The Caspian Sea is located at the junction of two parts of the Eurasian continent - Europe and Asia. The Caspian Sea is shaped like the Latin letter S, its length Caspian Sea from north to south - approximately 1200 kilometers (36°34" - 47°13" N), from west to east - from 195 to 435 kilometers, on average 310-320 kilometers (46° - 56° E).
The Caspian Sea is conventionally divided according to physical and geographical conditions into 3 parts - the Northern Caspian, the Middle Caspian and the Southern Caspian. The conditional border between the Northern and Middle Caspian Seas passes along the Chechen line (island)- Tyub-Karagansky Cape, between the Middle and Southern Caspian Seas - along the Zhilaya line (island)- Gan-Gulu (Cape). The area of the Northern, Middle and Southern Caspian Sea is 25, 36, 39 percent, respectively.
According to one hypothesis, the Caspian Sea received its name in honor of the ancient tribes of horse breeders - the Caspians, who lived BC on the southwestern coast of the Caspian Sea. Throughout the history of its existence, the Caspian Sea had about 70 names among different tribes and peoples: Hyrcanian Sea; Khvalynskoe Sea or Khvalisskoe Sea - Old Russian name, derived from the name of the inhabitants of Khorezm who traded in the Caspian Sea - hvalis; Khazar Sea - name in Arabic (Bahr al-Khazar), Persian (Darya-e Khazar), Turkish and Azerbaijani (Khazar denizi) languages; Abeskun Sea; Sarayskoye Sea; Derbent Sea; Sihai and other names. In Iran, the Caspian Sea is still called the Khazar or Mazandaran Sea. (after the name of the people inhabiting the coastal province of Iran of the same name).
The coastline of the Caspian Sea is estimated at approximately 6,500 - 6,700 kilometers, with islands - up to 7,000 kilometers. The shores of the Caspian Sea in most of its territory are low-lying and smooth. In the northern part, the coastline is indented by water streams and islands of the Volga and Ural deltas, the shores are low and swampy, and the water surface in many places is covered with thickets. The east coast is dominated by limestone shores adjacent to semi-deserts and deserts. The most winding shores are on the western coast in the area of the Absheron Peninsula and on the eastern coast in the area of the Kazakh Gulf and Kara-Bogaz-Gol.
Large peninsulas of the Caspian Sea: Agrakhan Peninsula, Absheron Peninsula, Buzachi, Mangyshlak, Miankale, Tub-Karagan.
There are about 50 large and medium-sized islands in the Caspian Sea with a total area of approximately 350 square kilometers. The largest islands: Ashur-Ada, Garasu, Gum, Dash, Zira (island), Zyanbil, Kur Dashi, Khara-Zira, Sengi-Mugan, Chechen (island), Chygyl.
Large bays of the Caspian Sea: Agrakhansky Bay, Komsomolets (bay) (formerly Dead Kultuk, formerly Tsesarevich Bay), Kaydak, Mangyshlak, Kazakh (bay), Turkmenbashi (bay) (formerly Krasnovodsk), Turkmen (bay), Gizilagach, Astrakhan (bay), Gyzlar, Girkan (formerly Astarabad) and Anzeli (formerly Pahlavi).
On the eastern coast is the salt lake Kara Bogaz Gol, which until 1980 was a bay-lagoon of the Caspian Sea, connected to it by a narrow strait. In 1980, a dam was built separating Kara-Bogaz-Gol from the Caspian Sea, and in 1984 a culvert was built, after which the level of Kara-Bogaz-Gol dropped by several meters. In 1992, the strait was restored, through which water flows from the Caspian Sea to Kara-Bogaz-Gol and evaporates there. Every year, 8 - 10 cubic kilometers of water flow from the Caspian Sea to Kara-Bogaz-Gol (according to other sources - 25 thousand kilometers) and about 150 thousand tons of salt.
130 rivers flow into the Caspian Sea, of which 9 rivers have a delta-shaped mouth. Large rivers flowing into the Caspian Sea - Volga, Terek (Russia), Ural, Emba (Kazakhstan), Kura (Azerbaijan), Samur (Russian border with Azerbaijan), Atrek (Turkmenistan) and others. Largest river, flowing into the Caspian Sea - the Volga, its average annual flow is 215-224 cubic kilometers. The Volga, Ural, Terek and Emba provide up to 88 - 90% of the annual runoff of the Caspian Sea.
The area of the Caspian Sea basin is approximately 3.1 - 3.5 million square kilometers, which is approximately 10 percent of the world's closed water basin area. The length of the Caspian Sea basin from north to south is about 2500 kilometers, from west to east - about 1000 kilometers. The Caspian Sea basin covers 9 states - Azerbaijan, Armenia, Georgia, Iran, Kazakhstan, Russia, Uzbekistan, Turkey and Turkmenistan.
The Caspian Sea washes the shores of five coastal states:
- Russia (Dagestan, Kalmykia and Astrakhan region)- in the trap and north-west, 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, coastline length - 724 kilometers
- Azerbaijan - in the southwest, the length of the coastline is 955 kilometers
The largest city and port on the Caspian Sea is Baku, the capital of Azerbaijan, which is located in the southern part of the Absheron Peninsula and has a population of 2,070 thousand people. (2003) . Other major Azerbaijani Caspian cities are Sumgait, which is located in the northern part of the Absheron Peninsula, and Lankaran, which is located near the southern border of Azerbaijan. To the South-East of the Absheron Peninsula, the oil workers’ settlement Neftyanye Kamni is located, the structures of which are located on artificial islands, overpasses and technological sites.
Large Russian cities - the capital of Dagestan, Makhachkala, and the southernmost city of Russia, Derbent - are located on the western coast of the Caspian Sea. 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 the northern coast of the Caspian Sea.
On the eastern shore of the Caspian Sea there is a Kazakh city - the port of Aktau, in the north in the Ural delta, 20 km from the sea, the city of Atyrau is located, south of Kara-Bogaz-Gol on the northern shore of the Krasnovodsk Bay - the Turkmen city of Turkmenbashi, former Krasnovodsk. Several Caspian cities are located in the southern (Iranian) coast, the largest of them is Anzeli.
The area and volume of water of the Caspian Sea varies significantly depending on fluctuations in water levels. At a water level of −26.75 m, the area was approximately 392,600 square kilometers, the volume of water was 78,648 cubic kilometers, which is approximately 44 percent 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 Lake Baikal (1620 m.) and Tanganyika (1435 m.). The average depth of 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.
The water level in the Caspian Sea is subject to significant fluctuations. According to modern science, over the past 3 thousand years the amplitude of changes in the water level of the Caspian Sea has amounted to 15 meters. Instrumental measurements of the level of the Caspian Sea and systematic observations of its fluctuations have been carried out since 1837, during which time the most high level water registered in 1882 (-25.2 m.), lowest - in 1977 (-29.0 m.), since 1978 the water level has risen and in 1995 reached −26.7 m; since 1996, a downward trend has emerged again. Scientists associate the reasons for changes in the water level of the Caspian Sea with climatic, geological and anthropogenic factors.
