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68-565: Borçka is reached by a winding road up from the Black Sea coast, alongside the Çoruh River ( Nigali valley ). There is a medieval stone arched bridge across the river just west of the town. Borçka Lake is a popular excursion from Artvin . This geographical article about a location in Artvin Province , Turkey is a stub . You can help Misplaced Pages by expanding it . Black Sea Unrecognised states: The Black Sea

136-527: 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. The base of the CIL is marked by a major pycnocline at about 100–200 metres (330–660 ft), and this density disparity

204-597: A coastline on the sea, its drainage basin includes parts of 24 countries in Europe. The Black Sea, not including the Sea of Azov , covers 436,400 km (168,500 sq mi), has a maximum depth of 2,212 m (7,257 ft), and a volume of 547,000 km (131,000 cu mi). Most of its coasts ascend rapidly. These rises are the Pontic Mountains to the south, bar the southwest-facing peninsulas,

272-455: A continental shelf differs significantly from the geological definition. UNCLOS states that the shelf extends to the limit of the continental margin , but no less than 200 nmi (370 km; 230 mi) and no more than 350 nmi (650 km; 400 mi) from the baseline . Thus inhabited volcanic islands such as the Canaries , which have no actual continental shelf, nonetheless have

340-556: A decrease in the flux of silicon associated with advection across isopycnal surfaces. This phenomenon demonstrates the potential for localized alterations in Black Sea nutrient-input to have basin-wide effects. Continental shelf A continental shelf is a portion of a continent that is submerged under an area of relatively shallow water, known as a shelf sea . Much of these shelves were exposed by drops in sea level during glacial periods . The shelf surrounding an island

408-832: A distance where the depth of waters admitted of resource exploitation were claimed by the marine nations that signed the Convention on the Continental Shelf drawn up by the UN's International Law Commission in 1958. This was partly superseded by the 1982 United Nations Convention on the Law of the Sea (UNCLOS). The 1982 convention created the 200 nautical miles (370 km; 230 mi) exclusive economic zone, plus continental shelf rights for states with physical continental shelves that extend beyond that distance. The legal definition of

476-484: A marked vertical stratification and a warm, shallow mixed layer. Day length and insolation intensity also control the extent of the photic zone . Subsurface productivity is limited by nutrient availability, as the anoxic bottom waters act as a sink for reduced nitrate , in the form of ammonia . The benthic zone also plays an important role in Black Sea nutrient cycling, as chemosynthetic organisms and anoxic geochemical pathways recycle nutrients which can be upwelled to

544-589: A strongly stratified vertical structure. Because of the extreme stratification, it is classified as a salt wedge estuary . Inflow from the Mediterranean Sea through the Bosporus and Dardanelles 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

612-433: A threat to health—and perhaps even life—for people living on the Black Sea coast. There have been isolated reports of flares on the Black Sea occurring during thunderstorms, possibly caused by lightning igniting combustible gas seeping up from the sea depths. The Black Sea supports an active and dynamic marine ecosystem, dominated by species suited to the brackish , nutrient-rich, conditions. As with all marine food webs,

680-529: A very thick convective bottom layer. 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 to be identified. The undersea river stems from salty water spilling through

748-496: A weaker mixed assemblage of community development below the seasonal thermocline during summer months, and surface-intensified autumn production. This pattern of productivity is augmented by an Emiliania huxleyi bloom during the late spring and summer months. Since the 1960s, rapid industrial expansion along the Black Sea coastline and the construction of a major dam on the Danube have significantly increased annual variability in

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816-631: Is a marginal mediterranean sea lying between Europe and Asia , east of the Balkans , south of the East European Plain , west of the Caucasus , and north of Anatolia . It is bounded by Bulgaria , Georgia , Romania , Russia , Turkey , and Ukraine . The Black Sea is supplied by major rivers, principally the Danube , Dnieper and Dniester . Consequently, while six countries have

