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Geology is a core component of two major multidisciplinary seabed-mapping initiatives in Norway (MAREANO, Marine Base Maps for the Coastal Zone). Helped by Norway’s Nature Diversity Act, which acknowledges geological and landscape diversity alongside biodiversity, geological information has gained recognition nationally as part of an essential foundation for knowledge-based management, both in the coastal zone and offshore. Recently, international focus on the United Nations Sustainable Development Goals has led to the proposal of Essential Geodiversity Variables, a framework for geological (geodiversity) information, intended to stand alongside Essential Variables already defined for climate, biodiversity and oceans (limited to ocean physics, biochemistry, biology, and ecosystems). Here we examine to what extent map products from the Geological Survey of Norway generated under these multidisciplinary mapping initiatives fit within this framework of Essential Geodiversity Variables and how well it is suited to information on marine geodiversity. Although we conclude that the framework is generally a good fit for the marine-relevant Essential Geodiversity Variable classes (geology and geomorphology), we examine opportunities for further highlighting quantitative geodiversity information. We present preliminary examples of substrate diversity and morphological diversity and discuss our experience of geological mapping as part of multidisciplinary initiatives. We highlight many benefits, which far outweigh any perceived or real compromises of this approach in monetary, practical and scientific terms.

Continental shelf sediments are places of both rapid organic carbon turnover and accumulation, while at the same time increasingly subjected to human-induced disturbances. Recent research suggests that shelf sediments might have a role to play as a natural climate solution, e.g. by storing organic carbon if left undisturbed from anthropogenic activity. However, we have an incomplete understanding about the centres of organic carbon accumulation and storage on continental shelves. To better constrain the rate of accumulation and the mass of organic carbon that is stored in sediments, we developed and applied a spatial modelling framework that allows us to estimate those quantities from sparse observations and predictor variables known or suspected to influence the spatial patterns of these parameters. This paper presents spatial distribution patterns of organic carbon densities and accumulation rates in the North Sea and Skagerrak. We found that organic carbon stocks and accumulation rates are highest in the Norwegian Trough, while large parts of the North Sea are characterised by low stocks and zero net accumulation. The total stock of organic carbon that is stored in the upper 0.1 m of sediments amounted to 230.5 ± 134.5 Tg C, of which approximately 26 % is stored in the Norwegian Trough. Rates of organic carbon accumulation in the Norwegian Trough are comparable with those reported from nearby fjords. We provide baseline datasets that could be used in marine management, e.g. for the establishment of “carbon protection zones”. Additionally, we highlight the complex nature of continental shelves with zones of rapid carbon cycling and accumulation juxtaposed, which will require further detailed and spatially explicit analyses to constrain sedimentary organic carbon stocks and accumulation rates globally.

Gas flares from natural sources of hydrocarbon gases escaping through the seafloor to the water column is a phenomenon observed in many parts of the World’s Oceans. The occurrence of these acoustically and visually observed seepages have been recorded by using various sensors onboard different platforms. But the use of multibeam echosounder systems, with the capability of recording the whole water column acoustic backscattering, in recent years have given the opportunity to cover large areas in a short time span along with bathymetric mapping in a cost-effective way. Even though the data sizes are multiple orders of magnitude larger, the use of dedicated software’s and high-performance processing systems have given the opportunity to find acoustic anomalies resulting from the streaming of gas bubbles in water column.The MAREANO programme which is aimed at mapping habitats through various methods has surveyed large areas of the Norwegian Arctic using multibeam systems. This has resulted in the acquisition of water column acoustic data covering a large area of Arctic Norway over in the last decade. These data have been interpreted and analysed together with other geological and ancillary data from other sensors such as photo/video observations, backscatter data, etc. leading us to relate these anomalies to various structural and geological formations. The database also gave us an opportunity to compare the differences between some of the multibeam systems in capturing these acoustic anomalies. More than approximately 5000 flares of varying magnitude and sizes were detected based on MAREANO water column data, in an area of about 139000 km2. We present the results from these comprehensive surveys and discuss various possibilities that such a database can provide for present and future understanding in the development of Arctic.