Water temperature is subject to significant latitudinal changes, most clearly expressed 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 difference in water temperature 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 off the west coast is 1 - 2 °C higher than that on the east, and in the open sea the water temperature is 2 - 4 °C higher than off the coast. Based on the nature of the horizontal structure of the temperature field in the annual cycle of variability, three time periods can be distinguished in the upper 2-meter layer. From October to March, the water temperature increases in the southern and eastern regions, which is especially noticeable in the Middle Caspian. Two stable quasi-latitudinal zones can be distinguished, where temperature gradients are increased. This is, firstly, the border between the Northern and Middle Caspian, and, secondly, between the Middle and Southern. At the ice edge, in the northern frontal zone, the temperature in February-March increases from 0 to 5 °C, in the southern frontal zone, in the area of the Absheron threshold, from 7 to 10 °C. During this period, the least cooled waters are in the center of the South Caspian Sea, which form a quasi-stationary core. In April-May, the area of minimum temperatures moves to the Middle Caspian Sea, which is associated with faster heating of waters in the shallow northern part of the sea. True, at the beginning of the season in the northern part of the sea a large amount of heat is spent on melting ice, but already in May the temperature here rises to 16 - 17 °C. In the middle part the temperature at this time is 13 - 15 °C, and in the south it increases to 17 - 18 °C. Spring warming of water evens out horizontal gradients, and the temperature difference between coastal areas and the open sea does not exceed 0.5 °C. Warming of the surface layer, which begins in March, disrupts the uniformity of temperature distribution with depth. In June-September, horizontal uniformity in the temperature distribution in the surface layer is observed. In August, which is the month of greatest warming, the water temperature throughout the sea is 24 - 26 °C, and in the southern regions it rises to 28 °C. In August, the water temperature in shallow bays, for example, in Krasnovodsk, can reach 32 °C. The main feature of the water temperature field at this time is upwelling. It is observed annually along the entire eastern coast of the Middle Caspian and partially penetrates even into the Southern Caspian. The rise of cold deep waters occurs with varying intensity as a result of the influence of northwest winds prevailing in the summer season. Wind this direction causes the outflow of warm surface waters from the coast and the rise of colder waters from the intermediate layers. Upwelling begins in June, but it reaches its greatest intensity in July-August. As a result, a decrease in temperature is observed on the water surface (7 - 15 °C). Horizontal temperature gradients reach 2.3 °C on the surface and 4.2 °C at a depth of 20 m. The source of upwelling gradually shifts from 41 - 42° N. in June to 43 - 45° N. in September. Summer upwelling is of great importance for the Caspian Sea, radically changing the dynamic processes in the deep-water area. In open areas of the sea, at the end of May - beginning of June, the formation of a temperature jump layer begins, which is most clearly expressed in August. Most often it is located between horizons of 20 and 30 m in the middle part of the sea and 30 and 40 m in the southern part. Vertical temperature gradients in the shock layer are very significant and can reach several degrees per meter. In the middle part of the sea, due to the surge off the eastern coast, the shock layer rises close to the surface. Since in the Caspian Sea there is no stable baroclinic layer with a large reserve of potential energy similar to the main thermocline of the World Ocean, then with the cessation of the prevailing winds causing upwelling and with the beginning of autumn-winter convection in October-November, a rapid restructuring of temperature fields to the winter regime occurs. In the open sea, the water temperature in the surface layer drops in the middle part to 12 - 13 °C, in the southern part to 16 - 17 °C. In the vertical structure, the shock layer is eroded due to convective mixing and disappears by the end of November.
The salt composition of the waters of the closed Caspian Sea differs from the oceanic one. There are significant differences in the ratios of concentrations of salt-forming ions, especially for waters in areas directly influenced by continental runoff. The process of metamorphization of sea waters under the influence of continental runoff leads to a decrease in the relative content of chlorides in the total amount of salts of sea waters, an increase in the relative amount of carbonates, sulfates, calcium, which are the main components in chemical composition river waters. The most conservative ions are potassium, sodium, chlorine and magnesium. The least conservative are calcium and bicarbonate ions. In the Caspian Sea, the content of calcium and magnesium cations is almost two times higher than in the Sea of Azov, and the sulfate anion is three times higher. Water salinity changes especially sharply in the northern part of the sea: from 0.1 units. psu in the mouth areas of the Volga and Ural up to 10 - 11 units. psu on the border with the Middle Caspian. Mineralization in shallow salty bays-kultuks can reach 60 - 100 g/kg. In the Northern Caspian, during the entire ice-free period from April to November, a salinity front of a quasi-latitudinal location is observed. The greatest desalination, associated with the spread of river flow across the sea, is observed in June. The formation of the salinity field in the Northern Caspian Sea is greatly influenced by the wind field. In the middle and southern parts of the sea, salinity fluctuations are small. Basically it is 11.2 - 12.8 units. psu, increasing in the southern and eastern directions. Salinity increases slightly with depth (by 0.1 - 0.2 psu units). In the deep-sea part of the Caspian Sea, in the vertical profile of salinity, characteristic deflections of isohalines and local extrema are observed in the area of the eastern continental slope, which indicate processes of bottom sliding of waters salinizing in the eastern shallow waters of the South Caspian. The salinity value also strongly depends on sea level and (which is related) on the volume of continental runoff.
The relief of the northern part of the Caspian Sea is a shallow undulating plain with banks and accumulative islands, the average depth of the Northern Caspian Sea is about 4 - 8 meters, the maximum does not exceed 25 meters. The Mangyshlak threshold separates the Northern Caspian from the Middle Caspian. The Middle Caspian is quite deep, the water depth in the Derbent depression reaches 788 meters. The Absheron threshold separates the Middle and Southern Caspian Seas. The Southern Caspian is considered deep-sea; the water depth in the South Caspian depression reaches 1025 meters from the surface of the Caspian Sea. Shell sands are widespread on the Caspian shelf, deep-sea areas are covered with silty sediments, and in some areas there is an outcrop of bedrock.
The climate of the Caspian Sea is continental in the northern part, temperate in the middle and subtropical in the southern part. In winter, the average monthly temperature of the Caspian Sea 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 was 44 degrees.
The average annual precipitation is 200 millimeters per year, ranging from 90-100 millimeters in the arid eastern part to 1,700 millimeters along the southwestern subtropical coast. Evaporation of water from the surface of the Caspian Sea is about 1000 millimeters per year, the most intense evaporation in the area of the Absheron Peninsula and in the eastern part of the South Caspian Sea is up to 1400 millimeters per year.
On the territory of the Caspian Sea, winds often blow, their average annual speed is 3-7 meters per second, and northern winds predominate in the wind rose. In the autumn and winter months, winds become stronger, with wind speeds often reaching 35-40 meters per second. The most windy areas are the Absheron Peninsula and the environs of Makhachkala - Derbent, where the highest wave was recorded - 11 meters.
