10.10.2019

>What is water salinity? Salinity of the waters of the World Ocean. Properties of sea water. Fresh balance Our planet is covered with water by 70%, of which more than 96% is occupied by oceans. It means that most of

The water on Earth is salty. What is water salinity? How is it determined and what does it depend on? Is it possible to use such water on the farm? Let's try to answer these questions.

What is water salinity? Most of the water on the planet has salinity. Usually it is called sea ​​water

and is found in oceans, seas and some lakes. The rest is fresh, its amount on Earth is less than 4%. Before you understand what the salinity of water is, you need to understand what salt is. Salts are complex substances

, which consist of cations (positively charged ions) of metals and anions (negatively charged ions) of acid bases. Lomonosov defined them as “fragile bodies that can dissolve in water.” There are many substances dissolved in sea water. It contains sulfates, nitrates, phosphates, cations of sodium, magnesium, rubidium, potassium, etc. Together these substances are defined as salts.

So what is water salinity? This is the content of substances dissolved in it. It is measured in parts per thousand - ppm, which are designated by a special symbol - %o. Permille determines the number of grams in one kilogram of water.

What determines the salinity of water? IN different parts hydrosphere and even in different times

• The salinity of the water varies throughout the year. It changes under the influence of several factors:
• evaporation;
• ice formation;
• precipitation;
• melting ice;
• river flow;

currents.

When water evaporates from the surface of the oceans, salts remain and do not erode. As a result, their concentration increases. The freezing process has a similar effect. Glaciers contain the largest reserve of fresh water on the planet. During their formation, the salinity of the waters of the World Ocean increases.

Melting glaciers have the opposite effect, reducing the salt content. In addition to them, the source of fresh water is precipitation and rivers flowing into the ocean. The level of salts also depends on the depth and nature of the currents. positive side, cold ones, on the contrary, reduce it.

Salinity of the World Ocean

What is the salinity of sea water? We already know that it is far from the same in different parts of the planet. Its indicators depend on geographic latitudes, climatic features of the area, proximity to river objects, etc.

The average salinity of the waters of the World Ocean is 35 ppm. Cold areas near the Arctic and Antarctic are characterized by lower concentrations of substances. Although in winter, when ice forms, the amount of salts increases.

For the same reason, the least saline ocean is the Arctic Ocean (32%). The highest content is noted Indian Ocean. It covers the Red Sea and Persian Gulf region, as well as the southern tropical zone, where salinity is up to 36 ppm.

The Pacific and Atlantic oceans have approximately equal concentrations of substances. Their salinity decreases in the equatorial zone and increases in subtropical and tropical regions. Some are warm and balance each other out. For example, the non-salty Gulf Stream and the salty Labrador Current in the Atlantic Ocean.

Salinity of lakes and seas

Most lakes on the planet are fresh, as they are fed mainly by sediments. This does not mean that there are no salts in them at all, just that their content is extremely low. If the amount of dissolved substances exceeds one ppm, then the lake is considered saline or mineral. The Caspian Sea has a record value (13%). The largest fresh lake is Baikal.

The concentration of salts depends on how the water leaves the lake. Fresh water bodies are flowing, while saltier ones are closed and subject to evaporation. The determining factor is also the rocks on which the lakes were formed. Thus, in the region of the Canadian Shield, rocks are poorly soluble in water, which is why the reservoirs there are “clean”.

The seas are connected to the oceans through straits. Their salinity is slightly different and affects the average values ​​of ocean waters. Thus, the concentration of substances in the Mediterranean Sea is 39% and is reflected in the Atlantic. The Red Sea, with an indicator of 41%o, greatly raises the average. The saltiest is the Dead Sea, in which the concentration of substances ranges from 300 to 350%o.

Properties and significance of sea water

Not suitable for economic activity. It is not suitable for drinking or watering plants. However, many organisms have long adapted to life in it. Moreover, they are very sensitive to changes in its salinity level. Based on this, organisms are divided into freshwater and marine.

Thus, many animals and plants that live in the oceans cannot live in the fresh water of rivers and lakes. Edible mussels, crabs, jellyfish, dolphins, whales, sharks and other animals are exclusively marine.

