The Caspian Sea is the most big lake On the Earth. It is called the sea because of its size and bed, which is folded like an ocean basin. The area is 371,000 square meters, the depth is 1025 m. The list of rivers flowing into the Caspian Sea includes 130 names. The largest of them are: Volga, Terek, Samur, Sulak, Ural and others.
Caspian Sea
It took 10 million years before the Caspian was formed. The reason for its formation is that the Sarmatian Sea, which lost its connection with the World Ocean, was divided into two reservoirs, which were called the Black and Caspian Seas. Between the latter and the World Ocean stretch thousands of kilometers of waterless path. It is located at the junction of two continents - Asia and Europe. Its length in the north-south direction is 1200 km, west-east - 195-435 km. The Caspian Sea is an internal drainless basin of Eurasia.
Near the Caspian Sea, the water level is below the level of the World Ocean, and besides, it is subject to fluctuations. According to scientists, this is due to many factors: anthropogenic, geological, climatic. At present, the average water level reaches 28 m.
The network of rivers and sewage is unevenly distributed along the coast. Few rivers flow into the part of the sea from the north side: Volga, Terek, Ural. From the west - Samur, Sulak, Kura. The east coast is characterized by the absence of permanent watercourses. Differences in space in the flow of water that rivers bring to the Caspian Sea is an important geographical feature of this reservoir.
Volga
This river is one of the largest in Europe. In Russia, it ranks sixth in size. Regarding the catchment area, it is second only to the Siberian rivers flowing into the Caspian Sea, such as the Ob, Lena, Yenisei, Irtysh. For the source, from where the Volga originates, the key is taken near the village of Volgoverkhovye, Tver Region, on the Valdai Upland. Now there is a chapel at the source, which attracts the attention of tourists, for whom it is a pride to step over the very beginning of the mighty Volga.
A small fast stream gradually gains strength and becomes a huge river. Its length is 3690 km. The source is 225 m above sea level. Among the rivers flowing into the Caspian Sea, the largest is the Volga. Her path runs through many regions of our country: Tver, Moscow, Nizhny Novgorod, Volgograd and others. The territories through which it flows are Tatarstan, Chuvashia, Kalmykia and Mari El. The Volga is the location of millionaire cities - Nizhny Novgorod, Samara, Kazan, Volgograd.
Volga Delta
The main riverbed is divided into channels. Formed certain form mouth. It's called the delta. Its beginning is the place of separation of the Buzan branch from the bed of the Volga river. The delta is located 46 km north of the city of Astrakhan. It includes channels, branches, small rivers. There are several main branches, but only Akhtuba is navigable. Among all the rivers of Europe, the Volga is distinguished by the largest delta, which is a rich fish region in this basin.
It lies lower than the ocean level, at 28 m. The mouth of the Volga is the location of the southernmost Volga city of Astrakhan, which in the distant past was the capital of the Tatar Khanate. Later, at the beginning of the 18th century (1717), Peter 1 gave the city the status of "the capital of the province of Astrakhan." During his reign, the main attraction of the city, the Assumption Cathedral, was built. Its Kremlin is made of white stone, brought from the capital of the Golden Horde, the city of Saray. The mouth is divided by branches, the largest of which are: Bolda, Bakhtemir, Buzan. Astrakhan is a southern city located on 11 islands. Today it is a city of shipbuilders, sailors and fishermen.
Currently, the Volga needs protection. For this purpose, a reserve has been established at the place where the river flows into the sea. The delta of the Volga, the largest river flowing into the Caspian Sea, abounds in unique flora and fauna: sturgeon, lotuses, pelicans, flamingos and others. Immediately after the revolution of 1917, a law was passed on their protection by the state as part of the Astrakhan Reserve.
Sulak River
It is located in Dagestan, flows through its territory. It feeds on the waters of melted snows that flow down from the mountains, as well as tributaries: Small Sulak, Chvakhun-bak, Akh-su. Water also enters Sulak through a canal from the Aksai and Aktash rivers.
The source is formed by the confluence of two rivers that originate in the basins: Didoyskaya and Tushinskaya. The length of the Sulak River is 144 km. Her pool has enough large area- 15,200 square meters. It flows through the canyon with the same name as the river, then through the Akhetlinsky gorge and finally comes to the plane. Going around the Agrakhan Bay from the south side, Sulak flows into the sea.
The river provides drinking water for Kaspiysk and Makhachkala, it is home to hydroelectric power plants, the urban-type settlements of Sulak and Dubki, and small town Kizilyurt.
Samur
The river got its name not by chance. The name translated from the Caucasian language (one of them) means "middle". Indeed, the border between the states of Russia and Azerbaijan is marked along the waterway along the Samur River.
The sources of the river are glaciers and springs, originating in the spurs of the Caucasus Range from the northeast side, not far from Guton Mountain. The height above sea level is 3200 m. Samur has a length of 213 km. The height in the upper reaches and the mouth differs by three kilometers. The catchment basin has an area of almost five thousand square meters.
The places where the river flows are narrow gorges located between the mountains. high altitude, composed of shale and sandstone, which is why the water here is muddy. The Samur basin has 65 rivers. Their length reaches 10 km or more.
Samur: the valley and its description
The valley of this river in Dagestan is the most densely populated region. Derbent is located near the mouth - ancient city peace. The banks of the Samur River are home to twenty or more species of relict representatives of the flora. Endemic, endangered and rare species listed in the Red Book grow here.
In the river delta, a relict forest is comfortably located, which is the only one in Russia. Liana forest is a fairy tale. Huge trees of the rarest and most common species grow here, intertwined with lianas. The river is rich in valuable species of fish: mullet, pike perch, pike, catfish and others.
Terek
The river got its name from the Karachay-Balkar peoples who lived along its banks. They called it "Terk Suu", which means "rushing water" in translation. Ingush and Chechens called it Lomeki - "mountain water".
The beginning of the river is the territory of Georgia, the Zigla-Khokh glacier - a mountain located on the slope of the Caucasus Range. It is under glaciers all year round. One of them melts when sliding down. A small stream is formed, which is the source of the Terek. It is located at an altitude of 2713 m above sea level. The length of the river flowing into the Caspian Sea is 600 km. At the confluence with the Caspian, the Terek is divided into many branches, as a result of which a vast delta is formed, its area is 4000 square meters. In some places it is very swampy.
The course in this place has changed several times. The old arms have now been turned into canals. The middle of the last century (1957) was marked by the construction of the Kargaly hydroelectric complex. It is used to supply water to the channels.
How is the Terek replenished?
The river has a mixed supply, but for the upper reaches, water from the melting of glaciers plays an important role, they fill the river. In this regard, 70% of the runoff occurs in spring and summer, that is, at this time the water level in the Terek is the highest, and the lowest - in February. The river freezes if the winters are characterized by a harsh climate, but the freeze-up is unstable.
The river is not distinguished by cleanliness and transparency. The turbidity of the water is large: 400-500 g/m 3 . Every year, the Terek and its tributaries pollute the Caspian Sea, pouring into it from 9 to 26 million tons of various suspensions. This is due to the rocks of which the shores are composed, and they are clayey.
Terek mouth
The Sunzha is the largest tributary flowing into the Terek, the lower reaches of which are measured precisely from this river. By this time, the Terek flows for a long time over the flat terrain, leaving the mountains located behind the Elkhot Gates. The bottom here is composed of sand and pebbles, the current slows down, and in some places stops altogether.
The mouth of the Terek River has an unusual appearance: the channel here is elevated above the valley, along appearance resembles a canal, which is fenced with an embankment of great height. The water level rises above the land level. This phenomenon is due to a natural cause. Since the Terek is a stormy river, it brings sand and stones from the Caucasian ridge to in large numbers. Given that the current in the lower reaches is weak, some of them settle here and do not reach the sea. For the inhabitants of the area, sediments are both a threat and a boon. When they are washed away by water, floods of great destructive power occur, this is very bad. But in the absence of floods, the soils become fertile.
