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This reconstruction of the Late Ordovician, glacigenic Pakhuis Formation of the Table Mountain Group is based on a variety of diverse datasets. Field observations were made over the full 300 km extent of exposure in a north-south direction. The thin glacigenic package constitutes a minor interlude in the development of a subcontinental, Palaeozoic, siliciclastic basin. The Pakhuis Formation is of special interest because it includes features like the extensive penecontemporaneous folding, an erosional unconformity and the uniform lithological character of the sandy diamictites. A model is presented by which an unusual concurrence of circumstances produced the special features of the Pakhuis glacigenics. These are the ice invasion of a developing basin, an onset zone within basin and a deep trough harboring an ice-stream. Subglacial, grounding zone and iceberg facies associations with their lateral variations are developed. The temperate, glaciation of relative short duration, comprised one major and a second minor advance. During the first advance the grounded ice sheet with slow-moving sheet-flow reached ice-stream characteristics along at least part of a trough. The occurrence of an ice-stream within a slow-moving, low-profile ice sheet provides the glaciological environment for ice-stream draw-down, flanking infill of ice, resulting in compressional ice-flow from the sides. The fundamental requirement for buckling (i.e. the development of the Fold Zone) is layer parallel shortening achieved by the compressional ice-flow. Ice-bed interface features like deforming–bed structures are developed, as well as outsize flutes for which an alternative bulk strain model is proposed. The glacial retreat was rapid, interrupted only by the second, minor advance. A marine environment is attested by the postglacial fauna of a black shale.

Seasonal evolution of the subglacial drainage system in the lower ablation area of the Hailuogou glacier ice tongue were revealed by repeated dye tracer (Rhodamine WT) experiments during the 2009 ablation season. Between April and October, 18 dye tracer experiments were conducted by injecting the tracer at one location of the lower ablation area of the Hailuogou Glacier to diagnose the seasonal variation of the subglacial drainage system of this section of glacier ice tongue. Using a simple advection-dispersion model (ADM), the flow velocity, hydrodynamic dispersion coefficient, and degree of tracer spreading were deduced. Tracer transit velocity through the tested subglacial channel varied from 0.148 to 0.555 m s&minus, 1 during the 2009 ablation season. Dispersivity showed a relatively high value than that found at other glaciers, which varied between 27.05 and 287.49 m2 s&minus, 1. Seasonal changes of these indexes indicated that the subglacial drainage system of the lower ablation area of the Hailougou Glacier is a relatively stable existing system in the case of its longitudinal shape, whereas its hydraulic efficiency is low in the early and late ablation seasons and high during the middle of summer due to subglacial channel expansion.

A 3700-km 2 area adjacent to the Firth of Clyde, Scotland, is examined to constrain the development and dynamics of the western central sector of the last British and Irish Ice Sheet. Results from geomorphological mapping, lithostratigraphic investigations, three-dimensional geological modelling and field observations are combined to produce an empirically constrained, five-stage conceptual model of ice sheet evolution. (A) Previously published dates on interstadial organic deposits and mammalian fossils suggest that the Main Late Devensian (MLD) (MIS 2) glaciation of central Scotland began after 35 ka cal BP. During build-up, ice advanced from the western Scottish Highlands into the Clyde and Ayrshire basins. Glaciomarine muds and shelly deposits scavenged from the Firth of Clyde were redeposited widely as shelly tills and glacial rafts. Ice advance against reverse slopes generated, and subsequently overtopped, ice-marginal sediment accumulations. We hypothesise that some of these formed pre-cursor ridges which were moulded into suites of ribbed moraine during the glacial cycle. (B) Sustained stadial conditions at the Last Glacial Maximum (LGM) (c 30–25 ka cal BP) resulted in development of a major dispersal centre over the Firth of Clyde and Southern Uplands. This dispersal centre locally preserved previously formed subglacial bedforms, and fed a wide corridor of fast-flowing ice east towards the Firth of Forth. (C) Initial deglaciation promoted a substantial re-configuration of the ice surface, with enhanced westward drawdown into the outer Firth of Clyde and eastward migration of an ice divide towards the Clyde-Forth watershed. (D) Renewed ice sheet thickening over the Firth of Clyde may have accompanied growth of the Irish Ice Sheet during the Killard Point Stadial (c 17.1–15.2 ka cal BP); it was associated with limited bed modification. Subsequent ice sheet retreat was characterised by substantial meltwater production, ponding and erosion. (E) Late stages of MLD ice sheet retreat were punctuated by one or more significant ice margin oscillations. Discovery of De Geer moraines at the site of a former proglacial lake in western Ayrshire allows glacier flow at the ice margin to be approximated as ≤290 m a −1 during one such oscillation. Such velocities were probably enabled by basal sliding and shallow sediment deformation. At this stage those parts of the MLD ice sheet margin that were grounded in the Firth of Clyde were extremely vulnerable to collapse. Final disintegration of glacier ice in the Clyde basin probably occurred early in the Lateglacial Interstadial (Greenland Interstadial-1), coinciding with marine incursion to c 40 m above present day sea level.

Glacier ice structures influence on moraines developement (Hørbye glacier, Central Spitsbergen) Geomorphological and basic sedimentological investigation of controlled moraine system was carried out at the ice surface and within the moraine complex zone of the Hørbye glacier (Central Spitsbergen). The Hørbye glacier creates controlled moraine chains regarding transversal fractures and longitudinal foliation. The forms parallel to the ice flow direction are represented by medial moraines, whereas transversal ones by thrustmoraines. Both arrangements are clearly visible. However, thrust and shear planes are more effective in creating forms, both on the ice surface and in the moraine complex. The longitudinal landforms are less distinct, moreover they are coarser-grained and worse rounded, in contrast to the material from shear and thrust plains which is finer and better rounded. The study area can be divided into three subzones: clean ice surface, debris covered ice fractures and moraine complex. The outer and inner sandur plain were not taken under consideration. It is suggested that present arrangement of both thrust or shear plains and longitudinal foliation controls formation of foreland relief. This hypothesis has a particular sense in understanding construction of modern sedimentary basins as well as the mechanism of terminoglacial relief formation with regend to ice structure.

Regional climate warming has caused several ice shelves on the Antarctic Peninsula to retreat and ultimately collapse during recent decades. Glaciers flowing into these retreating ice shelves have responded with accelerating ice flow and thinning. The Wordie Ice Shelf on the west coast of the Antarctic Peninsula was reported to have undergone a major areal reduction before 1989. Since then, this ice shelf has continued to retreat and now very little floating ice remains. Little information is currently available regarding the dynamic response of the glaciers feeding the Wordie Ice Shelf, but we describe a Chilean International Polar Year project, initiated in 2007, targeted at studying the glacier dynamics in this area and their relationship to local meteorological conditions. Various data were collected during field campaigns to Fleming Glacier in the austral summers of 2007/08 and 2008/09. In situ measurements of ice-flow velocity first made in 1974 were repeated and these confirm satellite-based assessments that velocity on the glacier has increased by 40–50% since 1974. Airborne lidar data collected in December 2008 can be compared with similar data collected in 2004 in collaboration with NASA and the Chilean Navy. This comparison indicates continued thinning of the glacier, with increasing rates of thinning downstream, with a mean of 4.1 ± 0.2 m a−1 at the grounding line of the glacier. These comparisons give little indication that the glacier is achieving a new equilibrium.

