1. Salinity. Ocean water is a solution containing all the chemical elements. Especially there is a lot of chlorine, sodium, magnesium, sulfur in ocean water, less - bromine, carbon, strontium, boron. The content of other elements is negligible - less than 1%.
The total amount of salts in the ocean is 5. 10 17 tons, they can cover the entire Earth with a layer of 45 m thick. Most of all in the ocean there are salts of sodium (NaCl) and magnesium (MgCl), which give the water a salty bitter taste.
The average salinity of the World Ocean is 35% o, i.e. 1 liter of ocean water contains 35 g of salts. Salinity depends on the ratio of atmospheric precipitation and evaporation, runoff from land (rivers), and ice melting. The distribution of salinity on the Earth shows latitudinal zoning. In equatorial latitudes, salinity is slightly less than average (about 34 o / oo), in tropical latitudes it increases to 37 o / oo. Further to the north and south, salinity decreases: in temperate latitudes to 35 o / oo, and in polar latitudes to 33-32 o / oo.
Latitudinal zoning in salinity distribution is disturbed by ocean currents. The Atlantic Ocean is considered the most salty - almost 35.5 o / oo, the least salty - the Arctic Ocean - about 32 o / oo (off the coast of Asia - only 20 o / oo). The saltiest are the Persian Gulf (39 o / oo), the Red Sea (42 o / oo), the Mediterranean Sea (39 o / oo).
At depths of more than 1500 m, the salinity of the World Ocean is unchanged - about 34.9 o / oo.
2. Temperature. The temperature of the entire mass of ocean water is approximately +4 o C. Water is the most heat-absorbing body on Earth, so the ocean slowly heats up and slowly cools down. As already mentioned, the ocean - powerful battery heat.
average temperature surface waters ocean +17 о С (average annual land temperature +14 о С). Highest temperatures the waters in the northern hemisphere are in August, the smallest in February (in the southern hemisphere, vice versa).
The surface water temperature is zonal. In near-equatorial latitudes the temperature is +27 o - +28 o C, in tropical - +15 o - +25 o C, in temperate latitudes - 0 o - +10 o C, in polar - 0 o - –2 o C. Most the Pacific Ocean is warm (average temperature +19 о С), and the warmest parts of the World Ocean are the Red Sea (+32 о С) and the Persian Gulf (+35 о С).
Daily and annual fluctuations in water temperature are small: daily - about 1 о С, annual in temperate latitudes - 5-10 о С.
Significant temperature changes occur only in the upper layers of the ocean water - 200-1000 m, deeper the temperature is +4 o +5 o C, at the bottom in polar latitudes - about 0 o, in equatorial latitudes - +2 o +3 o C.
3. Ice in the ocean. The freezing point of water depends on its salinity. Ice formation begins with the formation of fresh crystals, which then freeze. In this case, drops of brine remain in the space between the crystals, so the ice is salty. The brine gradually flows down between the crystals, and over time the ice is desalinated.
In calm water, a needle-like structure of ice is formed, with stirring, a spongy structure is formed. The ice is submerged at 9/10.
Salted ice is less durable than fresh ice, but it is more plastic and viscous.
The initial stage of ice formation is ice crystals. Further, an ice film is formed - fat, when snow falls, a snowball is formed. A strip of ice is growing along the coast - coastal fast ice. Adult ice has a thickness of 50-70 cm and more.
In the polar latitudes of the northern hemisphere, the ice formed in winter does not have time to melt over the summer. Among the polar ice there are annual and perennial ones. The thickness of first-year ice in the Arctic is 2-2.5 m, in the Antarctic is 1-1.5 m. Perennial ice is 3-5 m or more thick.
When compressed, ice forms hummocks. Non-moving ice is located only at the coast, the rest is drifting. Perennial layers of drifting ice in the Arctic are called pack ice (5 m or more thick). These ice cover about 75% of the total ice area in the North Arctic Ocean(they are not in the Southern Ocean).
When the ice melts, lakes form on it - puddles, then at temperatures above 0 ° C, polynyas are formed, etc.
except sea ice, in the ocean there can be river ice, carried out in spring by rivers, as well as continental ice - icebergs.
Ice cover almost 15% of the entire water area of the World Ocean. In the Arctic, the greatest distribution of ice reaches by April-May, and the smallest by the end of August. In the Antarctic in winter (from May to October), ice surrounds the continent in a ring, and in summer, this ring (January-February) collapses.
Icebergs reach 50 o N. in the northern hemisphere and 30 o S latitude. in the southern hemisphere. An iceberg 170 km long and 100 m high was discovered in the Weddell Sea.
4. Density. As the salinity of the water increases, its density increases. This is facilitated by the cooling of water, as well as evaporation, the formation of ice. Cold water has a higher density than warm water, so it sinks down. The average density of ocean water is approximately 1; it increases from the equator to the poles and into the ocean.
5. Pressure. The air puts tremendous pressure on the ocean. In addition, the water itself creates pressure, and the deeper, the greater the pressure. For every 10 m depth, the pressure increases by 1 atm. All processes at great depth are carried out under strong pressure.
6. Transparency. The least transparency of water near the coast. It also decreases during the plankton period. V clear water sunlight passes to a depth of about 600 m, then complete darkness. The central parts of the oceans are the most transparent and the Sargasso Sea is the most transparent.
7. Color. A layer of clear ocean water is blue or blue ("the color of the oceanic desert"). The presence of plankton gives the water a greenish tint, various impurities - yellowish-green (near river mouths the water may even be brown).
8. Gas composition. Gases are always dissolved in ocean water. The higher the temperature and salinity, the less gases can dissolve in the water. Gases enter water from the atmosphere, during chemical and biological processes in the ocean, with river water, during underwater eruptions. Oxygen, carbon dioxide, hydrogen sulfide, ammonia, methane are dissolved in water.
Ocean waters movement
The water in the oceans is in constant movement... This ensures mixing of water, redistribution of heat, salinity and gases.
Let us consider individual water movements.
1. Wave movements(waves). main reason the occurrence of waves - the wind, but they can be caused and abrupt change atmospheric pressure, earthquake, volcanic eruptions on the coast and ocean floor, tidal force.
The highest part of the wave is called the crest; the most in-depth part is the sole. The distance between two adjacent ridges (bottoms) is called the wavelength - (l).
The height of the wave (H) is called the excess of the crest of the wave over its base. The period of the wave (t) is the period of time during which each point of the wave moves a distance equal to its length. Velocity (n) is the distance traveled per unit of time by any point of the wave.