Ural river
In ancient times (until the second half of the 18th century), the river was called Yaik. It was renamed into the Russian style by the decree of Catherine II in 1775. Just at this time, the Peasant War was suppressed, the leader of which was Pugachev. The name is still preserved in the Bashkir language, and in Kazakhstan it is official. The Urals are the third longest in Europe, only the Volga and the Danube are larger than this river.
The Ural originates in Russia, on the slope of the Kruglyaya Sopka of the Uraltau Ridge. The source is a spring gushing out of the ground at an altitude of 637 m above sea level. At the beginning of its journey, the river flows in a north-south direction, but after the plateau encountered on the way, it makes sharp turn and continues to flow in a northwesterly direction. However, beyond Orenburg, its direction again changes to the southwestern, which is considered the main one. Having overcome the winding path, the Ural flows into the Caspian Sea. The length of the river is 2428 km. The mouth is divided into branches and tends to shallow.
The Ural is a river along which the natural water boundary between Europe and Asia passes, with the exception of the upper reaches. This is an inland European river, but its upper reaches east of Ural Range are the territory of Asia.
Importance of the Caspian rivers
The rivers flowing into the Caspian Sea are of great importance. Their waters are used for human and animal consumption, domestic needs, agricultural and industrial needs. Hydroelectric power plants are being built on the rivers, the energy of which is in demand by man for various purposes. River basins are full of fish, algae, shellfish. Even in ancient times, people chose river valleys for future settlements. And now cities and towns are being built on their banks. Rivers ply passenger and transport ships, performing important tasks for the transport of passengers and goods.
Caspian Sea- the largest lake on Earth, located at the junction of Europe and Asia, called the sea because of its size. Caspian Sea represents drainless lake, and the water in it is salty, from 0.05% near the mouth of the Volga to from 11-13% in the southeast.
The water level is subject to fluctuations, at present - about 28 m below the level of the World Ocean.
Square Caspian Sea currently - approximately 371,000 sq. km, maximum depth - 1025 m.
coastline length Caspian Sea estimated at about 6500 - 6700 kilometers, with the islands - up to 7000 kilometers. coast Caspian Sea in most of its territory - low-lying and smooth. In the northern part, the coastline is indented by water channels and islands of the Volga and Ural deltas, the shores are low and swampy, and the water surface is covered with thickets in many places. The east coast is dominated by limestone shores adjacent to semi-deserts and deserts. The most winding coasts are on the west coast in the area of the Apsheron Peninsula and on the east coast in the area of the Kazakh Gulf and Kara-Bogaz-Gol.
V Caspian Sea 130 rivers flow into it, of which 9 rivers have a mouth in the form of a delta. Large rivers flowing into the Caspian Sea are the Volga, Terek (Russia), Ural, Emba (Kazakhstan), Kura (Azerbaijan), Samur (Russian border with Azerbaijan), Atrek (Turkmenistan) and others.
Map of the Caspian Sea
The Caspian Sea washes the shores of five coastal states:
Russia (Dagestan, Kalmykia and Astrakhan region) - in the west and northwest, the length of the coastline is 695 kilometers
Kazakhstan - in the north, northeast and east, the length of the coastline is 2320 kilometers
Turkmenistan - in the southeast, the length of the coastline is 1200 kilometers
Iran - in the south, the length of the coastline - 724 kilometers
Azerbaijan - in the southwest, the length of the coastline is 955 kilometers
Water temperature
is subject to significant latitudinal changes, most pronounced in winter, when the temperature varies from 0 - 0.5 °C at the ice edge in the north of the sea to 10 - 11 °C in the south, that is, the water temperature difference is about 10 °C. For shallow water areas with depths less than 25 m, the annual amplitude can reach 25 - 26 °C. On average, the water temperature near the western coast is 1 - 2 °C higher than that of the eastern coast, and in the open sea the water temperature is 2 - 4 °C higher than near the coasts.
Climate of the Caspian Sea- continental in the northern part, temperate in the middle part and subtropical in the southern part. In winter, the average monthly temperature of the Caspian varies from -8 -10 in the northern part to +8 - +10 in the southern part, in summer - from +24 - +25 in the northern part to +26 - +27 in the southern part. The maximum temperature recorded on the east coast is 44 degrees.
Animal world
The fauna of the Caspian is represented by 1809 species, of which 415 are vertebrates. V Caspian Sea 101 species of fish have been registered, and most of the world's sturgeon stocks are concentrated in it, as well as such freshwater fish as roach, carp, pike perch. Caspian Sea- habitat for fish such as carp, mullet, sprat, kutum, bream, salmon, perch, pike. V Caspian Sea also inhabited by a marine mammal - the Caspian seal.
Vegetable world
Vegetable world Caspian Sea and its coast is represented by 728 species. From plants to Caspian Sea algae predominate - blue-green, diatoms, red, brown, char and others, from flowering ones - zoster and ruppia. By origin, the flora belongs mainly to the Neogene age, however, some plants were brought into Caspian Sea by a person consciously or on the bottoms of ships.
Oil and gas
V Caspian Sea many oil and gas fields are being developed. Proven oil resources in Caspian Sea are about 10 billion tons, the total resources of oil and gas condensate are estimated at 18 - 20 billion tons.
Oil production in Caspian Sea began in 1820, when the first oil well was drilled on the Absheron shelf. In the second half of the 19th century, oil production began on an industrial scale on the Absheron Peninsula, and then on other territories.
In addition to oil and gas production, on the coast Caspian Sea and the Caspian shelf, salt, limestone, stone, sand, and clay are also being mined.
Ecological problems
Ecological problems Caspian Sea associated with water pollution as a result of oil production and transportation on the continental shelf, the flow of pollutants from the Volga and other rivers flowing into Caspian Sea, the vital activity of coastal cities, as well as the flooding of individual facilities due to an increase in the level Caspian Sea. Predatory harvesting of sturgeons and their caviar, rampant poaching lead to a decrease in the number of sturgeons and forced restrictions on their production and export.
, Kazakhstan, Turkmenistan, Iran , Azerbaijan
Geographical position
Caspian Sea - view from space.
The Caspian Sea is located at the junction of two parts of the Eurasian continent - Europe and Asia. The length of the Caspian Sea from north to south is approximately 1200 kilometers (36°34 "-47°13" N), from west to east - from 195 to 435 kilometers, on average 310-320 kilometers (46°-56° v. d.).
The Caspian Sea is conditionally divided according to physical and geographical conditions into 3 parts - the North Caspian, the Middle Caspian and the South Caspian. The conditional border between the North and Middle Caspian runs along the line of about. Chechnya - Cape Tyub-Karagansky, between the Middle and South Caspian - along the line of about. Residential - Cape Gan-Gulu. The area of the Northern, Middle and Southern Caspian is 25, 36, 39 percent respectively.
Coast of the Caspian Sea
Coast of the Caspian Sea in Turkmenistan
The territory adjacent to the Caspian Sea is called the Caspian Sea.
Peninsulas of the Caspian Sea
- Ashur-Ada
- Garasu
- Zyanbil
- Hara Zira
- Sengi-Mugan
- Chygyl
Bays of the Caspian Sea
- Russia (Dagestan, Kalmykia and Astrakhan region) - in the west and north-west, the length of the coastline is about 1930 kilometers
- Kazakhstan - in the north, northeast and east, the length of the coastline is about 2320 kilometers
- Turkmenistan - in the southeast, the length of the coastline is about 650 kilometers
- Iran - in the south, the length of the coastline is about 1000 kilometers
- Azerbaijan - in the southwest, the length of the coastline is about 800 kilometers
Cities on the coast of the Caspian Sea
On the Russian coast there are cities - Lagan, Makhachkala, Kaspiysk, Izberbash and the southernmost city of Russia Derbent. Astrakhan is also considered a port city of the Caspian Sea, which, however, is not located on the shores of the Caspian Sea, but in the Volga Delta, 60 kilometers from north coast Caspian Sea.
