Salinity of waters oceans, is the main feature that distinguishes them from the waters of the land.
In oceanology, deer sea water is defined as the total amount of solids in grams (all substances dissolved in water, not just salts) dissolved in 1 kg of sea water, provided that all halogens are replaced by an equivalent amount of chlorine, all carbonates are converted to oxides, organic matter is burned. Salinity measured in "‰" ("ppm").
The average salinity of the world's oceans is 35 ‰. , that is, in 1 kg of sea water, an average of 35 grams of various substances are dissolved. A water sample taken in the Bay of Biscay, with a salinity close to 35 ‰, is taken as a standard. It is used to calibrate instruments.
The salinity of sea waters is of ancient origin; salts entered the ocean water simultaneously with the emergence of the oceans themselves. During the period of education earth's crust, which occurred at high temperatures, various substances were released from the earth into the atmosphere in the form of gases. The subsequent cooling of the earth's crust caused heavy rains. They took those substances with them and filled huge pits on the surface of the earth.
The salinity of the ocean waters is not the same everywhere. Salinity is influenced by the following processes:
1.Evaporation of water.
2. Formation of ice.
3. Precipitation.
4.River water runoff.
5. Melting ice.
At the same time, evaporation and ice formation contribute to an increase in salinity, while precipitation, river water runoff, and melting ice lower it.
The influence of biochemical processes on salinity is negligible.
Water mixing (diffusion) and advection of salts by currents are also involved in the formation of salinity. The salinity of deep and near-bottom waters is determined exclusively by these 2 processes, since there are no internal sources and sinks of salts at depths and at the bottom of the ocean.
The main role in the change in salinity belongs to evaporation and precipitation. Therefore, the salinity of the surface layers, as well as the temperature, depends on climatic conditions associated with geographical location seas.
The Red Sea is the saltiest sea in the world's oceans. Its salinity reaches 42 ‰. This is due to its location in tropical latitudes. There is very little atmospheric precipitation here, the evaporation of water from strong heating by the sun is very large. The water evaporates from the sea, but the salt remains. Not a single river flows into the Red Sea, and the only source of replenishment of the water balance is the flow of water from Gulf of Aden. Approximately 1,000 cubic meters of gas is brought into the sea through the Bab el-Mandeb Strait during the year. km of water is more than is taken out of it. According to calculations, it takes 15 years for the complete exchange of the waters of the Red Sea.
The water in the Red Sea is evenly mixed all year round. In winter, surface waters cool down, become denser and sink down, and rise up warm waters from depth. In summer, water evaporates from the surface of the sea, and the rest becomes more salty, heavy and sinks down. Less salty water rises in its place. Therefore, the Red Sea is the same in temperature and salinity throughout its volume.
Hot brine troughs have also been found in the Red Sea. Currently, more than 20 such depressions are known. The depressions are heated from below by the internal heat of the Earth. The brines in the depressions do not merge with the surrounding water, but are clearly distinguished from it and look like muddy ground covered with ripples, or like swirling fog. The content of many metals, including precious ones, in the brines of the Red Sea is hundreds and thousands of times higher than in ordinary sea water.
The absence of river runoff and rain streams, and hence dirt from land, ensures the transparency of the Red Sea water and the constancy of its salinity.
In the Baltic Sea, water forms layers of different salinity. Average salinity Baltic Sea not higher than 1%o, and its surface waters -5-8°/oo. This is due to the fact that this sea is located in a climatic zone where evaporation is less, but more precipitation falls. In coastal areas for salinity big influence renders river runoff, and in the polar regions - the processes of formation and melting of ice. When water freezes and sea ice builds up, part of the salts drain into the water and salinity increases; when melting sea ice and icebergs, it is decreasing. Fresh water enters the Baltic Sea from 250 rivers, while salt water enters only from the narrow Danish straits. As a result, salinity is highest in
Southwest of the Baltic, and decreases as you move to the east. However, the overall picture can be disturbed by currents.
Salty waters, falling into the Baltic Sea, sink to the bottom, forming a highly saline layer there. At depths of 70-80 meters, the salt content increases dramatically. This jump is called a halocline. A halocline occurs where the movements of the water mass caused by storms cease to reach.
Dead organic matter constantly sinks to the bottom of the sea. About once every 15 years, such large masses of water enter the Baltic Sea from the North Sea that stagnant water is pushed aside. The stagnant waters pushed into the northern and deepest parts of the Baltic gradually mix with the surrounding water there. At the beginning of the movement of stagnant waters, an increase in the salinity of the waters of the Baltic Sea occurs.
