It is broadest in the west and at the head of Kerch Strait but elsewhere forms a rim about 6 to 7 miles (10 to 11 km) wide, and the depth of the edge is usually less than 360 feet (110 metres).
The shelf gives way at its edge to a slope, which is broken by submarine valleys and is steep in its upper parts.
As mountains—the Pontic, Caucasus, Crimean, and Carpathians—rose around it, outwashed sediments filled the basin.
Further earth movements and changes in sea level associated with Pleistocene glaciers then occurred and led to intermittent connections with the Mediterranean.
The present connection to the Mediterranean Sea—and to salt water—is believed to have emerged some 6,500 to 7,500 years ago.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.In winter, spurs of the Siberian anticyclone (a clear, dry, high-pressure air mass) create a strong current of cold air, and the northwestern Black Sea cools down considerably, with regular ice formation.The winter invasion of polar continental air (which prevails for an average of 185 days annually) is accompanied by strong northeasterly winds, a rapid temperature drop, and frequent precipitation, with the air becoming warm and moist after passing over the milder eastern portions of the sea.
The mountains of southern Crimea form the only precipitous cliff areas.