Caspian Sea (largest lake). Caspian Sea
The Caspian Sea is the largest lake on our planet, which is located in a depression of the earth’s surface (the so-called Aral-Caspian Lowland) on the territory of Russia, Turkmenistan, Kazakhstan, Azerbaijan and Iran. Although they consider it as a lake, because it is not connected with the World Ocean, but by the nature of the formation processes and history of origin, by its size, the Caspian Sea is a sea.
The area of the Caspian Sea is about 371 thousand km 2. The sea, stretching from north to south, has a length of about 1200 km and an average width of 320 km. The length of the coastline is about 7 thousand km. The Caspian Sea is located 28.5 m below the level of the World Ocean and its greatest depth is 1025 m. There are about 50 islands in the Caspian Sea, mostly small in area. The large islands include such islands as Tyuleniy, Kulaly, Zhiloy, Chechen, Artem, Ogurchinsky. There are also many bays in the sea, for example: Kizlyarsky, Komsomolets, Kazakhsky, Agrakhansky, etc.
The Caspian Sea is fed by more than 130 rivers. The largest amount of water (about 88% of the total flow) is brought by the rivers Ural, Volga, Terek, Emba, which flow into the northern part of the sea. About 7% of the flow comes from the large rivers Kura, Samur, Sulak and small ones that flow into the sea on the west coast. The rivers Heraz, Gorgan, and Sefidrud flow into the southern Iranian coast, bringing only 5% of the flow. Not a single river flows into the eastern part of the sea. The water in the Caspian Sea is salty, its salinity ranges from 0.3‰ to 13‰.
Shores of the Caspian Sea
The shores have different landscapes. The shores of the northern part of the sea are low and flat, surrounded by low-lying semi-desert and somewhat elevated desert. In the south, the shores are partly low-lying, they are bordered by a small coastal lowland, behind which the Elburz ridge runs along the coast, which in some places comes close to the shore. In the west, the Greater Caucasus ranges approach the coast. In the east there is an abrasion coast, carved out of limestone, and semi-desert and desert plateaus approach it. The coastline changes greatly due to periodic fluctuations in water levels.
The climate of the Caspian Sea is different:
Continental in the north;
Moderate in the middle
Subtropical in the south.
At the same time, there are severe frosts and snowstorms on the northern shore, while fruit trees and magnolias bloom on the southern shore. In winter, strong storm winds rage at sea.
On the coast of the Caspian Sea there are large cities and ports: Baku, Lankaran, Turkmenbashi, Lagan, Makhachkala, Kaspiysk, Izberbash, Astrakhan, etc. 
The fauna of the Caspian Sea is represented by 1809 species of animals. More than 70 species of fish are found in the sea, including: herring, gobies, stellate sturgeon, sturgeon, beluga, white fish, sterlet, pike perch, carp, bream, roach, etc. Of the marine mammals, only the smallest in the world, the Caspian seal, is found in the lake. not found in other seas. The Caspian Sea lies on the main migratory route of birds between Asia, Europe and the Middle East. Every year, about 12 million birds fly over the Caspian Sea during migration, and another 5 million usually winter here.
Vegetable world
The flora of the Caspian Sea and its coast includes 728 species. Basically, the sea is inhabited by algae: diatoms, blue-greens, red, characeae, brown and others, of the flowering ones - rupee and zoster.
The Caspian Sea is rich in natural resources; many oil and gas fields are being developed in it; in addition, limestone, salt, sand, stone and clay are also mined here. The Caspian Sea is connected by the Volga-Don Canal with the Sea of Azov, and shipping is well developed. A lot of different fish are caught in the reservoir, including more than 90% of the world's sturgeon catch.
The Caspian Sea is also a recreation area; on its shores there are holiday homes, tourist centers and sanatoriums.
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8th grade
The Caspian Sea belongs to the internal closed basin of Eurasia. It was formed due to the disintegration of a single large basin that existed in the Neogene on the site of the Black and Caspian Seas, the connection of which with the World Ocean was repeatedly lost and restored again. The final isolation of the Caspian Sea occurred at the beginning of the Quaternary as a result of uplifts in the area of the Kuma-Manych depression. Nowadays the Caspian Sea is the largest endorheic sea on Earth.
Due to its geographical location, isolation and uniqueness of waters, the Caspian Sea belongs to a special type of “sea-lake” reservoir. Its hydrological regime and organic world, unlike other seas, depend to a greater extent on nature and its changes within the sea basin itself, in particular the Volga basin, located entirely within Russia.
The basin of the Caspian Sea consists of three parts: the northern shelf part of the sea with depths of less than 50 m lies on the lowered edge of the Russian and Scythian plates and has a smooth, calm bottom topography; the middle basin with depths in the central part of 200-788 m is confined to the Terek-Caspian marginal trough; the southern deep-sea basin (up to 1025 m) occupies the intermountain depression of the Alpine fold belt.
The sea extends from north to south within the temperate and subtropical climate zones for 1200 km with an average width of about 300 km. The large length along the meridian (10°34"), together with the volume of sea waters, determines the differences in its climate. In winter, the sea is under the influence of the Asian High, so northeastern winds blow over it, bringing cold continental air from temperate latitudes. The average air temperature in January - February reaches -8...-10°С in the northern part of the sea, -3...+ 5°С — in the middle and +8...+ 10°С in the south. The increase in air temperature towards the middle and southern parts of the sea is mainly due to the fact that sea waters accumulate significant reserves of heat in the summer, therefore they warm the air flows passing over the sea, thereby softening the winter. The shallow northern part of the sea is covered with ice from January to March. Cyclones of the Iranian branch of the polar front passing over the Southern Caspian Sea in winter bring precipitation.
Summer is characterized by more stable and clear weather compared to the autumn-winter period. Temperature differences between the North and South Caspian Sea in summer are small. The average July temperature in the north is 24-25°C, and in the south 26-28°C. The annual precipitation over the waters of the Northern Caspian Sea is 300-350 mm, in the southwestern part of the sea it exceeds 1200-1500 mm.
The hydrological regime, water balance and level of the Caspian Sea are closely related to surface runoff within its basin. More than 130 rivers bring about 300 km 2 of water to the sea annually. The main flow comes from the Volga (more than 80%). Thanks to the flow of the Volga, northeastern winds and the Coriolis force, there is a constant counterclockwise current along the shores of the Caspian Sea. There are two more cyclonic currents in the middle and southern basins.
