Seas washing the territory of Russia
Russia is a great maritime power. Its territory is washed by the waters of three oceans:
- the Arctic;
- Atlantic;
- Quiet.
And almost in the center of the mainland is the largest sea-lake in the world - the Caspian Sea. It belongs to the inland flow basin of Eurasia. The seas washing the territory of the country are located within four lithospheric plates:
- Eurasian (Eurasian);
- North American;
- Sea of Okhotsk;
- Amur.
Due to the vast area of Russia, these seas are located at different latitudes, respectively, in different climatic conditions. They have a different origin and structure of the bottom. The temperature and salinity of the waters, the climate determined the originality organic world seas.
Typology of the seas
In physical geography, all the seas of the World Ocean are conditionally divided into two groups: marginal and inland.
Definition 1
Marginal seas are called parts of the World Ocean adjacent to the mainland and only slightly separated by land.
Their nature (bottom structure, water temperature and salinity, composition and abundance of the organic world) is largely determined by the nature of the ocean of which they are a part. Marginal seas, for example, include:
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- Barents Sea;
- Kara Sea;
- Japanese Sea.
Definition 2
Inland seas are seas that are largely separated by land from the oceans.
The nature of the inland seas depends on the nature of the land surrounding them and the rivers flowing into them. The inland seas are:
- White Sea;
- Baltic Sea;
- Black Sea;
- Sea of Azov.
White Sea
Of all the seas of the Arctic Ocean, only the White Sea can be called inland, since it goes deep into the land. The basin of this sea is a flooded piece of land. Its connection with the Barents Sea is rather limited. Because of this, warm Atlantic waters do not penetrate into it. Therefore, despite the more southerly position compared to the Barents Sea, the White Sea is much colder and freezes completely in winter (another reason is its relatively shallow depth).
Such large rivers as the Northern Dvina, Onega, Mezen flow into the White Sea. The salinity of the water does not exceed $26$ ‰. The weather is characterized by frequent storms. Reduced salinity and the richness of water with oxygen determined the originality and richness of the organic world of the White Sea. Until recently, a unique craft of soft pearls was widespread here. But with the deterioration of the ecological situation, soft pearls ceased to form.
Inland seas of the Atlantic Ocean
The territory of Russia is washed by three seas belonging to the Atlantic Ocean basin:
- Baltic;
- Black;
- Azov.
All of them belong to the inland seas because they go deep into the mainland. In this regard, they have a rather peculiar hydrological regime. Communication with the World Ocean is mediated by a number of straits and other seas. The climate of the seas is largely determined by the western transfer of air masses and the influence of adjacent land areas.
The westernmost sea of Russia is the Baltic Sea. It arose in the Quaternary in a tectonic trough at the junction of the East European lithospheric plate and the Baltic Shield. The maximum depth of the sea is $470$ m (near Stockholm). Off the coast of Russia, the depths are about $50$ m.
The climate is formed under the influence of Atlantic air masses. Weather conditions are characterized by frequent cyclones and heavy rainfall. The Gulf of Finland can freeze completely in winter.
More than $250$ of rivers flow into the Baltic. This determines the low salinity of the water (about $7-8$ ‰). The desalinization of the waters led to the poverty of plankton. The main fish resources are herring, Baltic sprat, cod, whitefish, chime, lamprey, smelt, salmon.
The Black Sea is almost equal in area to the Baltic Sea. It is connected to the Atlantic through a system of inland seas and straits. It is located in a tectonic basin of the oceanic type (the bottom has an oceanic type of the earth's crust). The maximum depth of the sea is $2210 m. The shelf zone is most developed off the coast of Ukraine.
The climate over the Black Sea is close to Mediterranean. But in winter, the influence of eastern continental air masses affects. It flows into the Black Sea a large number of rec. The largest are the Danube and the Dnieper. The average water salinity is $17-18$ ‰. The waters are rich in fish resources (beluga, stellate sturgeon, sturgeon, herring, mullet, mackerel, horse mackerel, red mullet, sprat, anchovy, tuna, stingray, ram, pike perch, bream).
The unique nature of the Black Sea lies in the fact that water masses deeper than $200$ m are saturated with hydrogen sulfide and poor in oxygen. This is an almost lifeless layer.
Remark 1
The smallest sea on our planet is the Sea of Azov. The ancient Greeks considered it a lake. Its maximum depth is about $13$ m. It is connected to the Black Sea by the narrow Kerch Strait. Due to its small size and shallow depths, the Sea of Azov practically does not affect the formation of the coastal climate. On the contrary, it is influenced by the climatic conditions of the land.
Two large rivers, the Don and the Kuban, flow into the Sea of Azov. The salinity of the water is approximately $11$ ‰. But recently the salinity of the water has been rising. Due to the shallow depths, the water warms up well. Therefore, the Sea of Azov was distinguished by high bioproductivity. The most important fish species are kilka, pike-perch, anchovy, bream, and sturgeon.