Physiography
Area, depth, volume of water
The area and volume of water in the Caspian Sea varies significantly depending on fluctuations in water levels. At a water level of -26.75 m, the area is approximately 371,000 square kilometers, the volume of water is 78,648 cubic kilometers, which is approximately 44% of the world's lake water reserves. The maximum depth of the Caspian Sea is in the South Caspian depression, 1025 meters from its surface level. In terms of maximum depth, the Caspian Sea is second only to Baikal (1620 m) and Tanganyika (1435 m). Average depth The Caspian Sea, calculated from the bathygraphic curve, is 208 meters. At the same time, the northern part of the Caspian Sea is shallow, its maximum depth does not exceed 25 meters, and the average depth is 4 meters.
Water level fluctuations
Vegetable world
The flora of the Caspian Sea and its coast is represented by 728 species. Of the plants in the Caspian Sea, algae predominate - blue-green, diatoms, red, brown, char and others, of flowering - zoster and ruppia. By origin, the flora belongs mainly to the Neogene age, however, some plants were brought into the Caspian Sea by man either consciously or on the bottoms of ships.
History of the Caspian Sea
Origin of the Caspian Sea
Anthropological and cultural history of the Caspian Sea
Finds in the Khuto cave near the southern coast of the Caspian Sea indicate that a person lived in these parts about 75 thousand years ago. The first mention of the Caspian Sea and the tribes living on its coast are found in Herodotus. Approximately in the V-II centuries. BC e. Saka tribes lived on the coast of the Caspian Sea. Later, during the period of the settlement of the Turks, in the period of the 4th-5th centuries. n. e. Talysh tribes (Talysh) lived here. According to ancient Armenian and Iranian manuscripts, the Russians sailed the Caspian Sea from the 9th-10th centuries.
Exploration of the Caspian Sea
The exploration of the Caspian Sea was started by Peter the Great, when, on his orders, an expedition was organized in 1714-1715 under the leadership of A. Bekovich-Cherkassky. In the 1720s, hydrographic studies were continued by the expedition of Karl von Werden and F.I. Soymonov, later by I.V. Tokmachev, M.I. Voinovich and other researchers. At the beginning of the 19th century, instrumental surveying of the banks was carried out by I.F. Kolodkin, in the middle of the 19th century. - instrumental geographic survey under the guidance of N. A. Ivashintsev. Since 1866, for more than 50 years, expeditionary research on the hydrology and hydrobiology of the Caspian Sea has been carried out under the leadership of N. M. Knipovich. In 1897, the Astrakhan Research Station was founded. In the first decades of Soviet power in the Caspian Sea, geological research by I. M. Gubkin and other Soviet geologists was actively carried out, mainly aimed at finding oil, as well as research on the study of the water balance and fluctuations in the level of the Caspian Sea.
Economy of the Caspian Sea
Oil and gas
Many oil and gas fields are being developed in the Caspian Sea. The proven oil resources in the Caspian Sea are about 10 billion tons, the total resources of oil and gas condensate are estimated at 18-20 billion tons.
Oil production in the Caspian Sea began in 1820, when the first oil well was drilled on the Absheron shelf near Baku. In the second half of the 19th century, oil production began on an industrial scale on the Absheron Peninsula, and then on other territories.
Shipping
Shipping is developed in the Caspian Sea. On the Caspian Sea ferry crossings, in particular, Baku - Turkmenbashi, Baku - Aktau, Makhachkala - Aktau. The Caspian Sea has a navigable connection with the Sea of Azov through the Volga and Don rivers and the Volga-Don Canal.
Fishing and seafood
Fishing (sturgeon, bream, carp, pike perch, sprat), caviar, and seal fishing. More than 90 percent of the world's sturgeon catch is carried out in the Caspian Sea. In addition to industrial production, illegal production of sturgeon and their caviar flourishes in the Caspian Sea.
Recreational resources
The natural environment of the Caspian coast with sandy beaches, mineral waters and therapeutic mud in the coastal zone creates good conditions for relaxation and treatment. At the same time, in terms of the degree of development of resorts and the tourism industry, the Caspian coast noticeably loses to the Black Sea coast of the Caucasus. At the same time, in recent years, the tourism industry has been actively developing on the coast of Azerbaijan, Iran, Turkmenistan and Russian Dagestan. Azerbaijan is actively developing resort area in the Baku region. At the moment, a world-class resort has been created in Amburan, another modern tourist complex is being built in the area of the village of Nardaran, recreation in the sanatoriums of the villages of Bilgah and Zagulba is very popular. A resort area is also being developed in Nabran, in the north of Azerbaijan. but high prices, in general, the low level of service and the lack of advertising lead to the fact that there are almost no foreign tourists in the Caspian resorts. The development of the tourism industry in Turkmenistan is hampered by a long policy of isolation, in Iran - by Sharia law, due to which the mass vacation of foreign tourists on the Caspian coast of Iran is impossible.
Ecological problems
The environmental problems of the Caspian Sea are associated with water pollution as a result of oil production and transportation on the continental shelf, the flow of pollutants from the Volga and other rivers flowing into the Caspian Sea, the vital activity of coastal cities, as well as the flooding of individual objects due to the rise in the level of the Caspian Sea. Predatory harvesting of sturgeons and their caviar, rampant poaching lead to a decrease in the number of sturgeons and forced restrictions on their production and export.
International status of the Caspian Sea
Legal status of the Caspian Sea
After the collapse of the USSR, the division of the Caspian Sea has long been and still remains the subject of unsettled disagreements related to the division of the resources of the Caspian shelf - oil and gas, as well as biological resources. For a long time there were negotiations between the Caspian states on the status of the Caspian Sea - Azerbaijan, Kazakhstan and Turkmenistan insisted on dividing the Caspian along the median line, Iran - on dividing the Caspian along one fifth between all the Caspian states.
With regard to the Caspian Sea, the key physical and geographical circumstance is that it is a closed inland water body that does not have a natural connection with the World Ocean. Accordingly, the norms and concepts of international maritime law, in particular, the provisions of the UN Convention on the Law of the Sea of 1982, should not automatically apply to the Caspian Sea. Based on this, it would be unlawful to apply such concepts as “territorial sea”, “exclusive economic zone”, “continental shelf”, etc.
The current legal regime of the Caspian Sea was established by the Soviet-Iranian treaties of 1921 and 1940. These treaties provide for freedom of navigation throughout the sea, freedom of fishing, with the exception of ten-mile national fishing zones, and a ban on navigation in its waters of ships flying the flag of non-Caspian states.
Negotiations on the legal status of the Caspian are currently ongoing.
Delimitation of sections of the bottom of the Caspian Sea for the purpose of subsoil use
The Russian Federation concluded an agreement with Kazakhstan on the delimitation of the bottom of the northern part of the Caspian Sea in order to exercise sovereign rights to subsoil use (dated July 6, 1998 and the Protocol dated May 13, 2002), an agreement with Azerbaijan on the delimitation of adjacent sections of the bottom of the northern part of the Caspian Sea (dated September 23, 2002), as well as the trilateral Russian-Azerbaijani-Kazakhstan agreement on the junction of the demarcation lines of adjacent sections of the Caspian Sea bottom (dated May 14, 2003), which established geographical coordinates dividing lines delimiting seabed areas within which the parties exercise their sovereign rights in the field of exploration and extraction of mineral resources.
CASPIAN SEA (Caspian), the largest the globe closed body of water, endorheic brackish lake. Located on the southern border of Asia and Europe, it washes the shores of Russia, Kazakhstan, Turkmenistan, Iran and Azerbaijan. Due to the size, peculiarity of natural conditions and the complexity of hydrological processes, the Caspian Sea is usually referred to the class of closed inland seas.
