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The North Atlantic Oscillation is the dominant atmospheric driver of North Atlantic climate variability with phases corresponding to droughts and cold spells in Europe. Here, we exploit a suggested anti-correlation of North Atlantic Oscillation-phase and north-eastern North Atlantic primary productivity by investigation of south-eastern Norwegian Sea sediment cores spanning the last 8000 years. Age model uncertainties between 2 and 13 years for the period 1992–1850 AD allows for the proxy to observational data calibration. Our data suggest that Ca/Fe core-scanning results reflect sedimentary CaCO3 variability in the region. Cross-correlating the Ca/Fe record with nearby phytoplankton counts and dissolved O2 data suggests that Ca/Fe can be used as a proxy for primary productivity variability in the region. Our data support an anti-correlation of primary productivity to the winter North Atlantic Oscillation index. Hence, we propose a sub-decadally resolved palaeo-North Atlantic Oscillation reconstruction based on an open-ocean record spanning the last 8000 years.

For the Last Glacial Maximum (LGM), there is a general consensus that the Fennoscandian Ice Sheet coalesced with the British–Irish Ice Sheet in the Central North Sea forming the southwestern part of the Eurasian Ice Sheet. It is also generally accepted that the ice margin at LGM was situated close to the shelf edge from the Kara Sea to the Irish margin and that the southern margin in the North Sea was located along the northeast–southwest-trending Dogger Bank in the Southern North Sea. In this review, we will first present some of the landforms and evidence representing the Weichselian/Devensian (Last Glacial Cycle) maximum position of the Eurasian Ice Sheet in the North Sea and along the Mid-Norwegian continental margin and then present some of the subglacial form elements that may partly be attributed to the LGM in these regions.

Submarine landslides are common at glaciated continental margins. The onset of large-scale landslides coincides with the initiation of Northern Hemisphere glaciations in the Quaternary. This implies that processes related to glacial cycling provide favourable conditions for submarine landslides at high-latitude margins. Potential processes include glacial deposition patterns and enhanced seismicity. It is also possible that advances and retreats of ice sheets, a highly dynamic process in geologic terms, makes slopes discernible to failure by modifying the stress regime. Here, we quantify this effect using 2D Finite Element modelling of a glaciated continental margin. Different model runs investigate the pore pressure development in homogeneous as well as layered slopes during glaciation when loaded by an ice stream with one or multiple ice advances. Ice streams cause significant variations in excess pore pressure in the very shallow sediment sequences at the continental shelf. However, lateral fluid flow is not efficient enough to increase pore pressures significantly at the slope, where large-scale submarine slides are observed. Hence, while ice sheet dynamics appear to favour the occurrence of shallow slides close to the shelf edge, ice sheets seem to be irrelevant for the generation of large-scale submarine landslides at the continental slope.

Sediments deposited during glacial-interglacial cycles through the Early to Mid-Pleistocene in the North Sea are chronologically poorly constrained. To contribute to the chronology of these units, amino acid racemization (AAR) and strontium (Sr) isotope analyses have been performed on samples from four shallow borings and one oil well along a transect in the northern North Sea. D/L Asp (aspartic acid) values obtained through reverse-phase liquid chromatography in the benthic foraminiferal species Elphidium excavatum is focused on because of consistent results and a good stratigraphic distribution of this benthic species. For the Early Pleistocene, an age model for the well 16/1–8, from the central part of the northern North Sea based on Sr ages allows for dating of the prograding wedges filling the pre-Quaternary central basin. A regional calibration curve for the racemization of Asp in Elphidium excavatum is developed using published ages of radiocarbon-dated samples and samples associated with the previously identified Bruhnes/Matuyama (B/M) paleomagnetic boundary and a Sr age from this study. Based on all the available geochronological evidence, samples were assigned to marine oxygen isotope stages (MIS) with uncertainties on the order of 10–70 ka. Sr ages suggest a hiatus of

Here we present the first compilation of sediment volumes, sedimentation rates, and chronology of Quaternary sediment packages along the entire marine margin of the Eurasian ice sheets (EurIS; British–Irish, Kara–Barents Sea–Svalbard, and Fennoscandian). This compilation allows for a subdivision of the EurIS development into three phases (2.6–1.5 Ma, 1.5–0.78 Ma, and 0.78–0 Ma). At the start of the Quaternary, sedimentation rates increased, relative to pre-Quaternary rates, by an order of magnitude. This abruptness in rate change excludes tectonic raising of landmasses as the main factor, but more likely reflects climate change through increased glacial erosion. The sediment distribution data suggest that the Kara–Barents Sea–Svalbard Ice Sheet (KBSIS) already was quite large at the beginning of the Quaternary, and well before 1.5 Ma it extended to the shelf edge and coalesced with the Fennoscandian Ice Sheet (FIS), which prior to 1.5 Ma most likely was located near the coast. Large ice streams and intense glacial erosion characterized the KBSIS in the 1.5–0.78 Ma time period, whereas the FIS at that time extended farther out on the continental shelf. After 0.78 Ma, a north-south change in EurIS development occurred. In the FIS and the British–Irish Ice Sheet (BIIS), large ice streams developed and shelf-edge glaciations occurred nearly 1 m.y. later compared to the KBSIS. The FIS and BIIS also repetitively coalesced in the North Sea. A significant drop in sediment input along the KBSIS marine margin, to the lowest Quaternary level, suggests a less erosive KBSIS.

In this study, identified mass transport deposits (MTDs) in previously analyzed as well as new sediment cores and seismic profiles from 22 fjord systems and six lakes in west and mid-Norway are compiled in order to close knowledge gaps in the understanding of how mass movements relate to seismic activity and climatic changes affecting the sedimentary systems. A total of 125 postglacial MTDs have been identified and dated in the studied systems. Mass movement frequency plots suggest high mass movement activity for two periods in the Early Holocene (11,000–9700 and 8300–7700 cal. yrs BP), a quiescent period in the mid-Holocene, and a mass movement reactivation at ~4200 cal. yrs BP. The evaluation of trigger mechanisms makes us infer that some of the mass movements identified are most likely related to climatic processes and tsunamis. However, most of the events seem to be caused by regional seismic activity, resulting in failure of climatically-preconditioned slopes. We suggest that at least 36 individual regional earthquakes (M > 6) have occurred in west and mid-Norway through the Holocene. Earthquake recurrence rates of 1/80 years are estimated for the period directly after the last deglaciation (~12,800–11,600 cal. yrs BP), 1/200 years for the Early Holocene and 1/200 years for the last 4000 years of the Holocene time period. Comparisons with studies from other previously glaciated settings indicate that both Scandinavia and the Alps show similar trends as west and mid-Norway, but not Eastern Canada. This most likely reflects a later deglaciation of the Laurentide Ice Sheet.

