hydrological’ glacier, and this affects the calculated specific mass balance. Using the glaciological boundary leads to reductions in mean annual winter and summer balance (when spatial differences are ignored) of 0.12 mw.e. (from 2.92 to 2.80mw.e.) and 0.15 mw.e. (from –2.32 to –2.47mw.e.), respectively. The reduction in mean net balance for the period 1970–2006 is 0.27mw.e. (from +0.59 to +0.32mw.e.) which is about 50% of the calculated mass surplus in this period. This illustrates that the choice of glacier outline can significantly influence the long-term cumulative mass balance and that results from outlet glaciers must be interpreted with care when used for regional estimates of glacier change.

Subglacial rock friction is an important control on the sliding dynamics and erosive potential of hard-bedded glaciers, yet it remains largely unconstrained. To explore the relative influence of basal melt rate, effective stress and ice temperature on frictional resistance, we conducted abrasion experiments in which limestone beds were slid beneath a fixed slab of ice laden with granitic rock fragments. Shear stress scales linearly with melt rate and cryostatic stress, confirming that both viscous drag and effective stress are first-order controls on the contact force in drained conditions. Furthermore, temperature gradients in the ice increase the contribution of viscous drag on basal shear stress. In all experiments, the relationship between melt rate and shear stress is best explained by a model that accounts for the effects of regelation and viscous creep on the bed-normal drag force. We interpret this to mean fluid flow around entrained clasts contributed to basal drag even at subfreezing temperatures. Incorporating premelting dynamics into the Watts/Hallet model for subglacial rock friction, we find that the predicted debris-bed drag decreases by approximately an order of magnitude, with a corresponding ~3.5 × increase in the transition radius. This is lower than we observe for ice slightly below the pressure melting point.

Over the course of the 2014/15 and 2015/16 austral summer seasons, the South Pole Ice Core project recovered a 1751 m deep ice core at the South Pole. This core provided a high-resolution record of paleoclimate conditions in East Antarctica during the Holocene and late Pleistocene. The drilling and core processing were completed using the new US Intermediate Depth Drill system, which was designed and built by the US Ice Drilling Program at the University of Wisconsin–Madison. In this paper, we present and discuss the setup, operation, and performance of the drill system.

Landsat-5 Thematic Mapper (TM) data from Dronning [Queen] Maud Land, Antarctica, have been analysed to provide insights into physical properties of the ice sheet. Brightness (at-satellite) temperatures calculated from digital numbers of the thermal band (TM band 6), using state-of-the-art equations and constants (Markham and Barker 1986), are 8° to 20°C lower than temperatures measured on the surface. Such differences cannot be ascribed to atmospheric absorption or to emissivity variations; instead, they suggest errors in either the sensor or instrument calibration for the temperature range 0° to −20°C. The results indicate an excess gain factor of about 1.63. The TM band 6 data seem to reproduce faithfully the relative temperature variations across the surface.

Principal components (PCs) calculated for TM bands 2, 3, 4, 5, and 7 are presented for a region of the interior ice sheet. PCs are superior to individual bands or combinations of bands for analysing the main characteristics of an image, such as rendition of surface topography (mostly given in PCl), and for distinguishing between different surface materials (mostly given in PCs 2 and 3). Band ratioing was most useful for enhancing subtle albedo variations, such as those caused by changes in surface properties due to melting.

TM data of the region, collected 18 d apart, show large changes on the snow surface; strong patterns shown in PC2 and TM bands 5 and 7 of the earlier image were nearly faded 18 d later. These strong patterns are not present at visual wavelengths or in the thermal band, and we believe they reflect wind-related variations in the physical properties of the snow.

The British Antarctic Survey, in collaboration with Laboratoire de Glaciologie et Géophysique de l’Environnement, has in recent years successfully drilled to bedrock on three remote sites around the Antarctic Peninsula. Based on the experience from the multi-season project at Berkner Island (948m depth, 2002–05) we optimized the drill set-up to better suit two subsequent single-season projects at James Ross Island (363m depth, 2008) and Fletcher Promontory (654m depth, 2012). The adaptations, as well as the reasons for them, are discussed in detail and include a drill tent set-up without a trench; drilling without a borehole casing with a relatively low fluid column height; and using a shorter drill. These optimizations were aimed at reducing cargo loads and installation time while maintaining good core quality, productivity and a safe working environment. In addition, we introduce a number of innovations, ranging from a new lightweight cable tensioning device and drill-head design to core storage and protection trays. To minimize the environmental impact, all the drill fluid was successfully recovered at both sites and we describe and evaluate this operation.

