The Sea-water and its Physical and Chemical Properties 



69 



hydrogen sulphide content at three stations in July in different places in the eastern 

 part of the Black Sea (Neumann, 1943). The station PM 298 lies in the southern 

 part, the station PM 308 lies in the northern part of the central eastern basin near an 

 area with little current, and the station PM 303 lies south-west of Sochum in the area 

 of the strong current along the Caucasian coast. 



Hi^}° 



t'7 9 II 13 15 17 19 

 5%«I7 IB 19 20 21 22 23 



a-fW 12 13 14 15 16 17 



7 cm' 

 2rc 



Ks'Y 



-^^ H,st 



5 6 7cmyi 



S%ol7 



t7>l| 



II 13 15 17 19 21 "C 

 19 20 21 22 23 %<. 

 13 14 6 16 17 



ri 9 II 13 15 17 19 21°C 



5%ol7 18 19 20 21 2 2 23 %o 



o-,ll 12 13 14 15 16 17 18 



100 

 200 



400 



600 



800 



1000 



1200 



1400- 

 1500 



P.M. 298 



42''00'IM 



38°00'E 



I6/I7-3ZII-1925 



Is 



It 

 !\ 

 li 

 j i 

 ! i 



P.M. 303 



42°23'N 

 40°33'E 

 20-2Ii925 



i ! 

 it 

 il 



ij 

 il 



il 



i 



I 



:i 

 — li- 



w 



^•^ 5%..' 

 H,S\. 



P.M. 308 



43''04-9N 

 38° 29-8'E 

 22-3ZIIi925 



Fig. 38. Vertical structure of the water masses in the eastern part of the Black Sea. (Sept, 1925 

 stations: P.M. 298, 303, 308; temperature, salinity, density, oxygen content and sulphur 



content.) 



The vertical structure of the Black Sea is characterized by two layers. The upper 

 layer shows a very rapid increase of density with depth and usually extends down to 

 about 200 m. After a sharp bend in the a^-curve the density changes little with depth. 

 The boundary between these two layers coincides approximately with the upper limit 

 of the hydrogen sulphide; its depth varies from place to place depending on the dy- 

 namics of the currents prevailing. The upper layer (the troposphere) is divided in 

 summer at a depth of about 50-70 m by a definite temperature minimum at 6-5°- 

 7-5 °C. This surface zone has a constant salinity and shows a pronounced vertical 

 thermal convection; it is well ventilated and has a rich oxygen supply from the at- 

 mosphere and also from plant assimilatory activity. In the lower part of the surface 

 layer the oxygen falls off rapidly with depth and finally disappears, and in places is 

 replaced by hydrogen sulphide. The oxygen of these upper layers comes partly from 

 above and partly from horizontal advection but the latter effect is limited to the 

 immediate vicinity of the Bosphorus. 



The whole of the layer from below the oxygen zone down to the bottom at about 

 2000 m has an almost constant temperature, about 8-8-9-0°C; the slight increase 

 from 300 m is largely an adiabatic effect. The principal characteristic of this lower 

 water is the hydrogen sulphide content which increases down to the bottom (see 

 Table 26). 



Similar conditions, though on a smaller scale, are shown by several Norwegian 

 fiords where in most cases there is a considerable depth, a fresh-water influx at the 