The Caspian Sea is located in a vast area of internal flow and occupies a deep tectonic depression. The water level in the sea is at around 27 m below the level of the World Ocean, the area is about 390 thousand km 2, the volume is about 78 thousand km 3. The greatest depth is 1025 m. With a width of 200 to 400 km, the sea is elongated along the meridian for 1030 km.
The largest bays: in the east - Mangyshlak, Kara-Bogaz-Gol, Turkmenbashi (Krasnovodsk), Turkmen; in the west - Kizlyar, Agrakhan, Kyzylagadzh, Baku Bay; in the south - shallow lagoons. There are many islands in the Caspian Sea, but almost all of them are small, with a total area of less than 2 thousand km 2. In the northern part, there are numerous small islands adjacent to the Volga delta; larger ones - Kulaly, Morskoy, Tyuleniy, Chechen. Off the western shores - the Apsheron archipelago, to the south lie the islands of the Baku archipelago, near east coast- narrow, elongated from north to south island Ogurchinsky.
The northern shores of the Caspian Sea are low-lying and very sloping, characterized by a wide development of droughts formed as a result of surge phenomena; deltaic shores are also developed here (the deltas of the Volga, the Urals, and the Terek) with an abundant supply of terrigenous material; the Volga delta stands out with extensive reed beds. The western shores are abrasion, to the south of the Absheron Peninsula, mostly accumulative deltaic type with numerous bays and spits. southern shores base. The eastern shores are mostly deserted and low-lying, composed of sands.
Relief and geological structure of the bottom.
The Caspian Sea is located in a zone of increased seismic activity. In the city of Krasnovodsk (now Turkmenbashi) in 1895 there was a strong earthquake measuring 8.2 on the Richter scale. Eruptions of mud volcanoes are often observed on the islands and the coast of the southern part of the sea, leading to the formation of new shoals, banks and small islands, which are washed away by waves and reappear.
According to the peculiarities of physical and geographical conditions and the nature of the bottom topography in the Caspian Sea, it is customary to distinguish the Northern, Middle and Southern Caspian. The Northern Caspian is characterized by exceptional shallow water, located completely within the shelf with average depths of 4-5 m. Even small changes in the level here at low coasts lead to significant fluctuations in the area of the water table, so the boundaries of the sea in the northeastern part on small-scale maps are shown by a dotted line. The greatest depths (about 20 m) are observed only near the conditional border with the Middle Caspian, which is drawn along the line connecting Chechen Island (to the north of the Agrakhan Peninsula) with Cape Tyub-Karagan on the Mangyshlak Peninsula. In the relief of the bottom of the Middle Caspian, the Derbent depression stands out (the greatest depth is 788 m). The boundary between the Middle and South Caspian passes over the Apsheron threshold with depths up to 180 m along the line from Chilov Island (to the east of the Absheron Peninsula) to Cape Kuuli (Turkmenistan). The basin of the South Caspian is the most extensive area of the sea with the greatest depths, almost 2/3 of the waters of the Caspian Sea are concentrated here, 1/3 falls on the Middle Caspian, in the North Caspian, due to shallow depths, there is less than 1% of the Caspian waters. In general, the shelf areas (the entire northern part and a wide strip along the eastern coast of the sea) predominate in the bottom relief of the Caspian Sea. The continental slope is most pronounced on the western slope of the Derbent Basin and almost along the entire perimeter of the South Caspian Basin. On the shelf, terrigenous-shell sands, shells, and oolitic sands are common; deep-water areas of the bottom are covered with silty and silty sediments with a high content of calcium carbonate. In some areas of the bottom, Neogene bedrocks are exposed. Mirabilite accumulates in the Ka-ra-Bogaz-Gol Bay.
In tectonic terms, within the Northern Caspian, the southern part of the Caspian syneclise of the East European platform is distinguished, which is framed in the south by the Astrakhan-Aktobe zone, composed of Devonian-Lower Permian carbonate rocks, lying on a volcanic base and containing large deposits of oil and natural combustible gas. Paleozoic folded formations of the Donets-Caspian zone (or the Karpinsky ridge) are pushed onto the syneclise from the southwest, which is a protrusion of the basement of the young Scythian (in the west) and Turan (in the east) platforms, which are separated at the bottom of the Caspian Sea by the Agrakhan-Guryev fault (left shift) of northeast strike. The Middle Caspian mainly belongs to the Turan platform, and its southwestern margin (including the Derbent depression) is a continuation of the Terek-Caspian foredeep of the Greater Caucasus fold system. The sedimentary cover of the platform and trough, composed of Jurassic and younger sediments, contains oil and combustible gas deposits in local uplifts. The Apsheron Sill, which separates the Middle Caspian from the South, is a connecting link of the Cenozoic folded systems of the Greater Caucasus and the Kopetdag. The South Caspian Basin of the Caspian Sea with crust of oceanic or transitional type is filled with a thick (over 25 km) complex of Cenozoic sediments. Numerous large hydrocarbon deposits are concentrated in the South Caspian Basin.
Until the end of the Miocene, the Caspian Sea was a marginal sea of the ancient Tethys Ocean (since the Oligocene, the relic oceanic basin of the Paratethys). By the beginning of the Pliocene, it lost contact with the Black Sea. The Northern and Middle Caspians were drained, and the paleo-Volga valley stretched through them, the delta of which was located in the area of the Apsheron Peninsula. Delta sediments have become the main reservoir of oil and natural combustible gas deposits in Azerbaijan and Turkmenistan. In the late Pliocene, due to the Akchagyl transgression, the area of the Caspian Sea greatly increased and the connection with the World Ocean temporarily resumed. The waters of the sea covered not only the bottom of the modern depression of the Caspian Sea, but also the adjacent territories. In the Quaternary, transgressions (Absheron, Baku, Khazar, Khvalyn) alternated with regressions. The southern half of the Caspian Sea is located in a zone of increased seismic activity.
Climate. The Caspian Sea, strongly elongated from north to south, is located within several climatic zones. In the northern part the climate is temperate continental, on the western coast - temperate warm, southwestern and south coast lie within the subtropics, on the east coast dominated by a desert climate. V winter time over the North and Middle Caspian, the weather is formed under the influence of the Arctic continental and sea air, and the South Caspian is often under the influence of southern cyclones. The weather in the west is unstable rainy, in the east it is dry. In summer, the western and northwestern regions are influenced by the spurs of the Azores atmospheric maximum, and the southeastern regions are influenced by the Iran-Afghan minimum, which together creates dry, stable warm weather. Winds from the north and northwest (up to 40%) and southeast (about 35%) directions prevail over the sea. The average wind speed is about 6 m/s, in the central regions of the sea up to 7 m/s, in the area of the Apsheron Peninsula - 8-9 m/s. Northern storm "Baku Nords" reach speeds of 20-25 m/s. The lowest average monthly air temperatures of -10 °С are observed in January - February in the northeastern regions (in the most severe winters they reach -30 °С), in southern regions 8-12 °C. In July - August, the average monthly temperatures over the entire sea area are 25-26 °С, with a maximum of up to 44 °С on the east coast. The distribution of atmospheric precipitation is very uneven - from 100 mm per year on the eastern shores to 1700 mm in Lankaran. In the open sea, on average, about 200 mm of precipitation falls annually.
hydrological regime. Changes in the water balance of an enclosed sea strongly affect the change in the volume of water and the corresponding level fluctuations. Average long-term components of the water balance of the Caspian Sea for the 1900-90s (km 3 / cm layer): river runoff 300/77, precipitation 77/20, underground runoff 4/1, evaporation 377/97, runoff in Kara-Bogaz- Goal 13/3, which forms a negative water balance of 9 km 3 or 3 cm layer per year. According to paleogeographic data, over the past 2000 years, the range of fluctuations in the level of the Caspian Sea has reached at least 7 m. -29 m (the lowest position in the last 500 years). The sea surface area has decreased by more than 40 thousand km 2, which exceeds the area Sea of Azov. Since 1978, a rapid rise in level began, and by 1996 a mark of about -27 m relative to the level of the World Ocean was reached. In the modern era, fluctuations in the level of the Caspian Sea are determined mainly by fluctuations in climatic characteristics. Seasonal fluctuations in the level of the Caspian Sea are associated with the uneven flow of river flow (primarily the flow of the Volga), so the lowest level is observed in winter, the highest in summer. Short-term sharp level changes are associated with surge phenomena, they are most pronounced in shallow northern regions and can reach 3-4 m during storm surges. Such surges cause flooding of significant coastal land areas. In the Middle and Southern Caspian, surge fluctuations in the level are on average 10-30 cm, under storm conditions - up to 1.5 m. The frequency of surges, depending on the area, is from one to 5 times a month, the duration is up to one day. In the Caspian, as in any closed reservoir, seiche level fluctuations are observed in the form of standing waves with periods of 4-9 hours (wind) and 12 hours (tidal). The magnitude of seiche fluctuations usually does not exceed 20–30 cm.