The Caspian Sea is a brackish water basin. Water salinity ranges from 0.3‰ at the mouth of the Volga to 13‰ in the southeastern part. The surface water temperature in summer is 22-24°C in the northern part of the sea and 26-28°C in the southern regions. In winter in the Northern Caspian Sea, water temperatures are approximately -0.4...-0.6 ° C, i.e. close to freezing temperature.
The organic world of the Caspian Sea is not rich in the number of species, but is deeply endemic. The main part of the fauna is Mediterranean, left over from the period when the sea had a connection with the World Ocean, but later underwent changes (herring, gobies, sturgeon). It was joined by younger forms from the northern seas (salmon, whitefish, seal). A significant part of the fauna is represented by freshwater forms (cyprinids, perch). Over 70 species of fish are now found in the Caspian Sea. Sturgeon, stellate sturgeon, beluga, sterlet, white fish, pike perch, bream, carp, and roach are of commercial importance. The Caspian sturgeon herd is considered the largest in the world. Fishing for Caspian seals is limited.
The Caspian Sea is also of transport and oil production importance. Changes in the level of the Caspian Sea negatively affect transport, fisheries, the entire nature of the coast and the lives of the population.
The Caspian Sea is remarkable in that its western shore belongs to Europe, and its eastern shore is located in Asia. This is a huge body of salt water. It is called a sea, but, in fact, it is a lake, since it has no connection with the World Ocean. Therefore, it can be considered the largest lake in the world.
The area of the water giant is 371 thousand square meters. km. As for the depth, the northern part of the sea is quite shallow, and the southern part is deep. The average depth is 208 meters, but it does not give any idea of the thickness of the water mass. The entire reservoir is divided into three parts. These are the Northern, Middle and Southern Caspian. The northern one is a sea shelf. It accounts for only 1% of the total volume of water. This part ends behind the Kizlyar Bay near the island of Chechen. The average depth in these places is 5-6 meters.
In the Middle Caspian, the seabed noticeably decreases, and the average depth reaches 190 meters. The maximum is 788 meters. This part of the sea contains 33% of the total volume of water. And the South Caspian is considered the deepest. It absorbs 66% of the total water mass. The maximum depth is noted in the South Caspian depression. She is equal 1025 meters and is considered the official maximum depth of the sea today. The Middle and Southern Caspian Seas are approximately equal in area and occupy a total of 75% of the area of the entire reservoir.
The maximum length is 1030 km, and the corresponding width is 435 km. The minimum width is 195 km. The average figure corresponds to 317 km. That is, the reservoir has an impressive size and is rightfully called a sea. The length of the coastline together with the islands reaches almost 7 thousand km. As for the water level, it is 28 meters below the level of the World Ocean.
The most interesting thing is that the level of the Caspian Sea is subject to cyclicity. The water rises and falls. Water level measurements have been carried out since 1837. According to experts, over the last thousand years the level has fluctuated within 15 meters. This is a very large number. And they associate it with geological and anthropogenic (human impact on the environment) processes. However, it has been noted that since the beginning of the 21st century, the level of the huge reservoir has been steadily rising.
The Caspian Sea is surrounded by 5 countries. These are Russia, Kazakhstan, Turkmenistan, Iran and Azerbaijan. Moreover, Kazakhstan has the longest coastline. Russia is in 2nd place. But the length of the coastline of Azerbaijan reaches only 800 km, but in this place there is the largest port in the Caspian Sea. This is, of course, Baku. The city is home to 2 million people, and the population of the entire Absheron Peninsula is 2.5 million people.
"Oil Rocks" - a city in the sea
These are 200 platforms with a total length of 350 kilometers
Notable is the oil workers' village, which is called " Oil Rocks". It is located 42 km east of Absheron in the sea and is a creation of human hands. All residential and industrial buildings are built on metal overpasses. People service drilling rigs that pump oil from the bowels of the earth. Naturally, there are no permanent residents in this village.
In addition to Baku, there are other large cities along the shores of the salty reservoir. At the southern tip is the Iranian city of Anzali with a population of 111 thousand people. This is the largest Iranian port on the Caspian Sea. Kazakhstan owns the city of Aktau with a population of 178 thousand people. And in the northern part, directly on the Ural River, is the city of Atyrau. It is inhabited by 183 thousand people.
The Russian city of Astrakhan also has the status of a seaside city, although it is 60 km from the coast and is located in the Volga River delta. This is a regional center with a population of more than 500 thousand people. Directly on the seashore there are such Russian cities as Makhachkala, Kaspiysk, Derbent. The latter is one of the oldest cities in the world. People have been living in this place for more than 5 thousand years.
Many rivers flow into the Caspian Sea. There are about 130 of them. The largest of them are the Volga, Terek, Ural, Kura, Atrek, Emba, Sulak. It is rivers, not precipitation, that feed the huge reservoir. They give him up to 95% of water per year. The basin of the reservoir is 3.626 million square meters. km. These are all rivers with their tributaries flowing into the Caspian Sea. The territory is huge, it includes Kara-Bogaz-Gol Bay.
It would be more correct to call this bay a lagoon. It means a shallow body of water separated from the sea by a sandbar or reefs. There is such a spit in the Caspian Sea. And the strait through which water flows from the sea is 200 km wide. True, people, with their restless and ill-considered activities, almost destroyed Kara-Bogaz-Gol. They fenced off the lagoon with a dam, and its level dropped sharply. But after 12 years the mistake was corrected and the strait was restored.
The Caspian Sea has always been shipping is developed. In the Middle Ages, merchants brought exotic spices and snow leopard skins from Persia to Rus' by sea. Nowadays, the reservoir connects the cities located on its banks. Ferry crossings are practiced. There is a water connection with the Black and Baltic Seas through rivers and canals.
Caspian Sea on the map
The body of water is also important from the point of view fisheries, because sturgeon live in large numbers there and provide caviar. But today the number of sturgeon has decreased significantly. Environmentalists propose to ban the fishing of this valuable fish until the population recovers. But this issue has not yet been resolved. The number of tuna, bream, and pike perch also decreased. Here you need to take into account the fact that poaching is highly developed at sea. The reason for this is the difficult economic situation of the region.
