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



deep layers of the Sea by hydrogen sulphide cannot be considered as char- 

 acteristic only of the present phase of the Black Sea history. When first dis- 

 covered this phenomenon was attributed to a mass destruction of the brackish- 

 water Pontic fauna due to the rise of salinity after the breaking through of 

 the Dardanelles strait, and further maintained by a constant formation of more 

 hydrogen sulphide resulting from the putrefaction of dead animals sinking 

 from the upper layers of the Sea. Lately, however, this opinion has been 

 abandoned and various investigators (A. Archangelsky, V. Vernadsky, 

 N. Knipovitch) have come to the conclusion that hydrogen sulphide fer- 

 mentation in the deep layers is one of the characteristics in the history of 

 the south-Russian geo-synclinal bodies of water. 



Water balance and the circulation of water masses 



The nature of the circulation of the Black Sea water masses and of its water 

 balance through the Bosporus is of great significance for a wide range of 

 biological phenomena in this semi-closed sea basin. 



These problems have arisen since the depth-gauge expedition of 1890-91, 

 when the contamination of the deep zones of the Black Sea with hydrogen 

 sulphide was discovered, and since S. Makarov's study of the Bosporus cur- 

 rents in 1881-82. Different views on the nature of the vertical mixing of the 

 Black Sea waters have existed from the beginning of these investigations. 

 Some workers maintained that the deep hydrogen sulphide zone was linked 

 with the upper layer only by diffusion and a gradual upwelling due to the 

 inflow of saline waters from the Sea of Marmora through the Bosporus. 

 In their opinion the upper aerated layer and the deep layer, containing hydro- 

 gen sulphide, are quite different in origin and structure. Other investigators 

 have considered it probable that the two main water masses are mixed by the 

 wind, a system of currents, by internal waves and by a process of turbulent 

 mixing of the deep layers. The peculiar curving of isolines in the middle parts 

 of two cyclonic vortices was noted; moreover, curves of the isoline were also 

 observed in the deep layers of the Sea. 



The estimation of Black Sea biological productivity depends on the solu- 

 tion of this problem. The first point of view leads to the assumption of a 

 low productivity for the water column caused by its constant loss of organic 

 matter, which is carried into the depths in every stage of decomposition, by its 

 mineralization and by its continuous accumulation in the deep stagnant zone. 

 The constant return of plant food substances into the inhabited layer of water 

 from the zone of accumulation and the existence of a sufficient supply for the 

 productive biological processes in the upper zone are comprehensible from 

 the second point of view. Hence there was a considerable difference of opinion 

 as regards the scale of biological production. 



A considerable change of opinion on the mixing of the Black Sea water was 

 introduced not long ago as a result of the work of V. Wodjanitzky (1941, 

 1948, 1954) and G. Neumann (1942, 1943). Both investigators recognize the 

 presence of an exchange between the inhabited and hydrogen sulphide layers. 



The former proposed the following scheme of water circulation for the 

 Black Sea, based on the analysis of hydrological data (Table 154) and the 