Distinguish:
a) wind waves - under the influence of the wind, the waves grow simultaneously in height and length, while the period (t) and speed (n) increase; as the waves develop, they change appearance and sizes. At the stage of wave attenuation, long gentle waves are called swell. Wind waves have a significant destructive force, thereby shaping the relief of the coast. The average water height of wind waves in the ocean is 3-4 m (maximum up to 30 m), in the seas the wave height is less - maximum no more than 9 m. With increasing depth, the waves quickly fade.
b) tsunamis - seismic waves covering the entire water column occur during earthquakes and underwater volcanic eruptions. Tsunamis have a very long wavelength, their height in the ocean does not exceed 1 m, so they are not noticeable in the ocean. But on the coasts, in bays, their height increases to 20-50 m. The average speed of tsunami propagation is from 150 km / h to 900 km / h. Before the arrival of a tsunami, the water usually recedes from the coast by several hundred meters (up to 1 km) within 10-15 minutes. Large tsunamis are rare. Most of them are located on the shores of the Pacific Ocean. The tsunami is associated with tremendous destruction. The strongest tsunami occurred in 1960 as a result of an earthquake in the Andes, on the coast of Chile. At the same time, tsunamis spread across the Pacific Ocean to the shores of North America (California), New Zealand, Australia, the Philippine, Japanese, Kuril, Hawaiian Islands and Kamchatka. The tsunami reached the shores of Japan and Kamchatka almost a day after the earthquake.
c) tidal waves (ebbs and flows) occur as a result of the influence of the moon and the sun. Hot flashes are extremely complex. They are constantly changing, so they cannot be considered periodic. For navigation, special tables of "tides" have been created, which is especially important for port cities located in the lower reaches of rivers (London on the River Temza, etc.). The energy of the tidal waves is used by building the TES (they are in Russia, France, USA, Canada, China).
2. Currents of the World Ocean (sea currents). These are horizontal movements of water in oceans and seas, characterized by a certain direction and speed. They are several thousand kilometers long, tens, hundreds of kilometers wide, and hundreds of meters deep.
The main cause of currents in the ocean is wind. Other reasons include tidal forces, gravity. All currents are influenced by the Coriolis force.
Currents can be classified according to a number of characteristics.
I. By origin, currents are distinguished
1) frictional - arise under the action of moving air on the surface of the water:
a) wind - caused by temporary winds (seasonal),
b) drift - caused by constant winds (prevailing);
2) gravitational - arise under the influence of gravity:
a) sewage - flows from areas of excess water and strives to level the surface,
b) density - are the result of differences in water density at the same depth;
3) tidal - arise under the influence of tidal forces; cover the entire water column.
II. Distinguish currents by duration
1) constant - they always have approximately the same direction and speed (North trade wind, South trade wind, etc.);
2) periodic - periodically change direction and speed (monsoon currents in the Indian Ocean, tidal currents, and others);
3) temporary (episodic) - there are no patterns in their changes; they change frequently, most often as a result of the action of the wind.
III. By temperature, one can distinguish (but relatively) currents
1) warm - for example, the temperature of the North Atlantic Current is +6 о С, and the temperature of the surrounding water is +4 о С;
2) cold - for example, the temperature of the Peruvian current is +22 o C, the surrounding water is +28 o C;
3) neutral.
Warm currents, as a rule, go from the equator to the poles, cold ones vice versa. Warm currents are usually saltier than colder ones.
IV. Depending on the depth of the location, currents are distinguished
1) superficial,
2) deep,
3) bottom.
At present, a definite system of ocean currents has been established, due primarily to the general circulation of the atmosphere. Their scheme is as follows. In each hemisphere, on both sides of the equator, there are large gyres of currents around permanent subtropical baric maxima (regions of increased atmospheric pressure are formed at these latitudes): clockwise in the northern hemisphere, counterclockwise in the southern. An equatorial countercurrent from west to east arises between them. In the temperate and subpolar latitudes of the northern hemisphere, small currents are observed around the baric minimum (areas of low atmospheric pressure: the Icelandic minimum and the Aleutian minimum). In similar latitudes of the southern hemisphere, there is a current from west to east around Antarctica (current of the Westerly winds).
The most stable currents are the North and South trade winds (equatorial) currents. On the eastern coasts of the continents in tropical latitudes, warm waste streams: Gulf Stream, Kurosivo, Brazilian, Mozambique, Madagascar, East Australian.
In temperate latitudes, under the influence of constant westerly winds, there are warm North Atlantic and North Pacific currents and a cold current of the Westerly winds (West Drift). Cold compensatory currents are observed near the western coasts of the continents in tropical latitudes: California, Canary, Peruvian, Benguela, and Western Australian.
In small rings of currents, the warm Norwegian and cold Labrador currents in the Atlantic and the Alaskan and Kuril-Kamchatka currents in the Pacific Ocean should be named.
In the northern Indian Ocean, the monsoon circulation generates seasonal wind currents: in winter - from east to west, in summer - vice versa (in summer it is a cold Somali current).
In the Arctic Ocean, the main direction of water and ice is from east to west, towards the Greenland Sea. The Arctic is replenished with waters from the Atlantic in the form of the North Cape, Spitsbergen, and Novaya Zemlya currents.
The sea currents are of great importance for the climate and nature of the Earth. The currents violate the zonal temperature distribution. Thus, the cold Labrador Current contributes to the formation of ice-tundra landscapes on the Labrador Peninsula. And the warm currents of the Atlantic make most of the ice-free Barents Sea... Currents also affect the amount of precipitation: warm currents contribute to the inflow of precipitation, cold currents do not. Sea currents also promote mixing of water and carry out the transfer nutrients; with their help, the migration of plants and animals occurs.
Life in the ocean
In the oceans, life exists everywhere. According to the conditions of existence in the ocean, 2 areas are distinguished:
1) pelagial (water column),
2) benthal (bottom) -
a) littoral (coastal part of the bottom to a depth of 200 m),
b) abyssal (deep part).
The organic ocean world consists of 3 groups:
1) benthos - bottom dwellers (plants, worms, molluscs, crabs, etc.),
2) plankton - inhabitants of the water column, unable to move independently (protozoa, bacteria, algae, jellyfish, etc.),
3) nekton - the inhabitants of the waters. Free swimming (fish, whales, dolphins, seals, squids, sea snakes and turtles, etc.).
Green plants can develop only where there is sufficient light for photosynthesis (up to a depth of no more than 200 m). Organisms that do not need light colonize the entire water column.
Plankton are subdivided into phytoplankton and zooplankton. Most of the mass of living matter in the ocean is phytoplankton (under favorable conditions, its amount can double in a day). Phytoplankton mainly inhabit the upper 100-meter layer of water. The average phytoplankton mass is 1.7 billion tons. The most common form of phytoplankton is diatoms, of which there are about 15 thousand species. Phytoplankton is the main food for most marine organisms. Areas of abundant phytoplankton development are places rich in life.
The distribution of life in the ocean is zonal:
- in polar latitudes, conditions for phytoplankton are unfavorable, therefore they are poor in life (cold-loving fish and seals live here);
- in subpolar latitudes, phytoplankton develops in summer, it feeds on zooplankton, they, in turn, fish, whales, so in summer there are a lot of cod, perch, haddock, herring and other fish;
- in temperate latitudes, the most favorable conditions are formed, these are the most productive zones of the ocean: an abundance of phyto- and zooplankton, an abundance of herring, cod, flounder, halibut, navaga, salmon, sardine, tuna, anchovy and other fish;
- in subtropical and tropical latitudes, conditions for life are unfavorable: increased salinity, little oxygen, a small amount of plankton and fish; only brown algae - sargassum are widespread here;
- in equatorial latitudes, conditions are improving, so the amount of plankton and fish is increasing here; a lot of corals.
The ocean has the following resources: biological (fish 90%, mammals, molluscs, algae), mineral (oil, gas, coal, iron and manganese ores, tin, phosphorites, salt, etc.) and energy.
