On an 11 m firn/ice core from Kongsvegen, Svalbard, we have used dielectric profiling (DEP) to measure electrical properties, and digital photography to measure a core optical stratigraphy (COS) profile. We also used a neutron-scattering probe (NP) to measure a density profile in the borehole from which the core was extracted. The NP- and DEP-derived density profiles were similar, showing large-scale (>30 cm) variation in the gravimetric densities of each core section. Fine-scale features (<10 cm) are well characterized by the COS record and are seen at a slightly lower resolution in both the DEP and NP records, which show increasing smoothing. A combination of the density accuracy of NP and the spatial resolution of COS provides a useful method of evaluating the shallow-density profile of a glacier, improving paleoclimate interpretation, mass-balance measurement and interpretation of radar returns.

Sea ice surviving the summer melt season to become multi-year ice in the Arctic Ocean is of interest because multi-year ice significantly affects the ice-thickness distribution and the dynamics and thermodynamics of the ice pack in subsequent seasons. However, the amount of ice surviving summer melting has not been well determined because the time of the minimum ice area varies from region to region. A concept of local temporal minimum (LTM) accounts for non-simultaneity of the melt–freeze transition by determining the minima ice concentrations (CLTM) on local spatial scales. CLTM are calculated for 25 km gridcells using 24 years (1979–2002) of satellite passive-microwave data. The total area of ice surviving the summer melt (ALTM) is given by spatial integration of CLTM. Over 24 years, the average ALTM is 2.6 × 106 km2 (excluding ∼0.7 × 105 km2 above 84° N). In contrast, the average area (3.8 × 106 km2) of all ice types (ASM), measured when the total (simultaneous) ice cover is a minimum in daily maps in mid-September, is an often-used estimate of ice surviving the summer melting that is ∼45% too large. Over 24 years, the ALTM decreased by 9.5 ± 2.2% (10 a)−1 (0.27 ± 0.06 × 106 km2 (10 a)−1), which is similar to the rate of decline of ASM and about three times the rate of the annual average. The time-of-occurrence of the LTM averaged over the perennial ice pack increased by 8 days from around 11 to 19 August, indicating a later ending of the melt season by about 3 days (10 a)−1 as the summer pack declines. Estimates of multi-year ice in midwinter from passive microwave observations are ∼17% smaller than ALTM, suggesting that the microwave algorithm does not measure all the multi-year ice.

Subglacial water threatens the stability of a deep ice sheet. The Greenland ice sheet has been the subject of extensive radar surveys under NASA’s PARCA program and others, yet the extent of basal water has not previously been explored in detail. This paper provides a method for recovering basal radar reflection characteristics that yield robust discrimination of subglacial water, using PARCA data, by narrowing the spread of measured echo intensities. Sources of validation are provided, and they support the procedure and its results. The method can be extended to the entire Greenland radar dataset. It is not dependent on details of radar characteristics but relies on sufficient penetration performance, high-fidelity data acquisition and appropriate treatment of signals and interface statistics.

Variations of snow surface and snowpack properties affect avalanche formation. In up to four north-facing slopes above the tree line near Davos, Switzerland, snow surface properties were characterized. Penetration resistance was measured with a snow micro-penetrometer. The sampling scheme was designed to allow a multi-scale approach covering the snowpack depth scale (0.5–5 m), the slope scale (5–100 m) and the basin scale (100–1000 m). Observations and measurements were compared to the data of a nearby automatic weather station (AWS). The AWS data were also used to model snow-cover stratigraphy and its evolution with the numerical snow-cover model SNOWPACK. Comparing the four slopes showed that surface properties observed manually were similar among the three slopes that were sheltered, and often different from the slope that was wind-exposed. However, the penetration resistance of the surface layer was in most cases significantly different among slopes, although most values were <0.1 N, indicating very low hardness. These seemingly contradictory results follow from the different measurement support of the two methods. It is presently unclear which amount of variation at a given scale is relevant for avalanche formation. The geostatistical analysis and an analysis aimed at identifying the causes of variability were not conclusive. No patterns emerged that would allow conclusions regarding the effect on avalanche formation. Finding the causes of variability seems to require high-resolution terrain and weather models that are presently not readily available.

