Correlations between pelagic distribution of Common and Brünnich's Guillemots and their prey in the Barents Sea

Correlations between guillemots (including Common Guillemots Uria aalge and Brünnich's Guillemots U. lomvia) and their prey (divided into five prey categories, capelin Mallotus villosus , herring Clupea harengus , polar cod Boreogadus saida , plankton, and a mixture of other prey species) at two depths (10-100 m and 100-200m) were estimated along an extended transect of 3,060 nautical miles (5,667 km) in the Barents Sea in April/May 1986. Spatial concordance was highest during daylight hours when the largest number of birds were seen on water (presumably feeding birds). Capelin was the single prey category which was most often associated with birds but no single prey category could alone explain the distribution of birds. Although only a small fraction of guillemots could be identified to species, there was some evidence that capelin were of greater importance to Common than to Brünnich's Guillemots. Overall correlation between birds and total prey density was statistically significant at the smallest scale of 5 nautical miles (n.m.). The removal of herring from the calculations increased the strength of the correlation. The depth at which prey was located had little effect on the distribution of birds. The correlation between birds and prey was scale dependent, and reached a maximum at 90 n.m., although there seemed to be some upper threshold in the coefficient at c. 40 n.m. Numerical concordance (including only 5 n.m. periods where both prey and birds were present) was significant at the 5 n.m. scale but was higher for high density than for low density prey patches. The results are discussed in relation to the few similar studies in other oceans and in relation to the severe reduction of important prey species in the Barents Sea.     

Ctenophora in the Arctic: the abundance, distribution and predatory impact of the cydippid ctenophore Mertensia ovum (Fabricius) in the Barents Sea

The Ctenophora Mertensia ovum and Beroe cucumis , collected using both conventional sampling gear and scuba divers, were studied in the Barents Sea east of Bjørnøya and North Norway in spring 1987 and summer 1988. Among the gelatinous zooplankton, Mertensia ovum was the most consistently abundant copepod predator.
Feeding experiments were conducted to evaluate the predation rate of M. ovum in various trophic regimes. This ctenophore can take prey varying in size from small copepods to amphipods and krill, but gut-content analyses from field-collected specimens as well as experimental results showed that the main food source for adults was large-sized copepods (e.g. Calanus finmarchicus, C. glacialis, C. hyperboreus, Metridia longa ). The robust tentacle arrray of M. ovum makes this species effective as a predator on large prey. The high potential predation rate of this ctenophore relative to its estimated metabolic cost of only 1.7% of the body energy content d⁻¹ suggests that M. ovum may be able to maintain a positive energy balance even in conditions of low prey abundance. It is suggested that a single exploitation of a zooplankton patch may provide energy for survival for a very long time.
The potential impact of M. ovum on Barents Sea copepod populations is estimated on the basis of the minimal observed average daily ration in experiments and from field data on gut contents. Using abundances of copepods for the area, and the actual predator biomass collected, it was estimated that an average of 0.7% of the copepod fauna per day could fall prey to this predator.     

Insights into the lithospheric structure and tectonic setting of the Barents Sea region from isostatic considerations

We study the tectonic setting and lithospheric structure of the greater Barents Sea region by investigating its isostatic state and its gravity field. 3-D forward density modelling utilizing available information from seismic data and boreholes shows an apparent shift between the level of observed and modelled gravity anomalies. This difference cannot be solely explained by changes in crustal density. Furthermore, isostatic calculations show that the present crustal thickness of 35–37 km in the Eastern Barents Sea is greater than required to isostatically balance the deep basins of the area (>19 km). To isostatically compensate the missing masses from the thick crust and deep basins and to adequately explain the gravity field, high-density material (3300–3350 kg m⁻³) in the lithospheric mantle below the Eastern Barents Sea is needed. The distribution of mantle densities shows a regional division between the Western and Eastern Barents and Kara Seas. In addition, a band of high-densities is observed in the lower crust along the transition zone from the Eastern to Western Barents Sea. The distribution of high-density material in the crust and mantle suggests a connection to the Neoproterozoic Timanide orogen and argues against the presence of a Caledonian suture in the Eastern Barents Sea. Furthermore, the results indicate that the basins of the Western Barents Sea are mainly affected by rifting, while the Eastern Barents Sea basins are located on a stable continental platform.     

