Despite being a key location for paleoglaciological research in north-central Asia, with the largest number of modern and Pleistocene glaciers, and in the transition zone between the humid Russian Altai and dry Gobi Altai, little is known about the precise extent and timing of Holocene and late Pleistocene glaciations in western Mongolia. Here we present detailed information on the distribution of modern and late Holocene glaciers, and new results addressing the geomorphological differentiation and numerical dating (by optically stimulated luminescence, OSL) of Pleistocene glacial sequences in these areas. For the Mongolian Altai, geochronological results suggest large ice advances correlative to marine isotope stages (MIS) 4 and 2. This is in contrast to results from the Khangai mountains, central Mongolia, showing that significant ice advances additionally occurred during MIS3. During the Pleistocene, glacial equilibrium-line altitudes (ELAs) were ~500 to >1000m lower in the more humid portion of the Russian and western Mongolian Altai, compared to 300-600 m in the drier ranges of the eastern Mongolian Altai. Pleistocene ELAs in the Khangai mountains were depressed by 700-1000 m, suggesting more humid conditions at times of major glaciation than in the eastern Mongolian Altai. This paleo-ELA pattern reveals that the precipitation gradient from the drier to the more humid regions was more pronounced during glacial times than at present.

Johnsons and Hurd Glaciers are the two main glacier units of Hurd Peninsula ice cap, Livingston Island, South Shetland Islands, Antarctica. They presently cover an area of about 10 km2. Johnsons is a tidewater glacier, while Hurd Glacier ends on emerged land. In this paper, we estimate the changes in ice volume during the period 1956–2000, and compare them with the regional meteorological records. The volume-change estimates are based on the comparison of digital terrain models for the glacier surface, constructed from aerial photographs taken by the British Antarctic Survey in 1956 and from our geodetic measurements in 1999/2000. The total volume estimates are based on an ice-thickness map constructed from radio-echo sounding profiles (18–25 MHz) done in 1999–2001, showing maximum ice thickness of about 200 m. We estimate the changes in ice volume during the period 1956–2000 to be –0.108±0.048km3, which represents a 10.0±4.5% decrease from the 1956 total volume of 1.076±0.055km3 and is equivalent to an average annual mass balance of –0.23±0.10mw.e. during 1956–2000. Ice-thickness changes range from –40 to +20 m, averaging –5.5±4.4 m. Most areas show ice thinning; the thickening is limited to a small area within Johnsons Glacier. All glacier fronts, except Johnsons’ calving front, show retreat. These changes are consistent with the regional meteorological records for mean summer temperature, which show a trend of +0.023±0.005˚Ca–1 during the period 1956–2000.

Tidewater calving glaciers can undergo large fluctuations not necessarily in direct response to climate, but rather owing to complex ice–water interactions at the glacier termini. One example of this process in Chilean Patagonia is Glaciar Jorge Montt, where two cameras were installed in February 2010, collecting up to four glacier photographs per day, until they were recovered on 22 January 2011. Ice velocities were derived from feature tracking of the geo-referenced photos, yielding a mean value of 13 ±4 md–1 for the whole lower part of the glacier. These velocities were compared to satellite-imagery-derived feature tracking obtained in February 2010, resulting in similar values. During the operational period of the cameras, the glacier continued to retreat (1 km), experiencing one of the highest calving fluxes ever recorded in Patagonia (2.4 km3 a–1). Comparison with previous data also revealed ice acceleration in recent years. These very high velocities are clearly a response to enhanced glacier calving activity into a deep water fjord.

