Early–mid Pliocene moraines in the McMurdo Dry Valleys, Antarctica, are more extensive than the present alpine glaciers in this region, indicating substantial climatic differences between the early–mid Pliocene and the present. To quantify this difference in the glacier–climate regime, we estimated the equilibrium-line altitude (ELA) change since the early–mid Pliocene by calculating the modern ELA and reconstructing the ELAs of four alpine glaciers in Wright and Taylor Valleys at their early–mid Pliocene maxima. The area–altitude balance ratio method was used on modern and reconstructed early–mid Pliocene hypsometry. In Wright and Victoria Valleys, mass-balance data identify present-day ELAs of 800–1600ma.s.l. and an average balance ratio of 1.1. The estimated ELAs of the much larger early–mid Pliocene glaciers in Wright and Taylor Valleys range from 600 to 950±170ma.s.l., and thus are 250–600±170m lower than modern ELAs in these valleys. The depressed ELAs during the early–mid-Pliocene most likely indicate a wetter and therefore warmer climate in the Dry Valleys during this period than previous studies have recognized.

The 2006/07 and 2007/08 US-ITASE traverses from Taylor Dome to South Pole in East Antarctica provided opportunities to survey the subglacial and englacial environments using 3 MHz and 200MHz radar. We present first results of these new ground-based radar data. A prominent basal deformation layer indicates different ice-flow regimes for the northern and southern halves of the Byrd Glacier drainage. Buried dune stratigraphy that appears to be related to the megadunes towards the west occurs at depths of up to 1500 m. At least two new water-filled subglacial lakes were discovered, while two recently drained lakes identified from repeat ICESat surface elevation surveys appear to be devoid of water.

Evans Ice Stream, West Antarctica, has five tributaries and a complex grounding zone. The grounding zone of Evans Ice Stream, between the landward and seaward limits of tidal flexing, was mapped using SAR interferometry. The width of the mapped grounding zone was compared with that derived from an elastic beam model, and the tidal height changes derived from interferometry were compared with the results of a tidal model. Results show that in 1994 and 1996 the Evans grounding zone was located up to 100 km upstream of its location in the BEDMAP dataset. The grounding line of Evans Ice Stream is subjected to 5 m vertical tidal forcing, which would clearly affect ice-stream flow.

The World Glacier Inventory (WGI) was conceived half a century ago as an activity to be completed during the International Geophysical Year, 1957/58. It consisted until very recently of nearly 70 000 glacier records covering slightly less than one-quarter of the glacier ice outside the ice sheets. A complete WGI must be a compromise if it is to be available and usable soon. A more complete version, called WGI-XF, is available and usable now and contains records for just over 131 000 glaciers and nearly half of the global extent of ice. The additional glaciers come mainly from the assimilation of existing inventories but also from rescuing inventories that have been lost and from new inventories in Canada and the Subantarctic. In WGI-XF, the XF stands for ‘extended format’, flagging the fact that WGI-XF conforms to a set of explicit specifications which enhance usefulness by eliminating low-level inconsistencies. Two important features are nominal glaciers and glacier complexes. A nominal glacier, of which there are about 5000 in WGI-XF, is one about which little is known other than its existence and approximate location. A glacier complex is one or more contiguous glaciers. This term embodies the idea, which is not new, that inventories can be preliminary, based upon vector outlines which await subdivision by trained glaciologists. Many regional studies have found that measurements of changes in single glaciers require accurate work and painstaking quality control. WGI-XF is not assuredly reliable as a source for such detailed work, but there are several other subjects in which less detail would be a price worth paying for more complete coverage. Incomplete information about the dates of imagery and maps is a hindrance to analysis, and the recovery of dates from metadata should have high priority.