Water circulation in the Caspian Sea is related to runoff and winds. Since most of the drainage occurs in the Northern Caspian Sea, northern currents predominate. An intense northern current carries water from the Northern Caspian along the western coast to the Absheron Peninsula, where the current divides into two branches, one of which moves further along the western coast, the other goes to the Eastern Caspian.
The fauna of the Caspian Sea is represented by 1810 species, of which 415 are vertebrates. 101 species of fish are registered in the Caspian world, where most of the world's sturgeon reserves are concentrated, as well as such freshwater fish as roach, carp, and pike perch. The Caspian Sea is the habitat of fish such as carp, mullet, sprat, kutum, bream, salmon, perch, and pike. The Caspian Sea is also home to a marine mammal - the Caspian seal. Since March 31, 2008, 363 dead seals have been found on the coast of the Caspian Sea in Kazakhstan.
The flora of the Caspian Sea and its coast is represented by 728 species. The predominant plants in the Caspian Sea are algae - blue-green, diatoms, red, brown, characeae and others, and flowering plants - zoster and ruppia. In origin, the flora is predominantly of Neogene age, but some plants were brought into the Caspian Sea by humans deliberately or on the bottoms of ships.
CaspAndyskoe mOre(Caspian) is the largest enclosed body of water on Earth. In size, the Caspian Sea is much larger than lakes such as Superior, Victoria, Huron, Michigan, and Baikal. According to formal characteristics, the Caspian Sea is an endorheic lake. However, given its large size, brackish waters and a regime similar to the sea, this body of water is called a sea.
According to one hypothesis, the Caspian Sea (among the ancient Slavs – the Khvalynsk Sea) received its name in honor of the Caspian tribes who lived BC on its southwestern coast.
The Caspian Sea washes the shores of five states: Russia, Azerbaijan, Iran, Turkmenistan and Kazakhstan.
The Caspian Sea is elongated in the meridional direction and is located between 36°33΄ and 47°07΄ N latitude. and 45°43΄ and 54°03΄ E. (without Kara-Bogaz-Gol Bay). The length of the sea along the meridian is about 1200 km; average width – 310 km. The northern coast of the Caspian Sea is bordered by the Caspian lowland, the eastern coast by the deserts of Central Asia; in the west the Caucasus Mountains approach the sea, in the south the Elburz ridge stretches near the coast.
The surface of the Caspian Sea is located significantly below the level of the World Ocean. Its current level fluctuates around -27...-28 m. These levels correspond to a sea surface area of 390 and 380 thousand km 2 (without the Kara-Bogaz-Gol Bay), a water volume of 74.15 and 73.75 thousand km 3, average depth approximately 190 m.
The Caspian Sea is traditionally divided into three large parts: the Northern (24% of the sea area), the Middle (36%) and the Southern Caspian (40%), which differ significantly in morphology and regime, as well as the large and isolated Kara-Bogaz-Gol Bay. The northern, shelf part of the sea is shallow: its average depth is 5–6 m, maximum depths are 15–25 m, the volume is less than 1% of the total water mass of the sea. The Middle Caspian is an isolated basin with an area of maximum depths in the Derbent depression (788 m); its average depth is about 190 m. In the South Caspian, the average and maximum depths are 345 and 1025 m (in the South Caspian depression); 65% of the sea's water mass is concentrated here.
There are about 50 islands in the Caspian Sea with a total area of approximately 400 km2; the main ones are Tyuleniy, Chechen, Zyudev, Konevsky, Dzhambaysky, Durneva, Ogurchinsky, Apsheronsky. The length of the coastline is approximately 6.8 thousand km, with islands - up to 7.5 thousand km. The shores of the Caspian Sea are diverse. In the northern and eastern parts they are quite rugged. Here are the large bays of Kizlyarsky, Komsomolets, Mangyshlaksky, Kazakhsky, Kara-Bogaz-Gol, Krasnovodsky and Turkmensky, many bays; off the west coast - Kyzylagachsky. The largest peninsulas are Agrakhansky, Buzachi, Tyub-Karagan, Mangyshlak, Krasnovodsky, Cheleken and Apsheronsky. The most common shores are accumulative; areas with abrasion coasts are found along the contour of the Middle and Southern Caspian Sea.
Over 130 rivers flow into the Caspian Sea, the largest of which are the Volga , Ural, Terek, Sulak, Samur, Kura, Sefidrud, Atrek, Emba (its flow enters the sea only in high-water years). Nine rivers have deltas; the largest are located at the mouths of the Volga and Terek.
The main feature of the Caspian Sea, as an endorheic reservoir, is instability and a wide range of long-term fluctuations in its level. This most important hydrological feature of the Caspian Sea has a significant impact on all its other hydrological characteristics, as well as on the structure and regime of river mouths and coastal zones. In the Caspian Sea level varied in the range of ~200 m: from -140 to +50 m BS; at -34 to -20 m BS. From the first third of the 19th century. and until 1977, sea level dropped by about 3.8 m - to the lowest level in the last 400 years (-29.01 m BS). In 1978–1995 The level of the Caspian Sea rose by 2.35 m and reached -26.66 m BS. Since 1995, a certain downward trend in level has been dominant - to -27.69 m BS in 2013.
During major events, the northern shore of the Caspian Sea shifted to the Samara Luka on the Volga, and perhaps further. At maximum transgressions, the Caspian Sea turned into a drainage lake: excess water flowed through the Kuma-Manych depression into the Sea of Azov and further into the Black Sea. During extreme regressions, the southern coast of the Caspian Sea shifted to the Absheron threshold.
Long-term fluctuations in the Caspian Sea level are explained by changes in the structure of the water balance of the Caspian Sea. Sea level rises when the incoming part of the water balance (primarily the water flow of rivers) increases and exceeds the outgoing part, and decreases if the influx of river water decreases. The total water flow of all rivers averages 300 km 3 /year; while the five largest rivers account for almost 95% (the Volga gives 83%). During the period of the lowest sea level, in 1942–1977, the river flow was 275.3 km 3 /year (of which 234.6 km 3 /year was the Volga runoff), precipitation - 70.9, underground flow - 4 km 3 /year, and evaporation and outflow into the Kara-Bogaz-Gol Bay are 354.79 and 9.8 km 3 /year. During the period of intense sea level rise, in 1978–1995, - respectively 315 (Volga - 274.1), 86.1, 4, 348.79 and 8.7 km 3 /year; in the modern period - 287.4 (Volga - 248.2), 75.3, 4, 378.3 and 16.3 km 3 /year.
Intra-annual changes in the level of the Caspian Sea are characterized by a maximum in June–July and a minimum in February; the range of intra-annual level fluctuations is 30–40 cm. Surge level fluctuations occur throughout the sea, but they are most significant in the northern part, where, with maximum surges, the level can rise by 2–4.5 m and the edge “retreat” by several tens kilometers inland, and during surges it will drop by 1–2.5 m. Seiche and tidal level fluctuations do not exceed 0.1–0.2 m.
