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Baltic sea coastline character. Baltic Sea: vacation

Østersøen, Finnish Itämeri, est. Läänemeri, Latvian. Baltijas jūra, lit. Baltijos jūra) is an inland sea of ​​Eurasia, located in Northern Europe (partially washing the shores of Western and Eastern Europe). Refers to the Atlantic Ocean basin.

The northernmost point of the Baltic Sea is located near the Arctic Circle (65°40" N), the southernmost point is near the city of Wismar (53°45" N).

The westernmost point is located in the Flensburg area (9°10" E), the easternmost point is in the St. Petersburg area (30°15" E)

Sea surface area (without islands) is 415 thousand km². The volume of water is 21.5 thousand km³. Due to the huge flow of rivers, the water has low salinity and therefore the sea is brackish. It is the largest sea in the world with such a feature.

Geological history

Ancylus Lake approximately 8.7 thousand years ago. Remains of a glacier are still visible on the tops of the Scandinavian mountains.

The weight of the ice caused a significant deflection of the earth's crust, part of which was below ocean level. With the end of the last ice age, these territories are freed from ice, and the depression formed by the depression of the crust is filled with water:

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Physiographical sketch

The Baltic Sea extends deep into the land of Europe, washing the shores of Russia, Estonia, Latvia, Lithuania, Poland, Germany, Denmark, Sweden and Finland.

Large bays of the Baltic Sea: Finnish, Bothnian, Riga, Curonian (a freshwater bay separated from the sea by the sandy Curonian Spit).

The major rivers flowing into the Baltic Sea are the Neva, Narva, Western Dvina (Daugava), Neman, Pregolya, Vistula, Oder and Venta.

Bottom relief

Relief of the Baltic Sea (meters)

The Baltic Sea lies within the continental shelf. The average sea depth is 51 meters. In areas of shallows, banks, and near islands, shallow depths are observed (up to 12 meters). There are several basins in which depths reach 200 meters. The deepest basin is the Landsort basin ( 58°38′ N. w. 18°04′ E. d. HGIO) with a maximum sea depth of 470 meters. In the Gulf of Bothnia the maximum depth is 293 meters, in the Gotland Basin - 249 meters.

The bottom in the southern part of the sea is flat, in the north it is uneven and rocky. In coastal areas, sands are common among bottom sediments, but most of the seabed is covered with sediments of green, black or brown clayey silt of glacial origin.

Hydrological regime

A feature of the hydrological regime of the Baltic Sea is a large excess of fresh water, formed due to precipitation and river flow. The brackish surface waters of the Baltic Sea flow through the Danish Straits into the North Sea, and the salty waters of the North Sea enter the Baltic Sea with the deep current. During storms, when the water in the straits is mixed to the very bottom, the water exchange between the seas changes - along the entire cross-section of the straits, water can flow into both the North and Baltic Seas.

In 2003, 21 incidents of chemical weapons entering fishing nets were recorded in the Baltic Sea - all in the form of clumps of mustard gas weighing approximately 1005 kg.

In 2011, paraffin was discharged into the sea, which spread throughout the sea. Tourists found large pieces of paraffin on the beach. [ ]

Natural resources

The development of deposits may be hampered by strict environmental requirements associated with insignificant water exchange between the sea and the ocean, and anthropogenic water pollution by runoff from the territory of coastal states, which contribute to increased eutrophication.

The Nord Stream gas pipeline was laid along the bottom of the Baltic Sea.

Maritime transport

Recreational resources

Titles

First time title Baltic Sea(lat. mare Balticum) found in Adam of Bremen in his treatise “Acts of the Archbishops of the Hamburg Church” (lat. Gesta Hammaburgensis Ecclesiae Pontificum) .

In the Tale of Bygone Years the Baltic Sea is named Varyazhsky by sea. Historically in Russian the sea was called Varyazhsky and then Sveisky(Swedish). Under Peter I, the German name became stronger - Ostzeyskoe sea. The modern name has been used since 1884.

Baltic Sea(also called the Eastern Sea) is considered an inland sea that extends deep into the continent.