Interannual variability of dense shelf water salinities in the north-western Barents Sea

The maximum dense shelf water salinity formed during winter in the Svalbard Bank area of the north-western Barents Sea is reconstructed for the period 1952–2000 by analysing the transformation of summer remnants. The variability of 34.7 - 35.4, waters being at the freezing point, is mainly generated by interannual variations in the near surface salinity. On interannual time scales the latter is strongly linked to the sea ice import. In contrast, no correlation of the salinity of the Atlantic Water (AW) throughflow to the Arctic Ocean with the ice import is found. Salinities of both the dense shelf water site in the north-west Barents Sea and the north-eastward AW throughflow show a long term decrease, which can partly be explained by a less saline inflow of AW from the Norwegian Sea. The unusually low dense water salinities in the north-west Barents Sea during the 1990s appear to have a different origin, consistent with a response to oceanic heat advection and decreasing sea ice extent.     

The onset of Pleistocene glaciation in the Barents Sea: implications for glacial isostatic adjustment

In this paper the effect of a delayed onset of glaciation in the Barents Sea on glacial isostatic adjustment is investigated. The model calculations solve the sea-level equation governing the total mass redistributions associated with the last glaciation cycle on a spherically symmetric, linear, Maxwell viscoelastic earth for two different scenarios for the growth phase of the Barents Sea ice sheet. In the first ice model a linear growing history is used for the Barents Sea ice sheet, which closely relates its development to the build-up of other major Late Pleistocene ice sheets. In the second ice model the accumulation of the Barents Sea ice sheet is restricted to the last 6 ka prior to the last glacial maximum.
The calculations predict relative sea levels, present-day radial velocities, and gravity anomalies for the area formerly covered by the Weichselian ice sheet. The results show that observed relative sea levels in the Barents Sea are appropriate for distinguishing between the different glaciation histories. In particular, present-day observables such as the free-air gravity anomaly over the Barents Sea, and the present-day radial velocities are sensitive to changes in the glaciation history on this scale.
A palaeobathymetry derived from relative sea-level predictions before the last glacial maximum based on the second ice model essentially agrees with a palaeobathymetry derived by Lambeck (1995). The additional emerged areas provide centres for the build-up of an ice sheet and thus support the theory of Hald, Danielsen & Lorentzen (1990) and Mangerud et al. (1992) that the Barents Sea was an essentially marine environment shortly before the last glacial maximum.     

Prey composition and feeding rate of Sagitta elegans var. arctica (chaetognatha) in the Barents Sea in early summer

Sagitta elegans var. arctica , the dominant and locally abundant chaetognath in the Barents sea, was collected from the upper 50 m in Arctic water masses during an ice edge bloom in early summer 1983. In situ sampling was made along a transect at discrete depths with a 375 μm mesh net mounted on a plankton pump. Prey composition and feeding rate were estimated from gut content analyses on preserved specimens combined with data on digestion times from previous studies. No diel variations were found in feeding activity. The diet reflected the composition of available prey in the zooplankton and consisted mainly of nauplii, small copepods (early stages of Calanus, Pseudocalanus, Oithona ) and appendicularians. Prey usually occurred as a single item in the gut.
Mean prey body width related to chaetognath head width yielded a power curve, with a large amount of scatter, showing that chaetognaths in the Barents Sea can use a wide spectrum of prey sizes. Similarly, maximum prey body width was related to chaetognath head width as a power curve, reflecting the existence of an upper prey size limitation due to the chaetognath mouth size. The highest abundance of S. elegans (5 specimens m⁻³), and the most intense feeding activity, were found within or beneath the maximum zooplankton biomass. Further, distribution and feeding were affected by light intensity, salinity, and the population structure of 5. elegans var. arctica.
Estimated feeding rates ranged between 0.30 and 1.05 prey items per chaetognath day⁻¹. This corresponds to an ingestion of 8-54 μg AFDW day⁻¹, and a consumption of 0.08–0.22% of the zooplankton standing stock day⁻¹. From these rates, the calculated yearly ingestion by S. elegans var. arctica was 3% of the annually secondary production.     

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.     

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.     

