Caspian Sea

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Caspian Sea

(kăs`pēən), Lat. Mare Caspium or Mare Hyrcanium, salt lake, c.144,000 sq mi (373,000 sq km), between Europe and Asia; the largest lake in the world. It is bordered on the northeast by Kazakhstan, on the southeast by Turkmenistan, on the south by Iran, on the southwest by Azerbaijan, and on the northwest by Russia. The Caspian's surface lies 92 ft (28 m) below sea level. It reaches its maximum depth, c.3,200 ft (980 m), in the south; the shallow northern half averages only about 17 ft (5 m). The Caucasus Mts. rise from the southwestern shore, and the Elburz Mts. parallel the southern coast. The Caspian receives the Volga (which supplies more than 75% of its inflow), Ural, Emba, Kura, and Terek rivers, but has no outlet. The rate of evaporation is particularly high in the eastern inlet called GarabogazkolGarabogazkol
or Kara-Bogaz-Gol
, shallow bay,, in Turkmenistan. An arm of the Caspian Sea, it acts as a natural evaporation basin, drawing off the water of the Caspian and depositing salts along its shores.
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, which is exploited for salt. Variations in evaporation account for great changes in the size of the sea during the course of history. The damming and diversion of the Volga's water for industrial and residential use have been the leading reasons for the lowering of the Caspian's water level, a problem of serious proportions, but increases in evaporation rates and decreases in precipitation due to climate change are expected to accelerate the drop in the water level during the 21st cent. The chief ports on the Caspian are BakıBakı
or Baku
, city (1991 pop. 1,782,000), capital of Azerbaijan, on the Caspian Sea. Greater Bakı includes almost the whole Absheron peninsula, on which Bakı proper is situated; the city is located below sea level.
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, a major oil center, and AstrakhanAstrakhan
, city (1990 pop. 521,000), capital of Astrakhan region, SE European Russia. A Caspian Sea port on the Volga River's southern delta, it is a center for river transport thanks to a canal built for barge traffic. Russia's Caspian flotilla is based at the port.
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, at the mouth of the Volga.

Underlying the Caspian are some of the world's largest oil reserves, and the five surrounding countries, all with major stakes in oil-field development, have disputed zones of control, although Russia has signed territorial agreements with Kazakhstan and Azerbaijan. The Caspian also has important fisheries. The northern part of the sea is the chief source of beluga caviar, but the destruction of spawning areas and illegal fishing has greatly reduced the number of sturgeon, and fishing quotas have been imposed. In 2003 a framework treaty for the protection of the sea's environment was signed by four of the surrounding nations; Turkmenistan did not sign. The Convention on the Legal Status of the Caspian Sea, signed in 2018 by the bordering nations, established different guidelines for the division of the surface waters, which are divided into territorial waters (15 nautical mi/28.8 km), fishing waters (an additional 10 nautical mi/18.5 km), and common waters, and the seabed, which is divided into exclusive zones determined by bilateral agreements.

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The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Caspian Sea


(from the Greek Kaspion pelagos, the Latin Caspium Mare), the world’s largest inland body of water, located on the territory of the USSR (RSFSR, Kazakh SSR, Turkmen SSR, and Azerbaijan SSR) and Iran. The Caspian is frequently considered the largest lake in the world; this is inaccurate, however, since by its size, the nature of its processes, and its developmental history the Caspian is a sea. It received its name from the ancient Caspi tribes who inhabited the eastern part of the Caucasus. Among its other historical names are the Hyrcanian, Khvalyn (Khvaliss), and Khazar seas—also derived from the names of ancient peoples who inhabited its shores.

Physical geographic survey. GENERAL INFORMATION. The Caspian Sea extends almost 1, 200 km from north to south, and it has an average width of 320 km and a shoreline of about 7, 000 km (including more than 6, 000 km within the ussr). Its area is about 371,000 sq km, and its level is 28.5 m below the level of the world ocean (1969). The maximum depth is 1, 025 m. in 1929, prior to the considerable drop in the level of the Caspian Sea, its area was 422, 000 sq km. The largest gulfs are Kizliar and Komsomolets in the north, Mangyshlak, Kenderli, Kazakh, Kara-Bogaz-Gol, and Krasnovodsk in the east, and Agrakhan and Baku in the west. In the south there are shallow lagoons. The Caspian has up to 50 islands, predominantly small ones (with a total area of about 350 sq km). The most important are Kulaly, Tiulenii, Chechen’, Artem, Zhiloi, and Ogurchinskii.

