In what part is the Caspian lake. temperature and salinity. Vertical water mixing

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 of the Caspian Sea

The Caspian Sea is located at the junction of Europe with Asia and is geographically 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.

Lake or sea?

In fact, the Caspian Sea is the world's largest lake, but it has a number of marine features. 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. The length of the coastline is 6600 km, with islands - about 7 thousand km.

coast

Basically, the coast of the Caspian Sea is low-lying and smooth. In the northern part, it is heavily indented by the river channels of the Urals and the Volga. The swampy local shores are located very low. The eastern shores are 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)

The average water temperature in the Caspian in winter ranges from 0 °C in the northern part to +10 °C in the south. 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.

In summer, the average surface water temperature 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, anomalously low water temperatures persist in the summer months.

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)

The largest bays of the Caspian include: Agrakhan, Kazakh, Kizlyar, Dead Kultuk and Mangyshlak. In the east is the 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 the 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 amenities. 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.

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 population of one of the most beautiful cities in 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. Smaller cities: the capital of Dagestan - 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.

This is how the Mediterranean Sea was formed, which then included the current Azov, Black and Caspian Seas. On the site of the modern Caspian, a huge Caspian lowland was formed, the surface of which was almost 30 meters below the water level in the World Ocean. When the next rise of land began to take place at the place where the Caucasus Mountains were formed, the Caspian Sea was finally cut off from the ocean, and in its place a closed drainless reservoir was formed, which today is considered the largest inland sea on the planet. However, some scientists call this sea a giant lake.
A feature of the Caspian Sea is the constant fluctuation of the level of salinity of its water. Even in different areas of this sea, the water has different salinity. This was the reason for the predominance of fish and crustaceans in the Caspian Sea, which more easily tolerate fluctuations in water salinity.

Since the Caspian is completely isolated from the ocean, its inhabitants are endermics, i.e. always live in its water area.

The fauna of the Caspian Sea can be conditionally divided into four groups.

The first group of animals includes the descendants of ancient organisms that inhabited Tethys about 70 million years ago. These animals include Caspian gobies (golovach, Knipovich, Berg, bubyr, pugolovka, Baer) and herring (Kessler, Brazhnikov, Volga, brazil, etc.), some mollusks and most crustaceans (long-sexed crayfish, orthemia crustacean, etc.). Some fish, mainly herring, periodically enter the rivers flowing into the Caspian to spawn, many never leave the sea. Gobies prefer to live in coastal waters, often found in estuaries.
The second group of animals of the Caspian Sea is represented by arctic species. penetrated into the Caspian Sea from the north in the postglacial period. These are such animals as the Caspian seal (Caspian seal), fish - Caspian trout, white salmon, nelma. Of the crustaceans, this group is represented by mysid crustaceans, similar to small shrimps, tiny sea cockroaches, and some others.
The third group of animals inhabiting the Caspian includes species that independently or with the help of humans migrated here from the Mediterranean Sea. These are molluscs mitisyaster and abra, crustaceans - amphipods, shrimp, Black Sea and Atlantic crabs and some types of fish: golden mullet (sharp nose), needle fish and Black Sea kalk (flounder).

And, finally, the fourth group - freshwater fish that penetrated into the Caspian Sea from fresh rivers and turned into marine or anadromous, i.e. periodically rising into the rivers. Some of the typically freshwater fish also occasionally enter the Caspian. Among the fish of the fourth group are catfish, pike perch, barbel, red-lipped asp, Caspian fish, Russian and Persian sturgeon, beluga, stellate sturgeon. It should be noted that the Caspian Sea basin is the main habitat of sturgeons on the planet. Almost 80% of all sturgeons in the world live here. Barbels and fish are also valuable commercial fish.

As for sharks and other fish that are predatory and dangerous to humans, they do not live in the Caspian Sea-Lake.

The length of the coastline of the Caspian Sea is estimated at about 6500-6700 kilometers, with islands - up to 7000 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 channels and islands of the Volga and Ural deltas, the shores are low and swampy, and the water surface is covered with thickets in many places. The east coast is dominated by limestone shores adjacent to semi-deserts and deserts. The most winding coasts are on the west coast in the area of ​​the Apsheron Peninsula and on the east coast in the area of ​​the Kazakh Gulf and Kara-Bogaz-Gol. The territory adjacent to the Caspian Sea is called the Caspian Sea.

