Currents of the Black Sea. Map of the currents of the Black Sea cold and warm currents Is there a current in the Black Sea

When measuring heights on land, the reading starts from sea level. This does not mean that the sea level is exactly the same in all areas of the oceans. In particular, the level of the Black Sea near Odessa is 30 cm higher than near Istanbul, for this reason water rushes from the Black Sea to the Mediterranean (through the Sea of ​​Marmara), and in the Bosphorus there is a constant current that carries the Black Sea water. It is known that the atmosphere is cold air moves down towards warmer, lighter air. The water in the Bosphorus moves in exactly the same way - the heavy Mediterranean flows from below towards the Black Sea. It is interesting that the Mediterranean water is warmer, but, despite this, heavier: the density of water depends more not on temperature, but on salinity. 0.03 sq. km. It is a bit crowded here for two opposite currents. Foreign scientists took measurements in the Bosphorus in the 40-50s of our century and stated that there is no permanent lower current in the strait. Mediterranean water enters the Black Sea allegedly only occasionally, in small quantities. The materials used for such a "revolution in science" turned out to be clearly insufficient. The authors of the "discovery" did not pay attention to such an obvious circumstance: the flow of river waters into the Black Sea far exceeds the evaporation from its surface. So, if the sea was not constantly salted with Mediterranean water, it would become fresh. This is typical for the Black Sea, since in the Mediterranean, for example, evaporation exceeds river runoff, and the dynamics of the salt balance there is different. Accurate Facts are decisive in scientific disputes, so Soviet scientists, starting in 1958, conducted many years of research, now no longer in the strait, but in the Bosphorus region of the Black Sea. Expedition work was headed by hydrologists of the Institute of Biology of the Southern Seas, located in Sevastopol; our scientific institutions, as well as Bulgarian and Romanian scientists, took part in them. Expeditions in the Bosphorus region made it possible to establish that in all seasons of the year the Mediterranean water enters the Black Sea. After leaving the strait, this heavy water goes near the bottom, to the east, forming a stream 2 to 8 m thick, turns to the northwest after 5-6 miles, and in the region of the continental slope it breaks into separate jets, gradually descends to a great depth and mixes with the Black Sea water. Studies have shown that in the Bosphorus both currents have a speed of about 80 cm / s. The Black Sea receives about 170 cubic meters per year. km of Mediterranean water, and about 360 cubic meters flow out. km of Black Sea water. To fully determine the water balance of the Black Sea, it is also necessary to take into account the exchange with the Sea of ​​Azov, the flow of river waters. precipitation and evaporation. The study of the water balance of the sea is reminiscent of solving a school problem about a pool with pipes. Only the problem of the sea is incomparably more difficult. Nevertheless, it is already possible to fairly accurately predict the changes that will occur to the sea during certain major transformations of nature. The regulation of rivers by dams, the creation of reservoirs and diversion channels leads to a decrease in river flow, since part of the water no longer reaches the sea. The scale of these transformations is enormous. If in the Black Sea salinity does not change very noticeably yet, then in the shallow Azov Sea salinization already leads to a noticeable decrease in fish stocks. The more salty Black Sea water enters the Sea of ​​Azov through the Kerch Strait, in which, as in the Bosporus, there are opposite currents. Previously, the Sea of ​​​​Azov took about 33 cubic meters. km Black Sea water per year and gave 51 cubic meters. km of its own, less salty water. After the regulation of the Don and Kuban, the ratio changed in favor of the Black Sea water, and the Sea of ​​Azov began to become saline. Salinity exceeded 12‰. This led to a decrease in the food supply for gobies and other fish. The most valuable freshwater fish for fishing began to stay closer to the mouths of the rivers, and immobile mollusks are killed by the saltier water going down. In order to improve the water balance of the Sea of ​​\u200b\u200bAzov, it was decided to regulate the exchange of water in the Kerch Strait. This will allow controlling the sea level, its salinity, and will create conditions for increasing the fish stocks of Azov. One of the difficulties is that with reduced river flow, there is nothing to compensate for evaporation. There is still no need to artificially change the water exchange in the Bosporus to regulate the salinity of the Black Sea. But, perhaps, such a problem will someday have to be solved by countries interested in its fate. Near the mouths of the rivers, the Black Sea water is less salty than in the central part of the sea. But in deep-sea regions, far from the coast, does the Black Sea water have the same composition throughout the entire thickness of the sea? Is the water stagnant here or does it mix? It has long been established that currents exist in the upper layers of the seas. They are caused by winds, level differences and differences in water density. Scheme of currents in the Black Sea Some currents are constant and resemble rivers, others often change speed and direction (for example, depending on the nature of the winds). In the Black Sea, one of the causes of currents is the difference in level between its northern and southern parts, which we have already discussed. Water from the northwestern region of the sea "flows" to the south. But the rotation of the earth causes this current to deviate to the west, and it runs counterclockwise along the coast. The width of the current is about 60 km, and the speed of water movement is 0.5 m/s. Part of the water goes into the Bosporus, and the rest of the mass moves on, turning north at the eastern coast of the sea. Where the current bends around the wide ledge of the Anatolian coast, part of the stream forms a branch, heading immediately north; there is a western annular current. The eastern half of the sea also has its own annular counterclockwise current. Currents in the Black Sea are often disturbed by strong winds that move significant masses of water and can noticeably change the water level, sometimes by half a meter. When the wind blows from the shore, it drives the surface warm water into the open sea. The water level is dropping. During such an offshore wind, stones covered with algae are exposed near the shore. Instead of the departed warm water at the surface it turns out to be cold, rising from the depths. A surge wind directed from the sea to the shore brings warm surface water and raises the water level near the coast. The ebbs and flows in the Black Sea are so small that the movement of water under the influence of the wind almost completely obscures them. (Tides arise in the World Ocean under the influence of lunar attraction, but in the inland seas the tidal wave does not reach great heights.)