The most important rivers—the Volga, Emba, Ural, and Terek—flow into the northern part of the sea. Their combined annual flow accounts for about 88 percent of all river water entering the Caspian. Large rivers—the Sulak, Samur, and Kura —and a number of smaller ones flow into the sea on the western shore (contributing 7 percent of the inflow). The remaining 5 percent of the inflow comes from the rivers of the Iranian shore (Gorgan, Aras, and Safid). On the eastern shore, including the coast of the Kara-Bogaz-Gol, there is not a single permanent stream.

SHORELINE. The shores of the northern Caspian are low and gently sloping and are characterized by the extensive development of low coastal areas that form as a result of sediments brought in by wind-driven waves. Delta shores have also developed here (the deltas of the Volga, Ural, and Terek). as a whole, the shores of the northern Caspian are growing intensively as a result of the drop in the level of the sea, the rapid growth of the deltas, and the abundant influx of terrigenous material. The western shores of the Caspian are also largely shores of accumulation (with numerous bars and spits), while some areas on the coasts of Dagestan and the Apsheron Peninsula are abrasion shores. The eastern coast consists predominantly of abrasion shores resulting from the cutting away of the limestone of the adjacent semidesert and desert plateaus by the sea. there are also accumulation forms such as the Kara-Bogaz Spit, which separates the largest gulf on the Caspian, Kara-Bogaz-Gol, from the sea, as well as the Krasnovodsk and Kenderli spits. South of the Krasnovodsk Peninsula accumulation shores prevail.

RELIEF. in terms of the character of the relief and the hydro-logical features, the caspian sea is usually divided into the north caspian, middle caspian, and south caspian. the north caspian (about 80, 000 sq km in area) is the shallowest part of the sea, with depths of 4–8 m. The bottom is formed by a slightly undulating accumulation plain and a series of shoals and accumulation islands, which are known as the Mangyshlak bank. This bank separates the north Caspian from the Middle Caspian. the middle Caspian (about 138, 000 sq km in area) is divided into the derbent basin (maximum depth, 788 m), the shelf, and the continental slope, which is complicated by underwater landslips and canyons. on the gentle northern slope remains of ancient river valleys have been discovered. in the south the basin of the middle caspian is separated from the basin of the south caspian by the apsheron bank, on which lie a number of shoals and islands. the south caspian basin (maximum depth, 1, 025 m), which covers about one-third of the area of the sea, has a narrow shelf along the western and southern (iranian) shores; along the eastern shore the shelf is considerably wider. the bottom of the basin forms a flat abyssal plain. in the northern part of the basin there are several underwater ranges with a northwestern and southeastern strike.

GEOLOGICAL STRUCTURE AND MINERALS. The northern section of the Caspian Sea forms the edge of the Caspian tectonic depression, which is a part of the Eastern European Platform. The Mangyshlak Bank is structurally linked to the underwater Karpinskii swell (which was uplifted during the hercynian orogeny) on the western shore and the Mangyshlak mountains on the eastern. The bottom of the Middle Caspian has a heterogeneous structure. Its eastern part is a submerged section of the Epihercynian Turan Platform. The Derbent Basin and the western parts of the shelf and the continental slope are the foredeep of the greater caucasus geosyncline. The Apsheron Bank corresponds to one of the branches of recent structures that formed on the subsided folded structures of the Greater Caucasus; it connects the folded structures of the Greater Caucasus with the folded structures of the Kopetdag. The South Caspian is characterized by a suboceanic-type crustal structure, and the granite layer is absent here. Beneath the sedimentary layer, which is up to 25 km thick (this indicates, obviously, the great age of the South Caspian basin), lies a basalt layer up to 15 km thick.

Until the upper Miocene, the Caspian Sea basin was closely connected with the Black Sea in its geological history. After the upper Miocene folding, this link was broken, and the Caspian became a landlocked body of water. The connection with the ocean was reestablished during the upper Pliocene, in the Ak-chagyl age. During Anthropogenic times, owing to the alternation of glacial and postglacial ages on the East European Plain, the Caspian Sea repeatedly underwent transgressions (Baku, Khazar, and Khvalyn) and regressions. Traces of the transgressions and regressions have survived in the form of terrraces on the seashore as well as in the stratigraphy of the ancient Caspian deposits.

On the shelf there are terrigenous shell sands, coquina, and oolitic sands. The deepwater sections of the floor are covered by aleurite and silt sediments with a high content of calcium carbonate. In certain sections of the floor, bedrock of Neocene age has been exposed. The floor of the Caspian Sea has rich deposits of oil and gas. The Apsheron Bank is oil- and gas-bearing, as are the Dagestan and Turkmen regions of the sea. The areas of the sea floor adjacent to Mangyshlak and the Mangyshlak Bank are promising for oil and gas. The gulf of Kara-Bogaz-Gol contains the richest deposits of chemical raw materials (in particular, mirabilite).