Glacial geomorphological mapping of Shuttle Radar Topography Mission (SRTM) data from the western Canadian Prairies demonstrates that during the last (late Wisconsinan) deglaciation of the Laurentide Ice Sheet terrestrial ice streams underwent a major reorganization of their flow configuration. This reorganization involved a 90° shift in flow direction and was accompanied by a corresponding increase in the influence of topography on streaming flow. Ice streams included both topographically confined and “pure” ice streams that flowed independent of topography. Streaming flow is recorded by suites of highly elongate (>60 km long) subglacial bedforms, bounded sharply at their lateral margins by prominent moraines. Initial streaming flow was unconfined by topography but was replaced progressively, and crosscut, by younger topographically confined flows. Flow reorganization is inferred to have been caused by temporal and spatial variations in the interaction between frozen and thawed bed conditions, with thinning and shutdown of one ice stream ultimately triggering initiation of others. This highlights the role of internal glaciodynamically driven reorganization in triggering streaming flow within large ice sheets and shows that large-scale flow reorganization can occur over the time scale of a single deglaciation in terrestrial ice streams.

Subglacial landsystems in and around Okanagan Valley, British Columbia, Canada are investigated in order to evaluate landscape development, subglacial hydrology and Cordilleran Ice Sheet dynamics along its southern margin. Major landscape elements include drumlin swarms and tunnel valleys. Drumlins are composed of bedrock, diamicton and glaciofluvial sediments; their form truncates the substrate. Tunnel valleys of various scales (km to 100s km length), incised into bedrock and sediment, exhibit convex longitudinal profiles, and truncate drumlin swarms. Okanagan Valley is the largest tunnel valley in the area and is eroded >300 m below sea level. Over 600 m of Late Wisconsin-age sediments, consisting of a fining-up sequence of cobble gravel, sand and silt fill Okanagan Valley. Landform–substrate relationships, landform associations, and sedimentary sequences are incompatible with prevailing explanations of landsystem development centred mainly on deforming beds. They are best explained by meltwater erosion and deposition during ice sheet underbursts. During the Late-Wisconsin glaciation, Okanagan Valley functioned as part of a subglacial lake spanning multiple connected valleys (few 100s km) of southern British Columbia. Subglacial lake development started either as glaciers advanced over a pre-existing sub-aerial lake (catch lake) or by incremental production and storage of basal meltwater. High geothermal heat flux, geothermal springs and/or subglacial volcanic eruptions contributed to ice melt, and may have triggered, along with priming from supraglacial lakes, subglacial lake drainage. During the underburst(s), sheetflows eroded drumlins in corridors and channelized flows eroded tunnel valleys. Progressive flow channelization focused flows toward major bedrock valleys. In Okanagan Valley, most of the pre-glacial and early-glacial sediment fill was removed. A fining-up sequence of boulder gravel and sand was deposited during waning stages of the underburst(s) and bedrock drumlins in Okanagan Valley were enhanced or wholly formed by this underburst(s). Subglacial lake development and drainage had an impact on ice sheet geometry and ice volumes. The prevailing conceptual model for growth and decay of the CIS suggests significantly thicker ice in valleys compared to plateaus. Subglacial lake development created a reversal of this ice sheet geometry where grounded ice on plateaus thickened while floating valley ice remained thinner (due to melting and enhanced sliding, with significant transfer of ice toward the ice sheet margin). Subglacial lake drainage may have hastened deglaciation by melting ice, lowering ice-surface elevations, and causing lid fracture. This paper highlights the importance of ice sheet hydrology: its control on ice flow dynamics, distribution and volume in continental ice masses.

Radar surveys of Bench Glacier, Alaska, collected over five field seasons between 2002 and 2006 reveal a surface layer of radar transparent ice in this temperate valley glacier. The transparent layer covers the up-glacier half of the ablation zone and is defined by a distinct lack of the radar scattering events considered typical of temperate ice. Radar scattering ice underlies the transparent zone, and extends to the surface elsewhere on the glacier. We observed the layering in constant offset radar surveys conducted with characteristic frequencies ranging from 5 MHz to 100 MHz. The radar transparent layer extends from the surface to 20 m depth on average, but up to 50 m in some places. Bench Glacier's transparent layer appears similar to the cold surface layer of polythermal glaciers, however, observations in over 50 boreholes on Bench Glacier suggest there is no cold ice corresponding to the radar transparent layer. We conclude that spatially extensive radar-transparent layers normally used to identify cold ice in polythermal glaciers are present in some temperate glaciers. Copyright © 2009 John Wiley & Sons, Ltd.

We analyze spatial and temporal variability of the surface velocity field of David Glacier and its floating seaward extension Drygalski Ice Tongue. We obtain velocity measurements by combinations of automated feature tracking, interferometry and speckle tracking using 1997 Antarctic Mapping Mission-1 and 2000 Modified Antarctic Mapping Mission RADARSAT-1 data. We compare short-term velocities, three-year averaged velocities, and earlier studies to investigate whether any significant changes have occurred. Drygalski Ice Tongue advanced 2200 m over the three-year time interval, increasing its area by almost 45 km2 (an area three times that size calved off in early 2005). Our comparison suggests that the velocity field remained relatively constant from about 1991 to 2000. The yearly advance rate is similar to the long-term rate derived from a 1960 map and earlier studies, suggesting long-term steady flow. The new velocity estimates are used in combination with isostatically derived ice thickness fro...

The highest resolution Holocene sediment core from the Antarctic Peninsula to date was collected during the first SHALDRIL cruise (NBP0502). Drilling yielded a 108.2-m-long core (87% recovery; site NBP0502–1B) from Maxwell Bay, South Shetland Islands. This high-resolution sediment record comes from a region that is currently experiencing dramatic climate change and associated glacial retreat. Such records can help to constrain the nature of past climate change and causal mechanisms, and to provide a context for evaluating current climate change and its impacts. The base of the drill site sampled till and/or proximal glacimarine sediments resting directly on bedrock. Glacimarine suspension deposits composed of dark greenish gray silty mud with variable diatom abundance and scattered very fine sand laminations make up the majority of the sedimentary section. Detailed sedimentological and geochemical analyses, including magnetic susceptibility, total organic carbon (TOC) content, carbon and nitrogen isotopic composition, pebble content, and biogenic silica content, allow subdivision of the glacimarine section into nine units, and seismic facies analyses resulted in the identification of six distinct seismic units. We used 29 radiocarbon ages to construct an age model and calculate sedimentation rates that vary by two orders of magnitude, from 0.7 mm/a to ?30 mm/a. Radiocarbon ages from glacimarine sediments just above the till date back to between 14.1 and 14.8 ka. Thus, ice was grounded in the fjord during the Last Glacial Maximum and eroded older sediments from the fjord. Following initial retreat of grounded ice from Maxwell Bay, the fjord was covered by a permanent floating ice canopy, probably an ice tongue. The highest sedimentation rate corresponds to an interval that contains abundant sand laminations and gravelly mud intervals and likely represents a melt-out phase or period of rapid glacial retreat from 10.1 ka to 8.2 ka. There is no evidence for an early Holocene climatic reversal, as recorded farther south at the Palmer Deep drill site. Minimum sea-ice cover and warm water conditions occurred between 8.2 and 5.9 ka. From 5.9 to 2.6 ka, there was a gradual cooling and more extensive sea-ice cover in the bay. After 2.6 ka, the climate varied slightly, causing only subtle variation in glacier grounding lines. There is no compelling evidence for a Little Ice Age readvance in Maxwell Bay. The current warming and associated glacial response in the northern Antarctic Peninsula appears to be unprecedented in its synchroneity and widespread impact.

