The corer consists of an open-ended

The corer consists of an open-ended tube with a lead weight and a trigger mechanism that releases the corer from its suspension cable when the corer is lowered over the seabed and a small weight touches the ground. The corer falls into the seabed and penetrates it to a depth of up to 10 m (33 ft). Sony Vaio PCG-5L1L Battery

By lifting the corer, a long, cylindrical sample is extracted in which the structure of the seabed’s layers of sediment is preserved. Recovering sediment cores allows scientists to see the presence or absence of specific fossils in the mud that may indicate climate patterns at times in the past, such as during the ice ages. Sony Vaio PCG-6S2L Battery

Samples of deeper layers can be obtained with a corer mounted in a drill. The drilling vessel JOIDES Resolution is equipped to extract cores from depths of as much as 1,500 m (4900 ft) below the ocean bottom. (See Ocean Drilling Program)^.

Echo-sounding instruments have also been widely used to determine the depth of the sea bottom since World War II. Sony Vaio PCG-6S3L Battery

This instrument is used primarily for determining the depth of water by means of an acoustic echo. A pulse of sound sent from the ship is reflected from the sea bottom back to the ship, the interval of time between transmission and reception being proportional to the depth of the water. Sony Vaio PCG-6V1L Battery

By registering the time lapses between outgoing and returning signals continuously on paper tape, a continuous mapping of the seabed is obtained. The majority of the ocean floor has been mapped in this way.^[19] Sony Vaio PCG-6W1L Battery

In addition, high-resolution television cameras, thermometers, pressure meters, and seismographs are other notable instruments for deep-sea exploration invented by the technological advance. These instruments are either lowered to the sea bottom by long cables or directly attached to submersible buoys. Sony Vaio PCG-7111L Battery

Deep-sea currents can be studied by floats carrying an ultrasonic sound device so that their movements can be tracked from aboard the research vessel. Such vessels themselves are equipped with state -of-art navigational instruments, such as satellite navigation systems, Sony Vaio PCG-71511M Battery

and global positioning systems that keep the vessel in a live position relative to a sonar beacon on the bottom of the ocean.^[2]

Because of the high pressure, the depth to which a diver can descend without special equipment is limited. The deepest recorded made by a skin diver is 127 meters (417 ft).^[14] Sony Vaio PCG-6W3L Battery

The deepest record made by a scuba diver is not much deeper, at 145 meters (475 ft).^[14] Revolutionary new diving suits, such as the "JIM suit," allows divers to reach depths up to approximately 600 meters (2,000 ft).^[20] Some additional suits feature thruster packs that boost a diver to different locations underwater.^[21] Sony Vaio PCG-7113L Battery

To explore even deeper depths, deep-sea explorers must rely on specially constructed steel chambers to protect them. The American explorer William Beebe, also a naturalist from Columbia University in New York, was the designer of the first practical bathysphere to observe marine species at depths that could not be reached by a diver.^[22] Sony Vaio PCG-7133L Battery

The Bathysphere, a spherical steel vessel, was designed by Beebe and his fellow engineer Otis Barton, an engineer at Harvard University.^[23] In 1930 Beebe and Barton reached a depth of 435 m (about 1425 ft), and 923 m (3028 ft) in 1934. The potential danger was that if the cable broke, the occupants could not return to the surface. Sony Vaio PCG-7Z1L Battery

During the dive, Beebe peered out of a porthole and reported his observations by telephone to Barton who was on the surface.^[17][24]

In 1948, Swiss physicist Auguste Piccard tested a much deeper-diving vessel he invented called the bathyscaphe, a navigable deep-sea vessel with its gasoline-filled float and suspended chamber or gondola of spherical steel. Sony Vaio PCG-7Z2L Battery

On an experimental dive in the Cape Verde Islands, his bathyscaphe successfully withstood the pressure on it at 1,402 meters (4,600 ft), but its body was severely damaged by heavy waves after the dive. In 1954, with this bathyscaphe, Piccard reached a depth of 4,000 m (13,125 ft).^[22] Sony Vaio PCG-8Y1L Battery

