The changing geometry and thermal structure of Scott Turnerbreen, a 3.3 km2 glacier located at 78° N in the Svalbard archipelago, is documented. A net mass balance of–0.58 m a–1w.e. is determined for the period 1936–93, by comparing a recent topographic survey with earlier maps. The thermal regime was investigated with multifrequency radar and borehole thermistors. Basal temperatures of–4.1° and –3.3°C were measured, and observed temperature gradients indicate that the entire bed is frozen. This interpretation is confirmed by continuous radar profiling, which demonstrates the absence of high-frequency scattering from temperate ice. However, with the reconstructed 1936 ice- thickness distribution, at least 2 km of the length of the glacier bed would be at the pressure-melting temperature. The 20th century mass-balance history of Scott Turnerbreen is likely to have been influenced by a surge occurring around 1930, which meant that the glacier was already in a state of disequilibrium before the abrupt climate perturbation marking the termination of the Little Ice Age. A significant loss of mass has been accompanied by a transition from inferred polythermal to entirely non-temperate thermal conditions. Current driving stress and velocity are very low, and the glacier has almost certainly fallen out of the surge cycle. Within 60 years, there has therefore been a wholesale transformation in the geometry, thermal structure and dynamics of Scott Turnerbreen.

The recent fluctuation of the central Asian climate, and its effect on the region’s glaciers, is poorly known, largely because of a lack of knowledge of the dynamic behaviour of so-called summer-accumulation-type glaciers. In this study, a one-dimensional numerical glacier model is used to simulate the dynamic response of Sofiyskiy glacier, Altai mountains, Russia, to climate forcing. A successful simulation of the observed historical front variations was accomplished by dynamic calibration. This resulted in a reconstruction of the recent mass-balance history of the glacier, showing a distinct decline in surface mass balance in the second half of the 19th century, a slightly higher mass balance at the beginning of the 20th century, followed by a steady decline towards present conditions. The future response of Sofiyskiy glacier was projected for six 21st-century climate scenarios. Under a “no-change” scenario, the glacier will retreat > 2 km by 2100. If air temperature gradually rises by > 5°C during this century, the glacier will vanish around 2100. Basic response characteristics of Sofiyskiy glacier were determined. These indicate rather low mass-balance sensitivity to temperature change, but a strong front reaction due to geometric conditions.

The evolution of glaciers and ice sheets depends on processes in the subglacial environment. Shear seismicity along the ice–bed interface provides a window into these processes. Such seismicity requires a rapid loss of strength that is typically ascribed to rate-weakening friction, i.e., decreasing friction with sliding or sliding rate. Many friction experiments have investigated glacial materials at the temperate conditions typical of fast flowing glacier beds. To our knowledge, however, these studies have all found rate-strengthening friction. Here, we investigate the possibility that rate-weakening rock-on-rock friction between sediments frozen to the bottom of the glacier and the underlying water-saturated sediments or bedrock may be responsible for subglacial shear seismicity along temperate glacier beds. We test this ‘entrainment-seismicity hypothesis’ using targeted laboratory experiments and simple models of glacier sliding, seismicity and sediment entrainment. These models suggest that sediment entrainment may be a necessary but not sufficient condition for the occurrence of basal shear seismicity. We propose that stagnation at the Whillans Ice Stream, West Antarctica may be caused by the growth of a frozen fringe of entrained sediment in the ice stream margins. Our results suggest that basal shear seismicity may indicate geomorphic activity.

Glacier sliding is commonly linked with elevated water pressure at the glacier bed. Ice surface motion during a 3 week period encompassing an outburst of ice-dammed Hidden Creek Lake (HCL) at Kennicott Glacier, Alaska, USA, showed enhanced sliding during the flood. Two stakes, 1.2 km from HCL, revealed increased speed in two episodes, both associated with uplift of the ice surface relative to the trajectory of bed-parallel motion. Uplift of the surface began 12 days before the flood, initially stabilizing at a value of 0.25 m. Two days after lake drainage began, further uplift (reaching 0.4 m) occurred while surface speed peaked at 1.2 md–1. Maximum surface uplift coincided with peak discharge from HCL, high water level in a down-glacier ice-marginal basin, and low solute concentrations in the Kennicott River. Each of these records is consistent with high subglacial water pressure. We interpret the ice surface motion as arising from sliding up backs of bumps on the bed, which enlarges cavities and produces bed separation. The outburst increased water pressure over a broad region, promoting sliding, inhibiting cavity closure, and blocking drainage of solute-rich water from the distributed system. Pressure drop upon termination of the outburst drained water from and depressurized the distributed system, reducing sliding speeds. Expanded cavities then collapsed with a 1 day time-scale set by the local ice thickness.

