The water balance of the Black sea.
The main feature of the water balance of the Black sea is a significant excess river runoff (river in the sea bring about 355 km 3 of water per year) and precipitation over evaporation, so the water level in the Black sea 9-12 cm higher than the Mediterranean sea. Elevated levels constant due to surface runoff from the Black sea of Marmara. Surface runoff and prevailing North-easterly winds are the main pathogens circular system of currents in the Black sea clockwise, emerging in the North-Western part. Tidal currents in the Black sea is weak, the oscillation amplitude no more than 8 cm, Often they are clouded wind-tide phenomena.
Demersal waters over the Mediterranean, flowing through the Bosporus (Marmara from the Black sea to flow over the year of around 193 km 3 of water) Strait and spreading over the deep basin, plays a significant role in the hydrological regime of the Black sea. Waters of the Mediterranean sea are higher than the average oceanic salinity (about 38%), the density is much greater than the freshened surface water (to 1,017). This leads to the stable layer-by-layer shallow water, poor mixing, different as salt, temperature and gas regimes of these layers. Thus, the salinity in niinemaa (deeper than 150-200 m) in the Black sea up to 22 % 0 and slightly more at the bottom and in tribesperson area. The surface layers have a salinity of 17-18%, declining to 16%on the coast and up to 13% 0 th North-Western part of the sea. There is water exchange between the Black and Azov seas.
The water temperature of the upper layer in summer in the open sea reaches 25°, and in the shallow waters and in estuaries up to 28° C. At depths of 100-200 m and deeper temperature do not experience seasonal changes and to the bottom remains constant year round (about 8-9°). In winter, the surface waters of the Black sea are very cool, but only in the North-West and North-East areas the temperature can drop below zero (to -1.4°), with the sea in some years is covered with ice. Throughout the rest of the sea, and especially in the southern parts, the surface layers retain a temperature of about 8° C, i.e. equal to a constant temperature of depths, which impedes the convective mixing of waters even in the winter.
Organic world of the Black sea
Stable stratification of the water masses of the Black sea is most clearly reflected in the gas mode. The surface layer (to a depth of— 200-150 m) contains water in such an amount of oxygen (a 7.62 2.71 cm 3 /l), which provides life. It is oxygen area. The bottom layer (from a depth of 150 m and to the bottom) — hydrogen sulfide zone where life is limited to anaerobic bacteria. With the depth of 300 m and to the bottom of the oxygen is completely replaced by sulfide.
The present population of the Black sea is represented by the following forms.
1. Ancient saltwater Pontic relict fauna of the Caspian type.
2. Mediterranean flora and fauna that has entered at a later time and the currently dominant, but depleted in species composition.
3. Freshwater forms.
The resettlement of plants and animals in the Black sea area is limited oxygen. Phytoplankton (about 350 species) and zooplankton (various crustaceans, larvae of benthic animals, fish eggs, etc.), at the coast, in bays and in the upper layer (50 m) presents more abundant than in the open sea and at great depths.
Phytobenthos of the Black sea contains many species of green, brown and red algae (Phyllophora), all inhabiting the shallow belt sea. The zoobenthos is represented with various crustaceans, worms, mollusks (mussels, Pasolini) — mainly Mediterranean forms. The process of colonization of the Black sea, Mediterranean fauna is far from being finished.
The productivity of the Black sea is rather high and it provides the sustenance of fish fauna (166 species), which in richer species diversity of the ichthyofauna of the Caspian sea; the number of species is twice that in the Barents sea. However, fishing opportunities in the Black sea is not fully used, especially away from the coast. Commercial value is Beluga, sturgeon, starred sturgeon, herring (Pontic relicts), anchovy, whitebait, mullet, barbula, mackerel, Bonito, tuna, mackerel, spiny shark, flounder, rays (Mediterranean form), perch, bream, roach (freshwater). Mass fishing is done in the ways of seasonal migration: in the spring of Marmara to the Black sea and from the Black to the Azov; with the onset of cold fish migrate by these ways back.
Economic importance of the Black sea is not limited to the fishing business. Sea is widely used for the transport of highly diverse industrial products and agricultural products of the South and the Caucasus, as well as for foreign trade turnover, passenger traffic, including foreign tourists. On the Crimean and Caucasian coasts of the sea water are widely used for health purposes.