Southern coast of the Baltic Sea. Seas of Russia - Baltic Sea
Baltic Sea(Old Russian Varangian, Lith./Lat. Baltijos/Baltijas jūra, Liv. Vālda mer, Est. Läänemeri, Finnish Itämeri, Swedish Östersjön, Dan. Østersøen, German Ostsee, Kashubian Bôłt, Polish Morze Bałtyckie, Bałtyk, Saami Nuortamearra) inland sea of the Atlantic Ocean. It is located off the coast of Northern and Central Europe. It is connected to the North Sea by the Danish Straits. Square- 419 thousand km2, almost equal to the area of the Black Sea (422 thousand km2). The length of the coastline of the Baltic is 7 thousand km. The northernmost point of the Baltic Sea is located near the Arctic Circle, the southernmost point is near Wismar, the westernmost point is in the Flensburg region, and the easternmost point is in the St. Petersburg region. The coast is distributed among the countries as follows: Sweden owns 35% of the coast, Finland - 17%, the former USSR had 25% of the coast, Russia now has about 7% (about 500 km). The rest belongs to Lithuania, Latvia, Estonia, Poland, Germany, Denmark.
Dominant Depths 40-100 m, maximum - 470 m. The greatest depths are in the north, off the coast of Sweden, on average 60-150 m. The Curonian Lagoon is considered the shallowest, where the depths do not exceed 5 meters. In some areas there are underwater shoals, which greatly complicates navigation.
From the history of the Baltic Sea
Formed at the site of a large tectonic trough earth's crust in the Alpine era of mountain building at the junction of the Baltic crystalline shield with the sedimentary sequence of the Russian Platform. After the melting of the ice sheet, there was a vast expanse of water that connected the North Sea with the White Sea. This process began 18-20 thousand years ago. 13 thousand years ago, the glacier finally left the territory of Lithuania. When the ice melted, the water filled the depressions in the Baltic Sea - this is how the cold glacial Baltic Lake was formed, which in different periods connected to the Atlantic Ocean. This lake existed 13-10 thousand years ago.
Somewhat later, the glacier left the Central Swedish lowland. The resulting channel connected the lake with the Atlantic Ocean. With the new arrival of the glacier, the level of the glacial lake began to rise, and with its departure it dropped by 40 - 50 m. Large areas of land were opened up. This is how the Yoldia Sea was formed, which got its name from the abundance of mollusks that lived in it (from lat. Yoldia arctica). The compensatory uplift of the continental plate, which took place in the southern part of the Baltic Sea basin, deprived the Yoldian Sea of communication with the Atlantic Ocean. The rivers have sharply reduced the salinity of this water basin and raised its level. So 9,000 years ago, Ancylus Lake was formed (the name comes from the name of the mollusks Ancylus fluviatilis). Its deposits were preserved at a depth of 16-18 m. At this stage of the formation of the Baltic Sea, the climate was warm and dry.
7.5 thousand years ago, the salty waters of the Atlantic Ocean broke into Lake Antsylovo, and the Littorina Sea was formed (the name comes from the name of the mollusks Littorina littoraea). 4 thousand years ago, the Baltic Sea gradually acquired a modern look: its salinity decreased, modern animals and plants begin to predominate.
Salinity
The Baltic Sea is the largest sea in the world with low
The presence of certain fish species in a particular area is also associated with varying degrees of salinity of the water. The flora and fauna of the Baltic Sea have a transitional character from the sea to a freshwater lake. So, often sea clams, like oysters, Mua
trunata, Littorina littoralis, etc. are only in the app. parts of the sea where the water is saltier. Along with marine fish, freshwater fish also live in this sea - perch, bream, grayling, whitefish and others. In areas of high salinity and with great depth, cod predominate, different kinds herring, herring, flounder, kalkan, goby, eelpout, sprat. Less often, but still there are salmon - sea trout (trout), whitefish and Baltic salmon (a kind of salmon). A lot of three-spined stickleback, small fish. The Aland Islands have seals.
