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Black Sea: Waters
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The Black Sea is the largest anoxic, or oxygen-free, marine system. This is a result of the great depth of the sea and the relatively high salinity (and therefore density) of the water at depth; freshwater and seawater mixing is limited to the uppermost 100 to 150 m, with the water below this interface (called the pycnocline) being exchanged only once every thousand years. There is therefore no significant gas exchange with the surface, and as a result decaying organic matter in the sediment consumes any available oxygen. In these anoxic conditions some extremophile microorganisms are able to use sulfate (SO42−) for oxidation of organic material, producing hydrogen sulfide (H2S) and carbon dioxide. This mix is extremely toxic (a lungful would be fatal to a human), resulting in a sea that has almost all of its ecology living in that top layer down to a depth of approximately 180 m (600 ft). The relative lack of micro-organisms and oxygen has allowed deep-sea expeditions to recover ancient (on the order of thousands of years) human artifacts, such as boat hulls and the remains of settlements.
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The cleanup of the massive oil spill in the Black Sea was inching slowly forward. Firemen, farmworkers and soldiers, armed with spades and pitchforks, spread out over the sands Wednesday along with about 1,000 volunteers. And 1,000 students were expected to join the effort today. A rescue helicopter hovered over the water, scanning the sea for signs of the five seamen still missing.
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During the last 50 years, the Black Sea ecosystem has changed dramatically. And human beings living around this nearly land-locked sea have played no small role. When it comes to the explosion of jellyfish and comb-jelly populations, over-fishing and uncontrolled agricultural runoff are the apparent culprits. As commercial fishermen took an ever-increasing number of carnivorous fish at the top of the food chain, their prey species, including jellyfish, were able to multiply with little resistance. In the late l960s and l970s, mackerel, a major predator, were eliminated from the Black Sea ecosystem, which may be why severe outbreaks occurred of a formerly uncommon jellyfish, Rhizostoma pulmo. The same animal seen gliding through a tranquil pool of water is not so attractive when heaped in decaying piles along favorite bathing beaches.
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The Black Sea is Europe's most polluted sea; rivers feeding it bring raw sewage, nitrates, phosphates, pesticides, heavy metals, and other pollutants from 13 countries. This is accelerating the natural accumulation at the bottom of the sea of a layer of hydrogen sulphide, ammonia, methane, and ethane, which is rising by 2 m/7 ft a year. Below a depth of 150 m/500 ft 90% of the water is anoxic (lacking in oxygen), mixing little with the surface water, and supporting little life. It constitutes the world's largest mass of anoxic water and is caused by bacterial action on rotting vegetation.
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The Black Sea was an important link in ancient trade routes between Greece, Egypt, and the Near East. It is possible that ancient ships lie completely intact on the bottom. It is ... possible that ancient settlements consumed by the rising waters may lie entombed in the oxygen-less “dead” layer—looking just as they did when the waters started rising.
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Black Sea is an inland sea covering an area of about 420thousand square kilometers reaching at 2206 meters in its deepest point. Below 200 meters the oxygen level in the water is very low so marine life is very limited below this depth. Most known fish they catch in the Black Sea are; Black Sea turbot, gurnard, and small sharks.
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