We compare interferometric synthetic aperture radar (InSAR) observations of tidal flexure on Antarctic and Greenland glaciers with a finite-element model simulation of tidal flexure on an elastic plate of ice. The results show that the elastic-plate model is able to reproduce with good fidelity the pattern of tidal flexure observed with InSAR. In the case of David Glacier, Antarctica, the model provides independent confirmation of its grounding-line position and unusual pattern of tidal flexure. A detailed analysis of temporal changes in tidal flexing on Petermann Gletscher, Greenland, and Pine Island Glacier, West Antarctica, however, reveals that Young’s elastic modulus of ice, E, employed in the simulations to match observations, needs to vary between 0.8 and 3.5 GPa. This time dependence of E is attributed to visco-plastic effects, not to a migration of the grounding line with tide, or measurement errors.

Comparison of the Ross Ice Shelf (RIS, Antarctica) response at near-front seismic station RIS2 with seismometer data collected on tabular iceberg B15A and with land-based seismic stations at Scott Base on Ross Island (SBA) and near Lake Vanda in the Dry Valleys (VNDA) allows identification of RIS-specific signals resulting from gravity-wave forcing that includes meteorologically driven wind waves and swell, infragravity (IG) waves and tsunami waves. The vibration response of the RIS varies with season and with the frequency and amplitude of the gravity-wave forcing. The response of the RIS to IG wave and swell impacts is much greater than that observed at SBA and VNDA. A spectral peak at near-ice-front seismic station RIS2 centered near 0.5 Hz, which persists during April when swell is damped by sea ice, may be a dominant resonance or eigenfrequency of the RIS. High-amplitude swell events excite relatively broadband signals that are likely fracture events (icequakes). Changes in coherence between the vertical and horizontal sensors in the 8–12 Hz band from February to April, combined with the appearance of a spectral peak near 10 Hz in April when sea ice damps swell, suggest that lower (higher) temperatures during austral winter (summer) months affect signal propagation characteristics and hence mechanical properties of the RIS.

Automated classification of sea-ice types in Synthetic Aperture Radar (SAR) imagery is complicated by the class-dependent decrease of backscatter intensity with Incidence Angle (IA). In the log-domain, this decrease is approximately linear over the typical range of space-borne SAR instruments. A global correction does not consider that different surface types show different rates of decrease in backscatter intensity. Here, we introduce a supervised classification algorithm that directly incorporates the surface-type dependent effect of IA. We replace the constant mean vector of a Gaussian probability density function in a Bayesian classifier with a linearly variable mean. During training, the classifier first retrieves the slope and intercept of the linear function describing the mean value and then calculates the covariance matrix as the mean squared deviation relative to this function. The IA dependence is no longer treated as an image property but as a class property. Based on training and validation data selected from overlapping SAR and optical images, we evaluate the proposed method in several case studies and compare to other classification algorithms for which a global IA correction is applied during pre-processing. Our results show that the inclusion of the per-class IA sensitivity can significantly improve the performance of the classifier.

To assess the safety against failure of rock slopes in cold regions, such as high mountain areas, where stability is potentially maintained by ice in rock discontinuities, the shear strength of ice-filled rock joints was investigated in a series of direct shear-box tests. To permit control and repeatability, the experiments were conducted using simulated rock specimens. These were cast in the laboratory using high-strength concrete. Laboratory measurements showed that at a constant rate of shearing, the interface shear strength between ice and a joint surface of repeatable roughness is a function of both temperature and normal stress.