Tidal fluctuations in the Baltic are only a few centimeters. This is explained by the fact that the tidal ocean wave, reaching the coast of Denmark, loses its strength by almost 90% or subsides completely. However, the water level in the Baltic Sea changes frequently and abruptly, due to the western and northwestern winds that drive water into the Kaliningrad and Curonian Lagoons, as if locking the weak river currents in the channels, preventing them from entering the sea. If the winds blow from the south and east, the opposite occurs, and in some places the sea moves away from the coast, forming islands of land, interspersed with areas of sandbars. This is also related to fluctuations in water temperatures. In summer, the water temperature is kept in the range from 14° to 20° (sometimes higher, but the average level is 18-19°). Heated warm water is driven away from the shore by frequent winds in these places, and bottom, deep currents bring colder layers of water. So in a short time the water temperature can drop to 8-9 °. Summer in the Baltic is not hot, but winter, in turn, is not cold. In winter, the Baltic Sea freezes, but this happens mainly along the coast, where solid ice forms in a small strip or fills the bays, and the Curonian Lagoon freezes earlier than the Kaliningrad Lagoon. It should be noted that the reliability of the ice cover of bays is not the same everywhere, so fishing from such ice is always associated with a certain risk to life. In addition, in some places the ice has large irregularities and has a significant drift speed. Often, cracks and faults can be observed along the coast, especially if windy weather has set in. The heap of ice sometimes takes on bizarre forms, especially if blocks of ice run into rocks or sandbars. Autumn and winter the role of the winds is increasing. South-westerly Atlantic winds carry heat, and long thaws come, accompanied by sleet and rain.
The most dangerous time for fishing is accompanied by strong winds. In a word, the wind is the decisive factor that "makes the weather" throughout the Baltic Sea. Winds in Palanga (Lithuania) have interesting names: maritime(western), predominant in this part of the coast; terrestrial- east wind blowing towards the sea; goat- southeast; Finnish- northwestern. And there is more amber wind(Bernsteinwind - German Bernsteinwind) a weakening north-west wind from the sea on the Baltic coast, which, with sea swell, helps to wash out the so-called amber grass from the exposed amber layers and drives algae with amber to the shore. They flow into the Baltic Sea rivers: Neva, Narva, Western Dvina (Daugava), Venta, Neman, Vistula, Oder. Large islands: Bornholm (Denmark), Gotland, Öland (Sweden), Saaremaa, Hiiumaa (Estonia), Rügen, Usedom (Germany), Alandia. bays: Botanical, Finnish, Riga, Curonian.
Gulf of Riga- a bay in the east of the Baltic Sea between Latvia and Estonia. Partially separated from the rest of the sea by the Estonian island of Ezel (Saaremaa). The most important cities along the coast of the Gulf of Riga are Riga and Pärnu. The Estonian island of Ruhnu is located in the Gulf of Riga. Total area: 16300 km², max. length: 174 km, max. width: 137 km, max. depth: 67 m, flowing rivers : Zap. Dvina (Daugava), Courland Aa (Lielupe), Livonian Aa (Gauja), Salis (Salats).Main ports: St. Petersburg, Kaliningrad (Russia), Tallinn (Estonia), Riga, Ventspils, Liepaja (Latvia), Klaipeda (Lithuania), Gdansk-Gdynia, Szczecin (Poland), Rostock, Kiel, Lübeck (Germany), Copenhagen, Malmö , Stockholm, Luleå, Umeå, Gävle, Sundsval, Hudikval (Sweden), Turku, Helsinki, Rauma, Pori, Vaasa, Kokkola (Finland).
Resorts: Pärnu (Estonia), Jurmala, Liepaja, Pavilosta (Latvia), Palanga, Sventoji, Neringa (Lithuania), Kolobrzeg, Ustka (Poland), Heringsdorf, Warnemünde, Binz (Germany), etc.
Østersøen, Fin. Itämeri, est. Läänemeri, Latvian. Baltijas jūra, lit. Baltijos jūra) - the inland sea of Eurasia, located in Northern Europe (partially washes 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 region (9°10"E), the easternmost point is in the St. Petersburg region (30°15"E)
The surface area of the sea (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
Antsyl Lake about 8.7 thousand years ago. The remains of a glacier are still visible on the peaks of the Scandinavian mountains
The severity of the ice caused a significant deflection of the earth's crust, part of which was below sea level. With the end of the last ice age, these territories are freed from ice, and the depression formed by the trough of the crust is filled with water:
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Physical-geographical sketch
The Baltic Sea goes deep into the land of Europe, washes the shores of Russia, Estonia, Latvia, Lithuania, Poland, Germany, Denmark, Sweden and Finland.
