What is the Baltic Sea. water temperature and salinity. Sea bays and straits

Salinity of waters oceans, is the main feature that distinguishes them from the waters of the land.

In oceanology, deer sea water defined as the total amount of solids in grams (all substances dissolved in water, not just salts) dissolved in 1 kg of sea water, provided that all halogens are replaced by an equivalent amount of chlorine, all carbonates are converted to oxides, organic matter is burned. Salinity measured in "‰" ("ppm").

The average salinity of the world's oceans is 35 ‰. , that is, in 1 kg of sea water, an average of 35 grams of various substances are dissolved. A water sample taken in the Bay of Biscay, with a salinity close to 35 ‰, is taken as a standard. It is used to calibrate instruments.

The salinity of sea waters is of ancient origin; salts entered the ocean water simultaneously with the emergence of the oceans themselves. During the formation of the earth's crust, which occurred at high temperatures, various substances were released from the earth into the atmosphere in the form of gases. The subsequent cooling of the earth's crust caused heavy rains. They took those substances with them and filled huge pits on the surface of the earth.

The salinity of the ocean waters is not the same everywhere. Salinity is influenced by the following processes:

1.Evaporation of water.

2. Formation of ice.

3. Precipitation.

4. Stock river waters.

5. Melting ice.

At the same time, evaporation and ice formation contribute to an increase in salinity, while precipitation, river water runoff, and melting ice lower it.

The influence of biochemical processes on salinity is negligible.

Water mixing (diffusion) and advection of salts by currents are also involved in the formation of salinity. The salinity of deep and near-bottom waters is determined exclusively by these 2 processes, since there are no internal sources and sinks of salts at depths and at the bottom of the ocean.

The main role in the change in salinity belongs to evaporation and precipitation. Therefore, the salinity of the surface layers, as well as the temperature, depends on climatic conditions associated with the geographical location of the sea.

The Red Sea is the saltiest sea in the world's oceans. Its salinity reaches 42 ‰. This is due to its location in tropical latitudes. There is very little atmospheric precipitation here, the evaporation of water from strong heating by the sun is very large. The water evaporates from the sea, but the salt remains. Not a single river flows into the Red Sea, and the only source of replenishment of the water balance is the flow of water from Gulf of Aden. Approximately 1,000 cubic meters of gas is brought into the sea through the Bab el-Mandeb Strait during the year. km of water is more than is taken out of it. According to calculations, it takes 15 years for the complete exchange of the waters of the Red Sea.

The water in the Red Sea is evenly mixed throughout the year. In winter, surface waters cool down, become denser and sink down, and rise up warm waters from depth. In summer, water evaporates from the surface of the sea, and the rest becomes more salty, heavy and sinks down. Less salty water rises in its place. Therefore, the Red Sea is the same in temperature and salinity throughout its volume.

Hot brine troughs have also been found in the Red Sea. Currently, more than 20 such depressions are known. The depressions are heated from below by the internal heat of the Earth. The brines in the depressions do not merge with the surrounding water, but are clearly distinguished from it and look like muddy ground covered with ripples, or like swirling fog. The content of many metals, including precious ones, in the brines of the Red Sea is hundreds and thousands of times higher than in ordinary sea water.

The absence of river runoff and rain streams, and hence dirt from land, ensures the transparency of the Red Sea water and the constancy of its salinity.

In the Baltic Sea, water forms layers of different salinity. The average salinity of the Baltic Sea is not higher than 1%o, and its surface water-5 - 8 ° / oo. This is due to the fact that this sea is located in climate zone where there is less evaporation but more precipitation. IN coastal areas for salinity big influence renders river runoff, and in the polar regions - the processes of formation and melting of ice. When water freezes and sea ice builds up, part of the salts drain into the water and salinity increases; when melting sea ​​ice and icebergs it decreases Fresh water enters the Baltic Sea from 250 rivers, while salt water enters only from the narrow Danish straits. As a result, salinity is highest in
Southwest of the Baltic, and decreases as you move to the east. However, the overall picture can be disturbed by currents.

