THE CASPIAN SEA 541 



mud deposits {batkaki) are formed — frequently right at the shore and in 

 shallow water — under favourable conditions (bottom topography, slow cur- 

 rents) from the large accumulation of detritus brought down by river water 

 and retained by vegetation. Detritus and fine-grained soil fractions moved 

 away from the shores and were carried into the deep Central and Southern 

 Caspian depressions, which thus become encircled by a wide belt of the coarse 

 fraction, mainly huge beds of shell gravel (Fig. 256). This peculiarity — the 

 transfer of detritus from shallows to depths, and an abundance of pure shell- 

 gravel floors — is of cardinal importance for the phenomena of biological 

 productivity taking place in the Sea; it decreases considerably its potential 

 level, both as regards benthos and also, apparently, as regards plankton. 



The organisms populating the Sea, the molluscs most of all, are of extreme 

 importance in the formation of the sea-bed. According to A. Kolokolov's 

 computations (1940) the ratio of plant nutrients to terrigenous substances in 

 the North Caspian sea-bed is about 1:1. Dead molluscs remain in those parts 

 of the Sea where they lived and sea-beds rich in shell gravel are formed, and 

 are thus most productive as regards benthos. 



Sea level 



The level of the Caspian Sea, averaged over the last century, has been 25-45 m 

 below the ocean level. Moreover, it is not constant from year to year, but 

 undergoes considerable seasonal variations and fluctuations which may last 

 for many years. The average level of the Caspian Sea (for the hundred years 

 1830 to 1929) is 327 cm from zero on the Baku sea-gauge (its level being 28-73 m 

 above sea-level). The highest level of the Sea, 363 cm above zero on the 

 Baku sea-gauge, was recorded in 1896, and the lowest in very recent years. 

 In 1945 the level of the Caspian Sea was only 134-26 cm, and it is continuing 

 to fall: Thus in the last 50 years the range of the fluctuations of the level of the 

 Caspian Sea has been 229 cm. In the last 17 years (1929-46) it has fallen by 

 almost 2 m (187 cm); the decrease is proceeding fairly uniformly. Only in 

 1942-44 was there some indication of a break in this uniformity, when the 

 level of the Sea rose by 1 1-5 cm as compared with 1941 ; by 1945, however, its 

 level had dropped again by 20-5 cm as compared to 1943. 



There is reason to suppose that the catastrophic drop in the level of the 

 Caspian Sea, caused by the considerable decrease of river inflow (from 1930 

 to 1943) has now been stabilized at the level of about 130 cm above zero on 

 the Baku sea-gauge. A further insignificant drop of the level to 1 10 to 115 cm 

 above zero on the Baku sea-gauge may be expected in the coming years. 



In the opinion of most investigators (L. Berg, S. P. Brujevitch and others) 

 these changes in the level of the Caspian Sea are the results of the fluctuations 

 in the amounts of fresh water received by the Sea from the rivers and from rain- 

 fall minus evaporation. According to a different view the changes are caused 

 by the movements of the earth's crust (I. Gubkin, P. Pravoslavlev and others). 



A number of mountain ranges in the Southern Caspian, stretching from 

 north to south (Fig. 257), were discovered by recent investigations (V. Solov'evt 

 1958) with the use of an echo sounder. In Solov'ev's opinion they are of recen, 

 formation ; this indicates the continuance of structural processes, which could 