Alexander Grin recalled in his Autobiographical Tale that he learned to read by looking at a geographical map, and the first word he read was "sea".

“The sea smelled of watermelon,” we read in the story of the great master of epithets and comparisons, Ivan Bunin. But Anton Chekhov most of all liked the simple childish definition: "The sea was big."

Indeed, is it possible to say more precisely about this "model of the universe"? As a happy moment of life, we remember the day when we first saw the Black Sea, that's what draws us to it, that's why we count in the middle of winter the days before vacation. But if not for us, then our children and grandchildren should know something about the sea, and besides the fact that it is “big”!

Origin of the Black Sea

The origin of the Black Sea is closely connected with the history of the whole earth. At the dawn of its history, the earth was a red-hot fire ball. Then the earth began to cool, moisture began to condense, and heavy rains began to fall over its surface, which began to fill all the depressions and land. Groundwater began to collect. This is how the world's seas and oceans were born.

Initially, sea water was not salty. But over the past millions of years, sea water has become salty. Water, evaporating from the sea surface, left all the salts and minerals, while being replenished with water. deep rivers, which eroded young rocks enriched with salts. Thus, the world ocean was filled with minerals and became salty.

Sea water contains all the elements of the periodic table known on earth. But the first place in terms of content is occupied by sodium chloride, known as table salt, and magnesium sulfate - bitter salt. Thanks to them, sea water has a salty taste.

The Black Sea is the heir to the world ocean Tethys, whose waters stretched from the modern Atlantic Ocean to the Pacific. Millions of years passed before the modern seas formed and the mountains that separated it grew.

About twenty thousand years ago, the Black Sea basin was completely isolated from the World Ocean. Numerous fresh rivers served as a source of replenishment of water reserves. In fact, the Black Sea at that time was a lake. Only ten thousand years later, the overflowing freshwater Black Sea reservoir joined the Sea of ​​Marmara through the Bosphorus. Ocean water, enriched with salts, rushed stormy stream tsunami actively fill it. This natural disaster is described in old testament and more commonly known as the Deluge.

IN sea ​​depths the water is colder and saltier than in the upper layers, and therefore cannot rise to the surface to be enriched with oxygen. Where there is a lack of oxygen, hydrogen sulfide accumulates. The Black Sea at a depth below two hundred and 200 meters is saturated with hydrogen sulfide, and black silt lies in a thick layer at the bottom. There is no life in the hydrogen sulfide layer, except for hydrogen sulfide bacteria. The latest measurements of the level of hydrogen sulfide in the Black Sea show that it has begun to rise.

For all the time of the formation of the modern appearance of the earth, the Black Sea has repeatedly merged with the Mediterranean Sea and the Caspian Sea. And only about six or seven thousand years ago the Black Sea became the way we see it today.

The history of the name of the Black Sea

The first known name of the Black Sea is "Temarinda", which means "Dark Abyss". So it was called Tauri, the most ancient inhabitants of the Crimea.

The Greeks, who appeared off the coast of Crimea in the 8th century BC, called the Black Sea Pont Aksinsky - the Inhospitable Sea. For them, it was a sea full of pirates, where the shores teemed with tribes of wild natives. But centuries passed, enterprising Hellenes gradually settled in the Crimean shores, founded cities, developed trade, and centuries later the Black Sea was called Pont Euxinus - the Hospitable Sea.

A thousand years ago, the Black Sea was called the Surozh Sea. Then, through the modern Sudak, and in the past Surozh - the great silk road. It was also called the Russian Sea.

The modern name "Black Sea" was strengthened only in the Middle Ages, when tribes of nomadic Turkic peoples invaded the Crimea. But it sounded different. Mare Negrum - the Genoese and Venetians called it. Karadenis - Arabs. Black sea - now foreigners say. But since then the name has always been the same - the Black Sea.

Currents of the Black Sea

Resting in the Crimea, you often hear the phrase that "the course has changed." What is the course of the Black Sea? It is possible to conduct an experiment, if somewhere in the region of Odessa a boat is allowed to float freely, from the current it will carry it to the Bosphorus Strait itself.