Structural analyses were conducted in the basal zone of an Antarctic glacier. The studied basal ice sequence was retrieved from a 20-m-long subglacial tunnel dug at the margin of the glacier and is at the temperature of −17°C. For the first time, rotating clast systems embedded within debris-rich ice were thin-sectioned using specially designed cutting techniques. The observed structures reflect the occurrence of pervasive shearing at the base of the glacier, and can be used as shear sense indicators. In addition, some of these structures provide evidence for the presence of thin liquid films at the time of formation despite the marked freezing temperature of the ice. It is showed here that cautious analysis of deformation structures present in debris-bearing ice may bring insights not only into the flow dynamics of the embedding matrix, but also into the behaviour of the interstitial fluid network at the base of cold glaciers and ice sheets.

Quincey, D.J., Glasser, N.F. (2009). Morphological and ice-dynamical changes on the Tasman Glacier, New Zealand, 1990-2007. Global and Planetary Change, 68 (3): 185-197

The Kuannersuit Glacier surged 11 km between 1995 and 1998. The surge resulted in the formation of an ice cored thrust moraine complex constructed by subglacial and proglacial glaciotectonic processes. Four main thrust zones are evident in the glacier snout area with phases of compressional folding and thrusting followed by hydrofracture in response to the build-up of compressional stresses and the aquicludal nature of submarginal permafrost and naled. Various types of stratified debris-rich ice facies occur within the marginal zone: The first (Facies I) comprises laterally continuous strata of ice with sorted sediment accumulations, and is reworked and thrust naled ice. The second is laterally discontinuous stratified debris-rich ice with distinct tectonic structures, and is derived through subglacial extensional deformation and localised regelation (Facies II), whilst the third type is characterised by reworked and brecciated ice associated with the reworking and entrainment of meteoric ice (Facies III). Hydrofracture dykes and sills (Facies IV) cross-cut the marginal ice cored thrust moraines, with their sub-vertically frozen internal contact boundaries and sedimentary structures, suggesting supercooling operated as high-pressure evacuation of water occurred during thrusting, but this is not related to the formation of basal stratified debris-rich ice. Linear distributions of sorted fines transverse to ice flow, and small stratified sediment ridges that vertically cross-cut the ice surface up-ice of the thrust zone relate to sediment migration along crevasse traces and fluvial infilling of crevasses. From a palaeoglaciological viewpoint, marginal glacier tectonics, ice sediment content and sediment delivery mechanisms combine to control the development of this polythermal surge valley landsystem. The bulldozing of proglacial sediments and the folding and thrusting of naled leads to the initial development of the outer zone of the moraine complex. This becomes buried in bulldozed outwash sediment and well-sorted fines through surface ablation of naled. Up-ice of this, the heavily thrust margin becomes buried in sediment melted out from basal debris-rich ice and subglacial diamicts routed along thrusts. These mechanisms combine to deliver sediment to supraglacial localities, and promote the initial preservation of structurally controlled moraines through insulation, and the later development of kettled dead ice terrain.

Two diagnostic, dynamic/thermodynamic ice-shelf models are applied to the Brunt Ice Shelf/Stancomb-Wills Ice Tongue system, located off Caird Coast, Coats Land, Antarctica. The Brunt Ice Shelf/Stancomb-Wills Ice Tongue system is characterized as a thin, unbounded ice shelf with an atypical and highly heterogeneous structure. In contrast to other ice shelves, a composite mass of icebergs that calved at the grounding line and were then locked within fast (sea) ice exists between the fast-moving Stancomb-Wills Ice Stream and the slow-moving Brunt Ice Shelf. We simulate the present flow regime of the ice shelf that results from the ice-thickness distribution and the inflow at the grounding line with two different models, and compare the model results with feature tracking and InSAR flow velocities. We then incorporate two observed features, a rift and a shear margin, into the models with two different approaches, and demonstrate the effects of variations in numerical values for the shear strength and viscosity in these zones on the simulated velocity field. A major result is that both kinds of implementation of the rifts lead to similar effects on the entire velocity field, while there are discrepancies in the vicinity of the rifts.

This paper presents a newly derived velocity field of the Brunt Ice Shelf and Stancomb-Wills Ice Tongue in East Antarctica. Velocity is derived using automated feature-tracking techniques on RADARSAT-1 imagery from the 1997 Antarctic Mapping Mission-1 (AMM-1) and 2000 Modified Antarctic Mapping Mission (MAMM). We measure velocities up to 1350 m a−1 at the ice front. Closer investigation of the velocity field and radar images reveals an obvious divergence of contemporary flowlines from relict flow stripes along a portion of Stancomb-Wills Ice Tongue. Analysis of relict flow stripes can reveal glacial events in the past. Assuming relatively steady flow since the event occurred, we utilize the current velocity field to reconstruct former stripe configuration. We believe the flowline deviation points to a change in dynamics that occurred approximately 140 years ago, perhaps due to thinning and an associated shift in grounding-line position. This seems to be supported by historic observations and bottom topography data.

This paper examines the basal ice sequence of Rhone Glacier, a cold-based glacier in the McMurdo Dry Valleys, Antarctica, using isotopic and solute chemistry data. Three different ice facies are identified: englacial, amber and stratified. The englacial facies is clean, bubbly ice of meteoric origin and is underlain by an amber facies. Amber ice is a characteristic of cold alpine glaciers in the McMurdo Dry Valleys and is distinctive for its high solute concentrations and much higher strain rates compared with the overlying englacial ice and the underlying stratified ice. Analysis of the stratified facies reveals an isotopic signature indicative of melt then refreeze processes and it is most likely associated with apron entrainment at the margin. By contrast, the amber facies has a co-isotopic slope of 8 and plots on a meteoric waterline. The inclusion of impurities in the amber ice reveals prolonged contact with the bed, and its depleted isotopic signature is consistent with ice formed during a cooler period. Comparison of the basal sequence of Rhone Glacier with other cold-based glaciers in the McMurdo Dry Valleys reveals strong similarities between valley-side glaciers (e.g. Meserve and Rhone Glaciers), whereas valley-floor glacier basal sequences (e.g. Suess Glacier) are characterized by structurally complex amalgamations of ice and debris.

A circular hole was discovered on the downstream side of a glacier dam in the Yatude Valley, Langhovde, East Antarctica, during the 2005–2006 austral summer. The opening of this hole is the first opportunity enabling us to observe the interior of the dam. The opening led to a large cave in the dam, raising the possibility of meltwater drainage through the dam. The Yatude Valley is an approximately U-shaped fluvial valley. The valley floor has been incised to form a box-shaped inner valley that contains fluvial terraces and large boulders upon the valley floor. The origin of these features can be explained by a large amount of running water; however, we consider it unlikely that a regular current has flowed through this site for a long period. Instead, it is more likely that large quantities of lake water have been periodically discharged due to collapse of the glacier dam or spilling out through a tunnel channel within the cave. The discovered hole and the ice cave are key features in understanding the historical development of the Yatude Valley in relation to the melting history of the Antarctic ice sheet.

