Why are the waters of the Black Sea dangerous? The Black Sea is the world's most dangerous storage site for hydrogen sulfide

This is perhaps the most known fact about the Black Sea. Almost all of its life is concentrated in the surface, 100-meter layer of the Black Sea. Deeper - to depths of over 2 kilometers, only a few species of bacteria are found; there are no animals or plants there, because there is no oxygen in the water. These bacteria, living in the water column and at the bottom, decomposing the remains falling from the surface (there is even such a term - corpse rain), release hydrogen sulfide. Its source is sulfur-containing amino acids that are part of proteins.

Seawater sulfates, used by some types of bacteria to oxidize organic matter instead of oxygen, also serve as a source of sulfur (to a lesser extent). Hydrogen sulfide is a poison for animals and plants - it paralyzes cellular respiration in mitochondria.

Hydrogen sulfide is found in soft sediments at the bottom of all seas - oxygen from the water penetrates there very slowly, and the processes of bacterial decay and chemosynthesis with the release of hydrogen sulfide proceed intensively, which is why hydrogen sulfide accumulates in the soil. Dive deeper, where the waves do not stir up the soil, dig the bottom with your palm, and you will see that yellow sand, multi-colored shell rock or gray silt already a few centimeters from the surface have the same black color.

We observed this by descending deeper than 40 meters - where the gurnard walked along the bottom with its “paws” and exposed black silt under the gray surface (chapter “Life on Underwater Rocks”). Black is the color of sulfides - salts that hydrogen sulfide, like a weak acid, forms with metals. Therefore, shells in hydrogen sulfide turn black, and any metal object turns black. One of the legends about the origin of the name “Black Sea” is connected with this: they say that people came up with it when they lowered a metal weight on a rope into the sea to measure the depth. They brought him to the surface - he became completely black. Perhaps that's how it was. But the hypothesis that the name “Black” reflects the impression of Mediterranean travelers about our sea during a winter storm seems more plausible.

Hydrogen sulfide is often present in the weakly mixed bottom layer of water in other seas, especially in deep enclosed bays, but the Black Sea is the only one where such a gigantic mass of water is saturated with this substance. The reason here is that, with a relatively small area, the Black Sea has greater depth; The underwater slopes of the coasts are steep - as a result, water exchange between deep and surface waters is insufficient - oxygen does not penetrate deep into the sea. In other words, the Black Sea does not mix well.

Oxygen penetrates into water through the surface of the sea - from the air; and also - it is formed in the upper illuminated layer of water (photic zone) during photosynthesis of plankton algae. In order for oxygen to reach the depths, the sea must mix - due to waves and vertical currents. And in the Black Sea, the water mixes very weakly; It takes hundreds of years for water from the surface to reach the bottom.

The surface layer of the Black Sea water – to a depth of approximately 100 meters – is predominantly river origin. At the same time, saltier (and therefore heavier) water from the Sea of ​​Marmara enters the depths of the sea - it flows along the bottom of the Bosphorus Strait (Lower Bosphorus Current) and sinks deeper. Therefore, the salinity of the bottom layers of the Black Sea water reaches 30‰ (grams of salt per liter of water).

The change in water properties with depth is not smooth: from the surface to 50-100 meters, salinity changes quickly - from 17 to 21‰, and then further - to the bottom - it increases evenly. The density of water also changes according to salinity.

The temperature at the sea surface is always determined by the air temperature. And the temperature of the deep waters of the Black Sea is all year round 8-9 o C. From the surface to a depth of 50-100 meters, the temperature, like salinity, changes quickly - and then remains constant until the very bottom.

These are the two masses of Black Sea water: superficial– desalinated, lighter and closer in temperature to air (in summer it is warmer than deep waters, and in winter it is colder); And deep– saltier and heavier, with a constant temperature.

The layer of water from 50 to 100 meters is called the boundary layer - this is the boundary between two masses of Black Sea water, the boundary that prevents mixing. Its more accurate name is the cold boundary layer: it is always colder than deep waters, since, cooling to 5-6 o C in winter, it does not have time to warm up during the summer. The layer of water in which its temperature changes sharply is called a thermocline; a layer of rapid changes in salinity - halocline, water density - pycnocline. All these sudden changes properties of water in the Black Sea are concentrated in the boundary layer region.

Stratification (stratification) of Black Sea water by salinity, density and temperature prevents vertical mixing of the sea and enrichment of the depths with oxygen. In addition, all the rapidly developing Black Sea life breathes - planktonic crustaceans, jellyfish, crabs, fish, dolphins breathe, even the algae themselves breathe - they consume oxygen.

When living organisms die, their remains become food for saprotrophic bacteria. Bacterial decomposition of dead organic matter (rotting) uses oxygen. With depth, decomposition begins to dominate the processes of creating living matter by planktonic algae, and oxygen consumption during respiration and decay becomes more intense than its production during photosynthesis. Therefore, the further from the surface of the sea, the less oxygen remains in the water. In the aphotic zone of the sea (where sunlight does not penetrate), under the cold intermediate layer - below a depth of 100 meters, oxygen is no longer produced, but only consumed; It does not penetrate here due to mixing - this is prevented by the stratification of waters.

As a result, there is only enough oxygen for animal and plant life in the upper 150 meters of the Black Sea. Its concentration decreases with depth, and the bulk of life in the sea - the biomass of the Black Sea - is concentrated above 100 meters depth. This is how it turns out that 90% of the water mass of the Black Sea is almost lifeless. But in any other sea or ocean, almost all life is concentrated in the upper, 100-200-meter layer of water. True, due to the lack of oxygen and the presence of hydrogen sulfide in the water, there is no deep-sea fauna in the Black Sea , this reduces its biodiversity even further, in addition to the effects of low salinity. For example, there are no predatory fish of the deep with huge toothy mouths, in front of which luminous baits are hung.