The currents of the Black Sea are closely connected with the large rivers flowing into it - the Dnieper, the Danube, Southern Bug. There, the water level rises significantly. Here it should be remembered that the globe rotates from east to west, and water flows into the Black Sea to the south, deflecting it to the west, directing it along the coasts of Turkey, the Caucasus, Crimea - and so on in a circle ...

The width of the Black Sea current is only sixty meters, the speed is half a meter per second. It is counteracted by the south-west wind (it is called "surge"), which raises the deep cold layers of water to the surface. It is this southwest wind that causes a short cooling of sea water near the southern coast of Crimea. This phenomenon has received local residents Crimea is called "Nizovka", when the temperature of sea water can drop sharply from 25 to 13 degrees. But just a couple of days are enough, and the Black Sea warms up again. You can devote your free time from the sea to excursions and mountain hikes.

In the Black Sea Bosporus, two currents operate simultaneously. On the surface, the water moves from the Black Sea to the Sea of ​​Marmara. But at depth, the water moves back to the Black Sea. If from a boat that is carried by the current to the Sea of ​​​​Marmara, a container of water is thrown on a cable, then, having sunk to a depth of about thirty meters, it will begin to move the boat along against the current on the surface - towards the Black Sea.

The relief of the Black Sea

The Black Sea water area connects Crimea with Turkey, Russia, Georgia, Romania, Bulgaria. Through the Kerch Strait, it is connected to the shallow Sea of ​​Azov, and through the Bosphorus Strait - to the Sea of ​​Marmara and then the oceans.

The Black Sea is one of the deepest inland seas the globe. 2245 meters reaches maximum depth, while the average depth of the Black Sea is 1280 meters. The area of ​​the Black Sea is 442 thousand square kilometers. In terms of water volume, it is six times larger than the Caspian Sea, and sixteen times the Baltic Sea, although their areas are approximately equal in size.

The largest island in the Black Sea is Zmeiny. It occupies an area of ​​only 1.5 square meters. kilometers. There are no other large islands in the Black Sea.

The Black Sea is inland. It almost imperceptible ocean ebbs and flows under the influence of lunar gravity.

The relief of the Black Sea bottom is characterized by three forms. This is a continental shelf - a shelf, a continental slope and a deep-water Black Sea basin.

The shoal occupies about 24% of the entire area of ​​the Black Sea bottom, and descends from the shore to a depth of 100 - 140 meters. The width of the Black Sea shelf in the northwest reaches 200 - 250 kilometers, near the eastern coast - no more than 6 - 10 kilometers. There are places where it does not exceed 500 meters from the coast.

About ten thousand years ago, the shelf was a plain through which rivers flowed. After the melting of the glaciers, these plains were flooded with sea waters.

The continental slope near the Crimean coast is steep, reaches 30° and is considered steep. It is characterized by deep depressions, wide underwater valleys, giant underwater rocks, uplands and stone faults. Sea water slides along the continental slope at high speeds up to 90 km per hour and destroys the soil.

At a depth of 2000 meters, the bottom of the Black Sea basin begins, which occupies about 30% of the entire water area. The hollow is ideally even, oval in shape, slightly inclined to the south.

The Black Sea captures land - one centimeter per year. For example, at the very edge of the Heracleian peninsula, there was an ancient temple, which at that time stood at a safe distance from the sea. Now he is hidden in the depths of the sea. According to scientists, by the end of the 21st century the level of the Black Sea will rise by 1-2 meters. This means that in the next 50 years, all city beaches will go under water.

Fauna of the Black Sea

The fauna of the Black Sea is quite diverse. First of all, these are various types of commercial and non-commercial commercial fish- sturgeon (the largest of them is beluga), Azov flounder-gloss, mullet, pelengas, Black Sea flounder-kalkan, red mullet, sea ​​bass, horse mackerel, mackerel, herring (the herring family also includes anchovy, sprat, sprat), goby, sea ​​ruff, greenfinch and others - about 180 species in total. From the Mediterranean Sea through the Bosporus and Dardanelles tuna, swordfish, bluefish, bonito, garfish enter the Black Sea.

Found here also black sea shark- katran, three species of dolphins - bottlenose dolphin (the largest of them, up to 3 m long and weighing up to 400 kg), common dolphin and azovka (the smallest), there are two types of rays, jellyfish, mussels, rapana, crabs and other inhabitants of the deep sea .

The Black Sea monk seal once lived on the Crimean shores. The last time he was seen in the Novy Svet bays was in 1927. But off the coast of Turkey and Bulgaria, he has survived to this day.
Oysters were also once found in the Black Sea, but the Pacific rapana, which accidentally got into the Black Sea from Far East fifty years ago, practically destroyed them. It's a pity. And the red mullet got its second name - the sultanka - because it was considered the favorite fish of the Turkish sultans due to the thin, delicate taste. Today red mullet is served in the most exquisite Crimean restaurants.

