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Using radio echo sounder, ice thickness of Keqikaer Glacier tongue was measured in 1981 and 2004. Data obtained by comparing topographical maps, aerial and satellite photographs at different times, illustrates changes of the thickness and advance/retreat of Keqikaer Glacier. Keqikaer Glacier has been in intensive retreat since the 1990s and become thinner since the 1980s. Measured thickness of the ice tongue indicates reducing with a speed of 0.5–1.5 m a−1 since 1981. The shrinkage of the glacier terminus is less than 2% of the total length during the last 30 years; however, the retreat of terminus position and the thinning of the ice thickness provides significant information that these glaciers on the south slope of Mt. Tuomuer are in an intensively decreasing phase in recent time.

Thick exposures of debris-rich ice at various Icelandic glaciers are central to the debate over the prevalence of glacial sediment transfer by glaciohydraulic supercooling. We present physical analyses of ice and debris at Kviarjokull, a temperate glacier in southeast Iceland with a terminal glacier-bed overdeepening, where stratified debris-rich ice forms up to metre-thick transverse englacial bands. Our results are not consistent with debris-rich ice formation predominantly by supercooling because: (1) 137Cs was absent from sediment filtered from debris-rich ice; (2) isotopic analysis (δD and δ18O) demonstrated no clear pattern of isotopic enrichment of debris-rich ice with respect to englacial ice; and (3) melt-out debris from debris-rich ice included large striated clasts from both fluvial and basal sources. We support transverse englacial debris-rich ice band formation by the thickening and elevation of basal materials in a region of longitudinally compressive ice flow situated between the reverse slope of the overdeepening and the base of an ice fall. Debris band form and distribution are likely to be controlled by thrusting along transverse englacial foliae associated with the formation of band ogives on the glacier surface.

SUMMARY We report the detection, principally by the French Polynesian seismic network, of hydroacoustic signals generated inside large icebergs, either ‘parked’ along the Wilkes coast of Antarctica in the Indian Ocean, or drifting in the Southern Pacific Ocean between latitudes of 55 ◦ and 65 ◦ S, during the years 2002‐2004. The signals can be classified into two very broad families, based on the nature of their spectra. A first group features prominently monochromatic signals, whose frequency can, however, fluctuate with time during a single sequence of emission (typically lasting a few to a few tens of minutes). Such signals are generally reminiscent of those detected in 2000 in the Ross Sea and are generated principally in the Indian Ocean ‘iceberg parking lot’, between longitudes 144 ◦ E and 156 ◦ E. A new family of signals features a much broader spectrum, superimposed on a number of preferential frequencies suggesting the background activation of a number of resonators; these signals occur both in the parking lot and in the Southern Pacific. Further variations in spectra are documented inside each family. On the basis of similar in situ observations on Ross Sea icebergs under project SOUTHBERG, the first family is generally interpreted as expressing a stick-and-slip process during collisions between large iceberg masses. The second family of signals are observed during exceptional episodes of the otherwise silent drift of the icebergs in the deep Pacific Basin, some of which correlate with their passage over the various fronts defining the oceanographic southern convergence zone. Finally, a most recent episode of activity, generally similar to the above first family, was detected on 2004 December 3‐4, at the ocean entry of the Dibble Ice Tongue, 600 km west of the parking lot along the coast of Antarctica. It is interpreted as resulting from collisions between large drifting icebergs and fragments of the ice tongue calved off during its disintegration, as documented by satellite imagery.

Massive tabular icebergs (∽1000km2surface area, ∽1011 kg mass) arrived in the southwest Ross Sea in early 2001 where they remained relatively immobile for the next 4 years. During the period of their presence, extensive landfast sea ice (fast ice) waxed and waned along the Victoria Land coast, with maximum coverage exceeding typical coverage prior to the arrival of the icebergs by a factor of 5. The purposes of this study are to determine (1) whether the extensive ‘iceberg blockade’ extending from Ross Island to Drygalski Ice Tongue was indeed, as intuition suggests, responsible for the unusual fast-ice conditions, and (2) how storm frequency, intensity and seasonal timing may have mitigated the effects of the icebergs. Our simple analysis of glaciological and atmospheric conditions observed during 2001–05 suggests that iceberg movement alone is not sufficient to explain fast-ice variability; and, in fact, it is the detailed interplay between storms and iceberg location that determine this variability.

1990年代後半から2005年までの間,南極リュツォ・ホルム湾では沿岸定着氷の崩壊・流出が頻繁に観測されている.南極沿岸海氷の変動特性を把握するために,同湾で生じる海氷流出の履歴に着目して衛星画像を解析した.その結果,流出発生の有無,つまり海氷の安定/不安定は数年間ずつ続いていること,それらの発現時期は海氷上積雪深や地上気温・風系の年々変化の傾向と符合していることが見出された.また,同湾南端に流れ込む白瀬氷河の浮氷舌の動態を加えて,過去50年間の沿岸定着氷の変動を推定したところ,1980年代初期以降の約25年間は不安定で,それ以前に長期間続いた安定な氷状と顕著に異なることがわかった.南極リュツォ・ホルム湾の沿岸定着氷の変動を解析した結果,以下のことがわかった.

Ice-marginal Hidden Creek Lake, Alaska, USA, outbursts annually over the course of 2–3 days. As the lake fills, survey targets on the surface of the ‘ice dam’ (the glacier adjacent to the lake) move obliquely to the ice margin and rise substantially. As the lake drains, ice motion speeds up, becomes nearly perpendicular to the face of the ice dam, and the ice surface drops. Vertical movement of the ice dam probably reflects growth and decay of a wedge of water beneath the ice dam, in line with established ideas about jökulhlaup mechanics. However, the distribution of vertical ice movement, with a narrow (50–100 m wide) zone where the uplift rate decreases by 90%, cannot be explained by invoking flexure of the ice dam in a fashion analogous to tidal flexure of a floating glacier tongue or ice shelf. Rather, the zone of large uplift-rate gradient is a fault zone: ice-dam deformation is dominated by movement along high-angle faults that cut the ice dam through its entire thickness, with the sense of fault slip reversing as the lake drains. Survey targets spanning the zone of steep uplift gradient move relative to one another in a nearly reversible fashion as the lake fills and drains. The horizontal strain rate also undergoes a reversal across this zone, being compressional as the lake fills, but extensional as the lake drains. Frictional resistance to fault-block motion probably accounts for the fact that lake level falls measurably before the onset of accelerated horizontal motion and vertical downdrop. As the overall fault pattern is the same from year to year, even though ice is lost by calving, the faults must be regularly regenerated, probably by linkage of surface and bottom crevasses as ice is advected toward the lake basin.

