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Recently, international focus on the United Nations Sustainable Development Goals has led to the proposal of Essential Geodiversity Variables (EGVs), a framework for geological (geodiversity) information, intended to stand alongside Essential Variables (EVs) already defined for Climate, Biodiversity and Oceans (limited to ocean physics, biochemistry, biology, and ecosystems). In Norway, the Nature Diversity Act, which acknowledges geological and landscape diversity alongside biodiversity, has helped establish geology as part of an essential foundation for knowledge-based management, on land, in the coastal zone and offshore. In keeping with this, geological mapping is a core component of two ongoing national multidisciplinary seabed mapping initiatives [MAREANO, Marine Base Maps for the Coastal Zone (pilot)].Here we examine to what extent marine geological map products from the Geological Survey of Norway generated under these mapping initiatives fit within this EGV framework and how well it is suited to information on marine geodiversity. Further, we examine opportunities for highlighting quantitative geodiversity information through the development of non-traditional marine geological map products. We present some thematic examples at different spatial scales which explore the potential for delivering seabed geodiversity and related geological information more directly. It is important that such information is available in forms that are readily accessible and understandable to a wide range of end users who are largely non-geologists, and that it complements existing information used in coastal and offshore management.

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.

The late Early to early Middle Ordovician Fjellvollen Formation, Central Norwegian Caledonides, is a part of the Ilfjellet Group volcano-sedimentary succession formed in a rift basin that opened along the Laurentian margin. Depositional facies and trace fossils indicate the Nereites ichnofacies, typically found in distal turbidites and deep marine deposits. The recovered trace fossils include ?Alcyonidiopsis, Chondrites, Dictyodora, Gordia, Helminthoidichnites, Macaronichnus, Monomorphichnus, Nereites, Oikobesalon, Palaeophycus, Protovirgularia and Treptichnus. No body-fossils have been reported from the Fjellvollen Formation, but the trace fossils indicate the presence of varied epi- and infaunas of arthropods, bivalves, gastropods and polychaets. The abundance of meandering and looping trace fossils is comparable to what is found in the inferrably time-equivalent Vuddudalen Group farther north, although lack of graphoglyptids like Megagrapton in the Fjellvollen Formation may indicate more proximal, unstable depositional conditions in fan-fringe and adjacent basin-plain settings.

Arc-continent collision, followed by subduction polarity flip, occurs during closure of oceanic basins and contributes to the growth of continental crust. Such a setting may lead to a highly unusual association of ultrapotassic and mid-ocean ridge basalt (MORB)-type volcanic rocks as documented here from an Ordovician succession of the Scandinavian Caledonides. Interbedded with deep-marine turbidites, pillow basalts evolve from depleted-MORB (εNdt 9.4) to enriched-MORB (εNdt 4.8) stratigraphically upward, reflecting increasingly deeper melting of asthenospheric mantle. Intercalated intermediate to felsic lava and pyroclastic units, dated at ca. 474−469 Ma, are extremely enriched in incompatible trace elements (e.g., Th) and have low εNdt (−8.0 to −6.6) and high Sri (0.7089−0.7175). These are interpreted as ultrapotassic magmas derived from lithospheric mantle domains metasomatized by late Paleoproterozoic to Neoproterozoic crust-derived material (isotopic model ages 1.7−1.3 Ga). Detrital zircon spectra reveal a composite source for the interbedded turbidites, including Archean, Paleo-, to Neoproterozoic, and Cambro-Ordovician elements; clasts of Hølonda Porphyrite provide a link to the Hølonda terrane of Laurentian affinity. The entire volcano-sedimentary succession is interpreted to have formed in a rift basin that opened along the Laurentian margin as a result of slab rollback subsequent to arc-continent collision, ophiolite obduction and subduction polarity flip. The association of MORBs and ultrapotassic rocks is apparently a unique feature along the Caledonian-Appalachian orogen. Near-analogous modern settings include northern Taiwan and the Tyrrhenian region of the Mediterranean, but other examples of strictly concurrent MORB and ultrapotassic volcanism remain to be documented.

As the smallest of the palaeo-ice stream systems along the northeastern Atlantic Margin, The Kveithola Palaeo-Ice Stream and its related remnants gives a unique opportunity for mapping the entirety of the system. Both due to its size and history, as a small ice stream nestled between its two major counterparts, the Bear Island and Storfjorden Ice Stream, has put the Kveithola System in the focus for several studies during the last decade. Following three recent cruises, the MAREANO-programme has collected new datasets, where this study is focusing on data retrieved from the end member of the Kveithola Palaeo-Ice Stream, the Kveithola Trough-Mouth Fan (TMF). The dataset contains new bathymetry data from the Kveithola TMF, with a higher resolution than previous studies (10 m cell size), and is covering an area of more than 2000 km2, from the shelf edge towards the deep ocean. The surface revealed by the new data display a morphology that is highly influenced by mass movement processes, where the majority are interpreted as either sliding events or glacigenic debris flows. Based on the bathymetry, the slides appear to differentiate in age, where both older and younger events are present (possibly pre- and post- Last Glacial Maximum), and to have occurred both as single or sequenced events. The Kveithola Slide display features that indicates a retrogressive development, and within the new data there have also been observed three minor retrogressive cracks that foreshadows the potential for the occurrence of new events in the future.