People use fresh water for drinking. Salted water is used for medicinal purposes. Water with sea salt is consumed in small quantities to restore the body. The healing effect comes from swimming and bathing in sea water.

Water is a very good solvent. Rain breaks down rocks on land, small debris, gravel, sand and dissolved chemical substances are carried by streams into rivers, which carry them to the seas and oceans. The water heated by the sun evaporates, and the brought sediments and chemicals accumulate in the seas and oceans. Therefore, almost all substances known on Earth are dissolved in sea water.

The majority of salts in it are chlorides (89%) and sulfates (11%), which give the water a bitter-salty taste. Even during round the world expedition The Challenger noted that the amount of salts dissolved in ocean waters can vary significantly, but the ratio of salts that determine the salinity of waters is the same in all areas of the World Ocean. The constancy of the salt composition is an important feature of sea water.

The salinity of sea water is the content in grams of all minerals dissolved in 1 liter of sea water. Salinity is expressed in g/l, that is, in thousandths - ppm and is designated S (% - approx.. The average salinity of the World Ocean is 35%, that is, each liter of water contains 35 grams of minerals. However, this indicator is not the same everywhere. Where there is more precipitation and evaporation is low, the salinity is lower, and it is also lowered by river waters and melting ice. The salinity of ocean waters is influenced by currents: they transport saltier and warmer waters towards high latitudes, and from temperate latitudes towards them. equatorial regions receive less saline waters.

For example, the waters of the Gulf Stream, a powerful warm current directed from equatorial latitudes to the Arctic Ocean, have a higher salinity than the salinity of the ocean waters through which this current passes. And the cold Labrador Current, originating in polar latitudes, reduces salinity off the eastern coast of North America.

In general, salinity decreases towards high latitudes; it is also low in equatorial regions, where there is a lot of precipitation and evaporation is somewhat reduced, while in tropical latitudes salinity is increased.

The salinity of inland seas, connected to the oceans only by narrow straits, is very different from open ocean basins. For example, average salinity Atlantic Ocean- 35.4%, and its internal Baltic Sea - 10-12% (in the bays 2-6% - approx. This is explained by the fact that in the temperate climate zone, where the Baltic Sea is located, there is a large amount of precipitation and, moreover, many rivers carrying fresh water flow into the sea. If little fresh water enters the sea, and evaporation is significant, then its salinity turns out to be greater than the salinity of the ocean to which the sea belongs, for example, the salinity of the Red Sea is 40-42%.

The average temperature of the surface layer of the World Ocean is +17.5 °C; the temperature drops with depth and does not exceed 2 °C deeper than 1 km. The sun heats only the surface of the ocean; this heat is transferred into the thickness of the ocean by mixing and currents. In equatorial latitudes, water heats up to 27-28 °C, and in polar regions it drops to 0 °C and below. The highest surface water temperature is in the Pacific Ocean (+19.4 °C), followed by the Indian (+17.3 °C) and Atlantic (+16.5 °C) oceans, the lowest water temperature is in the Arctic Ocean ( -1 °C).

Extraction of sea salt. Antique engraving

THE MOST IMPORTANT WEALTH OF THE OCEAN

If all the salt from the waters of the World Ocean is evaporated and then evenly distributed over the surface of the land, you will get a layer about 150 m thick. According to rough estimates, the cost of the chemical elements contained in 1 km3 of sea water is estimated at 1 billion euros. But how to obtain these substances? Scientists offer different methods, but they are all extremely expensive and labor-intensive, since the composition of sea water is very complex and the content of useful substances per unit volume is negligible.

Today, only magnesium, bromine, and table salt are extracted from sea water on an industrial scale, which is evaporated in the sun in artificial shallow reservoirs. Every year, up to 60 million tons of table salt are obtained from sea water, which is about 3 5% of world production.

WHY IS SEA WATER BLUE?

