A series of ice-sheet-model intercomparison exercises have been organized as part of EISMINT. One such set of experiments investigated the implications of thermomechanical coupling on the flow of ice sheets with idealized geometry The results of these experiments are discussed by Payne and others (in press). They indicate that local concentrations of ice flow may develop as a consequence of interactions between ice flow, temperature and viscosity The nature of the intercomparison exercise meant that only a limited number of experiments could be performed by the ten contributing groups. Many of the implications arising from the results could not therefore be investigated. This paper focuses on four. They are the initiation of the patterning, its reversibility the influence of the relationship between ice temperature and viscosity and dependence on numerical time-step and horizontal grid size.

We report the results of a comparative analysis focusing on grain size, mineralogical composition and spectral reflectance values (400-2500 nm) of cryoconite samples collected from Jakobshavn Isbræ, West Greenland, and Canada Glacier, McMurdo Dry Valleys, Antarctica. The samples from the Greenland site were composed of small particles clumped into larger rounded agglomerates, while those from the site in Antarctica contained fragments of different sizes and shapes. Mineralogical analysis indicates that the samples from Jakobshavn Isbræ contained a higher percentage of quartz and albite, whereas those from Canada Glacier contained a higher percentage of amphibole, augite and biotite. Spectral measurements confirmed the primary role of organic material in reducing the reflectance over the measured spectrum. The reflectance of the samples from the Antarctic site remained low after the removal of organic matter because of the higher concentration of minerals with low reflectance. The reflectance of dried cryoconite samples in the visible region was relatively low (e.g. between ∼0.1 and ∼0.4) favouring increased absorbed solar radiation. Despite high reflectance values in the shortwave infrared region, the effect of the presence of cryoconite is negligible at infrared wavelengths where ice reflectance is low.

The transformation of ocean water masses at high latitudes is closely related to the freezing and melting processes during the year. Downward salt fluxes from brine rejection during freezing increase the salinity and density of the water column underneath. Fresh-water input from river run-off and melting of sea ice reduces the density, mainly of the surface layer. Hydrographic profiles collected in Storfjorden, Svalbard, in spring and summer, show the strong seasonal and interannual variability of the water masses. Using, in addition, data from moorings, a ship-borne acoustic Doppler current profiler and drifting buoys, and results from models of ice drift, polynya evolution, ice formation and convection processes during freezing, we document the seasonal water-mass transformation and try to explain its interannual variability. The advection of ice and water through the two northern sounds and over the sill in the south of the fjord is examined. The release of brine-enriched bottom water over the sill must be balanced by advection from the Barents Sea in the upper layers. The interannual variability of the brine-enriched bottom layer is very high, and higher salinities are observed in a milder winter. The density anomaly resulting from freezing might depend more on the ice cover and geographical position of the polynya than on the total atmospheric forcing during winter.

Many of the large outlet glaciers of Vatnajökull ice cap, Iceland, have a history of regular surges. The mass transport during surges can be up to 25% of the total ice flux. This is a considerable amount that affects the whole ice cap, the location of the ice divides, the flow field and the size and shape of the ice cap. Data from the surging outlet Dyngjujökull, on the northern side of Vatnajökull, which surged during the period 1998-2000, are presented: surface elevation changes, displacement and total mass tr ansport. The total gain in ice volume in the receiving area, due to the surge, is considerably smaller than the loss in the reservoir area. The difference is mainly due to enhanced melting rates on the larger surface area of the crevassed glacier surface, and increased turbulent fluxes above the surface, but also due to increased frictional melting at the bed during the surge. A two-dimensional vertically integrated numerical flow model, of standard shallow-ice approximation type, is used to show that a modeled glacier that is similar in size to Dyngjujökull and subject to the same mass balance has three times higher velocities than the measured velocity during the quiescent phase. Adding surges in the numerical model, by periodically increasing the sliding velocity, causes the glacier to retreat and oscillate around a smaller state when subject to the same mass-balance regime. Lowering the equilibrium line by 50 m lets the modeled surging glacier oscillate around a size similar to that of the present glacier, indicating that surging is an efficient long-term ablation mechanism.