Results from geological mapping within the MAREANO (Marine Areal Database for Norwegian Coasts and Sea Areas) programme and mapping projects in the coastal zone reveal a rich and diverse seafloor in Norwegian territories. The geomorphology and sediment distribution patterns reflect a complex geological history, as well as various modern-day hydrodynamic processes. By early 2019, MAREANO has mapped more than 200 000 km 2 ( c. 10%) of Norwegian offshore areas, spanning environmental gradients from shallow water to more than 3000 m depth, with ocean currents in places exceeding 1 m s −1 and water temperatures below −1°C. Inshore, along the 100 000 km-long Norwegian coastline, the Geological Survey of Norway (NGU) has conducted a series of seabed mapping projects in collaboration with local communities, industry and other stakeholders, resulting in detailed seabed and thematic maps of seabed properties covering c. 10 000 km 2 (11% of the areas). Bathymetric and geological maps produced by MAREANO and coastal mapping projects provide the foundation for benthic habitat mapping when combined with biological and oceanographic data. Results from the mapping conducted over the past decade have significantly increased our understanding of Norway's seabed and contributed to the knowledge base for sustainable management. Here we summarize the main results of these mapping efforts.

Hundreds of newly discovered gas seeps, craters, and mounds are presented from the central Barents Sea, Norway. Where they occur together, the crater-mound pairs have a preferred orientation towards the southeast. According to complex cross-cutting relationships with iceberg ploughmarks, both the craters and mounds formed during deglaciation (ca. 11–13 ka BP). Free gas, trapped beneath shallow gas hydrates in discrete areas, deformed or displaced overlying bedrock and sediment, forming mounds. Over-steepened slopes, weak layers, fractured bedrock, and unstable sediment resulted in small landslides towards the southeast: the direction of regional slope. In some cases, the highly buoyant, hydrate-cored sediment mounds may have instead, detached and floated with bottom currents before being re-deposited, either locally or distally. In this scenario, southeasterly flowing bottom currents would also explain the preferred orientation of the observed crater-mound pairs. Crater collapse would have occurred simultaneously or subsequently to landslide or detachment and floating due to the rapid dissociation of any remaining gas hydrates; a result of attendant regional changes in temperature and pressure following deglaciation and local removal of overlying sediment. The model of formation developed in this study explains the southeasterly trend in crater-mound orientation, but differs from other studies that interpret modern mounds, located elsewhere in the Barents Sea, as gas hydrate-cored.

In 2016, through a collaboration between marine mapping programmes in Norway, Ireland, and the UK, we published a new classification scheme to aid the characterisation of seabed geomorphology (Dove et al., 2016). The classification scheme was developed to address shared objectives and challenges in seabed mapping, particularly to enable more consistent classification where required. The novel aspect of this framework was the effort to independently describe seabed features according to their observed physical 1-Morphology, and the more subjective interpretation of their origin and evolution (2-Geomorphology). Initial application of the approach within our own groups and externally proved promising, and through the welcome involvement of colleagues from Geoscience Australia, we continued to progress and improve the approach.We are now within the second phase of the project, which involves the development of glossaries for both parts of the classification scheme. The glossary for part-1 Morphology was recently completed and published (Dove et al., 2020). This glossary includes a revised list of feature names, with definitions and representative diagrams for each feature. Feature definitions are in-part drawn from the International Hydrographic Organization (IHO) guide for undersea feature names, which were modified and augmented with additional terms to ensure the final feature catalogue and glossary encompasses the diversity of morphologies observed at the seabed.Part-2 Geomorphology glossary is now in development. We anticipate it to be more complicated than the Morphology glossary due to the (often) variable meaning of different terms between different fields and individual scientists. But as for Part 1, our primary objective is to produce a useful and robust framework (applicable from the coastal zone to the abyss), that minimises duplication and/or ambiguity as much as possible. The Geomorphology glossary will include example bathymetry images to add further value.Dove, D., Bradwell, T., Carter, G., Cotterill, C., Gafeira Goncalves, J., Green, S., Krabbendam, M., Mellett, C., Stevenson, A., Stewart, H. and Westhead, K., Scott, G., Guinan, J., Judge, M., Monteys, X., Elvenes, S., Maeten, N., Dolan, M., Thorsnes, T., Bjarnadottir, L., Ottesen, D., 2016. Seabed geomorphology: a two-part classification system. British Geological Survey, Open Report OR/16/001.Dove, D., Nanson, R., Bjarnadóttir, L.R., Guinan, J., Gafeira, J., Post, A., Dolan, M.F.J., Stewart, H., Arosio, R. and Scott, G., 2020. A two-part seabed geomorphology classification scheme:(v. 2). Part 1: morphology features glossary.