CLIMATE. The chief baric centers that determine atmospheric circulation in the Caspian Sea region are the spur of the Asiatic high-pressure center in the winter and the spurs of the azores high-pressure and the South Asian low-pressure centers in the summer. The characteristic climatic features are considerable continentality, predominance of anti-cyclonic weather conditions, dry winds, severe frosty winters (particularly in the northern part), sharp temperature fluctuations during the year, and little precipitation (excluding the southwestern part of the sea). Cyclonic activity develops on the atmospheric fronts and is also an important element in the climate and weather on the Caspian. in the northern and middle parts of the Caspian Sea, easterly winds prevail from October through April, and northwesterly winds prevail from May through September. in the southern part of the sea, the monsoon character of the winds is most sharply expressed. The strongest winds are found near the Apsheron Peninsula (the Baku northerly, which blows primarily in the autumn), the eastern shore of the middle section, and the northwestern part of the northern section. Here there are frequent storms during which the wind velocity reaches more than 24 m per sec.

The mean air temperature over many years during the warm months (July and August) over the entire sea is 24°-26°C, with an absolute maximum (up to 44°C) on the eastern coast. During the winter months temperatures range from — 10°C in the north to 12°C in the south. Over the sea average annual precipitation is 200 mm, with up to 400 mm on the western coast, 90-100 mm on the arid eastern coast, and up to 1, 700 mm on the subtropical southwestern coast. Evaporation from the greater part of the sea surface is very high, reaching 1,000 mm a year; in the eastern part of the South Caspian and near the Apsheron Peninsula it is up to 1, 400 mm a year.

HYDROLOGICAL REGIME. A cyclonic circulation of water prevails in the Caspian Sea, and it is caused chiefly by the inflow of rivers and the prevailing winds. Masses of water move from north to south along the western coast toward the Apsheron Peninsula, where the current splits. One branch continues along the western coast; the other branch crosses the Caspian near the Apsheron Bank, and off the eastern coast it joins the waters moving north along that coast from the South Caspian. The circulation in the South Caspian is also cyclonic but is less clearly expressed, and between Baku and the mouth of the Kura River it is complicated by a local anticyclonic circulation. In the North Caspian unstable wind-driven currents of different directions prevail. Their speed is usually 10–15 cm per sec, and during strong winds that coincide with the direction of the currents, the speed can reach 30–40 and even 100 cm per sec. Owing to the frequent occurrence of moderate and strong winds, there is a large number of days with heavy seas. The maximum observed wave height is 11 m near the Apsheron Bank.

During the summer, average water temperature on the surface is 24°-26°C; it is up to 29°C in the south and up to 32°C in Krasnovodsk Gulf. Along the eastern shores the temperature sometimes drops to 10°-12°C in July and August. This phenomenon is due to the driving influence of the winds and the upwelling of deep water. In winter significant temperature contrasts are observed. In the north there are negative temperatures (down to —0.5°C), in the Middle Caspian the temperature is 3°-7°C, and in the South Caspian it is 8°-10°C. The northern part of the sea usually freezes for two or three months, with ice thickness reaching 2 m. In the Middle Caspian individual shallow bays freeze during severe winters. The ice is frequently broken up by the wind and then drifts from the North Caspian south along the western shore. In some years floating ice reaches the Apsheron Peninsula region and is capable of causing significant damage to hydraulic engineering structures in the sea.

The average salinity of the water is 12.7–12.8 %o (parts per thousand), with a maximum (excluding Kara-Bogaz-Gol) of up to 13.2 along the eastern shores and a minimum of 1–2 %o in the northwest. Salinity fluctuations over the area of the sea, on the vertical, and in time are insignificant, and only in the north are they more noticeable due to fluctuations in the Volga’s drainage. The composition of the salts differs from ordinary sea salt by a greater content of sulfates, calcium carbonate, and magnesium carbonate and by a lower chloride content. This is caused by the influence of the inflow of rivers.

A vertical mixing of the water in the winter takes place throughout the entire vertical section in the North Caspian and a layer of 200–300 m in the deepwater regions; in the summer and autumn the mixing is limited to an upper layer of 15–30 m. During these seasons an intensive thermocline is formed (several degrees per meter) on the lower edge of the upper well-warmed and mixed layer (15–30 m), and this obstructs the spread of heat into the deep layers of the sea.

