Caspian Sea
Mazandaran sea
Caspian Sea from orbit.jpg
The Caspian Sea as taken by the MODIS on the orbiting Terra satellite, June 2003
Caspian Sea is located in Asia
Caspian Sea
Caspian Sea
LocationWestern Asia and eastern Europe
Coordinates41°40′N 50°40′E / 41.667°N 50.667°E / 41.667; 50.667Coordinates: 41°40′N 50°40′E / 41.667°N 50.667°E / 41.667; 50.667
TypeAncient lake, Endorheic, saline, permanent, natural
Primary inflowsVolga River, Ural River, Kura River, Terek River
Primary outflowsEvaporation, Kara-Bogaz-Gol
Catchment area3,626,000 km2 (1,400,000 sq mi)[1]
Basin countriesAzerbaijan, Iran, Kazakhstan, Russia, Turkmenistan
Max. length1,030 km (640 mi)
Max. width435 km (270 mi)
Surface area371,000 km2 (143,200 sq mi)
Average depth211 m (690 ft)
Max. depth1,025 m (3,360 ft)
Water volume78,200 km3 (18,800 cu mi)
Residence time250 years
Shore length17,000 km (4,300 mi)
Surface elevation−28 m (−92 ft)
SettlementsBaku (Azerbaijan), Nowshahr Rasht (Iran), Aktaw (Kazakhstan), Makhachkala (Russia), Türkmenbaşy (Turkmenistan) (see article)
1 Shore length is not a well-defined measure.

The Caspian Sea is the world's largest inland body of water, variously classed as the world's largest lake or a full-fledged sea. It is an endorheic basin (a basin without outflows) located between Europe and Asia, to the east of the Caucasus Mountains and to the west of the broad steppe of Central Asia. The sea has a surface area of 371,000 km2 (143,200 sq mi) (excluding the detached lagoon of Garabogazköl) and a volume of 78,200 km3 (18,800 cu mi). It has a salinity of approximately 1.2% (12 g/l), about a third of the salinity of most seawater. It is bounded by Kazakhstan to the northeast, Russia to the northwest, Azerbaijan to the west, Iran to the south, and Turkmenistan to the southeast. The Caspian Sea is home to a wide range of species and may be best known for its caviar and oil industries. Pollution from the oil industry and dams on rivers draining into the Caspian Sea have had negative effects on the organisms living in the sea.

The wide and endorheic Caspian Sea has a north–south orientation and its main freshwater inflow, the Volga River, enters at the shallow north end. Two deep basins occupy its central and southern areas. These lead to horizontal differences in temperature, salinity, and ecology. The Caspian Sea spreads out over nearly 1,200 kilometres (750 mi) from north to south, with an average width of 320 km (200 mi). It covers a region of around 386,400 km2 (149,200 sq mi) and its surface is about 27 m (89 ft) below sea level. The sea bed in the southern part reaches as low as 1,023 m (3,356 ft) below sea level, which is the second lowest natural depression on Earth after Lake Baikal (−1,180 m or −3,870 ft). The ancient inhabitants of its coast perceived the Caspian Sea as an ocean, probably because of its saltiness and large size.


The word Caspian is derived from the name of the Caspi, an ancient people who lived to the southwest of the sea in Transcaucasia.[2] Strabo wrote that "to the country of the Albanians belongs also the territory called Caspiane, which was named after the Caspian tribe, as was also the sea; but the tribe has now disappeared".[3] Moreover, the Caspian Gates, which is the name of a region in Iran's Tehran province, possibly indicates that they migrated to the south of the sea. The Iranian city of Qazvin shares the root of its name with that of the sea. In fact, the traditional Arabic name for the sea itself is Baḥr Qazwin (Sea of Qazvin).[4]

In classical antiquity among Greeks and Persians it was called the Hyrcanian Ocean.[5] In Persian middle age, as well as in modern Iran, it is known as درياى خزر, Daryā-e Khazar, which was named after Khazars an ancient nomadic tribe in the region. it is also sometimes referred to as Mazandaran Sea (Persian: دریای مازندران‎) in Iran.[6]

Some Turkic peoples refer to the lake as Khazar Sea. In Turkmen, the name is Hazar deňizi, in Azeri, it is Xəzər dənizi, and in modern Turkish, it is Hazar denizi. In all these cases, the second word simply means "sea", and the first word refers to the historical Khazars who had a large empire based to the north of the Caspian Sea between the 7th and 10th centuries. Some other Turkic ethnic groups refer to the lake as Caspian Sea. In Kazakh, where it is called Каспий теңізі, Kaspiy teñizi, in Kyrgyz: Каспий деңизи (Kaspiy deñizi), in Uzbek: Kaspiy dengizi.

Renaissance European maps labelled it as Abbacuch Sea (Oronce Fine's 1531 world map), Mar de Bachu (Ortellius' 1570 map), or Mar de Sala (Mercator's 1569 map).

Old Russian sources call it the Khvalyn or Khvalis Sea (Хвалынское море / Хвалисское море) after the name of Khwarezmia.[7] In modern Russian, it is called Каспи́йское мо́ре, Kaspiyskoye more.

