The Black Sea, a strange geography

The Black Sea is the largest inland sea that still maintains regular communication with the world's oceans.

This communication takes place through the narrow Bosphorus Strait that leads to the Mediterranean Sea, which in turn connects it to the Atlantic Ocean.

It has a more or less oval shape. Its longitudinal axis is approximately 1,150 km long, and its latitudinal axis is 611 km. It has an area of ​​423,000 km2. The average depth is 1,300 m, and the greatest depth is 2,245 m. The volume is 547,000 km3.

Geological history.

The Black Sea is considered a residual basin of the Tethys Sea of ​​Central Europe, which existed from the end of the Paleozoic era to the Middle Tertiary period. As a result of alpine orogenic movements in the Triassic period, the Tethys Sea was divided into a series of basins. One of them was Pontus, which stretched from Moldavia in the west to the Aral Sea in the east. At the end of the Tertiary period, this basin separated from the Caspian Sea and was reduced to the dimensions of today's Black Sea.

During the Ice Age of the Pleistocene epoch, the level of the Black Sea rose and the sea was connected several times with the Mediterranean and Caspian seas. But in the postglacial period, the Black Sea shrank, became a freshwater sea, and its water level fell below that of the ocean. The Bosphorus Strait was formed 6,000-8,000 years ago. Salt water from the Mediterranean Sea entered the Black Sea and filled its basin. It destroyed the freshwater fauna of the Black Sea, which was replaced by the saltwater fauna of the Mediterranean Sea. Sea levels rose, and salt water flooded the lower reaches of river valleys, creating lime.

The continental shelf is the outer coastal ring, less than 200 m deep. It slopes gently away from the coast and is covered with terrigenous deposits from the mountains. It covers about a quarter of the sea area and is widest in the northwest and in the Kerch Strait.

The continental slope is the ring that separates the continental shelf and the core of the basin. The steepness of the slope usually varies between 5° and 6°. At a depth of about 2,000 m, the steepness of the slope suddenly decreases and the slope merges with the bottom of the basin. The surface of the slope is usually very uneven and covered with a layer of sticky mud, black on top and light gray below. The color is due to ferrous sulfide, which is deposited as very fine grains or fine needles.

There are hardly any islands in the Dnipro-Boh estuary, and the island of Zmiinyi, near the Danube River delta, is small in size.

Climate. The climate of the Black Sea is predominantly continental. Only the southern coast of Crimea and the northwestern coast of Caucasia are protected by mountains from cold northerly winds and are visited by gentle winds from the Black Sea. Therefore, they have a temperate Mediterranean climate. The Atlantic Ocean has a great influence on the climate of the Black Sea. In winter, northeasterly winds generally prevail over the sea, lowering the temperature and causing frequent storms. On the northeast coast, near Novorossiisk, cold and violent mountain winds develop. The temperature of the northern part of the Black Sea averages about -3°C in January, but occasionally drops to -30°C. Coastal waters freeze for a month or more, while shallow bays, river mouths and lemons are frozen for two to three months. During this season, the southern coast of Crimea and the sheltered eastern coast enjoy a temperature of 6-8°C, well above freezing. The average July temperature in the north is 22-23 °C, and in the south - 24 °C. The northwestern coast has the lowest annual precipitation (300 mm), and the Caucasus coast has the highest ( up to 1,500mm).

The waters

The average volume of water in the Black Sea is 547,000 km3. The volume changes according to the following factors: precipitation, which is usually 230,000 km²; the inflow from the mainland - 310,000 cubic km; the flow from the Azov Sea - 25,000 cubic km; evaporation loss: 357,000 cubic km; and exit through the Bosphorus Strait - 208,000 km3.

Due to the relatively young geological age of the Black Sea and the large inflow of freshwater and semi-fresh water from the Sea of ​​Azov, the salinity of the Black Sea is almost 50 percent less than the salinity of the ocean. It is lowest in the Northwest (13 parts per thousand) and rises to 17-18 parts per thousand elsewhere. Salinity also varies: it is lowest at the surface and increases with depth to about 23 parts per thousand at 730 m, beyond which it remains almost constant.

