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Its northern part lies within the Chernozem belt (black soil belt) which goes from eastern Croatia (Slavonia), along the Danube (northern Serbia, northern Bulgaria (Danubian Plain) and southern Romania (Wallachian Plain)) to northeast Ukraine and further across the Central Black Earth Region and southern Russia into Siberia.
The Black Sea's circulation patterns are primarily controlled by basin topography and fluvial inputs, which result in a strongly stratified vertical structure.
Important cities along the coast include Batumi, Burgas, Constanța, Giresun, Istanbul, Kerch, Novorossiysk, Odessa, Ordu, Poti, Rize, Samsun, Sevastopol, Sochi, Sukhumi, Trabzon, Varna, Yalta, and Zonguldak.
The Black Sea has a positive water balance; that is, a net outflow of water 300 km (72 cu mi) per year through the Bosphorus and the Dardanelles into the Aegean Sea.
The Black Sea drains into the Mediterranean Sea, via the Aegean Sea and various straits, and is navigable to the Atlantic Ocean.
The modern basin is divided into two sub-basins by a convexity extending south from the Crimean Peninsula.
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 – as a result of differences in density caused by differences in salinity – leading to a significant anoxic layer well below the surface waters.
During the Ottoman Empire period, the Black Sea was called either Bahr-e Siyah or Karadeniz, both meaning "the Black Sea" in the Ottoman Turkish.
It is worthy to note, that in the tenth-century geography book Hudud al-'Alam, written in the Persian language by an unknown author, the Black Sea is called "Georgian Sea", "Sea of Georgians" ("daryä-yi Gurziyan").