884-593: Is also minimal, at less than 20 m (66 ft). Though the continental shelf is treated as a physiographic province of the ocean , it is not part of the deep ocean basin proper, but the flooded margins of the continent. Passive continental margins such as most of the Atlantic coasts have wide and shallow shelves, made of thick sedimentary wedges derived from long erosion of a neighboring continent. Active continental margins have narrow, relatively steep shelves, due to frequent earthquakes that move sediment to

952-753: 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

1020-469: Is evidence that changing wind, rainfall, and regional ocean currents in a warming ocean are having an effect on some shelf seas. Improved data collection via Integrated Ocean Observing Systems in shelf sea regions is making identification of these changes possible. Continental shelves teem with life because of the sunlight available in shallow waters, in contrast to the biotic desert of the oceans' abyssal plain . The pelagic (water column) environment of

1088-719: Is generally accepted to be a rendering of the Iranian word * axšaina- ("dark colored"). Ancient Greek voyagers adopted the name as Á-xe(i)nos , identified with the Greek word áxeinos (inhospitable). The name Πόντος Ἄξεινος Póntos Áxeinos (Inhospitable Sea), first attested in Pindar ( c.  475 BC ), was considered an ill omen and was euphemized to its opposite, Εὔξεινος Πόντος Eúxeinos Póntos (Hospitable Sea), also first attested in Pindar. This became

1156-462: Is known as an insular shelf . The continental margin , between the continental shelf and the abyssal plain , comprises a steep continental slope, surrounded by the flatter continental rise , in which sediment from the continent above cascades down the slope and accumulates as a pile of sediment at the base of the slope. Extending as far as 500 km (310 mi) from the slope, it consists of thick sediments deposited by turbidity currents from

1224-414: Is often cut with submarine canyons . The physical mechanisms involved in forming these canyons were not well understood until the 1960s. Continental shelves cover an area of about 27 million km (10 million sq mi), equal to about 7% of the surface area of the oceans. The width of the continental shelf varies considerably—it is not uncommon for an area to have virtually no shelf at all, particularly where

1292-590: 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. Beneath the surface waters—from about 50 to 100 metres (160 to 330 ft)—there exists

1360-460: 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). 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

1428-587: The Bosporus ) Burgas , Varna , Constanța , Odesa , Sevastopol , Novorossiysk , Sochi , Poti , Batumi , Trabzon and Samsun . The Black Sea has a positive water balance , with an annual net outflow of 300 km (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

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1496-749: 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 farther north. The longest east–west extent is about 1,175 km (730 mi). Important cities along the coast include (clockwise from

1564-917: 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 . The littoral zone of the Black Sea is often referred to as the Pontic littoral or Pontic zone . The largest bays of the Black Sea are Karkinit Bay in Ukraine; the Gulf of Burgas in Bulgaria; Dnieprovski Bay and Dniestrovski Bay, both in Ukraine; and Sinop Bay and Samsun Bay, both in Turkey. The largest rivers flowing into

1632-748: The North Atlantic oscillation , the climatic mechanisms resulting from the interaction between the north Atlantic and mid-latitude air masses. While the exact mechanisms causing the North Atlantic Oscillation remain unclear, it is thought the climate conditions established in western Europe mediate the heat and precipitation fluxes reaching Central Europe and Eurasia, regulating the formation of winter cyclones , which are largely responsible for regional precipitation inputs and influence Mediterranean sea surface temperatures (SSTs). The relative strength of these systems also limits

1700-632: The Santonian . 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. During the Messinian salinity crisis in the neighboring Mediterranean Sea , water levels fell but without drying up

1768-516: The Turkish Straits ) is out of the Black Sea, water generally flows in both directions simultaneously: Denser, more saline water from the Aegean flows into the Black Sea underneath the less dense, fresher water that flows out of 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

1836-484: The shelf break ). The sea floor below the break is the continental slope . Below the slope is the continental rise , which finally merges into the deep ocean floor, the abyssal plain . The continental shelf and the slope are part of the continental margin . The shelf area is commonly subdivided into the inner continental shelf , mid continental shelf , and outer continental shelf , each with their specific geomorphology and marine biology . The character of