Very often the question arises about the Black Sea jellyfish - what are they? We will answer. There are two types of jellyfish in the Black Sea: Aurelia and Cornerot. Aurelia has a flat umbrella shape, 10-20 cm in diameter, along the edges of which numerous thread-like tentacles are located. Cornerot is a larger jellyfish with a dome diameter of up to 40-50 cm, from which 8 large processes extend. The tentacles of jellyfish are equipped with so-called stinging cells; from touching them, a person gets a burn, as from nettles, traces of which remain on the body for up to several hours.

Due to hydrogen sulfide contamination organic world The Black Sea, although diverse, is not rich. Here you will not find corals, sea stars, urchins and lilies, cephalopods and other groups of animals that are typical for "ordinary", and even more so - tropical seas.

But, like any sea, the Black Sea is shrouded in many secrets. What can you not hear! Exciting stories about ancient Greek sailors and bloodthirsty Taurus pirates; romantic stories about lovers separated by sea and circumstances; legends about countless treasures stored at the bottom of the sea in sunken ships...

This phenomenon is scientifically called Knipovich glasses. Nikolai Mikhailovich Knipovich was the first hydrologist who noticed and described this phenomenon in detail.

The acceleration imparted to sea water by the rotation of the planet is the basis of the characteristic direction of this motion. In physics, this effect is called the Coriolis force. But, due to the fact that the Black Sea has a relatively small water area, a significant impact on the main also exerts the force of the wind. Due to this factor, the main flow The Black Sea is very variable. Sometimes it happens that it becomes faintly noticeable against the background of other sea currents, of a smaller scale. And it happens that the speed of the main Black Sea Current exceeds one hundred centimeters per second.

In the coastal Black Sea waters, eddy currents are formed with the opposite to the main the Black Sea current orientation - the so-called anticyclonic gyres. Such eddies are especially pronounced near the Anatolian and Caucasian coasts. In these regions, alongshore currents in the surface layer of the Black Sea are usually determined by the wind. The direction of such currents can change during the day.

There is a special type of local Black Sea current, which is called traction. The draft is formed during a storm (strong sea waves) near the gently sloping sandy shores. The principle of such currents is that the sea water running ashore retreats not equally evenly over the entire area of ​​the tide, but along the channels formed in the sandy bottom. It is very dangerous to get into the jet of such a drag, because, despite all the efforts of the swimmer, it can be carried away far from the coast right into the open sea.

To get out of such a current, one must swim not directly to the shore, but obliquely, so it is easier to overcome the force of the receding water.

The flow of "dragons" is one of the little-studied phenomena that is associated with waves.

The flow of "tyagun" is the most dangerous view coastal currents, it is formed due to the outflow of sea water, which was brought to the coast by waves. There is a well-established opinion that the "tyagun" pulls under water, it's not like these waves carry away from the shore.

The strength of the pull is high, it can drag even very experienced and strong swimmers with it from the shore. A person who has fallen into a “pull” should not fight it and try to swim straight to the shore by any means, the best way to save is to move diagonally. So it will be possible to gradually get out of the zone of action of the traction, this will save strength and stay afloat, as well as wait for help. It is also possible for the victim himself to gradually get to the shore on his own, trying not to return to the zone of action of this dangerous phenomenon.

This phenomenon can be observed, in many ports of the Black Sea, moored ships to the berth suddenly begin to move from time to time and move along the berths, it seems under the influence of some kind of force. It happens that such a movement is so powerful that the steel mooring lines cannot withstand the pressure, because of this, cargo ships are forced to stop loading and unloading operations and lay down the raid. A draft can form, not only during a storm, but also in complete calm at sea.

There are several hypotheses about the formation of lagoons, but they all define lagoons as a result of the approach to the port gates of a special type of sea waves that are difficult to notice with the naked eye. These waves are called long-period waves, they create an oscillation period much longer than ordinary ones. visible to people waves. By periodically creating strong fluctuations in the mass of water located in the water area of ​​the port, these waves cause the movement of ships moored at the berth.

The study of the formation of this phenomenon, which creates a danger to the ships of the fleet, is carried out both in our country and abroad. Held research work give scientific and practical recommendations on the rules for the mooring of ships during the “jagun”, as well as advice on the construction of safe ports that will extinguish the energy of this wave.

Main course of the Black Sea, the most extensive, is called - "main Black Sea current". Having a counterclockwise direction, it extends to the entire perimeter of the sea. This current forms two rings, in the scientific community called "Knipovich glasses". Knipovich- this is the first hydrologist who noticed and described such a phenomenon in his works. The movement, as well as its characteristic directionality, arises due to the acceleration transmitted to the water from the rotation of the Earth. "Coriolis Force" is the scientific name for such an effect in physics.

An additional significant impact on water flows is exerted by both the strength of the wind and its direction, because the water area near the Black Sea is relatively small in area. Considering these factors, one can speak of a strong variability of the main Black Sea current. It happens that its severity drops sharply compared to other, smaller currents. And at other moments, the speed of its flow can reach 100 cm per second.