The northern extreme point of the Baltic Sea is located near the Arctic Circle, the southern - near the German city of Wismar, the western - near the city of Flensburg, and the eastern - near St. Petersburg. This sea belongs to the ocean.

General information about the Baltic

The area of ​​the sea (not including islands) is 415 km. sq. It washes the shores of the following states:

  • Estonia;
  • Russia;
  • Lithuania;
  • Germany;
  • Latvia;
  • Poland
  • Latvia;
  • Denmark;
  • Finland;
  • * Sweden.

Large bays are considered to be: Bothnian, Finnish, Riga, Kursk (separated by an oblique). The largest islands: Öland, Wolin, Alandia, Gotland, Als, Saaremaa, Muhu, Men, Usedom, Fore and others. The largest rivers: Zapadnya Dvina, Neva, Vistula, Venta, Narva, Pregolya.

The Baltic Sea, through the Volga-Baltic basin, opens onto and is located on the continental shelf. In the area of ​​islands, shallows and banks, the depth varies within 12 meters. There are a couple of basins where the depth reaches 200 meters. The Landsort Basin is considered the deepest (470 meters), the depth of the basin reaches 250 meters, and in the Gulf of Bothnia - 254 meters.

In the southern region the seabed is flat, and in the north it is predominantly rocky. A huge part of the bottom is covered with sediments of glacial origin of various colors (green, brown, black).

A special feature of the Baltic Sea is that there is an excess of fresh water, which is formed due to river runoff and precipitation.

Its surface brackish waters constantly flow into. During storms, the exchange between these seas changes, as water is mixed from the bottom in the straits. The salinity of the sea is decreasing from the Danish Straits (20 ppm) to the east (in the Gulf of Bothnia it is 3 ppm, and in the Gulf of Finland – 2 ppm). Tides can be diurnal or semidiurnal (do not exceed 20 cm).

When compared with other seas, the disturbances in the Baltic Sea are completely insignificant. In the central parts of the sea, waves can reach 3-3.5 meters, less often - 4 meters. During large storms, waves 10-11 meters high were recorded. The clearest water with a bluish-green tint is observed in the Gulf of Bothnia; in coastal areas it is more turbid and has a yellowish-green color. Due to the development of plankton, the lowest water transparency is observed in summer. The soils of the coastal zone are varied: in the southern regions there is sand, in the east there is silt and sand, and on the northern coast there is stone.

Climate of the Baltic Sea

The sea temperature is generally lower than other seas. In the mornings in the summer, thanks to the southern winds that drive the upper warm layers into the ocean, the temperature sometimes drops below 12 degrees. When northerly winds begin to blow, surface waters become significantly warmer. The highest temperature is in August - about 18 C. In January it varies from 0 to 3 C.

Due to its low salinity, harsh winters and shallow depth, the Baltic Sea often freezes, although not every winter.

Flora and fauna

The water in the Baltic Sea changes from sea salt to fresh water. Marine mollusks live only in the western region of the sea, where the water is saltier. Fish here include sprat, cod, and herring. The Gulf of Finland is home to smelt, vendace, salmon and others. Seals live in the area of ​​the Åland Islands.

Due to the presence of many islands, rocks, and reefs in the sea, sailing in the Baltic Sea is quite dangerous. This danger is somewhat reduced due to the presence of a large number of lighthouses here (most of them). The largest cruise ships leave the Danish Straits and enter the Atlantic Ocean. The Great Belt Bridge is considered the most difficult place. The largest ports: Tallinn, Baltiysk, Lubeck, Riga, Stockholm, Szczecin, Rostock, Kiel, Vyborg, Gdansk, St. Petersburg;

  • Ptolemy called this sea the Venedian, which comes from the name of the Slavic peoples who lived in ancient times in the southern part of the coast - the Wends or Wends;
  • The famous route from the Varangians to the Greeks ran through the Baltic Sea;
  • "The Tale of Bygone Years" calls it Varangian Sea;
  • The name "Baltic Sea" appears for the first time in the treatise of Adam of Bremen in 1080;
  • This sea is rich in oil, manganese, iron and amber. The Nord Stream gas pipeline runs along its bottom;
  • Every year on March 22, Baltic Sea Environmental Protection Day is celebrated. This decision was made by the Helsinki Commission in 1986.