Despite the relatively small size of the reservoir, there is strong excitement in the Caspian Sea. The highest wave heights in the Southern Caspian Sea can reach 10–11 m. Wave heights decrease in the direction from south to north. Storm waves can develop at any time of the year, but they are more frequent and more dangerous in the cold half of the year.
In the Caspian Sea as a whole, wind currents predominate; Nevertheless, in the estuary coastal zones of large rivers, runoff currents play a significant role. In the Middle Caspian, cyclonic water circulation predominates, in the Southern Caspian - anticyclonic. In the northern part of the sea, patterns of wind currents are more irregular and depend on the characteristics and variability of the wind, bottom topography and coastal contours, river flow and aquatic vegetation.
Water temperature is subject to significant latitudinal and seasonal changes. In winter, it varies from 0–0.5 o C at the ice edge in the north of the sea to 10–11 o C in the south. In summer, the water temperature in the sea averages 23–28 o C, and in shallow coastal waters in the Northern Caspian Sea it can reach 35–40 o C. At depths, a constant temperature is maintained: deeper than 100 m it is 4–7 o C.
In winter, only the northern part of the Caspian Sea freezes; in severe winter - the entire Northern Caspian and coastal zones of the Middle Caspian. Freeze-up in the Northern Caspian lasts from November to March.
Water salinity changes especially sharply in the northern part of the sea: from 0.1‰ at the mouths of the Volga and Urals to 10–12‰ on the border with the Middle Caspian. In the Northern Caspian Sea, the temporal variability of water salinity is also great. In the middle and southern parts of the sea, salinity fluctuations are small: it is generally 12.5–13.5‰, increasing from north to south and from west to east. The highest water salinity is in the Kara-Bogaz-Gol Bay (up to 300‰). With depth, the salinity of water increases slightly (by 0.1–0.3‰). The average salinity of the sea is about 12.5‰.
More than a hundred species of fish live in the Caspian Sea and the mouths of the rivers flowing into it. There are Mediterranean and Arctic invaders. The fish species are goby, herring, salmon, carp, mullet and sturgeon. The latter include five species: sturgeon, beluga, stellate sturgeon, thorn and sterlet. The sea can produce up to 500–550 thousand tons of fish annually, if overfishing is not allowed. Of the marine mammals, the endemic Caspian seal lives in the Caspian Sea. 5–6 million waterfowl migrate through the Caspian region annually.
The economy of the Caspian Sea is associated with oil and gas production, shipping, fishing, seafood, various salts and minerals (Kara-Bogaz-Gol Bay), and the use of recreational resources. The explored oil resources in the Caspian Sea amount to about 10 billion tons, the total resources of oil and gas condensate are estimated at 18–20 billion tons. Oil and gas production is carried out on an ever-increasing scale. The Caspian Sea is also used by water transport, including along the river-sea and sea-river routes. The main ports of the Caspian Sea: Astrakhan, Olya, Makhachkala (Russia), Aktau, Atyrau (Kazakhstan), Baku (Azerbaijan), Noushehr, Bandar-Anzeli, Bandar-Torkemen (Iran) and Turkmenbashi (Turkmenistan).
Economic activities and hydrological features of the Caspian Sea create a number of serious environmental and water management problems. Among them: anthropogenic pollution of river and sea waters (mainly with petroleum products, phenols and surfactants), poaching and reduction of fish stocks, especially sturgeon; damage to the population and coastal economic activities due to large-scale and rapid changes in the level of the reservoir, the impact of numerous dangerous hydrological phenomena and hydrological-morphological processes.
The total economic loss for all Caspian countries associated with the rapid and significant recent rise in the level of the Caspian Sea, the flooding of part of the coastal land, and the destruction of coastlines and coastal structures, amounted to approximately 15 to 30 billion US dollars. Urgent engineering measures were required to protect the coast.
A sharp drop in the level of the Caspian Sea in the 1930s–1970s. resulted in less damage, but it was still significant. Navigable approach channels became shallow, the shallow seaside at the mouths of the Volga and Ural became heavily overgrown, which became an obstacle to the passage of fish into the rivers to spawn. Fish passages had to be built through the mentioned seashores.
Among the unresolved problems is the lack of an international agreement on the international legal status of the Caspian Sea, the division of its waters, bottom and subsoil.
The Caspian Sea is the object of many years of research by specialists from all Caspian states. Such domestic organizations as the State Oceanographic Institute, the Institute of Oceanology of the Russian Academy of Sciences, the Hydrometeorological Center of Russia, the Caspian Research Institute of Fisheries, the Faculty of Geography of the Moscow State University took an active part in the study of the Caspian Sea. state university etc.
The 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 in past geological eras it had connections with the ocean.
The sea area 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 the landscapes, climatic conditions and the types of rivers are different. Despite its vastness, only 62.6% of its area is in waste areas; about 26.1% - for non-drainage. 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). The largest river in the Caspian basin is the Volga, which provides 78% of the river waters 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 other features of the waters of the Caspian Sea), as well as the Kura River , Zhaiyk (Ural), Terek, Sulak, Samur.
Physiographically and according to the nature of the underwater relief, the sea is divided into three parts: northern, middle and southern. The conventional border between the northern and middle parts runs along the line Chechen Island–Cape Tyub-Karagan, and between the middle and southern parts along the line Zhiloy Island–Cape Kuuli.
The shelf of the Caspian Sea is on average limited to depths of about 100 m. The continental slope, which begins below the shelf edge, ends in the middle part at approximately 500–600 m depths, in the southern part, where it is very steep, at 700–750 m.
The northern part of 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 topography is complicated by the presence of banks, islands, and grooves.
The middle part of the sea is an isolated 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 by the Absheron threshold, which is a continuation Greater Caucasus. The depths above this underwater ridge do not exceed 180 m. The deepest part of the South Caspian depression 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.
The shores of the Caspian Sea are diverse. In the northern part of the sea they are quite indented. Here are the Kizlyarsky, Agrakhansky, Mangyshlaksky bays and many shallow bays. Notable peninsulas: Agrakhansky, Buzachi, Tyub-Karagan, Mangyshlak. Large islands in the northern part of the sea are Tyuleniy and Kulaly. In the deltas of the Volga and Ural rivers, the coastline is complicated by many islands and channels, often changing 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. The Absheron Peninsula is located on the western coast, on the border with the southern part of the sea. To the east of it there are islands and banks of the Absheron archipelago, of which the largest island is Zhiloy. The eastern coast of the Middle Caspian is more indented; the Kazakh Gulf with Kenderli Bay and several capes stand out here. 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 on the bottom of the sea. On the eastern shore there are large bays of Turkmenbashi and Turkmensky, and near it 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 level lower 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 sea level, the amplitude of its fluctuations has been almost 4 m, from –25.3 m in the eighties of the 19th century. to –29 m in 1977. In the last century, the level of the Caspian Sea changed significantly twice. In 1929 it stood at about -26 m, and since it had been close to this level for almost a century, this level position was considered to be a long-term or secular average. In 1930 the level began to decline rapidly. By 1941 it had dropped by almost 2 m. This led to the drying out of vast coastal areas of the bottom. The decrease in level, with slight fluctuations (short-term slight rises in level in 1946–1948 and 1956–1958), continued until 1977 and reached a level of –29.02 m, i.e. the level reached its lowest position in history the last 200 years.