We have assembled an elevation grid for the Greenland ice sheet using a combination of the best current digital elevation model (DEM) (Bamber and others, 2000a, 2001) and 44 Advanced Very High Resolution Radiometer satellite images acquired in spring 1997. The images are used to quantitatively enhance the representation of surface undulations through photoclinometry. Gridcell spacing of the new DEM is 625 m. To validate the new DEM, we compared profiles extracted from it and the Bamber and others DEM with airborne laser altimetry profiles collected in the 1990s by the Airborne Topographic Mapper (Krabill and others, 1995). The image-enhanced DEM has a greatly improved representation of decameter-relief surface features <15 km in lateral extent, and reduces the mean elevation error in regions having these features by 20–50%. Root-mean-squared errors are typically 7–15m in the Bamber DEM, and 4–10m after image enhancement. However, the photoclinometry process adds some noise. In very smooth portions of the ice sheet where decameter undulationsare absent, the photoclinometry process caused a slight increase in the rms error, from ~1 min the Bamber and others DEM to ∼2.5 min the image-enhanced DEM. The image-enhanced DEM will be useful for inferring accumulation-rate variations over the undulation field, or for improving maps of bedrock elevation through inversion of surface elevation, for example. We briefly explore the preliminary steps of this latter application.

Temperature profiles of first-year landfast sea ice have been recorded continuously over the 2003 winter growth season at McMurdo Sound, Antarctica. The temperature gradients in the ice were used to calculate the growth rate due to conductive heat flux, which is shown to account for only part of the total ice growth. Remaining ice growth must be due to a negative oceanic heat flux. Significantly, this oceanic heat flux is shown to occur episodically, sometimes with sustained daily rates in excess of –30Wm–2. There is no direct correlation between oceanic heat flux and water temperature. Times of increased oceanic heat flux do coincide with the appearance of platelet ice in cores, and appear to account for the growth of 35% of the total platelet ice depth measured in ice cores.

Most dynamic ice-sheet studies currently use either empirically based parameterizations or simple energy-balance climate models for the surface mass-balance forcing. If three-dimensional global climate models (GCMs) could be used instead, they would greatly improve the potential realism of coupled climate ice-sheet simulations. However, there are two serious problems in simulating realistic mass balances on ice sheets from GCM simulations: (i) dynamic ice-sheet models and the underlying bedrock topography need horizontal resolution of 50–100 km or less, but the finest practical resolution of atmospheric GCMs is currently ˜250 km, and (ii) GCM surface physics usually neglects the local refreezing of meltwater on ice sheets.

Two techniques are described that address these problems: an elevation correction applied to the atmospheric GCM fields interpolated to the ice-sheet grid, and a refreezing correction involving the annual totals of snowfall, rainfall and local melt at each grid-point. As an example of their use, we have used the GENESIS version 2 GCM at 3.75° × 3.75° resolution to simulate the climate at the end of the last interglaciation at ˜116 000 years ago. The atmospheric climate is then used to drive a standard two-dimensional dynamic ice-sheet model for 10 000 years on a 0.5° × 0.5° grid spanning northern North America. The model successfully predicts ice-sheet initiation over the Baffin Island highlands and the Canadian Archipelago, but at a slower rate than observed. A large ice sheet nucleates and grows rapidly over the northwestern Rockies, in conflict with geologic evidence. Possible reasons for these discrepancies are discussed.

The Mackenzie GEWEX Study (MAGS) is a Canadian investigation that has the objective of understanding and modelling the water and energy cycles and their roles in the climate system in the high-latitude Mackenzie River basin, including assessing potential changes due to climate variability and change. The Climate Research Branch (CRB) of the MeteorologicalService of Canada has investigated snow-cover variations over the MAGS region using snow water equivalent (SWE) datasets derived from Special Sensor Microwave/Imager (SSM/I) passive-microwave satellite data for the winter seasons 1988–98. The SWE datasets were derived using four CRB algorithms for prairie, coniferous-forest, deciduous-forest and sparse-forest land-cover types and then evaluated against available in situ SWE measurements for MAGS subbasins. Overall, the SWE algorithms produce reliable estimates (within 10–20mm of in situ SWE measurements) for the validated part of the MAGS region, although some areas exhibit underestimations of > 30 mm, which may be due to the presence of a high density of lakes or a decreased microwave sensitivity to high-SWE conditions (>100mm). A time-series dataset of SSM/I-derived SWE for1 March of each year from 1988 to 1998 has been produced as a MAGS deliverable, which provides important information on the spatial and temporal variability in snow cover over the Mackenzie River basin. This dataset has been used in the assessment of snow-cover outputs from MAGS hydrological and climate-modelling investigations.

