Deep-sea zones. The world's oceans and its parts Study of the ocean floor

The euphotic zone is the upper (on average 200 m) zone of the ocean, where the illumination is sufficient for the photosynthetic activity of plants. Phytoplankton is abundant here. The process of photosynthesis occurs most intensively at depths of 25-30 m, where the illumination is at least 1/3 of the illumination of the sea surface. At a depth of more than 100 m, the lighting intensity decreases to 1/100. In areas of the World Ocean where the waters are especially clear, phytoplankton can live at depths of up to 150-200 m.[...]

The deep waters of the World Ocean are highly homogeneous, but at the same time, all types of these waters have their own characteristic features. Deep waters are formed mainly in high latitudes as a result of the mixing of surface and intermediate waters in areas of cyclonic gyres located near continents. The main centers of formation of deep waters include the northwestern regions of the Pacific and Atlantic oceans and areas of Antarctica. They are located between intermediate and bottom waters. The thickness of these waters is on average 2000-2500 m. It is maximum (up to 3000 m) in the equatorial zone and in the area of ​​the subantarctic basins.[...]

Depth D is called the friction depth. At a horizon equal to twice the friction depth, the directions of the drift current velocity vectors at this depth and on the ocean surface will coincide. If the depth of the reservoir in the area under consideration is greater than the friction depth, then such a reservoir should be considered infinitely deep. Thus, in the equatorial zone of the World Ocean, depths, regardless of their real value, should be considered small and drift currents should be considered as currents in a shallow sea.[...]

Density changes with depth due to changes in temperature, salinity and pressure. As temperature decreases and salinity increases, density increases. However, normal density stratification is disrupted in certain areas of the World Ocean due to regional, seasonal and other changes in temperature and salinity. In the equatorial zone, where surface waters are relatively desalinated and have a temperature of 25-28 ° C, they are underlain by more salty cold waters, so the density increases sharply to a horizon of 200 m, and then slowly increases to 1500 m, after which it becomes almost constant. In temperate latitudes, where surface waters cool in the pre-winter period, density increases, convective currents develop and denser water sinks, while less dense water rises to the surface - vertical mixing of layers occurs. [...]

About 139 deep hydrothermal fields (65 of them active, see Fig. 5.1) have been identified in the rift zones of the World Ocean. It can be expected that the number of such systems will increase as further research into rift zones continues. The presence of 17 active hydrothermal systems along a 250 km stretch of neovolcanic zone in the Icelandic rift system and at least 14 active hydrothermal systems along a 900 km stretch in the Red Sea indicates a spatial range in the distribution of hydrothermal fields between 15 and 64 km.[...]

A unique zone of the World Ocean, characterized by high fish productivity, is upwelling, i.e. the rise of water from the depths to the upper layers of the ocean, as a rule, on the western shores of the contingents.[...]

The surface zone (with a lower boundary at an average depth of 200 m) is characterized by high dynamism and variability of water properties, caused by seasonal temperature fluctuations and wind waves. The volume of water contained in it is 68.4 million km3, which is 5.1% of the volume of water in the World Ocean.[...]

The intermediate zone (200-2000 m) is distinguished by a change in surface circulation with its latitudinal transfer of matter and energy to deep circulation, in which meridional transport prevails. In high latitudes, this zone is associated with a layer of warmer water that penetrated from low latitudes. The volume of water in the intermediate zone is 414.2 million km3, or 31.0% of the World Ocean.[...]

The uppermost part of the ocean, where light penetrates and where primary production is created, is called euphotic. Its thickness in the open ocean reaches 200 m, and in the coastal part - no more than 30 m. Compared to kilometer depths, this zone is quite thin and is separated by a compensation zone from a much larger water column, right down to the very bottom - the aphotic zone.[ .. .]

Within the open ocean, three zones are distinguished, the main difference of which is the depth of penetration of solar rays (Fig. 6.11).[...]