The coastal zones of the Black Sea are the place frequent occurrence eddies directed in the direction opposite to the main Black Sea current. This anticyclonic gyres, which are most characteristic of the Anatolian and Caucasian coasts. Coastal currents on the surface of the water, as a rule, depend on the wind. Their direction may change during the day.

Tyagun or reverse current in the Black Sea

One of the types of such flows is called "dragging". The place of its appearance is gentle shores with sandy beaches, formed during a storm. After hitting the shore, the water recedes unevenly, and flows in strong streams along the channels formed in the sandy bottom. Such jets are very dangerous for swimmers, because they carry them very far from the shore. Tyagun is rare in the Black Sea.

Located deep in the mainland, the Black Sea (together with the Sea of ​​Azov) is the most isolated part of the World Ocean. In the southwest, it communicates with the Sea of ​​Marmara through the Bosphorus Strait, the border between the seas runs along the line of Cape Rumeli - Cape Anadolu. The Kerch Strait connects the Black and Azov Seas, the boundary between which is the line between Cape Takil and Cape Panagia.

The area of ​​the Black Sea is 422 thousand km 2, the volume is 555 thousand km 3, the average depth is 1315 m, the greatest depth is 2210 m.

The coastline, with the exception of the north and northwest, is slightly indented. The eastern and southern shores are steep and mountainous, the western and northwestern shores are low and flat, sometimes steep. The only large peninsula is the Crimean. In the east, the spurs of the ridges of the Greater and Lesser Caucasus, separated by the Colchis lowland, come close to the sea. The Pontic Mountains stretch along the southern coast. In the Bosporus region, the coasts are low, but steep, in the southwest the Balkan Mountains approach the sea, further to the north is the Dobruja Upland, gradually turning into the lowlands of the vast Danube Delta. The northwestern and partially northern shores up to the mountainous Southern coast of Crimea are low, dissected by gullies, vast estuaries at the mouths of the rivers (Dniester, Dnieper-Bug), separated from the sea by spits.

Coast near Pitsunda

In the northwestern part of the sea there are the largest bays - Odessa, Karkinitsky, Kalamitsky. In addition to them, Samsun and Sinop bays are located on the southern coast of the sea, and Burgas on the western coast. The small islands of Serpent and Berezan are located in the northwestern part of the sea, Kefken - to the east of the Bosphorus.

The main part of the river runoff (up to 80%) enters the northwestern part of the sea, where the waters are most major rivers: Danube (200 km 3 / year), Dnieper (50 km 3 / year), Dniester (10 km 3 / year). On Black Sea coast Caucasus, the Inguri, Rioni, Chorokh and many small rivers flow into the sea. On the rest of the coast, runoff is negligible.

Climate

Far from the ocean, surrounded by land, the Black Sea has a continental climate, which is manifested in large seasonal changes in air temperature. On climatic features individual parts of the sea are significantly influenced by orography - the nature of the relief of the coastal strip. So, in the northwestern part of the sea, open to the impact air masses from the north, the steppe climate manifests itself (cold winters, hot, dry summers), and in a protected high mountains the southeastern part - the climate of humid subtropics (abundance of precipitation, warm winters, humid summers).

In winter, the sea is affected by the spur of the Siberian anticyclone, which causes intrusions of cold continental air. They are accompanied by northeast winds (at a speed of 7 - 8 m/s), often reaching storm strength, sharp drops in air temperature, and precipitation. Particularly strong northeast winds are characteristic of the Novorossiysk region (boron). Here, masses of cold air accumulate behind the high coastal mountains and, having crossed the peaks, fall with great force down to the sea. The wind speed during the bora reaches 30-40 m/s, the frequency of the bora is up to 20 or more times a year. When the spur of the Siberian anticyclone weakens in winter, Mediterranean cyclones enter the Black Sea. They cause unsettled weather with warm, sometimes quite strong southwesterly winds and temperature fluctuations.

In summer, the influence of the Azores high extends to the sea, clear, dry and hot weather sets in, thermal conditions become uniform for the entire water area. This season is dominated by weak northwestern winds (2-5 m/s), only in rare cases in the coastal strip of the northeastern part of the sea, northeastern winds of storm strength arise.

The most low temperature in January - February it is noted in the northwestern part of the sea (–1-5°), on the southern coast of Crimea it rises to 4°, and in the east and south - up to 6-9°. Minimum temperatures in the northern part of the sea reach -25 - 30°, in the southern part -5 - 10°. In summer the air temperature is 23-25°, the maximum values ​​in different places reach 35-37°.