Large bays of the Baltic Sea: Finnish, Bothnian, Riga, Curonian (freshwater bay, separated from the sea by the sandy Curonian Spit).
Major rivers emptying into the Baltic Sea are the Neva, Narva, Zapadnaya 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 depth of the sea is 51 meters. Small depths (up to 12 meters) are observed in the areas of shoals, banks, near the islands. There are several basins in which depths reach 200 meters. The deepest basin is Landsortskaya ( 58°38′ N. sh. 18°04′ in. 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 - uneven, rocky. In coastal areas, sands are common among the bottom sediments, but most of the seabed is covered with deposits 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 runoff. The brackish surface waters of the Baltic Sea through the Danish Straits go to the North Sea, and the salty waters of the North Sea enter the Baltic Sea with a 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 go both to the North and to the Baltic Sea.
In 2003, 21 cases of chemical weapons in fishing nets - all are clots of mustard gas with a total weight of approximately 1005 kg.
In 2011, paraffin was released 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 hindered by stringent environmental requirements associated with an insignificant water exchange between the sea and the ocean, anthropogenic pollution of water with runoff from the territory of coastal states, contributing to enhanced eutrophication.
The Nord Stream gas pipeline is laid along the bottom of the Baltic Sea.
Sea transport
Recreational resources
Titles
First time title Baltic Sea(lat. mare balticum) is 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 Varangian by sea. Historically, in Russian the sea was called Varangian, and then Sveisky(Swedish). Under Peter I, the German name was strengthened - Ostsee sea. Since 1884, the modern name has been used.
BALTIC SEA (Late Latin - Mare Balticum, among the ancient Slavs - the Varangian Sea or the Svean Sea), the inland sea of the Atlantic Ocean, between the Scandinavian Peninsula and the mainland shores of North-Western Europe. Washes the shores of Sweden, Finland, Russia, Estonia, Latvia, Lithuania, Poland, Germany, Denmark. In the southwest it is connected to the North Sea by the Danish Straits. The maritime boundary of the Baltic Sea runs along the southern entrances of the Øresund, Great Belt and Small Belt straits. The area is 419 thousand km 2, the volume is 21.5 thousand km 3. The greatest depth is 470 m. Depths above the rapids of the Danish Straits: Darser - 18 m, Drogden - 7 m. The cross section above the rapids is 0.225 and 0.08 km 2, respectively, which limits water exchange with the North Sea. The Baltic Sea juts deep into the Eurasian continent. The heavily indented coastline forms numerous bays and coves. The largest bays: the Gulf of Bothnia, the Gulf of Finland, the Gulf of Riga, the Curonian Lagoon, the Szczecin Bay, the Gulf of Gdansk. The shores of the Baltic Sea in the north are high, rocky, mostly of skerry and fjord types, in the south and southeast - for the most part low-lying, lagoon type, with sandy and pebble beaches. The largest islands: Gotland, Bornholm, Saaremaa, Muhu, Hiiumaa, Eland, Rügen. There are many small rocky islets - skerries, located along the northern shores (there are over 6 thousand in the Aland Islands group).
Relief and geological structure of the bottom. The Baltic Sea is shallow, lies completely within the shelf, depths up to 200 m occupy 99.8% of its area. The most shallow are the Gulfs of Finland, Bothnia and Riga. These areas of the bottom have a leveled accumulative relief and a well-developed cover of loose sediments. Most of the bottom of the Baltic Sea is characterized by a strongly dissected relief. The bottom of its basin has depressions delimited by elevations and the bases of the islands: in the west - Bornholmskaya (105 m) and Arkonskaya (53 m), in the center - Gotlandskaya (249 m) and Gdanskaya (116 m); to the north of the island of Gotland, the deepest depression - Landsortskaya (up to 470 m) stretches from the northeast to the southwest. Numerous stone ridges, ledges are traced in the central part of the sea - continuations of glints stretching from the northern coast of Estonia to the northern tip of the island of Öland, underwater valleys, glacial-accumulative landforms flooded by the sea.
