The Black Sea has a positive water balance, with an annual net outflow of 300km3 (72cumi) per year through the Bosporus and the Dardanelles into the Aegean Sea.[6] While the net flow of water through the Bosporus and Dardanelles (known collectively as 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 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 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 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.[citation needed]
Name
Coast of the Black Sea at OrduKapchik Cape in CrimeaThe Black Sea near Constanța, RomaniaCoast of the Black Sea at Burgas
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:[7]
The earliest known name of the Black Sea is the Sea of Zalpa, so called by both the Hattians[9] 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."[10]
The principal Greek name Póntos Áxeinos is generally accepted to be a rendering of the Iranian word *axšaina- ("dark colored").[8] Ancient Greek voyagers adopted the name as Á-xe(i)nos, identified with the Greek word áxeinos (inhospitable).[8] The name Πόντος ἌξεινοςPóntos Áxeinos (Inhospitable Sea), first attested in Pindar (c.475 BC), was considered an ill omen and was euphemized to its opposite, Εὔξεινος ΠόντοςEúxeinos Póntos (Hospitable Sea), also first attested in Pindar. This became the commonly used designation in Greek, although in mythological contexts the "true" name Póntos Áxeinos remained favoured.[8]
Strabo's Geographica (1.2.10) reports that in antiquity, the Black Sea was often simply called "the Sea" (ὁ πόντοςho Pontos).[11] He thought that the sea was called the "Inhospitable Sea Πόντος ἌξεινοςPóntos Áxeinos by the inhabitants of the Pontus region of 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 Milesianscolonised the region, bringing it into the Greek world.[12]
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 the cardinal directions, with black or dark for north, red for south, white for west, and green or light blue for east.[8] 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).[8]
In the Greater Bundahishn, a Middle PersianZoroastrian scripture, the Black Sea is called Siyābun.[13] In the tenth-century Persian geography book Hudud al-'Alam, the Black Sea is called Georgian Sea (daryā-yi Gurz).[14]The Georgian Chronicles use the name zğua sperisaზღუა სპერისა (Sea of Speri) after the Kartvelian tribe of Speris or Saspers.[15] Other modern names such as Chyornoye more and Karadeniz (both meaning Black Sea) originated during the 13th century.[8] A 1570 map Asiae Nova Descriptio from Abraham Ortelius's Theatrum Orbis Terrarum labels the sea Mar Maggior (Great Sea), compare Latin Mare major.[16]
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.[19]
The littoral zone of the Black Sea is often referred to as the Pontic littoral or Pontic zone.[20]
These rivers and their tributaries comprise a 2-millionkm2 (0.77-millionsqmi) Black Sea drainage basin that covers wholly or partially 24 countries:[24][25][26][27][28]
Short-term climatic variation in the Black Sea region is significantly influenced by the operation of the North Atlantic oscillation, the climatic mechanisms resulting from the interaction between the north Atlantic and mid-latitude air masses.[29] While the exact mechanisms causing the North Atlantic Oscillation remain unclear,[30] 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[31] and influence Mediterranean sea surface temperatures (SSTs).[32]
The relative strength of these systems also limits the amount of cold air arriving from northern regions during winter.[33] 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.[34]
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 Albianvolcanic 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 20million years later in the Santonian.[35][36][37] 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.[38]
The Yavuz Sultan Selim Bridge in Istanbul, Turkey, crosses the Bosporus strait near its entrance to the Black Sea. Connecting Europe and Asia, it is one of the tallest suspension bridges in the world.
During the Messinian salinity crisis in the neighboring Mediterranean Sea, water levels fell but without drying up the sea.[39] 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,[38] which features enhanced subsidence in the Black Sea basin and significant volcanic activity in the Anatolian region.[40] 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 190km (120mi) 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 20km (12mi) 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.[41]
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 EemianInterglacial (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.[42]
The Neoeuxinian transgression began with an inflow of waters from the Caspian Sea. Neoeuxinian deposits are found in the Black Sea below −20m (−66ft) 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 slopeturbidite sediments.[43]
Hydrology
This SeaWiFS view reveals the colorful interplay of currents on the sea's surface.
The Black Sea is the world's largest body of water with a meromictic basin.[44] 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.[45] 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.
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 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 11,000m3/s (390,000cuft/s) or around 350km3/a (84cumi/a).[46]
The following water budget can be estimated:[when?]
The southern sill of the Bosporus is located at 36.5m (120ft) 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 38,000m2 (410,000sqft).[46] Inflow and outflow current speeds are averaged around 0.3 to 0.4m/s (1.0 to 1.3ft/s), but much higher speeds are found locally, inducing significant turbulence and vertical shear. This allows for turbulent mixing of the two layers.[49] 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.[49]
Mean surface circulation is cyclonic; 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 50–100cm/s (20–39in/s). Within this feature, two smaller cyclonic gyres operate, occupying the eastern and western sectors of the basin.[49] 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.[50]
Beneath the surface waters—from about 50 to 100 metres (160 to 330ft)—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.[49] The base of the CIL is marked by a major pycnocline at about 100–200 metres (330–660ft), 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).[49] 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.[50]
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.[51] 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.[51]
Hydrochemistry
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 the region.[52] 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 a threat to health—and perhaps even life—for people living on the Black Sea coast.[53]
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.[54]
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, 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.[55]
During winter, strong wind promotes convective overturning and upwelling of nutrients, while high summer temperatures result in a marked vertical stratification and a warm, shallow mixed layer.[56] 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 the photic zone, enhancing productivity.[57]
In total, the Black Sea's biodiversity contains around one-third of the Mediterranean's and is experiencing natural and artificial invasions or "Mediterranizations".[58][59]
Phytoplankton
Phytoplankton blooms and plumes of sediment form the bright blue swirls that ring the Black Sea in this 2004 image.