Rutford Ice Stream, West Antarctica, drains a catchment of >45 000 km2 into the Ronne Ice Shelf through a 26 km wide, 2.4 km deep subglacial trough adjacent to the Ellsworth Mountains. Forty-two per cent of its catchment boundary is common with Pine Island Glacier, where rapid change to ice dynamics is currently underway. These changes may eventually affect adjacent catchments such as Rutford. Radar sounding data were acquired over the Rutford ice-drainage basin that show the internal structure. In particular, distinctive reflector groups were identified that mark the boundaries between four different flow elements. The flow-margin reflector groups include curvilinear events that cross-cut isochrones and are therefore likely to be post-depositional. These reflections may arise from crystal orientation fabrics generated by localized strain in a flow margin. One of the sectors of the ice-drainage basin supplies the largest share (38%) of the ice volume flux through the main trunk of Rutford Ice Stream. This sector may be preferentially affected by continuing surface lowering in the Pine Island Glacier catchment.

Optical matching of ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) satellite image pairs is used to determine the surface velocities of major glaciers across the central Karakoram. The ASTER images were acquired in 2006 and 2007, and cover a 60×120km region over Baltoro glacier, Pakistan, and areas to the north and west. The surface velocities were compared with differential global position system (GPS) data collected on Baltoro glacier in summer 2005. The ASTER measurements reveal fine details about ice dynamics in this region. For example, glaciers are found to be active over their termini even where they are very heavily debris-covered. The characteristics of several surge-type glaciers were measured, with terminus advances of several hundred meters per year and the displacement of trunk glaciers as surge glaciers pushed into them. This study is the first synthesis of glacier velocities across this region, and provides a baseline against which both past and future changes can be compared.

Glacier changes in the Karlik Shan, eastern Tien Shan, from 1971/72 to 2001/02 were monitored in this study. Topographic maps of 1 : 50 000 scale based on aerial photographs from 1971/72 and satellite images (Landsat TM, Landsat ETM+ and ASTER) from 1992, 2001 and 2002 were used to map glacier extent through a process of manual digitizing. The total glacier area decreased by 5.3% from 1971/72 to 2001/02. The rate of glacier area shrinkage was 0.13% a–1 between 1972 and 1992, but it was 0.27% a–1 from 1992 to 2001/02, suggesting accelerated glacier retreat in recent decades. Glacier changes in the region are a response to summer temperature increase. Annual precipitation also showed an upward trend, but this could not compensate for the mass loss due to ablation.

A new method was developed to estimate the mass balance in unsampled areas from existing datasets. Three years of mass-balance data from two glaciers in the central Italian Alps were used to develop and test a multiple-regression method based exclusively on a 10m resolution digital terrain model. The introduction of a relative elevation attribute, which expresses the degree of wind exposure of the gridcells, notably increased the amount of explainable variance in winter balance with respect to altitude itself. The summer balance is highly correlated with elevation, but, in order to obtain reliable extrapolations, the clear-sky shortwave radiation and the diurnal cloud-cover cycle had to be taken into account. The net annual mass balance on a glacier system comprising the two monitored glaciers was calculated by applying both a single regression of winter and summer balance with altitude and the new regression method. The consistency of results was assessed against measured net balances and snow-cover maps drawn in the ablation season. The results of the new method were in close agreement with observations and proved to be less sensitive to the spatial representation of the sampled areas.

Geometric changes on a sample of Svalbard glaciers were studied using subtraction of repeat digital terrain models to determine early surge-stage dynamics. Changes in surface features were also analyzed. A number of new surges were found for glaciers not known to have surged previously. The surge development could be followed through three stages, of which the first two had not been previously described in Svalbard. The first two stages are mainly identified from glacier thickness changes and showed little visual evidence. In stage 1, initial surface lowering was found in the upper part of the glacier, followed by a thickening further down-glacier in stage 2. Stage 3 represents the period of well-developed surge dynamics that is usually reported. Some surges ceased at stage 2 as a partial surge and never developed into a fully active surge. These partial surges could be misinterpreted as rapid response to climate change. The results of this study further support previous findings that the majority of Svalbard glaciers are of surge type.

