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 a relatively recent human activity. Compared to the other areas of geophysical research, the depths of the sea have been investigated only during comparatively recent years. Even nowaday, the depths of the sea are still a largely unexplored part of the planet earth, and they still form a relatively unexplored domain.

Modern scientific Deep-sea exploration can be said to have begun when French scientist Pierre Simon de Laplace calculated the average depth of the Atlantic ocean, by observing tidal motions registered on Brazilian and African coasts. He determined this depth to be 3,962 m (13,000 ft), a value later proven quite accurate by soundings measurement . Because of the need for submarine cables installment, accurate soundings was required and the first investigations of the sea bottom were undertaken. Deep-sea life forms were discovered in 1864 when Norwegian researchers sampled a stalked crinoid at a depth of 3,109 m (10,200 ft). More important discoveries have been made since 1870, the British Government sent out the Challenger expedition (a ship called the HMS Challenger) in 1872 which discovered 715 new genera and 4,417 new species of marine organisms over the space of 4 years.

The first instrument used for deep-sea investigation was the sounding weight, used by British explorer Sir James Clark Ross. It reached a depth of 3,700 m (12,140 ft) in 1840. The Challenger expedition used similar instruments called Baillie sounding machines to extract samples from the sea bed. The sounding weights had a tube on the base which forced the seabed in when it hit. Viking soldiers also used this instrument in a similar fashion. Using a lead weight, they measured the length of the rope when they hauled in on board in fathoms, the unit of measure still used today for nautical depths. In 1934 William Beebe made a record descent of 923m (3,028 ft) in his bathysphere.

Brief History

Throughout history, scientists have relied on a number of hand-made tools to measure, map, and view the ocean's depths. One of the first instruments used to examine the seafloor was the sounding weight. Ancient Viking sailors took measurements of sea depth and sampled seafloor sediments with this piece of equipment, which consisted of a lead weight with a hollow bottom attached to a line. Once the weight reached the sea bottom and collected a sample of the seabed, the line was hauled back onboard ship and measured in fathom. Cornelius van Drebel, a Dutch architect, is generally credited with construction of the first submarine. His submergible boat consisted of a wooden frame sheathed in animal skin. Oars extending out the sides propelled the craft through the water, at depths up to 4.6 meters (15 ft). The oar openings were sealed with tight-fitting leather flaps. Drebel tested the submarine in the Thames River in England in sometime between 1620 and 1624. It is believed that King James I have enjoyed a short ride in the craft.

The nature of the sea bottom was remained an unrevealed mystery until the mid-19th century. Scientists and artists alike imagined the deep sea as a lifeless soup of placid water, French author Jules Verne who helped pioneer the science-fiction genre portrayed the deep ocean as contained in a bowl of static rock in his “Twenty Thousand Leagues under the Sea”. However, by the late 1860s, controversial modern scientific theories, the origin of life by evolution and the enormity of geologic time had created a foundation of scientific curiosity and provoked a rising interest in marine exploration. The Royal Society of England thus initiated an ambitious oceanographic expedition to expand a scarce collection of existing marine data that included Charles Darwin's observations during the expedition of the HMS Beagle (1831–1836), a bathymetric chart created by U.S. Navy Lt. Matthew Maury to aid installation of the first trans-Atlantic telegraph cables in 1858, and a few examples of deep marine life. From 1872 to 1876, a landmark ocean study was undertaken by British scientists aboard HMS Challenger, a sailing vessel that was redesigned into a laboratory ship. The HMS Challenger expedition covered 127,653 km (68,890 nautical miles), and shipboard scientists collected hundreds of samples, hydrographic measurements, and specimens of marine life. They are also credited with providing the first real view of major seafloor features such as the deep ocean basins. The British researchers employed wire-line soundings to investigate sea depths and collected hundreds of biological samples from all the oceans except the Arctic. They discovered more than 4,700 new species of marine life, including deep-sea organisms.

Deep-sea exploration advanced considerably in the 1900s thanks to a series of inventions, ranging from sonar system to detect the presence of objects underwater through the use of sound to manned deep-diving submersibles such as DSV Alvin. Operated by the Woods Hole Oceanographic Institution, Alvin is designed to carry a crew of three people to depths of 4,000 meters (13,124 ft). The submarine is equipped with lights, cameras, computers, and highly maneuverable robotic arms for collecting samples in the darkness of the ocean's depths. However, the voyage to the ocean bottom takes time in a submersible. A cold, four-hour roundtrip to hydrothermal vent sites 2.4 kilometers (1.5 mi) below the water surface, and 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 one day may explore the deep sea from a computer screen in the lab rather than out of a porthole.

Oceanographic Instrumentation

The first instruments used for the investigation of the sea bottom was the sounding weight, with which British explorer Sir James Clark Ross reached a depth of 3,700 m (12,140 ft) in 1840. The sounding weights used on the HMS Challengerwere called "Baillie sounding machine", which were provided with a tube into which a sample of the seabed was forced when the weight hit the bottom of the ocean. Also used on the 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 modern version of the Baillie sounding machine is the gravity corer. 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). By lifting the corer, a long, cylindrical sample is extracted in which the structure of the seabed’s layers of sediment is preserved. Samples of deeper layers can be obtained with a corer mounted in a drill. The drilling vessel JOIDES Resolution (see Ocean Drilling Program,) is equipped to extract cores from depths of as much as 1500 m (4900 ft) below the ocean bottom.

