Calanus in North Norwegian fjords and in the Barents Sea

The Physical environment of a North Norwegian fjord and of the Atlantic and Arctic domains of the Barents Sea are described. The seasonal variation of primary production and biomass of the most important copepod species are described in order to contrast regional differences in the timing of the plankton cycles. Analysis of the seasonal variation in the biomass of six different copepod species in Balsfjorden clearly demonstrate the importance of Calanus finmarchkus as a spring and early summer form, whereas Pseudoculanus acuspes , the most important smaller form, reaches the highest biomass later during the productive season. In the Atlantic part of the Barents Sea, C. finmarchkus is the dominant herbivorous form. The next most important species, Pseudocalanus sp. and M. longa , play a less important role here than in Balsfjorden. In the Arctic domain, the smaller copepod forms appear to have been replaced in trophodynamic terms by the youngest year-group (C-CIII) of C. glacialis , which prevails during the Arctic summer and autumn periods. The coupling between primary producers and Calanus on a seasonal basis is addressed through the grazing and the vertical organisation of the plant-herbivore community. The productivity of these two Calanus species is considered in relation to the seasonal and inter-annual variation in climate; although different mechanisms are utilised, cold periods tend to lower Calanus productivity both in the Arctic and the Atlantic domains of the Barents Sea. Interannual variations in Calanus biomass and productivity are discussed in the perspective of endemic and advective processes.     

Architecture of the evaporite accumulation and salt structures dynamics in Tiddlybanken Basin,southeastern Norwegian Barents Sea

An extensive, reprocessed two‐dimensional (2D) seismic data set was utilized together with available well data to study the Tiddlybanken Basin in the southeastern Norwegian Barents Sea, which is revealed to be an excellent example of base salt rift structures, evaporite accumulations and evolution of salt structures. Late Devonian–early Carboniferous NE‐SW regional extensional stress affected the study area and gave rise to three half‐grabens that are separated by a NW‐SE to NNW‐SSE trending horst and an affiliated interference transfer zone. The arcuate nature of the horst is believed to be the effect of pre‐existing Timanian basement grain, whereas the interference zone formed due to the combined effect of a Timanian (basement) lineament and the geometrical arrangement of the opposing master faults. The interference transfer zone acted as a physical barrier, controlling the facies distribution and sedimentary thickness of three‐layered evaporitic sequences (LES). During the late Triassic, the northwestern part of a salt wall was developed due to passive diapirism and its evolution was influenced by halite lithology between the three‐LES. The central and southeastern parts of the salt wall did not progress beyond the pedestal stage due to lack of halite in the deepest evaporitic sequence. During the Triassic–Jurassic transition, far‐field stresses from the Novaya Zemlya fold‐and‐thrust belt reactivated the pre‐salt Carboniferous rift structures. The reactivation led to the development of the Signalhorn Dome, rejuvenated the northwestern part of the salt wall and affected the sedimentation rates in the southeastern broad basin. The salt wall together with the Signalhorn Dome and the Carboniferous pre‐salt structures were again reactivated during post‐Early Cretaceous, in response to regional compressional stresses. During this main tectonic inversion phase, the northwestern and southeastern parts of the salt wall were rejuvenated; however, salt reactivation was minimized towards the interference transfer zone beneath the centre of the salt wall.     

The influence of halokinesis on prograding clinoforms: Insights from the Tiddlybanken Basin,Norwegian Barents Sea

Although the trajectory and geometry of clinoforms in different types of basins have been described in many studies, few studies discuss the influence of halokinesis on clinoforms in salt-related basins. In this study, we analyse the Lower Cretaceous clinoforms in the Tiddlybanken Basin, Norwegian Barents Sea to evaluate the impact of salt mobilization on the geometry and trajectory of clinoforms as well as its implications on sediment partitioning. To accomplish this objective, we use a multidisciplinary approach consisting of seismic and well-interpretation, 3D structural restoration, and forward stratigraphic modelling. The results show that salt mobilization affects prograding clinoforms by: (a) causing lateral variations in progradation rates, resulting in complex palaeogeography, (b) increasing slope angles, which affect the equilibrium of the clinoform profile and can trigger slope-readjustment processes and (c) producing lateral and temporal variations in accommodation space, leading to different clinoform trajectories, stacking patterns and reservoir distribution along the basin. Forward stratigraphic modelling shows that in salt-related basins and other tectonically active basins, the isolated use of conventional methods for clinoform analysis might lead to potential interpretation pitfalls such as misinterpretation of trajectories and overestimation of foreset angles, which can have negative consequences for exploration models.     

