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The Eurasian ice sheet extended across the Barents and Kara Seas during the late Quaternary, yet evidence on past ice dynamics and thermal structure across its huge eastern periphery remains largely unknown. Here we use three-dimensional seismic data sets covering ∼4500 km2 of the Kara Sea west of Yamal Peninsula, Siberia (71°–73°N), to identify, for the first time in the Russian Arctic seas, several buried generations of vast subglacial tunnel valley networks. Individual valleys are up to 50 km long and are incised as much as 400 m deep; among the largest tunnel valleys ever reported. This discovery represents the first documentation of an extensively warm-based eastern margin of the Eurasian ice sheet during the Quaternary glaciations. The presence of major subglacial channel networks on the shallow shelf, with no evidence of ice streaming, suggests that significant meltwater discharge and subsequent freshwater forcing of ocean circulation may be long-lived rather than catastrophic, occurring during the latest stages of deglaciation in areas where the ice sheet flows slowly and is grounded largely above sea level. Furthermore, the first account of an extensive hydrological network across large areas of the Kara Sea provides important empirical evidence for active subglacial hydrological processes that should be considered in future numerical modeling of the eastern margin of the Quaternary Eurasian ice sheet.

We present PATICE, a GIS database of Patagonian glacial geomorphology and recalibrated chronological data. PATICE includes 58,823 landforms and 1,669 geochronological ages, and extends from 38°S to 55°S in southern South America. We use these data to generate new empirical reconstructions of the Patagonian Ice Sheet (PIS) and subsequent ice masses and ice-dammed palaeolakes at 35 ka, 30 ka, 25 ka, 20 ka, 15 ka, 13 ka (synchronous with the Antarctic Cold Reversal), 10 ka, 5 ka, 0.2 ka and 2011 AD. At 35 ka, the PIS covered of 492.6 x103 km2, had a sea level equivalent of ~1,496 mm, was 350 km wide and 2090 km long, and was grounded on the Pacific continental shelf edge. Outlet glacier lobes remained topographically confined and the largest generated the suites of subglacial streamlined bedforms characteristic of ice streams. The PIS reached its maximum extent by 33 – 28 ka from 38°S to 48°S, and earlier, around 47 ka from 48°S southwards. Net retreat from maximum positions began by 25 ka, with ice-marginal stabilisation then at 21 – 18 ka, which was then followed by rapid, irreversible deglaciation. By 15 ka, the PIS had separated into disparate ice masses, draining into large ice-dammed lakes along the eastern margin, which strongly influenced rates of recession. Glacial readvances or stabilisations occurred at least at 14 – 13 ka, 11 ka, 6 – 5 ka, 2 – 1 ka, and 0.5 – 0.2 ka. We suggest that 20th century glacial recession (% a-1) is occurring faster than at any time documented during the Holocene.

Bathymetry (seafloor depth), is a critical parameter providing the geospatial context for a multitude of marine scientific studies. Since 1997, the International Bathymetric Chart of the Arctic Ocean (IBCAO) has been the authoritative source of bathymetry for the Arctic Ocean. IBCAO has merged its efforts with the Nippon Foundation-GEBCO-Seabed 2030 Project, with the goal of mapping all of the oceans by 2030. Here we present the latest version (IBCAO Ver. 4.0), with more than twice the resolution (200 × 200 m versus 500 × 500 m) and with individual depth soundings constraining three times more area of the Arctic Ocean (∼19.8% versus 6.7%), than the previous IBCAO Ver. 3.0 released in 2012. Modern multibeam bathymetry comprises ∼14.3% in Ver. 4.0 compared to ∼5.4% in Ver. 3.0. Thus, the new IBCAO Ver. 4.0 has substantially more seafloor morphological information that offers new insights into a range of submarine features and processes; for example, the improved portrayal of Greenland fjords better serves predictive modelling of the fate of the Greenland Ice Sheet., Measurement(s)depthTechnology Type(s)digital curationFactor Type(s)geographic locationSample Characteristic - Environmentocean floorSample Characteristic - LocationArctic Ocean Machine-accessible metadata file describing the reported data: 10.6084/m9.figshare.12369314

Fast-flowing outlet glaciers currently drain the Greenland Ice Sheet (GIS), delivering ice, meltwater and debris to the fjords around Greenland. Although such glaciers strongly affect the ice sheet's mass balance, their glacimarine processes and associated products are still poorly understood. This study provides a detailed analysis of lithological and geophysical data from Disko Bay and the Vaigat Strait in central West Greenland. Disko Bay is strongly influenced by Jakobshavn Isbrae, Greenland's fastest-flowing glacier, which currently drains ∼7% of the ice sheet. Streamlined glacial landforms record the former flow of an expanded Jakobshavn Isbrae and adjacent GIS outlets through Disko Bay and the Vaigat Strait towards the continental shelf. Thirteen vibrocores contain a complex set of lithofacies including diamict, stratified mud, interbedded mud and sand, and bioturbated mud deposited by (1) suspension settling from meltwater plumes and the water column, (2) sediment gravity flows, and (3) iceberg rafting and ploughing. The importance of meltwater-related processes to glacimarine sedimentation in West Greenland fjords and bays is emphasised by the abundance of mud preserved in the cores. Radiocarbon dates constrain the position of the ice margin during deglaciation, and suggest that Jakobshavn Isbrae had retreated into central Disko Bay before 10.6 cal ka BP and to beyond Isfjeldsbanken by 7.6–7.1 cal ka BP. Sediment accumulation rates were up to 1.7 cm a−1 for ice-proximal glacimarine mud, and ∼0.007–0.05 cm a−1 for overlying distal sediments. In addition to elucidating the deglacial retreat history of Jakobshavn Isbrae, our findings show that the glacimarine sedimentary processes in West Greenland are similar to those in East Greenland, and that variability in such processes is more a function of time and glacier proximity than of geographic location and associated climatic regime.

