Caspian Sea

The Caspian Sea is one of the most amazing enclosed bodies of water on Earth.

Over the centuries, the sea has changed more than 70 names. The modern came from the Caspians - the tribes inhabiting the central and southeastern part of Transcaucasia 2 thousand years BC.
Geography Caspian Sea

The Caspian Sea is located at the junction of Europe with Asia and geographic location is divided into the South, North and Middle Caspian.
The middle and northern part of the sea belongs to Russia, the southern part to Iran, the eastern part to Turkmenistan and Kazakhstan, and the southwestern part to Azerbaijan.

For many years, the Caspian states have been dividing the Caspian water area among themselves, and quite sharply at that.

Caspian sea map

Lake or sea?

In fact, the Caspian Sea is the world's largest lake, but has a number of nautical signs.
These include: a large body of water, strong storms with high waves, high and low tides.

But the Caspian has no natural connection with the World Ocean, which makes it impossible to call it a sea.
At the same time, thanks to the Volga and artificially created channels, such a connection appeared.

The salinity of the Caspian Sea is 3 times lower than the usual sea level, which does not allow classifying the reservoir as a sea.

There were times when the Caspian Sea was indeed part of the World Ocean.
Several tens of thousands of years ago, the Caspian was connected to the Sea of ​​Azov, and through it to the Black and Mediterranean.
As a result of long-term processes occurring in the earth's crust, the Caucasus Mountains formed, which isolated the reservoir.
Communication between the Caspian and Black Seas for a long time was carried out through the strait (Kumo-Manych depression) and gradually ceased.

Physical quantities

Area, volume, depth

The area, volume and depth of the Caspian Sea are not constant and directly depend on the water level.
On average, the area of ​​\u200b\u200bthe reservoir is 371,000 km², the volume is 78,648 km³ (44% of all world lake water reserves).

Depth of the Caspian Sea in comparison with lakes Baikal and Tanganyika

The average depth of the Caspian is 208 m, the northern part of the sea is considered the shallowest. The maximum depth is 1025 m, noted in the South Caspian depression.
In depth, the Caspian is second only to Baikal and Tanganyika.

The length of the lake from north to south is about 1200 km, from west to east an average of 315 km. Length coastline- 6600 km, with islands - about 7 thousand km.

coast

Mostly, the coast of the Caspian Sea is low-lying and smooth.
In the northern part- heavily indented by the river channels of the Urals and the Volga. The swampy local shores are located very low.
Eastern Shores adjacent to semi-desert zones and deserts, covered with limestone deposits.
The most winding coasts are in the west in the region of the Apsheron Peninsula, and in the east - in the area of ​​the Kazakh Gulf and Kara-Bogaz-Gol.

sea ​​water temperature

The temperature of the Caspian Sea at different times of the year

Average water temperature in winter in the Caspian it fluctuates from 0 °С in the northern part and up to +10 °С in the southern part.
In the waters of Iran, the temperature does not fall below +13 °C.
With the onset of cold weather, the shallow northern part of the lake is covered with ice, which lasts for 2-3 months. The thickness of the ice cover is 25-60 cm, at especially low temperatures it can reach 130 cm. In late autumn and winter, drifting ice floes can be observed in the north.

Summer average temperature the surface of the water in the sea is + 24 °C.
Most of the sea warms up to +25 °C ... +30 °C.
Warm water and beautiful sandy, occasionally shell and pebble beaches create excellent conditions for a full-fledged beach holiday.
In the eastern part of the Caspian Sea near the city of Begdash, during the summer months, abnormally low water temperature.

Nature of the Caspian Sea

Islands, peninsulas, bays, rivers

The Caspian Sea includes about 50 large and medium-sized islands, the total area of ​​which is 350 km².
The largest of them are: Ashur-Ada, Garasu, Gum, Dash and Boyuk-Zira. The largest peninsulas are: Agrakhansky, Absheronsky, Buzachi, Mangyshlak, Miankale and Tyub-Karagan.

Tyuleniy Island in the Caspian Sea, part of the Dagestan Reserve

To the largest bays of the Caspian include: Agrakhan, Kazakh, Kizlyar, Dead Kultuk and Mangyshlak.
In the east is salt Lake Kara-Bogaz-Gol, previously a lagoon connected to the sea by a strait.
In 1980, a dam was built on it, through which water from the Caspian goes to Kara-Bogaz-Gol, where it then evaporates.