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 a weaker mixed assemblage of community development below the seasonal thermocline during summer months, and surface-intensified autumn production.[56][60] This pattern of productivity is augmented by an Emiliania huxleyi bloom during the late spring and summer months.
Annual dinoflagellate distribution is defined by an extended bloom period in subsurface waters during the late spring and summer. In November, subsurface plankton production is combined with surface production, due to vertical mixing of water masses and nutrients such as nitrite.[55] The major bloom-forming dinoflagellate species in the Black Sea is Gymnodinium sp.[61] Estimates of dinoflagellate diversity in the Black Sea range from 193[62] to 267 species.[63] This level of species richness is relatively low in comparison to the Mediterranean Sea, which is attributable to the brackish conditions, low water transparency and presence of anoxic bottom waters. It is also possible that the low winter temperatures below 4°C (39°F) of the Black Sea prevent thermophilous species from becoming established. The relatively high organic matter content of Black Sea surface water favor the development of heterotrophic (an organism that uses organic carbon for growth) and mixotrophic dinoflagellates species (able to exploit different trophic pathways), relative to autotrophs. Despite its unique hydrographic setting, there are no confirmed endemic dinoflagellate species in the Black Sea.[63]
The Black Sea is populated by many species of the marine diatom, which commonly exist as colonies of unicellular, non-motile auto- and heterotrophic algae. The life-cycle of most diatoms can be described as 'boom and bust' and the Black Sea is no exception, with diatom blooms occurring in surface waters throughout the year, most reliably during March.[55] In simple terms, the phase of rapid population growth in diatoms is caused by the in-wash of silicon-bearing terrestrial sediments, and when the supply of silicon is exhausted, the diatoms begin to sink out of the photic zone and produce resting cysts. Additional factors such as predation by zooplankton and ammonium-based regenerated production also have a role to play in the annual diatom cycle.[55][56] Typically, Proboscia alata blooms during spring and Pseudosolenia calcar-avis blooms during the autumn.[61]
Coccolithophores are a type of motile, autotrophicphytoplankton that produce CaCO3 plates, known as coccoliths, as part of their life cycle. In the Black Sea, the main period of coccolithophore growth occurs after the bulk of the dinoflagellate growth has taken place. In May, the dinoflagellates move below the seasonal thermocline into deeper waters, where more nutrients are available. This permits coccolithophores to utilize the nutrients in the upper waters, and by the end of May, with favorable light and temperature conditions, growth rates reach their highest. The major bloom-forming species is Emiliania huxleyi, which is also responsible for the release of dimethyl sulfide into the atmosphere. Overall, coccolithophore diversity is low in the Black Sea, and although recent sediments are dominated by E. huxleyi and Braarudosphaera bigelowii, Holocene sediments have been shown to also contain Helicopondosphaera and Discolithina species.
Cyanobacteria are a phylum of picoplanktonic (plankton ranging in size from 0.2 to 2.0 μm) bacteria that obtain their energy via photosynthesis, and are present throughout the world's oceans. They exhibit a range of morphologies, including filamentous colonies and biofilms. In the Black Sea, several species are present, and as an example, Synechococcus spp. can be found throughout the photic zone, although concentration decreases with increasing depth. Other factors which exert an influence on distribution include nutrient availability, predation, and salinity.[64]
The Black Sea along with the Caspian Sea is part of the zebra mussel's native range. The mussel has been accidentally introduced around the world and become an invasive species where it has been introduced.
The common carp's native range extends to the Black Sea along with the Caspian Sea and Aral Sea. Like the zebra mussel, the common carp is an invasive species when introduced to other habitats.
Another native fish that is also found in the Caspian Sea. It preys upon zebra mussels. Like the mussels and common carp, it has become invasive when introduced to other environments, like the Great Lakes in North America.
Marine mammals present within the basin include two species of dolphin (common[65] and bottlenose[66]) and the harbour porpoise,[67] although all of these are endangered due to pressures and impacts by human activities. All three species have been classified as distinct subspecies from those in the Mediterranean and the Atlantic and are endemic to the Black and Azov seas, and are more active during nights in the Turkish Straits.[68] However, construction of the Crimean Bridge has caused increases in nutrients and planktons in the waters, attracting large numbers of fish and more than 1,000 bottlenose dolphins.[69] However, others claim that construction may cause devastating damages on the ecosystem, including dolphins.[70]
Ongoing Mediterranizations may or may not boost cetacean diversity in the Turkish Straits[68] and hence in the Black and Azov basins.
Various species of pinnipeds, sea otter, and beluga whale[74][75] were introduced into the Black Sea by mankind and later escaped either by accidental or purported causes. Of these, grey seals[76] and beluga whales[74] have been recorded with successful, long-term occurrences.
