Background

Overview of the ecosystem

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The Barents Sea is a sub-Arctic ecosystem located between 70 and 80ºN. It connects with the Norwegian Sea to the west and the Arctic Ocean to the north. The average depth is 230 m and the maximum depth is approximately 500 m at the western entrance. The general pattern of circulation (Figure 2.1.1) is strongly influenced by this topography, and is characterised by inflow of relatively warm Atlantic water, and coastal water from the west. This current divides into two branches: 1) a southern branch that flows parallel to the coast and eastwards towards Novaya Zemlya; and 2) a northern branch that flows into the Hopen Trench. The Coastal Water has more fresh-water runoff and a lower salinity than the Atlantic water; it also has a stronger seasonal temperature signal. In the northern region of the Barents Sea, fresh and cold Arctic waters flow from northeast to southwest. Atlantic and Arctic water masses are separated by the Polar Front, which is characterised by strong gradients in both temperature and salinity. There is large inter-annual variability in ocean climate related to variable strength of the Atlantic water inflow, and exchange of cold Arctic water. Thus, seasonal variations in hydrographic conditions can be quite large.

Geographical description

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The Barents Sea is on the continental shelf surrounding the Arctic Ocean. It connects with the Norwegian Sea to the west and the Arctic Ocean to the north. Its contours are delineated by the continental slope between Norway and Spitsbergen to the west, the top of the continental slope towards the Arctic Ocean to the north, Novaya Zemlya archipelago to the east, and the coasts of both Norway and Russia to the south (see Figure 2.1.1). It covers an area of approximately 1.4 million km2, has an average depth of 230 m, and a maximum depth of about 500m at the western end of Bear Island Trough (Figure 2.1.1). Its topography is characterized by troughs and basins (300 m – 500m deep), separated by shallow bank areas, with depths ranging from 100-200 m. The three largest banks are Central Bank, Great Bank and Spitsbergen Bank. Several troughs over 300 m deep run from central Barents Sea to the northern (e.g. Franz Victoria Trough) and western (e.g. Bear Island Trough) continental shelf break. These troughs allow the influx of Atlantic waters to the central Barents Sea.

Meteorological conditions

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Atmospheric forcing exerts influence on marine ecosystems through winds and air-sea interactions. Variations in large-scale atmospheric circulation cause changes in upper ocean circulation, ice extent, and hydrographic properties of the water column. Changes in marine environments in turn cause biological responses such as timing of spring phytoplankton bloom, zooplankton production, patterns of fish eggs and larvae drift, encounter rate of larvae and their prey, survival and recruitment (Ottersen et al., 2004; Rey, 1993; Skjoldal and Rey, 1989; Sundby, 1991; 1995; 2000).

Bacteria and viruses

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In the biogeochefmical cycles of the ocean, a multitude of processes are catalyzed by Bacteria and Archaea, and the fufnctioning of these cycles in the Barents sea do not differ qualitatively from those at lower latitudes. The carbon cycle may well serve as an example of the biogeochemical cycles (Figure 2.4.1). The heterotrophic procaryotes, denoted bacteria for simplicity, are the major degraders of dissolved organic carbon (DOC), which is their principle source of energy and carbon. At high latitudes, DOC accumulates in the photic zone during the productive season, and the concentration decreases in September/October due to the combination of bacterial degradation and physical mixing processes (Børsheim and Myklestad 1997; Børsheim 2000).

Human activities (introduction)

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The aim of this chapter, is to give a background description of the different human activities as they are generally performed in the Barents Sea. The general impact that these activities have on the ecosystem will be dealt with in a later chapter Human impact and is thus not discussed with here.

Ecosystem interaction (Introduction)

admin@barentsportal.com (Administrator) — Wed, 03 Feb 2010 09:14:00 +0000

To understand the overall dynamics of an ecosystem and the way it is affected by human activities, it is important to consider both the impact of natural environmental variations and multispecies interactions. This chapter therefore starts (Abiotic impact) with a description of effects from environmental variation on the biological groups described earlier in chapter Biotic components. It then goes on to describe multipsecies interactions within and between these groups (Biotic interactions).

Oceanographic conditions - General circulation

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The Norwegian Atlantic Current carries warm and salty Atlantic water northwards along the Norwegian continental shelf break outside the Norwegian Coastal Current (Figure 2.1.1). When entering the Barents Sea it splits into two main branches. The first branch flows northeast along the Hopen Trench. The second branch flows eastward parallel to the coastal current towards Novaya Zemlya archipelago; this branch is called the Murman Current. Eventually, the modified Atlantic Water enters the Arctic Ocean between Novaya Zemlya and Franz Josef Land. The relative strength of these two branches depends on local wind conditions in the Barents Sea. Smaller Atlantic water currents also enter the Barents Sea from north-west region; they generally branch into subsurface flows, and do not extend very far south, but may have substantial impact on climate conditions in the northwestern Barents Sea.

Phytoplankton

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As the main primary producer, phytoplankton is an important link between the physical and chemical elements and higher tropic levels in the marine food web. Changes in the environment could affect the annual succession and species composition of the phytoplankton, as well as the overall primary production in the area. Phytoplankton monitoring will give important information regarding biological changes on the lowest level in the food web with environmental impact and climatic changes.

Human activities - Fisheries and other harvesting

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Fishing is the largest human impact to the fish stocks in the Barents Sea, and thereby the functioning of the whole ecosystem. However, the observed variation in both fish species and ecosystem is also impacted by other effects such as climate and predation (see chapter Predation by mammals).

Abiotic impact

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This subchapter describes effects of variation in the physical part of the ecosystem on biological groups. Such links are strong and important for the overall dynamics of the Barents Sea ecosystem. For example, variation in temperature has significant effects on reproduction and recruitment of several of the large fish stocks, and variation in ice cover may have considerable effects on primary productivity.