The history of Lake Vostok, the huge East Antarctic subglacial lake, is critical to the unique biota expected in this extreme environment. One theory is that the lake existed prior to the mid-Miocene glaciation of the continent at around 15 million years ago, survived the subsequent period of ice growth intact, and then remained relatively stable beneath its thick ice cover to the present day. The alternative is that the lake was formed by subglacial water flow into an existing and/or glacially eroded trough after the ice sheet reached its present configuration. Here, the onset of persistent ice cover in Antarctica is reviewed and a simple model for continental ice growth discussed. This information is used to argue against the preglacial origin of subglacial lakes. Lake Vostok is large because ice flows essentially perpendicular to the trough’s long axis, permitting the slopes of the ice surface and the ice-water interface to be low. During the onset of glaciation ice flow across Lake Vostok would have been more akin to flow across an ice marginal trough such as the Astrolabe Subglacial Basin, which holds the thickest ice in Antarctica: 4776 m where the bed is over 2 km below the sea level. Hence, regardless of whether Lake Vostok was a lake prior to glaciation, its trough is likely to have been occupied by grounded ice during the period of ice growth. Although the lake is stable today, its size and extent will be affected by ice sheet changes that occur over glacial-interglacial cycles. Such changes are reviewed and the potential consequences for the lake’s volume are discussed.

The surface velocity field of Devon Ice Cap, Nunavut, Canada, was mapped using interferometric synthetic aperture radar (InSAR). Ascending European Remote-sensing Satellite 1 and 2 (ERS-1/-2) tandem mode data were used for the western and southeast sectors, and 3 day repeat pass ERS-1 imagery for the northeast sector. Speckle-tracking procedures were used with RADARSAT 1 imagery to obtain surface velocities over the terminus of Belcher Glacier (a major calving front) where decorrelation between ERS data occurred. The InSAR data highlight a significant contrast in ice-flow dynamics between the east and west sides of the ice cap. Ice movement west of the main north–south divide is dominated by relatively uniform ‘sheet’ flow, but three fast-flowing outlet glaciers that extend 14–23km beyond the ice-cap margin also drain this region. Several outlet glaciers that extend up to 60 km inland from the eastern margin drain the eastern side of the ice cap. The dominant ice-flow regimes were classified based on the relationship between the driving stress (averaged over a length scale of ten ice thicknesses) and the ratio of surface velocity to ice thickness. The mapped distribution of flow regimes appears to depict the spatial extent of basal sliding across the ice cap. This is supported by a close relationship between the occurrence of flow stripes on the ice surface and flow regimes where basal sliding was found to be an important component of the glacier motion. Iceberg calving rates were computed using measured surface velocities and ice thicknesses derived from airborne radio-echo sounding. The volume of ice calved between 1960 and 1999 was estimated to be 20.5 ± 4.7 km3 (or 0.57 km3 a–1). Approximately 89% of this loss occurred along the eastern margin. The largest single source is Belcher Glacier, which accounts for ~50% of the total amount of ice calved.

We present results of a detailed investigation of surface motion across the tongue of a polythermal glacier, midre Lovenbreen, Svalbard, during the 1999 summer. Surface velocities in the warm-based upper tongue increased during periods of enhanced surface melting and rainfall events, and force-balance analysis indicates that these velocity variations were locally forced, probably by fluctuations in subglacial water pressure. Surface speed-ups were also observed on the cold-based lower tongue (which acted as a sticky spot, through which there was minimal subglacial drainage for most of the summer), but these were largely non-locally forced by longitudinal coupling to the faster-moving ice up-glacier. On one occasion, however, a large, rapid input of surface water to the glacier reduced the basal drag beneath the cold-based lower tongue, presumably due to hydraulic jacking. This resulted in locally forced enhanced surface velocities across the entire tongue, accompanied by a breaching of the lower tongue and an outburst of subglacially stored water.

Ice-dammed Hidden Creek Lake, Alaska, USA, outbursts annually in about 2–3 days. As the lake fills, a wedge of water penetrates beneath the glacier, and the surface of this ‘ice dam’ rises; the surface then falls as the lake drains. Detailed optical surveying of the glacier near the lake allows characterization of ice-dam deformation. Surface uplift rate is close to the rate of lake-level rise within about 400 m of the lake, then decreases by 90% over about 100 m. Such a steep gradient in uplift rate cannot be explained in terms of ice-dam flexure. Moreover, survey targets spanning the zone of steep uplift gradient move relative to one another in a nearly reversible fashion as the lake fills and drains. Evidently, the zone of steep uplift gradient is a fault zone, with the faults penetrating the entire thickness of the ice dam. Fault motion is in a reverse sense as the lake fills, but in a normal sense as the lake drains. As the overall fault pattern is the same from year to year, even though ice is lost by calving, the faults must be regularly regenerated, probably by linkage of surface and bottom crevasses as ice is advected toward the lake basin.

A mass balance calculation was made for the floating part of Byrd Glacier, using 1978–79 ice elevation and velocity data, over the 45 km of Byrd Glacier from its grounding line to where it leaves its fjord and merges with the Ross Ice Shelf. Smoothed basal melting rates were relatively uniform over this distance and averaged 12 ± 2 m yr−1.

The late Holocene retreat of the West Antarctic ice sheet is crucial information for assessing its current dynamics. However, data from this period for parts of the ice sheet where significant change has taken place, mainly the Ross Sea, are very sparse. Some significant dated deposits are from lakes dammed by valley glaciers, themselves dammed by the Ross Ice Sheet. The least age of these deposits is somewhat later than the retreat of the Ross Ice Sheet from the locality on account of the lagged response of the glacier. We present a model of the Hatherton Glacier, which examines its relationship to the Ross ice sheet, using dated margin data from ice-dammed lakes. Problems in modelling are the coupling with the Darwin Glacier, the unknown bed topography and the poorly known surface mass balance, which include blue ice areas. We infer the bed topography by tuning a valley glacier model, and use this model to (i) estimate the thickness of the Last Glacial Maximum (LGM) Ross Ice Sheet; and (ii) estimate the response time of the Hatherton Glacier to changes in the Ross Sea ice sheet. The best fit of the glacier surface profile to the geological data occur if the LGM Ross Ice Sheet elevation is assumed to be 800 m higher than the present-day ice shelf surface. If the decay of the Ross Ice sheet is linear with time, the response time is of the order of several centuries. Step changes in the elevation of the Ross Ice Sheet lead to a response time around one thousand years. The dated deposits in the Hatherton Valley cannot be used directly as dates of Ross Ice Sheet grounding line retreat.