An early study of the various components of the Greenland, Antarctic and Canadian Arctic ice-cap cores (Koerner, 1989) suggested that during the last interglacial period, the Greenland ice sheet suffered massive retreat and Canadian ice caps melted completely. Since then, modeling has helped support this interpretation (Cuffey and Marshall, 2000). Ice-core records of stable isotopes, melt layering and chemistry from the same Canadian ice cores, and others from the Russian Arctic islands, Svalbard and Greenland are presented as evidence for a more modest, but still substantial, retreat in the early Holocene. the sections representing the first half of the Holocene in many cores have less negative δ18O values (d values) and a higher percentage of melt layers than recently deposited ice, suggesting that temperatures were 1.3–3.5˚C warmer than today. Given that glacier balances are slightly negative today, they must have been substantially more negative during the early-Holocene thermal maximum, leading to retreat of the circumpolar ice caps. Evidence is presented to suggest that, with the exception of Academii Nauk ice cap, the ice in the Russian Arctic islands and Svalbard must have almost disappeared. In the Canadian Arctic, the larger Canadian ice caps retreated but survived. the cooling trend that followed this thermal maximum promoted re-expansion and new growth of most of the ice caps in the Russian Arctic islands and Svalbard.

We present results from a greenhouse warming experiment obtained from an atmosphere–ocean–sea-ice general circulation model that is interactively coupled with a three-dimensional model of the Greenland ice sheet. the experiment covers the period 1970–2099 and is driven by the mid-range Intergovernmental Panel on Climate Change SRESB2 scenario. the Greenland model is a thermomechanical high-resolution (20 km) model coupled with a viscoelastic bedrock model. the melt-and-runoff model is based on the positive degree-day method and includes meltwater retention in the snowpack and the formation of superimposed ice. the atmospheric–oceanic general circulation model (AOGCM) is a coarse-resolution model without flux correction based on the Laboratoire de Météorologie Dynamique (Paris) LMD 5.3 atmospheric model coupled with a primitive-equation, free-surface oceanic component incorporating sea ice (coupled large-scale ice–ocean (CLIO)). By 2100, average Greenland annual temperature is found to rise by about 4.5˚C and mean precipitation by about 35%. the total fresh-water flux approximately doubles over this period due to increased runoff from the ice sheet and the ice-free land, but the calving rate is found to decrease by 25%. the ice sheet shrinks equivalent to 4 cm of sea-level rise. the contribution from the background evolution is not more than 5% of the total predicted sea-level rise. We did not find significant changes in the patterns of climate change over the North Atlantic region compared with a climate-change run without Greenland fresh-water feedback.

We have compiled and analysed available records and data on the shrinkage of Satopanth (SPG) and Bhagirath Kharak (BKG) Glaciers, Uttarakhand, India, during the period 1936–2013. We estimate the mean retreat rates of the snouts of SPG and BKG for this period at 9.7±0.8m a–1 and 7.0±0.6m a–1 respectively. We have also revised the estimates of the area vacated during the period 1956–2013 to be 0.27 ± 0.05 km2 and 0.17 ± 0.04 km2 for SPG and BKG respectively, corresponding to front-averaged retreat rates of 5.7±0.6m a–1 and 6.0±0.9m a–1. The study revealed an average thinning of glacial ice in the lower ablation zone of SPG of 9 ± 11 m in the past 51 years. We observed that while the fronts of SPG and BKG depicted in the Survey of India topographic map published in 1962 are inconsistent with other available records, the elevation contours are consistent with them.

A suite of Arctic and Antarctic products is being prepared from Advanced Very High Resolution Radiometer (AVHRR) and ancillary data as part of NASA’s Polar Pathfinder effort. These products consist of twice-daily gridded fields of clear-sky surface temperature, surface albedo and cloud fraction, as well as daily ice velocities, for 1983–96. The products and their production methodology are summarized here, with examples demonstrating applications of the Pathfinder products for process studies and modeling.