Resorts

Among the resorts of the Baltic Sea, the most famous are: Zelenogorsk, Svetlogorsk, Zelenogradsk, Pionersky (Russia), Saulkrasti and

The Baltic Sea and its coast are an interesting place, imbued with memories of the Vikings, and tranquil with its northern landscapes. It differs from other seas in the nature of its relief, temperature and features of the coastline. The Baltic has great historical and geopolitical significance for Russia.

Geographical location

The Baltic Sea on the map is located in northern Europe and belongs to the Atlantic basin. Bounded by latitudes 54°46′ and 65°56′ north and longitudes 9°57′ and 30°00′ east. The extreme points that the Baltic Sea has on the map are: near the Arctic Circle in the north, near Wismar in the south, the eastern point is located near St. Petersburg and the western extreme point is located in the Flensburg area.

Relief and depths

The bottom topography has minor differences from the outlines of the shores bordering the Baltic Sea. Depths, in turn, also depend on the nature of the surrounding area. The southern side of the sea, belonging to Germany, Poland and Denmark, is gentle, level, with sandy beaches. The rocky coast and uneven rocky bottom are in the northern part. The depth and topography of the Baltic Sea varies in different areas. The bottom has a very complex dissected surface. There are depressions that delimit the highlands and bases of the islands that the Baltic Sea includes.

The depths in other places are shallow. For example, there are areas of pronounced accumulative relief - these are the shallow Gulfs of Finland, Riga and Bothnia.

Thus, the Baltic Sea has a depth of less than 200 meters. The Landsort depression is different. The maximum depth of the Baltic Sea is in this area and is about 470 meters. The Landsort depression extends in a southwestern direction. The rest are of lesser depth: Gotland - 249 m and Gdansk - 116 m in the central part of the sea, Arkona - 53 m and Bornholm - 105 m (in the western part).

Sea bays and straits

Refers to inland seas. In the southwest it adjoins the North Sea through the Danish straits (Little and Great Belt, Sound), Skagerrak and Kattegat.

In the east it is located between Estonia and Latvia. The Estonian island of Saaremaa partially separates the bay from the rest of the sea. There are also large Gulfs of Finland and Bothnia

Neva Bay is the eastern part of the Gulf of Finland. At a distance of about 50 km from St. Petersburg, the city of Kronstadt is located. The dam connects the island city and St. Petersburg, the highway is laid along the dam, so people have the opportunity to get to the mainland and back by car.

In the northeastern part, where the border between Russia and Finland passes, the Gulf of Finland is connected to the Vyborg Gulf. The Saimaa Canal, leased by Finland, originates there. It serves as a transport route and is also popular with tourists in warm weather. Guests come here for the beauty of the landscapes and duty-free shopping.

Coast

The Baltic Sea coast is diverse. Latvia has accumulation-type shores, formed as a result of the accumulation of sand on the coasts. The lagoon coast, formed by a bay and separated from the sea by a narrow spit, is located near Kaliningrad. The leveled shores border most of the sea, in particular, they belong to Poland. And they are formed under the influence of prevailing winds and coastal currents. Fjords are narrow and deep sea bays with towering steep and rocky shores that surround the sea from the north. They are formed by the flooding of tectonic faults and river valleys. The skerry coast appeared as a result of the flooding of areas with smoothed glaciers composed of crystalline rocks. These hills protrude above the sea surface in the form of many islands-skerries with traces of glacial activity.

The following countries have access to the Baltic Sea: Russia, Latvia, Estonia, Lithuania, Germany, Poland, Sweden, Denmark, Finland. After the collapse of the USSR, Russia was left with a small stretch of coastline, only 7%, instead of the previous 25%, which brings annual losses to the state. Therefore, one port has been established in Primorsk near Vyborg, which will specialize in coal and dry cargo. And the second port is located in Luga Bay, it will be an oil loading port.