The movement of the waters of the oceans
In their own way physical condition water is a very mobile medium, so in nature it is in continuous motion. This movement is caused by various reasons, primarily the wind. Acting on ocean waters, it stimulates surface currents that carry huge masses of water from one area of the ocean to another. The energy of the translational movement of surface waters due to internal friction is transferred to the underlying layers, which are also involved in movement. However, the direct influence of the wind extends over a relatively small (up to 300 m) distance from the surface. Lower in the water column and in the bottom horizons, movement occurs slowly and has directions associated with the bottom topography.
Surface currents form two large gyres, separated by a countercurrent in the equatorial region. The whirlpool of the northern hemisphere rotates clockwise, and the southern one - counterclockwise. When comparing this scheme with the currents of the real ocean, one can see a significant similarity between them for the Atlantic and Pacific oceans. At the same time, it should be noted that the real ocean has a more complex system of countercurrents at the borders of continents, where, for example, the Labrador Current (North Atlantic) and the Alaska Return Current (Pacific Ocean) are located. In addition, currents near the western edges of the oceans are distinguished by higher rates of water movement than those of the eastern ones. The winds apply a couple of forces to the surface of the ocean, rotating the water clockwise in the northern hemisphere and against it in the southern hemisphere. Large eddies of ocean currents arise as a result of the action of this pair of rotating forces. It is important to emphasize that winds and currents are not one-to-one. For example, the presence of the fast current of the Gulf Stream off the western shores of the North Atlantic does not mean that particularly strong winds blow in this area. The balance between the rotating pair of forces of the mean wind field and the resulting currents is added over the area of the entire ocean. In addition, currents accumulate great amount energy. Therefore, a shear in the mean wind field does not automatically lead to a shear of large oceanic eddies.
On the whirlpools, set in motion by the wind, another circulation is superimposed, thermohaline (“khalina” - salinity). Together, temperature and salinity determine the density of the water. The ocean transfers heat from tropical latitudes to polar ones. This transport is carried out with the participation of such large currents as the Gulf Stream, but there is also a return flow of cold water towards the tropics. It occurs mainly at depths below the layer of wind-driven eddies. Wind and thermohaline circulation are components of the general circulation of the ocean and interact with each other. So, if thermohaline conditions explain mainly convective movements of water (the sinking of cold heavy water in the polar regions and its subsequent flow to the tropics), then it is the winds that cause the divergence (divergence) of surface waters and actually "pump out" cold water back to the surface, completing the cycle ...
The concept of thermohaline circulation is less complete than that of wind circulation, but some features of this process are more or less known. The formation of sea ice in the Weddell Sea and in the Norwegian Sea is believed to be important for the formation of cold, dense water spreading at the bottom in the South and North Atlantic. Both regions receive water of increased salinity, which is cooled down to freezing in winter. When water freezes, a significant part of the salts it contains is not included in the newly formed ice. As a result, the salinity and density of the remaining unfrozen water increases. This heavy water sinks to the bottom. It is commonly referred to respectively as Antarctic bottom water and North Atlantic deep water.
Another important feature of thermohaline circulation is associated with the density stratification of the ocean and its effect on mixing. The density of water in the ocean increases with depth and the lines of constant density run almost horizontally. Water with different characteristics is much easier to mix in the direction of lines of constant density than across them.
Thermohaline circulation is difficult to characterize with certainty. In fact, both horizontal advection (water transport by sea currents) and diffusion should play an important role in thermohaline circulation. Determining the relative importance of these two processes in any area or situation is an important task.
I. Waves and tides
The waves are regular and have some General characteristics- length, amplitude and period. The speed of wave propagation is also noted.
The wavelength is the distance between the peaks or troughs of the waves, the wave height is the vertical distance from the trough to the top, it is equal to twice the amplitude, the period is equal to the time between the moments when two successive peaks (or troughs) pass through the same point.
The ripple height is measured in approximately one centimeter, and the period is about one second or less. Surf waves reach several meters in height with periods from 4 to 12 s.
Ocean waves have different shapes and shapes.
Waves caused by local wind are called wind waves. Another type of waves are swell waves, which slowly shake the ship even in calm weather. The swell is formed by waves that persist after they leave their area of \ u200b \ u200bthe wind.
At any wind speed, a certain equilibrium state is achieved, which is expressed in the phenomenon of fully developed waves, when the energy transmitted by the wind to the waves is equal to the energy transmitted by the wind to the waves, equal to the energy lost when the waves break. But in order for a fully developed wave to form, the wind must blow for a long time and over a large area. The space exposed to the wind is called the acceleration region.
II. Tsunami
Tsunamis travel in waves from the epicenter of underwater earthquakes. The area affected by tsunami waves is huge.
Tsunamis are directly related to movements crust... A shallow earthquake that causes significant crustal displacement at the bottom of the oceans will also trigger a tsunami. But an equally strong earthquake, not accompanied by any noticeable movements of the crust, will not cause a tsunami.
Tsunami occurs in the form of a single pulse, the leading edge of which propagates with the speed of a shallow water wave. The initial impulse does not always provide concentric propagation of energy, and with it the wave.
III. Tides
Tides are the slow rise and fall of the water level and movement of its edge. The tidal forces are the result of the attraction of the Sun and the Moon. When the Sun and Moon are approximately in line with the Earth, that is, during the full moon and new moon, the tides are greatest. Because the planes of revolution of the Sun and the Moon are not parallel, the action of the forces of the Moon and the Sun changes with the seasons, as well as depending on the phase of the Moon. The tidal force of the moon is approximately twice the tidal force of the sun. Large differences in the amplitude of tides in different parts of the coast are mainly determined by the shape of the oceanic basins.
Properties of the waters of the World Ocean
Water is a "universal solvent": any of the elements can dissolve in it, at least to a small extent. Water has the highest heat capacity among all ordinary liquids, that is, to heat it by one degree, more heat is required compared to other liquids. More heat is required for its evaporation. These and other features of water are of great biological importance. So, due to the high heat capacity of water, seasonal fluctuations in air temperature are less than it would be otherwise.
The temperature of the entire mass of ocean water is about 4 degrees Celsius. The oceans are cold. The water in them warms up only at the very surface, and with depth it becomes colder. Only 8% of ocean waters are warmer than 10 degrees, more than half are colder than 2.3 degrees. Temperature varies unevenly with depth.
Water is the most heat-absorbing body on Earth. Therefore, the ocean slowly heats up and slowly gives off heat, serves as a heat accumulator. It accounts for more than 2/3 of the absorbed solar radiation... It is consumed for evaporation, for heating the upper layer of water to a depth of about 300 m, as well as for heating the air.
The average temperature of the surface waters of the ocean is more than +17 degrees, and in the northern hemisphere it is 3 degrees. higher than in the south. The highest water temperatures in the northern hemisphere are observed in August, the lowest in February, and vice versa in the southern hemisphere. Daily and annual fluctuations in water temperature are insignificant: daily fluctuations do not exceed 1 deg., Annual ones are no more than 5..10 deg. in temperate latitudes.
The surface water temperature is zonal. In near-equatorial latitudes the temperature is 27 ... 28 degrees throughout the year, in tropical regions in the west of the oceans 20 ... 25 degrees, in the east 15 ... 20 degrees. (due to currents). In temperate latitudes, the water temperature gradually decreases from 10 to 0 degrees. in the southern hemisphere, in the northern hemisphere, with the same tendency, the western coasts of the continents are warmer than the eastern ones, also due to currents. In the polar regions, the water temperature all year round is 0 ...- 2 degrees, in the center of the Arctic perennial ice up to 5-7 m thick.