The Baltic Sea occupies a depression in the west of the ancient East European Platform. The northern part of the sea is located on the southern slope of the Baltic Shield; the central and southern parts belong to a large negative structure of the ancient platform - the Baltic syneclise. The extreme southwestern part of the sea enters the limits of the young Western European platform. The bottom in the north of the Baltic Sea is composed mainly of Precambrian age complexes overlain by a discontinuous cover of glacial and modern marine deposits. Silurian and Devonian sediments take part in the bottom structure in the central part of the sea. The ledges traced here are formed by the Cambrian-Ordovician and Silurian rocks. The Paleozoic complexes in the south are overlain by a thick layer of glacial and marine sediments.
During the last ice age (late Pleistocene), the Baltic Sea depression was completely covered by an ice sheet, after which the Baltic Glacial Lake was formed. At the end of the late Pleistocene, about 13 thousand years ago, the lake joined the ocean, and the depression was filled with sea water. Communication with the ocean was interrupted in the interval of 9-7.5 thousand years ago, followed by a marine transgression, the deposits of which are known on the modern coast of the Baltic Sea. Uplift continues in the northern part of the Baltic Sea, at a rate of up to 1 cm per year.
Bottom sediments at depths of more than 80 m are represented by clayey silts, under which lies banded clay on glacial deposits; at shallower depths, silt is mixed with sand; sands are common in coastal areas. There are boulders of glacial origin.
Climate. The Baltic Sea is characterized by a temperate maritime climate with continental features. Its seasonal features are determined by the interaction of baric centers: the Icelandic Low and the Azores High in the west and the Siberian High in the east. Cyclonic activity reaches its greatest intensity in the autumn-winter months, when cyclones bring cloudy, rainy weather with strong western and southwestern winds. The average air temperature in February is from -1.1°С in the south, -3°С in the central part of the sea, to -8°С in the north and east, in the northern part of the Gulf of Bothnia to -10°С. Rarely and for a short time, the cold arctic air penetrating the Baltic Sea lowers the temperature to -35°C. In summer, westerly winds also blow, but of low strength, bringing cool, humid weather from the Atlantic. The air temperature in July is 14-15°C in the Gulf of Bothnia and 16-18°C in the rest of the sea. Rare inflows of warm Mediterranean air cause short-term temperature rises up to 22-24°C. Annual precipitation varies from 400 mm in the north to 800 mm in the south. The greatest number of days with fogs (up to 59 days a year) is observed in the south and in the central part of the Baltic Sea, the smallest (22 days a year) - in the north of the Gulf of Bothnia.
Hydrological regime. The hydrological conditions of the Baltic Sea are determined by its climate, significant inflow of fresh water and limited water exchange with the North Sea. About 250 rivers flow into the Baltic Sea. River flow averages 472 km 3 per year. The largest rivers: Neva - 83.5 km 3, Vistula - 30, Neman - 21, Western Dvina - 20 km 3 per year. Freshwater runoff is unevenly distributed throughout the territory. The Gulf of Bothnia receives 181, the Gulf of Finland - 110, the Gulf of Riga - 37, central part Baltic Sea - 112 km 3 per year. The amount of fresh water coming with precipitation (172 km 3 per year) is equal to evaporation. Water exchange with the North Sea averages 1660 km 3 per year. Fresher waters with a surface runoff flow from the Baltic Sea to the North Sea, salty North Sea water with a near-bottom current flows through the straits from the North Sea. Strong westerly winds usually increase the inflow, east winds - the outflow of water from the Baltic Sea through the Danish straits.
The hydrological structure of the Baltic Sea in most areas is represented by surface and deep water masses separated by a thin intermediate layer. The surface water mass occupies a layer from 20 to (in some places) 90 m, its temperature during the year varies from 0 to 20 ° C, salinity is usually in the range of 7-8‰. This water mass is formed in the sea itself as a result of the interaction of sea water with fresh water, precipitation and river runoff. It has winter and summer modifications, which differ mainly in temperature. In the warm season, the presence of a cold intermediate layer is noted, which is associated with the summer heating of water on the surface. The deep water mass occupies a layer from 50-100 m to the bottom, its temperature varies from 1 to 15°C, salinity - from 10.0 to 18.5‰. Deep water is formed in the bottom layer as a result of mixing with high salinity water coming from the North Sea. The renewal and ventilation of bottom waters are highly dependent on the inflow of North Sea water, which is subject to interannual variability. With a reduction in the inflow of salt water into the Baltic Sea at great depths and in the depressions of the bottom topography, conditions are created for the appearance of dead sea phenomena. Seasonal changes in water temperature capture the layer from the surface to 50-60 m and usually do not penetrate deeper.
