Moving Ice Sheet Research Articles

Cryogenic Pits and Quaternary Glacial Evidence in Central Iran

Quaternary glaciation studies in Central Iran reveal that it is not implausible to anticipate glaciation traces in this region. It is feasible to provide conclusive evidence about the behavior of ice sheets by referring to geomorphological factors and climatic statistical analyses. Factors such as flatness and accidental geographical features contribute to the existence of ice sheets in the Namdan Fars region. The digital reconstruction of past climatic conditions، using the Wright method، along with the absence of lake terraces around Kaftar Lake، signifies the presence of ice instead of water in the lake. The multi-axial morphology of the Namdan Plain، the shape and form of main valleys and passes، and the existence of numerous glacial cirque traces in the surrounding heights are also indicators of this phenomenon. The lack of evidence of ancient settlements in the plain، despite the availability of water and fertile soil، can be attributed to the region's historical thermal conditions. Investigating ancient glaciers helps us understand the natural history of the land. This knowledge can aid planners in devising macro strategies for regional development and water resource management، as glacial performance has always been associated with optimal water levels. Although glacial activities can create aquifers، the movement of ice sheets or ice surfaces does not support the accumulation of sediments required for creating aquifers with sufficient water storage. Instead، their performance leads to the creation of suitable agricultural soil layers. In summary، regional glaciers play a positive role in transforming and creating favorable agricultural soils and can be beneficial in adapting to climatic changes and extending statistical periods.

The Pleistocene ice-sheet dynamics in north-central Poland based on magnetic fabrics of tills and landform analysis

Abstract This research was carried out in north-central Poland, which was occupied by the ice sheet of the Saalian (Marine Isotope Stage [MIS] 6) and Upper Stadial of the Weichselian (MIS 2) glaciation. The application of the anisotropy of magnetic susceptibility (AMS) method supported by a digital elevation model (DEM) analysis of the orientation of glacial landforms allowed for the reconstruction of ice-sheet extent and ice movement directions of these two Pleistocene glaciations. The research used an innovative method of collecting AMS till samples from the glacial plateau areas. Based on the research, it was found that during the general recession of the ice sheet of the Saalian glaciation, a previously undescribed glacial transgression occurred, characterized by a different direction of ice-sheet movement. On the basis of detailed geomorphological studies of the area of terminal moraines, previously described in fragments, the maximum extent of the ice sheet during the Weichselian glaciation was clarified. The recession of the ice sheet of the Weichselian glaciation from the area of north-central Poland took place in four regressive or transgressive–regressive stages with variable directions of ice-sheet movement. The results obtained indicate the great potential of the AMS method in paleoenvironmental studies of glaciated areas.

Electron microscope loading and in situ nanoindentation of water ice at cryogenic temperatures.

Interest in the technique of low temperature environmental nanoindentation has gained momentum in recent years. Low temperature indentation apparatuses can, for instance, be used for systematic measurements of the mechanical properties of ice in the laboratory, in order to accurately determine the inputs for the constitutive equations describing the rheologic behaviour of natural ice (i.e., the Glen flow law). These properties are essential to predict the movement of glaciers and ice sheets over time as a response to a changing climate. Herein, we introduce a new experimental setup and protocol for electron microscope loading and in situ nanoindentation of water ice. Preliminary testing on pure water ice yield elastic modulus and hardness measurements of 4.1 GPa and 176 MPa, respectively, which fall within the range of previously published values. Our approach demonstrates the potential of low temperature, in situ, instrumented nanoindentation of ice under controlled conditions in the SEM, opening the possibility for investigating individual structural elements and systematic studies across species and concentration of impurities to refine to constitutive equations for natural ice.