By temperature, the waters of the Black Sea are divided into two unequal layers: the upper layer, which extends to a 

By temperature, the waters of the Black Sea are divided into two unequal layers: the upper layer, which extends to a depth of about 500 m, the lower layer, 500 m to the bottom. The bottom layer maintains a nearly constant temperature of 9°C.

In winter, the temperature of the upper layer increases with depth, and in summer it decreases with depth. Vertical temperature changes are unequal. On the surface, the temperature is lower in February: from -0.5 ° C in the north, where coastal waters freeze 10–20 km from the coast, to 5–8 ° C in the south. The waters reach their highest temperature in August, from 20°C in the north to 25°C or more in the south. In the Sea of ​​Azov, the waters reach 26–27 ° C, and even 30 ° C.

The density of water depends on salinity and temperature. It is lowest at the mouths of rivers and the Kerch Strait (1,010–1,014 g/cc on average) and increases towards the open sea and downwards – it is 1,017 g/cc on average at a depth of 150 m and almost constant below. of that depth.

Oxygen is the most important gas in seawater because it supports organic life. In the upper layer it reaches 4–7 cc per litre. The amount of oxygen decreases rapidly with depth: at 200 m only 0.5 cc is found in a liter of water. This is not enough to support life and therefore only a few bacteria (Microspira aestuarii) live at this depth. Another obstacle to life below 200 m is the high concentration of hydrogen sulfide, which increases to 6–7 cc per liter at a depth of 2,000 m.

The transparency of the water in the Black Sea is 16 to 22 m deep on average. It is lowest near the coast (2–3 m) and highest in the middle of the sea (20–27 m).

Water movements.

The surface of the Black Sea is usually calm, but waves arise in windy weather, particularly in winter. During storms, waves can reach heights of 15 m or more and pose a threat to small boats. The tide is almost imperceptible, since it reaches barely 10 cm in height.

There are two types of sea currents in the Black Sea: the surface currents, caused by the cyclonic pattern of the winds, and the double currents in the Bosphorus Strait and the Kerch Strait, caused by the exchange of waters with adjacent seas. The surface currents form two closed circles. The width of the western circle, facing the Danube Delta, reaches 100 km and decreases towards the south. The speed of the current is about 0.5 km per hour. The width of the eastern circle varies between 50 and 100 km, and the speed is 1 km per hour.

The double current of the Bosphorus Strait consists of the exchange of waters between the Black Sea and the Sea of ​​Marmara. The less saline and clearer waters of the Black Sea flow as a surface current into the Sea of ​​Marmara at a speed of 1 to 2 m per second. In return, the more saline and denser waters of the Sea of ​​Marmara flow at a depth of 50-120 m into the Black Sea at a speed of 4-6 m per second. In the Kerch Strait, the surface current flows from the Sea of ​​Azov to the Black Sea at 1–2 m per second, while the lower current flows in the opposite direction at a depth of about 5 m.

In addition to horizontal currents, there are also vertical currents, which are limited to surface waters up to 200 meters,

Flora and fauna.

The most peculiar feature of the Black Sea is the absence of marine life at depths greater than 150-200 m, except for some anaerobic bacteria. Living organisms are concentrated in the shallow waters of the continental shelf and the mouths of rivers along the northwest coast.

The plant world consists of phytoplankton (350 unicellular species occur), bottom macrophytes (280 species), various species of grasses and seagrasses. The grass Phillophora rubens, which covers more than 15,000 square kilometers of the seabed and is harvested in quantities of more than five million tons, has commercial value. Zostera seagrass, which is eaten by fish, grows on the silt and sand bottoms of calm bays.

The number of animal species in the Black Sea is small compared to the number in the Mediterranean Sea: 350 species of simple creatures, 650 species of crustaceans, more than 200 species of mollusks, about 180 species of fish and 4 species of mammals. (the monk seal and 3 species of dolphins). Mammals and fish are of commercial value. The fishing industry brings rich catches of sturgeon, mackerel, sardine, herring, anchovy, mullet and other fish.

Reference:

http://www.encyclopediaofukraine.com/display.asp?linkpath=pages%5CB%5CL%5CBlackSea.htm