And, of course, I need to say a few words about oil. The extraction of “black gold” at sea began in 1873. The areas adjacent to Baku have become a real gold mine. There were more than 2 thousand wells here, and oil production and refining was carried out on an industrial scale. At the beginning of the 20th century it was the center of the international oil industry. In 1920, Azerbaijan was captured by the Bolsheviks. Oil wells and factories were requisitioned. The entire oil industry came under the control of the USSR. In 1941, Azerbaijan supplied 72% of all oil produced in the socialist state.
In 1994, the “Contract of the Century” was signed. He marked the beginning of the international development of the Baku oil fields. The main Baku-Tbilisi-Ceyhan pipeline allows Azerbaijani oil to flow directly to the Mediterranean port of Ceyhan. It was put into operation in 2006. Today, oil reserves are estimated at 12 trillion. US dollars.
Thus, it is clear that the Caspian Sea is one of the most important economic regions of the world. The political situation in the Caspian region is quite complicated. For a long time, there have been disputes about the maritime borders between Azerbaijan, Turkmenistan and Iran. There were many inconsistencies and disagreements, which negatively affected the development of the region.
This came to an end on August 12, 2018. On this day, the states of the “Caspian Five” signed the Convention on the Legal Status of the Caspian Sea. This document delimited the bottom and subsoil, and each of the five countries (Russia, Kazakhstan, Iran, Turkmenistan, Azerbaijan) received its share in the Caspian basin. Rules for navigation, fishing, scientific research, and pipeline laying were also approved. The boundaries of territorial waters received state status.
Yuri Syromyatnikov
V. N. MIKHAILOVThe Caspian Sea is the largest closed lake on the planet. This body of water is called the sea for its huge size, brackish water and a regime similar to the sea. The level of the Caspian Sea-lake lies much lower than the level of the World Ocean. At the beginning of 2000, it was around -27 abs. m. At this level, the area of the Caspian Sea is ~ 393 thousand km2 and the volume of water is 78,600 km3. The average and maximum depths are 208 and 1025 m, respectively.
The Caspian Sea stretches from south to north (Fig. 1). The Caspian Sea washes the shores of Russia, Kazakhstan, Turkmenistan, Azerbaijan and Iran. The reservoir is rich in fish, its bottom and shores are rich in oil and gas. The Caspian Sea has been studied quite well, but many mysteries remain in its regime. The most characteristic feature of a reservoir is the instability of the level with sharp drops and rises. The last increase in the level of the Caspian Sea occurred before our eyes from 1978 to 1995. It gave rise to many rumors and speculation. Numerous publications appeared in the press talking about catastrophic floods and an environmental disaster. They often wrote that the rise in the level of the Caspian Sea led to the flooding of almost the entire Volga delta. What is true in the statements made? What is the reason for this behavior of the Caspian Sea?
WHAT HAPPENED TO THE CASPIAN IN THE XX CENTURY
Systematic observations of the level of the Caspian Sea began in 1837. In the second half of the 19th century, the average annual values of the Caspian Sea level were in the range from – 26 to – 25.5 abs. m and had a slight downward trend. This trend continued into the 20th century (Fig. 2). In the period from 1929 to 1941, sea level dropped sharply (by almost 2 m - from - 25.88 to - 27.84 abs. m). In subsequent years, the level continued to fall and, having decreased by approximately 1.2 m, reached in 1977 the lowest level during the observation period - 29.01 abs. m. Then the sea level began to rise rapidly and, having risen by 2.35 m by 1995, reached 26.66 abs. m. In the next four years, the average sea level dropped by almost 30 cm. Its average levels were - 26.80 in 1996, - 26.95 in 1997, - 26.94 in 1998 and - 27.00 abs. m in 1999.
The decrease in sea level in 1930-1970 led to the shallowing of coastal waters, the extension of the coastline towards the sea, and the formation of wide beaches. The latter was perhaps the only positive consequence of the drop in level. There were significantly more negative consequences. As the level dropped, the areas of feeding grounds for fish stocks in the northern Caspian Sea decreased. The shallow-water estuarine coastal area of the Volga began to quickly become overgrown with aquatic vegetation, which worsened the conditions for the passage of fish to spawn in the Volga. Fish catches have sharply decreased, especially valuable species: sturgeon and sterlet. Shipping began to suffer due to the fact that the depths in the approach channels decreased, especially near the Volga delta.
The rise in levels from 1978 to 1995 was not only unexpected, but also led to even greater negative consequences. After all, both the economy and the population of coastal areas have already adapted to the low level.
Many sectors of the economy began to suffer damage. Significant areas were in the flood and flood zone, especially in the northern (plain) part of Dagestan, Kalmykia and the Astrakhan region. The cities of Derbent, Kaspiysk, Makhachkala, Sulak, Kaspiysky (Lagan) and dozens of other smaller settlements suffered from the rise in level. Significant areas of agricultural land have been flooded and submerged. Roads and power lines, engineering structures of industrial enterprises and public utilities are being destroyed. A threatening situation has developed with fish farming enterprises. Abrasion processes in the coastal zone and the influence of seawater surges have intensified. In recent years, the flora and fauna of the seaside and coastal zone of the Volga delta have suffered significant damage.
Due to the increase in depth in the shallow waters of the Northern Caspian and the reduction in the areas occupied by aquatic vegetation in these places, the conditions for the reproduction of stocks of anadromous and semi-anadromous fish and the conditions for their migration to the delta for spawning have somewhat improved. However, the predominance of negative consequences from rising sea levels has led to talk of an environmental catastrophe. The development of measures to protect national economic facilities and settlements from the advancing sea began.
HOW UNUSUAL IS THE CURRENT BEHAVIOR OF THE CASPIAN SEA?
Research into the life history of the Caspian Sea can help answer this question. Of course, there are no direct observations of the past regime of the Caspian Sea, but there is archaeological, cartographic and other evidence for historical time and the results of paleogeographic studies covering a longer period.