Highlights • Increased glacial sedimentation rates do not generate sufficient overpressure to trigger a landslide. • Simulated overpressures for different sedimentation scenarios do not significantly differ. • A glacimarine layer underneath rapidly-deposited sediments is important for overpressure build-up. • An earthquake of M6.9 or larger at a short distance from the Tampen Slide headwall could have triggered the Tampen Slide. Abstract Trough mouth fans are environments characterized by high sediment supply during glacial stages and the occurrence of large-scale instabilities. The geological record indicates that several of these environments have failed repeatedly resulting in large submarine landslides. The roles of sedimentation rate, weak layers, glacial loading and unloading as well as seismic activity on triggering megaslides in trough-mouth-fan systems is still unclear. A better understanding of the preconditioning factors, triggers and consequences of these landslides is crucial due to the hazard they pose to coastal communities and offshore industries. In this paper, we focus on the North Sea Trough Mouth Fan, which is the result of massive glacial sediment input delivered to the shelf edge through the Norwegian Channel, southeast Nordic Seas margin. The Tampen Slide, one of several large paleo-landslides that have happened within the North Sea Trough Mouth Fan, took place at c. 130 ka (end of MIS 6), and removed an estimated 1800 km3 of sediment. Here, we use boundary conditions from the Tampen Slide and 2D Finite Element Modeling (Abaqus software from Simulia) to evaluate the effects of variations in sedimentation rates as well as sediment properties on the generation of excess pore pressure, fluid flow, and slope stability along the axis of the trough-mouth-fan system. The model domain, 40 km in length and 2 km in height, is dominated by glacigenic debris flows and glacimarine sediment deposits. We use geotechnical data measured on samples of glacigenic and glacimarine sediment deposits from the nearby Ormen Lange gas field area to constrain the model. We evaluate the stability of the slope under various scenarios, including constant sediment loading, episodic changes in sedimentation rates and abrupt pulses in sediment delivery for a 61 kyr period (MIS 6). The models show that increased sedimentation rates during glacial stages do not generate sufficient excess pore pressure to set off a landslide. Furthermore, the simulated overpressures for the different sedimentation scenarios do not significantly differ at the end of the model runs. The results also highlight the importance of a basal glacimarine sediment layer underneath the rapidly-deposited sediments for the build-up of overpressure. Consequently, this glacimarine sediment layer has the inherited potential to act as a weak layer facilitating instability. However, as overpressure due to sediment deposition alone does not result in slope failure, we couple the preconditioned slope with earthquake ground shaking. Based on attenuation models, an earthquake of approximately M6.9 or larger at a short distance from the Tampen Slide headwall could have triggered the landslide. Therefore, we suggest glacial sedimentation and a glacimarine sediment layer to represent preconditioning factors, and seismic shaking as the final trigger mechanism for the Tampen Slide, i.e. similar to the situation that lead to the development of the Storegga Slide in the same area.

The timing, rates and patterns of retreat of western sectors of the last Eurasian Ice Sheet (EurIS) are poorly constrained, hampered by limited observations from the marine domain. A better knowledge of the deglaciation of the NW European marine areas/continental margins is essential for efforts to understand the role of different controlling factors (such as ice streams, atmospheric and oceanic conditions, relative sea level, morphology and substrate) on the stability of the EurIS, and also for ice-sheet stability in general. Based on new and existing mapping of glacial landforms, together with a compilation of existing and recalibrated dates from the NW European shelf, a new reconstruction of the retreating EurIS between 20 and 14 ka BP will be presented. Our reconstruction suggests an initial modest withdrawal from maximum extent to c. 19 ka BP along the entire western marine-terminating margin. From 19ka the two major marine-terminating ice streams, in the Norwegian Channel and Bear Island Trough, begin to retreat/collapse. This destabilisation leads to rapid interior downdraw and the eventual unzipping of the British-Irish and Fennoscandian ice sheets at c. 18.5 ka BP, and the Barents-Kara and Fennoscandian ice sheets between 16 and 15 ka BP. Based on our new reconstruction and modelling results, the importance of factors controlling the nonsynchronous and rapid deglaciation of marine-based sectors and the implications for the stability of the ice sheet, will be discussed. The chronology and patterns of past marine deglaciations provide contextual insight into ice sheet instabilities and the mechanisms behind, underpinning the ongoing retreat of the Greenland and Antarctic ice sheets today.

The aminostratigraphy of up to 1000 m of glacial and interglacial sediments in the North Sea Basin (NSB) is compiled from multiple boreholes sites and dated using strontium isotope (Sr) analysis to provide a chronological framework extending throughout the Quaternary. The Quaternary aminostratigraphy within the NSB can be divided into five amino zones (AZ), AZ1 (youngest) to AZ5 based on alle/Ile ratios which are used to correlate depositional events recorded in sedimentary facies from multiple borehole sites. The new relative and absolute chronology also ties to seismostratigraphy and multi-generational tunnel valley fill. Early Pleistocene sediments produce AZ5 ratios with Sr ages around 1.4–1.5 Ma deposited in marine to glacimarine conditions. Sediments with AZ4 ratios are constrained by Sr ages and magnetic polarity to 1.3–0.9 Ma, spanning the eccentricity to axial tilt insolation periodicity change of the Mid Pleistocene Transition (MPT). Some coarse-grained sedimentary units with AZ4 ratios may be linked to ice proximal deposition during the MPT. Sediments with AZ3 ratios are poorly chronologically constrained to between 1.1 and 0.26 Ma. At least one episode of diminished coarse clasts and increased foraminiferal diversity during this Mid Pleistocene time suggests a progression from ice proximal to warmer, possibly interglacial conditions. Furthermore, the stratigraphically deepest generation of tunnel valleys cut strata with AZ3 ratios indicating subglacial conditions at least once during the Mid Pleistocene. Sediments with AZ2 ratios corresponding to MIS7-5 are tied to seismic units including a thick (up to 40 m) deformation till, suggesting glacial incursion into the NSB during MIS6 followed by tunnel valley cutting of the this till, thought to be an MIS6 event also. The geometry and cross-cutting complexities of such tunnel valleys precludes further correlation of this ice extent. The youngest aminostratigraphic zone, AZ1, is recognised in all boreholes and well constrained to MIS4-2 and the youngest set of tunnel valleys, attributed to a single or multiple glacial advances at this time.

