The Black Sea is an inland sea of the Atlantic Ocean, washing the shores of Ukraine, Russia, Georgia, Romania, Bulgaria, and Turkey.
Area - 422 thousand km2, length between western and eastern points - about 1167 km, between northern and southern - 624 km. The largest peninsula is Crimean, the largest bays (off the coast of Ukraine) are Karkinitsky, Kalamitsky, Feodosiyskaya, Dzharylgachsky. The largest island off the coast of Ukraine is Zmeiny. The average depth is 1271 m, the maximum is 2245 m. The shores of the Black Sea are poorly dissected, most often mountainous, steep, but within the continental part of Ukraine they are flat.
Within Ukraine they flow into the Black Sea large rivers: Danube, Dniester, Southern Bug, Dnieper. Many resorts: Sochi, Gelendzhik, resorts of Crimea, Abkhazia, Bulgaria.
Most of the sea is located in the subtropical zone. Winter is warm and humid. The air temperature in January over the Black Sea is -1 ... + 8 ° C, the surface water temperature is + 8 ° ... 9 ° C, except in the northwestern and northeastern parts, where the sea freezes in severe winters. Summer is hot and dry. Air temperature +22 ... 25 ° C, surface water temperature H24 ... 26 ° C. Average precipitation increases from west to east from 200-600 to 2000 mm or more. Average salinity is 21.8%.
The waters of the Black Sea at depths of more than 50-100 m are saturated with hydrogen sulfide, which negatively affects its organic life.
In the Black Sea there are more than 300 species of algae and over 180 species of fish, living mainly in the upper layer (above the hydrogen sulfide zone). Anchovy, horse mackerel, mullet, flounder, mackerel, algae and invertebrates (mussels, shrimp, oysters) are of industrial importance. Every year the sea provides up to 300 thousand tons of biological resources. Industrial reserves of natural gas and oil have been explored. The mud of the Black Sea estuaries has medicinal value. The Black Sea has a number of bays convenient for ships.
The Black Sea extends from west to east for 1160 km, its greatest width is 580 km. The total water area exceeds 420 thousand km2. The sea fills a large tectonic depression. Its maximum depth is 2245 m. The largest bays are Dzharylgachsky, Karkinitsky, Kalamitsky, Feodosiyskaya, Sivash, Obitichna, Berdyansk. The rivers Danube, Dnieper, Dniester, and Southern Bug flow into the Black Sea. In areas between the rivers of the coast there are bodies of water connecting to the sea - estuaries. Of these, on the Black Sea coast there are the Dniester, Khadzhibey, Kuyalnitsky, Tiligulsky, Dnieper estuaries, and on the Azov coast - Utlyutsky, Molochny. The most peninsula of the Black Sea is the Crimean, which is connected to the mainland by the Perekop Isthmus. In the Sea of Azov, elongated areas of land - spits - attract attention. The largest among them is the Arabat Strelka Spit. In the Black Sea, the largest island is Dzharylgach.
The Kerch Strait connects the Black Sea with the Azov Sea. The depth of the strait is up to 4 m.
The climatic conditions of the Black Sea are characterized by subtropical features. Summer is dry and hot, winter is wet and warm. In winter, Mediterranean and Atlantic cyclones move over it, which are associated with rain and foggy weather. In summer, the Black Sea is under the influence of the Azores High, due to which cloudless weather prevails here, thunderstorms and tornadoes are rare occurrences.
Sea level fluctuations associated with high and low tides are insignificant, their amplitude is only 10 cm. Fluctuations under the influence of wind activity reach 1.5 m. Water temperature in summer is +24, + 26 ° C, and in winter it drops to +6, +7 ° C. From a depth of 150 m. The temperature became (8 ° C). In years with severe winters, the northwestern part of the Black Sea freezes.
The salinity of the upper layer of water in the Black Sea is 17-18%. With depth, salinity increases to 22.5%. Compare these indicators with the following: the average salinity of the World Ocean is 35% o, the Mediterranean Sea - up to 38, and the Red Sea - 40% o. Find out why the salinity of the Black Sea waters is much lower.
Characteristic feature natural conditions The Black Sea is the existence of a permanent layer of hydrogen sulfide at depths below 100-120 m. This layer is inhabited by bacteria that use hydrogen sulfide. An important fact is that the hydrogen sulfide layer makes up 87% of the volume of the entire Black Sea. And only 13% of the Black Sea water contains oxygen; it is in this small layer that animals are found. Researchers note that hydrogen sulfide rises to the surface.
