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interconnected mass of saltwater covering 70.78% of the surface of the earth, often called the world ocean. It is subdivided into four (or five) major units that are separated from each other in most cases by the continental masses. See also oceanographyoceanography,
study of the seas and oceans. The major divisions of oceanography include the geological study of the ocean floor (see plate tectonics) and features; physical oceanography, which is concerned with the physical attributes of the ocean water, such as currents and
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The World Ocean

Of the major units that comprise the world ocean, three—the Atlantic, Indian, and Pacific oceans—extend northward from Antarctica as huge "gulfs" separating the continents. The fourth, the Arctic Ocean, nearly landlocked by Eurasia and North America and nearly circular in outline, caps the north polar region. The Southern Ocean (also called the Antarctic Ocean) is now often considered a fifth, separate ocean, extending from the shores of Antarctica northward to about 60°S. The major oceans are further subdivided into smaller regions loosely called seas, gulfs, or bays. Some of these seas, such as the Sargasso Sea of the North Atlantic Ocean, are only vaguely defined, while others, such as the Mediterranean Sea or the Black Sea, are almost totally surrounded by land areas. Large and totally landlocked saltwater bodies such as the Caspian Sea are actually salt lakes.

The boundaries between oceans are usually designated by the continental land masses bordering them or by ridges in the ocean floor, which also serve as geographic boundaries. Where these features are absent (such as the ill-defined northern boundary of the Antarctic Ocean), the boundary is somewhat arbitrarily fixed by fluctuating zones of opposing currents that act as partial barriers to the mixing of waters between the two adjacent oceans.

The oceans are not uniformly distributed on the face of the earth. Continents and ocean basins tend to be antipodal, or diametrically opposed to one another, i.e., continents are found on the opposite side of the earth from ocean basins. For example, Antarctica is antipodal to the Arctic Ocean; Europe is opposed by the South Pacific Ocean. Furthermore, over two thirds of the earth's land area is found in the Northern Hemisphere, while the oceans comprise over 80% of the Southern Hemisphere.

The world ocean has an area of about 361 million sq km (139,400,000 sq mi), an average depth of about 3,730 m (12,230 ft), and a total volume of about 1,347,000,000 cu km (322,280,000 cu mi). Each cubic mile of seawater weighs approximately 4.7 billion tons and holds 166 million tons of dissolved solids. One of the most unique and intriguing aspects of ocean water is its salinity, or dissolved salt content. The measurement of salinity is essentially the determination of the amount of dissolved salts in 1 kg of ocean water and is expressed in parts per thousand (‰). Ocean salinities commonly range between 33 ‰ to 38 ‰, with an average of about 35 ‰. Thirty-five parts per thousand salinity is equivalent to 3.5% by weight. Six elements (chlorine, sodium, magnesium, sulfur, calcium, and potassium) constitute over 90% of the total salts dissolved in the oceans. Pressure in the ocean waters increases with increasing depth due to the weight of the overlying water. The pressure increases at the rate of 1 atmosphere for every 10 m (33 ft) of depth (1 atm=15 lb per sq in. or 1,016 dynes per sq cm). The average temperature of the oceans is 3.9°C; (39°F;).

It now appears that the waters making up the present oceans (and the gases that make up the present atmosphere) were not of cosmic origin, i.e., were not present in the primordial atmosphere. Instead, they were derived from the interior of the earth sometime in the first one or two billion years after the earth's formation. It is now also generally accepted that a new ocean crust has been forming more or less continuously for at least the past 200 million years through a process of volcanic activity along the midocean ridge system (see seafloor spreadingseafloor spreading,
theory of lithospheric evolution that holds that the ocean floors are spreading outward from vast underwater ridges. First proposed in the early 1960s by the American geologist Harry H.
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), which consists of a series of underwater mountains. On the basis of present knowledge it seems highly probable that all ocean waters and atmospheric gases were gradually released by the separation of these volatile components from the silicate rocks of the crust and upper mantle through volcanic activity. (Molten lava is known to contain appreciable amounts of water and other volatiles that are released upon solidification.) With the passage of time, water released by volcanic activity gradually filled oceanic depressions.

Continental Shelves, Slopes, and Rises

Virtually all continents are surrounded by a gently sloping submerged plain called the continental shelf, which is an underwater extension of the coastal plain. The continental shelves are the regions of the oceans best known and the most exploited commercially. It is this region where virtually all of the petroleum, commercial sand and gravel deposits, and fishery resources are found. It is also the locus of waste dumping. Changes in sea level have alternatingly exposed and inundated portions of the continental shelf. Continental shelves vary in width from almost zero up to the 1,500-km-wide (930-mi) Siberian shelf in the Arctic Ocean. They average 78 km (48 mi) in width. The edge of the shelf occurs at a depth that ranges from 20 to 550 m (66 to 1,800 ft), averaging 130 m (430 ft). The shelves consist of vast deposits of sands, muds, and gravels, overlying crystalline rocks or vast thicknesses of consolidated sedimentary rocks. Although there is a great variation in shelf features, nonglaciated shelves are usually exceptionally flat, with seaward slopes averaging on the order of 205 m per km (10 ft per mi), or less than 1° of slope. The edge of the shelf, called the shelf break, is marked by an abrupt increase in slope to an average of about 4°.

The continental slopes begin at the shelf break and plunge downward to the great depths of the ocean basin proper. Deep submarine canyons, some comparable in size to the Grand Canyon of the Colorado River, are sometimes found cutting across the shelf and slope, often extending from the mouths of terrestrial rivers. The Congo, Amazon, Ganges, and Hudson rivers all have submarine canyon extensions. It is assumed that submarine canyons on the continental shelf were initially carved during periods of lower sea level in the course of the ice ages. Their continental slope extensions were carved and more recently modified by turbidity currents—subsea "landslides" of a dense slurry of water and sediment.

Many continental slopes end in gently sloping, smooth-surfaced features called continental rises. The continental rises usually have an inclination of less than 1-2°. They have been found to consist of thick deposits of sediment, presumably deposited as a result of slumping and turbidity currents carrying sediment off the shelf and slope. The continental shelf, slope, and rise together are called the continental margin.

Trenches, Plains, and Ridges

One of the most surprising findings of the early oceanographers was that the deepest parts of the oceans were not in the centers, as they had expected, but were in fact quite close to the margins of continents, particularly in the Pacific Ocean. Further exploration showed that these deeps were located in long V-shaped trenches bordering the seaward edge of volcanic island arcs. These trenches are one of the most striking features of the Pacific floor. Trenches virtually encircle the rim of the Pacific basin. The trenches have lengths of thousands of kilometers, are generally hundreds of kilometers wide, and extend 3 to 4 km (1.9–2.5 mi) deeper than the surrounding ocean floor. The greatest ocean depth has been sounded in the Challenger Deep of the Marianas TrenchMarianas trench,
 Marianas trough,
or Marianas deep
, elongated depression on the Pacific Ocean floor, 210 mi (338 km) SW of Guam. It is the deepest known depression on the earth's surface, having been measured by various means at 35,760–36,089 ft
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, a distance of 10,911.5 m (35,798.6 ft) below sea level.

The deep ocean floor begins at the seaward edge of the continental rise or marginal trench, if one is present, and extends seaward to the base of the underwater midocean mountains. Many relief features of great importance are present in this region. Vast abyssal plains cover significant portions of the deep ocean basin. Such plains are occasionally broken by low, oval-shaped abyssal hills. The abyssal plains cover about 30% of the Atlantic and nearly 75% of the Pacific ocean floors. They are among the flattest portions of the earth's crust and appear to be formed by the deposition of fine sediment carried by turbidity currents that have covered and smoothed out irregularities in the ocean floor.

One of the most significant features of the ocean basins is the midocean ridge. First discovered in the Atlantic Ocean on the Challenger expeditionChallenger expedition,
British oceanographic expedition under the direction of the Scottish professor Charles Wyville Thompson and the British naturalist Sir John Murray. Taking place from 1872 to 1876, it opened the era of descriptive oceanography.
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, its relief features were further investigated during the German Meteor expedition of 1925–26. By the early 1960s it had been confirmed that the Mid-Atlantic Ridge was only part of a continuous feature that extended 55,000 km (34,000 mi) through the Atlantic, Indian, South Pacific, and Arctic oceans. The ridge is a broad bulge in the ocean floor that rises 1 to 3 km (0.6–2 mi) above the adjacent abyssal plains. It has a variable width averaging more than 1,500 km (c.900 mi). It is crossed by a number of fracture zones (transform faultsfault,
in geology, fracture in the earth's crust in which the rock on one side of the fracture has measurable movement in relation to the rock on the other side. Faults on other planets and satellites of the solar system also have been recognized.
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) and displays a deep rift 37 to 48 km (23–30 mi) wide and about 1.6 km (1 mi) deep at its very crest.

Relationship of the Ocean and the Atmosphere

The atmosphere affects the oceans and is in turn influenced by them. The action of winds blowing over the ocean surface creates waves and the great current systems of the oceans. When winds are strong enough to produce spray and whitecaps, tiny droplets of ocean water are thrown up into the atmosphere where some evaporate, leaving microscopic grains of salt buoyed by the turbulence of the air. These tiny particles may become nuclei for the condensation of water vapor to form fogs and clouds.

In turn, the oceans act upon the atmosphere—in ways not clearly understood—to influence and modify the world's climate and weather systems. When water evaporates, heat is removed from the oceans and stored in the atmosphere by the molecules of water vapor. When condensation occurs, this stored heat is released to the atmosphere to develop the mechanical energy of its motion. The atmosphere obtains nearly half of its energy for circulation from the condensation of evaporated ocean water.

Because the oceans have an extremely high thermal capacity when compared to the atmosphere, the ocean temperatures fluctuate seasonally much less than the atmospheric temperature. For the same reason, when air blows over the water, its temperature tends to come to the temperature of the water rather than vice versa. Thus maritime climates are generally less variable than regions in the interiors of the continents.

The relationships are not simple. The pattern of atmospheric circulation largely determines the pattern of oceanic surface circulation, which in turn determines the location and amount of heat that is released to the atmosphere. Also, the pattern of atmospheric circulation determines in part the location of clouds, which influences the locations of heating of the ocean surface.

Currents and Ocean Circulation

Surface Circulation

The surface circulation of the oceans is intimately tied to the prevailing wind circulation of the atmosphere (see windwind,
flow of air relative to the earth's surface. A wind is named according to the point of the compass from which it blows, e.g., a wind blowing from the north is a north wind.
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). As the planetary winds flow across the water, frictional stresses are set up which push huge rivers of water in their path. The general pattern of these surface currents is a nearly closed system of currents, called gyres, which are approximately centered on the horse latitudeshorse latitudes,
two belts of latitude where winds are light and the weather is hot and dry. They are located mostly over the oceans, at about 30° lat. in each hemisphere, and have a north-south range of about 5° as they follow the seasonal migration of the sun.
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 (about 30° latitude in both hemispheres). Major circulation of water in these gyres is clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere. In the North Pacific and North Atlantic oceans, smaller counterclockwise gyres are developed partly due to the presence of the continents. These are centered on about 50°N lat. The most dominant current in the Southern Ocean is the West Wind Drift, which circles Antarctica in an easterly direction. The northern and southern hemispheric gyres are divided by an eastward flowing equatorial countercurrent, which essentially follows the belt of the doldrums. This countercurrent is caused by the return flow of water piled up along the eastward portion of the equatorial seas, and its return flow is uninhibited by the weak and erratic winds of the doldrums. Analysis of current records shows that a number of major currents, such as the Gulf Stream, have strong fast-moving currents beneath them trending in the opposite direction to the surface current. Such undercurrents, or countercurrents, appear to be as important and pervasive as the surface currents. In 1952 the Cromwell current was found flowing eastward beneath the south equatorial current of the Pacific. In 1961 a similar current was discovered in the Atlantic. See also tidetide,
alternate and regular rise and fall of sea level in oceans and other large bodies of water. These changes are caused by the gravitational attraction of the moon and, to a lesser extent, of the sun on the earth.
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Thermohaline Circulation

Thermohaline circulation refers to the deepwater circulation of the oceans and is primarily caused by differences in density between the waters of different regions. It is mainly a convection process where cold, dense water formed in the polar regions sinks and flows slowly toward the equator. Most of the deep water acquires its characteristics in the Antarctic region and in the Norwegian Sea. Antarctic bottom water is the densest and coldest water in the ocean depths. It forms and sinks just off the continental slope of Antarctica and drifts slowly along the bottom as far as the middle North Atlantic Ocean, where it merges with other water. The circulation of ocean waters is vitally important in dispersing heat energy around the globe. In general, heat flows toward the poles in the surface currents, while the displaced cold water flows toward the equator in deeper ocean layers.