130 rivers flow into the Caspian Sea located mainly in its northern part. The largest of them: Volga, Terek, Sulak, Samur and Ural.
The average annual runoff of the Volga is 220 km³. 9 rivers have a delta-shaped mouth.

Flora and fauna

About 450 species of phytoplankton live in the Caspian Sea, including algae, aquatic and flowering plants. Of the 400 species of invertebrates, worms, crustaceans and mollusks predominate. There are a lot of small shrimp in the sea, which is an object of fishing.

More than 120 species of fish live in the Caspian and Delta. Fishing objects are sprat (“Kilkin fleet”), catfish, pike, bream, pike perch, kutum, mullet, vobla, rudd, herring, white fish, pike perch, goby, grass carp, burbot, asp and pike perch. Stocks of sturgeon and salmon are currently depleted, however, the sea is the largest supplier of black caviar in the world.

Fishing in the Caspian Sea is allowed all year round except for the period from late April to late June. On the coast there are many fishing bases with all conviniences. Fishing in the Caspian is a great pleasure. In any part of it, including in large cities, the catch is unusually rich.

The lake is famous for its large variety of waterfowl.. Geese, ducks, loons, gulls, waders, sea eagles, geese, swans and many others come to the Caspian during migration or nesting.
The largest number of birds - over 600 thousand individuals is observed in the mouths of the Volga and the Urals, in the bays of Turkmenbashi and Kyzylagach. During the hunting season, a huge number of fishermen come here not only from Russia, but also from countries near and far abroad.

Nerpa Caspian

The only mammal lives in the Caspian Sea. This is the Caspian seal or seal. Until recently, the seals swam close to the beaches, everyone could admire the amazing animal with round black eyes, the seals behaved very friendly.
Now the seal is on the verge of extinction.

Cities on the Caspian Sea

Baku is the largest city on the coast of the Caspian Sea..
The number of one of the most most beautiful cities of the world is over 2.5 million people. Baku is spread out on the most picturesque Absheron peninsula and is surrounded on three sides by the waters of the warm and oil-rich Caspian Sea.
Less big cities: the capital of Dagestan is Makhachkala, Kazakh Aktau, Turkmen Turkmenbashi and Iranian Bandar Anzeli.

Baku Bay, Baku - a city on the Caspian Sea

Interesting Facts

Scientists are still arguing about whether to call a reservoir a sea or a lake.
The level of the Caspian Sea is gradually decreasing.
The Volga delivers most of the water to the Caspian.
90% of black caviar is mined in the Caspian Sea. Among them, the most expensive is Almas beluga caviar ($2,000 per 100 g).

Companies from 21 countries are participating in the development of oil fields in the Caspian Sea. According to Russian estimates, hydrocarbon reserves in the sea amount to 12 billion tons.

American scientists claim that one fifth of the world's hydrocarbon reserves are concentrated in the depths of the Caspian Sea. This is more than the combined reserves of such oil-producing countries as Kuwait and Iraq.

On Sunday, August 12, in Kazakhstan's Aktau, the presidents of Azerbaijan, Iran, Kazakhstan, Russia and Turkmenistan signed the Convention on the Legal Status of the Caspian Sea. Previously, its status was regulated by the Soviet-Iranian treaties, in which the Caspian Sea was defined as a closed (inland) sea, and each Caspian state had sovereign rights to a 10-mile zone and equal rights to the rest of the sea.

Now, according to the new convention, each country has its own territorial waters (zones 15 miles wide). In addition, the provisions of the UN Convention on the Law of the Sea of ​​1982 will not apply to the Caspian Sea, the seabed will be delimited into sectors, as is done by neighbors on the seas, and sovereignty over the water column will be established on the basis of the principle that this is a lake.

Why is the Caspian considered neither a lake nor a sea?

To be considered a sea, the Caspian must have access to the ocean, this is one of the most important conditions for a body of water to be called a sea. But the Caspian has no access to the ocean, so it is considered a closed body of water, not connected to the oceans.

