Black Sea–Caspian Steppe Black Sea–Caspian Steppe The Black Sea-Caspian Steppe is an informal name for that part of the Eurasian Steppe that extends south between the Black and Caspian Seas. It is usually treated as part of the Pontic-Caspian steppe which includes the area north of the Black and Caspian Seas, but there is some reason to treat it as a distinct place. Its natural boundaries are the Sea of Azov and Black Sea on the west, the Caucasus Mountains on the south and the Caspian Sea on the east. Its northern boundary may be taken as the triangle formed by the lower
Caspian Sea human settlements. The Caspian has characteristics common to both seas and lakes. It is often listed as the world's largest lake, although it is not a freshwater lake. It contains about 3.5 times more water, by volume, than all five of North America's Great Lakes combined. The Caspian was once part of the Tethys Ocean, but became landlocked about 5.5 million years ago due to plate tectonics. The Volga River (about 80% of the inflow) and the Ural River discharge into the Caspian Sea, but it has no natural outflow other than by evaporation. Thus the Caspian ecosystem is a