The maximum surface water temperatures are observed in tropical seas and bays: more than 35 degrees in the Persian Gulf, 32 degrees in the Red Sea. In the bottom layers of the World Ocean (MO), temperatures at all latitudes are low: from +2 at the equator to -2 in the Arctic and Antarctic.
When seawater cools below freezing point, sea ice forms.
Ice is constantly covered 3 - 4% of the ocean. Sea ice differs from freshwater ice in a number of ways. In saline water, the freezing point decreases as salinity increases. In the salinity range from 30 to 35 ppm, the freezing point varies from -1.6 to -1.9 degrees.
The formation of sea ice can be considered as the freezing of fresh water with the displacement of salts into the cells of sea water within the ice mass. When the temperature reaches the freezing point, ice crystals form, which “surround” the unfrozen water. Unfrozen water is enriched with salts displaced by ice crystals, which leads to a further decrease in the freezing point of water in these cells. If ice crystals do not completely surround the salt-rich unfrozen water, it will sink and mix with the underlying sea water... If the freezing process is extended over time, almost all of the brine-rich brine will leave the ice and its salinity will be close to zero. When it freezes quickly, most of the brine will be trapped in the ice and its salinity will be almost the same as the salinity of the surrounding water.
Typically, the strength of sea ice is one-third the strength of freshwater ice of the same thickness. However, old sea ice (with very low salinity) or ice formed below the crystallization point of sodium chloride is as strong as freshwater ice.
Freezing of seawater occurs at negative temperatures: at an average salinity - about -2 degrees. The higher the salinity, the lower the freezing point.
For seawater to freeze, it is necessary that either the depth is shallow, or below the surface layer by no great depths there was water with a higher salinity. In the presence of a shallow halocline, surface water, even when cooled to the freezing point, will be lighter than the warmer but saltier underlying water.
When the surface layer of water cools down to the freezing point and stops deepening, ice formation will begin. The sea surface takes on an oily appearance with a special lead tint. As the ice crystals grow, they become visible and take the shape of needles. These crystals or needles freeze to each other and form a thin layer of ice. This layer bends easily under the action of waves. With increasing thickness, the ice loses its elasticity, and then the ice cover breaks into separate pieces that drift on their own. Colliding with each other during the excitement, pieces of ice take on rounded shapes. These rounded chunks of ice from 50 cm to 1 m in diameter are called pancake ice. At the next stage of freezing, pieces of pancake ice freeze and form fields of drifting ice. Waves and tides break the ice fields again, forming ridges of hummocks, which are many times thicker than the original ice cover. In the ice cover, areas of clear water are formed - polynyas, which allow submarines to float to the surface even in the Central Arctic.
Ice formation significantly reduces the interaction of the ocean with the atmosphere, delaying the propagation of convection into the ocean. The transfer of heat should be carried out already through ice - a very poor conductor of heat.
Thickness arctic ice about 2 m, and the air temperature in winter in the North Pole area drops to -40 degrees. The ice acts as an insulator, keeping the ocean from cooling.
Sea ice plays another important role in the energy budget of the ocean. Water is a good absorber of solar energy. On the contrary, ice, especially fresh, and snow - very good reflectors... If clean water absorbs about 80% of the incident radiation, then sea ice can reflect up to 80%. So the presence of ice significantly reduces the heating of the earth's surface.
Ice complicates navigation, and ship accidents are associated with icebergs.
Icebergs extend well beyond the sea ice boundary. They form on land. Although ice is solid, it still flows slowly. Snow accumulates in Greenland, Antarctica and the high-latitude mountains, giving rise to glaciers sliding down. On the coastline, huge blocks of ice are breaking away from the glacier, giving birth to icebergs. Since the density of ice is about 90% of the density of seawater, icebergs remain afloat. Approximately 80 - 90% of the iceberg's volume is under water. This volume also depends on the amount of air inclusions. After their formation, icebergs are carried away by ocean currents and, falling into lower latitudes, gradually melt.
Most of the icebergs that pose a danger to navigation originate on the western coast of Greenland, north of 6830 N. Here, about a hundred glaciers produce about 15,000 icebergs a year. Initially, these icebergs drift northward along with the West Greenland Current, and then turn southward, carried away by the Labrador Current. Greatest impression produce icebergs that have broken away from the Ross Ice Shelf, one of the unique phenomena of Antarctica. It is a very thick layer of ice that descends from the mainland and is afloat. Huge Antarctic icebergs break off from the Ross Glacier.
The sea ice is brackish, but its salinity is several times less than the salinity of the M.O. In addition to slightly salted sea ice, the oceans contain freshwater river and continental (icebergs) ice. Under the influence of winds and currents, ice from the polar regions is carried to temperate latitudes and melts there. dissolved in it chlorides (more than 88%) and sulfates (about 11%). Salty taste to water is given by table salt, bitter - by magnesium salts. The ocean water is characterized by a constant percentage of different salts, despite the different salinity. Salts, like the water of the oceans itself, came to the earth's surface primarily from the bowels of the earth, especially at the dawn of its formation. Salts are brought into the ocean by river waters rich in carbonates (over 60%). However, the amount of carbonates in ocean water does not increase and is only 0.3%. This is due to the fact that they precipitate, and are also spent on the skeletons and shells of animals, are consumed by algae, which, after dying off, sink to the bottom.
In the distribution of surface water salinity, zoning is traced, primarily due to the ratio of precipitation and evaporation. Salinity is reduced by river runoff and melting icebergs. In the equatorial latitudes, where more precipitation falls than evaporates, and river runoff, salinity 34-35 ppm. In tropical latitudes, there is little rainfall, but evaporation is high, so the salinity is 37 ppm. In temperate latitudes, salinity is close to 35, and in circumpolar latitudes - the lowest (32-33 ppm), because the amount of precipitation here is greater than evaporation, the river runoff is great, especially of the Siberian rivers, there are many icebergs, mainly around Antarctica and Greenland.
The latitudinal regularity of salinity is disturbed by sea currents. For example, in temperate latitudes, salinity is higher on the western coasts of the continents, where tropical waters enter, and less - on the eastern shores washed by polar waters. Coastal waters near river mouths have the lowest salinity. Maximum salinity is observed in tropical inland seas surrounded by deserts. Salinity affects other properties of water such as density, freezing point, etc.
The density of seawater depends on pressure, temperature and salinity. The density of seawater is close to 1.025 g / cm3. As it cools, the water becomes even heavier. The pressure also increases the density of the seawater. Therefore, at a depth of 5000 m, the density of seawater increases to 1.050 g / cm3. As a rule, oceanographers do not measure density directly, preferring to calculate it from data on temperature, salinity and pressure. Often they are interested in the dependence of the density of seawater only on temperature and salinity.
Typically, density, which does not include pressure in the calculation, increases with depth. In this case, the water is said to be stably stratified. In a stratified ocean, it is difficult to move water across lines of constant density; it is much easier to do this along such lines. In the language of physics, to move water across lines of constant density, you need to do work - to increase the potential energy. To move water along lines of constant density, it is only necessary to overcome the friction of the water, and sea water has an increased "fluidity".