1904-643: The 13th century. A 1570 map Asiae Nova Descriptio from Abraham Ortelius 's Theatrum Orbis Terrarum labels the sea Mar Maggior (Great Sea), compare Latin Mare major . English writers of the 18th century often used Euxine Sea ( / ˈ j uː k s ɪ n / or / ˈ j uː k ˌ s aɪ n / ). During the Ottoman Empire , it was called either Bahr-e Siyah ( Perso-Arabic ) or Karadeniz ( Ottoman Turkish ), both meaning "Black Sea". The International Hydrographic Organization defines

1972-567: The Asian mainland. Other familiar bodies of water that overlie continental shelves are the North Sea and the Persian Gulf . The average width of continental shelves is about 80 km (50 mi). The depth of the shelf also varies, but is generally limited to water shallower than 100 m (330 ft). The slope of the shelf is usually quite low, on the order of 0.5°; vertical relief

2040-582: The Black Sea Depression they are terrigenous non-carbonate silts , and at the foot of the continental slope turbidite sediments. The Black Sea is the world's largest body of water with a meromictic basin. 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. The Black Sea's circulation patterns are primarily controlled by basin topography and fluvial inputs, which result in

2108-404: The Black Sea are: These rivers and their tributaries comprise a 2-million km (0.77-million sq mi) Black Sea drainage basin that covers wholly or partially 24 countries: Unrecognised states: Some islands in the Black Sea belong to Bulgaria, Romania, Turkey, and Ukraine: Short-term climatic variation in the Black Sea region is significantly influenced by the operation of

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2176-585: The Black Sea features a range of trophic groups, with autotrophic algae, including diatoms and dinoflagellates , acting as primary producers. The fluvial systems draining Eurasia and central Europe introduce large volumes of sediment and dissolved nutrients into the Black Sea, but the distribution of these nutrients is controlled by the degree of physiochemical stratification, which is, in turn, dictated by seasonal physiographic development. During winter, strong wind promotes convective overturning and upwelling of nutrients, while high summer temperatures result in

2244-510: 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

2312-478: The Black Sea is called Siyābun . In the tenth-century Persian geography book Hudud al-'Alam , the Black Sea is called Georgian Sea ( daryā-yi Gurz ). The Georgian Chronicles use the name zğua sperisa ზღუა სპერისა (Sea of Speri) after the Kartvelian tribe of Speris or Saspers . Other modern names such as Chyornoye more and Karadeniz (both meaning Black Sea) originated during

2380-503: 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 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. Current names of

2448-525: The Bosporus Strait from the Mediterranean Sea into the Black Sea, where the water has a lower salt content. Because of the anoxic water at depth, organic matter, including anthropogenic artifacts such as boat hulls, are well preserved. During periods of high surface productivity, short-lived algal blooms form organic rich layers known as sapropels . Scientists have reported an annual phytoplankton bloom that can be seen in many NASA images of

2516-483: 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 m (410,000 sq ft). 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

2584-576: The N:P:Si ratio in the basin. Coastal areas, accordingly, have seen an increase in the frequency of monospecific phytoplankton blooms, with diatom-bloom frequency increasing by a factor of 2.5 and non-diatom bloom frequency increasing by a factor of 6. The non-diatoms, such as the prymnesiophytes Emiliania huxleyi (coccolithophore), Chromulina sp., and the Euglenophyte Eutreptia lanowii , can out-compete diatom species because of

2652-464: 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. 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

2720-471: The amount of cold air arriving from northern regions during winter. Other influencing factors include the regional topography , as depressions and storm systems arriving from the Mediterranean are funneled through the low land around the Bosporus, with the Pontic and Caucasus mountain ranges acting as waveguides, limiting the speed and paths of cyclones passing through the region. The Black Sea

