Barents Sea Waters Research Articles

Double-diffusive layering in the Eurasian Basin of the Arctic Ocean

The central basins of the Arctic Ocean, below the surface mixed layer and remote from peripheral boundary currents, comprise an extremely low energy oceanic environment. Water masses having distinctly different Θ– S characteristics are organised throughout the central basins in extensive layers, consistent with occurrence of double-diffusive convection. In the Eurasian Basin, these structures can be explained by invoking formation along the narrow frontal region associated with the confluence of Fram Strait and Barents Sea waters north of the Kara Sea, and subsequent advection by the main circulation field. The presence of features in the interior of the basins requires a combination of processes that could include self-induced migration, through double-diffusive convection, as well as advection, across the central regions having weak horizontal gradients in temperature and salinity.

Synthesis of particulate and extracellular carbon by phytoplankton at the marginal ice zone in the Barents Sea

Large phytoplankton biomass accumulates during ice‐edge blooms in Arctic waters, where taxa such as diatoms or the prymnesiophyte Phaeocystis pouchetii usually dominate. Based on characteristics from temperate phytoplankton, we hypothesized that in Barents Sea waters, a larger fraction of primary production would be extracellular (for synthesis of colonial mucilage) during periods of dominance by P. pouchetii as opposed to periods when diatoms dominated. This alternation of P. pouchetii and diatoms would affect the relationship between the particulate and dissolved carbon pools in the upper water column of the marginal ice zone (MIZ). Results presented in this paper do not support this hypothesis. Although P. pouchetii contributed strongly to the extracellular carbon pool (mucilage and dissolved organic carbon, DOC) during an ice‐edge bloom in May 1993, arctic diatoms contributed an equal amount of exuded carbon. Three process stations visited along a north‐south transect in the MIZ in the Barents Sea, presented between 36% and 55% of the primary production as extracellular carbon, defined as labeled organic matter which passes through a Whatman GF/C filter. No difference in the carbon allocation between diatom‐ and P. pouchetii‐rich phytoplankton was observed in these stations. In contrast, the station located in ice‐free waters had 18% of primary production in the extracellular fraction. These results (1) highlight similar carbon allocation for diatom‐ and P. pouchetii‐dominated phytoplankton in surface waters of the Barents Sea during the spring and/or ice‐edge bloom at the MIZ and (2) suggest that polar phytoplankton may be stronger producers of extracellular carbon, and possibly DOC, than previously thought.

Seabirds and marine mammals in the eastern Barents Sea: late summer at-sea distribution and calculated food intake

The at-sea distribution of seabirds and marine mammals in the eastern Barents Sea was determined using standardized transect counts during three cruises of RV“Dalnie Zelentsy” (Murmansk) in late summer 1991, 1992 and 1993. Totals of 32,268 seabirds, 485 pinnipeds, 25 cetaceans and 4 polar bears were counted during 554 half-hour counts. Numbers were converted into densities, total biomass and calculated daily food intake. Mean total food intake in kg fresh weight/km2.day was 3.1 for the entire zone and all years; fish eaters dominated the whole region, with an intake of 1.3 (mainly Brunnich’s guillemot, Uria lomvia, and harp seal, Phoca groenlandica), followed by zooplankton eaters (0.85, mainly fulmar, Fulmarus glacialis) and mixed zooplankton and fish feeders (0.75, mainly minke whale, Balaenoptera acutorostrata, and kittiwake, Rissa tridactyla). Year-to-year variations were of little importance, while geographic differences were obvious between Norwegian coastal, Atlantic and Barents Sea water masses, both quantitatively and qualitatively (relative importance of main diets). Within each zone, a strong geographic heterogeneity was noted, with high local concentrations at fronts between water masses and at ice edges.

Reduction of fish by-catch in shrimp trawl using a rigid separator grid in the aft belly

