The Black Sea also known as the Euxine Sea is an inland sea between southeastern Europe and Asia Minor. It is connected to the Mediterranean Sea by the Bosporus and the Sea of Marmara, and to the Sea of Azov by the Strait of Kerch.
There is a net inflow of seawater through the Bosporus, 200 km≥ per year. There is an inflow of freshwater from the surrounding areas, especially central and middle-eastern Europe, totalling 320 km≥ per year. The most important river entering the Black Sea is the Danube. The Black Sea has an area of 422,000 km≤ and a maximum depth of 2210 m.
Countries bordering on the Black Sea are Turkey, Bulgaria, Romania, Ukraine, Russia, Georgia. The Crimea is an Autonomous Republic of Ukraine.
Important cities along the coast : Istanbul (formerly Constantinople and Byzantium), Burgas, Varna, Constanta, Yalta, Odessa, Sevastopol, Batumi, Trabzon, Samsun, Zonguldak.
Geology : The Black Sea is the largest anoxic, or oxygen-free, marine system. This is a result of the great depth of the Deep Sea and the relatively low salinity (and therefore density) of the water flowing into it from rivers and the Mediterranean; freshwater and seawater mixing is limited to the uppermost 100 to 150 m, with the water below this interface (called the pycnocline) being exchanged only once every thousand years. There is therefore no significant gas exchange with the surface, and as a result decaying organic matter in the sediment consumes any available oxygen. In these anoxic conditions some extremophile microorganisms are able to use sulfate (SO42-) for oxidation of organic material, producing hydrogen sulfide (H2S) and carbon dioxide. This mix is extremely toxic (a lungful would be fatal to a human), resulting in a sea that has almost all of its ecology living in that top layer down to a depth of approximately 180 m (600 ft).
The Bulgarian coastline of the Black Sea doesn't have many islands. Those that exist are mostly small, uninhabited and covered with algae.Large amounts of organic material reach the bottom of the sea and accumulate in the sediments in concentrations of up to 20%. These kinds of sediments are called sapropel.
While it is agreed that the Black Sea has been a sweetwater lake with a considerably lower level during the last glaciation, its postglacial development into a marine sea is still a subject of intensive study and debate. There are catastrophic scenarios such as put forward by Ryan and Pitman as well as models emphasizing a more gradual transition to saline conditions and transgression in the Black Sea. They are based on different theories about the level the sweetwater lake had reached by the time the Mediterranean Sea was high enough to flow over the Dardanelles and the Bosphorus.
Black Sea today and in 5600 BC according to Ryan's and Pitman's theories"Ten cubic miles [42 km≥] of water poured through each day, two hundred times what flows over Niagara Falls. ... The Bosporus flume roared and surged at full spate for at least three hundred days."
Although neolithic agriculture had by that time already reached the Pannonian plain, the authors link its spread with people displaced by the postulated flood. It has been suggested that the survivors' memory of this event was the source of the legend for Noah's Flood. Initial resistance came from those who looked for more detailed correlation with the Book of Genesis (see Noah's Ark and Mount Ararat) or preferred as prototype the similar marine ingression that formed the Persian Gulf in the lower Tigris and Euphrates valley.
Subsequent work by marine archeologist Robert Ballard has identified ancient shorelines, freshwater snail shells, drowned river valleys and tool-worked timbers in 300 feet (100 m) of water off the coast of modern Turkey.