Sometimes they say that hydrogen sulfide appeared in the Black Sea as a result of its pollution, that hydrogen sulfide is becoming more and more abundant, that the sea is on the verge of disaster... Indeed, overfertilization (eutrophication) of the Black Sea with runoff from agricultural fields in the 1970-80s e years caused a rapid growth of “weed” marine vegetation - some types of phytoplankton, filamentous algae- “mud”, more organic remains began to form, from which hydrogen sulfide is formed during decay. But this “extra” hydrogen sulfide did not bring significant changes to the equilibrium that had developed over millennia. And there is certainly no danger of an explosion of hydrogen sulfide - in order for a gas bubble to form, the concentration of molecules of this substance in water must be orders of magnitude greater than the real one (8-10 mg/l at depths of 1000-2000 m, that is, for 1 molecule of hydrogen sulfide there is not less than 200,000 water molecules) - this is easy to check using formulas from school chemistry and physics courses.

The Black Sea is a deep-sea basin with relatively steep slopes. The profile, that is, a vertical section of the Black Sea, is shown in the figure. When considering this profile, it should be taken into account that for greater clarity of the image, the vertical scale is taken to be much larger than the horizontal one, so the bottom profile turned out to be steep, but in reality the bottom is not inclined as much as shown in the figure.

Many people think that in the Black Sea, immediately from the shore, a sharp drop in the bottom begins, and where gliders and boats, clearly visible from the beach, sail (about 500-1000 meters from the shore), the depths are already measured in hundreds of meters. However, this is far from the case. The 100-meter depth line runs at a distance of 200 kilometers from the coast in the northwestern part of the sea, 10-15 kilometers in the main part and only in certain areas (Crimea) at a distance of one kilometer. The sea bed is mostly flat, but there are small cracks and ledges, and there are also hills with very gentle slopes.

The greatest depth of the Black Sea is 2211 meters. The area of ​​maximum depths is located in the central part of the sea, somewhat closer to the Turkish shores.

At the bottom of the Black Sea, in one of its deepest depressions, the so-called Yalta, at a depth of over 2 kilometers, a man visited the first dive in the last century (1971) on a special deep-sea vehicle"North-2". Its length is 4 meters, displacement is 15 tons. The device had a crew of 4 people under the leadership and with the participation of M. N. Diomidov, a famous Soviet designer of deep-sea vehicles.

What do aquanauts see when diving into the depths of the Black Sea? Only in the surface layer - up to 100 meters - does life exist. Deeper in complete darkness, under the rays of a spotlight, only organic remains glow, slowly sinking to the bottom and resembling snow flakes. But here you can also find human creations - sunken ships from different eras rest in the darkness of the depths.

There are two types of structure of the earth's crust - oceanic and continental. In the ocean, under a layer of water there is a layer of sediment that gradually accumulates there; the thickness of this layer is from 2 to 5 kilometers. Then comes a basalt layer of the same thickness and, finally, magma, which comes to the surface during volcanic eruptions. There is no sedimentary layer under the continents, but the basalt layer there is thicker, up to 20 kilometers, and, in addition, there is another layer - granite, 10-15 kilometers thick, located above the basalt.

Under the Black Sea, the structure of the earth's crust resembles that of the ocean, but the layer of sedimentary rocks there is more than 10 kilometers, that is, thicker than in the ocean, and the layer of basalts is 10-20 kilometers thick (less than under the continents, but more than under the oceans). The granite layer extends only near the shore.

Since it is known that the Black Sea is geologically young, the structure of the earth’s crust underneath makes it possible to confirm one of the contradictory assumptions about the formation of continents and oceans. Some scientists believe that the oceans were formed before the continents, that the primary type of the earth’s crust was basaltic, and therefore these rocks lie shallow in the ocean. Then granite magma flowed through the cracks, which formed the continents. Other scientists take the opposite view. They believe that the seas are more modern than the continents. This point of view is confirmed by the oceanic structure of the bottom of the “young” Black Sea. If the continents were younger than the oceans, then under the Black Sea, as well as under other inland seas, there would be a large layer of granites.

Now, having been under the bottom of the Black Sea, let's rise higher and get acquainted with the composition of the soils covering its bottom from above. The soils of the Black Sea were formed as a result of the interaction of three main factors: destruction of the coast, river runoff and deposition of organic residues. Coastal soils consist of pebbles, gravel, sand, and silt (very small particles). The bottom at a depth of 20 to 150 meters is covered with silts with shells of mussels and phaseolina. Deep-sea silts are clayey and calcareous. The bottom at a depth of 200 to 1500 meters is covered with dark (gray, brown, brown) silts.

Having been to the bottom of the sea, we will rise even higher and get acquainted with the bottom topography near the sea shores. Before you give general characteristics coastal areas of the Black Sea bottom, it is necessary to dwell on the enormous role that waves play in their change. The figure shows with a dotted line what the original profile of the coast was. Sea waves cut off part of it, forming a steep ledge, or cliff, while the soil sank down the slope, creating sediments here, and part of the soil moved along the shore under the influence of the waves. Thus, the destructive and creative activity of waves in the surf zone exists simultaneously.

Let us now turn to the characteristics of the bottom of individual areas of the Black Sea.

Bottom characteristics

The shores of the northwestern part are shallow; on the western coast of Crimea there are also extensive sandy beaches. On the southern coast of Crimea, the beaches are small, since the rocks there are made of very strong rocks that even the thousand-year work of the sea could not destroy. For example, the “Monk” rock stood near Simeiz for several centuries, and only in 1927 was it destroyed by an earthquake.

An interesting feature of the Caucasian coast are the huge protrusions, for example, at the Pitsunda and Sukhumi capes. Their base lies at a depth of up to 200 meters. They were formed in the process of accumulation of soil, which is carried by rivers into the sea, and then moves under the influence of waves along the coast. Approaching the ledges, sediments fall into the sea, gradually building up the capes. A peculiarity of the Caucasian and Anatolian coasts of the sea is the presence of submerged deltaic ledges of rivers that form underwater shoals, such as the Gudauta River.