Marine sediment cores were obtained from in front of the tidewater glaciers in Marian and Potter coves in the South Shetland Islands in the austral summer of 1998–1999. Sedimentological and geochemical data from these cores document an advance of ice tongue for the deposition of clast-supported, massive diamicton, interpreted as having been produced by ice rafting in front of glacier margin and/or releasing of clasts from basal debris zones in the sub-ice tongue setting. A C-14 chronology for a core indicates that glacial advance took place ca. 1450–1700 yrs B.P., coincident with warm, humid phase in the study area. During this period, the glacier margin was likely to advance and release diamicton clasts, inferred from a reduction in the total organic carbon content, and an increase in sand and clasts within the diamicton facies. The glacial advance probably caused enhanced ice-edge blooms near the core sites, resulting in increased abundance of sea-ice related diatoms i.e.,Fragilariopsis curta andFragilariopsis cylindrus in the diamicton. The warm and humid conditions between 1450–1700 yrs B.P. might allow the intrusion of warm circumpolar deep water within the fjords, bringing about increased abundance of warm water form, i.e.,Fragilariposis kerguelensis. On the other hands, this warming condition probably prohibited the intrusion of Weddell Ice shelf water from the fjord, as evidenced by lack of cold water form,Thalassiosira antarctica, in the diamicton. Clearly, the response of the outlet glacier system along the periphery of the South Shetland Islands Ice Sheet during the late Holocene warm, humid period (1450–1700 yrs B.P.) was expansion. Thus the process of clast-supported massive diamicton formation is likely to be applicable to a number of areas of the modern and Quaternary Antarctic Peninsula.

Geomorphological and Quaternarygeological field- and laboratory data (Fig.1) are introduced and interpreted with regard to the maximum Ice Age (LGM) glaciation of the Central-and South Karakoram in the Braldu-, Basna-, Shigar-and Indus valley system as well as on the Deosai plateau between the Skardu Basin and the Astor valley (Fig.2). These data result from two research expeditions in the years 1997 and 2000. They show that between c. 60 and 20 Ka the Central Karakorum and its south slope were covered by a continuous c. 125,000 km2 sized ice stream network. This ice stream network flowed together to a joint parent glacier, the Indus glacier. The tongue end of the Indus glacier reached down to 850 ∼ 800 m a.s.l. In its centre the surface of this Indus ice stream network reached a height of a good 6000 m. Its most important ice thicknesses amounted to c. 2400 ∼ 2900 m.

This paper shows the results of chemical and crystallographic analyses carried out on a core drilled within the frontal pan of the Foscagno rock glacier in the Italian Alps. We use 58 vertical thin sections spaced along the massive ice core, found between depths of 2.5 and 7.65 m, to describe the ice fabric of the core. We also discuss the results of chemical analyses of more than 50 samples. The lower part of the massive ice core between 4 and 7.65 In shows a mean crystal size of 1.5 cm and a crystal shape predominantly elongated along the horizontal plane with c-axes. These characteristics are similar to those of firn ice. In contrast, the upper core between 2.5 and 4 m displays vertical elongation of large bubbles, indicating superimposed ice and the influence of melting and refreezing processes. The presence of a seasonal signal in sulfate distribution and the strong correlation between sodium and chloride in the lower part of the core confirm cold firnification without appreciable phase changes. This well-preserved glacier ice body is probably younger than 2200 +/- 60 yr B.P., a minimum age for the rock glacier as indicated by the C-14 age of a buried paleosoil, although the possibility that it may be older age cannot be excluded. The glacier ice body seems to be a relict of a former glacier preserved within a larger permafrost body that characterizes almost all of the rock glacier and also occurs beneath the massive ice. This finding points out that different types of ice can be preserved within a single rock glacier, reflecting a complex geological and paleoclimatic history.

Airborne radio-echo sounding investigations in the upper reaches of Bailey Ice Stream and Slessor Glacier, Coats Land, East Antarctica, have shown that enhanced-flow tributaries are associated with well-defined areas of relatively thicker ice, and are separated from each other by areas of relatively thinner ice. A numerical modelling study has revealed that while internal ice deformation might account for all the observed flow in inter-tributary areas and the majority in the Slessor tributaries, a significant proportion of the flow of Bailey tributary is attributable to basal motion. Further, investigations of depth-corrected basal reflection power indicate that the bed underlying both Bailey and Slessor enhanced-flow tributaries is significantly smoother than in the slower-moving inter-tributary areas. It is thus proposed that enhanced motion within Bailey tributary (and also perhaps Slessor) may be facilitated by a reduction in basal roughness, caused by the accumulation of water and/or sediments within subglacial valleys, or by the erosion and smoothing of bed obstacles.

Observations between 1997 and 2001, of a 30% velocity increase and up to 60 m thinning of downstream parts of Jakobshavn Isbræ, Greenland, immediately following calving of about 4 km of its 15 km floating ice tongue, suggest that acceleration may have been initiated by the calving. Assuming that the force perturbation associated with such weakening is swiftly transmitted far up-glacier, I develop equations to estimate the perturbation. Initially, the observed changes are consistent with the comparatively small perturbation associated with the calving. Thereafter, it was probably sustained by thinning of the remaining ice tongue at rates of about 80 ma–1. Otherwise, the force perturbation would soon have been balanced by reduction in the hydrostatic driving force for longitudinal creep as the glacier thinned, with velocities dropping to their former values. The calculated force perturbation increases to a maximum about 10 km inland of the grounding line, consistent with decreasing weight forces as the glacier thins over bedrock that slopes uphill seawards. Further inland, it progressively decreases, probably because marginal drag increased as the glacier accelerated. Both here and on the floating tongue, marginal ice appears to have been softened by the influence of locally intense shear on ice temperature and/or fabric. More recent observations show continued acceleration and thinning, and most of the remaining ice tongue calved away in April 2003, so thinning is likely to continue.

Mertz Glacier, East Antarctica, is characterized by a 140 km long, 25 km wide floating ice tongue. In this paper, we combine a large number of remotely sensed datasets, including in situ global positioning system measurements, satellite radar altimetry, airborne radio-echo sounding and satellite synthetic aperture radar imagery and interferometry. These various datasets allow us to study the interaction of the ice tongue with the tides and currents. However, the inverse barometer effect needs to be applied to sea-level variations affecting the tongue. We find that the tide-induced currents exert a small lateral pressure on the tongue which, when integrated over the large surface of the tongue, induce a flexure of up to 2 m amplitude per day. Simple elastic modelling of the flexure confirms the observations and helps validate the boundary conditions necessary to explain different eastward and westward tongue deflections. In addition, the along-flow velocity of the tongue does vary daily from 1.9 to 6.8 md-1 depending on the tidal current. When the current pushes the tongue toward the eastern boundary of the fjord, the tongue is retarded by the drag and the velocity decreases. The accumulated stress is released, allowing the tongue to flow very rapidly when the current pushes the tongue westward. These forcing and boundary conditions on the floating ice flow are important and must be taken into account when studying glacier discharge and calving.