With a total of 723 km2 of glaciers (1970) the Cordillera Blanca includes the largest glacier-covered area in the tropics. The climate is characterized by relatively large daily and small seasonal temperature variations as well as by a distinct succession between a dry (May–September) and a wet season (October–April). Since the early 1970s an ablation stake network has been installed on the tongues of the glaciers Uruashraju and Yanamarey. The determination of the equilibrium-line altitude at each end of a wet season was possible, showing a fair correlation with temperature, but not with the precipitation records of the nearby climatological station Querococha. Mean ablation rates at the lowest parts of the glacier tongues are markedly higher during the wet season than during the dry season. Reasons are presumably to be found in the seasonal variation of cloudiness and air moisture rates. Terminus variations of four glaciers in the Cordillera Blanca have been monitored since the early seventies, earlier positions are reconstructed back to 1948 by vertical air photographs. For the glaciers Uruashraju and Yanamarey the terminus positions of 1939 are known from an early map. The general retreat of glaciers in the Cordillera Blanca during the last five decades correlates with the global attitude of glaciers and especially with the attitude of glaciers in other tropical areas. Decreased recession rates with minor advances (1974–79 and 1985–86) are accompanied by lower annual temperatures and preceded and accompanied by years with relatively high annual precipitation sums.

The Baltic Sea is a semi-enclosed brackish water basin where sea ice occurs annually. The sea-ice study discussed here was conducted as a Finnish-Japanese cooperative research programme entitled "Ice Climatology of the Okhotsk and Baltic Seas’’ to investigate the structure and properties of the brackish ice in the Baltic Sea. Ice, snow and water samples were collected at Santala Bay, near the mouth of the Gulf of Finland, once a week from 20 January to 12 April 1999. The salinity and oxygen isotopic composition (δ18O) of the samples were measured. The ice samples were analyzed stratigraphically. The ice was composed of a granular upper layer, occupying approximately one-third of the entire ice thickness, and underlying columnar ice toward the bottom. The crystallography structure and δ18O values reveal that the granular ice consisted of two layers with different origins, i.e. snow ice and superimposed ice. The fraction of snow relative to the total thickness was estimated. The limited data show a significant contribution of the snow cover to the sea-ice development. The salinity of the granular ice was higher than that of the columnar ice, implying that the mechanism of entrapment of brine may be different between the two ice types.

Based on a time series of European remote-sensing satellite (ERS-2) synthetic-aperture radar (SAR) images from 1996/97, ablation on the King George Island (Antarctica) ice cap is documented. Snowmelt patterns were monitored by mapping the dynamic evolution of radar glacier zones and their boundaries. On the ice cap, all major radar glacier zones except the dry-snow radar zone were identified during the observed period While winter was characterized by a frozen-percolation radar zone, the ablation season was characterized by wet-snow and bare-ice radar zones. A striking bright backscatter signature indicated the presence of a highly reflective zone in the lower parts of the wet-snow zone. It was attributed to a phase 2 melt (P2) radar zone, which is characterized by a metamorphosed and roughened surface of a melting snow cover. Due to the absence of simultaneously acquired ground-truth information, concurrent meteorological data proved to be essential for interpreting the SAR images. Although the maximum elevation of the ice cap does not exceed 680 ma.s.L, ablation patterns obviously reflect altitudinal control. Melt onset up to 530 m a.s.l. was initiated by an advection event at the end of October 1996. A wet snowpack on the entire ice cap corresponds with a prolonged period of high temperatures in January 1997. However, the highest parts of the ice cap were affected by occasional melt-freeze cycles. The transient snowline at the end of February was determined as being at 250 m a i l. This late-summer snowline was regarded as an approximation of the equilibrium-line altitude for the 1996/97 ablation season.

Radio-wave velocity measurements in temperate and polythermal glaciers, combined with dielectric mixture formulae by Looyenga or Paren, have been used during the last decade to estimate the water content in temperate ice. We have used a similar mixture formula by Riznichenko, but based on elastic properties of the material, to estimate the water content from seismic velocity data. To compare the suitability of the two methods, we have used seismic and radar data from a temperate glacier on an Antarctic island. The estimated water contents are within 0.4–2.3% (average 1.2 ±0.6%) when radio-wave velocities are used, and within 0.9–3.2% (average 2.2±0.9%) when seismic velocities are used. These results are similar to those directly measured from ice cores and to those estimated from radar data on other temperate glaciers. The water-content estimates from seismic data are higher than those from radar data, which we attribute to the different behaviour of seismic and radar velocities as functions of density. Near-surface conditions (ice–firn conditions, presence of crevasses, etc.) have a strong influence on the propagation of elastic and electromagnetic waves, and thus on the accuracy of the velocity determinations and water-content estimates, and so should not be disregarded.