The Ocean as a Biological Environment

The oceans hold the answers to many important questions about the development of the earth and the history of life on earth. For instance, within the rocks and sediment of the ocean floors the geological history of the earth is recorded. Fossils in this sediment record a portion of the biological history of the earth at least back to the Jurassic period, which ended about 140,000,000 years ago. The first appearance of life on the earth is thought to have occurred in the oceans 2 or 3 billion years ago. The modern marine environment is divided into two major realms, the benthic and the pelagic, based upon the ecological characteristics and marine life associated with them. See also marine biologymarine biology,
study of ocean plants and animals and their ecological relationships. Marine organisms may be classified (according to their mode of life) as nektonic, planktonic, or benthic. Nektonic animals are those that swim and migrate freely, e.g.
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The Benthic Realm

The benthic realm refers to the floor of the oceans, extending from the high tide line to the greatest ocean depths. The organisms that live in or on the bottom are called benthos. The benthic realm is subdivided on the basis of depth into the littoral zone, which extends from high tide to a depth of about 200 m (660 ft), and the deep-sea realm. The benthic life forms are both sessile (attached) and motile (mobile). They are distributed from near-shore littoral regions to the ocean depths and play an important role in the food chain. Some benthic life forms live by predation, others sift organic matter from the water, and others scavenge the bottom for organic debris that has settled there. Benthic plants can live only in the euphotic zone, the uppermost 100–200 m (330–660 ft) of the ocean, where sunlight penetrates. Benthic animals that live below the euphotic zone often must depend on the rain of organic debris from above to supply their food needs, and thus the deep regions of the benthic realm are not highly populated except in the areas around hydrothermal ventshydrothermal vent,
crack along a rift or ridge in the deep ocean floor that spews out water heated to high temperatures by the magma under the earth's crust. Some vents are in areas of seafloor spreading, and in some locations water temperatures above 350°C; (660°F;) have
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 where chemosynthesischemosynthesis,
process in which carbohydrates are manufactured from carbon dioxide and water using chemical nutrients as the energy source, rather than the sunlight used for energy in photosynthesis. Much life on earth is fueled directly or indirectly by sunlight.
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 provides an alternative food source.

The Pelagic Realm

The pelagic realm consists of all of the ocean water covering the benthic realm. It is divided horizontally into the neritic, or fertile near-shore, province and the oceanic province. Vertically it is divided into the euphotic, or photic, zone and the aphotic (without sunlight) zone. Drifting, free-floating organisms, called plankton, and organisms with poor mobile ability populate the euphotic zone. Most plankton are microscopic or near-microscopic in size. Phytoplankton are photosynthetic bacteria (cyanbacteriacyanobacteria
or blue-green algae,
photosynthetic bacteria that contain chlorophyll. For many years they were classified in the plant kingdom along with algae, but discoveries made possible by the electron microscope and new biochemical techniques have shown them to be
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) and floating algae, such as diatoms, dinoflagellates, and coccolithopores. Heterotrophic plankton (zooplankton) are floating animals and protozoansprotozoan
, informal term for the unicellular heterotrophs of the kingdom Protista. Protozoans comprise a large, diverse assortment of microscopic or near-microscopic organisms that live as single cells or in simple colonies and that show no differentiation into tissues.
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 of the sea and rely on the phytoplankton as food sources. Foraminifera and radiolaria are the dominant protozoan zooplankton that secrete tests (shells), which become incorporated into the sediment of the ocean floor. Many juvenile forms of swimmers (such as shrimp) or bottom dwellers (such as barnacles) pass through a planktonic phase. Marine organisms capable of self-locomotion are called nektonic life forms. Fish, squid, and whales are examples of marine nekton.

Importance of the Ocean

Throughout history humans have been directly or indirectly influenced by the oceans. Ocean waters serve as a source of food and valuable minerals, as a vast highway for commerce, and provide a place for both recreation and waste disposal. Increasingly, people are turning to the oceans for their food supply either by direct consumption or indirectly by harvesting fish that is then processed for livestock feed. It has been estimated that as much as 10% of human protein intake comes from the oceans. Nevertheless, the food-producing potential of the oceans is only partly realized. Other biological products of the oceans are also commercially used. For example, pearls taken from oysters are used in jewelry, and shells and coral have been widely used as a source of building material.

Ocean water is processed to extract commercially valuable minerals such as salt, bromine, and magnesium. Although nearly 60 valuable chemical elements have been found dissolved in ocean water, most are in such dilute concentrations that commercial extraction is not profitable. In a few arid regions of the world, such as Ascension Island, Kuwait, and Israel, ocean water is desalinated to produce freshwater.

The shallow continental shelves have been exploited as a source of sands and gravels. In addition, extensive deposits of petroleum-bearing sands have been exploited in offshore areas, particularly along the Gulf and California coasts of the United States and in the Persian Gulf. On the deep ocean floor manganese nodules, formed by the precipitation of manganese oxides and other metallic salts around a nucleus of rock or shell, represent a potentially rich and extensive resource. Research is currently being conducted to explore nodule mining and metallic extraction techniques. Ocean water itself could prove to be a limitless source of energy in the event that nuclear fusion reactors are developed, since the oceans contain great quantities of deuterium.

The oceans also are important for recreational use, as each year more people are attracted to the sports of swimming, fishing, scuba diving, boating, and waterskiing. Ocean pollution, meantime, has escalated dramatically as those who use the oceans for recreational and commercial purposes, as well as those who live nearby, have disposed of more and more wastes there (see water pollutionwater pollution,
contamination of water resources by harmful wastes; see also sewerage, water supply, pollution, and environmentalism. Industrial Pollution
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See also R. Carson, The Sea around Us (1961); J. Bardach, Harvest of the Sea (1968); J. R. Moore, ed., Oceanography (1971); R. Perry, The Unknown Ocean (1972); L. Paine, The Sea and Civilization (2013).



(world ocean).

The ocean is the interconnecting body of salt water that surrounds the earth’s continents and islands. It constitutes 94 percent of the hydrosphere and occupies about 70.8 percent of the earth’s surface. The parts of the earth’s crust and mantle that underlie the ocean water are often included in the concept of “ocean.” In terms of its physical and chemical properties and the qualitative chemical composition of its water, the ocean is a single entity, but the quantitative indexes of its hydrological and hydrochemical conditions are highly diverse. As part of the hydrosphere the ocean is constantly interacting with the atmosphere and the earth’s crust, both of which determine many of its fundamental characteristics.

The ocean is an enormous accumulator of solar heat and moisture. By evening out fluctuations in temperature and bringing moisture to distant land areas, the ocean creates conditions conducive to the development of life. The ocean is an extremely rich source of protein food. It also contains energy, chemical, and mineral resources, which man has already begun to exploit, for example, the energy of tides, certain chemical elements, petroleum, and gas.

Since ancient times the ocean and its seas have been used to establish contact among peoples. This led to the great geographic discoveries and the exploration of areas far from the centers of culture, a process that was facilitated by technical progress in the means of transportation. About four-fifths of the world’s freight cargo is carried along ocean routes.

The ocean is playing an increasingly important role in human life. The problem of using the ocean in different branches of the economy is a global one and is connected with the resolution of important economic, political, and legal questions relating to navigation, fishing, the efficient exploitation of the ocean’s resources, the development of the shelf, the laying of intercontinental cables, the desalinization of water, and the protection of the marine environment and prevention of pollution.

The world ocean has been divided into separate oceans, seas, gulfs, bays, and straits on the basis of physicogeographic characteristics expressed in hydrological conditions. The most generally accepted subdivision of the ocean is based on the morphological, hydrological, and hydrochemical characteristics of the ocean basins, which are separated by continents and islands. The boundaries of the world ocean are clearly marked only by the shorelines of the land areas; the water boundaries between separate oceans, seas, and parts of seas are to some extent arbitrary. Guided by specific physical geographic conditions, some scholars have classified as a separate ocean the Southern Ocean, with its boundary along the line of the subtropical or subantarctic convergence or along latitudinal segments of the mid-ocean ridges. (The primary morphometric indexes of the oceans, including their seas, and of the world ocean as a whole are given in Table 1.)

Table 1. Primary morphometric indexes of the oceans
 Surface areaVolume (million cu km)Average depth (m)Maximun depth (m)
 million sq kmpercent
1 According to other sources, 91,14,338, and 3,332, respectively, for the first four columns
2 according to other sources, 14, 7, 16.7, and 1,130, respectively
Pacific . . . . . . . . . . . . .179.68507243,98411,022
Atlantic1 . . . . . . . . . . .93.36253373,9268,428
Indian . . . . . . . . . . . . . .74.92212923,8977,130
Arctic2 . . . . . . . . . . . . .13.104171,2055,449
World ocean . . . . . . .361.061001,3703,79511,022

Water occupies 61 percent of the surface of the globe in the northern hemisphere and 81 percent in the southern hemisphere. North of 81° N lat. in the Arctic Ocean and between roughly 56° and 63° S lat. ocean waters cover the globe in an unbroken sheet. The globe is divided into an oceanic and a continental hemisphere according to the distribution of water and land. The pole of the oceanic hemisphere is in the Pacific Ocean southeast of New Zealand, and the pole of the continental hemisphere is in northwestern France. The waters of the ocean occupy 91 percent of the oceanic hemisphere and 53 percent of the continental hemisphere.

Topography of the ocean floor and structure of the earth’s crust. A general idea of the distribution of different ocean depths is given by the hypsographic curve, which shows that 73.8 percent of the ocean floor lies between 3,000 and 6,000 m. The planetary morphostructures of the ocean floor are identified on the basis of differences in the structure and development of individual sections of the earth’s crust. The parts of the ocean floor that are adjacent to the continents have a continental crust and constitute the underwater margin of the continents, in which the main relief features are the shelf, the continental slope, and the continental rise. The continental rise is bounded by the ocean floor or by the floor of the basins of marginal seas, if the underwater margin of the continent is framed by a zone of island arcs. The ocean floor typically has a comparatively thin oceanic crust consisting of three layers: an upper layer of loose sediments (or first seismic layer), a second (upper basalt) layer, and a lower basalt layer. The topography of the ocean floor includes flat sedimentary abyssal plains and dissected hilly surfaces with a volcanic relief. Other major features are individual volcanic mountains, mountain chains, arched uplifts (swells), and block uplifts (aseismic ridges). The relative depth of the ocean floor ranges from 2,000–4,000 m to 11,000 m. Among the negative forms on the ocean floor are the narrow trenches that are confined to huge fractures and depressions in the earth’s crust, descending to a depth of 7,000 m or more.

