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Black Sea

Sea between Europe and Asia

Top 10 Black Sea related articles

Black Sea
The location of the Black Sea
Map of the Black Sea with bathymetry and surrounding relief
LocationEurope and Western Asia
Coordinates44°N 35°E / 44°N 35°E / 44; 35Coordinates: 44°N 35°E / 44°N 35°E / 44; 35
TypeSea
Primary inflowsDanube, Dnieper, Don, Dniester, Kuban
Primary outflowsBosporus
Basin countriesBulgaria, Georgia, Romania, Russia, Turkey, Ukraine
A large number of countries included in drainage basins for inflow rivers
Max. length1,175 km (730 mi)
Surface area436,402 km2 (168,500 sq mi)[1]
Average depth1,253 m (4,111 ft)
Max. depth2,212 m (7,257 ft)
Water volume547,000 km3 (131,200 cu mi)
Islands10+
The estuary of the Veleka in the Black Sea. Longshore drift has deposited sediment along the shoreline which has led to the formation of a spit, Sinemorets, Bulgaria
Black Sea coast of western Georgia, with the skyline of Batumi on the horizon
Coastline of Samsun in Turkey
A sanatorium in Sochi, Russia

The Black Sea is a marginal sea of the Atlantic Ocean lying between Europe and Asia; east of the Balkans (Southeast Europe), south of the East European Plain in Eastern Europe, west of the Caucasus, and north of Anatolia in Western Asia. It is supplied by major rivers, principally the Danube, Dnieper, and Don. The watersheds of many countries drain into the sea beyond the six that share its coast.[2]

The Black Sea covers 436,400 km2 (168,500 sq mi) (not including the Sea of Azov),[3] a maximum depth of 2,212 m (7,257 ft),[4] and a volume of 547,000 km3 (131,000 cu mi).[5] Most of its coasts rapidly ascend. These rises are the Pontic Mountains to the south, bar the southwest facing peninsulas, the Caucasus Mountains to the east, and the Crimean Mountains to the mid-north. In the west the coast is generally small floodplains below foothills such as the Strandzha; Cape Emine, a dwindling of the east end of the Balkan Mountains; and the Dobruja Plateau considerably further north. The longest east–west extent is about 1,175 km (730 mi).[6] Important cities along the coast include Istanbul, Odessa, Varna, Samsun, Sochi, Sevastopol, Constanța, Trabzon, Novorossiysk, Burgas, Batumi, etc.

The Black Sea is bordered by Bulgaria, Georgia, Romania, Russia, Turkey, and Ukraine. It has a positive water balance with an annual net outflow of 300 km3 (72 cu mi) per year through the Bosporus and the Dardanelles into the Aegean Sea. While the net flow of water through the Bosporus and Dardanelles (known collectively as the Turkish Straits) is out of the Black Sea, generally water is flowing in both directions simultaneously. Denser, more saline water from the Aegean flows into the Black Sea underneath the less dense, fresher outflowing water from the Black Sea. This creates a significant and permanent layer of deep water that does not drain or mix and is therefore anoxic. This anoxic layer is responsible for the preservation of ancient shipwrecks which have been found in the Black Sea.

The Black Sea ultimately drains into the Mediterranean Sea, via the Turkish Straits and the Aegean Sea. The Bosporus Strait connects it to the small Sea of Marmara which in turn is connected to the Aegean Sea via the Strait of the Dardanelles. To the north, the Black Sea is connected to the Sea of Azov by the Kerch Strait.

The water level has varied significantly over geological time. Due to these variations in the water level in the basin, the surrounding shelf and associated aprons have sometimes been dry land. At certain critical water levels, connections with surrounding water bodies can become established. It is through the most active of these connective routes, the Turkish Straits, that the Black Sea joins the world ocean. During geological periods when this hydrological link was not present, the Black Sea was an endorheic basin, operating independently of the global ocean system (similar to the Caspian Sea today). Currently, the Black Sea water level is relatively high; thus, water is being exchanged with the Mediterranean. The Turkish Straits connect the Black Sea with the Aegean Sea and comprise the Bosporus, the Sea of Marmara, and the Dardanelles. The Black Sea undersea river is a current of particularly saline water flowing through the Bosporus Strait and along the seabed of the Black Sea, the first of its kind discovered.