The use of habitat distribution models (HDMs) has become common in benthic habitat mapping for combining limited seabed observations with full-coverage environmental data to produce classified maps showing predicted habitat distribution for an entire study area. However, relatively few HDMs include oceanographic predictors, or present spatial validity or uncertainty analyses to support the classified predictions. Without reference studies it can be challenging to assess which type of oceanographic model data should be used, or developed, for this purpose. In this study, we compare biotope maps built using predictor variable suites from three different oceanographic models with differing levels of detail on near-bottom conditions. These results are compared with a baseline model without oceanographic predictors. We use associated spatial validity and uncertainty analyses to assess which oceanographic data may be best suited to biotope mapping. Our results show how spatial validity and uncertainty metrics capture differences between HDM outputs which are otherwise not apparent from standard non-spatial accuracy assessments or the classified maps themselves. We conclude that biotope HDMs incorporating high-resolution, preferably bottom-optimised, oceanography data can best minimise spatial uncertainty and maximise spatial validity. Furthermore, our results suggest that incorporating coarser oceanographic data may lead to more uncertainty than omitting such data.

Continental shelf sediments are places of both rapid organic carbon turnover and accumulation, while at the same time increasingly subjected to human-induced disturbances. Recent research suggests that shelf sediments might have a role to play as a natural climate solution, e.g. by protecting the seafloor against human-induced disturbance. However, we have an incomplete understanding about the centres of organic carbon accumulation and storage on continental shelves. To better constrain the rate of accumulation and the mass of organic carbon that is stored in sediments, we developed and applied a spatial modelling framework that allows to estimate those quantities from sparse observations and predictor variables known or suspected to influence the spatial patterns of these parameters. This paper presents spatial distribution patterns of organic carbon densities and accumulation rates in the North Sea and Skagerrak. We found that organic carbon stocks and accumulation rates are highest in the Norwegian Trough, while large parts of the North Sea are characterised by low stocks and zero net-accumulation. The total stock of organic carbon that is stored in the upper 0.1 m of sediments amounted to 230.5 ± 134.5 Tg, of which approximately 26 % are stored in the Norwegian Trough. Rates of organic carbon accumulation in the Norwegian Trough are on par with those reported from nearby fjords. We provide baseline datasets that could be used in marine management, e.g. for the establishment of carbon protection zones. Additionally, we highlight the complex nature of continental shelves with zones of rapid carbon cycling and accumulation juxtaposed, which will require further detailed and spatially explicit analyses to constrain sedimentary organic carbon stocks and accumulation rates globally.

In this paper, we describe the species composition of biotopes occurring in a wide range of environments and present their geographic distribution based on results from quantitative analyses of video-records collected as part of the Norwegian seabed mapping program MAREANO. We present results from an analysis of annotated video records at 757 stations from an area exceeding 100,000 km2 in the Barents Sea and Norwegian Sea. A two-way indicator species analyses (TWINSPAN) was used to identify sample groups and species assemblages for biotope classification. Environmental conditions were compared for the station groups identified at different similarity levels to detect environmental drivers behind each division and hence biotopes indicated by the analysis. In total, 27 groups were identified as potential biotopes in the study area giving a geographic resolution suitable for management needs and subsequent predictive modeling. The faunal composition was mainly correlated with water masses (temperature and salinity). The most distinct biotope identified occurred on Spitsbergenbanken, a shallow area (600 m) NSDW, separating into two TWINSPAN groups. Further divisions of these groups reflected variations in sediment and terrain attributes. Ten biotopes were characterized by indicators species of vulnerable marine ecosystems (e.g., coral gardens, sea pen communities, and sponge aggregations). Knowledge about megafauna composition and biotopes is poor for deep-water benthic habitats in the Arctic region, and better classification of benthic biotopes will be valuable for management purposes such as design of monitoring program for documenting the effects of climate change on ecosystems.