It has been proven that during the Pleistocene (the last 700-500 thousand years), the level of the Caspian Sea underwent large-scale fluctuations in the range of about 200 m: from -140 to + 50 abs. m. During this period of time, four stages are distinguished in the history of the Caspian Sea: Baku, Khazar, Khvalyn and Novo-Caspian (Fig. 3). Each stage included several transgressions and regressions. The Baku transgression occurred 400-500 thousand years ago, sea level rose to 5 abs. m. During the Khazar stage, there were two transgressions: early Khazar (250-300 thousand years ago, maximum level 10 abs. m) and late Khazar (100-200 thousand years ago, highest level -15 abs. m). The Khvalynian stage in the history of the Caspian Sea included two transgressions: the largest during the Pleistocene period, the Early Khvalynian (40-70 thousand years ago, maximum level 47 absolute meters, which is 74 m higher than the modern one) and the Late Khvalynian (10-20 thousand years ago, rise level up to 0 absolute m). These transgressions were separated by the deep Enotayev regression (22-17 thousand years ago), when sea level dropped to -64 abs. m and was 37 m lower than the modern one.
Rice. 4. Fluctuations in the level of the Caspian Sea over the past 10 thousand years. P is the natural range of fluctuations in the level of the Caspian Sea under climatic conditions characteristic of the sub-Atlantic Holocene era (risk zone). I-IV - stages of the New Caspian transgression; M - Mangyshlak, D - Derbent regression
Significant fluctuations in the level of the Caspian Sea also occurred during the New Caspian stage of its history, which coincided with the Holocene (the last 10 thousand years). After the Mangyshlak regression (10 thousand years ago, the level dropped to – 50 abs. m), five stages of the New Caspian transgression were noted, separated by small regressions (Fig. 4). Following fluctuations in sea level—its transgressions and regressions—the outline of the reservoir also changed (Fig. 5).
Over historical time (2000 years), the range of change in the average level of the Caspian Sea was 7 m – from – 32 to – 25 abs. m (see Fig. 4). The minimum level in the last 2000 years was during the Derbent regression (VI-VII centuries AD), when it decreased to – 32 abs. m. During the time elapsed after the Derbent regression, the average sea level changed in an even narrower range - from – 30 to – 25 abs. m. This range of level changes is called the risk zone.
Thus, the level of the Caspian Sea has experienced fluctuations before, and in the past they were more significant than in the 20th century. Such periodic fluctuations are a normal manifestation of the unstable state of a closed reservoir with variable conditions at the outer boundaries. Therefore, there is nothing unusual in the decrease and increase in the level of the Caspian Sea.
Fluctuations in the level of the Caspian Sea in the past, apparently, did not lead to irreversible degradation of its biota. Of course, sharp drops in sea level created temporary unfavorable conditions, for example for fish stocks. However, as the level rose, the situation corrected itself. The natural conditions of the coastal zone (vegetation, bottom animals, fish) experience periodic changes along with sea level fluctuations and, apparently, have a certain margin of stability and resistance to external influences. After all, the most valuable sturgeon stock has always been in the Caspian basin, regardless of sea level fluctuations, quickly overcoming temporary deterioration in living conditions.
Rumors that rising sea levels caused floods throughout the Volga delta were not confirmed. Moreover, it turned out that the increase in water levels even in the lower part of the delta is inadequate to the magnitude of the sea level rise. The increase in water level in the lower part of the delta during the low-water period did not exceed 0.2-0.3 m, and during the flood it almost did not appear at all. At the maximum level of the Caspian Sea in 1995, the backwater from the sea extended along the deepest branch of the delta, Bakhtemiru, no more than 90 km, and along other branches no more than 30 km. Therefore, only the islands on the seashore and the narrow coastal strip of the delta were flooded. Flooding in the upper and middle parts of the delta was associated with high floods in 1991 and 1995 (which is a normal phenomenon for the Volga delta) and with the unsatisfactory condition of protective dams. The reason for the weak influence of sea level rise on the regime of the Volga delta is the presence of a huge shallow coastal zone, which dampens the impact of the sea on the delta.
As for the negative impact of sea level rise on the economy and life of the population in the coastal zone, the following should be recalled. At the end of the last century, sea levels were higher than they are now, and this was in no way perceived as an environmental disaster. And before the level was even higher. Meanwhile, Astrakhan has been known since the middle of the 13th century, and here in the 13th - mid-16th centuries the capital of the Golden Horde, Sarai-Batu, was located. These and many other settlements on the Caspian coast did not suffer from high levels, since they were located on elevated places and during abnormal flood levels or surges, people temporarily moved from low places to higher places.
Why is it that now the consequences of sea level rise, even to lower levels, are perceived as a catastrophe? The reason for the enormous damage suffered by the national economy is not the rise in level, but the thoughtless and short-sighted development of a strip of land within the mentioned risk zone, freed (as it turned out, temporarily!) from under sea level after 1929, that is, when the level decreased below the mark - 26 abs. m. The buildings erected in the risk zone, naturally, turned out to be flooded and partially destroyed. Now, when a territory developed and polluted by humans is flooded, a dangerous ecological situation is actually created, the source of which is not natural processes, but unreasonable economic activity.
ABOUT THE REASONS FOR CASPIAN LEVEL FLUCTUATIONS
When considering the reasons for fluctuations in the level of the Caspian Sea, it is necessary to pay attention to the confrontation between two concepts in this area: geological and climatic. Significant contradictions in these approaches emerged, for example, at the international conference "Caspian-95".
According to the geological concept, the causes of changes in the level of the Caspian Sea include processes of two groups. The processes of the first group, according to geologists, lead to changes in the volume of the Caspian basin and, as a consequence, to changes in sea level. Such processes include vertical and horizontal tectonic movements of the earth's crust, accumulation of bottom sediments and seismic phenomena. The second group includes processes that, as geologists believe, affect the underground flow into the sea, either increasing or decreasing it. Such processes are called periodic extrusion or absorption of waters that saturate bottom sediments under the influence of changing tectonic stresses (changes in periods of compression and extension), as well as technogenic destabilization of the subsurface caused by oil and gas production or underground nuclear explosions. It is impossible to deny the fundamental possibility of the influence of geological processes on the morphology and morphometry of the Caspian basin and underground flow. However, at present, the quantitative connection of geological factors with fluctuations in the level of the Caspian Sea has not been proven.