Kaliningraders are lucky to live near Baltic Sea . After all, your own sea is very cool! Especially when it is so interesting and always different: harsh and merciless in the season of storms, quiet and friendly on hot summer days. Also, depending on the weather, the waters of the Baltic often change their color. Sometimes it is of warm blue hues, then it suddenly turns into greenish-gray colors, and in stormy weather the sea is completely blue-black. For many of us, the outline of the Baltic Sea is quite familiar from maps, but few people think about how the Baltic Sea works under the surface of the water, what kind of bottom topography does it have? The answer to this question can be found on the third floor Sea Aquarium Gdynia (Polish) Aquarium Gdynskie), where the unique layout of the Baltic Sea and the coast is located.
Located at the end of the South Pier of Gdynia, Seawater aquarium, opened in 1971, is one of the most significant sights of the city. In addition to a three-dimensional map of the Baltic Sea and all kinds of marine exhibits, here you can observe the life of more than 1600 aquatic inhabitants from different parts of the globe. They will be the subject of a separate report.
In the meantime, let's look at the model of the relief of the bottom of the Baltic Sea, on which all significant depths (troughs) are indicated, the largest (459 m) of which is called - Landsort(Polish Głębię Landsort). The average depth of the sea is 52.3 m.
The Baltic Sea, sometimes called the Mediterranean Sea of the North, due to its location in the middle of the land, covers a surface of 415 thousand square meters. km. Geographically, it is part of the Atlantic Ocean and is connected to the North Sea by the Danish Straits.
03. Bothnian and Finnish Gulfs.
04. St. Petersburg.
Along the northern coast of the Baltic Sea, in the Gulf of Finland and the Gulf of Bothnia, there are many thousands of islands and rocks. This is the famous area of skerries, unparalleled in its length and originality in any other part of the oceans.
06. Aland Islands.
07. The capital of Norway is Oslo.
Despite the fact that the Baltic Sea lies in the middle of the land, the ocean noticeably influences it. The coastal inhabitants of the Baltic feel the influence of the ocean every day. Deep cyclones coming from the Atlantic Ocean often visit the Baltic. During their passage, strong southwestern winds blow, often turning into storms. The maximum summer temperature of the Baltic is only +18 +20 degrees, which makes it not the most popular sea for a beach holiday.
08. Closest to the Kaliningrad region, a large depression is located in the area of Polish Gdansk - Głębię Gdanską(118 m). Three spits are also visible: Curonian, Vistula and Hel.
09. Gdynia.
10. Kaliningrad and the Curonian Spit.
11. The northern and eastern parts of the sea are "adorned" with powerful bays - Bothnian, Finnish and Riga.
12. The Gulf of Finland and the capitals of Estonia and Finland.
13. The Baltic Sea is rich in amber. The world's largest amber deposit is located in our Kaliningrad region, near the village. Amber.
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The Baltic Sea is the northern marginal body of water in Eurasia. It cuts deep into the land, and due to this it belongs to the water flows of the internal type. The sea fills the waters of the Atlantic. It is located in Northern Europe. The Baltic countries have access to the Baltic Sea. And also such states as: Denmark, Sweden, Finland, Germany, Russia and Poland. The stream connects with the ocean through the system and the North Sea.
The area of the reservoir is about 415 thousand square km. The volume of the water mirror is more than 20 thousand cubic meters. km. The deepest gutter is 470 meters.
Hydrology
The Baltic Sea, whose salinity greatly affects the flora and fauna, is filled with huge amount fresh water. Precipitation is their constant source. Salt streams penetrate into the reservoir due to bays and tributaries. The tides have insignificant levels and, as a rule, their magnitude is not more than 20 cm.
Constantly located within a radius of one mark. Air masses can exert a strong influence on it. Near the coast, the water level can rise up to 50 cm, in narrower places - up to 2 meters.
There are practically no storms on the water stream. Like other seas washing Russia, the Baltic reservoir is calm, and rarely when its waves are able to reach a height of 4 meters. Most of all it storms in autumn, in November. Maximum fluctuations - 7-8 points. In winter, they practically stop, this is facilitated by ice.
The constant flow of the Baltic Sea is small. Within 10-15 cm/s. The maximum current increases during storms up to 100-150 cm/s.
The tides of the Baltic Sea are almost imperceptible. This is facilitated by the isolation of the water flow to a greater extent. Their level varies within 20 meters. The maximum increase in water level is in August and September.
A significant part of the coast is covered with ice from October to April. The southern part and the center of the sea, but glaciers can drift along them during the thawing period (June-August).
The Baltic Sea is rich in natural resources. Oil reserves are hidden here, new deposits are being developed. Large deposits of amber have also recently been found. The Nord Stream gas route runs along the bottom of the sea.
And the Baltic Sea is rich in fish and seafood. AT last years the ecology of the stream has deteriorated significantly. The waters are clogged with toxins coming from large rivers. The presence of dumps of chemical weapons is also recorded.
Due to the shallow depth of the sea, shipping is not very developed here. Only light craft are able to cross the watercourse without problems. The largest ports of the Baltic Sea: Vyborg, Kaliningrad, Gdansk, Copenhagen, Tallinn, St. Petersburg, Stockholm.