River flow in the Caspian Sea is distributed extremely unevenly. More than 130 rivers flow into the sea, which, on average, bring about 290 km 3 of fresh water per year. Up to 85% of the river flow falls on the Volga with the Urals and enters the shallow Northern Caspian. The rivers of the western coast - Kura, Samur, Sulak, Terek, etc. - give up to 10% of the runoff. Another approximately 5% of fresh water is brought to the South Caspian by the rivers of the Iranian coast. The eastern desert shores are completely devoid of constant fresh water.
The average speed of wind currents is 15-20 cm/s, the highest - up to 70 cm/s. In the North Caspian, the prevailing winds create a flow directed along the northwestern coast to the southwest. In the Middle Caspian, this current merges with the western branch of the local cyclonic circulation and continues to move along the western coast. At the Absheron Peninsula, the current bifurcates. Its part in the open sea flows into the cyclonic circulation of the Middle Caspian, and the coastal part goes around the shores of the South Caspian and turns to the north, joining the coastal current, enveloping the entire eastern coast. The average state of the movement of the Caspian surface waters is often disturbed due to the variability of wind conditions and other factors. Thus, in the northeastern shallow area, a local anticyclonic gyre can occur. Two anticyclonic eddies are often observed in the South Caspian. In the Middle Caspian, during the warm season, steady northwest winds create southward transport along the east coast. In light winds and during calm weather, the currents may have other directions.
Wind waves develop very strongly, since the prevailing winds have a large acceleration length. The excitement develops mainly in the northwestern and southeastern directions. Severe storms are observed in the open waters of the Middle Caspian, in the areas of Makhachkala, the Apsheron Peninsula and the Mangyshlak Peninsula. Average Height waves of the greatest frequency of 1-1.5 m, with wind speeds of more than 15 m/s increases to 2-3 m. .
The water temperature on the sea surface in January - February in the North Caspian is close to freezing (about -0.2 - -0.3 °C) and gradually rises southward to 11 °C off the coast of Iran. In summer, surface waters warm up to 23-28 °С everywhere, except for the eastern shelf of the Middle Caspian, where seasonal coastal upwelling develops in July-August and the water temperature on the surface drops to 12-17 °С. In winter, due to intense convective mixing, the water temperature changes little with depth. In summer, under the upper heated layer at the horizons of 20-30 m, a seasonal thermocline (a layer of sharp temperature change) is formed, separating deep cold waters from warm surface waters. In the near-bottom layers of the waters of the deep-water depressions, the temperature is maintained all year round at 4.5-5.5 °C in the Middle Caspian and 5.8-6.5 °C in the South. The salinity in the Caspian Sea is almost 3 times lower than in the open areas of the World Ocean, and averages 12.8-12.9‰. It should be especially emphasized that the salt composition of the Caspian water is not completely identical to the composition ocean waters due to the isolation of the sea from the ocean. The waters of the Caspian Sea are poorer in sodium salts and chlorides, but richer in calcium and magnesium carbonates and sulfates due to the unique composition of salts entering the sea with river and underground runoff. The highest salinity variability is observed in the Northern Caspian, where in the estuarine sections of the Volga and the Urals the water is fresh (less than 1‰), and as you move south, the salt content increases to 10-11‰ at the border with the Middle Caspian. The greatest horizontal salinity gradients are characteristic of the frontal zone between sea and river waters. Differences in salinity between the Middle and South Caspian are small, salinity slightly increases from northwest to southeast, reaching 13.6‰ in the Turkmen Gulf (up to 300‰ in Kara-Bogaz-Gol). Salinity changes along the vertical are small and rarely exceed 0.3‰, which indicates good vertical mixing of waters. Water transparency varies over a wide range from 0.2 m in the mouth areas of large rivers to 15-17 m in the central regions of the sea.
According to the ice regime, the Caspian Sea belongs to partially freezing seas. Ice conditions are observed annually only in the northern regions. The Northern Caspian is completely covered with sea ice, the Middle - partially (only in severe winters). Middle border sea ice passes along an arc, turned by a bulge to the north, from the Agrakhan Peninsula in the west to the Tyub-Karagan Peninsula in the east. Usually, ice formation begins in mid-November in the extreme northeast and gradually spreads to the southwest. In January, the entire Northern Caspian is covered with ice, mostly landfast ice (fixed). Drifting ice borders the fast ice with a strip 20-30 km wide. The average thickness of ice is from 30 cm at the southern border to 60 cm in the northeastern regions of the Northern Caspian, in hummocky heaps - up to 1.5 m. The destruction of the ice cover begins in the 2nd half of February. In severe winters, drifting ice is carried to the south, along the western coast, sometimes as far as the Absheron Peninsula. In early April, the sea is completely free of ice cover.
Research History. It is believed that the modern name of the Caspian Sea comes from the ancient tribes of the Caspians, who inhabited the coastal regions in the 1st millennium BC; other historical names: Hyrkan (Irkan), Persian, Khazar, Khvalyn (Khvalis), Khorezm, Derbent. The first mention of the existence of the Caspian Sea dates back to the 5th century BC. Herodotus was one of the first to argue that this reservoir is isolated, that is, it is a lake. In the works of Arab scientists of the Middle Ages, there is information that in the 13-16 centuries the Amu Darya partially flowed into this sea by one of the branches. The well-known numerous ancient Greek, Arabic, European, including Russian, maps of the Caspian Sea until the beginning of the 18th century did not reflect reality and were in fact arbitrary drawings. By order of Tsar Peter I, an expedition was organized in 1714-15 under the leadership of A. Bekovich-Cherkassky, who explored the Caspian Sea, in particular its eastern shores. The first map, on which the contours of the coasts are close to modern ones, was compiled in 1720 using astronomical definitions by Russian military hydrographers F. I. Soymonov and K. Verden. In 1731, Soimonov published the first atlas, and soon the first printed sailing direction of the Caspian Sea. A new edition of the maps of the Caspian Sea with corrections and additions was carried out by Admiral A. I. Nagaev in 1760. The first information on the geology and biology of the Caspian Sea was published by S. G. Gmelin and P. S. Pallas. Hydrographic research in the 2nd half of the 18th century was continued by I.V. Tokmachev, M.I. Voinovich, at the beginning of the 19th century - by A.E. Kolodkin, who was the first to perform instrumental compass survey of the coast. Published in 1807 new map of the Caspian Sea, compiled taking into account the latest inventories. In 1837, systematic instrumental observations of sea level fluctuations began in Baku. In 1847 the first Full description Gulf of Kara-Bogaz-Gol. In 1878, the General Map of the Caspian Sea was published, which reflected the results of the latest astronomical observations, hydrographic surveys, and depth measurements. In 1866, 1904, 1912–13, and 1914–15, under the leadership of N. M. Knipovich, expeditionary studies were carried out in the hydrology and hydrobiology of the Caspian Sea; in 1934, a Commission for the Comprehensive Study of the Caspian Sea was established under the Academy of Sciences of the USSR. A great contribution to the study of the geological structure and oil content of the Apsheron Peninsula and the geological history of the Caspian Sea was made by Soviet geologists I. M. Gubkin, D. V. and V. D. Golubyatnikovs, P. A. Pravoslavlev, V. P. Baturin, S. A . Kovalevsky; in the study of water balance and sea level fluctuations - B. A. Appolov, V. V. Valedinsky, K. P. Voskresensky, L.S. Berg. After the Great Patriotic War, systematic diversified studies were launched in the Caspian Sea, aimed at studying the hydrometeorological regime, biological conditions and the geological structure of the sea.
