Several airborne radar-sounding surveys are used to trace internal reflections around the European Project for Ice Coring in Antarctica Dome C and Vostok ice core sites. Thirteen reflections, spanning the last two glacial cycles, are traced within 200 km of Dome C, a promising region for million-year-old ice, using the University of Texas Institute for Geophysics High-Capacity Radar Sounder. This provides a dated stratigraphy to 2318 m depth at Dome C. Reflection age uncertainties are calculated from the radar range precision and signal-to-noise ratio of the internal reflections. The radar stratigraphy matches well with the Multichannel Coherent Radar Depth Sounder (MCoRDS) radar stratigraphy obtained independently. We show that radar sounding enables the extension of ice core ages through the ice sheet with an additional radar-related age uncertainty of ~1/3–1/2 that of the ice cores. Reflections are extended along the Byrd-Totten Glacier divide, using University of Texas/Technical University of Denmark and MCoRDS surveys. However, core-to-core connection is impeded by pervasive aeolian terranes, and Lake Vostok's influence on reflection geometry. Poor radar connection of the two ice cores is attributed to these effects and suboptimal survey design in affected areas. We demonstrate that, while ice sheet internal radar reflections are generally isochronal and can be mapped over large distances, careful survey planning is necessary to extend ice core chronologies to distant regions of the East Antarctic ice sheet.

Scientific investigations on valley glaciers engaged some of the greatest natural philosophers of the nineteenth century. Among these, Louis Agassiz has unique importance for he personifies the transition from the protoscientific period of de Saussure and Scheuchzer to the scientific one of Forbes and his successors. In this brief history I have attempted to connect the achievements of the past 50 years with the aspirations of our predecessors.

Stable-water-isotope data (δD and δ18O) from three groups of samples (fresh-snow and snow-pit samples collected on Qomolangma (Mount Everest) and Xixa-bangma during field seasons 1997, 1998 and 2001, and precipitation samples collected at Tingri station during summer 2000) are presented and used to survey the isotopic composition of precipitation over the northern slope of the central Himalaya. Multi-year snow-pit samples on Qomolangma have a local meteoric water-line (slope = 8) close to the global value. Deuterium excess (d = δD – 8δ18O) values at Tingri are much lower than those in fresh snow from Qomolangma, probably due to differences in moisture source and air-mass trajectories as well as local weather conditions. There is no obvious seasonal trend for d values in the Qomolangma region. A negative relationship exists between δ18O and d values in both fresh snow on Qomolangma and precipitation at Tingri. Fresh-snow samples collected from different altitudes on Xixabangma allow us to investigate the altitude effect on δ18O values in snow. Of four storm events, only one has an obvious altitude effect on δ18O variation and a very low gradient of −0.1 % per 100 m elevation.

The subglacial water system of lower Whillans Ice Stream on the Siple Coast, West Antarctica, contains numerous connected subglacial lakes in three hydrological basins (northern, central and southern). We use Ice, Cloud and land Elevation Satellite (ICESat) data to derive estimates of lake volume change and regional thickness changes. By combining these results with a water budget model, we show that a uniform, localized thickness increase perturbed the hydropotential, resulting in a change in course of a major flow path within the system in 2005. Water originating from upper Whillans and Kamb Ice Streams that previously supplied the southern basin became diverted toward Subglacial Lake Whillans (SLW). This diversion led to a tenfold filling rate increase of SLW. Our observation suggests that water piracy may be common in the Siple Coast region, where the gentle basal relief makes the basal hydropotential particularly sensitive to small changes in ice thickness. Given the previously inferred connections between water piracy and ice-stream slowdown elsewhere in the region, the subtle and complex nature of this system presents new challenges for numerical models.