The waters of this reservoir are unsuitable for the development of resort tourism, but nevertheless there are sanatoriums and clinics on the coastal part. These are the Russian resort cities of Svetlogorsk, Zelenogorsk, Sestroretsk, the Latvian Jurmala, the Lithuanian Neringa, the Polish Koszalin and Sopot, the German Albek and Binz.
Brief description of water temperature and sea salinity
In the central part of the Baltic Sea, as a rule, the temperature rarely exceeds 15-18 ° C. At the bottom, it is about 4 degrees. The bay often has calm weather and +9..+12 o C.
The Baltic Sea, whose salinity decreases in the direction from west to east, at the beginning of the current has an official indicator of 20 ppm. At depth, this figure increases by 1.5 times.
Name
For the first time, the etymological name "Baltic" is found in a historical treatise of the 11th century. The earlier name of the sea is Varangian. It is it that is mentioned in the famous Tale of Bygone Years.
extreme points
Extreme points of the Baltic Sea:
- southern - Wismar (Germany), coordinates - 53° 45` N. sh.;
- north - Arctic Circle coordinates - 65° 40` s. sh.;
- eastern - St. Petersburg (Russia), coordinates - 30 ° 15` in. d.;
- western - Flensburg (Germany), coordinates - 9 ° 10` in. d.
Geographical characteristics: territory, tributaries and bays
The Baltic Sea (salinity and its characteristics are described below) is extended from the southwest to the northeast for 1360 km. The greatest width is located between the cities of Stockholm and St. Petersburg. It is 650 kilometers.
According to historical data, the Baltic Sea has existed for about 4 thousand years. In the same period of time, the Neva (74 km) begins its existence, which flows into this reservoir. In addition to it, more than 250 rivers merge with the stream. The largest of them are Vistula, Oder, Narva, Neman, Zapadnaya Dvina.
Some ports of the Baltic Sea lie on its large bays. In the north is the Gulf of Bothnia, the largest and deepest. In the east - Riga, located between Estonia and Latvia, Finnish, washing the shores of Finland, Estonia, Russia, and Due to the fact that the latter is separated from the sea by a sandy spit, the water in the stream is almost fresh. This is a unique feature.
The average depth of the Baltic Sea is 50 meters, the bottom is completely within the mainland. This nuance makes it possible to attribute it to inland continental water bodies.
Islands
More than 200 islands of different sizes are located in the sea. They are located unevenly both near the coast and far from them. The largest islands in the Baltic are Zealand, Falster, Mön, Langeland, Lolland, Bornholm, Funen (belong to Denmark); Öland and Gotland (Swedish islands); Fehmarn and Rügen (refers to Germany); Hiiumaa, Saaremaa (Estonia).
Coastline
The Baltic Sea (the ocean strongly affects it with its waters) has a different coastline along the entire perimeter of the waters. In the northern part, the bottom is uneven, rocky, and the coast is indented with small bays, ledges and small islands. The southern part, on the contrary, has a flat bottom, and a low-lying coast, with a sandy beach, which in some areas is represented by small dunes. A frequent occurrence on the young coast is sandy spits, deeply cutting into the sea.
The sedimentary bottom is represented by green, black silt (of glacial origin) and sand, and the soil consists of stones and boulders.
Salinity and its regular changes
Due to the large amount of precipitation and powerful water runoff from the rivers, the Baltic Sea (the salinity of the reservoir is relatively low) is filled with excess fresh water. It is distributed unevenly. Where the Baltic reservoir enters deep into the shore, the water is practically fresh, and the North Sea influences its salinity. This position is not permanent. Storm winds contribute to the mixing of water.
Based on this, the salinity of the Baltic Sea is low. A decrease in its level is typical for the coastline, the largest number of ppm is at the bottom.
In the territory where the watercourse meets the straits in the west, the salinity of the waters is up to 20 ‰ on the sea surface, at the bottom - 30 ‰. Off the coast of the Gulf of Bothnia and the Gulf of Finland, the lowest indicator. It does not exceed 3‰. The level from 6 to 8‰ is characteristic of the waters of the central part.
Seasonality also affects the distribution of salinity in the Baltic Sea. So, in the spring-summer season, it decreases by 0.5-0.2 ppm. This is due to the fact that melted rivers carry fresh water to the sea. And in autumn and winter, on the contrary, it increases due to the influx of cold northern masses.
Salinity change in the sea is one of important reasons, which regulate biological, physical and chemical processes on the coast. Partly due to the freshness of the water, the coast has a loose structure.
Deeply cut into the land, the Baltic Sea has a very complex outline of the coast and forms large bays: Bothnian, Finnish and Riga. This sea has land borders almost everywhere, and only from the Danish Straits (Great and Small Belt, Sound, Farman Belt) it is separated by conditional lines passing between certain points on their coasts. Due to the peculiar regime, the Danish Straits do not belong to the Baltic Sea. They link it to the North Sea and through it to the Atlantic Ocean. Depths above the thresholds separating the Baltic Sea from the straits are small: above the Darser threshold - 18 m, above the Drogden threshold - 7 m. The cross-sectional area in these places is 0.225 and 0.08 km 2, respectively. The Baltic Sea is weakly connected with the North Sea and has limited water exchange with it, and even more so with the Atlantic Ocean.