Observations over past decades show a sudden switch of Jakobshavn Isbrae—a large outlet glacier feeding a deep-ocean fjord on Greenland’s west coast—from slow thickening to rapid thinning in 1997. This switch is associated with a doubling in glacier velocity. Hydrographic data show a concurrent sudden increase in subsurface ocean temperatures along the entire west coast of Greenland, suggesting that the changes in Jakobshavn Isbrae were triggered by the arrival of relatively warm water originating from the Irminger Sea. Observations over the past decades show a rapid acceleration of several outlet glaciers in Greenland and Antarctica1. One of the largest changes is a sudden switch of Jakobshavn Isbrae, a large outlet glacier feeding a deep-ocean fjord on Greenland’s west coast, from slow thickening to rapid thinning2 in 1997, associated with a doubling in glacier velocity3. Suggested explanations for the speed-up of Jakobshavn Isbrae include increased lubrication of the ice–bedrock interface as more meltwater has drained to the glacier bed during recent warmer summers4 and weakening and break-up of the floating ice tongue that buttressed the glacier5. Here we present hydrographic data that show a sudden increase in subsurface ocean temperature in 1997 along the entire west coast of Greenland, suggesting that the changes in Jakobshavn Isbrae were instead triggered by the arrival of relatively warm water originating from the Irminger Sea near Iceland. We trace these oceanic changes back to changes in the atmospheric circulation in the North Atlantic region. We conclude that the prediction of future rapid dynamic responses of other outlet glaciers to climate change will require an improved understanding of the effect of changes in regional ocean and atmosphere circulation on the delivery of warm subsurface waters to the periphery of the ice sheets.

We use a time-dependent two-dimensional ice-flow model to explore the development of the Green Bay Lobe, an outlet glacier of the southern Laurentide Ice Sheet, leading up to the time of maximum ice extent and during subsequent deglaciation (c. 30 to 8 cal. ka BP). We focus on conditions at the ice-bed interface in order to evaluate their possible impact on glacial landscape evolution. Air temperatures for model input have been reconstructed using the GRIP δ8O record calibrated to speleothem records from Missouri that cover the time periods of c. 65 to 30 cal. ka BP and 13.25 to 12.4 cal. ka BP. Using that input, the known ice extents during maximum glaciation and early deglaciation can be reproduced reasonably well. The model fails, however, to reproduce short-term ice margin retreat and readvance events during later stages of deglaciation. Model results indicate that the area exposed after the retreat of the Green Bay Lobe was characterized by permafrost until at least 14 cal. ka BP. The extensive drumlin zones that formed behind the ice margins of the outermost Johnstown phase and the later Green Lake phase are associated with modeled ice margins that were stable for at least 1000 years, high basal shear stresses (c. 100 kPa) and permafrost depths of 80–200 m. During deglaciation, basal meltwater and sliding became more important.

The lipid and hydrocarbon composition of natural populations of diatom communities collected during the austral spring bloom of 1985 in the sea-ice at McMurdo Sound, Antartica was analyzed by TLC-FID, GC and GC-MS. Sea-ice diatom communities were dominated by Amphiprora sp., Nitzschia stellata Manguin and Berkeleya sp. at Cape Armitage; N. stellata, Amphiprora, Pleurosigma, N. kerguelensis (O'Meara) Hasle and some small centric diatoms adjacent to the Erebus Ice Tongue; and Porosira pseudodenticulata (Hustedt) Jouse at Wohlschlag Bay. Lipid distributions of the sea ice diatom communities from the Cape Armitage and Ereus sites were characterized by high concentrations of tracylaglecycerol (triacylglycerolplar lipid = 1.0 to 1.5). The hydrocarbon n-C21:6, common in temperate diatoms, and an isoprenoid C25 diunsaturated alkene were the dominant hydrocarons detected at these two sites. Hydrogenation of the C25 diene produced the known alkane 2, 6, 10, 14-tetramethyl-7- (3-methylpentyl)-pentadecane. The C25 diene is one of several structurally related hydrocarbons reported in many estuarine, coastal and ocean ic sediments. We propose that certain species of diatoms are a likely source of these alkenes in sediments. The first reported biological occurrence of the C25 diene in the green seaweed Enteromorpha prolifera may have been due to the presence of epiphytic microalgae in the field sample analysed.

Arc-shaped scours, sandwaves and channels on the Hudson Bay seafloor suggest that the catastrophic drainage of lake Agassiz–Ojibway occurred as a subglacial flood beneath the Laurentide Ice Sheet, which covered northern North America.

The southwestern part of the Laurentidc Ice Sheet, in central North America, repeatedly surged during the last part of the Wisconsin Glaciation. Evidence includes the extreme lobation of the ice margin, the gentle slopes of lateral moraines and other marginal features, a radiocarbon chronology indicating extremely rapid marginal advance and retreat, and the abundance of supraglacial flow till. Rapid ice movement was caused by subglacial water and was probably limited to areas of slowly permeable substrate, which slowed the escape of the water.

A revised lithostratigraphy of Skane, South Sweden, constitutes the basis of an alternative Weichselian glaciation model for southern Scandinavia, progressively anchored to the stratigraphy. Skane was not glaciated during the Weichselian until 21,000 B.P. The concepts, outlet surge and marginal dome (the main tools of the model) are defined. The palaeogeography of the Baltic and Kattegatt basins during the Mid-Weichselian are reconstructed. Shorelines, during the advance stage, are calculated from an inferred proglacial depression. Outlet surges, which occurred in three basins of the Baltic, guided the ice sheet during its growth. The growth of marginal domes on the outlet surge lobes resulted in changes in the configuration of the ice sheet and in the lowering of its surface profile. The South Scandinavian ice divide became located over a former outlet surge lobe NNE-NE of the island of Gotland in the northern Baltic. This gave the main ice in South Sweden and Denmark a NE ice movement during the whole glaciation until the deglaciation of SE Sweden. The Kattegatt Ice Lake was formed due to damming in the Skagerack area. Surging ice tilled in the basin resulting in the formation of vast areas of stagnant ice in front of the advancing NE-ice. Marginal domes were formed on these giving rise to the early glacial episodes in the southwest of Sweden and Denmark. During the deglactanon, tnree pnases of marginal dome formation are recorded in the soutnern Baltic area and the growth of these domes resulted in the East Jylland advance, the Baelthav readvance and the Simrishamn readvance. The marginal domes were formed on vast fields of stagnant ice left behind by the receding main ice. Baltic erratics, englacially present in the main ice as well as in the stagnant ice in front of it, were transported (stepwise) towards the west and northwest, partly by the advancing marginal domes and partly by ice streams formed between the marginal domes and the main (NE-) ice. It is argued that the classical, so-called Low Baltic ice stream in the sense of a readvancing glacier lobe never existed. The first two marginal domes collapsed due to starvation and the ice movement returned gradually to the independent NE ice movement of the main ice. The third marginal dome collapsed due to a downdraw caused by a large transgression recorded in the Kattegatt and the Oresund regions. The transgression took place roughly around 13,300 B.P. and was possibly caused by damming of the Kattegatt basin in the north in connection with a marine downdraw. The collapse of the third marginal dome and the subsequent ‘ice lake downdraw’ of the dome centre NNE-NE of Gotland took place during a cold period of the deglaciation. This resulted in an extremely high recessional rate on the Swedish cast coast compared with the west coast and a contemporaneous westwards displacement of the South Scandinavian ice divide. After the downdraw, the recession rate on the east coast slowed down markedly and became more or less equal to that of the west coast. Pure dynamic causes for the extremely high recession rate in SE Sweden are expected because the decrease in this rate coincides with the onset of a recorded, marked climatic amelioration at around 12,600 B.P. Formation of the marginal domes during the deglaciation indicates periods of increased cyclon activity at the southwest margin of the Weichsclian Scandinavian ice sheet alternating with periods of ice sheet starvation. Detailed modelling of the marginal domes is therefore expected to have significant palaeoclimatic implications. The marginal dome concept is believed to he useful also in the reconstruction of earlier glaciations.