This paper describes the application of an automated cross-correlation technique to pairs of 85.5 GHz Special Sensor Microwave Imager (SSM/I) images to obtain ice motion over the entire Arctic Basin for a contiguous two month period between December 1993 and January 1994. Although the surface ice information in the imagery is coarse and noisy, the area cross-correlation method is quite successful in picking up ice-motion information. The accuracy of 85.5 GHz SSM/I derived ice motions is evaluated by comparing results with Arctic buoy drift. Over 390 comparisons with buoy-drift estimates of ice displacement were made with an overall correlation of 0.75 and an average vector magnitude error in ice velocity of 3.5 km d−1. The main difficulty with the automated technique is the tendency to overestimate ice displacement compared to buoy data by about 14%. Two detailed examples of ice motion are presented. The first occurred in December 1993, when a major westward shift in the ice pack took place in the Canada Basin and opened up a very large lead off Banks and Prince Patrick Islands. The second example occurred in January 1994, when an intense anticyclone over the Canada Basin produced a strong Beaufort Gyre.

Mass-balance investigations on glaciers in Svalbard at high latitudes (78°N) show that the ice masses have been steadily decreasing during the period 1950–88. Detailed annual observations have been carried out on Brøggerbreen since 1966 and Lovénbreen since 1967. The mean specific net balances are −0.46 and −0.37 m year−1 water equivalent respectively. Only one year had positive net balance in this period. The cumulative mass lost in the period is then more than 10% of the volume in 1967. Zero net balance would be obtained if the summer temperature was lowered about 1°C or if the winter precipitation increased about 50%. There is a strong correlation between the net mass balance and the height of the equilibrium-line altitude (ELA). Because of the high amount of superimposed ice (10–30% of winter balance) stake readings are necessary to find the ELA. There is no sign of climatic warming through increased melting. The trend analysis of the data from the last 20 years shows stable conditions with a slight increase of the winter balance. The net balance is then slightly increasing and thus less negative than 20 years ago.

We have recorded reflection profiles of firn through large areas of West Antarctica and part of the East Antarctic plateau using 400MHz short-pulse radar. The locations show accumulation rates that vary from well above to well below the vertical radar resolution. Most reflection horizons have extensive lateral continuity, and are composed of distinctive wavelets with a consistent phase polarity sequence within their successive half-cycles. We modeled these waveforms, and conclude that they arise from thin, double layers of ice over hoar, which is consistent with the standard model of firn stratification. In addition, we conclude that ice/hoar layers are extensive throughout West Antarctica and also present (although more sparsely) beneath the Antarctic Plateau.

Contrary to prior expectations that warming would cause mass addition averaged over the Greenland and Antarctic ice sheets and over the next century, the ice sheets appear to be losing mass, at least partly in response to recent warming. With warming projected for the future, additional mass loss appears more likely than not.

Continuum damage mechanics describes the progressive deterioration of material subjected to loading. Jointly used with a level-set method, it proves to be a promising approach to computing the interface motion of a damaged material. For polycrystalline ice, a local isotropic damage evolution law (generalized Kachanow’s law) applied to Glen’s flow law allows the description of tertiary creep and facilitates the modeling of crevasse opening using a failure criterion based on damage accumulation. The use of a level-set method permits the description, in a continuum approach, of the motion of a fractured glacier surface. Using these methods, a model is developed. The ability of this model to describe phenomena connected to crevasse opening is presented. The rupture of a large ice block from a hanging glacier is computed and analyzed. The regular acceleration of such an unstable ice block prior to its collapse is calculated and compared to the acceleration function obtained from observations. A good agreement between the two acceleration functions was found.

Data on the mass balance of Xiao Dongkemadi glacier in the Tanggula mountains, central Tibetan Plateau, were obtained over 5 5 years from 1989 to 1995. These are the first continuous mass-balance data for a continental-type glacier on the Tibetan Plateau, where the glacier accumulates during the summer monsoon (summer-accumulation-type glacier). Mass-balance vs altitude profiles were steeper in the negative than in the positive mass-balance years. This is considered to have resulted from the effect of summer accumulation. The annual mass balance is compared with air temperature, precipitation, and black-body temperature in the area including the glacier, which is calculated from infrared radiation observations by theJapanese Geostationary Meteorological Satellite. It was found that the interannual variation in the glacier mass balance was not closely related to maximum monthly mean air temperature, while it did have a relatively good correlation with maximum monthly mean black-body temperature.