Great white sharks are known to reach into the Sea of Marmara and Bosporus Strait and basking sharks into the Dardanelles, although it is unclear whether or not these sharks may reach into the Black and Azov basins.[77][78]
Ecological effects of pollution
Since the 1960s, rapid industrial expansion along the Black Sea coastline and the construction of a major dam has significantly increased annual variability in the N:P:Si ratio in the basin. In coastal areas, the biological effect of these changes has been 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, are able to out-compete diatom species because of the limited availability of silicon, a necessary constituent of diatom frustules.[79] As a consequence of these blooms, benthic macrophyte populations were deprived of light, while anoxia caused mass mortality in marine animals.[80][81]
The decline in macrophytes was further compounded by overfishing during the 1970s, while the invasive ctenophore Mnemiopsis reduced the biomass of copepods and other zooplankton in the late 1980s. Additionally, an alien species—the warty comb jelly (Mnemiopsis leidyi)—was able to establish itself in the basin, exploding from a few individuals to an estimated biomass of one billion metric tons.[82] 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 were also significantly reduced, due to 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.
Pollution reduction and regulation efforts have led to a partial recovery of the Black Sea ecosystem during the 1990s, and an EU monitoring exercise, 'EROS21', revealed decreased nitrogen and phosphorus values, relative to the 1989 peak.[83] Recently, scientists have noted signs of ecological recovery, in part due to the construction of new sewage treatment plants in Slovakia, Hungary, Romania, and Bulgaria in connection with membership in the European Union. Mnemiopsis leidyi populations have been checked with the arrival of another alien species which feeds on them.[84]
The Black Sea is connected to the World Ocean by a chain of two shallow straits, the Dardanelles and the Bosporus. The Dardanelles is 55m (180ft) deep, and the Bosporus is as shallow as 36m (118ft). By comparison, at the height of the last ice age, sea levels were more than 100m (330ft) lower than they are now.
There is evidence that water levels in the Black Sea were considerably lower at some point during the post-glacial period. Some researchers theorize that the Black Sea had been a landlocked freshwater lake (at least in upper layers) during the last glaciation and for some time after.
In the aftermath of the last glacial period, water levels in the Black Sea and the Aegean Sea rose independently until they were high enough to exchange water. The exact timeline of this development is still subject to debate. One possibility is that the Black Sea filled first, with excess freshwater flowing over the Bosporus sill and eventually into the Mediterranean Sea. There are also catastrophic scenarios, such as the "Black Sea deluge hypothesis" put forward by William Ryan, Walter Pitman and Petko Dimitrov.
The Black Sea deluge is a hypothesized catastrophic rise in the level of the Black Sea c.5600BC due to waters from the Mediterranean Sea breaching a sill in the Bosporus Strait. The hypothesis was headlined when The New York Times published it in December 1996, shortly before it was published in an academic journal.[85] While it is agreed that the sequence of events described did occur, there is debate over the suddenness, dating, and magnitude of the events. Relevant to the hypothesis is that its description has led some to connect this catastrophe with prehistoric flood myths.[86][87]
A 16th-century map of the Black Sea by Diogo HomemGreek colonies (8th–3rd century BCE) of the Black Sea (Euxine, or "hospitable" sea)
The Black Sea was a busy waterway on the crossroads of the ancient world: the Balkans to the west, the Eurasian steppes to the north, the Caucasus and Central Asia to the east, Asia Minor and Mesopotamia to the south, and Greece to the southwest.
The land at the eastern end of the Black Sea, Colchis (in present-day Georgia), marked for the ancient Greeks the edge of the known world.
Greek presence in the Black Sea began at least as early as the 9th century BC with colonies scattered along the Black Sea's southern coast, attracting traders and colonists due to the grain grown in the Black Sea hinterland.[92][need quotation to verify][93] By 500 BC, permanent Greek communities existed all around the Black Sea, and a lucrative trade-network connected the entirety of the Black Sea to the wider Mediterranean. While Greek colonies generally maintained very close cultural ties to their founding polis, Greek colonies in the Black Sea began to develop their own Black Sea Greek culture, known today as Pontic. The coastal communities of Black Sea Greeks remained a prominent part of the Greek world for centuries,[94][pageneeded] and the realms of Mithridates of Pontus, Rome and Constantinople spanned the Black Sea to include Crimean territories.
The Crimean War, fought between 1853 and 1856, saw naval engagements between the French and British allies and the forces of Nicholas I of Russia. On the 2 March 1855 death of Nicholas I, Alexander II became Tsar. On 15 January 1856, the new tsar took Russia out of the war on the very unfavourable terms of the Treaty of Paris (1856), which included the loss of a naval fleet on the Black Sea, and the provision that the Black Sea was to be a demilitarized zone similar to a contemporaneous region of the Baltic Sea.
The Black Sea was a significant naval theatre of World War I (1914–1918) and saw both naval and land battles between 1941 and 1945 during World War II. For example, Sevastopol was obliterated by the Nazis, who even brought Schwerer Gustav to the Siege of Sevastopol (1941–1942). The Soviet naval base was one of the strongest fortifications in the world. Its site, on a deeply eroded, bare limestone promontory at the southwestern tip of the Crimea, made an approach by land forces exceedingly difficult. The high-level cliffs overlooking Severnaya Bay protected the anchorage, making an amphibious landing just as dangerous. The Soviet Navy had built upon these natural defenses by modernizing the port and installing heavy coastal batteries consisting of 180mm and 305mm re-purposed battleship guns which were capable of firing inland as well as out to sea. The artillery emplacements were protected by reinforced concrete fortifications and 9.8-inch thick armored turrets.