Limitations of access have long restricted exploration and investigation of the cavities beneath ice shelves to a small number of drillholes. Studies of sea-ice underwater morphology are limited largely to scientific utilization of submarines. Remotely operated vehicles, tethered to a mother ship by umbilical cable, have been deployed to investigate tidewater-glacier and ice-shelf margins, but their range is often restricted. The development of free-flying autonomous underwater vehicles (AUVs) with ranges of tens to hundreds of kilometres enables extensive missions to take place beneath sea ice and floating ice shelves. Autosub2 is a 3600 kg, 6.7 m long AUV, with a 1600 m operating depth and range of 400 km, based on the earlier Autosub1 which had a 500 m depth limit. A single direct-drive d.c. motor and five-bladed propeller produce speeds of 1–2 m s−1. Rear-mounted rudder and stern-plane control yaw, pitch and depth. The vehicle has three sections. The front and rear sections are free-flooding, built around aluminium extrusion space-frames covered with glass-fibre reinforced plastic panels. The central section has a set of carbon-fibre reinforced plastic pressure vessels. Four tubes contain batteries powering the vehicle. The other three house vehicle-control systems and sensors. The rear section houses subsystems for navigation, control actuation and propulsion and scientific sensors (e.g. digital camera, upward-looking 300 kHz acoustic Doppler current profiler, 200 kHz multibeam receiver). The front section contains forward-looking collision sensor, emergency abort, the homing systems, Argos satellite data and location transmitters and flashing lights for relocation as well as science sensors (e.g. twin conductivity–temperature–depth instruments, multibeam transmitter, sub-bottom profiler, AquaLab water sampler). Payload restrictions mean that a subset of scientific instruments is actually in place on any given dive. The scientific instruments carried on Autosub are described and examples of observational data collected from each sensor in Arctic or Antarctic waters are given (e.g. of roughness at the underside of floating ice shelves and sea ice).

The retreat of Laika Glacier (4.4 km2), part of a small ice cap situated on Coburg Island, Canadian Arctic Archipelago, is analyzed using field data, satellite remote sensing and mass-balance modelling. We present a methodology for merging various data types and numerical models and investigate the temporal and spatial changes of a remote glacier during the past five decades. A glacier mass-balance and surface-evolution model is run for the period 1959–2006, forced with in situ weather observations and climate re-analysis data (ERA-40, NARR). The model is calibrated using the ice-volume change observed between 1959 and 1971, and measured seasonal mass balances. Calculated glacier surface elevation is validated against ICESat GLAS altimeter data and ASTER-derived elevation. Landsatderived glacier outlines are used to validate calculated ice extent. The piedmont tongue of Laika Glacier has retreated considerably and is in a state of disintegration. The modelled glacier mass balance between 1959 and 2006 was −0.41 m w.e. a−1, on average. Model results indicate a significant trend towards higher mass-balance gradients. A complete wastage of Laika Glacier by 2100 is predicted by model runs based on climate scenarios.

Snowpack base temperatures vary during accumulation and diurnally. Their measurement provides insight into physical, biological and chemical processes occurring at the snow/soil interface. Recent advances in Raman-spectra instruments, which use the scattered light in a standard telecommunications fiber-optic cable to infer absolute temperature along the entire length of the fiber, offer a unique opportunity to obtain basal snow temperatures at resolutions of 1 m, 10 s and 0.1°C. Measurements along a 330 m fiber over 24 hours during late-spring snowmelt at Mammoth Mountain, California, USA, showed basal snow temperatures of 0 ± 0.2°C using 10 s averages. Where the fiber-optic cable traversed bare ground, surface temperatures approached 40°C during midday. The durability of the fiber optic was excellent; no major damage or breaks occurred through the winter of burial. Data from the Dry Creek experimental watershed in Idaho across a small stream valley showed little variability of temperature on the northeast-facing, snow-covered slope, but clearly showed melting patterns and the effects of solar heating on southwest-facing slopes. These proof-of-concept experiments show that the technology enables more detailed spatial and temporal coverage than traditional point measurements of temperature.

