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We investigate the mesoscopic electron transport through multiple quantum dot systems in a T-shaped configuration and analyse the effect of the number of quantum dots on transport observables. Analytically, the expressions for the transmission probability and current have been derived, in the presence of intradot Coulomb interaction, using non-equilibrium Green function techniques. The higher-order Green functions containing the Coulomb interaction term have been decoupled using the mean-field approximation. The analytical, as well as the numerical, calculations have been presented for single, double and triple quantum dot systems in T-shaped configuration and then the results have been generalised for N number of quantum dots in the same configuration. The transport observables, such as transmission coefficient, I–V characteristics and differential conductance, have been numerically analysed. Numerical results show a systematic variation in the number of transmission spectrum peaks as the number of quantum dots side-coupled to the active dot increases. It is found that the number of the transmission probability peaks is directly related to the number of quantum dots and the peak spacings are controlled by the inter-dot coupling strength. However, the magnitude of the current is hardly affected by the increase in the number of side-coupled dots in T-shaped quantum dot systems. [ABSTRACT FROM AUTHOR]

Gas seeps and fluid-flow related seabed features are found over the entire Norwegian exclusive economic zone (EEZ). Multibeam water-column data from c. 136 000 km2 has revealed more than 5 000 gas seeps. Most of the gas seeps seem to have biogenic, thermogenic or mixed origin; some may be of abiotic origin. The spatial distribution of the gas seeps appears to correlate with: 1 - structural highs with associated faulting, exposing hydrocarbon reservoir rocks at or near the seabed; 2 - faults serving as conduits for fluid flow; 3 - settings where reservoir rocks overlain by less permeable cap rocks sub-crop at the seabed. Other mechanisms involve seepage around abandoned exploration wells, and possible abiotic gas generation from serpentinisation of ultramafic rocks near mid-oceanic ridges. The gas seeping from the Norwegian cold seeps is mostly methane and has, in many places, led to the formation of methane-derived authigenic carbonate crusts, which give evidence for either extensive gas seepage in the past or long-lived seepage. Chemosynthetic communities are commonly associated with cold seeps and may form special habitats together with the carbonate crusts. Methane seepage has been proposed to contribute significantly to the global carbon budget and may be associated with gas hydrates giving rise to potential geohazards. Gas seeps have been identified and spatially mapped as acoustic gas flares, using multibeam echosounder systems, which have the ability to record reflections from both the water column and the seabed. Water-column data have been recorded in the MAREANO seabed mapping program since 2010, covering an area of c. 262 000 km2, with a data volume in the order of 210 Tb. The observations of extensive gas flares in the Norwegian EEZ are available to the scientific community and other users through a dedicated MAREANO data and web access system. [ABSTRACT FROM AUTHOR]

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

Abstract The Harstad Basin is a structural block on the continental shelf of SW Barents Sea where gas hydrates likely occurred below the grounded ice-sheet during the last glaciation and it hosts active gas seepage at numerous seafloor sites. We present an integrated study of fluid flow systems in the Harstad Basin by combining seismic profile interpretations and gas flare mapping data with the geochemical results obtained on seafloor seeping gas and methane-derived carbonate crusts. More than 190 acoustic gas flares were registered in water column, many of them in association with pockmarks and carbonate crust fields. However, weak or absent seepage observed during remotely operated underwater vehicle transects across many pockmarks and crust fields suggests that seepage activity may have decreased since the last deglaciation. In the western Harstad Basin, seeps of microbial methane occur mainly above Tertiary formations that are pinching out below the glacial sediments. High amplitude seismic anomalies suggest the presence of gas pockets at the base of the glacial sediments and within Tertiary deposits. In contrast, gas seeping in the eastern Harstad Basin originates from a biodegraded thermogenic source tentatively connected to the deeply faulted Mesozoic rocks occurring below glacial sediments. This spatial variability in fluid sources is also recorded in the carbon isotope data of seafloor carbonate crusts, with δ13C values typically between −55 and −42‰ and −40 and −20 ‰VPDB for carbonate crusts associated with microbial and thermogenic fluids, respectively. U-Th chronology combined with the stable isotope data suggests that this discrepancy in fluid sources over a distance of about 20 km has been stable since the last glaciation and highlights the significance of regional underlying geology in mediating fluid supply to the seafloor. Highlights • More than 190 flares identified over the course of multiple surveys. • Large pockmarks formed by a combination of fluid flow and erosional processes focused around exposed carbonate crusts. • Geochemical heterogeneity of seeping gas and seafloor carbonates over a short distance reflects variations in underlying geology. • Carbonate U-Th ages as old as 13.8 kyr suggest seepage and related carbonate formation started shortly after the deglaciation. [ABSTRACT FROM AUTHOR]