Dynamic response of East Antarctic ice sheet to Late Pleistocene glacial–interglacial climatic forcing

Knowledge regarding the response of the East Antarctic Ice Sheet to glacial–interglacial climatic cycles in the late Pleistocene is critical to understanding the global climate system and projections of future sea level rise. Here, we observed notable glacial–interglacial cyclicity in magnetic properties, bulk detrital Sr–Nd isotopes, and Fe/Ti ratios over the previous 530 kyr in three well-dated gravity cores from the continental rise offshore of Prydz Bay (East Antarctica). Our results show that Antarctic continental sources with more Ti-rich magnetite, less radiogenic epsilon neodymium (εNd), and higher Fe/Ti ratios were predominant during glacials in comparison with interglacials. Specifically, the εNd amplitude through MIS 11–5 differs from that in the remainder of the records, which is also expressed in the magnetic coercivity cycles with subdued patterns. Following source identification on the basis of the detrital Sr–Nd distribution, we recognize two main (rock type) sources and infer two types of ice drainage flow pattern (“flank” and “channelized”), which follow different pathways in the Lambert Glacier–Amery Ice Shelf system (LG-AISS). The first follows an eastern path connecting the Ingrid Christensen Coast (flank), while the second follows a central channel via the LG-AISS (channelized) during MIS 11–5. Regular dynamics on glacial–interglacial timescales, manifested by changes in magnetic coercivity, are closely related to the modeled Antarctic ice volume and ice sheet movement, in which the second channelized pathway during MIS 11–5 corresponds to a 340-kyr-long episode with contiguous warmer-than-present Antarctic interglacials (MIS 11, 9, 7, and 5). Our records thus provide the clearest evidence so far of variable patterns of ice sheet dynamics during the late Pleistocene in the Prydz Bay sector of East Antarctica, which coincided with similar variation of ice drainage during the late Miocene–early Pliocene at around 1.13 Ma (ODP188). Similar ice drainage changes in these two periods imply that major ice flow reconfiguration can be triggered repeatedly by abrupt changes from a stable warm period to a cold one. The presented data not only reveal glacial–interglacial cyclicity in ice sheet advance and retreat in the meridional direction, but also implicate latitudinal adjustment (lateral) within a thin elongated drainage basin of the LG-AISS.

Everything you always wanted to ask about the Lapa do Picareiro Aurignacian and should not be afraid to know: A reply to ‘The early Aurignacian at Lapa do Picareiro really is that old’

Knowledge regarding the response of the East Antarctic Ice Sheet to glacial–interglacial climatic cycles in the late Pleistocene is critical to understanding the global climate system and projections of future sea level rise. Here, we observed notable glacial–interglacial cyclicity in magnetic properties, bulk detrital Sr–Nd isotopes, and Fe/Ti ratios over the previous 530 kyr in three well-dated gravity cores from the continental rise offshore of Prydz Bay (East Antarctica). Our results show that Antarctic continental sources with more Ti-rich magnetite, less radiogenic epsilon neodymium (εNd), and higher Fe/Ti ratios were predominant during glacials in comparison with interglacials. Specifically, the εNd amplitude through MIS 11–5 differs from that in the remainder of the records, which is also expressed in the magnetic coercivity cycles with subdued patterns. Following source identification on the basis of the detrital Sr–Nd distribution, we recognize two main (rock type) sources and infer two types of ice drainage flow pattern (“flank” and “channelized”), which follow different pathways in the Lambert Glacier–Amery Ice Shelf system (LG-AISS). The first follows an eastern path connecting the Ingrid Christensen Coast (flank), while the second follows a central channel via the LG-AISS (channelized) during MIS 11–5. Regular dynamics on glacial–interglacial timescales, manifested by changes in magnetic coercivity, are closely related to the modeled Antarctic ice volume and ice sheet movement, in which the second channelized pathway during MIS 11–5 corresponds to a 340-kyr-long episode with contiguous warmer-than-present Antarctic interglacials (MIS 11, 9, 7, and 5). Our records thus provide the clearest evidence so far of variable patterns of ice sheet dynamics during the late Pleistocene in the Prydz Bay sector of East Antarctica, which coincided with similar variation of ice drainage during the late Miocene–early Pliocene at around 1.13 Ma (ODP188). Similar ice drainage changes in these two periods imply that major ice flow reconfiguration can be triggered repeatedly by abrupt changes from a stable warm period to a cold one. The presented data not only reveal glacial–interglacial cyclicity in ice sheet advance and retreat in the meridional direction, but also implicate latitudinal adjustment (lateral) within a thin elongated drainage basin of the LG-AISS.

