Barents Sea Shelf Research Articles

Patterns and drivers of megabenthic secondary production on the Barents Sea shelf

Megabenthos plays a major role in the overall energy flow on Arctic shelves, but information on megabenthic secondary production on large spatial scales is scarce. Here, we estimated for the first time megabenthic secondary production for the entire Bar- ents Sea shelf by applying a species-based empirical model to an extensive dataset from the joint Norwe- gianRussian ecosystem survey. Spatial patterns and relationships were analyzed within a GIS. The environ- mental drivers behind the observed production pattern were identified by applying an ordinary least squares regression model. Geographically weighted regression (GWR) was used to examine the varying relationship of secondary production and the environment on a shelf- wide scale. Significantly higher megabenthic second- ary production was found in the northeastern, season- ally ice-covered regions of the Barents Sea than in the permanently ice-free southwest. The environmental parameters that significantly relate to the observed pat- tern are bottom temperature and salinity, sea ice cover, new primary production, trawling pressure, and bottom current speed. The GWR proved to be a versatile tool for analyzing the regionally varying relationships of benthic secondary production and its environmental drivers (R 2 = 0.73). The observed pattern indicates tight pelagicbenthic coupling in the realm of the productive marginal ice zone. Ongoing decrease of winter sea ice extent and the associated poleward movement of the seasonal ice edge point towards a distinct decline of benthic secondary production in the northeastern Barents Sea in the future.

Thermochronological constraints to late Cenozoic exhumation of the Barents Sea Shelf

The Cenozoic evolution of the Barents Sea has been widely debated for its implications on hydrocarbon exploration. In this paper, we provide the first, for the area, apatite (U–Th)/He thermochronology data on Early-Middle Jurassic and Early Cretaceous sandstone reservoir samples obtained from three wells located on the western part of the Barents Shelf. A large range of grain ages have been detected, ranging from 1.58 to 50.65 Ma. These thermochronological data, initially integrated with vitrinite reflectance measurements to properly constrain the burial history evolution, have been modelled on the basis of estimated maximum temperature in order to evaluate the cooling path to present-day temperatures. Outputs from modelling indicate that: 1) the amount of net uplift and denudation is in the order of 1000 m, and 2) the last important phase of exhumation occurred during late Miocene-early Pliocene time, therefore challenging the prevailing idea of substantial uplift linked to the observed shelf-progradation along the margin as a result of the Plio-Pleistocene glaciations. The timing of the distinct exhumation event documented here may be, instead, attributed to different mechanisms. These may include basin inversion widespread on the NW European margin that is probably related to local changes in the North Atlantic spreading vector, while other mechanisms may include thermal and lithospheric-scale anomalies observed at the northwestern corner of the Barents-Svalbard Shelf.

Evolution of a high-latitude sediment drift inside a glacially-carved trough based on high-resolution seismic stratigraphy (Kveithola, NW Barents Sea)

Abstract Kveithola is a glacially-carved, E-W trending trough located in the NW Barents Sea, an epicontinental shelf sea of the Arctic Ocean located off northern Norway and Russia. A set of confined sediment drifts (the “Kveithola Drift”) is located in the inner part of the trough. In general, drift deposits are commonly characterized by high lateral continuity, restricted occurrence of hiatuses and relatively high accumulation rates, and thus represent excellent repositories of paleo-environmental information. We provide for the first time a detailed morphological and seismostratigraphic insight into this sediment drift, which is further supported by some preliminary lithological and sedimentological analyses. The complex morphology of the drift, imaged by combining all available multibeam data, includes a main and a minor drift body, two drift lenses in the outer part of the trough, more or less connected drift patches in the innermost part and small perched sediment patches in a structurally-controlled channel to the north. The seismic (PARASOUND) data show that the main and minor drift bodies are mainly well-stratified, characterized by sub-parallel reflections of moderate to high amplitude and good lateral continuity. The reflectors show an abrupt pinch-out on the northern edge where a distinct moat is present, and a gradual tapering to the south. Internally we identify the base of the drift and four internal horizons, which we correlate throughout the drift. Two units display high amplitude reflectors, marked lensoidal character and restricted lateral extent, suggesting the occurrence of more energetic sedimentary conditions. Facies typical for contourite deposition are found in the sediment cores, with strongly bioturbated sediments and abundant silty/sandy mottles that contain shell fragments. These characteristics, along with the morphological and seismic information, suggest a strong control by a bottom current flowing along the moat on the northern edge of the drift. Though both Atlantic and Arctic waters are known to enter the trough, from the west and the north respectively, brine-enriched shelf water (BSW) produced during winter and flowing westward in the moat, is suggested to be responsible for the genesis of the Kveithola Drift. The formation of BSW is inferred to have started around 13 cal ka BP, the onset of drift deposition, suggesting that conditions leading to atmospheric cooling of the surface waters and/or the presence of coastal polynyas and wind or floating ice shelves have persisted on the western Barents Shelf since that time. The units inferred to have been deposited under more energetic sedimentary conditions (tentatively dated to the Younger Dryas and to 8.9–8.2 cal ka BP) are suggestive of stronger BSW formation. In general, we infer that variations in the bottom current regime were mainly related to BSW formation due to atmospheric changes. They could also have been a response to successive episodes of grounded and sea ice retreat that allowed for a first limited, later open shelf current, which progressively established on the western Barents Sea shelf.