Gas seepage through the seafloor into the water column is inferred based on acoustic mapping, video observations and geochemical analyses at multiple locations in the Viking Graben and Utsira High areas of the central North Sea. Flares in the Viking Graben occur both inside and along the periphery of a submarine melt water channel where pockmarks (up to 500 m in diameter) and methane-derived carbonate crusts are found on the seafloor, indicating focussing of fluid flow in the vicinity of the channel. The flares can be related to gas accumulations close to the seafloor as well as in Quaternary and deeper strata, observed as high-amplitude reflections on seismic data. Many palaeo-channels, which act as accumulation zones, are observed in the subsurface of both the Viking Graben and Utsira High areas. The deeper origin of gas is partially supported by results of isotope analyses of headspace gas collected from sediment samples of the Viking Graben, which show a mixed microbial/thermogenic origin whereas isotope data on free seeping gas in the Viking Graben indicate a predominantly microbial origin. Based on these lines of evidence, a structure-controlled fluid flow model is proposed whereby hydrocarbons migrate in limited amount from deep thermogenic reservoirs along faults, and these deep fluids are strongly diluted by microbial methane. Moreover, the existence of subsurface pockmarks at several stratigraphic levels indicates long-term fluid flow, interpreted to be caused by gas hydrate destabilisation and stress-related high overpressures. [ABSTRACT FROM AUTHOR]

We present a theoretical study of the role of asymmetry and magnetic flux on electronic transport through various configurations of coupled quantum dot system, by using Non-Equilibrium Green Function formalism. Transport properties (Transmission Probability, Current–Voltage Characteristics and Differential Conductance) of the different configurations of coupled quantum dot system have been studied by self-consistent approach, in the presence of on-dot Coulomb interaction. Fano effect, appearing in Transmission probability, has been explored during transition of the system from series to symmetric parallel configuration and in response to the variation in magnetic flux threading the system. The results show Fano peaks for asymmetric and symmetric parallel configurations. By adjusting the magnetic flux, swapping effect in Fano peaks appears due to the exchange of states, which sustains despite strong Coulomb blockade effect. The transmission probability spectrum shows mirror symmetry whenever the sum of two values of magnetic flux threading the system is 2 π . [ABSTRACT FROM AUTHOR]

Multibeam bathymetric data and reflection-seismic profiles from Varangerfjorden, East Finnmark, have yielded a wealth of new information, particularly on morphological features of the seafloor, many of which can be readily linked to bedrock geological elements mapped in nearby onshore areas. The seismic profiles, in particular, have revealed the presence of a concealed half-graben in the hangingwall of the offshore extension of the Trollfjorden-Komagelva Fault Zone. Although the age of the c. 600 m-thick, sedimentary infill in the half-graben is, as yet, unknown, from the regional geological picture recorded offshore on the Finnmark Platform we consider that deposition in the fault-bounded basin is likely to date to Carboniferous time, possibly extending down into the Late Devonian. Internal folding in the succession close to the fault may relate to Mesozoic inversion. The bathymetric data show several interesting features: (1) two deep, glacially eroded basins and a shallower central basin; (2) a prominent NW-SE to NNW-SSE structural grain on the seabed in the outermost parts of the fjord which links with a similar trend of Timanian age on nearby Rybachi Peninsula, NW Russia; (3) the inferred southeastward trace of the Trollfjorden-Komagelva Fault Zone offshore from Varanger Peninsula; and (4) a series of subparallel, seafloor escarpments trending ESE-WNW south of the fault zone which can be linked to specific, Neoproterozoic, quartzitic sandstone formations onshore. The boundary between the Archaean basement and the well-stratified Neoproterozoic succession, representing an unconformity, can be identified on the seismic profiles and bathymetric image. [ABSTRACT FROM AUTHOR]

Abstract: Transport through coupled quantum dot system has been studied, using non-equilibrium Green function formalism. Inter-dot tunneling with on-dot Coulomb repulsion is included while inter-dot Coulomb interaction is neglected. Behavior of system in transition from series configuration to symmetric parallel and in T-shaped coupled quantum dot system has been explored. Transmission coefficient as a function of Fermi energy shows Fano effect during transition. The system shows negative differential conductance and reverse current at low bias in series. It has been shown that the existence of negative differential conductance during transition from series to asymmetric parallel configuration is regulated by a competition between inter-dot tunneling and dot-lead coupling. Effect of inter-dot tunneling on negative differential conductance and on transport properties of T-shaped double dot has been studied. [Copyright &y& Elsevier]

Transport through symmetric parallel coupled quantum dot system has been studied, using non-equilibrium Green function formalism. The inter-dot tunnelling with on-dot and inter-dot Coulomb repulsion is included. The transmission coeffcient and Landaur-Buttiker like current formula are shown in terms of internal states of quantum dots. The effect of inter-dot tunnelling on transport properties has been explored. Results, in intermediate inter-dot coupling regime show signatures of merger of two dots to form a single composite dot and in strong coupling regime the behaviour of the system resembles the two decoupled dots. [ABSTRACT FROM AUTHOR]

