The bottom of Black sea from a surf and up to depth of 120-200 meters represents, for small exceptions, a gentle slope. It is a so-called shelf. All of us we dive in the most shallow part of a shelf where there are rocks and sand. More deeply at the bottom of a shelf there lies silt.

The shelf breaks in area of Caucasus rather abrupt ledge in 2.5-10 kilometers from coast, seldom further. The bottom part of a ledge is shipped on 500 meters. The ledge is almost deprived deposits - they accumulate at its bottom in the form of a wide loop - and represents as though the wall which has been strongly cut up by underwater canyons, usually settling down against the large rivers.

Such ledges are observed not only in Black sea, but also around of all continents and the majority of islands. Their depths slightly differ from each other, that has given the basis to think about increase of a level of the World ocean during last geological time.

Geologists and oceanologists connect this phenomenon with thawing a glacier of the Europe in the Quaternary period. The volume of an ice of a glacier by the most minimal calculations was sufficient, that after thawing to raise a level of oceans on 75-100 meters. If the glacial cover of Antarctica, for example, has thawn, the level of oceans would raise on 60 meters.

Simultaneously with increase of a level of oceans, possibly, there was a lowering coast around the Black sea hollow filled glacial water and water of the rivers. (water of Black sea during ancient epoch was basically desalinated and only from time to time a little salinate.) Continuation of valleys of the rivers at the bottom of the sea (underwater canyons) up to depth of 500 meters confirms with places this assumption.

Behind a ledge, from depth of 500 meters, the bottom becomes flat and goes deep aside exhausting gradually. This abyssal, i.e. deep-water, area is covered by layers of silt of a various antiquity.

On depth about 2 kilometers, approximately to in parallel Caucasian coast, under a bottom of Black sea the continental slope - multikilometer thickness of a granite environment of an earth's crust comes to an end. Further the continental slope passes in more thin basalt environment covering a bottom of oceans and consequently named bark of oceanic type.

In an antiquity the seafarers ploughed waters of Black sea, were surprised, why the metal anchor lifted from greater depths always appeared covered black for a short while. Were surprised, but could not explain this phenomenon.

In 1890, the deep-water expedition of Russian hydrographer of I.B.Shpindler spent measurements and studying of sea depths on Black sea. Expedition has established, that from depth of 100-200 meters and up to the bottom water thickness of Black sea is sated by hydrogen sulphide. Became clear why anchors from metal blackened. Having got in the hydrosulphuric environment, they became covered by a pellicle of sulfide of iron.

One time considered, that Black sea in this respect is the only thing. But now hydrosulphuric infection is established in deep hollows of Caspian sea and in east part Arabian sea - near east part of the Arabian peninsula. A number of scientists assume, that hydrosulphuric infection of deep hollows of sea pools during the last geological epoch has been more widely widespread.

Depth of the top border of hydrosulphuric infection of Black sea is non-uniform. In a median part of the sea it makes 80-100 meters, at coast of Caucasus - 200, Crimea - 150 meters. Thus, the surface of this section has the convex form. Downwards hydrogen sulphide sates water up to the biggest depth, i.e. up to 2245 meters.

The hydrosulphuric zone of Black sea is uninhabited. In such, deprived oxygen, water there can not live organisms, except for some bacteria. Ability to live of these bacteria is based on mastering of inorganic connections of sulfur, iron and other elements, therefore them call sulfobacteriums, ferrobacteriums and so on - depending on that, what they eat.

Thickness of water of Black sea is subdivided into three layers: top, average and bottom - hydrosulphuric.

The top layer, up to depth of 40-60 meters, is subject to seasonal fluctuations of temperature of water at a surface: from 7 degrees of Celsius in the winter up to 24 summer, and at coast of Caucasus up to 29-30 degrees. With depth of fluctuation of temperature of water decrease. On depth of 40 meters the temperature varies from 8 degrees in the winter up to 11 degrees in the summer. This layer of water has lower salinity, than laying below.

The average layer reaches from depth 40-60 up to 100-150 meters. Here reigns a constant cold. On ours taste, certainly. For some fishes temperature of water of this layer just suitable - 6-8 degrees the year round. It is interesting, that the lowest temperature of water is observed in the middle of an average layer. Here half it is less than oxygen, than in near-surface parts of the sea. More deeply water is a little bit warmer - up to 9 degrees - and such remains and in a layer hydrosulphuric.

Why the temperature of water goes down with depth non-uniformly and even raises in the bottom part of a median layer a little?

The matter is that on depth of 100 meters in Black sea there is a section of waters: overlying less salty, diluted by rains, the rivers, and deep heavy salty, acting here through passages Dardanelless and Bosporus from Mediterranean sea. Vertical circulation of water occurs to different temperature only within the limits of the top layer as less salty water, even the most dense cold, all is easier salty. Here it also accumulates in the form of a cold layer above a salty layer of water. On depth about 100 meters of intensive hashing does not occur, and the border of the top and average layers rather sharp and is easily found out by analyses of water from different depths or measurements of temperature.

Thus, in the winter cold water plunges up to salty water thickness, superseding farmed for a summer up to 9.5 degrees water upwards, forming the cellary cold while will not get warm up to the same of 9.5 degrees in the summer and will not be superseded, in turn, again by colder water.

Thus, Black sea represents as though a two-storeyed building with the sated hydrogen sulphide a cellar where sea organisms fall at dying off.

The top floor of this building, warm in summertime and cold in the winter, is occupied by fishes from Mediterranean sea in the summer.

The ground floor is constantly populated coldphilic fishes - so-called Boreary-Atlantic forms. In the winter when the temperature of layers is equalized, coldphilic fishes occupy also the top floor.

Coldphilic fishes are some kind of owners of Black sea. First, because live in it the year round, secondly, because have occupied earlier, having arrived from Atlantic ocean in the end of Tertiary - the beginning of Quaternary epoch after break of waters from Mediterranean sea through straits of Dardanelless and Bosporus.

It has occured in a Ice Ages when water thicknesses of the Black and Mediterranean seas have been cooled enough and consequently have involved northern kinds of fishes of Atlantic ocean. Later, during postglacial warming, from them in Black sea there were only eight kinds. But then through passages there was a mass installation of thermophilic fishes.

Created: 03/17/1999 Last modified: 04/26.2008 19:02 MSK