Геодинамическая эволюция и морфоструктурный анализ западной части арктического шельфа России

The paper considers issues of the Barents Sea shelf geodynamic evolution and influence of basement geologic structural processes on seabed morphology in their interaction. The obtained data have made possible to assume that the Norwegian-Mezenskaya rift system, Voronin graben, St. Anne and Victoria grabens were formed at the expense of the lithosphere stretching processes, but the Vostochno-Barentsevomorskaya basin and MedvezinskoEdzinskaya area of depressions developed on the initial stage of lithosphere plate evolution due to collision of several island arcs and now all of them are outliers of the ancient oceanic crust. The technique of morphostructural analysis developed by the authors has allowed solve the inverse problem, and under morphological approach split all largest depressions on two main genetic types that confirm received geodynamic conclusion. Ключевые слова: геодинамика, морфоструктурный анализ, Баренцевоморский шельф, рельеф.

TRANSGRESSIONS ON THE MURMAN AND WHITE SEA COASTS IN THE LATE PLEISTOCENE–HOLOCENE IN CONNECTION WITH DEGLACIATION

Continental ice had blocked the sea advance onto land till the end of the Allerod. Transgression began to the Murmansk coast in the Bolling after deglaciation of south-east part of the Barents Sea shelf. The farthest spread of the sea onto Murmansk coast and in the White Sea Basin took place in the end of the Allerod after deglaciation of the coasts and the White Sea depression. Then, regression took place on the most part of the coasts. The following transgression flooded the previously glaciated area and its vicinity in the Younger Dryas. The subsequent regression began at the end of the Younger Dryas. The third transgression (Tapes) took place in the Holocene.

The application of cluster analysis to the structural studies of the sedimentary layer in the northeast of the Barents Sea shelf

During the recent decade, new data were obtained on the structure of the sedimentary layer in the northeast of the Barents Sea shelf. Spatial modeling is one of the promising methods for studying spatial, structural, and tectonic features. The spatial structural–tectonic model of the sedimentary layer of the Barents Sea shelf was interpreted using cluster analysis based on the obtained information on the morphometric characteristics of seismo-stratigraphic complexes.

Commercial fish and shellfish in the Barents Sea: Have introduced crab species affected the population trajectories of commercial fish?

The Barents Sea shelf system, particularly the southwestern, western and southern parts, is one of the most productive ocean regions in the world due to the influence of warm Atlantic water. We conducted an analysis of long-term data based on original and published sources focused on the trends in abundance of key commercial species in the Barents Sea. We specifically examined the patterns and characteristics of both invasive species and invasion processes, using the example of two introduced crabs: the red king crab (Paralithodes camtschaticus) and the snow crab (Chionoecetes opilio), which in polar ecosystems may provide an important case study for improving our ability to predict the impact of new invaders. Warm temperature anomalies were observed in the Barents Sea in the 20th century and in the early twenty-first century, with peaks from 2001 to 2007 and in 2012, associated with a pronounced decrease in total ice cover since 1999. Since their introduction, the stock biomass of red king crabs has varied widely. These fluctuations were associated with high levels of illegal fishing of red king crab. The total biomass of commercial snow crabs increased exponentially in the last decade. Since the late 1990s the stock of northern shrimp has varied with an overall rising trend, although landings in more recent years were relatively stable. Cod, haddock, and saithe stocks remained at relatively high levels. Capelin stock size is characterized by large fluctuations that are likely to reflect natural processes. Cross-correlation analysis suggests that neither crab species had negative effects on the stocks of important fish. However, a potential negative impact of snow crab on the northern shrimp population could not be rejected due to their overlapping distribution and predator–prey interactions. The high overall productivity of the Barents Sea in recent years, as evidenced by high abundances of major fish stocks, is more likely associated with warming in the Arctic region, and the introduction of both crab species has had no apparent detrimental effects on fish stocks while resulting in positive economic benefits.