High-resolution ground-penetrating radar surveys at 50 MHz on the polythermal glaciers Hornbreen, Hambergbreen and several surrounding glaciers in southern Spitsbergen, Svalbard, are presented and interpreted. Accurate positioning was obtained using differential global positioning system (DGPS). Digital elevation models (DEMs) of the bedrock and surface were constructed. Comparison of DGPS data and surface DEMs with data from the topographic mappings from 1936 oblique stereoscopic aerial photographs and from Mission Russe in 1899–1901 shows that the Hornbreen and Hambergbreen surfaces are about 60–100 m thinner today in the upper part than at the beginning of the 20th century. Hornbreen has retreated by 13.5 km from the central part of the front, and Hambergbreen by 16 km. All the fronts of the nearby east-coast glaciers in this area have retreated. The bedrock DEM shows that the Hornbreen and Hambergbreen beds lie at –25 to 25 m a.s.l. The combination of sub-sea-level fronts and increasing steepness of the glaciers suggests that the low-lying glaciated valley filled by Hornbreen and Hambergbreen may become a partially inundated ice-free isthmus within perhaps 100 years.

The release of a dry-snow slab avalanche involves brittle fracture. It is therefore essentially a non-linear fracture mechanics problem. Traditional snow-stability evaluation has mainly focused on snow strength measurements. Fracture toughness describes how well a material can withstand failure. The fracture toughness of snow is therefore a key parameter to assess fracture propagation propensity, and hence snows lope stability. Fracture toughness in tension KIc and shear KIIc was determined with notched cantilever-beam experiments in a cold laboratory. Measurements were performed at different temperatures and with different snow types of density ρ = 100–300 kgm–3, corresponding to typical dry-snow slab properties. The fracture toughness in tension KIc was found to be larger (by about a factor of 1.4) than in shear KIIc. Typical values of the fracture toughness were 500–1000 Pam1/2 for the snow types tested. This suggests that snow is one of the most brittle materials known to man. A power-law relation of toughness KIc on relative density was found with an exponent of about 2. The fracture toughness in tension KIc decreased with increasing temperature following an Arrhenius relation below about –8°C with an apparent activation energy of about 0.16 eV. Above –6°C the fracture toughness increased with increasing temperature towards the melting point, i.e. the Arrhenius relation broke down. The key property in dry-snow slab avalanche release, the critical crack size under shear at failure, was estimated to be about 1 m.

Sea ice is distinguished from many other porous composites, such as sandstones or bone, in that its microstructure and bulk material properties can vary dramatically over a small temperature range. For brine-volume fractions below a critical value of about 5%, which corresponds to a critical temperature of about −5°C for salinity of 5 ppt, columnar sea ice is effectively impermeable to fluid transport. For higher brine volumes, the brine phase becomes connected and the sea ice is permeable, allowing transport of brine, sea water, nutrients, biomass and heat through the ice. Over the past several years it has been found that brine transport is fundamental to such processes as sea-ice production through freezing of flooded ice surfaces, the enhancement of thermal and salt fluxes through sea ice, nutrient replenishment for sea-ice algal communities, and to sea-ice remote sensing. Motivated by these observations, recently we have shown how percolation theory can be used to understand the critical behavior of fluid transport in sea ice. We applied a percolation model developed for compressed powders of large polymer particles with much smaller metal particles, which explains the observed behavior of the fluid permeability in the critical temperature regime, as well as Antarctic data on surface flooding and algal growth rates. Moreover, the connectedness properties of the brine phase play a significant role in the microwave signature of sea ice through its effective complex permittivity and surface flooding. Here we review our recent results on brine percolation and its role in understanding the fluid and electromagnetic transport properties of sea ice. We also briefly report on measurements of percolation we made on first-year sea ice during the winter 1999 Mertz Glacier Polynya Experiment.

A robotic submarine was used for the first observations of a grounding-line area of a floating glacier. The site was Mackay Glacier which terminates as a floating glacier tongue in the Ross Sea, at latitude 77°S. Half of the 20 m thick basal debris layers in Mackay Glacier are deposited as subglacial till in the last 1.8 km that the glacier remains grounded. Subglacial till observed at and beyond the grounding line varies rapidly in texture and rheology spatially, occurring as a flat sheet, as flow-parallel flutes, or as bank forms into which it has been pushed at the grounding line. Very little free- flowing subglacial water was present during the observations, and no major subglacial water discharges appear to have occurred in the past. The other half of the basal debris is melted out up to 1.5 km in front of the grounding line, producing a sheet of glacimarine sediment as shelfstone diamicton and mud draped on subglacial till. Both till and glacimarine sediment may be turbated by icebergs. This simple model of till overlain by shelfstone diamicton and mud is a direct contrast to sedimentary depositional systems at tide-water termini of temperate glaciers.