Based on high-resolution TOPAS acoustic data, bathymetric data sets and sediment cores from the Norwegian Channel, the last retreat of the Norwegian Channel Ice Stream has been investigated. Mapping of ice-marginal features such as grounding-zone wedges and terminal moraines off western Norway suggest that the retreat of the grounding line in this part of the channel was interrupted by frequent stillstands, whereas the channel south of the threshold at Jaeren does not have crossing ice-marginal landforms. Three main seismic units have been identified, and, based on their seismic characteristics, in addition to study of sediment cores, these units are interpreted as till (U1), glacial marine sediment (U2) and Holocene hemipelagic sediment (U3). Based on new and published radiocarbon dates of the lower part of U2, combined with dates from the adjacent areas, it is concluded that the grounding line started to retreat from the shelf edge at about 19 ka and that the inner part of Skagerrak was ice free at 17.6 ka. This gives an average retreat rate of 450 m a−1, which is generally higher than mean retreat rates estimated for other palaeo-ice streams (15–310 m a−1).

High resolution acoustic data and a 15.7 m long sediment core from the Hardangerfjorden system, western Norway, have been analyzed to increase our knowledge on depositional environments, submarine mass movement trigger mechanisms and submarine mass movement frequencies in high latitude fjord systems. The seismic profiles analyzed show that an up to 160 m thick glacimarine-dominated unit, of probably Younger Dryas age, has been deposited above the acoustic basement. A < 55 m thick unit, comprising stacked mass transport deposits (MTDs) has been deposited atop the glacimarine unit. The identified mass movement events comprise 19 MTDs (MTD1–19), which have transported sediment volumes of up to 0.4 km3 and initiated turbidity currents resulting in the deposition of up to 13 m thick turbidite layers. The established chronostratigraphical framework reveals high mass movement activity in Hardangerfjorden at 11100–8200 cal. yrs BP (Early Holocene) and at 4100 cal. yrs BP to present (Late Holocene). 14 MTDs have been dated to the Early Holocene, which is a time period characterized by high sedimentation rates (1.1 mm/yr), giving a mass movement recurrence rate of 1/200 years. Several of these failure events are suggested to have been triggered by regional mechanisms such as earthquakes linked to glacioisostatic uplift. Some of the MTDs of that time could potentially be caused by rock avalanches. Furthermore, it seems that the identified 8200 cal. yrs BP MTD5 coincides with the age of the Storegga tsunami, suggesting that processes related to this event may have caused sediment failure in the inner Hardangerfjorden. During the mid-Holocene (8200–4100 cal. yrs BP), a time period which was characterized by low sedimentation rates of 0.1–0.2 mm/yr and a warmer and wetter climate, mass movement events were absent in the study area. The renewed slide activity in the Late Holocene, comprising four MTDs, is probably related to climatic processes, earthquakes and rock avalanches, resulting in a mass movement recurrence rate of 1/1000 years for this time period. This study, thus, underlines the importance of high-latitude fjords, also in a global context, as systems where local, regional and external geological forces interact to impose highly dynamic postglacial depositional environments. publishedVersion

This study describes the distribution and stratigraphic range of the Upper Palaeozoic–Mesozoic succession in the NE Atlantic region, and is correlated between conjugate margins and along the axis of the NE Atlantic rift system. The stratigraphic framework has yielded important new constraints on the timing and nature of sedimentary basin development in the NE Atlantic, with implications for rifting and the break-up of the Pangaean supercontinent. From a regional perspective, the Permian–Triassic succession records a northwards transition from an arid interior to a passively subsiding, mixed carbonate–siliciclastic shelf margin. A Late Permian–earliest Triassic rift pulse has regional expression in the stratigraphic record. A fragmentary paralic to shallow-marine Lower Jurassic succession reflects Early Jurassic thermal subsidence and mild extensional tectonism; this was interrupted by widespread Mid-Jurassic uplift and erosion, and followed by an intense phase of Late Jurassic rifting in some (but not all) parts of the NE Atlantic region. The Cretaceous succession is dominated by thick basinal-marine deposits, which accumulated within and along a broad zone of extension and subsidence between Rockall and NE Greenland. There is no evidence for a substantive and continuous rift system along the proto-NE Atlantic until the Late Cretaceous. publishedVersion

Recent reconstructions suggest that the British-Irish and Fennoscandian ice sheets coalesced and covered the central and northern North Sea from ca. 26 cal. ka BP and until ca. 19 cal. ka BP. At ca. 19 cal. ka BP the Norwegian Channel Ice Stream started to retreat and the ice sheets broke apart at ca. 18.7 cal. ka BP. This led to a drainage of an ice-dammed lake in the southern North Sea northwards via the Norwegian Channel into the SE Nordic Seas. In this paper we combine information from high resolution TOPAS profiles, bathymetric records and shallow borings to study the ice-dammed lake outburst, a common deglaciation process but which rarely has been evidenced in such a detail from the marine realm. A 12 m deep and 3 km wide incision at the northeastern part of the Dogger Bank is suggested to represent the point where the ice-dammed lake breached. The glacial lake outburst flood, which had an estimated peak discharge of 9.8 × 104–2.9 × 105 m3/s and lasted for about 5–15 months, flowed between the withdrawing British-Irish and Fennoscandian ice sheets following the crest of the Ling Bank northwards. Along this path, about 300 km downstream of the break-through point, an up to 10 m thick sediment package with a prograding-aggrading sedimentation pattern, typical for ice-dammed lake outburst deposits, has been deposited. This sediment package was deposited in a high-energy environment, immediately following extensive erosion of the underlying till unit of Last Glacial Maximum age. An oxygen isotope anomaly and an associated ultra-rapidly deposited meltwater plume on the Norwegian continental margin, dated to ca. 18.7 cal. ka BP, also witness this lake outburst. The ice-dammed lake outburst flood occurred when evidence suggest a sea level at least 110 m lower than at present in the region. As the sea level rose, following the melting of the Last Glacial Maximum ice sheet, the Ling Bank Delta developed on top the outburst deposits. The delta, indicating a sea level close to 80 m below present, has an extent of 80 km and up to 12 m deep fluvial channels are associated with the topset beds. This fluvial environment may have lasted until the end of the Younger Dryas time period when the Ling Bank was submerged and attained its present water depth.

Sediment cores from the south-eastern Nordic Seas simultaneously archive the variability of the Fennoscandian Ice Sheet (FIS), the British-Irish Ice Sheet (BIIS) and the regional oceanic conditions. This study aims to contribute to our understanding of the marine-based section of the FIS and the BIIS between 35,000 and 15,000 years BP, by using cores MD99-2283, MD99-2284 and MD99-2289, retrieved along the upper continental slope between the Faroe-Shetland Channel and the Wiring Plateau. For this, we present a revised, radiocarbon based, Bayesian modelled chronological framework and a compilation of new and published sedimentological, geochemical and micro-paleontological datasets. Our results show a possibly first Weichselian FIS/BIIS confluence at ca. 25,500 years BP in the central North Sea, which buttressed the BIIS to the East, potentially leading to a northwards BIIS deflection via the Shetlands. The Norwegian Channel Ice Stream (NCIS) most likely only reached the shelf edge after 23,300 +/- 500 years BP, possibly for the first time during the Weichselian. The NCIS onset directly preceded a pronounced influx of warm Atlantic water to the northern North Sea margin possibly implying forcing through ocean melt. We find a highly variable NCIS, with three similar to 1400 yearlong episodes of increased ice rafted debris flux interrupted by similar to 600 yearlong minima. When compared to other sides of the European Ice Sheet, these episodes appear to correlate well, suggesting a common forcing mechanism. In conclusion, our data supports recent suggestions that the last glacial stage of the BIIS was more extensive in the central North Sea and the confluence later than previously thought.