Baltic Seaaccording to its location it belongs to the Atlantic Ocean, and according to the classification of the seas - to the Mediterranean inland seas. It is surrounded by land on all sides, and only through the narrow and shallow straits of Øresund, the Great Belt and the Small Belt it connects to the North Sea, and then to the Atlantic.
The area of the Baltic Sea is 386 thousand square kilometers. It is relatively shallow (depths of 40 to 100 meters predominate), and the greatest depth is 459 meters (Landsort depression north of Gotland). Due to the influx of a large amount of river water and poor water exchange with the ocean, the Baltic Sea has low salinity: a liter of water contains from 4 to 11 grams of salts (the waters of the World Ocean contain up to 35 grams of salts).
Coastline The Baltic Sea is indented by numerous bays. These include the Curonian and Kaliningrad bays - shallow lagoons separated from the sea by narrow spits. They are connected to the sea by straits only 300-400 meters wide.
The Curonian Lagoon has total area 1.6 square kilometers. Of these, 1.3 thousand square kilometers belongs to the Kaliningrad region. The bay is shallow - its average depth is about four meters, and the largest, southeast of the village of Rybachy, is six meters.
The volume of the water masses of the bay exceeds six cubic kilometers, but three and a half times more river water flows here every year. Water is brought into the sea through a narrow strait near Klaipeda. A large inflow of water determines a higher water level than in the sea in the Curonian Lagoon - the average excess is fifteen centimeters. The flow of water in the strait is directed from the bay to the sea, and sea water almost never enters the bay. Therefore, it is freshwater, except for the northernmost part.
The temperature regime of the waters of the Curonian Lagoon differs from that of the open part of the southeast Baltic. It is known that the sea near the Kaliningrad coast freezes only in severe winters. In the Curonian Lagoon, the ice lasts from two to five months, and its thickness can reach 70-100 centimeters. Ice usually forms in early December, and melts in March - April. In summer, due to shallow water, the bay warms up well, in July the water temperature reaches 22-27 ° C. This is much higher than in the coastal part of the open sea, where the average monthly temperatures of the warmest month are 18 C.Coast of the Baltic Sea
The Kaliningrad seashore is an integral part of the "Golden Frame" of Europe. It stretches for almost 150 km and includes the coast of the Sambian Peninsula, parts of the Vistula and Curonian sand spits. The latter, with their dune landscape and great length (about 100 km), are unique natural formations of the Baltic Sea.
Within the Kaliningrad region is the northern part of the Vistula Spit 25 km long and the southern part curonian spit 49 km long. The indigenous shores of the Sambian Peninsula account for 74 km. The total length of the sea coast is 148 km. Its formation took place earlier and is taking place now under the influence of storm waves, coastal currents and wind. It is directly related to the history of the development of the Baltic Sea, which appeared as a modern body of water only in the late glacial period.
The Sambian Peninsula is formed by an uplifted ledge of Cenozoic rocks overlain by glacial deposits, and therefore sea shore bordered by coastal cliffs. The height of the coastal ledges reaches 50-61 m at Cape Taran, gradually decreasing to 5-7 m as it approaches the marginal areas of the peninsula and the city of Baltiysk in the south and the city of Zelenogradsk in the east, where the Cenozoic rocks are much or partially cut off by the glacier. The coastline of the peninsula is poorly dissected, which is explained by the peculiarities of the geological structure of the coast. Capes separating gentle bays are usually confined to outcrops of boulder moraine loams in the coastal ledge (Capes Taran, Obzorny, Bakalinsky, Kupalny, Gvardeisky). The concavities of the coast correspond to the areas of distribution of easily eroded sandy-clayey water-glacial deposits (bush Pokrovskaya, Yantarnenskaya, Donskaya, Filinskaya, Svetlogorskaya, Pionerskaya).
Along the coast of the Sambian Peninsula, with the exception of its individual sections, there is a beach, the width of which varies from 5-7 m within the ledges of the coast and capes to 40-50 m - in bays and concavities. In front of the coastal protection walls on Cape Taran, near the village. Lesnoye beach is practically absent as a result of the wave breaking effect. A sharp expansion of the beach (up to 150 m) is noted in those areas where it is artificially replenished with loose material.
On the capes, where the coast is deep and the waves easily reach the coastal cliffs, the beaches are composed of boulder-pebble material. In the concavities of the coast and bays, where the coast is shallow and protected from the onslaught of waves by a wide beach, their structure is dominated by sand accumulations with an admixture of pebbles and gravel in the waterfront zone. The thickness of beach deposits ranges from 0 to 2.4 m.
