Nautical Archaeology
Nautical Archaeology
Techniques for underwater surveyance, retrieval, and analysis
The development of nautical archaeology
Other uses of nautical archaeology
Recent techniques of nautical excavation
Nautical archaeology is the branch of archaeology (the study of the past by investigating what people left behind) concerned with the excavation, identification, and study of the remains of sunken sites such as ships and cities. The techniques used in nautical archaeology can be applied to the study of submerged ports, lost cities, sacrificial wells, and other underwater sites.
The ocean conceals a vast number of unexplored, and potentially valuable, archaeological sites. However, the technology needed to explore these sites was not perfected until the mid-twentieth century. With the development of scuba gear, underwater transport, and other underwater devices, archaeologists have improved their ability to survey and retrieve objects underwater.
The artifacts, or archaeological finds, removed from the ocean have enriched scientific understanding of the history of boat building and navigation, as well as broadened human knowledge of everyday life on land. Because of the lower oxygen content of cold water, objects preserved in the ocean deteriorate much less rapidly than they do on land. A 1,000-year-old shipwreck still might contain the wooden implements and food used to cook the sailors’ last meal, as well as the clothes they wore to dinner. The chances of finding such objects preserved on land would be extremely slim.
However, not all objects that sink into the ocean are preserved. If an object sinks near shore, it stands a chance of being shattered against the rocks or of being picked up by a curious diver. The movement of large waves can destroy even an object that sinks to depths of up to 50 ft (15 m). In addition, organisms inhabiting the lower regions of the sea such as teredos (ship worms) can bore through the object. In a process known as encrustation, barnacles and coral can grow in a thick layer over the object, also causing it to deteriorate.
Techniques for underwater surveyance, retrieval, and analysis
Before objects can be removed from a shipwreck, the diver must map their precise location in relation both to the other objects and to the surrounding ocean terrain. Because the average diver can move through the water at a rate of only 0.5 mph (1 km/h), apparatus have been developed to speed up surveyance. A diver may ride in a hydrodynamic cradle, a flat metal one-diver bobsled with a window in front, which can be maneuvered to lower depths. A team of two divers may ride in a towvane, a top-shaped vessel with Plexiglas® observation windows and hydrodynamic steering, similar to a diving bell. Or they may descend in a cubmarine, a small electrical battery-powered vessel steered by water jets that can submerge to depths of 164–197 ft (50–60 m).
At great ocean depths or in areas with poor visibility other devices may be employed. Sonar may be used to determine the location of large or encrusted objects by calculating the time it takes echoes to bounce off them. Underwater cameras may be towed by the boat to take pictures of a site in water with good visibility.
The method used to remove the objects will depend on their size and fragility. Ordinary objects may be brought up in plastic or net bags. Heavy objects may be lifted with chains and pulleys or with balloon-like air bags. These bags contain a small amount of compressed air that enables them to expand and rise to the surface as the water pressure decreases.
To determine the age of these objects, archaeologists had to develop new strategies. Pottery phases and stratigraphy (the analysis of the origin, distribution, and succession of layers or strata of earth) can be used to date objects found on land. However, neither technique works reliably for objects found in the sea, where water may distort the shape of a jar or may carry away rocks and silt from the scene of the wreck. Instead, archaeologists use anchors (and sometimes ship nails) to determine the age of a shipwreck. Like pottery, anchors were produced in different sizes and shapes and made of different kinds of materials (such as stone or iron) that conform to historical phases. Archaeologists use these features to assign the shipwreck a date.
The development of nautical archaeology
In the first century AD, two large Roman ships sank to the bottom of Lake Nemi, southwest of Rome, Italy. Rumored to be carrying treasure, and lying at the relatively shallow depth of 49–75 ft (15–23 m), they were not entirely forgotten. In 1446, at the request of a church official, Italian architect and theorist Leon Battista Alberti (1404–1472), assisted by divers, attempted to tow one of the ships to shore but succeeded only in raising a large statue. In 1556, a diver wearing a primitive diving apparatus consisting of a wooden hood and crystal face plate visited the site. He returned with a description of the ships, claiming that the decks were paved with red brick. In the late nineteenth century, antiquities dealer Eliseo Borghi began to remove objects from the vessel and sell them at high prices to the Italian government, but the government soon halted Borghi’s financial venture. It was not until 1928 that Italian dictator Benito Mussolini, intrigued by rumors of the buried treasure, decided to raise the ships by draining the lake, partially by means of an old Roman overflow tunnel. Four years later, the water level had been lowered more than 70 ft (229.5 m), and the ships were raised, cleaned, and moved to a museum. No treasure was found, but the ships themselves were a spectacular find: they contained heated baths, private cabins, and paved mosaic decks. Both ships were destroyed during World War II.