Content and fluxes of ice transported sand-sized and gravel-sized, lithic particles in marine sediment cores are a common tool used to reconstruct glacial variability. Ice-rafted debris datasets are currently acquired in several different and often time consuming ways, and within various grain size fractions. This paper proposes a novel workflow using an automated method to count ice-rafted debris to reduce analysis time and subjectivity. The described method is based on the instrument ‘Morphologi G3’ from Malvern Instruments Limited, and includes all pre-processing and post-processing steps. This particle characterization tool is an automated microscope combined with a proprietary software package. In the present study, the analysis was performed on the 150 to 1000 μm fraction. If desired, grain counts can be carried out on the entire sand and silt fractions, but then at the expense of considerably greater turnover time. A total of 350 sediment samples from core MD99-2283, taken on the upper continental slope at the southern part of the north-east Atlantic margin, were counted with this automated method. In addition, a total of 161 samples were counted manually as a control on the reliability of the scanning. The comparison of automated versus manually counted biogenic and lithic material shows a convincing correlation between both methods. The turnover time per automatically counted sample is around 20 minutes, the method requiring less experience and skills than manual counting. The results yield a promising, time saving new technique to achieve high-resolution ice-rafted debris counting records with acceptable error margins. This article is protected by copyright. All rights reserved.

Highlights • The basement at the mid-Norwegian More Margin is dominantly felsic in composition. • A lower crustal body is interpreted as a mixture of continental blocks and eclogite. • The thickness of the outer lower crustal body is twice as thick on the East Greenland Margin. • The thinning during this first phase of post-Caledonian extension was highest for proto Norway. Abstract The inner part of the volcanic, passive More Margin, mid-Norway, expresses an unusual abrupt thinning from high onshore topography with a thick crust to an offshore basin with thin crystalline crust. Previous P-wave modeling of wide-angle seismic data revealed the presence of a high-velocity (7.7–8.0 km/s) body in the lower crust in this transitional region. These velocities are too high to be readily interpreted as Early Cenozoic intrusions, a model often invoked to explain lower crustal high-velocity bodies in the region. We present a Vp/Vs model, derived from the modeling of wide-angle seismic data, acquired by use of Ocean Bottom Seismograph horizontal components. The modeling suggests dominantly felsic composition of the crust. An average Vp/Vs value for the lower crustal body is modeled at 1.77, which is compatible with a mixture of continental blocks and Caledonian eclogites. The results are compiled with earlier results into a transect extending from onshore Norway to onshore Greenland. Back-stripping of the transect to Early Cenozoic indicates asymmetric conjugate magmatism related to the continental break-up. Further back-stripping to the time when most of the Caledonian mountain range had collapsed indicates that the thinning during the first phase of extension was about 25% higher for proto Norway than proto Greenland.

Palaeoglaciological reconstructions of the North Sea sector of the last British Ice Sheet have, as other shelf areas, suffered from a lack of dates directly related to ice-front positions. In the present study new high-resolution TOPAS seismic data, bathymetric records and sediment core data from the Witch Ground Basin, central North Sea, were compiled. This compilation made it possible to map out three ice-marginal positions, partly through identification of terminal moraines and partly through location of glacial-fed debrisflows. The interfingering of the distal parts of the glacial-fed debrisflows with continuous marine sedimentation enabled the development of a chronology for glacial events based on previously published and some new radiocarbon dates on marine molluscs and foraminifera. From these data it is suggested that after the central Witch Ground Basin was deglaciated at c. 27 cal. ka BP, the eastern part was inundated by glacial ice from the east in the Tampen advance at c. 21 cal. ka BP. Subsequently, the basin was inundated by ice from northeast during the Fladen 1 (c. 17.5 cal. ka BP) and the Fladen 2 (16.2 cal. ka BP) events. It should be emphasized that the Fladen 1 and 2 events, individually, may represent dynamics of relatively small lobes of glacial ice at the margin of the British Ice Sheet and that the climatic significance of these may be questioned. However, the Fladen Events probably correlate in time with the Clogher Head and Killard Point re-advances previously documented from Ireland and the Bremanger event from off western Norway, suggesting that the British and Fennoscandian ice sheets both had major advances in their northwestern parts, close to the northwestern European seaboard, at this time.

2D multichannel seismic data and bathymetric records from the glaciated western Svalbard margin and the rift valley region of the ultraslow, and oblique-spreading, Knipovich Ridge are in this study interpreted to infer differences in seafloor spreading mechanisms and to identify sedimentary processes. Our results show that the rift flank geometry, the rift valley elevation and the active magmatism are closely linked. The inferred magmatic segments of the Knipovich Ridge exhibit high and steep rift flanks, whereas the rift flank heights of the proposed tectonic-dominated segments are lower and less steep. In addition, we observe significant rift flank asymmetry across the rift valley which can be partly explained by subsidence due to sediment loading. The identification of a huge sedimentary wedge on the western rift flank suggests that the oldest parts of these sediments have been transported from the western Svalbard margin and across the rift valley. However, we suggest that most of these sediments are glacimarine/hemipelagic sediments which have been deposited in the time period after the rift valley flanks had developed sufficiently to cut off the direct transport routes from the western Svalbard margin. We also observe thick current depositions on the western side, suggesting a strong along-slope influence of the West Spitsbergen Current during the Plio–Pleistocene time period.

Fjords commonly hold sediment basins with high temporal resolution that mirror land- and marine-based processes and depositional environments during a glacial–interglacial cycle. Here, we present TOPAS seismic profiles, with a vertical resolution of

Throughout the last 1.1 million years repeated glaciations have modified the southern Fennoscandian landscape and the neighbouring continental shelf into their present form. The glacigenic erosion products derived from the Fennoscandian landmasses were transported to the northern North Sea and the SE Nordic Seas continental margin. The prominent sub-marine Norwegian Channel trough, along the south coast of Norway, was the main transport route for the erosion products between 1.1 and 0.0 Ma. Most of these erosion products were deposited in the North Sea Fan, which reaches a maximum thickness of 1500 m and has nearly 40 000 km3 of sediments. About 90% of the North Sea Fan sediments have been deposited during the last 500 000 years, in a time period when fast-moving ice streams occupied the Norwegian Channel during each glacial stage. Back-stripping the sediment volumes in the northern North Sea and SE Nordic Seas sink areas, including the North Sea Fan, to their assumed Fennoscandian source area gives an average vertical erosion of 164 m for the 1.1–0.0 Ma time period. The average 1.1–0.0 Ma erosion rate in the Fennoscandian source area is estimated to be 0.15 mm a−1. We suggest, however, that large variations in erosion rates have existed through time and that the most intense Fennoscandian landscape denudation occurred during the time period of repeated shelf edge ice advances, namely from Marine Isotope Stage 12 (c. 0.5 Ma) onwards.