The ocean is not only cold but also dark. At a depth of over 100 m, it is impossible to see anything during the day except rare bioluminescent flashes of light from passing fish and zooplankton. Unlike the atmosphere, which is relatively transparent to all waves of the electromagnetic spectrum, the ocean is impenetrable to them. Neither long radio waves nor short-wave ultraviolet radiation can penetrate into its depths.
In any fluid, including seawater, the loss of solar radiation is fairly well described by the so-called Beer's law, which states that the amount of energy absorbed at a certain distance is proportional to its initial amount. This makes it possible to characterize seawater in terms of the relative transmittance. The transmittance changes near water depending on the wavelength of the radiation, and in particular the visible part of the spectrum sunlight transmitted by water is much better than radiation with shorter or longer wavelengths. The distinction between fresh and salt sea water is irrelevant in this respect.
It has been found that less than 1% of the solar energy that reaches the surface of the water penetrates into the ocean at a depth of 100 meters.
Due to the opacity of the ocean for electromagnetic radiation we are unable to use radio waves and radars to study the ocean. A submerged submarine can receive radio communications only through an antenna floating on the surface or with the help of radio devices operating at waves of such a length at which Beer's law no longer holds. On the other hand, the ocean is much more permeable to sound waves than the atmosphere, and due to a peculiar change in the speed of sound in the water column, it can propagate in the ocean over extremely long distances.
The speed of sound in the ocean changes depending on pressure, temperature and salinity - 1500 m / s, which is 4 - 5 times higher than the speed of sound in the atmosphere. With increasing temperature, salinity and pressure, the speed of sound increases. The speed of sound in water is independent of its pitch or frequency.
Sound in the ocean does not travel in a straight line, it always deflects to the side where the speed is slower.
In accordance with the increase in pressure, the speed of sound increases with depth. The combined effect of temperature and pressure usually leads to the fact that somewhere in the intermediate layer between the surface and the ocean floor, the speed of sound takes a minimum value. This layer of the minimum velocity is called the sound channel. Due to the fact that the path of sound always bends towards the water layer with a lower propagation velocity, the layer of the minimum velocity channels the sound.
The sound channel in the ocean has the property of continuity. It extends almost from the surface of oceanic waters in polar latitudes to a depth of about 2000 m off the coast of Portugal, with an average depth of about 700 m. The long-range sound propagation in the ocean is explained by the fact that both the sound source and the catcher are located near the axis of the sound channel.
Ocean water contains salts, gases, and particulate matter of organic and inorganic origin. By weight, they make up only 3.5%, but certain properties of water depend on them.
Table 1. Composition of sea water
|
Component |
Concentrated g / kg |
Component |
Concentration g / kg |
|
Bicarbonate |
|||
|
Strontium |
|||
Table 2. Chemical composition of plankton (in micro grams of element per gram of dry weight of plankton)
Most of the metals in ocean waters are present in seawater in extremely small amounts. As the table shows, living organisms extract metals from seawater. Most often, the concentration of metals in living organisms in comparison with their content in seawater does not exceed the concentration of phosphorus.
Substance sinking from the ocean surface includes many particles with a large reaction surface. Kichi manganese and iron particles also have extensive active surfaces. Some of them are deposited from the upper layers of the ocean, while others are formed by the oxidation of reduced iron and manganese, diffusing from bottom sediments or brought in by hot waters from the region of the expanding mid-ocean ridges. Such compounds trap metals. The most striking confirmation of this is the ferromanganese nodules at the bottom of the oceans, which contain up to 1% nickel and copper, as well as many other metals.
Such capture of metals occurs even more efficiently in coastal waters, where constant roiling of sediments and biological processing of sediment strata provide a continuous flow of oxidizing iron and manganese in solution from bottom sediments.
After the ingress of metals into the bottom sediments, the likelihood of their reappearance in the upper water column is very small, although some redistribution within the sediments themselves is observed.
Salinity. Ocean water consists by weight of 96.5% pure water and less than 4% of dissolved salts, gases and suspended insoluble particles. The presence of a relatively small amount of various substances makes it significantly different from other natural waters.
In total, 44 chemical elements are found in the dissolved state in the water of the Ocean. It is assumed that all substances found in nature are dissolved in it, but due to negligible amounts, they cannot be detected. Distinguish between the main components of the salinity of ocean water (Cl, Na, Mg, Ca, K, etc.) and minor, contained in negligible amounts (among them gold, silver, copper, phosphorus, iodine, etc.).
A remarkable feature of the Ocean's water is the constancy of its salt composition. The reason for this may be the continuous mixing of the waters of the World Ocean. However, this explanation cannot be considered exhaustive.
The total amount of salts contained in the water of the World Ocean is 48 * 10 in 15 tons. This amount of salts is enough to cover the entire surface of the Earth with a layer of 45 m, and the surface of the land with a layer of 153 m.
With a very low silver content (0.3 mg per 1 m3), its total amount in the ocean water is 20,000 times greater than the amount of silver mined by people for the entire historical period. Gold is contained in ocean water in the amount of 0.006 mg per 1 m3, while its total amount reaches 10 billion tons.
In terms of the composition of salts, ocean water differs significantly from river water (Table 19).
The ocean water contains the most (27 g in 1 liter of water) common table salt (NaCl), so the ocean water tastes salty; magnesium salts (MgCl2, MgSO4) give it a bitter taste.
Significant differences in the ratio of salts in the water of the Ocean and in the water of the rivers cannot but seem surprising, since the rivers continuously carry salts into the Ocean.
It is assumed that the salt composition of the Ocean waters, released from the earth's interior, is associated with their origin. Ocean waters were already distinguished with the original salinity. Subsequently, a certain salt composition was balanced. The amount of salts carried out by the rivers is to some extent balanced by their consumption. In the consumption of salts, the formation of iron-manganese nodules, the carry-over of salts by the wind and, of course, the activity of organisms extracting salts (primarily calcium salts) from the Ocean water to build skeletons and shells are important. Skeletons and shells of dead organisms partially dissolve in water, and partially form bottom sediments and, thus, fall out of the cycle of matter.
Plants and animals living in the Ocean absorb and concentrate in their bodies various substances in the water, including those that man has not yet been able to detect. Calcium and silicon are absorbed especially vigorously. Algae bind billions of tons of carbon annually and release billions of tons of oxygen. Water passes through the gills of fish when breathing; many animals, filtering food, pass through gastrointestinal tract a large amount of water, all animals swallow water with food. Ocean water somehow passes through the body of animals and plants, and this ultimately determines its modern salt composition.
Ocean waters have an average salinity of 35 ‰ (35 g of salt per 1 liter of water). Salinity changes are caused by changes in the input and output balance of salts or fresh water.
Salts enter the Ocean together with water flowing down from the land, are brought in and carried away during water exchange with neighboring parts of the Ocean, are released or consumed as a result of various processes occurring in the water. The constant influx of salts from land into the Ocean should have caused a gradual increase in the salinity of its waters. If this does happen, then so slowly that it remains undetected to this day.
The main reason for the differences in the salinity of the Ocean's water is the change in the balance of fresh water. Precipitation on the surface of the Ocean, runoff from land, melting of ice cause a decrease in salinity; evaporation, ice formation, on the contrary, increase it. The influx of water from land has a noticeable effect on salinity near the banks and especially near the confluence of rivers.