The upper 20—30 m of ice-rich permafrost at three sites overridden by the northwest margin of the Laurentide ice sheet in the Tuktoyaktuk Coastlands, western Arctic Canada, comprise massive ice beneath ice-rich diamicton or sandy silt. The diamicton and silt contain (1) truncated ice blocks up to 15 m long, (2) sand lenses and layers, (3) ice veins dipping at 20—30°, (4) ice lenses adjacent and parallel to sedimentary contacts, and (5) ice wedges. The massive ice is interpreted as intrasedimental or buried basal glacier ice, and the diamicton and silt as glacitectonite that has never thawed. Deformation of frozen ground was mainly ductile in character. Deformation was accompanied by sub-marginal erosion of permafrost, which formed an angular unconformity along the top of the massive ice and supplied ice clasts and sand bodies to the overlying glacitectonite. After deformation and erosion ceased, postglacial segregated ice and ice- wedge ice developed within the deformed permafrost.

The huge cavities beneath floating Antarctic ice shelves have only been explored recently by autonomous underwater vehicles (AUVs). Oceanic waters above the in situ freezing point melt those faces of marine-terminating glaciers and ice shelves with which they come into contact. This, in turn, impacts the dynamics of ice sheets as the reduction in buttressing allows the ice to flow faster into the ocean, increasing their contribution to eustatic sea-level rise (Shepherd et al. 2012). Pine Island Glacier (PIG) in West Antarctica (Fig. 1a, d) is an example, and has been accelerating and thinning over past decades, and still appears to be in retreat. This is driven by unpinning from a seabed ridge and exposure to high ocean temperatures of up to 1°C at the grounding line (Jenkins et al. 2010) that are subject to climatically forced variability (Dutrieux et al. 2014 a ). Fig. 1. ( a ) Surface elevation of Pine Island Glacier ice shelf (colour) (Dutrieux et al. 2013) overlays a Moderate Resolution Imaging Spectroradiometer image obtained on 28 December 2008. Thick black line shows the boundary between floating and grounded ice …

Byrd Glacier has one of the largest ice catchment areas in Antarctica, delivers more ice to the Ross Ice Shelf than any other ice stream, and is the fastest of these ice streams. A force balance, combined with a mass balance, demonstrates that stream flow in Byrd Glacier is transitional from sheet flow in East Antarctica to shelf flow in the Ross Ice Shelf. The longitudinal pulling stress, calculated along an ice flowband from the force balance, is linked to variations of ice thickness, to the ratio of the basal water pressure to the ice overburden pressure where Byrd Glacier is grounded, and is reduced by an ice-shelf buttressing stress where Byrd Glacier is floating. Longitudinal tension peaks at pressure-ratio maxima in grounded ice and close to minima in the ratio of the pulling stress to the buttressing stress in floating ice. The longitudinal spacing of these tension peaks is rather uniform and, for grounded ice, the peaks occur at maxima in surface slope that have no clear relation to the bed slope. This implies that the maxima in surface slope constitute a “wave train” that is related to regular variations in ice-bed coupling, not primarily to bed topography. It is unclear whether these surface “waves” are “standing waves” or are migrating either upslope or downslope, possibly causing the grounding line to either retreat or advance. Deciding which is the case will require obtaining bed topography in the map plane, a new map of surface topography, and more sophisticated modeling that includes ice flow linked to subglacial hydrology in the map plane.

Storglaciaren is a 3.2 km long polythermal valley glacier in northern Sweden. Since 1994 a number of small (1–2 m high) transverse debris‐charged ridges have emerged at the ice surface in the termi...

Geo-electrical resistivity surveys have been carried out at recently deglaciated sites in front of three glaciers in southern Iceland: Skeiðarajokull, Hrutarjokull, and Virkisjokull. The results show the presence of old glacier ice beneath debris mantles of various thickness. We conclude that buried glacier ice has survived for at least 50 years at Virkisjokull and Hrutarjokull, and probably for over 200 years at Skeiðarajokull. Additional data from a further site have identified a discontinuous ice core within 18th-century jokulhlaup deposits. Photographic and lichenometric evidence show that the overlying debris has been relatively stable, and hence melting of the ice at all four sites is proceeding slowly due to the heat-shielding properties of the overburden. The geomorphic implications are pertinent when considering the potential longevity of buried ice. The possible implications for dating techniques, such as lichenometry, radiocarbon dating and cosmogenic surface-exposure dating are also important, as long-term readjustments of surface forms may lead to dating inaccuracy. Finally, it is recognised that landscape development in areas of stagnant ice topography may post-date initial deglaciation by a considerable degree.

This paper describes a major calving of the Ninnis Glacier tongue in January 2000. This event, which took 10 years to complete, produced a major change in the George V Land coastline and a large iceberg (∼800 km2). By grounding or becoming “locked in” by fast ice, bergs produced locally and drifting in from afar reside for long periods (10–20 years) in the region ∼146 to 154°E to have a profound impact on sea ice distribution, both locally and 100s of kilometres up- and downstream. They are responsible for the formation of a lens of thick perennial ice to the east (∼14 000 km2 in area), and polynyas. Iceberg movement is sporadic, with intermittent ungroundings of large bergs occurring every 5–13 years. “Escaping” bergs have a temporary impact on the Mertz Glacier polynya to the west. Although public attention focuses on vast bergs, assemblages of small bergs appear to be equally important in terms of their impact on regional fast and pack ice distribution. Possible global change scenarios are discussed. The need for field observations and improved bathymetric and oceanographic data is emphasized.

In North America, the last (Laurentide) Ice Sheet retreated from much of the Canadian Shield by ‘zonal stagnation’. Masses of dead ice, severed from the main ice sheet by emerging bedrock highs, downwasted in situ within valleys and lake basins and were commonly buried by sediment. Consequently, the flat sediment floors of many valleys and lakes are now pitted by steep-sided, enclosed depressions (kettle basins) that record the melt of stagnant ice blocks and collapse of sediment. At Mazinaw Lake in eastern Ontario, Canada, high-resolution seismic reflection, magnetic and bathymetric surveys, integrated with onland outcrop and hammer seismic investigations, were conducted to identify the types of structural disturbance associated with the formation of kettle basins in glaciolacustrine sediments. Basins formed as a result of ice blocks being trapped within a regionally extensive proglacial lake (Glacial Lake Iroquois ∼12,500 to 11,400 years BP) that flooded eastern Ontario during deglaciation. Kettles occur within a thick (>30 m) succession of parallel, high-frequency acoustic facies consisting of rhythmically laminated (varved?) Iroquois silty-clays. Iroquois strata underlying and surrounding kettle basins show large-scale normal faults, fractures, rotational failures and incoherent chaotically bedded sediment formed by slumping and collapse. Mazinaw Lake lies along part of the Ottawa Graben and while neotectonic earthquake activity cannot be entirely dismissed, deformation is most likely to have occurred as a result of the rapid melt of buried ice blocks. Seismic data do not fully penetrate the entire basin sediment fill but the structure and topography of bedrock can be inferred from magnetometer data. The location and shape of buried ice masses was closely controlled by the graben-like form of the underlying bedrock surface.