Every year, up to 300 thousand tons are taken out of the Black Sea. Biological resources. Construction sand, gravel, and flammable gas are also mined here; The search for oil fields on the shelf continues.
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When measuring heights on land, the count starts from sea levels. This does not mean that sea level is exactly the same in all areas of the World Ocean. In particular, the level of the Black Sea near Odessa is 30 cm higher than that of Istanbul, for this reason water rushes from the Black Sea to the Mediterranean (via Mramornoe), and in the Bosphorus Strait there is a constant current carrying Black Sea water. It is known that the atmosphere is cold the air moves downwards towards warmer, lighter air. The water in the Bosphorus moves in exactly the same way - the heavy Mediterranean water flows below towards the Black Sea. It is interesting that Mediterranean water is warmer, but despite this, it is heavier: the density of water depends more on salinity rather than temperature. The smallest width of the Bosphorus is 730 m, and the depth in some places does not exceed 40 m, so the smallest section of the strait is only 0.03 sq. km. The two opposing currents are a bit crowded here. Foreign scientists took measurements in the Bosporus in the 40-50s of our century and stated that a constant lower current does not exist in the strait. Mediterranean water supposedly enters the Black Sea 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 this obvious circumstance: the flow of river water into the Black Sea far exceeds evaporation from its surface. So, if the sea were not constantly salted in the Mediterranean sea water, it would become insipid. This is typical specifically for the Black Sea, since in the Mediterranean, for example, evaporation exceeds river flow, 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. The expedition work was led by hydrologists from 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 Mediterranean water flows into the Black Sea in all seasons of the year. After leaving the strait this heavy the water is flowing at the bottom, to the east, forming a stream with a thickness of 2 to 8 m, after 5-6 miles it turns to the northwest, and in the area of the continental slope it breaks up into separate streams, gradually descends to great depths and mixes with the Black Sea water. Research has shown that that in the Bosphorus both currents have a speed of about 80 cm/sec. About 170 cubic meters enter the Black Sea annually. km of Mediterranean water, and about 360 cubic meters flow out. km of Black Sea water. To fully define water balance Black Sea, we also need to take into account the exchange with the Sea of Azov, the flow of river waters. precipitation and evaporation rates. Studying the water balance of the sea is reminiscent of solving a school problem about a swimming pool with pipes. Only the problem about the sea is incomparably more difficult. Nevertheless, it is already possible to quite accurately predict the changes that will occur to the sea during certain major transformations of nature. The regulation of rivers with dams, the creation of reservoirs and diversion canals leads to a decrease in river flow, since some of the water no longer reaches the sea. The scale of such transformations is enormous. If in the Black Sea salinity does not yet change very noticeably, then in the shallow Azov Sea salinity is already leading to a noticeable decrease in fish stocks. The saltier Black Sea water enters the Sea of Azov through the Kerch Strait, which, like the Bosphorus, has opposing currents. Previously, the Sea of Azov received about 33 cubic meters. km of 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 saltier. 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 rivers, and immobile mollusks are destroyed by the saltier water going below. In order to improve the water balance of the Sea of Azov, it was decided to regulate the exchange of water in the Kerch Strait. This will make it possible to control the sea level, its salinity, and 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 no need yet to artificially change water exchange in the Bosphorus to regulate the salinity of the Black Sea. But perhaps this problem will someday have to be solved by countries interested in its fate. Near the mouths of rivers, the Black Sea water is less salty than in the central part of the sea. But in deep-sea areas, far from the coast, does the Black Sea water have the same composition throughout the entire thickness of the sea? Is the water here stagnant or mixed? It has long been established that there are currents 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 reasons causing 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 flows along the coast counterclockwise. The width of the current is about 60 km, and the speed of water movement is 0.5 m/sec. Part of the water goes into the Bosphorus, and the rest of the mass moves further, turning north near the eastern shore of the sea. Where the current bends around the broad protrusion of the Anatolian coast, part of the stream forms a branch heading immediately to the north; a western ring current arises. The eastern half of the sea also has its own ring current, running counterclockwise. Currents in the Black Sea are often disrupted by strong winds, which move significant masses of water and can noticeably change the water level, sometimes by half a meter. When the wind blows offshore, it pushes warm surface water out to the open sea. The water level is falling. During such a driving wind, rocks covered with algae are exposed near the shore. Instead of the warm water that has gone away, cold water appears at the surface, rising from the depths. The surge wind directed from the sea to the shore drives warm surface water and increases the water level near the shore. The ebbs and flows in the Black Sea are so small that water movements under the influence of the wind almost completely obscure them. (Tides arise in the World Ocean under the influence of lunar gravity, but in inland seas the tidal wave does not reach a great height.)