The second feature that distinguishes sea water from lake water is their high salinity. The water in the Caspian Sea is indeed salty, but in terms of its salt composition it occupies an intermediate position between a river and an ocean. In addition, in the Caspian, salinity increases towards the south. The Volga delta contains from 0.3‰ salts, and in the eastern regions of the South and Middle Caspian, salinity already reaches 13-14‰. And if we talk about the salinity of the World Ocean, then it averages 34.7 ‰.

Due to the specific geographical and hydrological characteristics, the reservoir received a special legal status. The summit participants decided that the Caspian Sea is an inland water body that has no direct connection with the World Ocean, and therefore cannot be considered a sea, and at the same time, due to its size, water composition and bottom features, it cannot be considered a lake.

What has been achieved since the signing of the Convention?

The new treaty expands the possibilities for cooperation between countries, and also involves limiting any military presence of third countries. According to political scientist, director of the Institute of Recent States Alexei Martynov, the main achievement of the last summit is that its participants managed to stop any talk about the possible construction of NATO military bases and infrastructure facilities in the Caspian Sea.

“The most important thing that has been achieved is to fix that the Caspian will be demilitarized for all the Caspian states. There will be no other military, except for those representing the countries that have signed the Caspian Agreement. This is a fundamental and main issue that was important to fix. Everything else, that is divided in proportion to the zone of influence, the zone of extraction of bioresources, the zone of extraction of shelf resources was not so important. As we remember, in the last twenty years, the military has been actively striving for the region. The US even wanted to build its own military base there,” says Martynov.

In addition to the distribution of the shares of each country in the oil and gas fields of the Caspian basin, the Convention also provides for the construction of pipelines. As stated in the document, the rules for their laying provide for the consent of only neighboring countries, and not all countries of the Caspian Sea. After the signing of the agreement, Turkmenistan, in particular, stated that it was ready to lay pipelines along the bottom of the Caspian Sea, which would allow it to export its gas through Azerbaijan to Europe. The consent of Russia, which previously insisted that the project could only be implemented with the permission of all five Caspian states, is no longer required. The gas pipeline is planned to be connected in the future to the Trans-Anatolian gas pipeline, through which natural gas will go through the territory of Azerbaijan, Georgia and Turkey to Greece.

“Turkmenistan is not a foreign country to us, but our partner, a country that we consider very important for us in the post-Soviet space. We cannot be against them receiving an additional impetus for development through such pipeline projects. Gas has been coming from Turkmenistan and other countries through a different pipeline system for a long time, somewhere it even mixes with Russian gas, and there is nothing wrong with that. If this project works, then everyone will benefit, including Russia. In no case should the project be considered as a kind of competition. The European market is so big and insatiable, I mean the energy market, that there is enough space for everyone,” says Martynov.

Today, almost all Turkmen gas is supplied to China, where Russia also intends to supply natural gas. For this purpose, in particular, a large-scale project for the construction of the Power of Siberia gas pipeline is being implemented. Thus, the geography of gas supplies from both countries may expand - Turkmenistan will gain access to the European market, and Russia will be able to increase its gas supplies to China.

The Caspian Sea is the world's largest endorheic body of water at a level of 28.5 m below the level of the World Ocean. The Caspian Sea stretches from north to south for almost 1200 km, the average width is 320 km, the length of the coastline is about 7 thousand km. The area of ​​the Caspian Sea as a result of lowering the level decreased from 422 thousand km2 (1929) to 371 thousand km2 (1957). The volume of water is about 76 thousand km3, the average depth is 180 m. The coefficient of indentation of the coast is 3.36. The largest bays: Kizlyar, Komsomolets, Kara-Bogaz-Gol, Krasnovodsk, Mangyshlak.

There are about 50 islands with a total area of ​​350 km2. The most significant of them: Kulaly, Tyuleniy, Chechen, Zhiloy. More than 130 rivers flow into the Caspian Sea. The rivers Volga, Ural, Emba, Terek (total annual flow of 88% of the total river flow into the sea) flow into the northern part of the sea. On its western coast, the Sulak, Samur, Kura and other smaller rivers provide 7% of the total runoff. The remaining 5% of the flow is supplied by the rivers of the Iranian coast.