The thermal regime of high-altitude accumulation areas in the Swiss Alps was systematically investigated on the Jungfraufirn, Bernese Alps, on the Breithornplateau, Valais Alps, and on Grenzgletscher, Valais Alps. In 1991, 1992 and 1994, temperatures were measured in a deep hole (120 m deep) and in several shallow holes (14–30 m deep). Whereas the wide névé of the Jungfraufirn at 3400–3600 m a.s.l. and the 3800 m high Breithornplateau seems to be predominantly temperate, cold firn and ice temperatures were measured throughout on Grenzgletscher (3900–4450 m a.s.l.). Mean firn temperatures on Grenzgletscher vary strongly and range between −3° and −14°C. A comparison between the measured temperature profiles and a one-dimensional heat-conduction calculation shows that the release of latent heat by penetrating and refreezing meltwater decisively influences the thermal pattern of the firn pack. A multiple linear regression model, based on measured firn temperatures from the European Alps and the parameters altitude and aspect, yields aspect-dependent lower boundaries for the occurrence of cold firn ranging between 3400 (northerly aspects) and 4150 m a.s.l. (southerly aspects). A total of 120 glaciers with cold-firn areas are found when applying the model to glacier inventory data from the European Alps.

A theory of erosion, transport and deposition of unlithified sediments by glaciers is presented. It predicts the large-scale areal distribution of zones and rates of erosion and deposition in time and space through a complete glacial cycle, together with the resultant intensity of large-scale lineations (drumlins) which will be incised in the landscape. The theory also predicts the dispersal patterns of subglacial lithologies, together with the form of dispersal trains derived from distinctive sources and the vertical and horizontal distribution of lithologies within a till. It predicts major erosional discontinuities within tills and the formation of boulder pavements. It suggests that the dominant proportion of the lowland tills produced by Pleistocene mid-latitude ice sheets was generated by subglacial deformation and explains why they are predominantly fine-grained.

The theory is based on an analysis of glacier-dynamic processes and therefore can be used to infer the dynamic behaviour of former ice sheets from the distribution of tills and their lithologic composition.

Between 1953 and 1955, 73 glaciers in the Olympic and Cascade Mountains of Washington State have been investigated to determine their present activity. 50 of these glaciers are now advancing at rates from 3 to 100 m. or more per annum. Of the remaining 23, 22 glaciers either demonstrate clear evidence of increasing thickness, or have remained so heavily snow-covered at the end of the ablation season that it has not been possible to locate their limits.

The present glacier growth, which appears to have started about 12 years ago, represents a radical change from conditions during the previous 20 years when glaciers of the Olympics and Cascades without exception were shrinking rapidly. An analysis of local climatic data demonstrates a present trend toward a cooler, wetter climate in western Washington. The ten year running mean annual temperature at Tatoosh Island off the Washington coast has decreased approximately o 8° C. from the period 1934–1943 to the period 1945–1954. In the same interval of time the ten year running mean annual precipitation at Tatoosh has increased about 38 cm., and during the last decade has reached its highest value since the period 1898–1907.

Spaceborne microwave radiometers are an attractive tool for observing Antarctic climate because their measurements are related to the snow temperature. However, the conversion from microwave emission to snow temperature is not simple and strongly depends on the emissivity through snow properties. This difficulty in predicting the snow property profile for Antarctic conditions is the main bottleneck in the retrieval of accurate climate information from microwave radiometers. We attempt to explain the vertically polarized emissivity at 19.3 and 37 GHz derived from brightness temperatures acquired by the Special Sensor Microwave/Imager (SSM/I) and physical temperature from the ERA-40 re-analysis. In Antarctica the snow emissivities at 19.3 and 37 GHz are nearly equal, although a decrease with frequency is expected. To explain this, we consider various profiles of snow grain size and density and predict their emissivity using a dense-medium radiative transfer (DMRT) model. The results show that the emissivities cannot be explained by constant profiles of grain size and density. Heterogeneous snowpacks need to be considered. We first test random variations of snow density and grain radius with depth and then monotonic and continuous variations in the snow grain radius. In both cases, we show that an overall increase of the snow grain radius with depth is required to match the observed emissivity in Antarctica. In addition, two parameters characterizing the snow grain profiles are retrieved and compared with (1) in situ measurements of grain size at various locations in East Antarctica, (2) grain size estimated using visible spaceborne radiometers and (3) a semi-empirical relationship for grain growth.