An equally interesting feature are canyons - deep valleys with relatively steep slopes, running from the shore into the sea and along its bottom. The canyons are located opposite the mouths of the Colchis rivers - Inguri, Khobi and Rioni. The slope of their slopes sometimes reaches 25 degrees (400 m/km), and the longitudinal slope is 12 degrees (200 m/km). The canyons extend to a depth of 1000 meters. Scientists from many countries are working to clarify the mystery of the origin of canyons (such landforms exist near California and against the mouths of African rivers).

Perhaps these are the hollows of the rivers that flowed here, which were flooded when the level of the World Ocean rose (by hundreds of meters) caused by the melting of ice after the last glaciation. Perhaps the canyons are cracks in the earth's crust formed during earthquakes. Perhaps the canyons were formed as a result of erosion of the bottom by artesian springs.

Usually, scientists, explaining the presence of a huge mass of hydrogen sulfide in the Black Sea (BS), explain this by the uniqueness of this body of water. The following arguments are given:

1. The Black Sea is a closed basin, it is connected to the world ocean by narrow straits.


2. Large rivers are discharged into the World Cup a large number of organics.


3. The World Cup has great depth and a sharp drop from continental shelf to depth.


4. The high salinity of the deep layers of the Black Sea does not allow oxygen to penetrate downwards and this contributes to the formation and accumulation of hydrogen sulfide.


5. Due to the unique hydrology of the Black Sea, there is no mixing of layers in it.

Fig 1. Cross-section of the Black Sea.

Looking at this map, we quickly become convinced that the World Cup is not unique in its characteristics.

Rice. 2 Reliefs of the seas.
The Mediterranean Sea (MS) is also closed and is connected to the ocean by the relatively narrow Gibraltar. At the same time, the maximum depth of the SM is 5121 m, which significantly exceeds the depth of the CM (2210 m). The average depths of both seas have approximately the same value - 1240 and 1541 m. At the same time, the map shows that the differences in depths in the SM are almost greater than in the WC.
Regarding salinity, the salinity of the SM is significantly higher than the salinity of the BS (36-39.5 ‰ versus 15-18 ‰), which will undoubtedly further prevent the penetration of oxygen to depth. At the same time, the contribution of organic matter by the rivers of the Mediterranean basin is undoubtedly greater, not even because more rivers flow into it, but because on the banks of this basin there are industrial the developed countries EU. They are densely populated, carry out intensive agricultural work, and big cities They dump enormous amounts of waste. At the same time, in the EU countries there was no such decline in all economic indicators as in the countries of the former USSR and Eastern Europe.
Despite all this, hydrogen sulfide reserves are not formed in the SM.
But let's take the Caspian Sea (CM). It is generally a salt lake.

Fig.3 Caspian Sea.

The depth of the CM is quite decent - 1025 m. At the same time, we observe a significant difference in depth, almost a cliff in the area of ​​​​the confluence of the Kura River. And in the middle part of the pool too. There is no doubt about organics - pollution from oil production is added to the drains of the mighty Volga, Kura and Ural. But there are no deep layers of hydrogen sulfide in the CM either! Although salinity in the southern part of the sea reaches 28 ‰.
There remains one and final argument for the uniqueness of the FM - the absence of mixing of layers. Why do they mix in other seas, but not in the Black Sea? It is worth noting that the methodology itself for determining the parameters of sea water, deep currents and salinities is very complex. The fact is that such work requires significant costs. Oceanographic vessels are incredibly expensive to operate. It would be much better to spend money on building cruise ships, sort of floating paradises, and then sink and burn them in hopes of receiving insurance.

Rice. 4 Oceanographic vessels.

In addition, the volume of such research is extremely large. With great difficulty, we only had some idea of ​​the surface of the oceans and seas, and if we also take their thickness... this is a colossal amount of information. Often even submarines die due to lack of such knowledge. They fall into deeper layers with a lower density, as if breaking through the ice of a denser layer. How these layers are formed, where they are located and why - all of this is still a mystery for oceanology.
Therefore, it is premature to say with confidence that there is no vertical mixing of layers in the Black Sea for such and such a reason. But it is missing, and that is a fact.
However, hydrogen sulfide is successfully formed in other seas and basins. Accelerated formation of hydrogen sulfide has been observed, for example, in the Norwegian fjords. Driving by car to Odessa past the estuaries, we are forced to plug our noses and close the car windows - the stink of hydrogen sulfide is unbearable. This gas is also formed in other seas and even in lakes.
Not far from the resort of Playa del Carmen there is a full fresh water Cave Cenote Angelita. Lost in the impenetrable jungle of Mexico, the cave is fraught with many surprises, one of which is an amazing underwater lake! At the bottom of this lake there is also a hydrogen sulfide layer.

Rice. 5 Underwater lake in Mexico.

From this we can conclude that the Black Sea basin is absolutely not unique in this regard and the presence of 3.1 billion tons of hydrogen sulfide in it is due to other reasons.
Here I would like to mention another strange event. Recently, the American Landstat satellite took another picture Dead Sea(MM), which shocked scientists. In just one orbital revolution, the color of this body of water changed to completely black. Oceanologists came to the conclusion that the sea instantly “turned over.” The surface layers went down, and those saturated with hydrogen sulfide floated up.

Rice. 6 Dead Sea.