As early as 29 April 2022 submarines of the Black Sea Fleet were used by Russia to bombard Ukrainian cities with KalibrSLCMs.[105][106] The Kalibr missile was so successful that on 10 March 2023 Defense Minister Sergey Shoigu announced plans to broaden the type of ship which carried it, to include the corvetteSteregushchiy and the nuclear-powered cruiser Admiral Nakhimov.[107]
On the morning of 14 March 2023, a Russian Su-27 fighter jet intercepted and damaged an American MQ-9 Reaper drone, causing the latter to crash into the Black Sea. At 13:20 on 5 May 2023 a Russian Su-35 fighter jet intercepted and threatened the safety of a Polish L-140 Turbolet on a "routine Frontex patrol mission.. and performed 'aggressive and dangerous' manoeuvres".[108] The incident, which occurred "in international airspace over the Black Sea about 60km" east of Romanian airspace,[109] "caused the crew of five Polish border guards to lose control of the plane and lose altitude."[110]
Yalta, CrimeaAmasra, Turkey, is located on a small island in the Black Sea.
The Black Sea plays an integral part in the connection between Asia and Europe.[111] In addition to sea ports and fishing, key activities include hydrocarbons exploration for oil and natural gas, and tourism.
According to NATO, the Black Sea is a strategic corridor that provides smuggling channels for moving legal and illegal goods including drugs, radioactive materials, and counterfeit goods that can be used to finance terrorism.[112]
The Turkish commercial fishing fleet catches around 300,000 tons of anchovies per year. The fishery is carried out mainly in winter, and the highest portion of the stock is caught in November and December.[114]
In the 1980s, the Soviet Union started offshore drilling for petroleum in the sea's western portion (adjoining Ukraine's coast). Independent Ukraine continued and intensified that effort within its exclusive economic zone, inviting major international oil companies for exploration. Discovery of the new, massive oilfields in the area stimulated an influx of foreign investments. It also provoked a short-term peaceful territorial dispute with Romania which was resolved in 2011 by an international court redefining the exclusive economic zones between the two countries.
The Black Sea contains oil and natural gas resources but exploration in the sea is incomplete. As of 2017[update], 20 wells are in place. Throughout much of its existence, the Black Sea has had significant oil and gas-forming potential because of significant inflows of sediment and nutrient-rich waters. However, this varies geographically. For example, prospects are poorer off the coast of Bulgaria because of the large influx of sediment from the Danube which obscured sunlight and diluted organic-rich sediments. Many of the discoveries to date have taken place offshore of Romania in the Western Black Sea and only a few discoveries have been made in the Eastern Black Sea.
During the Eocene, the Paratethys Sea was partially isolated and sea levels fell. During this time sand shed off the rising Balkanide, Pontide and Caucasus mountains trapped organic material in the Maykop Suite of rocks through the Oligocene and early Miocene. Natural gas appears in rocks deposited in the Miocene and Pliocene by the paleo-Dnieper and paleo-Dniester rivers, or in deep-water Oligocene-age rocks. Serious exploration began in 1999 with two deep-water wells, Limanköy-1 and Limanköy-2, drilled in Turkish waters. Next, the HPX (Hopa)-1 deepwater well targeted late Miocene sandstone units in Achara-Trialet fold belt (also known as the Gurian fold belt) along the Georgia-Turkey maritime border. Although geologists inferred that these rocks might have hydrocarbons that migrated from the Maykop Suite, the well was unsuccessful. No more drilling happened for five years after the HPX-1 well. In 2010, Sinop-1 targeted carbonate reservoirs potentially charged from the nearby Maykop Suite on the Andrusov Ridge, but the well-struck only Cretaceous volcanic rocks. Yassihöyük-1 encountered similar problems.