Annual proglacial solute fluxes and chemical weathering rates at a polythermal high-Arctic glacier are presented. Bulk meltwater chemistry and discharge were monitored continuously at gauging stations located at the eastern and western margins of the glacier terminus and at “the Outlet”, 2.5 km downstream where meltwaters discharge into the fjord. Fluxes of non-snowpack HCO3−, SO42−, Ca2+ and Mg2+ increase by 30–47% between the glacier terminus and the Outlet, indicating that meltwaters are able to access and chemically weather efflorescent sulphates, carbonates and sulphides in the proglacial zone. Smaller increases in the fluxes of non-snowpack-derived Na+, K+ and Si indicate that proglacial chemical weathering of silicates is less significant. En3hanced solute fluxes in the proglacial zone are mainly due to the chemical weathering of active-layer sediments. The PCO2 of active-layer ground-waters is above atmospheric pressure. This implies that solute acquisition in the active layer involves no drawdown of CO2. The annual proglacial chemical weathering rate in 1999 is calculated to be 2600 meqΣ+ m−2. This exceeds the chemical weathering rate for the glaciated part of the catchment (790 meqΣ+ m−2) by a factor of 3.3. Hence, the proglacial zone at Finster-walderbreen is identified as an area of high geochemical reactivity and a source of CO2.

We investigate causes of the stratigraphic variation revealed in a 177 km, 400 MHz short-pulse radar profile of firn from West Antarctica. The profile covers 56 m depth, and its direction was close to those of the ice flow and mean wind. The average, near-surface accumulation rates calculated from the time delays of one radar horizon consistently show minima on leeward slopes and maxima on windward slopes, confirming an earlier study based on stake observations. The stratigraphic variation includes up to 30 m depth variation in individual horizons over tens of km, fold limbs that become progressively steeper with depth, and fold-hinge loci that change direction or propagate down-ice with depth over distances far less than predicted by the ice speeds. We use an accumulation rate model to show how local rate anomalies and the effect of ice speed upon a periodic variation in accumulation rate cause these phenomena, and we reproduce two key features seen in the stratigraphic variations. We conclude that the model provides an explanation of changes in spatial stratigraphy and local measures of accumulation history given the constraints of surface topography, ice and wind velocities, and a general accumulation rate for an area.

We use data from four automatic weather stations (AWSs) in Dronning Maud Land, East Antarctica, to study the surface mass balance and its components. Distinct differences were found between the moisture climates of the high plateau, the katabatic wind zone and the coastal ice shelves: significant undersaturation occurs year-round in the katabatic wind zone, while on the high plateau and on the coastal ice shelf the air is usually close to saturation. In summer, absorption of shortwave radiation at the snow surface enhances surface sublimation at all sites, removing 3-9% of the annual solid precipitation. Significant summer melting is an equally important ablation term near the coast, but vanishes inland. Vertically integrated column drifting-snow sublimation was estimated using two different methods. This process appears to be similar to or greater in magnitude than surface sublimation. Because intervals between significant precipitation events may last as long as several months, sublimation and melt cause extended periods of surface ablation in summer. In summer, all ablation processes together remove 15-56% of the solid precipitation, or 6-27% on an annual basis.

Between 2003 and 2007, North Gasherbrum Glacier on the northeastern slope of the Karakoram mountains in Asia underwent a dramatic acceleration, during which a velocity wave propagated down the glacier. There was a significant transfer of ice from up-glacier downstream, which resulted in a strong surface elevation increase over the lower tongue, but only a moderate advance of the glacier snout. We interpret this behaviour as that of a glacier surge, and we explain the observations by means of a simple version of the Kamb drainage-switching theory.

Discharge from marine-terminating outlet glaciers accounts for up to half the recent mass loss from the Greenland ice sheet, yet the causal factors are not fully understood. Here we assess the factors controlling the behaviour of Humboldt Glacier (HG), allowing us to evaluate the influence of basal topography on outlet glacier response to external forcing since part of HG’s terminus occupies a large overdeepening. HG’s retreat accelerated dramatically after 1999, coinciding with summer atmospheric warming of up to 0.19°C a–1 and sea-ice decline. Retreat was an order of magnitude greater in the northern section of the terminus, underlain by a major basal trough, than in the southern section, where the bedrock is comparatively shallow. Velocity change following retreat was spatially non-uniform, potentially due to a pinning point near HG’s northern lateral margin. Consistent with observations, numerical modelling demonstrates an order-of-magnitude greater sensitivity to sea-ice buttressing and crevasse depth (used as a proxy for atmospheric warming) in the northern section. The trough extends up to 72 km inland, so it is likely to facilitate sustained retreat and ice loss from HG during the 21st century.