2788-551: The cardinal directions , with black or dark for north, red for south, white for west, and green or light blue for east. Hence, "Black Sea" meant "Northern Sea". According to this scheme, the name could only have originated with a people living between the northern (black) and southern (red) seas : this points to the Achaemenids (550–330 BC). In the Greater Bundahishn , a Middle Persian Zoroastrian scripture,

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2856-532: 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 . 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

2924-567: The coast; sand is limited to shallow, wave-agitated waters, while silt and clays are deposited in quieter, deep water far offshore. These accumulate 15–40 centimetres (5.9–15.7 in) every millennium, much faster than deep-sea pelagic sediments . "Shelf seas" are the ocean waters on the continental shelf. Their motion is controlled by the combined influences of the tides , wind-forcing and brackish water formed from river inflows ( Regions of Freshwater Influence ). These regions can often be biologically highly productive due to mixing caused by

2992-469: The commonly used designation in Greek, although in mythological contexts the "true" name Póntos Áxeinos remained favoured. Strabo 's Geographica (1.2.10) reports that in antiquity, the Black Sea was often simply called "the Sea" ( ὁ πόντος ho Pontos ). He thought that the sea was called the "Inhospitable Sea Πόντος Ἄξεινος Póntos Áxeinos by the inhabitants of the Pontus region of

3060-420: The continental shelf constitutes the neritic zone , and the benthic (sea floor) province of the shelf is the sublittoral zone . The shelves make up less than 10% of the ocean, and a rough estimate suggests that only about 30% of the continental shelf sea floor receives enough sunlight to allow benthic photosynthesis. Though the shelves are usually fertile, if anoxic conditions prevail during sedimentation,

3128-418: The deep sea. The continental shelves are covered by terrigenous sediments ; that is, those derived from erosion of the continents. However, little of the sediment is from current rivers ; some 60–70% of the sediment on the world's shelves is relict sediment , deposited during the last ice age, when sea level was 100–120 m lower than it is now. Sediments usually become increasingly fine with distance from

3196-433: The deposits may over geologic time become sources for fossil fuels . The continental shelf is the best understood part of the ocean floor, as it is relatively accessible. Most commercial exploitation of the sea, such as extraction of metallic ore, non-metallic ore, and hydrocarbons , takes place on the continental shelf. Sovereign rights over their continental shelves down to a depth of 100 m (330 ft) or to

3264-618: The forward edge of an advancing oceanic plate dives beneath continental crust in an offshore subduction zone such as off the coast of Chile or the west coast of Sumatra . The largest shelf—the Siberian Shelf in the Arctic Ocean —stretches to 1,500 kilometers (930 mi) in width. The South China Sea lies over another extensive area of continental shelf, the Sunda Shelf , which joins Borneo , Sumatra, and Java to

3332-512: 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. 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

3400-518: The late 1980s. Additionally, an alien species—the warty comb jelly ( Mnemiopsis leidyi )—established itself in the basin, exploding from a few individuals to an estimated biomass of one billion metric tons. The change in species composition in Black Sea waters also has consequences for hydrochemistry, as calcium-producing coccolithophores influence salinity and pH, although these ramifications have yet to be fully quantified. In central Black Sea waters, silicon levels also reduced significantly, due to

3468-407: The limited availability of silicon, a necessary constituent of diatom frustules. As a consequence of these blooms, benthic macrophyte populations were deprived of light, while anoxia caused mass mortality in marine animals. Overfishing during the 1970s further compounded the decline in macrophytes, while the invasive ctenophore Mnemiopsis reduced the biomass of copepods and other zooplankton in

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3536-702: The limits of the Black Sea as follows: 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). 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

3604-752: The others being the Red Sea , the White Sea and the Yellow Sea . The earliest known name of the Black Sea is the Sea of Zalpa, so called by both the Hattians and their conquerors, the Hittites . The Hattic city of Zalpa was "situated probably at or near the estuary of the Marrassantiya River, the modern Kızıl Irmak , on the Black Sea coast." The principal Greek name Póntos Áxeinos

