A glacier moving by deformation of subglacial sediments will tend to exhaust its own sediment supply, unless new sediment is generated subglacially. We explore the potential for deforming sediments to overcome this difficulty and replenish themselves by abrading their beds. We review abrasion experiments and theory for brittle materials and conclude that a theoretical calculation of abrasion is not possible yet. Instead, we use fault-gouge production data to estimate a likely upper bound to abrasion rates, and conclude that sufficient erosion to maintain a steady deforming-layer thickness is difficult to achieve, and will only be possible if the substrate is very soft and if there is a moderate rate of slip at the base of the deforming layer. Slow abrasion, which can leave a geologic signature, is possible under most deforming layers that are deforming at the sediment/bedrock interface.

A method to estimate the flexural stiffness and effective elastic modulus of floating ice is described and analysed. The method is based on the analysis of water pressure records at two or three locations below the bottom of floating ice when flexural-gravity waves propagate through the ice. The relative errors in the calculations of the ice flexural stiffness and the water depth are analysed. The method is tested using data from field measurements in Tempelfjorden, Svalbard, where flexural-gravity waves were excited by an icefall at the front of the outflow glacier Tunabreen in February 2011.

Glaciers in the Bugyai Kangri are located in a transition zone from southeast Tibet, where monsoonal temperate glaciers dominate, to inner Tibet, where continental glaciers dominate. Here we analyze glacier and glacial lake changes in this region using multi-year inventories based on Landsat images from 1981–2013. Results show that the total area of 141 glaciers in the region decreased by 30.44 ±0.89 km2 from 198.35 ±9.54 km2 (1980s) to 167.93 ±4.52 km2 (2010s). The annual area shrinkage rate (–0.48% a–1) is lower than that reported for southeastern Tibet but higher than that of inner Tibet. Both the number and total area of glacial lakes increased between 1981 and 2013. Among all lakes, proglacial lakes contribute most (~81 %) to the expansion. The total area of ten proglacial lakes increased by 150.3 ± 13.17% and of these ten lakes the four that expanded most sharply showed increased calving at their upper margins, resulting in more rapid retreat of lake-terminating glaciers than land-terminating glaciers. Owing to rapid calving, several lakes may undergo further growth in the near future, increasing the potential risk of glacial lake outburst floods.

The long series of mass-balance data obtained by the Norsk Polarinstitutt on Brøggerbreen for the period 1967–88 has been correlated to climatological parameters from the meteorological station in Ny-Ålesund. The best multiple correlation coefficient was obtained between mass balance and positive summer and autumn temperatures combined with winter precipitations, for which R = 0.90. The regression equation gives a very good agreement between observed and estimated mass balance for Brøggerbreen. A test for 8 years which includes summer long-wave radiation, gives a coefficient of R = 0.98. Based on the good correlation between temperatures at several stations, we reconstructed summer temperatures in Longyearbyen and Brøggerbreen mass balances for 1912–88. The end of the cold period before 1918 is connected with historical observations of the maximum advance of cirque glaciers. After an increase between 1912 and 1920, summer and autumn temperatures decreased slowly. From 1920 this decay has been of −0.7°C. Mass balance has been negative since 1918, and the total mass lost at Brøggerbreen is 34.35 m of water equivalent. For the period with available data in Ny-Ålesund (1969–88), a very slight cooling during the ablation period and an increase in winter precipitation has maintained the reduction of the net balance deficit.

The physical, chemical and biological characteristics of surface and freeboard habitats in the summer pack ice in the eastern Ross Sea, Antarctica, were documented in a continuing effort to determine the factors controlling the distribution, production and succession of sea-ice biota. Three longitudinal transects from approximately 65° to 74° S in the western Ross Sea along 135°, 150° and 165° W were visited where samples of slush and slush interstitial water from surface and freeboard habitats as well as sea water were collected at every degree of latitude. Freeboard and surface habitats, found at all stations in the pack ice, contained a large range (five orders of magnitude) of microalgal biomass (measured as chlorophyll a concentrations) and nutrients ranging from below levels of detection to those of the surrounding sea water. The geophysical attributes of the freeboard habitat (i.e. a layer of semi-consolidated ice overlying a layer containing unconsolidated ice crystals and sea water) are consistent with previous descriptions of this environment. However, additional information is presented on the range of biomass concentrations as well as the small-scale distributions of the habitat and biota.