Cyanobacteria inhabit the Antarctic continent and have even been observed in the most southerly ice-free areas of Antarctica (86–87° S). The highest molecular diversity of cyanobacterial communities was found in the areas located between 70° S and 80° S. Further south and further north from this zone, the diversity abruptly decreased. Seventy-nine per cent (33 of 42 operational taxonomic units) of Antarctic terrestrial cyanobacteria have a cosmopolitan distribution. Analysis of the sampling efforts shows that only three regions (southern Victoria Land, the Sør Rondane Mountains and Alexander Island) have been particularly well studied, while other areas did not receive enough attention. Although cyanobacteria possess a capacity for long-range transport, regional populations in Antarctic ice-free areas seem to exist. The cyanobacterial communities of the three most intensively studied regions, separated from each other by a distance of 3000–3400 km, had a low degree of similarity with each other. Further development of microbial biogeography demands a standardized approach. For this purpose, as a minimal standard, we suggest using the sequence of cyanobacterial 16S rRNA gene between Escherichia coli positions 405 and 780.

Observations from along the length of Bench Glacier, Alaska, USA, show that the subglacial water-pressure field undergoes a multiphase transition from a winter mode to a summer mode. Data were collected at the glacier surface, the outlet stream, and in a network of 47 boreholes spanning the length of the 7 km long glacier. The winter pressure field was near overburden, with low-magnitude (centimeter to meter scale) and long-period (days to weeks) variations. During a spring speed-up event, boreholes showed synchronous variations and a slight pressure drop from prior winter values. Diurnal pressure variations followed the speed-up, with their onset associated with a glacier-wide pressure drop and flood at the terminus stream. Diurnal variations with swings of up to 80% of overburden pressure were typical of mid-summer. Several characteristics of our observations contradict common conceptions about the seasonal development of the subglacial drainage system and the linkages between subglacial hydrology and basal sliding: (1) increased water pressure did not accompany high sliding rates; (2) the drainage system showed activity characteristic of the spring season long before abundant water was available on the glacier surface; (3) the onset of both spring activity and diurnal variations of the drainage system did not show a spatial progression along the length of the glacier.

King George Island is the largest of the South Shetland Islands, close to the tip of the Antarctic Peninsula. The annual mean temperature on the island has increased by 1°C during the past three decades, and the ice cap that covers the majority of the island is sensitive to climatic change. We present data from two field campaigns (1997 and 2007): 700 km of global positioning system (GPS) and ground-penetrating radar (GPR) profiles were collected on Arctowski Icefield and on the adjacent central part. The data were analysed to determine the surface and bed topography and the thermal regime of the ice. Average ice thickness is 250 m and maximum thickness is 420 m. The GPR profiles show isochrones throughout the ice cap which depict the uparching of Raymond bumps beneath or close to the ice divides. A water table from percolation of meltwater in the snowpack shows the firn-ice boundary at ∼ 3 5 m depth. The firn layer may be temperate due to the release of latent heat. In the area below 400ma.s.l., backscatter by water inclusions is abundant for ice depths below the water table. We interpret this as evidence for temperate ice. Scatter decreases significantly above 400 m. Ice temperatures below the water table in this part of the ice cap are subject to further field and modelling investigations.

We use the upper 81 mof the record of stable isotopes of water from a 122m long ice core from Lomonosovfonna, central Spitsbergen, Svalbard, to construct an ice-core chronology and the annual accumulation rates over the icefield. the isotope cycles are counted in the ice-core record using a model that neglects short-wavelength and low-amplitude cycles. We find approximately the same number of δ18O cycles as years between known reference horizons, and assume these cycles represent annual cycles. Testing the validity of this assumption using cycles in δD shows that both records give similar numbers of cycles. Using the δ18O chronology, and decompressing the accumulation records using the Nye flow model, we calculate the annual accumulation for the ice-core site back to AD 1715. We find that the average accumulation rate from 1715 to 1950 was on average 0.30 mw.e. Accumulation rates increased about 25% during the later part of the 20th century to an average of 0.41 mw.e. for the period 1950–97. the accumulation rates show highly significant 2.1 and 21 year periodicities, which gives credibility to our time-scale.

