Saturday, February 18, 2012

FTV 2/18/2-12 Ocean Zones

Two major ocean features are shallow continental margins and the deep sea. Sea level changes through time have exposed and submerged the upper portion of continental margins, called the continental shelf. Continental shelves of the world vary greatly in their width from a few kilometers to a hundred or more, but are relatively shallow in depth. Most extend offshore to water depths of 100 to 200 m. Just beyond the shelf, the sea floor slope is much steeper. This is the continental slope. At the base of the slope lies the continental rise, which is less steep and quite broad in places. The shelf, slope and rise together make up the entire continental margin. Many continental margins have steep-walled submarine canyons cutting through them. Some canyons may have formed during lowered sea levels as rivers ran out across the shelf, cutting into it.

Out in the open ocean is what is called the pelagic zone, which is where many species of fish and marine mammals, plankton, and floating seaweed are found. The area under the pelagic zone is called the benthic zone, or deep-sea. This zone consists of silt, sand, and slowing decomposing organisms. This area is very cold because the sunlight does not reach into its depth. There are few plants at this level, and the animals include mostly bottom feeding organisms such as starfish, anemones, sponges, and various micro organisms.

The deepest part of the ocean is called the abyssal zone. Many invertebrate species and fish live here. The Coelacanth is a prehistoric fish one thought to be extinct but has been found deep in the Indian Ocean. This zone also is the home to other fish that glow in the dark by a process of photoluminescence. The abyssal zone is very cold and the pressure from the weight of the deep water is very high. In this zone the floor contains vents which are formed by spreading tectonic plates. These vents release hydrogen sulfide and other minerals which are converted to food by bacteria. These bacteria are eaten by other micro-organisms, which are consumed by invertebrates and fish that live near these vents.

Scientists thought the coelacanth died out 66 million years ago, because it vanishes from the fossil record then. But in 1938 a live coelacanth was hauled up in a fisherman nets off South Africa. Since then, another surviving species has turned up in Indonesia. Here, is our clickable coelacanth, see what makes this ancient fish stand out from all others.

Try this challenge
What groups of marine organisms produce substances that may be helpful in treating human diseases?

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