In February 1995 an automatic weather station (AWS) was placed on Thyssen Hohe, the south dome of Berkner Island, Antarctica. A fairly complete 3 year meteorological dataset of hourly average data was obtained. The mean annual temperature is about –24°C. The annual mass balance is about +180 mm we. Summer temperatures stay below 0°C, which implies that no melt takes place. Because the AWS is located on a dome, katabatic winds are not active, the wind direction is variable (directional constancy 0.38) and the wind speed relatively low (4.5 ms−1). Annual average variables are compared with data from Recovery Glacier AWS and Halley station.

The measurements are used to evaluate the surface energy fluxes for the 3 year period by using a surface energy-balance model. The annual average gain of energy from the sensible-heat flux ( + 10.8 W m–2) is balanced by a negative net radiative flux (–9.1 W m−2) and a small negative latent-heat flux (-1.7 W rrT2). The annual subsurface flux is small.

Snow sublimation is a fundamental process that affects the snow crystal structure and is important for ice-core interpretation, remote sensing, snow hydrology and chemical processes in snow. Prior studies have shown that sublimation can change the isotopic content of the remaining snow; these studies have inferred sublimation rates using field data, and were unable to control many of the environmental parameters that determine sublimation rate (e.g. temperature, relative humidity, snow microstructure). We present sublimation rate measurements on snow samples in the laboratory, where we have controlled many of these parameters simultaneously. We use the same experimental apparatus to determine sublimation rate, investigate the isotopic effects of sublimation, and study the isotopic exchange between vapor and solid. Our results suggest that pore spaces in snow are almost always at saturation vapor pressure; undersaturation may be possible in large pore spaces or in regions of rapid interstitial airflow. We present a revised formulation for determining the mass-transfer coefficient for snow as a linear function of Reynolds number (hm = 0.566Re + 0.075), estimate the fractionation coefficient for sublimating snow, and provide evidence for isotopic exchange between vapor and solid.

Accumulation rates and their spatio-temporal variability are important boundary conditions for ice-flow models. The depths of radar-detected internal layers can be used to infer the spatial variability of accumulation rates. Here we infer accumulation rates from three radar layers (26, 35 and 41 ka old) in the Vostok Subglacial Lake region using two methods: (1) the local-layer approximation (LLA) and (2) a combination of steady-state flowband modeling and formal inverse methods. The LLA assumes that the strain-rate history of a particle traveling through the ice sheet can be approximated by the vertical strain-rate profile at the current position of the particle, which we further assume is uniform. The flowband model, however, can account for upstream strain-rate gradients. We use the LLA to map accumulation rates over a 150 km × 350 km area, and we apply the flowband model along four flowbands. The LLA accumulation-rate map shows higher values in the northwestern corner of our study area and lower values near the downstream shoreline of the lake. These features are also present but less distinct in the flowband accumulation-rate profiles. The LLA-inferred accumulation-rate patterns over the three time periods are all similar, suggesting that the regional pattern did not change significantly between the start of the Holocene and the last ~20 ka of the last Glacial Period. However, the accumulation-rate profiles inferred from the flowband model suggest changes during that period of up to 1 cma–1 or ~50% of the inferred values.

Bering Glacier, Alaska, USA, has a ∼20 year surge cycle, with its most recent surge reaching the terminus in 2011. To study this most recent activity a time series of ice velocity maps was produced by applying optical feature-tracking methods to Landsat-7 ETM+ imagery spanning 2001-11. The velocity maps show a yearly increase in ice surface velocity associated with the down-glacier movement of a surge front. In 2008/09 the maximum ice surface velocity was 1.5 ±0.017 km a-1 in the mid-ablation zone, which decreased to 1.2 ±0.015 km a-1 in 2009/10 in the lower ablation zone, and then increased to nearly 4.4 ± 0.03 km a-1 in summer 2011 when the surge front reached the glacier terminus. The surge front propagated down-glacier as a kinematic wave at an average rate of 4.4 ±2.0 km a-1 between September 2002 and April 2009, then accelerated to 13.9 ± 2.0 km a-1 as it entered the piedmont lobe between April 2009 and September 2010. The wave seems to have initiated near the confluence of Bering Glacier and Bagley Ice Valley as early as 2001, and the surge was triggered in 2008 further down-glacier in the mid-ablation zone after the wave passed an ice reservoir area.