Abstract In 1989 and 1990, a new concept to avoid the by-catch of fish in a shrimp trawl was developed in Norway. The system consists of a rectangular aluminium grid with longitudinal bars. The grid is installed in the extension piece, just in front of the codend, angled 48°, with a fish outlet on the top. In front of the grid a guiding funnel or flapper is mounted. Investigations into different grid sizes, bar distances, size of fish outlets, and guiding funnel or flapper constructions during practical tests, have led to several recommended measures. Smaller coastal shrimpers should use grids at least 0.7 m wide and 1.40 m long, while the bigger offshore trawlers should use a 1.0 m wide and 1.5 m long grid, both with a recommended bar separation of 19 mm, which gives an acceptable shrimp loss below 5%. RCTV-observations of the sorting grid system during fishing have shown that most of the shrimps (Pandalus borealis) passed in a straight line through the grid, while fish were guided upwards towards the fish outlet, either by swimming in front of the grid, or sliding along the bars. Some of the smaller fish passed through the grid and ended up in the codend. A combined speed and angle sensor, mounted just behind the grid, measured the horizontal speed of water through the grid to be 0.7 of the towing speed, and the angle of the grid to be 3–5° less than the theoretical mounting angle of 48°. The separator grid allowed an increasing escape of cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) up to a length of 20 cm, whereby all fish escaped. The 100% escape lengths for redfish (Sebates sp.), long rough dab (Hippoglossoides platessoides), and polar cod (Boreogadus saida) were 18, 24 and 24 cm, respectively. The Greenland halibut (Reinhardtius hippoglossoides) gave a rather high 100% escape length of 30–32 cm, probably due to the behaviour of this flatfish which swims on its side. The handling of the separator system has so far caused only minor problems, and the pre-sorting of fish by the separator grid results in less sorting work on deck. The separator grid was made compulsory in the northern coastal shrimp fishery from 1 March 1990, from 1 January 1992 in the offshore fisheries and will be compulsory in the Barents Sea and Spitsbergen waters from 1 January 1993.

Bio-physical oceanographic interactions at the edge of the Arctic ice pack

About 7% of the world ocean is subject to the seasonal advance and retreat of sea ice. Physical processes at ice edges, interacting with biological phenomena, have been observed to promote phytoplankton blooms in both the Arctic (e.g., Bering and Greenland Seas) and the Antarctic. This interaction occurs primarily in spring with the retreating and melting sea ice laying down low-salinity derived stratification that reduces mixing in the photic zone which encourages a phytoplankton bloom. However other physical processes, such as oceanic eddys and fronts also play a role in enhancing primary productivity at the ice edge. This paper reviews biophysical oceanographic and meteorological interactions observed in both the eastern (Greenland Sea) and western (Bering Sea) Arctic. Comparisons of the physical and biological characteristics for these areas, as well as additional comparisons with the Barents Sea and Antarctic waters and other regions of the world ocean are presented. An estimate of some outstanding marginal ice edge research problems is also included.

Long‐term variations of biotic and abiotic conditions in the ecosystem of the Barents Sea

Synchronism of year‐class strength was noted for the majority of commercial fish in the Barents Sea. The reason for this is probably connected with a common factor, namely the intensity of water inflow which influences spawning efficiency, zooplankton food production, fish larval drift to the feeding grounds, and consequent survival of juvenile fish. Consequently, the established regular relationships of hydrological and weather processes in the ecosystem can serve as basis for long‐term fishing forecasts. The overall pattern of the Barents Sea water circulation, long‐term climatic changes in this region, and their effect on the fish stock reproduction are considered, using Arctic cod as an example.

Ecological significance of individual variability in copepod bioenergetics

High interstage variability in body length and mass, reproductive state, and metabolic activity is characteristic of copepod populations from the Barents Sea and coastal waters in Sweden and Norway. The dry weight of a given copepodite stage, sampled at a given time from a homogeneous water mass, may vary by a factor of 4–5 between extreme individuals, protein and particularly lipid content being even more variable. Similarly, high variability in gut fullness and grazing rate within defined copepodite stages typically occurs at all times of the year, both when measured as in situ rate or experimentally determined rate, using homogeneous food suspensions. In accordance with this, maturation state (measured as length of gonads) and spawning (measured as rate of egg production over 24 h) are highly variable factors at the individual level. Since all these factors also influence the metabolic rate of the animals the respiratory rate (measured as ETS activity) of comparable individuals may vary by a factor of 5 or more. The results indicate that high individual variability in size and activity parameters is universal. This can not be explained by existing models of feeding behaviour, growth and development, and calls for new models, in which the nutritional history of the individual may play an important role.

A characteristic of growth of Greenland halibut, Reinhardtius hippoglossoides (Walbaum), from the North Atlantic

Results of studies on length distribution, length and weight growth rates, and length-weight relationship in Greenland halibut are presented. The populations concerned are those inhabiting the New Foundland ICNAF fishing grounds as well as those in the ICES areas of the Barents Sea and Icelandic waters.