It belongs to the type of inland seas. Its area is 419 thousand km 2, volume - 21.5 thousand km 3, average depth - 51 m, maximum depth - 470 m.
Bottom relief
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. In the western part of the sea there are shallow Arkon (53 m) and Bornholm (105 m) depressions, separated by about. Bornholm. In the central regions of the sea, rather vast areas are occupied by the Gotland (up to 250 m) and Gdansk (up to 116 m) basins. North of about. Gotland lies the Landsort Depression, where the greatest depth of the Baltic Sea is recorded. This depression forms a narrow trench with depths of more than 400 m, which stretches from the northeast to the southwest, and then to the south. Between this trough and the Norrköping depression located to the south, an underwater hill stretches with depths of about 112 m. Further south, the depths again increase slightly. On the border of the central regions with the Gulf of Finland, the depth is about 100 m, with the Bothnian - about 50 m, and with the Riga - 25-30 m. The bottom relief of these bays is very complex.
Bottom relief and currents of the Baltic Sea
Climate
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 air temperature in the central part of the sea is -3° in the north and -5-8° 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° and even to -35°.
In the spring-summer season, the Siberian High collapses, and the Baltic Sea is affected by the Icelandic Low, the Azores and, to some extent, the Polar High. The sea itself is located in a zone of low pressure, along which cyclones from the Atlantic Ocean are less deep than in winter. In this regard, in spring the winds are very unstable in direction and low in speed. Northerly winds are responsible for the usually cold spring in the Baltic Sea.
In summer, predominantly western, northwestern and southwestern weak to moderate winds blow. They are associated with the cool and humid summer weather characteristic of the sea. The average monthly temperature of the warmest month - July - is 14-15° in the Gulf of Bothnia and 16-18° in other areas of the sea. Hot weather is rare. It is caused by short-term inflows of warm Mediterranean air.
Hydrology
About 250 rivers flow into the Baltic Sea. The largest amount of water is brought per year by the Neva - an average of 83.5 km 3, the Vistula - 30 km 3, the Neman - 21 km 3, the Daugava - about 20 km 3. The runoff is unevenly distributed across the regions. So, in the Gulf of Bothnia it is 181 km 3 /year, in Finland - 110, in Riga - 37, in the central part of the Baltic - 112 km 3 /year.
Geographical position, shallow water, complex bottom topography, limited water exchange with the North Sea, significant river runoff, and climate features have a decisive influence on hydrological conditions.
The Baltic Sea is characterized by some features of the eastern subtype of the subarctic structure. However, in the shallow Baltic Sea, it is represented mainly by surface and partially intermediate waters, significantly transformed under the influence of local conditions (limited water exchange, river runoff, etc.). The water masses that make up the structure of the waters of the Baltic Sea are not identical in their characteristics in different areas and change with the seasons. This is one of the distinguishing features of the Baltic Sea.
Water temperature and salinity
In most areas of the Baltic Sea, surface and deep water masses are distinguished, between which lies a transitional layer.
Surface water (0-20 m, in some places 0-90 m) with a temperature of 0 to 20 °, salinity of about 7-8‰ is formed in the sea itself as a result of its interaction with the atmosphere (precipitation, evaporation) and with the waters of the continental runoff. This water has winter and summer modifications. In the warm season, a cold intermediate layer is developed in it, the formation of which is associated with a significant summer heating of the sea surface.
The temperature of deep water (50-60 m - bottom, 100 m - bottom) - from 1 to 15 °, salinity - 10-18.5‰. Its formation is associated with the entry of deep waters into the sea through the Danish straits and with mixing processes.
The transitional layer (20-60 m, 90-100 m) has a temperature of 2-6°C, salinity of 8-10‰, and is formed mainly by mixing surface and deep waters.
In some areas of the sea, the structure of the waters has its own characteristics. For example, in the Arkon region, there is no cold intermediate layer in summer, which is explained by the relatively shallow depth of this part of the sea and the influence of horizontal advection. The Bornholm region is characterized by a warm layer (7-11°) observed in winter and summer. It is formed by warm waters coming here from the slightly warmer Arkona basin.
In winter, the water temperature is somewhat lower near the coast than in the open parts of the sea, while it is slightly higher near the western coast than near the eastern one. Thus, the average monthly water temperature in February near Ventspils is 0.7°, at the same latitude in the open sea - about 2°, and near the western coast - 1°.
Water temperature and salinity at the surface of the Baltic Sea in summer
In summer, the temperature of surface waters is not the same in different parts of the sea.
The decrease in temperature near the western shores, in the central and southern regions is explained by the predominance of westerly winds, which drive the surface layers of water away from the western shores. Colder underlying waters rise to the surface. In addition, a cold current from the Gulf of Bothnia passes along the Swedish coast to the south.
Clearly pronounced seasonal changes in water temperature cover only the upper 50-60 m; deeper, the temperature changes very little. In the cold season, it remains approximately the same from the surface to the horizons of 50-60 m, and deeper it drops somewhat to the bottom.