There is no doubt that tectonic movements played a decisive role in the initial stages of the formation of the Caspian basin. However, if we take into account that the Caspian Sea basin is located within a geologically heterogeneous territory, which results in a periodic rather than linear nature of tectonic movements with repeated changes in sign, then one should hardly expect a noticeable change in the capacity of the basin. The tectonic hypothesis is not supported by the fact that the coastlines of the New Caspian transgressions on all sections of the Caspian coast (with the exception of certain areas within the Absheron archipelago) are at the same level.
There is no reason to believe that the cause of fluctuations in the level of the Caspian Sea is a change in the capacity of its depression due to the accumulation of sediments. The rate of filling of the basin with bottom sediments, among which the main role is played by river discharges, is estimated, according to modern data, to be about 1 mm/year or less, which is two orders of magnitude less than the currently observed changes in sea level. Seismic deformations, which are noted only near the epicenter and attenuate at close distances from it, cannot have any significant effect on the volume of the Caspian basin.
As for the periodic large-scale discharge of groundwater into the Caspian Sea, its mechanism is still unclear. At the same time, this hypothesis is contradicted, according to E.G. Maevu, firstly, the undisturbed stratification of silt waters, indicating the absence of noticeable migrations of water through the thickness of bottom sediments, and secondly, the absence of proven powerful hydrological, hydrochemical and sedimentation anomalies in the sea, which should have accompanied large-scale discharge of groundwater that could influence changes in reservoir level.
The main proof of the insignificant role of geological factors at present is the convincing quantitative confirmation of the plausibility of the second, climatic, or more precisely, water-balance concept of Caspian level fluctuations.
CHANGES IN THE COMPONENTS OF THE CASPIAN WATER BALANCE AS THE MAIN REASON FOR FLUCTUATIONS IN ITS LEVEL
For the first time, fluctuations in the level of the Caspian Sea were explained by changes in climatic conditions (more specifically, river flow, evaporation and precipitation on the sea surface) by E.Kh. Lentz (1836) and A.I. Voeikov (1884). Later, the leading role of changes in the components of the water balance in sea level fluctuations was proven again and again by hydrologists, oceanologists, physical geographers and geomorphologists.
The key to most of the studies mentioned is the development of a water balance equation and the analysis of its components. The meaning of this equation is as follows: the change in the volume of water in the sea is the difference between the incoming (river and underground runoff, precipitation on the sea surface) and outgoing (evaporation from the sea surface and outflow of water into the Kara-Bogaz-Gol Bay) components of the water balance. The change in the level of the Caspian Sea is the quotient of the change in the volume of its waters divided by the area of the sea. The analysis showed that the leading role in the water balance of the sea belongs to the ratio of the runoff of the Volga, Ural, Terek, Sulak, Samur, Kura rivers and visible or effective evaporation, the difference between evaporation and precipitation on the sea surface. Analysis of the components of the water balance revealed that the largest contribution (up to 72% of the variance) to the level variability is made by the influx of river water, and more specifically, the zone of runoff formation in the Volga basin. As for the reasons for the change in the Volga runoff itself, many researchers believe that they are associated with the variability of atmospheric precipitation (mainly winter) in the river basin. And the precipitation regime, in turn, is determined by atmospheric circulation. It has long been proven that the latitudinal type of atmospheric circulation contributes to an increase in precipitation in the Volga basin, and the meridional type contributes to a decrease.
V.N. Malinin revealed that the root cause of moisture entering the Volga basin should be sought in the North Atlantic, and specifically in the Norwegian Sea. It is there that an increase in evaporation from the sea surface leads to an increase in the amount of moisture transferred to the continent and, accordingly, to an increase in atmospheric precipitation in the Volga basin. The latest data on the water balance of the Caspian Sea, obtained by employees of the State Oceanographic Institute R.E. Nikonova and V.N. Bortnik, are given with clarifications by the author in table. 1. These data provide convincing evidence that the main causes of both the rapid drop in sea level in the 1930s and the sharp rise in 1978-1995 were changes in river flow, as well as visible evaporation.
Bearing in mind that river flow is one of the main factors influencing the water balance and, as a consequence, the level of the Caspian Sea (and the Volga flow provides at least 80% of the total river flow into the sea and about 70% of the incoming part of the Caspian water balance), It would be interesting to find a connection between sea level and the flow of the Volga alone, measured most accurately. Direct correlation of these quantities does not give satisfactory results.
However, the connection between sea level and Volga runoff is clearly visible if we take into account the river flow not for every year, but take the ordinates of the difference integral runoff curve, that is, the sequential sum of normalized deviations of annual runoff values from the long-term average value (norm). Even a visual comparison of the course of the average annual levels of the Caspian Sea and the difference integral curve of the Volga runoff (see Fig. 2) allows us to identify their similarities.
Over the entire 98-year period of observations of the Volga runoff (the village of Verkhnee Lebyazhye at the top of the delta) and sea level (Makhachkala), the correlation coefficient between the sea level and the ordinates of the difference integral runoff curve was 0.73. If we discard years with small changes in level (1900-1928), then the correlation coefficient increases to 0.85. If we take for analysis a period with a rapid decline (1929-1941) and a rise in level (1978-1995), then the overall correlation coefficient will be 0.987, and separately for both periods 0.990 and 0.979, respectively.
The above calculation results fully confirm the conclusion that during periods of a sharp decrease or rise in sea level, the levels themselves are closely related to the runoff (more precisely, to the sum of its annual deviations from the norm).
A special task is to assess the role of anthropogenic factors in fluctuations in the level of the Caspian Sea, and first of all, the reduction of river flow due to irreversible losses due to the filling of reservoirs, evaporation from the surface of artificial reservoirs, and water intake for irrigation. It is believed that since the 40s, irreversible water consumption has steadily increased, which has led to a reduction in the influx of river water to the Caspian Sea and an additional decrease in its level compared to the natural one. According to V.N. Malinin, by the end of the 80s, the difference between the actual sea level and the restored (natural) reached almost 1.5 m. At the same time, the total irrecoverable water consumption in the Caspian basin was estimated in those years at 36-45 km3/year (of which the Volga accounted for about 26 km3/year). If it were not for the withdrawal of river flow, sea level rise would have begun not in the late 70s, but in the late 50s.