Black Sea Intro articles: 41

Extent

The International Hydrographic Organization defines the limits of the Black Sea as follows:[7]

On the Southwest. The Northeastern limit of the Sea of Marmara [A line joining Cape Rumili with Cape Anatoli (41°13'N)]. In the Kertch Strait. A line joining Cape Takil and Cape Panaghia (45°02'N).

Black Sea Extent articles: 4

Coastline and exclusive economic zones

Coastline length and area of exclusive economic zones
Country Coastline length (km)[1] Exclusive economic zones area (km2)[8]
 Russia 800 67,351
 Turkey 1,329 172,484
 Ukraine 2,782 132,414
 Bulgaria 354 35,132
 Georgia 310 22,947
 Romania 225 29,756
Total 5,800 460,084

Largest bays

The largest bays on the Black Sea are Karkinit Bay, in Ukraine; Burgas Bay, in Bulgaria; Dnieprovski Bay and Dniestrovski Bay, both in Ukraine; and Sinop Bay and Samsun Bay, both in Turkey.[1]

Black Sea Coastline and exclusive economic zones articles: 6

Drainage basin

The 2-million km2 (0.77-million sq mi) drainage basin that flows into the Black sea covers wholly or partially 25 countries:[9][10][11][12][13]

Largest rivers

The largest rivers flowing into the Black Sea are:[1]

Black Sea Drainage basin articles: 49

Geology and bathymetry

The bay of Sudak, Crimea
Yavuz Sultan Selim Bridge is on the Black Sea connecting Europe to Asia. One of the longest suspension bridges in the world.

The Black Sea is divided into two depositional basins—the Western Black Sea and Eastern Black Sea—separated by the Mid-Black Sea High, which includes the Andrusov Ridge, Tetyaev High, and Archangelsky High, extending south from the Crimean Peninsula. The basin includes two distinct relict back-arc basins which were initiated by the splitting of an Albian volcanic arc and the subduction of both the Paleo- and Neo-Tethys Oceans, but the timings of these events remain uncertain. Arc volcanism and extension occurred as the Neo-Tethys Ocean subducted under the southern margin of Laurasia during the Mesozoic. Uplift and compressional deformation took place as the Neotethys continued to close. Seismic surveys indicate that rifting began in the Western Black Sea in the Barremian and Aptian followed by the formation of oceanic crust 20 million years later in the Santonian.[14][15][16] Since its initiation, compressional tectonic environments led to subsidence in the basin, interspersed with extensional phases resulting in large-scale volcanism and numerous orogenies, causing the uplift of the Greater Caucasus, Pontides, Southern Crimean Peninsula and Balkanides mountain ranges.[17]

During the Messinian salinity crisis in the neighboring Mediterranean Sea, water levels fell but without drying up the sea.[18]

The ongoing collision between the Eurasian and African plates and westward escape of the Anatolian block along the North Anatolian Fault and East Anatolian Faults dictates the current tectonic regime,[17] which features enhanced subsidence in the Black Sea basin and significant volcanic activity in the Anatolian region.[19] These geological mechanisms, in the long term, have caused the periodic isolations of the Black Sea from the rest of the global ocean system.

The large shelf to the north of the basin is up to 190 km (120 mi) wide and features a shallow apron with gradients between 1:40 and 1:1000. The southern edge around Turkey and the eastern edge around Georgia, however, are typified by a narrow shelf that rarely exceeds 20 km (12 mi) in width and a steep apron that is typically 1:40 gradient with numerous submarine canyons and channel extensions. The Euxine abyssal plain in the centre of the Black Sea reaches a maximum depth of 2,212 metres (7,257.22 feet) just south of Yalta on the Crimean Peninsula.[20]

The littoral zone of the Black Sea is often referred to as the Pontic littoral or Pontic zone.[21]

The area surrounding the Black Sea is commonly referred to as the Black Sea Region. Its northern part lies within the Chernozem belt (black soil belt) which goes from eastern Croatia (Slavonia), along the Danube (northern Serbia, northern Bulgaria (Danubian Plain) and southern Romania (Wallachian Plain)) to northeast Ukraine and further across the Central Black Earth Region and southern Russia into Siberia.[22]