Since the salinity on the surface of the Ocean in its open part depends mainly on the ratio of precipitation and evaporation (i.e., on climatic conditions), latitudinal zoning is found in its distribution. It can be clearly seen on the map. isohaline- lines connecting points with the same salinity. In equatorial latitudes, the surface layers of water are somewhat freshened (34-35 ‰) due to the fact that precipitation is greater than evaporation. In subtropical and tropical latitudes, salinity surface layers increased and reaches a maximum for the surface of the open Ocean (36-37 ‰. This is due to the fact that the water consumption for evaporation is not covered by precipitation. The ocean loses moisture, while salts remain. To the north and south of tropical latitudes, the salinity of ocean waters gradually decreases to 33 -32 ‰, which is determined by a decrease in evaporation and an increase in precipitation. A decrease in salinity on the surface of the Ocean is facilitated by melting floating ice. Latitudinal zoning in the distribution of salinity on the surface of the Ocean is disturbed by currents. Warm currents increase salinity, cold currents, on the contrary, lower it.
The average salinity on the surface of the oceans varies. The Atlantic Ocean has the highest average salinity (35.4 ‰), the lowest is the Arctic Ocean (32 ‰). The increased salinity of the Atlantic Ocean is explained by the influence of the continents with its comparative narrowing. In the Arctic Ocean, Siberian rivers have a freshening effect (near the coast of Asia, salinity drops to 20 ‰).
Since the changes in salinity are mainly associated with the income and expenditure balance of water, they are well expressed only in the surface layers that directly receive (precipitation) and give up water (evaporation), as well as in the mixing layer. Mixing covers a water column with a thickness of up to 1500 m. Deeper, the salinity of the World Ocean remains unchanged (34.7-34.9 ‰). The nature of salinity changes depends on the conditions that determine the salinity at the surface. There are four types of vertical changes in salinity in the Ocean: I - equatorial, II - subtropical, III - moderate and IV - polar,
I. In equatorial latitudes, where the water on the surface is freshened, salinity gradually increases, reaching a maximum at a depth of 100 m, where more saline waters come to the equator from the tropical part of the Ocean. Deeper than 100 m, salinity decreases, and from a depth of 1000-1500 m it becomes almost constant. II. In subtropical latitudes, salinity rapidly decreases to a depth of 1000 m, deeper it is constant. III. In temperate latitudes, salinity changes little with depth. IV. In polar latitudes, the salinity on the surface of the Ocean is the lowest, with depth it first increases rapidly, and then, from about a depth of 200 m, almost does not change.
The salinity of water on the surface of the seas can be very different from the salinity of water in the open part of the Ocean. It is also determined primarily by the balance of fresh water, which means it depends on climatic conditions. The sea is influenced by the land it washed in significantly to a greater extent than the Ocean. The deeper the sea juts into the land, the less it is associated with the Ocean, the more its salinity differs from the average ocean salinity.
Seas in polar and temperate latitudes have positive balance water, and therefore the salinity on their surface is reduced, especially at the confluence of rivers. Seas in subtropical and tropical latitudes, surrounded by land with few rivers, have increased salinity. The high salinity of the Red Sea (up to 42 ‰) is explained by its position among the land, in a dry and hot climate. Precipitation on the sea surface is only 100 mm per year, there is no runoff from land, and evaporation reaches 3000 mm per year. Water exchange with the Ocean takes place through the narrow Bab el-Mandeb Strait.
Increased salinity Mediterranean Sea(up to 39 ‰) is a result of the fact that runoff from land and precipitation does not compensate for evaporation, water exchange with the Ocean is difficult. In the Black Sea (18 ‰), on the contrary, evaporation is almost compensated by runoff (annual runoff layer 80 cm), and precipitation makes the water balance positive. The lack of free water exchange with the Sea of Marmara contributes to the preservation of the reduced salinity of the Black Sea.
In the North Sea, experiencing, on the one hand, the influence of the Ocean, and on the other - strongly freshened Baltic Sea, salinity increases from southeast to northwest from 31 to 35 ‰. All the margins of the sea, closely connected with the Ocean, have a salinity close to the salinity of the adjacent part of the Ocean. In the coastal parts of the seas that receive rivers, the water is strongly freshened and often has a salinity of only a few ppm.
The change in salinity with depth in the seas depends on the salinity on the surface and the associated water exchange with the Ocean (or with a neighboring sea).
If the salinity of the sea is less than the salinity of the Ocean (neighboring sea) at the connecting strait, denser ocean water penetrates through the strait into the sea and sinks, filling its depths. In this case, the salinity in the sea increases with depth. If the sea is saltier than the neighboring part of the Ocean (sea), the water in the strait moves along the bottom towards the Ocean, along the surface towards the sea. The surface layers acquire the salinity and temperature characteristic of the sea in the given physical and geographical conditions. The salinity of the bottom waters corresponds to the salinity at the surface during the period of the lowest temperatures.
Various cases of changes in salinity with depth are clearly visible on the example of the Mediterranean, Marmara and Black seas. The Mediterranean Sea is saltier than the Atlantic Ocean. In the Strait of Gibraltar (depth 360 m) there is a deep current from the sea to the Ocean. The Mediterranean water descends from the threshold, creating an area of increased salinity at some depth in the Ocean near the threshold. On the surface in the strait, ocean water flows into the sea. The salinity of the water at the bottom of the Mediterranean Sea along its entire length is 38.6 ‰, while on the surface it varies from 39.6 ‰ in the eastern part to 37 ‰ in the western part. Accordingly, salinity decreases with depth in the eastern part, and increases in the western part.
The Sea of Marmara is located between two seas, the saltier Mediterranean and the less salty Black. The salty Mediterranean water, penetrating through the Dardanelles, fills the depths of the sea, and therefore the salinity at the bottom is 38 ‰. The Black Sea water, moving along the surface, enters the Sea of Marmara through the Bosphorus and freshens the water of the surface layers up to 25 ‰.
The Black Sea is heavily freshened. Therefore, water of Mediterranean origin penetrates from the Sea of Marmara into the Black Sea along the bottom of the Bosphorus and, sinking, fills its depths. The salinity of water in the Black Sea increases with depth from 17-16 to 22.3 ‰.
The water of the World Ocean contains colossal quantities of the most valuable chemical raw materials, the use of which is still very limited. About 5 million tons of table salt is annually extracted from the water of the oceans and seas, including more than 3 million tons - in countries South-East Asia... Potassium and magnesium salts are extracted from sea water. Bromide gas is obtained as a by-product in the extraction of sodium chloride and magnesium.
To extract chemical elements from water, which are contained in very small quantities, you can use the amazing ability of many inhabitants of the Ocean to absorb and concentrate certain elements in their bodies, for example, the concentration of iodine in a number of algae is thousands and hundreds of thousands of times higher than its concentration in the water of the Ocean. Molluscs absorb copper, aspidia - zinc, radiolarians - strontium, jellyfish - zinc, tin, lead. Fucus and kelp contain a lot of aluminum, sulfur bacteria - sulfur. By selecting certain organisms and enhancing their properties to concentrate elements, it will be possible to create artificial deposits of minerals.