In addition to the equatorial upwelling zone, upwelling of deep waters occurs where strong, persistent winds drive surface layers away from the shores of large bodies of water. Taking into account the conclusions of Ekman's theory, it can be stated that upwelling occurs when the wind direction is tangential to the coast (Fig. 7.17). A change in wind direction to the opposite leads to a change from upwelling to downwelling or vice versa. Upwelling zones account for only 0.1% of the area of ​​the World Ocean.[...]

Deep ocean rift zones are found at depths of about 3,000 m or more. Living conditions in the ecosystems of deep-sea rift zones are very unique. This is complete darkness, enormous pressure, low water temperature, lack of food resources, high concentrations of hydrogen sulfide and toxic metals, hot underground water outlets, etc. As a result, the organisms living here have undergone the following adaptations: reduction of the swim bladder in fish or filling it cavities with adipose tissue, atrophy of the organs of vision, development of light-emitting organs, etc. Living organisms are represented by giant worms (pogonophora), large bivalves, shrimp, crabs and certain species of fish. The producers are hydrogen sulfide bacteria living in symbiosis with mollusks.[...]

The continental slope is the zone of transition from the continents to the ocean floor, located within the range of 200-2440 m (2500 m). It is characterized by a sharp change in depth and significant bottom slopes. Average bottom slopes are 4-7°, in some areas they reach 13-14°, as, for example, in the Bay of Biscay; Even greater bottom slopes are known near coral and volcanic islands.[...]

When ascending along the fault zone with expansion to depths of 10 km or less (from the ocean floor), which approximately corresponds to the position of the Mohorovicic boundary in the oceanic lithosphere, the ultra-basic mantle intrusion can enter the thermal water circulation zone. Here, at T = 300-500°C, favorable conditions are created for the process of serpentinization of ultrabasites. Our calculations (see Fig. 3.17, a), as well as the increased values ​​of heat flow observed over such fault zones (2-4 times higher than the normal values ​​of q for the oceanic crust) suggest the presence of a temperature range of serpentinization at depths of 3-10 km (these depths strongly depend on the position of the top of the high-temperature intrusive mantle material). The gradual serpentinization of peridotites reduces their density to values ​​lower than the density of the surrounding rocks of the oceanic crust, and leads to an increase in their volume by 15-20%.[...]

In the future, it will be seen that the depth of friction in middle latitudes and at average wind speeds is small (about 100 m). Consequently, equations (52) can be applied in simple form (47) in any sea with any significant depth. The exception is the region of the world's oceans adjacent to the equator, where ¡sin φ tends to zero and the depth of friction tends to infinity. Of course, for now we are talking about the open sea; As for the coastal zone, we will have to talk a lot about it in the future.[...]

Bathial (from Greek - deep) is a zone occupying an intermediate position between the continental shallows and the ocean bed (from 200-500 to 3000 m), i.e. it corresponds to the depths of the continental slope. This ecological area is characterized by a rapid increase in depth and hydrostatic pressure, a gradual decrease in temperature (in low and middle latitudes - 5-15 ° C, in high latitudes - from 3 ° to - 1 ° C), the absence of photosynthetic plants, etc. Bottom sediments are represented by organogenic silts (from the skeletal remains of foraminifera, coccolithophores, etc.). Autotrophic chemosynthetic bacteria rapidly develop in these waters; Characteristic are many species of brachiopods, sea feathers, echinoderms, decapod crustaceans; among benthic fish, longtails, sable fish, etc. are common. Biomass is usually grams, sometimes tens of grams/m2. [...]

The seismically active zones of mid-ocean ridges described above differ significantly from those located in the regions of island arcs and active continental margins framing the Pacific Ocean. It is well known that a characteristic feature of such zones is their penetration to very great depths. The depths of earthquake foci here reach 600 kilometers or more. At the same time, as studies by S. A. Fedotov, L. R. Sykes and A. Hasegawa have shown, the width of the seismic activity zone going deep does not exceed 50-60 km. Another important distinctive feature of these seismically active zones is the mechanisms in the earthquake foci, which clearly indicate compression of the lithosphere in the area of ​​the outer edge of island arcs and active continental margins. [...]