Outburst floods from subglacial lakes beneath the Antarctic Ice Sheet modulate ice-flow velocities over periods of months to years. Although subglacial lake drainage events have been observed from satellite-altimetric data, little is known about their role in the long-term evolution of ice-sheet basal hydrology. Here, we systematically map and model past water flow through an extensive area containing over 1000 subglacial channels and 19 former lake basins exposed on over 19 000 km2 of seafloor by the retreat of Pine Island and Thwaites glaciers, West Antarctica. At 507 m wide and 43 m deep on average, the channels offshore of present-day Pine Island and Thwaites glaciers are approximately twice as deep, 3 times as wide, and cover an area over 400 times larger than the terrestrial meltwater channels comprising the Labyrinth in the Antarctic Dry Valleys. The channels incised into bedrock offshore of contemporary Pine Island and Thwaites glaciers would have been capable of accommodating discharges of up to 8.8×106 m3 s−1. We suggest that the channels were formed by episodic discharges from subglacial lakes trapped during ice-sheet advance and retreat over multiple glacial periods. Our results document the widespread influence of episodic subglacial drainage events during past glacial periods, in particular beneath large ice streams similar to those that continue to dominate contemporary ice-sheet discharge.

Basal hydrological systems play an important role in controlling the dynamic behaviour of ice streams. Data showing their morphology and relationship to geological substrates beneath modern ice streams are, however, sparse and difficult to collect. We present new multibeam bathymetry data that make the Anvers-Hugo Trough west of the Antarctic Peninsula the most completely surveyed palaeo-ice stream pathway in Antarctica. The data reveal a diverse range of landforms, including streamlined features where there was fast flow in the palaeo-ice stream, channels eroded by flow of subglacial water, and compelling evidence of palaeo-ice stream shear margin locations. We interpret landforms as indicating that subglacial water availability played an important role in facilitating ice stream flow and controlling shear margin positions. Water was likely supplied to the ice stream bed episodically as a result of outbursts from a subglacial lake located in the Palmer Deep basin on the inner continental shelf. These interpretations have implications for controls on the onset of fast ice flow, the dynamic behaviour of palaeo-ice streams on the Antarctic continental shelf, and potentially also for behaviour of modern ice streams.

Bathymetric data of unprecedented resolution are used to provide insights into former ice dynamics and glacial processes in a western Antarctic Peninsula embayment. An assemblage of submarine glacial landforms, which includes subglacially produced streamlined features and ice-marginal ridges, reveals the former pattern of ice flow and retreat. A group of more than 250 small (< 1–3 m high, 10–20 m wide) and relatively evenly spaced recessional moraines was identified beyond the margin of Philippa Glacier. The small recessional moraines are interpreted to have been produced during short-lived, possibly annual re-advances of a grounded ice margin during overall retreat. This is the first time that these features have been shown to be part of the assemblage of landforms produced by tidewater glaciers on the Antarctic Peninsula. Glacier-terminus changes during the last four decades, mapped from LANDSAT satellite images, were analysed to determine whether the moraines were produced during recent still-stands or re-advances of Philippa Glacier and to further investigate the short-term (annual to decadal) variability in ice-marginal position in tidewater glacier systems. The asynchronous response of individual tidewater glaciers in Darbel Bay is interpreted to be controlled mainly by local topography rather than by glacier catchment-area size.

© 2016 Regents of the University of Colorado. Previous advances and retreats of Blomstrandbreen within the cold period known as the Little Ice Age, between approximately 1400 and 1920, are relatively well documented. The seafloor characteristics associated with these glacier fluctuations, and their importance for the identification of similar surge-type tidewater glaciers, are discussed. We use detailed multibeam-bathymetric data acquired within Nordvågen, the marine area offshore of Blomstrandbreen, to provide a new understanding of the style and pattern of deglaciation around Blomstrandhalvøya since Blomstrandbreen's neoglacial maximum. Glacial landforms on the seafloor of Nordvågen comprise overridden moraines, glacial lineations, terminal moraines, and annual recessional moraines. Crevasse-fill ridges, which are often regarded as a characteristic landform of surging tidewater glaciers, are present on only restricted areas of Nordvågen. Significantly, this study shows that large terminal surge moraines and numerous crevasse-fill ridges may not always be well developed in association with glacier surges, with implications for the identification of surges in the geological record. Using historical observations, aerial photographs, and satellite imagery of Blomstrandbreen, we have correlated former ice-marginal positions with mapped submarine landforms. Three surge events occurred during a pattern of overall retreat, with a spacing of about 50 years between active advance phases; this represents a relatively short quiescent phase for Svalbard glaciers. Average retreat rates of 10-50 m yr-1 are typical of the quiescent phase of the surge cycle, whereas surge advances vary from 200 m to over 725 m.

