Frontal zones in the Barents

The structure and characteristics of the North Polar Frontal Zone in different regions of the Barents Sea differ rather strongly. There was very little information on the frontal zones in the Barents Sea in the literature. Detailed definitions of these zones are either absent in the literature or have a local and incidental character. An attempt to distinguish and describe the system of frontal zones of the Barents Sea based on a number of large-scale surveys was undertaken by Chvilev (1990, 1991).

According to the joint analysis of the USSR Hydrometeocenter's archive data of 1984-1987 (approximately 10,000 stations) and published information, the following main frontal zones or groups of frontal zones, included in the climatic NPFZ system, can be revealed in the Barents Sea (Rodionov and Kostianoy 1998):

1. The Bear Island Frontal Zone (BIFZ) is a zone of interaction of the Bear Current water with the North Cape Current water. It is located along the edge of the Bear Island shelf. The Spitsbergen Frontal Zone is a zone of interaction of the East Spitsbergen Current with enclosing water masses located along the southern and eastern edges of the Spitsbergen Archipelago shelf.

2. The Western Trough Frontal Zone (WTFZ) is located along the periphery of the western trough of the Barents Sea, and is caused by the interaction of the northern branch of the North Cape Current with enclosing waters.

3. The Central Rise Frontal Zone (CRFZ) is formed by the interaction of water of the central branch of the North Cape Current with the Barents Sea water formed above the Central Rise.

4. The Central Trough Frontal Zones (CTFZ) are located at the periphery of the Central Trough, and are formed by the interaction of the Barents Sea water, flowing down to the Central Trough, with waters of Atlantic and coastal origin.

5. The Marginal Ice or Arctic Frontal Zones (AFZ) are formed on the periphery of a lens of cold freshened waters, formed by ice melting.

6. The Eastern Barents Sea Frontal Zones (EBSFZ) are caused by the interaction of the waters of the Murmansk and Novaya Zemlya Currents with waters of the Novaya Zemlya shelf, and waters of the area between Kanin Nos Peninsula and Novaya Zemlya.

7. The Coastal Frontal Zones of the Barents Sea (CFZBS) are formed by the interaction of the Barents Sea water, waters of the coastal branch of the North Cape Current, waters of the Murmansk Current, and waters of the river discharge.

The pattern of the main currents and the location of the main frontal zones of the Barents Sea are presented in Fig. 5. The main parameters of the frontal zones of the Barents Sea were determined using a technique similar to that used for the frontal zones of the Norwegian and Greenland seas, and can be found in (Rodionov and Kostianoy 1998; Kostianoy et al. 2004).

Considerably fewer hydrological surveys and sections with a spatial resolution permitting to determine the characteristics of fronts were conducted in the Barents Sea than in the Norwegian and Greenland Seas.

It is worth to note that analyzing the data for every April of 1984-1987 in the area of the boundary of the Norwegian and the Barents seas, Rodionov and Kostianoy (1998) detected an extended thermohaline frontal zone stretching from the area of the Bear Island shelf up to the North Cape, which they named as the North Cape frontal zone (Fig. 6). To the west are the waters with T ~ 5-6°C, S ~ 35.1-35.2 psu, corresponding to the Atlantic waters, to the east waters with T ~ 2-3°C, S ~ 34.8-34.9 psu, very close to the coastal waters of the Kola Peninsula, according to their characteristics. Despite of a great amount of observations in the given region all the year round, this zone was never surveyed in other months. The

Fig. 5. The main current pattern and the frontal zones of the Barents Sea. The Roman numerals indicate the following frontal zones:

- I - Bear Island Frontal Zone, II - Western Trough Frontal Zone, III - Central Rise Frontal Zone, IV - Central Trough Frontal Zone, V - Eastern Barents Sea Frontal Zones, VI - Marginal Ice (Arctic) and Deep Frontal Zones, VII - Coastal Frontal Zones.

- The Arabic numerals indicate the currents: 1 - North Cape Current, 2 - Bear Current, 3

- East Spitsbergen Current, 4 - Murmansk Current, 5 - Central Current, 6 - Novaya Zemlya Current, 7 - Deep Current, 8 - Kolguev-Pechora Current, 9 - Kanin Current, 10

- Litke Current, 11 - Murmansk Coastal Current.

Fig. 6. Position of the high-gradient zones in the field of temperature (dotted line) and salinity (solid line) in April (total sum of observations for 1984-1987). Arrow shows the North Cape frontal zone.

existence of this zone was not mentioned in any literature known to the authors. This could be explained by the fact that many hydrological sections (even standard ones) have been made essentially along the line joining the North Cape and Bear Island, i.e. along this frontal zone and not across it. That is why, probably, the North Cape frontal zone was not observed earlier. The question of the origin of this frontal zone requires an additional and detailed research, however its presence only in April implies a relation with a synchronous uppermost southwestern position of the ice margin in the Barents Sea, at least in 1984-1987.

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