Other Turkish wells, Sürmene-1 and Sile-1 drilled in the Eastern Black Sea in 2011 and 2015 respectively tested four-way closures above Cretaceous volcanoes, with no results in either case. A different Turkish well, Kastamonu-1 drilled in 2011 did successfully find thermogenic gas in Pliocene and Miocene shale-cored anticlines in the Western Black Sea. A year later in 2012, Romania drilled Domino-1 which struck gas prompting the drilling of other wells in the Neptun Deep. In 2016, the Bulgarian well Polshkov-1 targeted Maykop Suite sandstones in the Polshkov High and Russia is in the process of drilling Jurassic carbonates on the Shatsky Ridge as of 2018.[115]
In August 2020, Turkey found 320billion cubic metres (11trillion cubic feet) of natural gas in the biggest ever discovery in the Black Sea, and hoped to begin production in the Sakarya Gas Field by 2023. The sector is near where Romania has also found gas reserves.[116]
In the years following the end of the Cold War, the popularity of the Black Sea as a tourist destination steadily increased. Tourism at Black Sea resorts became one of the region's growth industries.[120]
The following is a list of notable Black Sea resort towns:
The 1936 Montreux Convention provides for free passage of civilian ships between the international waters of the Black and the Mediterranean seas. However, a single country (Turkey) has complete control over the straits connecting the two seas. Military ships are categorised separately from civilian vessels and can pass through the straits only if the ship belongs to a Black Sea country. Other military ships have the right to pass through the straits if they are not in a war against Turkey and if they stay in the Black Sea basin for a limited time. The 1982 amendments to the Montreux Convention allow Turkey to close the straits at its discretion in both war and peacetime.[122]
The Montreux Convention governs the passage of vessels between the Black, the Mediterranean and Aegean seas and the presence of military vessels belonging to non-littoral states in the Black Sea waters.[123]
The Soviet hospital ship Armenia was sunk on 7 November 1941 by German aircraft while evacuating civilians and wounded soldiers from Crimea. It has been estimated that approximately 5,000 to 7,000 people were killed during the sinking, making it one of the deadliest maritime disasters in history. There were only eight survivors.[125]
In December 2018, the Kerch Strait incident occurred, in which the Russian navy and coast guard took control of three Ukrainian vessels as the ships were trying to transit from the Black Sea into the Sea of Azov.[126]
In April 2022, during the Russian invasion of Ukraine, the Russian cruiser Moskva was sunk in the western Black Sea by sea-skimming Neptune missiles of the Ukrainian armed forces[127] while the Russians claimed that an onboard fire had caused munitions to explode and damage the ship extensively.[128] She was the largest ship to be lost in naval combat in Europe since World War II.[129]
In late 2023, Russia announced plans to build a naval base on the Black Sea coast of Abkhazia.[130][131][132]
↑ The Journal of Indo-European Studies, p.79. United States, n.p, 1985. Google Books
↑ Burney, Charles. Historical Dictionary of the Hittites, p.333. United States, Rowman & Littlefield Publishers, 2018. Google Books. Accessed 26 February 2024.
↑ Aydin, Mustafa (2005). "Europe's new region: The Black Sea in the wider Europe neighbourhood". Southeast European and Black Sea Studies. 5 (2): 257–283. doi:10.1080/14683850500122943. S2CID154395443.
↑ Svitoch, Alexander A. (2010). "The Neueuxinian basin of the Black Sea and Khvalinian transgression". Quaternary International. 225: 230–234. doi:10.1016/j.quaint.2009.03.005.
↑ "Meromictic". Merriam-Webster. Retrieved 14 January 2014.
1 2 3 4 Gregg, M. C., and E. Özsoy (2002), "Flow, water mass changes, and hydraulics in the Bosporus", Journal of Geophysical Research 107(C3), 3016, doi:10.1029/2000JC000485
1 2 Korotaev, G. (2003). "Seasonal, interannual, and mesoscale variability of the Black Sea upper layer circulation derived from altimeter data". Journal of Geophysical Research. 108 (C4): 3122. Bibcode:2003JGRC..108.3122K. doi:10.1029/2002JC001508.
↑ Schuiling, Roelof Dirk; Cathcart, Richard B.; Badescu, Viorel; Isvoranu, Dragos; Pelinovsky, Efim (2006). "Asteroid impact in the Black Sea. Death by drowning or asphyxiation?". Natural Hazards. 40 (2): 327–338. doi:10.1007/s11069-006-0017-7. S2CID129038790.
↑ Uysal, Z. (2006). "Vertical distribution of marine cyanobacteria Synechococcus spp. in the Black, Marmara, Aegean, and eastern Mediterranean seas". Deep-Sea Research Part II. 53 (17–19): 1976–1987. Bibcode:2006DSRII..53.1976U. doi:10.1016/j.dsr2.2006.03.016.
↑ Emek Inanmaz, Özgür; Değirmenci, Özgür; Gücü, Ali Cemal (2014). "A new sighting of the Mediterranean Monk Seal, Monachus monachus (Hermann, 1779), in the Marmara Sea (Turkey)". Zoology in the Middle East. 60 (3): 278–280. doi:10.1080/09397140.2014.944438. S2CID83515152.
↑ Humborg, Christoph; Ittekkot, Venugopalan; Cociasu, Adriana; Bodungen, Bodo v. (1997). "Effect of Danube River dam on Black Sea biogeochemistry and ecosystem structure". Nature. 386 (6623): 385–388. Bibcode:1997Natur.386..385H. doi:10.1038/386385a0. S2CID4347576.
↑ Sburlea, A.; L. Boicenco; etal. (2006). "Aspects of Eutrophication as a Chemical Pollution with Implications on Marine Biota at the Romanian Black Sea Shore". Chemicals as Intentional and Accidental Global Environmental Threats. NATO Security through Science Series. pp.357–360. doi:10.1007/978-1-4020-5098-5_28. ISBN978-1-4020-5096-1.
↑ Gregoire, M.; C. Raick; etal. (2008). "Numerical modeling of the central Black Sea ecosystem functioning during the eutrophication phase". Progress in Oceanography. 76 (3): 286–333. Bibcode:2008PrOce..76..286G. doi:10.1016/j.pocean.2008.01.002.