Validation of GPS-Based Monitoring and Remote Sensing of Ice-Shelf and Ice-Sheet Movement Changes.

The north and south poles of the earth (hereinafter referred to as the polar regions) are important components of the earth system. Changes in the material balance and movement of the polar ice shelf reflect the influence of the polar regions on global climate change and are also a response to global climate change. Through a comprehensive investigation of ice-shelf kinematics, with sufficient accuracy, it is possible to obtain ice-shelf elevation, movement-state data, ice-shelf material balance state, and the ice-shelf movement dynamics mechanism. Due to the extremely harsh environment in polar regions, remote sensing is currently widely used. Manual and equipment monitoring methods show insufficient accuracy or discontinuous time series. There is an urgent need to obtain continuous real-time ice-shelf kinematics-related parameters on the ground to verify the reliability of the parameters obtained by satellite remote sensing. These parameters should be combined with remote sensing monitoring to provide data support. In this paper, a monitoring system for the movement of polar ice and shelf ice cover is developed, and it is proposed that various data can be acquired by integrating high-precision GPS (global positioning system) and other sensors. Solutions to the problem of low-temperature power supply in the polar regions, data acquisition and storage strategies, and remote communication methods are proposed. Testing and remote sensing validation verified that the developed acquisition system can fulfill the requirements for monitoring the movement of the polar unmanned ice shelves and ice sheets.

Revisiting the Nantuo Formation in Shennongjia, South China: A new depositional model and multiple glacial cycles in the Cryogenian

Increasing sedimentary records and non-glacial facies reported from various regional glaciations suggest diverse interpretation against the ‘hard’ snowball Earth. At Shennongjia, in northern Yangtze Craton, glaciogenic strata of the Nantuo Formation (~649–635 Ma) are widely outcropped, which represents the Marinoan glacial record. In this study, sedimentary logging of eight high-quality exposed sections of the Nantuo Formation were systematically conducted. Four facies associations were recognized: (i) diamictites, (ii) heterolithics, (iii) lonestone-bearing siltstone, and (iv) clast-free siltstone. The succession reveals significant spatial and lateral facies variation, therefore, the stratigraphic framework of Nantuo Formation could be compartmentalized into western, central and eastern types. Based on the facies associations analysed, the sequence stratigraphic method was applied to determine ice advance-retreat cycles in the region. Our data suggest the ice dynamic evolution is three-fold, comprising: (i) ice sheet moved from continental environment from eastern to the subglacial grounding zone in the western Shennongjia features first ice advance-retreat cycle, which is recorded by the lower member of Nantuo Formation; (ii) the second glacial episode is illustrated by glaciolacustrine and non-glacial lacustrine deposits in periglacial environment, which is indicated by the middle member of Nantuo Formation in western Shennongjia, though situation in rest parts of Shennongjia is unclear; (iii) the appearance of ice rafted deposits (IRD) in both western and eastern Shennongjia suggests ice-distal environments, alongside the siltstone on the top Nantuo Formation, representing final deglaciation period. Altogether three glacial advance systems tracts (GAST) were identified, separated by three glacial retreat systems tracts (GRST). Meanwhile, a general east–west direction ice sheet movement could also be reconstructed. Besides, based on sedimentology, notably the stacking patterns and clast character, we tentatively interpret the Nantuo glacier as the transitional type between temperate and polythermal glacier.

