Features of the coastline of the Baltic Sea. Baltic Sea: salinity, depth, coordinates, description

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 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 somewhat lower near the coast than in the open parts of the sea, while it is slightly higher near the western coast than near the eastern one. Thus, the average monthly water temperature in February near Ventspils is 0.7°, at the same latitude in the open sea - about 2°, and near the western coast - 1°.

Water temperature and salinity at the surface of the Baltic Sea in summer

In summer, the temperature of surface waters is not the same in different parts of the sea.

The decrease in temperature near the western shores, in the central and southern regions is explained by the predominance of westerly winds, which drive the surface layers of water away from the western shores. Colder underlying waters rise to the surface. In addition, a cold current from the Gulf of Bothnia passes along the Swedish coast to the south.

Clearly pronounced seasonal changes in water temperature cover only the upper 50-60 m; deeper, the temperature changes very little. In the cold season, it remains approximately the same from the surface to the horizons of 50-60 m, and deeper it drops somewhat to the bottom.

Water temperature (°С) on a longitudinal section in the Baltic Sea

In the warm season, the increase in water temperature as a result of mixing extends to horizons of 20–30 m. From 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 northern and central regions of the basin, salinity somewhat decreases from east to west, since in cyclonic circulation, saline waters are transported from south to northeast along the eastern coast of the sea further than along the western one. A decrease in surface salinity can also be traced from south to north, as well as in bays.

In the autumn-winter season, 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 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. Storm 7-8-point winds develop waves up to 5-6 m high and 50-70 m long. In the Gulf of Finland, strong winds of these directions form waves 3-4 m high. In the Gulf of Bothnia, storm waves reach a height of 4-5 m. big waves come in November. In winter, with stronger winds, the formation of high and long waves is prevented by ice.

As in other seas of the northern hemisphere, the surface circulation of the Baltic Sea has a general cyclonic character. Surface currents are formed in the northern part of the sea as a result of the confluence of waters leaving the Gulf of Bothnia and the Gulf of Finland. The general flow is directed along the Scandinavian coast to the southwest. Going around on both sides about. Bornholm, he is heading through the Danish Straits to the North Sea. At the southern coast, the current is directed to the east. Near the Gulf of Gdansk, it turns north and moves along the eastern coast to about. Khnum. Here it branches into three streams. One of them goes through the Irben Strait to the Gulf of Riga, where, together with the waters of the Daugava, it creates a circular current directed counterclockwise. Another stream enters the Gulf of Finland and along its southern coast extends almost to the mouth of the Neva, then turns to the north-west and, moving along the northern coast, leaves the bay together with river waters. The third flow goes to the north and through the straits of the Aland skerries penetrates into the Gulf of Bothnia. Here, along the Finnish coast, the current rises to the north, goes around the northern coast of the bay and descends to the south along the coast of Sweden. In the central part of the bay, there is a closed circular counterclockwise current.

The speed of the permanent currents of the Baltic Sea is very low and is approximately 3-4 cm/s. Sometimes it increases to 10-15 cm/s. The current pattern is very unstable and is often disturbed by the wind.

The prevailing wind currents in the sea are especially intense in autumn and winter, and during strong storms their speed can reach 100-150 cm/s.

Deep circulation in the Baltic Sea is determined by the flow of water through the Danish straits. The inlet current in them usually passes to horizons of 10-15 m. Then this water, being denser, descends into the underlying layers and is slowly transported by the deep current, first to the east and then to the north. With strong westerly winds, water from the Kattegat flows into the Baltic Sea almost along the entire cross section of the straits. East winds, on the contrary, increase the outlet current, which extends to the horizons of 20 m, and the inlet current remains only near the bottom.

Due to the high degree of isolation from the World Ocean, the tides in the Baltic Sea are almost invisible. Fluctuations in the level of the tidal character in individual points do not exceed 10-20 cm. The average sea level experiences secular, long-term, interannual 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 of the Baltic Sea regime.