The importance of within-system spatial variation in drivers of marine ecosystem regime shifts

Comparative analyses of the dynamics of exploited marine ecosystems have led to differing hypotheses regarding the primary causes of observed regime shifts, while many ecosystems have apparently not undergone regime shifts. These varied responses may be partly explained by the decade-old recognition that within-system spatial heterogeneity in key climate and anthropogenic drivers may be important, as recent theoretical examinations have concluded that spatial heterogeneity in environmental characteristics may diminish the tendency for regime shifts. Here, we synthesize recent, empirical within-system spatio-temporal analyses of some temperate and subarctic large marine ecosystems in which regime shifts have (and have not) occurred. Examples from the Baltic Sea, Black Sea, Bengula Current, North Sea, Barents Sea and Eastern Scotian Shelf reveal the largely neglected importance of considering spatial variability in key biotic and abiotic influences and species movements in the context of evaluating and predicting regime shifts. We highlight both the importance of understanding the scale-dependent spatial dynamics of climate influences and key predator–prey interactions to unravel the dynamics of regime shifts, and the utility of spatial downscaling of proposed mechanisms (as evident in the North Sea and Barents Sea) as a means of evaluating hypotheses originally derived from among-system comparisons.

Объёмная геолого-геотермическая модель осадочного чехла северо-восточной части Баренцевоморского шельфа в связи с освоением ресурсов углеводородов

Объёмная геолого-геотермическая модель осадочного чехла северо-восточной части Баренцевоморского шельфа в связи с освоением ресурсов углеводородов

Late Mesozoic magmatism and Cenozoic tectonic deformations of the Barents Sea continental margin: Effect on hydrocarbon potential distribution

The paper is focused on the two tectonic-geodynamic factors that made the most appreciable contribution to the transformation of the lithospheric and hydrocarbon potential distribution at the Barents Sea continental margin: Jurassic-Cretaceous basaltic magmatism and the Cenozoic tectonic deformations. The manifestations of Jurassic-Cretaceous basaltic magmatism in the sedimentary cover of the Barents Sea continental margin have been recorded using geological and geophysical techniques. Anomalous seismic units related to basaltic sills hosted in terrigenous sequences are traced in plan view as a tongue from Franz Josef Land Archipelago far to the south along the East Barents Trough System close to its depocentral zone with the transformed thinned Earth’s crust. The Barents Sea igneous province has been contoured. The results of seismic stratigraphy analysis and timing of basaltic rock occurrences indicate with a high probability that the local structures of the hydrocarbon (HC) fields and the Stockman-Lunin Saddle proper were formed and grew almost synchronously with intrusive magmatic activity. The second, no less significant multitectonic stress factor is largely related to the Cenozoic stage of evolution, when the development of oceanic basins was inseparably linked with the Barents Sea margin. The petrophysical properties of rocks from the insular and continental peripheries of the Barents Sea shelf are substantially distinct as evidence for intensification of tectonic processes in the northwestern margin segment. These distinctions are directly reflected in HC potential distribution.

Magnetic properties of Triassic rocks of Svalbard Archipelago - preliminary results