Wind waves develop especially strongly in autumn and winter with long and strong southwestern winds, when waves 5-6 m high and 50-70 m long are observed. The highest waves are observed in November. In winter, sea ice prevents the development of waves.
In the Baltic Sea, cyclonic (counterclockwise) water circulation is everywhere, complicated by eddy formations of different scales. The velocities of constant currents are usually about 3-4 cm/s, but in some areas they sometimes increase to 10-15 cm/s. Due to the low velocities of the current, they are unstable, their pattern is often disturbed by the action of winds. Storm winds cause strong wind currents with speeds of up to 150 cm/s, which quickly fade after a storm.
The tides in the Baltic Sea are weakly expressed due to a slight connection with the ocean, the height is 0.1-0.2 m. The surge fluctuations in the level reach significant values (at the tops of the bays up to 2 m). The combined action of the wind and sudden changes in atmospheric pressure cause seiche level fluctuations with a period of 24-26 hours. The magnitude of such fluctuations is from 0.3 m in the open sea to 1.5 m in the Gulf of Finland. Seiche waves with surge western winds sometimes cause a rise in the level at the top of the Gulf of Finland up to 3-4 m, which delays the flow of the Neva and leads to floods in St. Petersburg, sometimes catastrophic: in November 1824, about 410 cm, in September 1924 - 369 cm
The water temperature on the surface of the Baltic Sea varies greatly from season to season. In August, in the Gulf of Finland the water warms up to 15-17°C, in the Gulf of Bothnia 9-13°C, in the central part of the sea 14-18°C, in southern regions reaches 20°C. In February, in the open part of the sea, the water temperature on the surface is 1-3°C, in bays and bays below 0°C. The salinity of water on the surface is 11‰ at the exit from the Danish Straits, 6-8‰ in the central part of the sea, 2‰ and less at the tops of the Gulf of Bothnia and the Gulf of Finland.
The Baltic Sea belongs to the so-called brackish basins, in which the temperature of the highest density is above the freezing point, which leads to an intensification of the formation process sea ice. Ice formation begins in November in the bays and along the coast, later - in the open sea. IN harsh winters The ice cover occupies the entire northern part of the sea and the coastal waters of its central and southern parts. The thickness of landfast (fixed) ice reaches 1 m, drifting - from 0.4 to 0.6 m. Ice melting begins at the end of March, spreads from southwest to northeast and ends in June.
Research history. The first information about the exploration of the Baltic Sea is associated with the Normans. In the middle of the 7th century they penetrated into the Gulf of Bothnia, discovered the Aland Islands, in the 2nd half of the 7th-8th centuries they reached west coast The Baltics discovered the Moonsund archipelago, for the first time penetrated the Gulf of Riga, in the 9th-10th centuries they used the coast from the mouth of the Neva to the Gdansk Bay for trade and piracy. Russian hydrographic and cartographic work began in the Gulf of Finland in the early 18th century. In 1738, F. I. Soymonov published an atlas of the Baltic Sea, compiled from Russian and foreign sources. In the middle of the 18th century, A. I. Nagaev conducted many years of research, who compiled a detailed sailing chart of the Baltic Sea. The first deep-sea hydrological studies in the mid-1880s were carried out by S. O. Makarov. Since 1920, hydrological work has been carried out by the Hydrographic Office navy, the State Hydrological Institute (Leningrad), and from the 2nd half of the 20th century, extensive comprehensive research was launched under the guidance of the Leningrad (St. Petersburg) Department of the State Oceanographic Institute of the Russian Academy of Sciences.
Economic use. Fish resources consist of freshwater species living in the fresh waters of the bays (crucian carp, bream, pike, pike perch, chub), the Baltic salmon herd and purely marine species distributed mainly in the central part of the sea (cod, herring, smelt, vendace, sprat). Baltic herring, sprat, herring, smelt, river flounder, cod, perch, etc. are fished for. Eel is a unique object of fishing. Placers of amber are common on the coast of the Baltic Sea, mining is carried out near Kaliningrad (Russia). Oil reserves have been discovered at the bottom of the sea, and industrial development has begun. Iron ore is mined off the coast of Finland. The significance of the Baltic Sea as a transport artery is great. Large volumes of liquid, bulk and general cargo are transported across the Baltic Sea. A significant part of the foreign trade of Denmark, Germany, Poland, Russia, Lithuania, Latvia, Estonia, Finland, Sweden is carried out through the Baltic Sea.