Distributed energy-balance melt models have rarely been applied to glaciers with extensive supraglacial debris cover. This paper describes the development of a distributed melt model and its application to the debris-covered Miage glacier, western Italian Alps, over two summer seasons. Sub-debris melt rates are calculated using an existing debris energy-balance model (DEB-Model), and melt rates for clean ice, snow and partially debris-covered ice are calculated using standard energy-balance equations. Simulated sub-debris melt rates compare well to ablation stake observations. Melt rates are highest, and most sensitive to air temperature, on areas of dirty, crevassed ice on the middle glacier. Here melt rates are highly spatially variable because the debris thickness and surface type varies markedly. Melt rates are lowest, and least sensitive to air temperature, beneath the thickest debris on the lower glacier. Debris delays and attenuates the melt signal compared to clean ice, with peak melt occurring later in the day with increasing debris thickness. The continuously debris-covered zone consistently provides 30% of total melt throughout the ablation season, with the proportion increasing during cold weather. Sensitivity experiments show that an increase in debris thickness of 0.035 m would offset 18C of atmospheric warming.

Using a combination of satellite sensors, field measurements and satellite-uplinked in situ observing stations, we examine the evolution of several large icebergs drifting east of the Antarctic Peninsula towards South Georgia Island. Three styles of calving are observed during drift: ‘rift calvings’, ‘edge wasting’ and ‘rapid disintegration’. Rift calvings exploit large pre-existing fractures generated in the shelf environment and can occur at any stage of drift. Edge wasting is calving of the iceberg perimeter by numerous small edge-parallel, sliver-shaped icebergs, preserving the general shape of the main iceberg as it shrinks. This process is observed only in areas north of the sea-ice edge. Rapid disintegration, where numerous small calvings occur in rapid succession, is consistently associated with indications of surface melt saturation (surface lakes, firn-pit ponding). Freeboard measurements by ICESat indicate substantial increases in ice-thinning rates north of the sea-ice edge (from <10 m a−1 to >30 m a−1), but surface densification is shown to be an important correction (>2 m freeboard loss before the firn saturates). Edge wasting of icebergs in ‘warm’ surface water (sea-ice-free, >−1.8°C) implies a mechanism based on waterline erosion. Rapid disintegration (‘Larsen B-style’ break-up) is likely due to the effects of surface or saturated-firn water acting on pre-existing crevasses, or on wave- or tidally induced fractures. Changes in microwave backscatter of iceberg firn as icebergs drift into warmer climate and experience increased surface melt suggest a means of predicting when floating ice plates are evolving towards disintegration.

This paper aims to interpret the temporal variations of microwave brightness temperature (at 19 and 37GHz and at vertical and horizontal polarizations) in Antarctica using a physically based snow dynamic and emission model (SDEM). SDEM predicts time series of top-of-atmosphere brightness temperature from widely available surface meteorological data (ERA-40 re-analysis). To do so, it successively computes the heat flux incoming the snowpack, the snow temperature profile, the microwaves emitted by the snow and, finally, the propagation of the microwaves through the atmosphere up to the satellite. Since the model contains several parameters whose value is variable and uncertain across the continent, the parameter values are optimized for every 50 km × 50 km pixel. Simulation results show that the model is inadequate in the melt zone (where surface melting occurs on at least a few days a year) because the snowpack structure and its temporal variations are too complex. In contrast, the accuracy is reasonably good in the dry zone and varies between 2 and 4 K depending on the frequency and polarization of observations and on the location. At the Antarctic scale, the error is larger where wind is usually stronger, suggesting either that meteorological data are less accurate in windy regions or that some neglected processes (e.g. windpumping, surface scouring) are important. At Dome C, in calm conditions, a detailed analysis shows that most of the error is due to inaccuracy of the ERA-40 air temperature (∼2 K). Finally, the paper discusses the values of the optimized parameters and their spatial variations across the Antarctic.