In 1978, contrary to all forecasts, sea level began to rise. As of 1994, the level of the Caspian Sea was at –26.5 m, that is, over 16 years the level rose by more than 2 m. The rate of this rise is 15 cm per year. Level increment in individual years was higher, and in 1991 reached 39 cm.
The general fluctuations in the level of the Caspian Sea are superimposed by its seasonal changes, the long-term average of which reaches 40 cm, as well as surge phenomena. The latter are especially pronounced in the Northern Caspian Sea. The northwestern coast is characterized by large surges created by prevailing storms from the eastern and southeastern directions, especially in the cold season. A number of large (more than 1.5–3 m) surges have been observed here over the past decades. 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 waters.
Climate. The Caspian Sea is located in temperate and subtropical climatic zones. Climatic conditions change in the meridional direction, since the sea stretches from north to south for almost 1200 km.
Various circulation systems interact in the Caspian region, however, winds from eastern directions predominate throughout the year (influence of the Asian High). The position at fairly low latitudes provides a positive balance of heat influx, so the Caspian Sea serves as a source of heat and moisture for passing air masses for most of the year. The average annual temperature in the northern part of the sea is 8–10°C, in the middle - 11–14°C, in the southern part - 15–17°C. However, in the northernmost areas of the sea, the average January temperature is from –7 to –10°C, and the minimum during intrusions of Arctic air is down to –30°C, which determines the formation of 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 dramatic temperature fluctuations.
The Caspian Sea is characterized by a very small amount of precipitation per year - only 180 mm, with most of it falling during 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 lower (for the western part only 137 mm), and the seasonal distribution is more uniform (10–18 mm per month). In general, we can talk about the proximity of climatic conditions to arid ones.
Water temperature. The distinctive features of the Caspian Sea (large differences in depths in different parts of the sea, the nature of the bottom topography, isolation) have a certain influence on the formation of temperature conditions. In the shallow Northern Caspian Sea, the entire water column can be considered homogeneous (the same applies to shallow bays located in other parts of the sea). In the Middle and Southern Caspian Sea, surface and deep masses can be distinguished, separated by a transition layer. In the Northern Caspian and in the surface layers of the Middle and Southern Caspian, water temperatures vary over a wide range. In winter, temperatures vary from north to south from less than 2 to 10°C, the water temperature off the west coast is 1–2°C higher than that on the east, in the open sea the temperature is higher than at the coasts: by 2–3°C in the middle part and by 3–4°С in the southern part of the sea. In winter, the distribution of temperature with depth is more uniform, which is facilitated by winter vertical circulation. During moderate and severe winters in the northern part of the sea and shallow bays of the east coast, the water temperature drops to freezing temperature.
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 Northern Caspian Sea. The zone where the lowest temperatures occur is adjacent to the east coast. This is explained by the rise of cold deep waters to the surface. Temperatures are also relatively low in the poorly heated deep-sea central part. In open areas of the sea, at the end of May–beginning of June, the formation of a temperature jump layer begins, which is most clearly expressed in August. Most often it is located between 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 off the eastern coast, the shock layer rises close to the surface. In the bottom layers of the sea, the temperature throughout the year is about 4.5°C in the middle part and 5.8–5.9°C in the southern part.
Salinity. Salinity values are determined by factors such as river flow, 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, bottom topography, which determines the location of waters with different salinities, mainly along isobaths, evaporation, which ensures a deficit of fresh water and an influx of saltier water. These factors collectively influence seasonal differences in salinity.
The Northern Caspian Sea 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 flow. Horizontal salinity gradients can reach 1‰ per 1 km.
The eastern part of the Northern Caspian Sea 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.
Based on the values of horizontal salinity gradients, it is possible to distinguish in the western part of the Northern Caspian the river-sea contact zone 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 strengthening 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 seashore in summer is 10–15°C higher than the bottom waters.
In the deep-sea depressions of the Middle and Southern Caspian Sea, fluctuations in salinity in the upper layer are 1–1.5‰. The largest difference between the maximum and minimum salinity was noted in the area of the Absheron threshold, where it is 1.6‰ in the surface layer and 2.1‰ at a 5 m horizon.
The decrease in salinity along the western coast of the South Caspian Sea in the 0–20 m layer is caused by the flow of the Kura River. The influence of the Kura runoff decreases with depth; at 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 there is a strip of desalinated water with a salinity of 10–12.5‰, coming from the Northern Caspian Sea.
In addition, in the Southern Caspian Sea, an increase in salinity occurs when salted waters are carried out from bays and bays on the eastern shelf under the influence of southeastern winds. Subsequently, these waters are transferred to the Middle Caspian Sea.
In the deep layers of the Middle and Southern Caspian Sea, the 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-water part of the Southern Caspian, the upper boundary of waters with high salinity drops to 250 m. Obviously, in these parts of the sea, vertical mixing of waters is difficult.
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 part - southwestern and southern ones. Currents caused by the runoff of the Volga and Ural rivers can be traced only within the estuary coastal area. The prevailing current speeds are 10–15 cm/s, in open areas of the Northern Caspian Sea the maximum speeds 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 northwest, north, southeast and southern directions, off the east coast there are often easterly currents. Along the western coast of the middle part of the sea, the most stable currents are southeastern and southern. Current speeds are on average about 20–40 cm/s, with maximum speeds reaching 50–80 cm/s. Other types of currents also play a significant role in the circulation of sea waters: gradient, seiche, and inertial.
Ice formation. The Northern Caspian Sea is covered with ice every year in November, the area of the frozen part of the water area depends on the severity of the winter: in severe winters the entire Northern Caspian Sea is covered with ice, in mild winters the ice remains within 2–3 meter isobath. The appearance of ice in the middle and southern parts of the sea occurs in December-January. On the eastern coast the ice is of local origin, while on the western coast it is most often brought in from the northern part of the sea. In severe winters, shallow bays freeze off the eastern coast of the middle part of the sea, shores and fast ice form off the coast, and on the western coast, drifting ice spreads to the Absheron Peninsula in abnormally cold winters. The disappearance of 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 patterns.
The central part of the waters of the Northern Caspian Sea is characterized by a fairly uniform distribution of oxygen. An increased oxygen content is found in the areas near the Volga River near the mouth, while a decreased oxygen content is found in the southwestern part of the Northern Caspian Sea.
In the Middle and Southern Caspian Sea, the highest concentrations of oxygen are confined to shallow coastal areas and pre-estuary coastal areas of rivers, with the exception of the most polluted areas of the sea (Baku Bay, Sumgait region, etc.).
In the deep-water areas of the Caspian Sea, the main pattern remains the same throughout all seasons - a decrease in oxygen concentration with depth.
Thanks to autumn-winter cooling, the density of the waters of the Northern Caspian Sea increases to a value at which it becomes possible for the flow of North Caspian waters from high content oxygen along the continental slope to significant depths of the Caspian Sea.