Caspian Sea is a unique ecological system. It is the largest lake on planet Earth. The diverse biosphere, beautiful nature and wealth of natural resources make it attractive in all aspects.

Caspian Sea: description, photo and video

Many people wonder what is the area of ​​the Caspian Sea. It is quite difficult to answer this question, since this parameter varies depending on seasonality. For example, when the level of the water surface is at around 27 meters, the reservoir covers an area of ​​370 thousand square kilometers. This is almost 45 percent of the volume of freshwater lakes on Earth.

The Caspian also has a non-uniform depth. In the north, maximum depth of the Caspian Sea only about 25 meters, and the average is within 4 meters. The southern region, on the contrary, is very deep - 1025 kilometers. This is the third indicator in the world among lakes, after Tanganyika and. Scientists cannot yet name the exact reasons for such fluctuations in the Caspian Sea. Among the most likely versions is climate change and the earth's crust in the region.

Caspian Sea - Azerbaijan (Baku)

Since the lake is not only an industrial reservoir, but also a recreational one, the water temperature in the Caspian Sea is also of great interest. In winter, the lake experiences significant temperature fluctuations. On the south side, it is kept at around 11 degrees, and in the north it can drop to 0.5 and below. Sometimes glaciation can be observed in this region.

During the summer period, which lasts here from early June to mid-September, the temperature is approximately the same throughout the reservoir. In the upper layers, the average values ​​are kept within 26-27 degrees, and in shallow water the reservoir can heat up to 32. The water is slightly salty, but the saturation depends on the regional factor and may change. The largest concentration is in the west and south, and in the northern part, thanks to freshwater rivers, it is the smallest. The local climate is also changeable.

The lake is located in three climatic zones at once:

• continental;
• moderate;
• subtropical.

Summer in the region is quite hot. The thermometer can reach up to 44 degrees Celsius. In winter, in the south, these figures fluctuate up to +10, and in the north - up to -10. The Caspian Sea on the map has quite even shores, but in fact, its borders are very indented with river mouths, peninsulas and straits. The length of the coast, taking into account the islands, is 7 thousand kilometers. In the north, the coast is low-lying, and marshland caused by channels is common on it. In the east, limestones are common, flowing into semi-deserts.

There are approximately 50 islands on the territory of the lake. The largest of them:

• Seals;
• Boyuk-Zira;
• Chechen;
• Ogurchinsky;
• Ashur-Ada.

Among the numerous bays, Kara-Bogaz-Gol can be noted. Until the end of the century before last, it was a kind of lagoon, but in 1980 the construction of a dam began here, because of this, the amount of water entering the lake decreased. To date, the strait has been restored.

What rivers flow into the Caspian Sea? The lake feeds a large number of rivers, the largest of which are:

• Volga;
• Sulak (Pro);
• Terek;
• Ural (Pro).

Every year they bring hundreds of cubic meters of fresh water into the lake.

The region has been actively developed for many centuries. Today, large ports operate on the Caspian Sea, linking trade routes. Of the Russian ones, the most important are Astrakhan and Makhachkala. Oil production is also carried out in the Caspian Sea. According to experts, the oil resources of the region are about 10 billion tons. There are also gas reserves here.

The Caspian Lake is a great place to relax. Local beaches amaze everyone who comes here. The quality of recreation on the Caspian Sea is in no way inferior. Pleasant climate, comfortable beaches and fresh air - all this the Caspian is ready to give to tourists. For those who decide to visit the Caspian Sea, the prices for holidays can pleasantly surprise you. For a low cost, you can get high-quality service.

Popular cities include: resorts of the Caspian Sea:

• Makhachkala;
• Kaspiysk;
• Astrakhan;
• Lagan;
• Derbent;
• Dagestan lights.

Derbent is very attractive from a historical point of view. Astrakhan allows you to enjoy outdoor activities and fishing, and Makhachkala attracts with comfortable and equipped beaches. Rest on the Caspian Sea in Russia allows you to restore your health and relax from the bustle of the city. Among foreign resorts, the most popular are Baku (Azerbaijan), Avaza (Turkmenistan) and Aktau.