The presence of gas hydrate in marine sediments alters their physical properties. In some circumstances, gas hydrate may cement sediment grains together and dramatically increase the seismic P- and S-wave velocities of the composite medium. Hydrate may also form a load-bearing structure within the sediment microstructure, but with different seismic wave attenuation characteristics, changing the attenuation behaviour of the composite. Here we introduce an inversion algorithm based on effective medium modelling to infer hydrate saturations from velocity and attenuation measurements on hydrate-bearing sediments. The velocity increase is modelled as extra binding developed by gas hydrate that strengthens the sediment microstructure. The attenuation increase is modelled through a difference in fluid flow properties caused by different permeabilities in the sediment and hydrate microstructures. We relate velocity and attenuation increases in hydrate-bearing sediments to their hydrate content, using an effective medium inversion algorithm based on the self-consistent approximation (SCA), differential effective medium (DEM) theory, and Biot and squirt flow mechanisms of fluid flow. The inversion algorithm is able to convert observations in compressional and shear wave velocities and attenuations to hydrate saturation in the sediment pore space. We applied our algorithm to a data set from the Mallik 2L–38 well, Mackenzie delta, Canada, and to data from laboratory measurements on gas-rich and water-saturated sand samples. Predictions using our algorithm match the borehole data and water-saturated laboratory data if the proportion of hydrate contributing to the load-bearing structure increases with hydrate saturation. The predictions match the gas-rich laboratory data if that proportion decreases with hydrate saturation. We attribute this difference to differences in hydrate formation mechanisms between the two environments. [ABSTRACT FROM AUTHOR]

The presence of gas hydrate in oceanic sediments is mostly identified by bottom-simulating reflectors (BSRs), reflection events with reversed polarity following the trend of the seafloor. Attempts to quantify the amount of gas hydrate present in oceanic sediments have been based mainly on the presence or absence of a BSR and its relative amplitude. Recent studies have shown that a BSR is not a necessary criterion for the presence of gas hydrates, but rather its presence depends on the type of sediments and thein situconditions. The influence of hydrate on the physical properties of sediments overlying the BSR is determined by the elastic properties of their constituents and on sediment microstructure. In this context several approaches have been developed to predict the physical properties of sediments, and thereby quantify the amount of gas/gas hydrate present from observed deviations of these properties from those predicted for sediments without gas hydrate.We tested four models: the empirical weighted equation (WE); the three-phase effective-medium theory (TPEM); the three-phase Biot theory (TPB) and the differential effective-medium theory (DEM). We compared these models for a range of variables (porosity and clay content) using standard values for physical parameters. The comparison shows that all the models predict sediment properties comparable to field values except for the WE model at lower porosities and the TPB model at higher porosities. The models differ in the variation of velocity with porosity and clay content. The variation of velocity with hydrate saturation is also different, although the range is similar. We have used these models to predict velocities for field data sets from sediment sections with and without gas hydrates. The first is from the Mallik 2L–38 well, Mackenzie Delta, Canada, and the second is from Ocean Drilling Program (ODP) Leg 164 on Blake Ridge. Both data sets haveVp andVs information along with the composition and porosity of the matrix. Models are considered successful if predictions from bothVp andVs match hydrate saturations inferred from other data. Three of the models predict consistent hydrate saturations of 60–80 per cent from bothVp andVs from log and vertical seismic profiling data for the Mallik 2L-38 well data set, but the TPEM model predicts 20 per cent higher saturations, as does the DEM model with a clay–water starting medium. For the clay-rich sediments of Blake Ridge, the DEM, TPEM and WE models predict 10–20 per cent hydrate saturation fromVp data, comparable to that inferred from resistivity data. The hydrate saturation predicted by the TPB model fromVp is higher. UsingVs data, the DEM and TPEM models predict very low or zero hydrate saturation while the TPB and WE models predict hydrate saturation very much higher than those predicted fromVp data. Low hydrate saturations are observed to have little effect onVs. The hydrate phase appears to be connected within the sediment microstructure even at low saturations. [ABSTRACT FROM AUTHOR]

The nature of isostasy along the Western Continental Margin of India (WCMI) and the Eastern Continental Margin of Madagascar (ECMM) and their conjugate nature are examined. The first part of the study deals with the estimation of effective elastic thickness (Te) of the lithosphere for the two margins through cross-spectral analysis of gravity and bathymetry data. The results bring out comparable Te values of 8–15 km for the WCMI and 10–13 km for the ECMM, despite the WCMI having been traversed along strike by a hotspot trace. We have also compared topographic profiles across the two margins extending inland, to examine the rift-flank uplift experienced by the two landmasses abutting the margins, which bear a striking similarity. These results establish the symmetrical rifting mechanism resulting in the formation of the two margins, and indicate that despite the presence of a hotspot trace along one margin (i.e. the WCMI), the two margins have comparable isostatic compensation mechanisms with low Te values. In the second part of the study we have examined the possible mechanism for the rift-flank uplifts using a process-oriented approach of backstripping the sediments along a traverse across the WCMI and reconstructing the original rift flank topography by flexurally backstacking the amount of eroded material on the present-day topography of the Western Ghats. The backstack load configuration is taken from the amount of erosion that took place over the Western Ghats, obtained from AFTA (Apatite Fission Track Analysis) studies. The reconstructed rift time topography and bathymetry are used to get the Moho configuration, which was used to calculate the gravity anomaly, and is compared with the observed anomaly to derive a possible evolution model for the region. We have tried to examine the observed gravity anomaly through two different processes. In the first process, a Te=15 km for backstripping and backstacking, and a compensated underplating for the topography give a best fit model to the observed gravity. In the second process, a necking model with a deep level of necking (20 km) with Te=15 km and without any underplating explains the topography as well as the observed gravity. The nature and amount of the Western Ghat topography and cratonic age (Archaen) of the pre-rifted crust of western India and eastern Madagascar are more in favor of the rifting mechanism (necking model) rather than due to the passage of the Reunion hotspot (underplating model). This is evidenced by the observed increase in topography away from the influence of the Reunion hotspot trace as well as the presence of a similar topography in Madagascar. [Copyright &y& Elsevier]