Physical characteristics


The Caspian Sea, like the Black Sea, is a remnant of the ancient Paratethys Sea. Its seafloor is, therefore, a standard oceanic basalt and not a continental granite body. 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 in the north, the Caspian Sea water is almost fresh in its northern portions, getting more brackish toward the south. It is most saline on the Iranian shore, where the catchment basin contributes little flow.[8] 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.[9]


Area around the Caspian Sea. Yellow area indicates the (approximate) drainage area.

The Caspian Sea is the largest inland body of water in the world and accounts for 40 to 44% of the total lacustrine waters of the world.[10] The coastlines of the Caspian are shared by Azerbaijan, Iran, Kazakhstan, Russia, and Turkmenistan. The Caspian is divided into three distinct physical regions: the Northern, Middle, and Southern Caspian.[11] The Northern–Middle boundary is the Mangyshlak Threshold, which runs through Chechen Island and Cape Tiub-Karagan. The Middle–Southern boundary is the Apsheron Threshold, a sill of tectonic origin between the Eurasian continent and an oceanic remnant,[12] that runs through Zhiloi Island and Cape Kuuli.[13] The Garabogazköl Bay is the saline eastern inlet of the Caspian, which is part of Turkmenistan and at times has been a lake in its own right due to the isthmus that cuts it off from the Caspian.

Differences between the three regions are dramatic. The Northern Caspian only includes the Caspian shelf,[14] and is very shallow; it accounts for less than 1% of the total water volume with an average depth of only 5–6 metres (16–20 ft). The sea noticeably drops off towards the Middle Caspian, where the average depth is 190 metres (620 ft).[13] The Southern Caspian is the deepest, with oceanic depths of over 1,000 metres (3,300 ft), greatly exceeding the depth of other regional seas, such as the Persian Gulf. The Middle and Southern Caspian account for 33% and 66% of the total water volume, respectively.[11] The northern portion of the Caspian Sea typically freezes in the winter, and in the coldest winters ice forms in the south as well.[15]

Over 130 rivers provide inflow to the Caspian, with the Volga River being the largest. A second affluent, the Ural River, flows in from the north, and the Kura River flows into the sea from the west. In the past, the Amu Darya (Oxus) of Central Asia in the east often changed course to empty into the Caspian through a now-desiccated riverbed called the Uzboy River, as did the Syr Darya farther north. The Caspian also has several small islands; they are primarily located in the north and have a collective land area of roughly 2,000 km2 (770 sq mi). Adjacent to the North Caspian is the Caspian Depression, a low-lying region 27 metres (89 ft) below sea level. The Central Asian steppes stretch across the northeast coast, while the Caucasus mountains hug the western shore. The biomes to both the north and east are characterized by cold, continental deserts. Conversely, the climate to the southwest and south are generally warm with uneven elevation due to a mix of highlands and mountain ranges; the drastic changes in climate alongside the Caspian have led to a great deal of biodiversity in the region.[9]

The Caspian Sea has numerous islands throughout, all of them near the coasts; none in the deeper parts of the sea. Ogurja Ada is the largest island. The island is 37 km (23 mi) long, with gazelles roaming freely on it. In the North Caspian, the majority of the islands are small and uninhabited, like the Tyuleniy Archipelago, an Important Bird Area (IBA), although some of them have human settlements.


Caspian Sea near Aktau, Mangystau Region, Kazakhstan

The Caspian has characteristics common to both seas and lakes. It is often listed as the world's largest lake, although it is not a freshwater lake. It contains about 3.5 times more water, by volume, than all five of North America's Great Lakes combined. The Caspian was once part of the Tethys Ocean, but became landlocked about 5.5 million years ago due to plate tectonics.[10] 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[who?] claim that a medieval rising of the Caspian, perhaps caused by the Amu Darya changing its inflow to the Caspian from the 13th century to the 16th century, caused the coastal towns of Khazaria, such as Atil, to flood. In 2004, the water level was 28 metres (92 feet) below sea level.

Over the centuries, Caspian Sea levels have changed in synchrony 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 kilometres to the northwest.[citation needed]

The last short-term sea-level cycle started with a sea-level fall of 3 m (10 ft) from 1929 to 1977, followed by a rise of 3 m (10 ft) from 1977 until 1995. Since then smaller oscillations have taken place.[16]

A study by the Azerbaijan Academy of Sciences estimated that the level of the sea was dropping by more than six centimetres per year due to increased evaporation due to rising temperatures caused by climate change.[17]

Environmental degradation

The Volga River, the largest in Europe, drains 20% of the European land area and is the source of 80% of the Caspian's inflow. Its lower reaches are heavily developed with numerous unregulated releases of chemical and biological pollutants. The UN Environment Programme warns that the Caspian "suffers from an enormous burden of pollution from oil extraction and refining, offshore oil fields, radioactive wastes from nuclear power plants and huge volumes of untreated sewage and industrial waste introduced mainly by the Volga River".[17]

The magnitude of fossil fuel extraction and transport activity in the Caspian also poses a risk to the environment. The island of Vulf off Baku, for example, has suffered ecological damage as a result of the petrochemical industry; this has significantly decreased the number of species of marine birds in the area. Existing and planned oil and gas pipelines under the sea further increase the potential threat to the environment.[18]


Iran's northern Caspian Hyrcanian mixed forests are maintained by moisture captured from the Caspian Sea by the Alborz Mountain Range.



