Ocean

When Ocean (plural the oceans, from the Greek Ὠκεανός ( " Ocean "), which the Earth disk circumfluent world power, as a personification of ancient god Oceanus ) is defined as the greatest oceans of the earth. Synonym and as a transfer in German also ocean.

  • 6.1 upwelling
  • 6.2 Open Ocean
  • 6.3 shelf
  • 6.4 deep Sea
  • 6.5 Ocean Floor

The location

A total of 71 percent of the earth's surface is covered by oceans ( the oceans and their marginal seas ). They focus on the water hemisphere whose center is located in the vast Pacific near New Zealand. On the opposite hemisphere country are only the Atlantic Ocean, the Arctic Ocean and parts of the Southern Ocean and the Indian Ocean.

The distribution of the oceans

The five oceans of the earth are

  • The Arctic Ocean ( Arctic Ocean ),
  • The Atlantic Ocean ( Atlantic )
  • The Indian Ocean ( Indian Ocean )
  • The Pacific Ocean ( Pacific, also called Pacific Ocean ) and
  • The Antarctic Ocean ( Southern Ocean ).

In common parlance, one speaks of only three oceans: Atlantic Ocean, Indian Ocean and Pacific Ocean. From this perspective, the Arctic Ocean is considered part of the Atlantic and the Southern Ocean, as delimited by the 60th parallel south is defined, counted among the three first-mentioned oceans.

An alternative approach divides the two largest oceans of the earth according to their affiliation to the north or south hemisphere in North and South Atlantic, North and South Pacific and is one of the Indian Ocean, the Arctic Ocean and the Southern Ocean to do so.

Historically, one speaks of the seven seas, in addition to the Pacific, Atlantic and Indian Oceans and the Caribbean Sea, the Mediterranean Sea, the Yellow Sea and the North Sea include (or other seas, which are considered dependent seas of the oceans, such as the Black Sea and the Baltic Sea ).

Another alternative is the " divine " with the number seven related approach from the Judeo- Christian world. It divides the earth into seven continents ( North America, South America, Europe, Africa, Asia, Oceania, Antarctica ) and the seven seas / oceans ( North Atlantic, South Atlantic Ocean, Arctic Ocean, the Southern Ocean, Indian Ocean, North Pacific, South Pacific ). → Seven Seas

Shape of the oceans

The individual oceans that lie between the continents, differ from one another by volume, salinity, private tidal system, waves ( swell ) and ocean currents as well as geologically from the other parts of the world ocean.

Within the oceans and their marginal seas or on the ocean floor are often very high and elongated mid-ocean ridges, sometimes very many, and lower thresholds, large and small ocean basins, deep-sea trenches and various marine lows and in the Pacific the Pacific Ring of Fire. In addition, numerous islands, island groups and archipelagos of these seas and peninsulas jut out into this. Northern and the Southern Ocean are partly or completely covered by pack and drift ice.

The bottom of the ocean is the top of a piece of oceanic crust. His figure is explained by the theory of plate tectonics. After that new ocean floor at mid-ocean ridges and flows arises away until he plunges into a deep trough ( subduction zones ) into the earth. This means that an ocean be larger, smaller, newly created and also can disappear. So it is believed that the Atlantic Ocean is approximately 150 million years old. Earlier oceans, for example, the Mirovia, the Panthalassa, the Rheische ocean, the Iapetus or the Tethys with the "European" marginal sea Paratethys.

The coastline depends not only on the shape and position of the continents, but also on the volume of sea water. So there is at low temperatures less sea water, as large amounts of water stored as ice sheets and glaciers on the continents, with rising temperatures, however, it is due to thermal expansion and the melting of ice sheets to sea level rise ( transgression ). Other factors include the rising and falling of the ocean floor due to geological events.

In the global average, the ocean has a depth of 3682.2 m. This value will be more accurate if in the future such as the underwater mountains are measured completely right, because currently there are many underwater mountains only indirect, as determined by Earth Satellite Measurements. This is possible because an underwater mountain range creates a locally increased gravity and so a slightly lower water level can be measured above (see geoid ).

Water movements

The body of water in an ocean is not uniform, but varies with depth. There are large, stable water movements, ocean currents. Most important, the so-called Global conveyor belt, a combination of ocean currents, the four of the five oceans is to be connected together to form a global water cycle in the surface currents and deep currents. This may come from several 1000 m to the formation of large water swirls or eddies at a depth. Even mid-ocean ridge can lead to turbulence. Large water eddy of 50 km to 200 km in diameter, which hold for several weeks and carry cold, nutrient-rich deep water to the sea surface, are also observed.

Water waves Show at the sea surface. It can be generated by the wind irregular water movements, which are quantifiable by a Seegangsskala. Individual waves or wave groups, the so-called " rogue waves ", are particularly dangerous waves that result from superposition of several modes and thereby can reach heights of over 25 m. The tsunamis are caused by earthquakes and volcanic eruptions waves, the only pile up to dangerous heights near the coast.

The problems caused in the course of the day by tidal sea level fluctuations are against regularly and in severity affects the specific geometric shape of the coastline.

The wind produces water transport in the ocean. Taking into account the Coriolis force occurs in the upper layers (up to about 50 m ) to a corkscrew flow.

Seawater

Basics

See also: halocline, thermocline, chemocline, chemocline, salinity and acidification of the oceans

60 cubic kilometers of sea water are chemically bound in the ocean floor per year by serpentinization. Add to that the saturation of the sediments on the sea floor with water. In subduction zones, this water is clear again.

Oxygen distribution

The oxygen content of the seawater near the sea surface is determined by the transfer of oxygen from the air into the water and the biological production of oxygen from carbon dioxide ( CO2) by marine phytoplankton. Therefore, it can be used to over-saturation (oxygen saturation > 100 percent) of the surface water are common in the tropics at times, so that oxygen is released more in the air. However, the phytoplankton consumed in the darkness itself a part of the oxygen produced.

With increasing water depth and the related decrease in the sun light, the oxygen saturation of the sea water decreases. In addition to respire the oxygen by the zooplankton and bacterioplankton also a part of the increasing biodegradation of biomass to reduce the oxygen content helps. In the ocean, it does not tip over the deep water, as in the Labrador Sea, in the Greenland Sea and the Weddell Sea oxygen-rich surface water is formed, which sinks into the deep ocean and is distributed over the low flow of the global conveyor belt worldwide. The oxygen distribution in the deep sea is not uniform; there exist so-called oxygen minimum zones, where it is used for example for anaerobic ammonia oxidation and denitrification ( by anaerobic respiration of bacteria produced molecular nitrogen, which escapes from the water into the air ). These areas are often found in the tropics, so there is a significant in the Arabian Sea oxygen minimum zone at a depth of 200 m to 1150 m.

Ocean ecosystem

For the ocean ecosystem the decreasing with increasing depth sunlight is of great importance. On the top, filled with the sunlight part of the ocean, the euphotic zone, plants use photosynthesis to absorb energy. It joins including the dysphotic zone, where sunlight is only sufficiently present to see. In the underlying layer, the aphotic zone, no sunlight is available.

Another important characteristic of the oceans is that the sea water chemically behaves differently at different depths. Marine organisms such as clams, corals, coralline algae and diatoms use calcium carbonate and silica biomineralization by the construction of shells and skeletons. However, these biominerals can be chemically broken down by the sea water. So there is for the calcium carbonates aragonite and calcite in the oceans a lower depth, from which they dissolve, calcite and aragonite compensation depth.

The depth profile of an ocean is divided into several stages. It begins with the up to 200 meters deep reaching down shelf area. This is followed by the continental slope connects which can occupy a depth of up to 2000 m or 3000 m. The following are the Abyssal with a maximum depth of 6000 m and below the Hadal.

Upwelling areas

The very rare, mostly seasonal upwelling areas are very rich in nutrients. In them cold deep current rises and replaces the nutrient-poor warm surface water.

Open Ocean

The Open Ocean covers about 80 percent of the surface of the ocean, but only 1 percent of the biomass is produced there. In this oligotrophic area limited mainly to the lack of nitrogen and phosphorus in the sea water, the growth of marine plants (phytoplankton ). But the lack of important metals such as iron, has a growth retardant, which is why experimenting with iron fertilization of HNLC areas.

At the surface of sea water, the neuston is found.

Large eddies, where cold, nutrient-rich water from the deep sea is promoted to the sea surface, seem like a briefly existing upwelling region and lead to an explosive growth of phytoplankton. The same effect of tropical cyclones.

Important are large surveys of the sea floor, sometimes to reach up to the water surface, such as single underwater mountains ( seamounts and guyots ) and large submarine mountain range. These surveys affect ocean currents, so that there transported over long distances, nutrient-rich deep water to ascend to a shallower depth and therefore may result in a oasis of life in an otherwise nutrient-poor part of an ocean.

Shelf

→ Main article: shelf

The transition between the mainland and the deep sea is formed by up to 200 meters water depth reaching down shelf, the continental slope and the continental rise followed.

The shelf waters of the oceans are rich in nutrients and of great economic importance to the bordering countries. In this respect, the legal construct of Exclusive Economic Zone was created to assume the now mostly over-fished fishing grounds and possible deposits of oil and gas areas of national jurisdiction. In the European Union, the Common Fisheries Policy applies.

Tangwälder grow on mostly peaceful, rocky, 15 m to 40 m deep shelf areas. The eponymous kelp is a multicellular algae, rooted on the seabed.

On soft soil in shallow sea or in the watt range form plants from the family of seagrass plants partially extended seagrass meadows. In addition to their great ecological significance, they are also important for coastal protection.