↑ Haak, Wolfgang; Lazaridis, Iosif; Patterson, Nick; Rohland, Nadin; Mallick, Swapan; Llamas, Bastien; Brandt, Guido; Nordenfelt, Susanne; Harney, Eadaoin; Stewardson, Kristin; Fu, Qiaomei; Mittnik, Alissa; Bánffy, Eszter; Economou, Christos; Francken, Michael; Friederich, Susanne; Pena, Rafael Garrido; Hallgren, Fredrik; Khartanovich, Valery; Khokhlov, Aleksandr; Kunst, Michael; Kuznetsov, Pavel; Meller, Harald; Mochalov, Oleg; Moiseyev, Vayacheslav; Nicklisch, Nicole; Pichler, Sandra L.; Risch, Roberto; Guerra, Manuel A. Rojo; Roth, Christina; Szécsényi-Nagy, Anna; Wahl, Joachim; Meyer, Matthias; Krause, Johannes; Brown, Dorcas; Anthony, David; Cooper, Alan; Alt, Kurt Werner; Reich, David (10 February 2015). "Massive migration from the steppe is a source for Indo-European languages in Europe". bioRxiv. 522 (7555): 207–211. arXiv:1502.02783. Bibcode:2015Natur.522..207H. bioRxiv10.1101/013433. doi:10.1038/NATURE14317. PMC5048219. PMID25731166. Retrieved 5 April 2023. This steppe ancestry persisted in all sampled central Europeans until at least ≈3,000 years ago, and is ubiquitous in present-day Europeans. These results provide support for the theory of a steppe origin [...] of at least some of the Indo-European languages of Europe.
↑ Allentoft, Morten E.; Sikora, Martin; Sjögren, Karl-Göran; Rasmussen, Simon; Rasmussen, Morten; Stenderup, Jesper; Damgaard, Peter B.; Schroeder, Hannes; Ahlström, Torbjörn; Vinner, Lasse; Malaspinas, Anna-Sapfo; Margaryan, Ashot; Higham, Tom; Chivall, David; Lynnerup, Niels; Harvig, Lise; Baron, Justyna; Della Casa, Philippe; Dąbrowski, Paweł; Duffy, Paul R.; Ebel, Alexander V.; Epimakhov, Andrey; Frei, Karin; Furmanek, Mirosław; Gralak, Tomasz; Gromov, Andrey; Gronkiewicz, Stanisław; Grupe, Gisela; Hajdu, Tamás; Jarysz, Radosław (2015). "Population genomics of Bronze Age Eurasia". Nature. 522 (7555): 167–172. Bibcode:2015Natur.522..167A. doi:10.1038/nature14507. PMID26062507. S2CID4399103. Our genomic evidence for the spread of Yamnaya people from the Pontic-Caspian steppe to both northern Europe and Central Asia during the Early Bronze Age [...] corresponds well with the hypothesized expansion of the Indo-European languages.
↑ Mathieson, Iain; Lazaridis, Iosif; Rohland, Nadin; Mallick, Swapan; Llamas, Bastien; Pickrell, Joseph; Meller, Harald; Guerra, Manuel A. Rojo; Krause, Johannes; Anthony, David; Brown, Dorcas; Fox, Carles Lalueza; Cooper, Alan; Alt, Kurt W.; Haak, Wolfgang; Patterson, Nick; Reich, David (14 March 2015). "Eight thousand years of natural selection in Europe". bioRxiv: 016477. doi:10.1101/016477. Retrieved 5 April 2023– via biorxiv.org. Most present-day Europeans can be modeled as a mixture of three ancient populations related to Mesolithic hunter-gatherers (WHG), early farmers (EEF) and steppe pastoralists (Yamnaya) [...].
↑ Asimov, Isaac (1970). Constantinople: The Forgotten Empire. Houghton-Mifflin. p.3.
↑ Braun, Thomas (6 December 2012) [1991]. "Ancient Mediterranean Food". In Spiller, Gene A. (ed.). The Mediterranean Diets in Health and Disease (reprinted.). New York: Springer (published 2012). p.29. ISBN978-1-4684-6497-9. Retrieved 2 April 2022. The wheat trade was the reason for Greek colonization of Olbia and other Black Sea ports from c. 615 B.C. on. [...] The Ukraine was the chief source of wheat imports to classical Athens: the sea route from the Crimea through the Bosporus and Dardanelles to the Aegean was Athens' lifeline.
↑ Birsay, Cem (2007). "The Integration of Regional Efforts for Strengthening Stability Initiatives in the Wider Black Sea Area and Turkey's Position". In Volten, Peter M. E.; Tashev, Blagovest (eds.). Establishing Security and Stability in the Wider Black Sea Area: International Politics and the New and Emerging Democracies. Volume 26 of NATO science for peace and security series: Human and societal dynamics, ISSN 1874-6276. Amsterdam: IOS Press. p.91. ISBN978-1-58603-765-9. Retrieved 12 April 2023. [...] from the 18th century onwards, Russian ambitions fueled Turkish-Russian power conflict over the control of the Turkish Straits and the Black Sea.
↑ McGowan, Bruce William (1981). "Chiftlik agriculture, western Macedonia, 1620-1830: The economic role of the district". Economic Life in Ottoman Europe: Taxation, Trade and the Struggle for Land, 1600-1800. Studies in Modern Capitalism, ISSN 0144-2333. Cambridge: Cambridge University Press. p.134. ISBN978-0-521-24208-0. Retrieved 5 April 2023. A virtual cotton boom began with the onset of the American Revolutionary War in 1776, followed by a wheat boom beginning with the relaxation of Ottoman export controls following the French Revolution in 1789.