There is a transitional zone between the underwater continental margin and the ocean floor along much of the Pacific margin, in the northeastern part of the Indian Ocean, and in parts of the Caribbean and Scotia seas. Here the major relief features are the basins of the marginal seas (depths to 4,000–5,000 m), island arcs (underwater mountain ranges with chains of islands along the crests), and deep trenches where the greatest depths are encountered, for example, the 11,022–meter Mariana Trench. In the island arc zones segments of continental, subcontinental, sub-oceanic, and oceanic crust (lithosphere) are intricately combined, and these regions typically have a high degree of seismic activity and active volcanoes. The fourth planetary morphostructure of the ocean bottom is the mid-ocean ridge, a system of large, greatly dissected underwater uplifts that extends through all the oceans and has a special type of crust. Typical topographic features of the mid-ocean ridges are rift valleys framing rift ridges, transverse faults, and large volcanic massifs, for example, the Azores.

The planetary morphostructures correspond to the largest tectonic categories of the earth’s crust. Tectonically, the underwater continental margins are the submerged parts of continental platforms and are characterized by relatively tranquil tectonic conditions with slow negative movements of the earth’s crust, isometric contours of geophysical fields, and weak positive anomalies of the force of gravity. Linear positive magnetic and gravitational anomalies are frequently observed at the outer edge of the shelf and continental slope. The transitional zone is a contemporary geosynclinal area with sharp differentiation and rapid vertical movement of the earth’s crust. The zone also has an intricate geophysical field picture, with deep trenches usually showing marked negative gravitational anomalies and the basins of marginal seas having significant positive anomalies.

In a geotectonic sense, the mid-ocean ridges correspond to “georiftogenals” and, like the transitional zone, are areas of intense seismic activity, volcanic activity, and mountain formation. Linear positive and negative magnetic anomalies alternate in the mid-ocean ridges. The ocean floor, which tectonically corresponds to the thalassocraton, is distinguished by fairly broad distribution of a special type of volcanic activity, by fault tectonics, by weak seismic activity, and by slow negative regional movements of the earth’s crust. The geophysical fields of the ocean floor are mostly isometric, and positive gravitational anomalies predominate. Many regions have a banded distribution of the magnetic field.

Marine sediments. Until recently, knowledge about the geological age, composition, and development of the sedimentary mantle of the ocean was limited to information about uppermost horizons of the layer of loose sediments, known as the first seismic layer. Beginning in 1968, as a result of systematic deep boring done from the ship Glomar Challenger, the volcanic rocks of the second (upper basalt) layer of the crust were reached in a number of places. Geological investigations and seismic soundings have established that the thickness of the sediments ranges from 2,000–3,000 m or more in the zones adjoining the continents to a few dozen meters or even an absence of sediment on the crests of the mid-ocean ridges, the steep slopes of uplifts, and the ledges of the continental slope.

In the central, pelagic parts of the ocean there are three latitudinal belts where the sedimentary mantle is more than 2,000 m thick: along the equator, north of 40°N lat., and south of 40°S lat. The stratigraphic range of the sedimentary layer increases as one moves from the mid-ocean ridges (Pleistocene-Pliocene) to the margin of the ocean (Upper Jurassic). More ancient marine sediments have not been discovered by boring, but there is a strong possibility that they will be found in rocks of the second layer, for example, in the Pacific Ocean.

The sediments of the ocean floor may be divided into terrigenous, biogenic (calcareous, siliceous), and volcanic sediments and those of mixed origin (polygenic), which include the deep-sea red clays. Terrigenous sediments tend to occur on the underwater continental margins, on the periphery of the ocean floor, and in the deep trenches. Turbidites, or sediments deposited from turbidity currents, are common among terrigenous sediments, which are relatively rich in organic matter. The decomposition of this matter causes a reduction situation and gives the sediment its gray color. Calcareous sediments are most common in the warm and moderate zones of the ocean, from 50°N lat. to 50°S lat. On the ocean floor they are represented by foraminiferal and coccolith-foraminiferal deposits, and in shallow water by shell and coral deposits. There are no calcareous sediments at depths of more than 4,500–5,000 m owing to the dissolution of CaCO3. Siliceous sediments, both radiolarian and diatomaceous, form three belts corresponding to the zones of high phytoplankton productivity, of which two are subpolar belts and one equatorial. Red deep-sea clay is characteristic of basins with depths of 4,500–5,000 m or more in zones of low biological productivity. Volcanic sediments form in areas adjoining zones of subaerial volcanic activity. Today, the largest areas are occupied by carbonate sediments (about 150 million sq km), deep-sea red clays (more than 110 million sq km), and siliceous silts (about 60 million sq km). The present distribution of different types of sediments in the surface layer is not always maintained at deeper, more ancient horizons. Material from boring attests to change in the conditions of oceanic sediment accumulation in past geological periods.

The presence of endogenic matter on the ocean bottom is not limited to regions with above-water volcanoes. Such matter also occurs near mid-ocean ridges and large faults, where there are metal-bearing and sometimes ore-bearing (Red Sea) layers with a high concentration of Fe (up to 20–40 percent), Mn, Co, Ni, Pb, Zn, Ag, Se, Hg, and other elements. Another type of oceanic ore formation is associated with sedimentary processes leading to the accumulation of ferromagnesian concretions. These concretions are found in the surface layer of sediments, but sometimes also occur in the deep horizons of the sedimentary mantle.

Unlike sea deposits, oceanic sediments usually accumulate at a slow rate—about 1 mm in a thousand years for red deep-sea clays and from 1 to 30 mm in a thousand years for siliceous and diatomaceous sediments. The maximum rate is observed at the foot of the continental slope in the zone of terrigenous sediments, which often accumulate at a rate of more than 100 mm per thousand years.

Most of the material of oceanic sediments comes from the continents in the form of suspensions or in solution. The quantitative distribution of sedimentary material and types of sediments are related to climatic, vertical, horizontal, and circumcontinental zonation and tectonic conditions. Climatic zonation and tectonic conditions determine the mass and composition of terrigenous and biogenic material; vertical zonation controls the dissolution of carbonates at great depths and the presence of coarser material on uplifts; and circumcontinental zonation determines the formation of terrigenous sediments near the continents.

Deposits similar to oceanic sediments are believed to exist in the geosynclinal strata of the ancient folded systems of the continents. They probably exist in geological formations dating from the early stages in the development of marginal geosynclines (for example, the Franciscan formation on the Pacific coast of the United States) and on such oceanic islands as Timor and Barbados.

Origin and geological history. Today the ocean is regarded as the product of the differentiation of the matter of the earth’s mantle. Various hypotheses have been suggested concerning the origin and evolution of ocean basins. According to one of them —the continentalization hypothesis—ocean basins are more ancient than the continents. In the development of the earth’s crust and relief the ocean is gradually shrinking and the continents are becoming larger, and oceanic crust is being transformed into continental crust within the geosynclinal belts. An opposing view—the oceanization hypothesis—holds that the ocean basins are relatively young formations that arose during the transformation of continental crust into oceanic crust. During the 1960’s a third hypothesis, called plate tectonics, gained many adherents. According to this view, the entire earth’s crust consists of a number of mobile plates whose boundaries are the mid-ocean ridges and deep trenches. In the rift zones of the mid-ocean ridges, abyssal matter is uplifted and then flows outward in both directions. After gradually cooling and solidifying, it is again submerged in the zones of the deep trenches. It is believed that this process has been occurring since the middle of the Mesozoic and is gradually leading to a greater separation of the opposite sides of the ocean. A number of facts support this hypothesis, but at the present time it has not sufficiently taken into account the enormous amount of data that has been accumulated during the study of the geology of land areas.

The present deep-sea basins have existed at least since the Jurassic period; more ancient rocks have not yet been discovered on the ocean floor. During the Cretaceous and Cenozoic the basins were deepened, and abyssal sediments continued to form. Continental margins were undoubtedly enlarged in recent times through the elimination of marginal geosynclinal basins. The enormous thickness of sediments in the basins of the geosynclinal seas attests to the ocean’s ancient origin. Vertical and horizontal movements of the earth’s crust played a significant part in formation of the major topographic features of the ocean floor.

Seawater is a salt solution with an average concentration of about 35 g per liter. The ocean contains a total of 5 × 1022 g of dissolved salts. The ions Na+, Mg2+, K+, Ca2+, Cl and SO42− make up 99 percent of the salts. Many other elements are found in millionths and billionths (see Table 2).

The composition of the salt mass of the ocean is regulated by

Table 2. Average content of chemical elements in seawater1
1Salinity S = 35.00‰ (g/kg), Chlorinity Cl = 19.375‰
H . . . . . . .10.7
He . . . . . . .5 × 10−10
Li . . . . . . .1.5 × 10−5
Be . . . . . . .6 × 10−11
B . . . . . . .4.6 × 10−4
C . . . . . . .2.8 × 10−3
N . . . . . . .5 × 10−5
O . . . . . . .85.8
F . . . . . . .1.3 × 10−4
Ne . . . . . . .1 × 10−8
Na . . . . . . .1.035
Mg . . . . . . .0.1297
Al . . . . . . .1 × 10−6
Si . . . . . . .3 × 10−4
P . . . . . . .7 × 10−6
S . . . . . . .0.089
Cl . . . . . . .1.93
K . . . . . . .0.038
Ca . . . . . . .0.04
Sc . . . . . . .4 × 10−9
Ti . . . . . . .1 × 10−7
V . . . . . . .3 × 10−7
Cr . . . . . . .2 × 10−9
Mn . . . . . . .2 × 10−7
Fe . . . . . . .1 × 10−6
Co . . . . . . .5 × 10−8
Ni . . . . . . .2 × 10−7
Cu . . . . . . .3 × 10−7
Zn . . . . . . .1 × 10−6
Ga . . . . . . .3 × 10−9
Ge . . . . . . .6 × 10−9
As . . . . . . .1 × 10−7
Se . . . . . . .1 × 10−8
Br . . . . . . .6.6 × 10−3
Kr . . . . . . .3 × 10−8
Rb . . . . . . .2 × 10−5
Sr . . . . . . .8 × 10−4
Y . . . . . . .3 × 10−8
Zr . . . . . . .5 × 10−9
Nb . . . . . . .1 × 10−9
Mo . . . . . . .1 × 10−6
Ag . . . . . . .3 × 10−3
Cd . . . . . . .1 × 10−8
In . . . . . . .1 × 10−9
Sn . . . . . . .3 × 10−7
Sb . . . . . . .5 × 10−8
I . . . . . . .6 × 10−6
Cs . . . . . . .3.7 × 10−8
Ba . . . . . . .2 × 10−6
La . . . . . . .2.9 × 10−10
Ce . . . . . . .1.3 × 10−10
Pr . . . . . . .6 × 10−11
Nd . . . . . . .2.3 × 10−11
Sm . . . . . . .4.2 × 10−11
Eu . . . . . . .1.1 × 10−10
Gd . . . . . . .6 × 10−11
Dy . . . . . . .7.3 × 10−11
Ho . . . . . . .2.2 × 10−11
Er . . . . . . .6 × 10−11
Fm . . . . . . .1 × 10−11
Yb . . . . . . .5 × 10−11
Lu . . . . . . .1 × 10−11
W . . . . . . .1 × 10−8
Au . . . . . . .4 × 10−10
Hg . . . . . . .3 × 10−9
Tl . . . . . . .1 × 10−9
Pb . . . . . . .3 × 10−9
Bi . . . . . . .2 × 10−8
Ra . . . . . . .1 × 10−14
Ac . . . . . . .2 × 10−20
Th . . . . . . .1 × 10−9
Pa . . . . . . .5 × 10−15
U . . . . . . .3 × 10−7

solubility, the removal of sediment from the continents, exchange processes with the atmosphere and bottom sediments (primarily carbonaceous and siliceous equilibriums), and the biological activity of marine organisms. One group of ions (Na+, Mg2+, Li+, Cl, SO4−2) does not form insoluble compounds in significant quantities. These ions accumulate in seawater to a much larger extent than in river water. A second group of ions precipitates comparatively rapidly in the form of slightly soluble compounds. Thus, in tropical seas the hot surface layers of the water are supersaturated with CaCO3, which settles to the bottom both chemically and biogenically. Barium may also be precipitated in the form of the slightly soluble salt BaSO4. The ions of such metals as Ti, Mn, and Zr coagulate through hydrolysis and are precipitated in the form of hydroxides. Various trace elements in seawater—Cu, Pb, Mo, Hg, Zn, U, Ag, and the rare earths—are precipitated through adsorption by various natural sorbents: organic matter, hydroxides of iron and manganese, calcium phosphates, and silicates. Consequently, the concentrations of heavy metals in seawater are significantly lower than would be expected from the solubility of their compounds. The ocean is a dynamic system in which the quantity of incoming matter (river flow, atmospheric dust, products of volcanic activity) is roughly equal to the amount lost (sedimentation, loss into the atmosphere). The equilibrium of the ocean is defined by the ratio of the mass of each component found in the ocean at a given moment to the mass of the component that has passed through the ocean. The size of the ratio depends on the average time the element spends in the ocean. With the exception of Na and Cl the ratio is small compared to the length of time that the ocean has existed.