Water temperature (°С) on a longitudinal section in the Baltic Sea
In the warm season, the increase in water temperature as a result of mixing extends to horizons of 20-30 m. From here it abruptly decreases to horizons of 50-60 m and then again rises somewhat towards the bottom. The cold intermediate layer persists in summer, when the surface layer warms up and the thermocline is more pronounced than in spring.
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 flow of river waters into the eastern part of the Baltic. In the northern and central regions of the basin, salinity somewhat decreases from east to west, since in cyclonic circulation, saline waters are transported from south to northeast along the eastern coast of the sea further than along the western one. A decrease in surface salinity can also be traced from south to north, as well as in bays.
In the autumn-winter season, salinity upper layers slightly increases due to the reduction of river runoff and salinization during ice formation. In spring and summer, salinity on the surface decreases by 0.2-0.5‰ compared to the cold half-year. This is explained by the desalination effect of continental runoff and the spring melting of ice. Almost throughout the sea, a significant increase in salinity from the surface to the bottom is noticeable.
For example, in the Bornholm Basin, salinity at the surface is 7‰ and about 20‰ at the bottom. 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 layer of a jump (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 70–80 m horizons; deeper, at 80–100 m horizons, there is a halo wedge, and then salinity slightly increases to the bottom. In the Gulf of Bothnia, salinity increases from the surface to the bottom by only 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 addition to seasonal fluctuations in salinity, the Baltic Sea, unlike many seas of the World Ocean, is characterized by its significant interannual changes.
Observations of salinity in the Baltic Sea from the beginning of this century to recent years show that it tends to increase, against which short-term fluctuations appear. Changes in salinity in the basins of the sea are determined by the inflow of water through the Danish Straits, which in turn depends on hydrometeorological processes. These include, in particular, the variability of large-scale atmospheric circulation. The long-term weakening of cyclonic activity and the long-term development of anticyclonic conditions over Europe lead to a decrease in precipitation and, as a consequence, to a decrease in river runoff. Changes in salinity in the Baltic Sea are also associated with fluctuations in the values of continental runoff. With a large river flow, the level of the Baltic Sea slightly rises and the sewage flow from it intensifies, which in the shallow zone of the Danish Straits (the smallest depth here is 18 m) limits the access of salt water from the Kattegat to the Baltic. With a decrease in river flow, saline waters more freely penetrate into the sea. In this regard, fluctuations in the inflow of saline waters into the Baltic are in good agreement with changes in the water content of the rivers of the Baltic basin. In recent years, an increase in salinity has been noted not only in the bottom layers of the basins, but also in the upper horizons. At present, the salinity of the upper layer (20-40 m) has increased by 0.5‰ compared to the average long-term value.
Salinity (‰) on a longitudinal section in the Baltic Sea
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. In the areas of distribution of the saline Kattegat waters, especially in the basins at the horizons of 50-70 m, a constant density jump layer (pycnocline) is created. Above it, in the surface horizons (20-30 m), a seasonal layer of large vertical density gradients is formed, due to a sharp change in water temperature at these horizons.
Water circulation and currents
In the Gulf of Bothnia and in the shallow water area adjacent to it, a density jump is observed only in the upper (20-30 m) layer, where it is formed in spring due to freshening by river runoff, and in summer due to heating of the surface layer of the sea. A permanent lower layer of the density jump is not formed in these parts of the sea, since deep saline waters do not penetrate here and year-round stratification of waters does not exist here.
Water circulation in the Baltic Sea
The vertical distribution of oceanological characteristics in the Baltic Sea shows that in the southern and central regions the sea is divided by a density jump layer into upper (0-70 m) and lower (from 70 m to the bottom) layers. In late summer - early autumn, when weak winds prevail over the sea, wind mixing extends to horizons of 10-15 m in the northern part of the sea and to horizons of 5-10 m in the central and southern parts and serves as the main factor in the formation of the upper homogeneous layer. During autumn and winter, with an increase in wind speeds over the sea, mixing penetrates to horizons of 20–30 m in the central and southern regions, and up to 10–15 m in the east, since relatively weak winds blow here. As autumn cooling intensifies (October - November), the intensity of convective mixing increases. During these months, in the central and southern regions of the sea, in the Arkon, Gotland and Bornholm depressions, it covers a layer from the surface to about 50-60 m. ) and is limited by the density jump layer. In the northern part of the sea, in the Gulf of Bothnia and in the west of the Gulf of Finland, where autumn cooling is more significant than in other areas, convection penetrates to horizons of 60-70 m.
The renewal of deep waters, the sea occurs mainly due to the inflow of the Kattegat waters. With their active inflow, the deep and bottom layers of the Baltic Sea are well ventilated, and with small amounts of salt water flowing into the sea at great depths, stagnation occurs in the depressions up to the formation of hydrogen sulfide.