Source at https://doi.org/10.1130/G38195.1. During the last glacial period large parts of the Arctic, including the Barents Sea, north of Norway and Russia, were covered by ice sheets. Despite several studies indicating that melting occurred beneath much of the Barents Sea ice sheet, very few meltwater-related landforms have been identified. We document ∼200 seafloor valleys in the central Barents Sea and interpret them to be tunnel valleys formed by meltwater erosion beneath an ice sheet. This is the first account of widespread networks of tunnel valleys in the Barents Sea, and confirms previous predictions that large parts of the ice sheet were warm based. The tunnel valleys are interpreted to be formed through a combination of steady-state drainage and outburst floods close to the ice margin, as a result of increased melting within a period of rapid climate warming during late deglaciation. This is the first study documenting widespread tunnel valley formation at the northern reaches of a Northern Hemisphere paleo–ice sheet, during advanced deglaciation and beneath a much reduced ice sheet. This indicates that suitable conditions for tunnel valley formation may have occurred more widely than previously reported, and emphasizes the need to properly incorporate hydrological processes in current efforts to model ice sheet response to climate warming. This study provides valuable empirical data, to which modeling results can be compared.

Processes occurring at the grounding zone of marine terminating ice streams are crucial to marginal stability, influencing ice discharge over the grounding‐line, and thereby regulating ice‐sheet mass balance. We present new marine geophysical data sets over a ~30×40 km area from a former ice‐stream grounding zone in Storfjordrenna, a large cross‐shelf trough in the western Barents Sea, south of Svalbard. Mapped ice‐marginal landforms on the outer shelf include a large accumulation of grounding‐zone deposits and a diverse population of iceberg ploughmarks. Published minimum ages of deglaciation in this region indicate that the deposits relate to the deglaciation of the Late Weichselian Storfjordrenna Ice Stream, a major outlet of the Barents Sea–Svalbard Ice Sheet. Sea‐floor geomorphology records initial ice‐stream retreat from the continental shelf break, and subsequent stabilization of the ice margin in outer‐Storfjordrenna. Clustering of distinct iceberg ploughmark sets suggests locally diverse controls on iceberg calving, producing multi‐keeled, tabular icebergs at the southern sector of the former ice margin, and deep‐drafted, single‐keeled icebergs in the northern sector. Retreat of the palaeo‐ice stream from the continental shelf break was characterized by ice‐margin break‐up via large calving events, evidenced by intensive iceberg scouring on the outer shelf. The retreating ice margin stabilized in outer‐Storfjordrenna, where the southern tip of Spitsbergen and underlying bedrock ridges provide lateral and basal pinning points. Ice‐proximal fans on the western flank of the grounding‐zone deposits document subglacial meltwater conduit and meltwater plume activity at the ice margin during deglaciation. Along the length of the former ice margin, key environmental parameters probably impacted ice‐margin stability and grounding‐zone deposition, and should be taken into consideration when reconstructing recent changes or predicting future changes to the margins of modern ice streams.

Recently acquired multibeam echosounder data from the shallowest part (26–53 m depth) of Spitsbergenbanken in the western Barents Sea reveal a variety of bedforms, including megaripples, sandwaves and sandbanks. The bedforms exhibit varying degrees of superimposition and differ in their age of formation and present depositional regime, being either active or moribund. These are the first observations of co-occurring current induced bedforms in the western Barents Sea and provide evidence of a high energy environment in the study area. The bedforms indicate both sediment erosion and transport and confirm that there is enough sand available in this area to maintain them. Such conditions are not known to be common in the western Barents Sea and reflect the unique oceanographic and benthic environment of Spitsbergenbanken. © 2019 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license

Distinct assemblages of landforms are produced by retreating ice streams (e.g. Stokes & Clark 1999; Wellner et al. 2006). The composition of landforms is governed by ice-stream retreat dynamics, implying that ice-stream dynamics can be reconstructed from these geomorphic patterns. This method has been used to decipher the retreat dynamics of an ice stream that occupied the Kveithola Trough on the western Barents Sea margin, presumably during the Late Weichselian deglaciation (Rebesco et al. 2011; Ruther et al. 2012; Bjarnadottir et al. 2013). Kveithola Trough contains a diverse assemblage of landforms related to the presence and withdrawal of an ice stream, as well as to postglacial processes (Fig. 1a, b), described in detail by Bjarnadottir et al. (2013). Here, the acoustic-stratigraphic units defined by Bjarnadottir et al. (2013) are used, with a focus on seafloor morphology relating to the ice-stream landform assemblage. Fig. 1. Multibeam swath bathymetry from Kveithola Trough, western Barents Sea. ( a ) Swath-bathymetric image showing trough geomorphology. White polygons indicate locations of detail images (c–f). White lines indicate profiles in Figures 2 and 3. VE×8. ( b ) Location of study area (red box; map from IBCAO v. 3.0). ( c ) Oblique view of ice-stream onset zone, showing drumlins and channels. VE×20. ( d ) Oblique image showing multiple generations of grounding-line fans downstream of a GZW. VE×20. ( e ) Oblique view of MSGLs on/beneath GZWs. VE×35. ( f ) Oblique view of diverging MSGLs, shelf edge and gullies on upper slope. VE×16. Images (c–f) are viewed from the black stippled lines. Acquisition system Kongsberg Simrad EM300. Frequency 30 kHz. Grid-cell size 10 m. Kveithola is on the western margin of the Barents Sea, 40 km NW of Bear Island (Fig. 1b). The trough is c. 90–120 km long, 10–15 km wide (slightly wider at the seaward end) and 200–700 …