Salty waters, falling into the Baltic Sea, sink to the bottom, forming a highly saline layer there. At depths of 70-80 meters, the salt content increases dramatically. This jump is called a halocline. A halocline occurs where the movements of the water mass caused by storms cease to reach.
Dead organic matter constantly sinks to the bottom of the sea. About once every 15 years, such large masses of water enter the Baltic Sea from the North Sea that stagnant water is pushed aside. The stagnant waters pushed into the northern and deepest parts of the Baltic gradually mix with the surrounding water there. At the beginning of the movement of stagnant waters, an increase in the salinity of the waters of the Baltic Sea occurs.

The Baltic Sea (from antiquity until the 18th century in Russia it was known as the "Varangian Sea") is an inland marginal sea, deeply protruding into the mainland. The Baltic Sea is located in northern Europe, belongs to the pool Atlantic Ocean.

extreme north point The Baltic Sea is located near the Arctic Circle, the extreme south - near the city of Wismar (Germany). extreme western point is located near the city of Flensburg (Germany), the extreme eastern one is in the region of St. Petersburg. Due to the large elongation along the meridian and the parallel, certain areas of the Baltic Sea are located in different physical and geographical climatic zones. This, in turn, affects the oceanological processes occurring in the sea and its individual regions.
Sea area: 415 thousand kilometers. Depth: average - 52 meters, maximum - 459 meters.

The Baltic Sea has three large bays: Bothnian, Finnish, Riga. About 250 rivers flow into it, including the Neva, Vistula, Neman, Daugava, Oder.

The connection of the Baltic Sea with the Atlantic Ocean is carried out through the North Sea, the Skagerrak, Kattegat and Danish Straits (Great and Small Belt, Øresund (Sund) and Fehmarn Belt), however, this connection is difficult due to the shallowness of the straits (depth at the thresholds of 7- 18 meters). Therefore, the waters of the Baltic are very slowly renewed due to the cleaner Atlantic waters. The period of complete water renewal in the Baltic Sea is about 30-50 years.

The Baltic Sea has a low salt content. Its waters are a mixture of salt water from the ocean and fresh water from numerous rivers. The degree of salinity of the sea in different places has different indicators from each other, which is due to the weak vertical movement of water layers. If in the southwestern part of the sea it is 8 ppm (i.e., each kilogram of water contains 8 g of salt), in the western part it is 11 ppm, then in the central water area it is 6 ppm, and in the Gulf of Finland, Riga and Bothnia it barely exceeds a mark of 2-3 ppm (the average salinity of the oceans is 35 ppm).

The length of the Baltic coastline is 7 thousand kilometers. The coast is distributed among the countries as follows: Sweden owns 35% of the coast, Finland - 17%, Russia - about 7% (about 500 kilometers). The rest of the coast is divided among themselves by Lithuania, Latvia, Estonia, Poland, Germany, Denmark. The coast of the sea and adjacent land areas are heavily populated and intensively used by humans. On the coast are transport complexes, large industrial enterprises. The Baltic basin accounts for one tenth of the world's maritime traffic.

The Baltic Sea is heavily polluted as a result of the active activities of the people living on its shores. The environmental problems of the Baltic Sea are related to many aspects of society, such as energy production and consumption, industry, forestry, agriculture, fisheries, tourism, transport, wastewater treatment.

Main ecological problems the Baltics

Firstly, the excess supply of nitrogen and phosphorus to the water area as a result of flushing from fertilized fields, municipal wastewater from cities and waste from some enterprises. Since the water exchange of the Baltic is not very active, the concentration of nitrogen, phosphorus and other wastes in the water becomes very strong. Due to nutrients in the sea, organic matter is not completely recycled, and due to a lack of oxygen, they begin to decompose, releasing harmful to marine life hydrogen sulfide. Dead hydrogen sulfide zones already exist at the bottom of the Gotland, Gdansk, and Bornholm depressions.