The sun's rays are partially reflected from the surface of the water, and refracted at the interface between the air and water. Getting into the water column, they are scattered and absorbed - approx. Violet and blue rays of the solar spectrum, which have a short wavelength, are scattered more strongly and are absorbed less than long-wavelength red and yellow rays. Due to the fact that red and yellow rays are poorly scattered and are more strongly absorbed by water, they are not visible. Sea water is colored blue, blue or greenish. Impurities change the color of the water towards green. Therefore, in shallow water and in the open ocean, where there are many impurities in the water, it has green tints. The water of the open ocean and deep seas, which contains fewer impurities, is blue.

Violet and blue rays of the solar spectrum are reflected from the surface of the water more than red and yellow ones, which are intensely absorbed

Among the properties of the waters of the World Ocean, temperature and salinity are distinguished.

Water temperature The world's oceans change in the vertical direction (decreases with depth, since the sun's rays do not penetrate to great depths) and horizontally (the temperature of surface waters decreases from the equator to the poles from +25 ° C to - 2 ° C due to the difference in the amount of water received solar heat).

Surface water temperature. Ocean water is heated by the influx of solar heat onto its surface. The temperature of surface waters depends on the latitude of the place. In some areas of the ocean, this distribution is disrupted by the uneven distribution of land, ocean currents, constant winds, and water runoff from the continents. Temperature naturally changes with depth. Moreover, at first the temperature drops very quickly, and then quite slowly. The average annual temperature of the surface waters of the World Ocean is +17.5 °C. At a depth of 3-4 thousand m it usually ranges from +2 to 0 °C.

Salinity of the water of the World Ocean.

Ocean water concentrates different salt: sodium chloride (gives water a salty taste) - 78% of the total amount of salts, magnesium chloride (gives water a bitter taste) - 11%, other substances. The salinity of sea water is calculated in ppm (the ratio of a certain amount of substance to 1000 weight units), denoted ‰. The salinity of the ocean varies, it varies from 32‰ to 38‰.

The degree of salinity depends on the amount of precipitation, evaporation, and desalination of rivers flowing into the sea. Salinity also changes with depth. To a depth of 1500 m, salinity decreases slightly compared to the surface. Deeper down, changes in water salinity are insignificant; it is 35‰ almost everywhere. The minimum salinity is 5‰ in the Baltic Sea, the maximum is up to 41‰ in the Red Sea.

Thus, water salinity depends : 1) on the ratio of precipitation and evaporation, which varies depending on geographical latitude(because temperature and pressure changes); Salinity may be lower where the amount of precipitation exceeds evaporation, where the influx of river water is large, where the ice is melting; 2) from depth.

Table “Properties of ocean waters”

Geological activity of oceans and seas

Features of the relief of the ocean floor

Destructive and accumulative activities of the sea

Sedimentation in seas and oceans

General information about the World Ocean

Ocean– continuous water shell Lands surrounding continents and islands and having a common salt composition. The World Ocean makes up 94% of the hydrosphere and occupies 70.8% of the earth's surface. It is a giant depression of the earth's surface, containing the bulk of the hydrosphere - about 1.35 km 3. Parts of the World Ocean separated by land or elevated underwater relief and differing from the open part of the ocean in hydrological, meteorological and climatic regime are called seas. Conventionally, some open parts of the oceans (Sargasso Sea) and large lakes (Caspian Sea) are also called seas. From a geological point of view, modern seas are young formations: all of them took shape close to modern ones in Paleogene-Neogene times, and were finally formed in the Anthropocene. The formation of deep seas is associated with tectonic processes; shallow seas usually arose when the marginal parts of continents (shelf seas) were flooded by the waters of the World Ocean. The flooding of these areas could be due to two reasons: 1) a rise in the level of the World Ocean (due to the melting of Quaternary glaciers) or 2) subsidence of the earth's crust.

Salinity and composition of sea waters. The average salinity of the waters of the World Ocean is about 35 g/kg (or 35 ‰ - 35 ppm). However, this value is different in different parts of the World Ocean and depends on the degree of connection with the open ocean, climate, proximity to the mouths of large rivers, melting ice, etc.: in the Red Sea salinity reaches 42‰, while in the Baltic it exceeds 3 -6‰. Maximum salinity is observed in lagoons and bays separated from the sea, located in arid regions. Another reason for abnormally high salinity may be the supply of salts with hot aqueous solutions, which is observed in areas with an active tectonic regime; in some bottom areas of the Red Sea, where thermal brines emerge, salinity reaches 310‰. Minimum salinity is typical for seas that have a difficult connection with the ocean and receive a significant amount of river water (the salinity of the Black Sea is 17-18‰), and water areas near the mouths of large rivers.

