During the last of the great glaciations, the Black Sea became a large freshwater lake.
Between the port cities of Sinop and Samsun (Turkey), the coastline is paralleled by a rugged range of underwater mountains extending for nearly 100 miles (160 km).
The hollow forming the basin’s core covers about a third of the total area and is a completely featureless flat plain, with depths increasing evenly toward the centre to a little more than 7,200 feet (2,200 metres), with the axis of maximum depth displaced toward the Turkish coast.
To the countries of the region, the Black Sea has been of immense strategic importance over the centuries; the advent of more-settled conditions has brought its economic importance to the fore.
The coastline of the Black Sea is only mildly indented, except for the northwestern and northern shores, which are low and furrowed by numerous ravines, valleys, and rivers, the mouths of which are often impeded by sandy spits.
The Turks, when they came to control the lands beyond the sea’s southern shores, encountered only the sudden storms whipped up on its waters and reverted to a designation reflecting the inhospitable aspect of what they now termed the Karadenız, or Black Sea.
To scientists, the Black Sea is a remarkable feature because its lower levels are, to all intents and purposes, almost biologically dead—not because of pollution but because of continued weak ventilation of the deep layers.Farther north, in the Burgaski Bay area, low mountains emerge where the Balkan Mountains of Bulgaria extend eastward.Continuing northward along the western shore, a flatter plateau region gives way to the great Danube River delta, which thrusts its mass out into the sea.shelf zone occupies about one-fourth of the entire area.The roughly oval-shaped Black Sea occupies a large basin strategically situated at the southeastern extremity of Europe but connected to the distant waters of the Atlantic Ocean by the Bosporus (which emerges from the sea’s southwestern corner), the Sea of Marmara, the Dardanelles, the Aegean Sea, and the Mediterranean Sea.The Crimean Peninsula thrusts into the Black Sea from the north, and just to its east the narrow Kerch Strait links the sea to the smaller Sea of Azov.In ancient Greek myths, the sea—then on the fringe of the Mediterranean world—was named Pontus Axeinus, meaning “Inhospitable Sea.” Later explorations made the region more familiar, and, as colonies were established along the shores of a sea the Greeks came to know as more hospitable and friendly, its name was changed to Pontus Euxinus, the opposite of the earlier designation.