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Black Sea, inland sea, c.159,600 sq mi (413,360 sq km), between SE Europe and Asia, connected with the Mediterranean Sea by the Bosporus, the Sea of Marmara, and the Dardanelles. It is c.750 mi (1,210 km) from east to west, up to 350 mi (560 km) wide, and has a maximum depth of 7,364 ft (2,245 m). Its largest arm is the Sea of Azov, which joins it through the Kerch Strait. The Black Sea is enclosed by Ukraine and Crimea on the north, Russia on the northeast, Georgia on the east, Turkey on the south, and Bulgaria and Romania on the west.
The Dnieper, Southern Buh, Dniester, and Danube rivers are its principal feeders; the Don and Kuban rivers flow into the Sea of Azov. The rivers flowing into the northern part of the Black Sea carry much silt and form deltas, sandbars, and lagoons along the generally low and sandy northern coast. The southern coast is steep and rocky. The Black Sea has two layers of water of different densities. The heavily saline bottom layer has little movement and contains hydrogen sulfide; it has no marine life. The top layer, much less saline and richer in fish, flows in a counterclockwise direction around the sea. There is little tidal action.
Pollution in the Black Sea has spurred surrounding nations to cooperate in instituting environmental safeguards, but remains a problem; overfishing is also a significant problem and has altered the sea's ecosystem. The sea is subject to severe winter storms, and waterspouts are common in summer. Ice-free, it is the chief shipping outlet of Ukraine and Russia; Odessa in Ukraine, Sevastopol in Crimea, and Novorossiysk in Russia are major ports. Other important ports are Constanţa in Romania; Varna and Burgas in Bulgaria; and Trabzon, Samsun, and Zonguldak in Turkey. The Black Sea region, especially in the S Crimea and W Caucasus, is a popular resort area.
The Black Sea was once part of a larger body that included the Caspian and Aral seas. In the Tertiary period, it was separated from the Caspian Sea and was linked to the Mediterranean Sea. Evidence suggests that more recently, about 7,600 years ago, at the end of a long dry period, it was flooded when the Mediterranean, having again become separate, broke through at the Bosporus, an event that may have scattered farmers from its shores into Europe and Asia. Some scientists have hypothesized that this event happened catastrophically and is the source of the biblical story of the Deluge.
The Pontus Euxinus [hospitable sea] of the ancients, the Black Sea was navigated and its shores colonized by the Greeks (8th–6th cent. B.C.) and later by the Romans (3d–1st cent. B.C.). Its importance increased with the founding of Constantinople (A.D. 330). In the 13th cent. the Genoese established colonies on the Black Sea, and from the 15th to the 18th cent. it was a Turkish “lake.” The rise of Russia led to protracted dispute with the Ottoman Empire over control and use of the Bosporus and Dardanelles. In 1783, Russia annexed the Tatar Khanate of Crimea, which blocked its access to the sea, but the Treaty of Paris, which ended the Crimean War of 1856, frustrated Russia's expansionist ambitions, and Russia and its successor, the Soviet Union, retained limited influence in the region. In 1992, after the breakup of the Soviet Union, the Black Sea Economic Cooperation was established by nations surrounding the sea (not all members actually border the sea); it became a formal international organization in 1998. The six nations bordering the sea established the Black Sea Naval Cooperation Task Group in 2001 to promote cooperation on naval and environmental issues.
See N. Ascherson, Black Sea (1995).
an inland sea of the Atlantic Ocean, between Europe and Asia Minor.
Physical geographic description.GENERAL INFORMATION. The Black Sea is bounded by the USSR, Rumania, Bulgaria, and Turkey. In the northeast it is connected with the Sea of Azov by way of Kerch’ Strait, and in the southwest it is connected with the Sea of Marmara by way of the Bosporus and then with the Aegean Sea and the Mediterranean Sea by way of the Dardanelles. The Black Sea’s greatest east-west length is 1,150 km, and the greatest north-south length, 580 km. At its narrowest point, the sea is 265 km wide. It has an area of 420,300 sq km and a water volume of 547,000 cu km. Its average depth is 1,300 m. The chief rivers that empty into the Black Sea are the Danube, Dnestr, Iuzhnyi Bug, Dnieper, Rioni, and Kizil (Kyzyl Irmak).