Tectonic processes

To this day, the Baltic Sea continues to change. Its depths are shallow compared to other parts of the Atlantic Ocean. Actually, this vast body of water during its existence several times became a lake and again a sea due to tectonic processes.

Currently, the next stage of separating the sea from the ocean and turning it into a fresh lake is underway. It is characterized by a rise in the bottom of the Gulf of Bothnia by several centimeters per year and flooding of the southern coasts. Such processes create a need for northern ports to lengthen their piers. To save low-lying parts of the coast, embankments are made.

Temperature layers

The temperature of the Baltic Sea, in turn, depends on the depth. The predominant part of the waters of a huge reservoir can be divided into surface, transitional and deep water masses.

The surface layer ranges from 0 to 20 meters, in places - from 0 to 90 meters with temperatures from 0 to 20 degrees. It is formed as a result of the interaction of the sea with the atmosphere and waters flowing from the mainland. The temperature of the Baltic Sea in this layer varies depending on the time of year. In summer, cold intermediate water masses formed due to significant warming of the sea surface are more pronounced.

The deep layer (bottom and 50-60 meters above it) has a temperature of 1 to 15 degrees. This layer is formed by the flow of water through the Small and Big Belt straits and their mixing.

The transition layer includes water at depths from 20-60 to 90-100 meters. They have a temperature of 2-6 degrees and are formed by mixing waters of deep and surface layers.

Features of water temperature in the Baltic Sea

Certain areas of the sea differ in their water structure. Thus, the Bornholm region has a warm layer (7-11 degrees) both in summer and winter. It is formed by warm waters coming here from the more heated Arkona basin. Due to the shallow depth of the sea and the movement of water in the horizontal plane, there is no cold intermediate layer in summer.

Temperature changes by season

In winter, in the open sea the water temperature is higher than near the coast, while it differs on the western and eastern shores. In February the temperature is 0.7 degrees near Ventspils, in the open sea of ​​the same latitude - approximately 2 degrees, off the western coast - 1 degree.

In summer, surface waters in different parts of the sea also differ in temperature. Prevailing westerly winds drive surface water masses away from the western shores. The underlying cold waters rise to the surface. As a result of this phenomenon, temperatures drop in the southern and central regions, as well as off the western coasts. In addition, there is a cold current from the Gulf of Bothnia to the south along the coast of Sweden.

Seasonal fluctuations in water temperature are pronounced only in the upper 50-60 meters; deeper, the indicators change slightly. There are no changes in temperature during cold times, but with increasing depth the indicators decrease slightly. In warm weather, the water temperature rises to horizons of 20-30 meters due to mixing. Even in summer, when the surface layer of water is warmed up and the thermocline is expressed more sharply than in spring, a cold intermediate layer remains.

The depth, relief and other features of the Baltic Sea depend on many factors. This is a geographical location, being in northern latitudes, as well as being located on a continental plate.

The Baltic Sea (from antiquity until the 18th century in Russia was known as the “Varangian Sea”) is an inland marginal sea that protrudes deeply into the mainland. The Baltic Sea is located in northern Europe and belongs to the Atlantic Ocean basin.

The northernmost point of the Baltic Sea is located near the Arctic Circle, the southernmost point is near the city of Wismar (Germany). The westernmost point is located in the area of ​​the city of Flensburg (Germany), the easternmost point is located in the St. Petersburg area. Due to the large elongation along the meridian and parallel, individual areas of the Baltic Sea are located in different physical-geographical and climatic zones. This, in turn, influences the oceanological processes occurring in the sea and its individual areas.
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, and Oder.

The connection between the Baltic Sea and the Atlantic Ocean is carried out through the North Sea, the Skagerrak, Kattegat and Danish straits (Great and Little Belt, Öresund (Sund) and Fehmarn Belt), however, this connection is difficult due to the shallowness of the straits (depth at the rapids is 7- 18 meters). Therefore, the Baltic waters 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 low salt content. Its waters are a mixture of salt water from the ocean and fresh water coming from numerous rivers. The degree of sea salinity in different places has different indicators, 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., every 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 mark of 2-3 ppm (the average salinity of the World Ocean is 35 ppm).