Caspian Sea on the map

Where is the Caspian Sea located? It is located on the continent of Eurasia. It is interesting that its eastern coast is located in Asia, and the western coast is in Europe. Conventionally, the sea is divided into several parts:

• Northern Caspian;
• South Caspian;
• Middle Caspian.

Of these, only the North Caspian is a sea shelf. It contains only 1 percent of the total volume of water and ends at Chechen Island, located near the Kizlyar Bay.

Which countries are washed by the Caspian Sea? There are 5 states on the shore of the lake:

• Azerbaijan;
• Iran;
• Turkmenistan;
• Kazakhstan;
• Russia.

The largest coastline runs through the territory of Kazakhstan, in second place, according to this indicator, is Russia. The coast of Azerbaijan has the smallest length, but it owns the largest port - Baku.

There are also other large settlements on the coast of the salt reservoir:

• Anzali (Iran) - 111 thousand people;
• Aktau (Kazakhstan) - 178 thousand people;
• Atyrau (Russia) - 183 thousand people

Astrakhan also belongs to the coastal cities of the Caspian Sea, although the city is located 69 kilometers from the coast. Other Russian cities on the coast include Makhachkala, Derbent and Kaspiysk.

Caspian Sea or lake?

The Caspian Sea is a geographical feature, the essence of which does not quite correlate with its name.

Why is the Caspian Sea considered a lake? Caspian Sea It is an endorheic and closed reservoir. It receives water from rivers and has no connection with oceans and other seas. Although the water here is salty, this figure is much lower than that of other seas. International maritime laws do not apply to the Caspian Sea.

On the other hand, the Caspian is quite large in size, which differs from traditional ideas about lakes. Even Baikal, and even more so, is inferior to it in terms of area. There are no other lakes in the world whose coast belongs to five states at the same time. The bottom structure is also very similar to the ocean type. With a high degree of probability, the waters of the Caspian Sea flowed into the Mediterranean Sea many centuries ago, but due to drying and tectonic processes, they were separated.

The water area of ​​the Caspian Sea is rich in islands, the size of which, even by international standards, is quite large.

Nature of the Caspian Sea

One of the most interesting mysteries of the Caspian Sea is the population of seals living on the territory of the lake, which are a small variety of those that live in the cold northern waters. However, their appearance on the coast, at least suggests that these places are beginning to recover ecologically after the negative consequences of oil production.

The flora and fauna of the Caspian Sea is very diverse. The underwater ecosystem boasts a large number of crustaceans, mollusks, gobies, herring and sprat. Many species are endemic, meaning they only live in this region and nowhere else.

Freshwater species also live in the waters of the lake. They were able to adapt to salt water. These are primarily carp and perch fish. At the end of the ice age, arctic fish and invertebrates penetrated here. In the 40s of the last century, the waters of the Caspian Sea were deliberately populated with mullet, nereis and abra, which are the food base for sturgeons.

Fish processing plants operate in the vicinity of the Caspian Sea, as well as purification stations designed to ensure water cycles. Systematic work is also underway to breed many varieties of underwater abodes that have industrial value. The region is of great interest for fishing tourism. This holiday is especially popular in the Astrakhan region on the Caspian Sea.

The flora of the lake is represented by more than 700 plant species. Some of them grow on land, others in water. Phytoplankton of the Caspian Sea consists of both marine and freshwater algae. According to rough estimates, about 440 species of algae live in the reservoir.

Historical facts

The Caspian coast was once home to an ancient civilization that has since disappeared. There is an opinion that in the vicinity of Dagestan, the waters hide Itil from human eyes - the capital city of the Khazar Khaganate, which completely disappeared in the 12th century. In Derbent, there is still a wall from an ancient settlement, going to a depth of 300 meters. For what purpose it was built and who built it is a mystery.

Another interesting feature of the Caspian Sea is the Sabail citadel, located under water in the Baku Bay. The building was flooded during an earthquake that happened in 1306. In 1723, the upper part of the highest tower became visible above the water surface - this was the result of a decrease in the water level. Today, the fortress is again hidden in the depths of the Caspian Sea, although in sunny weather it can be seen in the water column.