New high-resolution multibeam bathymetry and sub-bottom profile datasets from Fingerdjupet are used for the first detailed geomorphological mapping of the seafloor in this area. The mapped landforms provide evidence for a palaeo-ice stream flowing in a southeasterly direction from Spitsbergenbanken into Fingerdjupet, merging with Bjornoyrenna ice stream, and confirm a theorised palaeo-ice divide located along the bank. The combined landform records and acoustic stratigraphy allow a detailed reconstruction of the glacial dynamics during the last deglaciation. The withdrawal of the Fingerdjupet ice stream from Bjornoyrenna was characterised by rapid retreat, punctuated by periods of stable ice marginal conditions. Five to six major ice margin stillstands and/or readvances associated with the last deglaciation are identified in the seafloor record and acoustic stratigraphy. During these events, large grounding zone wedges were deposited at the ice stream margin. The seabed geomorphology indicates that ice stream dynamics changed as the ice stream retreated from the trough onto the shallower bank. Here, numerous retreat moraines indicate that a grounded ice margin retreated slowly, with several minor stillstands, towards north-northwest. Several controls and/or drivers on the style of ice flow and retreat have been suggested, including catchment size reduction, sea level rise, bedrock topography, drawdown of bank ice and/or migration of the main ice divide over the bank.

Our understanding of processes relating to the retreat of marine-based ice sheets, such as the West Antarctic Ice Sheet and tidewater-terminating glaciers in Greenland today, is still limited. In particular, the role of ice stream instabilities and oceanographic dynamics in driving their collapse are poorly constrained beyond observational timescales. Over numerous glaciations during the Quaternary, a marine-based ice sheet has waxed and waned over the Barents Sea continental shelf, characterized by a number of ice streams that extended to the shelf edge and subsequently collapsed during periods of climate and ocean warming. Increasing availability of offshore and onshore geophysical data over the last decade has significantly enhanced our knowledge of the pattern and timing of retreat of this Barents Sea ice sheet (BSIS), particularly so from its Late Weichselian maximum extent. We present a review of existing geophysical constraints that detail the dynamic evolution of the BSIS through the last glacial cycle, providing numerical modelers and geophysical workers with a benchmark data set with which to tune ice sheet reconstructions and explore ice sheet sensitivities and drivers of dynamic behavior. Although constraining data are generally spatially sporadic across the Barents and Kara Seas, behaviors such as ice sheet thinning, major ice divide migration, asynchronous and rapid flow switching, and ice stream collapses are all evident. Further investigation into the drivers and mechanisms of such dynamics within this unique paleo-analogue is seen as a key priority for advancing our understanding of marine-based ice sheet deglaciations, both in the deep past and in the short-term future.

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.

A better understanding of marine geomorphology is a common goal for seabed mapping programmes, with various mapping approaches, methodologies and challenges associated with systematically describing geomorphological features. To address these issues, and highlight the overall value of geomorphological mapping, a group of representatives from the seabed mapping programmes of the geological surveys of Norway, Ireland and the United Kingdom have formed a partnership to share their knowledge, expertise and technologies. Here we describe the first year of collaboration by outlining the background to and motivation for the groups’ national seabed mapping programmes, and presenting several case studies as well as tests to potentially adopt a harmonised classification scheme.