Modern chemistry has received ion exchangers (exchange resins), which have the property of absorbing various substances from solution and retaining on their surface. A pinch of ion exchanger can desalinate a bucket of salt water, extract salts from it. The use of ion exchangers will make the richness of the Ocean salts more accessible for people to use.
Gases in the water of the Ocean. Gases are dissolved in the water of the Ocean. These are mainly oxygen, nitrogen, carbon dioxide, as well as hydrogen sulfide, ammonia, and methane. Water dissolves the gases of the atmosphere in contact with it, gases are released during chemical and biological processes, are brought by land waters, and enter the water of the Ocean during underwater eruptions. Redistribution of gases in water occurs when it is stirred. Due to the high dissolving power of water, the Ocean has a great influence on chemical composition atmosphere.
Nitrogen is present in the Ocean everywhere, and its content almost does not change, since it poorly enters into compounds and is consumed little. Some infiltrating bacteria convert it to nitrates and ammonia.
Oxygen enters the Ocean from the atmosphere and is released during photosynthesis. It is consumed in the process of respiration, for the oxidation of various substances, and is released into the atmosphere. The solubility of oxygen in water is determined by its temperature and salinity. When the surface of the Ocean is heated (spring, summer), water gives oxygen to the atmosphere; when it cools (autumn, winter), it absorbs it from the atmosphere. There is less oxygen in ocean water than in fresh water.
Since the intensity of the processes of photosynthesis depends on the degree of illumination of the water by the sun's rays, the amount of oxygen in the water fluctuates during the day, decreasing with depth. Below 200 m there is very little light, there is no vegetation and the oxygen content in the water decreases, but then, at great depths (> 1800 m), as a result of the circulation of ocean waters, it increases again.
The oxygen content in the surface layers of water (100-300 m) from the equator to the poles increases: at a latitude of 0 ° - 5 cm3 / l, at a latitude of 50 ° - 8 cm3 / l. The water of warm currents is poorer in oxygen than the water of cold currents.
The presence of oxygen in the water of the Ocean is a necessary condition for the development of life in it.
Carbon dioxide, in contrast to oxygen and nitrogen, is found in the water of the Ocean mainly in a bound state - in the form of carbonic compounds (carbonates and bicarbonates). It enters the water from the atmosphere, is released during the respiration of organisms and during decomposition organic matter, comes from the earth's crust during underwater eruptions. Like oxygen, carbon dioxide dissolves better in cold water. When the temperature rises, water gives off carbon dioxide to the atmosphere; when the temperature drops, it absorbs it. A significant part of the water dissolves in the Ocean. carbon dioxide atmosphere. The reserves of carbon dioxide in the Ocean are 45-50 cm3 per 1 liter of water. A sufficient amount of it is a prerequisite for the vital activity of organisms.
In the water of the seas, the amount and distribution of gases can be significantly different than in the water of the oceans. In the seas, the depths of which are not supplied with oxygen, hydrogen sulfide accumulates. This occurs as a result of the activity of bacteria using oxygen of sulfates for the oxidation of nutrients under anaerobic conditions. Normal organic life does not develop in a hydrogen sulfide environment.
An example of a sea whose depths are contaminated with hydrogen sulfide is the Black Sea. Increase in the density of water With depth, the balance of the water mass in the Black Sea is ensured. Complete mixing of water does not occur in it, oxygen gradually disappears with depth, the content of hydrogen sulfide increases, reaching 6.5 cm3 per 1 liter of water at the bottom.
Inorganic and organic compounds containing necessary for organisms elements are called nutrient.
The distribution of nutrients and energy (solar radiation) in the Ocean determines the distribution and productivity of living matter.
Ocean water density with an increase in salinity, it always increases, since the content of substances that have a greater specific gravity than water increases. The increase in density on the surface of the Ocean is facilitated by cooling, evaporation and the formation of ice. As the density of water increases, convection occurs. When heated, as well as when salt water is mixed with precipitation water and melted water, its density decreases.
On the surface of the Ocean, a change in density is observed in the range from 0.996 to 1.083. In the open Ocean, density is usually determined by temperature and therefore increases from the equator to the poles. The density of water in the Ocean increases with depth.
Pressure. For every square centimeter of the Ocean's surface, the atmosphere presses with approximately 1 kg (one atmosphere). The same pressure on the same area is exerted by a column of water only 10.06 m high. Thus, we can assume that for every 10 m depth, the pressure increases by 1 atmosphere. If we take into account that water contracts with depth and becomes denser, it turns out that the pressure at a depth of 10,000 m is equal to 1119 atmospheres. All processes occurring at great depths are carried out under strong pressure, but this does not prevent the development of life in the depths of the Ocean.
Ocean water transparency. The radiant energy of the Sun, penetrating into the water column, is scattered and absorbed. The transparency of water depends on the degree of its dispersion and absorption. Since the amount of impurity contained in water is not the same everywhere and varies over time, the transparency also does not remain constant (Table 20). The least transparency is observed off the coast in shallow water, especially after storms. Water transparency decreases significantly during the period of massive plankton development. The decrease in transparency is caused by the melting of ice (ice always contains impurities, in addition, the mass of air bubbles trapped in ice passes into water). It is noticed that the transparency of water increases in places where deep waters rise to the surface.
Currently, transparency measurements at different depths are performed using a universal hydrophotometer.
The color of the water of the oceans and seas. The clear water column of the Ocean (sea), as a result of the collective absorption and scattering of light, has a blue or blue color. This color of water is called "the color of the sea desert". The presence of plankton and inorganic suspended matter is reflected in the color of the water, and. it takes on a greenish tint. Large quantities impurities make the water yellowish-green, near river mouths it can even be brownish.
To determine the color of the Ocean water, use the scale of the color of the sea (the Trout-Ole scale), which includes 21 test tubes with liquid of different colors - from blue to brown.
In equatorial and tropical latitudes, the dominant color of the Ocean's water is dark blue and even blue. For example, the Bay of Bengal, the Arabian Sea, the southern part of the China Sea, and the Red Sea have such water. Blue water in the Mediterranean Sea, the Black Sea water is close to it in color. In temperate latitudes, in many places, the water is greenish (especially off the coast), it turns green noticeably in areas of melting ice. In polar latitudes, the greenish color predominates.
The properties of ocean water include temperature, clarity, and salinity.
Temperature. The temperature of the upper layers of the ocean differs slightly from the temperature of the surface environment. In warm latitudes, the ocean water temperature ranges from 25 to 30 ° C. In cold polar latitudes, it drops to -1-1.5 ° C, water at this temperature does not freeze due to salinity. With depth, the temperature of the water in the ocean decreases from 1 ° C to - 1 ° C.
Transparency.Sunlight penetrates the ocean waters to a depth of 200 m. Then visibility deteriorates, and darkness reigns at a depth of 500 m and deeper. For this reason aquatic plants live only in the illuminated part of the ocean depths. In the deep-sea parts of the ocean, living organisms are rare.
Salinity. The water in the oceans and seas is bitter-salty. Such water is not suitable for human consumption. Each liter of ocean and sea water contains an average of 35 grams of salt, mostly table salt.