A systematic generalised approach to find transport observables for a linear array of different quantum dot (QD) systems has been discussed, using non-equilibrium Green function (NEGF) formalism, in the presence of on-dot Coulomb interaction and inter-dot tunnelling. The equation of motion (EOM) method has been used to derive expressions for Green functions (GFs) within the simplest mean-field approximation to tackle the Coulomb correlation term. Starting from the mathematical structures of GFs for single, double and triple quantum dot systems, the expressions for GFs and transport observables have been generalised for the quantum dot systems containing N number of quantum dots in series as well as parallel linear array of dots. Further, the formulae so obtained have been used for numerical calculations of transmission probability and the I–V characteristics of linear arrays of quantum dots in series as well as parallel configuration containing up to three dots. The results show that, with the increase in number of dots in the scattering region, transmission probability and electron current decrease in series case, while both quantities increase in parallel configuration of dots. The inter-dot tunnelling leads to the splitting of transmission peaks in double QD system in series case whereas, it induces Fano effect in triple QD system in parallel configuration. [ABSTRACT FROM AUTHOR]

Gas hydrates occur within sediments on the western Svalbard continental margin and the Vestnesa Ridge, a large sediment drift that extends in a west‐northwest direction from the margin toward the mid‐ocean ridge. We acquired multicomponent ocean‐bottom seismic (OBS) data at 10 locations on the crest area of the eastern segment of the Vestnesa Ridge, an area with active gas seepage. P and S wave velocities are estimated using traveltime inversion, and self‐consistent approximation/differential effective medium rock physics modeling is used to estimate gas hydrate and free gas saturation at OBS stations. We apply 1‐D full waveform inversion at a selected OBS station to study detailed variations of P wave velocity near the bottom simulating reflection (BSR). High interval P wave velocity (Vp ≈ 1.73–1.82 km/s) and S wave velocity (>0.35 km/s) are observed in a layer above the BSR and low interval P wave velocity (Vp ≈ 1.28–1.53 km/s) in a layer below the BSR. We estimate 10–18% gas hydrate and 1.5–4.1% free gas saturation at different OBS stations in a layer above and below the BSR, respectively. We find significant variation in gas hydrate and free gas saturation across faults suggesting a structural control on the distribution of gas hydrate and free gas in the Vestnesa Ridge. Differences in gas hydrate saturation derived from P wave velocities and earlier estimates obtained from electromagnetic surveys indicate the presence of gas hydrates in faults and fractures. Moreover, beneath some OBS sites, the combined study of P and S waves, resistivity and seismic quality factor (Q), suggests the coexistence of free gas and gas hydrates. Key Points: Multicomponent OBS data show variations in gas hydrate distribution in contourite drift sediments of Vestnesa RidgeP and S wave velocities and 1‐D FWI models provide better constraints on gas hydrate and free gas saturation estimatesThe distribution of gas hydrates and free gas in Vestnesa Ridge is controlled by the presence of shallow faults [ABSTRACT FROM AUTHOR]

Integrated petrography, mineralogy, geochronology and geochemistry of cold seep carbonate crusts and free gas from the Alvheim channel elucidate diagenetic carbonate precipitation and related seepage histories in the central North Sea. Free gas isotope characteristics coupled with carbonate δ 13 C values as low as − 66‰ VPDB, indicate a predominantly microbial methane source with minor thermogenic contribution. We estimate that ~ 70% of the carbon sequestered into carbonate precipitates was derived from local oxidation of methane. The early stage of crust growth is represented by microcrystalline aragonite and Mg-calcite (10 to 40% mol MgCO 3 ) cementing seafloor sediments consisting of clays, quartz, feldspar, and minor detrital low Mg-calcite and dolomite. Typical association of aragonite cement with coarse-grained detritus may reflect elevated fluid flow and flushing of fine particles prior to cementation close to the seafloor. Middle rare earth element enrichment in early generation microcrystalline cements containing framboidal pyrite indicates diagenetic precipitation within the zone of anaerobic methane oxidation contiguous to iron reduction. The later generation diagenetic phase corresponds to less abundant radial fibrous and botryoidal aragonite which lines cavities developed within the crusts. In contrast to early generation cements, late generation cavity infills have rare earth elements and Y patterns with small negative Ce anomalies similar to seawater, consistent with carbonate precipitation in a more open, seawater dominated system. Aragonite U–Th ages indicate carbonate precipitation between 6.09 and 3.46 kyr BP in the northern part of the channel, whereas in the southern part precipitation occurred between 1.94 and 0.81 kyr BP reflecting regional changes in fluid conduit position. [ABSTRACT FROM AUTHOR]