The second significant problem in the Baltic is water pollution by oil. Thousands of tons of oil annually enter the water area with various effluents. The film of oil that covers the surface of the water mirror does not allow oxygen to pass into the depths. Also, toxic substances harmful to living organisms accumulate on the surface of the water. Oil spills in most cases occur in coastal and shelf zones, the most productive and at the same time vulnerable areas of the sea.

The third problem in the Baltic Sea is the accumulation of heavy metals. Mercury, lead, copper, zinc, cobalt, nickel mainly enter the Baltic waters with atmospheric precipitation, the rest gets through direct discharge into the water area or with river runoff of household and industrial waste. The amount of copper entering the water area is annually about 4 thousand tons, lead - 3 thousand tons, cadmium - about 50 tons, and mercury - 33 tons, per 21 thousand cubic kilometers of the water volume of the water area.

The Baltic Sea, due to its geographical position, has always been at the crossroads historical events. There is more than one ship graveyard at the bottom of the Baltic. Many wrecks carry dangerous goods. The containers in which the goods are located are destroyed over time.

For decades, the Baltic practiced the flooding and disposal of obsolete bombs, shells, chemical munitions. After the end of World War II, by a joint decision of the countries of the anti-Hitler coalition (USSR, Great Britain and the USA) and in accordance with the decision of the Potsdam Conference in 1951, in various parts of the Baltic, as well as in the straits connecting the Baltic Sea with the North Sea, more than 300 thousand tons were flooded German chemical weapons and ammunition.

For more than half a century, ammunition has been lying on the bottom of the Baltic, creating a potential mortal threat. Metal in sea water is corroded by rust, and toxic substances can enter the water at any time.

The material was prepared on the basis of information from open sources

The Baltic Sea washes the shores Russian Federation, Denmark, and the Baltic countries. The Russian Federation owns small water areas in the eastern part of the Baltic Sea - the Kaliningrad Bay and part Curonian Lagoon(territory Kaliningrad region) and the eastern edge of the Gulf of Finland (the territory Leningrad region).

The Baltic Sea is deeply incised into the northwestern part of Eurasia. This is an inland sea, connected to the North Sea of ​​the Atlantic Ocean by the system of the Øresund (Sund), Great Belt, Small Belt straits, known as common name Danish Straits. They pass into the deep and wide straits of the Skagerrak, Kattegat, which already belong to the North Sea, which is directly connected with.

The area of ​​the Baltic Sea is 419 thousand km2, the volume is 21.5 thousand km3, average depth- 51 m, greatest depth- 470 m.

About 250 rivers flow into the Baltic Sea. The largest rivers are Vistula, Oder, Neman, Daugava, Neva. The Neva brings the largest amount of water per year - an average of 83.5 km3.
The Baltic Sea stretched from the southwest to the northeast, and its maximum length is equal to 1360 km. The widest point of the sea is at 60° N. sh., between St. Petersburg and Stockholm, it stretches for almost 650 km.

The bottom relief of the Baltic Sea is uneven. The sea lies entirely within the shelf. The bottom of its basin is indented by underwater depressions, separated by hills and socles of islands.

The Baltic Sea is characterized by a long coastline. It has many bays, bays and a large number of islands. The sea is a collection of individual basins: the zone of the Danish Straits, the open or central part of the sea and three large bays - Bothnian, Finnish and Riga, which account for almost half of the sea.

Numerous islands of the Baltic Sea are located both off the mainland coast and in the open sea; in some parts of the sea the islands are grouped in large archipelagos, in others they stand alone.

The largest of the islands: Danish - Zealand, Fyn, Lolland, Falster, Langeland, Mön, Bornholm; Swedish - Gotland, Eland; German - Rügen and Fehmarn; - Saaremaa and Hiiumaa.

The shores of the northern and southern half seas. The skerry shores of Sweden and Finland are indented with small bays and gulfs, framed by islands composed of crystalline rocks. They for the most part low, sometimes naked, and in some places overgrown coniferous forest. The southern shores are low-lying, consist of sand and have a large number of shoals. In some places, along the coast, chains of sand dunes stretch here, and long spits protrude into the sea, forming large lagoons desalinated by the flow of rivers. The largest of these shallow bays are Curonian and Vistula.