During spring 2013, we performed 500 MHz, helicopter-borne impulsive ground-penetrating radar surveys of several glaciers and glacier forelands in south-central Alaska, USA. These surveys were designed to obtain spatially distributed measurements of snow accumulation spanning a broad range of continental and maritime climatic zones. Visual assessment of radar images shows that data quality varied with the terrains and was optimal for snow that covered smooth glacier ice and firn, smooth debris-covered areas and moraines, freshwater lake and river ice, tundra, and taiga. Conversely, returns from the base of the snowpack were unrecognizable over rough debris-covered glacier termini, icefalls and some high-altitude accumulation basins. Optimal flying speed was 15-20ms–1 (30–40kt). At these speeds, which are two to three times faster than previously reported for such surveys, we could still identify snow-depth data with confidence, at a point spacing of ~1.5-2.0m. Data quality on glaciers decreased with increased air speed, though useful echoes from the base of the snowpack were still obtained at 40-45 ms–1 (87 kt; data point spacing of 6-8 m). Similar high-speed surveys over non-glacial terrains were unsuccessful, as basal reflections were no longer recognizable.

During the deformation of polar ice, a fabric develops which results in a macroscopically anisotropic behaviour. Since the plastic anisotropy of the ice single crystal is very high, the effect of a strong (single maximum) fabric on the macroscopic flow law cannot be neglected when simulating the flow of an ice sheet. As this is already a difficult task when using the familiar isotropic power law for ice, the fabric evolution and related macroscopic mechanical behaviour model, to be implemented in such a simulation, must be realistic yet simple enough to achieve results within a reasonable level of complexity, at least as a first step.

To this aim, we propose to model polar ice as a transversely isotropic medium; while simplifying the problem, this captures the essential features of the in-situ observed fabrics. The macroscopic mechanical behaviour of the ice polycrystal is obtained by using an orientation distribution function (ODF) for the c axes of the grains, which characterizes the fabric, and a self-consistent scheme, considering each single crystal as transversely isotropic. The evolution of the ODF is described by a conservation equation. In the first stage, this model was run in the simple cases of uniaxial compression and tension along the orthotropy symmetry axis.

Although the formation and melt of sea ice are primarily functions of the annual radiation cycle, atmospheric sensible-heat forcing does serve to delay or advance the timing of such events. Additionally, if atmospheric conditions in the Arctic were to vary due to climate change it may have significant influence on ice conditions. Therefore, this paper investigates a methodology to determine melt-onset dale distribution, both spatially and temporally, in the Arctic Ocean and surrounding sea-ice covered regions.

Melt determination is made by a threshold technique using the spectral signatures of the horizontal brightness temperatures (19 GHz horizontal channel minus the 37 GHz horizontal channel) obtained from the Special Sensor Microwave Imager (SSM/I) passive-microwave sensor. Passive-microwave observations are used to identify melt because of the large increase in emissivity that occurs when liquid water is present. Emissivity variations are observed in the brightness temperatures due to the different scattering, absorption and penetration depths of the snowpack from the available satellite channels during melt. Monitoring the variations in the brightness temperatures allows the determination of melt-onset dates.

Analysis of daily brightness temperature data allows spatial variations in the date of the snow inch onset for sea ice to be detected. Since the data are gridded on a daily basis, a climatology of daily melt-onset dates can be produced for the Arctic region. From this climatology, progression of melt can be obtained and compared inter-annually.

