Deep-sea exploration


Deep-sea exploration is the investigation of physical, chemical, and biological conditions on the sea bed, for scientific or commercial purposes. Deep-sea exploration is considered a relatively recent human activity compared to the other areas of geophysical research, as the depths of the sea have been investigated only during comparatively recent years. The ocean depths still remain a largely unexplored part of the planet, and form a relatively undiscovered domain.
In general, modern scientific deep-sea exploration can be said to have begun when French scientist Pierre Simon de Laplace investigated the average depth of the Atlantic ocean by observing tidal motions registered on Brazilian and African coasts. He calculated the depth to be, a value later proven quite accurate by echo-sounding measurement techniques. Later on, due to increasing demand for the installment of submarine cables, accurate measurements of the sea floor depth were required and the first investigations of the sea bottom were undertaken. The first deep-sea life forms were discovered in 1864 when Norwegian researchers obtained a sample of a stalked crinoid at a depth of.
From 1872 to 1876, a landmark ocean study was carried out by British scientists aboard the HMS Challenger, a sailing vessel that was redesigned into a laboratory ship. The Challenger expedition covered, and shipboard scientists collected hundreds of samples and hydrographic measurements, discovering more than 4,700 new species of marine life, including deep-sea organisms. They are also credited with providing the first real view of major seafloor features such as the deep ocean basins.
The first instrument used for deep-sea investigation was the sounding weight, used by British explorer Sir James Clark Ross. With this instrument, he reached a depth of in 1840. The Challenger expedition used similar instruments called Baillie sounding machines to extract samples from the sea bed.
In the 20th century, deep-sea exploration advanced considerably through a series of technological inventions, ranging from the sonar system, which can detect the presence of objects underwater through the use of sound, to manned deep-diving submersibles. In 1960, Jacques Piccard and United States Navy Lieutenant Donald Walsh descended in the bathyscaphe Trieste into the deepest part of the world's oceans, the Mariana Trench. On 25 March 2012, filmmaker James Cameron descended into the Mariana Trench in the Deepsea Challenger, and, for the first time, is expected to have filmed and sampled the bottom.
Despite these advances in deep-sea exploration, the voyage to the ocean bottom is still a challenging experience. Scientists are working to find ways to study this extreme environment from the shipboard. With more sophisticated use of fiber optics, satellites, and remote-control robots, scientists hope to, one day, explore the deep sea from a computer screen on the deck rather than out of a porthole.

Milestones of deep sea exploration

The extreme conditions in the deep sea require elaborate methods and technologies to endure, which has been the main reason why its exploration has had a comparatively short history.
Some important milestones of deep sea exploration are listed below:
The sounding weight, one of the first instruments used for the sea bottom investigation, was designed as a tube on the base which forced the seabed in when it hit the bottom of the ocean. British explorer Sir James Clark Ross fully employed this instrument to reach a depth of in 1840.
Sounding weights used on were the slightly more advanced "Baillie sounding machine". The British researchers used wire-line soundings to investigate sea depths and collected hundreds of biological samples from all oceans except the Arctic. Also used on HMS Challenger were dredges and scoops, suspended on ropes, with which samples of the sediment and biological specimens of the seabed could be obtained.
A more advanced version of the sounding weight is the gravity corer. The gravity corer allows researchers to sample and study sediment layers at the bottom of oceans. 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. 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. 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 below the ocean bottom.
Echo-sounding instruments have also been widely used to determine the depth of the sea bottom since World War II. 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. 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.
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. 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, and global positioning systems that keep the vessel in a live position relative to a sonar beacon on the bottom of the ocean.

Oceanographic submersibles

Because of the high pressure, the depth to which a diver can descend without special equipment is limited. The deepest recorded descent made by a skin diver is. Revolutionary new diving suits, such as the "JIM suit," allow divers to reach depths up to approximately. Some additional suits feature thruster packs that can boost a diver to different locations underwater.
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, working with fellow engineer Otis Barton of Harvard University, designed the first practical bathysphere to observe marine species at depths that could not be reached by a diver. In 1930 Beebe and Barton reached a depth of, and in 1934. The potential danger was that if the cable broke, the occupants could not return to the surface. During the dive, Beebe peered out of a porthole and reported his observations by telephone to Barton who was on the surface.
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. On an experimental dive in the Cape Verde Islands, his bathyscaphe successfully withstood the pressure on it at, but its body was severely damaged by heavy waves after the dive. In 1954, with this bathyscaphe, Piccard reached a depth of. In 1953, his son Jacques Piccard joined in building a new and improved bathyscaphe, which dived to in field trials. The United States Navy acquired Trieste in 1958 and equipped it with a new cabin to enable it to reach deep ocean trenches. In 1960, Jacques Piccard and United States 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:.
An increasing number of occupied submersibles are now employed around the world. For example, the American-built, operated by the Woods Hole Oceanographic Institution, is a three-person submarine that can dive to about and is equipped with a mechanical manipulator to collect bottom samples.Operated by the Woods Hole Oceanographic Institution, Alvin is designed to carry a crew of three people to depths of. The submarine is equipped with lights, cameras, computers, and highly maneuverable robotic arms for collecting samples in the darkness of the ocean's depths. Alvin made its first test dive in 1964, and has performed more than 3,000 dives to average depths of. Alvin has also been 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.

Unmanned submersibles

One of the first unmanned deep sea vehicles was developed by the University of California with a grant from the Allan Hancock Foundation in the early 1950s to develop a more economical method of taking photos miles under the sea with an unmanned steel high-pressure 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 until it became wedged between some rocks and could not be retrieved.
Remote operated vehicles are also seeing increasing use in underwater exploration. These submersibles are piloted through a cable which connects to the surface ship, and can reach depths of up to. New developments in robotics have also led to the creation of AUVs, or autonomous underwater vehicles. The robotic submarines are programmed in advance, and receive no instruction from the surface. A Hybrid ROV combines features of both ROVs and AUV, operating independently or with a cable. was employed in 1985 to locate the wreck of ; the smaller was also used to explore the shipwreck.

Scientific results

In 1974, Alvin, the French bathyscaphe Archimède, and the French diving saucer CYANA, assisted by support ships and, explored the great rift valley of the Mid-Atlantic Ridge, southwest of the Azores. 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 the rift valley, giving additional proof that the seafloor spreads at this site at a rate of about per year.
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 high and about across, discharging a mixture of hot water and dissolved metals in dark, smoke-like plumes. These hot springs play an important role in the formation of deposits that are enriched in copper, nickel, cadmium, chromium, and uranium.