Dynamics of the last glaciation in eastern Svalbard as inferred from glacier-movement indicators

Glacial striae and other ice movement indicators such as roche moutonées, glacial erratics, till fabric and glaciotectonic deformation have been used to reconstruct the Late Weichselian ice movements in the region of eastern Svalbard and the northern Barents Sea. The ice movement pattern may be divided into three main phases: (1) a maximum phase when ice flowed out of a centre east or southeast of Kong Karls Land. At this time the southern part of Spitsbergen was overrun by glacial ice from the Barents Sea; (2) the phase of deglaciation of the Barents Sea Ice Sheet, when an ice cap was centred between Kong Karls Land and Nordaustlandet. At the same time ice flowed southwards along Storfjorden; and (3) the last phase of the Late Weichselian glaciation in eastern Svalbard is represented by local ice caps on Spitsbergen, Nordaustlandet, Barentsoya and Edgeøya.
The reconstructed ice flow pattern during maximum glaciation is compatible with a centre of uplift in the northern Barents Sea as shown by isobase reconstructions and suggested by isostatic modelling.     

Anomalous propagation of surface waves in the Barents Sea as inferred from NORSAR recordings

Summary. NORSAR recordings of Rayleigh waves generated by presumed nuclear explosions on central and southern Novaya Zemlya and in northwestern Siberia have been studied. Using a frequency time analysing technique and correcting for presumed known dispersion effects across the Baltic Shield, dispersion curves for two different paths across the southern part of the Barents Sea were obtained. The curves are very unusual in that they give extremely low velocities even for periods up to 20 s. For the path to the middle part of the island, the inversion of the data gives a model with sediments and consolidated sediments down to 25 km, followed by a 15-km thick basaltic layer and an upper mantle with a P velocity as low as 7.9 km/s. For the path to the southern part of Novaya Zemlya the data inversion gives a somewhat different model with sediments and consolidated sediments down to 8 km, followed by a 17-km thick zone with velocities close to granitic and a 15-km thick layer with basaltic velocities. Again the upper-mantle P velocity is only 7.9 km/s. Other indications of lateral inhomogeneities in the Barents Sea are obtained by utilizing the array's capability to determine the angle of approach of seismic waves. It is demonstrated that reflections both from inhomogeneities in the Barents Sea and the continental margin off Norway can be detected. For waves from the southern end of the island, a reflection from a strong discontinuity close to the direct path to the middle part of the island is found, whereas signals from this area include a reflected wave possibly coming from the edge of the Svalbard platform.     

南北极海冰变化及其影响因素的对比分析

海冰是海洋-大气交互系统的重要组成部分,与全球气候系统间存在灵敏的响应和反馈机制。本文选用欧洲空间局发布的1992—2008年海冰密集度数据分析了南北极海冰在时间和空间上的变化规律与趋势,并结合由美国环境预报中心(National Centers for Environmental Prediction,NCEP)和美国大气研究中心(National Center for Atmospheric Research, NCAR)联合制作的NCEP/NCAR气温数据和ENSO指数探讨了南北极海冰变化的影响因素。结果表明,北极海冰面积呈明显的减少趋势,其中夏季海冰最小月的减少更快。北冰洋中央海盆区、巴伦支海、喀拉海、巴芬湾和拉布拉多海的减少最明显。南极海冰面积呈微弱增加趋势,罗斯海、太平洋扇区和大西洋扇区的海冰增加。北极海冰面积与气温有显著的滞后1个月的负相关关系(P0.01)。北极升温显著,北冰洋中央海盆区、喀拉海、巴伦支海、巴芬湾和楚科奇海升温趋势最大,海冰减少很明显。南极在南大西洋、南太平洋呈降温趋势,海冰增加。北极海冰减少与39个月之后ONI的下降、40个月之后SOI的上升密切相关;南极海冰增加与7个月之后ONI的下降、6个月之后SOI的上升存在很好的响应关系。南北极海冰变化与三次ENSO的强暖与强冷事件有很好的对应关系。     

Ice draft and current measurements from the north-western Barents Sea, 1993–96

From 1993 to 1996, three oceanographic moorings were deployed in the north-western Barents Sea, each with a current meter and an upward-looking sonar for measuring ice drafts. These yielded three years of currents and two years of ice draft measurements. An interannual variability of almost I m was measured in the average ice draft. Causes for this variability are explored, particularly its possible connection to changes in atmospheric circulation patterns. We found that the flow of Northern Barents Atlantic-derived Water and the transport of ice from the Central Arctic into the Barents Sea appears to be controlled by winds between Nordaustlandet and Franz Josef Land, which in turn may be influenced by larger-scale variations such as the Arctic Oscillation/North Atlantic Oscillation.     

