Euxine Sea

The Black Sea 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 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 , has a maximum depth of , and a volume of .
Most of its coasts ascend rapidly.
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 farther north. The longest east–west extent is about . Important cities along the coast include (clockwise from 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 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, 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.

Name

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:
* ,
* ,
* ,
* ,
* ,
* ,
*
* ,
* Laz and , , or simply , , , "Sea"
* ,
* ,
* ,
* ,

Such names have not yet been shown conclusively to predate the 13thcentury.

In Greece, the historical name "Euxine Sea", which holds a different literal meaning (see below), is still widely used:
* , ; the name , , is used, but is much less common.

The Black Sea is one of four seas named in English after common color terms – the others being the Red Sea, the White Sea and the Yellow Sea.

Historical names and etymology

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'' is generally accepted to be a rendering of the Iranian word ("dark colored"). Ancient Greek voyagers adopted the name as , identified with the Greek word (inhospitable). The name (Inhospitable Sea), first attested in Pindar (), was considered an ill omen and was euphemized to its opposite, (Hospitable Sea), also first attested in Pindar. This became the commonly used designation in Greek, although in mythological contexts the "true" name remained favored.

Strabo's ''Geographica'' (1.2.10) reports that in antiquity, the Black Sea was often simply called "the Sea" ( ). He thought that the sea was called the "Inhospitable Sea" by the inhabitants of the Pontus region of the southern shoreline before Greek colonization due to its difficult navigation and hostile barbarian natives (7.3.6), and that the name was changed to "hospitable" after the Milesians colonized 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 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. 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). This interpretation has been labeled as folk etymology and may reflect a primitive historical understanding of the "P/Bla" phoneme originally associated with the name.Beekes, R. S. P. (2002). "The Origin of the Etruscans." Koninklijke Nederlandse Akademie van Wetenschappen,Amsterdam
Robert Beekes
/ref>

In the Greater Bundahishn, a Middle Persian Zoroastrian scripture, the Black Sea is called . In the tenth-century Persian geography book , the Black Sea is called ''Georgian Sea'' (). '' The Georgian Chronicles'' use the name (Sea of Speri) after the Kartvelian tribe of Speris or Saspers. Other modern names such as and (both meaning Black Sea) originated during the 13th century. A 1570 map from Abraham Ortelius's labels the sea (Great Sea), compare Latin .

English writers of the 18th century often used ''Euxine Sea'' ( or ). During the Ottoman Empire, it was called either (Perso-Arabic) or (Ottoman Turkish), both meaning "Black Sea".

Geography

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

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.

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; Dnieprovska Gulf and Dniestrovsky Liman, both in Ukraine; and Sinop Bay and Samsun Bay, both in Turkey.

Coastline and exclusive economic zones

Drainage basin

The largest rivers flowing into the Black Sea are:

# Danube
# Dnieper
# Don
# Dniester
# Kızılırmak
# Kuban
# Sakarya
# Southern Bug
# Çoruh/Chorokhi
# Yeşilırmak
# Rioni
# Yeya
# Mius
# Kamchiya
# Enguri/Egry
# Kalmius
# Molochna
# Tylihul
# Velykyi Kuialnyk
# Veleka
# Rezovo
# Kodori/Kwydry
# Bzyb/Bzipi
# Supsa
# Mzymta

These rivers and their tributaries comprise a Black Sea drainage basin that covers wholly or partially 24 countries:

*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
Unrecognized states:
*

Islands

Some islands in the Black Sea belong to Bulgaria, Romania, Turkey, and Ukraine:

* St. Thomas Island – Bulgaria
* St. Anastasia Island – Bulgaria
* St. Cyricus Island – Bulgaria
* St. Ivan Island – Bulgaria
* St. Peter Island – Bulgaria
* Sacalinu Mare Island – Romania
* Sacalinu Mic Island – Romania
* K Island – Romania and Ukraine
* Utrish Island
* Krupinin Island
* Sudiuk Island
* Kefken Island
* Oreke Island
* Giresun Island – Turkey
* Dzharylhach Island – Ukraine
* Zmiinyi (Snake) Island – Ukraine

Climate

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. 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 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.

Geology and bathymetry

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 20million years later in 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 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 the Black Sea from the rest of the global ocean system.

The large shelf to the north of the basin is up to 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 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 center of the Black Sea reaches a maximum depth of just south of Yalta on the Crimean Peninsula.

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.

The Neoeuxinian transgression began with an inflow of waters from the Caspian Sea. Neoeuxinian deposits are found in the Black Sea below 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.