A large and diverse dataset has been compiled and analysed in the Barents Sea and Finnmark fjords in northern Norway in order to map and characterise pockmarks. The main data sources are regional side-scan sonar and deep-towed boomer lines and extensive bathymetric datasets of multibeam echo sounding. Small to medium-sized pockmark fields occur in several basins west of Nordkappbanken. The most extensive is in Ingøydjupet, where the largest pockmarks are nearly 100 m wide and up to 8 m deep. Small to medium-sized pockmarks are, however, more common (20-50 m wide, 2-5 m deep). The pockmark density is typically 150-200 per km². North of the Finnmark coast, from Magerøya/Nordkapp to the Russian border, pockmark distribution is nearly continuous. The density varies mainly between 300 and 600 per km², and most pockmarks are small (15-40 m wide, 1.5-4 m deep). Recent studies suggest that the pockmarks in the southwestern Barents Sea were formed from seabed expulsion of gas due to dissociation of gas hydrates during the last deglaciation. Locally, gas has been observed to leak from the Barents Sea floor, but not from pockmarks, suggesting recent inactivity. We further explore the possibility that the pockmarks were formed during a short-lived event and that their shapes have been preserved due to low sedimentation rates and turbulent ocean currents. Numerous small pockmarks also occur in four studied Finnmark fjords. They are most common in Varangerfjorden and Porsangerfjorden where non-gas generating Proterozoic rocks subcrop. The origin of these pockmarks is most likely related to groundwater seepage. [ABSTRACT FROM AUTHOR]

Litho-stratigraphic variation of sedimentary units constructed from seismic sections and gravity anomaly in the Konkan and Kerala basins of the western continental margin of India (WCMI) have been used to model processes such as lithospheric rifting mechanism, its strength, and evolution of flank uplift topography that led to the present-day Western Ghats escarpment. Based on the process-oriented approach, two lithospheric models (necking and magmatic underplating) of evolution of the margin were tested. Both, necking and underplating models suggest an effective elastic thickness (Te) of 5 km and 10 km along Konkan and Kerala basins, respectively and a deep level of necking at 20 km at both basins. Model study suggests that the necking model better explains the observed gravity anomalies in the southern part of the WCMI. A synthesis of these results along with the previously published elastic thickness estimates along the WCMI suggests that a low-to-intermediate strength lithosphere and a deeper level of necking explains the observed flank-uplift topography of the Western Ghats. Process-oriented gravity modelling further suggests that the lateral variations in the lithospheric strength, though not very significant, exist from north to south within a distance of 600 km in the Konkan and Kerala basins along the WCMI at the time of rifting. A comparison with previous Te estimates from coherence analysis along the WCMI indicates that the lithospheric strength did not change appreciably since the time of rifting and it is low both onshore and offshore having a range of 5-15 km. [ABSTRACT FROM AUTHOR]

Abstract: With the recently recovered organic-rich sediments of early Tertiary age from the Lomonosov Ridge by the Integrated Ocean Drilling Program (IODP) Expedition 302, the first data collection directly from source rocks of the central basins of the Arctic Ocean is now available. Using the results of seismic interpretations and published sedimentological and organic geochemical data from Expedition 302, the framework for the first quantitative assessment of source-rock quality and distribution of the Palaeogene sediments was modelled in the central Arctic Ocean. The modelling results suggest that an approximately 100-m-thick Early to Middle Eocene sedimentary sequence of good to very good source rocks exists along a 75km long transect across the Lomonosov Ridge. In-situ generation of hydrocarbons is unlikely because the overburden (∼200–250m) and consequently the thermal maturity are too low. Burial history and thermal modelling reveal that an additional overburden of at least 1000m is necessary to start hydrocarbon generation along the ridge. However, source-rock modelling results show that good source-rock potential may exist in correlative units in the adjacent Amundsen Basin. Simulated organic carbon contents of 1.5–5%, coupled with an overburden of ∼1000–1200m, and heat flow anomalies (117 and 100mWm−2) due to the vicinity to the Gakkel Ridge spreading centre indicate that necessary conditions for hydrocarbon expulsion are already reached, and point to viability of a potential petroleum system. Our results support the hypothesis that deposition of a potentially good hydrocarbon source rock occurred across the entire Arctic Basin and adjacent margins during the early Tertiary. [Copyright &y& Elsevier]