The first large-scale salvage of a shipwreck was carried out by the Greek Navy in 1900. In about 80 BC, a Roman vessel carrying a cargo of Greek amphorae (two-handled storage jars) sank to a depth of 197 ft (60 m) near the island of Antikythera, between Crete and southern Greece. Divers worked under extremely dangerous conditions to excavate the wreck. Laboring in storm-tossed seas, and able to remain submerged for only five minutes at a time, the divers nevertheless brought up a number of valuable objects. These objects included a statute by the Greek sculptor Lycippus and an early astronomical computer.
The first systematic archaeological excavation of a shipwreck was carried out in 1952 under the direction of French researcher, ecologist, and explorer Jacques-Yves Cousteau (1910–1997) and Fre´de´ric Dumas. The French team excavated a Roman amphora carrier that had sunk in the second century BC at Grand Congloué, near Marseilles. To assist in surveying the wreck, they decided to employ underwater photographic equipment. They also used a method known as an airlift to bring the amphorae to the surface. In this method, unbroken amphorae were filled with air, causing them to rise to the top of the water. To clear off debris from the wreck, the team used a vacuum pump attached to the ship.
Photojournalist Peter Throckmorton and archaeologist George Bass employed underwater photography and precise methods of surveyance to excavate the Gelidonya wreck off the coast of Turkey. In about 1200 BC, a trade vessel loaded with more than a ton of metal hit rocks and sank to the bottom of the sea on its journey to Phoenicia (modern-day Syria, Lebanon, and Israel). Explorers worked at a depth of 90 ft (27 m). They pinpointed the location of each object before bringing it to the surface. Heavy objects were raised with a winch and borne to the surface by air bags.
Between 1961 and 1964, Bass led the first excavation to be conducted completely underwater. Divers explored a wreck located off the coast of Turkey. Not far from the island of Yassi Ada, a seventh-century Byzantine amphora carrier lay buried in the sand, its wooden structure partially devoured by teredos. Rescuers excavated the ship by using bicycle spokes to keep the fragile wood from breaking off and drifting away until their work could be completed. To give them a better picture of the site, they built a metal scaffold overhead, complete with photographic towers that were 16-ft (5-m) high. The undamaged part of the ship was salvaged and completely reassembled on land.
All of the wrecks discussed above were excavated in the Mediterranean Sea. Many wrecks have been excavated in other parts of the world—for example, China. In 1973, a shipwreck was discovered off the coast of Quanzhou in east China. Its cargo contained pottery and fragrant wood. Dated to 1277, the ship is one of the earliest examples of Chinese nautical design. Examination of the wreck brought to light a new fact about Chinese ship construction. Chinese ships were not flat-bottomed, as formerly believed, but rather V-shaped, with a keel that tapered inward.
Whole-ship retrieval
Early excavations succeeded in raising only the contents of shipwrecks or portions of the ships. Recent excavations have focused on raising the entire ship, with its contents intact.
One such project was carried out under the leadership of Anders Franze´n, with the support of the Swedish government. In the seventeenth century, Swedish king Gustavus II Adolph (ruled from 1611 to 1632) decided to improve Sweden’s military capability by building a powerful naval fleet. The pride of this fleet was the Vasa, an enormous 1,400-ton vessel that was set to depart on its first voyage from Stockholm Harbor. No sooner had it set out from port than it sank, within full view of the king.
Franze´n believed that the ship lay at the bottom of the coldwater harbor in an excellent state of preservation. He made several attempts to locate the vessel— one with sonar—all of which failed. Then he made a lucky discovery. He came across a letter from the Swedish Parliament to the king that described the ship’s exact location.
Various plans to raise the vessel were discussed. Rescuers decided that the safest plan would be to run cables through tunnels dug by divers beneath the ship. The divers would then swim through the tunnels with the cables and attach them to pontoons on either side of the ship. The pontoons would be filled with water until their decks were even with the water’s surface. When the water was pumped out of the pontoons, the Vasa would begin to rise from the bottom of the harbor.
This plan was tried and it worked. The process was repeated several times, and the Vasa was pumped out of the water. A floating hall was built around it. Enshrined in the hall, and still containing its centuries-old cargo, the Vasa was floated to a museum site, where it remains on view today. Among the items found inside the ship were casks containing the sailors’ original food and ale, implements for daily use, and twelve skeletons, many of them with their clothing still on, undisturbed down to the coins in their pockets.