The bottom sediments of the Baltic Sea are represented mainly by silts and sand. The soils of the Baltic Sea are characterized by stones and boulders, often found at the bottom of the sea. Sandy deposits are common in coastal areas. IN Gulf of Finland most of the bottom is covered with sands with separate patches of silt, occupying small depressions and forming a field of sediments of the Neva delta front, somewhat elongated along the strike of the bay. The construction of the dam, which fenced off a significant part of the water area from the open sea, significantly changed the composition and distribution of precipitation that existed in natural conditions.

The climate of the Baltic Sea is of maritime temperate latitudes with features of continentality. The peculiar configuration of the sea and a significant length from north to south and from west to east create differences in climatic conditions in different areas of the sea.

The Icelandic low, as well as the Siberian and Azores anticyclones, most significantly affect the weather. The nature of their interaction determines the seasonal features of the weather. In autumn and especially winter time Icelandic Low and Siberian High interact intensively, which enhances cyclonic activity over the sea. In this regard, in autumn and winter, deep cyclones often pass, which bring with them cloudy weather with strong southwestern and western winds.

In the coldest months - January and February - the average in the central part of the sea is -3°С in the north and -5...-8°С in the east. With rare and short-term intrusions of cold Arctic air associated with the strengthening of the Polar High, the air temperature over the sea drops to –30°С and even to –35°С.

In summer, predominantly western, northwestern weak to moderate winds blow. They are associated with the cool and humid summer weather characteristic of the sea. Average monthly temperature of the warmest month is 14–15°С in the Gulf of Bothnia and 16–18°С in the rest of the sea. Hot weather is rare. It is caused by short-term inflows of warm Mediterranean air.

The temperature conditions of the waters of the Baltic Sea in different parts of it are not the same and depend not only on geographical location places, but also from meteorological and hydrological features area. The highest value for temperature regime The Baltic Sea have surface heating by the rays of the sun, the runoff of river waters and the inflow of deep oceanic waters. This determines the general picture of the temperature conditions of the sea. In the surface layers, the water temperature varies widely. At depths exceeding 50 meters, the water temperature is kept within 3–4 ° C all year round in the southern part of the sea and near zero in the northern Bothnian region.

During the summer months, surface water temperatures are generally close to air temperatures. Near the eastern shores, the water temperature is higher due to the influence of warm, southward land masses, and along the western, Swedish, shores, it is lower due to the flow of cold waters from the north, from the Gulf of Bothnia. In winter, on the contrary, the eastern parts of the sea are colder than the western ones; they are subject to the influence of the chilled land masses of the mainland, and the western parts of the sea during this period experience a regular influx of warm air masses from the Atlantic.

Limited water exchange with the North Sea and significant river runoff result in low salinity. On the sea surface, it decreases from west to east, which is associated with the predominant inflow of river waters from the eastern Baltic. In the northern and central regions of the basin, salinity decreases somewhat from east to west, since in cyclonic circulation, saline waters are transported from south to northeast along east coast sea ​​further than along the western. A decrease in surface salinity is also traced from south to north in the bays.

Almost throughout the sea, a significant increase in salinity from the surface to the bottom is noticeable. The change in salinity with depth is basically the same throughout the sea, with the exception of the Gulf of Bothnia. In the southwestern and partly central regions of the sea, it gradually and slightly increases from the surface to horizons of 30–50 m; below, between 60–80 m, there is a sharp shock layer (halocline), deeper than which the salinity again slightly increases towards the bottom. In the central and northeastern parts, salinity increases very slowly from the surface to horizons of 70–80 m; deeper, at 80–100 m, there is a halocline, and then salinity slightly increases to the bottom. In the Gulf of Bothnia, salinity increases from the surface to the bottom only by 1–2‰.