Ice cores provide a valuable archive of climate history. for a complete understanding of this archive, it is important to understand air–snow exchange processes through the snow and firn in order to fully decode the ice-core record. Transport processes through the snow and firn are dependent upon their physical properties. In this paper, bidirectional permeabilities from selected sections of a 13 mcore from Summit, Greenland, are presented. Differences between lateral and vertical permeabilities are evident throughout the core in permeameter data and in microstructure statistics. Both lateral and vertical permeabilities are consistent with overall patterns of previous polar permeability data with depth. the differences between lateral and vertical permeability measurements for some samples can be attributed to equivalent sphere radius. Further studies examining mean free-path length may be helpful in chemical modeling and in deriving an equation relating permeability to microstructure.

Changes in the shear strength of faceted crystals were measured and parameterized under equi-temperature conditions in the laboratory. The air temperature and bottom temperature of the snow layer were controlled to create a large temperature gradient for 8.8 days to make faceted crystals. Subsequently, the temperature gradient was eliminated and the snow was kept under equi-temperature conditions (–5°C and –10°C) for 55 days. During the experiments, the snow density and shear strength were measured six times. The measured shear strength was compared with two empirical relationships based on density. One of these relationships addresses the strength of round grains, whereas the other refers to faceted grains. The measured shear strength approached the calculated value for faceted crystals when the temperature gradient was large, whereas it approached that for rounded grains after the temperature gradient was removed. The dry snow metamorphism factor (DSM factor), which expresses the developmental stage of faceted crystals, was used to model the shear strength increase under equi-temperature conditions. The DSM factor indicates shear strength using an empirical equation based on rounded grains or faceted crystals. It is approximately 0 for rounded grains and 1 for faceted crystals. It decreased from 1.04 to 0.84 and 0.79 at –10°C and –5°C, respectively, in 55 days. These results were incorporated into the numerical snowpack model SNOWPACK, which successfully reproduced the experimentally observed increase in shear strength under equi-temperature conditions.

The aim of the paper is (1) to develop theory to describe sea ice as a collection of finite-sized floes and (2) to construct a rheology based on this description.

Successful sea-ice models have considered the ice to be a two-dimensional continuum with a nonlinear plastic rheology, a two-dimensional yield curve being used to determine the internal ice stresses as functions of the strain-rate (Hibler 1979). In this paper, the shape but not the size of such a yield curve is derived from an idealized picture of floes as moving discs, randomly distributed in a plane. The expected collision rate, which determines the energy loss, is calculated in terms of the average floe size, the areal floe-number density, and the strain-rate. For the case in which the ice strength is low, the dependence of the energy loss upon the strain-rate implies a lens-shaped yield curve, the curved portions being parts of a sine wave. This compares with circular, tear drop-shaped and elliptical yield curves that have been used in sea-ice models to date (Coon 1974, Colony 1976, Hibler 1979). The applicability of the derived yield curve to cases where the ice strength is not low and significant ridging takes place, such as in a continuous ice cover is discussed.

This study examines a new method for reconstructing mean summer temperature variations by using an ice core from a wet-snow zone on a summer-accumulation-type glacier. In July 2001, a 25.1 m deep ice core was recovered from the accumulation area of Sofiyskiy glacier (49°47’ N, 87°43’ E; 3435m a.s.l.), located in the southern Chuyskiy range of the Russian Altai mountains, and a 4.5 m deep pit was excavated about 5 0m northwest of the drill site. The observation site has a positive balance even during summer when melting occurs. The summer balance for each year from 1990 to 2000 was estimated from Pinaceae and Artemisia pollen peaks in these samples. Pinaceae pollen marks spring, whereas Artemisia pollen marks autumn. Moreover, meltwater intrusion did not reach the previous year’s accumulation. Thus, the ice between these pollen peaks in the same year was used to estimate a summer balance. The reconstructed summer balance variations were negatively correlated with mean summer temperature variations (r = –0.72, P< 0.05). This study shows that, for summer-accumulation-type glaciers such as Sofiyskiy glacier, the most important climate factor controlling the glacier’s surface mass balance is mean summer temperature. Therefore, the summer layer thickness in an ice core can be used as a proxy for reconstructing mean summer temperature variations.