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.

Densely spaced high-resolution TOPAS seismic profiles and EM1002 bathymetric data reveal the presence of numerous pockmarks, mound-like structures and elongated seabed cracks at Nyegga, offshore mid-Norway. The seabed cracks are located adjacent to the northern escarpment of the Storegga Slide, appearing as graben-like structures in the TOPAS data. Unlike the cracks, pockmarks and mound-structures are largely associated with vertical zones of acoustic blanking at depth, interpreted as pathways for vertically migrating gaseous fluids. Based on the TOPAS data, a new seismostratigraphic framework has been established and correlated to previously published age models of IMAGES cores MD99-2291 and MD99-2289. Seismic facies interpretation suggests repeated and rapid deposition of up to 40 m thick glacigenic wedges in the eastern part of the study area around 18.2 14 C ka BP (21.8 cal. ka), 17.5 14 C ka BP (20.8 cal. ka) and 16.9 14 C ka BP (20 cal. ka). Towards the west, glacimarine deposition has prevailed, characterized by progressively increasing sedimentation rates with peak values of 30 m/ka during the period from 15.0 14 C ka BP (18.2 cal. ka) to 15.8 14 C ka BP (19 cal. ka). As the distribution of the Nyegga pockmarks closely coincides with the main Late Weichselian sediment depocenters, we suggest a relation between rapid and repeated sedimentation and periodic overpressure generation at depth, ultimately leading to fluid expulsion at the seabed and the formation of the Nyegga pockmark field. In contrast, seabed cracks at Nyegga appear to have formed due to local extension which we relate to horizontal stress reduction as a consequence of the Storegga Slide event. Potentially, this event has been accompanied by renewed vertical fluid migration and the most recent stage of pockmark development.

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.

Pockmark G11 is the most spectacular one among the pockmarks located at the southern border of Voring Plateau and 1–2 km away from the northern flank of the Storegga Slide, mid-Norwegian continental margin. For the first time, detailed pore-water geochemical studies were conducted to address methane hydrate occurrence, methane seepage and associated geochemical processes, and methane characteristics in the pockmark. Pore-waters collected from five sediments cores inside and one sediment core outside the pockmark, were analyzed for dissolved Cl−, sulfate (SO42−), total hydrogen sulfide (ΣH2S), Ca2+, Mg2+, dissolved inorganic carbon (DIC), δ13CDIC and δ18O. Methane hydrates were recovered in all sediments below 0.75 m in a core inside pockmark G11, which is in good accordance with heavy oxygen isotope (1.9 to 2.3‰SMOW) and low Cl−concentrations (84.9 to 16.1 mM) in pore-waters. Pore-water profiles indicate that upward-migrating methane fluids are spatially variable in the pockmark, with methane fluxes ranging from below detection in the center and outside, to 0.30–0.54 mol m− 2 a− 1 inside. In the cores with active methane fluxes, maximum DIC concentrations (19.4 to 21.5 mM) and corresponding minimum δ13CDIC values (− 52.3 to − 54.6 ‰ PDB) occur within sulfate-methane-transition (SMT) zones from ∼ 0.40 to 0.50 m below seafloor (mbsf), close to the seafloor. Simple mass balance modeling and δ13CDIC measurements within the SMT zones suggest that methane in shallow sediments within pockmark G11 is microbial in origin. Pore-water geochemistry and seabed observations suggest that methane fluxes inside pockmark G11 are episodic, and derived mostly from the recycling of methane hydrate at depth during sediment burial.

Lysa, A., Hjelstuen, B. O. & Larsen, E. 2009: Fjord infill in a high-relief area: Rapid deposition influenced by deglaciation dynamics, glacio-isostatic rebound and gravitational activity. Boreas, 10.1111/j.1502-3885.2009.00117.x. ISSN 0300-9483. Seismic profiles and gravity cores have been collected from the previously glaciated Nordfjord system on the west coast of Norway. The results give new information about the deglaciation history of the area and contribute to our understanding of fjord fill in high relief areas. During the last deglaciation, up to 360 m of sediments was deposited in the 135 km long fjord system. Shortly after the coastal area became ice-free, ∼12 300 14C years BP, the first ice-marginal deposits were formed, probably due to a minor glacier re-advance. The greatest volume of sediments in the fjord was deposited during the Allerod ice recession period, the Younger Dryas re-advance and the succeeding ice retreat period until the ice disappeared from the fjord in early Preboreal. During the Allerod, the fjord was ice-free and glaciomarine stratified sediments were deposited. The ice margin is suggested to have been located just west of Lake Strynevatnet before the advance during the Younger Dryas. In the late phase of the Younger Dryas, and within the succeeding ∼1000 years, the glacio-isostatic rebound was rapid, and extensive re-sedimentation took place. Slide activities continued into mid-Holocene, albeit with less intensity and were followed by normal and calm marine conditions that prevailed until the present. One huge rock avalanche into the fjord took place between 2200 and 1800 14C yr BP, probably triggering a tsunami and several slides in the fjord. Even though glacigenic sediments totally dominate in terms of sediment volume, the present study underlines the importance of re-sedimentation and other gravitational processes in such fjord settings.

The Nyegga region, located at water depths of about 600–800 m on the NW European continental margin, contains more than 200 pockmarks. Recently collected TOPAS seismic profiles and EM1002 bathymetric records now provide high-resolution information on their seabed and shallow sub-seabed geological setting. The identified pockmarks are up to 15 m deep, between 30 m and 600 m across and reach a maximum area of ca. 315,000 m2. The pockmarks are sediment-empty features. They do not have any preferred direction of orientation and show large variations in their shape. The pockmarks are restricted to a

Based on a revised chronostratigraphy, and compilation of borehole data from the Barents Sea continental margin, a coherent glaciation model is proposed for the Barents Sea ice sheet over the past 3.5 million years (Ma). Three phases of ice growth are suggested: (1) The initial build-up phase, covering mountainous regions and reaching the coastline/shelf edge in the northern Barents Sea during short-term glacial intensification, is concomitant with the onset of the Northern Hemisphere Glaciation (3.6–2.4 Ma). (2) A transitional growth phase (2.4–1.0 Ma), during which the ice sheet expanded towards the southern Barents Sea and reached the northwestern Kara Sea. This is inferred from step-wise decrease of Siberian river-supplied smectite-rich sediments, likely caused by ice sheet blockade and possibly reduced sea ice formation in the Kara Sea as well as glacigenic wedge growth along the northwestern Barents Sea margin hampering entrainment and transport of sea ice sediments to the Arctic–Atlantic gateway. (3) Finally, large-scale glaciation in the Barents Sea occurred after 1 Ma with repeated advances to the shelf edge. The timing is inferred from ice grounding on the Yermak Plateau at about 0.95 Ma, and higher frequencies of gravity-driven mass movements along the western Barents Sea margin associated with expansive glacial growth.