The length of the Baltic coastline is 7 thousand kilometers. The coast is distributed between the countries as follows: Sweden owns 35% of the coast, Finland - 17%, Russia - about 7% (approximately 500 kilometers). The remaining part of the coast is shared by Lithuania, Latvia, Estonia, Poland, Germany, and Denmark. The sea coast and adjacent land areas are heavily populated and intensively used by humans. Transport complexes and large industrial enterprises are located on the coast. The Baltic Basin accounts for one tenth of global maritime trade.

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

The main environmental problems of the Baltic

Firstly, the excess supply of nitrogen and phosphorus into the water area as a result of washout from fertilized fields, with 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 biogenic elements in the sea, organic substances are not completely processed, and due to a lack of oxygen, they begin to decompose, releasing hydrogen sulfide, which is harmful to marine life. At the bottom of the Gotland, Gdansk, and Bornholm depressions, dead hydrogen sulfide zones already exist.

The second significant problem of the Baltic is water pollution with oil. Thousands of tons of oil enter the water area annually through various discharges. The film of oil that covers the surface of the water mirror does not allow oxygen to penetrate deeper. Toxic substances that are harmful to living organisms also accumulate on the surface of the water. Accidental 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 enter mainly into the Baltic waters with precipitation, the rest ends up through direct discharge into the water area or with river runoff of household and industrial waste. The amount of copper entering the water area annually is about 4 thousand tons, lead - 3 thousand tons, cadmium - about 50 tons, and mercury - 33 tons, per 21 thousand cubic kilometers of water volume of the water area.

Due to its geographical location, the Baltic Sea has always been at the crossroads of historical events. There is more than one ship graveyard at the bottom of the Baltic. Many sunken ships contain dangerous cargo. Containers containing cargo deteriorate over time.

For decades in the Baltic, the practice of sinking and burying obsolete bombs, shells, and chemical munitions was practiced. 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 of 1951, over 300 thousand tons were sunk in various areas of the Baltic, as well as in the straits connecting the Baltic Sea with the North Sea German chemical weapons and ammunition.

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

The material was prepared based on information from open sources

The Baltic Sea is connected to the North Sea by the Øresund Straits (Zund), Greater and Lesser Belta, Kattegat and Skagerrak. It washes the shores of Russia, Estonia, Latvia, Lithuania, Poland, Germany, Denmark, Sweden, and Finland.

The maritime border of the Baltic Sea runs along the southern entrances of the Öresund, Greater and Lesser Belta straits. Area 386 thousand km². The average depth is 71 m. The shores of the Baltic Sea in the south and south-east. predominantly low-lying, sandy, lagoon-type; on the land side there are dunes covered with forest, on the sea side there are sandy and pebble beaches. In the north, the shores are high, rocky, predominantly of the skerry type. The coastline is heavily indented and forms numerous bays and bays.

The largest bays: Bothnian (according to physical and geographical conditions, it is a sea), Finnish, Riga, Curonian, Gdansk Bay, Szczecin, etc.

Islands of the Baltic Sea of ​​continental origin. There are many small rocky islands - skerries, located along the northern shores and concentrated in the groups of Vasiya and Åland islands. The largest islands are: Gotland, Bornholm, Sarema, Muhu, Hiuma, Öland, Rügen, etc. A large number of rivers flow into the Baltic Sea, the largest of which are the Neva, Western Dvina, Neman, Vistula, Odra, etc.

The Baltic Sea is a shallow shelf sea. The predominant depths are 40-100 m. The shallowest areas are the Kattegat Straits (average depth 28 m), Oresund, the Greater and Lesser Belts, the eastern parts of the Gulf of Finland and the Gulf of Bothnia and the Gulf of Riga. These areas of the seabed have a leveled accumulative topography and a well-developed cover of loose sediments. Most of the bottom of the Baltic Sea is characterized by highly dissected relief; there are relatively deep basins: Gotland (249 m), Bornholm (96 m), in the Södra-Kvarken Strait (244 m) and the deepest - Landsortsjupet south of Stockholm (459 m). There are numerous stone ridges; in the central part of the sea, ledges are traced - continuations of the Cambrian-Ordovician (from the northern coast of Estonia to the northern tip of the island of Öland) and Silurian cliffs, underwater valleys, glacial-accumulative landforms flooded by the sea.