Terminal-moraine ridges up to 6 m high have been forming at the snout of Styggedalsbreen for two decades. Based on intermittent observations during this period, combined with a detailed study of ridge morphology, sedimentary structures and composition during the 1993 field season, a model of terminal-moraine formation that involves the interaction of glacial and glacio-fluvial processes at a seasonally oscillating ice margin is presented. In winter, subglacial debris is frozen-on to the glacier sole; in summer, ice-marginal and supraglacial streams deposit sediments on the wasting ice tongue. The ice tongue overrides an embryonic moraine ridge during a late-winter advance and a double layer of sediment (diamicton overlain by sorted sands and gravels) is added to the moraine ridge during the subsequent ablation season. Particular ridges grow incrementally over many years and exert positive feedback by enhancing snout up-arching during the winter advance and constraining the course of summer meltwater streams close to the ice margin. The double-layer annual-meltout model is related to moraine formation by the stacking of subglacial frozen-on sediment slabs (Kruger 1993). Moraine ridges of this type have a complex origin. are not push moraines, and may be characteristic of dynamic high-latitude and high-altitude temperate glaciers.

Ice-divide migration may explain the pattern of Holocene glacier fluctuations around the Mýrdalsjokull ice cap in southern Iceland. On at least three occasions Solheimajokull, the principal outlet glacier on the southwest flank of the ice cap, has exceeded the Little Ice Age limits of recent centuries that mark the maximum extent of neighbouring glaciers in the Holocene. Bedrock divides beneath the Mýrdalsjokull ice cap do not coincide with present ice divides. It is suggested that the ice divide migrated during the course of ice-cap growth. At various stages during the Holocene (7000-4500, c. 3100, 1400-1200 BP) Solheimajokull could have drained more of the ice cap than today, so becoming more advanced than neighbouring glaciers. In the Little Ice Age (c. AD 1600–1900) the glacier could have had a smaller catchment as a result of ice-divide migration, resulting in a more inhibited advance compared with neighbouring glaciers which reached their Holocene maximum at that time. Identification of ice-divide migration is important for palaeoclimatic reconstructions because of the need to recognize different responses of glaciers to climate if one is to use their fluctuations as indicators of change.

Large embankments, typically several kilometers in lateral extent and many tens of meters high, choke the mouths of each alpine valley of the central Cascade Range, Washington State, U.S.A., at or near their junctions with the Puget Lowland. They comprise till and bedded gravel, sand, and silt, aggraded into ice-dammed lakes. The embankments lie within the late-Pleistocene Cordilleran ice-sheet limit and so do not mark the location of the ice-maximum terminus. Reconstruction of the subglacial hydraulic potential field indicates that these ice-dammed lakes would have drained subglacially via spillways located near the junction of each alpine valley and the Lowland. Physical processes tended to stabilize the grounding line for each ice tongue close to its respective spillway location. Because sedimentation rates are highest adjacent to the grounding line, subaqueous sedimentation formed a growing embankment there. In some valleys, subsequent subaerial lake drainage or decay of the active-ice dam resulted in late-stage deposition of deltas or valley trains. This analysis of ice-water behavior is based on physical principles that should be generally applicable to any environment where glaciers terminate against ice-dammed bodies of water.

Glacial drifts perched alongside outlet glaciers that drain through the Transantarctic Mountains constrain inland polar plateau ice elevations. The Taylor Glacier, which heads in the Taylor Dome (a peripheral dome of the East Antarctic Ice Sheet), drains East Antarctic ice into the Dry Valleys sector of Transantarctic Mountains and terminates in central Taylor Valley, about 24 km west of the Ross Sea. Five gravel-rich drifts (including 39 distinct moraine ridges) fringe a lateral lobe of the Taylor Glacier in the lower Arena Valley, Quartermain Mountains, southern Victoria Land. 3He and 10Be exposure age dating (from Brook et al. 1992), together with Arena Valley stratigraphy and soil morphologic data, provide chronologic control for these drifts and constrain maximum Quaternary thickening of the inland Taylor ice dome to less than 160 m. These minor Quaternary expansions of Taylor Glacier were out-of-phase with outlet glaciers that pass through the Transantarctic Mountains and terminate in the Ross Sea north and south of the Dry Valleys region. Textural analyses suggest that drift deposition occurred from cold-based ice, even though Taylor Glacier advances most likely occurred during global interglaciations. The thermal regime of former Taylor Glacier ice lobes, the character of geomorphic features superimposed on individual drifts, the chemical composition of soils developed on Taylor drifts, and the stability of in situ moraine ridges on steep valley walls suggest that the present cold-desert climate in Arena Valley has persisted for at least the last 2.2 Ma.

The deglaciation at the end of the Weichselian in the Danish area has previously been considered to occur as a frontal wastage. Since the glacier ice was assumed to be debris-free, the wasting should be characterized by outwash plains and successions of end-moraines. The almost complete lack of sandur plains in the eastern part of the area and indications from recent investigations of widespread occurrence of flow till justify a re-evaluation of the mentioned deglaciation model. Two morphological features have a general occurrence: the plains and the ‘tunnel’ valleys. The plains appear stepwise in the landscapes, and are frequently limited by steep slopes. Topmost is a subcircular kame-like hill. Sedimentologically, the plains mainly consist of melt water deposits, and the scattered occurrences of till are interpreted as flow till. The plains continue from the open landscape into the ‘tunnel’ valleys where they appear as terraces. These features are considered to have been formed during the deglaciation. The almost horizontal surface of the ice sheet over large areas caused a sensitivity to changes in the climate. The wasting of the ice may therefore be expected to affect large areas almost simultaneously. On the assumption that the ice contained debris, an increasing amount of clastic matter was released on the ice surface. This material was concentrated in the depressions. If such a depression perforated the ice, the content of sediments settled on the substratum and a plain was established. During continued wasting the thickness of the ice decreased and the depressions were enlarged. They assumed the character of sandur plains. As still larger areas of these supraglacial sandurs rested on the basement the successive lower situated plains were formed. The latest ice was preserved where the ‘tunnel’ valleys are situated to-day.

Detailed field mapping of different lateral phenomena, striae, texture and till fabric forms the basis of a reconstruction of five deglaciation phases in the east Jotunheimen-Gudbrandsdalen area, a land scape with moderate relief in the vicinity of the ice divide. During wastage, the inland ice sheet separated into several ice lobes situated in valleys enclosed by large ice-free uplands. The slope of the ice surface varied with local changes in the ice movement pattern and with the breaking of ice dams, which caused reversal of drainage from ice-dammed lakes. Non-climatic, large margianl moraines are thought to have fomed as a result of locally increased steepness of the ice surface. By tracing the deglaciation phases through two different valley systems which converge in the lake Mjosa area, deglaciation events in the ice divide zone are correlated with marginal deposits at the front of the ice lobes.