The vertical concentration distribution of frazil-ice crystals in a stream during the formation and growth of frazil ice was discussed in a preliminary way by Gosink and Osterkamp (1981). This paper extends and completes the analysis of buoyant rise velocities of frazil-ice crystals and applies the results to an interpretation of measured velocity profiles in rivers during frazil-ice events. Additional experimental data are also presented. Two time scales are defined: the buoyant time scale TB, which represents the time required for a frazil crystal to rise, buoyantly, from the river bottom to the water surface, and the diffusive tine scale TD, which represents the time required for a frazil crystal to he transported by turbulence through the depth. It is shown that the ratio of the time scales TB/TD defines the nature of the layering processes; in particular, if TB/TD<1, then buoyant forces Till lift a frazil crystal faster than turbulent diffusion can redistribute it and the flow will be layered. Conversely, if TB./TD>1, turbulent mixing will proceed faster than buoyant lifting and the flow will be well-mixed. This ratio, for frazil particles of diameter 2 mm or more, corresponds to rule-of-thumb velocity criteria developed in Norway and Canada to distinguish layered frazil-ice/water flow from well-mixed flow.

The development of this theory depends in large part upon the determination of TB, which depends upon the rise velocity of frazil-ice crystals. A force balance .nodel was developed for the rise velocity of a frazil crystal. Field observations during frazil -ice formation in Goldstream Creek and in the Chatanika River north of Fairbanks are reported, including a series of measurements of the rise velocities of frazil-ice crystals. Typical particle size of frazil ice was about 2 mm with a rise velocity of about 10.0 mm s -1. The agreement of measured rise velocities with the theoretical model is good considering uncertainties in the drag coefficient and in the determination of frazil crystal sizes under field conditions.

Velocity profiles in the Chatanika River and in Goldstream Creek during frazil formation suggest that the time-scale ratio may serve as a transition criterion between layered frazil-ice/water flow and well-mixed flow. This ratio was calculated with the rise velocity of frazil-ice crystals arbitrarily chosen to be 0.01 m s−1.

Over the perennial Sea ice in the western and central Weddell Sea, Antarctica, the onset of Summer is accompanied by a Significant decrease of Sea-ice brightness temperatures (Tb) as observed by passive-microwave radiometers Such as the Special Sensor Microwave/Imager (SSM/I). The Summer-specific Tb drop is the dominant feature in the seasonal cycle of Tb data and represents a conspicuous difference to most Arctic Sea-ice regions, where the onset of Summer is mostly marked by a rise in Tb. Data from a 5 week drift Station through the western Weddell Sea in the 2004/05 austral Summer, Ice Station POLarstern (IsPOL), helped with identifying the characteristic processes for Antarctic Sea ice. In Situ glaciological and meteorological data, in combination with SSM/I Swath Satellite data, indicate that the cycle of repeated diurnal thawing and refreezing of Snow (‘freeze–thaw cycles’) is the dominant process in the Summer Season, with the absence of complete Snow wetting. The resulting metamorphous Snow with increased grain Size, as well as the formation of ice layers, leads to decreasing emissivity, enhanced volume Scattering and increased backscatter. This causes the Summer Tb drop.

Dome C was chosen by the European Project for Ice Coring in Antarctica (EPICA) as the site for the drilling of a deep ice core. This paper presents results from geodetic surveys of ice velocities (absolute and relative) at Dome C and along a transect to Terra Nova Bay. The purpose of the surveys was to provide accurate data for the study of ice dynamics, particularly a strain network comprising 37 poles surveyed in 1995 and again in 1999. Data indicate that the ice surface at the poles closest to the topographic summit moves horizontally by up to a few mm a–1 in a direction consistent with downslope motion of the ice sheet, while 25 km from the summit it moves up to 211 mma–1. The EPICA drilling site yields an interpolated velocity of about 15 ±10mma–1 in a north-northwesterly direction. Analysis of the velocity field and surface topography reveals that the surface flow centre is nearly co-located with the dome summit, and that both are in a steady-state condition. The measured horizontal velocities are consistent with the remote-sensing result and provide accurate ground-truth control for flow mapping. Seven snow–firn cores, up to 53m deep, were drilled during the Terra Nova Bay–Dome C traverse. Submerged velocity systems were installed at the borehole and measured using the global positioning system (GPS). First results show a steady-state condition. Measured (horizontal) ice velocities increase from the summit of the ice sheet to the coast, reaching about 28 ma–1 at site GPS2A.