This can happen when a critical density gradient is reached and is quite possible with our FM. Water saturated with hydrogen sulfide is black. Here is your explanation - why the World Cup is called black. But before it was called Russian, the Greeks called it hospitable. Only then did it suddenly turn black. Did a “turning over” of layers happen in ancient times?
It is worth noting, and scientists always point out this, that the bottom of the World Cup does not have a solid granite slab. That is, the Black Sea lies directly on the basalts of the mantle and is a remnant of an ancient ocean. The true depth of the Black Sea reaches 16 km, the depression is filled with sediments.
A simple calculation shows that the volume of sedimentary substances is:
The area of ​​the deep-sea part is 211,000 sq. km. * the thickness of the sedimentary layer is 16 km. = 3 million 376 thousand cubic meters km.
Which exceeds the volume of the entire World Cup by more than 6 times.
At the same time, research by the expedition of J. Murray in 1910, part of the Meteor expedition, research on the cable steamer Lord Kelvin, the expedition of W. Snell and many others showed that the layer of sedimentary substances at the bottom of the world's oceans is 23-35 cm. That is, precipitation accumulate extremely long and slowly.
How could a layer of sediment 16 km thick accumulate in the World Cup?
It should be noted that back in the early 1920s, hydrogen sulfide was located much deeper. In 1891, Professor A. Lebedintsev raised the first water sample from the depths of the Black Sea. The sample showed that the water below 183 meters is saturated with hydrogen sulfide. Nowadays, poisonous and explosive gas is located at depths of 18 m, and sometimes even breaks through to the surface, as happened during the Crimean earthquake of 1927. Then an entire flotilla of fishermen burned in flames on the surface of the sea.

Rice. 7 World Cup.
This means that the process of hydrogen sulfide formation continues and proceeds quite quickly. And this is not due to an increase in the discharge of organic substances into the Black Sea - it has even decreased. This is the result of rotting without oxygen of a huge amount of sediment that ended up in the World Cup unknown, as in the recent past.
We know that the breakthrough of the Bosporus and Dardanelles occurred in historical period, this is noted in the chronicles. It is also known that on ancient maps the World Cup is depicted as a rounded basin, without peninsulas, and Crimea is depicted as a flat coast.

There is no need to make idiots out of our ancestors, as if they, when drawing Crimea, did not see that it was a peninsula jutting out 300 km into the sea. It’s just that the old maps show the World Cup as it was. And this was a lake in the deep-water part of the modern World Cup. I have already written (http://alexandrafl.livejournal.com/5078.html) that presumably, as a result of a huge tsunami, and even more likely - hyper-precipitation, super-powerful rains, all the biomass from the Central Russian Upland, the southern part of Ukraine, was washed away into Black Sea basin. As a result, we have the absence of thick layers of fertile soils in the Non-Black Earth Region, wide river floodplains that do not correspond to their geological history, accumulations of black soil in places where it was washed, absence of trees in steppe zone Ukraine, a thick layer of sediment in the steppe part of Crimea.
At the bottom of the World Cup lie the remains of our ancient civilization. There is vegetation, soil, dead animals and people, flooded cities and river beds. The once wooded, wildlife-filled, fertile south of Ukraine has turned into a dry steppe. This happened not as long ago as scientists would like us to believe. You can still find references to this fertile land in historical documents. Our ancestors tried to protect themselves from the elements, they built along large rivers colossal hydraulic structures - the Serpentine Shafts, which they are now trying to pass off as defensive structures against the small number of nomads, capable of gathering only as a gang, but not into an army.

Rice. 8 Serpentine shafts.

The Crimean Isthmus was also dug up, and a shaft was made separating the Kerch Peninsula. Everything for protection from powerful mudflows and floods.
The remnants of our civilization continue to “gas” at the bottom of the World Cup. This is precisely the uniqueness that is inherent in the former Russian, and now Black Sea.

• All rights reserved Alexandra Lorenz

Looking at the azure surface of the Black Sea, it is difficult to even imagine that in its waters, from a depth of 200 meters to the very bottom, there is a layer of hydrogen sulfide, which is deadly to all living things. And if dolphins, fish and other marine organisms live in the upper layers of the sea, then the remaining 90% of the water is almost lifeless. Only some types of bacteria are able to survive in such unbearable conditions.

The Black Sea has a very interesting structure. The fact is that the water column in it is divided into several layers that do not mix with each other. The thin surface layer of the sea is fresher, rich in oxygen and organic matter. It is here that all the diversity of the Black Sea fauna is concentrated. But, starting from a depth of 100 meters, there is a decrease in the amount of dissolved oxygen, and from about a depth of 200 meters, the Black Sea is a toxic hydrogen sulfide environment.

The basin of the sea looks like a bowl up to 2000 meters deep, the entire water mass of which communicates with Mediterranean Sea through the narrow and shallow Bosphorus Strait. The sea is fed by precipitation and the fresh water of the tributaries flowing into it. Not long ago, scientists discovered an underwater river that carries its waters at a speed of about 6.5 km/s from the Sea of ​​Marmara to the central parts of the Black Sea basin and increases the salinity of the bottom layer to 30‰. At the same time, in the surface part there is a watercourse that carries water from the Black Sea to the Mediterranean and further to the Atlantic. But this water exchange, as it turned out, is not enough to reduce the concentration of hydrogen sulfide in most of the sea.

The hydrogen sulfide content increases with depth and reaches a maximum at around 2000 meters - 9.6 mg/l of water. Further at the very bottom, gradually decreasing to 5.7 mg/l. According to experts, this caustic gas with an odor rotten eggs the Black Sea contains about 3 billion tons, more than any other sea on the planet. Accumulations of hydrogen sulfide are also found in oceanic depressions, but nowhere are there such a large number of people inhabiting the shores of a reservoir as in the case of the Black Sea coast.

Some studies indicate that the Black Sea, in addition to hydrogen sulfide, also contains large amounts of methane. Due to slow water exchange, these gases rarely come to the surface, although cases of poisoning sea ​​creatures sometimes observed in the shallow part of the sea. But at least one large-scale case has been reliably recorded in which deadly gases escaped to the surface. This happened in 1927 during the Crimean earthquake, when, due to fluctuations earth's surface the balance between the layers was disrupted and the gas cloud burst out. Eyewitnesses smelled a strong odor of hydrogen sulfide and also observed a huge flame above the surface of the sea. The fact is that during the earthquake there was a thunderstorm, which, in all likelihood, ignited the gases that rose to the surface. But the mixture of hydrogen sulfide with air is itself explosive, and the presence of methane could have played a role in this fire.

But where did so much hydrogen sulfide come from in the water of the Black Sea? There are several theories on this matter, and they all have a right to exist.