The increase in water consumption in the Caspian basin by 2000 was predicted first to 65 km3/year, and then to 55 km3/year (36 of which were accounted for by the Volga). Such an increase in irretrievable losses of river flow should have reduced the level of the Caspian Sea by more than 0.5 m by 2000. In connection with assessing the impact of irreversible water consumption on the level of the Caspian Sea, we note the following. Firstly, estimates in the literature of the volumes of water intake and losses due to evaporation from the surface of reservoirs in the Volga basin are apparently significantly overestimated. Secondly, forecasts for the growth of water consumption turned out to be erroneous. The forecasts included the pace of development of water-consuming sectors of the economy (especially irrigation), which not only turned out to be unrealistic, but also gave way to a decline in production in recent years. In fact, as A.E. points out. Asarin (1997), by 1990, water consumption in the Caspian basin was about 40 km3/year, and has now decreased to 30-35 km3/year (in the Volga basin up to 24 km3/year). Therefore, the “anthropogenic” difference between the natural and actual sea level is currently not as great as predicted.
ABOUT POSSIBLE FLUCTUATIONS IN THE CASPIAN SEA LEVEL IN THE FUTURE
The author does not set himself the goal of analyzing in detail the numerous forecasts of fluctuations in the level of the Caspian Sea (this is an independent and difficult task). The main conclusion from assessing the results of forecasting Caspian level fluctuations can be drawn as follows. Although the forecasts were based on completely different approaches (both deterministic and probabilistic), there was not a single reliable forecast. The main difficulty in using deterministic forecasts based on the sea water balance equation is the lack of development of the theory and practice of ultra-long-term climate change forecasts over large areas.
When sea levels dropped in the 1930s to 1970s, most researchers predicted they would fall further. In the last two decades, when sea level rise began, most forecasts predicted an almost linear and even accelerating rise in sea level to -25 and even -20 abs. m and higher at the beginning of the 21st century. Three circumstances were not taken into account. Firstly, the periodic nature of fluctuations in the level of all closed reservoirs. The instability of the Caspian Sea level and its periodic nature is confirmed by an analysis of its current and past fluctuations. Secondly, at a sea level close to – 26 abs. m, the flooding of large bays-sors on the north-eastern coast of the Caspian Sea - Dead Kultuk and Kaydak, as well as low-lying areas in other places on the coast - will begin to flood, which have dried out at low levels. This would lead to an increase in the area of shallow waters and, as a consequence, to an increase in evaporation (up to 10 km3/year). At higher sea levels, the outflow of water into Kara-Bogaz-Gol will increase. All this should stabilize or at least slow down the level increase. Thirdly, level fluctuations under the conditions of the modern climatic era (the last 2000 years), as shown above, are limited by the risk zone (from – 30 to – 25 abs. m). Taking into account the anthropogenic decrease in runoff, the level is unlikely to exceed the level of 26-26.5 abs. m.
The decrease in average annual levels in the last four years by a total of 0.34 m may indicate that in 1995 the level reached its maximum (- 26.66 abs. m), and a change in the trend of the Caspian level. In any case, the prediction is that sea level is unlikely to exceed 26 absolute. m, apparently, is justified.
In the 20th century, the level of the Caspian Sea changed within 3.5 m, first falling and then rising sharply. This behavior of the Caspian Sea is the normal state of a closed reservoir as an open dynamic system with variable conditions at its inlet.
Each combination of incoming (river flow, precipitation on the sea surface) and outgoing (evaporation from the surface of a reservoir, outflow into the Kara-Bogaz-Gol Bay) components of the Caspian water balance corresponds to its own level of equilibrium. Since the components of the water balance of the sea also change under the influence of climatic conditions, the level of the reservoir fluctuates, trying to reach an equilibrium state, but never reaches it. Ultimately, the trend of changes in the level of the Caspian Sea at a given time depends on the ratio of precipitation minus evaporation in the catchment area (in the basins of the rivers that feed it) and evaporation minus precipitation above the reservoir itself. There is actually nothing unusual about the recent rise in the Caspian sea level by 2.3 m. Such level changes have happened many times in the past and have not caused irreparable damage to the natural resources of the Caspian Sea. The current rise in sea level has become a disaster for the economy of the coastal zone only because of the unreasonable development by man of this risk zone.
Vadim Nikolaevich Mikhailov, Doctor of Geographical Sciences, Professor of the Department of Land Hydrology, Faculty of Geography, Moscow State University, Honored Scientist of the Russian Federation, Full Member of the Academy of Water Sciences. Area of scientific interests: hydrology and water resources, interaction of rivers and seas, deltas and estuaries, hydroecology. Author and co-author of about 250 scientific works, including 11 monographs, two textbooks, four scientific and methodological manuals.
CASPIAN SEA (Caspian), the largest enclosed body of water on the globe, an 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 its size, unique natural conditions and the complexity of hydrological processes, the Caspian Sea is usually classified as a closed inland sea.
The Caspian Sea is located in a vast area of internal drainage and occupies a deep tectonic depression. The water level in the sea is about 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 extends along the meridian for 1030 km.
The largest bays: in the east - Mangyshlaksky, Kara-Bogaz-Gol, Turkmenbashi (Krasnovodsky), Turkmensky; in the west - Kizlyarsky, Agrakhansky, Kizilagaj, Baku Bay; in the south there are 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 are Kulaly, Morskoy, Tyuleniy, Chechen. Off the western coast is the Absheron archipelago, to the south lie the islands of the Baku archipelago, off the eastern coast is the narrow island of Ogurchinsky, stretched from north to south.
The northern shores of the Caspian Sea are low-lying and very sloping, characterized by the widespread development of drying areas formed as a result of surge phenomena; deltaic shores are also developed here (deltas of the Volga, Ural, Terek) with an abundant supply of terrigenous material; the Volga delta with extensive reed thickets stands out. The western shores are abrasive, south of the Absheron Peninsula, mostly accumulative deltaic type with numerous bay bars and spits. The southern shores are low. The eastern shores are mostly deserted and low-lying, composed of sand.
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, a powerful earthquake measuring 8.2 on the Richter scale occurred. On the islands and coast of the southern part of the sea, eruptions of mud volcanoes are often observed, leading to the formation of new shoals, banks and small islands, which are eroded by waves and appear again.
