. Biology of the seas of the Marine biology -- Soviet Union; Hydrology -- Soviet Union. THE BLACK SEA 385 Kerch Strait, is noted in recent literature (S. P. Brujevitch, 1953; A. Bog- danova, 1959). A certain rise in salinity in the upper layer and a fall in salinity throughout the water-column have been observed in the Black Sea for a period of 25 years (1924-51). The decrease of salt content through that period for the whole Sea was determined as 2 milliards of tons (A. Bogdanova, 1959). This is caused primarily by the loss of salts through the Bosporus being greater than the supply,
. Biology of the seas of the Marine biology -- Soviet Union; Hydrology -- Soviet Union. THE BLACK SEA 385 Kerch Strait, is noted in recent literature (S. P. Brujevitch, 1953; A. Bog- danova, 1959). A certain rise in salinity in the upper layer and a fall in salinity throughout the water-column have been observed in the Black Sea for a period of 25 years (1924-51). The decrease of salt content through that period for the whole Sea was determined as 2 milliards of tons (A. Bogdanova, 1959). This is caused primarily by the loss of salts through the Bosporus being greater than the supply, a fact which is linked in its turn with a 19%0 rise in salinity in the upper layer of the sea as a result of a decrease of the mainland run-off. In Bogdanova's opinion the decrease in salinity of the deep layers is connected with the slackening of the deep Bosporus current. The change in salinity of the upper layer and the main column of water should have im- proved vertical circulation. In addition, cool- ing of the intermediate layer (75 to 300 m) and some warming up of the deeper layers were recorded. In the off-shore zone animals were found at depths of a little more than 200 m; on the other hand in the halistatic area patches were found where plankton animals disappeared at a depth of no more than 87-5 m. Hence the length of the Black Sea water column populated by animals varies greatly in different parts of the 2 J o-o-oo-o^ Fluctuations of water level The ' fluctuations in the amount of water coming from the mainland, or from rainfall, evaporated from the sea surface, entering the Sea as a result of water exchange with the neighbouring seas through the straits may affect the volume of sea-water. During recent decades changes in the Black Sea level, with an amplitude of about 32-5 cm, have been observed. Seasonal changes in the sea-level have been observed with ranges of 15 to 27-5 cm. Finally, the changes of sea-level may be due to the wind and tides. The latter d
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