The rising level of the Caspian Sea between 1994 and 1996 reduced the number of habitats for rare species of aquatic vegetation. This has been attributed to a general lack of seeding material in newly formed coastal lagoons and water bodies.[citation needed]


Most tadpole gobies (Benthophilus) are only found in the Caspian Sea basin.[19]

The Caspian turtle (Mauremys caspica), although found in neighboring areas, is a wholly freshwater species. The zebra mussel is native to the Caspian and Black Sea basins, but has become an invasive species elsewhere, when introduced. The area has given its name to several species, including the Caspian gull and the Caspian tern. The Caspian seal (Pusa caspica) is the only aquatic mammal and is endemic to the Caspian Sea, being one of very few seal species that live in inland waters, but it is different from the those inhabiting freshwaters due to the hydrological environment of the sea. A century ago the Caspian was home to more than one million seals. Today, fewer than 10% remain.[17]

Archeological studies of Gobustan Rock Art have identified what may be dolphins[20] and porpoises,[21][22] or a certain species of beaked whales[23] and what may be a whaling scene indicates large baleen whales[24] likely being present in Caspian Sea at least until when the Caspian Sea ceased being a part of the ocean system or until the Quaternary or much more recent periods such as until the last glacial period or antiquity.[25] Although the rock art on Kichikdash Mountain is assumed to be of a dolphin[26] or of a beaked whale,[23] it might instead represent the famous beluga sturgeon due to its size (430 cm in length), but fossil records suggest certain ancestors of modern dolphins and whales, such as Macrokentriodon morani (bottlenose dolphins) and Balaenoptera sibbaldina (blue whales) were presumably larger than their present descendants. From the same artworks, auks, like Brunnich's Guillemot could also have been in the sea as well, and these petroglyphs suggest marine inflow between the current Caspian Sea and the Arctic Ocean or North Sea, or the Black Sea.[26] This is supported by the existences of current endemic, oceanic species such as lagoon cockles which was genetically identified to originate in Caspian/Black Seas regions.[24]

The sea's basin (including associated waters such as rivers) has 160 native species and subspecies of fish in more than 60 genera.[19] About 62% of the species and subspecies are endemic, as are 4–6 genera (depending on taxonomic treatment). The lake proper has 115 natives, including 73 endemics (63.5%).[19] Among the more than 50 genera in the lake proper, 3–4 are endemic: Anatirostrum, Caspiomyzon, Chasar (often included in Ponticola) and Hyrcanogobius.[19] By far the most numerous families in the lake proper are gobies (35 species and subspecies), cyprinids (32) and clupeids (22). Two particularly rich genera are Alosa with 18 endemic species/subspecies and Benthophilus with 16 endemic species.[19] Other examples of endemics are four species of Clupeonella, Gobio volgensis, two Rutilus, three Sabanejewia, Stenodus leucichthys, two Salmo, two Mesogobius and three Neogobius.[19] Most non-endemic natives are either shared with the Black Sea basin or widespread Palearctic species such as crucian carp, Prussian carp, common carp, common bream, common bleak, asp, white bream, sunbleak, common dace, common roach, common rudd, European chub, sichel, tench, European weatherfish, wels catfish, northern pike, burbot, European perch and zander.[19] Almost 30 non-indigenous, introduced fish species have been reported from the Caspian Sea, but only a few have become established.[19]

Six sturgeon species, the Russian, bastard, Persian, sterlet, starry and beluga, are native to the Caspian Sea.[19] The last of these is arguably the largest freshwater fish in the world. The sturgeon yield roe (eggs) that are processed into caviar. Overfishing has depleted a number of the historic fisheries.[27] In recent years, overfishing has threatened the sturgeon population to the point that environmentalists advocate banning sturgeon fishing completely until the population recovers. The high price of sturgeon caviar—more than 1,500 Azerbaijani manats[17] (US$880 as of April 2019) per kilo—allows fishermen to afford bribes to ensure the authorities look the other way, making regulations in many locations ineffective.[28] Caviar harvesting further endangers the fish stocks, since it targets reproductive females.



Many rare and endemic plant species of Russia are associated with the tidal areas of the Volga delta and riparian forests of the Samur River delta. The shoreline is also a unique refuge for plants adapted to the loose sands of the Central Asian Deserts. The principal limiting factors to successful establishment of plant species are hydrological imbalances within the surrounding deltas, water pollution, and various land reclamation activities. The water level change within the Caspian Sea is an indirect reason for which plants may not get established.

These affect aquatic plants of the Volga Delta, such as Aldrovanda vesiculosa and the native Nelumbo caspica. About 11 plant species are found in the Samur River Delta, including the unique liana forests that date back to the Tertiary period.[citation needed]


Illustration of two Caspian tigers, extinct in the region since the 1970s.

Reptiles native to the region include spur-thighed tortoise (Testudo graeca buxtoni) and Horsfield's tortoise.