Evidence for former fast glacier flow (ice streaming) in the southwest Laurentide Ice Sheet is identified on the basis of regional glacial geomorphology and sedimentology, highlighting the depositional processes associated with the margin of a terrestrial terminating ice stream. Preliminary mapping from a digital elevation model of Alberta identifies corridors of smoothed topography and corridor-parallel streamlined landforms (megaflutes to mega-lineations) that display high levels of spatial coherency. Ridges that lie transverse to the dominant streamlining patterns are interpreted as: (a) series of minor recessional push moraines; (b) thrust block moraines or composite ridges/hill–hole pairs constructed during readvances/surges; and (c) overridden moraines (cupola hills), apparently of thrust origin. Together these landforms demarcate the beds and margins of former fast ice flow trunks or ice streams that terminated as lobate forms. Localised cross-cutting and/or misalignment of flow sets indicates temporal separation and the overprinting of ice streams/lobes. The fast-flow tracks are separated by areas of interlobate or inter-stream terrain in which moraines have been constructed at the margins of neighbouring (competing) ice streams/outlet glaciers; this inter-stream terrain was covered by more sluggish, non-streaming ice during full glacial conditions. Thin tills at the centres of the fast-flow corridors, in many places unconformably overlying stratified sediments, suggest that widespread till deformation may have been subordinate to basal sliding in driving fast ice flow but the general thickening of tills towards the lobate terminal margins of ice streams/outlet glaciers is consistent with subglacial deformation theory. In this area of relatively low relief we speculate that fast glacier flow or streaming was highly dynamic and transitory, sometimes with fast-flowing trunks topographically fixed in their onset zones and with the terminus migrating laterally. The occurrence of minor push moraines and flutings and associated landforms, because of their similarity to modern active temperate glacial landsystems, are interpreted as indicative of ice lobe marginal oscillations, possibly in response to seasonal climatic forcing, in locations where meltwater was more effectively drained from the glacier bed. Further north, the occurrence of surging glacier landsystems suggests that persistent fast glacier flow gave way to more transitory surging, possibly in response to the decreasing size of ice reservoir areas in dispersal centres and also locally facilitated by ice-bed decoupling and drawdown initiated by the development of ice-dammed lakes. Copyright © 2008 John Wiley & Sons, Ltd.

We describe field measurements (ground-penetrating radar (GPR), geodetic survey and ice-core drilling) to provide new information on the movement mechanism and internal structure of a polar rock glacier on James Ross Island, Antarctic Peninsula. We collected GPR data along longitudinal and transverse profiles. The longitudinal GPR profiles identify inter-bedded debris-rich layers that dip up-glacier, similar to the thrust structures in the compression zone of a valley glacier. The transverse GPR profiles indicate a syncline structure inclined towards the central part of the rock glacier, resembling the transverse foliation of a valley glacier. The stratigraphy of two boreholes shows that the rock glacier consists primarily of bubbly ice with thin debris-rich layers, an internal structure similar to the ‘nested spoons’ structure common in the interior of valley glaciers. These results indicate that the glacier motion is controlled by shear movement, common in valley glaciers. The geodetic survey confirms that flow velocities decrease towards the lower part of the rock glacier. Such heterogeneous movement causes longitudinal compression and forms thrusts which then create the debris-rich layer by uplifting basal ice and debris. Pushing of the upstream ice against the downstream ice bends the surface layers, forming transverse ridges on the rock glacier surface.

During 2000–07, five giant icebergs (B15A, B15J, B15K, C16 and C25) adrift in the southwestern Ross Sea, Antarctica, were instrumented with global positioning system (GPS) receivers and other instruments to monitor their behavior in the near-coastal environment. The measurements show that collision processes can strongly influence iceberg behavior and delay their progress in drifting to the open ocean. Collisions appear to have been a dominant control on the movement of B15A, the largest of the icebergs, during the 4-year period it gyrated within the limited confines of Ross Island, the fixed Ross Ice Shelf and grounded C16. Iceberg interactions in the near-coastal regime are largely driven by ocean tidal effects which determine the magnitude of forces generated during collision and break-up events. Estimates of forces derived from the observed drift trajectories during the iceberg-collisioninduced calving of iceberg C19 from the Ross Ice Shelf, during the iceberg-induced break-off of the tip of the Drygalski Ice Tongue and the break-up of B15A provide a crude estimate of the stress scale involved in iceberg calving. Considering the total area the vertical face of new rifts created in the calving or break-up process, and not accounting for local stress amplification near rift tips, this estimated stress scale is 104 Pa.

In the Schiantala Valley of the Maritime Alps, the relationship between a till-like body and a contiguous rock glacier has been analyzed using geomorphologic, geoelectric and ice-petrographic methodologies. DC resistivity tomographies undertaken in the till and in the rock glacier show the presence of buried massive ice and ice-rich sediments, respectively. Ice samples from a massive ice outcrop show spherical gas inclusions and equidimensional ice crystals that are randomly orientated, confirming the typical petrographic characteristics of sedimentary ice. The rock glacier formation began after a phase of glacier expansion about 2550"50 14C yr BP. Further ice advance during the Little Ice Age (LIA) overrode the rock glacier root and caused partial shrinkage of the pre-existing permafrost. Finally, during the 19th and 20th centuries, the glacial surface became totally debris covered. Geomorphological and geophysical methods combined with analyses of ice structure and fabric can effectively interpret the genesis of landforms in an environment where glaciers and permafrost interact. Ice petrography proved especially useful for differentiating ice of past glaciers versus ice formed under permafrost conditions. These two mechanisms of ice formation are common in the Maritime Alps where many sites of modern rock glaciers were formerly occupied by LIA glaciers.

Ice exposed in ablation zones of ice sheets can be a valuable source of samples for paleoclimate studies and information about long-term ice dynamics. We report a 28-km long stable isotope sampling transect along a flowline on lower Taylor Glacier, Antarctica, and show that ice from the last glacial period is exposed here over tens of kilometers. Gas isotope analyses on a small number of samples confirm our age hypothesis. These chronostratigraphic data contain information about past ice dynamics and in particular should be sensitive to the longitudinal strain rate on the north flank of Taylor Dome, averaged over millennia. The imprint of climatic changes on ice dynamics may be discernible in these data.

One of the key elements in reconstructing the palaeoglaciology of the northeastern sector of the Fennoscandian Ice Sheet is the Keiva ice marginal zone (KIZ) along the southern and eastern coast of Kola Peninsula, including the Keiva I and II moraines. From detailed geomorphological mapping of the KIZ, primarily using aerial photographs and satellite images, combined with fieldwork, we observed the following. (1) The moraines display ice contact features on both the Kola side and the White Sea side along its entire length. (2) The Keiva II moraine is sloping along its length from c. 100 m a.s.l. in the west (Varzuga River) to c. 250 m a.s.l. in the east (Ponoy River). (3) The KIZ was partly overrun and fragmented by erosive White Sea-based ice after formation. From these observations we conclude that the KIZ is not a synchronous feature formed along the lateral side of a White Sea-based ice lobe. If it was, the moraines should have a reversed slope. Rather, we interpret it to be time transgressive, formed at a northeastward-migrating junction between a warm-based Fennoscandian Ice Sheet expanding from the west and southwest into the White Sea depression, and a sluggish cold-based ice mass centred over eastern Kola Peninsula. In contrast to earlier reconstructions, we find it unlikely that an ice expansion of this magnitude was a mere re-advance during the deglaciation. Instead, we propose that the KIZ was formed during a major expansion of a Fennoscandian Ice Sheet at a time pre-dating the Last Glacial Maximum.