The cargo turnover is dominated by oil products (from the ports of Russia and from the Atlantic Ocean), coal (from Poland, Russia), timber (from Finland, Sweden, Russia), pulp and paper (from Sweden and Finland), iron ore (from Sweden); important role also play machines and equipment, the major producers and consumers of which are countries located on the shores and in the basin of the Baltic Sea. The largest ports of the Baltic Sea: St. Petersburg, Kaliningrad (Russia), Tallinn (Estonia), Riga (Latvia), Gdansk, Gdynia, Szczecin (Poland), Rostock - Warnemünde, Lubeck, Kiel (Germany), Copenhagen (Denmark), Malmö , Stockholm, Luleå (Sweden), Turku, Helsinki, Kotka (Finland). In the Baltic Sea, maritime passenger and ferry traffic: Copenhagen - Malmö, Trelleborg - Sassnitz (railway ferries), Nortelje - Turku (car ferry), etc. There are many resort places on the southern and southeastern coasts.
Ecological state. The Baltic Sea, which has a difficult water exchange with the World Ocean (water renewal lasts about 30 years), is surrounded by industrialized countries and is experiencing an extremely intense anthropogenic load. Main ecological problems associated with the disposal of chemical weapons at the bottom of the sea, the discharge of sewage from large cities into the sea, the washing off of chemical fertilizers used in agriculture, and especially with shipping - one of the most intensive in the world (mainly oil tankers). After the entry into force of the Convention for the Protection of the Marine Environment of the Baltic Sea in 1980, the ecological situation improved due to the introduction of a large number of treatment facilities sewage, reducing the use of chemical fertilizers, monitoring the technical condition of ships. The concentration of toxic substances such as DDT and polychlorinated biphenyls, petroleum hydrocarbons has decreased. The content of dioxins in the Baltic herring is 3 times lower than the MPC, the gray seal population has recovered. The issue of giving the Baltic Sea the status of a particularly vulnerable sea area is being considered.
Lit.: Terms. Concepts. Reference tables. M., 1980; Hydrometeorological conditions of the shelf zone of the seas of the USSR. L., 1983. T. 1. Issue. 1: Baltic Sea without bays; Atlantic Ocean. L., 1984; Biological resources of the Atlantic Ocean. M., 1986; Pushcharovsky Yu. M. Tectonics of the Atlantic with elements of nonlinear geodynamics. M., 1994; Hydrometeorology and hydrochemistry of the seas of the USSR. SPb., 1994. T. 3. Issue. 2; Zalogin B. S., Kosarev A. N. Morya. M., 1999.
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) is it 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. The depths above the rapids 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 in winter, the Icelandic Low and the Siberian High interact intensively, which intensifies 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 distinguishing features 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 places 0-90 m) with a temperature of 0 to 20°C, salinity of approximately 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 inflow 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 (°C) 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 there, 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 north and central regions In the basin, salinity decreases somewhat 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 coast. A decrease in surface salinity can also be traced from south to north, as well as in bays.
In the autumn-winter season, the salinity of the upper layers slightly increases due to a decrease in 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 until 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 result, 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 runoff, 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 saline Kattegat waters, especially in basins at levels of 50-70 m, a constant layer of a density jump (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 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 up 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. Stormy 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 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 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 northwest 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 flow 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 at individual points do not exceed 10–20 cm. Average level sea 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. 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 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 drive 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 (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, 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 spread of motionless 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. In severe winters, the thickness still ice reaches 1 m, and floating ice - 40-60 cm.
Melting begins in late March - early April. The release of the sea from ice goes from the southwest to the 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 sea views fish 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 and its coastline is an interesting place, saturated with memories of the Vikings, pacifying with its northern landscapes. It differs from other seas in the nature of the relief, temperature and features of the coastline. The Baltic is of great historical and geopolitical importance for Russia.