According to one version, hydrogen sulfide is formed at the bottom during the decay of organic residues. And due to poor circulation, water accumulates there in large quantities. Moreover, the source of organic matter in this case is not so much the fauna of the Black Sea as the anthropogenic load on the reservoir. According to experts, organic matter entering with the waters of the Danube, Dnieper and other tributaries has a significant negative impact on the ecological state of the reservoir.

According to another version, hydrogen sulfide is released from fractures in the earth's crust at the bottom of the sea. And the third version boils down to the fact that the culprit of such a high concentration of dangerous gas was anaerobic sulfate-reducing bacteria, which convert sulfates from organic residues into hydrogen sulfide.

Today, experts dealing with the problem of hydrogen sulfide and methane in the Black Sea are concerned about the increasing frequency of these gases coming to the surface. Such phenomena can pose a danger not only to the Black Sea fauna, but also to coastal residents if the event takes on alarming proportions, as it did in 1927.

Interestingly, as one of the solutions to the hydrogen sulfide problem in the Black Sea, a method of using this gas as a source of electricity is proposed.

There were reports in the mass media about the possibility of a sulfur explosionhydrogen in the Black Sea. Are such statements legitimate and what is needed?take to reduce the amount of hydrogen sulfide in deep andsurface layers of water? These issues are discussed in the publication below.article.

V. I. BELYAEV, E. E. SOVGA

HYDROGEN SULFIDE WILL NOT EXPLODE IN THE BLACK SEA

In 1890, a Russian oceanographic expedition, working under the leadership of an academician, discovered in the depths of the Black Sea a noticeable concentration of dissolved hydrogen sulfide, a poisonous gas with the smell of rotten eggs. As further studies have shown, this gas is present throughout the deep waters of the Black Sea, approaching the surface at approximately 100 m in the central part of the sea and 150-250 m off the coast. This difference in the position of the upper boundary of the hydrogen sulfide zone is due to the specific circulation of water masses, in which water rises (upwelling) in the center of the sea and falls (deepening) on ​​its periphery.

The Black Sea is the only one on globe, in which hydrogen sulfide constantly Huge amounts of water are contaminated. There are areas in the seas and oceans where hydrogen sulfide contamination occurs periodically or even persists throughout the year, for example in the Norwegian fjords and the Karjako depression in the Caribbean Sea. Vast deep anaerobic water masses contaminated with hydrogen sulfide sometimes appear in the oceans. They migrate across the water area, sometimes invading shelf areas, which has a detrimental effect on the state of coastal ecological systems. So, in the early 50s in Walvis Bay ( Atlantic coast southwest Africa), upwellings brought to the surface a water mass formed in the depths containing hydrogen sulfide. Massive fish deaths were observed, and a smell was noted along the coast up to 40 miles inland.

© BELYAEV Valery Ivanovich - academician Academy of Sciences of the Ukrainian SSR, Chairman of the Commission of the Academy of Sciences of the Ukrainian SSR on the problems of the World Ocean. SOVGA Elena Evgenievna - candidate of geological and mineralogical sciences, senior Researcher Marine Hydrophysical Institute of the Ukrainian SSR Academy of Sciences.

IN. AND. Belyaev, HER. Sovga

hydrogen sulfide, which caused concern among the population. Water masses contaminated with hydrogen sulfide systematically invade the shelf of the Arabian Sea - in the northwestern part Indian Ocean. At the same time, massive fish deaths also occur. Local formations of hydrogen sulfide are recorded in the Caspian Sea and even in the shallow Baltic Sea.

In the geological history of the Black Sea, the formation of hydrogen sulfide has always been associated with the penetration of saltier waters through the Bosphorus Strait Mediterranean waters into the deep layers of the Black Sea. At the same time, a significant volume of river runoff also enters the sea, resulting in a sharp jump in density - a halocline - between the desalinated surface and saline deep waters. The variable circulation of water masses shifts the halocline: sometimes it lifts it closer to the surface, sometimes it lowers it into the depths. As a rule, the upper boundary of the hydrogen sulfide zone begins immediately below the halocline, which impedes the flow of oxygen into this zone from upper layers. During climatic fluctuations in ocean level, the connection between the Black Sea and the Mediterranean through the Bosphorus Strait was either disrupted or resumed. Last time it was restored approximately 6-7 thousand years ago. During this time, a deep water column containing hydrogen sulfide formed in the Black Sea. It occupies about 90X the volume of the sea.

There are three main sources of hydrogen sulfide in the Earth's water bodies. Firstly, it is formed due to the reduction of sulfates present in water during the anoxic decomposition of organic substances. Decomposition is carried out with the participation of anaerobic sulfate-reducing bacteria, which use the oxygen of sulfates in the process of their life, releasing hydrogen sulfide. Secondly, this gas occurs during the decay of organic substances containing sulfur. And thirdly, it can come from the earth's crust through crevices of the seabed and with hydrothermal waters.

A well-known oceanologist summarized the research materials on the hydrogen sulfide zone of the Black Sea. He analyzed all the material available on this issue up to 1965, that is, before the development of the process of eutrophication of the sea, which has now spread to its entire water area. suggested that if the flow of organic matter into the Black Sea increases (for example, due to an increase in its biological productivity or a large influx of low-persistence organic compounds entering the sea with river waters), then the chemical composition of the sea will change. The consequence of these changes will be possible local rises in the upper boundary of the deep hydrogen sulfide zone, that is, a rise in the “limit of life” in the sea.

Now these assumptions are beginning to come true. According to data obtained over the past decade and a half, the environmental situation in the Black Sea has worsened. Not only in coastal areas, but also in open waters sea, an excess of organic matter was discovered. The structure of biological communities has also changed: large predator fish have practically disappeared, the number of dolphins has decreased, the aurelia jellyfish and the microalgae nocturnal have multiplied unusually, the bottom field of phyllophora algae and mussel colonies have decreased in the northwestern shallow part of the sea, where in the summer now extensive frozen zones. Clear,

that such a situation should sooner or later affect the balance of hydrogen sulfide in the sea. But to what extent this balance is determined by the influence of natural and to what extent by anthropogenic factors is not yet reliably known. The answer to the question can only be obtained as a result of long-term observations of the hydrogen sulfide zone of the sea. The solution to this interdisciplinary problem required the involvement of specialists from various fields: hydrophysicists, hydrochemists, hydrobiologists, as well as specialists in the field of mathematical modeling of ecological systems.