Systematic palaeontology and biostratigraphy of two Early Cretaceous condensed sections from the Barents Sea

Bivalve, brachiopod and cirripede faunas from the latest Jurassic and Early Cretaceous Barents Sea boreholes 7320/3-U-l and 7425/9-U-l are systematically described and illustrated. Microfossils have also been studied and the cores arc dated on the basis of the fossil recovery. The bivalve Buchia whose zonal sequence has been used for correlation of boreal marine sections is the most important biostratigraphic marker group in the condensed Boreal Berriasian-Hauterivian intervals of these cores. A new species of cirripede Zeugmatolepas? borealis Collins sp. nov. and dinoflagellate cyst Muderongia aequicornus Århus sp. nov. are described.
The Late Jurassic fine-grained elastics of core 7320/3-U-l are overlain by about 3 m of grey dolomitic limestone of Valanginian and Hauterivian age. The lowermost part of 7425/9-U-l is represented by a latest Volgian-earliest Berriasian fossiliferous greyish green marl. It is followed by a reddish brown fossilifcrous claystone of Berriasian and perhaps partly Valanginian age. Core 7425/9-U-l also contains a mainly Valanginian greyish green marly limestone which changes into a dark grey to black limestone of Early Barremian age in its upper part. The sedimentological change from condensation to dark grey clay deposition took place in the middle Barremian H. rude-fissicostatum ammonite Zone in 7425/9-U-l and probably slightly earlier in 7320/3-U-l. This was commenced at about the same time as deposition of the inaccurately and only indirectly dated fluvio-deltaic Festningen Sandstone Member on Spitsbergen. The dark claystone may thus be a distal equivalent to this sandstone unit.     

Seabirds in the Greenland, Barents and Norwegian Seas, February-April 1982

The pelagic distributions of seabirds in the Greenland, Norwegian and western Barents Seas are poorly known, especially in winter. This paper describes quantitative observations made in the course of an oceanographic cruise between 60°-79°13'N and 15°W-18°30'E from 25 February to 4 April 1982. Seabirds were generally scarce: the principal species were Fulmarus glacialis, Rissa tridactyla, Pagophila eburnea, Una spp. and Alle atle . Numbers were greatest in the south and east, where the sea surface temperatures were warmest. Pagophila eburnea and Cepphus grylle were most commonly seen near the edge of the pack-ice in the Greenland Sea. In the pack-ice zone Fulmarus glacialis and Alle alle were commonest where the sea surface was 40–60% covered with ice. These late-winter observations are compared with published accounts of summer distributions. Preliminary quantitative comparisons also suggest that the size of the population of Uria spp. wintering in the survey area, and especially in the western Barents Sea, is significantly larger than that which winters off Nova Scotia, eastern Canada; the reverse is true of Alle alle. R. G. B. Brown, Canadian Wildlife Service, Bedford Institute of Oceanography, P.O. Boxlø06, Dartmouth, Nova Scotia, Canada, B2Y 4A2 .     

Lithological description of subcropping Lower and Middle Triasic rocks from the Svalis Dome, Barents Sea

Eleven shallow cores display 315 m of the >700 m thick Lower and Middle Triasic successional of the Svalis Dome, a Salt diapir in the central south-western Barents Sea. The Svalis Dome was uplifted in the late Mesozoic. and Trisassic rocks suherop below Quaternary till around the Upper Palaeozoic core of the dome. Deposition of the Triassic succession took place in deep shelf to basinal environments below storm wave base. The succession is dated by macrofossils and palynomorphs and can be assigned to four formations. The basal beds of the shaly greenish grey Havert Formation (Griesbachian) occur above Permian bioclastic carbonate. The Klappmyss Formation (Smithian) in the lower part contains gravity flow sands deposited as submarine fans pussible triggered by tectonic movements along the adjacent ault zones overlian by silty claystones. An organic-rich dark shale unit is here formally defined as the Steinkobbe overlain by silty claystones. An organic-rich dark shale unit is here formally defined as the Steinkobbe Formation, and was deposited in a large bight by restricted water circulation. The Snadd Formation. on top, representes a marine shelf unit deposited in front of an emerging land area in the north-east. A minimum of six higher order transgressive-regressive sequences are recognized at the Svalis Dome and these are correlated with other Arctic areas.     

A review of variability in the distribution and abundance of Norwegian spring spawning herring and Barents Sea capelin

The historic data on the fisheries on Norwegian spring spawning herring and Barents Sea capelin show that the migration pattern and time of spawning have changed for these species. Furthermore, modern techniques like tagging, hydroacoustic abundance estimation and virtual population analysis have shown that the abundance, both of the adult and the immature parts of the population, fluctuates widely. Predators (other fish, seabirds, sea mammals) of pelagic fish must have experienced corresponding fluctuations in food availablilty.     