This paper presents the first attempt to measure the calving rate and flow velocity of the front of a glacier using ground-based high-range resolution interferometric radar at a high temporal rate (2 Hz). The radar, operating at 5.75 GHz, is located ∽4 km from the calving front of Kronebreen, Svalbard. The radar measures a horizontal width of ∽700m of the front, and a range of 300 m. The latter includes the calving front and 250m up-glacier. We find that the glacier surface provides permanent scatterers, so spatially continuous movements at the front and at locations further up-glacier can be tracked. For ∽8 hours we measured a large increase in velocity at the calving front, which extended 30 m up-glacier, while further up-glacier the velocity was stable (∽2.5md–1) during the entire period. Two large calving events were identified during this survey, removing 25m of ice in the radar range direction normal to the ice front. The velocity of the front slowed to a stable 2.5md–1 after the events. During another data series the velocities were stable (∽2.5md–1) and no calving events were identified. The method is promising for carrying out studies of processes at a calving front, as it provides spatially continuous, high-frequency accurate velocities from a safe distance to the glacier.

A new approach to glacier inventory, based on airborne laser-scanner data, has been applied to South Tyrol, Italy: it yields highly accurate results with a minimum of human supervision. Earlier inventories, from 1983 and 1997, are used to compare changes in area, volume and equilibrium-line altitude. A reduction of 32% was observed in glacier area from 1983 to 2006. Volume change, derived from the 1997 and 2006 digital elevation models, was –1.037 km3, and an ELA rise of 54 m, to almost 3000 m a.s.l., was calculated for this period. Losses vary widely for individual glaciers, but have accelerated for all South Tyrolean glaciers since the first inventory in 1983.

We present the results of low-frequency (20 MHz) radio-echo sounding (RES) carried out in December 2000 and December 2006 on the main ice divides of Livingston Island, South Shetland Islands (SSI), Antarctica, and Bowles Plateau, Antarctica, respectively, as well as high-frequency (200 MHz) RES on the latter, aimed at determining the ice thickness, internal structure and subglacial relief. Typical ice thickness along the main ice divides is ~150 m, reaching maxima of ~200 m. On Bowles Plateau the ice is much thicker, with an average of 265 m and maxima of ~500 m. The bed below the main ice divides is above sea level, while part of the outlet glaciers from Bowles Plateau lies significantly below sea level, down to –120 m. The strong scattering of the radio waves in the areas under study constitutes further evidence that the ice in the accumulation area of the ice masses of the SSI is temperate. Typical thickness of the firn layer in Bowles Plateau is 20–35 m, similar to that found in King George ice cap. A strong internal reflector within the firn layer, interpreted as a tephra layer from the 1970 eruption at Deception Island, has allowed a rough estimate of the specific mass balances for Bowles Plateau within 0.20–0.40ma–1w.e., as average values for the period 1970–2006.

We present 1 and 100 MHz ground-based radar data from the onset region of Rutford Ice Stream, West Antarctica, which indicate the form and internal structure of isochrones. In the flow-parallel lines, modelled isochrone patterns reproduce the gross pattern of the imaged near-surface layers, assuming steady-state flow velocity from GPS records and the current accumulation rate for the last 200 years. We interpret this as indicating overall stability in flow in the onset region of Rutford Ice Stream throughout this period. However, in the cross-flow lines some local variability in accumulation is seen in areas close to the ice-stream margin where a number of tributaries converge towards the ice-stream onset zone. Episodic surface lowering events are observed followed by rapid fill episodes. The fill events indicate deposition towards the northwest, most likely generated by storm winds, which blow at an oblique angle to ice flow. More problematic is explaining the generation of episodic surface lowering in this area. We speculate this may be due to: changing ice-flow direction in the complex tributary area of the onset zone; a change in basal sediments or sedimentary landforms; a change in basal melt rates or water supply; or episodic lake drainage events in the fjord systems of the Ellsworth Subglacial Highlands. The study highlights the difficulty of assessing flow stability in the complex onset regions of West Antarctic ice streams.