An inventory of the surface area and volume of the world’s glaciers, outside Greenland and Antarctica, was part of the International Hydrological Decade (1965–74). It was considered essential to an understanding of the role played by glaciers in the hydrological cycle and was to be repeated every 50 years to detect change. To date, 46% of the estimated total glacier area has been inventoried and made available through the World Glacier Monitoring Service and the US National Snow and Ice Data Center. As the original inventory method was too time-consuming and inapplicable for some areas, a simplified method was developed in the early 1980s using satellite images. The Global Land Ice Measurements from Space (GLIMS) project now covers 34% of the estimated glacierized area outside Greenland and Antarctica. Both inventory efforts have made good progress and contributed substantially to our knowledge of glaciology and its related sciences, but global coverage is still incomplete. If both inventories are combined, 46% of the world’s glacierized area is still missing; 26% is covered by both methods, which allows the quality of the satellite-based and semi-automatic inventories to be assessed by comparison. About 95 000 glaciers remain to be inventoried, of which about half are in the Canadian Cordillera, South America and the Canadian Arctic Islands. As the cryosphere is changing rapidly, it is of the utmost importance to complete the global glacier inventory as soon as possible, and identify an appropriate repeat cycle.

Daily acquisitions from satellite microwave sensors can be used to observe the spatial and temporal characteristics of the Arctic sea-ice snowmelt onset because the initial presence of liquid water in a dry snowpack causes a dramatic change in the active-and passive-microwave response. A daily sequence of backscatter coefficient images from the NASA scatterometer (NSCAT) clearly shows the spatially continuous progression of decreasing backscatter associated with snowmelt onset across the Arctic Ocean during spring 1997. A time series of the active NSCAT backscatter and a scattering index from the passive Special Sensor Microwave/Imager (SSM/I) show similar trends during the time of the melt onset. An NSCATsnowmelt-onset detection algorithm is developed using the derivative of the backscatter with respect to time to select a melt-onset date for each pixel, generating a melt map for the Arctic sea ice. Comparison between this melt map and one previously generated from an SSM/I scattering index shows the NSCAT algorithm predicts the onset occurs 1−10 days earlier than the SSM/I-based algorithm for most portions of multi-year ice.

High-resolution digital elevation models of Finland and Sweden based on LiDAR (Light Detection and Ranging) reveal subglacial landforms in great detail. We describe the ice-sheet scale distribution and morphometric characteristics of a glacial landform that is distinctive in morphology and occurs commonly in the central parts of the former Scandinavian Ice Sheet, especially up-ice of the Younger Dryas end moraine zone. We refer to these triangular or V-shaped landforms as murtoos (singular, ‘murtoo’). Murtoos are typically 30–200 m in length and 30–200 m in width with a relief of commonly <5 m. Murtoos have straight and steep edges, a triangular tip oriented parallel to ice-flow direction, and an asymmetric longitudinal profile with a shorter, but steeper down-ice slope. The spatial distribution of murtoos and their geomorphic relation to other landforms indicate that they formed subglacially during times of climate warming and rapid retreat of the Scandinavian Ice Sheet when large amounts of meltwater were delivered to the bed. Murtoos are formed under warm-based ice and may be associated with a non-channelized subglacial hydraulic system that evacuated large discharges of subglacial water.

A novel flow-through microparticle detector was deployed concurrently with continuous flow analyses of major ions during the North Greenland Icecore Project 2000 field season. the easy-handling detector performs continuous counting and sizing. In this deployment the lower size-detection limit was conservatively set to 1.0 μm equivalent spherical particle diameter, and a depth resolution of ≤1cm was achieved for microparticle concentrations. the dust concentration usually followed the Ca2+ variability. Here results are presented from an inspection of the Ca/dust mass ratio in 23 selected intervals, 1.65 m long each, covering different climatic periods including Holocene and Last Glacial Maximum (LGM). A (Ca2+)/(insoluble dust) mass ratio of 0.29 was found for the Holocene and 0.11 for LGM. Changes to the Ca/dust ratio occur on an annual to multi-annual time-scale exhibiting the same pattern, i.e. a lower Ca/dust ratio for higher crustal concentrations. Moreover, the Ca2+/dust ratio may increase significantly during episodic events such as volcanic horizons due to enhanced dissolution of CaCO3. This calls into question the notion of deploying Ca2+ as a quantitative mineral dust reference species and shows the importance of variable source properties or fractionating processes during transport and deposition.