Aerial photography was conducted in the high Arctic Ocean during a Chinese research expedition in summer 2010. By partitioning the images into three distinct surface categories (sea ice/snow, water and melt ponds), the areal fraction of each category, ice concentration and the size and geometry of individual melt ponds, are determined with high-spatial resolution. The ice concentration and melt pond coverage have large spatial deviations between flights and even between images from the marginal ice zone to the pack ice zone in the central Arctic. Ice concentration and pond coverage over high Arctic (from 84°N to north) was ~75% and ~6.8%, respectively, providing ‘ground truth’ for the unusual transpolar reduction strip of ice indicated concurrently by AMSR-E data and for the regions (north of 88°N) where no passive microwave sensors can cover. Melt pond size and shape distributions are examined in terms of pond area (S), perimeter (P), mean caliper dimension (MCD) (L), roundness (R), convex degree (C), the ratio of P/S and fractal dimension (D). Power-law relationships are developed between pond size and number. Some general trends in geometric metrics are identified as a function of pond area including R, C, P/S and D. The scale separation of pond complexity is demonstrated by analyzing area-perimeter data. The results will potentially help the modelling of melt pond evolution and the determination of heterogeneity of under-ice transmitted light fields.

In situ measurements of water depth and optical properties of a melt pond in East Greenland were collected to verify a previously developed algorithm for determining supraglacial water depths using satellite imagery. That algorithm made five simplifying assumptions which we have tested using the in situ data and laboratory analysis of water samples. We conclude that three assumptions were justified, one was not and the remaining one (substrate homogeneity) requires further study, but probably has a minor effect on the retrieved water depths and volumes. Measured water depths of 0.2–3.0m agree well with those derived from a satellite image using the algorithm. Numerically modeled depths also agree well with those from the satellite image. This new analysis demonstrates the validity of our algorithm as a means for determining meltwater volumes in supraglacial ponds and lakes.

Nearly 9000 individual lineations (drumlins and flutes) from two ice- flow systems have been mapped over a 22 500 km2 area of northern Sweden by interpretation of aerial photographs.The lineations were classified according to their size and orientation to allow a quantitative analysis of their distribution. The two glacial lineation systems, separated in time by at least 100 000 years and two individual overriding ice sheets, cross-cut at a high angle. The older system occurs over the entire study area and is interpreted to have formed by prolonged sheet flow during Marine Isotope Stage 5d, while the youngest system is spatially restricted, marking the presence of a laterally constrained zone of faster ice flow, developed near the end of the last deglaciation. The effect of the younger ice flow was erosion and elimination of smaller lineations in the older system, while the larger drumlinoid forms survived more or less intact, thus creating an apparent increase in average drumlin size of the older lineation system. One possible explanation for the unaltered shape of these larger drumlins is that the glacier bed of the younger ice sheet only reached the pressure melting point in the lower parts of the terrain, thus eroding the smaller forms, while the larger forms protruded into colder parts of the ice mass and were protected from erosion and deformation. There was no evidence of the deformation of older drumlins into barchanoid shapes or the development of lee-side tail features on the distal side of pre-existing lineations, as has previously been described for crossing drumlin systems. The lack of any such deformational features suggests that the younger lineation system was formed by net erosion, rather than deformation or deposition.

Detailed studies on temporal changes of crevasses and their linkage with glacier dynamics are scarce in the Himalayan context. Observations of temporally changing surficial crevasse patterns and their orientations are suggestive of the processes that determine seasonal glacier flow characteristics. In the present study, on a Himalayan valley glacier, changing crevasse patterns and orientations were detected and mapped on Landsat 8 images in an automated procedure using the ratio of Thermal Infrared Sensor (TIRS) band 10 to Optical Land Imager (OLI) shortwave infrared (SWIR) band 6. The ratio was capable of mapping even crevasses falling under mountain shadows. Differential GPS observations suggested an average error of 3.65% and root-mean-square error of 6.32m in crevasse lengths. A year-round observation of these crevasses, coupled with field-based surface velocity measurements, provided some interesting interpretations of seasonal glacier dynamics.