Geographical position
The Baltic Sea on the map is located in northern Europe and belongs to the Atlantic basin. It is limited to 54°46′ and 65°56′ North latitude and 9°57′ and 30°00′ East longitude. The extreme points that the Baltic Sea has on the map: near the Arctic Circle in the north, near Wismar in the south, the eastern one is near St. Petersburg and the western extreme point located in the Flensburg area.
Relief and depths
The bottom relief has slight differences from the outlines of the shores that limit 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 gently sloping, flat, with sandy beaches. The rocky shore and uneven rocky bottom are located in the northern part. The depth and relief of the Baltic Sea are different in different areas. The bottom has a very complex dissected surface. There are depressions that demarcate the uplands and bases of the islands that the Baltic Sea includes.
Depths elsewhere are shallow. For example, there are areas of pronounced accumulative relief - these are the shallow Gulfs of Finland, Riga and Bothnia.
Thus, the depth of the Baltic Sea is less than 200 meters. The Landsortskaya depression is different. The maximum depth of the Baltic Sea is located in this area and is about 470 meters. The Landsort Basin extends in a southwesterly direction. The rest are of lesser depth: Gotlandskaya - 249 m and Gdanskaya - 116 m in the central part of the sea, Arkonskaya - 53 m and Bornholmskaya - 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 (Small 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
The Neva Bay is the eastern section of the Gulf of Finland. At a distance of about 50 km from St. Petersburg is located on which the city of Kronstadt was built. The dam connects the island city and St. Petersburg, the highway is laid along the dam, so that 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, also originates there. It performs the function of a transport route, and is also popular with tourists in warm weather. Guests come here for the beauty of landscapes, and for duty-free shopping.
Coast
The coast of the Baltic Sea is diverse. Latvia has an accumulation-type coast 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. Leveled shores border most of the sea, in particular, 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 were formed by flooding of tectonic faults and river valleys. The skerry shore appeared as a result of flooding of territories with smoothed glaciers composed of crystalline rocks. These hills protrude above the sea surface in the form of many 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 segment of the coast, only 7%, instead of the former 25%, which brings annual losses to the state. Therefore, one port was laid in Primorsk near Vyborg, which will specialize in coal and dry cargo. And the second port is located in the Luga Bay, it will be oil loading.
Tectonic processes
To this day, the Baltic Sea continues to change. It has shallow depths compared to other parts of the Atlantic Ocean. Actually, this vast reservoir during its existence several times became a lake and again a sea due to tectonic processes.
At present time is running the next stage of separating the sea from the ocean and turning it into a fresh lake. It is characterized by the rise of the bottom of the Gulf of Bothnia during the year by several centimeters and flooding. southern coasts. Such processes create a need for northern ports to lengthen their piers. To save the low parts of the coast, embankments are being 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 is from 0 to 20 meters, in some places - from 0 to 90 meters with a temperature of 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 with the seasons. In summer, cold intermediate water masses are more pronounced, formed in connection with a significant warming of the sea surface.
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 straits of the Small and Great Belt and their mixing.
The transition layer includes water at a depth of 20-60 to 90-100 meters. They have a temperature of 2-6 degrees, are formed by mixing the waters of the deep and surface layers.
Features of water temperature in the Baltic Sea
Separate areas of the sea are distinguished by the peculiarities of the structure of the waters. So, Bornholmsky district has a warm layer (7-11 degrees) both in summer and in winter. It is formed by warm waters coming here from the more heated Arkona basin. In it, due to the shallow depth of the sea and the movement of waters in the horizontal plane, there is no cold intermediate layer in summer.
Seasonal change in temperature
In winter, in the open sea, the water temperature is higher than near the coast, while it differs from the western and eastern coasts. In February, the temperature is 0.7 degrees near Ventspils, in the open sea of the same latitude - approximately 2 degrees, near the western coast - 1 degree.
In summer, surface waters different parts The seas also differ in temperature. The 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, in the southern and central regions, as well as near the western coasts, the temperature drops. In addition, a cold current from the Gulf of Bothnia flows south along the coast of Sweden.
Seasonal fluctuations in water temperature are pronounced only in the upper 50-60 meters, deeper indicators change slightly. There are no temperature changes in cold weather, but with increasing depth, the indicators slightly decrease. 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 warm and the thermocline is more pronounced than in spring, a cold intermediate layer is preserved.
The depth, relief and other features of the Baltic Sea depend on many factors. This geographical position, being in northern latitudes, as well as being located on the continental plate.
