All the seas have a certainly deep points. It is called "the deep sea". How many do you know about the deep sea?
First, A strict definition does not exist in deep sea. Suppose in many cases that the depth of water of 200 meters or less is generally deep sea. Then, I start to explain why did people come to dive into the deep sea. A continental shelf is at a point with a depth of about 200 meters in the sea of Japan. In 1996, it was said that the oil natural gas in a continental shelf ,so need to develop the resources. So, the necessity that human actually sees and works by the eye rather than the robot which can you only indirect operation was born.
The thing of deep sea has been solved little by little in recent years. The deep sea has the different big features from the shallower seas. A lower picture is a picture which the depth of deep sea understands well.
First, it has a big water pressure. In water, water pressure bigger as it goes underwater deeply comes to be poured. Since it goes up by 1 atmosphere every 10 meters, the intensity to which the submarine can respond to it is called for. For example, when human incidentally works, diving directly, in order to bear the water pressure of a 300 meters point, you have to pressurize the own body for about 10 hours. Moreover for returning water pressure (decompression), thing time is required for 12 days. Submarine prospecting is not easy in the present of 2012 because of very huge water pressure.
Second, it has a low temperature. The first thing, water temperature dives at a stretch 1000 meters from 0 meters. This layer is called thermocline. In the abyssal zone at the point of thermocline, water temperature hardly changes. So water temperature will become fixed per 1.5 degrees, passes over the depth of water of 3000 meters. As an exception, a hydrothermal vent exists in deep sea. So near this vent, there is also a place where water temperature will be 300 degrees. This hydrothermal vent is anew introduced with another report again.
Third, It has a darkness. Sunlight required for photosynthesis does not reach in deep sea. Therefore, an ecosystem and and environment differ from near surface of the earth greatly. Furthermore, phytoplankton does not exist, either. It is environment just severe for a living thing making a living. It become a limit that human perceives light with the depth of water of 400 meter depth. However, since few sunlight has arrived, the depth of water of 1000 meters has many things with a big eye, in order that deep sea fish may detect it. What kind of the world is the deepest-water place really in the sea? It is very interesting in what what of the world of the darkness which light does not reach at all has.
Did you get interested about the deep sea? There are many wonderful things in deep sea.
Next time , I am going to introduce in more detail.
reference
Wikipedia ( http://ja.wikipedia.org/wiki/Deep_sea )
JAMSTEC ( http://www.jamstec.go.jp/j/museum/umihoshi/index2.html )
( http://www.jamstec.go.jp/j/kids/tazunete/index.html )