Studies were carried out in three rock formations: the Vardebukta Formation (Early Triassic) and the Bravaisberget Formation (Middle Triassic) from Spitsbergen and the Botneheia Formation (Middle Triassic) from Edgeoya (Eastern Svalbard). Collected samples are diversified and represent various lithologies with different thermal and tectonic histories. Magnetic properties of the specimens were studied using rock-magnetic methods including: thermal demagnetization of saturated isothermal remanent magnetization (SIRM), hysteresis loops and analysis of magnetic susceptibility variations at high temperatures. Subsequently anisotropy of magnetic susceptibility (AMS) and analysis of the structure of natural remanent magnetization (NRM) using thermal and alternating field (AF) demagnetization were investigated. The obtained results show that magnetite represents the main magnetic mineral in all studied rocks, whereas pyrrothite, as a second magnetic information carrier, was noted in some of specimens only. The samples from Edgeoya possess the highest magnetic susceptibility (ca. 240∙10−6 SI) which tends to decrease in sites located further to the west and reaches the minimum value for samples from western Spitsbergen (ca. 30–40∙10−6 SI). AMS studies revealed that the Middle Triassic samples are characterized by inverse magnetic fabric and prolate AMS ellipsoids, whereas the Early Triassic specimens represent normal sedimentary fabric and oblate AMS ellipsoids. Inverse magnetic fabric can be carried by many minerals including: tourmaline, cordierite or goethite (Chadima et al., 2006). For investigated samples two models proposed by Rochette (1988) are highly probable: (1) presence of single-domain elongated magnetite grains or (2) presence of ferroan carbonates whose maximum susceptibility is parallel to the c-axis. Paleomagnetic results of the Botneheia Formation revealed only one characteristic NRM component characterized by steep inclination and maximal unblocking temperatures in range of 425–450°C. In turn, the Early Triassic rocks record several NRM components with partially overlapping unblocking temperatures. We have concluded that different magnetic properties observed in studied rocks might be related to various lithologies but also to distinct tectonic and thermal histories associated with complex tectonic evolution of the Barents Sea Shelf.

Diurnal tides on the Barents Sea continental slope

Measurements of diurnal tides over the continental slope between the Norwegian Sea and the Barents Sea shelf are presented. Numerical 3D simulations, in agreement with field data, show strong cross-slope velocities and large vertical displacements of the interface between Atlantic Water and intermediate water over the slope. The striking correspondence between the prominent observed and modeled diurnal oscillations gives confidence that this is well represented by the model. This variability, interpreted as tidally induced diurnal period topographic waves, is confined to the diverging topography of the continental slope west of Tromsøflaket. The model results reveal highly variable magnitudes of the oscillations and the cross shelf currents in time, related to variable strength of the background flow, the Norwegian Atlantic Current. We suggest that the diurnal topographic wave can be an effective mechanism for cross slope exchange between the Norwegian Sea and the Barents Sea shelf, and important for benthic and pelagic biological processes on the shelf and slope.

Issue of the genesis of recent sediments on the Barents Sea shelf

This paper is a reply to the comment on our two previous publications (Krapivner, 2009a, 2009b) devoted to the genesis of recent sediments on the Barents Sea shelf in (Epshtein et al., 2011a, 2011b). It is substantiated that the physical nature of the reflection of recent sediments in seismoacoustic records, a very important point for the lithofacies analysis, is incorrectly interpreted by the above opponents. The paper presents geochronological and paleomagnetic data confirming invalidity of the popular concepts about the link between the cover of poorly consolidated sediments and the epoch of the last deglaciation. We show incorrectness of the statement of the opponents about the redeposited character of Pliocene-Quaternary marine biota of diamictons and the glacial processing of coarse-clastic material therein. Diverse properties of recent sediments and their topography artificially united into a complex of indicators of the glacial paragenesis are either simply explained in terms of the natural (for the Barents Sea) icemarine sedimentation or attributed to postsedimentary processes during intense neotectonic activity of the Barents Sea shelf.

Towards an improved organic carbon budget for the western Barents Sea shelf

Abstract. There is generally a lack of knowledge on how marine organic carbon accumulation is linked to vertical export and primary productivity patterns in the Arctic Ocean. Despite the fact that annual primary production in the Arctic has increased as a consequence of shrinking sea ice, its effect on flux, preservation, and accumulation of organic carbon is still not well understood. In this study, a multi-proxy geochemical and organic-sedimentological approach is coupled with organic facies modelling, focusing on regional calculations of carbon cycling and carbon burial on the western Barents Shelf between northern Scandinavia and Svalbard. OF-Mod 3-D, an organic facies modelling software tool, is used to reconstruct and quantify the marine and terrestrial organic carbon fractions and to make inferences about marine primary productivity changes across the marginal ice zone (MIZ). By calibrating the model against an extensive set of sediment surface samples, we improve the Holocene organic carbon budget for ice-free and seasonally ice-covered areas in the western Barents Sea. The results show that higher organic carbon accumulation rates in the MIZ are best explained by enhanced surface water productivity compared to ice-free regions, implying that shrinking sea ice may reveal a significant effect on the overall organic carbon storage capacity of the western Barents Sea shelf.