In the 1980s, another remarkable vessel was raised from the sea. This time researchers worked to rescue a sixteenth-century naval vessel, the Mary Rose. In a tragedy strikingly similar to that which befell the Vasa, King Henry VIII watched from Southsea Castle as the pride of his fleet sank with its crew of 700 men on its way to battle in France. Historian and archaeologist Alexander McKee believed that the Mary Rose was preserved in a deep bed of silt. He decided to raise the ship by attaching cables to a floating crane that lifted the ship out of the water. The ship was, then, continuously sprayed with water to keep it from drying out until it could be safely moved to shore. Medical equipment, pocket sundials, fishing gear, and leftover food from the ship broadened knowledge of daily life in the sixteenth century.
Other uses of nautical archaeology
Techniques used in nautical archaeology have been applied to other kinds of underwater archaeology. Submerged ports and lost cities are also subjects of research. Excavated by a team from the United States in 1960, the enormous Port of Caesarea was built by King Herod of Judaea in the first century BC to improve commerce with foreign merchants. Destroyed by an earthquake, the port still remains visible underwater. To construct the port, enormous stone blocks were lowered into the water to form a foundation for the 5-mi (8 km) long pier built on top, which included a large curved wall with towers and arched shelters for the merchants.
Destroyed by an earthquake in 1692, Port Royal was a flourishing center of commerce in the Caribbean. After the earthquake, the port sank to a distance of 65 ft (20 m) below sea level. A field school established to study the site has employed seventeenth-century maps to explore the submerged city and port.
The Maya are a Central American people who built an extensive civilization that flourished until the arrival of the Spaniards in the sixteenth century. The natural wells found in the limestone Yucatan Peninsula provided the Maya with a source of drinking water, but some wells were also the site of human sacrifice. In the early twentieth century, attracted by the prospect of finding treasure in the sacred wells, American archaeologist Edward Herbert Thompson (1860–1935) purchased one of them for $70. To excavate the well, he employed the highly unsystematic method of lifting objects out with a bucket. When this method proved unsatisfactory, Thompson dove down into the murky well with two Greek sponge divers, but the extremely low level of visibility thwarted any hope of finding the treasure. Thompson’s mission did, however, bring to light a number of important archaeological finds— headdresses, wooden spears, and fabric-that would have otherwise perished had they been left to deteriorate on land.
More than one-half century later, the National Institute of Anthropology and History made its own
Key Terms
Amphora (plural: amphorae)— A tall, graceful, two-handled jar with a narrow neck used to store wine, grain, etc., in classical times.
Artifact— An artificially made object that has been shaped and fashioned for human use.
Teredo— A kind of mollusk with a wormlike body, which burrows through wood and other materials on ships.
attempt to excavate the sacrificial well. This time, the water was chemically treated and filtered so that rescuers could see to a depth of 15.5 ft (5 m). The two-and-a-half-month excavation project produced other exciting finds. These finds included carved wooden stools, stone jaguars and serpents, and human remains.
Recent techniques of nautical excavation
To search for objects underwater, nautical archaeologists now employ robots and improved sonar technology. These methods were employed to excavate the Titanic, a supposedly indestructible ocean vessel than sank in 1912. To search for the Titanic, an American-French team employed three robots: Alvin, Angus, and Argo. Alvin was a midget submarine that could descend to the 13-ft (4 m) depth where the ship lay buried. The photographic craft Angus and the television camera craft Argo assisted in pinpointing the location of the Titanic.
During the Titanic mission, the French researchers used a new kind of sonar known as side-scanning sonar. Ordinary sonar surveys a narrow field that must be carefully mapped out in advance. Side-scanning sonar eliminates this drawback, by picking up signals at a diagonal.
Resources
BOOKS
Ashmore, Wendy, and Robert J. Sharer. Discovering Our Past: A Brief Introduction to Archaeology. 3rd ed. Mountain View, CA: Mayfield Publishing, 2000.
Bass, George F., ed. Beneath the Seven Seas: Adventures with the Institute of Nautical Archaeology. London, UK: Thames & Hudson, 2005.
Finamore, Daniel, ed. Maritime History as World History. Salem, MA: Peabody Essex Museum; and Gainesville, FL: University Press of Florida, 2004.
Marx, Robert F. Treasure Lost at Sea: Diving to the World’s Great Shipwrecks. Buffalo, NY: Firefly Books, 2004.
McGrail, Sean. Boats of the World: From the Stone Age to Medieval Times. Oxford, UK, and New York: Oxford University Press, 2002.
Throckmorton, Peter, ed. The Sea Remembers: Shipwrecks and Archaeology from Homer’s Greece to the Rediscovery of the Titanic. New York: Smithmark, 1991.