Located in the depths of the continent, 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 Rumeli Cape - Anadolu Cape. The Kerch Strait connects the Black and Azov Seas, the border between which is the line Cape Takil - 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, steep in places. The only large peninsula is Crimean. In the east, spurs of the Greater and Lesser Caucasus ranges, separated by the Colchis Lowland, come close to the sea. The Pontic Mountains stretch along the southern coast. In the Bosphorus area, the shores are low but steep; in the southwest the Balkan Mountains approach the sea; further to the north is the Dobrudzha 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 ravines, extensive estuaries at the mouths of rivers (Dniester, Dnieper-Bug), fenced off from the sea by spits.
Beach near Pitsunda
In the northwestern part of the sea there are the largest bays - Odessa, Karkinitsky, Kalamitsky. In addition to them, on the southern coast of the sea there are Samsun and Sinop bays, and on the western coast - Burgas. The small islands of Zmeiny and Berezan are located in the northwestern part of the sea, Kefken - east of the Bosphorus.
The main part of the river flow (up to 80%) flows into the northwestern part of the sea, where the largest rivers carry water: Danube (200 km 3 / year), Dnieper (50 km 3 / year), Dniester (10 km 3 / year) . On the Black Sea coast of the Caucasus, the Inguri, Rioni, Chorokh and many small rivers flow into the sea. On the rest of the coast, the flow is negligible.
Climate
Remote from the ocean and surrounded by land, the Black Sea has a continental climate, which is manifested in large seasonal changes in air temperature. The climatic characteristics of individual parts of the sea are significantly influenced by orography - the nature of the relief of the coastal strip. Thus, in the northwestern part of the sea, open to influence air masses from the north, the climate of the steppes appears (cold winters, hot, dry summers), and in the southeastern part, protected by high mountains, the climate of humid subtropics (abundance of precipitation, warm winter, wet summer).
In winter, the sea is affected by the spur of the Siberian anticyclone, which causes intrusions of cold continental air. They are accompanied by northeastern winds (at a speed of 7 - 8 m/s), often reaching storm force, sharp drops in air temperature, and precipitation. Particularly strong northeastern winds are typical for the Novorossiysk (Bora) region. Here, masses of cold air accumulate behind the high coastal mountains and, having passed over the peaks, fall with great force down to the sea. The wind speed during bora reaches 30-40 m/s, the frequency of 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 unstable weather with warm, sometimes very strong southwesterly winds and temperature fluctuations.
In summer, the sea is influenced by the Azores High, clear, dry and hot weather, thermal conditions become uniform for the entire water area. During this season, weak northwestern winds (2-5 m/s) predominate; only in rare cases do northeastern winds of storm force occur in the coastal strip of the northeastern part of the sea.
The most low temperature in January - February it is observed 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 - 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°, maximum values at different points reach 35-37°.
Atmospheric precipitation falls very unevenly on the coast. In the southeastern part of the sea, where the Caucasus ridges block the path of 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, off the southern and western coasts and on the southern coast of Crimea - 600-700 mm/year. 340-360 km 3 of Black Sea water flows annually through the Bosphorus, and about 170 km 3 of Mediterranean water enters the Black Sea. Water exchange through the Bosphorus experiences seasonal changes, determined by the difference in 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 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. Depending on the wind speed and wave acceleration length, waves with a height of 1-3 m predominate in the sea. In open areas, maximum wave heights 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 over 3 m high.
Crimean coast
Seasonal changes in sea level are created mainly due to intra-annual differences in river flow input. Therefore, in the warm season the level is higher, in the cold season it is lower. The magnitude of these fluctuations is not the same and is most significant in areas influenced by continental runoff, where it reaches 30-40 cm.
The greatest magnitude in the Black Sea is the surge level fluctuations associated with the impact steady winds. They are especially often observed in autumn-winter in western and northwestern parts seas, where they can exceed 1 m. In the west, strong surges are caused by easterly and northeasterly winds, and in the northwest - southeasterly ones. Strong surges in these parts of the sea occur during northwestern winds. Along 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 longer.
In the Black Sea, seiche level fluctuations up to 10 cm in height are often observed. Seiches with periods of 2-6 hours are excited by wind, and 12-hour seiches are associated with tides. The Black Sea is characterized by irregular semidiurnal tides.