The salinity of the inland seas is somewhat different from the salinity of ocean water. In warm latitudes, where evaporation is high, the salinity of water in the inland seas increases. For example, the salinity of the Red Sea, surrounded on all sides by sandy deserts, is 42 grams per liter (g / L). This is the saltiest part of the oceans. In less warm latitudes, as well as in places of confluence large rivers the salinity of the inland seas is decreasing due to the reduction of evaporation and the influx of fresh water. For example, the salinity of the Black Sea is 17-22 g / l.
Waves. The water in the oceans is rarely calm. As you approach the sea, the sound of the surf becomes noticeable. Waves approach the shore, foam and crash on it. The wind is the cause of rough seas. During the eruption of underwater volcanoes and earthquakes, huge waves with a ten-story building, called "tsunamis", arise.
Ocean currents. In ancient times, before the invention of radio, sailors from a ship in distress reported their fate with a note, which was sealed in a bottle and thrown overboard. The bottle with the tragic message was caught by people who lived thousands of kilometers from the site of the shipwreck. For example, thrown overboard off the coast South America a bottle with a message was found off the coast of the African continent, etc.
Subsequently, when people learned about the existence of ocean currents, they became aware of the reason why the bottle with the message traveled great distances.
As it turned out, there are permanent currents in the oceans. The constant movement of oceanic waters in a certain direction is called sea, or oceanic currents. The emergence of ocean currents is caused by constant winds. For example, the current of the westerly winds, the Tradewinds arise in this way. The current of the westerly winds bends around Antarctica. Its length is over 30 thousand kilometers. Ocean currents are divided into warm and cold. On geographical maps warm ocean currents are usually denoted with red arrows, and cold ones - blue.
Resources of the World Ocean. The ocean is home to a diverse flora and fauna. Seafood (fish, crabs, shellfish, seaweed etc.) are included in the human diet and serve as raw materials for the food industry.
The ocean is rich in plankton (microorganisms), which feed on the inhabitants of the sea. The largest mammal on Earth, the whale, also feeds on plankton. The whale reaches 30 m in length and weighs about 150 tons. The ocean is also rich in game animals (walrus, seal, sea otter, etc.), the fur, fat and fangs of which people use in everyday life.
There are many minerals in the ocean, for example, oil, gas, gold, etc. Life requires a caring attitude from a person natural resources Of the World Ocean. Overfishing and hunting can cause irreparable damage to the ocean. For example, due to uncontrolled hunting, whales are on the verge of extinction. Pollution of the ocean with oil products and toxic industrial waste leads to the death of the flora and fauna of the oceans.
The depths of the ocean are studied using special underwater vehicles - bathyscaphes. The Swiss scientist Jacques Picard in the bathyscaphe "Trieste" in 1960 sank 11,000 m deep into the ocean in the Mariana Trench.
Attention! If you find an error in the text, select it and press Ctrl + Enter to notify the administration.
Salinity is an the most important feature ocean water. This solution contains almost all chemical elements known on Earth. The total amount of salts is 50-10 16 tons. They can cover the ocean floor with a layer, they can cover the ocean floor with a layer of 60 m, the entire Earth - 45 m, land - 153 m. The ratio of salts in ocean water remains constant, this is ensured by the high dynamics of ocean waters. The composition is dominated by NaCl (77.8%), MgCl (10.9%), etc.
The average salinity of the ocean water is 35 0/00. The deviation from the average salinity in one direction or another is caused by changes in the incoming and outgoing balance of fresh water. So, atmospheric precipitation, water from glaciers, runoff from land reduce salinity; evaporation - increases salinity.
There are both zonal and regional features in the distribution of salinity in the ocean. Zonal features are associated with climatic conditions (distribution of precipitation and evaporation). In the equatorial zone, the waters are slightly saline (O> E), in tropical and subtropical latitudes (E> O), the salinity is maximum for ocean surface waters - 36-37 0/00, to the north and south of this zone salinity decreases. Melting of ice contributes to the decrease in salinity in high latitudes.
Latitudinal zoning in the distribution of salinity on the ocean surface is disturbed by currents. Warm ones increase salinity, cold ones lower it. The average salinity of the oceans on the surface is different. The highest salinity is in the Atlantic Ocean - 35.4 0/00, the least in the Arctic Ocean - 32 0/00 (the desalination role of Siberian waters is great). Salinity changes are mainly associated with surface layers directly receiving fresh water and determined by the depth of mixing. All changes in salinity occur in the upper layers to a depth of 1500 m, deeper salinity does not change.
World ocean water temperature.
Changes in the course of heat balance elements determine the course of water temperature. The daily amplitudes of water temperature fluctuations on the ocean surface do not exceed, on average, 0.5 0 C. The largest daily amplitude is at low latitudes (up to 1 0 C), the smallest - at high latitudes (up to 0 0 C). Daily fluctuations in ocean temperature play a subordinate role.
Annual amplitudes of temperature fluctuations on the ocean surface are greater than daily ones. Annual temperature fluctuations are small at low (1 0) and high (2 0) latitudes. In the first case large quantities it is evenly distributed throughout the year, in the second - during the short summer, the water does not have time to heat up very much. The largest annual amplitudes (from 10 0 to 17 0) are noted in temperate latitudes. The highest average annual water temperatures (27-28 0) are observed in equatorial and tropical latitudes, to the north and south of them the temperature drops to 0 0 C and below in polar latitudes. The thermal equator is located at about 5 ° С N. Ocean currents violate the zonal temperature distribution. Currents that transfer heat towards the poles (for example, the Gulf Stream) stand out as positive temperature anomalies. Therefore, in tropical latitudes, under the influence of currents, the water temperature at the eastern coasts is higher than at the western ones, and in temperate latitudes, on the contrary, at the western ones it is higher than at the eastern ones. In the southern, more seaward hemisphere, the zoning in the distribution of water temperatures is almost not disturbed. The most heat on the ocean surface (+32 0 С) was observed in August in the Pacific Ocean, the lowest in February in the Arctic Ocean (-1.7 0 С). On average, per year, the ocean surface in the southern hemisphere is colder than in the northern (the influence of Antarctica). The average annual temperature on the ocean surface is + 17.4 0 С, which is higher than the annual air temperature +14 0. The warmest is the Indian Ocean - about +20 0 C. The heat of solar radiation, heating the upper layer of water, is extremely slowly transferred to the underlying layers. The redistribution of heat in the ocean water column occurs due to convection and mixing by waves and currents. Hence, the temperature decreases with depth. At a depth of about 100-200 m, the temperature drops sharply. The layer of a sharp drop in water temperature with depth is called a thermocline.
Thermocline in the ocean from the equator to 50-60 0 s. and y.sh. exists constantly at depths from 100 to 700 m. In the Arctic Ocean, the water temperature drops to a depth of 50-100 m, and then rises, reaching a maximum at a depth of 200-600 m. This increase in temperature is caused by penetration from temperate latitudes warm waters saltier than the upper layers of water.
Ice in the ocean appears at high latitudes when the water temperature drops below freezing point. The freezing point depends on its salinity. The higher the salinity, the lower the freezing point. Ice is less dense than fresh ice. Salted ice is less durable than fresh ice, but more plastic and viscous. It does not break on swell (weak excitement). It acquires a greenish tint, in contrast to the blue color of fresh ice. Ice in the ocean can be stationary and buoyant. Fixed ice is a continuous ice sheet associated with land or shoals. This is usually ice fast ice. Floating ice (drifting) is not connected to the shore and is moved by wind and currents.