Atmospheric precipitation on the coast falls very unevenly. In the southeastern part of the sea, where the Caucasus ranges block the way for the western and southwestern humid Mediterranean winds, the greatest amount of precipitation falls (in Batumi - up to 2500 mm / year, in Poti - 1600 mm / year); on the flat northwestern coast it is only 300 mm/year, near the southern and western coasts and on the southern coast of Crimea - 600-700 mm/year. 340-360 km 3 of the Black Sea water annually flows through the Bosphorus, and about 170 km 3 of the Mediterranean water enters the Black Sea. Water exchange through the Bosphorus experiences seasonal changes, determined by the difference in the levels of the Black and Marmara Seas and the nature of the winds in the area of ​​the strait. The Upper Bosphorus current from the Black Sea (occupying a layer of about 40 m at the entrance to the strait) reaches its maximum in summer, and its minimum is observed in autumn. The intensity of the lower Bosphorus current into the Black Sea is greatest in autumn and spring, least of all in early summer. In accordance with the nature of wind activity over the sea, strong waves most often develop in autumn and winter in the northwestern, northeastern and central parts of the sea. Waves 1-3 m high prevail in the sea, depending on the wind speed and the length of the wave acceleration. In open areas maximum heights waves reach 7 m, and in very strong storms they can be higher. The southwestern and southeastern parts of the sea are the calmest, strong waves are rarely observed here, and there are almost no waves higher than 3 m.

Crimean coast

Seasonal changes in sea level are created mainly due to intra-annual differences in the inflow of river runoff. Therefore, in the warm season, the level is higher, in the cold - lower. The magnitude of these fluctuations is not the same and is most significant in the areas of influence of the continental runoff, where it reaches 30–40 cm.

The greatest magnitude in the Black Sea are surge fluctuations in the level associated with the impact of stable winds. They are especially often observed in autumn and winter in the western and northwestern parts of the sea, where they can exceed 1 m. Strong surges in these parts of the sea occur during northwestern winds. Near the Crimean and Caucasian coasts, surges and surges rarely exceed 30-40 cm. Usually their duration is 3-5 days, but sometimes it can be more.

In the Black Sea, seiche level fluctuations up to 10 cm high are often observed. Seiches with periods of 2-6 hours are excited by the action of the wind, and 12-hour seiches are associated with tides. The Black Sea is characterized by irregular semidiurnal tides.

ice coverage

Ice forms annually only in a narrow coastal strip of the northwestern part of the sea. Even in harsh winters it covers less than 5%, and in moderate winters - 0.5-1.5% of the sea area. In very severe winters, fast ice along the western coast extends to Constanta, and floating ice is carried to the Bosphorus. Over the past 150 years, ice floes have been observed in the strait 5 times. In mild winters, only estuaries and individual bays are covered with ice.

Ice formation usually begins in mid-December, and the maximum extent of ice occurs in February. The boundary of immobile ice in moderate winters in the northwestern part of the sea runs from the Dniester Estuary to the Tendrovskaya Spit at a distance of 5-10 km from the coast. Further, the ice edge crosses the Karkinit Bay and reaches the middle part of the Tarkhankut Peninsula. The sea is cleared of ice in March (early - at the beginning of March, later - at the beginning of April). The duration of the ice period varies greatly: from 130 days in very severe winters to 40 days in mild ones. Ice thickness on average does not exceed 15 cm, in severe winters it reaches 50 cm.

Bottom relief

Underwater canyon in the Black Sea

In the topography of the sea bottom, three main structures are clearly distinguished: the shelf, the continental slope, and the deep-sea basin. The shelf occupies up to 25% of the total bottom area and, on average, is limited to depths of 100–120 m. It reaches its greatest width (more than 200 km) in the northwestern part of the sea, which is entirely located within the shelf zone. Almost throughout the mountainous eastern and southern coasts of the sea, the shelf is very narrow (only a few kilometers), and in the southwestern part of the sea it is wider (tens of kilometers).

The continental slope, which occupies up to 40% of the bottom area, descends approximately to a depth of 2000 m. It is steep and indented by underwater valleys and canyons. The bottom of the basin (35%) is a flat accumulative plain, the depth of which gradually increases towards the center.

Water circulation and currents

Water circulation throughout the year has a cyclonic character with cyclonic gyres in the western and eastern parts of the sea and the main along-shore Black Sea current that envelops them. Seasonal changes in circulation are manifested in the velocities and in the details of this system of currents. The main Black Sea current and cyclonic gyres are most clearly expressed in winter and summer. In spring and autumn, water circulation becomes weaker and more complex in structure. A small anticyclonic gyre forms in the southeastern part of the sea in summer.

Three characteristic areas can be distinguished in the water circulation system, the structure of currents in which is distinguished by its originality: the coastal part, the zone of the main Black Sea current and the open parts of the sea.

The boundaries of the coastal part of the sea are determined by the width of the shelf. The current regime here depends on local factors and is significantly variable in space and time.

The zone of the main Black Sea current, 40-80 km wide, is located above the continental slope. The currents in it are very stable and have a cyclonic direction. The current velocities on the surface are 40-50 cm/s, sometimes exceeding 100 and even 150 cm/s (in the core of the flow). In the upper hundred-meter layer of the main current, the velocities decrease slightly with depth, the maximum vertical gradients fall on the 100–200 m layer, below which the velocities slowly fade.

In the open parts of the sea, the currents are weak. The average velocities here do not exceed 5-15 cm/s on the surface, slightly decreasing with depth to 5 cm/s at the horizons of 500-1000 m. The boundaries between these structural regions are rather arbitrary.