The relief of the bottom of the Caspian Sea

By the nature of the underwater relief and features hydrological regime in the Caspian Sea, the North, Middle and South Caspian are distinguished. The Northern Caspian (about 80,000 km2) is a shallow, slightly undulating, accumulative plain with prevailing depths of 4–8 capes. Within the Middle Caspian (138 thousand km2) shelf, continental slope and Derbent depression (maximum depth 788 m). The Apsheron threshold - a chain of banks and islands with depths of 170 m between them - limits the Middle Caspian from the south. The Southern Caspian (1/3 of the area of ​​the sea) is distinguished by a very narrow shelf near the western and southern coasts and a much more extensive shelf near the eastern coast. In the depression of the South Caspian, the deepest sea depth of 1025 m was measured. The bottom of the depression is a flat abyssal plain.

Climate in the Caspian Sea

The main oaric centers that determine the atmospheric circulation over the Caspian Sea: in winter - the spur of the Asian maximum, and in summer - the crest of the Azores maximum and the trough of the South Asian depression. Characteristic features of the climate are the predominance of anticyclonic weather conditions, dry winds, and sharp changes in air temperature.

In the northern and middle parts of the Caspian Sea, from October to April, the winds of the eastern quarter prevail, and from May to September, the winds of the northwestern rhumbs prevail. In the southern part of the Caspian Sea, the monsoon character of the winds is clearly expressed.

The long-term average air temperature of the warm months (July-August) over the entire sea is 24-26°C. The absolute maximum (up to 44°C) is noted on the east coast. On average, 200 mm of precipitation falls over the sea per year, with 90-100 mm on the arid eastern coast and 1700 mm in the subtropical southwestern part of the coast. Evaporation in most of the water area is about 1000 mm/year, and in the eastern part of the South Caspian and in the area of ​​the Apsheron Peninsula up to 1400 mm/year.

Hydrological regime

The currents of the Caspian Sea are formed as a result of the combined effect of the wind regime, river runoff and density differences in individual areas. In the northern part of the Caspian Sea, the waters of the Volga River are divided into two branches. The smaller of them goes along the northern coast to the east, merges with the waters of the Ural River and forms a closed circulation. The main part of the waters of the Volga runoff goes along the western coast to the south. Somewhat to the north of the Absheron Peninsula, part of the waters of this current separates and, crossing the sea, goes to its eastern shores and flows into the waters moving to the north. Thus, in the Middle Caspian, a water cycle is formed, moving counterclockwise. The bulk of the waters spreading to the south. along west coast, enters the South Caspian and, having reached the southern coast, turns to the east, and then along the eastern coasts goes to the north.
The speed of the currents is on average about 10–15 cm/s. Frequent repetition of moderate and strong winds causes a large number of days of great excitement.

The maximum wave height (11 m) is observed in the area of ​​the Apsheron threshold. The water temperature of the surface layer of the sea in August is about 24-26 ° C in the North and Middle Caspian, up to 29 ° C in the South, 32 ° C in the Krasnovodsk Bay and over 35 ° C in the Kara-Bogaz-Gol Bay. In July-August, upwelling and associated temperature drops to 8-10°C are observed off the eastern shores.

Ice formation in the northern part of the Caspian Sea begins in December, and the ice remains for 2–3 months. In cold winters, drifting ice is carried south to the Absheron Peninsula.
Isolation from the World Ocean, the influx of river waters and the precipitation of salts as a result of intense evaporation in the Kara-Bogaz-Gol Bay determine the peculiarity of the salt composition of the Caspian Sea water - a reduced content of chlorides and an increased concentration of carbonates in comparison with the waters of the World Ocean. The Caspian Sea is a brackish water basin, the salinity of which is three times less than the normal ocean.

The average salinity of the waters of the northwestern part of the Caspian Sea is 1-2 ppm, in the region of the northern border of the Middle Caspian 12.7-12.8 ppm, and in the South Caspian 13 ppm, the maximum salinity (13.3 ppm) is observed near the eastern shores. In the Gulf of Kara-Bogaz-Gol, the salinity is 300 ppm; In the Northern and Southern Caspian, due to the reduction in inflow and salinization during ice formation, salinity increases in winter. In the South Caspian at this time, salinity decreases due to a decrease in evaporation. In summer, an increase in river flow causes a decrease in the salinity of waters in the North and Middle Caspian, and increasing evaporation leads to an increase in the salinity of the waters of the South Caspian. Changes in salinity from the surface to the bottom are small. Therefore, seasonal fluctuations in temperature and salinity of water, causing an increase in density, determine the winter vertical circulation of water, which in the Northern Caspian extends to the bottom, and in the Middle Caspian to a depth of 300 m. in winter, the waters of the Middle Caspian through the Apsheron threshold and the sliding of cooled waters of high salinity from the eastern shallow water. Studies have shown that due to the increase in water salinity over the past 25 years, the mixing depth has significantly increased, the oxygen content has correspondingly increased, and hydrogen sulfide contamination of deep waters has disappeared.