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

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.

Arctic and Antarctic polynyas are crucial sites for deep-water formation, which helps sustain global ocean circulation. During glacial times, the occurrence of polynyas proximal to expansive ice sheets in both hemispheres has been proposed to explain limited ocean ventilation and a habitat requirement for marine and higher-trophic terrestrial fauna. Nonetheless, their existence remains equivocal, not least due to the hitherto paucity of sufficiently characteristic proxy data. Here we demonstrate polynya formation in front of the NW Eurasian ice sheets during the Last Glacial Maximum (LGM), which resulted from katabatic winds blowing seaward of the ice shelves and upwelling of warm, sub-surface Atlantic water. These polynyas sustained ice-sheet build-up, ocean ventilation, and marine productivity in an otherwise glacial Arctic desert. Following the catastrophic meltwater discharge from the collapsing ice sheets at ~17.5 ka BP, polynya formation ceased, marine productivity declined dramatically, and sea ice expanded rapidly to cover the entire Nordic Seas., Polynyas potentially played a role in sustaining marine life during the last glacial, yet their presence and importance remains equivocal. This multi-proxy study reconstructs a corridor of polynyas in the Nordic Seas during the last glacial maximum, and reveals a strong association with biological productivity.

Accepted manuscript version. Published version available at https://doi.org/10.1016/j.margeo.2018.05.006. Accepted manuscript version, licensed CC BY-NC-ND 4.0. Arctic Ocean trough mouth fans (TMFs) represent a valuable archive of glacial-interglacial sedimentary processes that are especially important when reconstructing pre-Weichselian glaciations that may lack distinct imprints on the shelves. In 2011, we acquired the first high-resolution 3D seismic cube (~3 m vertical and 6 m horizontal resolution) on the continental slope of the SW Barents Sea by use of a P-Cable 3D system, to study in detail the seismic stratigraphy and glacial depositional history of the Bear Island Trough Mouth Fan. This technology provides data with a resolution that, for the first time on the western Barents Sea slope, enables detailed mapping of deposits of different glacial cycles. The dataset provides entire spatially coverage, allowing us to reconcile multiple generations of glacigenic deposits and channel systems. High-resolution 3D seismic data is crucial to describe buried channels, glacial units, as well as low relief landforms such as sediment waves accurately. The 30 km2 seismic cube is located at the southern flank of the Bear Island TMF at water depths from 592 to 660 m where sandwaves dominate the present seafloor. The data covers the glacially derived stratigraphy in the uppermost ~700 m below the seafloor. We establish a robust stratigraphic framework by interpreting seismic reflectors along 2D tie-in lines to previously well-constrained seismic and well data. We find that our data provide a record of progradation of glacigenic debris flows (GDFs) since MIS 12 (0.5 Ma) to present. Horizon slices reveal a range of gullies and channels at different depths overlying the GDFs. We describe the paleoenvironment and sedimentary processes throughout this time-span (that covers seven glacial cycles) and discuss the impact of the Barents Sea Ice Sheet waxing and waning on erosion, sedimentation, and deposition along the continental slope. Abundant buried gullies were hitherto unknown at the Bear Island TMF, with previous work describing this succession as a debris-flow dominated unit where meltwater-related features are lacking, and interpreting this to represent low average temperatures. By use of the relatively small high-resolution 3D seismic dataset, we provide new evidence for the presence of gullies and channels indicating that periods of ice sheet melting and meltwater runoff existed throughout the middle-late Pleistocene succession. The work offers new insight into the stratigraphic evolution of a continental margin dominated by GDFs and demonstrates the value of high-resolution seismic, such as the P-Cable system, in resolving important details of paleo-slope-environments.

We integrate morphological, geological and geophysical observations with oceanographic measurements and modelling results to interpret the processes behind the origin and evolution of sandwaves on the upper continental slope of the southwestern Barents Sea. Seven sandwave fields covering c. 130 km2 and with a volume of c. 72 × 106 m3 occur in water depths of c. 475–800 m. Individual sandwaves reach heights up to 6 m. The sandwaves are sinusoidal with asymmetric stoss–lee side relationships, and time lapse multibeam bathymetry analysis indicates that some sandwaves have migrated up to 10 m towards the NNW over a 4-year time period. This contour current parallel migration is counteracted by currents in several other directions, and the sand unit is thus not a simple contourite. Measurements show prominent diurnal period oscillations and clear spring-neap variations of current direction and speed with along-slope and cross-slope current velocities up to 75 cm s−1 and 65 cm s−1, respectively. Numerical ocean modelling results produce eddies travelling along the slope, positionally stable, daily recurring vortices and bottom current velocity up to 100 cm s−1 in the sandwave fields. Sandwave migration towards the SE is also observed, and the cross-slope currents are capable of transporting sand up and down the slope, as evidenced by ripples migrating normal to the sandwaves. Eroded sand accumulates in the sandwave fields along the boundary between North Atlantic Water and Norwegian Sea Arctic Intermediate Water. This is a consequence of the combined effect of the NNW directed along-slope Norwegian Atlantic Current and tidally induced topographic waves. The sandwave fields started to form 11 000–13 000 14C yrs BP or possibly later by current erosion of glacial sediments on the continental shelf and slope.