The downwasting of the Weichselian ice sheet in the Klalalven valley and its continuation southwards has been studied. The meltwater drainage below the highest coastline (HCL) on the plain of Lake Vanern took place subglacially causing breaking-up and calving around tunnel mouths in the ice margin. When the ice margin reached into the extension of the Klaralven valley, the drainage pattern changed to lateral. The ice disappeared as a narrow ice tongue later than in the surrounding highland. When the tongue receded northwards it left dead-ice bodies behind, that remained in the valley after the general retreat. Along the tongue and dead-ice bodies glaciofluvial sediments accumulated as kame terraces, deriving from esker trains in tributary valleys. At the mouths of the tributaries, deltas were deposited. Halts in the retreat occurred at a few places marked by thresholds of till. According to the present study the HCL rises northwards, from 180 m a.s.l. at Brattforsheden to 228 m at Holjes 170 km to the north. At halts in the ice recession it dropped a few metres. A tentative dating based on the level of the HCL, the tilt of raised shorelines and the rate of shoreline regression has given the time 10900 to 10360 calibrated years BP for the retreat of the ice margin from Brattforsheden to Holjes.

The Cairngorm Mountain area of Scotland is a classic example of a landscape of selective linear glacial erosion, with sharp contrasts in the intensity of glacial erosion between the deeply incised troughs and valleys and the undulating high plateau. This article examines the Quaternary development of Glen Avon, a 200 m deep glacial trough set within the high plateau of the mountains. Evidence concerning the aggregate basal thermal regimes of the topographically controlled ice streams that formerly developed in this area is reconstructed from the geomorphological record, including bedforms indicative of wet-based, sliding ice and of dry-based ice frozen to its bed. This mapping indicates that basal sliding was not confined exclusively to the troughs but extended towards valley heads and on to parts of the plateau adjacent to troughs. The extent of basal sliding appears to have been greatest beneath pre-Late Devensian ice sheets. Basal ice temperatures are modelled under steady-state conditions for the last ice sheet at c. 18 ka BP. Basal thermal regimes are predicted using a reconstruction of the preglacial relief and for the current topography of the area. Convergent flow of ice through the preglacial valley system appears to have been sufficient to induce basal melting and therefore to initiate valley deepening. This effect is enhanced when the model is run across the present topography. Comparison of results of the geomorphological mapping and the modelling reveals significant differences between the actual and predicted extent of basal sliding outside the main ice stream. The overall conclusion is that many ice streams in mountainous terrain are inherited from the locations of preglacial valleys, which serve to accelerate ice flow and promote frictional heating beneath ice sheets.

Glacial bedform patterns and sediments deposited by the temperate and polythermal Late Devensian ice sheet in north-central Ireland record changes in the processes, location, and magnitude of subglacial meltwater throughout the last full glacial cycle (∼21–14 14C kyear BP). Meltwater characteristics are related directly to basal ice thermal regime and ice dynamics, including ice velocity and shifts in the location of ice centres. Therefore, reconstructed meltwater characteristics may provide insight into wider controls on dynamic ice behaviour. A range of meltwater-related features are present across north-central Ireland. These include tunnel valleys, drumlin leeside sequences, eskers, and boulder lags. Other bedforms including Rogen moraines were modified by meltwater activity along ice streams. Meltwater was stored subglacially in two contrasting regions located beneath or near ice centres in north-central Ireland. (1) The Lough Erne Basin is developed in a lowland depression occupied partly by subglacial Rogen moraine ridges which were formed around the time of the last glacial maximum. Meltwater was stored between Rogen ridge crests and released by hydraulic jacking associated with drumlinisation (∼16.6 14C kyear BP) and ice streaming (∼13.8 14C kyear BP). (2) The Lough Neagh Basin occupies a similar lowland depression and was the location of an ice sheet centre throughout the last glacial cycle. No bedforms are present beneath or immediately surrounding Lough Neagh. A larger, more continuous meltwater lake existed in the Lough Neagh depression, probably sealed by a region of cold-based ice outside lake margins. Water escaped through regional-scale tunnel valleys, particularly the Poyntzpass channel which was active during the Carlingford ice readvance (Killard Stadial, correlated with Heinrich event 1 at ∼14.5 14C kyear BP). Overall, reconstructed subglacial lake characteristics and drainage mechanisms are related closely to basal ice thermal regime and substrate relief (controlling lake geometry), and provide insight into controls on overall ice sheet dynamics.

Lake Vostok, located beneath more than 4 km of ice in the middle of East Antarctica, is a unique subglacial habitat and may contain microorganisms with distinct adaptations to such an extreme environment. Melting and freezing at the base of the ice sheet, which slowly flows across the lake, controls the flux of water, biota and sediment particles through the lake. The influx of thermal energy, however, is limited to contributions from below. Thus the geological origin of Lake Vostok is a critical boundary condition for the subglacial ecosystem. We present the first comprehensive maps of ice surface, ice thickness and subglacial topography around Lake Vostok. The ice flow across the lake and the landscape setting are closely linked to the geological origin of Lake Vostok. Our data show that Lake Vostok is located along a major geological boundary. Magnetic and gravity data are distinct east and west of the lake, as is the roughness of the subglacial topography. The physiographic setting of the lake has important consequences for the ice flow and thus the melting and freezing pattern and the lake’s circulation. Lake Vostok is a tectonically controlled subglacial lake. The tectonic processes provided the space for a unique habitat and recent minor tectonic activity could have the potential to introduce small, but significant amounts of thermal energy into the lake.

Our understanding of Lake Vostok, the huge subglacial lake beneath the East Antarctic Ice Sheet, has improved recently through the identification of key physical and chemical interactions between the ice sheet and the lake. The north of the lake, where the overlying ice sheet is thickest, is characterized by subglacial melting, whereas freezing of lake water occurs in the south, resulting in ∼210 m of ice accretion to the underside of the ice sheet. The accreted ice contains lower concentrations of the impurities normally found in glacier ice, suggesting a net transfer of material from meltwater into the lake. The small numbers of microbes found so far within the accreted ice have DNA profiles similar to those of contemporary surface microbes. Microbiologists expect, however, that Lake Vostok, and other subglacial lakes, will harbour unique species, particularly within the deeper waters and associated sediments. The extreme environments of subglacial lakes are characterized by high pressures, low temperatures, permanent darkness, limited nutrient availability, and oxygen concentrations that are derived from the ice that provides the meltwater. Copyright © 2002 John Wiley & Sons, Ltd.

Patterns of late Midlandian ice retreat in the Tempo Valley, north-central Ireland, are reconstructed from field morphological and sedimentary evidence. Ice retreat stages reflect the splitting up of the regional Omagh Basin ice mass into separate Omagh Basin and Clogher Valley components, and the formation and later drainage of glacial lakes which are controlled by the mutual interactions of these ice masses. The Tempo Valley area illustrates some generic problems in reconstructing ice retreat stages in Ireland, including the historical overemphasis of the presence of end-moraines, the possibility of ice lobe interactions following ice sheet division, and the likelihood of ice stagnation as a major mode of deglaciation.