The catastrophic St. Petersburg floods are connected with sea level fluctuations. They occur when the level rise is due to the simultaneous action of several factors. Cyclones that cross the Baltic Sea from the southwest to the northeast cause winds that drive water from the western regions of the sea and overtake it into the northeastern part of the Gulf of Finland, where the sea level rises. Passing cyclones also cause seiche fluctuations in the level, at which the level rises in the Aland region. From here, a free seiche wave, driven by western winds, enters the Gulf of Finland and, together with the surge of water, causes a significant increase (up to 1-2 m and even 3-4 m) in the level at its top. This prevents the flow of the Neva water into the Gulf of Finland. The water level in the Neva is rapidly rising, which leads to floods, including catastrophic ones.

ice coverage

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

The distribution of fixed and floating ice in the Baltic Sea depends on the severity of the winter. Moreover, in mild winters, ice, having appeared, may completely disappear, and then appear again. In severe winters, the thickness of immobile 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 marine fish species are common in the central regions of the Baltic, where salinity is relatively high, although some of them also enter fairly fresh bays. For example, herring lives in the Gulf of Finland and Riga. More saltwater fish - Baltic cod - do not enter the fresh and warm bays. Eel is a unique species.

In fishing, the main place is occupied by herring, sprat, cod, river flounder, smelt, perch and various types of freshwater fish.

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

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

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

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

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

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

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

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

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

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

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

The Icelandic low, as well as the Siberian and Azores anticyclones, most significantly affect the weather. The nature of their interaction determines the seasonal features of the weather. In autumn and especially 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 in the central part of the sea is -3°С in the north and -5...-8°С in the east. With rare and short-term intrusions of cold Arctic air associated with the strengthening of the Polar High, the air temperature over the sea drops to –30°С and even to –35°С.

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

The temperature conditions of the waters of the Baltic Sea in different parts of it are not the same and depend not only on the geographical location of the place, but also on the meteorological and hydrological features of the area. water. This determines the general picture of the temperature conditions of the sea. In the surface layers, the water temperature varies widely. At depths exceeding 50 meters, the water temperature is kept within 3–4 ° C all year round in the southern part of the sea and near zero in the northern Bothnian region.

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

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

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

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

The strongest wind waves are observed in autumn and winter in open, deep areas of the sea with prolonged and strong southwestern winds. Stormy 7–8-point winds develop waves up to 5–6 m high and 3–4 m long. The largest waves occur in November. In winter, with 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 leaving the Gulf of Bothnia and the Gulf of Finland. The speed of the permanent currents of the Baltic Sea is very low and is approximately 3–4 cm/s. Sometimes it increases to 10–15 cm/s. The current pattern is very unstable and is often disturbed by the wind. The wind currents prevailing in the sea are especially intense in autumn and winter, and during strong storms their speed can reach 100–150 cm/s.

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

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

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

Catastrophic floods are associated with fluctuations in sea level.

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

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

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

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

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

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

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

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

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 formation of the earth's crust, which occurred at high temperatures, various substances were released from the earth into the atmosphere in the form of gases. The subsequent cooling of the earth's crust caused heavy rains. They took those substances with them and filled huge pits on the surface of the earth.

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

1.Evaporation of water.

2. Formation of ice.

3. Precipitation.

4.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 the climatic conditions associated with the geographical location of the sea.

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

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

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

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

In the Baltic Sea, water forms layers of different salinity. The average salinity of the Baltic Sea is not higher than 1%o, and that of its surface waters is -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, salinity is greatly influenced by river runoff, and in polar regions, by the processes of ice formation and melting. When water freezes and sea ice builds up, part of the salts drain into the water and salinity increases; when sea ice and icebergs melt, it decreases. Fresh water enters the Baltic Sea from 250 rivers, while salt water enters only from the narrow Danish straits. As a result, salinity is highest in
Southwest of the Baltic, and decreases as you move to the east. However, the overall picture can be disturbed by currents.

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

History of the Baltic Sea is estimated in tens of thousands of years. The Baltic Sea is not one of the large or deep seas. Its area is only 430 thousand square kilometers, and the maximum depth is only about 470 meters. And even then depths of hundreds of meters are a rarity in this sea. Its average depth is 55 meters. Buildings having more than 18 floors would protrude when placed at the average depth of this sea. And the needle of the Moscow television tower could not have been hidden even by its maximum depth.

Salinity of the Baltic Sea

It cannot be said that the water Baltic Sea has a special salinity. No, the high-water rivers that flow into it sharply reduce its salinity, it is much lower than in the ocean. And narrow and shallow straits do not allow deep mixing of salt and fresh waters. Especially freshwater is the Gulf of Finland, into which the full-flowing Neva flows.