Abstract: The convergence tectonics of the Ninetyeast Ridge (NER), upon the Andaman island arc–trench system is examined through an analysis of ETOPO2 bathymetry, satellite-derived free air gravity and seismic data. Oblique subduction and the buoyancy forces arising from subduction of the NER render the subduction processes near the Andaman arc highly complex. The bathymetric expression of the NER is visible up to Lat. 10°N but seismic reflection data indicate that it extends up to about Lat. 17°N. The gravity anomalies are strongly positive over the exposed segment of the ridge but are subdued over the buried portion. There is a prominent break in the continuity of the trench gravity low, where the NER seems to impinge upon the island arc. Further, a strong curvilinear belt of negative anomalies just behind and running parallel to the island arc, associated with the forearc basin, is a dominant feature of the gravity map. An offset in the continuity of this strong negative anomaly occurs at about the same latitude where the NER seems to be converging upon the island arc. Seismic reflection data indicate that the NER is very close to the trench. Flexural modeling of the gravity anomalies for the subducting Indian ocean lithosphere, loaded by sediments and the NER, indicates that the NER is at the starting phase of its collision with the island arc and may not have started affecting the subduction process itself. We infer that the en-echelon block structure of the NER in the proximity of the convergent zone is a consequence of complex strike-slip and subduction-related tectonic forces. [Copyright &y& Elsevier]

Joint analysis of electrical resistivity and seismic velocity data is primarily used to detect the presence of gas hydrate-filled faults and fractures. In this study, we present a novel approach to infer the occurrence of structurally controlled gas hydrate accumulations using azimuthal seismic velocity analysis. We perform this analysis using ocean-bottom seismic data at two sites on Vestnesa Ridge, W-Svalbard Margin. Previous geophysical studies inferred the presence of gas hydrates at shallow depths (up to ~190-195 m below the seafloor) in marine sediments of Vestnesa Ridge. We analyze azimuthal P-wave seismic velocities in relation with steeply dipping near-surface faults to study structural controls on gas hydrate distribution. This unique analysis documents directional changes in seismic velocities along and across faults. P-wave velocities are elevated and reduced by ~0.06-0.08 km/s in azimuths where the raypath plane lies along the fault plane in the gas hydrate stability zone (GHSZ) and below the base of the GHSZ, respectively. The resulting velocities can be explained with the presence of gas hydrate- and free gas-filled faults above and below the base of the GHSZ, respectively. Moreover, the occurrence of elevated and reduced (>0.05 km/s) seismic velocities in groups of azimuths bounded by faults suggests compartmentalization of gas hydrates and free gas by fault planes. Results from gas hydrate saturation modeling suggest that these observed changes in seismic velocities with azimuth can be due to gas hydrate saturated faults of thickness greater than 20 cm and considerably smaller than 300 cm. [ABSTRACT FROM AUTHOR]

Frænfjorden, a fjord on the west coast of Norway, has been studied to increase our knowledge of the environmental effects of submarine tailings placement (STP). Fine-grained tailings consisting primarily of calcite are disposed of by Omya Hustadmarmor. The dataset, including multibeam echosounder data, shallow seismic, video data, grab samples and sediment cores, demonstrates that tailings are primarily deposited in an up to 2 km-wide area with a tailings thickness of up to 20 m. Minor quantities of tailings are spread outside the STP by tidal currents. Sediment cores show the difference in colour, mineralogy and grain size between the natural sediments and the tailings. The tailings have a white/grey colour, are very fine grained, contain high amounts of calcite and have a lower water content than the natural sediments. A series of multibeam echosounder data from 2013 to 2017 show that deposition of tailings has triggered several small gravity flows and slides. The tailings within the STP have a low stability compared to the natural sediments outside the STP because of their fine grain size and higher sensitivity, high slope angles, high sediment accumulation rates preventing normal consolidation, and loading of tailings causing overpressure in the underlying sediments. [ABSTRACT FROM AUTHOR]

Submarine groundwater discharge could impact the transport of critical solutes to the ocean. However, its driver(s), significance over geological time scales, and geographical coverage are poorly understood. We characterize a submarine groundwater seep from the continental slope off northern Norway where substantial amount of meteoric water was detected. We reconstruct the seepage history from textural relationships and U‐Th geochronology of authigenic minerals. We demonstrate how glacial‐interglacial dynamics have promoted submarine groundwater circulation more than 100 km offshore and result in high fluxes of critical solutes to the ocean. Such cryosphere‐hydrosphere coupling is likely common in the circum‐Arctic implying that future decay of glaciers and permafrost in a warming Arctic is expected to attenuate such a coupled process and thus decreases the export of critical solutes. Plain Language Summary: Occurrence of meteoric groundwater (freshwater originated from precipitation such as rain and snow) in the global ocean is an unexpected but seemingly common phenomenon. Here, we report evidence for meteoric groundwater flow at ~800‐m water depth from the coast of northern Norway. Dating of the chemically formed carbonate rocks on the seafloor, an oxidation product of methane, reveals that the groundwater flow was strongest when large ice sheets occupied the nearby shelf. Our results confirm the temporal and geographical scales of meteoric groundwater flow in the Arctic region and highlight its impact on carbon cycling and ocean chemistry. Key Points: We document the connection between glacial dynamics and the discharge of meteoric water from the eastern Norwegian SeaA large quantity of critical solutes discharge to the ocean as a result of water circulationOffshore presence/discharge of freshwater is a common phenomenon in the circum‐Arctic Ocean that have profound impact on ocean chemistry [ABSTRACT FROM AUTHOR]