In the shallow northwestern part of the sea, the circulation is mainly driven by the wind. The northern and northeastern winds determine the cyclonic nature of the currents, and the winds of the western directions are anticyclonic. In accordance with the nature of the winds, the establishment of anticyclonic circulation is possible in the summer season.

The general circulation of the sea waters has a unidirectional character to a depth of about 1000 m. In deeper layers, it is very weak, and it is difficult to talk about its general character.

An important feature of the main Black Sea current is its meandering, which can lead to the formation of isolated eddies that differ in temperature and salinity from the surrounding waters. The sizes of eddies reach 40-90 km, the phenomenon of eddy formation is essential for water exchange not only in the upper, but also in the deep layers of the sea.

Inertial currents with a period of 17-18 hours are widespread in the open sea. These currents affect the mixing in the water column, since their velocities even in the 500-1000 m layer can be 20-30 cm/s.

Water temperature and salinity

The water temperature on the sea surface in winter rises from -0.5-0° in the coastal areas of the northwestern part to 7-8° in central regions and 9-10° in the southeastern part of the sea. In summer, the surface layer of water warms up to 23-26°C. Only during the ebb can there be short-term significant drops in temperature (for example, near the southern coast of Crimea). During the warming of the sea, a layer of temperature jump is formed at the lower boundary of wind mixing, which limits the spread of heat to the upper homogeneous layer.

Salinity on the surface throughout the year is minimal in the northwestern part of the sea, where the main volume of river waters enters. In the estuarine areas, salinity increases from 0-2 to 5-10‰, and in most of the open sea it is 17.5-18.3‰.

During the cold season, vertical circulation develops in the sea, by the end of winter covering a layer with a thickness of 30-50 m in the central to 100-150 m in the coastal areas. The waters cool most strongly in the northwestern part of the sea, from where they spread by currents to intermediate horizons throughout the sea and can reach the regions most remote from the cold centers. As a consequence of winter convection, a cold intermediate layer is formed in the sea during subsequent summer heating. It persists throughout the year at horizons of 60-100 m and is distinguished by temperature at the boundaries of 8 °, and in the core - 6.5-7.5 °.

Convective mixing in the Black Sea cannot extend deeper than 100-150 m due to the increase in salinity (and, consequently, density) in deeper layers as a result of the entry of salty Marble Sea waters there. In the upper mixed layer, salinity increases slowly, and then sharply increases from 18.5 to 21‰ at 100-150 m. This is a permanent salinity jump layer (halocline).

Starting from the horizons of 150-200 m, salinity and temperature slowly increase towards the bottom due to the influence of the more saline and warm Marble Sea waters entering the deeper layers. At the exit from the Bosporus, they have a salinity of 28-34‰ and a temperature of 13-15°, but quickly change their characteristics, mixing with the Black Sea water. In the near-bottom layer, a slight increase in temperature also occurs due to the geothermal heat inflow from the sea bottom. Deep waters, located in the layer from 1000 m to the bottom and occupying in the Black Sea in winter (II) and summer (VIII) more than 40% of the volume of the sea, are characterized by a large constancy of temperature (8.5-9.2 °) and salinity (22- 22.4‰.

Vertical distribution of water temperature (1) and salinity (2)

Thus, in the vertical hydrological structure of the Black Sea waters, the main components are distinguished:

the upper homogeneous layer and the seasonal (summer) thermocline, associated mainly with the process of wind mixing and the annual cycle of heat flux through the sea surface;

a cold intermediate layer with a temperature minimum in depth, which in the northwest and northeast of the sea arises as a result of autumn-winter convection, and in other areas is formed mainly by the transfer of cold waters by currents;

permanent halocline - a layer of maximum increase in salinity with depth, located in the contact zone of the upper (Black Sea) and deep (Marmara) water masses;

deep layer - from 200 m to the bottom, where there are no seasonal changes in hydrological characteristics, and their spatial distribution is very uniform.

The processes occurring in these layers, their seasonal and interannual variability determine the hydrological conditions of the Black Sea.

The Black Sea has a two-layer hydrochemical structure. Unlike other seas, only the upper well-mixed layer (0-50 m) is saturated with oxygen (7-8 ml/l). Deeper, the oxygen content begins to decrease rapidly, and already at the horizons of 100-150 m it is equal to zero. At the same horizons, hydrogen sulfide appears, the amount of which increases with depth up to 8-10 mg / l at a horizon of 1500 m, and further to the bottom it stabilizes. In the centers of the main cyclonic gyres, where water rises, the upper boundary of the hydrogen sulfide zone is located closer to the surface (70-100 m) than in coastal areas (100-150 m).

On the border between the oxygen and hydrogen sulfide zones, there is an intermediate layer of the existence of oxygen and hydrogen sulfide, which is the lower "boundary of life" in the sea.