Tidal fluctuations in the level of the Caspian Sea do not exceed 3 cm. about 0.7 m. The range of seasonal level fluctuations is about 30 cm. A characteristic feature of the hydrological regime of the Caspian Sea is sharp interannual fluctuations in the average annual level. The average level from zero of the Baku footstock for a century (1830-1930) was 326 cm. The highest level (363 cm) was observed in 1896. cm. In the last decade, the level of the Caspian has stabilized at low levels with interannual fluctuations of the order of ±20 cm. Fluctuations in the level of the Caspian Sea are associated with climate changes over the entire basin of this sea.

To prevent a further drop in sea level, a system of measures is being developed. There is a project to transfer the waters of the northern rivers Vychegda and Pechora to the Volga river basin, which will increase the flow by about 32 km3. A project was developed (1972) to regulate the flow of Caspian waters into the Kara-Bogaz-Gol Bay.

Many geographical names, can mislead people who are not fond of geography. Could it be that the object marked on all maps as the sea is in fact a lake? Let's figure it out.

The history of the appearance of the Caspian Sea?

14,000,000 years ago, the Sarmatian Sea existed on the planet. It included modern, Black, Caspian and Sea of ​​Azov. About 6,000,000 years ago, due to the rise of the Caucasus Mountains and the lowering of the water level in the Mediterranean Sea, it split, forming four different seas.

The Caspian is inhabited by many representatives of the fauna of Azov, which once again confirms that once these reservoirs were one. This is one of the reasons why the Caspian Sea is considered a lake.

The name of the sea comes from the ancient tribes of the Caspians. They inhabited its shores in the first millennia BC and were engaged in horse breeding. But over the long hundreds of years of its existence, this sea has had many names. It was called Derbent, Sarai, Girkan, Sigay, Kukkuz. Even in our time, for the inhabitants of Iran and Azerbaijan, this lake is called Khazar.

Geographic location

Two parts of the world - Europe and Asia, are washed by the waters of the Caspian Sea. The coastline covers the following countries:

• Turkmenistan
• Russia
• Azerbaijan
• Kazakhstan

The length from north to south is about one thousand two hundred kilometers, the width from west to east is about three hundred kilometers. The average depth is about two hundred meters, the greatest depth is about a thousand kilometers. The total area of ​​the reservoir is more than 370,000 square kilometers and is divided into three climatic and geographical zones:

1. Northern
2. Average
3. South Caspian

The water area has six large peninsulas and about fifty islands. Their total area is four hundred square kilometers. Most major islands- Dzhambaysky, Ogurchinsky, Chechen, Tyuleniy, Konevsky, Zyudev and Apsheron Islands. About one hundred and thirty rivers flow into the Caspian, including the Volga, Ural, Atrek, Sefirud, Terek, Kura and many others.

Sea or lake?

The official name used in documentation and cartography is the Caspian Sea. But is this true?

In order to have the right to be called a sea, any body of water must be connected to the oceans. In the case of the Caspian, this is not the reality. From the nearest sea, the Black Sea, the Caspian Sea is separated by almost 500 km of land. This is a completely enclosed reservoir. The main differences of the seas:

• The seas can be fed by water arteries - rivers.
• The outer seas are directly connected with the ocean, that is, they have access to it.
• The inland seas are connected to other seas or oceans by straits.

The Caspian received the right to be called a sea primarily because of its impressive size, which is more characteristic of seas rather than lakes. In terms of area, it surpasses even Azov. Also, the fact that not a single lake washes the shores of five states at once played a significant role.

It should be noted that the structure of the bottom of the Caspian Sea belongs to the oceanic type. This happened due to the fact that it was once part of the ancient oceans.