Ice cover
Ice is formed annually only in a narrow coastal strip in the northwestern part of the sea. Even in severe winters it covers less than 5%, and in moderate winters - 0.5-1.5% of the sea area. In very severe winters, the fast ice along the western coast extends to Constanta, and the floating ice is carried to the Bosphorus. Over the past 150 years, ice floes in the strait have been observed 5 times. In mild winters, only estuaries and individual bays are covered with ice.
Ice formation usually begins in mid-December, with maximum ice expansion observed in February. The boundary of stationary 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 Karkinitsky Bay and reaches the middle part of the Tarkhankut Peninsula. Clearing of the sea from ice occurs in March (early - in early March, later - in early April). The duration of the ice period varies greatly: from 130 days in very severe winters to 40 days in mild ones. The 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 seabed, 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 is on average 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 all located within the shelf zone. Almost along the entire length of 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, occupying up to 40% of the bottom area, descends to approximately 2000 m depth. 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 is cyclonic in nature with cyclonic gyres in the western and eastern parts of the sea and the main Black Sea alongshore current that goes around them. Seasonal changes in circulation are reflected in the speeds and details of this current system. 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. In the southeastern part of the sea, a small anticyclonic gyre is formed in the summer.
In the water circulation system, three characteristic areas can be distinguished, 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 orientation. Current speeds on the surface are 40-50 cm/s, sometimes exceeding 100 and even 150 cm/s (in the flow core). In the upper hundred-meter layer of the main current, velocities decrease slightly with depth; the maximum vertical gradients occur in the 100-200 m layer, below which the velocities slowly attenuate.
In open parts of the sea, currents are weak. Average velocities here do not exceed 5-15 cm/s on the surface, slightly decreasing with depth to 5 cm/s at horizons of 500-1000 m. The boundaries between these structural regions are quite arbitrary.
In the shallow northwestern part of the sea, circulation is mainly driven by the wind. Northern and northeastern winds determine the cyclonic nature of the currents, and winds from the western directions determine the anticyclonic nature. In accordance with the nature of the winds, the establishment of anticyclonic circulation is possible in the summer season.
The general circulation of sea waters is unidirectional to a depth of about 1000 m. In deeper layers it is very weak, and it is difficult to talk about its general nature.
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 size of the eddies reaches 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 influence mixing in the water column, since their speeds even in a layer of 500-1000 m 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 north-western part to 7-8° in the central regions and 9-10° in the south-eastern part of the sea. In summer, the surface layer of water warms up to 23-26°. Only during surges can short-term significant drops in temperature occur (for example, off the southern coast of Crimea). During the period of sea warming, a temperature jump layer is formed at the lower boundary of wind mixing, limiting the spread of heat to the upper homogeneous layer.
Salinity on the surface is minimal all year round in the northwestern part of the sea, where the bulk of river water flows. In the estuary 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, a vertical circulation develops in the sea, which by the end of winter covers a layer with a thickness of 30-50 m in central to 100-150 m in coastal areas. The waters cool most strongly in the northwestern part of the sea, from where they are distributed by currents at intermediate horizons throughout the sea and can reach areas farthest from the centers of cold. As a consequence of winter convection, with subsequent summer heating, a cold intermediate layer is formed in the sea. It persists throughout the year at horizons of 60-100 m and is distinguished by its 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 an increase in salinity (and therefore density) in deeper layers as a result of the influx of salty Marmara Sea waters there. In the upper mixed layer, salinity increases slowly, and then at 100-150 m it sharply increases from 18.5 to 21‰. This is a permanent salinity jump layer (halocline).
Starting from horizons of 150-200 m, salinity and temperature slowly increase towards the bottom due to the influence of saltier and warmer Marble Sea waters entering the deeper layers. At the exit from the Bosphorus they have a salinity of 28-34‰ and a temperature of 13-15°, but quickly change their characteristics when mixed with Black Sea water. In the bottom layer, a slight increase in temperature also occurs due to geothermal heat influx from the seabed. Deep waters, located in a layer from 1000 m to the bottom and occupying more than 40% of the sea volume in the Black Sea in winter (II) and summer (VIII), are characterized by great constancy of temperature (8.5-9.2 °) and salinity (22- 22.4‰.