Various gases both from the atmosphere and formed in the water layer itself are dissolved in ocean water. The most important gases are O2 and CO2, which condition biological activity in the ocean. There are also a number of inert gases—N2, Ar, Kr, and Xe—whose solubility is inversely related to their atomic weight. The content of O2 reaches a maximum of 7–8 milliliters per liter in the surface layers of the water (to depths of 100–150 m) and drops to 3.0–0.5 milliliters per liter at greater depths (the layer of minimum oxygen). In some places there is a complete absence of O2. In contrast, the maximum amount of CO2 occurs in the deep water layers. The solubility of carbon dioxide increases in cold water and decreases as it becomes warmer. For this reason, some of the CO2 passes from the atmosphere into ocean water during the winter months and returns to the atmosphere during the summer. CO2 participates in chemical reactions; in particular it regulates the carbonate balance. Waters enriched with CO2 tend to dissolve CaCO3, and the removal of CO2 from water when it is warmed promotes the precipitation of carbonates. CO2 plays an important role in photosynthesis, during which organic matter is formed. As a result of photosynthesis about 1017g of phytoplankton biomass is formed each year.

The photosynthetic activity of phytoplankton determines the content of gases dissolved in the surface layers of the water (to depths of 100–150 m) by saturating them with oxygen and absorbing CO2. In addition to carbon, organisms extract such elements as Si, Ca, Mg, K, Br, I, P, and Na, as well as a number of heavy metals that are physiologically important, including V, Zn, Cu, Co, and Ni. When organisms die a portion of these elements enters the bottom mud where, under appropriate conditions, the elements may become concentrated. Cu, Zn, Ni, Co, Mo, Ag, Tl, Pb, and other elements also accumulate in ferromagnesian concretions. The total amount of ferromagnesian concretions is estimated at 1013.

Many scientists have divided the geochemical history of the ocean into three stages: an initial stage, a transitional stage, and a contemporary stage. The initial stage is a hypothetical stage encompassing the pregeological period that ended about 3.5 billion years ago. During this period most of the water and the acid products of degasification (Cl, F, Br, I, S) were removed from the earth’s interior, and the acid products were later neutralized through interaction with the rocks of the ocean floor. The transitional stage, which probably lasted about 2 billion years, from 3.5 to 1.7 billion years ago, was marked by the emergence and development of life, the appearance and gradual increase of photosynthetic oxygen in the atmosphere, and the oxidation of reduced sulfur and other polyvalent elements. The contemporary stage probably began between the Early and Late Proterozoic, about 1.7 billion years ago, and has continued to the present. During this stage the composition of ocean water and atmospheric gases has been similar to that of the present, and a state of equilibrium has prevailed, with brief and limited fluctuations in salinity during periods of salt accumulation (the Cambrian, Devonian, and Permian). The bottom sediments form under the influence of the processes taking place in ocean water, which penetrates the sediments to a considerable depth. The buried water of the bottom sediments and its composition undergo change.

The ocean contains rich mineral resources, which may be subdivided into the chemical elements dissolved in seawater, the minerals found under the sea floor, both on the continental shelves and elsewhere, and the minerals occurring on the surface of the floor.

Until the 1970’s the chief products extracted from seawater were common salt (about 8 million tons a year), sodium sulfate, magnesium chloride, potassium chloride, and bromine. The scientific and technological revolution is facilitating the production of chemicals from seawater.

Petroleum and natural gas account for more than 90 percent of the value of mineral raw material taken from the ocean. The total petroleum- and gas-bearing area within the continental shelf is estimated to be 13 million sq km, or about half of the shelf s area. The geological reserves of petroleum in the ocean (to depths of 305 m) have been estimated at 280 billion tons, and natural gas reserves have been estimated at 140 trillion cu m. Converted to petroleum, the potential reserves of petroleum and gas are estimated at 1,410 billion tons. Until the early 1970’s the extraction of petroleum and gas was restricted to depths of 100–110 m and a distance of about 150 km from the shore. In the near future more extensive drilling at greater depths and farther from the shore is expected. In 1970 petroleum extraction on the shelf accounted for 19.2 percent of total world production, and offshore drilling operations have been expanding rapidly. In 1973 petroleum and gas were being extracted from marine deposits in 25 countries, and exploratory work in the shelf zones of the seas and oceans was under way in almost 100 countries. The largest petroleum- and gas-producing regions are the Persian Gulf and the Gulf of Mexico. Petroleum and gas are also being extracted from the floor of the North Sea.

The shelf is also rich in surface deposits, represented by numerous placers on the floor containing metallic ores, as well as by nonmetallic minerals. Important among them are the titanium minerals ilmenite and rutile, as well as zircon and monazite. The largest deposits are worked on the east coast of Australia, where more than 1 million tons of titanium minerals are extracted annually; 1,245,000 tons were mined in 1970, including 877,000 tons of ilmenite. Similar placers also occur near the coasts of India, Sri Lanka, Malaysia, and elsewhere. Among other important minerals extracted from the ocean are tin (on the shelf adjacent to Malaysia, Indonesia, Thailand, Vietnam, and other Asian countries), iron ore (Japan, Newfoundland in Canada), native sulfur (Mexico), and coal (Canada). Gold and platinum have been found in many places, for example, along the coast of Alaska and California in the United States, as well as columbite-tantalite, magnetite, titanomagnetite, chromites, and diamonds. Diamond deposits are worked along the southwestern coast of Africa, in Namibia. Deposits of phosphorite concretions are widely found along the coasts of Mexico, Peru, Chile, and the Republic of South Africa.

Rich deposits of ferromagnesian concretions have been found over vast areas of the ocean floor. They are unique multicomponent ores containing nickel, cobalt, and copper whose potential reserves are estimated at several trillion tons. It is estimated that the reserves of manganese, nickel, and cobalt in these ores are many times greater than the explored reserves on land. Several countries have begun experimenting with the industrial extraction of concretions from depths reaching 4,000 m. Furthermore, studies have indicated that there may be large deposits of various metals in the bedrock beneath the ocean floor.

In addition to petroleum and gas, other forms of energy resources are potentially important. The force of waves, the difference in water level caused by tides, and the differences in temperature on and below the surface may be used to obtain energy from the ocean. The use of the energy of tides, estimated at 1 billion kilowatts, has only begun. The first tidal power plant was built in France in 1967 at the mouth of the Ranee River, which empties into the English Channel. In the USSR, the experimental Kislogubskaia tidal power plant was built in 1968 on the northern Kola Peninsula, and more powerful stations are being planned. Canada, the United States, and Great Britain are also developing plans to construct such plants. Attempts to harness the energy of waves have not progressed beyond the experimental stage. Solving the extremely difficult problem of concentrating the diffused energy of waves would give man a major new source of energy. The tropical regions have the greatest potential for harnessing the thermal energy of the ocean. Here the surface temperature of the coastal zone reaches 30°C, and at depths of 400–500 m the temperature falls to 8–10°C. Construction of the first hydrothermal power station began in 1969 near Abidjan in the Ivory Coast.

The ocean is the principal reservoir of heavy hydrogen (deuterium) which may become an inexhaustible source of energy if the problem of controlling thermonuclear reactions is solved.

Heat balance. The main components of the ocean’s heat balance are the radiation balance (total solar radiation minus the reverse radiation of the ocean), the loss of heat by evaporation, turbulent heat exchange between the surface of the ocean and the atmosphere, and the internal heat exchange between the surface of the ocean and the lower layers. In addition, the overall heat balance of the ocean includes transmission by the ocean of the internal heat of the earth, the warming and cooling of the ocean

Table 3. Average values of basic components of the heat balance (according to M. I. Budyko)
LatitudeTotal radiationRadiation balanceLoss of heat by evaporationTurbulent heat exchangeInternal heat exchange
70°–60° N . . . . .69233316−26
60°–50° N . . . . .68293916−26
50°–40° N . . . . .90515314−16
40°–30° N . . . . .126838613−16
30°–20° N . . . . .1561131059−1
20°–10° N . . . . .16411999614
10°–0° N . . . . . .15711580431
0°–10° S . . . . . .16011584427
10°–20° S . . . . .16011310454
20°–30° S . . . . .1491011007−5
30°–40° S . . . . .12882809−7
40°–50° S . . . . .9357559−7
50°–60° S . . . . .6728318−11
70°–60° S . . . . .127827480

caused by the chemical processes taking place, the conversion of kinetic energy into thermal energy, and the release of heat during the condensation of water vapor on the surface of the ocean. Since these heat gains and losses are extremely small, each totaling less than one-thousandth of the amount of solar radiation, they are not usually taken into account in considering the overall heat balance of the ocean. (Table 3 gives the average values of the basic components of the ocean’s heat balance by latitudinal belts in kilocalories per sq cm per year.)

The total radiation increases from the high latitudes to the low, reaching a maximum at about 20° N lat. and 20° S lat. owing to the minimal cloud cover in these regions of high atmospheric pressure. The greatest loss of heat by evaporation also occurs in regions of high atmospheric pressure. In the tropical and temperate latitudes the turbulent heat exchange is less than the other main components of the heat balance, and its increase in the higher latitudes is related to increasingly greater differences between the temperature of the water and the air. The ocean absorbs heat in the belt between 30° N lat. and 30° S lat. and releases it into the atmosphere in the higher latitudes, an important factor in making the climate of the temperate and polar latitudes less severe during the cold half of the year. As a result of evaporation and turbulent heat exchange, 82 kilocalories per sq cm per year are released from the surface of the ocean into the atmosphere, in contrast to 49 kilocalories per sq cm per year from the surface of dry land. Thus, the ocean is the principal factor in determining climate and weather on earth. The uneven transfer of solar heat to the surface of the ocean and the variability of atmospheric processes directly influence temperature, salinity, and other properties of the ocean.

Water balance. The ocean’s water balance is governed by the loss of water from the surface by evaporation and its gain of water from precipitation and runoff (see Table 4).

Table 4. Water balance (according to M. I. L’vovich)
 Annual volume (cu km)Annual water layer (mm)
Precipitation . . . . . . . . . . . . . . .411,0001,140
River runoff . . . . . . . . . . . . . . .41,000111
Evaporation . . . . . . . . . . . . . . .452,0001,251

The ratio between the components of the water balance determines salinity distribution and changes in the salinity of ocean water. The annual totals of the components of the water balance for different latitudes are given in Table 5, expressed in cm as a layer of water.

