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).
The North Atlantic Oscillation (NAO) (e.g. Hurrell et al., 2003) is a predominant, recurrent atmospheric pattern of seasonal and long-term variability in the North Atlantic (Figure 2.3.1). However, climatic conditions of the Barents Sea are determined by both Atlantic and Arctic climatic systems, the winter NAO index explains only about 15-20% (R2=0.14-0.22) of interannual variability in air and sea temperature in the southern Barents Sea (Ozhigin et al., 2003).
During cold seasons, a typical feature of atmospheric pressure is a low-pressure trough stretching from Iceland to the central Barents Sea. Pressure lows frequently travel along it bringing warm air from the Atlantic towards Novaya Zemlya archipelago (Figure 2.3.2). The southern Barents Sea is usually dominated by southwesterly winds, which contribute to increased advection of warm Atlantic water into the area. In the northern part of the sea, cold northeasterly winds predominate. During summer, contrasts in sea level pressure are pronounced over the northeast Atlantic (Figure 2.3.2). In both Norwegian and Barents Seas horizontal gradients of pressure are relatively small; as a result, light winds of different directions blow over the Barents Sea. In some years, cold northerly and northeasterly winds prevail – even in the southern part of the sea – during May-August.
Level pressure patterns greatly influence the spatial variation of air temperature in the Barents Sea. Figure 2.3.3 shows the climatic seasonal cycle of air temperature at different stations around the Barents Sea: Svalbard Airport (78.2°N, 15.5°E), Bear Island (74.5°N, 19.0°E), Murmansk (69.0°N, 33.0°E), Malye Karmakuly (72.4°N, 52.7°E), and Heiss Island (Franz Josef Land Archipelago) (80.6°N, 58.0°E). The long-term mean air temperature over the Barents Sea ranges from -7 °C in the south to -25 °C in the north during January, and from 12 °C to 1 °C in corresponding regions of the sea during July (Figure 2.3.3). Long-term seasonal mean sea.