Сейсмостратиграфический анализ и перспективы нефтегазоносности юрских отложений Баренцевоморского шельфа

Сейсмостратиграфический анализ и перспективы нефтегазоносности юрских отложений Баренцевоморского шельфа

EUNAseis: A seismic model for Moho and crustal structure in Europe, Greenland, and the North Atlantic region

We present a new digital crustal model for Moho depth and crustal structure in Europe, Greenland, Iceland, Svalbard, European Arctic shelf, and the North Atlantic Ocean (72W–62E, 30N–84N). Our compilation is based on digitization of original seismic profiles and Receiver Functions from ca. 650 publications which provides a dense regional data coverage. Exclusion of non-seismic data allows application of the database to potential field modeling. EUNAseis model includes Vp velocity and thickness of five crustal layers, including the sedimentary cover, and Pn velocity. For each parameter we discuss uncertainties associated with theoretical limitations, regional data quality, and interpolation. By analyzing regional trends in crustal structure and links to tectonic evolution illustrated by a new tectonic map, we conclude that: (1) Each tectonic setting shows significant variation in depth to Moho and crustal structure, essentially controlled by the age of latest tectono-thermal processes; (2) Published global averages of crustal parameters are outside of observed ranges for any tectonic setting in Europe; (3) Variation of Vp with depth in the sedimentary cover does not follow commonly accepted trends; (4) The thickness ratio between upper-middle (Vp < 6.8 km/s) and lower (Vp > 6.8 km/s) crystalline crust is indicative of crustal origin: oceanic, transitional, platform, or extended crust; (5) Continental rifting generally thins the upper-middle crust significantly without changing Vp. Lower crust experiences less thinning, also without changing Vp, suggesting a complex interplay of magmatic underplating, gabbro-eclogite phase transition and delamination; (6) Crustal structure of the Barents Sea shelf differs from rifted continental crust; and (7) Most of the North Atlantic Ocean north of 55°N has anomalously shallow bathymetry and anomalously thick oceanic crust. A belt of exceptionally thick crust (ca. 30 km) of probable oceanic origin on both sides of southern Greenland includes the Greenland–Iceland–Faeroe Ridge in the east and a similar “Baffin Ridge” feature in the west.

Cenozoic microfossils in northern Finland: Local reworking or distant wind transport?

Allochthonous Cenozoic microfossils have been reported from Late Pleistocene lake and mire host sediments across an area of >30,000km2 in northern Finland. Two main groups of microfossils are recognised: Palaeogene marine diatoms, silicoflagellates and ebridians that include taxa from around the time of the Palaeocene–Eocene Thermal Maximum and Pliocene to early Pleistocene freshwater diatoms. The presence of these microfossils has been regarded as evidence that Eocene marine and late Neogene freshwater sediments formerly existed on the shield surface. Both groups have been referred to frequently in reconstructions of the sea level, tectonic and erosion history of the northern Fennoscandian shield. The questions raised by the presence of allochthonous Cenozoic microfossils in northern Finland are, however, strongly resonant of the debate over the biota, origin and age of the Pliocene Sirius Group in Antarctica where competing hypotheses have been put forward of local deposition and reworking versus distant wind transport of marine diatoms from the continental shelf.This review explores alternative origins for the allochthonous Cenozoic microfossils in northern Finland. Local reworking of Palaeogene marine sediments during Pleistocene glaciation is unlikely, as no source rocks of Palaeogene age are known from the shield surface or from surrounding sedimentary basins in the Baltic and White Sea. Moreover, at all sites except Akanvaara, the marine diatom taxa cover wide age ranges and occur only as minor components in diatom assemblages that are dominated by Quaternary freshwater taxa. Local reworking of Pliocene–Pleistocene freshwater diatoms is, however, compatible with the widespread survival of pre-Pleistocene deep weathering although no in situ or unmixed, ice-rafted Pliocene–Pleistocene lacustrine sediment has yet been found. An alternative origin for the marine Palaeogene microfossils by distant wind transport is proposed. In this hypothesis, Palaeogene diatomites on the Barents Sea shelf were exposed to deep glacial and fluvioglacial erosion during the Pliocene and Early Pleistocene and in low sea level stages of the Middle and Late Pleistocene. Intense wind action acting on comminuted mudstones on outwash plains carried dust including microfossils into northern Fennoscandia to be deposited by rain-out in lakes and wetlands. This material may have been later further recycled by glacial and meltwater transport and more localised wind action, processes that also may help to account for the distribution of Eemian marine diatoms well beyond Eemian shorelines. The distant wind transport hypothesis implies that the presence of marine Palaeogene diatoms on the shield surface in northern Finland cannot be regarded as vestiges of former marine sediments and so do not constrain the tectonic and geomorphic history of the northern Fennoscandian shield in the Cenozoic.