An erosional origin for drumlins of NW Poland

AbstractDrumlins are landforms essential to understanding of ice sheet movement over soft beds, sediment transport along the ice/bed interface, and the formation of a wide range of glacial deposits. Although investigated more than any other glacial landform, the origin of drumlins remains contentious. Using high‐resolution LiDAR imagery and field data, we investigate the geomorphology and internal composition of one of the biggest drumlin fields in the North European Lowland. The Stargard drumlin field consists of over 1300 drumlins and related streamlined subglacial bedforms in a terminal part of a major Weichselian palaeo‐ice stream of the southern Scandinavian Ice Sheet. The drumlins are typically 600‐800 m long, 200‐250 m wide, 3‐6 m high and have axial elongation ratios ~2 but in some cases exceeding 15. Several subzones inferred from drumlin morphometry exist reflecting different ice flow dynamics. The most elongated drumlins occur in areas where ice moved down‐slope and where thick fine‐grained deposits of low hydraulic conductivity occur in the substratum. The largest portion of land occupied by drumlins and the greatest frequency density of drumlins occur where the ice moved up‐slope. Stargard drumlins are composed of a wide variety of glacial deposits including various types of tills and meltwater sediments, which range from undisturbed to heavily deformed. There is no correlation between the deposits in the drumlins and the drumlin forms indicating that the deposits pre‐date the drumlinizing process. It is suggested that the drumlin field was generated by a combination of direct glacial erosion and subglacial meltwater erosion by removing antecedent material from the inter‐drumlin areas and streamlining the resultant bumps. Our data support the search for a unifying theory of drumlin formation and suggest erosion as the most plausible single mechanism generating drumlin landscapes. © 2019 John Wiley & Sons, Ltd.

Estimation of Paleo-ice Sheet Thickness and Evolution of Landforms in Schirmacher Oasis and Adjoining Area, cDML, East Antarctica

ABSTRACT Quaternary period has witnessed perceptible climatic change in Schirmacher region, central Dronning Maud Land (cDML), East Antarctica. There were buildup of ice sheet and its recession throughout the period. The Schirmacher Oasis, Baalsrudfjellet, Veteheia and Veten nunataks are the prominent northernmost exposures in cDML area and play a major role in controlling the ice flow in this region resulting in glacial erosional as well as depositional landforms. These developments reveal vital information about the evolution of the region in Quaternary period. Erosional features such as roche-moutonees, glacially polished and abraded rocky outcrops with excellent preservation of glacial striations indicates the paleo-movement of overriding glaciers. Striations are generally preserved on polished surfaces of bedrock exposed on the high lands, however, glacial striations are also preserved over some mafic and resistant hard rocks in low lying areas. In general, the glacial striations indicate north-northeast movement of paleo ice sheet. Majority of the boulders in east-central valley show their longer axis trending in NNE-WSW to NE-SW directions. The cross cutting relation of striations give the changing directions of paleo ice sheet movement. Further, back calculation of depth of indentation and corresponding ice load gives a value of 100 to 500 m thick paleo-ice sheet in different parts of this region, documenting vast deglaciation in this region.

Sedimentary processes at ice sheet grounding‐zone wedges revealed by outcrops, Washington State (USA)

AbstractGrounding‐zone wedges (GZWs) mark the grounding terminus of flowing marine‐based ice streams and, in the presence of an ice shelf, the transition from grounded ice to floating ice. The morphology and stratigraphy of GZWs is predominantly constrained by seafloor bathymetry, seismic data, and sediment cores from deglaciated continental shelves; however, due to minimal constraints on GZW sedimentation processes, there remains a general lack of knowledge concerning the production of these landforms. Herein, outcrop observations are provided of GZWs from Whidbey Island in the Puget Lowlands (Washington State, USA). These features are characterized by prograded diamictons bounded by glacial unconformities, whereby the lower unconformity indicates glacial advance of the southern Cordilleran Ice Sheet and the upper unconformity indicates locally restricted ice advance during GZW growth; the consistent presence of an upper unconformity supports the hypothesis that GZWs facilitate ice advance during landform construction. Based on outcrop stratigraphy, GZW construction is dominated by sediment transport of deformation till and melt‐out of entrained basal debris at the grounding line. This material may be subsequently remobilized by debris flows. Additionally, there is evidence for subglacial meltwater discharge at the grounding line, as well as rhythmically bedded silt and sand, indicating possible tidal pumping at the grounding line. A series of GZWs on Whidbey Island provides evidence of punctuated ice sheet movement during retreat, rather than a rapid ice sheet lift‐off. The distance between adjacent GZWs of 102–103 m and the consistency in their size relative to modern ice stream grounding lines suggests that individual wedges formed over decades to centuries. © 2018 John Wiley & Sons, Ltd.

Characteristics of the under-ice soundscape in the southern Beaufort Sea during Ice Exercise 2016

Ice Camp SARGO was the remote hub of operations for the multi-national naval operation Ice Exercise 2016 (ICEX-16), held in March of that year. Over a three-day period in early March, continuous recordings of the under-ice soundscape were collected with receivers deployed at various depths through first-year ice in the vicinity of the ice camp as it drifted westward across the Beaufort Sea approximately 175 nm north of Prudhoe Bay, Alaska. A significant reduction in the strength of easterly winds resulted in deceleration of the ice sheet during the period of observation, inducing notable ice cracking and ridging events near the camp. Ice sheet movement slowed from about 0.5 knots early in the test to virtually coming to a halt near the end of the recording period. Sounds from naturally occurring and anthropogenic sources in the 10-Hz to 10-kHz band detected in the recordings were analyzed in connection to the origins of the sound and correlated to varying environment conditions including wind speed and ice motion. Results show a wide variety of persistent and transient sound sources contribute to the total soundscape at this remote location. Comparisons to other soundscape observations in the region are discussed.

Directional properties of glacial relief and sediments as an effect of multi-stage evolution: Case study of the Tczew Hump, northern Poland

This paper focuses on the upland territory south-west of the Gulf of Gdańsk characterized by the existence of numerous hills with distinct ordering of their crest-line orientation. Characteristic features of relief in the Tczew Hump were analysed using GIS-based tools. Directional properties and morphometric characteristics are not uniform throughout the study area. Therefore, subsequent detailed analyses were performed after dividing it into three zones: north-western (NW), central and south-eastern (SE). The highest hills are situated in the central part of the Hump. The landforms analysed are mostly elongated, but they show varying elongation ratios (1.0–4.05). In general a NE-SW orientation is observed, however, the azimuthal distribution of their crest-lines shows considerable variation (from N-S to E-W). Two main systems of the crest-line orientation are distinguished: System A (NNE-SSW) and System B (NE-SW/ENE-WSW).The landforms considered are covered with till consisting of two subunits, what reflects two subsequent ice-sheet movement periods in the Late Weichselian but without releasing the area from ice-sheet cover. The subunits can be identified by changes in their petrographic composition – up to ten times more erratics of local provenance in the upper one than in the lower one. Ice flow direction during deposition of both till subunits, based on the till fabric of each of the three analysed sections, coincides with System A of the crest-lines. However, most of the till-covered hills fit System B, which suggests that they retained their previous (older than Late Weichselian) orientation. The complex relief of the Tczew Hump has a palimpsest nature and its arrangement emerged in several stages: (1) formation of the primeval relief before the Late Weichselian (hills built of sediments of heterogeneous ages); (2) partial relief reshaping in subglacial conditions during the two, successive, ice-flow events in the Late Weichselian (till-covered hills, clear bipartition of the till); (3) development of additional landforms during deglaciation − typically not covered with till (or with flow till on the slopes only), showing an orientation determined by the crevasse system developed in the ice.

Elsterian ice sheet dynamics in a topographically varied area (southern part of the Racibórz–Oświęcim Basin and its vicinity, southern Poland)

During the Elsterian Glaciation, the Scandinavian Ice Sheet, before reaching its maximum extent, advanced over the mountainous foreland of Southern Poland, which was characterized by a substrate of increasingly varied relief. One such area was the hilly Rybnik Plateau of the southern part of the Raciborz–Oświecim Basin, located directly north of the Ostrava Basin and Moravian Gate, where the ice sheet advanced far south and formed a large lobe. In this study, till from the Łaziska site, located in southern part of the Rybnik Plateau, was analysed and interpreted. The till was deposited at the top of an W–E oriented ridge composed of Neogene clays. The study indicates that a high basal water pressure occurred at the base of the ice sheet, favouring a basal mechanism of ice sheet movement. Till fabric and kinematic structures indicate that ice flowed easily from the west over the ridge, parallel to its axis. Reconstructed patterns of ice flow direction reflect an ice sheet that was characterized by a strong spatially varied dynamics. The Odra Valley was the main corridor of fast flowing ice to the Ostrava Basin, from where ice was distributed radially in different directions. The second corridor of actively flowing ice was probably located in the Ruda palaeovalley to the north of the Rybnik Plateau. In the central part of the Rybnik Plateau, ice flow was restricted. This less dynamic ice sheet behaviour resulted mostly from the much higher location of the area. This study indicates that the large morphological and lithological variations of the ice sheet substrate induced varied frictional resistance, producing a spatially varied stress field within the ice sheet. This generated active zones of streaming ice adjacent to more passive zones. Potential switching between neighbouring active zones transporting ice towards the ice sheet margin is postulated.

Subglacial conditions and Scandinavian Ice Sheet dynamics at the coarse-grained substratum of the fore-mountain area of southern Poland

Abstract The fore-mountain areas of southern Poland are locally composed of the coarse-grained sediments of alluvial fans, which created unusual conditions under the advancing Scandinavian Ice Sheet during the Elsterian glaciation. This highly permeable substratum potentially enabled rapid outflow of meltwater from the ice sheet base, thereby reducing the water pressure and strongly influencing the ice sheet dynamics. The subglacial conditions and the relationship between the ice sheet behaviour and its coarse-grained substratum were studied at the foreland of the western Carpathian Mountains. The sedimentological and structural analysis of the till and related sediments that were deposited above the alluvial gravel of the fore-mountain fans are presented. The study indicates that despite the high permeability of the coarse-grained substratum, it did not slow the ice sheet movement. Conversely, the ice sheet moved mainly due to basal slip and locally shallow deformations. This was a consequence of very high basal water pressure, which resulted largely from the presence of permafrost that restricted subglacial groundwater outflow. In addition, the ice sheet substratum was inclined opposite to the direction of its movement, increasing the pressure of the subglacial water. Numerous subhorizontal sandy laminae within the till indicate that the meltwater from the ice sheet base was drained by a water film along the ice/bed interface. The water escape structures within the till and subtill sediments indicate the occasional instability of the ice sheet hydrological system and suggest that the meltwater was periodically stored in the ice sheet base. Temporal changes occurring in the ice sheet hydrological system might indicate variations in the ice sheet behaviour; i.e. phases of relatively fast ice flow and phases of ice stagnation. The latter were probably correlated with the freezing of the ice margin to its base. The study shows how the coarse-grained substratum could potentially influence ice sheet behaviour and provides a broader look on the factors controlling the dynamics of the Pleistocene ice sheets, which soft-sediment substrata in many areas were texturally varied.

Antarctic ice velocities from GPS locations logged by seismic stations

AbstractIn 2007–08, seismologists began deploying passive seismic stations over much of the Antarctic ice sheet. These stations routinely log their position by navigation-grade global positioning system (GPS) receivers. This location data can be used to track the stations situated on moving ice. For stations along the traverse from Zhongshan station to Dome A in East Antarctica and at the West Antarctic Ice Sheet divide the estimated velocities of the ice surface based on positions recorded by navigation-grade GPS are consistent with those obtained by high-accuracy geodetic GPS. Most of the estimated velocities have an angle difference of <28° with the steepest downhill vector of the ice surface slope at the stations. These results indicate that navigation-grade GPS measurements over several months provide reliable information on ice sheet movement of ≥1 m yr-1. With an uncertainty of ~0.3–1 m yr-1, this method is able to resolve both very slow ice velocities near Dome A and velocities of >100 m yr-1 on Thwaites Glacier. Information on ice velocity at three locations for which no data from satellite-based interferometric synthetic aperture radar are available have also been provided using this method.