The strongest wind waves are observed in autumn and winter in open, deep areas of the sea with prolonged and strong southwestern winds. Storm 7-8-point winds develop waves up to 5-6 m high and 50-70 m long. In the Gulf of Finland, strong winds of these directions form waves 3-4 m high. In the Gulf of Bothnia, storm waves reach a height of 4-5 m. big waves come in November. In winter, with stronger 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 waters 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 leaving the Gulf of Bothnia and the Gulf of Finland. The general flow is directed along the Scandinavian coast to the southwest. Going around on both sides about. Bornholm, he is heading through the Danish Straits to the North Sea. At the southern coast, the current is directed to the east. Near the Gulf of Gdansk, it turns north and moves along the eastern coast to about. Khnum. Here it branches into three streams. One of them goes through the Irben Strait to the Gulf of Riga, where, together with the waters of the Daugava, it creates a circular current directed counterclockwise. Another stream enters the Gulf of Finland and along its southern coast extends almost to the mouth of the Neva, then turns to the north-west and, moving along the northern coast, leaves the bay together with river waters. The third flow goes to the north and through the straits of the Aland skerries penetrates into the Gulf of Bothnia. Here, along the Finnish coast, the current rises to the north, goes around the northern coast of the bay and descends to the south along the coast of Sweden. In the central part of the bay, there is a closed circular counterclockwise current.
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 prevailing wind currents 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 horizons 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. With strong westerly winds, water from the Kattegat flows into the Baltic Sea almost along the entire cross section of the straits. East winds, on the contrary, increase the outlet current, which extends to the horizons of 20 m, and the inlet current remains only near the bottom.
Due to the high degree of isolation from the World Ocean, the tides in the Baltic Sea are almost invisible. Fluctuations in the level of the tidal character in individual points do not exceed 10-20 cm. The average sea level experiences secular, long-term, inter-annual and intra-annual fluctuations. They can be associated with a change in the volume of water in the sea as a whole and then have the same value for any point in the sea. The secular level fluctuations (except for changes in the volume of water in the sea) reflect the vertical movements of the shores. These movements are most noticeable in the north of the Gulf of Bothnia, where the rate of land rise reaches 0.90-0.95 cm/year, while in the south the rise is replaced by the sinking of the coast at a rate of 0.05-0.15 cm/year.
In the seasonal course of the Baltic Sea level, two minima and two maxima are clearly expressed. lowest level 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 height difference between the summer maximum and the spring minimum is 22-28 cm. It is greater in the bays and less in the open sea.
Surge fluctuations in the level occur quite quickly and reach significant values. In 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. -26 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 regime of the Baltic Sea.
The catastrophic St. Petersburg floods are connected with sea level fluctuations. They occur when the level rise is due to the simultaneous action of several factors. Cyclones that cross the Baltic Sea from the southwest to the northeast cause winds that drive water from the western regions of the sea and overtake it into the northeastern part of the Gulf of Finland, where the sea level rises. Passing cyclones also cause seiche fluctuations in the level, at which the level rises in the Aland region. From here, a free seiche wave, driven by western winds, enters the Gulf of Finland and, together with the surge of water, causes a significant increase (up to 1-2 m and even 3-4 m) in the level at its top. This prevents the flow of the Neva water into the Gulf of Finland. The water level in the Neva is rapidly rising, which leads to floods, including catastrophic ones.
ice coverage
The Baltic Sea is covered with ice in some areas. The earliest (approximately in early 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, motionless ice occupies the northern part of the 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 distribution of fixed and floating ice in the Baltic Sea depends on the severity of the winter. Moreover, in mild winters, ice, having appeared, may completely disappear, and then appear again. AT harsh winters the thickness of immobile ice reaches 1 m, and floating ice - 40-60 cm.
Melting begins in late March - early April. Liberation of the sea ice is coming from southwest to northeast.
Only in severe winters in the north of the Gulf of Bothnia, ice can be found in June. However, the sea is cleared of ice every year.
Economic importance
Freshwater fish species live in the significantly freshened waters of the bays of the Baltic Sea: crucian carp, bream, chub, pike, etc. There are also fish that spend only part of their lives in fresh waters, the rest of the time they live in the salty waters of the sea. These are now rare Baltic whitefish, typical inhabitants of the cold and clean lakes of Karelia and Siberia.
A particularly valuable fish is the Baltic salmon (salmon), which forms an isolated herd here. The main habitats of salmon are the rivers of the Gulf of Bothnia, the Gulf of Finland and the Gulf of Riga. She spends the first two or three years of her life mainly in the southern part of the Baltic Sea, and then goes to spawn in the rivers.
Purely marine fish species are common in the central regions of the Baltic, where salinity is relatively high, although some of them also enter fairly fresh bays. For example, herring lives in the Gulf of Finland and Riga. More saltwater fish - Baltic cod - do not enter the fresh and warm bays. Eel is a unique species.
In fishing, the main place is occupied by herring, sprat, cod, river flounder, smelt, perch and various types of freshwater fish.
The Baltic Sea, also known as Varangian, is located in the northern part of Eurasia. It is distinguished by a low concentration of salts, since its full flow is provided by a large amount of river flows that flow into the reservoir, dilute it to a slightly saline level.
This is the largest sea in the world, which has the status of brackish water. It plays a key role in the socio-economic and military-strategic spheres of most of the Nordic countries.