Fjords situated in past, or present, glacial regimes represent important repositories between land masses (source systems) and the open oceans (sink systems). Newly collected TOPAS high-resolution seismic profiles from the previously glaciated Nordfjord system, on the west coast of Norway, reveal sedimentary processes and depositional environments within fjords in more detail than before. The seismic data show that the fjord basins are characterised by a well-laminated lower unit that is overlain by acoustic transparent lensoidal bodies. We infer the lower unit, which is up to 350 m thick, to be composed of glacimarine sediments. The transparent bodies represent up to 0.25 km 3 large slide debrites that comprise 14 C yr BP (c. 15 000 cal. yr BP), during the last deglaciation. The entire Nordfjord system was ice free for a short time period before the ∼ 1000 year long Younger Dryas readvance halted the main Fennoscandian deglaciation and over-ran the eastern part of Nordfjord. In contrast to the Last Glacial Maximum, we suggest that the sediments in the ice-covered fjord basins were preserved during Younger Dryas. The rapid isostatic adjustments accompanying the withdrawal of the Younger Dryas ice sheet promoted conditions for failures. We relate the identified Nordfjord slide bodies to this paraglacial environment. This implies that the acoustic well-laminated glacimarine fjord unit has been deposited in about 2000 yr, and that sediment rates as high as 20 cm/yr have existed during deposition.

Mass movements are a frequent sedimentary process in the marine realm, affecting both glaciated and non-glaciated continental margins. Here a 3D seismic data set from the North Sea Fan, NE Atlantic margin, is used to study internal architecture, external geometry and surface geomorphology of different types of buried sediment transport. We identify three mass transport deposits, at a depth of ca 100–1000 m below seabed, corresponding to the previously mapped Tampen (~130 ka) and M½re (~300 ka) slides and the Stad (~400 ka) Slide, identified in this study. These slides all eroded underlying sedimentary units and their surfaces include curvilinear ridges up to 20 m high and 10–15 km long. Locally, the slide surfaces also include rafted slide blocks, up to 200 m wide, 300 m long and 30 m high. We relate the curvilinear ridges and the slide blocks to submarine spreading. Intervals of glacigenic debris flows are identified between the mass transport deposits. These lens-shaped bodies are seen in plan to be flows that widen downslope and which are fed from 10 to 20 m deep, 50–200 m wide and >2 km long transport channels that extend from the paleo-shelf edge. Analyses of time slices suggest that such flows may have been operating on the North Sea Fan for the last ~1.1 million years.

Based on high-resolution bathymetric records, sub-bottom profiles and sediment cores, we study postglacial mass transport deposits, slide scar complexes, cyclic steps and rockfall deposits as indicators of mass failures in the inner Hardangerfjorden system, western Norway. The stacked mass transport deposits show thicknesses of up to 4 m and witness that the inner Hardangerfjorden has been a site of repetitive mass failure events, potentially triggered by earthquakes related to glacioisostatic uplift. The cyclic steps, affecting an area of about 2 km2 in the innermost fjord, have wave lengths of 40 m, heights of 5 m and are most likely related to fluvial sediment supply. Seven slide scar complexes, with stratigraphy-cutting scar heights of 6–34 m, are identified on the basin plain of the fjord. These are all associated with large depocenters along the fjord flanks, suggesting a link between locations of high sediment supply and mass failure. Although rapid deposition might, by itself, induce failures, an external trigger mechanism, such as an earthquake, should also be considered.

Submarine slides have been instrumental in shaping the Late Neogene NE Atlantic continental margin. We document a margin setting north of 70°N capable of generating recurrent huge Pleistocene mass-movements. The 1.0–0.2 Ma old Bjornoya Fan Slide Complex includes three buried mega-slides, which have left scars containing up to 500 m-thick debris units. The two largest slides may have had a retrogressive development, cover areas of the order of ∼ 120 × 10 3 km 2 , and involved ∼ 25 × 10 3 km 3 of sediments. Thus, the failures involved an order of magnitude more sediment than the Storegga Slide, the world's largest exposed slide. The mega-slides occurred during the Northern Hemisphere Glaciations, characterized by greatly enhanced deposition rates leading to the construction of the 3-km-thick Bjornoya Trough Mouth Fan that progressively loaded a softer Miocene–Oligocene substratum. This setting induced excess pore pressure and sediment instability, conditions favorable for sliding. External trigger mechanisms, such as earthquakes, may have facilitated the mass-wasting process.

Based on studies of sediment accumulations deposited from-and erode by-alongslope flowing ocean currents on the European continental margin from Porcupine (Ireland) to Lofoten (Norway), the evolution of the Cenozoic paleocirculation was reconstructed as part of the STRATAGEM project. There is evidence of ocean current-controlled erosion and deposition in the Rockall Trough, in the Faeroe-Shetland Channel and on the Voring Plateau since the late Eocene, although the circulation pattern remains ambiguous. The late Palaeogene flow in the Rockall Trough was almost probably driven by southerly-derived Tethyan Outflow Water. The extent and strength of any northerly-derived flow is uncertain. From the early Neogene (early-mid-Miocene), there was a massive regional expansion of contourite drift development both in the North Atlantic and in the Norwegian-Greenland Sea. This was most probably related to the development of the Faroe Conduit, the opening of the Fram Strait and the general subsidence of the Greenland-Scotland Ridge. These may have combined to cause a considerable acceleration in the exchange and overflow of deep waters between the Arctic and Atlantic Oceans. An early late Neogene (late early Pliocene) regional erosional event has been ascribed to a vigorous pulse of bottom-current activity, most probably the result of a global reorganisation of ocean currents associated with the closure of the Central American Seaway. During the late Neogene, contourites and sediment drifts developed in deep-water basins, between units of glacigenic sediments as well as infill of several paleo-slide scars. These sediments were derived from areas of bottom-current erosion as well as from the development of Plio-Pleistocene prograding sediment wedges, incorporating the extensive sediment supply derived from shelf-wide ice sheets. Presently a profound winnowing prevails along the shelf and upper slope due to the inflowing currents of Atlantic water. Depocentres of sediments derived from the winnowing are located (locally) in lower slope embayments and in slide scars.