The snow-cover model SNOWPACK was applied to the wet-snow areas of Japan. Simulated variations of snow type, snow depth and weight, profiles of snow density, temperature and liquid-water content were compared with snow-pit measurements. The snow-depth simulation during early winter agreed with the measurements, but the differences between the simulation and the measurements increased during the course of the melt season. These differences were caused by underestimation of the energy balance at the snow surface, mainly that regarding sensible-heat flux during the melt season. The underestimation was caused by the implicit numerical treatment of the heat-transport equation. Consistent with the underestimation of snowmelt, simulated metamorphosis of compacted particles into melt forms was slower than the change shown by the measurements, and faceted snow particles, which constitute a snow type not actually found in the study area, sometimes appeared in the model. The inaccurate melt treatment also influenced simulated densities, which were larger than the measurements at small densities, while they were smaller than the measurements at large densities. Greater accuracy was achieved when an empirical compressive viscosity formulation for wet snows in Japan was introduced. A new version of SNOWPACK, with an accurate treatment of melt processes, is available.

In heavy-snowfall areas facing the Sea of Japan, winter seasons with lower volumes of snow occurred from 1986/87 to 1999/2000. In this paper, the changes induced by these warmer winters in snowy areas in Japan are investigated using two datasets. One set was normalized for the period 1971–2000 from manned surface meteorological observations by the Japan Meteorological Agency, and the other set was for 1961– 90. Winter climatic monthly values for the first dataset were thought to be affected by the warmer winter seasons since almost half the relevant period coincides with them. By comparing each monthly climatic value in both datasets, the following results were obtained: (1) At each meteorological observation site the bimonthly average temperature fromJanuary to February increased and the amounts of increase were about 0.4°C on average. (2) The bimonthly maximum snow depth for the same period increased at a number of sites, but usually by only a few centimeters, the maximum increase being 0.05 m. (3) In contrast, the decreases in snow depth in heavy-snowfall areas facing the Japan Sea, which belong to a temperate climate zone, were large, ranging from about 0.05 to 0.22 m in climatic bimonthly maximum snow depth during January and February. The last result shows that snow covers in such warm snowy areas are very sensitive to climatic changes. An attempt is also made in this paper to estimate the amounts of decrease in snow depth from the increases in air temperature and the decreases in precipitation amounts.

Seasonal variations of firn density in ice-sheet firn layers have been attributed to variations in deposition processes or other processes within the upper firn. A recent high-resolution (mm-scale) density profile, measured along a 181 m core from Antarctica, showed small-scale density variations with a clear seasonal cycle that apparently was not related to seasonal variations in deposition or known near-surface processes (Gerland and others, 1999). A recent model of surface elevation changes (Zwally and Li, in press) produced a seasonal variation in firn densification, and explained the seasonal surface elevation changes observed by satellite radar altimeters. In this study, we apply our one-dimensional time-dependent numerical model of firn densification that includes a temperature-dependent formulation of firn densification based on laboratory measurements of grain growth. The model is driven by a steady-state seasonal surface temperature and a constant accumulation rate appropriate for the measured Antarctic ice core. The modeled seasonal variations in firn density show that the layers of snow deposited during spring to mid-summer that have the highest temperature history compress to the highest density, and the layers deposited during later summer to autumn that have the lowest temperature history compress to the lowest density. The initial amplitude of the seasonal difference of about 0.13 reduces to about 0.09 in 5 years and asymptotically to 0.0 at greater depth, which is consistent with the core measurements.

In this paper, a molecular-dynamics sea-ice model is used to study contact and force networks in fragmented sea ice, composed of separate floes with power-law size distribution. The momentum equations for individual floes, taking into account floe/floe collisions (with Hertzian contact mechanics), are formulated in a way suitable for a computationally efficient numerical algorithm, allowing simulation of systems of thousands of floes. The simulations are performed for a number of scenarios: pure convergence without wind, through a jamming phase transition; constant wind at a constant ice concentration; and an idealized marginal ice zone. An analysis of the statistical properties of the contact and force networks reveals a highly localized, intermittent character of internal stress in the ice, as well as the role of the size-dependent response of floes to the forcing in formation of spatial patterns of internal stress at lower ice concentrations. The results provide a valuable starting point for formulating improved rheology models for fragmented sea ice.