In autumn-winter time, the flow of North Sea waters into the Baltic Sea increases, and in summer-autumn it somewhat decreases, which leads to an increase or decrease in the salinity of deep waters, respectively. In the autumn-winter season, the salinity of the upper layers slightly increases due to reduction and deviation during ice formation. In spring and summer, salinity on the surface decreases by 0.2–0.5‰ compared to the cold half of the year. This is explained by the desalination effect of continental runoff and the spring melting of ice. In addition to seasonal fluctuations in salinity, the Baltic Sea, unlike many seas of the World Ocean, is characterized by its significant interannual changes. Salinity variability in the Baltic Sea is one of the most important factors regulating many physical, chemical and biological processes. Due to the low salinity of the surface waters of the sea, their density is also low and decreases from south to north, varying slightly from season to season. Density increases with depth.

The strongest wind waves are observed in autumn and winter in open, deep areas of the sea with prolonged and strong southwestern winds. Stormy 7–8-point winds develop waves up to 5–6 m high and 3–4 m long. The largest waves occur in November. In winter, with more strong winds the formation of high and long waves is prevented by ice. As in other seas of the northern hemisphere, the surface circulation of the Baltic Sea has a general cyclonic character.

Surface currents are formed in the northern part of the sea as a result of the confluence of waters emerging from the Gulf of Bothnia and the Gulf of Finland. The speed of the permanent currents of the Baltic Sea is very low and is approximately 3–4 cm/s. Sometimes it increases to 10–15 cm/s. The current pattern is very unstable and is often disturbed by the wind. The wind currents prevailing in the sea are especially intense in autumn and winter, and during strong storms their speed can reach 100–150 cm/s.

Deep circulation in the Baltic Sea is determined by the flow of water through the Danish straits. The inlet current in them usually passes to a horizon of 10–15 m. Then this water, being denser, descends into the underlying layers and is slowly transported by the deep current, first to the east and then to the north.

Due to the high degree of isolation from the World Ocean, the tides in the Baltic Sea are almost invisible. Fluctuations in the tidal level at individual points do not exceed 10–20 cm. Two minimums and two maxima are clearly expressed in the seasonal course of the Baltic Sea level. The lowest level is observed in spring. With the arrival of spring flood waters, it gradually rises, reaching a maximum in August or September. After that, the level goes down. The secondary autumn low is coming. With the development of intense cyclonic activity, westerly winds drive water through the straits into the sea, the level rises again and reaches a secondary, but less pronounced maximum in winter. The difference in level heights between the summer maximum and the spring minimum is 22–28 cm. It is larger in bays and smaller in the open sea.

Surge fluctuations in sea level occur quite quickly and reach significant values. In the open areas of the sea, they are approximately 0.5 m, and at the tops of bays and bays they are 1–1.5 and even 2 m. h. Level changes associated with seiches do not exceed 20–30 cm in the open part of the sea and reach 1.5 m in the Neva Bay. Complex seiche level fluctuations are one of the characteristic features of the Baltic Sea regime.

Catastrophic floods are associated with fluctuations in sea level.

The Baltic Sea is covered with ice in some areas. The earliest (around the beginning of November) ice forms in the northeastern part of the Gulf of Bothnia, in small bays and off the coast. Then the shallow areas of the Gulf of Finland begin to freeze. The maximum development of the ice cover reaches in early March. By this time, the still ice occupies northern part Gulf of Bothnia, the region of the Aland skerries and the eastern part of the Gulf of Finland. Floating ice occurs in the open areas of the northeastern part of the sea.

The main problems of the Baltic Sea are related to the gradual deterioration of oxygen conditions in the deep layers of the sea, which has been observed in recent decades. In some years, oxygen disappears completely already at a depth of 150 m, where it forms hydrogen sulfide. These changes are the result of both natural changes in the environment, mainly temperature, water salinity and water exchange, and anthropogenic impact, which is expressed mainly in an increase in the supply of nutrient salts in the form of various forms of nitrogen and phosphorus.

The significance of the Baltic Sea in the national economy of the countries of the region and the ever-increasing negative impact of anthropogenic factors on the quality of the marine environment require urgent measures to be taken to guarantee the cleanliness of the sea.

