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Oceans and Water
Factfile |
 Oceans and Water |
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The Ocean floor |
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Because deep water is pitch-dark, near-freezing and under immense pressure, the ocean depths have remained virtually unexplored. But if you could drain all the oceans of their water, you would find an amazing landscape: long mountain ranges; big plains; deep gorges and volcanoes. Because all these amazing features are hidden under the sea, we know very little about them. But thanks to modern technology like sonar equipment, we are finding out more about them.
Ocean Floor - HMS Endurance
HMS Endurance uses sonar equipment and satellite location devices to map the ocean floor. An instrument on or near the surface beams a sound pulse at a wide strip of seabed, then records how long the sound takes to return. From the timed readings, depths can be calculated, then turned into three-dimensional computer maps of the ocean floor, Other sonar instruments, towed very near the ocean floor, pick up detailed features on it, such as mineral growths.
About half of the seabed under the oceans has huge flat plains. These are between 4000m and 6000m below the surface and are called abyssal plains (from the word `abyss’, meaning very deep down). On these plains lies a thick layer of mud made from the remains of billions of tiny plants and sea animals. However, these plains can also support life and all kinds of creatures live here – including angler fish, deep-sea starfish, sponges and giant sea spiders.
All the large oceans have under-sea mountain ridges. The longest is the Mid-Atlantic Ridge that stretches from north of Iceland to Antarctica. It is over 11,000km, with mountains 4km high – which is as high as the Rockies in Canada or the Alps in Switzerland. It is along these ridges that hot molten rock seeps up through cracks in the seabed and cools as it hits the water, to become new mountains or volcanoes. This process is called sea-floor spreading and scientists estimate that the Atlantic is getting wider by between 2 - 4 cm each year because of it!
However, there is a process that balances out sea-floor spreading and this is called subduction. As we have already mentioned, there are deep-sea trenches on the ocean floor, which look like huge gashes. Some of them are over 10 km deep, while the deepest of all is the Mariana Trench in the Pacific Ocean, which reaches down to a depth of 10,920 m below sea level. Trenches are produced when a piece of seabed is pushed under another, and then melts back into the Earth. This process of subduction stops the Earth getting bigger and bigger.
Scientists now use manned or unmanned submersibles (small submarines) to explore the ocean floor and gather samples. Some of these submersibles can dive up to 4,000 m deep and were used to explore the wreck of the Titanic, when it was discovered in 1986 in 3,800m off the US coast.
Also, to determine past climatic changes, scientists have drilled and collected sediment cores to obtain records of Earth’s climate history. A core from the ocean floor can tell scientists what periods in our Earth’s history have gone though interglacial (the warmer period between each ice age) or glacial periods. These samples of seabed contain the fossils of microscopic organisms known to be sensitive to sea temperatures and are therefore thought to be good indicators of past climate change.
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