Looking at the physical map of the hemispheres, you can see the uneven distribution of land and water on the surface of the planet. Huge continents are scattered across the expanses of the oceans like islands. In the Southern Hemisphere, land accounts for less than 20%, in the Northern Hemisphere - about 40%. What is called the oceans in geography, ecology and other earth sciences? This is the most significant part of the hydrosphere - the water shell of our planet. How many oceans on Earth exist, which one is the largest in area and the warmest? These and many other questions are answered in the proposed article.
What is called the World Ocean (MO)?
All water on Earth forms a single shell, parts of which are connected by a cycle of H 2 O molecules and other substances. MO is a continuous part of the hydrosphere, which accounts for over 94% of the total water area on the planet (oceans, seas, bays, straits, rivers, lakes and ponds). Usually, Russian geographers distinguish 4 main parts of the oceans. We list them in decreasing order of surface area (million km 2 ): Pacific (179), Atlantic (92), Indian (76), Arctic (15).
How did people learn about the relationship between the oceans?
Since ancient times, man has been attracted by the vast expanses of the sea. Already in ancient times, on fragile boats, rafts and catamarans, fishermen went on dangerous water trips. The history of the oceans mentions ancient descriptions, legends, legends of overcoming vast distances on rafts, rowing and sailing ships. It is believed that the settlement of continents and islands in ancient times was due to the ability of people to overcome oceans and seas.
The first known round-the-world trip was made by the Spanish squadron under the leadership of Fernand Magellan in 1519-1522. Moving from the Iberian Peninsula to the west, ships crossed the Atlantic Ocean, circled South America, entered unknown waters. The weather was calm, so Magellan called the Pacific Ocean. In a clash with the aborigines in the Philippines, many Spanish sailors along with the head of the expedition died. Companions of Magellan continued their journey west in search of spices, gold, jewelry for the Spanish crown.
One of the ships, led by Captain Juan Elcano, crossed the central part of the Indian Ocean, circled Africa from the south and returned to Europe. So the sphericity of the Earth was proved, the existence of another part of the World Ocean was established. Circumnavigation and other trips in the era of the Great Geographical Discoveries marked the beginning of a large-scale study of water spaces in the interests of trade, science, industry and fisheries.
MO - the main part of the hydrosphere
When studying the topic “World Ocean” (Grade 7), it is necessary to recall the previously studied material of Grade 6 (“Hydrosphere”). The single water shell of the Earth is two parts of unequal size - MO and land water. They are interconnected by a cycle of matter and energy, moisture transfer, surface and underground runoff. What is called the oceans in modern science? The term itself has been used in relation to large bodies of water since the 17th century thanks to the work of the German-Dutch explorer Bernhard Varenius.
At the beginning of the 20th century, the Russian scientist Yu. M. Shokalsky introduced the term “World Ocean” into scientific use and identified 4 main parts of the Moscow Region. These are huge oceanic natural complexes, separated from each other by continents and archipelagos (chains of islands). Minor branches of the MO are bays, straits, and seas (marginal and inland).
The traditional division of MO into parts
Borders are often conditional, since there is a single body of water - the oceans. The MO map gives an idea of the variety of dividing lines. For example, the Pacific Ocean and the Arctic Ocean are separated from each other by peninsulas (Chukotsky and Alaska), connected by a narrow Bering Strait. The border between the Atlantic and Indian oceans south of Africa is drawn at 20 ° c. d.
In a number of countries it is customary to divide the bulk of the hydrosphere into 5 or even 7 separate regions. In these cases, the Southern Ocean and two parts of the Atlantic are added. Depending on the country of residence, the answer to the usual question for the school curriculum is “What is called the World Ocean?” differs in the number of allocated parts (oceans of the Earth).
Science of the oceans and parts thereof
The study of the bottom topography, temperature, salinity of water, currents and other features of large water spaces is carried out by oceanology (section of geography). Different parts of MO differ in the content of dissolved substances, densities, the measurements of which are carried out using modern instruments at tens of thousands of points.
Determination of depths using echolocation made it possible to calculate the total amount of sea water on the Earth and the compounds dissolved in it (chlorides, sulfates, iodides of practical importance). The waters of the oceans have an average density of 1,024 g / cm 3 . Such a liquid does not freeze at 0 ° , but at –1 ... –3 ° . The deeper, the less temperature readings depend on geographic latitude.
Depth of the oceans
How to find out the largest and smallest distances to the bottom surface? What are the depths on which the oceans differ? Map MO contains information about the average and maximum depth. Sea spaces are indicated by various shades of blue. Dark color on the maps corresponds to the deepest places.
Light blue color is used to display shallows, mid-ocean ridges. The Pacific Ocean is considered the deepest; in its northwestern part there is the Mariana Trench with a depth of over 11 km. Off the western coast of Chile runs the Peruvian Trench (about 7 km). And the average depth of the MO is 3.7 km.
Bottom relief
The continuation of the surface of the continents under water is a continental shallow, in some places its depth reaches 1 km. The oceans around the perimeter has another transition zone - the continental slope. Within the mainland shallows, plains of different origin are distinguished; there are deeply lowered plots in the Sea of Okhotsk, Barents and Japan. The ocean bed covers the central parts of the bottom and is different in shape and size of the basin, the hill. Deep-water troughs arose in the areas of collision of oceanic lithospheric plates with continental ones.
Among the mountain structures of the seabed, mid-oceanic shafts and ridges prevail, which are connected into a single continuous chain with a length of over 40 thousand km. In addition, block and volcanic ridges, massifs and single underwater peaks are distinguished on the ocean floor. Other forms of bottom topography are plateaus and hills.