Sibelco Nordic's mine on Stjernøya, North Norway, disposes mine tailings into the fjord Stjernsundet. The tailings, discharged at the shoreline in the bay of Lillebukt, comprise c. 85% fine silt to medium-grained sand (0.01-0.5 mm). Upon discharge of the mine tailings into the fjord, they are redistributed by slides and density currents along major channels with pronounced levees. Multibeam echosounder data show sand waves in the channels, while seabed samples and cores document sand ripples and layers of mud between the sand layers. Mud accumulates outside of the channels on the seabed in Lillebukt and as a thin veneer along the shores to the east and west. The bathymetry data show partly buried slide escarpments and slide deposits, while smaller slide scars are evident in the levees. Three slide events in the tailings are documented of which the most recent occurred 9th October 2017. Comparison of bathymetry data collected in 2016 and 2018 show changes in bathymetry in the channels of ± 3 m. Slides are partly initiated along fine-grained layers and caused by hypersedimentation. From 60 m depth, one single channel continues down to 100 m, where the sediment transport is along a gully in the steep (45°) bedrock slope down to c. 400 m depth. A sand-dominated submarine fan has accumulated at the foot of the slope, extending to c. 463 m depth. Bathymetric data, seismic data and core analysis show that the fan has a radius of up to 1500 m and covers an area of c. 1.5 km2. Comparison of bathymetry data collected in 1998 and 2016 shows that a large part of the tailings disposed of in that 18-year period (4 million tons) have accumulated on the submarine fan. [ABSTRACT FROM AUTHOR]

Recent observations of extensive methane release into the oceans and atmosphere have raised concern as to whether rising temperatures across the Arctic could drive rapid destabilization of gas hydrate reservoirs. Here, we report modelling results from hydrate-modulated methane seepage from Vestnesa Ridge, offshore western Svalbard, suggesting that continuous leakage has occurred from the seafloor since the early Pleistocene up until today. Sustained by modelled deep subsurface thermogenic sources of Miocene age, large scale hydrocarbon fluid migration started ∼6 million years ago and reached the seafloor some 4 million years later. The modelling results indicate that widespread methane seepage offshore western Svalbard commenced in earnest during early Pleistocene, significantly older than late Holocene as previously reported. We propose that the onset of vertical hydrocarbon migration is the response of rapid burial of potential hydrocarbon sources induced by increased sediment deposition following the onset of Northern Hemisphere glaciations, ∼2.7 million years ago. From the modelling results we propose that source rock intervals capable of generating hydrocarbons and hydrocarbon reservoirs buried kilometers deep have continuously fueled the gas hydrate system off western Svalbard for the past 2 million years. It is this hydrocarbon system that primarily controls the thermogenic methane fluxes and seepage variability at the seabed over geological times. [ABSTRACT FROM AUTHOR]

We investigated active methane seeps in a water depth of 200 m in the Hola area off the coast of Vesterålen, northern Norway, to assess (1) hydrocarbon sources, (2) migration pathways and (3) the influence of hydrocarbon seepage on sediment pore water and water column chemistry. The seepage area is characterised by the presence of gas flares in the water column as revealed by hydro acoustic surveys and elevated methane concentrations of up to 42 nM ca. 5 m above the seafloor. Pore water analyses of three gravity cores from the seepage area show varying depths of the sulphate–methane-transition zone (SMTZ) between 80 cm and > 250 cm indicating spatially heterogeneous methane ascent. The isotopic composition of methane (δ 13 C from − 40‰ to − 63‰ and δ 2 H from − 191‰ to − 225‰) and δ 13 C depth profiles of methane and dissolved inorganic carbon show that the hydrocarbons are predominantly of thermogenic origin, consistent with δ 13 C values of C 2 to C 4 hydrocarbons. Isotope data also indicate considerable biodegradation of propane. Seismic profiles from the study area reveal major faults and steeply dipping unconformities between the basement and overlying Mesozoic sedimentary rocks. We propose that these act as migration pathways for the hydrocarbons from late Jurassic to early Cretaceous source rocks. [ABSTRACT FROM AUTHOR]

We present an account of the glacial dynamics from late Marine Isotope Stage (MIS) 3 to the Heinrich Stadial (HS) 1 on the Lofoten–Vesterålen margin, Northern Norway. This account is based on an analysis of the sedimentary stratigraphy on the upper slope close to the ice sheet grounding line at the continental shelf edge, and an analysis of the glacial morphology on the shelf areas. Our results point to a dynamic ice sheet that waxed and waned on the Lofoten–Vesterålen continental shelf from the late MIS-3, through the Last Glacial Maximum (LGM) and the HS 1. Glacigenic debris flows and deposition of laminated diamicts suggest that the ice sheet reached the shelf edge on several occasions. These are dated to ∼25.5 ka BP (HS3), between 21.1 and 21.7 ka BP, ∼19.5 ka BP, 15.6 ka BP and 14.4 ka BP (uncorrected 14 C ages). A contouritic sorted sand sediment unit that formed in a relatively warm interval during Late MIS-3 suggests that a strong Norwegian Atlantic Slope Current also developed during glacial interstadials implying that the oceanic circulation in the eastern Norwegian Sea was similar as today. The general pattern is that the ice sheet advanced onto the shelf during cold period with little influx of Atlantic Water to the Norwegian Sea and that it retreated toward the coast during intervals with higher temperatures and higher influx of warm Atlantic Water. The last ice advance to the edge of the continental shelf occurred during HS 1. [ABSTRACT FROM AUTHOR]