The surface mass balance (SMB) at Dome Fuji, East Antarctica, was estimated using 36 bamboo stakes (grid of 6 × 6, placed at 20 m intervals) from 1995 to 2006. The heights of the stake tops from the snow surface were measured at 0.5 cm resolution twice monthly in 1995, 1996, 1997 and 2003, and once a year for the rest of the study period. To account for snow settling, the average snow density at the stake base during the measurements was used for converting the stake-height data to SMB. The annual SMB from 1995 to 2006 at Dome Fuji was 27.3 ± 1.5 kg m−2 a−1. This result agrees well with the annual SMB from AD 1260 to 1993 (26.4 kg m−2 a−1) estimated from volcanic signals in the Dome Fuji ice core. Over the period 1995–2006, there were 37 (8.6% of the measurements) negative or zero annual SMB results. Variation in the multi-year averages of annual SMB decreased with the square root of the number of observation years, and 10 years of observations of a single stake allowed the estimation of annual SMB at ±10% accuracy. The frequency distributions of annual and monthly SMB were examined. The findings clarify the complex behavior of the annual and monthly SMB at Dome Fuji, which will be common phenomena in areas of low snow accumulation of the interior of the Antarctic ice sheet.

Water levels were measured in boreholes spaced along the entire length of Bench Glacier, Alaska, USA, for a period in excess of 2 years. Instrumented boreholes were arranged as nine pairs along the center line of the glacier and an orthogonal grid of 16 boreholes in a 3600 m2 region at the center of the ablation area. Diurnal fluctuations of the water levels were found to be restricted to the late melt season. Pairs of boreholes spaced along the length of the ablation area often exhibited similar fluctuations and diurnal changes in water levels. Three distinct and independent types of diurnal fluctuations in water level were observed in clusters of boreholes within the grid of boreholes. Head gradients suggest water did not flow between clusters, and a single tunnel connecting the boreholes could not explain the observed pattern of diurnal water-level fluctuations. Inter-borehole and borehole-cluster connectivity suggests the cross-glacier width of influence of a segment of the drainage system connected to a borehole was limited to tens of meters. A drainage configuration whereby boreholes are connected to a somewhat distant tunnel by drainage pipes of differing lengths, often hundreds of meters, is shown with a numerical test to be a plausible explanation for the observed borehole behavior.

This study adjusts and compares digital elevation models (DEMs) created from photogrammetric and interferometric synthetic aperture radar techniques to determine volume and surface elevation changes of five icefields in a remote region of southwest British Columbia, Canada, between the mid-1980s and 1999. Preliminary differences between the DEMs in ice-free and vegetation-free areas indicated variable elevation offsets with increasing altitude (11 m km−1) and with increasing slope (2.7 m (10°)−1). Results indicate a surface elevation change of −6.0 ± 2.7 m (−0.5 ± 0.2 m a−1) and a total volume loss of −19.4 ± 8.8 km3 (−1.5 ± 0.7 km3 a−1), which represents a potential sea-level rise contribution of 0.004 ± 0.002 mm a−1. Temperature and snowfall data from four nearby meteorological stations indicate that increased temperatures and decreased snowfall throughout the late 1980s and 1990s are a likely cause of the thinning. Glacier terminus positions were compared between a historical map (1927) and satellite images (1974, 1990/91 and 2000/01). All observed glaciers were in retreat between 1927 and 1974, as well as between 1990/91 and 2000/01, but many glaciers advanced or significantly slowed in their retreat between 1974 and 1990/91.

Ice-core records of methanesulphonic acid (MSA) provide a potentially powerful tool for producing proxy records of sea ice, a critical but poorly understood component of the Earth’s climate system. However, MSA is able to diffuse through solid ice, and here we examine the effect of two different methods of frozen storage on the preservation of MSA in archived ice-core samples. Re-analysis of archived ice sticks confirms that MSA diffuses out of ice cores archived in this manner. Despite MSA losses of up to 39% after 7 years storage, the ice sticks studied here preserve much of the variability of the original MSA record, suggesting that useful proxy records can be obtained from archived ice sticks. Furthermore, re-analysis of ice-core samples that had been refrozen into discrete bottled samples for storage demonstrates that it is possible to archive ice samples in a way that prevents MSA loss. In this case, accurate records of MSA variability and concentration were preserved even over storage periods of 15 years. This has important implications for the storage of ice cores and subsequent determination of MSA, and demonstrates that ice storage history needs to be considered when interpreting MSA records.

The seasonal deuterium excess signal of fresh snow samples from Neumayer station, coastal Dronning Maud Land, Antarctica, was studied to investigate the relationship between deuterium excess and precipitation origin. An isotope model was combined with a trajectory model to determine the relative influence of different moisture sources on the mean annual course of the deuterium excess, focusing on the phase lag between δ18O and excess d. Whereas the annual course of δ18O always shows an austral summer maximum, which clearly depends on local temperature and the annual course of moisture source-area parameters, the deuterium excess of the fresh snow samples shows maximum values already in spring. There can be many different reasons for the time lag between δ18O and deuterium excess in an ice core, including post-depositional processes and changes in the moisture source of precipitation. The use of fresh snow samples enabled us to exclude post-depositional processes and study solely the influence of precipitation origin. Changes in the moisture source connected to systematic changes in the general atmospheric circulation can have a strong influence on the phase lag between deuterium excess and δ18O, which has to be taken into account for climatic interpretation of stable-isotope profiles from ice cores.

