Caspian Sea
The Caspian Sea, like the Black Sea, Namak Lake, and Lake Urmia, is a remnant of the ancient Paratethys Sea. It became landlocked about 5.5 million years ago due to tectonic uplift and a fall in sea level. During warm and dry climatic periods, the landlocked sea almost dried up, depositing evaporitic sediments like halite that were covered by wind-blown deposits and were sealed off as an evaporite sink when cool, wet climates refilled the basin. (Comparable evaporite beds underlie the Mediterranean.) Due to the current inflow of fresh water, the Caspian Sea is a freshwater lake in its northern portions, and is most saline on the Iranian shore, where the catchment basin contributes little flow. Currently, the mean salinity of the Caspian is one third that of Earth's oceans. The Garabogazköl embayment, which dried up when water flow from the main body of the Caspian was blocked in the 1980s but has since been restored, routinely exceeds oceanic salinity by a factor of 10.
Kura (Caspian Sea)
People have inhabited the Caucasus region for thousands of years, and first established agriculture in the Kura Valley over 4,500 years ago. Large, complex civilizations eventually grew up on the river, but by 1200 CE, most were reduced to ruin by natural disasters and foreign invaders. The increasing human use, and eventual damage, of the watershed’s forests and grasslands contributed to a rising intensity of floods through the 20th century. In the 1950s, the Soviet Union started building many dams and canals on the river. Previously navigable up to Tbilisi in Georgia, it is now much slower and shallower, as it has been harnessed by irrigation projects and hydroelectric power stations. The river is now moderately polluted by major industrial centers like Tbilisi and Rustavi in Georgia.