Changes in the taxonomic composition of diatoms in fast ice as well as in the underlying platelet layer were followed from June to December 1995 in Atka Bay Antarctica. Four communities were clearly distinguished: (1) an interior community dominated by flagellates in spring; (2) a bottom community dominated by a small form of Fragilariopsis cylindrus; (3) a platelet-ice layer dominated by Amphiprora Kufferathii and Thalassionema sp. growing attached to the ice platelets; and (4) an interstitial community dominated by Chaetoceros neglectus growing in the water between the platelets. Species composition distribution and succession in these communities were related to changes in silicate concentration, pore space and ice-formation processes and the ability of some cells to grow attached to ice platelets. The presence of the platelet-layer communities may have implications for paleoglaciology

Dome A, the highest point on the Antarctic ice sheet at just over 4000 ma.s.l., is located near the centre of East Antarctica. Chinese National Antarctic Research Expeditions have studied ice-sheet dynamics and mass balance along a traverse route from Zhongshan station to Dome A during the austral summers from 1996/97 to 2004/05. Nineteen GPS sites were occupied on at least two occasions at approximately 50 km intervals. The purpose of the surveys was to provide accurate ice-dynamics data. A dual-frequency GPS receiver was used and each site was occupied for 1–12 hours. GPS data were processed using GAMIT/GLOBK software, and horizontal accuracies were within 0.1 m. Repeat GPS measurements provided ice velocities. The horizontal surface ice velocities increase from the summit of the ice sheet to the coast. In the Dome A area, the velocities are <10ma–1; in the plateau area, velocities range from 8 to 24 ma–1 and reach about 98.2 ma–1 at a site (LT980) near the coast. The flow directions are roughly perpendicular to the ice-sheet surface elevation contours, primarily toward the Lambert Glacier basin.

This paper presents an overview of internal layering across Pine Island Glacier, West Antarctica, as measured from airborne-radar data acquired during a survey conducted by the British Antarctic Survey and the University of Texas in the 2004/05 season. Internal layering is classified according to type (continuous/discontinuous/missing) and the results compared with InSAR velocities. Several areas exhibit disruption of internal layers that is most likely caused by large basal shear stresses. Signs of changes in flow were identified in a few inter-tributary areas, but overall the layering classification and distribution of layers indicate that only minor changes in ice-flow regime have taken place. This is supported by bed-topography data that show the main trunk of the glacier, as well as some of the tributaries, are topographically controlled and located in deep basins.

The microstructural evolution of brine inclusions in granular and columnar sea ice has been investigated through magnetic resonance imaging (MRI) for temperatures between –28 and –3˚C. Thin-section and salinity measurements were completed on core samples obtained from winter sea ice near Barrow, Alaska, USA. Subsamples of granular (2–5cm depth in core) and columnar sea ice (20–23 cm depth) were investigated with morphological spin-echo and diffusion-weighted imaging in a Bruker 4.7T MRI system operating at field gradients of 200 mTm–1 at temperatures of approximately –28, –15, –6 and –3˚C. Average linear pore dimensions range from 0.2 to 1 mm and increase with bulk liquid volume fraction as temperatures rise from –15 to –3˚C. Granular ice pores are significantly larger than columnar ice pores and exhibit a higher degree of connectivity. No evidence is found of strongly non-linear increases in pore connectivity based on the MRI data. This might be explained by shortcomings in resolution, sensitivity and lack of truly three-dimensional data, differences between laboratory and field conditions or the absence of a percolation transition. Pore connectivity increases between –6 and –3˚C. Pore-number densities average at 1.4±1.2mm–2. The pore-number density distribution as a function of cross-sectional area conforms with power-law and lognormal distributions previously identified, although significant variations occur as a function of ice type and temperature. At low temperatures (< –26˚C), pore sizes were estimated from 1H self-diffusivity measurements, with self-diffusivity lower by up to an order of magnitude than in the free liquid. Analysis of diffusional length scales suggests characteristic pore dimensions of <1 μm at < –26˚C.