In this paper new and previously published data on the Pleistocene glacial impact on the NW European margin from Ireland to Svalbard (between c. 48°N–80°N) are compiled. The morphology of the glaciated part of the European margin strongly reflects repeated occurrence of fast-moving ice streams, creating numerous glacial troughs/channels that are separated by shallow bank areas. End-moraines have been identified at several locations on the shelf, suggesting shelf-edge glaciation along the major part of the margin during the Last Glacial Maximum. Deposition of stacked units of glacigenic debris flows on the continental slope form fans at a number of locations from 55°N and northwards, whereas the margin to the south of this is characterised by the presence of submarine canyons. Glaciation curves, based primarily on information from the glacial fed fan systems, that depict the Pleistocene trends in extent of glaciations along the margin have been compiled. These curves suggest that extensive shelf glaciations started around Svalbard at 1.6–1.3 Ma, while repeated periods of shelf-edge glaciations on the UK margin started with MIS 12 (c. 0.45 Ma). The available evidence for MIS 2 suggest that shelf-edge glaciation for the whole margin was reached between c. 28 and 22 14 C ka BP and maximum positions after this were more limited in some regions (North Sea and Lofoten). The last glacial advance on the margin has been dated to 15–13.5 14 C ka BP, and by c. 13 14 C ka BP the shelf areas were completely deglaciated. The Younger Dryas (Loch Lomond) advance reached the coastal areas in only a few regions.

The lower Neogene stratigraphy of the NW European Atlantic margin, from the Voring to the Porcupine basins, is interpreted to record a discrete phase of compressional tectonism that spanned at least 8 Ma from the earliest to the early mid-Miocene. This compressional tectonism may be coeval with a local reorganisation of the NE Atlantic plate system with the transfer of the Jan Mayen micro-plate from Greenland to Europe. The compressional tectonics has resulted in a number of stratigraphic sequences of complex character bounded by regional base Neogene and intra-Miocene unconformities. These are traceable across a range of depths and record distortion of the basin margins and changes in deep-water circulation patterns. This episode of compressional tectonics has also resulted in the creation of a number of anticlinal domes along the Norwegian, Faroese and UK Atlantic margins. The stratigraphic and structural evidence are interpreted to record two stages in the development of the margin: the first being characterised by a prolonged period of regional flexure in response to the build-up of compressive stresses; the second stage is the development of anticlinal structures that led to a rapid release of stress. In the Wyville–Thomson–Faroes region, compressional deformation influenced the creation of the present-day deep-water conduit of the Faroe Bank Channel, which is interpreted to be an early Neogene syncline. Together, the Faroe Bank and Faroe–Shetland channels represent the deepest water passageway across the Greenland–Scotland Ridge. The early Neogene development of this conduit is considered to mark the onset of deep-water exchange across this oceanic gateway.

The North Atlantic margins are archetypally passive, yet they have experienced post-rift vertical movements of up to kilometre scale. The Cenozoic history of such movements along the NW European margin, from Ireland to mid-Norway, is examined by integrating published analyses of uplift and subsidence with higher resolution tectono-stratigraphic indicators of relative movements (including results from the STRATAGEM project). Three episodes of epeirogenic movement are identified, in the early, mid- and late Cenozoic, distinct from at least one phase of compressive tectonism. Two forms of epeirogenic movement are recognised, referred to as tilting (coeval subsidence and uplift, rotations

Rapidly deposited laminated sediments dated between 18 and 21 cal. ka BP have been observed at several core locations in the Northern North Sea and the Southern Norwegian Sea. Sedimentation rates range from 20 cm/ka up to 2000 cm/ka, compared to a normal background sedimentation rate in the area of 5–10 cm/ka. Dropstones, in situ paired bivalves and grain size distribution indicate a hemipelagic origin for the laminae in core MD99-2291, from the upper continental slope of Southern Norway. AMS radiocarbon dating and cyclic changes in the number of planktonic foraminifera and lithological parameters suggest that the laminations in the core are annual varves. The laminated sediments are interpreted to be suspension plume deposits and two phases of plume deposition have been dated to 21.5 and 18.6 cal. ka BP. Large fluxes of meltwater were generated during this period, as reflected in oxygen and carbon isotopes records from cores in the area. The meltwater and the laminated plume deposits are interpreted to be associated with the presence and disintegration of the Norwegian Channel Ice Stream. Observations from other regions demonstrate that laminated high rate deposition is very widespread on glaciated continental margins. Around 18.6 cal. ka BP increases in sediment fluxes also occurred on the Barra Fan, the North Sea Fan, the Lofoten contourite drift and the Svalbard margin, preceding increased sediment and meltwater fluxes on the Greenland margin and the Labrador Sea, associated with Heinrich event 1. Warm water inflow to the Norwegian Sea together with rising sea level probably triggered the destabilisation of the ice streams of the Fennoscandian Ice Sheet, while a similar response of the Laurentide ice sheet was delayed by 500–1000 yr.

A regional stratigraphic framework for the Neogene succession along and across the NW European margin is presented, based on a regional seismic and sample database. The stratigraphy provides constraints on the timing and nature of the mid- to late Cenozoic differential tectonic movements that have drivenmajor changes in sediment supply, oceanographic circulation and climate (culminating in continental glaciation). The overall context for Neogene deposition on the margin was established in the mid-Cenozoic, when rapid, km-scale differential subsidence (sagging) created the present-day deep-water basins. The Neogene is subdivided into lower (Miocene–lower Pliocene) and upper (lower Pliocene–Holocene) intervals. The lower Neogene contains evidence of early to mid-Miocene compressive tectonism, including inversion anticlines and multiple unconformities that record uplift and erosion of basin margins, as well as changes in deep-water currents. These movements culminated in a major expansion of contourite drifts in the mid-Miocene, argued to reflect enhanced deep-water exchange across the Wyville-Thomson Ridge Complex, via the Faroe Conduit. The distribution and amplitude of the intra-Miocene movements are consistent with deformation and basin margin flexure in response to enhanced intra-plate compressive stresses during a local plate reorganization (transfer of the Jan Mayen Ridge from Greenland to Europe). The upper Neogene records a seaward tilting (