The suite of sedimentary landforms produced on continental shelves by fast-flowing ice streams is typified by features that are elongate and streamlined in the direction of past ice flow (e.g. Stokes & Clark 2001; Ottesen et al. 2005 a ; Livingstone et al. 2012). By contrast, the slower-flowing parts of an ice sheet, located between ice streams and fed by drainage basins that are often an order of magnitude or more smaller than the interior basins feeding the ice stream, have a very different set of characteristic submarine landforms; these are orientated predominantly transverse to the direction of past ice flow (Ottesen & Dowdeswell 2009; Klages et al. 2013, 2016). In addition, on many high-latitude shelf-banks glacial landforms produced beneath and at the margins of ice sheets are often reworked by the ploughing action of iceberg keels, sometimes to the point where these primary depositional landforms are almost obliterated (e.g. Dowdeswell et al. 1993, 2014). Submarine landforms from the western margin of the former Eurasian Ice Sheet, which extended across the shallow banks and deeper intervening troughs on the continental shelves of Norway and Svalbard at the Last Glacial Maximum (LGM) (Svendsen et al. 2004; Ottesen et al. 2005 a ), are used to illustrate this inter-ice stream palaeo-glacial setting (Fig. 1). In these locations, ice flux is limited by relatively small drainage-basin size and ice flow is likely to be slow relative to the 103–104 m a−1 velocities of adjacent ice streams (Dowdeswell & Siegert 1999). Fig. 1. ( a ) Location of study areas offshore of Norway and Svalbard (red boxes; map from IBCAO v. 3.0). Bathymetric data showing the pattern of shallow banks and intervening cross-shelf troughs offshore of ( b ) NW Norway and ( c ) NW Spitsbergen. WI, Wijdefjorden; KR, Krossfjorden. ### Description The …

Svalbard has about 800 km of ice cliffs where tidewater glaciers reach the sea (Blaszczyk et al. 2009). A number of these glaciers are of surge type (Dowdeswell et al. 1991; Hagen et al. 1993) and have undergone rapid advances of a few years in duration followed by slow retreat over decades, in response to variations in their basal hydrological system driven largely by geometric and thermal changes (e.g. Murray et al. 1998, 2000). These fluctuations, which take place over beds composed mainly of soft sediments, have been monitored using satellite imagery, aerial photographs and early maps (e.g. Ottesen et al. 2008; Flink et al. 2015). The seafloor geomorphology of surging tidewater glaciers in Svalbard, revealed after glacier-terminus retreat, contains a well-defined landform assemblage (e.g. Solheim & Pfirman 1985; Ottesen & Dowdeswell 2006; Ottesen et al. 2008; Flink et al. 2015). Seafloor sediments in two Spitsbergen fjords, inner Van Keulenfjorden and Borebukta (Fig. 1), exemplify the landforms typically deposited by recent tidewater-glacier surges in Svalbard. Van Keulenfjorden is 40 km long and 5 km wide, and is subdivided into two basins. Several glaciers with a total area of about 900 km2 drain into inner Van Keulenfjorden (Fig. 1a). Here, Van Keulenfjorden is about 2.5 km wide with a maximum depth of 80 m before shallowing to a prominent ridge about 10 km from the 2002 tidewater-glacier termini (Fig. 1a). Borebukta is a 10 km long inlet on the north side of Isfjorden (Fig. 1b), about 1 km wide and 50 m deep at the present tidewater-glacier front, deepening to about 70 m offshore (Fig. 1b). Further out it shallows once more to a 10 m deep threshold at the fjord entrance. The 22 km long Borebreen and 14 …

The Antarctic Peninsula comprises a thin spine of mountains and islands presently covered by an ice sheet up to 500 m thick that drains eastward and westward via outlet glaciers (Davies et al. 2012). The peninsula has undergone recent rapid warming, resulting in the collapse of fringing ice shelves and the retreat, thinning and acceleration of marine-terminating outlet glaciers (e.g. Pritchard & Vaughan 2007). At the Last Glacial Maximum (LGM), the ice sheet expanded to the continental shelf break around the peninsula, and was organized into a series of ice streams that drained along cross-shelf bathymetric troughs (O Cofaigh et al. 2014). Marguerite Bay is located on the west side of the Antarctic Peninsula, at about 66–70° S (Fig. 1). A 12–80 km wide and 370 km long trough extends across the bay from the northern terminus of George VI Ice Shelf to the continental shelf edge. Extensive marine-geophysical surveys of the trough reveal a suite of glacial landforms which record past flow of an ice stream which extended to the shelf edge at, or shortly after, the LGM. Subsequent retreat of the ice stream was underway by c. 14 ka ago and proceeded rapidly to the mid-shelf, where it slowed before accelerating once again to the inner shelf at c. 9 ka (Kilfeather et al. 2011). Fig. 1. Regional bathymetry and shelf architecture of the Marguerite Trough shelf–slope system, Antarctic Peninsula (AP). The location of subsequent figures is shown. ( a ) Multibeam-bathymetric coverage of the Marguerite Trough system. Light grey is grounded ice; dark grey is floating ice. Inset: location of study area on the Antarctic Peninsula (red box; map from IBCSO v. 1.0). Regional bathymetry from IBCAO v. 3.0. Arrows denote perspective of oblique views in Figures 2a and 3a. ( b ) 130 km along-dip seismic-reflection profile showing Antarctic …