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.

Accepted manuscript version. Published version available at https://doi.org/10.1016/j.margeo.2014.04.003.Accepted manuscript version, licensed CC BY-NC-ND 4.0. Seabed data acquired from the southern Barents Sea continental margin offshore Norway reveal detailed morphology of large sandwave fields. Multibeam echosounder bathymetry and backscatter, shallow seismic, sediment samples and seabed video data collected by the MAREANO program have been used to describe and interpret the morphology, distribution and transport of the sandwaves. The bedforms lie on a slope dominated by relict glacial forms and muddy/sandy/gravelly sediments. Sandwave migration across small gravity mass failures of the glacial mud constrains the field initiation as early post glacial or later. The contour-parallel nature of the fields and crestlines normal to the bathymetry contours and the geostrophic Norwegian Atlantic Current (NwAC) demonstrate that the NNW-flowing oceanographic circulation is the primary driving current. The fields coincide with the depth range at which a transition between warm, saline and underlying cooler, less saline waters fluctuate across the seabed. Statistically rigorous measurements of height, width and various parameters of slope and symmetry confirm a tendency to downstream (NNW) sandwave migration but with significant exceptions. Anomalous bedform symmetry domains within the fields are tuned to meso-scale topography along (relict) glacial debris flow chutes, indicating current focusing. Upstream and upper slope-derived winnowed sand transport eroded from the glacial sediments is the supposed source. Sandwave flank slope values are comparable to the regional slope such that the gravitational vector would have a cumulative downslope migration affect unless balanced by upslope drivers. Perpendicular cross-cutting of stoss face 3-D ripples by linear (2-D) ripples in the sandwave troughs and lee faces is evidence for non-synchronous, episodic current variations. Though deep Ekman transport and internal wave action are unproven here, these could explain chute-related tuning of bedform symmetry through funneling in the debris flow chutes and favor sand recycling, thus contributing to long-term maintenance of the sandwave field.

High-resolution multibeam bathymetry acquired on the steep continental slope off Lofoten-Vesteralen (LV), North Norway, reveals approximately 15 canyons, some of which are incised 500–1100 m into a sedimentary succession of mainly Quaternary–Cenozoic age. The shape and size of canyons vary considerably, particularly in the southwest where the average slope gradient is 3–5° and where two of the canyons have reached a mature stage and are filled by 200–450 m of sediments. Three canyons confined to the lower-mid slope were probably initiated at the lowermost slope. The initiation process is poorly understood. There is a marked change to steeper slopes (5–8°) northwards, where most of the canyons transect the entire continental slope and are V-shaped in cross section. The majority of the canyons are deeply eroded, with branches formed by slides. Erosion by various mass-movement processes along thalwegs have steepened slopes and reduced stability, causing a retrogressive development by sliding both at canyon heads and at sidewalls. The age of the present canyons, and how they started to form, cannot be determined from the present data. We suggest that the initiation of canyons by mass movements from the shelf edge are most likely in the north. New 2D seismic data reveal several palaeocanyons. Some are partly or totally filled by younger sediments, while others have been rejuvenated. The data indicate that a marked uplift of the LV margin occurred in Mid Miocene time, causing reduced slope stability and formation of the first canyons. Successions of submarine fan/slide deposits up to 700 m thick interbedded with hemipelagic/turbiditic sediments occur on the continental rise at the outlets of canyons where the seabed slope gradient is around 1°. The last phase of significant canyon activity was during the Late Pleistocene, while minor mass movements may have occurred into the Holocene.

Video inspection of the seabed on the continental rise (ca. 2200 m water depth) off Vesteralen–Troms, North Norway has revealed several remarkable features, including large tunnels, small tunnels, chimney tunnels, carbonate crusts and bacterial mats. The structures occur in landslide areas with slide blocks up to 2 km long, 1 km wide and 100 m high. We hypothesize that the large seabed tunnels, in and between slide blocks and with opening diameters up to 1 m and apparent inner diameters of 10–20 cm, are formed by dewatering of fine-grained sediments buried by the slide masses and possibly venting of underground gas reservoirs related to sliding and loading. This process probably occurred instantaneously after sliding. Numerous small tunnels with diameters up to a few centimetres, in slide blocks of compacted sediments, may have formed by dewatering following sudden pressure release or by decomposition of gas hydrates following off-loading of sediments due to sliding. Bacterial mats and carbonate crusts indicate active leakage of subsurface fluids and methane through the seabed and the gas hydrate stability zone, either from thermogenic sources or from shallow reservoirs. Cemented chimney tunnels up to 15 cm tall, and with inner diameters up to a few centimetres occur both on slide blocks and on flat and even seabed. The presence of apparently both inactive and active chimney tunnels indicates that gas and fluid release is a process that has been periodically active, possibly from before sliding up to the present.