Based on the peculiarities of physical-geographical conditions and the nature of the bottom topography in the Caspian Sea, it is customary to distinguish the Northern, Middle and Southern Caspian Seas. The Northern Caspian Sea is distinguished by exceptionally shallow waters, located entirely within the shelf with average depths of 4-5 m. Even small changes in the level here on low-lying coasts lead to significant fluctuations in the area of the water surface, therefore the boundaries of the sea in the north-eastern part are shown with a dotted line on small-scale maps. The greatest depths (about 20 m) are observed only near the conventional border with the Middle Caspian, which is drawn along a line connecting the island of Chechen (north of the Agrakhan Peninsula) with Cape Tyub-Karagan on the Mangyshlak Peninsula. The Derbent depression (maximum depth 788 m) stands out in the bottom topography of the Middle Caspian Sea. The border between the Middle and Southern Caspian Sea passes over the Absheron threshold with depths of up to 180 m along the line from Chilov Island (east of the Absheron Peninsula) to Cape Kuuli (Turkmenistan). The Southern Caspian basin 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 is in the Middle Caspian, and less than 1% of the Caspian waters are located in the Northern Caspian due to shallow depths. In general, the topography of the Caspian Sea bottom is dominated by shelf areas (the entire northern part and a wide strip along the eastern coast of the 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-shelly sands, shell, and oolitic sands are common; deep-sea areas of the bottom are covered with siltstone and silty sediments with a high content of calcium carbonate. In some areas of the bottom, bedrock of Neogene age is exposed. Mirabilite accumulates in the Kara-Bogaz-Gol Bay.
Tectonically, within the Northern Caspian Sea, the southern part of the Caspian syneclise of the Eastern European Platform is distinguished, which in the south is framed by the Astrakhan-Aktobe zone, composed of Devonian-Lower Permian carbonate rocks that lie on a volcanic base and contain large deposits of oil and natural combustible gas. From the southwest, Paleozoic folded formations of the Donetsk-Caspian zone (or Karpinsky ridge) are thrust onto the syneclise, which is a protrusion of the foundation of the young Scythian (in the west) and Turanian (in the east) platforms, which are separated at the bottom of the Caspian Sea by the Agrakhan-Gurievsky fault (left shear) of northeastern strike. The Middle Caspian mainly belongs to the Turanian 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 deposits of oil and combustible gas in local uplifts. The Absheron threshold, separating the Middle Caspian from the South, is a connecting link of the Cenozoic folded systems of the Greater Caucasus and 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 (from the Oligocene - the relict oceanic basin of the Paratethys). By the beginning of the Pliocene, it lost contact with the Black Sea. The Northern and Middle Caspian Seas were drained, and the paleo-Volga valley stretched through them, the delta of which was located in the Absheron Peninsula region. Delta sediments have become the main reservoir of oil and natural combustible gas deposits in Azerbaijan and Turkmenistan. In the late Pliocene, in connection with the Akchagyl transgression, the area of the Caspian Sea greatly increased and the connection with the World Ocean was 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 Quaternary time, transgressions (Apsheron, 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 west coast it is warm temperate, the southwestern and southern coasts lie within the subtropics, and on the east coast a desert climate prevails. In winter, over the Northern and Middle Caspian, the weather is formed under the influence of Arctic continental and sea air, and the Southern Caspian is often under the influence of southern cyclones. The weather in the west is unstable and 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 ones are influenced by the Iran-Afghan minimum, which together creates dry, stable warm weather. Over the sea, winds prevail in the northern and northwestern (up to 40%) and southeastern (about 35%) directions. 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 Absheron Peninsula - 8-9 m/s. Northern storm “Baku Nords” reach speeds of 20-25 m/s. The lowest average monthly air temperatures -10 °C are observed in January - February in the northeastern regions (in the most severe winters they reach -30 °C), in the southern regions 8-12 °C. In July - August, average monthly temperatures over the entire sea area are 25-26 °C, with a maximum of 44 °C 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. The open sea receives an average of about 200 mm of precipitation per year.
Hydrological regime. Changes in the water balance of an enclosed sea greatly influence changes in the volume of water and corresponding fluctuations in level. 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 to Kara-Bogaz- Gol 13/3, which forms a negative water balance of 9 km 3, or 3 cm of 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. Since the beginning of the 20th century, level fluctuations have shown a steady downward trend, as a result of which over 75 years the level dropped by 3.2 m and in 1977 reached -29 m (lowest position in the last 500 years). The sea surface area has decreased by more than 40 thousand km 2, which exceeds the area of the 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 unevenness of river flow (primarily the Volga runoff), therefore the lowest level is observed in winter, the highest in summer. Short-term sharp changes in level are associated with surge phenomena; they are most pronounced in shallow northern areas and during storm surges can reach 3-4 m. Such surges cause flooding of large coastal areas of land. In the Middle and Southern Caspian Sea, surge fluctuations in level average 10-30 cm, under storm conditions - up to 1.5 m. The frequency of surges, depending on the region, is from one to 5 times a month, lasting up to one day. In the Caspian Sea, as in any closed body of water, 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 vibrations 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 and the Urals and enters the shallow Northern Caspian Sea. The rivers of the western coast - Kura, Samur, Sulak, Terek, etc. - provide up to 10% of the flow. Another approximately 5% of fresh water is brought to the South Caspian by rivers on the Iranian coast. The eastern desert shores are completely deprived of constant fresh flow.
The average speed of wind currents is 15-20 cm/s, the highest - up to 70 cm/s. In the Northern Caspian Sea, 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. Near 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 Southern Caspian and turns north, joining the coastal current that goes around the entire eastern coast. The average state of movement of Caspian surface waters is often disturbed due to variability in wind conditions and other factors. Thus, in the northeastern shallow area, a local anticyclonic gyre may arise. Two anticyclonic eddies are often observed in the Southern Caspian Sea. In the Middle Caspian in the warm season, stable northwest winds create southerly transport along the eastern coast. In light winds and during calm weather, currents may have other directions.
Wind waves develop very strongly, since the prevailing winds have a long acceleration length. The disturbance develops mainly in the northwest and southeast directions. Strong storms are observed in the open waters of the Middle Caspian Sea, in the areas of Makhachkala, the Absheron Peninsula and the Mangyshlak Peninsula. The average wave height of greatest frequency is 1-1.5 m; at wind speeds of more than 15 m/s it increases to 2-3 m. The highest wave heights are recorded during strong storms in the area of the Neftyanye Kamni hydrometeorological station: annually 7-8 m, in some cases up to 10 m.
