6 The Gulf of Finland
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Fig. 6.6 Salinity distribution (‰) in the surface layer (upper panel) and bottom layer (lower panel)
in the Gulf of Finland based on a high-resolution dataset from June 1 to September 1 1996 (Myrberg et al. 2010b). The scale at right is linear from 0 to 10 ‰
6.2.4 Temperature
In the Gulf of Finland, as in the whole Baltic Sea, the water temperature follows
the two-layer structure determined by the salinity (Fig. 6.4). The most remarkable
feature is the strong seasonal cycle of the temperature in the upper layer, forced by
the radiation budget and air–sea interaction. The temperature in the lower layer is
decoupled from atmospheric forcing due to the halocline and largely dictated by the
advection from the North Sea. The latter is most pronounced in the southern Baltic
but is felt also in the gulf.
As expected, the seasonal evolution of temperature in the Gulf of Finland
(Fig. 6.7) is very different in the upper and lower layers. Due to the large seasonal
variations in the energy budget of the upper layer, the water temperature at sea surface reaches its maximum in summer and minimum in winter, whereas in winter
at least a part of the gulf freezes. The seasonal variability of the temperature in the
lower layer is weak because of the decoupling from atmospheric forcing. The tem-