The Cenozoic seismic stratigraphy and geological development of the south Voring margin are analyzed to understand their relation to fluid flow and margin stability. The regional stratigraphy and palaeomorphology of the More and Voring basins indicate gradual changes in depositional environment and tectonic compression between 55 Ma to 2.8 Ma during Brygge and Kai periods, and abrupt changes associated with glacial/interglacial cycles from last 2.8 Ma during Naust period. These changes resulted in deposition of various types of sediments and led to processes such as polygonal faulting and dewatering, inter-fingering of contouritic, stratified and glacigenic sediments, and margin progradation. A gas hydrate related bottom simulating reflector (BSR) occurs at Nyegga and within the central Voring Basin while pockmarks are observed at Nyegga only. Diagentic reflectors due to Opal A - Opal CT conversion (DBSRs) occur along a wider area beyond the shelf edge. The DBSRs are located in oozes within the Kai and late Brygge Formations. The gas hydrate BSR occurrence is concentrated above Eocene depocenters in hemipelagic and contouritic sediments deposited during Late Plio-Pleistocene. The BSR overlies polygonal faults and DBSRs but are confined to the slope of anticlines indicating its formation being related to fluid pathways from methanogenic rocks through focused fluid flow. Microbial gas production in Kai, Brygge and deeper formations may have supplied the gas for gas hydrate formation. Fluid expulsion due to DBSR formation and polygonal faulting in oozes may have created overpressure development in permeable layers belonging to the overlying Naust Formation. Slide headwalls are also located close to the anticlines in the study area, implying that over pressured oozes and focussed fluid flow may have been important in creating weak surfaces in the overlying Naust sediments, promoting conditions for failures to occur.

Late Cenozoic seismic stratigraphy of the Voring continental margin has been studied in detail, with emphasis on the geological development of the Naust Formation deposited during the last 3 million years. The Kai Formation (15–3 Ma) comprises mainly biogenic ooze deposited in the More and Voring Basins. In Naust time, there was a marked increase in supply of sediments from the inner shelf areas and the western part of the Scandinavian mountain range, and glaciers expanded to the shelf and reached the shelf edge several times during the last 1.5–2 million years. During early to mid Naust time the shelf was widened by westerly prograding sediment units, but for a long period the shallowest part of the Helland-Hansen Arch (HHA) formed a barrier preventing glacially derived debris from being distributed farther west. West of the HHA, mainly stratified marine and glacimarine sediments were deposited. A substantial part of these sediments were transported by the north-flowing Norwegian Atlantic Current, which redistributed suspended particles from ice streams, rivers, coastal erosion and seabed winnowing. After burial of the crest of the HHA at c. 0.5 Ma, glacial debris and slide deposits were also deposited west of this high. In the north, massive units of glacial debris were distributed beyond the crest of the HHA, also in mid Naust time, thinning westwards and interfingering with fine-grained sediments on the lower slope. The Sklinnadjupet Slide, inferred to be c. 250,000 years old, corresponds in age with an earlier huge slide in the Storegga area. An elongated area of uneven seabed topography previously interpreted as diapirs (Vigrid diapirs) on the slope west of the HHA is shown to be formed by ooze eruption from the crest of the arch and submarine sliding.

Multibeam bathymetry acquired under the MAREANO programme from the continental shelf off Nordland and Troms, northern Norway, show bedforms that we have interpreted as rippled scour depressions. They occur in three areas offshore on bank slopes facing southeast, more than 15 km from land. They are generally found where the slope gradient is low, in water depths of 70–160 m. Individual depressions are up to 3 km long, 1 m deep and up to 300 m wide. They occur in areas where sediments evolve quickly from glacial deposits on the banks to post-glacial muddy sediments on the glacial troughs. Multibeam backscatter and underwater video data show that depression floors are covered by rippled, gravelly, shelly sand. Ripple crests are parallel or slightly oblique to the depression axis orientation. Sand without bedforms is observed between the depressions. TOPAS seismic lines show that the uppermost seismic unit consists of the sand between the depressions. The base of this unit may be the last transgressive/tidal/wave ravinement surface. Physical oceanographic modelling indicates that maximum current velocities are up to 0.6 m/s in the rippled scour depression areas. Stronger currents appear to inhibit the building of these features. Tidal currents play an important role as they trend parallel to the southeast banks slopes and are likely responsible of the gravelly ripples formation inside the depressions as well as the persistence of these depressions which are not covered by finer sediments. On Malangsgrunnen bank, some of the rippled scour depressions are in the extension of NW–SE furrows located on the bank. Simulated bottom currents indicate currents mainly perpendicular to these furrows, as for the rippled scour depressions on the bank slopes. Nevertheless, these features could also highlight currents coming from the northwest which reach the bank margin and continue down to the areas of the rippled scour depressions. These currents could be responsible for the formation of some of the bedforms, together with tidal currents.

Seabed data acquired from the Hola glacial trough off Vesteralen, North Norway, reveal the morphology of spectacular sandwave fields and large sandwaves in great detail. The sandwave fields are among the deepest known, occurring in water depths of 200–260 m. Multibeam bathymetry and backscatter, shallow seismic, sediment samples and video data collected by the MAREANO programme and bottom current modelling results have been used to interpret morphology, transport and distribution of the seabed sediments. Sand supply to the Hola trough was initially from wave and current reworking of glacial and glaciomarine deposits during the eustatic sea level lowstand and sea level rise after the last glaciation. More recently deposited bioclastic sand dominates the upper part of the sand unit, which locally reaches 10 m thickness. Sand predominantly accumulates behind ridges, where current strength decreases, and in topographic lows. Straight-crested and barchan-type sandwaves up to 3 km long and 7 m high are interpreted to form by tidal and geostrophic currents with bottom current speeds reaching 0.7–0.8 m s − 1 . A large cluster of coral reefs occur immediately east of the barchan-type sandwaves, where modelling shows bottom current velocities up to c. 1 m s − 1 . Sandwaves occur in four major sandwave fields. Strong variation in the nature of sandwaves over short distances, e.g., migration direction, between neighbouring sandwave fields point to important local variations in current regime and sedimentary processes. The present work demonstrates how local topography and interaction of several current systems may produce complex depositional patterns on a local scale. Detailed multibeam mapping and video inspection of open shelf troughs in other narrow shelf settings worldwide may reveal similar sandwave fields.