The territory of the Caspian Sea was an "apple of discord" between the adjacent countries. Disputes over the distribution of the possessions and resources of the lake have been going on for 22 years. In 2018, the countries finally came to a common denominator. On August 12, the Convention on the Legal Status of the Caspian Sea was signed. Prior to this, in the legal field, regulation was carried out on the basis of the Soviet-Iranian agreements that define the Caspian as a closed body of water, and each border state had an independent right to a 10-mile zone. The rest of the lake was divided equally.

How the Caspian Sea was divided? The new agreement assigns 15 miles of territorial waters to each state. Also, the bottom of the Caspian Sea is divided into sectors, as happens with the seas, and the sovereignty of the water column is established on the principle of a lake.

For the current day Caspian Sea is an economically important region. Without it, it is impossible to imagine Eurasia, including Russia. Everyone should visit the Caspian Sea, and the protection of the reservoir should be carried out at the state level. Only by joint efforts can this natural pearl be preserved.

The Caspian Sea is inland and is located in a vast continental depression on the border of Europe and Asia. The Caspian Sea has no connection with the ocean, which formally allows it to be called a lake, but it has all the features of the sea, since it had connections with the ocean in past geological epochs.

The area of ​​the sea is 386.4 thousand km2, the volume of water is 78 thousand m3.

The Caspian Sea has a vast drainage basin, with an area of ​​about 3.5 million km2. The nature of landscapes, climatic conditions and types of rivers are different. Despite its vastness, only 62.6% of its area is in waste areas; about 26.1% - for drainless. The area of ​​the Caspian Sea itself is 11.3%. 130 rivers flow into it, but almost all of them are located in the north and west (and the eastern coast does not have a single river reaching the sea at all). The largest river in the Caspian basin is the Volga, which provides 78% of the river water entering the sea (it should be noted that more than 25% of the Russian economy is located in the basin of this river, and this undoubtedly determines many other features of the waters of the Caspian Sea), as well as the Kura River , Zhaiyk (Ural), Terek, Sulak, Samur.

In physical and geographical terms and according to the nature of the underwater relief, the sea is divided into three parts: northern, middle and southern. The conditional boundary between the northern and middle parts runs along the line of Chechen Island–Cape Tyub-Karagan, between the middle and southern parts - along the line of Zhiloy Island–Cape Kuuli.

The shelf of the Caspian Sea, on average, is limited to depths of about 100 m. The continental slope, which begins below the edge of the shelf, ends in the middle part at about 500–600 m, in the southern part, where it is very steep, at 700–750 m.

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 relief is complicated by the presence of banks, islands, furrows.

The middle part of the sea is a separate basin, the region of maximum depths of which - the Derbent depression - is shifted to the western coast. The average depth of this part of the sea is 190 m, the greatest is 788 m.

The southern part of the sea is separated from the middle part by the Apsheron threshold, which is a continuation of the Greater Caucasus. Depths above this underwater ridge do not exceed 180 m. The deepest part of the South Caspian basin with a maximum sea depth of 1025 m is located east of the Kura delta. Several underwater ridges up to 500 m high rise above the bottom of the basin.

The shores of the Caspian Sea are diverse. In the northern part of the sea, they are quite strongly indented. Here are the bays of Kizlyar, Agrakhan, Mangyshlak and many shallow bays. Notable peninsulas: Agrakhansky, Buzachi, Tyub-Karagan, Mangyshlak. Large islands in the northern part of the sea are Tyuleniy, Kulaly. In the deltas of the Volga and Ural rivers, the coastline is complicated by many islets and channels, which often change their position. Many small islands and banks are located on other parts of the coastline.

The middle part of the sea has a relatively flat coastline. On the western coast, on the border with the southern part of the sea, the Apsheron Peninsula is located. To the east of it, islands and banks of the Apsheron archipelago stand out, of which the largest is Zhiloy Island. The eastern shore of the Middle Caspian is more indented, the Kazakh Bay stands out here with the Kenderli Bay and several capes. The largest bay of this coast is Kara-Bogaz-Gol.

South of the Absheron Peninsula are the islands of the Baku archipelago. The origin of these islands, as well as some banks off the eastern coast of the southern part of the sea, is associated with the activity of underwater mud volcanoes lying at the bottom of the sea. On the eastern shore are the large bays of Turkmenbashi and Turkmensky, and near it is the island of Ogurchinsky.