In the 21st century in Russia, two major scientific centers. The Caspian Marine Research Center (CaspMNIC), established in 1995 by a decree of the Government of the Russian Federation, conducts research work in hydrometeorology, oceanography and ecology. The Caspian Research Institute of Fisheries (CaspNIRKH) traces its history from the Astrakhan Research Station [established in 1897, since 1930 the Volga-Caspian Scientific Fisheries Station, since 1948 the Caspian Branch of the All-Russian Research Institute of Fisheries and Oceanography, since 1954 the Caspian Research Institute of Marine Fisheries and Oceanography (KaspNIRO), modern name since 1965]. CaspNIRKh is developing the foundations for the conservation and rational use of the biological resources of the Caspian Sea. It consists of 18 laboratories and scientific departments - in Astrakhan, Volgograd and Makhachkala. It has a scientific fleet of more than 20 vessels.
Economic use. Natural resources The Caspian Sea is rich and varied. Significant hydrocarbon reserves are being actively developed by Russian, Kazakh, Azerbaijani and Turkmen oil and gas companies. There are huge reserves of mineral self-saddle salts in the Kara-Bogaz-Gol Bay. The Caspian region is also known as a massive habitat for waterfowl and near-water birds. About 6 million migratory birds migrate through the Caspian Sea every year. In this regard, the Volga delta, Kyzylagadzh, Northern Cheleken and Turkmenbashi bays are recognized as sites of international rank under the Ramsar Convention. The mouth sections of many rivers flowing into the sea have unique species vegetation. The fauna of the Caspian Sea is represented by 1800 animal species, of which 415 species are vertebrates. More than 100 species of fish live in the sea and estuaries of rivers. are of commercial importance sea views- herring, sprat, gobies, sturgeons; freshwater - carp, perch; arctic "invaders" - salmon, white salmon. Major ports: Astrakhan, Makhachkala in Russia; Aktau, Atyrau in Kazakhstan; Turkmenbashi in Turkmenistan; Bandar Torkemen, Bandar Anzeli in Iran; Baku in Azerbaijan.
Ecological state. The Caspian Sea is under a powerful anthropogenic impact due to the intensive development of hydrocarbon deposits and the active development of fishing. In the 1980s, the Caspian Sea produced up to 80% of the world's sturgeon catch. Predatory catches of recent decades, poaching and a sharp deterioration in the ecological situation have put many valuable fish species on the brink of extinction. Habitat conditions have deteriorated not only for fish, but also for birds and marine animals (Caspian seal). The countries washed by the waters of the Caspian Sea are faced with the problem of creating a set of international measures to prevent pollution of the aquatic environment and developing the most effective environmental strategy for the near future. A stable ecological state is noted only in parts of the sea remote from the coast.
Lit.: Caspian Sea. M., 1969; Complex studies of the Caspian Sea. M., 1970. Issue. one; Gul K.K., Lappalainen T.N., Polushkin V.A. The Caspian Sea. M., 1970; Zalogin B. S., Kosarev A. N. Morya. M., 1999; International tectonic map of the Caspian Sea and its framing / Ed. V. E. Khain, N. A. Bogdanov. M., 2003; Zonn I. S. Caspian Encyclopedia. M., 2004.
M. G. Deev; V. E. Khain (geological structure of the bottom).
Caspian Sea is inland and located in a vast continental depression on the border of Europe and Asia. The Caspian Sea has no connection with the ocean, which formally allows it to be called a lake, but it has all the features of the sea, since it had connections with the ocean in past geological epochs.
Today, Russia has access only to the Northern Caspian and the Dagestan part of the western coast of the Middle Caspian. The waters of the Caspian Sea wash the shores of such countries as Azerbaijan, Iran, Turkmenistan, Kazakhstan.
The area of the sea is 386.4 thousand km2, the volume of water is 78 thousand m3.
The Caspian Sea has a vast drainage basin, with an area of about 3.5 million km2. The nature of landscapes, climatic conditions and types of rivers are different. Despite the vastness of the drainage basin, only 62.6% of its area falls on waste areas; about 26.1% - for drainless. The area of the Caspian Sea itself is 11.3%. 130 rivers flow into it, but almost all of them are located in the north and west (and the eastern coast does not have a single river reaching the sea at all). largest river the Caspian basin - the Volga, which provides 78% of the river water entering the sea (it should be noted that more than 25% of the Russian economy is located in the basin of this river, and this undoubtedly determines many hydrochemical and other features of the waters of the Caspian Sea), as well as the Kura River, Zhaiyk (Ural), Terek, Sulak, Samur.
In physical and geographical terms and according to the nature of the underwater relief, the sea is divided into three parts: northern, middle and southern. The conditional boundary between the northern and middle parts runs along the line of Chechen Island–Cape Tyub-Karagan, between the middle and southern parts - along the line of Zhiloy Island–Cape Kuuli.
The shelf of the Caspian Sea, on average, is limited to depths of about 100 m. The continental slope, which begins below the edge of the shelf, ends in the middle part at about 500–600 m, in the southern part, where it is very steep, at 700–750 m.
Northern part The sea is shallow, its average depth is 5–6 m, the maximum depths of 15–20 m are located on the border with the middle part of the sea. The bottom relief is complicated by the presence of banks, islands, furrows.
The middle part of the sea is a separate basin, the region of maximum depths of which - the Derbent depression - is shifted to the western coast. The average depth of this part of the sea is 190 m, the greatest is 788 m.
The southern part of the sea is separated from the middle part by the Apsheron threshold, which is a continuation of the Greater Caucasus. Depths above this underwater ridge do not exceed 180 m. The deepest part of the South Caspian basin with a maximum sea depth of 1025 m is located east of the Kura delta. Several underwater ridges up to 500 m high rise above the bottom of the basin.
coast The Caspian Sea are diverse. In the northern part of the sea, they are quite strongly indented. Here are the bays of Kizlyar, Agrakhan, Mangyshlak and many shallow bays. Notable peninsulas: Agrakhansky, Buzachi, Tyub-Karagan, Mangyshlak. Large islands in the northern part of the sea are Tyuleniy, Kulaly. In the deltas of the Volga and Ural rivers, the coastline is complicated by many islets and channels, which often change their position. Many small islands and banks are located on other parts of the coastline.
The middle part of the sea has a relatively flat coastline. On the west coast, on the border with southern part sea located Absheron Peninsula. To the east of it, islands and banks of the Apsheron archipelago stand out, of which the largest is Zhiloy Island. The eastern shore of the Middle Caspian is more indented, the Kazakh Bay stands out here with the Kenderli Bay and several capes. The largest bay of this coast is Kara-Bogaz-Gol.
South of the Absheron Peninsula are the islands of the Baku archipelago. The origin of these islands, as well as some banks off the eastern coast of the southern part of the sea, is associated with the activity of underwater mud volcanoes lying at the bottom of the sea. On the east coast the large bays of Turkmenbashi and Turkmensky are located, and near it is the island of Ogurchinsky.