Sea water is a solution containing more than 40 chemical elements. The sources of salts are river runoff and salts entering during the process of volcanism and hydrothermal activity, as well as during underwater weathering of rocks - halmyrolysis. The total mass of salts is about 49.2 * 10 15 tons, this mass is enough for the evaporation of all ocean waters to cover the surface of the planet with a layer 150 m thick. The most common anions and cations in waters are the following (in descending order): among the anions Cl -, SO 4 2-, HCO 3 -, among the anions Na +, Mg 2+, Ca 2+. Accordingly, in terms of layers greatest number accounts for NaCl (about 78%), MgCl 2, MgSO 4, CaSO 4. The salt composition of sea water is dominated by chlorides (while river water contains more carbonates). It is noteworthy that the chemical composition of sea water is very similar to the salt composition of human blood. The salty taste of water depends on the sodium chloride content in it; the bitter taste is determined by magnesium chloride, sodium and magnesium sulfates. The slightly alkaline reaction of sea water (pH 8.38-8.40) is determined by the predominant role of alkaline and alkaline earth elements - sodium, calcium, magnesium, potassium.

A significant amount of gases are also dissolved in the waters of the seas and oceans. These are mainly nitrogen, oxygen and CO 2 . At the same time, the gas composition of sea waters is somewhat different from the atmospheric one - sea water, for example, contains hydrogen sulfide and methane.

Most of all, nitrogen is dissolved in sea water (10-15 ml/l), which, due to its chemical inertness, does not participate and does not significantly influence sedimentation processes and biological processes. It is assimilated only by nitrogen-fixing bacteria that are capable of converting free nitrogen into its compounds. Therefore, compared to other gases, the content of dissolved nitrogen (as well as argon, neon and helium) changes little with depth and is always close to saturation.

Oxygen entering waters during gas exchange with the atmosphere and during photosynthesis. It is a very mobile and chemically active component of sea waters, therefore its content is very different - from significant to negligible; in the surface layers of the ocean its concentration usually ranges from 5 to 9 ml/l. The supply of oxygen to the deep ocean layers depends on the rate of its consumption (oxidation of organic components, respiration, etc.), on the mixing of waters and their transfer by currents. The solubility of oxygen in water depends on temperature and salinity; in general, it decreases with increasing temperature, which explains its low content in the equatorial zone and higher content in the cold waters of high latitudes. With increasing depth, the oxygen content decreases, reaching values ​​of 3.0-0.5 ml/l in the oxygen minimum layer.

Carbon dioxide is contained in seawater in small concentrations (no more than 0.5 ml/l), but the total content of carbon dioxide is approximately 60 times higher than its amount in the atmosphere. At the same time, it plays a crucial role in biological processes (being a source of carbon during the construction of a living cell), influences global climatic processes (participating in gas exchange with the atmosphere), and determines the characteristics of carbonate sedimentation. In seawater, carbon oxides are common in free form (CO 2), in the form of carbonic acid and in the form of the HCO 3– anion. In general, the content of CO 2, as well as oxygen, decreases with increasing temperature, so its maximum content is observed in cold waters of high latitudes and in deep zones of the water column. With depth, the concentration of CO 2 increases, since its consumption decreases in the absence of photosynthesis and the supply of carbon monoxide increases during the decomposition of organic residues, especially in the oxygen minimum layer.

Hydrogen sulfide in seawater is found in significant quantities in water bodies with difficult water exchange ( famous example“hydrogen sulfide contamination” serves as the Black Sea). Sources of hydrogen sulfide can be hydrothermal waters coming from the depths to the ocean floor, the reduction of sulfates by sulfate-reducing bacteria during the decomposition of dead organic matter, release of sulfur-containing organic residues during decay. Oxygen reacts quite quickly with hydrogen sulfide and sulfides, ultimately oxidizing them to sulfates.

