276 



BIOLOGY OF THE SEAS OF THE U.S.S.R, 



Fig. 117. Ice chart of the Baltic Sea (Bliitgen, 1938). 1 Fast ice; 2 Periodical 

 drift pack ice ; 3 Periodical floes ; 4 Periodical drift ice ; 5 Episodical fast ice ; 

 6 Episodical pack ice ; 7 Episodical drift ice. 



of their surface : in the inner parts for 2 to 5 months and more, at the inner 

 end of the Gulf of Finland for 3 to 6 months and at the top of the Gulf of 

 Bothnia for as much as 5 to 7 months. The ice conditions of the Baltic Sea 

 are shown in Fig. 117. 



Such temperatures are unknown in the North Sea, which lies alongside the 

 Baltic and in the same latitude (Fig. 118). During the warmest time of the 

 year (August) the surface temperatures of both Seas are practically the same. 

 The heat conditions of the deepest parts of the sea undergo slight variations 

 in temperature in the course of the year. Below 50 m and down to the bottom 