Compared to other seas, the percentage of salt saturation in it is very weak and does not exceed 0.05%. The Caspian is fed only by rivers flowing into it, like all lakes on the globe.

Like many seas, the Caspian is famous for its powerful storms. The height of the waves can reach eleven meters. Storms can occur at any time of the year, but they are most dangerous in autumn and winter.

In fact, the Caspian Sea is the most big lake in the world. Its waters are not subject to international maritime laws. The territory of the waters is divided between countries on the basis of laws adopted for lakes, and not for seas.

The Caspian Sea has rich mineral resources such as oil and gas. Its waters are inhabited by more than one hundred and twenty species of fish. Among them are the most valuable sturgeons, such as stellate sturgeon, sturgeon, sterlet, beluga, and spike. 90% of the world's sturgeon catch goes to the Caspian Sea.

Interesting features:

• Scientists around the world have not come to an unambiguous opinion why the Caspian Sea is considered a lake. Some experts even suggest considering it a "lake-sea" or "inland" sea, like the Dead Sea in Israel;
• The deepest point of the Caspian is more than one kilometer;
• Historically, it is known that the general water level in the reservoir has changed more than once. The exact reasons for this are still not understood;
• This is the only body of water separating Asia and Europe;
• The largest waterway that feeds the lake is the Volga River. It is she who carries the bulk of the water;
• Thousands of years ago the Caspian Sea was part of the Black Sea;
• In terms of the number of fish species, the Caspian Sea loses to some rivers;
• The Caspian Sea is the main supplier of the most expensive delicacy - black caviar;
• The water in the lake is completely renewed every two hundred and fifty years;
• Territory of Japan less area the Caspian Sea.

Ecological situation

Intervention in the ecology of the Caspian Sea regularly occurs due to the extraction of oil and natural resources. There are also interventions in the fauna of the reservoir, cases of poaching and illegal catching of valuable species of fish are frequent.

The water level in the Caspian Sea is falling every year. This is due to global warming, due to the influence of which the water temperature on the surface of the reservoir increased by one degree and the sea began to actively evaporate.

It is estimated that the water level has fallen by seven centimeters since 1996. By 2015, the fall was about one and a half meters, and the water continues to fall.

If this continues, in a century the smallest part of the lake may simply disappear. This will be the part that washes the borders of Russia and Kazakhstan. In the case of increased global warming, the process can accelerate and this will happen much earlier.

It is known that long before the onset of global warming, the water level in the Caspian was undergoing changes. The water stayed and then fell. Scientists still cannot say exactly why this happened.

CaspAndmOre(Caspian) - the largest enclosed body of water on Earth. In size, the Caspian Sea is much larger than such lakes as the Upper, Victoria, Huron, Michigan, Baikal. According to formal features, the Caspian Sea is an endorheic lake. However, considering it big sizes, brackish waters and a regime similar to the sea, this body of water is called the sea.

According to one hypothesis, the Caspian Sea (among the ancient Slavs - the Khvalyn Sea) got its name in honor of the Caspian tribes who lived before our era 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; the average width is 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 mountains of the Caucasus approach the sea, in the south, near the coast, the Elburz ridge stretches.

The surface of the Caspian Sea is much lower than the level of the World Ocean. Its current level fluctuates around -27 ... -28 m. These levels correspond to the sea surface area of ​​​​390 and 380 thousand km 2 (without the Kara-Bogaz-Gol Bay), the volume of water is 74.15 and 73.75 thousand km 3, average depth is about 190 m.

The Caspian Sea is traditionally divided into three large parts: the North (24% of the sea area), the Middle (36%) and the South 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, and the volume is less than 1% of the total water mass of the sea. The Middle Caspian is a separate basin with the 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 water mass of the sea 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 strongly indented. There are large bays Kizlyarsky, Komsomolets, Mangyshlaksky, Kazakhsky, Kara-Bogaz-Gol, Krasnovodsky and Turkmensky, many bays; off the western coast - Kyzylagach. The largest peninsulas are Agrakhansky, Buzachi, Tyub-Karagan, Mangyshlak, Krasnovodsky, Cheleken and Apsheronsky. The most common banks are accumulative; areas with abrasion shores are found along the contour of the Middle and South Caspian.