Seismic signals from artificially released avalanches were studied in an attempt to characterize them for avalanche-monitoring purposes. The seismic signals generated by different sizes and types of avalanches were recorded and analyzed in the time and frequency domains. Synchronized recordings of the corresponding seismic signals and the video images of the evolution of the avalanches were obtained together with a detailed cartography. Characteristic signatures in the frequency and time domains were found to depend on the characteristics of the avalanche path and measuring location, but to be mostly independent of avalanche size. The source of the different parts of the recorded seismic signals was determined. A relationship was observed between the avalanche size and the amplitude of the signals. Given the presence of local site effects, a prior seismic characterization of the avalanche path in relation to the recording sites is necessary for monitoring purposes. Moreover” it was found that sliding slabs in the early phase of acceleration produce little seismic energy, resulting in a time lapse between the observable start of the avalanche and the arrival of the detectable seismic waves at the receiving station.

Avalanche forecasters can better anticipate avalanche extremes if they understand the relationships between those extremes and atmospheric circulation patterns. We investigated the relationship between extreme avalanche days and atmospheric circulation patterns at four sites in the western United States: Bridger Bowl, Montana; Jackson Hole, Wyoming; Alta, Utah; and Taos, New Mexico. For each site, we calculated a daily avalanche hazard index based on the number and size of avalanches, and we defined abnormal avalanche events as the top 10% of days with recorded avalanche activity. We assessed the influence of different variables on avalanche extremes, and found that high snow water equivalent and high snowfall correspond most closely to days of high avalanche hazard. Composite-anomaly maps of 500 hPa heights during those avalanche extremes clearly illustrate that spatial patterns of anomalous troughing prevail, though the exact position of the troughing varies between sites. These patterns can be explained by the topography of the western United States, and the low-elevation pathways for moisture that exist to the west of each of the sites. The methods developed for this research can be applied to other sites with long-term climate and avalanche databases to further our understanding of the spatial distribution of atmospheric patterns associated with extreme avalanche days.

The Subglacial Antarctic Lakes Scientific Access (SALSA) Project accessed Mercer Subglacial Lake using environmentally clean hot-water drilling to examine interactions among ice, water, sediment, rock, microbes and carbon reservoirs within the lake water column and underlying sediments. A ~0.4 m diameter borehole was melted through 1087 m of ice and maintained over ~10 days, allowing observation of ice properties and collection of water and sediment with various tools. Over this period, SALSA collected: 60 L of lake water and 10 L of deep borehole water; microbes >0.2 μm in diameter from in situ filtration of ~100 L of lake water; 10 multicores 0.32–0.49 m long; 1.0 and 1.76 m long gravity cores; three conductivity–temperature–depth profiles of borehole and lake water; five discrete depth current meter measurements in the lake and images of ice, the lake water–ice interface and lake sediments. Temperature and conductivity data showed the hydrodynamic character of water mixing between the borehole and lake after entry. Models simulating melting of the ~6 m thick basal accreted ice layer imply that debris fall-out through the ~15 m water column to the lake sediments from borehole melting had little effect on the stratigraphy of surficial sediment cores.

Changes in the discharge of West Antarctic ice streams are of potential concern with respect to global sea level. The six relatively thin, fast-flowing Ross ice streams are of interest as low-slope end-members among Antarctic ice streams. Extensive research has demonstrated that these “rivers of ice” have a history of relatively high-frequency , asynchronous discharge variations with evolving lateral boundaries. Amidst this variability, a ∼1300 km grounding-line retreat has occurred since the Last Glacial Maximum. Numerical studies of Ice Stream D (Parizek and others, 2002) indicate that a proposed thermal-regulation mechanism (Clarke and Marshall, 1998; Hulbe and MacAyeal, 1999; Tulaczyk and others, 2000a, b), which could buffer the West Antarctic ice sheet against complete collapse, may be over-ridden by latent-heat transport within melt-water from beneath inland ice. Extending these studies to Ice Stream A, Whillans Ice Stream and Ice Stream C suggests that further grounding-line retreat contributing to sea-level rise is possible thermodynamically However, the efficiency of basal water distribution may be a constraint on the system. Because local thermal deficits promote basal freeze-on (especially on topographic highs), observed short-term variability is likely to persist.