The solubility of carbonates in seawater is important for ocean sedimentation processes. Calcium in sea water contains an average of 400 mg/l, but a huge amount of it is bound in the skeletons of marine organisms, which dissolve when the latter die. Surface waters are typically saturated with calcium carbonate, so it does not dissolve in the upper part of the water column immediately after organisms die. With depth, waters become increasingly undersaturated with calcium carbonate, and eventually, at a certain depth, the rate of dissolution of carbonate matter is equal to the rate of its supply. This level is named depth of carbonate compensation. The depth of carbonate compensation varies depending on the chemical composition and temperature of sea water, averaging 4500 m. Below this level, carbonates cannot accumulate, which determines the replacement of essentially carbonate sediments with non-carbonate ones. The depth where the concentration of carbonates is equal to 10% of the dry matter of the sediment is called the critical depth of carbonate accumulation ( carbonate compensation depth).

Features of the relief of the ocean floor

Shelf(or mainland shoal) is a slightly inclined, leveled part of the underwater margin of continents, adjacent to the shores of land and characterized by a common geological structure. The shelf depth is usually up to 100-200 m; The shelf width ranges from 1-3 km to 1500 km (Barents Sea shelf). The outer boundary of the shelf is delineated by an inflection of the bottom topography - the edge of the shelf.

Modern shelves were mainly formed as a result of flooding of the margins of continents when the level of the World Ocean rose due to the melting of glaciers, as well as due to the subsidence of areas of the earth's surface associated with recent tectonic movements. The shelf existed in all geological periods, in some of them it grew sharply in size (for example, in the Jurassic and Cretaceous times), in others, occupying small areas (Permian). The modern geological era is characterized by moderate development of shelf seas.

continental slope is the next of the main elements of the underwater continental margins; it is located between the shelf and the continental foot. It is characterized by steeper surface slopes compared to the shelf and ocean bed (on average 3-5 0, sometimes up to 40 0) and significant dissected relief. Typical forms of relief are steps parallel to the edge and base of the slope, as well as underwater canyons, usually originating on the shelf and extending to the continental foot. Seismic studies, dredging and deep-sea drilling have established that, in terms of geological structure, the continental slope, like the shelf, is a direct continuation of the structures developed in adjacent areas of the continents.

Mainland foot is a plume of accumulative sediments that arose at the foot of the continental slope due to the movement of material down the slope (through turbidity currents, underwater landslides and landslides) and the deposition of suspended matter. The depth of the continental foot reaches 3.5 km or more. Geomorphologically, it is a sloping hilly plain. Accumulative deposits that form the continental foot are usually superimposed on the ocean floor, represented by oceanic crust, or are located partly on continental and partly on oceanic crust.

Next are structures formed on oceanic-type crust. The largest elements of the relief of the oceans (and the Earth as a whole) are the ocean floor and mid-ocean ridges. The ocean floor is divided by ridges, swells and hills into basins, the bottom of which is occupied by abyssal plains. These areas are characterized by a stable tectonic regime, low seismic activity and flat topography, which allows them to be considered as oceanic plates - Thalassocratons. Geomorphologically, these areas are represented by abyssal (deep-sea) accumulative and hilly plains. Accumulative plains have a leveled, slightly inclined surface and are developed primarily along the periphery of the oceans in areas of significant influx of sedimentary material from the continents. Their formation is associated with the supply and accumulation of material by suspension flows, which determines their inherent features: a depression of the surface from the continental foot toward the ocean, the presence of underwater valleys, gradational layering of sediments, and leveled relief. Last feature is determined by the fact that, moving deeper into the ocean basins, sediments bury the primary dissected tectonic and volcanic relief. The hilly abyssal plains are characterized by dissected topography and low sediment thickness. These plains are typical of the inner parts of basins, distant from the shores. An important element The relief of these plains are volcanic uplifts and individual volcanic buildings.

