Rapp. P.-v. Réun. Cons. int. Explor. Mer, 188: 23-35. 1989 Climatic fluctuations in the Barents Sea Lars Midttun Midttun, Lars. 1989. Climatic fluctuations in the Barents Sea. Rapp. P.-v. Réun. Cons. int. Explor. Mer, 188: 23—35. The circulation system of the Barents Sea is described. Warm water flows into the sea from the west and is gradually transformed into Arctic water, which then flows out of the sea, partly as surface currents, partly as dense bottom water. The climatic conditions of the Barents Sea are determined both by the variations in the inflow and by processes taking place in the sea itself. The great variations in temperature and salinity observed along standard sections crossing the inflowing water masses are examined, and possible explanations are discussed. Lars Midttun: Institute of Marine Research, P.O. Box 1870 - Nordnes, N-5024 Bergen, Norway. Introduction The main purpose of this paper is to present and discuss been the most intensively studied area, and several stan­ the rather marked climatic variations observed in the dard sections have been established in order to investi­ Barents Sea. However it may be worth while first to gate variations in the inflowing water masses. Measure­ give a short description of the circulation system as ments in the Kola section were started as early as 1900 known from the literature. by Dr N. Knipowich and have been regularly continued Based on early observations, Knipowich (1905) gave since 1920. Bochkov (1976) studied temperature var­ a description of the water masses of the Barents Sea, iations in relation to solar activity. Three sections ob­ and Nansen (1906) devised theories on the formation of served by the Institute of Marine Research were ana­ bottom water in the northern seas, including the Bar­ lysed by Blindheim and Loeng (1981) and later by ents Sea. Nansen also believed that dense water formed Loeng and Midttun (1984). The section Fugløya- in the eastern Barents Sea could supply the bottom Bjørnøya (Bear Island) was studied by Dickson and water of the Arctic Ocean through the channel between Blindheim (1984). Variability at the fixed station Nord- Novaya Zemiya and Franz Josef Land, as indicated by kapp was analysed by Midttun (1969), while Blindheim Admiral Makaroffs temperature observations in that et al. (1981) compared the climatic variations in Norwe­ area. Recently. Midttun (1985) has confirmed Nansen’s gian coastal water with the observations from the Kola hypothesis. Mosby (1938) studied the waters between sections. Dickson et al. (1970) presented results from Svalbard and Franz Josef Land. This area is mainly the hydrographic work done during the joint 0-group dominated by Atlantic water masses, although some fish surveys in the Barents Sea from 1965 to 1969. The outflow from the Barents Sea may take place near Franz climatic variations in the Barents Sea were studied by Josef Land. Midttun and Loeng (1987). The majority of the contributions to the oceanog­ raphy of the Barents Sea are presented by scientists from the USSR. Tantsiura (1959) made a comprehen­ sive analysis of the currents in the Barents Sea. Agene- General description of physical rov (1946) studied a large number of current observa­ conditions tions. The detailed work by Novitskiy (1961) dealt with the currents of the northern Barents Sea. Sarynina Principally on the basis of the above-mentioned litera­ ( 1972) was concerned with the bottom water of the Bear ture, Loeng (1987) gave a brief review of the main Island Channel, and Kislyakov (1964) studied the condi­ circulation and water masses of the Barents Sea. This tions at the western inlet to the Barents Sea. review is summarized below. Naturally, the southern part of the Barents Sea has 23 Figure 1. Bottom topography of the Barents Sea. The current systems The Norwegian Coastal Current flows along the west­ The bottom topography is given in Figure 1. Figure 2 ern and northern coast of Norway. Outside, and parallel shows a simplified picture of the surface current system, to, the coastal current flows the Norwegian Atlantic based mainly on current maps made by Tantsiura (1959) Current along the Norwegian continental shelf. Off the and Novitskiy (1961). Only minor corrections have been coast of northern Norway the Atlantic Current splits made as a result of some recent observations. The map into two branches, one continuing northwards along the indicates two main current directions. In the southern continental slope as the West Spitsbergen Current, and part, the currents are towards the east, while the current the other entering the Barents Sea along the Bear Island directions in the north are westwards and southwest- Channel as the Nordkapp Current. wards. The southern part of this current continues eastwards 24 FRANZ JOSEFS LAND K VITÖYA \ NORDAUSTLANDET / KONG KARLS LAND VEST - SPITSBERGEN HOPEN SENT KAL Bk THOR IVERSEN Bk NORDKAPP Bk J