The Caspian Sea is the largest enclosed body of water on
Earth by area, variously classed as the world's largest
lake or a full-fledged
sea. It has a surface area of 371,000
square kilometers (143,244 sq mi) and a volume of 78,200
cubic kilometers (18,761 cu mi).It is an
endorheic body of water (has no outflows), and lies between the southern areas of the
Russian Federation and northern
Iran. It has a maximum depth of about 1025 meters (3,363 ft).
It was perceived as a sea by its ancient coastal inhabitants because it is salty and seemed boundless. It has a
salinity of approximately 1.2%, about a third the salinity of most
seawater. According to
Strabo, it is named after an ancient people called
Black Sea and the
Mediterranean, the Caspian Sea is a remnant of the
Tethys Ocean. It became landlocked about 5.5 million years ago due to continental drift. The Caspian owes what reduced salinity it has to its origins as a remnant of the
World Ocean. During warm and dry climatic periods, the landlocked sea has all but dried up, depositing
evaporitic sediments like
halite that became covered by wind-blown deposits and were sealed off as an evaporite sink when cool, wet climates refilled the basin.Due to the inflow of fresh water, the Caspian Sea is a fresh-water lake in its northern portions. It is more saline on the Iranian shore, where the catchment basin contributes little flow. Currently, the mean salinity of the Caspian is three times less than the Earth's oceans. The largely dried-up
embayment routinely exceeds oceanic salinity.
The Caspian Sea is the largest inland body of water in the world and accounts for 40 to 44 percent of the total
lacustrine waters of the world. The coastlines of the Caspian are shared by
Turkmenistan. The Caspian is divided into three distinct physical regions: Northern, Middle, and Southern Caspian. The North-Middle boundary is the Mangyshlak threshold, which runs through Chechen Island and Cape Tiub-Karagan. The Middle-South boundary is the Apsheron threshold, which runs through Zhiloi Island and Cape Kuuli.
Over 130 rivers provide inflow to the Caspian, with the
Volga River being the largest. The Caspian also has several small islands; they are primarily located in the North and have a collective land area of roughly 2000 square kilometers.
The Caspian Sea holds great numbers of
sturgeon, which yield
eggs that are processed into
caviar. In recent years overfishing has threatened the sturgeon population to the point that
environmentalists advocate banning sturgeon fishing completely until the population recovers. However, the high price of sturgeon caviar allows fisherman to afford bribes to ensure the authorities look the other way, making regulations in many locations ineffective.Caviar harvesting further endangers the fish stocks, since it targets reproductive females.
Caspian seal, (Phoca caspica,
Pusa caspica in some sources) which is
endemic to the Caspian Sea, is one of very few
seal species that live in inland waters (see also
Baikal seal). The area has given its name to several species of birds, including the
Caspian gull and the
Caspian tern. There are several species and subspecies of fish endemic to the Caspian Sea, including the
Kktum (also known as
Caspian white fish), Caspian
bream (some report that the Bream occurring in the
Aral Sea is the same subspecies), and a Caspian "salmon" (a subspecies of trout,
Salmo trutta caspiensis). The "Caspian salmon" is critically endangered.
The Caspian has characteristics common to both seas and
lakes. It is often listed as the world's largest lake, though it is not a
freshwater lake. The Caspian became landlocked about 5.5 million years ago due to
plate tectonics. The
Volga River (about 80% of the inflow) and the
Ural River discharge into the Caspian Sea, but it has no natural outflow other than by
evaporation. Thus the Caspian
ecosystem is a
closed basin, with its own sea level history that is independent of the
eustatic level of the world's oceans. The level of the Caspian has fallen and risen, often rapidly, many times over the centuries. Some Russian historians claim that a
medieval rising of the Caspian caused the coastal towns of
Khazaria, such as
Atil, to flood. In 2004, the water level was -28 metres, or 28 metres (92 ft) below
Over the centuries, Caspian Sea levels have changed in synchronicity with the estimated discharge of the Volga, which in turn depends on rainfall levels in its vast catchment basin. Precipitation is related to variations in the amount of North Atlantic depressions that reach the interior, and they in turn are affected by cycles of the
North Atlantic Oscillation. Thus levels in the Caspian sea relate to atmospheric conditions in the North Atlantic thousands of miles to the north and west. These factors make the Caspian Sea a valuable place to study the causes and effects of global climate change.
The last short-term sea-level cycle started with a sea-level fall of 3 m from 1929 to 1977, followed by a rise of 3 m from 1977 until 1995. Since then smaller oscillations have taken place.