Seasonal cycles of the chemical species Na+, Κ+ , Mg2+, Ca2+, CH3SO3 (MSA) Cl− NO3− and NO3− in the Dome Summit South (DSS) ice core from Law Dome were measured for a number of epochs (AD 1809-15, 1821-31 1980-92) span-nine a total of 28 years. These preliminary trace-chemical patterns show that the DSS site is mainly affected by marine air. The main features found in the seasonal pattern of sea-salt concentrations (e.g. Na+, Cl− and Mg2+) were a winter peak and a summer minimum. The variations in sea salts are believed to reflect aerosol production and transport due to the level of storminess, and are less affected by sea-ice extent. The seasonal cycles of marine biogenic compounds, non-sea-salt SO42- and MSA are in good agreement. They show a characteristic summer maximum arid a winter minimum, due to variations in biological activity. While the main sources of nitrate in polar snow remain unclear, the seasonal signal, including sub-seasonal structure, at DSS resembles that found m the atmosphere at coastal Antarctic sites. However, the timing of the nitrate maximum is different in the ice-core record compared with the aerosol records. Overall, the results indicate that the DSS core, with sub-seasonal resolution, contains a sensitive record for investigating climate variability.

Time series of satellite radar backscatter coefficients of the European Remote-sensing Satellite (ERS-1/-2) scatterometer are presented for perennial sea-ice regions in the Antarctic from June 1991 to June 1999. There is a pronounced seasonal cycle, with higher backscatter in summer than in winter. On average, backscatter increases from spring values of −16.3 dB to summer values of −10.7 dB within 96 days. This rapid rise and the summer maximum are occasionally interrupted by sudden strong signal drops. After late summer/early autumn, backscatter decreases again and slowly approaches winter values. The seasonal cycle is interpreted in terms of processes at the ice surface. The spring backscatter rise is associated with internal snowmelt and the formation of superimposed ice. This process commences once the surface energy balance becomes positive. Sudden backscatter drops are caused by temporary meltwater saturation of the snow during episodic events of warm-air advection. In the autumn, when superimposed-ice formation ceases due to surface cooling, gradual surface flooding with sea water becomes the dominant process, causing the observed decreasing backscatter. The reoccurrence of the seasonal backscatter cycle in most regions points to the widespread formation of superimposed ice on perennial Antarctic sea ice.

Ice-sheet modelling is an important tool for predicting the possible response of ice sheets to climate change in the past and future. An established ice-sheet model is SICOPOLIS (SImulation COde for POLythermal Ice Sheets), and for this study the previously grounded-ice-only model was complemented by an ice-shelf module. The new version of SICOPOLIS is applied to the Antarctic ice sheet, driven by standard forcings defined by the SeaRISE (Sea-level Response to Ice Sheet Evolution) community effort. A crucial point for simulations into the future is to obtain reasonable initial conditions by a palaeoclimatic spin-up, which we carry out over 125 000 years from the Eemian until today. We then carry out a set of experiments for 500 years into the future, in which the surface temperature and precipitation are kept at their present-day distributions, while sub-ice-shelf melting rates between 0 and 200 ma–1 are applied. These simulations show a significant, but not catastrophic, sensitivity of the ice sheet. Grounded-ice volumes decrease with increasing melting rates, and the spread of the results from the zero to the maximum melting case is ~0.65ms.l.e. (metres sea-level equivalent) after 100 years and ~2.25ms.l.e. after 500 years.