Since World War II, echo-sounding techniques have been widely used to measure the depth of the sea bottom. Acoustic pulses are transmitted from the ship; the time registered for the reflection of the sound wave is a measure of the water’s depth. By registering the time lapses between outgoing and returning signals continuously on paper tape, a continuous mapping of the seabed is obtained. Much of the ocean floor has been mapped in this way.

Other instruments for deep-sea exploration are high-resolution television cameras, movie cameras, thermometers, pressure meters, flow meters, and seismographs. These instruments are either lowered to the sea bottom on long cables or attached to submersible buoys; they sometimes are provided with a sound source, making depth determination possible. Deep-sea currents can be determined by floats carrying an ultrasonic sound source so that their movements can be followed aboard the research vessel. Such vessels themselves require precise navigational instrumentation, such as satellite navigation devices, and global positioning systems that keep the vessel in a fixed 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 severely limited. The deepest recorded dive by a skin diver is 127 meters (417 ft). The deepest recorded dive by a scuba diver is not much farther, at 145 meters (475 ft). Revolutionary new diving suits, such as the "JIM suit," enable divers to reach depths up to about 600 meters (2,000 ft). Some 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 Charles William Beebe was the first to observe marine species at depths that could not be reached by a diver. He and engineer Otis Barton designed a spherical steel vessel called a Bathysphere, that could be lowered from the attached ship by a suspended cable. In 1930 Beebe and Barton reached a depth of 435 m (about 1425 ft), and in 1934 a depth of 923 m (3028 ft). The danger of this submersible 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 a colleague who was on the surface.

In 1948, Swiss physicist Auguste Piccard began testing a much deeper-diving vessel he invented called the bathyscaphe (This word is derived from the Greek words bathos -"deep" and scaphos -"ship".), a navigable deep-sea vessel consisting of a pressure sphere that is kept buoyant by a float (a large container filled with gasoline). On an unpiloted dive in the Cape Verde Islands, his invention successfully withstood the pressure on it at 1,402 meters (4,600 ft), but its float was severely damaged by heavy waves after the dive. In 1954, with this bathyscaphe, Piccard reached a depth of 4000 m (13,125 ft). In 1953, Jacques Piccard, a son of Auguste Piccard, joined his father in building new and improved bathyscaphe Trieste, which dived to 3,139 meters (10,300 ft) in field trials. The U.S. 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 Navy Lieutenant Donald Walsh descended in Trieste to the deepest known point on Earth - the Challenger Deep in the Mariana Trench. The two men made the deepest dive in history: 10,915 meters (35,810 ft).

A large number of occupied submersibles for deep-sea exploration are now employed by different countries around the world. Among them is the American-built DSV Alvin that is operated by the Woods Hole Oceanographic Institution. This three-person submarine can dive to about 3600 m (about 12,000 ft) and is equipped with underwater lights, cameras, a television system, and a mechanical manipulator to collect bottom samples. Alvin made its first dive in 1964, and has made more than 3,000 dives to average depths of 1,829 meters (6,000 ft). Alvin has conducted a wide variety of research missions, such as one where giant tube worms were discovered on the Pacific Ocean floor near the Galápagos Islands. Unmanned, robot submersibles, capable of descending to depths of as much as 6000 m (20,000 ft), are also being used for underwater exploration. Argo was used in 1985 to locate the wreck of the Titanic; the smaller Jason was used to explore it.

Scientific Results

The first large exploration using occupied submersibles was the French-American Mid-Ocean Undersea Study (FAMOUS) project. In 1974 the Alvin (operated by the Woods Hole Oceanographic Institution), 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 the Azores. The Rift Valley is considered by geologists as the separation between the Eurasian plate and the North American plate of the earth’s crust, and it constitutes one of the many sites in the ocean bottom where molten rock oozes forth to form new crust. About 5200 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 2.5 cm (about 1 in) per year (see plate tectonics,).

In a series of dives conducted between 1979–1980 into the Galápagos rift, off the coast of Ecuador, French, Mexican, and U.S. scientists found chimneylike 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) and dissolved metals in dark, smokelike 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.

See also

• Census of Marine Life

External links

• Deep Sea Exploration - MSN Encarta (Archived 2009-10-31)
• http://www.floridasmart.com/subjects/ocean/deepsea.htm
• http://www.learnersonline.com/weekly/archive99/week25/index.htm
• http://www.eurekalert.org/features/kids/2005-03/aaft-det030205.php
• http://www.ocean.udel.edu/deepsea/level-2/tools/history.html
• http://www.encyclopedia.com/doc/1E1-diving-d.html
• http://www.oceanexplorer.noaa.gov/
• http://oceanexplorer.noaa.gov/history/history.html
• http://oceanexplorer.noaa.gov/gallery/gallery.html
• http://www.explore.noaa.gov/
• http://celebrating200years.noaa.gov/rarebooks/challenger/welcome.html
• http://celebrating200years.noaa.gov/rarebooks/depth/welcome.html
• http://www.titanic-titanic.com/discovery_of_titanic.shtml
• http://www.factmonster.com/ce6/people/A0848555.html