THE BALTIC SEA 



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the temperature usually ranges between 3° and 5° in the southern parts of the 

 Sea, and between 1° and 5° in the northern ones (Aland depression). 



The phenomenon of dichothermia is very common in the Baltic Sea ; the 

 coldest layer of water (intermediate cold layer) lies usually not at the bottom 



Fig. 118. Surface isotherms of the North and Baltic Seas in February 

 (A) and August (B) (Schulz). 



but at a depth of 60 to 100 m. At the bottom the temperature rises again from 

 3° to 5° (Gotland and Danzig depressions). In this respect the diagram in 

 Fig. 119 is most instructive; it gives the changes of temperature at different 

 depths in the depression situated at the entrance to Danzig Bay, which has a 

 maximum depth of 113 m. The range of July temperatures in the area of the 

 Island of Gotland is given in Fig. 120. 



Salinity 



The most characteristic features of the hydrology of the Baltic Sea comprise 

 the instability of its saline conditions, especially in its transitional areas, the 

 movement of the more saline near-bottom water from west to east along the 

 deep troughs with a simultaneous surface discharge current in the opposite 

 direction and, in consequence, a sharp division of salinity in two layers of the 