The continental component is important only in coastal regions. In the open ocean the governing factor is the relation between precipitation and evaporation. In the northern hemisphere evaporation totals 111.9 cm per year, and precipitation 116.7 cm per year; the corresponding figures in the southern hemisphere are 113.0 cm and 91.6 cm. In the temperate and

Table 5. Annual totals of the components of the water balance (according to L. I. Zubenok)
LatitudeEvaporationPrecipitationContinental runoff
60°–50° N . . . . . . . .105.057.447.6
50°–40° N . . . . . . . .114.086.327.7
40°–30° N . . . . . . . .96.2121.225.0
30°–20° N . . . . . . . .81.5141.159.6
20°–10° N . . . . . . . .124.7148.824.1
10°–0° N . . . . . . . .193.0127.066.0
0°–10° S . . . . . . . .119.3134.214.9
10°–20° S . . . . . . . .98.6162.163.5
20°–30° S . . . . . . . .83.5144.260.7
30°–40° S . . . . . . . .87.5128.440.9
40°–50° S . . . . . . . .105.695.110.5
50°–60° S . . . . . . . .91.562.229.3
60° N–60° S . . . . . . . .112.7102.410.3

polar latitudes, the intake and loss of fresh water during the thawing and formation of ice is important in the water balance.

Temperature. The thin uppermost layer of the water, 1 cm thick, absorbs 94 percent of the solar energy that reaches the ocean surface. Through intermixing, the heat is transmitted to the entire water body. Differences in the heat balance determine regional and zonal characteristics in the distribution of temperature (see Table 6).

Table 6. Average water temperature on the ocean surface
LatitudeTemperature (°C)
70°–60° N . . . . . . . . . . . . . .. . . . .2.9
60°–50° N . . . . . . . . . . . . . .. . . . . .6.1
50°–40° N . . . . . . . . . . . . . .. . . . . .11.2
40°–30° N . . . . . . . . . . . . . .. . . . . .19.1
30°–20° N . . . . . . . . . . . . . .. . . . . .23.6
20°–10° N . . . . . . . . . . . . . .. . . . . .26.4
10°–0° N . . . . . . . . . . . . . .. . . . . .27.3
0°–10° S . . . . . . . . . . . . . .. . . . . .26.7
10°–20° S . . . . . . . . . . . . . .. . . . . .25.2
20°–30° S . . . . . . . . . . . . . .. . . . . .22.1
30°–40° S . . . . . . . . . . . . . .. . . . . .17.1
40°–50° S . . . . . . . . . . . . . .. . . . . .9.8
50°–60° S . . . . . . . . . . . . . .. . . . . .3.1
70°N–60° S . . . . . . . . . . . . . .. . . . . .19.32

The average annual temperature of the surface water of the ocean is 17.5°C, and the air temperature above the ocean averages 14.4°C. The water temperature in the northern hemisphere is higher than in the southern hemisphere owing to continental influences. The thermal equator—the line of maximum temperatures—lies north of the equator. Here the average annual temperature reaches 28°C, rising to 32°C in landlocked tropical seas. Moving from the equator toward the poles, the temperature gradually drops to –1.5° or –1.9°C in the polar regions. The distribution of temperature on the surface and in the upper layer of the ocean is generally zonal. However, in the temperate latitudes, under the influence of warm and cold currents, the temperature in the eastern part of the ocean is 5°–8°C higher than in the western part; in contrast, in the subtropical latitudes, the temperature is 5°–10°C lower in the east than in the west. Seasonal variations in temperature occur to depths of 100–150 m. On the ocean surface seasonal variations range from 1°C or less at the equator to 10°C or more in the temperate and subtropical latitudes.

At great depths temperature distribution is determined by abyssal circulation, which carries waters that have come from the surface. The higher the latitude at which waters submerge, the greater the depths they will occupy (because of their greater density) and the lower their temperatures will be. Thus, the temperature drops with increasing depth, becoming 1.4°–1.8°C in the bottom layer (below 0°C in the polar regions). But the drop in temperature with depth does not occur evenly. Substantial temperature changes are observed only to depths of 1,000 m (from 200 m to 2,000 m, depending on the region). In the open ocean, with the exception of the polar regions, the temperature varies considerably from the surface to depths of 300–400 m; then down to 1,500 m temperature changes are very slight (10°–12°) at depths of 400–450 m, 3°–7°at 1,000 m, and 2.5°–3° at 2,000 m); and below 1,500 m the temperature hardly changes at all. In the temperate and polar latitudes the drop in temperature is disrupted in some cases by incoming warm or cold waters in abyssal currents. In depressions more than 7,000 m deep the temperature does not drop but rather rises several tenths of a degree near the bottom as a result of adiabatic processes.

Salinity. Depending on the ratio of the components of the water balance, salinity ranges from almost 0 near the mouths of large rivers to 39–42 parts per thousand ‰ in tropical seas such as the Red Sea, the Persian Gulf, and the Mediterranean Sea. The latitudinal zonation of the distribution of salinity on the ocean surface is also disrupted by currents and the formation and melting of ice. Table 7 shows the average salinity on the ocean surface for different latitudes.

Table 7. Average salinity at the ocean surface
LatitudeSalinity (‰)
80°–60° N . . . . . . . . . . . . . . . . . . . .32.87
60°–50° N . . . . . . . . . . . . . . . . . . . .33.03
50°–40° N . . . . . . . . . . . . . . . . . . . .33.91
40°–30° N . . . . . . . . . . . . . . . . . . . .35.30
30°–20° N . . . . . . . . . . . . . . . . . . . .35.71
20°–10° N . . . . . . . . . . . . . . . . . . . .34.95
10°–0° N . . . . . . . . . . . . . . . . . . . .34.58
0°–10° S . . . . . . . . . . . . . .. . . . . .35.16
10°–20° S . . . . . . . . . . . . . .. . . . . .35.52
20°–30° S . . . . . . . . . . . . . .. . . . . .35.71
30°–40° S . . . . . . . . . . . . . .. . . . . .35.25
40°–50° S . . . . . . . . . . . . . .. . . . . .34.34
50°–60° S . . . . . . . . . . . . . .. . . . . .33.95
70° N–60° S . . . . . . . . . . . . . .. . . . . .34.89

The salinity is lower in the northern hemisphere than in the southern hemisphere. The greatest salinity in the open ocean occurs in the tropical latitudes of the Atlantic Ocean, where it reaches 37.25‰. In the polar regions the salinity decreases to 31.4‰ in the north and 33.93‰ in the south; at the equator the salinity decreases to 32–34‰. Seasonal variations in salinity occur to depths of 100–150 m and are most apparent in the 10–25 m layer, where they exceed 2–3‰. Below 150 m the distribution of salinity, as of temperature, is determined by abyssal circulation and varies only slightly, from 34.6‰ to 34.9‰. Between 40° N lat. and 40° S lat there is a layer of minimum salinity (34.0‰ to 34.5‰), associated with the distribution of subpolar waters that have sunk from the surface.

Circulation of ocean waters. A number of factors contribute to the circulation of ocean waters. Under the influence of atmospheric circulation, surface currents to depths of 150–200 m form anticyclonic circulations in the subtropical and tropical latitudes and cyclonic circulations in the temperate and high latitudes. Anticyclonic circulations are formed in the tropical latitudes by the strong trade-wind currents that develop under the influence of the northeasterly and southeasterly trade winds. These currents cross the ocean from east to west. Along the eastern coasts of the continents they turn north in the northern hemisphere and south in the southern hemisphere and move along the continents to a latitude of about 40°–45°. Here, under the influence of westerly winds, the surface currents turn eastward and again cross the ocean, forming a continuous stream of surface water in the southern hemisphere—the West Wind Drift—and the strong North Atlantic and North Pacific currents in the northern hemisphere.

Along the western coasts of continents, branches of the easterly surface currents flow toward the equator, where they merge with the trade-wind currents and complete the subtropical anticyclonic circulations. In the northern hemisphere, as the easterly surface currents move to higher latitudes, they form branches that flow in a westerly direction. These branches merge with the surface currents coming from the high latitudes into the temperate latitudes along the eastern coasts of continents and complete the cyclonic circulations. In the high southern latitudes, near Antarctica, a current flows from east to west. Between this current and the easterly current of the temperate latitudes cyclonic circulations also form, owing to the general cyclonic circulation of the atmosphere in these latitudes.

The currents of the northern and southern hemispheres are separated at the equator by the zone of equatorial countercur-rents, which move from west to east. The equatorial countercurrents are seasonal, and only in the Pacific Ocean do they exist throughout the year. In the monsoon regions of the ocean—the northern part of the Indian Ocean and the northwestern part of the Pacific Ocean—the currents undergo seasonal changes. In these systems of circulation, the movement of water from lower to higher latitudes and from higher to lower latitudes produces warm and cold ocean currents whose temperature differs from that of the surrounding water. Examples include the warm Gulf Stream and Kuroshio Current in the northern Atlantic and Pacific oceans and the cold Labrador, Benguela, Kuril, and Peru currents.

At depths of more than 150–200 m, the circulation of waters is caused primarily by differences in water density. These differences arise because waters that have sunk from the ocean surface in convergence zones have different temperature and salinity characteristics corresponding to the latitude at which they have submerged. The temperature and salinity differences of these waters are also the result of winter cooling and flowing along the continental slope. At depths to 1,000–1,500 m the submerged waters appear to circulate in a manner resembling surface circulation. Above this circulation in a number of regions flow strong countercurrents, such as the subsurface Lomonosov and Cromwell currents, which originate in the equatorial latitudes of the Atlantic and Pacific oceans. At great depths the meridional component in the direction of currents prevails, causing water exchange between the northern and southern parts of the ocean. Abyssal waters return to the surface of the ocean in zones where surface currents diverge or in areas from which surface waters move away, such as in places of cyclonic circulation. Thus, there is a constant replacement of water at all depths and a transfer of its hydrological and hydrochemical characteristics from the surface to the bottom and vice versa.

Waves. In addition to the horizontal and vertical movements of water masses, the dynamics of the ocean includes waves caused by winds, tides, or earthquakes. Wind waves occur only in the upper layer of the ocean to average depths of 50–60 m; these waves are 12–13 m or more high. The prevailing height of ocean waves is about 4 m in the temperate latitudes and 1.5 m in the tropical latitudes. Tidal and seismic (tsunami) waves encompass the entire water mass. Tidal waves are a constant phenomenon in the ocean. There are also internal waves, formed at the boundary between water layers with different densities. Internal waves reach a height of several dozen meters. If the upper layer is thin and there is a large difference in density between the upper layer and the one beneath it, “dead water” occurs, making sailing difficult, especially in sailboats.

Tides. Tidal phenomena, both regular, almost periodic fluctuations in water level and tidal currents, play an important part in the ocean regimen. Semidiurnal tides predominate. Although they are not more than 1 m high in the open ocean, they reach 3–6 m along the coast. High tides are typical along the coasts of bays and marginal seas. In the Bay of Fundy along the Atlantic coast of Canada tides reach 18 m. In the western part of the Gulf of Mexico, the Java Sea, and other areas tides are diurnal and reach a height of 5.9 m (Sea of Okhotsk). In some places there are mixed tides—irregular semidiurnal or diurnal tides. In Pen-zhin Bay of the Sea of Okhotsk mixed tides reach 12.9 m. Tidal currents are particularly important in narrows, where they may reach velocities of more than 7 m per sec.