Pollution enters the sea directly with sewage or from ships, diffusely through rivers or. The main mass of pollutants is brought into the sea with the flow of rivers (Neva, Vistula) both in a dissolved state and adsorbed on suspension. In addition, sources of pollution of the marine environment with oil products are seaside towns, St. Petersburg, Kronstadt, Vyborg and, to the greatest extent, the merchant and military fleets.

The greatest harm to the marine environment is caused by toxic substances (salts of heavy metals, DDT, phenols, etc.), oil products, organic and biogenic substances. Every year, about 300 tons of oil products enter the Gulf of Finland from various sources. The main mass of nitrogenous compounds enters the sea diffusely, as well as sulfur compounds, which enter the marine environment mainly through the atmosphere. Toxic substances are discharged mainly by industry. The different nature of pollution complicates the struggle for the purity of the marine environment and requires the implementation of a complex set of water protection measures.

Monitoring of the marine environment is, first of all, the organization of systematic observations of the physicochemical and biological indicators of the marine environment at constant representative points of the reservoir.

The quality of the marine environment of the Baltic Sea generally meets the requirements of water users, but about many major cities and areas of contamination. It is alarming that over the past decades the content of toxic substances in marine living organisms has increased to two orders of magnitude, which once again indicates the need for urgent water protection measures. Great harm is caused by accidental spills of oil products from tankers. The monitoring results will make it possible to periodically check the state of the marine environment, i.e., to identify the dynamics of marine pollution.

Two small sections of the bottom of the coastal part of the Baltic Sea belonging to Russia are sharply different in terms of geoecological conditions. The most anthropogenic pressure is experienced by internal, East End Gulf of Finland within the Leningrad region. The main area of ​​pollution was that part of the bay, which is located east of the island Kotlin, between it and the Neva delta. This happened several years ago after the construction of a dam running from Kotlin Island to the northern and southern mainland shores. An important element of the geoecological situation in the eastern part of the Gulf of Finland are numerous underwater quarries for the extraction of construction raw materials, mainly sand, which in the future may pose a threat to the stability of the coastal part of the bottom and coasts.

The Baltic Sea washes nine countries: Latvia, Lithuania, Estonia, Russia, Poland, Germany, Finland, Sweden and Denmark.

The coastline of the sea is 8.000 km. , and the area of ​​the sea is 415.000 sq. km.

It is believed that the sea was formed 14,000 years ago, but in the modern outline of the boundaries there are 4,000 years.

The sea has four bays, the largest Bothnian(washes Sweden and Finland), Finnish(washes Finland, Russia and Estonia), Riga(washes Estonia and Latvia) and freshwater Curonian(washes Russia and Lithuania).

Window to Europe

The Baltic Sea is inland sea basin of the Atlantic Ocean and is located in a shallow depression between the Scandinavian Peninsula and European continent. Through the system of the Danish Straits, through the North Sea, the Baltic Sea is connected to the ocean.

The surface area is 386 thousand sq. km, the average depth is 71 m, the maximum depth is 459 m (Landsortsupet basin south of Stockholm).

The ancient Slavs called this sea the Varangian.

As a result of studying the bottom topography and the nature of the soils, scientists came to the conclusion that in the preglacial period, there was land on the site of the Baltic Sea. Then, during the ice age, the depression in which the sea is now located was filled with ice, the process of melting of which led to the formation of a lake with fresh water.

About 14 thousand years ago, this lake joined the ocean as a result of the sinking of land areas - the lake turned into a sea. Then, after the next rise of land in the area Central Sweden the connection of the sea with the ocean was broken, and it again turned into a closed lake-type reservoir.

Approximately 7 thousand years ago, another land subsidence occurred in the area of ​​​​the modern Danish Straits and the connection of the lake with the Atlantic resumed.

Subsequent fluctuations in land level led to the formation of the modern Baltic Sea.

The rise of land in the area continues at the present time. Thus, in the area of ​​the Gulf of Bothnia, the bottom rise is approximately 1 m per 100 years.