One of the most striking phenomena of the Caspian Sea is the periodic variability of its level. In historical times, the Caspian Sea had a lower level than the World Ocean. Fluctuations in the level of the Caspian Sea are so great that for more than a century they have attracted the attention of not only scientists. Its peculiarity is that in the memory of mankind its level has always been below the level of the World Ocean. Since the beginning of instrumental observations (since 1830) of the sea level, the amplitude of its fluctuations has been almost 4 m, from -25.3 m in the eighties of the XIX century. to -29 m in 1977. In the last century, the level of the Caspian Sea has changed significantly twice. In 1929 it stood at a mark of about -26 m, and since it had been close to this mark for almost a century, this position of the level was considered as a long-term or secular average. In 1930, the level began to decline rapidly. Already by 1941, it had dropped by almost 2 m. This led to the drying up of vast coastal areas of the bottom. The decrease in the level, with its small fluctuations (short-term insignificant rises in the level in 1946-1948 and 1956-1958), continued until 1977 and reached the mark of -29.02 m, i.e., the level took the lowest position for last 200 years.

In 1978, contrary to all forecasts, the sea level began to rise. As of 1994, the level of the Caspian Sea was at -26.5 m, that is, in 16 years the level has risen by more than 2 m. The rate of this rise is 15 cm per year. The level increment in some years was higher, and in 1991 it reached 39 cm.

The general fluctuations in the level of the Caspian Sea are superimposed by its seasonal changes, the average long-term of which reaches 40 cm, as well as surge phenomena. The latter are especially pronounced in the Northern Caspian. The northwestern coast is characterized by large surges created by the prevailing, especially in the cold season, storms of eastern and southeastern directions. Over the past decades, a number of large (more than 1.5–3 m) surges have been observed here. A particularly large surge with catastrophic consequences was noted in 1952. Fluctuations in the level of the Caspian Sea cause great damage to the states surrounding its water area.

Climate. The Caspian Sea is located in the temperate and subtropical climatic zones. Climatic conditions change in the meridional direction, since the sea stretches for almost 1200 km from north to south.

In the Caspian region, various circulation systems interact, however, easterly winds prevail throughout the year (the influence of the Asian high). The position at rather low latitudes provides a positive balance of heat inflow, so the Caspian Sea serves as a source of heat and moisture for passing air masses for most of the year. The average annual temperature in the northern part of the sea is 8–10°С, in the middle part - 11–14°С, in the southern part – 15–17°С. However, in the northernmost parts of the sea, the average January temperature is from –7 to –10°C, and the minimum temperature during arctic air intrusions is up to –30°C, which determines the formation of the ice cover. In summer, rather high temperatures dominate over the entire region under consideration - 24–26°С. Thus, the Northern Caspian is subject to the most sharp temperature fluctuations.

The Caspian Sea is characterized by a very small amount of precipitation per year - only 180 mm, and most of it falls on the cold season of the year (from October to March). However, the Northern Caspian differs in this respect from the rest of the basin: here the average annual precipitation is less (only 137 mm for the western part), and the distribution over the seasons is more even (10–18 mm per month). In general, we can talk about the proximity of climatic conditions to arid ones.

Water temperature. The distinctive features of the Caspian Sea (great differences in depths in different parts of the sea, the nature of the bottom relief, isolation) have a certain influence on the formation of temperature conditions. In the shallow North Caspian, the entire water column can be considered as homogeneous (the same applies to shallow bays located in other parts of the sea). In the Middle and South Caspian, surface and deep masses separated by a transitional layer can be distinguished. In the Northern Caspian and in the surface layers of the Middle and Southern Caspian, the water temperature varies over a wide range. In winter, temperatures vary from north to south from less than 2 to 10°С, the water temperature near the western coast is 1–2°С higher than near the eastern one, in the open sea the temperature is higher than near the coasts: by 2–3°С in the middle part and by 3–4°С in the southern part of the sea. In winter, the temperature distribution is more uniform with depth, which is facilitated by the winter vertical circulation. During moderate and severe winters in the northern part of the sea and shallow bays on the east coast, the water temperature drops to freezing.