This is an inland sea that washes the following states located in northern, eastern and western parts of the European continent:
- Poland;
- Lithuania;
- Denmark;
- Finland;
- Sweden;
- Estonia;
- Latvia;
- Germany;
- Russia.
The northernmost cape of the Baltic Sea is located directly at the polar circle of the globe. The southern point is the outskirts of the city of Wismar. The Western Cape is near locality Flensburg.
The easternmost point is located in the area of the Russian city of St. Petersburg. The reservoir is part of the Atlantic basin. If we consider the total surface of the sea without taking into account the island land, then its area is 415 thousand square meters. km.
The volume of water is 21.5 thousand km. cube The maximum depth of the sea reaches 470 m. The length of the coastline passing through the territory of the above states is 8 thousand km.
The average distance from the surface of the sea surface to the bottom of the reservoir is 51 m. In the Precambrian period, the Baltic craton was located on the site of the current sea, which had the appearance of high mountains and was the core of the northern part of the Eurasian continent.
After the earth's crust sank under the weight of the glacier, a large basin formed. Water from the district rivers, as well as their tributaries, began to flow into the naturally formed depression. So a new sea appeared, which was named the Baltic Sea in honor of the craton.
In Russia, this inland reservoir was called the Varangian, since the ships of the northern navigators from the Scandinavian Peninsula passed through its waters. They entered the mouths of the rivers and reached the shores of the current states of Ukraine, Belarus and Russia.
Geography of the Baltic Sea
The Baltic Sea, which is located in the North of Europe, like any other natural object, has its own physical and geographical characteristics. Below is detailed information about the ecology of this reservoir, its climatic conditions, features of hydrology, as well as the concentration of mineral salts.
Relief
The Baltic Sea is located within the borders of the Eurasian continent. The bottom level consists of shoals, medium depressions (51 m), as well as large bottom gorges, the depressions of which are at least 200 m. 
One of the deepest depressions is Landsortskaya, which is also the area where the greatest distance from the sea surface to the bottom, namely, 470 m. It is also worth noting the basin off the coast of about. Gotland (249 m), as well as located in the Gulf of Bothnia (293 m).
On the south side, the bottom topography is distinguished by a plateau landscape, while in the north, on the contrary, it is uneven, with many hills and rock formations. In the coastline zone, the bottom of the Baltic Sea is lined with sand. 
The rest of the bottom part of the reservoir consists of layers of the Ice Age. This is silt, consisting of clay-type soils that have black, greenish, and brown hues.
Hydrological features
The Baltic Sea is located in a region where a large amount of river runoff is concentrated. Their presence is the main feature of the reservoir, since due to oversaturation with fresh water, its salty currents overflow into the North Sea through the Danish Strait.
The main volume of river flows remains in the Baltic, which play a key role in the desalination of the reservoir. During sea storms, currents can change, mixing of the waters of the North and Baltic Seas is observed. Tides are divided into 2 types. These are semi-diurnal as well as diurnal. Their height is not more than 20 cm. One of the features of the Baltic Sea is the presence of surge phenomena.
Depending on the degree of fullness of the rivers that saturate the reservoir, the level of the sea itself can fluctuate significantly. So, off the coast of the Gulf of Finland, the water area can rise up to 5 m, near the city of Ventspils up to 1.5 m, the sea level near the coast of Kronstadt increases by 3.6 m.
Temperature
The Baltic Sea is located in the north of the European continent, so its waters do not have a high temperature regime. In the summer season, the surface of the water area in the area of the Gulf of Finland warms up to 17 °C. 
The waters of the Gulf of Bothnia are colder and are in the temperature range of 9–13 °C. At a depth of 30 meters, the thermocline effect appears. In the bottom part of the Baltic Sea, water heating does not exceed 5 °C.
Salinity
The degree of concentration of mineral salts in the Baltic Sea is minimized as the water area moves away from the Danish straits. If water is taken directly from these channels, where they connect with the North Sea, then the salinity level will be 20% of the water area and 30% at the very bottom. In the central part of the Baltic, the salt concentration does not exceed 8%. 
If you examine the waters of the Gulf of Bothnia, you will find that their salinity is not higher than 3%. The freshest water area is the Gulf of Finland, and the level of its mineralization is at the level of 2%. Closer to the bottom salinity rises to 13%. The distinctive uniqueness of the Baltic Sea is that in the event of an emergency, its water can be consumed inside.
Ecology
At the end of the Second World War in the Baltic Sea, there was a burial of ships carrying dangerous chemical substances. Most often it was mustard gas, which is considered a weapon of mass destruction. 
During 2003, at least 21 cases were recorded in the reservoir when fishing schooners pulled out bundles of chemical weapons in their nets, the average tonnage of which was 1000 kg.
In 2011, there was an unauthorized discharge of paraffin compounds, which spilled over tens of square meters. km. and their pieces were found for a long time on the coast of the sea.
Map of sunken chemical weapons at the bottom of the Baltic Sea Currently, the ecological situation in the Baltic Sea is unsatisfactory, as the sunken ships with chemical weapons on board have become unusable, and toxic substances are gradually released from metal containers.
