AbstractIce, Cloud and land Elevation Satellite (ICESat) repeat-track laser altimetry has identified 17 sites within the Byrd Glacier catchment, East Antarctica, where rapid ice-surface height changes have occurred, which have been interpreted as evidence for ‘active’ subglacial lakes. Here we present evidence from a new radio-echo sounding (RES) survey at 11 of these locations to understand the bed conditions associated with the proposed hydrological activity. At none of the sites examined did we find evidence in support of substantial pooled basal water. In the majority of cases, along-track RES bed reflection amplitudes either side of the locations of surface height change are indistinguishable from those within the features. These results indicate that, in most cases, hypothesized ‘active’ lakes are not discrete radar targets and are therefore much smaller than the areas of surface height change. In addition, we have identified three new relatively large subglacial lakes upstream of the region where most ‘active’ subglacial lakes are found, in an area where the hydraulic gradient is significantly lower. Our results suggest that substantial and long-lasting basal water storage in the Byrd Glacier catchment occurs only under low hydraulic gradients, while coast-proximal sites of hydraulic activity likely involve small or temporary accumulations of basal water.

Antarctic subglacial highlands are where the Antarctic ice sheets first developed and the “pinning points” where retreat phases of the marine-based sectors of the ice sheet are impeded. Due to low ice velocities and limited present-day change in the ice-sheet interior, West Antarctic subglacial highlands have been overlooked for detailed study. These regions have considerable potential, however, for establishing the locations from which the West Antarctic Ice Sheet originated and grew, and its likely response to warming climates. Here, we characterize the subglacial morphology of the Ellsworth Subglacial Highlands, West Antarctica, from ground-based and aerogeophysical radio-echo sounding (RES) surveys and the Moderate-Resolution Imaging Spectroradiometer (MODIS) Mosaic of Antarctica. We document well-preserved classic landforms associated with restricted, dynamic, marine-proximal alpine glaciation, with hanging tributary valleys feeding a significant overdeepened trough (the Ellsworth Trough) cut by valley (tidewater) glaciers. Fjord-mouth threshold bars down-ice of two overdeepenings define both the northwest and southeast termini of paleo-outlet glaciers, which cut and occupied the Ellsworth Trough. Satellite imagery reveals numerous other glaciated valleys, terminating at the edge of deep former marine basins (e.g., Bentley Subglacial Trench), throughout the Ellsworth Subglacial Highlands. These geomorphic data can be used to reconstruct the glaciology of the ice masses that formed the proto–West Antarctic Ice Sheet. The landscape predates the present ice sheet and was formed by a small dynamic ice field(s), similar to those of the present-day Antarctic Peninsula, at times when the marine sections of the West Antarctic Ice Sheet were absent. The Ellsworth Subglacial Highlands represent a major seeding center of the paleo–West Antarctic Ice Sheet, and its margins represent the pinning point at which future retreat of the marine-based West Antarctic Ice Sheet would be arrested.

We present a detailed analysis of bed roughness beneath Institute and Möller Ice Streams, west Antarctica, using radio-echo sounding data (RES) acquired in the austral summer of 2010/11. We assess roughness using a two-parameter approach and also assess the directionality of roughness relative to present-day ice flow. Our work highlights the wealth of additional information that resides in analyses of bed roughness. Employing these multiple approaches we show that spatially variable roughness patterns are partly a consequence of the ability of flowing ice not only to smooth the bed but also to redistribute and remove sediments, and to do this along-flow. Accordingly, we identify some fast-flow tributaries underlain by topography that has been streamlined and other tributaries that are underlain by sediments. We also identify locations that are currently protected from erosion, but where more ancient erosion may once have occurred. We conclude that detailed roughness analysis is a useful tool for landscape interpretation; and we suggest that the roughness of an ice-sheet's bed should be viewed not only as the consequence of ancient marine sedimentation, but also as a product of more contemporary erosion and redistribution of sediments, as well as bedrock-smoothing that is ongoing because of continuing dynamic activity. In this way, basal roughness has the potential to evolve continually with ice sheet form and flow, and should not be viewed simply as a snapshot of either present-day or palaeo-basal conditions.

A recent ocean modelling study indicates that possible changes in circulation may bring warm deep-ocean water into direct contact with the grounding lines of the Filchner–Ronne ice streams, suggesting the potential for future ice losses from this sector equivalent to ~0.3 m of sea-level rise. Significant advancements have been made in our knowledge of both the basal topography and ice velocity in the Weddell Sea sector, and the ability to accurately model marine ice sheet dynamics, thus enabling an assessment to be made of the relative sensitivities of the diverse collection of ice streams feeding the Filchner–Ronne Ice Shelf. Here we use the BISICLES ice sheet model, which employs adaptive-mesh refinement to resolve grounding line dynamics, to carry out such an assessment. The impact of realistic perturbations to the surface and sub-shelf mass balance forcing fields from our 2000-year "reference" model run indicate that both the Institute and Möller ice streams are highly sensitive to changes in basal melting either near to their respective grounding lines, or in the region of the ice rises within the Filchner–Ronne Ice Shelf. These same perturbations have little impact, however, on the Rutford, Carlson or Foundation ice streams, while the Evans Ice Stream is found to enter a phase of unstable retreat only after melt at its grounding line has increased by 50% of likely present-day values.