In summer, the temperature varies in space from 20 to 28°C. The highest temperatures are observed in the southern part of the sea; temperatures are also quite high in the well-warmed shallow North Caspian. The zone of distribution of the lowest temperatures is adjacent to the east coast. This is due to the rise of cold deep waters to the surface. Temperatures are also relatively low in the poorly heated deep-water central part. In the open areas of the sea, in late May–early June, the formation of a temperature jump layer begins, which is most clearly expressed in August. Most often it is located between 20 and 30 m in the middle part of the sea and 30 and 40 m in the south. In the middle part of the sea, due to the surge near the eastern coast, the shock layer rises close to the surface. In the bottom layers of the sea, the temperature during the year is about 4.5°C in the middle part and 5.8–5.9°C in the south.

Salinity. Salinity values ​​are determined by such factors as river runoff, water dynamics, including mainly wind and gradient currents, the resulting water exchange between the western and eastern parts of the Northern Caspian and between the Northern and Middle Caspian, the bottom topography, which determines the location of waters with different salinity, mainly along the isobaths, evaporation, which ensures the shortage of fresh water and the inflow of more saline ones. These factors collectively affect the seasonal differences in salinity.

The Northern Caspian can be considered as a reservoir of constant mixing of river and Caspian waters. The most active mixing occurs in the western part, where both river and Central Caspian waters directly enter. In this case, horizontal salinity gradients can reach 1‰ per 1 km.

The eastern part of the Northern Caspian is characterized by a more uniform salinity field, since most of the river and sea (Middle Caspian) waters enter this area of ​​the sea in a transformed form.

According to the values ​​of horizontal salinity gradients, in the western part of the Northern Caspian, a river-sea contact zone can be distinguished with water salinity from 2 to 10‰, in the eastern part from 2 to 6‰.

Significant vertical salinity gradients in the Northern Caspian are formed as a result of the interaction of river and sea waters, with runoff playing a decisive role. The intensification of vertical stratification is also facilitated by the unequal thermal state of the water layers, since the temperature of the surface desalinated waters coming from the coast in summer is 10–15°C higher than that of the bottom ones.

In the deep basins of the Middle and South Caspian, salinity fluctuations in the upper layer are 1–1.5‰. The largest difference between the maximum and minimum salinity was noted in the area of ​​the Apsheron threshold, where it is 1.6‰ in the surface layer and 2.1‰ at the 5 m horizon.

The decrease in salinity along the western coast of the South Caspian in the 0–20 m layer is caused by the runoff of the Kura River. The influence of the Kura runoff decreases with depth; at the horizons of 40–70 m, the range of salinity fluctuations is no more than 1.1‰. Along the entire western coast to the Absheron Peninsula stretches a strip of desalinated water with a salinity of 10–12.5‰ coming from the Northern Caspian.

In addition, salinity increases in the South Caspian due to the removal of saline waters from bays and inlets on the eastern shelf under the action of southeasterly winds. In the future, these waters are transferred to the Middle Caspian.

In the deep layers of the Middle and South Caspian, salinity is about 13‰. In the central part of the Middle Caspian, such salinity is observed at horizons below 100 m, and in the deep part of the South Caspian, the upper boundary of waters with increased salinity drops to 250 m. Obviously, vertical mixing of waters is difficult in these parts of the sea.

Surface water circulation. Currents in the sea are mainly wind-driven. In the western part of the Northern Caspian, currents of the western and eastern quarters are most often observed, in the eastern - southwestern and southern. The currents caused by the runoff of the Volga and Ural rivers can be traced only within the estuarine coast. The prevailing current velocities are 10–15 cm/s; in the open areas of the Northern Caspian, the maximum velocities are about 30 cm/s.

In the coastal areas of the middle and southern parts of the sea, currents of the northwestern, northern, southeastern, and southern directions are observed in accordance with the wind directions; eastward currents often occur near the eastern coast. Along the western coast of the middle part of the sea, the most stable currents are southeast and south. Current velocities are on average about 20–40 cm/s, the maximum ones reach 50–80 cm/s. Other types of currents also play a significant role in the circulation of sea waters: gradient, seiche, inertial ones.

ice formation. The Northern Caspian is covered with ice annually in November, the area of ​​the freezing part of the water area depends on the severity of the winter: in severe winters, the entire Northern Caspian is covered with ice, in soft ice it stays within the 2–3 meter isobath. The appearance of ice in the middle and southern parts of the sea falls on December-January. Near the eastern coast, ice is of local origin, near the western coast - most often brought from the northern part of the sea. In severe winters, shallow bays freeze off the eastern coast of the middle part of the sea, coasts and landfast ice form off the coast, and drift ice spreads to the Absheron Peninsula in abnormally cold winters off the western coast. The disappearance of the ice cover is observed in the second half of February–March.

