THE SEA OF AZOV 471 



Ice conditions 



The considerable fall of temperature in December, January and February 

 leads to the formation of ice, which proceeds the more readily owing to the 

 shallow water and the low salinity of the Sea of Azov. Ice formation begins 

 at the Gulf of Taganrog, where it remains longer than anywhere else. Ice 

 formation is weakest off the southern shores. 



In some years an almost continuous ice cover persists for 4 to A\ months. 

 In 1923-28 the period of ice varied in different parts of the Sea from 38 to 

 138 days, while the thickness of the cover ranged from 9 to 90 cm. Ice usually 

 appears in the first half of December and disappears in the second half of 

 March. 'Taking into consideration the considerable thickness of the ice 

 fields', wrote N. M. Knipovitch (1932), 'which are 80 or even 90 cm thick, the 

 masses of hummocks and the piling up of ice which sometimes reaches down 

 to the sea bottom, one cannot help seeing that the freezing of such great 

 masses of water with the separating out of large amounts of salts, would 

 increase to a considerable degree the salinity of the sea in winter, particularly 

 in so shallow a sea as the Sea of Azov.' 



Salinity * 



The mean salinity of the Sea of Azov may be taken as 1 1 -2% ; seasonal 

 fluctuations of salinity are observed with a maximum in winter and a mini- 

 mum in summer (Fig. 223a). 



The salinity of the Sivash is unusual for the Sea of Azov. In the Northern 

 Sivash a salinity of 400% has been observed and it increases even more 

 farther south and west. 



In the Sea of Azov itself maximum salinity (17-5% ) is found in the bottom 

 layers in the area of the Kerch Strait — this is Black Sea water which is only 

 slightly diluted. 



The salinity of the Sea of Azov fluctuates considerably during the course of 

 the year. Maximum salinity is found in the winter months when its rise is 

 caused by the decrease in the river inflow and the freezing up of large masses 

 of fresh water. Salinity begins to decrease gradually with the melting of the 

 snows, and a period of minimum salinity is reached by the end of summer 

 (September). In the eastern part of the Gulf of Taganrog the water is often 

 almost fresh, while in the west, close to the entrance into the Sea of Azov, 

 salinity rises to 4 to 5% (chlorine). 



Gas conditions 



The surface layers of the Sea of Azov usually contain an adequate amount 

 of oxygen, owing to its shallow waters and its good aeration. Annual changes 

 of oxygen content in the water-column are shown in Fig. 224a where they 

 are compared with the course of phytoplankton development. Fluctuations 

 of oxygen content are small (92 to 1 14 per cent saturation). The deep-water 

 layers, however, owing to the abundant life in the Sea, the accumulation of 

 huge masses of decomposed organic substances and the high temperature, 

 may easily lose their oxygen and pass to a state of oxygen deficiency. This 