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 km 2 and with a volume of c. 72 × 10 6 m 3 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 14 C yrs BP or possibly later by current erosion of glacial sediments on the continental shelf and slope. [ABSTRACT FROM AUTHOR]

Abstract: The SW Barents Sea is a large hydrocarbon-prone epi-continental Sea of the Norwegian Arctic region. A significant portion of the hydrocarbon gases generated in deep source rocks has leaked or migrated into the shallow subsurface and is now trapped in gas hydrate and shallow gas reservoirs. The evolution of sedimentary basins of this region has controlled the leakage of these fluids through marine sediments. Understanding the distribution of various fluid-flow systems may enhance our knowledge of the evolution of different basins in the SW Barents Sea and could help find potential targets for future hydrocarbon exploration. We analyze approximately 3000 2D multi-channel seismic profiles and data from 60 wells covering the entire SW Barents Sea, to identify and classify fluid-flow features, and study their relationship to tectonic elements and geological history. Gas chimneys are the most abundant feature among various other fluid-flow features such as fluid leakage along faults and fractures, seepage pipes, and high amplitude anomalies potentially indicating trapped fluids. Large fluid-flow features, covering areas as large as 600 km2, occur close to known hydrocarbon fields such as Snøhvit, Skrugard, and Havis. The fluid-flow features occur above major deep-seated faults in the area suggesting a close relation to it. The number of fluid-flow features in the western part of the study area is significantly higher than in the eastern part. The amount of net erosion in the study area shows no direct control over the distribution of fluid-flow features, suggesting that the faults and distribution of mature source rocks control the fluid flow. The strong correlation between the locations of fluid-flow features and structural elements indicates that extensional tectonics, uplift and glaciations could have played major roles in the timing and activity of the fluid leakage, although erosion might have had an added effect. [Copyright &y& Elsevier]

Abstract: Video inspection of the seabed on the continental rise (ca. 2200 m water depth) off Vesterålen–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. [Copyright &y& Elsevier]

Abstract: Seafloor pockmarks are common indicators for vertical fluid flow and frequently associated with methane discharge through the gas-hydrate stability zone (GHSZ). The present-day flux through these degassing systems is presumably at a low level on most rifted continental margins. A pockmark-field on the NW-Svalbard passive margin is located on young ocean crust (<20 Ma) and shows evidence of ongoing, episodic degassing. New geophysical data from the Vestnesa Ridge (∼79°N), a mounded and elongated sediment drift in the eastern Fram Strait, reveal a gas-hydrate, free-gas and venting system that is exceptionally more dynamic than documented elsewhere along the northeastern North Atlantic margin. The prominent bottom-simulating reflection (BSR), about 200 mbsf, separates anomalously high P-wave velocities in the GHSZ from a remarkable underlying low-velocity zone, indicating the presence of gas hydrate and gas in the pore space. Inversion of P-wave velocity data using the differential effective medium theory yields a two-dimensional concentration model of methane hydrate and free gas. The model predicts saturations of up to 11% in the hydrate reservoir, which due to the seafloor topography forms a large anticlinal permeability-barrier. Below, in the low-velocity zone (i.e., 1350–1500 m/s), up to 3% of free gas is predicted across the apex of the Vestnesa Ridge and in the immediate vicinity of extensional faults. A conservative estimate indicates that 225 kg/m2 of pure methane is stored in hydrate and gas in the upper 230 m of the sedimentary column. An elongated pockmark-field, consisting of >100 individual pockmarks up to 600 m wide, systematically aligns the apex of the Vestnesa Ridge. Active, vigorous degassing from the topography-controlled pressure-valve system was evident from a 750-m-high and ∼150-m-wide gas flare observed in the water column during a cruise with R/V Jan Mayen in October 2008. The gas flare documents dynamic degassing through the corresponding chimney, which penetrates the entire GHSZ and into the underlying free gas zone. Cruises in 2006 and 2007 did not detect active gas venting above the pockmark-field. Accordingly, vigorous degassing may operate in an episodic mode, where hydrothermal circulation systems through young ocean crust may play a significant role. [Copyright &y& Elsevier]

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. • Detailed description of different kinds of megaripples as small as 4 cm high and 1 m long • Study of sandwaves and sandbanks in a high latitude sea (Barents Sea) • Evolution of large sandwaves and sandbanks since the last deglaciation [ABSTRACT FROM AUTHOR]