Glaciar Perito Moreno (GPM) and Glaciar Ameghino (GA), Southern Patagonia Icefield, are in contact in the accumulation area, but have shown contrasting frontal variations in the past few decades. To investigate recent changes of the two glaciers and processes controlling the different responses to similar climate conditions, we measured surface elevation change from 2000 to 2008 and terminus positions from 1999 to 2012 using several types of satellite data. GPM shows no significant changes in terminus position and 0.4 ± 0.3 m a–1 thickening over the period, whereas GA retreated 55 ± 2 m a–1 and thinned 2.6 ± 0.3 m a–1. Mass-balance measurements over the period 1999/2000 show that accumulation at GPM was ten times greater than that at GA, but ablation was only three times greater. The mass-balance–altitude profile is similar for the two glaciers; differences in the mass-balance distribution are caused by differences in the accumulation–area ratio (AAR). Our results suggest that the AAR and the calving flux exert strong control on the evolution of glaciers in the region.

The deep ice-sheet coring (DISC) drill was used for production ice-core drilling at WAIS Divide in Antarctica for six field seasons between 2007 and 2013. Continuous ice-core samples were obtained between the snow surface and 3405 m depth. During the 2012/13 austral summer, the DISC drill’s newly designed replicate ice-coring system was utilized to collect nearly 285m of additional high-quality core samples at depths of high scientific interest. Annual progress graphs are described, as well as milestones achieved over the course of the project. Drilling operations, challenges encountered, drill fluid usage, drilling results, and the drill crew’s experiences with the DISC drill and replicate coring system during production drilling are described and discussed in detail. Core-processing operations are described briefly, as well as the logistical undertaking of the DISC drill’s deployment to Antarctica.

Calving mechanisms are still poorly understood and stress states in the vicinity of ice-shelf fronts are insufficiently known for the development of physically motivated calving laws that match observations. A calving model requires the knowledge of maximum tensile stresses. These stresses depend on different simulation approaches and material models. Therefore, this study compares results of a two-dimensional (2-D) continuum approach using finite elements with results of a one-dimensional (1-D) beam model elaborated in Reeh (1968). A purely viscous model, as well as a viscoelastic Maxwell model, is applied for the 2-D case. The maximum tensile stress usually appears at the top surface of an ice shelf. Its location and magnitude are predominantly influenced by the thickness of the ice shelf and the height of the freeboard, the traction-free part at the ice front. More precisely, doubling the thickness leads to twice the stress maximum, while doubling the freeboard, based on changes of the ice density, results in an increase of the stress maximum by 61%. Poisson's ratio controls the evolution of the maximum stress with time. The viscosity and Young's modulus define the characteristic time of the Maxwell model and thus the time to reach the maximum principal stress.

Analysis of satellite images (Landsat 1 MSS, 4 TM and SPOT 1 XS), of U.S. Navy aerial photographs (TMA) and of U.S.G.S. maps has made it possible to assess a number of parameters relating to the surface dynamics (between 1956 and 1990) of eight ice tongues and of two ice shelves in the Terra Nova Bay area. The study shows that between 1960–63 and 1972–73 there was a decided decrease in the areas of some of the tongues and shelves: −53 km2 for the Aviator Glacier Tongue and −124 km2 for the Nansen Ice Sheet. On the other hand, the areas generally increased in the period 1972–73 to 1988. An exception to this situation is the small Hells Gate ice shelf whose area diminished by 1.15 km2 between 1956–57 and 1988. The calculated surface velocity of the ice tongues shows that they increase from the grounding line to their outer limit. Values of longitudinal strain rate generally increase from the grounding line to just after the start of the ice tongue, after which they diminsh proceeding towards its outer limit. Integration of the areal values with radio-echo sounding data has enabled the ice discharges of the southern flow of the David Glacier (12km3a−1) and of the Aviator Glacier Tongue (0.62 km3 a−1) to be calculated. Furthermore, on the basis of the data available, basal melting values of between 25 cm a−1 and 100 cm a−1 are deduced for these two ice tongues, and bottom freezing values of 20 cm a−1 for the Drygalski Ice Tongue. Different spectral responses of the glacial areas have made it possible to discriminate ablation areas from those of accumulation and to differentiate various typologies of ice (glacier ice, melt lake ice, and sea ice formed at the ice shelf-ocean interface).