The seasonal distribution of oxygen is mainly associated with the annual course and seasonal relationship of production-destruction processes occurring in the sea.
In spring, the production of oxygen during photosynthesis very significantly covers the decrease in oxygen caused by a decrease in its solubility with increasing water temperature in spring.
In the areas of the mouths of the coastal rivers feeding the Caspian Sea, in the spring there is a sharp increase in the relative oxygen content, which in turn is an integral indicator of the intensification of the photosynthesis process and characterizes the degree of productivity of the mixing zones of sea and river waters.
In summer, due to the significant warming of water masses and the activation of photosynthesis processes, the leading factors in the formation of the oxygen regime are photosynthetic processes in surface waters, and biochemical oxygen consumption by bottom sediments in bottom waters.
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 minimal entry into the lower layers of the sea, resulting in the formation of an oxygen deficiency zone in the Northern Caspian Sea. Intense photosynthesis in the open waters of the deep-sea regions of the Middle and Southern Caspian Sea covers the upper 25-meter layer, where oxygen saturation is more than 120%.
In autumn, in the well-aerated shallow areas of the Northern, Middle and Southern Caspian Sea, the formation of oxygen fields is determined by the processes of water cooling and the less active, but still ongoing process of photosynthesis. The oxygen content is increasing.
The spatial distribution of nutrients in the Caspian Sea reveals the following patterns:
- increased concentrations of nutrients are characteristic of areas near the mouth of the coastal rivers that feed the sea and shallow areas of the sea subject to active anthropogenic influence (Baku Bay, Turkmenbashi Bay, water areas adjacent to Makhachkala, Fort Shevchenko, etc.);
- 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 Sea, the cyclonic nature of the circulation contributes to the rise of deep waters with a high content of nutrients into the overlying layers of the sea;
- in the deep-water regions of the Middle and Southern Caspian Sea, the vertical distribution of nutrients depends on the intensity of the convective mixing process, and their content increases with depth.
The dynamics of nutrient concentrations throughout the year in the Caspian Sea are influenced by such factors as seasonal fluctuations in nutrient runoff into the sea, the seasonal ratio of production-destructive processes, the intensity of exchange between soil and water mass, ice conditions in winter in the Northern Caspian, winter processes vertical circulation in deep sea areas.
In winter, a significant area of the Northern Caspian Sea is covered with ice, but biochemical processes actively develop in subglacial water and ice. The ice of the Northern Caspian, being a kind of accumulator of nutrients, transforms these substances entering the sea from and from the atmosphere.
As a result of the winter vertical circulation of water in the deep-water regions of the Middle and Southern Caspian Sea during 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 Sea 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 Sea during floods, are due to intensive washing by river waters.
In the spring season, in the area of water exchange between the Northern and Middle Caspian Seas in the subsurface layer, with a maximum oxygen content, the phosphate content is minimal, which, in turn, indicates the activation of the photosynthesis process in this layer.
In the Southern Caspian, the distribution of nutrients in spring is basically similar to their distribution in the Middle Caspian.
In summer, a redistribution is detected in the waters of the Northern Caspian various forms biogenic compounds. Here the content of ammonium nitrogen and nitrates decreases significantly, 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 Southern Caspian Sea, the concentration of phosphates has decreased due to their consumption during photosynthesis and the difficulty of water exchange with the deep-sea accumulation zone.
In autumn in the Caspian Sea, due to the cessation of activity of some types of phytoplankton, the content of phosphates and nitrates increases, and the concentration of silicon decreases, as there is an autumn outbreak of the development of diatoms.
Oil has been extracted on the Caspian Sea shelf for more than 150 years.
Currently, large hydrocarbon reserves are being developed on the Russian shelf, the resources of which on the Dagestan shelf are estimated at 425 million tons in oil equivalent (of which 132 million tons of oil and 78 billion m3 of gas), on the shelf of the Northern Caspian Sea - at 1 billion tons of oil .
In total, about 2 billion tons of oil have already been produced in the Caspian Sea.
Losses of oil and its products during production, transportation and use reach 2% of the total volume.
The main sources of pollutants, including petroleum products, entering the Caspian Sea are removal with river runoff, discharge of untreated industrial and agricultural wastewater, municipal waste waste water cities and towns located on the coast, shipping, exploration and exploitation of oil and gas fields located at the bottom of the sea, oil transportation by sea. The places where pollutants enter with river runoff are 90% concentrated in the Northern Caspian Sea, industrial wastewater is confined mainly to the area of the Absheron Peninsula, and increased oil pollution of the Southern Caspian Sea is associated with oil production and oil exploration drilling, as well as with active volcanic activity (mud) in zone of oil and gas bearing structures.
From the territory of Russia, about 55 thousand tons of petroleum products enter the Northern Caspian annually, including 35 thousand tons (65%) from the Volga River and 130 tons (2.5%) from the runoff of the Terek and Sulak rivers.
Thickening of the film on the water surface to 0.01 mm disrupts gas exchange processes and threatens the death of hydrobiota. The concentration of petroleum products is toxic for fish at 0.01 mg/l and for phytoplankton at 0.1 mg/l.
The development of oil and gas resources on the bottom of the Caspian Sea, the forecast reserves of which are estimated at 12–15 billion tons of standard fuel, will become the main factor in the anthropogenic load on the sea ecosystem in the coming decades.
Caspian autochthonous fauna. Total number autochthons - 513 species or 43.8% of the entire fauna, which include herring, gobies, mollusks, etc.
Arctic species. The total number of the Arctic group is 14 species and subspecies, or only 1.2% of the entire Caspian fauna (mysids, sea cockroach, whitefish, Caspian salmon, Caspian seal, etc.). The basis of the Arctic fauna are crustaceans (71.4%), which easily tolerate desalination and live at great depths of the Middle and Southern Caspian Sea (from 200 to 700 m), since the lowest water temperatures are maintained here throughout the year (4.9– 5.9°C).
Mediterranean species. These are 2 types of mollusks, needle fish, etc. At the beginning of the 20s of our century, the mollusk mytileaster entered here, later 2 types of shrimp (with mullet, during their acclimatization), 2 types of mullet and flounder. Some Mediterranean species entered the Caspian Sea after the opening of the Volga-Don Canal. Mediterranean species play a significant role in the food supply of fish in the Caspian Sea.
Freshwater fauna (228 species). This group includes anadromous and semi-anadromous fish (sturgeon, salmon, pike, catfish, carp, and also rotifers).
Marine species. 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 bodies of water on the planet.
The Caspian Sea produces more than 80% of the world's sturgeon catches, the bulk of which occur in the Northern Caspian Sea.
To increase sturgeon catches, which sharply decreased during the years of falling sea levels, a set of measures is being implemented. Among them are a complete ban on sturgeon fishing in the sea and its regulation in rivers, and an increase in the scale of sturgeon factory farming.
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The Caspian Lake is one of the most unique places on Earth. It keeps many secrets related to the history of the development of our planet.