Seasonal distribution of harp seals (Phoca groenlandica) in the Barents Sea

The distributional patterns of Barents Sea harp seals (Phoca groenlandica) throughout the year are presented based on existing literature and recent Norwegian and Russian field observations. The harp seals breed in February-March in the White Sea. Moulting occurs during April to June in the White Sea and southern Barents Sea. Feeding.behaviour is closely related to the configuration and localisation of the drifting sea-ice during summer and autumn (June-October) when the seals follow the receding ice edge, retiring gradually northwards and northeastwards in the Barents Sea. The southward movement of the population in autumn probably takes place in November prior to the advance of the ice edge, and is likely related to food-search. Apparently, most Barents Sea harp seals seems to concentrate at the southern end of their range in winter and spring.     

Ottar Basin, SW Barents Sea: a major Upper Palaeozoic rift basin containing large volumes of deeply buried salt

Seismic mapping and gravity modelling of the Ottar Basin - a little studied Upper Palaeozoic graben in the south-western Barents Sea - demonstrates the presence of a major rift basin with large accumulations of unmobilized salt. Buried beneath thick, flat-lying Mesozoic strata, the NE-trending fault-bounded basin is at least 170 km long, varies in width between 50 and 80 km and coincides with a negative gravity anomaly of more than — 10 mgal. Seismic observations show that the south-western part is a half-graben tilted to the north-west whereas the north-eastern part appears to be more symmetric in shape. A large mass deficiency in the north-eastern part of the basin, indicated by a gravity anomaly of more than — 30 mgal, makes it necessary to postulate large amounts of salt within the basin. The preferred gravity model shows a total basin depth of 9.5 km, basin relief of 4.2 km and a salt volume of 6800 km³ corresponding to a 2.4-km-thick salt layer. Similar basin depths, but only 500–600 km³ of salt, are indicated beneath the Samson Dome in the south-western part of the basin. Unlike salt bodies in other Barents Sea basins, the thick salt deposit in the north-eastern part of the Ottar Basin is relatively unaffected by halokinesis. Interfingering of different basin facies, lack of tectonic reactivation of the basin and a relatively late differential loading by protruding cover strata probably explain these differences in development. The large size and voluminous salt deposits establish the Ottar Basin as one of the major Barents Sea evaporite basins and an important structural component of the Upper Palaeozoic rift system.     

Surface wave tomography of the Barents Sea and surrounding regions

The goal of this study is to refine knowledge of the structure and tectonic history of the European Arctic using the combination of all available seismological surface wave data, including historical data that were not used before for this purpose. We demonstrate how the improved data coverage leads to better depth and spatial resolution of the seismological model and discovery of intriguing features of upper-mantle structure. To improve the surface wave data set in the European Arctic, we extensively searched for broad-band data from stations in the area from the beginning of the 1970s until 2005. We were able to retrieve surface wave observations from regional data archives in Norway, Finland, Denmark and Russia in addition to data from the data centres of IRIS and GEOFON. Rayleigh and Love wave group velocity measurements between 10 and 150 s period were combined with existing data provided by the University of Colorado at Boulder. This new data set was inverted for maps showing the 2-D group-velocity distribution of Love and Rayleigh waves for specific periods. Using Monte Carlo inversion, we constructed a new 3-D shear velocity model of the crust and upper mantle beneath the European Arctic which provides higher resolution and accuracy than previous models. A new crustal model of the Barents Sea and surrounding areas, published recently by a collaboration between the University of Oslo, NORSAR and the USGS, constrains the 3-D inversion of the surface wave data in the shallow lithosphere. The new 3-D model, BARMOD, reveals substantial variations in shear wave speeds in the upper mantle across the region with a nominal resolution of 1°× 1°. Of particular note are clarified images of the mantle expression of the continent-ocean transition in the Norwegian Sea and a deep, high wave speed lithospheric root beneath the Eastern Barents Sea, which presumably is the remnant of several Palaeozoic collisions.     

Are bacteria active in the cold pelagic ecosystem of the Barents Sea?

