海域

The ocean is divided into sub-zones. The names depend on the amount of sunlight each of the zone gets. The first zone is called the sunlit zone, or the euphotic zone. This is the zone with the most sunlight. More than 90 percent of marine life lives here because there is enough light to support photosynthesis. The next zone is the twilight zone, or the disphotic zone. Very little light reaches this part of the ocean. The water pressure begins to increase the deeper. No plants live here. The last zone is the twilight zone, or the aphotic zone. No light reaches this part of the ocean. Surprisingly, some animals still live here. The live off of the bacteria seeping out of cracks at the bottom of the ocean. At this zone, the water pressure is extreme with temperatures dropping to freezing.

The layers of the ocean are divided by temperature and light. The first zone is the epipelagic zone, or the sunlight zone. The depth ranges from the surface to 200 meters. There is a wide range of temperatures here.

The second zone is the mesopelagic zone (they all end with "pelagic", which means relating to the open sea), also known as the twilight zone. The depth ranges from 200 to 1,000 meters. There is very little light. You also begin to see bioluminescent creature's lights.

The third is the bathypelagic zone, the midnight zone. The depth ranges from 1,000 to 4,000 meters. There is no light except from organisms. The water pressure is 5,850 pounds per square inch!

The fourth is the abyssopelagic zone, the abyssal zone. The depth ranges from 4,000 to 6,000 meters. The temperature is near freezing, with no light at all. There are very few organisms here. Three quarters of the ocean floor is found in this range.

The fifth and final is the hadalpelagic zone, the trenches. The depth ranges from 6,000 meters to the ocean floor. This is mainly just the underwater canyons and water trenches. The pressure is an amazing eight tons per square inch! Surprisingly, quite a bit of organisms live here, such as tubeworms and starfish, which live near hydrothermal vents.

The Challenger Deep is the deepest known point in the Earth's seabed hydrosphere, with a depth of 10,898 to 10,916 m (35,755 to 35,814 ft) by direct measurement from submersibles, and slightly more by sonar bathymetry. It is in the Pacific Ocean, at the southern end of the Mariana Trench near the Mariana Islands group. The Challenger Deep is a relatively small slot-shaped depression in the bottom of a considerably larger crescent-shaped oceanic trench, which itself is an unusually deep feature in the ocean floor. Its bottom is about 11 km (7 mi) long and 1.6 km (1 mi) wide, with gently sloping sides.[1] The closest land to the Challenger Deep is Fais Island (one of the outer islands of Yap), 287 km (178 mi) southwest, and Guam, 304 km (189 mi) to the northeast. It is located in the ocean territory of the Federated States of Micronesia, 1.6 km (1 mi) from its border with ocean territory associated with Guam.[2]

The depression is named after the British Royal Navy survey ship HMS Challenger, whose expedition of 1872–1876 made the first recordings of its depth. According to the August 2011 version of the GEBCO Gazetteer of Undersea Feature Names, the location and depth of the Challenger Deep are 11°22.4′N 142°35.5′E and 10,920 m (35,827 ft) ±10 m (33 ft).[3]

June 2009 sonar mapping of the Challenger Deep by the Simrad EM120 (sonar multibeam bathymetry system for 300–11,000 m deep water mapping) aboard the RV Kilo Moana indicated a depth of 10,971 metres (35,994 ft). The sonar system uses phase and amplitude bottom detection, with a precision of 0.2% to 0.5% of water depth; this is an error of about 22 to 55 m (72 to 180 ft) at this depth.[4][5][6] Further soundings made by the US Center for Coastal & Ocean Mapping in October 2010 are in agreement with this figure, preliminarily placing the deepest part of the Challenger Deep at 10,994 m (36,070 ft), with an estimated vertical uncertainty of ±40 m (131 ft).[7][8] A 2014 study concludes that with the best of 2010 multibeam echosounder technologies a depth uncertainty of ±25 m (82 ft) (95% confidence level) on 9 degrees of freedom and a positional uncertainty of ±20 to 25 m (66 to 82 ft) (2drms) remain and the location of the deepest depth recorded in the 2010 mapping is 10,984 m (36,037 ft) at 11.329903°N 142.199305°E (11°19′47.650″N 142°11′57.498″E).[6]

Only four descents have ever been achieved. The first descent by any vehicle was by the manned bathyscaphe Trieste in 1960. This was followed by the unmanned ROVs Kaikō in 1995 and Nereus in 2009. In March 2012 a manned solo descent was made by film director James Cameron in the deep-submergence vehicle Deepsea Challenger.[9][10][11] These expeditions measured very similar depths of 10,898 to 10,916 metres (35,755 to 35,814 ft).