This paper presents a seabed sediments (grain size) map of the Nordland VI area (25,000 km2) off the Lofoten islands, north Norway. The map is based on multibeam echosounder data (bathymetry and backscatter), visual analysis of 215 video transects (each 700-m long), and visual and grain-size analysis of seabed sediment samples from 40 sampling stations acquired by grabs, boxcores and multicores. A total of 14 sediment classes were identified, with sediments varying in grain size from mud to boulders. Seabed types also include bedrock and bioclastic sediments from degrading cold-water coral reefs. The continental shelf is mostly characterised by coarse-grained sediments such as gravelly sand and sandy gravel, especially in till areas. In basins and glacial troughs, finer-grained sediments such as sandy mud and muddy sand dominate. The upper continental slope (300–600-m water depth) is characterised by coarse-grained sediments related to the influence of the strong north-east flowing Norwegian Atlantic Current. In deeper areas, finer-grained sediments are prominent. Below 1000-m depth, mostly mud and mud with sediment blocks occur.

The Barents Sea Ice Sheet (BSIS) is a good palaeo-analogue for the present day West Antarctic Ice Sheet. Both were marine-based ice sheets, particularly vulnerable to ocean warming and sea-level rise. Understanding the BSIS ice dynamics and patterns of retreat since the Last Glacial Maximum (LGM) is useful in developing our knowledge of spatial and temporal variations during marine-based ice sheet retreat. While the western margins of the Barents Sea have been extensively studied, few studies have focused on the central regions, which hosted key ice stream tributaries and major ice domes and divides. Presenting a new high-resolution (5 m) bathymetric dataset, this glacial geomorphological study focuses on the Sentralbankrenna palaeo-glacial system in the central Barents Sea. A large number of grounding zone wedges, mega-scale glacial lineations and areas with tunnel valleys and palaeo-subglacial basins were identified. These form the basis for a six-stage reconstruction of ice stream retreat through deglaciation since the LGM. In reconstructing the retreat of the Sentralbankrenna Ice Stream, we document the rapid but highly spatially variable pattern of retreat of a marine-based ice sheet margin. The presence of several tunnel valleys and interconnected palaeo-subglacial basin systems indicates an abundance of meltwater, likely to have been stored and released through several discharge events, significantly influencing the ice stream margin dynamics. This study provides insight into the behaviour and dynamics of ice during the late stages of the BSIS deglaciation within the central Barents Sea, increasing our understanding of grounding line processes.

Palaeo-records of rapid ice stream retreat are important as they can be used to identify the processes involved, and inform investigations of present-day ice masses. Here we document a previously unknown retreat stage in northernmost Bjornoyrenna (Bear Island Trough) in the northern Barents Sea, representing the youngest stage in a stepwise retreat of the Bjornoyrenna Ice Stream. We present a descriptive landsystem model for retreat of a marine-based ice stream, which provides new insights into the glacial dynamics of the episodic retreat stages. This model captures the landforms produced during a cycle of 1) fast ice stream flow, 2) intense calving of large icebergs locked in a dense matrix of smaller icebergs, probably from a collapsed ice shelf, 3) ice-stream stagnation, 4) ice-stream floating off, forming an ice shelf as the grounding line retreats, and eventually 5) ice-shelf disintegration. We hypothesize that the presented ice-stream retreat model reflects glacial surging. The formation of corrugated furrows in the study area is consistent with interpretation of similar features in Pine Island Bay, West Antarctica, which are interpreted to have been formed during a massive ice shelf break-up and associated grounding line retreat. Two directions of past ice flow are indicated from streamlined glacial landforms in the study area. Ice flow from north north-east is indicated for the Last Glacial Maximum and an early phase of deglaciation, whereas a shift to flow from north north-west, from an ice dome located over Hinlopenstretet, Svalbard is indicated for the latest deglaciation phases of the Bjornoyrenna Ice Stream.

