The IceCube Neutrino Observatory and its prototype, AMANDA, were built in South Pole ice, using powerful hot-water drills to cleanly bore >100 holes to depths up to 2500 m. The construction of these particle physics detectors provided a unique opportunity to examine the deep ice sheet using a variety of novel techniques. We made high-resolution particulate profiles with a laser dust logger in eight of the boreholes during detector commissioning between 2004 and 2010. The South Pole laser logs are among the most clearly resolved measurements of Antarctic dust strata during the last glacial period and can be used to reconstruct paleoclimate records in exceptional detail. Here we use manual and algorithmic matching to synthesize our South Pole measurements with ice-core and logging data from Dome C, East Antarctica. We derive impurity concentration, precision chronology, annual-layer thickness, local spatial variability, and identify several widespread volcanic ash depositions useful for dating. We also examine the interval around ∼74 ka recently isolated with radiometric dating to bracket the Toba (Sumatra) supereruption.

Ice shelves and ice tongues are dynamically coupled to their cavities. Here we compute normal modes (eigenfrequencies and eigenfunctions) of this coupled system using a thin-plate approximation for the ice shelf and potential water flow in the ice-shelf cavity. Our results show that normal modes depend not only on the ice-shelf parameters (length, thickness, Young’s modulus, etc.) but also on the cavity depth. The dominant eigenmodes are higher for ice shelves floating over deeper cavities; they are also higher for shorter ice shelves and ice tongues (<50 km long). The higheigenfrequency eigenmodes are primarily controlled by the ice flexure and have similar periods to sea swell. These results suggest that both long ocean waves with periods of 100–400 s and shorter sea swell with periods of 10–20 s can have strong impacts on relatively short ice shelves and ice tongues by exciting oscillations with their eigenfrequencies, which can lead to iceberg calving and, in some circumstances, ice-shelf disintegration.

The roughness of the bed beneath ice streams exerts an important control on their dynamics. Here the first in-depth analysis of roughness beneath the Greenland ice sheet is presented. Much of the interior is underlain by a smooth bed, while the margins are much rougher; this is particularly pronounced in the east where more mountainous topography dominates and fast-flow features are laterally constrained in deep narrow valleys. In contrast, fast flow in the west is much less laterally constrained and areas of high roughness are less extensive and pronounced. It is proposed that there is a major geological control on the distribution of bed variability since a significant thrust-fault coincides approximately with the boundary between rough terrain in the east and the smooth central region. Furthermore there is an abrupt change in roughness approximately coinciding with the crossing of this fault line. This suggests a limiting factor on the extent of fast flow in the east, which is lacking in the west. The size of many glaciers draining Greenland makes their local bed conditions difficult to determine with great confidence. However, the much larger Petermann Glacier lies in a deep trough characterized by a smooth bed that extends some distance into the ice sheet. The smooth bed may be due to deformable marine sediments which facilitate faster flow, although smoothing could also result from ice dynamics and subglacial erosion. That the smooth bed of Petermann Glacier extends some considerable distance raises concerns about the possible stability of this feature, and perhaps others in Greenland too.

Many glaciological and hydrological studies require outlines of individual glaciers rather than total ice cover. Here we develop a new semiautomatic algorithm that uses a digital elevation model (DEM) and outlines of glacier complexes to calculate the extents of individual glaciers. The algorithm first applies hydrological modeling tools to a modified DEM to calculate flowsheds. It then merges flowsheds that belong to individual glaciers using a distance-based approach, whose required empirical parameters are derived from the Juneau Icefield area in Alaska. In this region, 2% of ~1300 glaciers were misclassified. The algorithm was validated on >25 000 km2 of ice in other regions in Alaska and on >40 000 km2 of ice in Arctic Canada, resulting in ~2% and ~3% misclassified glaciers, respectively. Results indicate that the algorithm is robust provided the DEM and the outlines are of good quality.

We combine the complementary characteristics of laser altimeter data and stereoscopic digital elevation models (DEMs) to construct high-resolution (∼100 m) maps of surface elevations and elevation changes over rapidly changing outlet glaciers in Greenland. Measurements from spaceborne and airborne laser altimeters have relatively low errors but are spatially limited to the ground tracks, while DEMs have larger errors but provide spatially continuous surfaces. The principle of our method is to fit the DEM surface to the altimeter point clouds in time and space to minimize the DEM errors and use that surface to extrapolate elevations away from altimeter flight lines. This reduces the DEM registration errors and fills the gap between the altimeter paths. We use data from ICESat and ATM as well as SPOT 5 DEMs from 2007 and 2008 and apply them to the outlet glaciers Jakobshavn Isbræ (JI) and Kangerdlugssuaq (KL). We find that the main trunks of JI and KL lowered at rates of 30–35 and 7–20 m a−1,respectively. The rates decreased inland. The corresponding errors were 0.3–5.2 m a−1for JI and 0.3–5.1 m a−1for KL, with errors increasing proportionally with distance from the altimeter paths.