Seafloor morphology beyond nine tidewater glaciers terminating in open-marine settings in eastern Svalbard has been investigated using multibeam swath-bathymetry. Historical information on tidewater glacier fluctuations over the past century or so shows that the seafloor offshore has been exposed only recently. Most glaciers have been observed to surge or have looped surface moraines indicating past surges. During these ice advances and subsequent retreat, a well-preserved submarine landform assemblage has been produced. (a) Subglacial landforms include: overridden moraine ridges, mega-scale glacial lineations (MSGLs), other streamlined lineations, elongate drumlins and medial moraines, small ridges forming a complex boxwork or rhombohedral pattern, and meltwater-related eskers and channels. (b) Ice-marginal landforms include: large terminal moraines with debris flow lobes on their outer flanks and indentations on their inner sides, small transverse retreat moraines, and crater-like kettle holes. (c) Glacimarine features include: iceberg ploughmarks and an otherwise relatively smooth sedimentary seafloor produced by fine-grained debris rain-out. A schematic plan-view landform assemblage model for tidewater glaciers advancing into open-marine settings is developed. Arcuate terminal moraines marking the ice-advance limit provide a distinctive component. Submarine basin(s) exposed inside these moraine ridges when ice retreats contain suites of individual landforms, produced subglacially and ice-marginally, with a consistent order of timing of deposition and stratigraphic superposition. The new schematic model is compared with earlier models based on submarine landforms associated with surges in the more topographically constrained setting of Spitsbergen fjords. Differences include: (i) the overall arcuate shape of the open-marine assemblage; (ii) the indented ice-proximal sides of terminal moraine ridges; (iii) the fan-shaped pattern of streamlined lineations; (iv) crater-like kettle holes at the inner lateral margins of many submarine basins; (v) prominent systems of eskers and channels. Modern glaciological analogues from ongoing surges of ice caps in eastern Svalbard and Severnaya Zemlya provide contemporary observations of ice advance into open-marine settings, including heavily crevassed ice lobes with finger-like termini.

The basal topography is largely unknown beneath most glaciers and ice caps and many attempts have been made to estimate a thickness field from other more accessible information at the surface. Here, we present a two-step reconstruction approach for ice thickness that solves mass conservation over single or several connected drainage basins. The approach performs well for a variety of test geometries with abundant thickness measurements including marine- and land-terminating glaciers as well as a 2400 km2 ice cap on Svalbard. Input requirements for the first step are comparable to other approaches that have already been applied world-wide. In the first step, a geometrically controlled, non-local flux solution is converted into thickness values relying on the shallow ice approximation. In a second step, the thickness reconstruction is improved along fast-flowing glacier trunks on the basis of velocity observations. In both steps, thickness measurements are assimilated as internal boundary conditions. Each thickness field is presented together with a map of error estimates which stem from a formal propagation of input uncertainties. These estimates point out that the thickness field is least constrained near ice divides or in other stagnant areas. The error-estimate map also highlights key regions for future thickness surveys as well as a preference for across-flow acquisition. Withholding parts of the thickness measurements indicates that error estimates show a tendency to overestimate actual mismatch values. For very sparse or non-existent thickness information, our reconstruction approach indicates that we have to accept an average uncertainty of at least 25 % in the reconstructed thickness field. For Vestfonna, previous ice volume estimates have to be corrected upward by 22 %. We also find that a 12 % area fraction of the ice cap are in fact grounded below sea-level as compared to the previous 5 %-estimate.

Feature tracking of approximately annually separated Landsat-7 ETM+ imagery acquired from 1999 to 2010 and speckle tracking of 24-day separated RADARSAT-2 imagery acquired from 2009 to 2015 reveal that motion of the major tidewater glaciers of Devon Ice Cap is more variable than previously described. The flow of almost half (six of 14) of the outlet glaciers slowed over the observation period, while that of the terminus regions of three of 14 of the glaciers sped up in the most recent years of observation. The North Croker Bay Glacier of southern Devon Ice Cap showed the greatest variability in motion, oscillating between multi-year (three or more) periods of slower and faster flow and exhibited a pattern of velocity variability that is different from that of the rest of the ice cap's outlet glaciers. Comparisons between areas of dynamic variability and glacier bed topography indicate that velocity variability is largely restricted to regions where the glacier bed is grounded below sea level. Derived velocities are combined with measurements of ice thickness at the fronts of tidewater glacier to determine a mean annual (2009; 2011–15) dynamic ice discharge of 0.41 ± 0.11 Gt a−1for Devon Ice Cap. The Belcher Glacier is becoming a larger source of mass loss via ice discharge.

Large icebergs leave evidence of their drift via ploughing of the seabed, thereby providing a geological record of episodes of calving from thick ice sheets. We interpret large-scale curvilinear depressions on the western Svalbard margin as ploughmarks produced by the keels of icebergs that grounded on the seafloor as they drifted through this area. Iceberg ploughmarks were identified at modern water depths between 300 m and 1000 m and in two distinct stratigraphic units. Combining data from sediment cores with seismic stratigraphy from sub-bottom profiler data suggests that the ploughmarks developed in two phases: (1) during Marine Isotope Stage (MIS) 6; and (2) during MIS 2, indicating the presence of large drifting icebergs on the western Svalbard margin during both the Late Saalian and Late Weichselian glaciations. Sediment-core data along the western Svalbard margin indicate a sharp increase in mass-transported sediments dated at 23.7 ± 0.2 ka, consistent with the MIS 2 age of the younger iceberg-ploughed surface. The ploughmarks are oriented in two main directions: SW-NE and S-N. S-N oriented ploughmarks, which shallow to the north, indicate iceberg drift from the south with a SW–NE component marking the zone of splitting of the West Spitsbergen Current (WSC) into the Yermak Slope Current (YSC) and North Spitsbergen Current (NSC). Large MIS 6 and MIS 2 icebergs most likely had an Arctic Ocean source. We suggest that these icebergs probably left the Arctic Ocean southward through Fram Strait and circulated within the Norwegian-Greenland Sea before being transported northwards along the Svalbard margin by the WSC. An additional likely source of icebergs to the western Svalbard margin during MIS 2 was the ice-sheet terminating in the western Barents Sea, from which icebergs drifted northward.