COASTLINE. The Black Sea coastline, which measures a total of 3,400 km, is relatively smooth, with only one major peninsula—the Crimean Peninsula. Some of its segments have their own name, for example, the Southern Coast (Iuzhnyi Bereg) of the Crimea and the Black Sea Coast (Chernomorskii Bereg) of the Caucasus in the USSR and the Rumelian and Anatolian coasts in Turkey. In the west and northwest the shores are low and, in places, steep; limans are characteristic of the shores in the northwest. The northern coast of the Crimean Peninsula is flat, while the southern coast is mountainous. In the east and south the mountains of the Greater and Lesser Caucasus and the Pontic Mountains extend to the very edge of the sea; there are a few low-lying areas here, formed by river deltas jutting out into the sea near the capes of Pitsunda and Kodor in Georgia and Civa and Bafra in eastern Anatolia. The largest bays and gulfs are Karkinitskii, Kalamitskii, Dnieper-Bug, Dnestr, Varna, and Burgas in the northwest and west and Sinop and Samsun in the south. Islands are few, the most important being Berezan’ and Zmeinyi.
TOPOGRAPHY OF THE BOTTOM AND GEOLOGICAL STRUCTURE. Three parts are identified in the topography of the bottom: the shelf, the continental slope, and the deep sea basin. The shelf extends to a depth of 110–160 m and reaches its greatest width, more than 200 km, in the northwest; elsewhere it usually extends to depths less than 110 m and ranges in width from 2.5 km (along the coast of Turkey) to 10–15 km.
The continental slope is strongly dissected by underwater valleys and canyons. Its average inclination is 5°–8°, but in the northwest and near Kerch’ Strait, the inclination is 1°–3°. Some parts reach a steepness of 20°–30°. A system of underwater ridges measuring more than 150 km in length stretches almost parallel to the shore between Sinop and Samsun.
The floor of the deep sea basin is a flat aggradation plain, whose depth gradually increases to more than 2,000 m at the center; the maximum depth is 2,211 m. Geologically, the bottom comprises parts of different type and age. Most of the Black Sea is located within the Alpide geosynclinal (folded) region. The earth’s crust beneath the deep sea basin consists of two layers: the sedimentary and “basalt” layers. The sedimentary layer is 10–16 km thick, and its upper part, at least 3–4 km thick, lies almost horizontally. In the central parts of the deep sea basin, the crust is 22–25 km thick, reaching 30–35 km along the periphery, where a granite layer appears above the “basalt” layer. In the northwest, the shelf encompasses the southern edge of the East European Platform and the Epipaleozoic Scythian Platform.
The formation of the Black Sea basin is linked with either the processes of “oceanization” of the continental crust or with the relict nature of the Black Sea basin as a remnant of the basin of the ancient ocean Tethys. The outlines of the modern basin had formed during the Oligocene, when uplifts in Asia Minor gradually separated the Black and Caspian seas from the ocean. During the Upper Miocene, the Black Sea was one of a chain of freshwater lake-seas (the Sarmatian Basin). After a short-lived connection with the Mediterranean Sea, during the Meotian stage, the freshwater Lake Pontus formed. In the late Pontian stage, the connection between the Black Sea and the Caspian was closed. During the Middle and Upper Pliocene, the Black Sea was probably a freshwater lake with an outlet. In the Middle Pleistocene, the Black Sea was twice connected with the Mediterranean for short periods and had more saline water. During the last glaciation, the New Euxine lake-sea formed, with relatively fresh water; 6,000–7,000 years ago, it was connected to the Mediterranean Sea by way of straits, giving rise to the modern Black Sea. Tectonic activity is manifested by earthquakes, whose epicenters are located along the margins of the basin and in the adjoining regions.
In the littoral zone, coarse deposits—pebbles, gravel, and sand—predominate. Farther out to sea, they are replaced quite rapidly by fine-grained sand and aleurites. In the northwest, coquinas and latter-day shell mounds inhabited by mytilids, oysters, and other mollusks are widespread. The continental slope and sea floor are characterized by pelitic oozes, whose carbonate content increases toward the open sea, exceeding 50 percent in some places; coccolithophores play a significant role in the carbonate material. At depths to 2,000 m in the southeast, aleuritic and sandy sediments deposited by turbidity currents are found.
