Major Seas of the World

Black Sea

The Black Sea is an inland sea between southeastern Europe and Anatolia that is actually a distant arm of the Atlantic Ocean by way of the Mediterranean Sea. It is connected to the Mediterranean by the Bosporus and the Sea of Marmara, and to the Sea of Azov by the Strait of Kerch. There is a net inflow of seawater through the Bosporus, 200 km³ per year. There is an inflow of freshwater from the surrounding areas, especially central and middle-eastern Europe, totalling 320 km³ per year. The most important river entering the Black Sea is the Danube. The Black Sea has an area of 436,400 km², with a maximum depth of 2200 m.
Countries bordering on the Black Sea are Turkey, Bulgaria, Romania, Ukraine, Russia, and Georgia. The Crimean peninsula is a Ukrainian autonomous republic. Important cities along the coast include: Istanbul, Burgas, Varna, Constanta, Yalta, Odessa, Sevastopol, Kerch, Novorossiysk, Sochi, Sukhumi, Poti, Batumi, Trabzon, Samsun and Zonguldak.

Geology and bathymetry
The Black Sea forms an enclosed basin, located between south-eastern Europe and Asia Minor. The basin was formed during the Miocene orogenies which uplifted the mountain ranges and divided the ancient Tethys Ocean into several brackish basins, including the Sarmatic Sea. The Caspian, Azov, Aral and Black Seas are the remnants of this evaporated basin.
The basin is divided into two sub-basins by a convexity extending south from the Crimean peninsula. The north-west of the basin is characterized by a relatively large shelf up to 190 km wide, which has a relatively shallow apron with gradients between 1:40 and 1:1000. The southern edge around Turkey and the eastern edge around Georgia however, are typified by a shelf that rarely exceeds 20km in width and an apron that is typically 1:40 gradient with numerous submarine canyons and channel extensions. The Euxine abyssal plain in the centre of the Black Sea reaches a maximum depth of 2,206m just south of Yalta on the Crimean peninsula. The basin is connected to the Mediterranean Sea via the Turkish Straits System (TSS) in the south-west, which includes the Bosporus and Dardanelles straits and the Sea of Marmara. The Black Sea is connected to the Sea of Azov in the north-east via the Kerch straits.

Hydrology and hydrochemistry
The Black Sea is the world’s largest meromictic basin, with 90% of its volume occupied by anoxic waters. The current hydrochemical configuration is primarily controlled by basin topography and fluvial inputs, which result in a strongly stratified vertical structure and a positive water balance. The upper layers are generally cooler, less dense and less salty than the deeper waters, as they are fed by large fluvial systems, whereas the deep waters originate from the warm, salty waters of the Mediterranean. This influx of dense water from Mediterranean is balanced by an outflow of fresher Black Sea surface-water into the Marmara Sea, maintaining the stratification and salinity levels.
The surface water has an average salinity of 18-18.5 ppt and contains oxygen and other nutrients required to sustain biotic activity. These waters circulate in a basin-wide anti-cyclonic shelfbreak gyre known as the Rim Current which transports water round the perimeter of the Black Sea. Within this feature, two smaller cyclonic gyres operate, occupying the eastern and western sectors of the basin. Outside the Rim Current, numerous quasi-permanent coastal eddies are formed due to upwelling around the coastal apron and ‘wind curl’ mechanisms. The intra-annual strength of these features is controlled by seasonal atmospheric and fluvial variations. Sea Surface Temperature of the surface waters varies seasonally from 8°C to 30°C.