In 1984, a voyage of the research vessel "Vityaz" of the Institute of Oceanology named after. Academy of Sciences of the USSR. Its participants explored the area of ​​the upper boundary of the hydrogen sulfide zone using the Argus underwater vehicle. The features of the distribution of chemical compounds in the contact layer of the oxygen and hydrogen sulfide zones, where the oxidation of hydrogen sulfide occurs, were studied. Visually, fish and other organisms were observed penetrating into this zone.

In 1985-1986 Work was carried out under the interdepartmental program of the Academy of Sciences of Ukraine "Study of the dynamics of the hydrogen sulfide zone of the Black Sea in order to develop methods and means of preventing negative restructuring of its ecological system." Within the framework of this program, six complex expeditions were carried out on the ships “Mikhail Lomonosov”, “Akademik Vernadsky”, “Professor Kolesnikov”, etc. During the expeditions, which worked in all seasons of the year, 430 deep-sea stations were completed. To detect possible geological sources of hydrogen sulfide in the Black Sea, samples of deep water were taken at a distance of 5-10 m from the bottom, as well as samples of bottom sediments. Not only the concentrations of hydrogen sulfide and oxygen were measured, but also the content of sulfur in other forms (thiosulfates, sulfates), samples of phyto- and zooplankton, bacteria, chlorophyll were taken, and optical and hydrological characteristics were determined.

The study of the hydrogen sulfide zone continued after the completion of this program. In all expeditions, deep water sampling was carried out at a spatial interval of 30 miles using bathometers of the MGI-4102 sounding complex (Istok) with a vertical measurement discreteness of 5-10 m in the zone of interaction of oxygen and hydrogen sulfide. Measuring hydrogen sulfide in deep seawater samples is not an easy task. The concentrations of hydrogen sulfide in these samples are low, and it quickly oxidizes upon accidental contact with atmospheric oxygen. Therefore, when taking samples of deep water containing hydrogen sulfide and other reduced forms of sulfur, their complete isolation from the atmosphere was ensured.

As a result of expeditionary research, the interseasonal and intraseasonal variability of the hydrogen sulfide zone boundary throughout the year was determined. Closest to the surface (70-90 m), the upper boundary of the zone is located in the spring in the area of ​​​​a single cyclonic circulation in the center of the sea. In summer and autumn, in the presence of two stationary cyclonic gyres in their center, the depth of the hydrogen sulfide boundary is 95-10 m. At the periphery of the gyres in all seasons, a deepening of the boundary to 150-190 m is noted. Data on the interannual variability of the sulfur boundary

hydrogen zone strongly depend on the duration of the time interval. Thus, judging by estimates of changes in the position of this boundary over a fairly long period (about 60 years), its average depth changed little. But within this period of time there were periods of both uplifting and deepening of the upper boundary of the hydrogen sulfide zone. In 1984-1986 a tendency of its rise was noted, and then, until 1990, a slight deepening. Academician T believes that against the background of recorded interannual variations, a constant unidirectional change in the position of the boundary of the hydrogen sulfide zone is not observed. This conclusion coincides with the opinion of most experts studying this problem. The highest position of the boundary of the hydrogen sulfide zone in the entire history of studying the Black Sea was noted in the spring of 1988, when hydrogen sulfide was recorded at a depth of 70 m in the center of a single cyclonic gyre. But this rise turned out to be short-lived. When the research vessel returned to this area 20 days later, the depth of water sampling, corresponding to the appearance of hydrogen sulfide, was already 90-95 m. Such local elevations are not stable in time and space and, as a rule, are caused by short-term active synoptic disturbances.

It should be emphasized that the very concept of “upper limit of the hydrogen sulfide zone” is rather arbitrary; it is determined by many difficult-to-control factors. The upper limit is the depth at which, in accordance with the accepted methodology, the presence of hydrogen sulfide in water samples is detected (concentration of about 0.1 ml/l). By the way, a more sensitive measurement technique detects traces of hydrogen sulfide in the Black Sea and at higher horizons, right up to the surface. The position of the upper boundary depends on the rate of the hydrogen sulfide oxidation reaction, the rate of delivery (due to vertical water exchange) of oxygen from the upper and hydrogen sulfide from the lower layers to the intermediate layer where oxidation occurs. Finally, the upper boundary of the hydrogen sulfide zone can move along with water when vertical currents occur. In addition to slow, climatic changes in vertical circulation in the sea, as already noted, rapid vertical rises and falls of water associated with vortex movements are observed. The intensity of these movements is due to the activity of atmospheric processes. Therefore, it is very difficult, without sufficiently long-term observational data, to determine what causes each time the anomalous vertical rises of the boundary of the hydrogen sulfide zone: the intensification of atmospheric processes, increased formation or weakening of the oxidation of hydrogen sulfide. The processes of hydrogen sulfide formation are associated with the activity of bacteria, which also depends on climatological factors, including solar activity.

From the point of view of mathematical statistics, in order to obtain a conclusion about the trend of changes in the positions of the upper boundary of the hydrogen sulfide zone, it is necessary to determine the average values ​​of the characteristics of non-stationary random fields based on a relatively small sample of observations. This circumstance reduces the problem of the dynamics of the upper boundary only to assessing the trends of its vertical displacements.