↑ Bruce McGowan (4 March 2010). Economic Life in Ottoman Europe: Taxation, Trade and the Struggle for Land, 1600–1800, Studies in Modern Capitalism. Cambridge University Press. p.134. ISBN978-0-521-13536-8.
↑ Compare: Bruce William McGowan (1981). Economic Life in Ottoman Europe: Taxation, Trade and the Struggle for Land, 1600–1800. Studies in Modern Capitalism ISSN 0144-2333. Cambridge: Cambridge University Press. p.23. ISBN978-0-521-24208-0. Retrieved 2 April 2022. [...] a new group of sea-going merchants - Greek and Albanian subjects of the Porte [...] flew the Russian flag after 1783 (making up the bulk of the first foreign flag commercial flotilla on the Black Sea since the departure of the Italians in the fifteenth century), taking up the slack after the collapse of French trade after 1789.
Stella Ghervas, "Odessa et les confins de l'Europe: un éclairage historique", in Stella Ghervas et François Rosset (ed), Lieux d'Europe. Mythes et limites (Paris: Editions de la Maison des sciences de l'homme, 2008), pp.107–124. ISBN978-2-7351-1182-4
Rüdiger Schmitt, "Considerations on the Name of the Black Sea", in: Hellas und der griechische Osten (Saarbrücken 1996), pp.219–224
West, Stephanie (2003). 'The Most Marvellous of All Seas': the Greek Encounter with the Euxine. Vol.50. Greece & Rome. pp.151–167.{{cite book}}: CS1 maint: location missing publisher (link)
The Bosporus or Bosphorus Strait is a natural strait and an internationally significant waterway located in Istanbul, Turkey. The Bosporus connects the Black Sea to the Sea of Marmara and forms one of the continental boundaries between Asia and Europe. It also divides Turkey by separating Asia minor from Thrace. It is the world's narrowest strait used for international navigation.
The Dardanelles, also known as the Strait of Gallipoli and in Classical Antiquity as the Hellespont, is a narrow, natural strait and internationally significant waterway in northwestern Turkey that forms part of the continental boundary between Asia and Europe and separates Asian Turkey from European Turkey. Together with the Bosporus, the Dardanelles forms the Turkish Straits.
The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Southern Europe and Anatolia, on the south by North Africa, on the east by the Levant in West Asia, and on the west almost by the Morocco–Spain border. The Mediterranean has played a central role in the history of Western civilization. Geological evidence indicates that around 5.9 million years ago, the Mediterranean was cut off from the Atlantic and was partly or completely desiccated over a period of some 600,000 years during the Messinian salinity crisis before being refilled by the Zanclean flood about 5.3 million years ago.
The Sea of Azov is an inland shelf sea in Eastern Europe connected to the Black Sea by the narrow Strait of Kerch, and sometimes regarded as a northern extension of the Black Sea. The sea is bounded by Russia on the east, and by Ukraine on the northwest and southwest. It is an important access route for Central Asia, from the Caspian Sea via the Volga–Don Canal.
Downwelling is the downward movement of a fluid parcel and its properties within a larger fluid. It is closely related to upwelling, the upward movement of fluid.
The Kerch Strait is a strait in Eastern Europe. It connects the Black Sea and the Sea of Azov, separating the Kerch Peninsula of Crimea in the west from the Taman Peninsula of Russia's Krasnodar Krai in the east. The strait is 3.1 kilometres (1.9 mi) to 15 kilometres (9.3 mi) wide and up to 18 metres (59 ft) deep. The most important harbor, the Crimean city of Kerch, gives its name to the strait, formerly known as the Cimmerian Bosporus or Straits of Taman. It has also been called the Straits of Yenikale after the Yeni-Kale fortress in Kerch.
Yalta is a resort city on the south coast of the Crimean Peninsula surrounded by the Black Sea. It serves as the administrative center of Yalta Municipality, one of the regions within Crimea. Yalta, along with the rest of Crimea, is internationally recognised as part of Ukraine, and is considered part of the Autonomous Republic of Crimea. However, it is under the control of Russia, which annexed Crimea in 2014 and regards the town as part of the Republic of Crimea. According to the most recent census, its population was 76,746 .
Europe is often divided into regions and subregions based on geographical, cultural or historical factors. Since there is no universal agreement on Europe's regional composition, the placement of individual countries may vary based on criteria being used. For instance, the Balkans is a distinct geographical region within Europe, but individual countries may alternatively be grouped into South-eastern Europe or Southern Europe.
The Black Sea deluge is the best known of three hypothetical flood scenarios proposed for the Late Quaternary history of the Black Sea. One other flood scenario proposes a rapid, even catastrophic, rise in sea level of the Black Sea.
The Crimean Tatar diaspora dates back to the annexation of Crimea by Russia in 1783, after which Crimean Tatars emigrated in a series of waves spanning the period from 1783 to 1917. The diaspora was largely the result of the destruction of their social and economic life as a consequence of integration into the Russian Empire.