Emerging paleoclimate records from proglacial lake Hvitarvatn, central Iceland, suggest that Langjokull ice cap attained its maximum Holocene extent within the last 400 years. With the aim of constructing glaciological models and appropriate model inputs for Holocene simulations of Langjokull, we begin by simulating the evolution of Langjokull through the Little Ice Age to present, a period for which we have some constraint on ice-cap geometry. Using modern measured mass balance distributions (1997–2003) and meteorological data from nearby Hveravellir, we derive a reference precipitation field for the period 1961–1990 over the ice cap. Our simulations suggest Langjokull attained its maximum Little Ice Age volume around 1840 with a second local maximum around 1890. The two outlet glaciers terminating in Hvitarvatn, Nor ð urjokull and Su ð urjokull, advance slowly into the lake, occupying their maximum lake area in the late 19th century, and retreat comparatively rapidly in the mid- to late 20th century. Simulations of Nor ð urjokull are much more faithful to the geomorphic evidence than are simulations of Su ð urjokull, potentially suggesting a difference in dynamics between these two glaciers. While only 35% of the Hvitarvatn catchment area is ice-covered, meltwater from Langjokull comprises ∼ 70 % of the water input to the lake. Two-thirds of this input from the ice cap is transported as groundwater. Simulated glacier-derived discharge to the lake through the Little Ice Age suggests that a sediment concentration of 1.5 kg m - 3 would have resulted in the transport of 1.5 × 10 11 kg of material to the lake over the last 300 years, comparable to the estimated mass of sediment in the most recently deposited sedimentary unit in the lake.

Advance of part of the margin of the Greenland ice sheet across a proglacial moraine ridge between 1968 and 2002 caused progressive changes in moraine morphology, basal ice formation, debris release, ice-marginal sediment storage, and sediment transfer to the distal proglacial zone. When the ice margin is behind the moraine, most of the sediment released from the glacier is stored close to the ice margin. As the margin advances across the moraine the potential for ice-proximal sediment storage decreases and distal sediment flux is augmented by reactivation of moraine sediment. For six stages of advance associated with distinctive glacial and sedimentary processes we describe the ice margin, the debris-rich basal ice, debris release from the glacier, sediment routing into the proglacial zone, and geomorphic processes on the moraine. The overtopping of a moraine ridge is a significant glaciological, geomorphological and sedimentological threshold in glacier advance, likely to cause a distinctive pulse in distal sediment accumulation rates that should be taken into account when glacial sediments are interpreted to reconstruct glacier fluctuations.

Several debris-covered glaciers occupy tributaries of upper Beacon Valley, Antarctica. Understanding their flow dynamics and ice thickness is important for palaeoclimate studies and for understanding the origins of ancient ice elsewhere in the McMurdo Dry Valleys region. We present the results of several shallow seismic surveys in Mullins Valley, where the largest of these debris-covered glaciers is located. Our results suggest that beneath a thin sublimation till and near-surface horizon of dirty glacier ice, lies relatively pure glacier ice (P-wave velocity ~3700–3800 m s-1), with total thickness estimates of ~90–95 m towards the valley head, and ~40–65 m near the entrance to Beacon Valley, ~2.5 km downglacier. P-wave velocities decrease downvalley, suggesting that the material properties of the ice change with increasing distance from the ice-accumulation zone. These new data are used to calibrate an ice thickness profile for the active portion of the Mullins Valley debris-covered glacier (upper ~3.5 km) and to shed light on the origin and spatial distribution of enclosed debris.

A marine sediment core collected from the Nordenskjold Basin, to the south of the Drygalski Ice Tongue, provides new sedimentological and chronological data for reconstructing the Pleistocene glacial history and palaeoenvironmental evolution of Victoria Land. The core consists of an over consolidated biogenic mud covered with glacial diamicton; Holocene diatomaceous mud lies on top of the sequence. Radiocarbon dates of the acid insoluble organic matter indicate a pre-Last Glacial Maximum age (>24kyr) for the biogenic mud at the base of the sequence. From this we can presume that at least this portion of the western Ross Sea was deglaciated during Marine Isotope Stage 3 and enjoyed open marine conditions. Our results are consistent with recent findings of pre-Holocene raised beaches at Cape Ross and in the Terra Nova Bay area.

Calving of icebergs is an important component of mass loss from the polar ice sheets and glaciers in many parts of the world. Calving rates can increase dramatically in response to increases in velocity and/or retreat of the glacier margin, with important implications for sea level change. Despite their importance, calving and related dynamic processes are poorly represented in the current generation of ice sheet models. This is largely because understanding the ‘calving problem’ involves several other long-standing problems in glaciology, combined with the difficulties and dangers of field data collection. In this paper, we systematically review different aspects of the calving problem, and outline a new framework for representing calving processes in ice sheet models. We define a hierarchy of calving processes, to distinguish those that exert a fundamental control on the position of the ice margin from more localised processes responsible for individual calving events. The first-order control on calving is the strain rate arising from spatial variations in velocity (particularly sliding speed), which determines the location and depth of surface crevasses. Superimposed on this first-order process are second-order processes that can further erode the ice margin. These include: fracture propagation in response to local stress imbalances in the immediate vicinity of the glacier front; undercutting of the glacier terminus by melting at or below the waterline; and bending at the junction between grounded and buoyant parts of an ice tongue. Calving of projecting, submerged ‘ice feet’ can be regarded as a third-order process, because it is paced by first- or second-order calving above the waterline. First-order calving can be represented in glacier models using a calving criterion based on crevasse depth, which is a function of longitudinal strain rate. Modelling changes in terminus position and calving rates thus reduces to the problem of determining the ice geometry and velocity distribution. Realistic solutions to the problem of modelling ice flow therefore depend critically on an appropriate choice of sliding law. Models that assume that basal velocities are controlled by basal drag can replicate much of the observed behaviour of calving glaciers with grounded termini, but an important limitation is that they cannot be used to model floating glacier termini or ice shelves. Alternative sliding laws that parameterise drag from the glacier margins provide more flexible and robust ways of representing calving in ice sheet models. Such models can explain a remarkable range of observed phenomena within a simple, unifying framework, including: downglacier increases in velocity and strain rates where basal and/or lateral drag diminishes; flow acceleration in response to thinning through time; the tendency for glaciers to stabilise at ‘pinning points’ in relatively shallow water or fjord narrowings; the constraints on ice shelf stability; and the contrasts in calving rates between tidewater and freshwater calving glaciers. Many unresolved issues remain, however, including the role played by the removal of backstress in the acceleration of retreating calving glaciers, and the controls on melting at and below the waterline.

Basal water pressure and water flow patterns are significant factors in controlling the behavior of an ice sheet, because they influence ice-sheet thickness, stability and extent. Water produced by basal melting may infiltrate the subsurface, or occur as sheet or channelized flow at the ice/bed interface. We examine subglacial groundwater conditions along a flowline of the Scandinavian ice sheet through Nordfjord, in the western fjords region of southern Norway, using a steady-state, twodimensional groundwater-flow model. Meltwater input to the groundwater model is calculated by a two-dimensional, time-dependent, thermomechanically coupled ice-flow model oriented along the same flowline. Model results show that the subglacial sediments could not have transmitted all the meltwater out of the fjord during times of ice advance and when the ice sheet was at its maximum position at the edge of the continental shelf. In order for pore-water pressures to remain below the overburden pressure of the overlying ice, other paths of subglacial drainage are necessary to remove excess water. During times of retreat, the subglacial aquifer is incapable of transmitting all the meltwater that was probably generated. Pulses of meltwater reaching the bed could explain nonclimatically driven margin readvances during the overall retreat phase.