On 16–18 June 2008 the US National Snow and Ice Data Center held a GLIMS workshop in Boulder, CO, USA, focusing on formulating procedures and best practices for operational glacier mapping using satellite imagery. Despite the progress made in recent years, there still remain many cases where automatic delineation of glacier boundaries in satellite imagery is difficult, error prone or time-consuming. This workshop identified six themes for consideration by focus groups: (1) mapping clean ice and lakes; (2) mapping ice divides; (3) mapping debris-covered glaciers; (4) assessing changes in glacier area and elevation through comparisons with older data; (5) digital elevation model (DEM) generation from satellite stereo pairs; and (6) accuracy and error analysis. Talks presented examples and work in progress for each of these topics, and focus groups worked on compiling a summary of available algorithms and procedures to address and avoid identified hurdles. Special emphasis was given to establishing standard protocols for glacier delineation and analysis, creating illustrated tutorials and providing source code for available methods. This paper summarizes the major results of the 2008 GLIMS workshop, with an emphasis on definitions, methods and recommendations for satellite data processing. While the list of proposed methods and recommendations is not comprehensive and is still a work in progress, our goal here is to provide a starting point for the GLIMS regional centers as well as for the wider glaciological community in terms of documentation on possible pitfalls along with potential solutions.

All climate models participating in the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, as made available by the Program for Climate Model Diagnosis and Intercomparison (PCMDI) as the Coupled Model Intercomparison Project 3 (CMIP3) archive, predict a significant surface warming of Antarctica by the end of the 21st century under a moderate (SRESA1B) greenhouse-gas scenario. All models but one predict a concurrent precipitation increase but with a large scatter of results. The models with finer horizontal resolution tend to predict a larger precipitation increase. Because modeled Antarctic surface mass balance is known to be sensitive to horizontal resolution, extrapolating predictions from the different models with respect to model resolution may provide simple yet better multi-model estimates of Antarctic precipitation change than mere averaging or even more complex approaches. Using such extrapolation, a conservative estimate of the predicted precipitation increase at the end of the 21st century is +30 kg m–2 a–1 on the grounded ice sheet, corresponding to a >1m ma–1 sea-level rise. About three-quarters of this rise originates from the marginal regions of the Antarctic ice sheet with surface elevation below 2250 m. This is where field programs are most urgently needed to better understand and monitor accumulation at the surface of Antarctica, and to improve and verify prediction models.

The resistance to sliding beneath soft-bedded glaciers depends on the effective stress, N, which is controlled by the subglacial hydrological system. While large-scale water transport is primarily through conduits, the effective stress profile beneath most of the glacier base is expected to be controlled by seepage flows through the permeable sediments. Models of the response to forced changes of the near-conduit effective stress demonstrate that perturbations in N decay over a characteristic lateral distance that is typically only a few times the sediment thickness. This implies that only relatively small changes to the spatially averaged effective stress, can be produced if conduit spacing is comparatively large and the glacier and sediments remain in contact. To produce larger changes to , it is likely that flotation must be achieved beneath a significant portion of the glacier base. At higher values, spatial variations in N can produce gradients in the thickness, h, of a fringe of ice-infiltrated sediments immediately adjacent to the glacier base; this has implications for the development of glacial landforms when sliding causes sediment transport.