Intermixing. Through intermixing, the hydrological and hydrochemical properties of ocean water are transmitted from one layer to another and are equalized. These processes occur both vertically and horizontally (lateral intermixing). Intermixing may be molecular or turbulent. Turbulent intermixing is further subdivided into friction and convection intermixing. Friction intermixing is caused by the movement of water layers against each other and primarily takes the form of wind or tidal intermixing. Whereas wind intermixing occurs as far as the depth of wind-driven waves, tidal intermixing may encompass the ocean’s entire water mass. Unlike wind intermixing, which develops sporadically, tidal intermixing occurs at fairly regular intervals.

Convection, or density, intermixing is associated with irregularities in the density stratification of water layers, when the density of a higher layer increases or the density of a lower layer decreases because of a drop in temperature or rise in salinity in the first case and a rise in temperature in the second. Especially important is the convection that develops during the winter as the surface of the ocean cools (winter vertical circulation). It reaches considerable depths, and in some enclosed seas with a high salinity, such as the Red and Mediterranean seas, it extends to the bottom. When waters of different temperature and salinity are mixed, the density of the mixture increases. The differences in temperature and their absolute values are the primary factors. The lower the temperature of the waters and the greater the temperature differences, the greater is the increase in density and the deeper the intermixing. The increase in density during intermixing in zones where surface currents of different temperature and salinity converge causes the surface waters to sink to the depths.

Intermixing is highly important for marine life. The solar heat absorbed by the thin surface layer is distributed to the depths, the salinity of seawater is equalized, the abyssal and bottom waters receive oxygen, and the surface waters are enriched with nutrient (biogenic) substances that have accumulated in the deep waters. The richest fishing grounds are shallow waters with intensive intermixing, such as the Barents, North, and Azov seas and the waters off the coast of Newfoundland.

Water level. The ocean’s water level is constantly fluctuating, especially near shore, owing to tides, changes in atmospheric pressure, coastal runoff, the density of seawater, and winds. Thus there are both periodic and nonperiodic fluctuations. The periodic fluctuations associated with tides are either semidiurnal or diurnal and may be quite large. Changes in atmospheric pressure and other factors operating over extended periods cause seasonal variations in the water level. In some enclosed seas (Black, Azov, and Baltic) these fluctuations are greater than the tidal ones. Nonperiodic changes in the level are caused by winds and range from 1 to 3 m. When combined with a tidal rise in level, a wind-driven rise in level may reach great heights and sometimes cause disastrous coastal flooding, for example, the floods along the North Sea. There are also fluctuations that occur over centuries related to oscillatory movements of the earth’s crust and fluctuations in the volume of the world ocean.

Ice. Ice forms in the ocean at the high and temperate latitudes. At high latitudes the ice lasts several years because of the small amount of solar heat. The ice packs are carried by currents and wind to the temperate latitudes, where they melt. The ice reaches its greatest thickness (3–5 m) in the arctic. Annual ice forms in the temperate latitudes, primarily in seas with severe winters. In addition to sea ice, enormous masses of continental ice (icebergs) are found in the ocean. Most of the icebergs have broken off the glaciers of Antarctica, Greenland, Spitsbergen, and other polar islands. They are most common in the antarctic and in the northwestern Atlantic Ocean.

Color and transparency. The color and transparency of seawater are determined by its ability to absorb and disperse light rays. They also depend on the conditions of illumination of the ocean surface, changes in spectral composition, and reduction in light intensity. Where the water is very transparent it acquires the intense deep blue color characteristic of the open ocean. If there are many suspended particles strongly dispersing the light, the water takes on the blue-green or green color typical of coastal regions and certain enclosed seas. In places where large rivers flow into the ocean carrying many suspended particles, the color of the water acquires yellow and brown tints. The maximum relative transparency, defined as the depth at which a white disc 30 cm in diameter vanishes, was recorded in the Sargasso Sea of the Atlantic Ocean (66 m). In the Indian Ocean the maximum transparency is 40–50 m, and in the Pacific it is about 59 m. In the open ocean transparency generally decreases as one moves from the equator toward the poles, but it may also be considerable in the polar regions. Luminescence occurs everywhere in the ocean.

Zonation. The distribution of the sun’s energy throughout the ocean is unequal and follows the patterns of zonation. Latitudinal zonation occurs within water layers 150–200 m deep. Like dry land, the ocean has polar, subpolar, temperate, subtropical, tropical, and equatorial belts. Often the boundaries between these zones are clearly marked by fronts (convergence zones), where the characteristics and dynamics of the waters change abruptly, for example, the Kuroshio front in the Pacific Ocean and the Gulf Stream front in the Atlantic Ocean, the antarctic front, and the southern subtropical front.

Vertical zonation manifests itself in the sequence of surface, subsurface, intermediate, deep, and bottom water masses. In surface water masses, the processes caused by the active exchange of energy and matter with the atmosphere occur more intensively. The depth of this layer averages 150–200 m. Subsurface water masses lie at depths of 200–500 m. In low and temperate latitudes these water masses are characterized by increased salinity, and in low latitudes only, by higher temperatures. The intermediate water masses differ sharply from the waters above and below them: in polar latitudes they have higher temperatures and in temperate and tropical latitudes they have a lower salinity and a minimum oxygen content. The lower boundary of the intermediate water masses varies from 1,000 to 1,500 m in different parts of the ocean.

The deep water masses are characterized by their great thickness. Their lower boundary has been established at depths of 3,000–3,500 m. Although the deep waters of the ocean show a high degree of homogeneity, four or five different types of water are distinguished. These waters differ according to formation and especially salinity and oxygen content.

The bottom water masses occupy the deepest parts of the ocean, flowing from the polar regions through the basins and underwater depressions connecting them. The average thickness of the bottom water is 1,000–1,500 m; in the deep-sea trenches it may exceed 6,000 m. The most common bottom water in the ocean is antarctic water, which has a low temperature and is relatively rich in oxygen. In the Atlantic Ocean, antarctic water is found as high as 40° N lat., and in the Pacific it extends to the equator and in places to 10°–20° N lat.

Living organisms inhabit the ocean from the surface to its greatest depths. Based on place of habitation, a distinction is made between pelagic organisms, which inhabit the water layers, and benthic organisms, which inhabit the ocean bottom. Pelagic organisms are subdivided into passively floating plankton and actively swimming nekton. Of the plant organisms, only bacteria and certain lower fungi are found everywhere in the ocean. Bacteria play a major role in the biological, chemical, and geological processes of the ocean. They participate in the cycle of matter, induce oxidation-reduction processes, and assimilate organic matter from the water and bottom sediments, thus making it suitable for use by animals. The other plant organisms inhabit only the uppermost, illuminated layer of the ocean, generally extending to about 50–100 m, in which photosynthesis can occur. The photosynthesizing plants create the primary food on which the rest of the ocean population depends for life. About 10,000 species of plants live in the ocean. Diatoms form a large part of the phytoplankton, and peridiniums and coccolitho-phores predominate among the flagellates. The bottom plants, or phytobenthos, include primarily diatomaceous, green, brown, and red algae, as well as species of grassy flowering plants, such as eelgrass.

The animal life of the ocean is even more varied. Representatives of almost all the classes of present-day free-living animals inhabit the ocean, and many classes live only in the ocean. The ocean fauna includes more than 160,000 species: about 15,000 species of protozoans (primarily radiolarians, foraminifers, and infusorians), 5,000 species of sponges, about 9,000 species of coelenterates, more than 7,000 species of worms, 80,000 species of mollusks, more than 20,000 species of crustaceans, 6,000 species of echinoderms and less numerous representatives of other invertebrate groups (bryozoans, brachiopods, Pogonofora, tuni-cates), and about 16,000 species of fish. Excluding fish, vertebrates are represented by about 50 species of turtles and snakes and more than 100 species of mammals, chiefly whales and pinnipeds. About 240 species of birds, including penguins, albatrosses, and gulls, depend on the ocean.

The tropical regions typically have the greatest number of animal species. The bottom fauna is especially varied on shallow coral reefs. With increasing depth the diversity of life in the ocean decreases. The deepest parts of the ocean (more than 9,000–10,000 m) are inhabited only by bacteria and several dozen species of invertebrates.

The quantitative development of life varies greatly in different parts of the ocean. The amount of phytoplankton depends on the abundance of biogenic elements in the surface layers, primarily compounds of nitrogen, phosphorus, and silica. Because the deep waters of the ocean are rich in these substances, areas of intensive vertical circulation and upwelling of deep waters are especially favorable for the development of phytoplankton. Such regions include the fronts where cold and warm currents meet (for example, the Gulf Stream and the Labrador, Kuroshio, and Oyashio currents), divergence zones (for example, the equatorial divergence zone), and areas where the water level near shore is constantly lowered by wind action. The regions that are rich in phytoplankton have the greatest amount of zooplankton, which feeds on the phytoplankton, and nektonic animals, which eat the zooplankton.

The greatest quantitative development of the bottom population is found in shallow coastal regions in the temperate zones, where 1 sq m of the ocean floor contains up to several dozen kg of phytobenthos and zoobenthos. At great depths the bottom population lives on the organic residue that settles from the surface layers or is washed down from shallow coastal waters. Thus the most populous parts of the ocean bottom are near the continents or in places where life has developed most abundantly in the surface layers. The vast areas of the tropical ocean far from the coast (the oligotrophic regions) are poor in life in the pelagic and bottom zones.

The conditions for life in the ocean vary at different depths. With increasing depth, illumination decreases rapidly, the temperature drops, the hydrostatic pressure increases, and the amount of food decreases, resulting in vertical biological zonation. The ocean bottom has been divided into the following zones based on the distribution of life: littoral (inter tidal), sublittoral (to 200 m, its lower part is sometimes called elittoral), bathyal (to 2,500–3,000 m), abyssal (to 6,000 m), and hadal (deeper than 6,000 m). The boundaries between these zones are classified as transitional horizons. The vertical zonation of the population of the ocean waters is less clearly marked because of the ability of many pelagic animals to make vertical migrations. The ocean waters as an environment are generally divided into three zones: a surface, or epipelagic zone (to 150–200 m), a transitional, or mesopelagic zone (to 750–1,000 m), and a deep zone. The deep zone is subdivided into the bathypelagic (to 2,500–3,000 m), the abyssopelagic (to 6,000 m), and the hadal (deeper than 6,000 m) zones. Animal life in the ocean is also divided into zoogeographic zones.

Calcareous and siliceous skeletons of organisms are a highly important component of the bottom sediments of the ocean. Many marine organisms are commercially important either as food or as industrial raw material.

The ocean contains large biological resources. It produces 12–15 percent of the world’s animal protein and 3–4 percent of its animal fat. Excluding mammals, the world catch of fish and other marine products was 59.9 million tons in 1971 (in 1965 it was 45.6 million tons, and in 1970 it was 60.6 million tons). The seas and oceans account for more than four-fifths of the total world catch. The fishing industry is constantly working new regions of the ocean. Prior to 1939 more than 83 percent of the world catch came from the area north of 20° N lat.; in 1970 this zone produced only 40 percent of the world catch. In 1971 the Pacific Ocean accounted for 56 percent of the catch, the Atlantic Ocean for 39 percent, and the Indian Ocean for 5 percent. Fish constitute 90 percent of all marine products; various mollusks account for about 5 percent, crustaceans for about 3 percent, and water plants for about 1.5 percent. Marine mammals (whales, seals) are also commercially important; the catch in 1970 was more than 540,000 tons. World marine fishing is concentrated in about 25 percent of the ocean’s area, the chief fishing regions being located on the shelf. In 1971 the countries with the largest fish catch were Peru (10,600,000 tons, with a sharp decline in 1972–73), Japan (9,900,000), USSR (7,300,000), Norway (3,100,000), USA (2,800,000), India (1,800,000), Thailand (1,600,000), Spain (1,500,000), Denmark (1,400,000), Canada (1,300,000), Indonesia (1,250,000), the Republic of South Africa (1,100,000), and Iceland (700,000). The growing demand for the biological resources of the ocean and the use of sophisticated equipment has presented certain dangers. Unregulated and inefficient use of the ocean’s biological resources could lead to a depletion of the resources or to irreplaceable losses. The necessity for efficient use of marine animals and plants has posed the question of international cooperation in this area, in particular the protection of certain species. Artificial reproduction of the most valuable species of marine animals and plants is expected to become increasingly important.