PERIODICALS
Gibbins, D. “Shipwrecks and Maritime Archaeology.” Archaeology Prospection 9, no. 2 (2002): 279-291.
Christine Molinari
Nautical Archaeology
Nautical archaeology
Nautical archaeology is the branch of archaeology concerned with the excavation, identification, and study of the remains of sunken ships. The techniques used in nautical archaeology can be applied to the study of submerged ports, lost cities, sacrificial wells, and other underwater sites.
The ocean conceals a vast number of unexplored, and potentially valuable, archaeological sites. But the technology needed to explore these sites was not perfected until the mid-twentieth century. With the development of scuba gear, underwater transport, and other underwater devices, archaeologists have improved their ability to survey and retrieve objects underwater.
The artifacts, or archaeological finds, removed from the ocean have enriched our understanding of the history of boat building and navigation, as well as broadened our knowledge of everyday life on land. Because of the lower oxygen content of cold water , objects preserved in the ocean deteriorate much less rapidly than they do on land. A 1,000-year-old shipwreck still might contain the wooden implements and food used to cook the sailors' last meal, as well as the clothes they wore to dinner. The chances of finding such objects preserved on land would be extremely slim.
However, not all objects that sink into the ocean are preserved. If an object sinks near shore, it stands a chance of being shattered against the rocks or of being picked up by a curious diver. Even an object that sinks to depths of up to 50 ft (15 m) can be destroyed by the movement of large waves. In addition, organisms inhabiting the lower regions of the sea such as teredos (ship worms) can bore through the object. In a process known as encrustation, barnacles and coral can grow in a thick layer over the object, also causing it to deteriorate.
Techniques for underwater surveyance, retrieval, and analysis
Before objects can be removed from a shipwreck, the diver must map their precise location in relation both to the other objects and to the surrounding ocean terrain. Because the average diver can move through the water at a rate of only 0.5 mi/h (1 km/h), apparatus have been developed to speed up surveyance. A diver may ride in a hydrodynamic cradle, a flat metal one-diver "bobsled" with a window in front, which can be maneuvered to lower depths. A team of two divers may ride in a towvane, a top-shaped vessel with Plexiglas observation windows and hydrodynamic steering, similar to a diving bell. Or they may descend in a cubmarine, a small electrical battery-powered vessel steered by water jets that can submerge to depths of 164-197 ft (50-60 m).
At great ocean depths or in areas with poor visibility other devices may be employed. Sonar may be used to determine the location of large or encrusted objects by calculating the time it takes echoes to bounce off them. Underwater cameras may be towed by the boat to take pictures of a site in water with good visibility.
The method used to remove the objects will depend on their size and fragility. Ordinary objects may be brought up in plastic or net bags. Heavy objects may be lifted with chains and pulleys or with balloon-like air bags. These bags contain a small amount of compressed air that enables them to expand and rise to the surface as the water pressure decreases.
To determine the age of these objects, archaeologists had to develop new strategies. Although pottery phases and stratigraphy (the analysis of the origin, distribution, and succession of layers or strata of earth ) can be used to date objects found on land, neither technique works reliably for objects found in the sea, where water may distort the shape of a jar or may carry away rocks and silt from the scene of the wreck. Instead, archaeologists use anchors (and sometimes ship nails) to determine the age of a shipwreck. Like pottery, anchors were produced in different sizes and shapes and made of different kinds of materials (such as stone or iron ) that conform to historical phases. Archaeologists use these features to assign the shipwreck a date.
The development of nautical archaeology
In the first century a.d., two large Roman ships sank to the bottom of Lake Nemi, southwest of Rome. Rumored to be carrying treasure, and lying at the relatively shallow depth of 49-75.5 ft (15-23 m), they were not entirely forgotten. In 1446, at the request of a church official, the noted Italian architect and theorist Leon Battista Alberti (1404-1472), assisted by divers, attempted to tow one of the ships to shore but succeeded only in raising a large statue. In 1556, a diver wearing a primitive diving apparatus consisting of a wooden "hood" and crystal face plate visited the site. He returned with a description of the ships, claiming that the decks were paved with red brick . In the late nineteenth century, the antiquities dealer Eliseo Borghi began to remove objects from the vessel and sell them at high prices to the Italian government, but the government soon halted Borghi's financial venture. It was not until 1928 that the Italian dictator Benito Mussolini, intrigued by rumors of the buried treasure, decided to raise the ships by draining the lake, partially by means of an old Roman overflow tunnel. Four years later, the water level had been lowered more than 70 ft (229.5 m), and the ships were raised, cleaned, and moved to a museum. No "treasure" was found, but the ships themselves were a spectacular find: they contained heated baths, private cabins, and paved mosaic decks. Both ships were destroyed during World War II.
