284 



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



part of the Sea. Thus in the deep layers of the Aland depression at a much 

 lower temperature (1-18° to 3-81°) and a lesser salinity (6-8 to 702% o ), the 

 deep-water salinity is only 1% higher than that of the surface water, the verti- 

 cal circulation reaches the bottom and the amount of oxygen at 300 m is still 

 6-5 to 8-7 cm 3 /l- at 73 to 93 per cent of saturation. In the southern depression 

 of the Gulf of Bothnia the deep-water salinity varies between 6 and 6-5% , 

 while in the northern depression it is about 4% . 

 As regards deep-water gas conditions, the area of the eastern part of the 



Fig. 128. Concentration of hydrogen ions in near- 

 bottom waters of Baltic in May to July 1922 (Schulz). 



deep trough, which extends from the Gotland depression to the entrance to 

 the Gulf of Finland, is most interesting. Deep saline waters from the Gotland 

 depression penetrate into this area, while the surface waters, by contrast, are 

 considerably diluted ; so that conditions are created which are extremely un- 

 favourable for vertical circulation. The following phenomena have been ob- 

 served in the area to the north of Dago Island at a depth of 180 m (Bogskar 

 depression): marked salinity fluctuations (9-20 to 10T4% o ), increased tem- 

 perature (3-71° to 4-96°) and changes in oxygen content from to 2-49 cm 3 /l. 

 (0 to 29 per cent of saturation). 



The range of deep-water salinity of the Gulf of Finland is shown in Fig. 129, 

 while the hydrological conditions of the most eastern part of the Gulf up to 

 Neva Guba are given in Fig. 130. 