Deep sea

→ Main article: Deep Sea

The deep sea is a hitherto little -researched area of the oceans. With manned deep-sea submarines for medium and large depths, as well as unmanned autonomous and remotely operated submersibles images are recorded and collected samples since the 20th century on the spot. Until then (1872-1876) from a depth of up to 8000 m or the Valdivia Expedition ( 1898-1899 ) made could only networks, for example on the Challenger Expedition caught about 4600 m depth, more or less squashed creatures from the deep sea.

In contrast to the exposed upper region of the ocean through the deep sea to be little or no sunlight reached, so that there is no possible photosynthesis. Most deep-sea animals migrate at sunset from the weak light zone up in the daytime by exposed area to where they feed on, and dive at sunrise again. During this migration they encounter lurking predators. The most frequent walkers are copepods, jellyfish and krill. Survival is important for the animals living here is that they do not stand out against the color coming from above weak blue light. Important stealth techniques are transparency and counter lighting by illuminating the body underside existing light organs depending on lighting conditions vary greatly in blue. This bioluminescence wins in the open sunlight zone of the deep sea even more important. So there are deep sea fish that attract prey with flares or partner.

The almost colorless, transparent jellyfish in the blue spotlight

Vampire squid hunt with light and push in the run glowing particles from.

Deep-sea angler fish with a light organ above the snout

Ghosts fish have large, upward eye

Ocean floor

→ Main article: Ocean Floor

The ocean floor is the largest area on earth habitat and includes the bottoms of the coasts, the shelves, the continental slopes, the great abyssal plains and deep-sea trenches.

The ocean floor at a continental slope is usually made ​​of sand and gravel, in the intertidal zone and of silt and mud. Of the continents farther it consists mainly of clay and remains of microorganisms that sink in the form of so-called sea snow from the surface to the bottom of an ocean slowly. In this way, a 800 m thick on the average layer of deep-sea sediments, which is an important part of the deep biosphere.

The organisms in the ocean floor feed on the falling down remains of plants and animals, and occasionally of dissolved volcanic gases. It is also conceivable that hydrogen produced by radiolysis of bacteria is used as a power source. In the top still oxygenated sediment layer live bacteria and archaea few, while including only archaea are still to be found. In the open ocean of the South Pacific Ocean, in an area where the annual accumulates little marine snow, a lot of oxygen could be measured in the sediment at depths of up to eight meters, while carbon in turn was hardly available. There a few but very active found in need of oxygen bacteria. Smaller animals in the upper sediment layer, for example, worms, snails and mussels.

On the ocean floor grow up to 50 meters deep tropical coral reefs and the highly endangered by the trawling cold water reefs on the continental slopes to depths of 1000 meters. Other typical living on the seabed marine animals are sea anemones, tube worms, sponges, sea urchins, sea cucumbers, starfish, brittle stars and ground-dwelling fish such as gurnard, flatfish or compound eyes fish.

At some undersea mountains, the mid-ocean ridges, there are hot springs. These are deposited ore slurry and form the basis for the sunlight completely independent ecosystem of the Black Smoker (see also Lost City). In the vicinity of deep-sea trenches and at sites where methane hydrates become unstable as a result of landslides, there are cold springs, the so-called cold seeps, also called methane sources. They arise because of the seabed water, enriched with methane and hydrogen sulfide, for example, flows. Bart worms that live in symbiosis with bacteria found in the hot and cold springs. At the hot springs there are a versatile and biomass of fauna, consisting for example of yeti crabs and certain types of clams, snails and shrimp. The ecosystem of the cold springs is similar to the hot springs, just missing there, the elevated temperature of the sea water, it is more durable and the transition to non-specialized fauna is easier. Another important ecosystem are the carcasses of large creatures, such as whales that sink to the ocean floor where they serve for months to decades different creatures as a food source. These are eg sharks, hagfish and bone -eating worms.

Conservation

→ Main article: Marine Protected See also: Garbage Patch, dumping of waste acid, nuclear waste, sewage from ships ( MARPOL), as well as underwater noise

International treaties

See: law of the sea, UNCLOS and Seabed Treaty

Oceans on other planets and satellites

There is probably hidden under a giant ice crust, a global ocean ( Eismondozean ) on Jupiter 's moon Europa, and perhaps also to the other moons Ganymede and Callisto. Much evidence suggests that Mars in the early period of its development contained open water. Smaller oceans or even lakes of hydrocarbons (methane, ethane ) could all year round or only exist on Saturn's moon Titan at times. Furthermore, if the gas planets Jupiter, Saturn, Uranus and Neptune perhaps layers of liquid phases, possibly of helium or hydrogen, accommodate, can only be speculated. On the origin of the oceans see origin of terrestrial water.

The only moon in the sea, which is called " ocean ", the Oceanus Procellarum, the Ocean of Storms.

Oceaneum

There are large aquariums that mimic different ecosystems of the oceans. These include the Oceanarium de Lisboa and the Oceaneum Stralsund.

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