In 1953, his son Jacques Piccard joined in building new and improved bathyscaphe Trieste, which dived to 3,139 meters (10,300 ft) in field trials.^[22] The U.S. Navy acquired Trieste in 1958 and equipped it with a new cabin to enable it to reach deep ocean trenches.^[5] Sony Vaio PCG-8Y2L Battery

In 1960, Jacques Piccard and Navy Lieutenant Donald Walsh descended in Trieste to the deepest known point on Earth - the Challenger Deep in the Mariana Trench, successfully making the deepest dive in history: 10,915 meters (35,810 ft).^[5]

An increasing number of occupied submersibles are now employed around the world. Sony Vaio PCG-8Z2L Battery

The American-built DSV Alvin that is operated by the Woods Hole Oceanographic Institution, is a three-person submarine that can dive to about 3,600 m (12,000 ft) and is equipped with a mechanical manipulator to collect bottom samples.^[25]Alvin made its first test dive in 1964, and has performed more than 3,000 dives to average depths of 1,829 meters (6,000 ft). Sony Vaio PCG-8Z1L Battery

Alvin has also involved in a wide variety of research projects, such as one where giant tube worms were discovered on the Pacific Ocean floor near the Galápagos Islands.^[25]

One of the first unmanned deep sea vehicles was developed by the University of California with a grant from the Alan Hancock Foundation in the early 1950s to develop a more Sony Vaio PCG-7112L Battery

economical method of taking photos miles under the sea with an unmanned steel high pressure 3,0000 lb sphere called a benthograph which contained a camera and strobe light. The original benthograph built by USC was very successful in taking a series of underwater photos till it became wedged between some rocks and could not be retrieved. ^[26] Sony Vaio PCG-6W2L Battery

ROVs, or Remote Operated Vehicles, are seeing increasing use in underwater exploration. These submersibles are piloted through a cable which connects to the surface ship, and they can reach depths of up to 6,000 meters. New developments in robotics have also led to the creation of AUVs, or Autonomous Underwater Vehicles. Sony Vaio PCG-5K1L Battery

The robotic submarines are programmed in advance, and receive no instruction from the surface. HROV combine features of both ROVs and AUV, operating independently or with a cable.^[27][28] Argo was employed in 1985 to locate the wreck of the RMS Titanic; the smaller Jason was also used to explore the ship wreck. Sony VAIO VGN-NW21EF/S Battery

In 1974 the Alvin (operated by the Woods Hole Oceanographic Institution and the (Deep Sea Place Research Center), the French bathyscaphe Archimède, and the French diving saucer Cyane, assisted by support ships and the Glomar Challenger, explored the great Rift Valley of the Mid-Atlantic Ridge, southwest of theAzores. Sony VAIO VGN-NW21JF Battery

About 5,200 photographs of the region were taken, and samples of relatively young solidified magma were found on each side of the central fissure of theRift Valley, giving additional proof that the seafloor spreads at this site at a rate of about 2.5 cm (about 1 in) per year (see plate tectonics,).^[29] Sony VAIO VGN-NW21MF Battery

In a series of dives conducted between 1979–1980 into the Galápagos rift, off the coast of Ecuador, French,Italian, Mexican, and U.S. scientists found vents, nearly 9 m (nearly 30 ft) high and about 3.7 m (about 12 ft) across, discharging a mixture of hot water (up to 300°C/570°F) Sony VAIO VGN-NW21MF/W Battery

and dissolved metals in dark, smoke-like plumes (see hydrothermal vent,). These hot springs play an important role in the formation of deposits that are enriched in copper, nickel, cadmium,chromium, and uranium.