Early knowledge about the ocean was accumulated along with geographic knowledge about the earth. The ancient Phoenicians, Egyptians, Greeks, Chinese, and other peoples who lived along seacoasts correctly understood some of the phenomena that they observed. Aristotle believed that the world ocean was a single entity and noted the presence of currents in the Kerch’, Bosporus, and Dardanelles straits. The further development of knowledge about the ocean is associated with the major geographic discoveries of the late 15th and early 16th centuries, primarily with the voyages of Vasco da Gama, Columbus, and Magellan. After the age of the great geographic discoveries, study of the ocean began developing rapidly. In 1650 the Dutch geographer B. Varenius was the first to divide the world ocean into five oceans: the Pacific, Atlantic, Indian, Arctic, and Antarctic. In 1845 the London Geographic Society confirmed this division. Subsequently O. Krümmel in Germany (1878) and Iu. M. Shokal’skii in Russia (1917) argued that there were only three oceans—the Pacific, Atlantic, and Indian—classifying the Arctic Ocean as a sea of the Atlantic. After conducting comprehensive studies of the arctic basin, the Soviet Union officially declared the Arctic to be a separate ocean in 1935.

In 1664 the German A. Kircher compiled the first map of marine currents-based on the observations of navigators. In 1725, L. Marsigli first described the ocean bottom as consisting of sedimentary rock and measured water temperature at different depths in the Mediterranean. In 1749, Captain H. Ellis was the first to measure temperature at depths to 1,630 m off the northwest coast of Africa. In 1770, B. Franklin in the American colonies compiled the first map of the Gulf Stream and established that wind was the principal cause of marine currents. Of great importance was the theory of tides put forward by the English scientist I. Newton in 1687 and subsequently developed by D. Bernoulli in Switzerland in 1740 and by P. S. Laplace in France between 1799 and 1825. During this period the theory of waves was being developed by Newton (1726), Laplace (1776), J. Lagrange (1786), and F. Gerstner (1802).

In the early 19th century the Russian scientists E. Lenz and E. Parrot invented the bathometer and depth gauge. In 1832 they conducted experiments demonstrating the effect of pressure on water temperature. In 1854 the American J. M. Brooke invented a sounding line with a disengaging lead and a dredge for collecting ground samples and bottom organisms.

I. F. Kruzenshtern and Iu. F. Lisianskii led the first Russian round-the-world expedition on the Nadezhda and Neva from 1803 to 1806. During the expedition they measured water temperatures at great depths, studied the density and color of ocean water and marine currents, conducted biological investigations, and made depth measurements. Equally important were the voyages of the Predpriiatie from 1823 to 1826, during which E. Lenz made the first precise oceanographic measurements. During the voyages of the Beagle the English naturalist C. Darwin conducted extensive biological research. The expedition headed by F. F. Bellingshausen and M. P. Lazarev on the Vostok and Mirnyi from 1819 to 1821 led to the discovery of the coast of Antarctica and made a significant contribution to the classification of antarctic ice and the study of its physical and chemical properties. The first coastal observation points were established at this time. A notable advance was the invention of the tide gauge for measuring sea level by the Russian navigator F. P. Litke in 1839; tide gauges were later installed along the Arctic and Pacific coasts.

In 1819 the French scientist A. Marcet established the temperature of water at its greatest density, and in 1837 the Belgian S. Depres determined the freezing point of water and demonstrated that both of these temperatures depended on the salinity of the water. In 1842, G. Airy in Great Britain expanded the theory of tides. In 1862 W. Froude, an Englishman, made numerous studies of sea waves using the spar buoy which he had designed. Between 1840 and 1850 M. F. Maury, an American, compiled several maps of currents for the pilot books that he was publishing. In 1845, Lenz proposed the first diagram of the vertical circulation of ocean waters. During the 1850’s Maury compiled the first map of the topography of the bottom in the northern part of the Atlantic Ocean, and in 1872 the English geologist J. Prestwich gave the first description of the temperature stratification of the ocean. In 1865 the Danish scientist J. Forchhammer established the constancy of the chemical composition of seawater, and from 1868 to 1870 W. B. Carpenter and W. Thomson of Great Britain chemically analyzed ocean water and the gases contained in it. Scientific study of the living organisms inhabiting the ocean began at this time, and it was shown that they inhabit not only the surface layer but also the depths. In 1851 the American D. V. Baley established that the organic part of bottom sediments consists of remnants of dead organisms (diatoms, radiolarians).

The first oceanographic expedition was made between 1872 and 1876 on the Challenger. The voyage marked the beginning of special oceanographic expeditions and the development of new equipment and observation methods. Between 1872 and 1882 the English scientist Dittmar, using the findings of the Challenger expedition, confirmed the constancy of the chemical composition of ocean water and the predominance of chlorides in it. In 1902 the Dane M. Knudsen developed a method for determining the salinity of water by its chlorine content and compiled tables of water salinity and density. In the late 19th and early 20th centuries international and national oceanographic institutions and coastal stations were organized. The International Council for the Exploration of the Sea, founded in 1902, introduced uniform methods for oceanographic measurements and standardized horizons and cross sections used for repeated observations.

The Challenger expeditions stimulated many other scientific voyages, including those of S. O. Makarov on the Vitiaz’ (Russia, 1886–89), A. Agassiz on the Albatross (United States, 1888–1905), the Meteor (Germany, 1925–27), the Manshu (Japan, 1925–28), and the Discovery II (Great Britain, 1929–39). The Gulf Stream, the Kuroshio Current, Antarctica, and the Arctic Ocean were systematically studied. In the USSR special attention was given to the study of adjacent seas, and by the late 1930’s they were the most thoroughly studied regions of the world ocean.

In 1905 the Swede V. W. Ekman developed the theory of drift currents. In 1903 the Norwegians J. W. Sandström and B. Helland-Hansen worked out a dynamic method of calculating currents based on V. Bjerkness’ theory. The method was perfected by the Soviet scientist N. N. Zubov in 1935. Between 1912 and 1916 Helland-Hansen developed a method of analyzing temperature-salinity curves in studying the structure of the ocean and the processes of water mixing. The Soviet scientist V. B. Shtokman later worked on this problem. In 1907 the English astronomer G. Darwin proposed a simplified method for the harmonic analysis of tides, and in 1922, Sterneck compiled the first map of cotidal lines for the world ocean. Important work on the theory of tides and the methods of forecasting them was done by A. Defant (Austria, 1923), J. Proudman (Great Britain, 1924), and A. Doodson (Great Britain, 1924, 1928), as well as by the Soviet scientists N. E. Kochin (1938), L. N. Sretenskii (1936), and V. V. Shuleikin (1938).

Oceanographic research in the USSR began after the founding of the Floating Marine Institute in accordance with a decree signed by V. I. Lenin in 1921 and the launching of the research ship Persei. In 1929 the Floating Marine Institute was transformed into the Oceanographic Institute, which was reorganized as the All-Union Institute of Fisheries and Oceanography in 1933. The Institute for the Study of the North, now the Arctic and Antarctic Scientific Research Institute, was established in 1925. In 1929 the first marine hydrophysical station was established in the Crimea under the direction of V. V. Shuleikin. It later became the Marine Hydrophysical Institute of the Academy of Sciences of the USSR. The State Oceanographic Institute was set up in 1943, and in 1946 P. P. Shirshov founded the Institute of Oceanography of the Academy of Sciences of the USSR.

Prior to the 1940’s oceanographic expeditions concentrated on describing ocean and sea basins and studying the most important physical and chemical properties of water, currents, tides, waves, ice, and other marine phenomena. The investigations were usually confined to specific regions or particular regimes and made extensive use of the methods of climatology, cartography, and other fields of geography. Major contributions to oceanography were made by the Soviet scientists Iu. M. Shokal’skii, N. M. Knipovich, K. M. Deriugin, Vs. A. Berezkin, and V. Iu. Vize; by the Norwegians H. Sverdrup and F. Nansen; by the Germans O. Krümmel, G. Wüst, and G. Schott; by the Japanese K. Suda; by the Swede S. O. Pettersson; and by the American R. Icelin.

The second half of the 1940’s saw the rapid development of all aspects of oceanography. By the 1970’s the world expeditionary fleet numbered more than 120 vessels with displacements of 500 tons or more, provided with the latest technical equipment and devices. Several major international expeditions have been undertaken since 1955. The NorPac Expedition of 1955 studied the northern Pacific, and oceanographic programs were part of the International Geophysical Year (1957–58). The equatorial zone of the Atlantic was studied by the Equalant Expedition in 1963–64, the Kuroshio Current by the Sic Expedition begun in 1965, and the tropical zone of the Atlantic by the Tropex Expedition in 1974.

Oceanographic research has begun to stress protection of the marine environment and its biological resources and the study of the ocean’s energy and mineral resources. Experimental and theoretical research is now directed primarily toward developing quantitative methods of. studying the ocean’s physical environment and toward working out methods of calculating and predicting waves, water level and temperature, and other properties of the ocean. During the 1950’s and 1960’s theoretical generalizations were derived from observations made on all the oceans and seas, and scientists discovered the principles of the formation and variability of the thermohaline and dynamic structure of oceans and seas. Oceanographers established the laws of the horizontal and vertical exchange of chemical substances (primarily nutrient salts) that depends on the state of the ocean’s physical environment. Among other important problems being studied are the chemical pollution of sea and ocean waters and the protection of the marine environment.

Biological research has greatly increased our knowledge about the morphology and ecology of marine organisms. The biological structure of the ocean has been determined, and estimates of the biomass are being made. Scientists are studying problems of controlling biological productivity and of forecasting and regulating commercial fishing.

Investigations of the topography of the ocean bottom have identified distinct relief forms and shown their distribution, and relief-forming factors have been determined. Oceanographers are studying the interaction of the ocean’s physical environment with the bottom’s complex topography. The general characteristics of the ocean floor’s geological structure have been determined, and deposits of minerals have been discovered in various regions.

In recent years major contributions to the study of the ocean have been made by Soviet and foreign scientists. The physical environment of the ocean has been studied by V. V. Shuleikin, N. N. Zubov, and V. V. Timonov in the USSR; H. M. Stommel and R. Revelle in the United States; N. J. Campbell and R. W. Stewart in Canada; G. E. Deacon, J. C. Swallow, and H. Charnock in Great Britain; H. Lacombe in France; and I. Matsuzawa, M. Uda, and K. Hidaka in Japan. Among prominent scientists studying the chemistry of the ocean are O. A. Alekin, L. K. Blinov, and S. V. Bruevich in the USSR; D. E. Fisher and R. H. Fleming in the United States; M. Waldichuk and W. L. Ford in Canada; and I. Imai and K. Sugawara in Japan. Important work in marine biology has been done by V. G. Bogorov and L. A. Zenkevich in the USSR; J. D. Isaacs and W. M. Chapman in the United States; C. E. Lucas in Great Britain; and R. Marumo and I. Matsui in Japan.