Ecosystem of deep ocean rift zones - this unique ecosystem was discovered by American scientists in 1977 in the rift zone of the underwater ridge of the Pacific Ocean. Here, at a depth of 2,600 m, in complete darkness, with abundant levels of hydrogen sulfide and toxic metals released from hydrothermal vents, “oases of life” were discovered. Living organisms were represented by giant (up to 1-1.5 m long) tube-living worms (pogonophora), large white bivalves, shrimp, crabs and individual specimens of peculiar fish. The biomass of pogonophora alone reached 10-15 kg/m2 (in neighboring areas of the bottom - only 0.1-10 g/m2). In Fig. 97 shows the features of this ecosystem in comparison with terrestrial biocenoses. Sulfur bacteria make up the first link in the food chain of this unique ecosystem, followed by pogonophora, whose bodies contain bacteria that process hydrogen sulfide into essential nutrients. In the rift zone ecosystem, 75% of the biomass consists of organisms living in symbiosis with chemoautotrophic bacteria. Predators are represented by crabs, gastropods, and certain species of fish (macrurids). Similar “oases of life” have been discovered in deep-sea rift zones in many areas of the World Ocean. More details can be found in the book of the French scientist L. Laubier “Oases on the ocean floor” (L., 1990).[...]

In Fig. Figure 30 shows the main ecological zones of the World Ocean, showing the vertical zonation of the distribution of living organisms. In the ocean, first of all, two ecological areas are distinguished: the water column - pelagial and the bottom - yoental. Depending on the depth, benthal is divided into littoral (up to 200 m), bathyal (up to 2500 m), abyssal (up to 6000 m) and ultra-abyssal (deeper than 6000 m) zones. The pelagic zone is also subdivided into vertical zones corresponding in depth to the benthic zones: epipelagic-al, bathypelagic and abyssopelagic.[...]

The steep continental slope of the ocean is inhabited by representatives of bathyal (up to 6000 m), abyssal and ultra-abyssal fauna; in these zones, outside the light available for photosynthesis, there are no plants.[...]

Abyssal (from Greek - bottomless) is an ecological zone of distribution of life on the bottom of the World Ocean, corresponding to the depths of the ocean floor (2500-6000 m).[...]

Until now, we have been talking about the impact on physical parameters: the ocean, and it was only indirectly assumed that through these parameters there is an impact on ecosystems. On the one hand, the rise of deep waters rich in biogenic salts can serve as a factor in increasing the bioproductivity of these otherwise poor areas. We can count on the fact that the rise of deep waters will reduce the temperature of surface waters at least in some local zones with a simultaneous increase in the oxygen content due to an increase in the solubility of oxygen. On the other hand, the discharge of cold water into the environment is associated with the death of heat-loving species with low thermal stability, changes in the species composition of organisms, food supply, etc. In addition, the ecosystem will be constantly exposed to biocides that prevent the fouling of the working elements of the station, the effects of various reagents, metals, pollutants and other by-product emissions.[...]

The main factor differentiating marine biota is the depth of the sea (see Fig. 7.4): the continental shelf abruptly gives way to the continental slope, smoothly turning into the continental foot, which descends lower to the flat ocean bed - the abyssal plain. The following zones roughly correspond to these morphological parts of the ocean: neritic - to the shelf (with littoral - tidal zone), bathyal - to the continental slope and its foot; abyssal - the region of oceanic depths from 2000 to 5000 m. The abyssal region is cut by deep depressions and gorges, the depth of which is more than 6000 m. The region of the open ocean outside the shelf is called oceanic. The entire population of the ocean, as in freshwater ecosystems, is divided into plankton, nekton, and benthos. Plankton and nekton, i.e. everything that lives in open waters forms the so-called pelagic zone.[...]

It is generally accepted that coastal stations are profitable if the required depths with suitable cooling water temperatures are located sufficiently close to the coast and the pipeline length does not exceed 1-3 km. This situation is typical for many islands in the tropical zone, which are the tops of seamounts and extinct volcanoes and do not have the extended shelf characteristic of continents: their shores descend rather steeply towards the ocean floor. If the coast is sufficiently remote from zones of required depths (for example, on islands surrounded by coral reefs) or is separated by a gently sloping shelf, then to reduce the length of pipelines, power units of stations can be placed on artificial islands or stationary platforms - analogues of those used in offshore oil and gas production. The advantage of land-based and even island stations is that there is no need to create and maintain expensive structures exposed to the open ocean - be they artificial islands or permanent foundations. However, two significant factors limiting coastal basing still remain: the limited nature of the corresponding island territories and the need to lay and protect pipelines.[...]

For the first time, the morphological characteristics and typification of oceanic fault zones based on morphological characteristics (using the example of faults in the northeastern part of the Pacific Ocean) were made by G. Menard and T. Chace. They defined faults as “long and narrow zones of highly dissected topography, characterized by the presence of volcanoes, linear ridges, scarps, and usually separating different topographic provinces with unequal regional depths.” The expression of transform faults in the topography of the ocean floor and anomalous geophysical fields is, as a rule, quite sharp and clear. This has been confirmed by numerous detailed studies conducted in recent years. High near-fault ridges and deep depressions, faults and cracks are characteristic of transform fault zones. Anomalies of A, AT, heat flow and others indicate the heterogeneity of the structure of the lithosphere and the complex dynamics of fault zones. In addition, lithosphere blocks of different ages located on different sides of the fault, in accordance with the V/ law, have different structures, expressed in different bottom depths and lithosphere thicknesses, which creates additional regional anomalies in geophysical fields.[...]

The continental shelf region, the neritic region, if its area is limited to a depth of 200 m, constitutes about eight percent of the ocean area (29 million km2) and is the richest fauna in the ocean. The coastal zone is favorable in terms of nutritional conditions; even in tropical rainforests there is no such diversity of life as here. Plankton is very rich in food due to the larvae of benthic fauna. Larvae that remain uneaten settle on the substrate and form either epifauna (attached) or infauna (burrowing). [...]

Plankton also exhibits pronounced vertical differentiation as different species adapt to different depths and different light intensities. Vertical migrations influence the distribution of these species, and therefore vertical layering is less obvious in this community than in the forest. Communities of illuminated zones on the ocean floor below high tide are differentiated in part by light intensity. Green algae species are concentrated in shallow waters, brown algae species are common at somewhat greater depths, and red algae are especially abundant lower still. Brown and red algae contain, in addition to chlorophyll and carotenoids, additional pigments, which allows them to use light of low intensity and different in spectral composition from light in shallow waters. Vertical differentiation is thus a common feature of natural communities.[...]

Abyssal landscapes are a kingdom of darkness, cold, slow-moving waters and very poor organic life. In olyshtrophic zones of the Ocean, benthos biomass ranges from 0.05 or less to 0.1 g/m2, increasing slightly in areas of rich surface plankton. But even here, at such great depths, “oases of life” are encountered. The soils of abyssal landscapes are formed by silts. Their composition, like that of terrestrial soils, depends on the latitude and height (in this case, depth). Somewhere at a depth of 4000-5000 m, the previously dominant carbonate silts are replaced by non-carbonate silts (red clays, radiolarian silts in the tropics and diatoms in temperate latitudes).[...]

Here x is the coefficient of thermal diffusion of lithospheric rocks, Ф is the probability function, (T + Cr) is the temperature of the mantle under the axial zone of the median ridge, i.e. at / = 0. In the boundary layer model, the depth of the isotherms and the base of the lithosphere, as well as the depth of the ocean bottom I, measured from its value on the ridge axis, increase in proportion to the value of V/.[...]

At high latitudes (above 50°), the seasonal thermocline is destroyed with convective mixing of water masses. In the subpolar regions of the ocean, there is an upward movement of deep masses. Therefore, these ocean latitudes belong to highly productive areas. As we move further towards the poles, productivity begins to decline due to a decrease in water temperature and a decrease in its illumination. The ocean is characterized not only by spatial variability in productivity, but also by widespread seasonal variability. Seasonal variability in productivity is largely due to the response of phytoplankton to seasonal changes in environmental conditions, primarily light and temperature. The greatest seasonal contrast is observed in the temperate zone of the ocean.[...]