The chief useful minerals in the Black Sea are petroleum and gas, found in the northwestern part of the basin, and titanomagnetite sands, found in the coastal waters off Taman’ and the Caucasus.
CLIMATE. In the course of the year, the Black Sea is affected primarily by continental polar, marine polar, and marine tropical air masses. Continental polar air predominates. In the winter its intrusion is accompanied by strong northerly and northeasterly winds, a drop in temperature, and frequent precipitation; the winds are especially strong in the vicinity of the city of Novorossiisk, where they are called boras. When marine polar air intrudes from the Atlantic Ocean, considerable cyclonic activity develops, accompanied by squalls and precipitation. The marine tropical air, which is always warm and has higher humidity, is brought in by southwesterly winds from the Mediterranean Sea basin.
Most of the Black Sea has warm, humid winters and hot, dry summers. The average air temperature in January is about 8°C in the central part of the sea, 6°C along the eastern coast, –3°C in the northwest, and 6°–9°C in the southeast and south. The temperatures in the northern part of the Black Sea may drop to as low as –30°C, and in the southern part, to –10°C. Snowfalls occur everywhere during the winter; Sochi and Khost have up to eight days of snow a year.
In the summer, part of the Azores high extends over the Black Sea, bringing consistently clear and warm weather. The average air temperature in July is 22°–24°C; temperatures sometimes reach 30–35°C. Average annual cloudiness is 60 percent, with a maximum in the winter and a minimum in the summer. Annual precipitation is 300–500 mm in the west and northwest, 750–800 mm in the south, and 1,800–2,500 mm in the east. Waterspouts occur in the fall.
HYDROLOGICAL REGIME. The sea’s water balance is governed by atmospheric precipitation (230 cu km per year), continental runoff (310 cu km per year), and the influx of water from the Sea of Azov (30 cu km per year), on the one hand, and evaporation from the surface of the sea (360 cu km per year) and outflow through the Bosporus (210 cu km per year), on the other. The general cyclonic atmospheric circulation over the Black Sea and continental runoff lead to the development of cyclonic circulation of water, moving counterclockwise along the shores at the surface. Internal cyclonic circulations develop deep within this cycle in the west, central part, and east. The surface currents have velocities up to 1 km/hr; in some areas, they increase to 5–6 km/hr as a result of strong winds.
The excess fresh water flowing into the Black Sea causes the water to be steadily discharged through the Bosporus into the Sea of Marmara by the upper (to a depth of 40 m) current, while the lower current carries transformed salt water from the Mediterranean Sea, by way of the Bosporus, to fill the deep layers of the Black Sea. As a result, the vertical exchange of water in the Black Sea is impeded. The surface and deep waters intermix as a result of vertical flows of water in the centers of the circulations and along the continental slope.
Water-level fluctuations as a result of wind-driven currents vary from 40–60 cm in the Crimea to 1.5 m in the northwest. Changes in level caused by tides do not exceed 10 cm, while seiches do not exceed 60 cm. Wind-driven currents can cause the temperature of the coastal surface water in the summer to drop from 25°C to 10° or less in a few hours as a result of the rising of the deep waters to the surface.
During the winter, the water temperature at depths of 60 m drops to 6°–7°C. In the northwest it reaches 0.5°C, and the inlets usually freeze at temperatures below zero. In the southeast the water temperature is higher, reaching 9°-H°C. In the summer, the surface water warms up to 24°–26°C, reaching 29°C along the shore. The temperature remains at about 7°C year-round at depths below 60–80 m.
The abundant continental runoff, the influx of relatively fresh water from the Sea of Azov, and atmospheric precipitation determine the salinity. The salinity of the surface water is 17–18‰ in the open sea and 3–9‰ near the mouths of rivers. At depths of 60–80 m it is 19–20‰, and at the bottom, 22–22.5‰. The water density at the surface is 1.013–1.015 g/cm3 in the winter and 1.0085–1.0120 g/cm3 in the summer. Dissolved oxygen is found only in the top layer of water; its content is 8–9 ml/l at the surface.
Below depths of 150–200 m, the water is “contaminated” by hydrogen sulfide, which reaches a concentration of 11–14 ml/l at the bottom. It is believed that hydrogen sulfide forms in the Black Sea primarily as a result of the vital activity of sulfate-reducing bacteria, the sharply delineated water stratification, and weak vertical exchange.