FLUCTUATIONS IN LEVEL. Brief nonperiodic fluctuations in the level of the Caspian Sea are caused by the winds, and in the north the winds can cause a temporary rise in the level by 2.5–2 m or a drop of up to 2 m. Seiches are observed with a period of from 10 minutes to 12 hours and an amplitude of up to 0.7 M. Small seasonal fluctuations in the level also occur (about 30 cm).

Over the years and centuries, the level of the Caspian Sea has undergone significant fluctuations which have been caused primarily by changes in the sea’s water balance. According to geological, archaeological, historical, and geomorphological data, it has been established that the Caspian Sea had a high level (up to 22 m below sea level) about 4, 000 to 6, 000 years ago, at the start of the Common Era, and at the beginning of the 19th century (the Neocaspian transgression). It is also known that there was a low level from the seventh through the 11th centuries a.d. (possibly 2–4 m below the present one). The last major drop in the level occurred between 1929 (when the level was at about —26 m) and 1956–57. At present the level fluctuates around the —28.5 m level by not more than several centimeters. The reasons for the latest drop in the level, aside from climatic changes that caused a reduction in the river inflow to the Caspian Sea and an increase in evaporation from its surface, were the hydraulic engineering construction on the Volga (the creation of large man-made reservoirs) and the use of river water for irrigating arid lands and for industrial needs. Another negative factor in the water balance is the flow of Caspian Sea water into Kara-Bogaz-Gol, which is 4 m lower than the Caspian. As a whole, the components of the water balance in 1970 were as follows. The input consisted of 66.8 cu km of precipitation, 266.4 cu km of river inflow, and 5 cu km of subterranean water. The consumption consisted of 357.3 cu km in evaporation, 4 cu km of flow into Kara-Bogaz-Gol, and 1 cu km of seawater used by man. Since the consumption exceeds the input, the water level has dropped by an average of 7 cm a year (over the 1966–67 period). A number of measures have been worked out for preventing a further drop in the sea level. (The level could decline another 2 m by the year 2000.) There are plans to divert the water of northern rivers such as the Vychegda and Pechora into the Volga Basin, which would give the Volga and the Caspian Sea about 32 cu km of water a year more. A plan has also been worked out (1972) for regulating the flow of Caspian waters into Kara-Bogaz-Gol.

FLORA AND FAUNA. The Caspian Sea is poor in terms of the species composition of the flora and fauna, but the biomass is large. The Caspian is inhabited by more than 500 plant and 854 fish and animal species, which are diverse in their origin. Among the plants in the Caspian the blue-green algae and diatoms (for example, Rhizosolenia) predominate. Among the recent arrivals are many red and brown algae. Zostera and Ruppia are the most widely distributed of the flowering marine plants. The algae Charophyta have the greatest biomass (up to 30 kg per sq m of bottom). Most of the fauna originated in Neocene times, and it has undergone great changes owing to the frequent and considerable fluctuations in salinity. This group includes sturgeons, herring, sprats, gobies, and “pugolovka” (Benthophilus) of the fish, zebra mussels and cockles of the mollusks, and gammarids, poly-chaetes, sponges, and one species of jellyfish from the other invertebrates. The Caspian is also inhabited by 15 species that migrated from the arctic and Mediterranean basins. An important group is made up of freshwater organisms (the pike perch of the fish). As a whole, a high degree of endemism is typical. Some organisms have settled in the Caspian quite recently either as a result of being carried in on the bottoms of seagoing vessels (chiefly various growths, for example, mytilaster, the Rhizosolenia algae, and barnacles and crabs) or of deliberate acclimatization by man (for example, the gray mullet of the fish and Nereis and Syndesmya of the invertebrates).

History of exploration. Documentary evidence concerning the acquaintance of Russians with the Caspian Sea and their voyages across it dates to the ninth and tenth centuries (ancient Arabic, Armenian, and Iranian manuscripts). Regular exploration of the Caspian Sea was begun by Peter I, upon whose initiative an expedition under the leadership of A. Bekovich-Cherkasskii was organized in 1714–15. In particular, Bekovich-Cherkasskii studied the eastern coast of the Caspian. In the 1720’s, I. F. Soimo-nov began to conduct hydrographic research in the Caspian, and, during the second half of the 18th century, this research was continued by I. V. Tokmachev and M. I. Voinovich. At the beginning of the 19th century further research was carried out by Kolodkin, who was the first to make an instrumental compass survey of the shores. In the middle of the 19th century a detailed hydrographic instrumental survey of the Caspian Sea was made under the leadership of N. A. Ivashintsev. The maps made as a result of these surveys served as the basis for the subsequent publications of maritime charts for the Caspian up to the 1930’s.

