Lack of oxygen (hypoxia) in polluted water bodies worries the population of all industrialized countries of the world. But how much does it threaten the entire world's oceans?

In fact, there is no clear evidence of an increase in oxygen deficiency and hydrogen sulfide poisoning of the World's oceans, since such observations are rarely conducted there. In the Black Sea, scientists have been monitoring the distribution of hydrogen sulfide in the water column for many decades ^* . Here, only the upper 150-200-meter layer of water contains oxygen - all the flora and fauna of the sea is concentrated in it. The vast majority of the water column contains hydrogen sulfide, which is incompatible with life. There are many projects for improving the waters of this pool. One of them suggests blocking the Bosphorus, which would lead to a decrease in the hydrogen sulfide zone, and in the distant future, to its disappearance, as happened in the past, when the strait was blocked due to a decrease in ocean level during the ice age.

Other projects on the Black Sea relate to the hydrological regime of the reservoir itself. Calculations have shown that if the lower Phosphor current is blocked, water will mix better vertically, and the exchange rate between the upper (oxygen) and lower (hydrogen sulfide) zones will increase. And sooner or later the latter will disappear. But even this project is not perfect, because there is an assumption that the main mechanism of water circulation in the Black Sea is not connected with the exchange through the Bosphorus and the slow displacement of water to the top, but with the atmosphere.

There are several other sulfur-containing areas in the world's oceans, such as Walvis Bay off the southwestern coast of Africa, in the Atlantic Ocean. There is an anaerobic (oxygen - free-hydrogen sulfide), almost lifeless zone with a width of more than 50 km, it stretches for more than 300 km parallel to the coast.

Similar places are located in some places in the Indian and Pacific Oceans. So, off the coast of Peru, the appearance of hydrogen sulfide zones has a periodicity of 7 years and is associated with the penetration of the warm El Nino current ^** . The second largest "Black Sea" was identified in the 50s by the staff of the Woodhall Oceanographic Institute (USA)-this is the Cariaco depression on the continental shelf in the Caribbean Sea north of Venezuela. A powerful hydrogen sulfide lens with a water half-turn time of about 24,000 years is registered here.

So, starting from the Arabian Sea and the Gulf of Oman, then to the northwest stretches a strip of hydrogen sulfide zones-the Caspian Sea and the Black Sea. The Gotland Depression in the Baltic Sea and the Norwegian fjords, then the tip of Kamchatka and the Philippines region, it ends with the mentioned Kariako depression. Perhaps there will be new areas where hydrogen sulfide zones are found - for example, in Alaska or the Aleutian Island arc.

Some scientists believe that modern hydrogen sulfide zones are confined to areas of geological activity with lively processes of mountain formation, volcanism, earthquakes and the formation of depressions in the World's oceans. But in any case, these areas should never be discounted today, because they affect, first, the entire ecology of the planet, second, fishing and, third, the distribution of oil deposits.

^* See: V. I. Avilov, S. D. Avilova. These mysterious Black Sea precipitation patterns. - Nauka v Rossii, 1995, N 2 (editor's note).

^{* *} See: A. B. Polonsky. The mysterious El Nino. Nauka v Rossii, 1993, No. 1 (ed.).

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