Bed topography is a critical boundary for the numerical\ud modelling of ice sheets and ice–ocean interactions.\ud A persistent issue with existing topography products for the\ud bed of the Greenland Ice Sheet and surrounding sea floor is\ud the poor representation of coastal bathymetry, especially in\ud regions of floating ice and near the grounding line. Sparse\ud data coverage, and the resultant coarse resolution at the ice–\ud ocean boundary, poses issues in our ability to model ice\ud flow advance and retreat from the present position. In addition,\ud as fjord bathymetry is known to exert strong control\ud on ocean circulation and ice–ocean forcing, the lack\ud of bed data leads to an inability to model these processes\ud adequately. Since the release of the last complete Greenland\ud bed topography–bathymetry product, new observational\ud bathymetry data have become available. These data can be\ud used to constrain bathymetry, but many fjords remain completely\ud unsampled and therefore poorly resolved. Here, as\ud part of the development of the next generation of Greenland\ud bed topography products, we present a new method for constraining\ud the bathymetry of fjord systems in regions where\ud data coverage is sparse. For these cases, we generate synthetic\ud fjord geometries using a method conditioned by surveys\ud of terrestrial glacial valleys as well as existing sinuous\ud feature interpolation schemes. Our approach enables the capture\ud of the general bathymetry profile of a fjord in north-west\ud Greenland close to Cape York, when compared to observational\ud data. We validate our synthetic approach by demonstrating\ud reduced overestimation of depths compared to past\ud attempts to constrain fjord bathymetry. We also present an\ud analysis of the spectral characteristics of fjord centrelines using\ud recently acquired bathymetric observations, demonstrating\ud how a stochastic model of fjord bathymetry could be parameterised\ud and used to create different realisations.

We derive the scattered component (hereafter referred to as the incoherent component) of glacier surface echoes from airborne radio-echo sounding measurements over Devon Ice Cap, Arctic Canada, and compare the scattering distribution to firn stratigraphy observations from ground-based radar data. Low scattering correlates to laterally homogeneous firn above 1800 m elevation containing thin, flat, and continuous ice layers and below 1200 m elevation where firn predominantly consists of ice. Increased scattering between elevations of 1200–1800 m corresponds to firn with inhomogeneous, undulating ice layers. No correlation was found to surface roughness and its theoretical incoherent backscattering values. This indicates that the scattering component is mainly influenced by the near-surface firn stratigraphy, whereas surface roughness effects are minor. Our results suggest that analyzing the scattered signal component of glacier surface echoes is a promising approach to characterize the spatial heterogeneity of firn that is affected by melting and refreezing processes.

The seafloor of inner continental shelves on glaciated margins is sometimes stripped of most of the softer sediments, leaving bedrock exposed (Wellner et al. 2001). Examples of such exposed bedrock regions have been observed in the inner parts of several cross-shelf troughs on the West Antarctica margin, including those in the Amundsen Sea (Lowe & Anderson 2003; Graham et al. 2009) and Marguerite Bay (Anderson & Fretwell 2008). The detailed morphology of these areas consists of various features of glacial origin, predominantly parallel grooves or striations. These areas can also contain sinuous channels that are incised deeply into the rock substrate. Some prominent examples of channels eroded into exposed bedrock are found in Pine Island Bay in the Amundsen Sea, West Antarctica (Fig. 1a–c). The channels were first reported by Lowe & Anderson (2003). They exhibit a range of sizes and orientations. The largest channels are as deep as 400–500 m and as wide as 1000–2000 m (Fig. 1e). Secondary channels are up to 10–100 m deep and up to hundreds of metres wide. …

The ice cap of Austfonna in eastern Svalbard is the largest in the Eurasian Arctic at 8000 km2 and has about 200 km of marine-terminating ice cliffs (Dowdeswell et al. 2008). Several of its drainage basins are of surge type (Meier & Post 1969) and, between 1936 and 1938, one of these basins (Brasvellbreen; 1100 km2) increased its velocity rapidly and underwent an advance of about 20 km along a 30 km wide front (Schytt 1969). Since that time the ice-cap terminus has stagnated and retreated, losing mass by a combination of surface melting, thinning and iceberg production. Retreat has revealed several distinctive and well-preserved submarine landforms (Fig. 1) linked to this recent surge activity (Solheim & Pfirman 1985; Solheim 1991). Fig. 1. ( a ) Rhombohedral ridges and a terminal moraine ridge on the seafloor offshore of Brasvellbreen, an outlet of the Austfonna ice cap in eastern Svalbard. Image courtesy of the Norwegian Hydrographic Service (Permission no. 14/G754). Acquisition system Kongsberg EM1002. Frequency 97 kHz. Grid-cell size 3 m. The ridges are interpreted to have been formed by the filling of basal crevasses with deforming diamictic sediment. ( b ) Oblique aerial photograph of the surge and rapid advance of Brasvellbreen in 1938 (Photo S38-1958; courtesy of Norsk Polarinstitutt). ( c ) Location of study area (red box; map from IBCAO v. 3.0). ( d …