The first large-scale salvage of a shipwreck was carried out by the Greek Navy in 1900. In about 80 b.c., a Roman vessel carrying a cargo of Greek amphorae (twohandled storage jars) sank to a depth of 60 m (197 ft) near the island of Antikythera, between Crete and southern Greece. Divers worked under extremely dangerous conditions to excavate the wreck. Laboring in storm-tossed seas, and able to remain submerged for only five minutes at a time, the divers nevertheless brought up a number of valuable objects. These included a statute by the Greek sculptor Lycippus and an early astronomical computer.
The first systematic archaeological excavation of a shipwreck was carried out in 1952 under the direction of Jacques-Yves Cousteau and Frédéric Dumas. The French team excavated a Roman amphora carrier that had sunk in the second century b.c. at Grand Congloué, near Marseilles. To assist in surveying the wreck, they decided to employ underwater photographic equipment. They also used a method known as an "airlift " to bring the amphorae to the surface. In this method, unbroken amphorae were filled with air, causing them to rise to the top of the water. To clear off debris from the wreck, the team used a vacuum pump attached to the ship.
The photojournalist Peter Throckmorton and the archaeologist George Bass employed underwater photography and precise methods of surveyance to excavate the Gelidonya wreck off the coast of Turkey. In about 1200 b.c., a trade vessel loaded with more than a ton of metal hit rocks and sank to the bottom of the sea on its journey to Phoenicia (modern-day Syria, Lebanon, and Israel). Explorers worked at a depth of 90 ft (27 m). They pinpointed the location of each object before bringing it to the surface. Heavy objects were raised with a winch and borne to the surface by air bags.
In 1961-64, Bass led the first excavation to be conducted completely underwater. Divers explored a wreck located off the coast of Turkey. Not far from the island of Yassi Ada, a seventh-century Byzantine amphora carrier lay buried in the sand , its wooden structure partially devoured by teredos. Rescuers excavated the ship by using bicycle spokes to keep the fragile wood from breaking off and drifting away until their work could be completed. To give them a better picture of the site, they built a metal scaffold overhead, complete with 16-ft-high (5 m) photographic towers. The undamaged part of the ship was salvaged and completely reassembled on land.
All of the wrecks discussed above were excavated in the Mediterranean Sea. Many wrecks have been excavated in other parts of the world-for example, China. In 1973 a shipwreck was discovered off the coast of Quanzhou in east China. Its cargo contained pottery and fragrant wood. Dated to 1277, the ship is one of the earliest examples of Chinese nautical design. Examination of the wreck brought to light a new fact about Chinese ship construction. Chinese ships were not flat-bottomed, as formerly believed, but rather V-shaped, with a keel that tapered inward.
Whole-ship retrieval
Early excavations succeeded in raising only the contents of shipwrecks or portions of the ships. Recent excavations have focused on raising the entire ship, with its contents intact.
One such project was carried out under the leadership of Anders Franzén, with the support of the Swedish government. In the seventeenth century, the Swedish king Gustavus II Adolph (ruled 1611-1632) decided to improve Sweden's military capability by building a powerful naval fleet. The pride of this fleet was the Vasa, an enormous 1,400-ton vessel that was set to depart on its first voyage from Stockholm Harbor. No sooner had it set out from port than it sank, within full view of the king.
Franzén believed that the ship lay at the bottom of the coldwater harbor in an excellent state of preservation. He made several attempts to locate the vessel—one with sonar—all of which failed. Then he made a lucky discovery. He came across a letter from the Swedish Parliament to the king that described the ship's exact location.
Various plans to raise the vessel were discussed. Rescuers decided that the safest plan would be to run cables through tunnels dug by divers beneath the ship. The divers would then swim through the tunnels with the cables and attach them to pontoons on either side of the ship. The pontoons would be filled with water until their decks were even with the water's surface. When the water was pumped out of the pontoons, the Vasa would begin to rise from the bottom of the harbor.
This plan was tried and it worked. The process was repeated several times, and the Vasa was pumped out of the water. A floating hall was built around it. Enshrined in the hall, and still containing its centuries-old cargo, the Vasa was floated to a museum site, where it remains on view today. Among the items found inside the ship were casks containing the sailors' original food and ale, implements for daily use, and twelve skeletons, many of them with their clothing still on, undisturbed down to the coins in their pockets.