Understanding the controls on the amount of surface meltwater that refreezes, rather than becoming runoff, over polar ice masses is necessary for modeling their surface mass balance and ultimately for predicting their future contributions to global sea level change. We present a modified version of a physically based model that includes an energy balance routine and explicit calculation of near‐surface meltwater refreezing capacity, to simulate the evolution of near‐surface density and temperature profiles across Devon Ice Cap in Arctic Canada. Uniquely, our model is initiated and calibrated using high spatial resolution measurements of snow and firn densities across almost the entire elevation range of the ice cap for the summer of 2004 and subsequently validated with the same type of measurements obtained during the very different meteorological conditions of summer 2006. The model captures the spatial variability across the transect in bulk snowpack properties although it slightly underestimates the flow of meltwater into the firn of previous years. The percentage of meltwater that becomes runoff is similar in both years; however, the spatial pattern of this melt‐runoff relationship is different in the 2 years. The model is found to be insensitive to variation in the depth of impermeable layers within the firn but is very sensitive to variation in air temperature, since the refreezing capacity of firn decreases with increasing temperature. We highlight that the sensitivity of the ice cap's surface mass balance to air temperature is itself dependent on air temperature.

Subglacial hydrology in East Antarctica is poorly understood, yet may be critical to the manner in which ice flows. Data from a new regional airborne geophysical survey (ICECAP) have transformed our understanding of the topography and glaciology associated with the 287,000 km(2) Aurora Subglacial Basin in East Antarctica. Using these data, in conjunction with numerical ice sheet modeling, we present a suite of analyses that demonstrate the potential of the 1000 km-long basin as a route for subglacial water drainage from the ice sheet interior to the ice sheet margin. We present results from our analysis of basal topography, bed roughness and radar power reflectance and from our modeling of ice sheet flow and basal ice temperatures. Although no clear-cut subglacial lakes are found within the Aurora Basin itself, dozens of lake-like reflectors are observed that, in conjunction with other results reported here, support the hypothesis that the basin acts as a pathway allowing discharge from subglacial lakes near the Dome C ice divide to reach the coast via the Totten Glacier.

Antarctic subglacial lakes are studied for three main scientific reasons. First, they form an important component of the basal hydrological system which is known to affect the dynamics of the ice sheet. Second, they are amongst the most extreme viable habitats on Earth and third, if sediments exist on their floors, they may contain high-resolution records of ice sheet history. Here we present a new inventory of locations, dimensions and data sources for 379 subglacial lakes. Several major advances are responsible for the rise in the total number of lakes from the 145 known at the time of the last inventory in 2005. New radar datasets have been collected in previously unexplored regions of the ice sheet while digital data collection and processing techniques have allowed improvements to lake identification methods. Satellite measurements of ice surface elevation change caused by the movement of subglacial water have also been found to be widespread in Antarctica, often in places where radar data are absent. These advances have changed our appreciation of the Antarctic subglacial environment and have expanded our understanding of the behaviour of subglacial lakes.

The fjords beneath The East Antarctic ice sheet has played a fundamental part in modulating climate and sea level during the past 30 million years. Understanding its history is crucial to evaluating its future behaviour and response to global warming. Airborne ice-penetrating radar studies now reveal a fjord-like landscape beneath several kilometres of ice in the East Antarctic Aurora subglacial basin. The data confirm, and provide a new constraint on, the magnitude and dynamics of the oscillations of the East Antarctic ice sheet during the late Cenozoic, which had previously been supported only by marine cores.

Ice thickness data over much of East Antarctica are sparse and irregularly distributed. This poses difficulties for reconstructing the homogeneous coverage needed to properly assess underlying sub-glacial morphology and fundamental geometric constraints on sea level rise. Here we introduce a new physically-based ice thickness interpolation scheme and apply this to existing ice thickness data in the Aurora Subglacial Basin region. The skill and robustness of the new reconstruction is demonstrated by comparison with new data from the ICECAP project. The interpolated morphology shows an extensive marine-based ice sheet, with considerably more area below sea-level than shown by prior studies. It also shows deep features connecting the coastal grounding zone with the deepest regions in the interior. This has implications for ice sheet response to a warming ocean and underscores the importance of obtaining additional high resolution data in these marginal zones for modelling ice sheet evolution.

