Seabed

The ocean floor (also called seabed or ocean floor ) is the area covered by sea water part of the lithosphere of the Earth and thus takes 71% of the planet's surface a. He is in the area of ​​the continental margin of the continental, in the other regions of oceanic crust.

Ocean floors are the global average in about 3.8 km depth below sea level ( Kossinna, 1921). The vast and deep ocean basin is offset by a much lower average height of the continents, which is only about 230 m, which is due to the extensive lowlands, which cover about ten times more area than the mountains.

  • 2.1 shallow sea deposits
  • 2.2 Deep-sea deposits

The relief of the ocean floor

The seabed is uniform on its nature here than the mainland, because it is exposed to only a few erosive forces. These are mainly to trends, but also icebergs can erode the seabed.

From the continental shelf to the deep sea

Like a belt framed a shallow lake region, the shelf, also called the continental shelf, the coasts of the continents. It arose in part as a result of lower water levels during the ice ages and averages up to 200 m below sea level, but can also reach depths between 50 m and 300 m. Its width varies from 10 km in the Bay of Biscay and 200 km at the northern coast of Siberia.

Where higher currents flow into the sea, their erosive power can deep canyon-like incisions tear in the shelf. These canyons that come from the current profile during the ice ages, but can still be deepened.

On the shelf seaward zones follows the 80 km wide continental waste, which is usually relatively smooth to a depth continues 3500-4000 meters.

Approx. 50 % of the ocean floor are located in around 4000 to 5000 m depth.

Islands and mid-ocean ridge

Between the individual ocean basins, there are often islands or island chains, but also individual underwater mountains exist in large numbers. The largest mountain range in the oceans is the mid-ocean ridge, with 60,000 kilometers of the longest continuous mountain range on earth that runs around the whole earth. But the Mid-Atlantic Ridge is already over 15,000 km long.

This long, narrow, mostly submarine mountain ranges running rarely reach such a large amount that they are visible as islands above the sea surface, as is the case for example in Iceland. The crest of these thresholds or back is criss-crossed along its entire length by a central grave zone that is several times offset from each other by transverse fractures, the transform faults.

The mid-ocean ridges owe their existence to the rupture of the oceanic crust along the plate boundaries. Here comes basaltic magma from the mantle and solidifies on the seabed. The ever nachdrängende magma pushes the ocean floor around 2-12 cm annually by both apart and fills the resulting gaps with solidifying basalts. The new oceanic crust that constantly forms by this so-called seafloor spreading, is subducted at the borders of the continents in each different strength, which is why the continents drift.

Deep-sea trenches and island chains

In some areas of the oceans, there are narrow, elongated, so-called deep-sea trenches (obsolete deep-sea trenches ), which is 40 km wide and 6 km deep on average. Here the greatest depths of the ocean floor are measured. At some of these places the deep sea reaches up to 11 km in depth.

Deep-sea trenches are found exclusively in areas of subduction zones and thus follow the plate boundaries of the Earth's crust: Here push heavier oceanic crust parts with a few centimeters per year under lighter continental crust. Here the ocean floor also crustal material is not only drawn to great depths, but postponed so as to form, accompanied by frequent earthquakes, often volcanic island chains in the country side facing the gutters. This " Pacific Ring of Fire " made ​​on Kamchatka in eastern Siberia continental mass and elsewhere led to the emergence of the islands of the Aleutian Islands, Japan, the Philippines, etc.

As deepwater channel of the Mariana Trench in the Pacific reached the record depth of 11,022 m below sea level. The deepest trough of the Atlantic is the Puerto Rico Trench at 9,219 m below sea level and the greatest depth in the Indian Ocean is 8,047 m below sea level.

Yet all forms of life are not explored that can live at the base of deep-sea trenches under the extreme conditions of the absence of light and the high pressure. Because lost almost all the sediments of the sea floor at the subduction past geological eras, relatively little is known about the life world of the deep sea.

Flat and inland seas

The floors of most inland seas are less structured, as can be observed about the examples Baltic Sea and Caspian Sea. An exception is the Mediterranean: It is in the tension of the African and Eurasian plate, which manifests itself particularly in its eastern neighboring countries. Before Greece it reaches almost 5000 meters depth, while it has only 200 m in the center of the Aegean. Separation from the western Mediterranean is Sicily with the great volcano Etna and many smaller volcanoes further north dar. As Africa moved steadily to the north, it collides with the Eurasian Plate and will raise the Mediterranean floor in the coming geological time and wrinkle. By currents sediments are supplied in deeper areas, until the bottom of the Aegean eventually silt up and will be involved in an orogenic phase already.

Sediments of the ocean floor

Ocean floors are usually covered with deep-sea sediments, whose thickness is 800 m on average, but varies in extreme cases between 0 and 5 km. As ocean floors are constantly replaced by the mid-ocean ridges forth and dive to the ocean margins in the subduction zones again, the sediment thickness increases with increasing distance to the back. The deposits are divided depending on the water depth in shallow sea and deep sea sediments.

Shallow sea deposits

The flat comprises the sea washed over the ocean part of the continental shelf, also called the continental shelf. This area is greatly moved by waves, tides and currents. Here, the ocean floor consists mainly of the Continent material. It is usually to sands and gravels, in the intertidal zones also silt and mud.

Deep-sea sediments

More than half of the seabed consists of deep-sea deposits. They contain almost no festländisches material and consist primarily of clays and remnants of microorganisms.

Grossly simplified, we can say that the size of sediment particles decreases as one moves away from the coast.

History of ocean floor research

The systematic exploration of the ocean floors began with depth measurements, which were carried out with sonar since 1922. In this case, it sends while driving the sound waves to the sea floor, which are reflected and recorded as the echo from a receiver.

The first depth chart was released in 1854, through the North Atlantic.

Later researchers tried to dive even greater depths. So Jacques Piccard and Don Walsh reached with a dive boat in the Mariana Trench to a depth of 10 916 m.

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