In the 1980s, another remarkable vessel was raised from the sea. This time researchers worked to rescue a sixteenth-century naval vessel, the Mary Rose. In a tragedy strikingly similar to that which befell the Vasa, King Henry VIII watched from Southsea Castle as the pride of his fleet sank with its crew of 700 men on its way to battle France. The historian and archaeologist Alexander McKee believed that the Mary Rose was preserved in a deep bed of silt. He decided to raise the ship by attaching cables to a floating crane that lifted the ship out of the water. The ship was then continuously sprayed with water to keep it from drying out until it could be safely moved to shore. Medical equipment, pocket sundials, fishing gear, and leftover food from the ship broadened our knowledge of daily life in the sixteenth century.
Other uses of nautical archaeology
Techniques used in nautical archaeology have been applied to other kinds of underwater archaeology. Submerged ports and lost cities are also subjects of research. Excavated by the United States in 1960, the enormous Port of Caesarea was built by King Herod of Judaea in the first century b.c. to improve commerce with foreign merchants. Destroyed by an earthquake , the port still remains visible underwater. To construct the port, enormous stone blocks were lowered into the water to form a foundation for the 5-mi-long pier (8 km) built on top, which included a large curved wall with towers and arched shelters for the merchants.
Destroyed by an earthquake in 1692, Port Royal was a flourishing center of commerce in the Caribbean. After the earthquake, the port sank to a distance of 65 ft (20 m) below sea level . A field school established to study the site has employed seventeenth-century maps to explore the submerged city and port.
The Maya are a Central American people who built an extensive civilization that flourished until the arrival of the Spaniards in the sixteenth century. The natural wells found in the limestone Yucatan Peninsula provided the Maya with a source of drinking water, but some wells were also the site of human sacrifice. In the early twentieth century, attracted by the prospect of finding treasure in the sacred wells, the American archaeologist Edward Herbert Thompson (1860-1935) purchased one of them for $70. To excavate the well he employed the highly unsystematic method of lifting objects out with a bucket. When this method proved unsatisfactory, Thompson dove down into the murky well with two Greek sponge divers, but the extremely low level of visibility thwarted any hope of finding the treasure. Thompson's mission did, however, bring to light a number of important archaeological finds-headdresses, wooden spears, and fabric-which would have otherwise perished had they been left to deteriorate on land.
More than half a century later, the National Institute of Anthropology and History made its own attempt to excavate the sacrificial well. This time, the water was chemically treated and filtered so that rescuers could see to a depth of 15.5 ft (5 m). The two-and-a-half-month excavation project produced other exciting finds. These included carved wooden stools, stone jaguars and serpents, and human remains.
Recent techniques of nautical excavation
To search for objects underwater, nautical archaeologists now employ robots and improved sonar technology. These methods were employed to excavate the Titanic, an "indestructible" ocean vessel than sank in 1912. To search for the Titanic, an American-French team employed three robots: Alvin, Angus, and Argo. Alvin was a midget submarine that could descend to the 13 ft (4 m) depth where the ship lay buried. The photographic craft Angus and the television camera craft Argo assisted in pinpointing the location of the Titanic.
During the Titanic mission, the French researchers used a new kind of sonar known as side-scanning sonar. Ordinary sonar surveys a narrow field that must be carefully mapped out in advance. Side-scanning sonar eliminates this drawback, by picking up signals at a diagonal.
Resources
books
Ashmore, Wendy, and Robert J. Sharer. Discovering Our Past: A Brief Introduction to Archaeology. 3rd ed. New York: McGraw Hill, 1999.
Lampton, Christopher. Undersea Archaeology. New York: Franklin Watts, 1988.
Sunk! Exploring Underwater Archaeology. Minnesota: Runeston Press, 1994.
Throckmorton, Peter, ed. The Sea Remembers: Shipwrecks and Archaeology from Homer's Greece to the Rediscovery of the Titanic. London: Wiedenfeld & Nicolson, 1987.
periodicals
Gibbins, D. "Shipwrecks and Maritime Archaeology." Archaeology Prospection 9, no. 2 (2002): 279-291.
Christine Molinari
KEY TERMS
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .- Amphora (plural: amphorae)
—A tall, graceful, two-handled jar with a narrow neck used to store wine, grain, etc., in classical times.
- Artifact
—A man-made object that has been shaped and fashioned for human use.
- Teredo
—A kind of mollusk with a wormlike body, which burrows through wood and other materials on ships.