History of the Baltic Sea
As the Baltic lowland was freed from ice, the formation of the Baltic Sea began. Hypsometry features of underwater terraces located at different depths of the sea, as well as spore-pollen analysis of vegetation growing along the shores of the Baltic Lake, and then the sea, made it possible to establish several stages in its development.
Following the melting of the glacier, the entire Baltic depression was occupied by a vast fresh Baltic glacial lake, which existed for about 4 thousand years; 10 thousand years ago, the lake through the Danish straits connected with the pool Atlantic Ocean and as a result of the transgression, the Yoldian Sea arose, which existed for about 500 years.
In the future, communication with the ocean is broken due to a drop in its level and the possible rise of Fennoscandia. During the period that took place 9500 - 8000 years ago, the freshwater lake Ancylus appeared. The filling of Lake Ancylus and the rise in the ocean level led to the erosion of the Danish Straits and the connection of the lake with the North Sea. As a result of the transgression that began, the Litorin Sea arose, which existed in the period of about 3.5 thousand - 4.5 thousand years ago. The next stage in the development of the basin is the Limnea Sea, the level of which gradually dropped, approaching the modern Mia Sea. The current sea level lies 6 m below the Littorina Sea, which has led to the swamping of the coastal lowland around the Baltic Sea.
At present, the level of the World Ocean, and hence the seas included in its basin, is rising at a rate of 1.5 mm per year, or 1.5 m per millennium. In combination with the tectonic lowering of the coast of the region at a rate of about 1-2 mm per year, the total level rise is 2.5 - 3.5 m per millennium. This means that on the territory of the Kaliningrad region, the coasts are in a transgressive regime, i.e. the sea comes to land.
In general, the Holocene is subdivided into five climatochronological phases: preboreal, boreal, Atlantic, subboreal, and subatlantic. This scheme was developed at the beginning of the 20th century. Scandinavian scientists on the basis of palynological studies of peat deposits in Scandinavia. It is widely used for the stratification of marine sediments of the post-glacial Baltic Sea and adjacent territories, including the Kaliningrad region.
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 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. V central regions In the sea, quite extensive spaces 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. Winds northern directions cause 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 number waters are 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°C, a 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 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 slightly lower near the coast than in open parts sea, while on the western coast it is slightly higher than on the eastern coast. 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 eastern part Baltics. 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 east coast sea further than along the western. 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 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 saline Kattegat waters, especially in basins at the horizons 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 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 in the east - up to 10-15 m, 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 south 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 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 the current along the Finnish coast rises to the north, bends around north coast bay and along the coast of Sweden descends to the south. 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. 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. The combined effect of wind and a sharp change atmospheric pressure(during the passage of cyclones) cause seiche fluctuations in the level surface with a period of 24-26 hours. 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 (around the beginning of November) ice forms in the northeastern part of the Gulf of Bothnia, in small bays and off the coast. Then the shallow areas of the Gulf of Finland begin to freeze. The maximum development of the ice cover reaches in early March. By this time, the still ice occupies northern part Gulf of Bothnia, the region of the Aland skerries and the eastern part of the Gulf of Finland. Floating ice occurs in the open areas of the northeastern part of the sea.
The 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 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 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. TO unique species applies to acne.
In fishing, the main place is occupied by herring, sprat, cod, river flounder, smelt, perch and various types of freshwater fish.
Heavily cut into the mainland. Its not as severe as the climate of the Arctic seas, although the Baltic Sea is located in the northwestern part of Russia. This sea is almost completely limited by land. Only from the southwest is this sea connected to the waters by various straits. The Baltic Sea belongs to the type of inland seas.
The shores that this sea washes have a different origin. Quite complicated and. The Baltic Sea has a rather small depth, due to the fact that it is located within the boundaries of the continental shelf.
The greatest depth of the Baltic Sea was recorded in the Landsort Basin. The Danish Straits are characterized by shallow depths. The depth of the Great Belt is 10 - 25 m, the Small Belt - 10 - 35 m. The waters of the Sound have a depth of 7 to 15 m. The shallow depths of the straits interfere with the unhindered exchange of water between the Baltic Sea and. The Baltic Sea covers an area equal to 419 thousand km2. The volume of water is 321.5 km3. The average water depth is about 51 m. The maximum sea depth is 470 m.
The climate of the Baltic Sea is influenced by its location in the zone of temperate latitudes, the proximity of the Atlantic Ocean and the location of a large part of the sea inside the mainland. All these factors contribute to the fact that the climate of the Baltic Sea is in many ways close to the maritime climate of temperate latitudes, and there are also some features of the continental climate. Due to the rather significant extent of the sea, there are some distinctive features of the climate in different parts of the sea.