Vertical distribution of water temperature (1) and salinity (2)
Thus, the main components are distinguished in the vertical hydrological structure of the Black Sea waters:
an upper homogeneous layer and a seasonal (summer) thermocline, associated mainly with the process of wind mixing and the annual cycle of heat flow through the sea surface;
a cold intermediate layer with a minimum temperature 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;
constant 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 horizons of 100-150 m it is equal to zero. Hydrogen sulfide appears at the same horizons, the amount of which increases with depth to 8-10 mg/l at a horizon of 1500 m, and then stabilizes towards the bottom. 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).
At the border between the oxygen and hydrogen sulfide zones there is an intermediate layer of the existence of oxygen and hydrogen sulfide, which represents the lower “limit 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 hampered by large vertical density gradients in the contact zone of the Black Sea and Marmara Sea water masses, limiting convective mixing by the upper layer.
At the same time, the exchange of water in the Black Sea occurs between all layers, although slowly. Deep salty waters, constantly replenished by the lower Bosphorus current, gradually rise and mix with the upper layers, which flow into the Bosphorus with the upper current. This 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.), causing vertical exchange in the water column: the rise of water in the centers of cyclonic gyres and the descent at their periphery; turbulent mixing and diffusion in the sea water column; autumn-winter convection in the upper 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 issue requires further research.
As the main mechanism for the formation of hydrogen sulfide in the Black Sea, most authors accept the reduction of sulfuric acid compounds (sulfates) during the decomposition of organic residues (dead organisms) under the influence of sulfate-reducing microspira bacteria. This process is possible in any reservoir, but the hydrogen sulfide formed in them quickly oxidizes. It does not disappear in the Black Sea due to the slow exchange of waters and the lack of 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 into sulfates. Thus, in the sea there is a steady equilibrium cycle of sulfur compounds, determined by the rate of water exchange and other hydrodynamic processes.
Currently, there is an opinion 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 flow and changes in the density structure of the sea. However, the available data so far only indicate natural interannual fluctuations in the position of the boundary of the hydrogen sulfide zone, which occur differently in different areas of the sea. Isolating an 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 plant and animal world The Black Sea is almost entirely concentrated in the upper layer 150-200 m thick, constituting 10-15% of the sea's volume. The deep water column, devoid 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 of different origins 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-water estuaries there are representatives of ancient fauna that have been preserved since the existence of the ancient Ponto-Caspian basin. The most valuable of them are sturgeon, as well as several types of herring. Third group Black Sea fish are immigrants from North Atlantic- these are cold-loving sprat, whiting, spiny dogfish 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 Mramornye and Mediterranean seas. These include bonito, mackerel, tuna, Atlantic horse mackerel, etc. Only 60 species of fish of Mediterranean origin that permanently live in the Black Sea can be considered Black Sea. These include anchovy, garfish, mullet, mackerel, red mullet, mackerel, flounder, stingrays, etc. Of the 20 commercial species of Black Sea fish, only anchovy, small mackerel and sprat, as well as the dogfish shark, are important.
Currently, the state of the Black Sea ecosystem is unfavorable. Depletion occurs species composition plants and animals, reduction of stocks useful species. This is primarily observed in shelf areas experiencing significant anthropogenic pressure. 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 (“blooming”). In the area influenced by the Danube runoff, the biomass of phytoplankton increased 10-20 times, cases "red tides". Due to the toxic effect of some algae, the death of fauna is observed during mass blooms. In addition, with intensive development of plankton, sediment settles to the bottom. a large number of dead organisms, 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, oxygen deficiency develops in it (hypoxia), which can lead to the death of organisms (deaths). Since 1970, death tolls of varying intensity have been repeated almost every year. Unfavorable environmental conditions have caused the death of a once vast field of phyllophora - an algae used to make agar-agar.
The deterioration of water quality and oxygen conditions is one of the main reasons for the decline in the number of commercial fish in the northwestern part of the Black Sea.
COLOR OF THE BLACK SEA
The Black Sea is "not the bluest in the world" (Sargasso Sea, some areas of the Indian Ocean) - even in the Red Sea the water is bluer than in the Black Sea. The color of water depends on the scattering of solar spectrum rays by water particles and impurities.
Rays of different colors have different wavelengths, red - long wavelengths are absorbed in the surface layer; blue - short wavelength - are reflected and enter the eye. Near the shore, where there are many impurities, green and yellow rays are reflected.
Also, the color of water depends on the number of suspended particles. There are more of them in the Azov Sea than in the Black Sea, so the water in the Azov Sea is greenish-brown, and in the Black Sea it is greenish-blue.