Copepod grazing and its potential impact on the phytoplankton development in the Barents Sea

Compiled data from published and unpublished sources on copepod grazing of the large-sized copepods in the Barents Sea give wide ranges in grazing rates. Approximate average values indicate daily rations of 7–18% for copepodite stages V and VI and considerably higher values for the earliest copepodite stages. It is demonstrated that individual variability in gut fullness of copepods from a given locality is typically very high and not closely related to variable food abundance or depth of occurrence. There is no diel feeding rhythm during the summer, and even when relating copepod grazing to a number of biotic and abiotic factors through stepwise linear regression analysis, much of the variability remains unexplained. It is suggested that feeding behaviour, food quality and feeding history of the copepods all play important roles as factors which regulate copepod grazing. Model simulations on the phytoplankton succession, using literature data on laboratory-determined growth characteristics for solitary cells and colonies of the prymnesiophyte Phaeocystis pouchetii and large diatoms, indicate that the extent of the mixed layer and selective grazing by zooplankton are important factors that may explain the occurrence of dense blooms of P. pouchetii colonies, frequently observed during the spring.     

Surface temperatures of the Barents Sea

Temperature conditions in the Barents Sea are determined by the quality and quantity of the inflowing Atlantic water from the west and by processes taking part in the Barents Sea itself, in particular as a consequence of winter cooling and ice formation. The field of inflow to the Barents Sea during the period 1977-1987 has been studied. The surface winter temperatures within the Barents Sea vary in parallel with variations in the deeper layers of the inflowing water masses, whereas the surface temperatures in summer have a different variation pattern which is most likely dependent on the summer heating process.     

The Klippfisk Formation—a new lithostratigraphic unit of Lower Cretaceous platform carbonates on the Western Barents Shelf

A new Lower Cretceous lithostratigraphic unit of the Western Barents Shelf, named the Klippfisk Formation, is formally introduced. The formation represents a condensed carbonate succession deposited on platform areas and structural highs, where it consists of limestones and marls, often glauconitic. The limestones may have a nodular appearance, and fossil debris, which are dominated by Inoceramus prisms, may be abundant. The Klippfisk Formation is composed of two members: the Kutling Member defined herein from cores drilled on the Bjarmeland Platform, and the coeval Tordenskjoldberget Member described on Kong Karls Land. The base of the formation is defined by the abrupt decrease in gamma-ray intensity, where the dark shales of the underlying Hekkingen or Agardhfjellet formations are replaced by marls. It is often unconformable. The Klippfisk Formation is of Berriasian to Early Barremian age and appears to be time-transgressive over parts of the Western Barents Shelf (including Kong Karls Land). It passes laterally into the basinal Knurr Formation. On Kongsøya (Kong Karls Land) a thin shale unit, bounded by unconformities, earlier included in the Tordenskjoldberget Member, represents the northernmost extension of the overlying Kolje Formation in the Barents Shelf.     

Structural evolution of sheared margin basins: the role of strain partitioning. Sørvestsnaget Basin,Norwegian Barents Sea

Spatio‐temporal analysis of basins formed along sheared margins has received much less attention than those formed along orthogonally extended margins. Knowledge about the structural evolution of such basins is important for petroleum exploration but there has been a lack of studies that document these based on 3D seismic reflection data. In this study, we demonstrate how partitioning of strain during deformation of the central and southern part of the Sørvestsnaget Basin along the Senja Shear Margin, Norwegian Barents Sea, facilitated coeval shortening and extension. This is achieved through quantitative analysis of syn‐kinematic growth strata using 3D seismic data. Our results show that during Cenozoic extensional faulting, folds and thrusts developed coevally and orthogonal to sub‐orthogonal to normal faults. We attribute this strain partitioning to be a result of the right‐lateral oblique plate motions along the margin. Rotation of fold hinge‐lines and indications of hinge‐parallel extension indicate that the dominating deformation mechanism in the central and southern Sørvestsnaget Basin during opening along the Senja Shear Margin was transtensional. We also argue that interpretation of shortening structures attributed to inversion along the margin should consider that partitioning of strain may result in shortening structures that are coeval with extensional faults and not a result of a separate compressional phase.     