A series of small moraine ridges in the central Niagara Peninsula, southern Ontario, were investigated in order to understand the impact the retreating Lauren- tide Ice Sheet had on this area of Canada, in terms of the Quaternary sedimentology, stratigraphy and geomorphology. As the ice retreated from the Lake Erie Basin, the area was simultaneously inundated by a series of glacial lakes. The only surface expression of this retreat phase of the ice sheet are suites of small moraine ridges. The morphology, stratigraphy, and sedimentology of these ridges indicates that they were probably formed, over a short period of time, in an ice proximal sub- aqueous environment at the rapidly retreating grounding-line margin of the ice sheet. The sediments reveal a stratigraphy that indicates an association of grounded ice sheet and sub- aqueous marginal conditions., Une série de petites crêtes morainiques situées au centre de la péninsule du Niagara a été étudiée afin de pré-ciser les effets du retrait de l'Inlandsis laurentidien dans cette région, en ce qui a trait à la sédimentologie, la stratigraphie et la géomorphologie du Quaternaire. Pendant le retrait même des glaces du bassin du lac Érié, la région a été inondée par une série de lacs glaciaires. La seule résultante morphologique de cette phase de retrait est l'édification de petites crêtes morainiques. La morphologie, la stratigraphie et la sédimentologie des crêtes montrent qu'elles se sont formées, en peu de temps, dans un milieu subaquatique de proximité glaciaire à la marge de la ligne d'ancrage de l'inlandsis en recul rapide. La stratigraphie des sédiments montre qu'il y a un rapport entre l'inlandsis ancré et les conditions subaquatiques à la marge., Man hat eine Serie kleiner Moränenkämme im Zentrum der Niagara-Halbinsel, Süd-Ontario untersucht, um die Auswirkung, welche der Rückzug der laurentischen Eisdecke auf dieses Gebiet Kanadas hatte, zu verstehen bezüglich der Quartär-Sedimentation, Stratigraphie und Geomorphologie. Während das Eis sich aus dem Lake Erie-Becken zurückzog, wurde das Gebiet gleichzeitig durch eine Serie glazialer Seen überschwemmt. Die einzige Oberflächenspur dieser Rückzugsphase der Eisdecke sind Reihen kleiner Moränenkämme. Die Morphologie, Stratigraphie und Sedimentation dieser Kämme zeigen, dass sie wahrscheinlich in einem kurzen Zeitraum gebildet worden sind, in einer Eis-proximalen subaquatischen Umgebung am Rand der rasch zurückweichenden Verankerungslinie der Eisdecke.

The fast ice flow characteristic of the low-gradient Lake Michigan Lobe of the southern Laurentide Ice Sheet during the last glaciation likely resulted from some combination of subglacial sediment deformation and sliding at the ice-bed interface. Both mechanisms require high basal water pressure relative to overlying ice pressure. To evaluate the basal water pressures of the Lake Michigan Lobe, we used the groundwater model MODFLOW to simulate groundwater flow along a 1040-km-long flow line corresponding to the flow path taken by the ice lobe. Our simulations show that groundwater flow directions and velocities were substantially different than modern conditions. Simulations also indicate that subglacial aquifers were not capable of evacuating the estimated basal meltwater, but that excess water draining through a basal drainage system such as one that may underlie Ice Stream B, West Antarctic Ice Sheet, would prevent basal water pressure from exceeding the ice-overburden pressure. The buried Mahomet bedrock-valley system near the distal end of the Lake Michigan Lobe could have drained enough subglacial water to substantially lower basal water pressure and thus affect the dynamics of the lobe. By draining basal meltwater away from the Lake Michigan Lobe, the buried Mahomet bedrock-valley system may have attenuated the effect of permafrost on basal water pressure. During the Last Glacial Maximum, groundwater-flow patterns and velocities were altered or reversed relative to present conditions.

An extensive terrestrial drainage system, centred on Algae Lake in southern Bunger Hills, is described. The 25-km-long Algae River is the third longest known in Antarctica after Onyx River (Wright Valley, Victoria Land) and Druzhby River (Vestfold Hills, Queen Elizabeth Land). Algae River receives meltwater from the Antarctic ice sheet, Apfel Glacier, and ephemeral and permanent snow banks in the ice-free area of the Bunger Hills. Water flows through a series of epiglacial lakes before reaching the extensive Algae Lake, which in turn has an outlet to Transkriptsii Gulf, a largely fresh-water, tidal epishelf lake connected to the ocean under the Edisto Ice Tongue and Shackleton Ice Shelf. Total flow from Algae Lake was estimated to be greater than 1 x 107m3a-1from data collected in the 1986/87 summer. Some portions of the drainage system that were flowing during the 1946/47,1985/86, 1986/87, 1994/95, 1995/96, and 1998/99 summers were not flowing during the 1999/2000 summer, indicating the variable nature of discharge in the river and emphasising that parts of the drainage network may become disconnected readily.

A 28 year record of lower Pine Island Glacier, West Antarctica, constructed from 15 Landsat images, shows changes at the terminus, grounding zone and both margins. The north margin has expanded 5 km into the adjacent ice shelf in a sustained event that was underway in 1973 and may have begun in 1957. Between 1991 and 1997, this expansion ceased and a new region of rifting was created associated with an ice rise on the glacier’s floating tongue. Changes in the topography of a nearby ice rise are used to deduce an upper-bound estimate of a 134 m thinning of the adjacent ice shelf. On the south margin, widening was limited to 1 km over the observation period and is seen propagating downstream in an intermediate-dated image. New areas of crevassing are also evident in the grounding zone of the glacier. Ice loss by the calving of large tabular bergs vastly exceeds mass loss by calving of many small bergs. These observations are consistent with reported changes of the 1990s and indicate that changes in the flow of Pine Island Glacier have occurred over the full period of satellite observations.

Freshwater produced by the surface melting of ice sheets is commonly discharged into ocean fjords from the bottom of deep fjord-terminating glaciers. The discharge of the freshwater forms upwelling plumes in front of the glacier calving face. This study simulates the meltwater plumes emanated into an unstratified environment using a nonhydrostatic ocean model with an unstructured mesh and subgrid-scale mixing calibrated by comparison to established plume theory. The presence of an ice face reduces the entrainment of seawater into the meltwater plumes, so the plumes remain attached to the ice front, in contrast to previous simple models. Ice melting increases with height above the discharge, also in contrast to some simple models, and the authors speculate that this “overcutting” may contribute to the tendency of icebergs to topple inwards toward the ice face upon calving. The overall melt rate is found to increase with discharge flux only up to a critical value, which depends on the channel size. The melt rate is not a simple function of the subglacial discharge flux, as assumed by many previous studies. For a given discharge flux, the geometry of the plume source also significantly affects the melting, with higher melt rates obtained for a thinner, wider source. In a wider channel, two plumes are emanated near the source and these plumes eventually coalesce. Such merged meltwater plumes ascend faster and increase the maximum melt rate near the center of the channel. The melt rate per unit discharge decreases as the subglacial system becomes more channelized.

Bedrock geometry is an essential boundary condition in ice sheet modelling. The shape of the bedrock on fine scales can influences ice sheet evolution, for example through the formation of pinning points that alter grounding line dynamics. Here we test the sensitivity of the BISICLES adaptive mesh ice sheet model to small amplitude height fluctuations on different spatial scales in the bed rock topography provided by bedmap2 in the catchments of Pine Island Glacier, the Amery Ice Shelf, and a region of East Antarctica including the Denman and Totten Glaciers. We generate an ensemble of bedrock topographies by adding random noise to the bedmap2 data with amplitude determined by the accompanying estimates of bedrock uncertainty. Lower frequency coherent noise, which generates broad spatial scale (over 10s of km) errors in topography with relatively gently slopes, while higher frequency noise has steeper slopes over smaller spatial scales. We find that the small amplitude fluctuations result in only minor changes in the way these glaciers evolve. However, lower frequency noise is more important than higher frequency noise even when the features have the same height amplitudes and the total noise power is maintained. This provides optimism for credible sea level rise estimates with presently achievable densities of thickness measurements. Pine Island Glacier appears to be the most sensitive to errors in bed topography, while Lambert–Amery is stable under the present day observational data uncertainty. Totten–Denman region may undergo a retreat around Totten ice shelf, where the bedrock is lower than the sea level, especially if basal melt rates increase.

We derived tide-corrected ice-flow velocity map (v-map) of Campbell Glacier Tongue (CGT) in East Antarctica from 14 COSMO-SkyMed one-day tandem interferometric SAR image pairs obtained in 2011. Ice-flow velocity was measured to increase from the upper part of Campbell Glacier (∼20 cm day−1) to the seaward edge of CGT (∼67 cm day−1). Ice thinning rate by flux of CGT was obtained by calculating ice flux divergence from the v-map and the ice thickness of 340±18 m estimated by the ICESat GLAS data. Basal melting of CGT was deduced from the ice thickening rate (−6.29±1.37 m a−1), surface mass balance (0.24±0.02 m a−1) and the ice flux divergence. Total amount of ice loss in CGT (330.9±72.0 Mt a−1) is more affected by ice flux divergence (214.6±26.7 Mt a−1) than basal melting (129.2±56.4 Mt a−1).

The Jakobshavn Effect is a series of positive feedback mechanisms that was first observed on Jakobshavn Isbrae, which drains the west-central part of the Greenland Ice Sheet and enters Jakobshavn Isfjord at 69°10'. These mechanisms fall into two categories, reductions of ice-bed coupling beneath an ice stream due to surface meltwater reaching the bed, and reductions in ice-shelf buttressing beyond an ice stream due to disintegration of a laterally confined and locally pinned ice shelf. These uncoupling and unbuttressing mechanisms have recently taken place for Byrd Glacier in Antarctica and Jakobshavn Isbrae in Greenland, respectively. For Byrd Glacier, no surface meltwater reaches the bed. That water is supplied by drainage of two large subglacial lakes where East Antarctic ice converges strongly on Byrd Glacier. Results from modeling both mechanisms are presented here. We find that the Jakobshavn Effect is not active for Byrd Glacier, but is active for Jakobshavn Isbrae, at least for now. Our treatment is holistic in the sense it provides continuity from sheet flow to stream flow to shelf flow. It relies primarily on a force balance, so our results cannot be used to predict long-term behavior of these ice streams. The treatment uses geometrical representations of gravitational and resisting forces that provide a visual understanding of these forces, without involving partial differential equations and continuum mechanics. The Jakobshavn Effect was proposed to facilitate terminations of glaciation cycles during the Quaternary Ice Age by collapsing marine parts of ice sheets. This is unlikely for the Antarctic and Greenland ice sheets, based on our results for Byrd Glacier and Jakobshavn Isbrae, without drastic climate warming in high polar latitudes. Warming would affect other Antarctic ice streams already weakly buttressed or unbuttressed by an ice shelf. Ross Ice Shelf would still protect Byrd Glacier.

The article of record as published may be located at http://dx.doi.org/10.1002/2013JC009070 In situ measurements of flow and stratification in the vicinity of the Erebus Glacier Tongue, a 12 km long floating Antarctic glacier, show the significant influence of the glacier. Three ADCPs (75, 300, and 600 kHz) were deployed close (

The right slope of the High Cismon Valley (Trento Province, Italy), carved into the poly-deformed phyllites of the South Alpine Basement, shows evidence of differential Quaternary slope evolution which highly depends on how the slope intersects the inherited structures. In the study area, the regional schistosity outlines a kilometer-scale NNW–SSE trending fold, with close flanks and an axial plane dipping to the NE. The structure obliquely intersects the NNE–SSW trending slope so that the northern part of the slope follows the upper limb of the fold and the southern sector coincides with the lower limb and the hinge. The secondary axial-plane foliation is typically incipient at the fold flanks, and much more pervasive and fan-shaped near the hinge zone. This foliation, as well as the asymmetric polyharmonic secondary folds, has significant consequences on rock mass mechanical properties and on mechanisms and timing of the gravitational phenomena developed along the slope. In particular the Joint Compressive Strength ( JCS ) and the Geological Strength Index ( GSI ), obtained on stable outcrops outside the deforming area, display a decrease from north to south. This points to a progressive deterioration of the rock mass strength which directly reflects the influence of the pre-existing fabric. The results obtained by the analysis of LiDAR-derived digital elevation model show evidence of two different gravitational movements, located in the northern and southern sectors of the slope respectively. The northern side is characterized by an ongoing deep-seated gravitational slope deformation (DSGSD) likely triggered by post-glacial unloading, derived from the retreat of the ice tongue that filled the Cismon Valley during the Last Glacial Maximum (LGM). Conversely, the southern part of the slope is the expression of a fully evolved pre-LGM gravitational collapse. This heterogeneous behavior of the slope is most likely controlled by the secondary foliation and asymmetric polyharmonic folds, the former being of paramount importance for the release of the mobilized mass at the crown area, and the latter easing or impeding the downslope movement. Although it is widely accepted that the regional foliation is the dominant controlling factor of DSGSDs on poly-deformed and highly foliated metamorphic basement, our work suggests that the secondary foliation, as well as parasitic folds, may also have remarkable effects on slope evolution if favorably oriented and sufficiently pervasive.

The most direct evidence of the areal extent of former glaciers is the distribution of erratic boulders, till, or ice-contact stratified deposits. Often the distribution of glacial landforms such as moraines, ice-contact deltas and fans, and drumlins can be identified from aerial photographs. Features formed by subglacial water such as tunnel channels, eskers, hummocky or pitted sand and gravel, and ice-marginal channels also provide evidence of former ice extent. Scoured bedrock surfaces with striations or other small-scale and large-scale abrasion and plucking marks may, in some areas, be the only evidence of former ice cover. The vertical extent, or thickness of ice, is more difficult to determine. Isostatic rebound can be used to calculate former ice thickness over broad areas and within broad limits. Commonly, the areal extent of former glacier ice is easily determined, but in some places there appears to be no till, very few erratics, deep weathering, and little sign of glacial erosion. In these areas, especially where there is also dispute over former ice thickness, the amount of over-consolidation of preglacial clay, the distribution of cosmogenic dates on boulders and striated bedrock surfaces, and modeling provide clues to former horizontal and vertical extent of glacier ice.

Major ice loss has recently been observed along coastal outlet glaciers of the West Antarctic ice sheet, mainly due to increased melting below the ice shelves. However, the behavior of this marine ice sheet is poorly understood, leading to significant shortcomings in ice-sheet models attempting to predict future sea-level rise. The stability of a marine ice sheet is controlled by the dynamics at the grounding line, the boundary between the grounded ice stream and the floating ice shelf. One of the largest contributors to current sea-level rise is the fast-flowing Thwaites Glacier, which flows into the Amundsen Sea. Here we use an ice-stream/ice-shelf model and perform a number of experiments along a central flowline to analyze the sensitivity of its grounding line on centennial timescales. In the absence of width and buttressing effects, we find that the grounding line retreats by ˜300 km in 200 years from the present day (rate of 1.5 km a–1). With variable glacier width implemented in the model, flow convergence slows the retreat of Thwaites grounding line at 0.3–1.2 km a–1. The parameterization of ice-shelf buttressing according to different observed scenarios further reduces the glacier retreat and can even lead to a slight advance in the most buttressed case.

The sudden breakup of ice shelves is expected to result in significant acceleration of inland glaciers, a process related to the removal of the buttressing effect exerted by the ice shelf on the tributary glaciers. In this paper, this process is analyzed by means of scaled analogue experiments reproducing the flow of a valley glacier draining an ice sheet grounded above sea level into an ice shelf, and analyzing the dynamic perturbations resulting from ice shelf disintegration and removal of buttressing effect. Models show a significant increase in glacier velocity close to its outlet following ice shelf breakup, a transient effect that does not significantly propagate upstream towards the ice sheet and rapidly decays with time. Basal lubrication and variations in ice thickness do not significantly influence the process that thus leaves the ice sheet almost unaffected by flow perturbations.

International audience; Glacier limits are usually mapped according to a spatial discrimination based on color of remote sensing images or aerial photography. What appears like ice (white or light colored areas) at the end of the ablation period (end of summer) corresponds to the glacier, while what appears as rock (dark areas) is identified as the slope. This kind of visual discretization seems to be insufficient in the case of small arctic glaciers. Indeed, the slopes have been described as very unstable parts of glacial basins. Debris are generated by the inclination of the slopes, and reach the glacier surface. Thus, the visible limit does not correspond to the ice extension: a significant amount of ice is potentially covered by rock debris, enlarging the actual glacier surface with respect to the observed area. Hence, we apply Ground Penetrating Radar (GPR) measurements for mapping, beyond the central parts of the glacier, the steep slopes of the Austre Lovénbreen (Spitsbergen, 79° N). The aim is to assess the discrepancy between the limits extracted from remote sensing methods – aerial photography, satellite images and derived digital elevation models – and the GPR data which exhibit significant ice thickness at locations considered outside the glacier itself. The ice is observed to extend typically from 25 to 30 m, and up to 100 m, under the slopes. These measurements allow for a new determination of the rock/ice interface location following criteria beyond the visual and morphological characteristics seen from the surface, as obtained by remote sensing techniques or in-situ observations.

The Odden ice tongue is an ice cover phenomenon in the Greenland Sea that covers all or part of the area of influence of the Jan Mayen Current and that encloses a bay of open water called Nordbukta. The yearly attributes of the spatial distribution of the Odden from 1979 through 1998 have been quantified in terms of average concentration, standard deviation of ice concentrations, persistence, maximum extent, and anomalies in extent, and the results show vastly different formation characteristics and seasonalities during different years. The monthly average extents of the Odden are shown to have a strong negative correlation with monthly surface air temperatures recorded at Jan Mayen Island and monthly temperatures retrieved from satellite infrared data, with correlation coefficients of 0.74 and 0.89, respectively. Wind effect is also shown to be an important factor at daily and shorter timescales, directly influencing size and shape and sometimes initiating the formation of Nordbukta. The Odden was most extensive in 1979, 1982, 1986, and 1997 and most persistent in 1988, 1989, and 1997 but did not appear in 1984, 1994, and 1995, suggesting decadal periodicity for the 20 year period. With the use of the 75 year temperature record at Jan Mayen Island as a proxy for Odden size, spectral analysis also shows a periodicity of 10–12 years. A correlation study of North Atlantic Oscillation (NAO) indices with extents of the Odden, as derived from satellite data, yields a correlation coefficient of 0.4, which suggests that the interannual variability of the Odden may be influenced but not controlled by NAO. Regression analysis of the Jan Mayen surface temperature record also yields a slight warming (0.06 K decade−1) and a decrease in Odden area (−0.14×104 km2 decade−1) from 1979 to 1996, but during the past 75 years, there has actually been a slight cooling (−0.15 K decade−1), suggesting either that the Odden had actually been smaller in size several decades ago or that it had occurred farther north.

We present newly acquired airborne radar data showing ice thickness and surface elevation for Pine Island Glacier, Antarctica. These data, when combined with earlier measurements, suggest the presence of a lightly grounded area immediately above the grounding line of Pine Island Glacier. We identify this region as an “ice plain”. It lies close to the centre line of the glacier, has an elevation above buoyancy of 28 km. The upstream edge of the ice plain is defined by a “coupling line”. The configuration of the ice plain implies that nearby thinning of the ice stream would result in substantial grounding-line retreat. We suggest that the grounding-line retreat of Pine Island Glacier, observed between 1992 and 1996, probably commenced sometime after 1981.

The accreted ice of subglacial Lake Vostok extends upward from the lake water level (a depth of 3750 m) to the bottom surface of the overlying Antarctic ice sheet. All of the accreted ice samples, taken from depths between 3541 and 3611 m, were found to contain pro- and eukaryotic microorganisms, whose number and diversity varied in different ice horizons and correlated, to a certain degree, with the occurrence of organic and inorganic impurities in a given horizon. Some biological objects found in the accreted lake ice, including bacteria, microalgae, and the pollen of higher plants, were morphologically similar to those found earlier in the glacier ice bulk. The others were not. It is suggested that the microorganisms found in the lake ice may come from different locations—the bottom layer of the glacier ice, the bedrock underlying the glacier, and the lake water.