• The Black Sea is bounded by Europe, Anatolia and the Caucasus and is ultimately connected to the Atlantic Ocean via the Mediterranean and the Aegean seas and various straits. The Bosphorus strait connects it to the Sea of Marmara, and the strait of the Dardanelles connects that sea to the Aegean Sea region of the Mediterranean. These waters separate eastern Europe and western Asia. The Black Sea is also connecte to the Sea of Azov by the Strait of Kerch.
• The Black Sea has an area of 436,400 km2 (168,500 sq mi) (not including the Sea of Azov), a maximum depth of 2,212 m (7,257 ft), and a volume of 547,000 km3.The Black Sea forms in an east-west trending elliptical depression which lies between Bulgaria, Georgia, Romania, Russia, Turkey , and Ukraine. It is constrained by the Pontic Mountains to the south, the Caucasus Mountains to the east and features a wide shelf to the northwest. The longest east-west extent is about 1,175 km.
• The Black Sea has a positive water balance; that is, a net outflow of water 300 km3 per year through the Bosphorus and the Dardanelles into the Aegean Sea. Mediterranean water flows into the Black Sea as part of a two-way hydrological exchange. The Black Sea outflow is cooler and less saline, and floats over the warm, more saline Mediterranean inflow -because of density difference due to salinity-, leading to a significant anoxic layer well below the surface waters. The Black Sea also receives river water from large Eurasian fluvial systems to the north of the Sea, of which the Don, Dnieper and Danube are the most significant.
Geology and bathymetry • The modern basin is divided into two sub-basins by a convexity extending south from the Crimean Peninsula. The large shelf to the north of the basin is up to 190 km wide, and features a shallow apron with gradients between 1:40 and 1:1000. The southern edge around Turkey and the western edge around Georgia, however, are typified by a narrow shelf that rarely exceeds 20 km 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 m (7,257.22 ft) just south of Yalta on the Crimean Peninsula.The littoral zone of the Black Sea is often referred to as the Pontic littoral.
Hydrology and hydrochemistry• The Black Sea is the world’s largest meromictic basin where 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 current hydrochemical configuration is primarily controlled by basin topography and fluvial inputs, which result in a strongly stratified vertical structure and a positive water balance. The upper layers are generally cooler, less dense and less salty than the deeper waters, as they are fed by large fluvial systems, whereas the deep waters originate from the warm, salty waters of the Mediterranean. This influx of dense water from Mediterranean is balanced by an outflow of fresher Black Sea surface-water into the Marmara Sea, maintaining the stratification and salinity levels.
• The Black Sea supports an active and dynamic marineEcology 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, includingdiatoms 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 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 a marked vertical stratification and a warm, shallow mixed layer. Day length and insolation intensity also controls 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
The effect of pollution on Black Seaecology Pollution reduction and • Since the 1960s, rapid industrial expansion along the Black Sea coast line and the regulation efforts have led to construction of a major dam a partial recovery of the has significantly increased Black Sea ecosystem during annual variability in the N:P:Si the 1990s, and an EU ratio in the basin. In coastal areas, the biological effect of monitoring exercise, these changes has been an EROS21, revealed increase in the frequency of decreased N and P values, monospecific phytoplankton relative to the 1989 blooms, with diatom bloom frequency increasing by a peak. Recently, scientists factor of 2.5 and non-diatom have noted signs of bloom frequency increasing by ecological recovery, in part a factor of 6. The non-diatoms, due to the construction of such as the prymnesiophytes Emiliania new sewage treatment plants huxleyi (coccolithophore), Chr in Slovakia, Hungary, omulina sp., and the Romania, and Bulgaria in Euglenophyte Eutreptia connection with membership lanowii are able to out- compete diatom species in the European because of the limited Union. Mnemiopsis availability of Si, a necessary leidyi populations have been constituent of diatom checked with the arrival of frustules. As a consequence of these blooms, benthic another alien species which macrophyte populations were feeds on them . deprived of light, while anoxia caused mass mortality in marine animals .
History• 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, Caucasus and Central Asia to the East, Asia Minor and Mesopotamia to the south, and Greece to the south-west. The oldest processed gold in the world, arguably left by Old Europeans, was found in Varna, and the Black Sea was supposedly sailed by the Argonauts. The land at the eastern end of the Black Sea, Colchis, (now Georgia), marked for the Greeks an edge of the known world. The steppes to the north of the Black Sea have been suggested as the original homeland (Urheimat) of the speakers of the Proto-Indo-European language, (PIE) the progenitor of the Indo-European language family, by some scholars (see Kurgan; others move the heartland further east towards the Caspian Sea, yet others to Anatolia). Numerous ancient ports line Black Seas coasts, some older than the pyramids.• The Black Sea was a significant naval theatre of World War I and saw both naval and land battles during World War II.