Supraglacial ponds on Tasman Glacier, New Zealand, initiated the development of the large Tasman Lake during the 1980s and still play an important role for ice loss and further terminus disintegration. Limnological and glaciological measurements between 2001 and 2003 reveal distinct differences between ponds. The hydraulic connection of a pond to the englacial water level exerts a key control on whether the pond contributes to longer-term terminus disintegration. In the earlier stages of pond development, ice loss occurs predominantly in the horizontal dimension by subaerial melt. Subaqueous calving at later stages plays a major role for ice loss. During the capture of a pond by the lake, substantial limnological changes lead to changes in relative significance and rates of ice loss processes, the most important being the change from melting to predominantly calving. As a result, ice loss accelerated from around 11 m a−1 of melt under partial debris cover to a retreat by calving and melting of 34 m a−1. Ice loss at the ponds accounted for only 10% of the surface loss in the lower terminus area, but is likely to increase in the future with enlargement and coalescence of ponds.

Annual equilibrium-line altitude (ELA) and surface mass balance of Glacier Blanc, Ecrins region, French Alps, were reconstructed from a 25 year time series of satellite images (1981–2005). The remote-sensing method used was based on identification of the snowline, which is easy to discern on optical satellite images taken at the end of the ablation season. In addition, surface mass balances at the ELA were reconstructed for the same period using meteorological data from three nearby weather stations. A comparison of the two types of series reveals a correlation of r > 0.67 at the 0.01 level of significance. Furthermore, the surface mass balances obtained from remote-sensing data are consistent with those obtained from field measurements on five other French glaciers (r = 0.76, p < 0.01). Also consistent for Glacier Blanc is the total mass loss (10.8 m w.e.) over the studied period. However, the surface mass balances obtained with the remote-sensing method show lower interannual variability. Given that the remote-sensing method is based on changes in the ELA, this difference probably results from the lower sensitivity of the surface mass balance to climate parameters at the ELA.

Surface-elevation change and ice velocities have been measured over the debris-covered tongue of Chacraraju, Peru. Elevation change was measured by reflectorless survey at a 1 m horizontal resolution over three separate areas of the glacier between 2004 and 2005. Area-averaged change revealed general lowering, with two of the surveyed areas experiencing surface lowering of 0.58 and 0.77 m, and the third a rise of 0.07 m. Combining all three areas (43 216 m2) resulted in a mean net lowering of 0.43 m a−1, which is at the higher end of the range of long-term studies in the region. Velocity was measured over 7 days by the repeated optical survey of 12 prisms attached to stakes inserted directly into the glacier’s surface. Results indicate that velocity increases approximately with distance squared from the glacier’s terminus, from <10 mm d−1 near the terminus to approaching 100 mm d−1 at the base of the glacier’s icefall, located ∼1.7 km up-glacier. Velocity vectors also changed systematically along the glacier, from a consistent down-glacier orientation near the icefall to more variable orientations within ∼300 m of the terminus. No up-glacier motion component was measured.

Based on the field data at Koryto glacier, Kamchatka Peninsula, Russia, we constructed a one-dimensional numerical glacier model which fits the behaviour of the glacier. The analysis of meteorological data from the nearby station suggests that the recent rapid retreat of the glacier since the mid-20th century is likely to be due to a decrease in winter precipitation. Using the geographical data of the glacier terminus variations from 1711 to 1930, we reconstructed the fluctuation in the equilibrium-line altitude by means of the glacier model. With summer temperatures inferred from tree-ring data, the model suggests that the winter precipitation from the mid-19th to the early 20th century was about 10% less than that at present. This trend is close to consistent with ice-core results from the nearby ice cap in the central Kamchatka Peninsula.