Deep sea communities currently remain largely unexplored, due the technological and logististical challenges and expense involved in visiting these remote biomes. Sony VAIO VGN-NW21ZF Battery

Because of the unique challenges (particularly the high barometric pressure, extremes of temperature and absence of light), it was long believed that little life existed in this hostile environment. Since the 19th century however, research has demonstrated that significant biodiversity exists in the deep sea. Sony VAIO VGN-NW31EF/W Battery

The three main sources of energy and nutrients for deep sea communities are marine snow, whale falls, and chemosynthesis athydrothermal vents and cold seeps.

Prior to the 19th century scientists assumed life was sparse in the deep ocean. In the 1870s Sir Charles Thompson and colleagues aboard the Challenger expedition discovered many deep-sea creatures of widely varying types. Sony VAIO VGN-NW31JF Battery

The first discovery of any deep-sea chemosynthetic community including higher animals was unexpectedly made at hydrothermal vents in the eastern Pacific Oceanduring geological explorations (Corliss et al., 1979).^[1] Two scientists, J. Corliss and J. van Andel, Sony VAIO VGN-NW320F/B Battery

first witnessed dense chemosynthetic clam beds from the submersible DSV Alvin on February 17, 1977, after their unanticipated discovery using a remote camera sled two days before.^[1]

The Challenger Deep is the deepest surveyed point of all of Earth's oceans; it is located at the southern end of the Mariana Trench near the Mariana Islandsgroup. Sony VAIO VGN-NW320F/TC Battery

The depression is named after HMS Challenger, whose researchers made the first recordings of its depth on 23 March 1875 at station 225. The reported depth was 4,475 fathoms (8184 meters) based on two separate soundings. In 1960, Don Walsh and Jacques Piccard descended to the bottom of the Challenger Deep in the Trieste bathyscaphe. Sony VAIO VGN-NW35E Battery

At this great depth a small flounder-like fish was seen moving away from the spotlight of the bathyscaphe.

The Japanese remote operated vehicle (ROV) Kaiko became the second vessel to reach the bottom of the Challenger Deep in March 1995. Nereus, a hybrid remotely operated vehicle (HROV) of the Woods Hole Oceanographic Institution, Sony VAIO VGN-NW380F/S Battery

is currently the only vehicle capable of exploring ocean depths beyond 7000 meters. Nereusreached a depth of 10,902 meters at the Challenger Deep on May 31, 2009. On 1 June 2009, sonar mapping of the Challenger Deep by the Simrad EM120 multibeam sonar bathymetry system aboard the R/V Kilo Moana indicated a maximum depth of 10971 meters (6.82 miles). Sony VAIO VGN-NW380F/T Battery

The sonar system uses phase and amplitude bottom detection, with an accuracy of better than 0.2% of water depth (this is an error of about 22 meters at this depth).

The ocean can be conceptualized as being divided into various zones, depending on depth, and presence or absence of sunlight.Sony VAIO VGN-NW50JB Battery

Nearly all life forms in the ocean depend on the photosynthetic activities of phytoplankton and other marine plants to convert carbon dioxide into organic carbon, which is the basic building block of organic matter. Photosynthesis in turn requires energy from sunlight to drive the chemical reactions that produce organic carbon.^[5] Sony VAIO VGN-NW51FB/N Battery

The stratum of the water column nearest the surface of the ocean (sea level) is referred to as the photic zone. The photic zone can be subdivided into two different vertical regions. The uppermost portion of the photic zone, where there is adequate light to support photosynthesis by phytoplankton and plants, Sony VAIO VGN-NW51FB/W Battery

is referred to as the euphotic zone (also referred to as theepipelagic zone, or surface zone).^[6] The lower portion of the photic zone, where the light intensity is insufficient for photosynthesis, is called the disphotic zone (disphotic means "poorly lit" in Greek).^[7] The disphotic zone is also referred to as the mesopelagic zone, or the twilight zone. Sony VAIO VGN-NW70JB Battery

Its lowermost boundary is at a thermocline of 12 °C (54 °F), which, in the tropics generally lies between 200 and 1000 meters.^[9]