Chronostratigraphy

The Paleo-Euxinian is described by the accumulation of eolian silt deposits (related to the Riss glaciation) and the lowering of sea levels (MIS 6, 8 and 10). The Karangat marine transgression occurred during the Eemian Interglacial (MIS 5e). This may have been the highest sea levels reached in the late Pleistocene. Based on this some scholars have suggested that the Crimean Peninsula was isolated from the mainland by a shallow strait during the Eemian Interglacial.[23]

The Neoeuxinian transgression began with an inflow of waters from the Caspian Sea. Neoeuxinian deposits are found in the Black Sea below −20 m (−66 ft) water depth in three layers. The upper layers correspond with the peak of the Khvalinian transgression, on the shelf shallow-water sands and coquina mixed with silty sands and brackish-water fauna, and inside the Black Sea Depression hydrotroilite silts. The middle layers on the shelf are sands with brackish-water mollusc shells. Of continental origin, the lower level on the shelf is mostly alluvial sands with pebbles, mixed with less common lacustrine silts and freshwater mollusc shells. Inside the Black Sea Depression they are terrigenous non-carbonate silts, and at the foot of the continental slope turbidite sediments.[24]

Black Sea Geology and bathymetry articles: 49

Name

Coast of the Black Sea at Ordu
Sunset on the Black Sea at Laspi, Crimea
The Black Sea near Constanța, Romania

Modern names

Current names of the sea are usually equivalents of the English name "Black Sea", including these given in the countries bordering the sea:[25]

Such names have not yet been shown conclusively to predate the 13th century.[26]

In Greece, the historical name "Euxine Sea", which holds a different meaning (see below), is still widely used:

Historical names and etymology

The principal Greek name Póntos Áxeinos is generally accepted to be a rendering of Iranian word *axšaina- (dark colored).[26] This became the commonly used designation in Greek, although in mythological contexts the "true" name Póntos Áxeinos remained favored.[26]

Strabo's Geographica (1.2.10) reports that in antiquity, the Black Sea was often simply called "the Sea" (ὁ πόντος ho Pontos). He also thought the Black Sea was called "inhospitable" before Greek colonization for its difficult navigation and hostile barbarian natives (7.3.6), and that the name was changed to "hospitable" after the Milesians colonized the Pontus region of the southern shoreline, bringing it within Greek civilization.

Popular supposition derives "Black Sea" from the dark color of the water or climatic conditions. Rather, it referred to a system of color symbolism representing the cardinal directions, with black or dark for north, red for south, white for west, and green or light blue for east.[26] Hence "Black Sea" meant "Northern Sea". According to this scheme, the name could not have originated with the Scythians, who principally roamed north of the sea, but only with a people living between the northern (black) and southern (red) seas: this points to the Achaemenids (550–330  BC).[26]

In the Greater Bundahishn, a Middle Persian Zoroastrian scripture, the Black Sea is called Siyābun.[27] In the tenth-century Persian geography book Hudud al-'Alam, the Black Sea is called Sea of the Georgians (daryā-yi Gurz).[28] The Georgian Chronicles use the name zğua sperisa ზღუა სპერისა (Sea of Speri) after the Kartvelian tribe of Speris or Saspers.[29] Other modern names such as Chyornoye more and Karadeniz, originated in the 13th century.[26] A 1570 map Asiae Nova Descriptio from Abraham Ortelius's Theatrum Orbis Terrarum labels the sea Mar Maggior (Great Sea), compare Latin mare major.[30]

English writers of the 18th century often used Euxine Sea (/ˈjksɪn/ or /ˈjkˌsn/).[31] During the Ottoman Empire, it was called either Bahr-e Siyah or Karadeniz, both meaning "Black Sea" in Turkish.[32]

Black Sea Name articles: 38

Hydrology

This SeaWiFS view reveals the colorful interplay of currents on the sea's surface

The Black Sea is the world's largest inland body of water,[a] and is the world's largest body of water with a meromictic basin.[33] The deep waters do not mix with the upper layers of water that receive oxygen from the atmosphere. As a result, over 90% of the deeper Black Sea volume is anoxic water.[34] The Black Sea's circulation patterns are primarily controlled by basin topography and fluvial inputs, which result in a strongly stratified vertical structure. Because of the extreme stratification, it is classified as a salt wedge estuary.

