Black Sea
The Black Sea is a marginal mediterranean sea of
the Atlantic Ocean lying
between Europe and Asia.
It lies to the east of the Balkans in Southeast Europe, south of the East European Plain in Eastern Europe; and north of Anatolia and west of the Caucasus, both in Western Asia. The Black Sea is supplied by major
rivers, principally the Danube, Dnieper, and Don. Consequently, while six countries have a coastline on the
sea itself, its drainage basin includes
parts of 24 countries across Europe.[2]
The Black Sea covers 436,400 km2 (168,500 sq mi) (not
including the Sea of Azov), has a maximum depth of
2,212 m (7,257 ft), and a volume of 547,000 km3 (131,000 cu mi).[5] Most of its coasts
ascend rapidly. These rises are the Pontic Mountains to the south, bar the southwest-facing
peninsulas, the Caucasus Mountains to
the east, and the Crimean Mountains to
the mid-north. In the west the coast is generally small floodplains below foothills such as the Strandzha; Cape Emine, a dwindling of the east end of the Balkan Mountains; and the Dobruja Plateau considerably further north. The longest
east–west extent is about 1,175 km (730 mi).[6] Important cities
along the coast include Odessa, Varna, Samsun, Sochi, Sevastopol, Constanța, Trabzon, Novorossiysk, Burgas, and Batumi.
The Black Sea is bordered by Bulgaria,
Georgia, Romania, Russia, Turkey, and Ukraine. It has a positive water balance, with an annual net outflow of 300 km3 (72 cu mi) per year through
the Bosporus and
the Dardanelles into the Aegean Sea. While the net flow of water through the
Bosporus and Dardanelles (known collectively as the Turkish Straits) is out of the Black Sea, water generally
flows in both directions simultaneously: Denser, more saline water from the Aegean flows into the Black Sea
underneath the less dense, fresher water that flows out of the Black Sea. This
creates a significant and permanent layer of deep water that does not drain or
mix and is therefore anoxic. This anoxic layer is responsible
for the preservation of ancient shipwrecks which
have been found in the Black Sea.
The Black Sea ultimately drains into
the Mediterranean Sea, via the
Turkish Straits and the Aegean Sea. The Bosporus strait connects it to the small Sea of Marmara which in turn is connected to the Aegean
Sea via the strait of the Dardanelles. To the north, the Black Sea is connected to
the Sea of Azov by the Kerch Strait.
The water level has varied significantly over
geological time. Due to these variations in the water level in the basin, the
surrounding shelf and associated
aprons have sometimes been dry land. At certain critical water levels,
connections with surrounding water bodies can become established. It is through
the most active of these connective routes, the Turkish Straits, that the Black Sea joins the world ocean. During geological periods when this hydrological
link was not present, the Black Sea was an endorheic basin, operating independently of the global ocean
system (similar to the Caspian Sea today). Currently, the
Black Sea water level is relatively high; thus, water is being exchanged with
the Mediterranean. The Black Sea undersea river is
a current of particularly saline water flowing through the Bosporus Strait and
along the seabed of the Black Sea, the first of its kind
discovered.
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