Geographical history of the Baltic Sea
After the gradual subsidence of the earth's crust under the weight of the ice during the great era of the ice age, history developed formation of the Baltic, which exists within its modern borders, namely:
| Name | Description |
| glacial lake | it was 14 thousand years ago in the territory where the southern part of the Baltic is located today |
| Yoldian Sea | a small glacial lake was filled with sea water that gushed from a strait located in central Sweden |
| Ancylus Sea | existed from 9 to 7.5 thousand years BC. |
| Littorina lake | there was an increase in the level of the ocean, and through the straits located near the territory of modern Denmark, streams of salt water poured into the Baltic |
The Baltic Sea was formed about 4 thousand years ago. Around the same time period, the Neva River appeared. The current boundaries of the reservoir are almost identical to prehistoric ones.
Notable explorers of the Baltic Sea
The first information about scientific research held in the Baltic Sea date back to 1738. The most famous scientists who have devoted their lives to studying the flora and fauna of the Baltic, its climate, currents and bottom topography are the following explorers and travelers:
If we consider the study of the Baltic in a broader format, then scientists believe that for the first time an active study of its water area began in the 7th century. At that time, the Normans living on the territory of the Scandinavian Peninsula for the first time entered the Gulf of Bothnia, discovered the Aland Islands and began to move further in the direction of the Neva.
Rivers flowing into the Baltic Sea
The Baltic Sea is located in a region that does not suffer from a lack of moisture, and its freshwater supply is provided by the following rivers:
If it were not for the presence of these water arteries, the Baltic Sea would not have such voluminous fresh water reserves, would lose its strategic importance as an inland water body that ensures the development of social, trade, economic and partnership relations between countries.
Currents of the Baltic Sea
The peculiarity of this inland reservoir is that its currents are surface, and are formed by the waters of large rivers flowing into the Gulf of Finland and Bothnia.
The speed of their advance is 3-4 cm per second. Due to the slow current, the direction of water movement can change in any direction with gusty winds. During storms, the speed of surface currents reaches 100 cm per second. The waters of the Baltic Sea move from east to north.
Flora and fauna of the Baltic Sea
The flora of the inland reservoir is represented by blue-green algae, which are found in shallow places where the water warms up quite well in the summer. 
The fauna of the sea is all freshwater and consists of the following fish species:
- crucian carp;
- zander;
- carp;
- pike;
- perch.
There are reptiles in the form of frogs, turtles, newts. During the period of seasonal migration of birds on the surface of the waters of the Baltic Sea, you can see wild geese, ducks, swans. Herons are common in shallow water and in the coastal zone.
Main ports
Given the fact that the Baltic Sea is washed by a large number of states, the following major port cities are located on their coasts, hosting passenger, merchant and military ships:
Ferry crossings run between the ports of Denmark, Sweden, and Germany on a regular basis. A new ferry terminal is currently under construction to open the Fermanbelt passenger route, which will be put into operation in 2028.
Natural resources
Oil deposits have been discovered in the bottom depths of the Baltic Sea. Geological exploration of the deposit, which received the code name D-6, is being actively carried out. Interlayers of ores of iron oxide and potassium permanganate were found. There are significant reserves of amber. Most of natural resources concentrated in the economic zone of the Russian Federation from the Kaliningrad region.
The main obstacles to the development of minerals are associated with strict labor protection requirements, since the Baltic is connected to the Atlantic by small straits, and there is no abundant water exchange. All this affects the degree of pollution of the reservoir.
Sea transport
The water area of the Gulf of Finland, as well as in the area of the Archipelago Sea, is characterized by shallow depths. This prevents the passage of large vessels. From the ports of Vyborg and St. Petersburg, timber and lumber, grain, and food products are transported to European cities. 
Machinery, industrial equipment, electronic devices come to the Russian Federation from the EU countries. Between the port cities there is a constant exchange of a wide variety of goods.
Recreational resources
Holidays in the Baltic attract tourists who prefer fresh sea air, like to lie on the beach, but cannot stand the unbearable heat. Summer near the coast of the Baltic Sea is warm and with a lot of precipitation. The weather can change several times within 10-15 minutes.
Below are the resorts on the coast of the Baltic Sea, which are most popular among residents of the European continent:
- Sestroretsk;
- Heiligendamm;
- Pärnu;
- Sopot;
- Koszalin;
- Neringa;
- Jurmala;
- Albek;
- Zelenogorsk;
- Saulkrasti.
The shores on which the Baltic resorts are located are strewn with golden sand, and the rest of the territory is covered with dense coniferous forests. In memory of the journey and vacation on the Baltic Sea, you can buy souvenirs made from locally mined amber.
In addition to the fact that the Baltic Sea is distinguished by physical and geographical features, there are also the following Interesting Facts which not everyone is aware of people of the country:
There is a unique place on the Danish coast of the Baltic Sea. This is the so-called Forest of Trolls, where there are coniferous trees, all the trunks of which are twisted into a bizarre shape and in one direction. This riddle of nature has not yet been solved by leading scientists of biology and botanists with a worldwide reputation.
Article formatting: Mila Fridan
Video about the Baltic Sea
Documentary about the wild nature of the Baltic: