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by Vladimir AVILOV, Dr. Sc. (Tech.), Svetlana AVILOVA, Dr. Sc. (Biol.), P.P. Shirshov Institute of Oceanology, RAS
During our voyage aboard the AKADEMIK KURCHATOV research vessel, we discovered a hitherto unknown phenomenon - biological life in hydrotherms (hot springs) on the floor of the Red Sea. That expedition of ours took place in the spring of 1976. Although our discovery gave us doctoral degrees, it was officially registered only twenty years after the event.
RED SEA TROUGHS
Our voyage to the northwestern part of the Indian Ocean was no joking matter, and so we spared no efforts to get ready in good earnest. Our technical equipment, quite behind the age, was a big headache - it was no good for the job at hand: it didn't perform now and then in the sea depths, and it wasn't watertight enough, which meant that our water samples were not reliable. In a nutshell, what we needed was a good bathymeter. And it was designed in due course by one of the authors of the present article. This apparatus was quite hermetic and could take water samples at prescribed depths. And it was superior to other bathymeters in that it had a ground tube equilibrating an increase in water or sediment samples - we call that "the compensative characteristic". So our samples had to be intact, authentic. Incidentally, we have patented these two innovative devices. In fact, before the spring of 1976 oceanologists here in this country and abroad had nothing of the kind in their panoply.
And thus off we were, equipped with reliable instruments and most up-to-date methods of exploration - geochemical and biochemical methods too. One merits special mention.
We made use of the ATP (adenosine triphosphate) assay technique - a high-precision, high-specificity method considered ultramodern in those times.* Now, ATP is contained in live cells only, and therefore it could serve as indisputable evidence for organic life. ATP is an organic compound, a carrier of microenergy bonds - in short, it is an energy pool in a living cell. Our comprehensive methodic approach proved all right, and it fructified.
Our itinerary took in the Black Sea and the Mediterranean; then, through the Suez Canal, we entered the Red Sea, our first destination, where we got busy with the investigation of deep- water hydrothermal troughs. According to the science authorities of those times - like the German oceanologists E. Degens and D. Ross, such sea depths were lifeless. We had to reckon with their opinion, sure, and so we had no thought of finding any tokens of biological life in the hydrotherms of the Red Sea. Yet everything turned out much otherwise.
Among other things, our expedition was to study the qualitative composition of water and bottom sediments within the famous troughs. Upon reaching the required depth (over 2,000 m), ourbathy-
* See: V. Avilov, S. Avilova, "Two Voyages Across Two Oceans", Science in Russia, No. 3, 2000. - Ed.
meter captured a water sample just a meter above the floor. Our explorers were on tenterhooks watching the operation on the deck, together with their counterparts from Sweden, Germany and the United States with test-tubes at the ready. The operation took two hours in all, counting in the descent and uplift. Everybody rushed in as soon as the bathymeter landed on board to see how tight it was. Yes, all correct!
But there was something else to amaze us: the bathymeter's walls were hot, which meant that it hit slap into the hydrotherms of the trough Atlantis-2, that is in the area where our sea party was working at the time. What a streak of good luck! The hot water, all of it, was drawn for assays and analyses of every kind. Its temperature was found at 62 0 С, salinity - at 242%o, or tenfold higher than in similar samples as deep as that.
Yet another big surprise: the data of geochemical and biochemical assays obtained then and there, in the onboard laboratory. These results amazed everybody. Just think of it: after all, there was life over there, in hot and so much salty water, and in the absence of oxygen at that. Even at that stage we saw that we hit the
right track in our experimental methods. Subsequently the presence of life in its new forms down in subwater hydro-therms was confirmed by researchers from the United States and other countries who described this discovery as the greatest breakthrough in the earth sciences of the 20th century.*
BIOSPHERE OF ANOTHER KIND
All that dashed the then persistent notions about the crucial role of photosynthetic processes in sea water - not only in-depth from surface to bottom, but also in the upper stratum of bottom sediments. Our on-the-spot experiments with the use of the latest instruments and research techniques made it possible to detect a community of marine organisms in hydrotherms deep under water. Their life was found to be based not on the energy of photosynthesis but on what we call chemolitothoautotrophy; in other words, in the absence of oxygen, i.e. under anaerobic conditions, and at depths inaccessible to sunlight, living organisms subsist on gases escaping from the earth's interior.