Changes in the ice fronts on the Antarctic Peninsula north of 70˚ S are currently being investigated through a comprehensive analysis of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and Landsat Thematic Mapper (TM) data as part of the international research initiative ‘Global land Ice Measurements from Space’ (GLIMS). Regional case studies are presented that cover a variety of glacial systems distributed over the northern Antarctic Peninsula and provide data on glacier front variations during the period 1986–2002. The results confirm a general trend of regional glacier front recession, but a range of different glacier variations are observed throughout the study area. Areas of predominant retreat are located in the northeastern and southwestern sectors, while stationary ice fronts characterize glacial behaviour on the northwestern coast of the peninsula. In addition, a significant increase in glacier recession is identified on James Ross Island, where retreat rates doubled during the period 1988–2001 compared to the previous investigation period, 1975–88. These observations are interpreted as being direct consequences of the rapidly changing climate in the region, which differentially affects the local accumulation and ablation patterns of the glacial systems.

This paper presents new data and interpretations of the structure, strength and behaviour of basal ice and the substrate of Suess Glacier, south Victoria Land, Antarctica, which is a small alpine dry-based glacier that has a basal temperature of—17°C. A tunnel excavated in the glacier revealed a substrate composed of frozen sand and gravel and a basal zone that was 3.8 m thick. From bottom to top, the basal zone was composed of 1.8 m of stratified, complexly deformed layers of ice and debris overlain by a 0.9 m thick layer of frozen sediment and a 0.8 m thick layer of discoloured ice lying immediately beneath clean glacier ice. Direct shear tests performed in the field on 36 samples show that the average peak shear strength of substrate samples was 2.53 MPa, which is almost twice as strong as the average value for basal ice (1.28 MPa) and the glacier ice samples (1.39 MPa). The direct shear tests suggest that the glacier substrate is unlikely to deform at the current temperature. However, observations of the structure and composition of the basal zone suggest that the substrate contains localized weaknesses that may reduce the peak strength sufficiently to permit bed deformation and entrainment. Two observed forms of weakness are ice lenses and layers in the permafrost and lenses of unsaturated permafrost, which may be inherited from the active zone of a former land surface or produced as pore ice sublimes into cavities which have formed at the glacier bed. Interpretation of data from this study suggests that glacier beds well below the freezing point can be deformed and eroded under certain conditions.

Large parts of the Arctic are covered by water bodies. Ice covers on lakes and rivers prohibit the exchange of heat and water vapor between the water body and the atmosphere. With melt onset, the ecosystem is subjected to changes, making it important to monitor the ice decay. As ground-based monitoring of these vast uninhabited areas is expensive and thus restricted to a few locations, remote-sensing techniques need to be applied. Here we evaluate the performance of the unsupervised k-means classification for dividing ice and water fractions on lakes and river channels from spaceborne radar data in comparison to threshold-based methods. The analysis is based on six TerraSAR-X and three RADARSAT-2 images, obtained during spring 2011 over the central Lena Delta in northern Siberia. The performance of the k-means classification is found to be similar to a fixed-threshold approach. As the k-means classification does not need prior statistical backscatter analyses to account for the radar configuration and ice conditions, it is easier to use than the threshold method. In addition, we found that the application of a low-pass filter prior to the classification of river channels and a closing filter on the classification results of lakes strongly improves the overall classification results.

The deformation of subglacial till is instrumental in causing certain glacier surges, the motion of rapid ice streams in ice sheets, and ice-sheet surges which are associated with Heinrich events, and consequent rapid climatic shifts, during the last ice age. It may also be the means whereby drumlins are formed, and these in turn may act as a brake on large-scale ice flow. It is therefore important in building models to understand the rate at which till deforms, and how this controls the basal ice velocity. In recent years, two paradigms have emerged. On the one hand, theoreticians have tended to use a viscous rheology, though this lacks quantitative support. On the other hand, field and laboratory studies suggest that till behaves plastically. In this paper I will examine some of the dynamic consequences of this latter assumption, and show how the dichotomy between viscous and plastic may be less clear-cut than previously thought.