Iceberg ploughmarks are produced when the keels of drifting icebergs impinge upon and cut into seafloor sediments. They are common landforms of high-latitude shelves and fjords, especially in water shallower than about 500 m where they are easily detected using modern multibeam echo-sounding and earlier side-scan sonar systems (e.g. Lien 1983; Dowdeswell et al. 1993). In addition, similar buried morphological features have been imaged within Quaternary sediments on palaeo-shelves using 3D seismic methods (e.g. Dowdeswell & Ottesen 2013). Five examples of unusual linear to curvilinear features from the seabed of the Norwegian continental shelf are presented (Fig. 1). The first and rather small feature is from outside Brasvellbreen (Fig. 1a), an outlet glacier of Austfonna in E Svalbard. The looped feature is about 15 m wide and 1 m deep and has small berms on either side. The diameter of the loop is about 1.2 km. The feature is found on top of a dense criss-crossing pattern of similar features on the seafloor in water depths of around 40 m. Fig. 1. Iceberg ploughmarks on the Norwegian continental shelf and upper slope (located in (g)). ( a ) An almost-circular iceberg ploughmark outside Brasvellbreen, Austfonna, Svalbard. ( b ) Peculiarly shaped iceberg ploughmark in the central Barents Sea. ( c ) Iceberg ploughmark demonstrating rotation, central Barents Sea. The many small round …

The shallow shelf waters of the Beaufort Sea have experienced marine transgression during the Holocene (Hill et al. 1985; Taylor et al. 2013). This has led to a warming of what was terrestrial permafrost by water incursion, and to the dissociation of subsurface gas hydrates which now vent into marine waters. Accompanying this change is the development of conical submarine landforms produced through the extrusion of sediments, combined with the continuing reworking of the seafloor by the ploughing action of the keels of drifting ice (Fig. 1). Fig. 1. Multibeam swath bathymetry and bathymetric profiles of mud volcanoes and ice-keel ploughmarks on the Beaufort Sea shelf, Arctic Canada. ( a ) Sun-illuminated multibeam-bathymetric image showing mud volcanoes and ice-keel ploughmarks. Acquisition system Kongsberg EM302. Frequency 30 kHz. Grid-cell size 5 m. White arrows denote a curvilinear ploughmark cross-cutting its previous track. The image is a compilation of data from CCGS Amundsen -based surveys in 2009 and 2011. The NW–SE narrow, linear artefacts arise from instrumentation employed in the initial survey. Wide, curvilinear artefacts arise from different instrumentation employed in a subsequent survey. ( b ) Sun-illuminated multibeam-bathymetric image showing a swarm of mud volcanoes. Acquisition system Kongsberg EM3002. Frequency 300 kHz. …

Linear to curvilinear depressions on high-latitude continental shelves have long been regarded as the signature of the ploughing action of iceberg keels impinging on the sedimentary seafloor (e.g. Woodworth-Lynas et al. 1991). These depressions vary in dimensions and pattern with the size of calved icebergs and their drift tracks through the polar seas. Two different sizes of iceberg have affected the shelf north of Svalbard, producing distinctive sets of ploughmarks (Dowdeswell et al. 2010). Large numbers of linear and curvilinear depressions are present on the seafloor of the northern Svalbard margin at water depths of

Turbid meltwater plumes and ice-proximal fans occur where subglacial streams reach the grounded marine margins of modern and ancient tidewater glaciers. However, the spacing and temporal stability of these subglacial channels is poorly understood. This has significant implications for understanding the geometry and distribution of Quaternary and ancient ice-proximal fans that can form important aquifers and hydrocarbon reservoirs. Remote-sensing and numerical-modelling techniques are applied to the 200 km long marine margin of a Svalbard ice cap, Austfonna, to quantify turbid meltwater-plume distribution and predict its temporal stability. Results are combined with observations from geophysical data close to the modern ice front to refine existing depositional models for ice-proximal fans. Plumes are spaced ca 3 km apart and their distribution along the ice front is stable over decades. Numerical modelling also predicts the drainage pattern and meltwater discharge beneath the ice cap; modelled water-routing patterns are in reasonable agreement with satellite-mapped plume locations. However, glacial retreat of several kilometres over the past 40 years has limited build-up of significant ice-proximal fans. A single fan and moraine ridge is noted from marine-geophysical surveys. Closer to the ice front there are smaller recessional moraines and polygonal sediment lobes but no identifiable fans. Schematic models of ice-proximal deposits represent varying glacier-terminus stability: (i) stable terminus where meltwater sedimentation produces an ice-proximal fan; (ii) quasi-stable terminus, where glacier readvance pushes or thrusts up ice-proximal deposits into a morainal bank; and (iii) retreating terminus, with short still-stands, allowing only small sediment lobes to build up at melt-stream portals. These modern investigations are complemented with outcrop and subsurface observations and numerical modelling of an ancient, Ordovician glacial system. Thick turbidite successions and large fans in the Late Ordovician suggest either high-magnitude events or sustained high discharge, consistent with a relatively mild palaeo-glacial setting for the former North African ice sheet.