Water clarity is determined by lowering a standard white disk with a diameter of 30 centimeters to a depth; the depth at which this disk is hidden from view is called water clarity. The largest is 27 meters, in the eastern part - in summer, the smallest 2-3 meters - in the northwestern part - in spring. At a depth of 25 meters, the illumination is 1-4 percent of the illumination on the surface.
BLACK SEA CURRENTS
1. Weak, the speed rarely exceeds 0.5 meters per second, their causes are river flow and the effects of winds. Under the influence of river flow and under the influence of the rotational force of the earth, it deviates to the right by 90 degrees (in the northern hemisphere) and runs along the banks counterclockwise. The main stream of currents has a width of 40-60 kilometers and passes at a distance of 3-7 kilometers from the coast.
2. Separate gyres are formed in the bays in a clockwise direction, their speed is 0.5 meters per second.
3. In the central part of the sea there are calm zones; there are 2 rings: in the eastern and western half.
4. Winds form temporary currents.
5. In the Bosphorus Strait, Admiral Makarov established 2 currents:
a) surface - carrying desalinated water from the Black Sea to Marmara, speed 1.5 meters per second;
b) deep - carrying dense salty water into Chernoye, speed 0.75 meters per second.
POLLUTION OF BLACK SEA WATER
a) semi-closed, weak exchange of water with the ocean.
b) absence of vertical movement of water.
c) oil (pouring of oil; ballast water provides the largest amount of oil; after unloading oil, tanker tanks are filled with ballast - sea water, and before loading it again, it is poured into the sea; oil has a neuroparalytic effect on marine organisms: fish - 15 milligrams of oil per 1 liter of water, mussels - 40 milligrams.
d) discharge into the sea of untreated Wastewater. We need purification systems, especially for water, for the production of plastics and other synthetic substances.
Material used for this article:
Encyclopedic Dictionary of Brockhaus and Efron: In 86 volumes - St. Petersburg, 1890-1907.
Agbunov M.V. Antique pilotage of the Black Sea. Academy of Sciences of the USSR. Science, Moscow, 1987.
Kuzminskaya G. Black Sea. Krasnodar 1977.
Beasts of the Black Sea. Simferopol: Tavria, 1996.
Wikipedia
In the Black Sea there is Main Black Sea Current(Rim Current) - it is directed counterclockwise along the entire perimeter of the sea, forming two noticeable rings (“Knipovich glasses”, named after one of the hydrologists who described these currents). The basis of this movement of water and its direction is the acceleration imparted to water by the rotation of the Earth - the Coriolis force. True, in such a relatively small water area as the Black Sea, the direction and strength of the wind are no less important. Therefore, the Rim Current is very variable, sometimes it becomes poorly distinguishable against the background of smaller-scale currents, and sometimes its jet speed reaches 100 cm/s.
In the coastal waters of the Black Sea, eddies of opposite direction to the Rim Current are formed - anticyclonic gyres, they are especially pronounced along the Caucasian and Anatolian coasts.
Local coastal currents in the surface layer of water are usually determined by the wind; their direction can change even during the day.
A special type of local coastal current - draft- forms on flat sandy shores during strong sea waves: the water flowing onto the shore does not retreat evenly, but along channels formed in the sandy bottom. Getting caught in such a current is dangerous - despite the efforts of the swimmer, he can be carried away from the shore; to get out, you need to swim not straight to the shore, but diagonally.
Vertical currents: rise of water from depth - upwelling, most often occurs when driven away coastal surface waters from the shore strong wind from the shore; at the same time, water from the depths rises to replace the surface water driven into the sea. Since the water of the depths is colder than the surface waters heated by the sun, as a result of the surge, the water near the shore becomes colder. The surge of water off the Caucasian coast of the Black Sea, caused by a strong northeast wind (this wind is called bora here), can be so powerful that the sea level near the coast can drop by forty centimeters per day.
In the oceans, upwellings arise from the action of the Coriolis force (created by the movement of the Earth around its axis) on masses of water carried by currents in the meridional direction (from the poles to the equator) along the coasts of the continents: the Peruvian current and the Peruvian upwelling (the most powerful in the world) off the Pacific coast South America, Benguela Current and Benguela Upwelling off the east coast of South Africa .
Upwellings lift into the surface, illuminated layer of the ocean (or sea) water enriched with biogenic minerals (salt ions containing nitrogen, phosphorus, silicon), necessary for the growth and reproduction of phytoplankton microalgae - the basis of life in the sea. Therefore, upwelling areas are the most productive water areas - there is more plankton, fish, and everything that lives in the ocean.