Debris-covered glaciers respond to atmospheric conditions in different ways from debris-free glaciers, due to the presence of debris at the surface during the ablation season and at the snow/ice interface during the accumulation season. Understanding the response of debris-covered glaciers to a variety of meteorological conditions in a physically sound manner is essential to quantify meltwater discharge and to predict their response to climate change. To tackle this issue, we developed the Crocus-DEB model as an adaptation of the detailed snowpack model Crocus, to simulate the energy and mass balance of debris-covered glaciers, including periods when debris is covered by snow. Crocus-DEB was evaluated with data gathered during a field experiment using artificial debris covering the snowpack at Col de Porte, France, with very good results in terms of conductive heat flux, both at the surface and at the interface between the debris and the underlying dense snow taken as a surrogate for ice, with and without snow overlying the debris. The model was also evaluated using field data from the debris-covered glacier Changri Nup, Nepal, Himalaya. This paper introduces the design of the model, its performance and its ability to explore relationships between model parameters, meteorological conditions and the critical debris thickness.

Remote sensing of ice motion by tracking displacement of surface features is a valuable tool in glaciology. Efficient image feature-tracking programs, such as IMCORR, based on fast Fourier transform methods can produce misleading correlations if there are data gaps in either or both of the reference and search images. This is particularly problematic if the data gaps are regular in character, such as for Landsat7 images collected after the failure of the Scan Line Corrector (SLC-off images). We demonstrate that this situation can be alleviated by filling the data gaps with suitably chosen random data. We modified IMCORR to achieve this automatically (source code is included), but generic image-processing software could be used to modify inputs for other correlation packages. We test our method using images of Pine Island Ice Shelf, Antarctica, and document the acceleration of the velocity field for the floating extension of Pine Island Glacier over the decade 2001–11. We also combine our velocities with recent NASA Operation IceBridge ice thickness data from CReSIS to estimate the basal melt rates.

The refreezing rate of a borehole drilled through a 252 m thick region of the Ross Ice Shelf, Antarctica, is determined using oceanographic measurements over two periods of a day. We first use a method based on the conservation of salt in the supercooled salt water of the borehole. This is compared to a model using a numerical solution of the heat equation to find the temperature distribution in the host ice, allowing ice growth to be calculated from the balance of heat fluxes at the ice/water interface. This second method broadly confirms the refreezing rates deduced from salinity measurements, giving confidence in the generalization of this simple heat-flux model to predict refreezing rates of other boreholes. Predictions from both are subject to uncertainty due to the poorly defined value of the solid fraction of ice that freezes in a supercooled volume of sea water. This is taken to be 0.5 ± 0.1 throughout this study. The predicted rates are also strongly dependent on the initial and boundary conditions chosen, but results show the initial diameter of 600 mm decreases at a rate of ~3–5 mm h−1 in an ice shelf with a minimum temperature of −22°C.

Stable isotopes are a primary tool for inferring past temperature changes and atmospheric moisture variability from ice cores. A 33 m ice core representing the period 1850–2004 was retrieved from the Tanggula Mountains, central Tibetan Plateau (5743 m a.s.l.), in August 2005. Annual average stable isotope (δ18O, δD) values generally increase during the period, while the second-order parameter of deuterium excess (d-excess) generally decreases. High annual average d-excess values (18.2‰) throughout the ice core suggest a significant contribution of continental recycled moisture. d-excess values shift from relatively higher values during 1850–1940 to lower values since the 1940s. Annual isotope values and reconstructed accumulation are compared with climate indices, local station temperature records and northern India monsoon precipitation. Significant correlation is observed between δ18O and the Southern Oscillation, NINO3.4 and Dipole Mode indices. Annual average d-excess values revealed a significant negative correlation with the Dipole Mode index. Results suggest a relatively greater contribution of westerly-dominated continental moisture prior to the 1940s and an increase in the contribution of moisture evaporated under more humid conditions since the 1940s.