Automated glacier mapping from thresholded band ratios of multispectral satellite data is a well-established technique to update glacier inventories over large and remote regions. The local glaciers and ice caps on Greenland are of particular interest for such efforts, as they have been only partly mapped, mainly during the 1940s–60s, and their potential contribution to global sea-level rise could be large. Here we use three Landsat ETM+ scenes from 2001 covering Disko Island (Qeqertarsuaq) and the Nuussuaq and Svartenhuk peninsulas, West Greenland, to map the glacier extent in 2001 of 1172 entities. We also manually digitize Little Ice Age (LIA) extents from clearly visible trimlines for a subsample of 500 entities. In this region with numerous surge-type glaciers, the related area-change calculation is challenging and we consider different samples with and without known surging glaciers. For the three regions the mean area changes are –28%, –20% and –23%, respectively, when known surge-type glaciers are excluded. The glaciers on smaller islands and peninsulas closer to the margin of the ice sheet show a lower mean area change of –15%. Moreover, lower (–16%) and upper (–21%) bounds are calculated for the overall area changes in the entire region between the LIA and 2001 using different upscaling assumptions. Cumulative length changes since the LIA are found to be slightly lower for surge-type glaciers.

It has been suggested that meteorological and climate models underestimate snow accumulation on the Antarctic plateau, because accumulation (or surface mass balance (SMB)) is dominated by clear-sky precipitation while this process is not properly taken into account in the models. Here, we show that differences between model and field SMB data are much reduced when the in situ SMB reports used to evaluate the models are filtered through quality-control criteria and less reliable reports are subsequently left out. We thus argue that, although not necessarily unsupported, model biases and their interpretations in terms of clear-sky vs synoptic precipitation on the Antarctic plateau may have been overstated in the past. To avoid such misleading issues, it is important that in situ SMB reports of insufficient or unassessed reliability are discarded, even at the cost of a strong reduction in spatial sampling and coverage.

We present the thermal distribution in the confluence area of Gorner- and Grenzgletscher, Valais, Switzerland. The area was mapped by ice-penetrating radar at 1–5 and 40 MHz. The higher-frequency data reveal a thick surface layer of low backscatter in the center of the Grenzgletscher branch. Based on datasets of borehole-temperature measurements and flow velocity, we interpret this as a thick layer of cold ice, advected from the accumulation region of Grenzgletscher. Along seven profiles the base of the low-backscatter zone can be found at a maximum depths between approximately 100 and 200 m. Laterally, the layer extends some 400 m, ∼1/3 of the width of the Grenzgletscher branch. The lower boundary of the low-backscatter zone is systematically higher than the cold–temperate transition surface found in the boreholes. This discrepancy is attributed to the direct sensitivity of radar backscatter to liquid-water inclusions, rather than to the temperature distributions as observed in boreholes. We present the current state of the cold layer and discuss its influence on other glacier characteristics.

We extend the application of control methods to a comprehensive three-dimensional thermomechanical ice-sheet model, SICOPOLIS (SImulation COde for POLythermal Ice Sheets). Lagrange multipliers, i.e. sensitivities, are computed with an exact, efficient adjoint model that has been generated from SICOPOLIS by rigorous application of automatic differentiation. The case study uses the adjoint model to determine the sensitivity of the total Greenland ice volume to various control variables over a 100 year period. The control space has of the order 1.2 × 106 elements, consisting of spatial fields of basal flow parameters, surface and basal forcings and initial conditions. Reliability of the adjoint model was tested through finite-difference perturbation calculations for various control variables and perturbation regions, ascertaining quantitative inferences of the adjoint model. As well as confirming qualitative aspects of ice-sheet sensitivities (e.g. expected regional variations), we detect regions where model sensitivities are seemingly unexpected or counter-intuitive, albeit ‘real’ in the sense of actual model behavior. An example is inferred regions where sensitivities of ice-sheet volume to basal sliding coefficient are positive, i.e. where a local increase in basal sliding parameter increases the ice-sheet volume. Similarly, positive (generally negative) ice temperature sensitivities in certain parts of the ice sheet are found, the detection of which seems highly unlikely if only conventional perturbation experiments had been used. The object of this paper is largely a proof of concept. Available adjoint-code generation tools now open up a variety of novel model applications, notably with regard to sensitivity and uncertainty analyses and ice-sheet state estimation or data assimilation.