Atlantic Water is commonly defined as having salinity >35.0 and temperatures >3oC. Between Norway and Bear Island, the temperature of Atlantic Water varies seasonally and inter-annually from 3.5-7.5 oC. As a rule, both temperature and salinity decrease in northwards and eastwards in the Barents Sea (Figure 2.3.6). For this reason, water with salinity as low as 34.95 is often classified as water of Atlantic origin. In the southwestern Barents Sea, Atlantic water is normally predominant. Interannual temperature variation in the Barents Sea is illustrated in Figure 2.3.7, which presents annual temperature observations during the last 100 years for the Kola region (Bochkov, 1982; 2005) in the southern Barents Sea.
Coastal Water resembles Atlantic Water but generally has lower salinity (<34.7) and a wider temperature range, particularly near the surface. Arctic water is characterised by low salinity, but is more easily classified by its low temperature. The core of the Arctic Water has temperature <–1.5 oC and salinity between 34.4 and 34.7.
The seasonal ocean temperature signal is strong, and lags behind air temperatures by 2-3 months (Figure 2.3.8). Maximum values are reached during September-October and minimum values during March-April.
Temperature in the upper 150 m layer of the water column reaches a seasonal minimum during April in the Kola region; this minimum occurs a bit later in deeper layers. The corresponding time delay – to reach a seasonal maximum temperature in deeper layers – is longer. In the upper 20 m layer of the water column, the seasonal maximum takes place in August; the timing is then gradually delayed with increasing depth.
As a result, the time of temperature maximum near-bottom is between October and January (Figure 2.3.9).This phenomenon was first noted by N.M.Knipovich (1906), and later described by many researchers (Sarynina, 1980; Tereshchenko and Bochkov, 1994; Tereshchenko, 1997; 2000; Boitsov, 2006).Seasonal variation of salinity in the Kola region differs from that of temperature. Salinity variation in the upper 50 m layer of the water column has a minimum during August-September and a maximum during January-April. Northern stations of this region are an exception; there the seasonal maximums at depths extending down to 50 m occur during December. The seasonal signal at lower depths and/or near-bottom layers has not been determined; long-term data indicate that at such depths salinity stays constant year round (amplitude of the change is less than 0.05) (Figure 2.3.9) (Karsakov, 2007).
Different processes – both external and local in origin – operating on different time scales, determine temperature regimes in the Barents Sea: advection of warm Atlantic water masses from the Norwegian Sea, temperature of these water masses, local heat exchange with the atmosphere, and differences in water density within the ocean itself. Inflow from the Norwegian Sea into the Barents Sea is influenced by wind conditions in the western Barents Sea, which again is related to wind conditions in the Norwegian Sea (Ingvaldsen et al., 2004). Both slowly moving advective propagation and rapid barotropic responses due to large-scale changes in air pressure must be con¬sidered when describing variation in temperature of the Barents Sea.
In ice-free waters, winter is characterised by an intense deep vertical mixing, which brings mineral nutrients to the upper layers of the water column. In late spring, the upper layer becomes stratified, which strongly impacts timing and development of the spring bloom. Different water masses differ considerably in terms of mixing and stratification.