The color of the water differs in different parts of the sea. It is greenish blue in the central and eastern parts and bluish green in the northwest. The transparency of the water averages 16–22 m; in the western and eastern parts it is 20–27 m, decreasing to 6–8 m in the coastal regions and even to 2–3 m in some areas.
L. M. FOMIN
PLANT AND ANIMAL LIFE. A characteristic feature of the Black Sea is the almost total absence of life at depths greater than 150–200 m, where the hydrogen sulfide zone begins, with the exception of anaerobic bacteria, primarily Microspira. Of the plants, 350 species of unicellular phytoplankton algae are known, including about 150 species of diatoms and 150 of peridinians, and about 280 species of benthic macrophytes, including 129 species of red algae, 71 of brown algae, 77 of green algae, and several species of marine grasses, primarily Zostera. The brown algae Cystoseira and the red algae Phyllophora are especially numerous, forming enormous accumulations at depths of 20–50 m in the northwestern part of the sea; they are commercially important, with estimated reserves of more than 5 million tons.
The fauna of the Black Sea is approximately one-third as rich as that of the Mediterranean Sea. Benthic species predominate, numbering about 1,700. The most typical biocenoses are the mytilid oozes and phaseoline (named for the mollusk Modiola phaseolina) oozes, the former occurring primarily at depths of 30–70 m, and the latter, at 50–200 m. With respect to origin, immigrant species from the Mediterranean Sea predominate, constituting more than 30 percent of all the species. Of lesser importance are relicts of the Pliocene brackish Pontic Basin and freshwater immigrant species that inhabit the parts with less saline water. Endemic species constitute about 12 percent. More than 2,000 species of animals are known, including about 300 species of protozoans, 650 of various types of worms (including 190 species of marine polychaetes), 640 of crustaceans, more than 200 of mollusks, 160 of fishes, and about 150 of animals of other groups, including four mammalian species—seals—and three species of dolphins. Because of the lowered salinity, many groups of stenohaline marine animals are represented by only a small number of species (for example, there are only 14 species of echinoderms and one species of radiolarian) or are completely absent (there are no cephalopod mollusks or brachiopods). Many fish (about 20 percent of the species) are commercially important, among them the anchovy, horse mackerel, Atlantic mackerel, bonito, sprat, and sturgeon.
G. M. BELIAEV
Economic geography. The Black Sea is an important artery, linking the USSR with foreign countries; one-fourth of all USSR imports and one-half of all exports are shipped by way of the sea. The Black Sea merchant fleet accounts for a significant share of USSR marine shipping. Considerable domestic cargo is also shipped on the Black Sea, often by way of the V. I. Lenin Volga-Don Ship Canal, which links the Black Sea with the Volga River and Caspian Sea. The largest port on the Black Sea is Odessa, which, together with the nearby port of Il’ichevsk, accounts for one-third of the total freight turnover on the Black Sea. Virtually all types of raw materials and industrial products pass through Odessa. Petroleum is shipped from Novorossiisk, Tuapse, and Batumi. Cement is shipped from Novorossiisk and manganese ore from Poti. Other large ports are Nikolaev, Kherson, Kerch’, Feodosiia, Sevastopol’, and Izmail.
The Black Sea is also very important for the economies of Bulgaria, Rumania, and Turkey. The main ports in Bulgaria are Burgas and Varna, and in Rumania, Constanfa. A large part of the cargo from the Balkan countries is transported to the Black Sea along the Danube. The most important Turkish ports are Trabzon, Samsun, and Zonguldak.
The Black Sea is a major commercial source of fish, algae, and mollusks.
The favorable climate of the Black Sea has favored the development of resorts and tourism. In the USSR, the Southern Coast of the Crimea, with its center in Yalta, is a major climatic resort area, as are the cities of Sochi, Pitsunda, Gagra, Sukhumi, Batumi, Anapa, and Gelendzhik on the Caucasian coast. The chief resorts in Bulgaria are Golden Sands and Sunny Coast; the main resort in Rumania is Mamaia.