In the Polish Lowlands, three main ice lobes, referred to as Odra, Vistula and Mazury, formed during the Last Scandinavian Glaciation. These lobes protruded at least several kilometres beyond the main ice margin and it is believed that they represent terminal parts of the ice streams. Applied geostatistical analysis based on numerous geological data has allowed an approximate reconstruction of the Odra ice lobe substratum in the area of northwest Poland and northeast Germany. A spatial representation of the Odra lobe substratum clearly illustrates the adverse slope of the glacier bed, but also indicates areas morphologically prone to ice streaming. It is suggested that the ice took advantage of local topography that enabled advance out of the Baltic basin; consequently, the ice followed a topographic low which, in combination with favourable hydraulic conditions of its substratum, likely initiated ice streaming.

Outlet glaciers grounded on a bed that deepens inland and extends below sea level are potentially vulnerable to ‘marine ice sheet instability’. This instability, which may lead to runaway ice loss, has been simulated in models, but its consequences have not been directly observed in geological records. Here we provide new surface-exposure ages from an outlet of the East Antarctic Ice Sheet that reveal rapid glacier thinning occurred approximately 7,000 years ago, in the absence of large environmental changes. Glacier thinning persisted for more than two and a half centuries, resulting in hundreds of metres of ice loss. Numerical simulations indicate that ice surface drawdown accelerated when the otherwise steadily retreating glacier encountered a bedrock trough. Together, the geological reconstruction and numerical simulations suggest that centennial-scale glacier thinning arose from unstable grounding line retreat. Capturing these instability processes in ice sheet models is important for predicting Antarctica’s future contribution to sea level change., Nature Communications, 6, ISSN:2041-1723

Jakobshavn Isbrae, one of Greenland’s major outlet glaciers, displayed rapid changes since the mid-1990s. Its floating ice tongue broke up around 1997, followed by a rapid calving front retreat over tens of kilometres, possibly linked to a prior warming of the ocean waters adjacent to the fjord. Parallel to this major retreat, a quasi-simultaneous process of acceleration and thinning of the glacier has been observed, currently making it a major contributor to eustatic sea-level rise. However, the causal interplay between the various factors involved has not yet been fully understood. Numerical studies of Jakobshavn Isbrae so far are either 2-D plan view ice flow models with a fixed calving front or 2-D flowline models, which have to parameterize lateral stresses. Hence the interaction between changes in calving front position and ice dynamics could not be studied consistently. To overcome this limitation, we implemented an implicit boundary tracking method in the Ice Sheet System Model (ISSM). This tool allows us to freely evolve the calving front by prescribing a calving rate, the ice front velocity being therefore the sum of ice velocity and calving rate. A suite of sensitivity experiments perturbing an initial steady-state calving rate has been performed to study its impact on the dynamics of the glacier. Our numerical results suggest a high sensitivity of the glacier dynamics to the applied calving rate. Changes in calving rate quickly affect upstream areas of the ice stream through a combination of changes in calving front position, ice velocity, thickness, grounding and ungrounding, and surface gradient change. Consequently, acceleration triggered at the calving front quickly affects the entire drainage basin. Moreover, the model results suggest that the ice stream does not recover from a short duration (about a year) calving rate perturbation over timescales on the order of a century. We present selected results of the sensitivity experiments to support the discussion clarifying the causes of the current changes occurring at this dynamic ice stream.

Hydrometeorological conditions of ice field onshore thrusting and its forms were explored in the Szczecin and Vistula lagoons. Five well-documented cases of ice sheet thrusting to more than 100 m inland are presented. Four cases (March 1, 1976; January 14, 1993; January 28, 2003; and February 1, 2004) were observed in the Szczecin Lagoon, one (February 8, 2011) occurring in the Vistula Lagoon. In both areas, the ice field onshore thrusting was driven mainly by strong winds following a cold front in a deep baric low. The longest thrusts, several to 150-m wide, pushed the ice sheet 140 m inland. Near the shore, the sheets were alternated by ice hummocks. The ice sheet base was usually flanked by elongated, low ice piles. The ice sheet tapered inland, its edges rounding off. The thrust ice sheets were finger, tongue, half-ellipse, or semicircle shaped, and they were distinctly rounded in the frontal part.

Very large volumes of ice break off regularly from Taconnaz hanging glacier, French Alps. During winter, when the snow mantle is unstable, these collapses can trigger very large avalanches that represent a serious threat to inhabited areas below. Photogrammetric measurements have been performed over 1 year to assess the volume and frequency of the largest collapses. Major collapses occur when the glacier reaches a critical geometry. After a major ice collapse, the glacier is in a minimal position and subsequently recharges over 6 months to reach the maximum position again. This critical geometry is a necessary but not sufficient condition for further large collapses. Large collapses do not systematically occur in the maximum position, as ice is often removed by disintegration into small ice blocks. For two major collapses, the volume of ice breaking off has been assessed at ~275 000 m3. Photogrammetric measurements were used to determine an ice flux of 820 000 m3 a–1 through the studied ice stream, in agreement with an assessment based on ice-flow modeling. This ice flux estimation was used to determine the average ice volumes breaking off over surveyed periods.

We investigated the evolution of two major rifts cutting across Mertz Glacier Tongue, East Antarctica, using a combination of satellite images and 60 day sets of GPS data from two stations deployed either side of the western rift in 2007. The eastern rift began to open in the early 1990s, and the western rift initiated in 2002 in conjunction with the collision of a large iceberg with the tongue. Velocity time series derived from the 2007 GPS data exhibited strong variations at tidal periods modulated by sea-surface height and sea-surface slope and reproduced here with a conceptually simple model. We found that opening of the western rift in 2002 leads to a dramatic change in behavior of the tongue as the large range in velocity (700–2400 m a−1) observed in 2000 was largely reduced (1075–1225 m a−1) in 2007. Opening of the western rift decoupled the glacier from the transverse loading on the tongue driven by east–west tidal circulation. This loading previously induced time-varying lateral drag, which caused the large velocity range. Our results suggest changes in the mechanical behavior of an ice tongue impact the dynamics of the outlet glacier system and should be considered in longer-term mass-balance evaluations.

The melting of tidewater outlet glaciers from the Greenland Ice Sheet contributes significantly to global sea level rise. Accelerated mass loss is related to melt-processes in front of calving glaciers, yet the role of ocean heat transports is poorly understood. Here we present the first direct measurements from a subglacial plume in front of a calving tidewater outlet glacier. Surface salinity in the plume corresponded to a meltwater content of 7 %, which is indicative of significant entrainment of warm bottom water and, according to plume model calculations, significant ice melt. Energy balance of the area near the glacier showed that ice melt was mainly due to ocean heat transport and that direct plume-associated melt was only important in periods with high meltwater discharge rates of ~100 m3 s−1. Ocean mixing outside of the plume area was thus the primary heat source for melting glacier ice.

International audience; The Mertz Glacier Polynya off George V Land, East Antarctica, is a source of Adélie Land Bottom Water, which contributes up to B25% of the Antarctic Bottom Water. This major polynya is closely linked to the presence of the Mertz Glacier Tongue that traps pack ice upstream. In 2010, the Mertz Glacier calved a massive iceberg, deeply impacting local sea ice conditions and dense shelf water formation. Here we provide the first detailed 250-year long reconstruction of local sea ice and bottom water conditions. Spectral analysis of the data sets reveals large and abrupt changes in sea surface and bottom water conditions with a B70-year cyclicity, associated with the Mertz Glacier Tongue calving and regrowth dynamics. Geological data and atmospheric reanalysis, however, suggest that sea ice conditions in the polynya were also very sensitive to changes in surface winds in relation to the recent intensification of the Southern Annular Mode.