ISOTOPE STUDIES IN THE CASPIAN SEA

The Caspian Sea is the world's largest inland water body with a surface area of 386400 km2 and a volume of 66780 km3. It is located in a large continental depression about 28 m below sea level and has no surface outlet. The drainage area of the Caspian Sea is approximately 3.7 million square kilometers. The Volga, Ural and Terek rivers empty into the North Caspian, and their combined annual flow accounts for 88 % of all water entering the sea. The Sulak, Samur, Kura rivers and a number of small rivers contribute about 7 % of the flow, the remainder comes in from the rivers of the Iranian shore [1]. The Caspian Sea is divided into three basins with approximately the same surface [2]. The North Caspian basin has a maximum depth of 15 m, an average depth of 5 m and contains 1 % of the total water. The bottom is formed of an unvarying rippling sedimentary plain, broken only by a line of southern barsand shoals, some of which are the foundations of Tyuleny, Kulaly and Zhemchuzhny islands reflecting underlying structural rises. The Central Caspian basin has a maximum depth 800 m and contains 22 % of the total water. It is an irregular depression with an abrupt western slope and a gentler eastern gradient. The bottom of the depression is formed by a plain that deepens to the west. The Apsheron Bank, a belt of shoals and islands rising fro