The Baltic Sea occupies a depression of tectonic origin, which is a structural element of the Baltic shield and its slope. According to modern concepts, the main irregularities of the seabed are caused by block tectonics and structural denudation processes. The latter, in particular, owe their origin to the underwater cliff ledges. The northern part of the seabed is composed predominantly of Precambrian rocks, overlain by an intermittent cover of glacial and recent marine sediments.

In the central part of the sea, the bottom is composed of Silurian and Devonian rocks, hiding to the south under a thickness of glacial and marine sediments of considerable thickness.

The presence of underwater river valleys and the absence of marine sediments under the glacial deposits indicate that in pre-glacial times there was land in place of the Baltic Sea. During at least the last ice age, the Baltic Sea basin was completely occupied by ice. Only about 13 thousand years ago there was a connection with the ocean, and sea waters filled the depression; The Ioldian Sea was formed (based on the mollusk Joldia). The Ioldian Sea phase is slightly earlier (15 thousand years ago) preceded by the phase of the Baltic glacial lake, which was not yet connected to the sea. About 9-7.5 thousand years ago, as a result of tectonic uplift in Central Sweden, the connection between the Ioldian Sea and the ocean ceased, and the Baltic Sea again became a lake. This phase of development of the Baltic Sea is known as Lake Ancylus (based on the mollusk Ancylus). A new subsidence of land in the area of ​​the modern Danish Straits, which occurred about 7-7.5 thousand years ago, and extensive transgression led to the resumption of communication with the ocean and the formation of the Littorina Sea. The level of the last sea was several meters higher than the modern one, and the salinity was greater. Deposits of the Littorina transgression are widely known on the modern coast of the Baltic Sea. The secular rise in the northern part of the Baltic Sea basin continues today, reaching 1 m per hundred years in the north of the Gulf of Bothnia and gradually decreasing to the south.

The climate of the Baltic Sea is maritime and temperate, strongly influenced by the Atlantic Ocean. It is characterized by relatively small annual temperature fluctuations, frequent precipitation fairly evenly distributed throughout the year, and fog in the cold and transitional seasons. During the year, westerly winds prevail, which are associated with cyclones coming from the Atlantic Ocean. Cyclonic activity reaches its greatest intensity in the autumn-winter months. At this time, cyclones are accompanied by strong winds, frequent storms and cause large rises in water levels near the coast. In the summer months, cyclones weaken and their frequency decreases. The invasion of anticyclones is accompanied by easterly winds.

The extension of the Baltic Sea by 12° along the meridian determines noticeable differences in the climatic conditions of its individual regions. Average air temperature in the southern part of the Baltic Sea: in January -1.1°C, in July 17.5°C; middle part: in January -2.3°C, July 16.5°C; Gulf of Finland: in January -5°C, in July 17°C; northern part of the Gulf of Bothnia: in January -10.3°C, in July 15.6°C. Cloudiness in summer is about 60%, in winter more than 80%. The average annual precipitation in the north is about 500 mm, in the south over 600 mm, and in some areas up to 1000 mm. The greatest number of days with fog falls on the southern and middle parts of the Baltic Sea, where it reaches an average of 59 days a year, the smallest - in the north. Gulf of Bothnia (up to 22 days a year).

The hydrological conditions of the Baltic Sea are determined mainly by its climate, excess fresh water and water exchange with the North Sea. Excess fresh water, equal to 472 km3 per year, is formed due to continental runoff. The amount of water entering precipitation (172.0 km³ per year), is equal to evaporation. Water exchange with the North Sea averages 1659 km3 per year (salt water 1187 km³ per year, fresh water - 472 km³ per year). Fresh water flows from the Baltic Sea into the North Sea through the runoff current, while salt water flows through the straits from the North Sea into the Baltic Sea through the deep current. Strong westerly winds usually cause an influx, and eastern winds cause a flow of water from the Baltic Sea through all sections of the Øresund, Greater and Lesser Belta straits.