Another element of the megarelief is mid-ocean ridges, representing a powerful mountain system, stretching across all the oceans. The total length of mid-ocean ridges (MORs) is more than 60,000 km, width 200-1200 km, height 1-3 km. In some areas, the peaks of the MOR form volcanic islands (Iceland). The relief is dissected, the relief forms are oriented mainly parallel to the extent of the ridge. The sedimentary cover is thin, represented by carbonate biogenic silts and volcanogenic formations. The age of sedimentary strata becomes older with distance from the axial parts of the ridge; in the axial zones the sedimentary cover is absent or represented by modern deposits. The MOR regions are characterized by intense endogenous activity: seismicity, volcanism, and high heat flow.

MOR zones are confined to the boundaries of the separation of lithospheric plates; here the process of formation of new oceanic crust occurs due to incoming mantle melts.

Special attention deserve zones of transition from continental to oceanic crust - the margins of continents. There are two types of continental margins: tectonically active and tectonically passive.

Passive outskirts represent a direct continuation of continental blocks, flooded by the waters of the seas and oceans. They include the shelf, continental slope and continental foot and are characterized by the absence of manifestations of endogenous activity. Active ocarinas are confined to the boundaries of lithospheric plates, along which the oceanic plates move under the continental ones. These ocarinas are characterized by active endogenous activity; areas of seismic activity and modern volcanism are confined to them. Among active ocarinas, two main types are distinguished by structure: Western Pacific (island arc) and Eastern Pacific (Andean). The main elements of Western Pacific type margins are deep-sea trenches, volcanic island arcs, and marginal (or inter-arc) marine basins. The region of the deep-sea trench corresponds to the boundary at which the subduction of a plate with oceanic crust occurs. Melting of part of the subducting plate and the above-lying rocks of the lithosphere (associated with the influx of water into the subducting plate, which sharply lowers the melting temperature of the rocks) leads to the formation of magma chambers, from which melts flow to the surface. Due to active volcanism, volcanic islands are formed, stretching parallel to the plate subduction boundary. The margins of the East Pacific type are distinguished by the absence of volcanic arcs (volcanism occurs directly on the edge of the land) and marginal basins. The deep-sea trench gives way to a steep continental slope and a narrow shelf.

Destructive and accumulative activities of the sea

Abrasion (from lat. “abrasion” – scraping, shaving) – the process of destruction of rocks by waves and currents. Abrasion occurs most intensely near the shore under the influence of the surf.

The destruction of coastal rocks consists of the following factors:

· wave impact (the force of which reaches 30-40 t/m2 during storms);

· abrasive effect of debris brought by the wave;

· dissolution of rocks;

· compression of air in the pores and cavities of the rock during the impact of waves, which leads to cracking of rocks under the influence of high pressure;

· thermal abrasion, manifested in the thawing of frozen rocks and ice shores, and other types of impact on the shores.

The impact of the abrasion process manifests itself to a depth of several tens of meters, and in the oceans up to 100 m or more.

The impact of abrasion on the shores leads to the formation of clastic deposits and certain forms of relief. The abrasion process proceeds as follows. Hitting the shore, the wave gradually creates a depression at its base - wave-breaking niche, over which the cornice hangs. As the wave-breaking niche deepens under the influence of gravity, the cornice collapses, the debris ends up at the foot of the shore and, under the influence of the waves, turns into sand and pebbles.

The cliff or steep ledge formed as a result of abrasion is called cliff. At the site of the retreating cliff, a abrasion terrace, or bench (English "bench"), consisting of bedrock. The cliff may border directly on the bench or be separated from the latter by a beach. The transverse profile of the abrasion terrace has the form of a convex curve with small slopes near the shore and large slopes at the base of the terrace. The resulting debris material is carried away from the shore, forming underwater accumulative terraces.

As abrasion and accumulative terraces develop, the waves end up in shallow water, become rough and lose energy before reaching the bedrock shore, and because of this, the abrasion process stops.

Depending on the nature of the ongoing processes, shores can be divided into abrasive and accumulative.

A B C - various stages retreat of the coastal cliff, destroyed by abrasion; A 1, B 2, C 3 - various stages of development of an underwater accumulative terrace.