Undersea Exploration
Undersea Exploration
Over the last two centuries there has been an explosion in our knowledge of the global underwater environment. This understanding of the world's oceans and seas has been accomplished by a variety of methods, including the use of both manned and unmanned (i.e., robotic) vehicles. When people use any of these modern methods to explore the undersea realm, they must, in one way or another, use a mathematical description of the under-sea environment in order to be successful. For example, scuba divers must be aware of such quantities as the depth below the surface and the total time they can remain submerged. Each of these quantities is expressed as a number: for example, depth in feet and total dive time in minutes. The use and application of mathematics is therefore an essential part of undersea exploration.
Oceanography is the branch of earth science concerned with the study of all aspects of the world's oceans, such as the direction and strength of currents, and variations in temperatures and depths. Oceanography also encompasses the study of the marine life inhabiting the oceans. As noted earlier, there are multiple ways to explore the oceans and oceanic life. When people and/or machines are sent to directly explore the ocean environment, several different properties of the oceans must be taken into account in order for the dive to be successful and safe. These properties include—but are not limited to—ocean depth and pressure, temperature, and illumination (visibility).
Ocean Properties
"Pressure" is a measurement related to force, and is especially useful when dealing with gases or liquids. When an object is immersed in a swimming pool, in a lake, or in the ocean, it experiences a force pushing inward over its entire surface. For instance, a balloon that is inflated, sealed, and then submerged will be pushed inward by water pressure. The pressure on the balloon is the force exerted by the water on every square inch of the balloon's surface. Pressure is therefore measured as the force-per-unit-area, such as pounds-per-square-inch. Due to Earth's atmosphere, all objects at sea level experience a pressure of approximately 14.7 pounds-per-square-inch (abbreviated 14.7 lbs/in2) over their entire surface.
Perhaps the greatest limitation to underwater exploration is water pressure, which increases with depth (i.e., the deeper one goes, the greater the pressures encountered). Moreover, the pressures within the ocean depths can be immense. A balloon lowered deeper and deeper into the ocean will continuously shrink in size as the water pressure increases. Just under the ocean's surface the water pressure is 14.7 lbs/in2, equal to one atmosphere . For every 10 meters (about 33 feet) of additional ocean depth, the pressure increases by one atmosphere.
"Visibility" refers to how well one can see through the water. As light from the Sun passes through seawater, it is both absorbed and scattered so that visibility due to sunlight decreases rapidly with increasing depth. Below about 100 meters (approximately 330 feet), most areas of the ocean appear dark.
"Temperatures" at the ocean surface vary greatly across the globe. Tropical waters can be quite comfortable to swim in, while polar waters are much colder. However, below a depth of about 250 meters most sea-water across the world hovers around the freezing point, from 3°C to −1°C.
The Development of Diving Equipment
In the past, people who wished to dive down and explore the oceans were limited by the extremes of pressure, visibility and temperature found there. Nevertheless, for thousands of years people have dove beneath the waves to exploit the sea's resources for things like pearls and sponges. However, divers without the benefit of mechanical devices are limited to the amount of air stored in their lungs, and so the duration of their dives is quite restricted. In such cases, diving depths of around 12 meters (less than 40 feet) and durations of less than two minutes are normal.
Various devices have been invented to extend the depth and duration of divers. All these devices provide an additional oxygen supply. Over 2,300 years ago Alexander the Great (356 b.c.e–323 b.c.e) was supposedly lowered beneath the waves in a device that allowed him an undersea view. Alexander may have used an early form of the diving bell, which is like a barrel with one end open and the other sealed. With the closed end at the top, air becomes trapped inside the barrel, and upon being lowered into the water the occupant is able to breathe.
About 2,000 years after Alexander's undersea excursion, Englishman Edmund Halley (1656–1742) constructed a modified diving bell, similar to Alexander's apparatus, but with additional air supplied to the occupant through hoses. Modern diving stations, like diving bells, are containers with a bottom opening to the sea. Water is prevented from entering the station because, like a diving bell, the air pressure inside the station is equal to the water pressure outside. Researchers can live in a diving station for long periods of time, allowing them immediate access to the ocean environment at depths of up to 100 meters (328 feet).
The Emergence of Diving Suits
To allow greater freedom of movement when submerged, various under-water suits and breathing devices have been invented. In the early 1800s, diving suits were constructed, and modern versions are still in use. These suits possess a hard helmet with a transparent front for visibility; an airtight garment that keeps water out but still allows movement; and connecting hoses linked to a surface machine that feeds a continuous flow of fresh air to the suit. Over the years, additional improvements have been added to diving suits, such as telephone lines running between the surface and diver for communication.