Oxygen content. The spatial distribution of dissolved oxygen in the Caspian Sea has a number of regularities.
The central part of the Northern Caspian is characterized by a fairly uniform distribution of oxygen. An increased oxygen content is found in the areas of the pre-estuary seashore of the Volga River, a lower one - in the southwestern part of the Northern Caspian.

In the Middle and South Caspian, the highest oxygen concentrations are confined to coastal shallow areas and pre-estuary seashores of rivers, with the exception of the most polluted areas of the sea (Baku Bay, Sumgait region, etc.).

In the deep-water regions of the Caspian Sea, the main pattern is preserved in all seasons - a decrease in oxygen concentration with depth.
Due to the autumn-winter cooling, the density of the waters of the North Caspian increases to a value at which it becomes possible for the flow of North Caspian waters with a high oxygen content along the continental slope to significant depths of the Caspian Sea.

The seasonal distribution of oxygen is mainly related to the annual course and seasonal ratio of production-destruction processes occurring in the sea.

In spring, the production of oxygen in the process of photosynthesis quite significantly covers the decrease in oxygen due to a decrease in its solubility with an increase in water temperature in spring.

In the areas of the estuarine coasts of the rivers feeding the Caspian Sea, in 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 significant warming of water masses and activation of photosynthesis processes, the leading factors in the formation of the oxygen regime in surface waters are photosynthetic processes, in near-bottom waters - biochemical oxygen consumption by bottom sediments.

Due to the high temperature of the waters, the stratification of the water column, the large influx of organic matter and its intense oxidation, oxygen is quickly consumed with its minimal entry into the lower layers of the sea, as a result of which an oxygen deficiency zone is formed in the Northern Caspian. Intensive photosynthesis in the open waters of the deep-water regions of the Middle and South Caspian covers the upper 25-meter layer, where oxygen saturation is more than 120%.

In autumn, in the well-aerated shallow water areas of the Northern, Middle and Southern Caspian, 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 rising.

The spatial distribution of nutrients in the Caspian Sea reveals the following patterns:

• increased concentrations of biogenic substances characterize the areas of pre-estuary seashores of 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, the cyclonic nature of the circulation contributes to the upwelling of deep waters with a high content of nutrients into the overlying layers of the sea;
• in the deep water areas of the Middle and South Caspian, the vertical distribution of nutrients depends on the intensity of the convective mixing process, and their content increases with depth.

The dynamics of nutrient concentrations during the year in the Caspian Sea is influenced by such factors as seasonal fluctuations in the biogenic runoff into the sea, the seasonal ratio of production-destruction processes, the intensity of exchange between soil and water mass, ice conditions in winter in the Northern Caspian, the processes of winter vertical circulation in the deep sea areas.

In winter, a significant area of ​​the Northern Caspian is covered with ice, but biochemical processes are actively developing in the under-ice water and ice. The ice of the Northern Caspian, being a kind of accumulator of biogenic substances, transforms these substances entering the sea from and from the atmosphere.

As a result of the winter vertical circulation of waters in the deep-sea regions of the Middle and Southern Caspian in the cold season, the active layer of the sea is enriched with nutrients due to their supply from the underlying layers.

Spring for the waters of the North Caspian is characterized by a minimum content of phosphates, nitrites and silicon, which is explained by the spring outbreak of phytoplankton development (silicon is actively consumed by diatoms). High concentrations of ammonium and nitrate nitrogen, characteristic of the waters of a large area of ​​the Northern Caspian during floods, are due to intensive flushing by river waters.

In the spring season, in the area of ​​water exchange between the Northern and Middle Caspian in the subsurface layer, with the maximum oxygen content, the content of phosphates is minimal, which, in turn, indicates the activation of the photosynthesis process in this layer.

In the South Caspian, the distribution of nutrients in spring is basically similar to their distribution in the Middle Caspian.