Ice phenology (freeze-up, break-up and duration) was monitored for five seasons between autumn 2001 and spring 2006 at 11 small, shallow ponds in the boreal forest of central Alaska, USA. The sequence in which freeze-up (FU; day of 100% ice cover) and break-up (BU; day of zero ice cover) occurred at the 11 ponds showed moderately high to very high coherence each season. This was probably due to FU and BU being poorly correlated with pond morphometry (area, depth). BU is strongly correlated with April mean air temperature; a ±1˚C change in mean April air temperature is equivalent to a ±1.86 day change in BU. FU and air-temperature relationships are inconclusive, primarily because post-FU warm intervals in two autumns cause an anticorrelation between mean September air temperature and FU. Mean ice duration varies between 205 and 225 days, and is strongly correlated with maximum ice thickness through its effect on BU. A ±10mm change in maximum ice thickness will cause a ±0.6 day change in ice duration. Maximum ice thickness and ice composition (snow ice, congelation ice) also have a strong influence on break-up when all data from all ponds and all years are considered. The predictability of FU and BU sequence, the minor role of morphometry in FU and BU, the strong role of April mean air temperature in BU, and the role of maximum ice thickness in duration suggests that these ponds would be good sites for continued long-term observation of phenology and the influence of weather/climate variation and change, and for freeze-up/break-up process studies, particularly the role of ice composition and albedo.

The causes of iceberg deterioration can be discussed under three broad headings: wave-induced melting at the water line; breaking; and melting at the top, bottom, and sides. A short summary of current understanding under the first two headings is presented. It is then argued, under the third heading, that the melt rate at the sides of a tabular Antarctic iceberg is likely to exceed that at the top and bottom. The behaviour of the entraining plume which forms at the side of an iceberg when it melts in water of uniform salinity is outlined. Another form of convection, occurring when the ambient water is stratified, is then described; in this case the melt water spreads out in a series of almost horizontal layers. Finally, field observations on iceberg melting are discussed.

Ice shelves regulate the rate of ice-sheet discharge along much of the Antarctic coastline. Pinning points, sites of localised grounding within floating ice, can in turn, regulate the flow and thickness of an ice shelf. While the net resistive effect of ice shelves has been quantified in a systematic way, few extant pinning points have been examined in detail. Here, complete force budgets are calculated and examined for ice rises and rumples in the Ross Ice Shelf, West Antarctica. The diverse features have different effects on ice shelf mechanics that do not depend simply on their size but may, we conclude, depend on the properties of seafloor materials.

New ice-velocity measurements are obtained for the main trunk of Byrd Glacier, East Antarctica, using recently acquired Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) imagery. The velocities are derived from the application of a cross-correlation technique to sequential images acquired in 2000 and 2001. Images were co-registered and ortho-rectified with the aid of a digital elevation model (DEM) generated from ASTER stereo imagery. This paper outlines the process of DEM generation, image co-registration and correction, and the application of the cross-correlation technique to obtain ice velocities. Comparison of the new velocity map with earlier measurements of velocity from 1978 indicates that the glacier has undergone a substantial deceleration between observations. Portions of the glacier flowing at speeds of ~850ma–1 in 1978/79 were flowing at ~650ma–1 in 2000/01. The cause of this change in ice dynamics is not known, but the observation shows that East Antarctic outlet glaciers can undergo substantial changes on relatively short timescales.

A one-dimensional evolution equation for the slope-normal velocity profile of a streamwise uniform avalanche over an entrainable bed is derived. The boundary conditions are no slip at the bed, a stress-free surface and constant bed shear stress equal to the shear strength of the snow cover. The resulting equation is solved numerically by means of finite differences on a regular grid with a superposed fine grid near the erosion front that is adjusted at each time-step. The first exploratory simulations yield realistic entrainment rates and show that the entrainment rate tends towards a constant value while the flow depth and the velocity increase linearly with time for all investigated rheologies. It is shown that there indeed exists a rheology-independent asymptotic solution to the equation of motion of an entraining slab if the bottom friction is equal to the bed shear strength; the asymptotic acceleration is found to be half the downslope gravitational acceleration. The model can easily be extended to general path profiles, non-uniform flows and variable snow properties.