Position on physical map
The Caspian Sea is an internal, drainless salt lake. The geographical location of the Caspian Lake is the continent of Eurasia at the junction of parts of the world (Europe and Asia).
The length of the lake shoreline ranges from 6500 km to 6700 km. Taking into account the islands, the length increases to 7000 km.
The coastal areas of the Caspian Lake are mostly low-lying. Their northern part is cut by the channels of the Volga and Ural. The river delta is rich in islands. The surface of the water in these areas is covered with thickets. Large areas of land are swampy.
The eastern coast of the Caspian Sea adjoins the On the shores of the lake there are significant deposits of limestone. The western and part of the eastern coasts are characterized by a winding coastline.
The Caspian Lake is represented on the map by its considerable size. The entire territory adjacent to it was called the Caspian Sea.
Some characteristics
The Caspian Lake has no equal on Earth in terms of its area and volume of water. It stretches from north to south for 1049 kilometers, and its longest length from west to east is 435 kilometers.
If we take into account the depth of the reservoirs, their area and volume of water, then the lake is comparable to the Yellow, Baltic and Black Seas. According to the same parameters, the Caspian Sea surpasses the Tyrrhenian, Aegean, Adriatic and other seas.
The volume of water available in the Caspian Lake is 44% of the supply of all lake waters on the planet.
Lake or sea?
Why is the Caspian Lake called a sea? Was it really the impressive size of the reservoir that led to the assignment of such a “status”? More precisely, this became one of these reasons.
Others include the huge mass of water in the lake and the presence of large waves during stormy winds. All this is typical for real seas. It becomes clear why the Caspian Lake is called a sea.
But one of the main conditions that must exist in order for geographers to classify a body of water as a sea is not mentioned here. We are talking about a direct connection between the lake and the World Ocean. It is precisely this condition that the Caspian Sea does not meet.
Where the Caspian Lake is located, a depression was formed in the earth’s crust several tens of thousands of years ago. Today it is filled with the waters of the Caspian Sea. According to scientists, at the end of the 20th century, the water level in the Caspian Sea was 28 meters below the level of the World Ocean. The direct connection between the waters of the lake and the ocean ceased to exist approximately 6 thousand years ago. The conclusion from the above is that the Caspian Sea is a lake.
There is one more feature that distinguishes the Caspian Sea from the sea - the salinity of its water is almost 3 times lower than the salinity of the World Ocean. The explanation for this is that about 130 large and small rivers carry fresh water to the Caspian Sea. The Volga makes the most significant contribution to this work - it “gives” up to 80% of all water to the lake.
The river played another important role in the life of the Caspian Sea. It is she who will help find the answer to the question of why the Caspian Lake is called a sea. Now that man has built many canals, it has become a fact that the Volga connects the lake with the World Ocean.
History of the lake
The modern appearance and geographical position of the Caspian Lake are determined by continuous processes occurring on the surface of the Earth and in its depths. There were times when the Caspian was connected to the Sea of Azov, and through it to the Mediterranean and Black Sea. That is, tens of thousands of years ago the Caspian Lake was part of the World Ocean.
As a result of processes associated with raising and lowering earth's crust, mountains appeared on the site of the modern Caucasus. They isolated a body of water that was part of a huge ancient ocean. Tens of thousands of years passed before the basins of the Black and Caspian Seas separated. But for a long time the connection between their waters was carried out through the strait, which was on the site of the Kuma-Manych depression.
Periodically, the narrow strait was either dried up or filled with water again. This happened due to fluctuations in the level of the World Ocean and changes in the appearance of the land.
In a word, the origin of the Caspian Lake is closely connected with the general history of the formation of the Earth's surface.
Yours modern name the lake received due to the Caspian tribes that inhabited the eastern parts of the Caucasus and steppe zones Caspian territories. Over the entire history of its existence, the lake has had 70 different names.
Territorial division of the lake-sea
The depth of the Caspian Lake is very different in different places. Based on this, the entire water area of the lake-sea was conditionally divided into three parts: the Northern, Middle and Southern Caspian.
Shallow water is the northern part of the lake. The average depth of these places is 4.4 meters. The highest level is 27 meters. And on 20% of the entire area of the Northern Caspian Sea the depth is only about a meter. It is clear that this part of the lake is of little use for navigation.
The Middle Caspian has the greatest depth of 788 meters. The deep-water part is occupied by lakes. The average depth here is 345 meters, and the greatest is 1026 meters.
Seasonal changes at sea
Due to the large extent of the reservoir from north to south, the climatic conditions on the coast of the lake are not the same. Seasonal changes in the areas adjacent to the reservoir also depend on this.
In winter on south coast lakes in Iran, the water temperature does not fall below 13 degrees. During the same period, in the northern part of the lake off the coast of Russia, the water temperature does not exceed 0 degrees. The Northern Caspian is covered with ice for 2-3 months of the year.
In summer, almost everywhere the Caspian Lake warms up to 25-30 degrees. Warm water, excellent sandy beaches, and sunny weather create excellent conditions for people to relax.
Caspian Sea on the political map of the world
There are five states on the shores of the Caspian Lake - Russia, Iran, Azerbaijan, Kazakhstan and Turkmenistan.
The western regions of the Northern and Middle Caspian Sea belong to the territory of Russia. Iran is located on the southern shores of the sea, it owns 15% of the entire coastline. The eastern coastline is shared by Kazakhstan and Turkmenistan. Azerbaijan is located in the southwestern territories of the Caspian region.
The issue of dividing the lake’s waters between the Caspian states has been the most pressing for many years. The heads of five states are trying to find a solution that would satisfy everyone's needs and requirements.
Natural resources of the lake
Caspian Sea since ancient times for local residents served as a water transport route.
The lake is famous for valuable fish species, in particular sturgeon. Their reserves account for up to 80% of the world's resources. The issue of preserving the sturgeon population is of international importance; it is being resolved at the level of the government of the Caspian states.
The Caspian seal is another mystery of the unique sea-lake. Scientists have still not fully unraveled the mystery of the appearance of this animal in the waters of the Caspian Sea, as well as other species of animals of northern latitudes.
A total of 1,809 species live in the Caspian Sea various groups animals. There are 728 species of plants. Most of them are “indigenous inhabitants” of the lake. But there is a small group of plants that were brought here intentionally by humans.
Of the mineral resources, the main wealth of the Caspian Sea is oil and gas. Some information sources The oil reserves of the Caspian Lake fields are compared with Kuwait. Industrial offshore mining black gold mining has been carried out on the lake since the end of the 19th century. The first well appeared on the Absheron shelf in 1820.
Today, governments unanimously believe that the region cannot be viewed only as a source of oil and gas, while leaving the ecology of the Caspian Sea without attention.
In addition to oil fields, in the Caspian region there are deposits of salt, stone, limestone, clay and sand. Their production also could not but affect the ecological situation of the region.
Sea level fluctuations
The water level in the Caspian Lake is not constant. This is evidenced by evidence dating back to the 4th century BC. The ancient Greeks, who explored the sea, discovered a large bay at the confluence of the Volga. The existence of a shallow strait between the Caspian and the Sea of Azov was also discovered by them.