Pockmarks are observed worldwide along the continental margins and are inferred to be indicators of fluid expulsion. In the present study, we have analysed multibeam bathymetry and 2D/3D seismic data from the south-western Barents Sea, in relation to gas hydrate stability field and sediment type, to examine pockmark genesis. Seismic attributes of the sediments at and beneath the seafloor have been analysed to study the factors related to pockmark formation. The seabed depths in the study area are just outside the methane hydrate stability field, but the presence of higher order hydrocarbon gases such as ethane and/or propane in the expelled fluids may cause localised gas hydrate formation. The selective occurrence of pockmarks in regions of specific seabed sediment types indicates that their formation is more closely related to the type of seabed sediment than the source path of fluid venting such as faults. The presence of high acoustic backscatter amplitudes at the centre of the pockmarks indicates harder/coarser sediments, likely linked to removal of soft material. The pockmarks show high seismic reflection amplitudes along their fringes indicating deposition of carbonates precipitated from upwelling fluids. High seismic amplitude gas anomalies underlying the region away from the pockmarks indicate active fluid flow from hydrocarbon source rocks beneath, which is blocked by overlying less permeable formations. In areas of consolidated sediments, the upward flow is limited to open fault locations, while soft sediment areas allow diffused flow of fluids and hence formation of pockmarks over a wider region, through removal of fine-grained material.

Acoustic equipment, including interferometric sonar and parametric sub-bottom profiler, have been used to determine the volume and lateral spread of dredged sediments disposed in the natural submarine depression in the Bekkelag Basin, inner Oslofjord since the beginning of the Oslo Harbor remediation project in 2006. This natural depression is used as a subaqueous confined disposal facility (CDF). Calculation of the volume of disposed sediments in the CDF is based on elevation change, derived from two high-resolution bathymetric datasets obtained in 2004, i.e. before the onset of the remediation project, and in April 2008. Seismic profiles across the CDF have been used to estimate the settlement of the original seabed, caused by loading-induced dewatering and compaction of the seabed sediments under the disposed masses. Detailed bathymetry and backscatter data demonstrate the lateral spread of disposed sediments within a well-confined area covering ca. 195,000 m 2 . The sea bottom within this area is distinctly softer than the surrounding seabed as shown by very low acoustic backscatter amplitude, signifying a very loose surface character of the disposed sediments. The thickness of the disposed sediments reaches 6 m the deepest part of the original depression. The volume calculation of the disposed sediments in the CDF, based solely on bathymetry data, gives a value of ca. 310,000–320,000 m 3 . Settlement of the original seabed as a result of loading has been estimated to be 30 cm at 5 m thickness of the disposed sediments. Under the condition that the settlement rate is linearly correlated to the thickness of disposed sediments, the settlement corrected volume of disposed sediments is ca. 330,000–340,000 m 3 . Presented results demonstrate high accuracy and good reproducibility of acoustic seafloor data, and indicate a great potential of such methods as monitoring tools in environmental projects that involve dredging and subaqueous disposal.

Based on seismic profiles, multibeam bathymetry and sediment cores, an improved understanding of the deglaciation/postglacial history of the southern part of the Norwegian Channel has been obtained. The Norwegian Channel Ice Stream started to recede from the shelf edge ca. 15.5 ka BP ( 14 C ages are used throughout). Approximately 500–1000 years later the ice margin was located east of the deep Skagerrak trough. At that time, the Norwegian Channel off southern Norway had become a large fjord-like embayment, surrounded by the grounded ice sheet along the northern slope and possibly stagnant ice remnants at the southern flank. The Norwegian Channel off southern Norway has been the main sediment trap of the North Sea, and south of Egersund more than 200 m of sediments have been deposited since the start of the deglaciation. Five seismic units are mapped. The oldest unit E occurs in some of the deepest troughs, and was deposited immediately after the ice became buoyant. Unit D is acoustically massive and comprises mass-movement deposits in eastern Skagerrak and south of Egersund. Unit C (in the channel southwest of Lista/Egersund) is interpreted to comprise mainly bottom current deposits derived from palaeo-rivers, e.g. Elben. During deposition of unit C (ca. 14.5–13 ka BP), there was limited inflow of Atlantic water. A change in depositional environment at ca. 13 ka BP is related to an increased inflow of saline water and more open hydrographic circulation. Widely distributed, acoustically stratified clays of unit B were deposited ca. 13–10 ka BP. The Holocene Unit A shows a depositional pattern broadly similar to that of unit B.

