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.
Caspian Depression
The depression lies at the southern end of the Ryn Desert, and is in both Kazakhstan and Russia. Most of the Russian Republic of Kalmykia lies in the Caspian Depression. The Volga River and the Ural River flow into the Caspian Sea through this region. The deltas of the Ural and Volga Rivers are extensive wetlands. The North Caspian depression is part of the continental or semi-arid desert biome. The area receives of rain per year, on average, and less than 10% of the region is irrigated.