Acoustically stratified sediments that infill glacially eroded bedrock basins are common in fjords (Seramur et al. 1997; Gilbert et al. 1998; Hogan et al. 2012; Dowdeswell & Vasquez 2013). Internally, such stratified sediments are often characterized by relatively smooth reflections that parallel the seafloor. Sills between basins usually comprise bedrock, sometimes covered by a thin veneer of glacimarine sediment and/or till. Fjords in West Greenland, including Rink Fjord and Vaigat, contain bedrock basins infilled by acoustically stratified sediment (Fig. 1). The basin fills are a product of rain-out from turbid meltwater plumes, probably supplemented by iceberg-rafting and downslope resedimentation. Fig. 1. Multibeam bathymetry and acoustic sub-bottom profiles of submarine basins close to the coast of West Greenland. ( a ) Multibeam bathymetry from Rink Fjord, West Greenland, with water depths >1000 m. ( b ) 3.5 kHz sub-bottom profile from Rink Fjord showing stratified, conformable basin fill (Facies 2) between basement pinnacles (Facies 1). VE×96. ( c , d ) Multibeam bathymetry in Vaigat strait and a coastal basin, West Greenland, respectively; arrows indicate ice-flow directions during the last glacial based on the orientation of sculpted …

Terminal moraines are relatively large ridges of diamictic glacial debris produced at the outermost margins of past glaciers and ice sheets. Their identification on land is important in mapping the maximum extent of Quaternary ice sheets (e.g. Svendsen et al. 2004; Benn & Evans 2010). In marine environments where fast-flowing ice streams reach the shelf edge during full-glacial intervals, moraine ridges are not usually present and the seafloor is characterized by parallel-to-flow streamlined sediments (Ottesen & Dowdeswell 2009). Submarine terminal moraine ridges, by contrast, appear more typical of slower-flowing marine ice margins (Dahlgren et al. 2002; Dowdeswell & Elverhoi 2002; Dowdeswell et al. 2016). A very large ridge, about 150 km long and up to approximately 200 m high relative to the adjacent shelf, is located on the outermost part of the mid-Norwegian continental shelf edge between about 65° and 66° N (Fig. 1a). It is known as Skjoldryggen (‘skjold’ means ‘shield’ and ‘ryggen’ means ‘the ridge’ in Norwegian). Along most of its length, the ridge has a steeper offshore slope relative to …

The Labrador Shelf is characterized by several cross-shelf troughs separated by intervening shallower banks. The troughs were probably occupied by fast-flowing ice streams in the Late Pleistocene. Hopedale Saddle trough has a long Quaternary history of till progradation at the shelf edge, and the modern continental slope developed over a major 0.3 Ma shelf-edge failure complex. The upper slope exhibits a series of relatively narrow and deep gullies, whereas the mid-slope contains wider and shallower channels that are locally anastomosing (Fig. 1a). The erosional submarine landforms on the slope are likely to be linked to the delivery of dense sediment-rich meltwater to the shelf edge from a full-glacial ice stream (Piper et al. 2012). Fig. 1. Multibeam bathymetry and seismic profile of gullies and channels on the continental slope in the central Hopedale Saddle region, offshore of Labrador. ( a ) Swath-bathymetric image. Examples of areas of convergent (C) and divergent (D) channel sections are labelled. IL, inner levee; T, incised-thalweg channel. White arrows indicate examples of artefacts. Acquisition system Kongsberg EM300. Frequency 30 kHz. Grid-cell size 10 m. ( b ) Location of study area (red box; map from GEBCO_08). ( c ) Seismic-reflection profile x–x′ across several channels along the mid-slope (located in (a)). VE×17. Acquisition system Sleeve-gun. Frequency 120–850 Hz. MIS, Marine Isotope Stage; GFD, glacigenic debris-flow; H, Heinrich Layer. ( d ) Enlarged oblique …

This is the author accepted manuscript. The final version is available from the Geological Society of London via https://doi.org/doi.org/10.1144/M46.70

Terminal and recessional moraine ridges are built up on high-latitude continental shelves and in fjords during glacial maxima and still-stands punctuating deglaciation. Such ridges are often found in association with relatively shallow banks and are seldom located in major crossshelf troughs where past ice streams tend to have produced subglacial landforms streamlined in the direction of former ice flow (e.g. Dahlgren et al. 2002; Dowdeswell & Elverhøi 2002; Ottesen & Dowdeswell 2009). Many of these ridges are relatively large, at tens of metres in height above the general level of the seafloor, and have been modified little during the Holocene (e.g. Ottesen et al. 2005). The preservation of these prominent submarine glacial landforms is often linked to relatively low interglacial sedimentation rates and to the lowenergy process environment that is typical of many polar shelves after deglaciation. An exception, however, is where moraine ridges are present at relatively shallow water depths, a situation sometimes enhanced by isostatic rebound during the Holocene. In these circumstances, current and wave action can result in significant modification of moraine ridges.

Grounding-zone wedges (GZWs) are asymmetrical depocentres built up beneath the grounding zone of marine-terminating ice streams through the delivery of soft, deforming subglacial till from upglacier. They are typically tens of metres thick, tens of kilometres in length and usually form subdued transverse-to-flow ridges across the long axes of fjords and cross-shelf troughs on high-latitude continental shelves (e.g. Dowdeswell & Fugelli 2012; Batchelor & Dowdeswell 2015). The ridges, representing the relatively steeper ice-distal face of the wedge, usually appear as small scarps or steps in multibeam imagery. The wedges thin in an ice-proximal direction, often becoming difficult to identify except by using acoustic-stratigraphic methods. Relatively large sedimentary wedges have been identified in multibeam data from several Greenland cross-shelf troughs (e.g. Dowdeswell et al. 2014). The features generally have a scarp at their ice-distal end, and a subdued, low-gradient ice-proximal slope which makes their termination difficult to pinpoint from bathymetric data. Where a basal reflection can be identified, there is some evidence that the wedges thin progressively over a few tens of kilometres away from the former ice margin and have a characteristic asymmetry along trough axes. A multibeam image of a modern wedge from the outer shelf of …