FUG LOY 4* Figure 2. Surface currents in the Barents Sea. Arctic currents (------->), Atlantic currents (—>), and coastal currents (• • •>). (Simplified after Tantsiura, 1959; and Novitskiy, 1961). Locations of sections discussed are indicated. together with the Norwegian Coastal Current and pro­ parallel to the Murmansk Current, turning northeast­ ceeds along the Murmansk coast as the Murmansk Cur­ wards along the axis of the eastern basins. A much less rent. The northern part of the Nordkapp Current di­ important inflow of Atlantic water to the Barents Sea vides along three major routes at about 30°E. One arm takes place along the Storfjordrenna between Bjørnøya turns northwards between Hopen Island and the Great and Spitsbergen. Bank where it submerges under the lighter Arctic wa­ The influx of Arctic water to the Barents Sea takes ter. The second branch continues eastwards in the place along two main routes: between Spitsbergen and deeper area between the Great Bank and the Central Franz Josef Land, and through the opening between Bank as an intermediate current. The third part turns Franz Josef Land and Novaya Zemlya (Dickson et al., southeastwards, south of the Central Bank, and flows 1970). The main part of the first-mentioned current 25 Figure 3. Distribution of salinity (left) and temperature (right) at 100-m depth, autumn 1984. flows as the East Spitsbergen Current southwards along and temperature in the core from 1966 to 1977 were the coast of Spitsbergen. The current flowing south- 35.13 and 6.2°C, respectively (Blindheim and Loeng, westwards south of Franz Josef Land, called the Persey 1981). Farther east in the Barents Sea the salinity and Current, splits north of the Central Bank. According to temperature were lower, as shown in Figure 3, and as Tantsiura (1959), one branch turns southwards to the clearly demonstrated by Loeng and Midttun (1984). As Central Bank, but this part is probably small. The main will be discussed later, there are also great long-term part of the Persey Current goes southwestwards along variations in the properties of the Atlantic inflow to the the eastern slope of the Svalbard Bank as the Bear Barents Sea, which again may influence the properties Island Current. The current turns around Bear Island of the locally formed water masses. and goes northeastwards around the Storfjordrenna. The coastal water is characterized by low salinity (S < The details of the current system are poorly known. 34.7) and relatively high temperature (t > 3°C). This Hydrographic observations indicate an anticyclonic vor­ mass is also most easily traced by the salinity (Fig. 3). tex above some of the bank areas, such as the Central The light coastal water spreads out in a wedge-shaped Bank and probably also the Svalbard Bank. This implies form above the heavier Atlantic water. The seaward a long residence time for the water masses and possibil­ extent of this wedge of coastal water varies seasonally ities for vertical mixing during the winter season (Nan­ and has its minimum in the winter (Sætre and Liøen, sen, 1906). Current measurements indicate almost the 1971). same direction from surface to bottom in areas with During the summer the Arctic water (or Barents Sea only one water mass (Blindheim and Loeng, 1978; winter water) is mainly found in the intermediate layer, Helle, 1979). However, in areas where the Atlantic between 20 and 150 m, in the northern Barents Sea. The water submerges beneath the lighter Arctic water, as it core is usually found between 30 and 60 m, with temper­ does west and south of the Great Bank, one must expect atures below — 1.5°C and the salinity between 34.4 and different current directions with depth. Also in areas 34.6. In the horizontal map (Fig. 3) most of the water with outflowing dense bottom water, the current direc­ with a temperature below 0°C is Arctic water. tions probably differ from surface to bottom. Therefore The area between the Atlantic and the Arctic water Figure 2 represents the current systems in intermediate masses is called the Arctic Front. In this area Arctic and and bottom layers only to a certain extent. Atlantic water mix. In the area west of the Central Bank, the Arctic Front is sharp and has features typical of the bottom topography. In the eastern Barents Sea the front area is less distinct, and a mixed water mass Water masses covers great areas. Following Helland-Hansen and Nansen (1909), Atlantic Bottom water of different kinds may be formed in water is defined by a salinity higher than 35.0. At the various places in the Barents Sea. Dense bottom water entrance to the Barents Sea, the mean autumn salinity is formed through brine rejection when ice freezes and 26 ^ MINIMUM EXTENSION ^ MAXIMUM EXTENSION Figure 4. Southern limit of sea ice at the end of the months February, April, June, August, October, and December during the period 1971-1980 (after Vinje, 1983).