Experts studying the hydrogen sulfide zone in the Black Sea judge its

Hydrogen sulfide V Black sea Not will explode 51

behavior based on independent observations of many processes in the sea (physical, chemical, biological), and field observations are combined with numerical experiments on mathematical models. To correctly understand the behavior of the hydrogen sulfide zone, reliable ideas about its origin are required. Expeditionary studies indicate sulfate reduction as the main process of hydrogen sulfide replenishment in the Black Sea. At the same time, the main reasons for the existence of the hydrogen sulfide zone here are considered to be density stratification, which impedes vertical exchange, and a large nutrient runoff from the coast per unit sea area. Both of these factors provide intense sulfate reduction, leading to the formation of hydrogen sulfide in the deep anaerobic zone. Expeditionary data confirm the focal nature of sulfate reduction, and the location of these foci is confined to places where dead organic matter arrives from the shelf.

At the same time, both mentioned factors are under strong anthropogenic pressure. Thus, regulation of river flow reduces the volume fresh water, entering the upper layer of the sea, evens out stratification and can improve vertical water exchange. Increased nutrient runoff as a result of industrial, domestic and agricultural pollution causes an increase in the production of dead organic matter, which stimulates the process of sulfate reduction and the replenishment of hydrogen sulfide in the sea. At the same time, in the aerobic zone, oxygen is spent on the decomposition of additional quantities of organic matter, which reduces the possibility of rapid oxidation of hydrogen sulfide in the event of its local rises. Since most of the organic matter is formed in the Black Sea on the shelf, the ecosystem of the latter largely determines the state of the hydrogen sulfide zone in the deep sea.

According to rough estimates, due to anthropogenic pollution in the Black Sea today, an additional amount of hydrogen sulfide may appear, comparable to that formed naturally. An increase in the supply of hydrogen sulfide in deep waters increases the likelihood of its invasion into the oxygen zone, accompanied by a detrimental effect on the fish, algae and shellfish living in it. There is an increased risk of hydrogen sulfide escaping directly onto the sea surface in coastal areas of resort water use. Although these phenomena can be short-lived, quite rare (like hurricanes in the atmosphere) and occur under certain hydrological and meteorological conditions, they are quite unpleasant. No matter how low the concentration of hydrogen sulfide in deep Black Sea water is, in contact with air it emits a quite noticeable odor. Sensing it already means that the concentration of hydrogen sulfide in the air exceeds the safety threshold for people. So far, such phenomena have not been observed in resort areas of the Black Sea. However, there is an urgent need to create a permanent monitoring service for the concentration of hydrogen sulfide in the Black Sea in order to promptly warn the population about an abnormal rise of hydrogen sulfide waters and inform about the rules of behavior in such situations.

Experts' concerns about the negative consequences of water sulfide development

native zone in conditions of anthropogenic pollution, in all likelihood, provoked the appearance in the mass press of articles about the possibility of a hydrogen sulfide explosion in the Black Sea. To prevent a catastrophe, it was proposed to “simply” extract hydrogen sulfide from the pumped deep water. The idea has been put forward that by burning hydrogen sulfide it is possible to obtain energy and commercial sulfur by building a chemical plant for this purpose on the Black Sea coast.

It should be noted that the dissolved gaseous phase of hydrogen sulfide in the Black Sea is only 0.24 g per ton of sea water at a depth of 300 m, 1.2 g at a depth of 1000 m and up to 2.2 g at the bottom. at depths of about 2000 m. Hydrogen sulfide has high solubility: even at atmospheric pressure can be dissolved up to 12 kg in 1 ton of water, and in deep waters under pressure of about 200 atm - many times more. Thus, the concentration of deep hydrogen sulfide raised to the surface is less than 0.0001 parts of the saturating value. At such low concentrations of the gas, it is not possible to talk about the possibility of its release in bubbles from the solution as a result of shaking.

Nevertheless, with an insignificant concentration of hydrogen sulfide, its total amount formed annually in the Black Sea basin naturally is about 107-10e tons, and maybe more. We do not know the exact value, but there is every reason to believe that it is variable, varying within wide limits along with changes in the position of the upper boundary of the hydrogen sulfide zone. To oxidize such a quantity of hydrogen sulfide, it is necessary to create a gigantic industrial installation through the pipes of which deep water is simultaneously pumped in an amount equal to several drains of rivers such as the Volga or Danube. Even with ideal environmental cleanliness of the main sulfur production, the construction of such a large-scale industrial complex in the resort area of ​​the Black Sea coast will not be without negative consequences for the environment. It is no coincidence that it is forbidden to build here industrial enterprises. At the same time, we cannot reliably calculate the impact of this installation on the hydrogen sulfide zone of the sea, guarantee the success of its operation and assess the long-term environmental consequences.

The absurdity of proposals to pump out deep-seated hydrogen sulfide reveals the vicious concept of using water resources practiced in our country. It practically ignored the fact that reservoirs are not just masses of water, but ecological systems formed as a result of long evolution - peculiar natural factories in which living organisms work, converting the energy of the Sun into products directly consumed by humans - fish, mollusks, crustaceans . The implementation of this concept of environmental management led to the death of the ecosystem of rivers, lakes, and inland seas. Our country has lost huge resources of valuable fish, which were previously obtained from rivers and lakes, the Black and Azov seas. At the same time, there was an opportunity, through careful, carefully justified stage-by-stage hydraulic engineering and drainage development of these reservoirs, to greatly enhance their natural ability to produce fish and other “gifts of nature.” Unfortunately, energy is taken from rivers like this

Hydrogen sulfide in the Black Sea will not explode 53

in a way that destroyed their ecosystems. With the help of this energy, metals were obtained, ships were built from them, which went “for hake” to distant seas...

It is more realistic to influence the hydrogen sulfide zone of the Black Sea, preventing pollution of waters that come with coastal runoff. It is important not to mix waste of different origins, then they can be directly passed through specialized recycling installations at each production site. After all, in principle, there is no waste that is not a raw material for some kind of production. All this costs additional costs, but this is the only way to ensure the cleanliness of rivers, lakes, and air, while the sea will become clean and cope with its problems on its own, as it has dealt with them for over 7 thousand years.