A 181 m long ice core was drilled at 79°36’51"S, 45°43’28" W, near the summit of Berkner Island, Antarctica (886 m a.s.L). Berkner Island is located between the Filchner and Ronne Ice Shelves, and the ice near the summit shows little lateral flow. The density of the ice core was measured every 3 mm along its length, using attenuation of a gamma-ray beam, which gave an absolute accuracy of 2%. As expected, there is a general density increase with depth, the maximum densities of > 900 kg m−3 being reached just above 100 m depth. Comparison with the electrical conductivity method (ECM) shows density variations with the same wavelength as the annual signals, which can be seen in the ECM log (higher acidity during summer). In the shallowest part of the core, the density of winter layers is higher than that of summer layers, a relationship which is reversed at greater depth. We assume that the densification rates for the two types of firn are different. Similar density phenomena were observed on ice cores from Greenland, showing that such phenomena are not a local effect.

This paper examines the topographic and geometric controls on glacier changes in area and equilibrium-line altitude (ELA) in the central Tien Shan, China, since the Little Ice Age (LIA). We delineate the extents of 487 modern glaciers and their corresponding maximum LIA glacial advances using satellite imagery in Google Earth, and analyze the relationships between the magnitude of glacier changes and a set of local topographic/geometric factors including glacier area, slope, aspect, shape, hypsometry and mean elevation. Our results show that: (1) glacier area decreased from 460.2 km2 during the LIA to 265.6 km2 in the 2000s (a loss of 42.3%), with an average ELA increase of ~100m; (2) relative area changes of glaciers are strongly affected by two of these local factors (glacier area and mean elevation); and (3) ELA change does not show a strong relationship with local factors, suggesting that it may be controlled mainly by climatic factors. This study provides important insights into the local controls on glacier changes at the centennial timescale, which are of critical importance to assess future glacier changes in this arid and semi-arid region.

Very small (ppm) amounts of soil dust in snow can significantly reduce snow albedo and thereby affect the snow-surface energy budget. Ice cores from Greenland show enhanced dust concentrations in ice from the last glacial maximum, in amounts capable of causing measurable effects on snow albedo. This enhanced dust is probably due in part to the expanded desert areas at that time.

Volcanic ash layers visible in the Byrd station core reduced the snow albedo in West Antarctica when they were on the surface. The ash is unlikely to have had a long-term effect on albedo because of the episodic nature of volcanic eruptions.

Very large amounts of dust on snow can inhibit snow-melt by insulating the snow. A debris cover probably slowed the melting of parts of the North American ice sheet during its most recent decay phase.

Snow in the Arctic Ocean is presently suffering large-scale contamination by carbon soot from anthropogenic sources. Preliminary estimates indicate that soot concentrations in Arctic snow are sufficient to reduce snow albedo measurably.

West Antarctic climate and surface mass balance (SMB) records are sparse. To fill this gap, regional atmospheric climate modelling is useful, providing that such models are employed at sufficiently high horizontal resolution and coupled with a snow model. Here we present the results of a high-resolution (5.5 km) regional atmospheric climate model (RACMO2) simulation of coastal West Antarctica for the period 1979–2015. We evaluate the results with available in situ weather observations, remote-sensing estimates of surface melt, and SMB estimates derived from radar and firn cores. Moreover, results are compared with those from a lower-resolution version, to assess the added value of the resolution. The high-resolution model resolves small-scale climate variability invoked by topography, such as the relatively warm conditions over ice-shelf grounding zones, and local wind speed accelerations. Surface melt and SMB are well reproduced by RACMO2. This dataset will prove useful for picking ice core locations, converting elevation changes to mass changes, for driving ocean, ice-sheet and coupled models, and for attributing changes in the West Antarctic Ice Sheet and shelves to changes in atmospheric forcing.

