Black Sea - Geography
The notion of the peculiarly stormy character of the Black Sea fast disappeared in early modern times. A short and troublesome sea is, indeed, produced by anything like a gale, but not in á greater degree than in other portions of the water of tho same limited extent. Another mistaken opinion of the ancients concerning the Black Sea, was that of its gradual subsidence. Polybius not only attested it, but has given his roasons for thinking it to be a fact. By comparing the accounts of these seas, as given by the ancient authors, with the limits assigned to them by recent observations, it appeared that they have sustained a most singular diminution, in consequence of some great convulsion.
The name of Kherson was given to the new town because it was erroneously supposed to stand on the site of the ancient Greek colony of that name, the ruins of which are to be seen close to Sevastopol, and similar mistakes are common in the case of many other Russian towns founded about the same time. Thus Sevastopol itself bears the name of the old Greek city on the shores of Abkhazia; the ruins of the real Eupatoria are at a long distance from the place which now bears its name; and nothing but a Tatar village of the name of Hadjibey ever stood on those steppes where Odessa is supposed to renew the memory of the ancient Odessus deserve admiration.
It is situated between Europe and Asia, and connected with the Mediterranean by the Bosporus of Thrace, the sea of Marmora, the Hellespont and Archipelago. This sea is divided into the Euxine proper, computed to be nine hundred and thirty-two miles long, and one hundred and twenty-six miles in the narrowest part; and the Palus Mæotis, now the sea of Azof, which is about two hundred and ten miles in length and from forty to sixty in breadth. The sea of Azov is united to the Black Sea by the Cimmerian Bosporus.
The coastal and shelf zones of the Black Sea are a mosaic of complex, interacting ecosystems with immense economic significance, rich natural resources and ecological communities, and concentrated human activities. They contain biologically productive, diverse ecosystems that provide a vital habitat for many commercial and endangered species. Until recently, the Black Sea supported fisheries almost five times richer than those of the neighboring Mediterranean.
The Black Sea has experienced the worst environmental degradation of all of the world’s oceans. The situation has become so severe that it has affected the health, well being, and standard of living of the people in the immediate area. About 160 million people live in the Black Sea catchment basin, including 80 million only in the Danube River basin. Although international agreements, strategic plans, and national environmental programs are in place, these severe economical problems have significantly slowed environmental monitoring, remediation, and restoration efforts.
The Black Sea is a landlocked basin with the exception of the relatively small flux of water and materials exchanged at the Bosphorus. The closed basin geometry of the Black Sea has important impacts on the regional hydrological cycle. The flow is constrained by the exchange at the Turkish Straits System.
By far the greatest quantity of water is received into this sea at its north-western corner, where the rivers Dniepr, Búg, Dniestr, and Danube fall into it. The catchment of large rivers covers almost half of the European continent, from where they derive the fresh water and pollutant inputs to the Black Sea. The Danube drains most of the Central and Eastern Europe to dominate the freshwater and sediment budget of the Black Sea. Per year, the Danube contributes about 209 km3 of water discharge, more than the entire freshwater supply to the North Sea, the Dniepr delivers 44 km3, and the Don contributes 22 km3.
It receives the drainage of a part of southern Russia, and there is probably no portion of the ocean which receives the drainage of a greater extent of country than the Black sea. As its basin is said to comprehend 960,000 square miles, and its surface to contain only 180,000, it follows that each square mile of its surface receives the drainage of five and one-third square miles, which will account for the small degree of saltness of its waters.
Air-sea exchange of a landlocked basin of continental/marine climate is all too significant in a climate sensitive region. Fine-scale features such as upwelling systems, boundary currents, jets and eddies represent high levels of dynamical variability. The ice covered north-western shelf and shallow Azov Sea in winter, and a river dominated regime competing with the Mediterranean influence, with all the interesting biological interactions make up a sensitive ecosystem.
The circulation of the Black Sea is mainly wind an buoyancy driven, and surface intensified, with a strong stratification that has evolved by great amounts of fresh water supplied by rivers such as the Danube, Dniepr, Dniester in the northwest, which form a coastal flow of low salinity water along with the rim current. There is a strong horizontal stratification across the front, both due to salinity, as well as temperature in the winter months when ice is formed in the northwest.
The Black Sea is very deep (about 2 km), and the only outlet is through the narrow, shallow (< 75 m deep) Bosphorus Strait. In the north, the Kerch Strait connects it to the shallow Sea of Azov, which has an area of 40,000 km2 and an average depth of 8 m. The Black Sea has a two-layer stratification, with a thin layer (~100 m) of fresher (~18 ppt salinity) and lighter water overlying a denser water (~22 ppt salinity and 1,017 kg/m3 density) at the bottom. A strong pycnocline, located at around 100 m depth, separates them. The difference in density and the lack of vertical currents prevent mixing and subsequent ventilation of the sub-pycnocline waters from the surface. Over the years, organic matter has been sinking and decomposing, causing a permanent anoxia beneath 100 to 150 m. This means that more than 90% of the Black Sea’s water is devoid of oxygen, making it the largest anoxic water body on our planet. Since dissolved oxygen is not sufficient, organic matter degradation uses oxygen bound in nitrates, and especially in sulfates, which generates hydrogen sulfide.
|
NEWSLETTER
|
| Join the GlobalSecurity.org mailing list |
|
|
|