The water temperature on the sea surface in January - February in the Northern Caspian Sea is close to freezing temperature (about -0.2 - -0.3 °C) and gradually increases southward to 11 °C off the coast of Iran. In summer, surface waters warm up to 23-28 °C everywhere, except for the eastern shelf of the Middle Caspian Sea, where in July - August seasonal coastal upwelling develops and the surface water temperature drops to 12-17 °C. In winter, due to intense convective mixing, the water temperature changes little with depth. In summer, under the upper heated layer at horizons of 20-30 m, a seasonal thermocline (a layer of sharp temperature changes) is formed, separating deep cold waters from warm surface ones. In the bottom layers of water in deep-sea depressions, the temperature remains 4.5-5.5 °C all year round in the Middle Caspian and 5.8-6.5 °C in the Southern Caspian. Salinity in the Caspian Sea is almost 3 times lower than in open areas of the World Ocean, averaging 12.8-12.9‰. It should be especially emphasized that the salt composition of Caspian water is not completely identical to the composition of ocean waters, which is explained by the isolation of the sea from the ocean. The waters of the Caspian Sea are poorer in sodium salts and chlorides, but richer in carbonates and sulfates of calcium and magnesium 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 areas of the Volga and Ural the water is fresh (less than 1‰), and as we 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. The differences in salinity between the Middle and Southern Caspian Seas are small; salinity increases slightly from northwest to southeast, reaching 13.6‰ in the Turkmen Gulf (in Kara-Bogaz-Gol up to 300‰). Vertical changes in salinity are small and rarely exceed 0.3‰, which indicates good vertical mixing of waters. Water transparency varies widely 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 is classified as a partially frozen sea. Ice conditions are observed annually only in the northern regions. The Northern Caspian is completely covered by sea ice, the Middle Caspian is partially covered (only in severe winters). The average boundary of sea ice runs along an arc convex to the north, from the Agrakhan Peninsula in the west to the Tyub-Karagan Peninsula in the east. Ice formation usually begins in mid-November in the extreme northeast and gradually spreads to the southwest. In January, the entire Northern Caspian Sea is covered with ice, mostly fast ice (immobile). Drifting ice borders the fast ice with a strip 20-30 km wide. The average ice thickness is from 30 cm at the southern border to 60 cm in the northeastern regions of the Northern Caspian Sea, in hummocky accumulations - 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 south, along the western coast, sometimes to the Absheron Peninsula. At the beginning of April, the sea is completely free of ice cover.
History of the study . It is believed that the modern name of the Caspian Sea comes from the ancient Caspian tribes who inhabited the coastal areas 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 claim that this body of water is isolated, that is, it is a lake. In the works of Arab scientists of the Middle Ages there is information that in the 13th-16th centuries the Amu Darya partially flowed into this sea through one of its 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 actually arbitrary drawings. By order of Tsar Peter I, in 1714-15, an expedition was organized 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. Soimonov and K. Verdun. In 1731, Soimonov published the first atlas, and soon the first printed sailing guide of the Caspian Sea. A new edition of 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, and at the beginning of the 19th century by A.E. Kolodkin, who for the first time carried out instrumental compass surveying of the coast. In 1807, a new map of the Caspian Sea was published, compiled taking into account the latest inventories. In 1837, systematic instrumental observations of sea level fluctuations began in Baku. In 1847, the first complete description of the Kara-Bogaz-Gol Bay was made. In 1878, a 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, 1914-15, under the leadership of N. M. Knipovich, expeditionary research was carried out on the hydrology and hydrobiology of the Caspian Sea; in 1934, the Commission for the Comprehensive Study of the Caspian Sea was created at the USSR Academy of Sciences. Soviet geologists I. made a great contribution to the study of the geological structure and oil content of the Absheron Peninsula and the geological history of the Caspian Sea. M. Gubkin, D. V. and V. D. Golubyatnikov, 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, comprehensive research was launched in the Caspian Sea, aimed at studying the hydrometeorological regime, biological conditions and geological structure of the sea.
In the 21st century in Russia, two large scientific centers are engaged in solving the problems of the Caspian Sea. The Caspian Marine Research Center (CaspMNRC), created in 1995 by 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 back to 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 Scientific Research Institute of Marine Fisheries and Oceanography (CaspNIRO), modern name since 1965]. CaspNIRH is developing the foundations for the conservation and rational use of 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. The natural resources of the Caspian Sea are 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-sedimented salts in the Kara-Bogaz-Gol Bay. The Caspian region is also known as a massive habitat for waterfowl and semi-aquatic birds. About 6 million migratory birds migrate across the Caspian Sea every year. In this regard, the Volga delta, Kyzylagaj, Northern Cheleken and Turkmenbashi bays are recognized as sites of international rank within the framework of the Ramsar Convention. The mouth areas of many rivers flowing into the sea have unique types of vegetation. The fauna of the Caspian Sea is represented by 1800 species of animals, of which 415 are vertebrate species. More than 100 species of fish live in the sea and river mouths. Marine species are of commercial importance - herring, sprat, gobies, sturgeon; freshwater - carp, perch; Arctic “invaders” - salmon, whitefish. Large ports: Astrakhan, Makhachkala in Russia; Aktau, Atyrau in Kazakhstan; Turkmenbashi in Turkmenistan; Bender-Torkemen, Bender-Anzeli in Iran; Baku in Azerbaijan.
Ecological state. The Caspian Sea is under powerful anthropogenic influence due to the intensive development of hydrocarbon deposits and the active development of fishing. In the 1980s, the Caspian Sea provided up to 80% of the world's sturgeon catch. Predatory fishing in recent decades, poaching and a sharp deterioration of the environmental situation have brought many valuable fish species to the brink of extinction. The living conditions of not only fish, but also birds and sea animals (Caspian seal) have deteriorated. 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 observed only in parts of the sea remote from the coast.
Lit.: Caspian Sea. M., 1969; Comprehensive studies of the Caspian Sea. M., 1970. Issue. 1; Gul K.K., Lappalainen T.N., Polushkin V.A. Caspian Sea. M., 1970; Zalogin B.S., Kosarev A.N. Seas. M., 1999; International tectonic map of the Caspian Sea and its frame / 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).