The currents of the Baltic Sea form a counterclockwise circulation. Along the southern coast the current is directed to the east, along the eastern coast to the north, along the western coast to the south and at the northern coast to the west. The speed of these currents ranges from 5 to 20 m/sec. Under the influence of winds, currents can change direction and their speed near the coast can reach 80 cm/sec or more, and in the open part - 30 cm/sec.

The surface water temperature in August in the Gulf of Finland is 15°C, 17°C; in the Gulf of Bothnia 9°C, 13°C and in the central part of the sea 14°C, 18°C, and in the south it reaches 20°C. In February - March, the temperature in the open part of the sea is 1°C-3°C, in the Bothnian, Finnish, Riga and other bays and bays below 0°C. The salinity of surface water decreases rapidly with distance from the straits from 11‰ to 6-8‰ (1‰-0.1%) in the central part of the sea. In the Gulf of Bothnia it is 4-5‰ (in the north of the bay 2‰), in the Gulf of Finland 3-6‰ (at the top of the bay 2‰ and less). In the deep and bottom layers of water, the temperature is 5°C or more, salinity varies from 16‰ in the west to 12-13‰ in the central part and 10‰ in the north of the sea. In years of increased water inflow, salinity increases in the west to 20‰, in the central part of the sea to 14-15‰, and in years of decreased influx it drops in the middle parts of the sea to 11‰.

Ice usually appears in early November in the north of the Gulf of Bothnia and reaches its greatest extent in early March. At this time, a significant part of the Riga, Finnish and Bothnian gulfs is covered with motionless ice. The central part of the sea is usually ice-free.

The amount of ice in the Baltic Sea varies from year to year. In exceptionally severe winters, almost the entire sea is covered with ice; in mild winters, only the bays. The northern part of the Gulf of Bothnia is covered with ice 210 days a year, the middle part - 185 days; Gulf of Riga - 80-90 days, Danish Straits - 16-45 days.

The level of the Baltic Sea is subject to fluctuations under the influence of changes in wind direction and atmospheric pressure (progressive-standing long waves, seiches), influx of river waters and waters of the North Sea. The period of these changes varies from several hours to several days. Rapidly changing cyclones cause level fluctuations of up to 0.5 m or more off the coast of the open sea and up to 1.5-3 m at the tops of bays and bays. Particularly large rises of water, which are, as a rule, a consequence of the superposition of a wind surge on the crest of a long wave, occur in the Neva Bay. The greatest rise in water in Leningrad was noted in November 1824 (about 410 cm) and in September 1924 (369 cm).

Level fluctuations associated with tides are extremely small. The tides have irregular semidiurnal, irregular diurnal and diurnal patterns. Their size varies from 4 cm (Klaipeda) up to 10 cm (Gulf of Finland).

The fauna of the Baltic Sea is poor in species, but rich in quantity. The Baltic Sea is home to a brackish-water race of Atlantic herring (herring), Baltic sprat, as well as cod, flounder, salmon, eel, smelt, vendace, whitefish, perch. Among mammals - the Baltic seal. Intensive fishing is carried out in the Baltic Sea.

Russian hydrographic and cartographic work began in the Gulf of Finland at the beginning of the 18th century. In 1738, F.I. Soimonov published an atlas of the Baltic Sea, compiled from Russian and foreign sources. In the middle of the 18th century. Many years of research in the Baltic Sea were carried out by A.I. Nagaev, who compiled a detailed navigation guide. First deep-sea hydrological exploration in the mid-1880s. were carried out by S. O. Makarov. Since 1920, hydrological work was carried out by the Hydrographic Directorate and the State Hydrological Institute, and after the Patriotic War of 1941-45, extensive comprehensive research was launched under the leadership of the Leningrad branch of the State Oceanographic Institute of the USSR.