City under the Ice: The Closed World of Camp Century in Cold War Culture

Located on the beeline between the two nuclear superpowers, Greenland took on vital strategic importance during the early phases of the Cold War. As part of its polar strategy, the USA constructed several bases in Greenland. Camp Century, known as ‘City under the Ice’, was an experimental-military American city built entirely inside the ice sheet in 1959–1960. A 225-person, nuclear-powered army base, Century was the precursor for a much larger installation of intercontinental ballistic missiles (which never materialized), but was also used to project popular images of techno-scientific control, nuclear containment, and American values into Cold War American culture. Applying Paul Edward's closed-world metaphor to photos, film, books, and articles about Camp Century enables us to see both the strengths and the fragility of public discourses about the camp. Century was depicted as an outstanding example of man's never-ceasing quest for knowledge, as the epic conquest of the harsh Arctic environment by US Army engineers, as an Arctic sword and shield against the Soviet aggressor, and as a friendly collaboration between the USA and Denmark (in 1953, the former colony of Greenland became part of the Danish Realm). In the end, Camp Century had to be abandoned due to the glaciological forces of the moving ice sheet which crushed the tunnels, but also due to changes in Cold War politics and the political difficulties underscoring nuclear installations on Danish territory.

Radionuclide transport during glacial cycles: Comparison of two approaches for representing flow transients

The effect of future, transient ice sheet movement and permafrost development on transport of radionuclides from a proposed repository site is investigated using numerical groundwater flow and radionuclide transport modelling. Two different transport approaches are compared, both utilizing groundwater flow simulations of future climate conditions. The first transport approach uses steady-state particle trajectories representing temperate climate conditions, but modifies the transport velocity along the trajectories according to the changing climate. The second approach is pseudo-transient by performing particle tracking in each individual flow field representing a given time epoch.Two different climate sequences are analyzed. First, a simplified sequence is assessed in order to understand if the two different transport approaches yield significantly different breakthrough characteristics. Second, a sequence representing conditions relevant for real safety assessment applications is considered.Results indicate that the transport approach using fixed trajectories tends to significantly over predict breakthrough during permafrost conditions relative to the pseudo-transient approach. The major difference between the two approaches is related to discharge locations. The fixed trajectory approach yields discharge locations constant in time whereas the pseudo-transient approach is characterized by discharge centres moving in time according to the different climate conditions.

Submarine geomorphology and glacial history of the Sea of the Hebrides, UK

The Sea of the Hebrides is an island-studded region of complex bathymetry on the UK continental shelf, west of the Scottish mainland. An extensive area (2200km2) of recently collected multibeam bathymetry data, combined with seismic reflection profiles reveal this part of the shelf to have been extensively modified by both glacial and modern processes. Our new geomorphological evidence strongly supports the contention that an ice stream drained ice from western Scotland and the Inner Hebrides towards the Barra Fan at the continental shelf break at the height of the last glaciation (Marine Isotope Stage 2–3). Convergent seabed glacial lineations and other subglacially streamlined features eroded in bedrock around the Islands of Canna and Rum preserve the direction of ice sheet movement, and strongly suggest the onset of ice streaming in a southwesterly direction on the continental shelf in the Sea of the Hebrides region. This fast-flow zone formed part of a larger convergent ice stream system draining much of western Scotland and the north of Ireland — the southern part of which has been postulated already. A number of rock basins, linear troughs and deeps west and south of Muck, kept sediment-free by the dominant modern tidal regime, are interpreted as being at least partly subglacial in origin. Similarly, a large complex of buried deeps between Eigg and Arisaig are interpreted as an overdeepened glacial drainage network. It is suggested that intense bedrock erosion by focused subglacial abrasion and subglacial meltwater discharge over multiple glacial advance and decay cycles led to significant modifications of the pre-Quaternary bedrock surface. Other features such as moraines are only found in shallower water (typically <50m), west of Canna, west of Rum and south of Skye. Their relative paucity indicates that the modern tidally dominated environment of the area may have removed much of the localised geomorphological evidence of offshore glacial limits within the Sea of the Hebrides, or alternatively that the ice sheet margin was floating and retreated predominantly by calving leaving little geomorphological evidence of its retreat.