In the 19th century major contributions to studying the natural conditions of the Caspian Sea were made by the scientists P. S. Pallas, S. G. Gmelin, G. S. Karelin, K. M. Baer, G. V. Abich, O. A. Grim, N. I. Andrusov, and I. B. Shpindler. In 1897 the Astrakhan Scientific Research Station (presently the Institute of Caspian Fisheries) was founded. In 1866, 1904, 1912–13, and 1914–15 expeditionary research on the hydrology and hydrobiology of the Caspian was carried out under the leadership of N. M. Knipovich. This work was continued after 1917 by the Caspian Expedition of the Academy of Sciences of the USSR, which was also led by Knipovich.

In the first decade after the October Revolution, the research of the Soviet geologists I. M. Gubkin, D. V. Golubiatnikov, V. D. Golubiatnikov, P. A. Pravoslavlev, V. P. Baturin, and S. A. Kovalevskii played an important role in the study of the geological structure of and presence of oil on the Apsheron Peninsula as well as the geological history of the Caspian Sea. At this time, B. A. Appolov, V. V. Valedinskii, K. P. Vos-kresenskii, and L. S. Berg made significant contributions to studying the water balance of and the fluctuations in the level oi* the Caspian.

After the Great Patriotic War of 1941–45 comprehensive systematic research was started on the Caspian Sea. It aimed at studying the hydrometeorological regime, biological conditions, and the geological structure of the sea. Among the institutions taking part in this research are Moscow State University, the Institute of Geography of the Academy of Sciences of the Azerbaijan SSR, the State Institute of Oceanography, the observatories of the Hydrometeorological Service, the Institute for Geology and Exploitation of Combustible Minerals (IGIRGI) of the Academy of Sciences of the USSR, the Institute of Geophysics of the Academy of Sciences of the USSR, the Aeromethods Laboratory and the All-Union Geophysics Scientific Research Institute of the Ministry of Geology of the USSR, the Caspian Institute for Sturgeon Fisheries, and other scientific institutions of the republic academies of sciences and ministries.

Economic and geographic survey. The Caspian Sea has long been famous as a region where valuable types of fish can be caught—in particular sturgeons (82 percent of the world catch) and herring, as well as freshwater fish (bream, pike perch, Caspian roach, and wild carp). As a result of the drop in the sea level (which has led to the disappearance of valuable spawning grounds) and the controlling of the flow of the Volga, Kura, and Araks rivers (which has worsened conditions for the breeding of diadromous and semidiadromous fish), the quantity and the catch primarily of the valuable types of fish (herring and sturgeons) have sharply declined. In 1936 the gross catch was about 500, 000 tons, and in 1956 it was 461,000 tons (21, 500 and 15, 000 tons of sturgeons, 197, 000 and 18, 000 for the roach, and 55, 000 and 8, 400 for the pike perch, respectively). The comparatively slight decline in the gross catch can be explained by a sharp increase in the catch of less valuable fish, mainly sprats. Owing to the decline in the number of sturgeons, work is being done to breed and replenish the valuable types of fish. In the North Caspian, seals are also hunted.

In 1924 oil began to be produced in Il’ich Bay (near Baku) for the first time, but output increased particularly after the Great Patriotic War of 1941–45. Petroleum is produced offshore from derricks (Neftianye Kamni) and man-made islands. The main regions are Apsheron and Sangachaly Raion on the western coast and Cheleken on the eastern. The offshore oil fields produce more than 50 percent of the total oil produced in the Azerbaijan SSR. The mining of sodium sulfate, mirabilite, and epsomite in the Kara-Bogaz-Gol region is also of great economic significance.

Owing to the ever increasing need for fresh water, units for desalinizing seawater have appeared on the Caspian Sea. The largest of them (for obtaining fresh water for industry and everyday needs in nearby desert and semidesert regions) are being built (1972) in the towns of Shevchenko and Krasnovodsk.

The Caspian Sea is of great importance for transportation, both domestically and in commerce with foreign countries. The main cargoes transported over the Caspian are oil, lumber, grain, cotton, rice, and sulfate. The most important ports are Astrakhan, Baku, Makhachkala, Krasnovodsk, and Shevchenko. They are also connected by regular passenger runs. Sea-rail ferries operate between Baku and Krasnovodsk. A ferry service is also planned (1972) between Makhachkala and Shevchenko. In Iran the main ports are Bandar-e Pahlavi and Bandar-e Shah.


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K. K. GIUL’ and O. K. LEONT’EV

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

Caspian Sea

a salt lake between SE Europe and Asia: the largest inland sea in the world; fed mainly by the River Volga. Area: 394 299 sq. km (152 239 sq. miles)
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005