History of the Baltic Sea from the Ice Age

Baltic Sea- the native child of the great one, who at one time advanced over Europe from the Scandinavian mountains and covered most of it. Then the entire Baltic Sea lay under a layer of ice many kilometers thick. But then the glaciers began to recede, opening up a black surface for the rays of the sun. They also discovered the bottom of the Baltic Sea, which was immediately filled with the waters of a melting glacier. This happened very recently, 13 thousand years ago.

The melting of the glacier was quite rapid, and the released waters covered the entire bowl of the sea that had been opened from ice. And an excess of water gushed through southern Sweden into the North Sea, which is part of the Atlantic Ocean. In those days there was an even more convenient way to connect the huge lake with the ocean, lying in Central Sweden, but it was clogged with the body of the glacier.

When the glacier left Central Sweden, this path opened up, and the water level in the freshwater lake quickly dropped, reaching the level of the ocean. But when this "equation" occurred, the outflow of fresh water into the ocean did not stop, because the sea continued to receive the flow of water from the melting glacier, but this flow "from the sea" occurred only in the upper part of the connecting strait. And in its lower part, a countercurrent was established: the heavy salty waters of the ocean flowed into the fresh sea. And the fresh glacial lake became the salty sea. And it happened about 10 thousand years ago.

The level of the sea that arose was fifty meters lower than the modern one. The Danish straits of the sea had not yet opened, and it was possible to come to the Scandinavian Peninsula from Denmark through the future island of Gotland without soaking your boots.

This first sea was very short-lived. It lasted only 600-700 years. The uplifts of the earth's crust interrupted the connections of the Young Sea with the oceans, and the sea again became a lake.

Formation of the Baltic Sea

Formation of the Baltic Sea started with lake Antsilyusa . Numerous rivers flowed into it, and thanks to this, it quickly lost its salinity. The lake became fresh water again. In its sediments, a freshwater mollusk ancilus was found, which gave the name to the lake.

But it also was not a long-liver of the planet: after about 1000 years, the waters of this fresh lake again began to overflow through Central Sweden into the Atlantic Ocean. Opened the passage of water through the Danish straits. And also towards the fresh waters of the lake in the lower part of the straits, a rather powerful countercurrent was established.

Powerful enough to ensure that flora and fauna, characteristic of the salty waters of the ocean, firmly reign in its waters. This second edition of the sea appeared in the same place about 7 thousand years ago. In those days, the salinity of the sea was greater than now, and the climate on its shores was warmer than today.
Of course, the formation of the Baltic Sea did not end there. There were rises, fluctuations in sea level, changes in its configuration and the nature of the coast.

Only 2-3 thousand years ago the sea took its modern shape, and they have a number of trends to change. After all, the earth's crust in the area of ​​the Baltic Sea is continuously rising. This cannot but affect the configuration of such a shallow sea as the Baltic.
More than 60 years ago, the greatest Russian poet Valery Bryusov wrote a poem

"To the North Sea":

I came to say goodbye to you, the sea, maybe for many years. You are again in a sparkling dress, in foam lace, as always.

Pass, oh sea, unchanged through the ages that consume us...

And one gets the impression that for an intelligent and deeply educated poet, the sea was a kind of symbol of constancy and immutability.
But today we are already well aware that this constancy is very conditional. That only when comparing the life of the sea with the life of an individual can one speak of a certain immutability of the sea. And already in the memory of several generations of people, the seas are not at all unchanged. Seas and lakes disappear and arise just like islands and continents.

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).

The coastline of 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 a total area of ​​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 almost no sea water enters the bay. Therefore, it is freshwater, except for the northernmost part.

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.

The northern part of the Vistula Spit, 25 km long, and the southern part of the Curonian Spit, 49 km long, are located within the Kaliningrad region. 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 elevated ledge of Cenozoic rocks, overlain by glacial deposits, and therefore is bordered by coastal ledges on the seashore. 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-argillaceous water-glacial deposits (bush Pokrovskaya, Yantarnenskaya, Donskaya, Filinsky, 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 basin of the Atlantic Ocean and as a result of 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 postglacial Baltic Sea and adjacent territories, including the Kaliningrad region.