Seismic data acquisition along the Nordland coast (Norway) has resulted in the discovery of two downfaulted sedimentary basins of Mesozoic age in an area of Precambrian–Lower Palaeozoic metamorphic rocks. The Stabbfjorden Basin (informal name) west of Meloya has a sedimentary rock succession that is up to 800 m thick, while the Lyngvaerfjorden Basin (informal name) northeast of Traena is at least 350 m deep. Microfossil dating of ice-transported erratic blocks thought to be eroded from these basins and found on nearby skerries range in age from Barremian to Triassic. The majority of the samples are of Middle-Late Jurassic age. The sedimentary blocks comprise conglomerates, sandstones, siltstones and mudstones, and frequently contain shells and coal fragments. Lithofacies analyses show that they reflect shallow marine deposition, but it is possible that the oldest samples were deposited in a continental environment. The lithofacies reflect the well-known tectonic phases and sea-level changes that have been reported for the Middle Jurassic–Early Cretaceous in the Nordland offshore region. Vitrinite reflectance measurements show that organic material in the samples can be classified as immature, and the newly discovered basins have no hydrocarbon exploration potential.

Multibeam data have been acquired on eastern Tromsoflaket, a bank in the southwestern Barents Sea comprising a plateau ( Detailed examination of the multibeam backscatter data however reveals a high variability of sediments, especially in and around iceberg ploughmarks. We observe coarser sediments on the levees either side of the ploughmarks than inside the furrows. Moreover we frequently note asymmetries in the distribution of fine sediments across these ploughmark features. Drawing inspiration from previous studies of bottom currents which use the distribution of sediments across bedforms (e.g. sand waves) we have interpreted the direction of bottom currents on Tromsoflaket by examining the local distribution of fine sediments across iceberg ploughmarks, which are the most prominent bedform in this area. Further integration of our results with existing grain-size - current-speed models have allowed estimates of the bottom current speeds to be obtained. Such interpretations are particularly valuable in this area where availability of bottom current measurements sparse. Our approach makes valuable and novel use of multibeam data and results show good agreement with the limited set of available current data and models. We can identify near bottom pathways for the Norwegian Atlantic Current and Norwegian Coastal Current, the two major current systems in this region, and the patterns of circulation help to explain the sedimentation regime and identify recent erosion and deposition areas.

Multibeam bathymetry and seismic data disclose three submarine slides in the outer Boknafjord area, SW Norway. The largest slide (Arsneset slide) has a volume of ca. 28 × 10 6 m 3 . The scar of this slide is 15–30 m high and it covers an area of ca. 1.4 × 10 6 m 2 . Seismic data on sediment thicknesses and sedimentation rate estimates from radiocarbon dating indicate that this slide occurred ca. 10 000 14 C yr BP. 2D and 3D simulations of the tsunami generated by the slide indicate run-up heights on the neighbouring Galta peninsula of 2.5–4 m at a slide velocity of 25 m s − 1 . Possible higher slide velocities would have caused waves reaching higher areas. An archaeological excavation on the Galta peninsula at Rennesoy yielded approximately 17 500 flint artefacts of Late Palaeolithic/Early Mesolithic age in an up to 1 m thick beach sediment sequence. The archaeological material combined with sedimentological and shoreline displacement data limit the occupation time of the settlements to approximately 10 000–9700 14 C yr BP, which makes them to one of the oldest known Stone Age settlements in southern Norway. There is no evidence of transgressions between 10 200 and 9500 14 C yr BP, which could explain erosion of settlements and the presence of flint artefacts within the beach sediment sequence. It is thus possible that the oldest settlements were flooded and eroded away by a slide-generated tsunami. Artefacts and sediments were transported downslope into the sea and were subsequently reworked by waves during continued isostatic uplift.

An erosional channel and upslope-climbing sediment waves have been observed in Ytre Orkdalsfjorden and the marine fjord branch Gaulosen off the mouth of Gaula River in Trondheimsfjorden, central Norway. The submarine channel (up to 100–150 m wide and 12 m deep) is interpreted as the pathway of hyperpycnal flows and turbidity currents. It can be traced for 20 km on the seafloor from the mouth of Gaula River down to 500 m of water depth. Based on swath bathymetry and seismic data, the sediment waves are shown to have an accumulated thickness of 50–60 m. They are up to 8 m high, have up to 1-km-long crests, and wavelengths of 100–900 m. The sediment waves are attributed to hyperpycnal flows and turbidity currents overflowing the banks of the channel. Many of the sediment waves were instigated by pre-existing topography created by mass movements since early Holocene times.

Interpretation of new seismic data from four inshore/nearshore areas along the coast of Mid-Norway yields important information on the geometry and stratigraphy of downfaulted Jurassic sedimentary rocks. Three seismic units have been identified. These are interpreted to be of Middle to Late Jurassic age (Fangst Group and Melke Formation). Half-graben geometries related to normal fault movement are common for the areas, although the Beitstadfjorden Basin and the Griptarane area also record possible strike-slip movements. The structural development of the four areas can be related to tectonic movements along the More–Trondelag Fault Complex. The Jurassic basins along the coast of Mid-Norway are directly comparable in size and geometry with previously unmapped, deep-seated basins in the Voring Basin. We suggest that the inshore, nearshore and offshore basins originated during the same extensional event in Late Jurassic–Early Cretaceous times, and that this basin-forming event was regionally very extensive.