Hydrology

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 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 or around , and the inflow is or around .Gregg, M. C., and E. Özsoy (2002), "Flow, water mass changes, and hydraulics in the Bosporus", ''Journal of Geophysical Research'' 107(C3), 3016,

The following water budget can be estimated:
* Water in:
** Total river discharge:
** Precipitation:
** Inflow via Bosporus:
* Water out:
** Evaporation: (reduced greatly since the 1970s)
** Outflow via Bosporus:

The southern sill of the Bosporus is located at 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 . Inflow and outflow current speeds are averaged around , but much higher speeds are found locally, inducing significant turbulence and vertical shear. This allows for turbulent mixing of the two layers.''Descriptive Physical Oceanography''. Talley, Pickard, Emery, Swift. 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 the Rim Current. The Rim Current has a maximum velocity of about . 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 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 —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. The base of the CIL is marked by a major pycnocline at about , 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 . 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.

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 1 August 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 the Bosporus Strait from the Mediterranean Sea into the Black Sea, where the water has a lower salt content.

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. 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.

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.

Ecology

Marine

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.

During winter, strong winds promote convective overturning and upwelling of nutrients, while high summer temperatures result in 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 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".

Phytoplankton

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. This pattern of productivity is augmented by an ''Emiliania huxleyi'' bloom during the late spring and summer months.
* Dinoflagellates
: 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. The major bloom-forming dinoflagellate species in the Black Sea is ''Gymnodinium'' sp. Estimates of dinoflagellate diversity in the Black Sea range from 193 to 267 species. 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 of the Black Sea prevent thermophilous species from becoming established. The relatively high organic matter content of Black Sea surface water favors 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.
* Diatoms
: 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. 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. Typically, blooms during spring and blooms during the autumn.
* Coccolithophores
: Coccolithophores are a type of motile, autotrophic phytoplankton 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 , 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 and , Holocene sediments have been shown to also contain Helicopondosphaera and Discolithina species.
* Cyanobacteria
: 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.

Animal species

* Zebra mussel
: 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.
* Common carp
: 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.
* Round goby
: 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 and marine megafauna
: Marine mammals present within the basin include two species of dolphin (common and bottlenose) and the harbour porpoise, 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.First stranding record of a Risso's Dolphin (Grampus griseus) in the Marmara Sea, Turkey
(pdf). Retrieved on 6 September 2017 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. However, others claim that construction may cause devastating damages to the ecosystem, including dolphins.
: Mediterranean monk seals, now a vulnerable species, were historically abundant in the Black Sea, and are regarded to have become extinct from the basin in 1997. Monk seals were present at Snake Island, near the Danube Delta, until the 1950s, and several locations such as the and Doğankent were the last of the seals' hauling-out sites post-1990. Very few animals still thrive in the Sea of Marmara.
: Ongoing Mediterranizations may or may not boost cetacean diversity in the Turkish Straits and hence in the Black and Azov basins.
: Various species of pinnipeds, sea otter, and beluga whale were introduced into the Black Sea by mankind and later escaped either by accidental or purported causes. Of these, grey seals and beluga whales 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.

Ecological effects of pollution

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 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 (coccolithophore), sp., and the Euglenophyte , can out-compete diatom species because of 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 the late 1980s. Additionally, an alien species—the warty comb jelly ()—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 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 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. 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 those countries' membership of the European Union. populations have been checked with the arrival of another alien species that feeds on them.

File:black sea fauna jelly 01.jpg, Jellyfish
File:black sea fauna actinia 01.jpg, Actinia
File:black sea fauna actinia 02.JPG, Actinia
File:black sea fauna goby 01.jpg, Goby
File:black sea fauna stingray 01.jpg, Stingray
File:Black sea mullus barbatus ponticus 01.jpg, Goat fish
File:Black sea fauna hermit crab 01.jpg, Hermit crab, '' Diogenes pugilator''
File:Black sea fauna blue sponge.jpg, Blue sponge
File:Squalus acanthias2.jpg, Spiny dogfish
File:Black Sea fauna Seahorse.JPG, Seahorse
File:Kitesurfer and Dolphins Cropped.jpg, Black Sea common dolphins with a kite-surfer off Sochi

History

Mediterranean connection during the Holocene

The Black Sea is connected to the World Ocean by a chain of two shallow straits, the Dardanelles and the Bosporus. The Dardanelles is deep, and the Bosporus is as shallow as . By comparison, at the height of the last ice age, sea levels were more than 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.

Deluge hypothesis

The Black Sea deluge is a hypothesized catastrophic rise in the level of the Black Sea 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. 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.

Archaeology

The Black Sea was sailed by Hittites, Carians, Colchians, Armenians, Thracians, Greeks, Persians, Cimmerians, Scythians, Romans, Byzantines, Goths, Huns, Avars, Slavs, Varangians