Climate in the area of ​​​​marine temperate, characterized by small seasonal temperature fluctuations, frequent precipitation in the form of rain, fog and snow.

Temperature surface water reaches +20 degrees C in summer. As you move north, the water is cooler and in the Gulf of Bothnia does not warm up above +9 - +10 degrees C. In winter, the water cools down to freezing temperature and the northern bays of the sea are covered with ice. Central and southern regions usually remain ice-free, but in exceptionally cold winters the sea can become completely ice-covered.

Water in the sea it is highly desalinated, especially in areas remote from the Danish Straits. Reason - numerous rivers and rivulets (almost 250) flowing into the sea.

Among the major rivers Neva, Narva, Vistula, Kemijoki, Zapadnaya Dvina, Neman, Odra can be noted.

currents in the sea they form a cyclonic circulation, often their direction and speed are corrected by the winds.

tides in the sea are very low - 5-10 cm, however, wind surges of water, especially in narrow bays, can exceed 3-4 meters.

Coastline The Baltic Sea is heavily indented. There are many large and small bays, bays, capes, spits. northern shores rocky, as you move south, rocks and stones are replaced by sand-pebble mixtures and sand. Here the shores are low and flat.

Islands mainland origin, especially many small rocky islets in the northern part of the sea. Large islands: Gotland, Bornholm, Sarema.

Bottom relief the sea is complex. There are many ups and downs here, which appeared as a result of the activity of glaciers, river beds, land fluctuations. However, the elevation changes are small - the sea is shallow.

Animal world The Baltic Sea is relatively poor in represented species. A feature of the sea fauna is the distribution of freshwater and marine species animals in different areas. In the northern, fresher regions, especially near the mouths of the rivers, live mainly freshwater animals and species that easily tolerate desalination. Closer to the Danish Straits, the waters of the sea are much saltier, so you can meet many typical marine life here. The general species composition of the sea is scarce, but rather rich in quantitative terms.

The poverty of the fauna of the sea is also explained by its youth, because in the form that it has now, its age is estimated at only five millennia. According to scientists, another 5,000 years will pass, and the Baltic Sea will again lose contact with the ocean and turn into a large fresh lake. many forms marine life in such a short time they simply did not have time to adapt to the local conditions of existence.

Nevertheless, the quantitative composition of animals living in the Baltic Sea is quite large.

Bottom animal species are represented mainly by worms, gastropods and bivalve mollusks, small crustaceans and bottom fish - flounder, gobies. In some places you can meet the mitten crab - an alien from the North Sea and accustomed here. Near the Danish Straits, there is even a giant among jellyfish - cyanide. And another type of jellyfish - eared aurelia in the Baltic Sea is found almost everywhere. Small schooling fish - three-spined stickleback, Baltic sprat.

In the desalinated areas of the sea, there are many river fish: roach, perch, pike, bream, ide, pike perch, migratory whitefish, burbot, etc.

In the Baltic Sea hunt such valuable fish as herring (about half of the total fish catch), sprat (sprat), salmon, eel, cod, flounder.

Marine mammals only three species of seals are represented in the Baltic Sea: the gray seal (tuvyak), the common seal (seal), and the harbor porpoise, which belongs to toothed cetaceans.

sharks in the Baltic Sea are represented only by the ubiquitous katrans - a small spiny shark, which is dangerous to humans only for its spines on the dorsal fins. But these fish are not settled in all areas of the sea - too desalinated and shallow areas are not suitable for them to live.

However, in the area of ​​​​the Danish Straits, connecting the Baltic with the North Sea, other predators are sometimes found - herring sharks. No such guests have been registered off the Russian shores of the Baltic Sea.

In conclusion, I would like to note that at present the Baltic Sea is intensively polluted by various chemical and biochemical effluents, as well as by trace elements contained in precipitation. This leads to the mass death of microflora and microfauna, in in large numbers settling to the bottom and processed by bacteria into hydrogen sulfide. And hydrogen sulfide has a detrimental effect on all living organisms in the bottom layer of water. If urgent measures are not taken, the number of aquatic animals in the sea will decrease significantly.