An important problem is the protection of the Black Sea from pollution. The main pollutants are petroleum, petroleum products, phenols, and detergents. Especially polluted by petroleum are the coastal waters and the western part of the sea, site of shipping lanes from Odessa, to the mouth of the Danube, and then to Istanbul or Varna. Measures have been undertaken to prevent the discharge of untreated industrial and household wastes into the sea; the dumping of petroleum, petroleum products, and other substances that pollute the water has been prohibited.
History of study. Opinions differ regarding the source of the modern name Black Sea. Greek navigators of the sixth and fifth centuries B.C. called the sea Pontus Axeinus, literally “inhospitable sea”; in the early part of the Common Era, it was called Pontus Euxinus, or “hospitable sea.” In the ninth and tenth centuries the Arabs called it the Russian Sea. In the 15th century the Turkish named it Karadeniz, literally “black sea” or “bad sea.” Another explanation links the word “black” to the color designation used by some peoples for the countries of the world: “black” signified the north. In Slavic, chermnoe means “bleak” or “stormy”; the ancient Persian name Achshaena literally means “dark sea,” which signifies a harsh sea.
Since ancient times the Black Sea has been an active sea route, well known to the Phoenicians and Greeks. In the third century B.C., the Greeks made the first map of the Black Sea. In the late ninth century A.D., Russians began using the sea to sail from the Baltic to Byzantium, the route “from the Varangians to the Greeks.”
The study and scientific development of the Black Sea began in the early 19th century. The first Russian expedition, led by G. P. Manganara, surveyed the coastline, took depth measurements, and studied the soil, and the results obtained were used to draw navigation charts and a map of the Black Sea. Similar studies were later carried out by numerous hydrographic expeditions, which also studied water temperature and currents. The first atlas of depths (down to 180 m), sediments, and currents was published in Russia in 1842. Important studies of the Bosporus were conducted in 1881–82 by S. O. Makarov. He established the two-layer current, the upper current flowing from the Sea of Marmara into the Black Sea and the lower from the Black Sea into the Sea of Marmara. In 1890–91 an expedition led by I. B. Shpindler on the ships Donets and Zaporozhets made the first deep-water observations and established the “contamination” of the deep sea waters by hydrogen sulfide. After the founding of the Sevastopol’ Biological Station in 1871, extensive biological research developed under the direction of A. O. Kovalevskii.
In the 1920’s, the Sevastopol’ Biological Station and the Marine Observatory embarked on a planned, coordinated study of the Black Sea. The largest expeditions were N. M. Knipovich’s scientific-commercial expedition of 1922–27, Iu. M. Shokal’skii’s hydrologic and hydrographic expedition of 1923–27, and the Marine Observatory expedition of 1928–38, headed by V. A. Snezhinskii. These expeditions contributed much to the study of the topography of the bottom and to the study of sediments, the vertical structure of the water, and the ichthiofauna of the Black Sea. The material they gathered enabled A. D. Arkhangel’skii and N. M. Strakhov to advance the first generalization of the stratigraphy and geological history of the Black Sea in the Cenozoic.
With the introduction of observations on standard cross sections in the 1930’s, the study of the Black Sea became systematic. The Hydrometeorological Observatory and the Azov–Black Sea Scientific Research Institute of Fishing and Oceanography became involved in studying the sea. In the late 1940’s and subsequent years observations on cross sections expanded greatly; hydrologic and hydrochemical observations are now made once a month or every ten days on standard cross sections. Since the late 1950’s, a systematic study of the geology and geophysics of the Black Sea, the geomorphology of the bottom, bottom sediments, and other aspects has been conducted. Regular seismic investigations of the structure of the earth’s crust beneath the Black Sea was begun in 1957. In 1975 a deep-sea drilling project that went down to a depth of 1 km was carried out by scientists from various countries on the ship Glomar Challenger. The State Oceanographic Institute has been systematically monitoring the pollution of the Black Sea since the mid-1960’s.
The following institutions are engaged in the study of the Black Sea: the Institute of the Biology of the Southern Seas (the former Sevastopol’ Biological Station), the Marine Hydrophysical Institute of the Academy of Sciences of the Ukrainian SSR, the Azov-Black Sea Scientific Research Institute of Fishing and Oceanography, the Sevastopol’ division of the State Oceanographic Institute, the Black Sea division of the Institute of Oceanography of the Academy of Sciences of the USSR, the All-Union Scientific Research Institute of Marine Geology, and the Marine Observatory.
A. M. MUROMTSEV
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