Bacterial biomass and activity indicators have been studied at low water temperatures (−1.9 to +4°C) in Barents Sea. Strong responses by indicators of bacterial activity, such as hydrolytic enzyme and substrate uptake potentials, were observed in association with the development of phytoplankton blooms. At late successional stages of blooms, observation by epifluorescence microscopy revealed heavy bacterial colonisation of detrital matter, in particular of senescent colonies of Phaeocystis pouchetii . Based on the retention of bacteria on filters of 1 μm pore size, up to 55% of the bacterial population was estimated to be attached to organic aggregates in some cases. Based on thymidine incorporation and a conventional conversion factor, bacterial generation times as short as one day were estimated at temperatures below zero. Changes in substrate availability governed by the successional stages of the planktonic ecosystem seem to be more important as controlling factors for bacterial growth than the low temperatures of the Barents Sea.     

The Quaternary record of eastern Svalbard - an overview

The eastern part Svalbard archipelago and the adjacent areas of the Barents Sea were subject to extensive erosion during the Late Weichselian glaciation. Small remnants of older sediment successions have been preserved on Edgeeya, whereas a more complete succession on Kongsøya contains sediments from two different ice-free periods, both probably older than the Early Weichselian. Ice movement indicators in the region suggest that the Late Weichselian ice radiated from a centre east of Kong Karls Land. On Bjørnøya, on the edge of the Barents Shelf, the lack of raised shorelines or glacial striae from the east indicates that the western parts of the ice sheet were thin during the Late Weichselian. The deglaciation of Edgeøya and Barentsøya occurred ca 10,300 bp as a response to calving of the marine-based portion of the ice sheet. Atlantic water, which does not much influence the coasts of eastern Svalbard today, penetrated the northwestern Barents Sea shortly after the deglaciation. At that time, the coastal environment was characterised by extensive longshore sediment transport and deposition of spits at the mouths of shallow palaeo-fjords.     

Deglacial land emergence and lateral upper-mantle heterogeneity in the Svalbard Archipelago—II. Extended results for high-resolution load models

In Paper I (Breuer & Wolf 1995), a preliminary interpretation of the postglacial land emergence observed at a restricted set of six locations in the Svalbard Archipelago was given. The study was based on a simple model of the Barents Sea ice sheet and suggested increases in lithosphere thickness and asthenosphere viscosity with increasing distance from the continental margin.
In the present paper, the newly developed high-resolution load model. BARENTS-2, and land-uplift observations from an extended set of 25 locations are used to study further the possibility of resolving lateral heterogeneity in the upper mantle below the northern Barents Sea. A comparison of the calculated and observed uplift values shows that the lithosphere thickness is not well resolved by the observations, although values above 110 km are most common for this parameter. In contrast to this, there are indications of a lateral variation of asthenosphere viscosity. Whereas values in the range 10¹⁸-10²⁰Pas are inferred for locations close to the continental margin, 10²⁰-10²¹ Pa s are suggested further away from the margin.
A study of the sensitivity of the values found for lithosphere thickness and asthenosphere viscosity to modifications of load model BARENTS-2 shows that such modifications can be largely accommodated by appropriate changes in lithosphere thickness, whereas the suggested lateral variation of asthenosphere viscosity is essentially unaffected. An estimate of the influence of the Fennoscandian. ice sheet leads to the conclusion that its neglect results in an underestimation of the thickness of the Barents Sea ice sheet by about 10 per cent.     

Sea ice algae in the White and Barents seas: composition and origin

To examine algae populations, three expeditions (in March 2001, April 2002 and February 2003) were conducted in the Guba Chupa (Chupa Estuary; north-western White Sea), and one cruise was carried out in the open part of the White Sea in April 2003 and in the northern part of the Barents Sea in July 2001. Sea ice algae and phytoplankton composition and abundance and the content of sediment traps under the land-fast ice in the White Sea and annual and multi-year pack ice in the Barents Sea were investigated. The community in land-fast sea ice was dominated by pennate diatoms and its composition was more closely related to that of the underlying sediments than was the community of the pack ice, which was dominated by flagellates, dinoflagellates and centric diatoms. Algae were far more abundant in land-fast ice: motile benthic and ice-benthic species found favourable conditions in the ice. The pack ice community was more closely related to that of the surrounding water. It originated from plankton incorporation during sea ice formation and during seawater flood events. An additional source for ice colonization may be multi-year ice. Algae may be released from the ice during brine drainage or sea ice melting. Many sea ice algae developed spores before the ice melt. These algae were observed in the above-bottom sediment traps all year around. Three possible fates of ice algae can be distinguished: 1) suspension in the water column, 2) sinking to the bottom and 3) ingestion by herbivores in the ice, at the ice-water interface or in the water column.