The Black Sea only experiences water transfer with the Mediterranean Sea, so all inflow and outflow occurs in the Bosporus and Dardanelles. Inflow from the Mediterranean has a higher salinity and density than the outflow, creating the classic estuarine circulation. This means that the inflow of dense water from the Mediterranean occurs at the bottom of the basin while the outflow of fresher Black Sea surface-water into the Marmara Sea occurs near the surface. The outflow is 16,000 m3/s (570,000 cu ft/s) (around 500 km3/a or 120 cubic miles per year) and the inflow is 11,000 m3/s (390,000 cu ft/s) (around 350 km3/a or 84 cubic miles per year), acc to Gregg (2002).[35]

The following water budget can be estimated:

  • Water IN: 900 km3/a (220 cu mi/a)
    • Total river discharge : 370 km3/a (90 cu mi/a)[36]
    • Precipitation : 180 km3/a (40 cu mi/a)[37]
    • Inflow via Bosporus : 350 km3/a (80 cu mi/a)[35]
  • Water OUT: 900 km3/a (220 cu mi/a)
    • Evaporation : 400 km3/a (100 cu mi/a) (reducing since the 1970s)[37]
    • Outflow via Bosporus : 500 km3/a (120 cu mi/a)[35]

The southern sill of the Bosporus is located at −36.5 m (−120 ft) below present sea level (deepest spot of the shallowest cross-section in the Bosporus, located in front of Dolmabahçe Palace) and has a wet section of around 38,000 m2 (410,000 sq ft).[35] Inflow and outflow current speeds are averaged around 0.3 to 0.4 m/s (1.0 to 1.3 ft/s), but much higher speeds are found locally, inducing significant turbulence and vertical shear. This allows for turbulent mixing of the two layers.[38] Surface water leaves the Black Sea with a salinity of 17 Practical salinity unit (PSU) and reaches the Mediterranean with a salinity of 34 PSU. Likewise, an inflow of the Mediterranean with salinity 38.5 PSU experiences a decrease to about 34 PSU.[38]

Mean surface circulation is cyclonic and waters around the perimeter of the Black Sea circulate in a basin-wide shelfbreak gyre known as the Rim Current. The Rim Current has a maximum velocity of about 50–100 cm/s (20–39 in/s). Within this feature, two smaller cyclonic gyres operate, occupying the eastern and western sectors of the basin.[38] The Eastern and Western Gyres are well-organized systems in the winter but dissipate into a series of interconnected eddies in the summer and autumn. Mesoscale activity in the peripheral flow becomes more pronounced during these warmer seasons and is subject to interannual variability.

Outside of the Rim Current, numerous quasi-permanent coastal eddies are formed as a result of upwelling around the coastal apron and "wind curl" mechanisms. The intra-annual strength of these features is controlled by seasonal atmospheric and fluvial variations. During the spring, the Batumi eddy forms in the southeastern corner of the sea.[39]

Beneath the surface waters—from about 50–100 metres (160–330 ft)—there exists a halocline that stops at the Cold Intermediate Layer (CIL). This layer is composed of cool, salty surface waters, which are the result of localized atmospheric cooling and decreased fluvial input during the winter months. It is the remnant of the winter surface mixed layer.[38] The base of the CIL is marked by a major pycnocline at about 100–200 metres (330–660 ft) and this density disparity is the major mechanism for isolation of the deep water.

Below the pycnocline is the Deep Water mass, where salinity increases to 22.3 PSU and temperatures rise to around 8.9 °C (48.0 °F).[38] The hydrochemical environment shifts from oxygenated to anoxic, as bacterial decomposition of sunken biomass utilizes all of the free oxygen. Weak geothermal heating and long residence time create a very thick convective bottom layer.[39]

The Black Sea undersea river is a current of particularly saline water flowing through the Bosporus Strait and along the seabed of the Black Sea. The discovery of the river announced on August 1, 2010, was made by scientists at the University of Leeds and is the first of its kind in the world.[40] The undersea river stems from salty water spilling through the Bosporus Strait from the Mediterranean Sea into the Black Sea, where the water has a lower salt content.[40]

Black Sea Hydrology articles: 13