The entry of magma into the magma chamber apparently occurs sporadically, and is a function of the release of large amounts of molten matter from depths of more than 30 - 40 km in the upper mantle. The concentration of molten matter in the central part of the segment leads to an increase in volume (swelling) of the magma chamber and migration of the melt along the axis to the edges of the segment. As the transform fault approaches, the depth of the roof, as a rule, decreases until the corresponding horizon near the transform fault completely disappears. This is largely due to the cooling influence of an older lithospheric block bordering the axial zone along a transform fault (transform fault effect). Accordingly, a gradual subsidence of the ocean floor level is observed (see Fig. 3.2).[...]

In the Antarctic region of the southern hemisphere, the ocean floor is covered with glacial and iceberg sediments and diatomaceous oozes, which are also found in the north Pacific Ocean. The bottom of the Indian Ocean is lined with silt with a high content of calcium carbonate; deep-sea depressions - red clay. The most diverse sediments are the bottom of the Pacific Ocean, where diatomaceous oozes dominate in the north, the northern half is covered at depths of over 4000 m with red clay; In the near-equatorial zone of the eastern part of the ocean, silts with siliceous residue (radiolarians) are common; in the southern half, at depths of up to 4000 m, calcareous-carbonate silts are found. red clay, in the south - diatomaceous and glacial deposits. In areas of volcanic islands and coral reefs, volcanic and coral sand and silt are found (Fig. 7).[...]

The change from the continental crust to the oceanic crust does not occur gradually, but spasmodically, accompanied by the formation of morphostructures of a special kind, characteristic of transitional, or more precisely, contact zones. They are sometimes called the peripheral regions of the oceans. Their main morphostructures are island arcs with active volcanoes, abruptly turning towards the ocean into deep-sea trenches. It is here, in the narrow, deepest (up to 11 km) depressions of the World Ocean, that the structural boundary of the continental and oceanic crust passes, coinciding with deep faults known to geologists as the Zavaritsky-Benoff zone. The faults falling under the continent go to a depth of up to 700 km.[...]

The second special experiment to study the synoptic variability of ocean currents (“Polygon-70”) was carried out by Soviet oceanologists led by the Institute of Oceanology of the USSR Academy of Sciences in February-September 1970 in the northern trade wind zone of the Atlantic, where continuous measurements of currents were carried out for six months at 10 depths from 25 to 1500 m at 17 moored buoy stations, forming a cross measuring 200X200 km with a center at point 16°ZG 14, 33°30W, and a number of hydrological surveys were also carried out.[...]

Thus, an amendment was made to the idea of ​​​​the non-renewability of mineral wealth. Mineral resources, with the exception of peat and some other natural formations, are non-renewable in depleted deposits at the depth of the continents’ interiors that can be reached by humans. This is understandable - those physico-chemical and other conditions in the deposit area, which in the distant past of geological history created mineral formations valuable to humans, have irrevocably disappeared. Mining granular ores from the bottom of an existing ocean is another matter. We can take them, and in the natural operating laboratory that created these ores, which is the ocean, the processes of ore formation will not stop.[...]

If gravitational anomalies in free air on continents and oceans do not have fundamental differences, then in the Bouguer reduction this difference is very noticeable. The introduction of a correction for the influence of the intermediate layer in the ocean leads to high positive values ​​of Bouguer anomalies, the greater the greater the depth of the ocean. This fact is due to the theoretical violation of the natural isostasy of the oceanic lithosphere when introducing the Bouguer correction (“backfilling” of the ocean). Thus, in the ridge zones of the MOR, the Bouguer anomaly is about 200 mGal, for abyssal oceanic basins - on average from 200 to 350 mGal. There is no doubt that the Bouguer anomalies reflect the general features of the ocean floor topography to the extent that they are isostatically compensated, since the main contribution to the Bouguer anomalies is made by the theoretical correction.[...]