Morskoi atlas, vols. 1–2. Leningrad, 1950–53.
Shokal’skii, Iu. M. Okeanografiia, 2nd ed. Leningrad, 1959.
Frolov, Iu. S. “Novye fundamental’nye dannye po morfometrii Mirovogo okeana.” Vestnik LGU, 1971, no. 6.
Carrington, R. Biografiia moria. Leningrad, 1966. (Translated from English.)
Istoshin, Iu. V. Okeanologiia. Leningrad, 1969.
Dietrich, G. Obshchaia okeanografiia. Moscow, 1962. (Translated from German.)
Okean (collection of articles). Moscow, 1971. (Translated from English.)
Shepard, F. P. Morskaia geologiia, 2nd ed. Leningrad, 1969. (Translated from English.)
Leont’ev, O. K. Dno okeana. Moscow, 1968.
Belousov, V. V. Zemnaia kora i verkhniaia mantiia okeanov. Moscow, 1968.
Geologiia i geofizika morskogo dna. Moscow, 1969. (Translated from English.)
Issledovaniia po probleme riftovykh zon Mirovogo okeana, vols. 1–2. Moscow, 1972.
Sistema riftov Zemli. Moscow, 1970. (Translated from English.)
Fourmarier, P. Problemy dreifa kontinentov. Moscow, 1971. (Translated from French.)
Vinogradov, A. P. Vvedenie v geokhimiiu okeana. Moscow, 1967.
Lisitsyn, A. P. Osadkoobrazovanie v okeanakh. Moscow, 1974.
Sovremennye osadki morei i okeanov. Moscow, 1961.
Mero, J. L. Mineral’nye bogatstva okeana. Moscow, 1969. (Translated from English.)
Kalinko, M. K. Neftegazonosnost’ akvatorii mira. Moscow, 1969.
Initial Reports of the Deep Sea Drilling Project, vols. 1–20. Washington, 1969–73.
Zubov, N. N. Dinamicheskaia okeanologiia. Moscow-Leningrad, 1947.
Ierlov, N. G. Opticheskaia okeanografiia. Moscow, 1970. (Translated from English.)
Shuleikin, V. V. Fizika moria, 4th ed. Moscow, 1968.
Alekin, O. A. Khimiia okeana. Leningrad, 1966.
Lacombe, H. Energiia moria. Moscow, 1972. (Translated from French.)
Lacombe, H. Fizicheskaia okeanografiia. Moscow, 1974. (Translated from French.)
Defant, A. Physical Oceanography, vols. 1–2. Oxford, 1961.
Sverdrup, H. U., M. W. Johnson, and R. H. Fleming. The Oceans, Their Physics, Chemistry, and General Biology. Englewood Cliffs, N.J., 1957.
Zenkevich, L. A. Fauna i biologicheskaia produktivnost’ moria, vols. 1–2. Moscow, 1947–51.
Moiseev, P. A. Biologicheskie resursy Mirovogo okeana. Moscow, 1969.
Bogorov, V. G. Plankton Mirovogo okeana. Moscow, 1974.
Hela, I., and T. Laevastu. Promyslovaia okeanografiia. Moscow, 1970. (Translated from English.)
Okean i chelovechestvo. Moscow, 1968.
Mikhailov, S. V. Mirovoi okean i chelovechestvo. Moscow, 1969.
Osokin, S. D. Mirovoi okean (Ocherki o prirode i ekonomike). Moscow, 1972.


The international law of the ocean includes the regulation of six important spheres of human activity connected with the world ocean: the use of ocean waters, merchant shipping, military navigation, scientific research in the ocean, study of the seabed, and protection of the marine environment. The law determines the rights, duties, and responsibilities of all countries, including those without a seacoast.

The legal regulation of the ocean is included in international treaties and customary laws, as well as in the domestic legislation of various countries. International organizations also play an important part in the legal regulation of the ocean. The principal organizations are the Intergovernmental Maritime Consultative Organization (IMCO), the UNESCO Oceanographic Commission, the UN Committee on the Peaceful Uses of the Seabed and the Ocean Floor Beyond the Limits of National Jurisdiction, and the UN Committee on Maritime Law.

The international law of ocean waters includes the regulation of the internal seas of countries with access to the sea, territorial waters, and the waters of the open sea.

There are also specially regulated zones in different parts of the ocean, such as fishing grounds, areas set aside for the protection of the living resources of the open sea, and areas that are temporarily dangerous for navigation because of weapons testing. The size of these areas and the procedure for their establishment must conform to the general principles and norms of contemporary international law, the UN Charter, the 1958 Geneva conventions on maritime law, and other international treaties and agreements. Of special importance is the legal regulation of international straits and canals.

Merchant shipping is regulated by international law to promote unrestricted commercial navigation by all countries on the basis of equality and mutual advantage and to ensure the safe conveyance of passengers and cargo. International maritime law also aims to ensure the legal status of commercial vessels and their crews, passengers, and cargo both on the open sea and in foreign waters and ports, as well as the immunity of state merchant ships. The norms that establish responsibility for violation of the rules of commercial navigation are highly important. Such matters are regulated by contracts and bilateral agreements concerning trade and navigation, for example, the 1973 agreements on maritime shipping between the USSR and the United States. Accountability is also treated in such international conventions as the convention on unifying certain rules relating to ship collisions (1910), the convention on standardizing certain rules regarding bills of lading (1924), and the convention on standardizing certain rules concerning accountability arising from ship collisions (1973). The international commercial navigation of the USSR and other socialist countries is regulated by the General Conditions for Delivery of Maritime Tonnage and Foreign-trade Cargoes of COMECON countries, adopted in 1972. In the USSR, the norms governing commercial navigation are contained in the Maritime Code of the USSR.

The international law of military navigation aims to promote freedom of military navigation by all countries, to ensure the safety of military navigation, to prevent incidents at sea, and to maintain law and order on the seas and oceans. The regulation of military navigation presupposes special rights for military ships on the high seas, such as the right to pursue violators of the law at sea and the right to combat piracy, slave trading, and certain other international crimes. Military ships enjoy immunity, privileges, and rights both on the high seas and in foreign territorial waters and ports. Norms have been established to regulate the procedure by which military ships may enter foreign waters (with authorization or notification) and the special legal status of the crew on shore in a foreign country. There are also norms that establish the rules of naval warfare and the rights of neutral countries in sea warfare, define the concept of contraband and naval blockade, and prescribe the procedure for stopping, examining, searching, and seizing foreign vessels. Military navigation is regulated by the Geneva conventions of 1958 and by treaties on demilitarized and neutral territories, for example, the 1971 seabed treaty and the 1972 agreement between the USSR and the United States on preventing incidents on the high seas and the air space above them. Military navigation is also regulated by the domestic legislation of the various countries, in the USSR, for example, by the 1960 Statute on the Protection of the State Border of the USSR, by the 1960 Rules for Visits by Foreign Military Ships to the Territorial Waters and Ports of the USSR, and by the Naval Regulations of the USSR.

The international law of fisheries has been established to ensure the efficient obtaining of marine resources without disrupting the reproduction of the ocean’s biomass. Coastal countries give their citizens preferential or exclusive rights to take fish and other marine products from fishing grounds adjoining their territorial waters. There are many multilateral and bilateral agreements regulating the taking of fish and other marine products on the high seas. Among the agreements to which the USSR has adhered are the 1949 Convention on Fishing in the Northwestern Atlantic Ocean, the 1958 Geneva Convention on Fishing and the Conservation of the Living Resources of the High Seas, the 1946 Convention on Regulation of Whaling, and the 1957 Convention on the Conservation of Fur Seals in the Northern Pacific Ocean. Of special importance is a 1972 declaration issued by six socialist countries concerning the principles of efficient exploitation of the living resources of the ocean in the common interest of all peoples.

The international law of scientific research, one of the less developed branches of maritime law, is intended to ensure favorable conditions for conducting comprehensive investigations of the ocean, as well as studies of the atmosphere and outer space from marine waters. The activity of research ships in various parts of the ocean is governed by the status of the bodies of water, the “right of the flag,” and the principle of freedom of the high seas. In 1973 an important agreement on cooperation in marine research was concluded between the USSR and the United States.

The international law of the seabed is also a little developed aspect of contemporary international maritime law. Unlike commercial and military navigation, for example, industrial activity on the ocean bottom (and also protection of the marine environment) is a “nontraditional” use of the sea that developed in the 1960’s and early 1970’s and necessitated legal regulation. In this branch of maritime law the most clearly resolved questions are those relating to the continental shelf. The seabed beyond the continental shelf may be used exclusively for peaceful purposes by all countries without any discrimination. Exploration and the exploitation of natural resources on the ocean bottom must not conflict with the principles of freedom of navigation, fishing, and scientific research.

The international legal protection of the ocean environment aims at preserving the marine environment and the ocean’s ecological balance and preventing contamination of the ocean, particularly radioactive contamination. It also seeks to prevent disruption of existing biological, chemical, and physical ratios and processes and damage to the ocean’s flora and fauna, seabed, and the atmosphere above the ocean. There are international conventions and domestic laws to combat pollution and contamination of the marine environment, for example, the 1954, 1962, 1969, 1972, and 1973 conventions on combating petroleum pollution. The radioactive contamination of the ocean is forbidden under the 1958 Geneva Convention on the High Seas and the 1963 Treaty Banning Nuclear Weapon Tests in the Atmosphere, Outer Space, and Under Water.

The legal regulation of the air space above ocean waters is closely related to the legal regime of those ocean waters. Thus, the air space above the internal or territorial waters of a particular country are under its full and exclusive jurisdiction, and no country has the right of “peaceful flight” over such waters without the permission of the coastal country. Regular international flights follow air routes established by international agreements, and occasional flights are made only with the permission of the appropriate country. The air space above the open sea is freely used by all countries and all aircraft.

Observation of the norms of international maritime law on the ocean is an important factor in developing international cooperation and securing peaceful coexistence among states with different social systems. It presupposes a stable rule of law—a system of relations among countries, established by international law, regulating international travel on the ocean and use of the ocean as a source of natural and mineral wealth and of scientific knowledge.


Aktual’nye problemy sovremennogo mezhdunarodnogo morskogo prava. Moscow, 1972.
Okean, tekhnika, pravo. Moscow, 1972.
Gureev, S. A. Kollizionnye problemy morskogo prava. Moscow, 1972.
Kolodkin, A. L. Mirovoi okean: Mezhdunarodno-pravovoi rezhim, Osnovnye problemy. Moscow, 1973.




an island in the western Pacific Ocean at 0° 52′ S lat. and 169° 32′ E long. Area, 6.5 sq km. Population, 2,100 (1969).

Ruled by Great Britain as part of the Gilbert Islands territory, Ocean Island is an atoll rising to 80 m above sea level and is fringed by coral reefs. Its large phosphorite deposits yielded 509,000 tons in 1970. The island was discovered in 1804 by British sailors, who named it after their ship.

What does it mean when you dream about the ocean?

The meaning of a dream about the sea can vary, depending on whether the ocean is a vast, imposing body of water, or a peaceful sea beside a resort. The sea can have waves as high as a thirty-story building, or be as calm and clear as a piece of glass. Sailing the high seas may give a sense of elation, or lead to a feeling of helplessness, especially if the dreamer is lost at sea. Unless tied to specific experiences near the water, the sea often represents the state of our emotions and/or the unconscious mind.


The interconnected body of salt water that occupies almost three-quarters of the earth's surface.


1. a very large stretch of sea, esp one of the five oceans of the world, the Atlantic, Pacific, Indian, Arctic, and Antarctic
2. the body of salt water covering approximately 70 per cent of the earth's surface


It traditionally represents our great unconscious, memories, emotions, and individual soul and collective experiences. Look at all of the details in this dream. Is the water clear or murky? Is it calm or turbulent? Are you catching fish, or are you stranded and afraid? Look, listen, and try to comprehend the messages in this dream. No one is in a better position to give meaning to your dreams than you. Concentrate and learn for yourself.
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