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 …

A marine geophysical study reveals a complex deglaciation pattern in the Kveithola trough, W Barents Sea. The data set includes multibeam swath bathymetry and sub-bottom sediment profiler (chirp) data acquired for the whole extent of a palaeo, marine-terminating ice stream, along with high-resolution single-channel seismic data from chosen profiles. The multibeam data show a geomorphic landform assemblage characteristic of ice streams. The results of a combination of seismic and chirp unit stratigraphy reveal that the seabed geomorphology is governed by a deeper-lying reflector. The reflector dominates surface expressions of several subglacial and ice-marginal units, each connected to a separate episode of ice-margin stillstand/advance. Analysis of the combined data set has resulted in a conceptual model of the ice-stream retreat. The model depicts complex deglaciation of a small, confined ice-stream system through episodic retreat. It describes the formation of several generations of grounding-zone systems, characterized by high meltwater discharges and the deposition of fine-grained grounding-line fans. The inferred style of grounding-zone deposition in Kveithola deviates from that of other accounts, and is suggested to be intermediate in the previously described continuum between morainal banks and grounding-line wedges. The results of this paper have implications for grounding-zone theory and should be of interest to modellers of grounding-line dynamics and ice-stream retreat.

The origin of two acoustic sediment units has been studied based on lithological facies, chronology and benthic stable isotope values as well as on foraminifera and clay mineral assemblages in six marine sediment cores from Kveithola, a small trough west of Spitsbergenbanken on the western Barents Sea margin. We have identified four time slices with characteristic sedimentary environments. Before c. 14.2 cal. ka, rhythmically laminated muds indicate extensive sea ice cover in the area. From c. 13.9 to 14.2 cal. ka, muds rich in ice-rafted debris were deposited during the disintegration of grounded ice on Spitsbergenbanken. From c. 10.3 to 13.1 cal. ka, sediments with heterogeneous lithologies suggest a shifting influence of suspension settling and iceberg rafting, probably derived from a decaying Barents Sea Ice Sheet in the inner-fjord and land areas to the north of Kveithola. Holocene deposition was episodic and characterized by the deposition of calcareous sands and shell debris, indicative of strong bottom currents. We speculate that a marked erosional boundary at c. 8.2 cal. ka may have been caused by the Storegga tsunami. Whilst deposition was sparse during the Holocene, Kveithola acted as a sediment trap during the preceding deglaciation. Investigation of the deglacial sediments provides unprecedented details on the dynamics and timing of glacial retreat from Spitsbergenbanken.

Mapping of well-preserved submarine glacial landforms has been used to decipher the pattern and dynamics of the retreat of the Bear Island Trough ice stream that drained the Barents Sea Ice Sheet during the Late Weichselian deglaciation (e.g. Andreassen et al. 2008, 2014; Winsborrow et al. 2010; Ruther et al. 2011; Bjarnadottir et al. 2014). However, the formation processes of some of the landforms identified are not fully understood; one example is that of an enigmatic linear sedimentary seafloor feature termed ‘needle’ by Bjarnadottir et al. (2014). A variety of subglacial landforms co-exist in the Bear Island Trough (BIT), including landforms typically associated with both active ice streams, such as mega-scale glacial lineations (MSGLs) and grounding-zone wedges (GZWs), and ice stagnation (e.g. Ruther et al. 2011; Andreassen et al. 2014; Bjarnadottir et al. 2014). Included among these are remarkably straight and elongate features, termed ‘needles’ by Bjarnadottir et al. (2014), which are described here. Needle-like features occur in the upper BIT at water depths of 230–280 m (Fig. 1a). They are

While there are numerous hypotheses concerning glacial interglacial environmental and climatic regime shifts in the Arctic Ocean, a holistic view on the Northern Hemisphere's late Quaternary ice-sheet extent and their impact on ocean and sea-ice dynamics remains to be established. Here we aim to provide a step in this direction by presenting an overview of Arctic Ocean glacial history, based on the present state-of-the-art knowledge gained from field work and chronological studies, and with a specific focus on ice-sheet extent and environmental conditions during the Last Glacial Maximum (LGM). The maximum Quaternary extension of ice sheets is discussed and compared to LGM. We bring together recent results from the circum-Arctic continental margins and the deep central basin; extent of ice sheets and ice streams bordering the Arctic Ocean as well as evidence for ice shelves extending into the central deep basin. Discrepancies between new results and published LGM ice-sheet reconstructions in the high Arctic are highlighted and outstanding questions are identified. Finally, we address the ability to simulate the Arctic Ocean ice sheet complexes and their dynamics, including ice streams and ice shelves, using presently available ice-sheet models. Our review shows that while we are able to firmly reject some of the earlier hypotheses formulated to describe Arctic Ocean glacial conditions, we still lack information from key areas to compile the holistic Arctic Ocean glacial history. (C) 2013 The Authors. Published by Elsevier Ltd.