The movement of water in the MO
Various causes and natural phenomena cause the movement of water masses in the oceans:
- water movements up and down occur under the influence of wind;
- constant air currents lead to the formation of currents;
- ebbs and flows causes the attraction of the oceans to the moon;
- as a result of eruptions of underwater volcanoes, giant waves appear - tsunamis.
On the maps of Moscow Oblast in the atlases, the currents are indicated by red and blue arrows. Color conveys such a feature as a higher or lower temperature in the course compared to the environment of the ocean. Largest warm streams: Gulf Stream in the northwestern Atlantic, Kuroshio near the Japanese Islands, North Atlantic Current. Cold water streams in the Moscow Region: current of the West winds, Peruvian, Bengel.
MO water temperature
The polar and circumpolar parts of the MO are the coldest. A significant surface area of the Arctic Ocean is covered with perennial ice of great thickness. In the Arctic and Antarctic there are ice fields and blocks in the water - icebergs. The coldest ocean is the Arctic Ocean, a significant part of which is frozen all year round. As you move from the Arctic Circle to the temperate zones, the Northern and Southern tropics, the water is more heated by the Sun. The Pacific Ocean is considered the warmest, the widest in the hot zone of illumination.
Surface water temperature changes faster. As a rule, the main flow of solar energy does not penetrate to the depth. Therefore, in summer in temperate and tropical latitudes, the surface water temperature is higher than in winter. At great depths, seasonal differences are almost not felt. When moving from the surface for the first hundreds of meters, a marked decrease in temperature is noticeable. Over 1 thousand meters, the changes are less pronounced, and below 3 thousand meters the temperature is constantly in the range + 2 ° ... 0 ° .
The impact of MO on the climate of the continents
The oceans are important for the formation of climate and weather on land. The average water surface temperature of the MO is 17.4 ° C, while at the Earth's surface this indicator is 14.4 ° C. Oceans can have a significant impact on the exchange of heat and moisture between the atmosphere and land. Water heats and cools more slowly than continents and islands, due to the large specific heat.
Currents move cold water masses to warmer regions, and vice versa. These processes have a large effect on the distribution of pressure and air temperature. In winter, Moscow Region is a kind of “stove” for heating the continents, and in summer - a “refrigerator." Existing problems of the oceans - melting ice, rising water levels - threaten a change in climatic conditions and vegetation on the continents, natural disasters.
Salinity
Almost all elements of the periodic table are present in different amounts in sea water. The average content of various salts is 3.5%. A special unit of measurement is used - ppm - showing the amount of dissolved substances in grams per 1 liter of seawater ( 0/00 ) . The average salinity of the MO is 35 0/00 . The connection between the geographical position, the distribution of surface currents, evaporation, salinity and other properties that distinguish the oceans is traced. MO water resources far exceed land reserves. Evaporation is used to extract useful compounds, and special desalination plants on sea vessels and in coastal areas of many countries are used to obtain drinking water.
A significant amount of salts accumulate ocean waters, which are between 45 ° C. w. and 10 ° s. w. The content of substances in sea water depends on the surface runoff from the mainland, the thickness of the ice and its melting. The most saline parts of the MO are confined to tropical latitudes. This is the northwestern part of the Indian Ocean - the Red Sea and the Bab el-Mandeb Strait (41 and 42 ‰, respectively). The salinity of the Mediterranean Sea is 39 ‰.
Natural Resources MO
A pantry of valuable chemicals, fuel, a source of energy, fresh water, products, a home for many living organisms - all this is the World Ocean. The geography of mineral reserves has not yet been sufficiently studied at great depths, and offshore development has been underway for many decades. The following natural resources of the MO are of great value:
- fuel (oil, gas, coal);
- metallic and non-metallic minerals (table salt, iron, manganese, bromine, calcium, gold, diamonds, amber, titanium, tin);
- energy (tides, waves, hot springs);
- building materials (sand, gravel);
- reserves of water for desalination;
- fish, marine mammals, crustaceans, mollusks, sponges;
- vegetable;
- recreational.
Since ancient times , the oceans, coastal zone resources have been used for shipping, marine fishing, cruise and beach recreation, and restoration of public health. Popular beaches are located on the warm sandy coasts of the Mediterranean, Red and Black Seas, the Atlantic, Indian, Pacific Oceans in the subtropical and tropical climatic zones.
The environmental problems of the oceans are largely associated with an increase in mining. When spilling oil and oil products, an airtight film forms on the surface of the water. The exchange of oxygen and carbon dioxide between the atmosphere and the ocean is disrupted, aquatic animals and plants die.
"Fish latitudes" of the oceans
Oceans and seas are areas of intensive fishing, coral and pearl mining. Approximately 10% of food raw materials account for marine fisheries. Commercial fish of the World Ocean are sardines, anchovies, herring, tuna, salmon, hake, capelin, mackerel, notothenia, pollock, cod, halibut, sprat, flounder.
In those latitudes where there are conditions for the development of plankton, an abundance of fish is observed. For the multiplication of small organisms suspended in water, it is necessary that the so-called biogenic elements (nitrogen, silicon, phosphorus, calcium and others) rise from the bottom. Nature created similar conditions in many regions of the Moscow Region:
- off the Pacific coast of South America south of the equator;
- in the area of the Labrador Peninsula, off East Greenland in the north;
- near the coasts of Europe and North America in the Atlantic Ocean, near 40 ° C. W .;
- from the shores of Morocco in West Africa to the extreme point in the south of the hot continent;
- off the coast of Burma in the Indian Ocean, in the region of the islands of Indonesia.
The world's oceans, as the most significant part of the Earth’s continuous water envelope, plays a huge role on the planet, and its wealth has been used by man since time immemorial. According to their individual characteristics, parts of the MO are different, but this is an integral natural complex of a planetary scale, which must be preserved for the well-being of the present and subsequent generations.