Waves carry out not only destructive work, but also work on the movement and accumulation of debris. The incoming wave carries out pebbles and sand, which remain on the shore when the wave recedes, thus forming beaches. Beach(from French “plage” - sloping seashore) called a strip of sediment on the sea coast in the zone of action of the surf flow. Morphologically, there are beaches with a full profile, which look like a gently sloping ridge, and beaches with an incomplete profile, which are an accumulation of sediment inclined towards the sea, adjacent to back side to the foot of the coastal cliff. Beaches with a full profile are typical for accumulative shores, while beaches with an incomplete profile are typical for abrasive shores.

When waves break up at depths of the first meters, the material deposited under water (sand, gravel or shell) forms an underwater sand bank. Sometimes an underwater accumulative shaft, growing, protrudes above the surface of the water, stretching parallel to the shore. Such shafts are called bars(from French "barre" - barrier, shallow).

The formation of a bar can lead to the separation of the coastal part of the sea basin from the main water area - lagoons are formed. Lagoon (from lat. "lacus" - lake) is a shallow natural water basin, separated from the sea by a bar or connected to the sea by a narrow strait (or straits). The main feature of lagoons is the difference in water salinity and biological communities.

Sedimentation in seas and oceans

Various sediments accumulate in the seas and oceans, which, based on their origin, can be divided into the following groups:

· terrigenous, formed due to the accumulation of products of mechanical destruction of rocks;

· biogenic, formed due to the vital activity and death of organisms;

· chemogenic, associated with precipitation from sea water;

· volcanogenic, accumulating as a result of underwater eruptions and due to eruption products brought from land;

· polygenic, i.e. mixed sediments formed by materials of different origins.

In general, the material composition of bottom sediments is determined by the following factors:

· depth of the sedimentation area and bottom topography;

· hydrodynamic conditions (presence of currents, influence of wave activity);

· the nature of the supplied sedimentary material (determined by climatic zonation and distance from the continents);

· biological productivity (marine organisms extract minerals from water and supply them to the bottom after dying (in the form of shells, coral structures, etc.));

· volcanism and hydrothermal activity.

One of the determining factors is depth, which makes it possible to distinguish several zones that differ in sedimentation characteristics. Littoral(from lat. "litoralis"- coastal) - a border strip between land and sea, regularly flooded at high tide and drained at low tide. The littoral zone is the area of ​​the seabed located between the levels of the highest high tide and the lowest low tide. Nerite zone corresponds to the depths of the shelf (from Greek. "erites"- sea mollusk). Bathyal zone(from the Greek “deep”) roughly corresponds to the area of ​​the continental slope and foot and depths of 200 – 2500 m. This zone is characterized by the following environmental conditions: significant pressure, almost complete absence light, minor seasonal fluctuations in temperature and water density; The organic world is dominated by representatives of zoobenthos and fish; the plant world is very poor due to the lack of light. Abyssal zone(from the Greek “bottomless”) corresponds to sea depths of more than 2500 m, which corresponds to deep-sea basins. The waters of this zone are characterized by relatively weak mobility, constantly low temperature (1-2 0 C, in the polar regions below 0 0 C), constant salinity; Here there is a complete absence of sunlight and enormous pressures are reached, which determine the originality and poverty of the organic world. Areas with a depth of more than 6000 m are usually identified as ultra-abyssal zones, corresponding to the deepest parts of basins and deep-sea trenches.

The main feature of the water of oceans and seas is its salinity. In science, it is customary to measure salinity by the number of grams of salts contained in a kilogram of sea water. Since a kilogram is equal to a thousand grams, when we measure salinity in grams per kilogram, we essentially express it in thousandths - ppm. Therefore, salinity is said to be “expressed in ppm.” Salinity was agreed upon to mean great Latin letter S, and ppm - °/00.

The salinity of the surface water of the Black Sea is eighteen ppm. This means that one kilogram of Black Sea water contains eighteen grams of various salts.

The average salinity of the water in the World Ocean is thirty-five ppm (S=35°/00). In the surface water of the oceans and seas, quite significant deviations from this average value are observed. This depends on the fact that the amount of water evaporating from any part of the ocean surface and the amount of precipitation falling on the same surface during the same time are not the same at different latitudes. In the equatorial zone, a layer of precipitation about 2 m high falls per year, but less water evaporates; therefore, an excess of fresh water is obtained, which lowers the salinity of the surface water to about 34 °/00.