Flat-topped mounds in western Ross Sea: Carbonate mounds or subglacial volcanic features?

Detailed multibeam bathymetry data in the western Ross Sea, Antarctica, delineate a field of unusual flat-topped seafloor mounds located ∼50 km west of Franklin Island and an arcuate zone of pockmarks to the northwest and west of Franklin Island. Sixteen mounds occur in an area about 30 km square at a depth of ∼500 m, within the Terror Rift, the active extensional part of the Victoria Land Basin. The mounds tend to be circular in the east and linear in the west, with their steepest slope to the southeast, and shallowest slope to the northwest, consistent with erosion by northwest ice-sheet movement. The largest mound is ∼4 km across and 100 m high. Five similar features were delineated to the south and east of Franklin Island at depths of 400–650 m. Seismic, gravity, and magnetic data indicate that the mounds are largely low-density, nonmagnetic bodies overlying a largely nondisrupted sedimentary section, but some mounds have an associated small (∼50 nT), short-wavelength, normal or reversed magnetic anomaly, indicating a magnetic core to the mounds. Their proximity to inferred subsurface gas hydrates suggests they may be carbonate banks, but they also occur close to volcanic centers including Franklin Island. Our preferred interpretation is that they are of volcanic origin, erupted during a geomagnetic reversal and under a grounded ice sheet forming hyaloclastite edifices, previously unknown under the Ross Sea. The pockmarks range from 200 m to 500 m in diameter.

Chapter 65 Neoproterozoic glacial deposits of the Kimberly Region and northwestern Northern Territory, Australia

Abstract Neoproterozoic glaciogenic formations are preserved in the Kimberley region and northwestern Northern Territory of northern Australia. They are distributed in the west Kimberley adjacent to the northern margins of the King Leopold Orogen, the Mt Ramsay area at the junction of the King Leopold and Halls Creek orogens, and east Kimberley, adjacent to the eastern margin of the Halls Creek Orogen. Small outlier glaciogenic deposits are preserved in the Litchfield Province, Northern Territory (Uniya Fm.) and Georgina Basin, western Queensland (Little Burke Fm.). Glaciogenic strata comprise diamictite, conglomerate, sandstone and pebbly mudstone and characterize the Walsh, Landrigan and Fargoo/Moonlight Valley formations. Thin units of laminated dolomite sit conformably at the top of the Walsh, Landrigan and Moonlight Valley formations. Glaciogenic units are also interbedded with the carbonate platform deposits of the Egan Fm. and Boonall Dolomite. δ 13 C data are available for all carbonate units. There is no direct chronological constraint on these successions, and dispute over the regional correlation of the Neoproterozoic succession has been largely resolved through biostratigraphic, chemostratigraphic and lithostratigraphic analysis. However, palaeomagnetic results from the Walsh Fm. are inconsistent with sedimentologically based correlations. Two stratigraphically defined glaciations are preserved in northwestern Australia: the ‘Landrigan Glaciation’, characterized by SW-directed continental ice-sheet movement and correlated with late Cryogenian glaciation elsewhere in Australia and the world; and, the ‘Egan Glaciation’, a more localized glaciation of the Ediacaran Period. Future research focus should include chronology, palaeomagnetic constraint and tectonostratigraphic controls on deposition.