In the summertime, the waters of the Northern Caspian reveal a redistribution of various forms of biogenic compounds. Here, the content of ammonium nitrogen and nitrates significantly decreases, while at the same time there is a slight increase in the concentrations of phosphates and nitrites and a rather significant increase in the concentration of silicon. In the Middle and South Caspian, the concentration of phosphates has decreased due to their consumption in the process of photosynthesis and the difficulty of water exchange with the deep water accumulation zone.

In autumn, in the Caspian Sea, due to the cessation of the activity of some types of phytoplankton, the content of phosphates and nitrates increases, and the concentration of silicon decreases, as an autumn outbreak of diatoms occurs.

Oil has been produced on the shelf of the Caspian Sea for more than 150 years.

Currently, large reserves of hydrocarbons are being developed on the Russian shelf, the resources of which on the Dagestan shelf are estimated at 425 million tons of oil equivalent (of which 132 million tons of oil and 78 billion m3 of gas), on the shelf of the Northern Caspian - 1 billion tons of oil .

In total, about 2 billion tons of oil have already been produced in the Caspian.

Losses of oil and products of its processing during extraction, transportation and use reach 2% of the total volume.

The main sources of pollutants, including oil products, entering the Caspian Sea are carry-over with river runoff, discharge of untreated industrial and agricultural effluents, domestic wastewater from cities and towns located on the coast, shipping, exploration and exploitation of oil and gas fields located at the bottom of the sea, transportation of oil by sea. 90% of pollutants with river runoff are concentrated in the Northern Caspian, industrial effluents are confined mainly to the area of ​​the Apsheron Peninsula, and increased oil pollution of the Southern Caspian is associated with oil production and oil exploration drilling, as well as active volcanic activity (mud) in zone of oil and gas bearing structures.

From the territory of Russia, about 55 thousand tons of oil products enter the Northern Caspian every year, including 35 thousand tons (65%) from the Volga River and 130 tons (2.5%) from the Terek and Sulak rivers.

The thickening of the film on the water surface up to 0.01 mm disrupts the processes of gas exchange and threatens the death of hydrobiota. Toxic for fish is the concentration of oil products 0.01 mg/l, for phytoplankton - 0.1 mg/l.

The development of oil and gas resources of the bottom of the Caspian Sea, the estimated reserves of which are estimated at 12–15 billion tons of standard fuel, will become the main factor in the anthropogenic load on the ecosystem of the sea in the coming decades.

Caspian autochthonous fauna. The total number of autochthons is 513 species or 43.8% of the entire fauna, which include herring, gobies, mollusks, etc.

arctic views. The total number of the Arctic group is 14 species and subspecies, or only 1.2% of the entire fauna of the Caspian (mysids, sea cockroach, white salmon, Caspian salmon, Caspian seal, etc.). The basis of the Arctic fauna is crustaceans (71.4%), which easily tolerate desalination and live at great depths of the Middle and South Caspian (from 200 to 700 m), since the lowest water temperatures (4.9– 5.9°C).

mediterranean views. These are 2 types of mollusks, needle-fish, etc. At the beginning of the 20s of our century, the mollusk mitilyastra penetrated here, later 2 types of shrimp (with mullets, during their acclimatization), 2 types of mullet and flounder. Some Mediterranean species entered the Caspian after the opening of the Volga-Don Canal. Mediterranean species play a significant role in the fish food base of the Caspian Sea.

Freshwater fauna (228 species). This group includes anadromous and semi-anadromous fish (sturgeon, salmon, pike, catfish, cyprinids, as well as rotifers).

sea ​​views. These are ciliates (386 forms), 2 species of foraminifera. There are especially many endemics among higher crustaceans (31 species), gastropod mollusks (74 species and subspecies), bivalve mollusks (28 species and subspecies) and fish (63 species and subspecies). The abundance of endemics in the Caspian Sea makes it one of the most unique brackish water bodies on the planet.

The Caspian Sea provides more than 80% of the world's sturgeon catch, most of which falls on the North Caspian.

To increase the catches of sturgeon, which dropped sharply during the years of sea level drop, a set of measures is being implemented. Among them - a complete ban on sturgeon fishing in the sea and its regulation in rivers, an increase in the scale of factory breeding of sturgeons.