Primary production of the northern Barents Sea

The majority of the arctic waters are only seasonally ice covered; the northern Barents Sea, where freezing starts at 80 to 81°N in September, is one such area. In March, the ice cover reaches its greatest extension (74-75°N). Melting is particularly rapid in June and July, and by August the Barents Sea may be ice free. The pelagic productive season is rather short, 3 to 3.5 months in the northern part of the Barents Sea (north of the Polar Front, 75°N), and is able to sustain an open water production during only half of this time when a substantial part of the area is free of ice. Ice algal production starts in March and terminates during the rapid melting season in June and July, thus equalling the pelagic production season in duration.
This paper presents the first in situ measurements of both pelagic and ice-related production in the northern Barents Sea: pelagic production in summer after melting has started and more open water has become accessible, and ice production in spring before the ice cover melts. Judged by the developmental stage of the plankton populations, the northern Barents Sea consists of several sub-areas with different phytoplankton situations. Estimates of both daily and annual carbon production have been based on in situ measurements. Although there are few sampling stations (6 phytoplankton stations and 8 ice-algae stations), the measurements represent both pelagic bloom and non-bloom conditions and ice algal day and night production. The annual production in ice was estimated to 5.3 g Cm^-2, compared to the pelagic production of 25 to 30 g Cm^-2 south of Kvitøya and 12 to 15 g Cm^-2 further north. According to these estimates ice production thus constitutes 16% to 22% of the total primary production of the northern Barents Sea, depending on the extent of ice-free areas.     

Source, density and composition of sympagic fauna in the Barents Sea

The sympagic fauna (= ice fauna) of the Barents Sea was investigated on nine different cruises in 1982-1988. Each cruise lasted from two to five weeks. Sampling techniques were based on scuba diving. The abundant sympagic organisms were the polar cod ( Boreogadus saida ) and the three amphipods Apherusa glacialis, Onisimus sp. and Gammarus wilkitzkii .
Mean biomass-values (wet weight) of the invertebrate sympagic fauna ranged from 0 to 2 g/m². Values above 0.001 g/m² were not recorded in five of the nine cruises. This is orders of magnitude lower than mean values recorded in multi-year ice north of Svalbard and in the Fram Strait where values between 1-10g/m² are quite common.
Apherusa glacialis seemed to have the best spreading capacity of the three most conspicuous amphipods. Gammarus wilkitzkii was most dependent on a passive transport with the ice.
Sympagic amphipods play an important part in a food chain from microalgae to polar cod and marine birds in areas covered with ice, especially in areas with multi-year ice.     

North Atlantic Water in the Barents Sea Opening, 1997 to 1999

North Atlantic Water (NAW) is an important source of heat and salt to the Nordic seas and the Arctic Ocean. To measure the transport and variability of one branch of NAW entering the Arctic, a transect across the entrance to the Barents Sea was occupied 13 times between July 1997 and November 1999, and hydrography and currents were measured. There is large variability between the cruises, but the mean currents and the hydrography show that the main inflow takes place in Bjørnøyrenna, with a transport of 1.6 Sv of NAW into the Barents Sea. Combining the flow field with measurements of temperature and salinity, this results in mean heat and salt transports by NAW into the Barents Sea of 3.9×10¹³ W and 5.7×10⁷ kg s⁻¹, respectively. The NAW core increased in temperature and salinity by 0.7 °C yr⁻¹ and 0.04 yr⁻¹, respectively, over the observation period. Variations in the transports of heat and salt are, however, dominated by the flow field, which did not exhibit a significant change.     

Russian iceberg observations in the Barents Sea, 1933– 1990

Seasonal variations of iceberg distribution in the Barents Sea have been studied on the basis of Russian observations for the period 1933-1990. The maximum southern distribution is observed in January and the minimum in September and October. A significant correlation coefficient of 0.5 is calculated for the relationship between the latitude of the southern ice cover expansion and the corresponding expansion of iceberg distribution. There is a general temporal trend of increased southern locations of iceberg observations during the period considered. Some analyses of iceberg dimensions in the western part of the Barents Sea are based on observations obtained in 1988–1990 under the Ice Data Acquisition Programme (IDAP) and under the Soviet-Norwegian Occanographic Programme (SNOP).     

A study of the climatic system in the Barents Sea

The climatic conditions in the Barents Sea are mainly determined by the influx of Atlantic Water. A homogeneous wind-driven numerical current model was used to calculate the fluctuations in the volume flux of Atlantic Water to the Barents Sea which are caused by local wind forcing. The study period is from 1970 to 86. When compared with observed variations in temperature, ice coverage, and air pressure, the results show remarkably good agreement between all three parameters. The climate system of the Barents Sea is discussed with emphasis on the interrelations and feedback mechanisms between air, sea, and ice.