Physically based projections of the Greenland ice sheet contribution to future sea-level change are subject to uncertainties of the atmospheric and oceanic climatic forcing and to the formulations within the ice flow model itself. Here a higher-order, three-dimensional thermomechanical ice flow model is used, initialized to the present-day geometry. The forcing comes from a high-resolution regional climate model and from a flowline model applied to four individual marine-terminated glaciers, and results are subsequently extended to the entire ice sheet. The experiments span the next 200 years and consider climate scenario SRES A1B. The surface mass-balance (SMB) scheme is taken either from a regional climate model or from a positive-degree-day (PDD) model using temperature and precipitation anomalies from the underlying climate models. Our model results show that outlet glacier dynamics only account for 6–18% of the sea-level contribution after 200 years, confirming earlier findings that stress the dominant effect of SMB changes. Furthermore, interaction between SMB and ice discharge limits the importance of outlet glacier dynamics with increasing atmospheric forcing. Forcing from the regional climate model produces a 14–31 % higher sea-level contribution compared to a PDD model run with the same parameters as for IPCC AR4.

There remain large regions of scientific interest in the Antarctic that are not instrumented. These include highly dynamic ice streams and glaciers that are difficult or impossible to reach safely because heavy crevassing impedes an overland trek or an aircraft landing. We have developed an alternative strategy for instrumenting these regions: an aerodynamic sensor that can be dropped from an overflying aircraft. During freefall the sensor accelerates to its terminal velocity of 42 m s−1 before impacting with the glacier. On impact it partially buries itself in the snow while leaving an antenna mast protruding high above the surface to ensure a long operating life. In this paper, we describe the design and results of testing this aircraft-deployable sensor. Finally we present the initial results of two campaigns to instrument inaccessible regions of Pine Island Glacier, West Antarctica, and Scar Inlet, Antarctic Peninsula, with GPS receivers.

Nanospray ionization Fourier transform ion cyclotron resonance mass spectrometry was developed as a tool for examining the dissolved organic matter (DOM) present in ice cores, significantly reducing the sample volume required for extraction compared with previous studies. Using smaller sample volumes is important for resolving temporal changes in ice-core DOM. We demonstrate that a small volume of ice-core meltwater can be extracted and analyzed with sufficient mass spectral sensitivity to describe the molecular composition of the DOM. Two different solid-phase extraction resins (PPL and C18) were compared to examine potential fractionation of the DOM. Over 2500 unique molecular formulas isolated from two different Greenland ice-core samples, dated to approximately AD 1660 and AD 1360, were obtained from the analyses. Method and sensitivity improvements provide an opportunity for organic matter characterization at higher temporal resolution than our previous analyses afforded and allows for examination of ice cores containing low levels of organic carbon.

The evolution of preferred crystal-orientation fabrics is strongly sensitive to the initial fabric and texture. A perturbation in climate can induce variations in fabric and texture in the firn. Feedbacks between fabric evolution and ice deformation can enhance these variations through time and depth in an ice sheet. We model the evolution of fabric under vertical uniaxial-compression and pure-shear regimes typical of ice divides. Using an analytic anisotropic flow law applied to an aggregate of distinct ice crystals, the model evolves the fabric and includes parameterizations of crystal growth, polygonization and migration recrystallization. Stress and temperature history drive the fabric evolution. Using this model, we explore the evolution of a subtle variation in near-surface fabric using both constant applied stress and a stress–temperature history based on data from Taylor Dome, East Antarctica. Our model suggests that a subtle variation in fabric caused by climate perturbations will be preserved through time and depth in an ice sheet. The stress history and polygonization rate primarily control the magnitude of the preserved climate signal. These results offer the possibility of extracting information about past climate directly from ice fabrics.

We present a new method for extracting the direction of surface flow for ice sheets, based on the detection of flow-induced features that are visible in satellite imagery. The orientation of linear features is determined using a Radon transform and only requires a single image. The technique is demonstrated by applying it to the RADARSAT mosaic of Antarctica, over the Lambert Glacier–Amery Ice Shelf region of East Antarctica. Comparisons with both existing flow-direction fields and traced streamlines over the same area provide an evaluation of the method. We also illustrate its application to Landsat 7 imagery.