Shallow seismic sections, multibeam bathymetric images and geotechnical investigations of the seafloor in Karmsundet and Skudenesfjorden, SW Norway, have revealed the occurrence of large slide scars and associated mass-movement deposits. The slide escarpments are up to 30–40 m high and 8 km long, with up to 20×10 6 m 3 of sediment released during a single event of retrogressive sliding. The slide scars show a range of associated seafloor topography, reflecting various modes of sediment displacement. The variation in the escarpment morphology and sediment deformation style can be attributed to the varied intensity of liquefaction. Sliding involved mud deposits of Allerod–Younger Dryas to early Holocene age, but partly also deposits older than ca. 12,000 14C years bp . The sediment failures were probably triggered by seismic reactivation of a local fault by postglacial regional isostatic rebound. Prior to failure, the seafloor deposits were undercompacted and metastable due to high pore pressure, the presence of shallow gas and the relatively steep local slope created by the formation of a major scour trough by sea currents. Minor gravitational sliding may still occur along some of the escarpments, although engineering slope-stability analysis indicates that the deposits can be regarded as stable in the present-day conditions of static load and the anticipated weak sporadic earthquakes with an occurrence likelihood of 10−4/year and a peak acceleration of 0.25 g.

In the deepest part of the Skagerrak, the sea-floor morphology and the subsurface geology have been mapped from multibeam echo sounder data, seismic data and bedrock cores. An area of high pockmark density occurs along the shallowest part of a gentle ridge in the central Norwegian Trench, where a Middle Jurassic sandstone unit subcrops below 30–40 m of Late Weichselian sediments. In contrast, few pockmarks occur at the seabed where Lower and Upper Jurassic shales and clayey siltstones subcrop. The concentration of pockmarks above the Middle Jurassic sandstone unit is thus attributed to seepage of gas or liquids migrating up-dip from deeper parts of the sedimentary basin. In the Skagerrak, more than 90% of the observed pockmarks occur above Mesozoic sedimentary rocks, while less than 10% occur in areas of Palaeozoic metasediments or crystalline rocks. A linear concentration of pockmarks is observed above a fault that terminates at the base of the Quaternary succession, and this is therefore attributed to seepage of gas or liquids along the fault plane. The density of pockmarks is low in areas with thick successions of Quaternary sediments, indicating that the pockmarks are not related to seepage of biogenic gas from these deposits. Pockmarks in the Skagerrak are thus caused by seepage of thermogenic gas and/or other pore fluids from deeper sources, and their distribution may help to improve our understanding of the fluid system and migration regime of this part of the North Sea.

The Mesozoic succession on the landward side of Griptarane, offshore mid-Norway, reflects an upward change from Lower Jurassic alluvial deposits to Middle Jurassic marine/continental deposits into Upper Jurassic-Lower Cretaceous marine deposits. In the latest Jurassic there was deposition of submarine fans along faults associated with major extensional deformation and fault block rotation, probably in Volgian times. This phase coincided with NW-SE extension and rifting in the Slorebotn Sub-basin and at Haltenbanken. An onlap surface is interpreted to represent the Kimmerian unconformity and to mark the approximate position of the Jurassic-Cretaceous boundary. Some WNW-ESE- to E-W-oriented faults exhibit reverse movements, while E-W-trending folds indicate N-S compression. This compression is interpreted to coincide with a late Early Cretaceous phase of sinistral transpression in the Gossa High and Slorebotn Sub-basin, and inversion and doming in the More and Voring Basins. The predominance of WNW-ESE- to NW-SE- and ENE-WSW- to NE-SW-trending structures indicates that the Griptarane area has been influenced by the stress regimes of the More-Trondelag Fault Complex as well as the stress regimes in the regions further offshore.

Multibeam echosounder surveys conducted on the southern slope of the Norwegian Trench between Norway and Denmark, show that elongate depressions interpreted as current-modified pockmarks are widespread in water depths of 100–500 m, in the Holocene–Recent succession. The long axes of the depressions are oriented at an angle of about 15° downslope, relative to the depth contours. The long axes appear to almost exactly parallel the effective bottom currents in this part of the Skagerrak. The present current directions were probably established about 4000 years ago, following a major shift in the oceanographic circulation pattern. The most characteristic feature of the depressions is their large size, with maximum depths of 45 m, widths of 400 m and lengths of 2 km. Strong bottom currents continuously transport particles thrown into suspension by the seepage process away from the pockmarks and prevent further deposition. Continuous seepage of shallow gas at fixed pockmark sites over long time periods combined with generally high sedimentation rates are thought to be responsible for the exceptional size of many depressions. The shallow gas probably has a mixed biogenic/thermogenic origin; however, the thermogenic component is considered to be most important for the formation of pockmarks. Seepage from permeable layers in the Jurassic–Cretaceous bedrock is evidenced by linear rows of depressions above these horizons, while pockmarks above sub-surface faults indicate gas seeps also from there. In shallow-water areas, the shape and size of pockmarks are locally dependent on their location with respect to giant sand waves, which trend sub-parallel to the depth contours and are interpreted to be of late Weichselian to early Holocene age. In deeper-water areas, the pockmarks have been further modified by gravity slides caused by collapse of steep pockmark walls.