In the Baltic, it is largely due to the influence of the Icelandic low, the Siberian and. Depending on whose influence is dominant, seasonal features differ. In autumn and winter, the Baltic Sea is influenced by the Icelandic Low and the Siberian High. As a result of this, the sea is in power, which spread in autumn from west to east, and in winter to the northeast. This period is characterized by cloudy weather with large southwestern and western winds.
In January and February, when the lowest temperature is observed, the average monthly temperature in the central part of the sea is -3°C, and in the north and east - 5-8°C. With the strengthening of the Polar High, cold ones enter the Baltic Sea. As a result, it drops to – 30 – 35°С. But such cold snaps are quite rare and, as a rule, they are short-lived.
In the spring-summer period, the Siberian High loses its strength, and the Azores and, to a lesser extent, the Polar High have a dominant effect on the Baltic Sea. At this time, the sea is observed. Cyclones coming to the Baltic from the Atlantic Ocean are not as significant as in winter. All this causes the unstable direction of the winds, which have low speeds. In the spring season, northerly winds have a great influence on the weather, they bring cold air.
In summer, winds from the western and northwestern directions prevail. These winds are predominantly weak or. Due to their influence, cool and humid weather is observed in summer. The average July temperature reaches + 14 - 15°С in the Gulf of Bothnia and +16 - 18°С in other areas of the sea. Very rarely, warm air masses enter the Baltic, which cause hot weather.
The temperature of the waters of the Baltic Sea depends on the specific location. In winter, the water temperature near the coast is lower than in the open sea. In the western part, the sea is warmer than in the eastern part, which is associated with the cooling effect of the land. In summer, the coldest waters are near the western coasts in the central and southern zones of the sea. Such a distribution of temperatures is due to the fact that the western ones move the heated upper waters from the western shores. Their place is taken by cold deep waters.
Coast of the Baltic Sea
Approximately 250 large and small rivers carry their waters into the Baltic Sea. During the year they give the sea about 433 km 3, which is 2.1% of the total volume of the sea. The most full-flowing are: the Neva, which pours 83.5 km 3 per year, the Vistula (30.4 km 3 per year), the Neman (20.8 km 3 per year) and the Daugava (19.7 km 3 per year). In different areas of the Baltic Sea, the proportion is not the same. For example, in the Gulf of Bothnia, rivers give 188 km 3 per year, the volume of continental waters is 109.8 km 3 / year. The Gulf of Riga receives 36.7 km 3 /year and in the central part of the Baltic is 111.6 km 3 /year. Thus, the eastern regions of the sea receive more than half of all continental waters.
During the year, rivers bring an unequal amount of water to the sea. If the full flow of rivers is regulated by a lake, as, for example, near the Neva River, then a greater flow occurs in the spring-summer period. If the full flow of rivers is not regulated by lakes, as, for example, near the Daugava River, then the maximum flow is noted in spring and a slight increase in autumn.
are practically not observed. The current affecting surface waters arises under the influence of winds and river runoff. In winter, the waters of the Baltic Sea are covered with ice. But during one and the same winter, the ice can melt several times and again bind the waters. This sea is never completely covered with ice.
Fishing is widely developed in the Baltic Sea. Baltic herring, sprat, cod, whitefish, lamprey, salmon and other types of fish are caught here. Also in these waters, a large amount of algae is mined. There are many marine farms on the Baltic Sea where the most sought-after fish species are grown. There are a large number of placers on the coast of the Baltic Sea. Amber mining works are carried out in the region. There is oil in the bowels of the Baltic Sea.
Navigation is widely developed in the waters of the Baltic Sea. Sea transportation of various goods is constantly carried out here. Thanks to the Baltic Sea, it maintains close economic and trade relations with Western European countries. There are a large number of ports on the coast of the Baltic Sea.
HGI AMOLExtreme north point The Baltic Sea is located near the Arctic Circle (65 ° 40 "N), the extreme south 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
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:
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
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 most deep basin- Landsortskaya ( 58°38′ N. sh. 18°04′ in. d. HGI AMOL) with a maximum sea depth of 470 meters. In the Gulf of Bothnia maximum depth- 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.
see also
Notes
- // Military encyclopedia: [in 18 volumes] / ed. V. F. Novitsky [i dr.]. - St. Petersburg. ; [ M. ] : Type. t-va I. D. Sytin, 1911-1915.