* See: A. Lisitsyn, A. Sagalevich, "Breakthrough Discovery in the Ocean", Science in Russia, No. 1, 2001. - Ed .
Chemolithoautotrophy means an absolute autonomy in the existence of such colonies of microorganisms: they in no way depend on the upper layers of water and photosynthetic processes occurring there. A new type biosphere? Yes!
Already in the early 1970s foreign oceanologists were searching, but all in vain, for tokens of organic life in marine hydrotherms. The trouble was that they employed conventional and rather primitive methods of oceanological research, no good for the identification of organisms in a biosphere other than we are used to, a biosphere not related to photosynthetic processes.
But our data on ATP obtained in 1976 show: the hydrothermal waters filling the Atlantis-2 trough in the Red Sea - a virtual subwater "lake", so to speak - have a fairly dense population of microorganisms. In two parallel samples their biomass amounted to 40.4 and 44.5 mkg x С x 1 -1 (depth, 2,121 m). It proved to be larger compared with the biomass present in the upper water layers: 4-4.5 times as large as in the passage (transition) layer (depth, 2,030 m), 6 times as large as in the intermediate layer (interlayer, depth - 1,000 m) and 1.5 fold as large as in the uppermost photic layer (depth, 50 m).
From these comparative data we see that hydrothermal waters are inhabited by active organisms whose vital activity could in no way be associated with phenomena taking place in the upper photic layers. The more so, that the passage (transition) layer with its high temperature, salinity and gas concentration gradients reliably separates the hydrothermal waters from the bulk of the Red Sea water above and prevents an intensive interchange. This is an important factor to explain the cause of the vigorous vital activity of benthic microorganisms.
Besides ATP, we also detected gases - carbon dioxide, hydrogen and methane - in the water samples from the Atlantis-2 trough; these gases are a nutrient substrate for the community of benthonic organisms. Thus we could trace the cause-and-effect link of suchlike processes. Cause and effect is a must for explaining any newly discovered phenomenon.
The microorganisms subsisting on the above gases are the core of biocommunities within deep-sea hydrotherms. These gases come thither from the bowels of the earth lithosphere to support the sustain-able and autonomous life of deep-water colonies with vital substances and energy.
Much later, in 1981, two American researchers, C. Jannas and C. Virsen, at long last found microorganisms in hydrotherms of the Pacific. But studying them by the conventional microbiological method (countup), the Americans could not explain how those organisms were growing and what they were feeding on. A plain statement of the fact, but no cause and effect! It was only a few years later that Dr. Jannas and other research scientists could confirm the presence of ATP by using a biochemical method similar to ours. They obtained the same concentrations of the biomass of active microorganisms as we did - both in the hydrotherm itself and in the waters around it.
The existence of colonies like that on the ocean floor, or of a biosphere most uncommon to us, may be of practical significance for enterprises consuming or processing natural or else spent gases in ecologically safe closed cycles. Simultaneously, there is a better chance for broader problem solving, what with new data on the migration of gases from the lithosphere. All that is essential to gas-and-oil industry workers in prospecting for fuel deposits with the use of geochemical methods.
We have now a novel vision concerning the adaptation of living organisms to the consumption of nonphotosynthetic energy; and we have studied animals feeding on chemosynthetic bacteria.
And last but not least. Organic life, especially at the level of microorganisms, might be possible even deep in the bowels of the earth in spite of the high pressure and temperature there. We have bits of hard evidence to this effect. In 1991 our party carried out ecological studies on the shore of the island of Sakhalin; and we inspected core samples of rock besides. Well, ATP was found in a sample recovered from a depth of 23 meters. But ATP is a sure sign of life. Besides, a flow of endogenic gases - helium, hydrogen, carbon dioxide - was registered there. It is beyond doubt that here, too, we deal with microorganisms endowed with the chemolithoautotrophic type of metabolism.
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