Publisher Summary The continental margin off Lofoten, Vesteralen, and Troms comprises a great variation of marine landscapes, ranging from 0 to 3,000 m in depth largely influenced by previous glaciations and oceanographic processes governed by three different water masses. The biological communities identified with multivariate analyses of results from visual surveys were strongly correlated with water mass distribution, sediment type, and various topographic indices. Broadscale geomorphic features such as canyons and troughs have a significant influence on the distribution of sediment types and biological communities through their modification of current patterns. Currents also influence the distribution of geomorphic features such as sand waves and coral reefs. At a broadscale, the largest faunistic change occurs between the warm Atlantic water and the cold intermediate water mass at depths around 700 m. Banks and plains are important geomorphic elements on the continental shelf off LVT. The biological communities identified with multivariate analyses of results from visual surveys were strongly correlated with water mass distribution, sediment type, and various topographic indices. Broadscale geomorphic features such as canyons and troughs have a significant influence on the distribution of sediment types and biological communities through their modification of current patterns. Currents also influence the distribution of geomorphic features such as sand waves and coral reefs. At a broadscale, the largest faunistic change occurs between the warm Atlantic water and the cold intermediate water mass at depths around 700 m.

Multibeam bathymetry, high-resolution seismic profiles and sediment cores were collected from the upper continental slope outside Andoya, the northernmost island in Vesteralen, northern Norway (69°N). Eight small slides are identified at water depths between 500 and 800 m. These are linked to a larger slide related to the development of the Andoya Canyon by high resolution seismic. Slope angles adjacent to the headwalls of the small slides are 3–4° while slide deposits have accumulated where slope angles are 2–3°. The slides occurred in parallel-stratified glacial marine sediments, and three seismic horizons are interpreted. One of these horizons coincides with failure planes in four of the slides. A 12 m long core terminates above this level, but penetrates another horizon representing a slip plane in two of the slides. The core comprises silty clay with varying content of ice rafted debris. The upper slope shallower than 450 m appears stable although it may be up to 8° steep. Tension cracks up to 2 m deep on the lower slopes may suggest that deformation is active near the canyon systems.

The Frohavet Basin, a newly discovered sedimentary basin on the innermost mid-Norwegian continental shelf, occurs in an area 60×20 km and contains a stratal sequence up to 1000 m thick. Dating by ice-transported erratic blocks suggests a Jurassic age. The sequence is preserved in half-grabens downthrown to the north-west, and is cut by numerous faults, some of which are interpreted as syndepositional. The sequence reflects an upward change from continental deposition, with the Frohavet area acting as a local depocentre, to more widespread continental and marine deposition. The predominant sediment transport direction was towards the north-west. The Frohavet sequence was deformed during a phase of extensional tectonism, probably in Late Jurassic—Early Cretaceous times.

The Asenvågoya Conglomerate is a thin (c. 6 m) conglomeratic body composed of mass-flow deposits and enveloped by braided-stream sandstones and conglomerates. The section studied represents the proximal part of a small-radius alluvial fan built out from the basin margin towards a flood basin. The fan was possibly generated by escarpment creation, or rejuvenation, in response to syndepositional faulting along the basin margin, and comprises sand-matrix-supported and clast-supported, sheet-like conglomerates. There is an upward change through the sequence from stream flow and surging mass-flow, through fully turbulent mass-flow and sheet flow to cohesive mass-flow deposits and then a return of braided-stream alluvium at the top of the sequence. The fan wedge demonstrates the wide range of textures possible within a ‘mass-flow” system.

The 1996 Finneidfjord slide was a combined submarine/subaerial, retrogressive flow/ quick clay slide that mobilized 1 mill, m3 of sediments and killed four people. Interpretation of the morphology of the submarine slide scar and the slide deposits combined with eyewitness observations suggest that the initial failure occurred on the steepest slope of the foreshore platform. Detachment along a weak layer within silty clay caused unloading, oversteepening and erosion and triggered retrogressive sliding. Outrunner blocks from the slide occur up to 1.6 km outside the main debris lobe. Excess hydrostatic pressure related to meteorological and anthropogenic influence is thought to have triggered the slide.

A combined sediment-sampling, high-resolution seismic, multiple echo sounder, and video survey was conducted offshore Vestarlen, northern Norway, in October 2007 as part of the ongoing Marine Area Database for Norwegian Coast and Oceanic Regions (MAREANO) program. MAREANO is a multidisciplinary seabed mapping program conducting physical, biological, and environmental mapping in the Lofoten/southern Barents Sea area. Data and analysis arising from this program will provide the basis for ecosystem- based management of Norway' coastal and offshore regions. The survey used multicorer, box corer, and grab samplers; a TOPAS parametric subbottom profiler; 18-, 38-, 70-, 120-, 200-, and 400- kilohertz echo sounders; and a CAMPOD camera system with two video cameras and lights mounted on an aluminum frame.

A seismic reflection profiling survey has indicated the existence of downfaulted Mesozoic sequences in Edoyfjorden south of Smola (Trondheimsleia) and in Beitstadfjorden. These rocks are preserved in halfgrabens within the More-Trondelag Fault Zone (MTFZ) which is interpreted as an important structural element in Central Norway. The MTFZ probably originated in the Palaeozoic, and at least two phases of reactivation can be recognized in the Mesozoic sequences.