Of course, one cannot categorically object to proposals to extract certain substances from sea water, including sulfur. In seawater, hydrogen sulfide is present not only in a free state, but also in a bound state, as part of hydrosulfides (salts). Taking into account the latter, 1 ton of deep water contains 9-12 g of hydrogen sulfide and its compounds. Let us note for comparison that 1 ton of coal can contain from two to 80 kg of sulfur. When such coal is burned, toxic sulfur oxides are formed, which poison environment. Therefore, first of all, it is necessary to solve the problem of extracting sulfur from coal. Nevertheless, its extraction from the Black Sea water may someday prove feasible. But since Black Sea coast- an all-Union health resort, plans to create the next industrial giants here affect the interests of the whole people and should, at the level of ideas, be subject to a thorough environmental assessment and broad public discussion. Of course, given the current state of production culture, such projects are harmful.

The authors of articles published in the mass media base their statement about the possibility of a hydrogen sulfide explosion in the Black Sea on information about the flame that appeared during the 1927 earthquake above the surface of the sea, opposite the southwestern part of Crimea. Eyewitness accounts of this phenomenon are provided. However, the fact that it has been studied and the research results have been published in the scientific press is completely ignored. An expedition was working in Crimea at that time under the leadership of. Its participants immediately went out to sea on a boat, took water samples, examined the bottom and determined that there had been a release of gaseous hydrocarbons mixed with hydrogen sulfide from the bowels of the earth. In other words, mud volcanoes at the bottom of the sea “triggered.” Thus, hydrogen sulfide dissolved in deep waters had nothing to do with the flame that broke out over the sea in 1927.

So, the natural hydrogen sulfide zone most likely does not threaten anyone in itself. At the same time, this is not dead water, but full of life bacterial ecological system, well balanced in its functions with the aerobic ecosystems of the sea. Its bacterial population ensures the cycle of carbon and nutrients no worse, and perhaps even better, than deep sea ecosystems without hydrogen sulfide.

Everyone knows the role of soil: without it, the Earth’s surface would quickly

Biosphere" href="/text/category/biosfera/" rel="bookmark">life itself would cease to exist in the biosphere. In the seas, the role of soil is played by deep ecosystems, and in the Black Sea - the ecosystem of the hydrogen sulfide zone, providing a very high potential biological productivity of the Black Sea shelf. Unfortunately, this natural potential is now poorly realized, since the ecosystems of bays, estuaries, and coastal waters where fish spawned or wintered have suffered a severe blow economic activity person. The proposal to destroy the hydrogen sulfide zone and destroy its ecosystem looks the same as the proposal to burn Ukrainian black soil to generate electricity.

The hydrogen sulfide zone has a complex vertical structure. Each “floor” is home to its own type of bacteria that perform a specific function, including creating biomass using the energy of hydrogen sulfide. The destruction of this zone through crude intervention will complete the destruction of the Black Sea ecosystem and ultimately lead to an environmental disaster. This consideration is expressed in case someone in the future comes up with the idea of ​​building several nuclear power plants on the Black Sea coast and using them to extract sulfur from Black Sea hydrogen sulfide.

Pollution entering the sea produces a massive combined effect. Pesticides washed off from fields kill zooplankton and fish, and fertilizers contribute to the massive proliferation of unicellular algae. Due to the death of zooplankton and fish, there is no one to eat the algae; they die and rot, absorbing oxygen. This leads to the death of the remaining zooplankton, fish and other aquatic animals. On the Black Sea shelf, vast oxygen-free “sore” zones are formed. Sometimes they cover almost the entire northwestern water area. In their oxygen-free environment, hydrogen sulfide is formed, rising to the surface of the sea. This hydrogen sulfide, caused by pollution, has nothing to do with the deep. However, the destruction by humans of oxygen in the surface layers of the sea also creates conditions for a local rise of deep-seated hydrogen sulfide with vertical jets in the centers of vortex movements. According to opinion, the emergence of dead zones is associated with the state of vertical water exchange, which, in turn, is determined by the general weather situation. Similar situations are repeated with the frequency of solar activity - approximately every 11 years. The last time severe kills in the Black Sea were observed was in 1983. Due to the fact that sea pollution has increased sharply over the past years, severe kills, the formation of hydrogen sulfide and its release to the surface in coastal waters in summer months(July-August) 1991 - 1995, with the next occurrence of a weather situation conducive to death. Their greatest probability occurs in 1994.

The fight against sea pollution contributes not only to the restoration of its fish stocks, the healing recreational properties of waters, the removal of coastal areas from a state of environmental disaster, but also to the prevention of local disasters associated with the formation of hydrogen sulfide in coastal sea waters. Let us emphasize again; sea ​​pollution has created a very real danger of local releases of hydrogen sulfide on the

Hydrogen sulfide in the Black Sea will not explode 55

the surface of the sea and into the atmosphere off its coast. The exit locations are determined by the weather situation and are not predictable in advance. Such disasters are not directly related to the deep hydrogen sulfide zone, so pumping hydrogen sulfide from it will not be able to prevent them.

Currently, theoretical studies are being carried out on the interaction of oxygen and hydrogen sulfide in the waters of the Black Sea in order to establish the mechanisms that determine the dynamics of the upper boundary of the hydrogen sulfide zone. The models established the basic patterns of behavior of this boundary depending on the characteristics of vertical exchange and the power of sources of oxygen and hydrogen sulfide. An analysis of the processes of formation of the vertical distribution of oxygen and hydrogen sulfide in the Black Sea, carried out by different authors, showed that the main influence on the concentration of oxygen and hydrogen sulfide at various depths is exerted by the dependence of the turbulent diffusion coefficient on depth. A decrease in this coefficient to almost zero in the halocline region causes a decrease in the oxygen flow into the hydrogen sulfide zone. An increase in the power of sources by an order of magnitude or even two orders of magnitude leads to a slight increase in its upper limit. These patterns are in good qualitative agreement with the data of expeditionary observations.

The Academy of Sciences of Ukraine has developed a model of the bacterial ecosystem of the hydrogen sulfide zone of the Black Sea)