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



Transparency 



The water of the Sea of Azov is only slightly transparent, owing to the large 

 amount of organic and inorganic matter suspended in it. The limits of the 

 fluctuations of transparency are ОТ to 5-0 m; in the overwhelming majority 

 of cases transparency does not extend farther than 2 m, and in 60 per cent of 

 them farther than 1 m. On the whole the water is more transparent in the 

 central and western parts of the Sea than in the east. 



Temperature 



Like the Black and Caspian Seas, the Sea of Azov, except for the Sivash, 

 belongs to the bodies of brackish water, in the sense used by N. M. Knipo- 

 vitch (1929), to which we referred earlier. 



Some features of the hydrological conditions of the Sea of Azov are due to 

 this brackishness of its waters. In winter time, with the surface water at 

 freezing temperature and partly covered with ice, warmer and at the same time 

 heavier waters are concentrated in the depths. At a salinity of 6% * (by 

 chlorine), the temperature at the surface at that time will be —0-58°, and at 

 the bottom 1-67°. When the circulation is vigorous and the whole column of 

 water has a temperature of about freezing point, then, in the spring, once the 

 surface layers are warmed to 1-67° they rapidly sink and quickly warm the 

 whole column of water to the temperature of the highest density, i.e. 1-67°. 

 Further heating is mainly concentrated in the upper layers of water and passed 

 over to the lower layers only gradually as a result of drifting circulations. 



The summer rise in temperature of the waters of the Sea of Azov, and the 

 mean annual temperature, are fairly high. Thus the mean annual temperature 

 of the surface of the Sea for the four years 1924-27 was 11-28° for Taganrog 

 and 12-4° for Temryuk. 



In the four summer months at Temryuk the water temperature is higher 

 than 20°, reaching 25° at times. The lowest average monthly temperature, 

 which sometimes occurs in January, but usually in February, is about 0°; 

 some lower temperatures have been recorded occasionally : —0-3° for Tagan- 

 rog, — 10 for Temryuk, — 1-3 for Genichensk. On the other hand the highest 

 average monthly temperature of water on the surface of the Sea, usually 

 occurring in July, reaches 25-9° at Taganrog, and the highest single observa- 

 tions were 29-6° at Taganrog, 31-2° at Eisk, and 29-3 at Temryuk. 



In autumn and winter as a rule an almost homothermic state is observed ; 

 the temperature varies only slightly with depth. Only in the spring, during the 

 period of a quick rise of water temperature, is a considerable decrease of 

 temperature with depth commonly observed. A strong wind brings about 

 considerable changes in the range of temperature right down to the bottom. 



* The salt ratio in the Sea of Azov, and especially in the Caspian, is somewhat different 

 from that of typical sea-water. Hence it is impossible to obtain an accurate expression of 

 its total salinity from the usual formula of the change in the chlorine content obtained by 

 titration (weight of chlorine in grammes per kilogramme of water). For the Sea of Azov 

 and still more for the Caspian Sea the so called ' chlorine numbers ' are commonly used 

 instead of salinity. The usual formula can be used to convert it into general salinity: 



S<L = 0-030+ 1-8050 CI 