The fjords of Chilean Patagonia are areas of relatively rapid Holocene sediment delivery from glacial, glacifluvial and fluvial systems. These systems are fed by substantial ice- and snow-melt on the flanks of the Andean mountains. Many fjords are infilled by tens of metres of fine-grained, acoustically laminated sediment leading to a relatively flat and undifferentiated appearance of the fjord floor except where mass-wasting and turbidity-current processes are operating (e.g. DaSilva et al. 1997; Araya-Vergara 1999, 2008; Boyd et al. 2008; Dowdeswell & Vasquez 2013). In some areas, pockmarks have been observed on the floor of fjords, whose origin has been linked to the escape of fluids from the underlying sediments. During the analysis and interpretation of almost 27 000 km2 of multibeam-bathymetric imagery from the fjords of Chilian Patagonia between 47° 35′ S and 50° 17′ S (Fig. 1a), several relatively small areas of the fjord floor were identified as containing crater-like pockmarks (Dowdeswell & Vasquez …

The ~ 200 km-wide Labrador continental shelf consists of a series of shallow banks and intervening cross-shelf troughs (Fig. 1b). Glacial reconstructions suggest that the banks were occupied by slow-flowing ice and the troughs by ice-streams during several Quaternary glaciations (Dyke et al. 2002; Josenhans et al. 1986; Margold et al. 2015). On the continental slope offshore of the Makkovik Bank - southern Hopedale Saddle region, several submarine canyons and interfluves with numerous sediment destabilisation features are visible in multibeam data (Fig. 1a).

At the Last Glacial Maximum (LGM), a 400 km long fast-flowing ice stream drained an interior basin of the Scandinavian Ice Sheet of about 150 000 km2 through Vestfjorden and the adjacent cross-shelf trough of Traenadjupet further downstream (Fig. 1) (Ottesen et al. 2005 a ). Evidence for past ice-stream activity comes from a variety of submarine sedimentary landforms that are streamlined in the direction of past ice flow (Ottesen et al. 2005 b ). Superimposed on these streamlined landforms are several wedge-like sedimentary features orientated transverse to flow. These submarine landforms suggest that deglacial retreat was punctuated by stillstands that produced substantial depocentres known as grounding-zone wedges (GZWs) (e.g. Anderson 1999; Dowdeswell et al. 2008; Dowdeswell & Fugelli 2012; Batchelor & Dowdeswell 2015). Fig. 1. Grounding-zone wedges in Vestfjorden, North Norwegian margin. ( a ) Shaded-relief swath-bathymetric image of a 5500 km2 area of Vestfjorden showing two large GZWs which both override MSGLs and have further MSGLs on their surfaces. The shallowest parts of the GZWs have been affected by the ploughing action of iceberg keels. Acquisition system Kongsberg EM100. Frequency 97 kHz. Grid-cell size 50 m. ( b …

The steep slopes of glacially eroded fjord walls are potential sites for slope failure and mass wasting (Syvitski et al. 1987). Slides of sedimentary material are relatively common but require that sediment is present on fjord sides, often deposited from glaciers before and during their retreat through fjord systems. This debris then fails, producing slides that run out onto fjord floors and leave scars on fjord side-walls. On the steep side-walls and floor of Smeerenburgfjorden, a 25 km long fjord in NW Spitsbergen, Svalbard, more than 30 slide scars and associated depositional zones are observed on both sides of the fjord (Fig. 1) (Ottesen & Dowdeswell 2009). The slide headwalls are usually located on slopes greater than 15°. The depositional zones of the slides are usually (but not always) blocky, and the scar surfaces are also relatively rough (Fig. 1a–d). Many of the slides appear to be composites of several individual failure events (Fig. 1b, c), whereas a few record only single failures (Fig. 1d). Examples of composite failures include at least four events in Figure 1b and three or more in …

The North Sea Basin has been subsiding during the Quaternary and contains hundreds of metres of fill. Seismic surveys (170 000 km2) provide new evidence on Early Quaternary sedimentation, from about 2.75 Ma to around the Brunhes-Matuyama boundary (0.78 Ma). We present an informal seismic stratigraphy for the Early Quaternary of the North Sea, and calculate sediment volumes for major units. Early Quaternary sediment thickness is > 1000 m in the northern basin and >700 m in the central basin (total about 40 000 km3). Northern North Sea basin-fill comprises several clinoform units, prograding westward over 60 000 km2. Architecture of the central basin also comprises clinoforms, building from the southeast. To the west, an acoustically layered and mounded unit (Unit Z) was deposited. Remaining accommodation space was filled with fine-grained sediments of two Central Basin units. Above these units, an Upper Regional Unconformity-equivalent (URU) records a conformable surface with flat-lying units that indicate stronger direct glacial influence than on the sediments below. On the North Sea Plateau north of 59°N, the Upper Regional Unconformity (URU) is defined by a shift from westward to eastward dipping seismic reflectors, recording a major change in sedimentation, with the Shetland Platform becoming a significant source. A model of Early Quaternary sediment delivery to the North Sea shows sources from the Scandinavian ice sheet and major European rivers. Clinoforms prograding west in the northern North Sea Basin, representing glacigenic debris flows, indicate an ice sheet on the western Scandinavian margin. In the central basin, sediments are generally fine-grained, suggesting a distal fluvial or glacifluvial origin from European rivers. Ploughmarks also demonstrate that icebergs, derived from an ice sheet to the north, drifted into the central North Sea Basin. By contrast, sediments and glacial landforms above the URU provide evidence for the later presence of a grounded ice sheet.