There are other data on the water level in the Caspian Lake. The facts suggest that the level was much lower than what exists now. The ancients are proof architectural structures, discovered on the seabed. The buildings date back to the 7th-13th centuries. Now the depth of their flooding ranges from 2 to 7 meters.
In 1930, the water level in the lake began to decline catastrophically. The process continued for almost fifty years. This caused great concern among people, since all economic activity in the Caspian region is adapted to the previously established water level.
From 1978 the level began to rise again. Today he has become more than 2 meters higher. This is also an undesirable phenomenon for people living on the coast of the lake-sea.
The main reason affecting fluctuations in the lake is climate change. This entails an increase in the volume of river water entering the Caspian Sea, the amount of precipitation, and a decrease in the intensity of water evaporation.
However, it cannot be said that this is the only opinion that explains the fluctuation in water level in the Caspian Lake. There are others, no less plausible.
Human activities and environmental issues
The area of the Caspian Lake's drainage basin is 10 times larger than the surface of the reservoir itself. Therefore, all changes occurring in such a vast territory in one way or another affect the ecology of the Caspian Sea.
An important role in the change environmental situation human activity plays a role in the Caspian Lake region. For example, pollution of a reservoir with harmful and dangerous substances occurs along with the influx of fresh water. This is directly related to industrial production, mining and other human activities in the watershed.
State environment The Caspian Sea and adjacent territories are of general concern to the governments of the countries located here. Therefore, the discussion of measures aimed at preserving the unique lake, its flora and fauna has become traditional.
Each state has an understanding that only through joint efforts can the ecology of the Caspian Sea be improved.
The Caspian Sea is the most big lake on Earth. It is a residual (relict) body of water of the much wider Khvalynsk Sea, which once occupied the entire Caspian lowland. During the era of the Khvalinsk transgression, when
The level of the Caspian Sea was much higher than the modern one; it was connected to the Black Sea through a strait that passed on the site of the Kuma-Manych lowland.
In summer, the waters of the Caspian Sea warm up greatly, and the water temperature above the surface reaches +25 ... +27 ° C. In winter, the sea slowly cools down and for the most part maintains above-zero temperatures. Only its shallow northern part freezes, where floating ice is formed annually and an ice cover is established. There are no ice phenomena in the middle and southern parts of the sea.
The huge basin of the Caspian Sea in a morphological sense is divided into three parts:
1) northern - shallow (less than 10 m), separated from the middle part of the line running from the mouth of the Terek to the Mangyshlak Peninsula;
2) medium - with an average depth of 200 m and the greatest depth of 790 m;
3) southern - deep, with greatest depth up to 980 m and with an average of 325 g. The depressions in the middle and southern parts of the sea are separated by an underwater threshold.
The Caspian Sea was named for its enormous size, brackish water and similar sea regime. It is his regime that keeps many secrets to this day. The most characteristic feature of a reservoir is a change in its level.
In 1930-1970 pp. There was a retreat of the sea, which led to shallowing of coastal waters and changes in the coastline. At the same time, the shallow water area of the Volga mouth began to become overgrown, which worsened the possibility of fish passing to spawn in the main river of Russia. Fish catches, in particular sturgeon and sterlet, have sharply decreased.
A further drop in sea level was predicted. In this regard, various projects began to be developed to reduce possible negative consequences. Projects were proposed for transferring part of the flow of northern rivers to the Volga basin, separating shallow water areas with the help of dams and blocking the strait connecting the Caspian Sea with the Kara-Bogaz-Gol Bay. Fortunately, only one of the grandiose plans has begun to be implemented - the construction of a blind dam to block the strait into the Kara-Bogaz-Gol Bay. Construction was completed in 1980, but still, contrary to forecasts, sea levels began to rise. This gave rise to many rumors. Publications appeared in the press talking about catastrophic floods. Scientists reassured us, suggesting that this process would stop. And indeed: since the summer of 1995, the Caspian Sea began to gradually retreat. But soon the sea presented another surprise - from December 2002, the water level began to rise again from average speed 14 centimeters per year.
The rise in the level of the Caspian Sea was not only unexpected, but also led to even greater negative consequences than its decrease. After all, many coastal areas were developed by people. The most active offensive was in the northern shallow part of the Caspian Sea, especially in the deltas of the Volga, Terek, and Sulak rivers, where valuable agricultural land, fishing areas and large industrial centers are concentrated. The cities of Derbent, Kaspiysk, Makhachkala, Kaspiysky (Lagan) and dozens of other smaller settlements were affected. Many fields were flooded. Roads and power lines were destroyed, and damage was caused to the flora and fauna of the seaside and coastal zone of the Volga delta. The likelihood of contamination of surface and groundwater has increased, and drinking water supply conditions have worsened.
It is expected that in the next 10-12 years the level of the Caspian Sea will fluctuate within the absolute range of -27.0 ... -27.58 m (the sea is below the level of the World Ocean). It is assumed that in 2016 it may decrease by an average of 50 cm. But today no one can say whether the next forecast will come true. After all, the Caspian Sea has repeatedly raised surprises for scientists, the leadership of coastal countries and local residents.
Most scientists express the opinion that the level of the Caspian Sea depends on the rivers that feed it, precipitation and evaporation, the state and regime of which are undergoing changes under the conditions of a changing climate.
The cities of Makhachkala, Kaspiysk, Derbent, Kaspiysky, the village are located in the zone of influence of sea level fluctuations. Sulak, the Astrakhan Nature Reserve in the coastal part of the Volga delta, as well as infrastructure facilities: sewer and water supply networks, the Kizlyar-Astrakhan railway, irrigation systems, fisheries facilities, dozens of communications and energy facilities, oil fields and other structures.
The fauna of the Caspian Sea can be divided into four parts. The first group includes the descendants of ancient forms that inhabited the Tethys (an ancient ocean that existed during the Mesozoic era between the ancient continents of Gondwanaland and Laurasia) about 70 million years ago. These species include Caspian gobies and herrings, some molluscs and most crustaceans. The second group consists of Arctic species - animals that entered the Caspian Sea from the north during the post-glacial period. Of the fish, this group includes the Caspian trout and white fish (the only representative of the whitefish family in the Caspian Sea). The Arctic species also includes the only marine mammal of the Caspian Sea - the Caspian seal (Caspian seal) from the family of true seals.
The third group of animals - Mediterranean species, independently or with the help of humans, penetrated into the Caspian Sea from the Black Sea. These are two types of shellfish, shrimp, Black Sea Atlantic crab and fish - singil and sharpnose from the mullet family, needle fish and Black Sea kalkan. The fourth group of local fauna is freshwater fish species. Having penetrated into the Caspian Sea, they turned into marine or migratory fish (they rise into rivers).
The Caspian Sea is crossed by the flyways of birds nesting both in the Caspian Sea itself and in Siberia, Kazakhstan, and northern Europe. During mild winters, some birds remain to spend the winter in the Caspian Sea.