The main processes that determine the profile of the margin that arose at the rear edge of the continent (passive margin) are almost permanent subsidence, especially significant in its distal, near-oceanic half. They are only partially compensated by the accumulation of precipitation. Over time, the margin grows both as a result of the involvement of continental blocks increasingly distant from the ocean into subsidence, and as a result of the formation of a thick sedimentary lens at the continental foot. The growth occurs mainly due to neighboring areas of the ocean floor and is a consequence of the ongoing erosion of areas adjacent to the edge of the continent, as well as its deep regions. This is reflected not only in the non-silting of the land, but also in the softening and leveling of the relief in the underwater sections of the transition zone. A kind of aggradation occurs: leveling of the surface of transition zones in areas with a passive tectonic regime. Generally speaking, this tendency is characteristic of any margin, but in tectonically active zones it is not realized due to orogenesis, folding, and the growth of volcanic edifices.[...]

In accordance with the characteristics of sea water, its temperature, even on the surface, is devoid of sharp contrasts characteristic of surface layers of air, and ranges from -2 ° C (freezing temperature) to 29 ° C in the open Ocean (up to 35.6 ° C in the Persian Gulf ). But this is true for the temperature of water at the surface, due to the influx of solar radiation. In the rift zones of the Ocean, powerful hydrotherms have been discovered at great depths with water temperatures under high pressure up to 250-300°C. And these are not episodic outpourings of superheated deep waters, but long-term (even on a geological scale) or permanently existing lakes of super-hot water at the bottom of the Ocean, as evidenced by their ecologically unique bacterial fauna, which uses sulfur compounds for their nutrition. In this case, the amplitude of the absolute maximum and minimum ocean water temperatures will be 300°C, which is twice the amplitude of the extremely high and low air temperatures at the earth’s surface. [...]

The dispersion of biostromal matter extends over a significant part of the thickness of the geographic envelope, and in the atmosphere even goes beyond its limits. Viable organisms have been found at altitudes of more than 80 km. There is no autonomous life in the atmosphere, but the air troposphere is a transporter, a carrier over vast distances of seeds and spores of plants, microorganisms, an environment in which many insects and birds spend a significant part of their lives. The dispersion of the water-surface biostrome extends throughout the entire thickness of oceanic waters down to the bottom film of life. The fact is that deeper than the euphotic zone, communities are practically devoid of their own producers; energetically they are completely dependent on the communities of the upper zone of photosynthesis and on this basis cannot be considered full-fledged biocenoses in the understanding of Yu. Odum (M. E. Vinogradov, 1977). With increasing depth, the biomass and abundance of plankton rapidly decrease. In the bathypelagic zone in the most productive areas of the ocean, the biomass does not exceed 20-30 mg/m3 - this is hundreds of times less than in the corresponding areas on the ocean surface. Below 3000 m, in the abyssopelagic zone, the biomass and abundance of plankton are extremely low.

DEEP WATER ZONES

Deep-sea (abyssal) zones - areas of the ocean more than 2000 m deep - occupy more than half of the earth's surface. Consequently, this is the most common habitat, but it also remains the least studied. Only recently, thanks to the advent of deep-sea vehicles, we are beginning to explore this amazing world.

Deep zones are characterized by constant conditions: cold, darkness, enormous pressure (more than 1000 atmospheres); due to the constant circulation of water in deep sea currents, there is no lack of oxygen. These zones exist for a very long time and there are no barriers to the spread of organisms.

In complete darkness it is not easy to find food or a partner, so the inhabitants of the deep sea have adapted to recognize each other using chemical signals; Some deep-sea fish have bioluminescent organs containing glowing symbiont bacteria. Deep-sea fish - anglers - went further: when the male (smaller) finds a female, he attaches to her and even their blood circulation becomes common. Another consequence of darkness is the absence of photosynthetic organisms, hence communities obtain nutrients and energy from dead organisms that fall to the seabed. These can be either giant whales or microscopic plankton. The fine particles often form "sea snow" flakes when they mix with mucus, nutrients, bacteria and protozoa. On the way to the bottom, most of the organic material is eaten or a lot of nitrogen is released from it, so by the time the remains finish their journey, they are not very nutritious. This is one of the reasons why the concentration of biomass on the seabed is very low.

An important focus of future deep-sea research should be the role of bacteria in the food chain.

See also the article "Oceans".