Digital elevation models (DEMs) of the ablation area of Hailuogou glacier, China, produced from Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data obtained in 2009, differential GPS (DGPS) data surveyed in 2008 and aerial photographs acquired in 1966 and 1989 are differenced to estimate long- and short-term glacier surface elevation change (dh/dt). The mean dh/dt of the ablation area over 43 years (1966–2009) is −1.1 ± 0.4 m a−1. Since 1989 the thinning has accelerated significantly. Ice velocities measured by DGPS at 28 fixed stakes implanted in the ablation area increase with distance from the glacier terminus, ranging from 41.0 m a−1 approaching the glacier terminus to a maximum of 205.0 m a−1 at the base of an icefall. Our results reveal that the overall average ice velocity in the ablation area has undergone significant temporal variability over the past several decades. Changes in glacier surface elevation in the ablation area result from the combined effects of climate change and glacier dynamics, which are driven by different factors for different regions and periods.

Basal radar reflectivity is the most important measurement for the detection of subglacial water. However, dielectric loss in the overlying ice column complicates the determination of basal reflectivity. Dielectric attenuation is a function of ice temperature and impurity concentration. Temperature distribution is a function of climate history, basal heat flow and vertical strain rate, all of which can be partially inferred from the structure of dated internal layers. Using 11 dated layers, isotope records from Dome C, East Antarctica, and a model of the spatial variation of geothermal flux, we calculate the vertical strain rate and accumulation-rate history, allowing identification of areas where the basal melt rate exceeds 1.5 mm a−1. The accumulation-rate history and vertical strain rates are then used as inputs for a transient temperature model. The model outputs for the present-day temperature distribution are then combined with depth-dependent ionic concentrations to model dielectric loss and infer basal reflectivity. The resulting reflection coefficients are consistent (∼−5 dB) across a variety of subglacial water bodies. We also identify a high reflectivity >−15 dB in Concordia Trench and along suspected subglacial water-flow routes in Vincennes Basin. Highland areas tend to have highly variable reflection coefficients near −30 dB, consistent with an ice–bedrock interface. This combined model also identifies three areas of enhanced basal melting along Concordia Ridge, Concordia Subglacial Lake and Vincennes Basin. Melt at Concordia Subglacial Lake exceeds 5 mm a−1. The inferred basal melt at these locations is not possible without enhanced geothermal flux. We demonstrate how radar-sounding data can provide both input and verification for a self-consistent model of vertical strain, vertical temperature distribution and meltwater distribution.

Here, we present a comprehensive assessment of Siachen Glacier (East Karakoram), in terms of its area and elevation change, velocity variations and mass budget, utilizing different satellite datasets including Landsat, Hexagon, Cartosat-I, Shuttle Radar Topography Mission, Envisat Advanced Synthetic Aperture Radar and Japanese Advanced Land Observing Satellite Phased Array-type L-band SAR. The total areal extent of Siachen Glacier did not change significantly between 1980 and 2014; however the exposed-ice area decreased during that period. The terminus of the glacier has experienced substantial downwasting (on average 30 m) over the period of 1999–2007, followed by a retreat of the transition between exposed and debris-covered ice by a distance of 1.3 km during the short span 2007–14. The spatial patterns of the elevation difference and velocity are heterogeneous over the large areal extent of Siachen Glacier. The average velocity of the entire glacier, as computed between 11 December 2008 and 26 January 2009, was 12.3 ± 0.4 cm d−1, while those estimated separately for the accumulation and ablation regions were 9.7 ± 0.4 cm d−1 and 20.4 ± 0.4 cm d−1, respectively. The mass budget of Siachen Glacier is estimated to be –0.03 ± 0.21 m w.e. a−1 for the period of 1999–2007.

In a two-dimensional model of an ice mass breaking off from a cliff, stresses and velocities are calculated numerically according to Glen's flow law. A tensile crack opens in the zone of maximum tensile principal stress σ1 and propagates to a depth where σ1, iɜ, zero. Ice flow then produces an overhang of the partly detached ice mass. Consequently, the stress σ1 below the tip of the crack becomes tensile again and the crack propagates for another small distance. This process goes on until the centre of gravity of the detaching ice mass has moved past the supporting edge of the bedrock. Velocities v of the ice mass calculated for different stages of the process are plotted as a function of time t. The plotted points lie in the vicinity of a curve given by

(1)

where vc, tA B and D are constants. The same type of function has been found for velocities measured at an ice mass breaking off the Grubengletscher.