Basal crevasses may play an important precursory role in determining both the location and propagation of rifts and iceberg dimensions. For example, icebergs calved recently from Thwaites Glacier, Antarctica, have the same width as surface undulations, strengthening the connection between basal crevasses, rifting and calving. We explore a novel method for estimating the heights of basal crevasses formed at the grounding lines of ice shelves and ice streams. We employ a thin-elastic beam (TEB) formulation and tensional yielding criterion to capture the physics of flexed ice at grounding lines. Observations of basal crevasse heights compare well with model predictions in the Siple Coast region of the Ross Ice Shelf. We find that the TEB method is most accurate in areas of low strain rate. We also test the method in other areas of Antarctica to produce order-of-magnitude maps of grounding-line basal crevasses and find general agreement with reported observations assuming basal crevasses develop in spatio-temporal sequence and are advected downstream. This method is computationally cheap and could be relatively easy to implement into damage-oriented large-scale ice models which aim at physically simulating calving and fracture processes.

We study the approximations underlying the macroscopic theory of glacier response to climate, and illustrate some basic properties of glacier response using two simple examples, a block on an inclined plane and a block with a more realistic terminal region. The properties include nonlinearity and the usefulness of linear approximations, sensitivity to bed slope, timescale, stability, characteristic elevations of the equilibrium line at which the properties of the response change, the limit of fast response in a changing climate, the minimum sustainable size, increased sensitivity to climate change as a glacier retreats, and finally the similarity in the responses of simple glaciers with the same product of length and square of bed slope.

Laser altimetry (lidar) is a remote-sensing technology that holds tremendous promise for mapping snow depth in snow hydrology and avalanche applications. Recently lidar has seen a dramatic widening of applications in the natural sciences, resulting in technological improvements and an increase in the availability of both airborne and ground-based sensors. Modern sensors allow mapping of vegetation heights and snow or ground surface elevations below forest canopies. Typical vertical accuracies for airborne datasets are decimeter-scale with order 1 m point spacings. Ground-based systems typically provide millimeter-scale range accuracy and sub-meter point spacing over 1 m to several kilometers. Many system parameters, such as scan angle, pulse rate and shot geometry relative to terrain gradients, require specification to achieve specific point coverage densities in forested and/or complex terrain. Additionally, snow has a significant volumetric scattering component, requiring different considerations for error estimation than for other Earth surface materials. We use published estimates of light penetration depth by wavelength to estimate radiative transfer error contributions. This paper presents a review of lidar mapping procedures and error sources, potential errors unique to snow surface remote sensing in the near-infrared and visible wavelengths, and recommendations for projects using lidar for snow-depth mapping.

Ice thickness estimates using advanced nadir sounding and tomographic radar processing techniques are compared and combined in a study of Isunnguata Sermia glacier, Greenland. Using an ensemble of Operation IceBridge flight lines spaced at 500 m intervals and running approximately along the flow direction, we find there is a statistically excellent comparison between subglacial terrains derived from two-dimensional tomography and gridded nadir sounding. Analysis shows that tomographic data better capture short wavelength (1–2 km) patterns in basal terrain, but interpolated nadir sounding data yield more spatially extensive and continuous coverage across the glacier, especially in deep subglacial troughs. Using derived surface and basal topography maps, we find that driving stress and measured and modeled surface velocity comparisons indicate that basal sliding is an important component of the glacier motion, but is also only weakly coupled to the detailed bed topography save for the deepest troughs. As might be expected for this land-terminating, relatively slow-moving glacier, the subglacial and proglacial topography is similar, suggesting the erosional processes acting on the modern glacier bed once helped sculpt the now exposed land.

Recent studies of Himalayan glacier recession indicate that there is wide variability in terminus retreat rate and mass balance in the different sectors of the mountain range, primarily linked to the topography and climate of the region. Variable retreat rates of glacier termini and inadequate supporting field data (e.g. mass balance, ice thickness, velocity, etc.) in the Himalayan glaciers make it difficult to develop a coherent picture of climate change impacts. In this study, the results of a detailed mapping campaign and ground-based measurements of ablation rate, terminus retreat and ice loss are reported for the period 2003–10. In addition, background information from an old glacier map (Survey of India, 1962) was compiled and terminus recession measurements were carried out from 1990 field photographs of Chorabari Glacier, central Himalaya. Our ablation stake network results suggest that the influence of debris cover is significant for Chorabari Glacier mass balance and terminus retreat. The terminus survey finds that the glacier is retreating, but at a lower rate than many other non-debriscovered glaciers in the region. The recession and ablation data (particularly in the upper ablation area at higher altitudes) suggest that the ice volume loss of the glaciers is of greater magnitude than the slow terminus retreat and, if the process continues, the lowermost part of the glacier may reduce to a quasi-stationary position while significant ice loss continues.