An anoxic event describes a period wherein large expanses of Earth's oceans were depleted of dissolved oxygen (O2), creating toxic, euxinic (anoxic and sulfidic) waters. Although anoxic events have not happened for millions of years, the geologic record shows that they happened many times in the past. Anoxic events coincided with several mass extinctions and may have contributed to them. These mass extinctions include some that geobiologists use as time markers in biostratigraphic dating. On the other hand, there are widespread, various black-shale beds from the mid-Cretaceous which indicate anoxic events but are not associated with mass extinctions. Many geologists believe oceanic anoxic events are strongly linked to the slowing of ocean circulation, climatic warming, and elevated levels of greenhouse gases. Researchers have proposed enhanced volcanism (the release of CO2) as the "central external trigger for euxinia."
Anoxic waters are areas of sea water, fresh water, or groundwater that are depleted of dissolved oxygen. The US Geological Survey defines anoxic groundwater as those with dissolved oxygen concentration of less than 0.5 milligrams per litre. Anoxic waters can be contrasted with hypoxic waters, which are low in dissolved oxygen. This condition is generally found in areas that have restricted water exchange.
Sapropel is a term used in marine geology to describe dark-coloured sediments that are rich in organic matter. Organic carbon concentrations in sapropels commonly exceed 2 wt.% in weight.
Proterorhinus marmoratus is a species of gobiid fish, a tubenose goby native to the brackish water parts of the Black Sea and the Sea of Azov, near the coasts of Bulgaria, Georgia, Romania, Ukraine and Russia. Also it is found in the Marmora Sea (Turkey). It can reach a length of 11.5 centimetres (4.5 in) TL.
The genus Ceratium is restricted to a small number of freshwater dinoflagellate species. Previously the genus contained also a large number of marine dinoflagellate species. However, these marine species have now been assigned to a new genus called Tripos. Ceratium dinoflagellates are characterized by their armored plates, two flagella, and horns. They are found worldwide and are of concern due to their blooms.
Siliceous ooze is a type of biogenic pelagic sediment located on the deep ocean floor. Siliceous oozes are the least common of the deep sea sediments, and make up approximately 15% of the ocean floor. Oozes are defined as sediments which contain at least 30% skeletal remains of pelagic microorganisms. Siliceous oozes are largely composed of the silica based skeletons of microscopic marine organisms such as diatoms and radiolarians. Other components of siliceous oozes near continental margins may include terrestrially derived silica particles and sponge spicules. Siliceous oozes are composed of skeletons made from opal silica SiO2·nH2O, as opposed to calcareous oozes, which are made from skeletons of calcium carbonate (CaCO3·nH2O) organisms (i.e. coccolithophores). Silica (Si) is a bioessential element and is efficiently recycled in the marine environment through the silica cycle. Distance from land masses, water depth and ocean fertility are all factors that affect the opal silica content in seawater and the presence of siliceous oozes.
The European anchovy is a forage fish somewhat related to the herring. It is a type of anchovy; anchovies are placed in the family Engraulidae. It lives off the coasts of Europe and Africa, including in the Mediterranean Sea, the Black Sea, and the Sea of Azov. It is fished by humans throughout much of its range.
L'Atalante basin is a hypersaline brine lake at the bottom of the Mediterranean Sea about 192 km (119 mi) west of the island of Crete. It is named for the French L'Atalante, one of the oceanographic research vessels involved in its discovery in 1993. L'Atalante and its neighbors the Urania and Discovery deep hyper saline anoxic basins (DHABs) are at most 35,000 years old. They were formed by Messinian evaporite salt deposits dissolving out of the Mediterranean Ridge and collecting in abyssal depressions about 3,000 m (9,800 ft) deep. L'Atalante is the smallest of the three; its surface begins at about 3,500 m (11,500 ft) below sea level.
The Mediterranean horse mackerel, also known as the Black Sea horse mackerel, horse mackerel, Mediterranean scad, common scad, or simply scad, is a species of mackerel in the family Carangidae found in the eastern Atlantic from Bay of Biscay to Mauritania, including the Mediterranean Sea. It is a benthopelagic, subtropical, marine fish that can reach up to 60 cm (24 in) in length. In the countries near the Mediterranean and Black Seas, it makes up a significant portion of fish catch, 54% of fish caught in the latter. Despite overfishing in the 1980s, catch numbers have leveled out and it is listed as least concern by the International Union for Conservation of Nature.
Euxinia or euxinic conditions occur when water is both anoxic and sulfidic. This means that there is no oxygen (O2) and a raised level of free hydrogen sulfide (H2S). Euxinic bodies of water are frequently strongly stratified; have an oxic, highly productive, thin surface layer; and have anoxic, sulfidic bottom water. The word "euxinia" is derived from the Greek name for the Black Sea (Εὔξεινος Πόντος (Euxeinos Pontos)) which translates to "hospitable sea". Euxinic deep water is a key component of the Canfield ocean, a model of oceans during part of the Proterozoic eon (a part specifically known as the Boring Billion) proposed by Donald Canfield, an American geologist, in 1998. There is still debate within the scientific community on both the duration and frequency of euxinic conditions in the ancient oceans. Euxinia is relatively rare in modern bodies of water, but does still happen in places like the Black Sea and certain fjords.
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