We investigate the glaciological and topographic setting of known Antarctic subglacial lakes following a previous assessment by Dowdeswell and Siegert (2002) based on the first inventory of 77 lakes. Procedures used to detect subglacial lakes are discussed, including radio echo sounding (RES) (which was first used to demonstrate the presence of subglacial lakes), surface topography, topographical changes, gravity measurements, and seismic investigations. Recent discoveries of subglacial lakes using these techniques are detailed, from which a revised new inventory of subglacial lakes is established, bringing the total number of known subglacial lakes to 387. Using this new inventory, we examine various controls on subglacial lakes, such as overlying ice thickness and position within the ice sheet and formulate frequency distributions for the entire subglacial lake population based on these (variable) controls. We show how the utility of RES in identifying subglacial lakes is spatially affected; lakes away from the ice divide are not easily detected by this technique, probably due to scattering at the ice sheet base. We show that subglacial lakes are widespread in Antarctica, and it is likely that many are connected within well-defined subglacial hydrological systems.

Ice within marine basins of East Antarctica, and their outlets, represent the ultimate limit on sea level change. The region of East Antarctica between the Ross Sea and Wilkes Land hosts a number of major basin, but has been poorly understood. Long range aerogeophysics from US, Australian and French stations, with significant British and IceBridge support, has, under the banner of the ICECAP project, greatly improved our knowledge of ice thickness, surface elevation, and crustal structure of the Wilkes and Aurora Subglacial Basins, as well as the Totten Glacier, Cook Ice Shelf, and Byrd Glacier. We will discuss the evolution of the Wilkes and Aurora Subglacial Basins, new constraints on the geometry of the major outlet glaciers, as well as our results from surface elevation change measurements over dynamic regions of the ice sheet. We will discuss the implications of our data for the presence of mid Pleistocene ice in central East Antarctica. Future directions for ICECAP will be discussed.

Recent technological advances in the study and dating of both land and marine glacial geologic features combined with improvements in both glaciological and post-glacial isostatic rebound modelling have led to significant improvements in our knowledge and understanding of the Antarctic Ice Sheets at the Last Glacial Maximum (LGM) and their subsequent changes throughout the Holocene. Here we review the geological evidence for the extent and timing of the maximum advance of the East and West Antarctic Ice Sheets and the ice cover of the Antarctic Peninsula during the most recent glacial cycle. We also discuss evidence for the rate and timing of Holocene Ice Sheet retreat. Geological data provide a very important 'first-hand' record of ice-sheet changes over a range of time periods. They are also useful for constraining and improving models which then have the potential to both fill in the gaps for which geological data are unavailable, and to make predictions of the future. Inspection of the geological record allows us to form qualitative scenarios concerning glacial history. Numerical modelling has been used on several occasions to test such hypotheses. We discuss such numerical studies, indicating both their importance and limitations in order to develop quantitative ideas about the late Quaternary history of the ice sheet. An important environmental aspect of Antarctica's glacial history is its contribution to global sea level rise since the LGM. The past decade has seen the range of estimates (from reconstructions based solely on geological evidence, on glaciological modelling constrained by geology and on modelling of the isostatic rebound) change from 0.5-38 m sea level equivalent to 5.9-19.2 m. Although the convergence of estimates is encouraging, there is a need for further glaciological modelling to take full account of the constraints placed on LGM ice expansion, particularly in East Antarctica, by new geological evidence.

Wind load factors incorporated in the ASCE 7-05 standard are based on rough approximations of wind effects and the uncertainties inherent in them. These factors are routinely applied to tall building design, even though the original calculations on which they are based disregard two important facts characterizing tall building response to wind. First, wind effects on flexible structures are proportional to the wind speeds raised to powers larger than two, instead of the power two, as is the case for rigid buildings. Second, dynamic response parameters, that is, the natural frequencies of vibration and the damping ratios affecting the response, exhibit significant uncertainties. It is shown that, for these reasons, the use of ASCE 7-05 wind load factors for the design of tall flexible buildings results in safety levels that can be significantly lower than safety levels typical of common, rigid structures.

The flow of water beneath the Antarctic Ice Sheet has recently been shown to involve drainage from and exchange between subglacial lakes, with flow routing over distances of >100km. As subglacial water is known to be important to ice‐sheet dynamics, changes to the flow routing of basal water may yield an ice‐sheet response. Here we show that the directions of subglacial hydrological flowpaths are highly sensitive to the ice‐sheet surface topography at certain sites in Antarctica. Surface elevation changes, of between 5 and 15 m, are found to be sufficient to produce significant changes to the subglacial water flowpaths, which affect the potential drainage routes of large subglacial lakes. We identify the reasons for this high sensitivity and recognise several locations in East Antarctica where changes to the drainage regime could have important effects on large‐scale basal water distribution.