One of the most striking phenomena of the Caspian Sea is the periodic variability of its level. In historical times, the Caspian Sea had a lower level than the World Ocean. Fluctuations in the level of the Caspian Sea are so great that for more than a century they have attracted the attention of not only scientists. Its peculiarity is that in the memory of mankind its level has always been below the level of the World Ocean. Since the beginning of instrumental observations (since 1830) of the sea level, the amplitude of its fluctuations has been almost 4 m, from -25.3 m in the eighties of the XIX century. to -29 m in 1977. In the last century, the level of the Caspian Sea has changed significantly twice. In 1929 it stood at a mark of about -26 m, and since it had been close to this mark for almost a century, this position of the level was considered as a long-term or secular average. In 1930, the level began to decline rapidly. Already by 1941, it had dropped by almost 2 m. This led to the drying up of vast coastal areas of the bottom. The decrease in the level, with its small fluctuations (short-term insignificant rises in the level in 1946-1948 and 1956-1958), continued until 1977 and reached the mark of -29.02 m, i.e., the level took the lowest position for last 200 years.
In 1978, contrary to all forecasts, the sea level began to rise. As of 1994, the level of the Caspian Sea was at -26.5 m, that is, in 16 years the level has risen by more than 2 m. The rate of this rise is 15 cm per year. The level increment in some years was higher, and in 1991 it reached 39 cm.
The general fluctuations in the level of the Caspian Sea are superimposed by its seasonal changes, the average long-term of which reaches 40 cm, as well as surge phenomena. The latter are especially pronounced in the Northern Caspian. The northwestern coast is characterized by large surges created by the prevailing, especially in the cold season, storms of the eastern and southeast directions. Here for recent decades a number of large (more than 1.5–3 m) surges were observed. A particularly large surge with catastrophic consequences was noted in 1952. Fluctuations in the level of the Caspian Sea cause great damage to the states surrounding its water area.
.gif) |
Climate. The Caspian Sea is located in the temperate and subtropical climatic zones. Climatic conditions change in the meridional direction, since the sea stretches for almost 1200 km from north to south.
In the Caspian region, various systems of atmospheric circulation interact, however, during the year, easterly winds prevail (the influence of the Asian maximum). The position at rather low latitudes provides a positive balance of heat inflow, so the Caspian Sea serves as a source of heat and moisture for passing air masses for most of the year. The average annual air temperature in the northern part of the sea is 8–10°С, in the middle part - 11–14°С, in the southern part – 15–17°С. However, in the northernmost parts of the sea, the average January temperature is from –7 to –10°C, and the minimum temperature during arctic air intrusions is up to –30°C, which determines the formation of the ice cover. In summer, rather high temperatures dominate over the entire region under consideration - 24–26°C. Thus, the Northern Caspian is subject to the most sharp temperature fluctuations.
The Caspian Sea is characterized by a very small amount of precipitation per year - only 180 mm, and most of it falls on the cold season of the year (from October to March). However, the Northern Caspian differs in this respect from the rest of the basin: here the average annual precipitation is less (only 137 mm for the western part), and the distribution over the seasons is more even (10–18 mm per month). In general, we can talk about proximity climatic conditions to the arid ones.
Water temperature. The distinctive features of the Caspian Sea (great differences in depths in different parts of the sea, the nature of the bottom relief, isolation) have a certain influence on the formation of temperature conditions. In the shallow North Caspian, the entire water column can be considered as homogeneous (the same applies to shallow bays located in other parts of the sea). In the Middle and South Caspian, surface and deep masses separated by a transitional layer can be distinguished. In the Northern Caspian and in the surface layers of the Middle and Southern Caspian, the water temperature varies over a wide range. In winter, temperatures vary from north to south from less than 2 to 10°С, the water temperature near the western coast is 1–2°С higher than near the eastern one, in the open sea the temperature is higher than near the coasts: by 2–3°С in the middle part and by 3–4°С in the southern part of the sea. In winter, the temperature distribution is more uniform with depth, which is facilitated by the winter vertical circulation. During moderate and severe winters in the northern part of the sea and shallow bays on the east coast, the water temperature drops to freezing.
In summer, the temperature varies in space from 20 to 28°C. The highest temperatures are observed in the southern part of the sea; temperatures are also quite high in the well-warmed shallow North Caspian. The zone of distribution of the lowest temperatures is adjacent to the east coast. This is due to the rise of cold deep waters to the surface. Temperatures are also relatively low in the poorly heated deep-water central part. In the open areas of the sea, in late May–early June, the formation of a temperature jump layer begins, which is most clearly expressed in August. Most often, it is located between the horizons of 20 and 30 m in the middle part of the sea and 30 and 40 m in the southern part. In the middle part of the sea, due to the surge near the eastern coast, the shock layer rises close to the surface. In the bottom layers of the sea, the temperature during the year is about 4.5°C in the middle part and 5.8–5.9°C in the south.
Salinity. Salinity values are determined by such factors as river runoff, water dynamics, including mainly wind and gradient currents, the resulting water exchange between the western and eastern parts of the Northern Caspian and between the Northern and Middle Caspian, the bottom topography, which determines the location of waters with different salinity, mainly along the isobaths, evaporation, which ensures the shortage of fresh water and the inflow of more saline ones. These factors collectively affect the seasonal differences in salinity.
The Northern Caspian can be considered as a reservoir of constant mixing of river and Caspian waters. The most active mixing occurs in the western part, where both river and Central Caspian waters directly enter. In this case, horizontal salinity gradients can reach 1‰ per 1 km.
The eastern part of the Northern Caspian is characterized by a more uniform salinity field, since most of the river and sea (Middle Caspian) waters enter this area of the sea in a transformed form.
According to the values of horizontal salinity gradients, in the western part of the Northern Caspian, a river-sea contact zone can be distinguished with water salinity from 2 to 10‰, in the eastern part from 2 to 6‰.
Significant vertical salinity gradients in the Northern Caspian are formed as a result of the interaction of river and sea waters, with runoff playing a decisive role. The intensification of vertical stratification is also facilitated by the unequal thermal state of the water layers, since the temperature of the surface desalinated waters coming from the coast in summer is 10–15°C higher than that of the bottom ones.
In the deep basins of the Middle and South Caspian, salinity fluctuations in the upper layer are 1–1.5‰. The largest difference between the maximum and minimum salinity was noted in the area of the Apsheron threshold, where it is 1.6‰ in the surface layer and 2.1‰ at the 5 m horizon.
The decrease in salinity along the western coast of the South Caspian in the 0–20 m layer is caused by the runoff of the Kura River. The influence of the Kura runoff decreases with depth; at the horizons of 40–70 m, the range of salinity fluctuations is no more than 1.1‰. Along the entire western coast to the Absheron Peninsula stretches a strip of desalinated water with a salinity of 10–12.5‰ coming from the Northern Caspian.
In addition, salinity increases in the South Caspian due to the removal of saline waters from bays and inlets on the eastern shelf under the action of southeasterly winds. In the future, these waters are transferred to the Middle Caspian.
In the deep layers of the Middle and South Caspian, salinity is about 13‰. In the central part of the Middle Caspian, such salinity is observed at horizons below 100 m, and in the deep part of the South Caspian, the upper boundary of waters with increased salinity drops to 250 m. Obviously, vertical mixing of waters is difficult in these parts of the sea.
Surface water circulation. Currents in the sea are mainly wind-driven. In the western part of the Northern Caspian, currents of the western and eastern quarters are most often observed, in the eastern - southwestern and southern. The currents caused by the runoff of the Volga and Ural rivers can be traced only within the estuarine coast. The prevailing current velocities are 10–15 cm/s; in the open areas of the Northern Caspian, the maximum velocities are about 30 cm/s.
In the coastal areas of the middle and southern parts of the sea, in accordance with the wind directions, currents of the northwestern, northern, southeastern and southern directions, currents often occur off the east coast east direction. Along the western coast of the middle part of the sea, the most stable currents are southeast and south. Current velocities are on average about 20–40 cm/s, the maximum ones reach 50–80 cm/s. Other types of currents also play a significant role in the circulation of sea waters: gradient, seiche, inertial ones.