Four long-term time series of seasonal mass-balance observations, all starting in 1914, have been compiled for two stakes on Claridenfirn and one stake on Grosser Aletschgletscher and Silvrettagletscher, Switzerland. These data represent the longest records of mass balance worldwide. A mass-balance model based on the temperature-index approach is used to correct field data for varying observation dates and data gaps and to separate accumulation and ablation. The homogenized continuous 93 year time series cover most of the 20th century and enable us to investigate temporal, regional and altitudinal variability in mass balance and changes in the climatic forcing on glaciers. A high-altitude site shows summer balance trends opposite to those at three stakes located near the equilibrium line. Since 1975, melt rates have increased by 10%(10 a)−1 periods of enhanced climatic forcing are detected: 1943–53 and 1987–2007. The energy consumed for melt was higher in the 1940s despite lower air temperatures compared to the years since 1987. We find evidence for a change in the glacier surface heat budget, which has important implications for the long-term stability of degree-day factors in empirical temperature-index modelling.

The major river systems of India, i.e. the Indus, Ganga and Brahmaputra river systems originating in the Himalayan region, are considered the lifeline of the Indian subcontinent. The main sources maintaining the flow of the Himalayan rivers are snow/glacial melt runoff, rainfall runoff and base flow. The Beas River originates from Beas Kund Glacier in the Himalayan region and flows down to join the Sutlej River, which is a tributary of the Indus River system. In the present study two approaches, namely hydrologic modelling and isotope analysis, have been applied to estimate the contribution of snow and glacier melt. Samples of streamflow, rainfall and snow for isotopic analysis were collected daily from April to September and weekly from October to March during 2010 and 2011. The isotope analysis of samples reveals that the snow/glacier melt contribution to the Beas River at Manali is 50% of the total flow during these 2 years. Snowmelt runoff modelling has been carried out using the SNOWMOD model, and the snow/glacier melt runoff contribution is calculated to be 52% of the total flow during the same period. These findings indicate that the results obtained from the two approaches are similar.

The U.S. Science Plan for Deep Ice Coring in West Antarctica calls for two ice cores to be collected. the first of these cores, from Siple Dome, was completed during the 1997/98 field season. the second core is to be collected from a site near the divide that separates ice flowing to the Ross Sea and to the Amundsen Sea.Using high-resolution, grid-based aerogeophysical surveys of the Ross/Amundsen ice-divide region, we identify seven candidate sites and assess their suitability for deep coring. We apply ice-flow and temperature calculations to predict time-scales and annual-layer resolution, and to assess the potential for basal melting for several selected sites. We conclude that basal melting is likely for sites with very thick ice, as was observed at the Byrd core site. Nevertheless, these sites are most attractive for coring since they promise recovery of a long climate record with comparatively high time resolution during the last glacial period.

SNOWPACK has been in operational use for five consecutive winters on approximately 100 automatic weather stations in the Swiss Alps. It calculates snow precipitation, snowdrift and the layered structure of the snow cover. An analysis routine has been implemented that gives a stability estimation for a model profile. We distinguish between slab instability and direct action or deformation-rate instability. Slab instability relies on a static force balance within the snowpack (stability index) and may be used to assess stability for both natural and skier-triggered slab avalanches. We heuristically improve the slab index by adding a term of overload correction for all grain types and scaling the stability index with the bond size. Deformation-rate instability means that the load of the snow cover increases faster than the snow gains strength. An index is formulated based on the snow deformation rate. It may be associated with large snowfall events and wet-snow situations as they occur in catastrophic situations, or with the effect of a sudden increase in temperature. The results of both stability indices are compared to the fore-casted avalanche danger. The indices are able to recognize cases of avalanching. It is shown that the inclusion of several locations, for which the indices are calculated, improves the correlation between stability indices and avalanche danger. A sufficient number of profiles could bridge the gap between snow-cover characteristics at a point and avalanche danger.