3672-454: The outflow of fresher Black Sea surface-water into the Sea of Marmara occurs near the surface. According to Gregg (2002), the outflow is 16,000 cubic metres per second (570,000 cubic feet per second) or around 500 cubic kilometres per year (120 cubic miles per year), and the inflow is 11,000 m /s (390,000 cu ft/s) or around 350 km /a (84 cu mi/a). The following water budget can be estimated: The southern sill of

3740-507: 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

3808-488: The photic zone, enhancing productivity. In total, the Black Sea's biodiversity contains around one-third of the Mediterranean's and is experiencing natural and artificial invasions or "Mediterranizations". The main phytoplankton groups present in the Black Sea are dinoflagellates , diatoms , coccolithophores and cyanobacteria . Generally, the annual cycle of phytoplankton development comprises significant diatom and dinoflagellate-dominated spring production, followed by

3876-681: The preservation of ancient shipwrecks which have been found in the Black Sea, which 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

3944-493: The region. As a result of these characteristics the Black Sea has gained interest from the field of marine archaeology , as ancient shipwrecks in excellent states of preservation have been discovered, such as the Byzantine wreck Sinop D , located in the anoxic layer off the coast of Sinop, Turkey . Modelling shows that, in the event of an asteroid impact on the Black Sea, the release of hydrogen sulfide clouds would pose

4012-469: The sea are usually equivalents of the English name "Black Sea", including these given in the countries bordering the sea: Such names have not yet been shown conclusively to predate the 13th century. In Greece , the historical name "Euxine Sea", which holds a different literal meaning (see below), is still widely used: The Black Sea is one of four seas named in English after common color terms –

4080-647: The sea. The collision between the Eurasian and African plates and the westward escape of the Anatolian block along the North Anatolian and East Anatolian faults dictates the current tectonic regime, which features enhanced subsidence in the Black Sea basin and significant volcanic activity in the Anatolian region. These geological mechanisms, in the long term, have caused the periodic isolations of

4148-400: The shallower waters and the enhanced current speeds. Despite covering only about 8% of Earth's ocean surface area, shelf seas support 15–20% of global primary productivity . In temperate continental shelf seas, three distinctive oceanographic regimes are found, as a consequence of the interplay between surface heating, lateral buoyancy gradients (due to river inflow), and turbulent mixing by

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4216-485: The shelf and slope. The continental rise 's gradient is intermediate between the gradients of the slope and the shelf. Under the United Nations Convention on the Law of the Sea , the name continental shelf was given a legal definition as the stretch of the seabed adjacent to the shores of a particular country to which it belongs. The shelf usually ends at a point of increasing slope (called

4284-428: The shelf changes dramatically at the shelf break, where the continental slope begins. With a few exceptions, the shelf break is located at a remarkably uniform depth of roughly 140 m (460 ft); this is likely a hallmark of past ice ages, when sea level was lower than it is now. The continental slope is much steeper than the shelf; the average angle is 3°, but it can be as low as 1° or as high as 10°. The slope

4352-441: The southern shoreline before Greek colonisation due to its difficult navigation and hostile barbarian natives (7.3.6), and that the name was changed to "hospitable" after the Milesians colonised the region, bringing it into the Greek world. Popular supposition derives "Black Sea" from the dark color of the water or climatic conditions. Some scholars understand the name to be derived from a system of colour symbolism representing

4420-407: The tides and to a lesser extent the wind. Indian Ocean shelf seas are dominated by major river systems, including the Ganges and Indus rivers. The shelf seas around New Zealand are complicated because the submerged continent of Zealandia creates wide plateaus. Shelf seas around Antarctica and the shores of the Arctic Ocean are influenced by sea ice production and polynya . There

4488-439: 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

4556-408: The two layers. Surface water leaves the Black Sea with a salinity of 17 practical salinity units (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. Mean surface circulation is cyclonic ; waters around the perimeter of the Black Sea circulate in a basin-wide shelfbreak gyre known as

4624-399: 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,

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