Vertical distribution of oxygen and hydrogen sulfide in the Black Sea. 1 - average oxygen content, 2 - average hydrogen sulfide content, 3 - deviation from the average

The spread of oxygen into the deep layers of the sea is hindered by large vertical density gradients in the contact zone of the Black Sea and Marble Sea water masses, which limit convective mixing by the upper layer.

At the same time, the exchange of waters in the Black Sea occurs between all layers, albeit slowly. Deep salty waters, constantly replenished by the lower Bosphorus current, gradually rise and mix with the upper layers, which go into the Bosphorus with upstream. Such circulation maintains a relatively constant salinity ratio in the sea water column.

In the Black Sea, the following main processes are distinguished (Vodyanitsky V.A. et al.) that determine the vertical exchange in the water column: the rise of water in the centers of cyclonic gyres and subsidence at their periphery; turbulent mixing and diffusion in the sea water column; autumn-winter convection in top layer; bottom convection due to heat flow from the bottom; mixing in synoptic eddies; surge phenomena in the coastal zone.

Estimates of the time of vertical water exchange in the sea are very approximate. This important question needs further research.

As the main mechanism for the formation of hydrogen sulfide in the Black Sea, most authors accept the reduction of sulfate compounds (sulfates) during the decomposition of organic residues (dead organisms) under the influence of sulfate-reducing microspira bacteria. Such a process is possible in any reservoirs, but the hydrogen sulfide formed in them quickly oxidizes. In the Black Sea, it does not disappear due to the slow exchange of water and the lack of the possibility of its rapid oxidation in the deep layers. When deep water rises into the upper oxygen layer of the sea, hydrogen sulfide is oxidized to sulfates. Thus, there is an established equilibrium cycle of sulfur compounds in the sea, determined by the rate of water exchange and other hydrodynamic processes.

At present, it is believed that in recent decades there has been a constant unidirectional rise (trend) of the upper boundary of the hydrogen sulfide zone to the sea surface, reaching tens of meters. This is associated with anthropogenic withdrawals of river runoff and changes in the density structure of the sea. However, the available data so far only testify to natural interannual fluctuations in the position of the boundary of the hydrogen sulfide zone, which occur differently in different areas of the sea. The isolation of the anthropogenic trend against the background of these fluctuations is difficult due to the lack of systematic observations of the topography of the boundary of the hydrogen sulfide layer and the imperfection of the methodology for its determination.

Fauna and environmental issues

Diverse vegetable and animal world The Black Sea is almost entirely concentrated in the upper layer 150-200 m thick, which is 10-15% of the volume of the sea. The deep water column, deprived of oxygen and containing hydrogen sulfide, is almost lifeless and inhabited only by anaerobic bacteria.

The ichthyofauna of the Black Sea was formed from representatives different origin and has about 160 species of fish. One of the groups is fish of freshwater origin: bream, crucian carp, perch, rudd, pike perch, ram and others, found mainly in the northwestern part of the sea. In desalinated areas and brackish estuaries there are representatives of the ancient fauna, preserved from the time of the existence of the ancient Ponto-Caspian basin. The most valuable of them are sturgeon, as well as several types of herring. The third group of Black Sea fish is made up of immigrants from the North Atlantic - these are cold-loving sprats, whiting, spiny katran shark, etc. The fourth, largest group of fish - Mediterranean invaders - has over a hundred species. Many of them enter the Black Sea only in summer, and winter in the Marmara and mediterranean seas. Among them are bonito, mackerel, tuna, Atlantic horse mackerel, etc. Only 60 species of fish of Mediterranean origin that constantly live in the Black Sea can be considered Black Sea. These include anchovy, garfish, mullet, horse mackerel, sultanka (red mullet), mackerel, flounder-kalkan, stingrays, etc. Of the 20 commercial species of Black Sea fish, only anchovy, small horse mackerel and sprat, as well as katran sharks, are of importance.

At present, the state of the Black Sea ecosystem is unfavorable. There is an impoverishment of the species composition of plants and animals, a reduction in the reserves of useful species. First of all, this is observed in the shelf areas experiencing a significant anthropogenic load. The greatest changes are observed in the northwestern part of the sea. A large amount of biogenic and organic substances coming here with continental runoff causes the massive development of planktonic algae (“bloom”). In the area of ​​influence of the Danube runoff, the phytoplankton biomass increased by 10-20 times; "red tides". Due to the toxic effect of some algae, the death of fauna is observed during the mass "blooming". In addition, with the intensive development of plankton, a large number of dead organisms settle to the bottom, the decomposition of which consumes dissolved oxygen. With a well-defined stratification of waters, which prevents the flow of oxygen from the surface layer to the bottom layer, an oxygen deficiency (hypoxia) develops in it, which can lead to the death of organisms (kills). Since 1970, deaths of varying intensity have been repeated almost annually. The unfavorable ecological situation caused the extinction of the once vast field of Phyllophora, an algae used to make agar-agar.

The deterioration of water quality and oxygen regime is one of the main reasons for the decline in the number of commercial fish in the northwestern part of the Black Sea.