Acoustic data and sediment cores collected from the Storegga Slide and its adjacent slide flanks, i.e. the Voring Plateau to the north and the North Sea Fan to the south, have been used to study the Late Cenozoic glacial history and geological development of this region. Age constrains obtained from the investigated cores show that the Fennoscandian Ice Sheet reached the shelf edge during Marine Isotope Stages (MIS) 12, 10, 8, 6 and 2. Ice sheet fluctuations within each glaciation might have occurred, as is evidenced for the Last Glacial Maximum (MIS 2). The first extensive ice advance is identified in the Early Pleistocene, at c. 1.1 Ma; however, between 2.6 and 0.5 Ma the ice sheets were largely restricted to the fjords and inner shelf. During each glacial maximum, glacigenic debris flows (GDFs) transported basal till, deposited at the shelf edge, into the deep sea along the entire studied margin. The most voluminous GDF sequences are found on the southern Storegga Slide flank (North Sea Fan), where the individual flows are found as far as 500 km from the shelf edge. On the Voring Plateau glacimarine/hemipelagic sedimentation has dominated the last c. 250,000 yr. During MIS 2 such sediments were rapidly deposited, covering the upper-slope-limited GDF units in this region. Between c. 15,700 and 15,000 14C yr BP, i.e. during the last deglaciation of the Norwegian margin, a presumed meltwater plume, released from the disintegrating Norwegian Channel Ice Stream, transported and rapidly deposited up to 20 m of fine-grained sediments in the region north of the North Sea Fan. The rapid deposition of large volumes of GDFs, glacimarine and meltwater related sediments might have influenced the stability of the slope sediments in the studied region, promoting conditions favorable for failure. Furthermore, these high sedimentation rates also partly account for the high subsidence rates observed on the Norwegian continental margin in the Late Cenozoic.

2D multichannel seismic and mini-sleeve gun profiles reveal that an up to 1.5 s(twt) thick sedimentary succession has been deposited on the Norwegian continental margin (62°N–68°N) during Neogene and Quaternary. Well-defined Miocene depocentres have evolved both in the North Sea Fan region and along the flanks of structural highs in the Voring Basin. Miocene sediments are, on the other hand, mainly absent within the Storegga Slide scar. Seismic facies analyses show that these deposits locally are characterised by a mounded and/or migration–aggradation pattern, which we relate to a current-influenced depositional environment. Hence, the early Neogene sediments on the Norwegian continental margin are classified as contourites. The contourites have most likely been deposited in connection with the establishment of a deep-water exchange in the Norwegian–Greenland Sea, due to the opening of the Fram Strait and subsidence of the Greenland–Scotland Ridge. At about 2.5 Ma, a significant change in this depositional environment took place. Down-slope sedimentary processes became now more important and throughout the late Plio-Pleistocene sediments were mainly sourced from the Norwegian mainland and the adjacent continental shelf, causing depocentres to evolve along the shelf edge.

Throughout the Pleistocene the sedimentary environment on the SE Nordic Seas continental slope/outer shelf, off western Norway, has been strongly controlled by variability in the Norwegian Atlantic Current (NwAC), glaciations of the shelf areas and sea level changes. Acoustic and core data from the southern Voring Plateau show a Pleistocene sequence characterised by hemipelagic sediments interfingered by diamictons on the upper slope. The area of the 7.25 14 C ka BP Storegga Slide shows evidence of a long history of Pleistocene mega-slides. During the last interglacial, and most likely also during previous interglacials, the slide region has been the locus of rapid deposition between water depths of 800 and 1200 m, as a result of NwAC winnowing along the upper slope. The North Sea Fan region is strongly influenced by glacigenic debris flows (GDFs) deposited during glacial advances reaching the shelf edge, when the Norwegian Channel was occupied by the Norwegian Channel Ice Stream. It appears that GDF activity was initiated at ca. Marine Isotope Stage 12. Interbedded between the debris flow sequences, mega-slide events such as the More and Tampen slides have been identified. During glaciations, when the entire SE Nordic Seas continental shelf was covered by extensive grounded ice sheets, basal till were transported to the shelf edge from where subsequent mass movement occurred. During late glaciation/early deglaciation meltwater plumes were released at the time of disintegration of ice streams in the Norwegian Channel, as is evidenced from the last deglaciation of the margin at ca. 15 14 C ka BP. The plume material was transported northwards by currents, before rapidly deposited as a thick package within the Storegga Slide area and on the south Voring Plateau. Based on identification and dating of iceberg scourings, glacial erosion surfaces and delta deposits on the shelf, subsidence rates between 0.7 and 1.2 m/ky have been calculated for the last ca. 250 ka.

High-resolution seismic data and sediment cores show that an up to 280 m thick sedimentary sequence has been deposited on the south Voring margin, off mid-Norway, the last ca 250 ka. The sedimentary succession has been divided into six seismic units, dominated by hemipelagic sediments. Five wedge-shaped massive sequences, of marine isotope stages 8, 6 and 2, interfinger the hemipelagic deposits on the upper slope. The wedge-shaped sequences represent glacigenic debris flows that have been fed by till transported to the shelf edge by grounded ice sheets during maximum glaciations. The hemipelagic units show well-defined depocentres, of various thicknesses, on the upper continental slope. Seismic facies interpretation indicates that the sediment distribution locally has been controlled by currents. Commonly, the hemipelagic units are characterised by parallel and continuous reflectors. However, the second youngest unit identified, deposited between 15.7 and 15.0 14 C ka BP, is acoustic transparent. We suggest that this unit has been sourced by along-slope transported meltwater plume deposits, released during the initial stage of the last deglaciation of the Norwegian Channel. The hemipelagic sedimentation rates have varied considerably throughout the studied time period. Until ca 21 14 C ka BP the rates did not exceed 1.4 m/kyr, whereas during the Last Glacial Maximum the rates increased and reached values of about 36 m/kyr before decreasing again at ca 15 14 C ka BP. Observation of iceberg scourings, of MIS 8 age, about 800 m below the present day sea level, suggest that the south Voring margin has subsided by a rate of 1.2 m/kyr in the Late Quaternary.

The Norwegian Channel between Skagerrak, in the southeast, and the continental margin of the northern North Sea, in the northwest, is the result of processes related to repeated ice stream activity through the last 1.1 m yr. In such periods the Skagerrak Trough (700 m deep) has acted as a confluence area for glacial ice from southeastern Norway, southern Sweden and parts of the Baltic. Possibly related to the threshold in the Norwegian Channel off Jaeren (250 m deep), the ice stream, on a number of occasions over the last 400 ka, inundated the coastal lowlands and left an imprint of NW-oriented ice directional features (drumlins, stone orientations in tills and striations). Marine interstadial sediments found up to 200 m a.s.l. on Jaeren have been suggested to reflect glacial isostasy related to the Norwegian Channel Ice Stream (NCIS). In the channel itself, the ice stream activity is evidenced by mega-scale glacial lineations on till surfaces. As a result of subsidence, the most complete sedimentary records of early phases of the NCIS are preserved close to the continental margin in the North Sea Fan region. The strongest evidence for ice stream erosion during the last glacial phase is found in the Skagerrak. On the continental slope the ice stream activity is evidenced by the large North Sea Fan, which is mainly a result of deposition of glacial-fed debris flows. Northwards of the North Sea Fan, rapid deposition of meltwater plume deposits, possibly related to the NCIS, is detected as far north as the Voring Plateau. The NCIS system offers a unique possibility to study ice stream related processes and the impact the ice stream development had on open ocean sedimentation and circulation.