In the subtropical zone at latitudes between 30-35°, clear, dry weather prevails, there is little precipitation, and evaporation is very high. The predominance of evaporation over precipitation leads to the fact that the salinity of the surface water of the World Ocean in the subtropics is above average: in the Northern Hemisphere 38 °/00, and in the Southern Hemisphere - 37 °/00.

In temperate latitudes, precipitation is greater than in the subtropics, and evaporation is less; therefore, as you move north from the tropics in the Northern Hemisphere and south in the Southern Hemisphere, the salinity gradually approaches normal. In the polar zones, where evaporation is sharply reduced, the salinity of surface water is less than the average salinity of the World Ocean. It does not exceed 33-34 °/00 here

Thus, on the surface of the World Ocean there is a decreased salinity in the equatorial zone and an increased salinity to the north and south of it - in the subtropical zones. Towards the poles, salinity gradually decreases, becoming normal in temperate latitudes (S = 35 °/00). This pattern is somewhat violated by ocean currents. Cold currents carry low-salinity water from the polar zones to temperate latitudes, while currents coming from the subtropics carry saltier water to temperate latitudes.

In the coastal parts of the World Ocean, especially near the mouths of large rivers, such as the Amazon, Congo, Yenisei, Lena, Ob, the salinity of water on the surface decreases sharply.

All the differences in the salinity of ocean water that we talked about are observed only on the surface of the World Ocean. They can be seen in a layer of water several hundred meters thick. The salinity of the deep waters of the World Ocean is almost the same everywhere and is equal to 35 °/00.

How did the salts in it get into sea water? On their way, rivers dissolve the salts that make up the rocks, and then carry the salts into the oceans and seas.

Careful chemical analyzes have shown that seawater contains all the common on land chemical elements. It is interesting that the relationships between them in different parts of the World Ocean are the same, i.e. chemical composition salts of the World Ocean is constant.

It turned out that salts dissolved in sea water are present in the following proportion (in%):

Chlorides (salts of hydrochloric acid). . . 88,7

Sulfates (salts of sulfuric acid). . . 10.8

Carbonates (salts of carbonic acid). . . 0.3

The rest of the salts………. 0.2

In all oceans these ratios are preserved. This once again shows the unity of the World Ocean and indicates that the water of the oceans mixes well.

In river water, unlike sea water, the majority is not of chlorides, but of carbonates. What happens to them in the ocean? They are used by living creatures living in seawater to build their shells and skeletons.

SEA WATER TEMPERATURE

It is known from physics that water has a very high heat capacity compared to air. To heat one by 1° cubic centimeter, or one gram of water, you need to expend one calorie of heat. The same calorie can heat more than three thousand cubic centimeters of air by 1°.

Therefore, the surface temperature of the water in the World Ocean greatly influences the temperature of the air above it, and therefore the climate of those areas where this air penetrates thanks to the prevailing winds.

The highest water temperature on the surface of the World Ocean far from the coast is observed in the equatorial zone. The average annual temperature there reaches 28°. In shallow waters off the coast, the water warms up even more. It is interesting that during the year in the equatorial zone the temperature of ocean water remains almost unchanged. The highest temperature is usually no more than one degree above the average. The minimum temperature is also much lower than the average. This happens because in the equatorial zone the arrival of solar heat throughout the year is very uniform, since the length of the day all year round is approximately 12 hours, and the sun at noon is near the zenith.

From the equatorial zone and to the north and south, average annual water surface temperatures begin to decrease and in the subtropics reach 20°. In the subtropical zone, the sun rises almost to its zenith at noon in summer. At this time, the day is much longer than the night. In winter, the days are shorter and the sun does not rise as high at midday. Therefore, the difference in solar heat gain in summer and winter is significant. The highest and lowest water temperatures can differ from the annual average by up to 5°. For example, the average annual water temperature is 22°, the highest (maximum) is 27°, and the lowest (minimum) is 17°. Accordingly, the air temperature also changes.

From the subtropics towards the polar circles, the average annual temperature of surface water decreases rapidly and, finally, in winter it reaches the temperature at which ice forms,

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