One common assumption in interpreting ice-core CO2 records is that diffusion in the ice does not affect the concentration profile. However, this assumption remains untested because the extremely small CO2 diffusion coefficient in ice has not been accurately determined in the laboratory. In this study we take advantage of high levels of CO2 associated with refrozen layers in an ice core from Siple Dome, Antarctica, to study CO2 diffusion rates. We use noble gases (Xe/Ar and Kr/Ar), electrical conductivity and Ca2+ ion concentrations to show that substantial CO2 diffusion may occur in ice on timescales of thousands of years. We estimate the permeation coefficient for CO2 in ice is ∼4 × 10−21 mol m−1 s−1 Pa−1 at −23°C in the top 287 m (corresponding to 2.74 kyr). Smoothing of the CO2 record by diffusion at this depth/age is one or two orders of magnitude smaller than the smoothing in the firn. However, simulations for depths of ∼930–950 m (∼60–70 kyr) indicate that smoothing of the CO2 record by diffusion in deep ice is comparable to smoothing in the firn. Other types of diffusion (e.g. via liquid in ice grain boundaries or veins) may also be important but their influence has not been quantified.

Ocean circulation under ice shelves and associated rates of melting and freezing are strongly influenced by the shape of the sub-ice-shelf cavity. We have refined an existing method and used additional in situ measurements to estimate the cavity shape under the Amery Ice Shelf, East Antarctica. A finite-element hydrodynamic ocean-tide model was used to simulate the major tidal constituents for a range of different sub-Amery Ice Shelf cavity water-column thicknesses. The data are adjusted in the largely unsurveyed southern region of the ice-shelf cavity by comparing the complex error between simulated tides and in situ tides, derived from GPS observations. We show a significant improvement in the simulated tides, with a combined complex error of 1.8 cm, in comparison with past studies which show a complex error of ∼5.3 cm. Our bathymetry incorporates ice-draft data at the grounding line and seismic surveys, which have provided a considerable amount of new data. This technique has particular application when the water column beneath ice shelves is inaccessible and in situ GPS data are available.

Spatio-temporal variations of the recently determined accumulation rate are investigated using ground-penetrating radar (GPR) measurements and firn-core studies. The study area is located on Ritscherflya in western Dronning Maud Land, Antarctica, at an elevation range 1400–1560 m. Accumulation rates are derived from internal reflection horizons (IRHs), tracked with GPR, which are connected to a dated firn core. GPR-derived internal layer depths show small relief along a 22 km profile on an ice flowline. Average accumulation rates are about 190 kg m−2 a−1 (1980–2005) with spatial variability (1σ) of 5% along the GPR profile. The interannual variability obtained from four dated firn cores is one order of magnitude higher, showing 1σ standard deviations around 30%. Mean temporal variations of GPRderived accumulation rates are of the same magnitude or even higher than spatial variations. Temporal differences between 1980–90 and 1990–2005, obtained from two dated IRHs along the GPR profile, indicate temporally non-stationary processes, linked to spatial variations. Comparison with similarly obtained accumulation data from another coastal area in central Dronning Maud Land confirms this observation. Our results contribute to understanding spatio-temporal variations of the accumulation processes, necessary for the validation of satellite data (e.g. altimetry studies and gravity missions such as Gravity Recovery and Climate Experiment (GRACE)).

A finite-volume model is used to simulate 9 years (1995–2003) of snow temperatures at the South Pole. The upper boundary condition is skin-surface temperature derived from routine upwelling longwave radiation measurements, while the lower boundary condition is set to the seasonal temperature gradient at 6.5 m depth, taken from prior measurements at the South Pole. We focus on statistics of temperature, heat fluxes, heating rates and vapour pressures in the top metre of snow, but present results from the full depth of the model (6.5 m). The monthly mean net heat flux into the snow agrees with results from previous studies performed at the South Pole. On shorter timescales, the heating rates and vapour pressures show large variability. The net heat flux into the snow, which is between ±5 W m−2 in the monthly mean, can be greater than ±20 W m−2 on hourly timescales. On sub-daily timescales, heating rates exceed 40 K d−1 in the top 10 cm of the snow. Subsurface temperatures, and therefore heating rates, are more variable during winter (April–September) due to increased synoptic activity and the presence of a strong, surface-based, atmospheric temperature inversion. The largest vapour pressures (60–70 Pa) and vertical gradients of vapour pressure are found in the top metre of snow during the short summer (December–January). In contrast, during the long winter, the low temperatures result in very small vapour pressures and insignificant vapour-pressure gradients. The high summertime vapour-pressure gradients may be important in altering the isotopic composition of snow and ice on the Antarctic plateau.