More than 130 rivers flow into the Caspian Sea, the largest of which is the Volga. , Ural, Terek, Sulak, Samur, Kura, Sefidrud, Atrek, Emba (its runoff 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 a drainless 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, on coastal zones. In the Caspian Sea level varied in the range of ~200 m: from -140 to +50 m BS; in from -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 point 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 has dominated - to -27.69 m BS in 2013.

During major periods, the northern shore of the Caspian Sea shifted to Samarskaya Luka on the Volga, and perhaps even further. At maximum transgressions, the Caspian turned into a sewage lake: excess water flowed through the Kuma-Manych depression into the Sea of ​​Azov and further into the Black Sea. In extreme regressions South coast The Caspian was shifted to the Apsheron threshold.

Long-term fluctuations in the level of the Caspian are explained by changes in the structure of the water balance of the Caspian Sea. The sea level rises when the incoming part of the water balance (primarily river runoff) increases and exceeds the outgoing part, and decreases if the inflow of river waters decreases. The total water flow of all rivers averages 300 km 3 /year; while the five largest rivers account for almost 95% (the Volga provides 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 is the flow of the Volga), precipitation - 70.9, underground flow - 4 km 3 /year, and evaporation and outflow to the Kara-Bogaz-Gol Bay - 354.79 and 9.8 km 3 /year. During the period of intensive 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.

The 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-surge level fluctuations are manifested 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 of kilometers inland, and in case of surges - to 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 in the Caspian Sea, there is strong excitement. highest heights waves in the South Caspian 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 more often and more dangerously in the cold half of the year.

The Caspian Sea is generally dominated by wind currents; nevertheless, on the estuarine coasts major rivers runoff currents play a significant role. Cyclonic water circulation prevails in the Middle Caspian, and anticyclonic circulation in the South Caspian. In the northern part of the sea, the patterns of wind currents are more irregular and depend on the characteristics and variability of the wind, bottom topography and coastlines, river runoff and aquatic vegetation.

The water temperature is subject to significant latitudinal and seasonal changes. IN winter period 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 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 the coastal zones of the Middle Caspian. Freezing in the Northern Caspian lasts from November to March.

The salinity of water changes especially sharply in the northern part of the sea: from 0.1‰ on the estuarine coasts of the Volga and Urals to 10–12‰ on the border with the Middle Caspian. In the Northern Caspian, the temporal variability of water salinity is also great. In the middle and southern parts of the sea, salinity fluctuations are small: it is mainly 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 object of fishing is goby, herring, salmon, carp, mullet and sturgeon fish. The latter number five species: sturgeon, beluga, stellate sturgeon, spike and sterlet. The sea is capable of producing 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. Every year 5-6 million waterfowl migrate through the Caspian region.

The economy of the Caspian Sea is connected with oil and gas production, shipping, fishing, extraction of seafood, various salts and minerals (Kara-Bogaz-Gol Bay), with the use of recreational resources. The explored oil resources in the Caspian Sea are about 10 billion tons, the total resources of oil and gas condensate are estimated at 18–20 billion tons. Oil and gas are being produced on an ever-increasing scale. Used by the Caspian Sea and 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), Nowshahr, Bender-Enzeli, Bender-Torkemen (Iran) and Turkmenbashi (Turkmenistan).

The economic activity 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 oil products, phenols and synthetic surfactants), poaching and reduction of fish stock, especially sturgeons; damage to the population and coastal economic activity due to large-scale and rapid changes in the level of the reservoir, the impact of numerous hazardous hydrological phenomena and hydrological and morphological processes.

The total economic damage for all the 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, the destruction of coasts and coastal structures, was estimated at 15 to 30 billion US dollars. It took urgent engineering measures to protect the coast.

A sharp drop in the level of the Caspian Sea in the 1930s–1970s. led to less damage, but they were significant. The navigable approach channels became shallow, the shallow seashore at the mouths of the Volga and the Urals became heavily overgrown, which became an obstacle to the passage of fish into the rivers for spawning. It was necessary to build fish passages through the seasides mentioned above.

Among the unresolved problems is the lack of an international agreement on the international legal status of the Caspian Sea, the division of its water area, bottom and subsoil.

The Caspian Sea is the object of many years of research by specialists of all littoral 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 Moscow State University, etc. took an active part in the study of the Caspian Sea.