Organic matter–apatite–pyrite relationships in the Botneheia Formation (Middle Triassic) of eastern Svalbard: Relevance to the formation of petroleum source rocks in the NW Barents Sea shelf

The Middle Triassic Botneheia Formation of eastern Svalbard (Edgeøya and Barentsøya) comprises an organic carbon-rich, fine-grained clastic succession (∼100 m thick) that makes the best petroleum source rock horizon in the NW Barents Sea shelf. The succession records a transgressive–regressive interplay between the prodelta depositional system sourced in the southern Barents Sea shelf (black shale facies of the lower and middle parts of the Muen Member) and the open shelf phosphogenic system related to upwelling and nutrient supply from the Panthalassic Ocean (phosphogenic black shale facies of the upper part of the Muen Member and the Blanknuten Member). The relationships between organic matter, authigenic apatite, and pyrite in these facies allow to characterize the relative roles of redox conditions and oceanic productivity in the organic carbon preservation. The accumulation of terrestrial and autochthonous marine organic matter in the black shale facies occurred under dominating oxic conditions and increasing-upward productivity related to early transgressive phase and retrogradation of the prodelta system. The phosphogenic black shale facies deposited in an oxygen-minimum zone (OMZ) of the open shelf environment during the late transgressive to regressive phases under conditions of high biological productivity, suppressed sedimentation rates, and changing bottom redox. The phosphatic black shales occurring in the lower and upper parts of the phosphogenic succession reveal depositional conditions indicative of the shallower part of OMZ, including high input of autochthonous organic matter into sediment, oxic-to-dysoxic (episodically suboxic and/or anoxic) conditions, intense phosphogenesis, and recurrent reworking of the seabed. The massive phosphatic mudstone occurring in the middle of the phosphogenic succession reflects the development of euxinia in the deeper part of OMZ during high-stand of the sea. High input of autochthonous organic matter in this environment was coupled with mineral starvation and intermittent phosphogenesis. In mature sections in eastern Svalbard, the petroleum potential of the Botneheia Formation rises from moderate to good in the black shale facies, and from good to very good in the phosphogenic black shale facies, attaining maximum in the massive phosphatic mudstone.

Seismostratigraphic complex of Jurassic deposits, Barents Sea shelf

The Jurassic deposits of the Barents Sea are very promising for hydrocarbon prospecting. This complex of deposits occurs at a depth that is accessible for drilling. Using the seismostratigraphic method, the environments and stages of sedimentation in Jurassic are found. The alimentary zones and migration routes are defined. The most promising zones for prospecting for new large hydrocarbon fields are determined.

Tectonics and magmatism of ultraslow spreading ridges

The tectonics, structure-forming processes, and magmatism in rift zones of ultraslow spreading ridges are exemplified in the Reykjanes, Kolbeinsey, Mohns, Knipovich, Gakkel, and Southwest Indian ridges. The thermal state of the mantle, the thickness of the brittle lithospheric layer, and spreading obliquety are the most important factors that control the structural pattern of rift zones. For the Reykjanes and Kolbeinsey ridges, the following are crucial factors: variations in the crust thickness; relationships between the thicknesses of its brittle and ductile layers; width of the rift zone; increase in intensity of magma supply approaching the Iceland thermal anomaly; and spreading obliquety. For the Knipovich Ridge, these are its localization in the transitional zone between the Gakkel and Mohns ridges under conditions of shear and tensile stresses and multiple rearrangements of spreading; nonorthogonal spreading; and structural and compositional barrier of thick continental lithosphere at the Barents Sea shelf and Spitsbergen. The Mohns Ridge is characterized by oblique spreading under conditions of a thick cold lithosphere and narrow stable rift zone. The Gakkel and the Southwest Indian ridges are distinguished by the lowest spreading rate under the settings of the along-strike variations in heating of the mantle and of a variable spreading geometry. The intensity of endogenic structure-forming varies along the strike of the ridges. In addition to the prevalence of tectonic factors in the formation of the topography, magmatism and metamorphism locally play an important role.