Ice formation. The Northern Caspian is covered with ice annually in November, the area of the freezing part of the water area depends on the severity of the winter: in severe winters, the entire Northern Caspian is covered with ice, in soft ice it stays within the 2–3 meter isobath. The appearance of ice in the middle and southern parts of the sea falls on December-January. Near the eastern coast, ice is of local origin, near the western coast - most often brought from the northern part of the sea. In severe winters, shallow bays freeze off the eastern coast of the middle part of the sea, coastlines and landfast ice form off the coast, and drifting ice spreads to the Absheron Peninsula in abnormally cold winters off the western coast. The disappearance of the ice cover is observed in the second half of February–March.
|
Oxygen content. The spatial distribution of dissolved oxygen in the Caspian Sea has a number of regularities. The central part of the Northern Caspian is characterized by a fairly uniform distribution of oxygen. An increased oxygen content is found in the areas of the pre-estuary seashore of the Volga River, a lower one - in the southwestern part of the Northern Caspian. In the Middle and South Caspian, the highest oxygen concentrations are confined to coastal shallow areas and pre-estuary seashores of rivers, with the exception of the most polluted areas of the sea (Baku Bay, Sumgait region, etc.). In summer, due to the significant heating of water masses and the activation of photosynthesis processes, the leading factors in the formation of the oxygen regime, in surface waters are photosynthetic processes, in the near-bottom - biochemical consumption of oxygen by bottom sediments. Due to the high temperature of the waters, the stratification of the water column, the large influx of organic matter and its intense oxidation, oxygen is quickly consumed with its minimal entry into the lower layers of the sea, resulting in the formation of an oxygen deficiency zone in the Northern Caspian. Intensive photosynthesis in the open waters of the deep-water regions of the Middle and South Caspian covers the upper 25-meter layer, where oxygen saturation is more than 120%. |
– The Northern Caspian, which is a vast mixing zone of river and sea waters, is characterized by significant spatial gradients in the distribution of nutrients;
- in the Middle Caspian, the cyclonic nature of the circulation contributes to the upwelling of deep waters with a high content of nutrients into the overlying layers of the sea;
– in the deep water areas of the Middle and South Caspian, the vertical distribution of nutrients depends on the intensity of the process of convective mixing, and their content increases with depth.
On the dynamics of concentrations nutrients during the year in the Caspian Sea are influenced by such factors as seasonal fluctuations in the biogenic runoff in the sea, the seasonal ratio of production-destruction processes, the intensity of the exchange between soil and water mass, ice conditions in winter in the Northern Caspian, the processes of winter vertical circulation in deep water areas seas.
In winter, a significant area of the Northern Caspian is covered with ice, but biochemical processes are actively developing in the under-ice water and ice. The ice of the Northern Caspian, being a kind of accumulator of biogenic substances, transforms these substances that enter the sea with river runoff and from the atmosphere.
As a result of the winter vertical circulation of waters in the deep-water regions of the Middle and Southern Caspian in the cold season, the active layer of the sea is enriched with nutrients due to their supply from the underlying layers.
Spring for the waters of the Northern Caspian is characterized by a minimum content of phosphates, nitrites and silicon, which is explained by the spring outbreak of phytoplankton development (silicon is actively consumed by diatoms). High concentrations of ammonium and nitrate nitrogen, characteristic of the waters of a large area of the Northern Caspian during floods, are due to intensive flushing of the Volga delta by river waters.
.gif)
In the spring season, in the area of water exchange between the North and Middle Caspian in the subsurface layer, with the maximum oxygen content, the content of phosphates is minimal, which, in turn, indicates the activation of the photosynthesis process in this layer.
In the South Caspian, the distribution of nutrients in spring is basically similar to their distribution in the Middle Caspian.
In the summertime, the waters of the Northern Caspian reveal a redistribution of various forms of biogenic compounds. Here, the content of ammonium nitrogen and nitrates significantly decreases, while at the same time, there is a slight increase in the concentrations of phosphates and nitrites and a rather significant increase in the concentration of silicon. In the Middle and South Caspian, the concentration of phosphates has decreased due to their consumption in the process of photosynthesis and the difficulty of water exchange with the deep water accumulation zone.
In the autumn in the Caspian Sea, due to the cessation of the activity of some types of phytoplankton, the content of phosphates and nitrates increases, and the concentration of silicon decreases, as an autumn outbreak of the development of diatoms takes place.
For more than 150 years, oil has been mined on the shelf of the Caspian Sea oil.
Currently, large reserves of hydrocarbons are being developed on the Russian shelf, the resources of which on the Dagestan shelf are estimated at 425 million tons of oil equivalent (of which 132 million tons of oil and 78 billion m3 of gas), on the shelf of the Northern Caspian - 1 billion tons of oil .
In total, about 2 billion tons of oil have already been produced in the Caspian.
Losses of oil and products of its processing during extraction, transportation and use reach 2% of the total volume.
Main sources of income pollutants, including oil products, into the Caspian Sea - this is the removal with river runoff, the discharge of untreated industrial and agricultural effluents, domestic wastewater from cities and towns located on the coast, shipping, exploration and exploitation of oil and gas fields located at the bottom of the sea, transportation of oil by sea. 90% of pollutants with river runoff are concentrated in the Northern Caspian, industrial effluents are confined mainly to the area of the Apsheron Peninsula, and increased oil pollution of the Southern Caspian is associated with oil production and oil exploration drilling, as well as with active volcanic activity (mud volcanism) in the zone of oil and gas bearing structures.
About 55 thousand tons of oil products enter the Northern Caspian every year from the territory of Russia, including 35 thousand tons (65%) from the Volga River and 130 tons (2.5%) from the Terek and Sulak rivers.
The thickening of the film on the water surface up to 0.01 mm disrupts the processes of gas exchange and threatens the death of hydrobiota. Toxic for fish is the concentration of oil products 0.01 mg/l, for phytoplankton - 0.1 mg/l.
The development of oil and gas resources of the bottom of the Caspian Sea, the estimated reserves of which are estimated at 12–15 billion tons of standard fuel, will become the main factor in the anthropogenic load on the ecosystem of the sea in the coming decades.
.gif)
Caspian autochthonous fauna. The total number of autochthons is 513 species or 43.8% of the entire fauna, which include herring, gobies, mollusks, etc.
arctic views. The total number of the Arctic group is 14 species and subspecies, or only 1.2% of the entire fauna of the Caspian (mysids, sea cockroach, white salmon, Caspian salmon, Caspian seal, etc.). The basis of the Arctic fauna is crustaceans (71.4%), which easily tolerate desalination and live at great depths of the Middle and Southern Caspian (from 200 to 700 m), since the lowest water temperatures (4.9– 5.9°C).
.gif)
Mediterranean views. These are 2 types of mollusks, needle-fish, etc. At the beginning of the 20s of our century, the mollusk mitilyastra penetrated here, later 2 types of shrimp (with mullets, during their acclimatization), 2 types of mullet and flounder. Some Mediterranean species entered the Caspian after the opening of the Volga-Don Canal. Mediterranean species play a significant role in the fish food base of the Caspian Sea.
freshwater fauna(228 species). This group includes anadromous and semi-anadromous fish (sturgeon, salmon, pike, catfish, cyprinids, as well as rotifers).
Marine views. These are ciliates (386 forms), 2 species of foraminifera. There are especially many endemics among higher crustaceans (31 species), gastropods (74 species and subspecies), bivalves (28 species and subspecies) and fish (63 species and subspecies). The abundance of endemics in the Caspian Sea makes it one of the most unique brackish water bodies on the planet.
The Caspian Sea provides more than 80% of the world's sturgeon catch, most of which falls on the North Caspian.
To increase the catches of sturgeon, which dropped sharply during the years of sea level drop, a set of measures is being implemented. Among them - a complete ban on sturgeon fishing in the sea and its regulation in rivers, an increase in the scale of factory breeding of sturgeons.
.gif) |