From an exploratory point-of-view, diving suits are limited because of their bulkiness, the cumbersome connecting lines that run to the surface, and the restriction of the diver to the seafloor. Skin diving (or "free diving") overcomes the mobility problem by allowing the diver to freely swim underwater. As the name implies, most skin divers are not completely covered by a suit, but rather use minimal equipment such as a facemask, flippers, and often a snorkel for breathing. A snorkel has tubes that allow the diver to breathe surface air while underwater. This type of diving (called snorkeling) must be performed close to the surface.
As compared to snorkeling, scuba diving considerably increases the diving depth of snorkeling by employing an oxygen supply contained in tanks (scuba is derived from "s elf c ontained u nderwater b reathing a pparatus"). Varying versions of scuba gear have been invented. Probably the most popular is the aqualung, introduced by the undersea explorer Jacques Cousteau (1910–1997). When the diver begins to inhale, compressed air is automatically fed into her or his mouthpiece by valves designed to assure a constant airflow at a pressure that matches the outside water pressure. The compressed air is contained in cylinders that are carried on the diver's back. Using conventional mixtures of oxygen and compressed air, divers can safely submerge to around 75 meters (almost 250 feet). With special breathing mixtures, such as oxygen with helium, scuba dives of greater than 150 meters (about 500 feet) have been safely accomplished. To illuminate their surroundings, scuba divers sometimes carry battery-powered lights.
Station, suit, and scuba divers utilize compressed gases for breathing. As divers go deeper, the pressure on their lungs increases, requiring that they breathe higher-pressure air. This process forces gases such as nitrogen into the cells of the diver's body. Divers who do not follow the proper procedure upon returning to the surface risk experiencing a painful, possibly fatal condition known as "the bends." The bends are the result of the pressurized gases inside the diver's body being released quickly, like carbon dioxide being released from a shaken soda can. A diver can avoid the bends by ascending to the surface in a controlled and timed manner, so that the gas buildup inside his or her cells is slowly dissipated. This procedure is called decompression. A competent diver uses gauges to be aware at all times of the depth of the dive, and ascends to the surface in a timed manner.
It is recommended that divers ascend no faster than 30 feet per minute. For example, if a diver is at a depth of 90 feet, it should take 3 minutes to
ascend. The use of numbers and measurements are therefore of utmost importance in all types of diving.
Underseas Exploration Using Submersibles
Although scuba divers can explore some shallow parts of the ocean, especially environments such as coral reefs, submersibles allow exploration of every part of the ocean, regardless of depth. Submersibles are airtight, rigid diving machines built for underwater activities, including exploration. They may be classified as being either manned or remotely operated.
Manned submersibles require an onboard crew. Unlike scuba or suit divers, the people inside submersibles usually breathe air at sea-level pressure. Therefore, people in submersibles are not concerned with decompressing at the end of a dive. In 1960, the Trieste submersible made a record dive of 10,914 meters (35,800 feet) into an area of the Pacific Ocean known as Challenger Deep. Mathematics was essential for both the construction of Trieste and for its record-breaking dive. For instance, the maximum pressure anticipated for its dives (over 80 tons per-square-inch) had to be correctly calculated, and then the vessel walls had to be built accordingly, or the craft would be destroyed. Today there are many new and sophisticated manned submersibles possessing their own propulsion system, life support system, external lighting, mechanical arms for sampling, and various recording devices, such as video and still cameras.
Remotely operated submersibles do not need a human crew onboard and they are guided instead by a person at a different location (hence its name). These vehicles are equipped with video cameras from which the remote operator views the underwater scene. Remote submersibles can byand-large duplicate the operations of a manned submersible but without endangering human life in the case of an accident.
Philip Edward Koth with
William Arthur Atkins
Bibliography
Carey, Helen H., and Judith E. Greenberg. Under the Sea. Milwaukee, WI: Raintree Publishers, 1990.
Davies, Eryl. Ocean Frontiers. New York: Viking Press, 1980.
Oleksy, Walter G. Treasures of the Deep: Adventures of Undersea Exploration. New York: J. Messner, 1984.
Stephen, R. J. Undersea Machines. London, U.K.: F. Watts, 1986.
IS AN OCEAN DIFFERENT FROM A SEA?
The words "ocean" and "sea" are often used interchangeably to refer to any of the large bodies of salt water that together cover a majority of Earth's surface. The word "undersea" refers to everything that lies under the surface of the world's seas or oceans, down to the seafloor.
USING PROPORTIONS WHEN DIVING
Scuba divers know that the deeper the dive, the greater the pressure—a direct proportion. Yet the deeper the dive, the less time they can safely stay underwater to avoid "the bends" —an inverse proportion.
Nautical Archaeology
Nautical archaeology
Nautical archaeology (pronounced NAW-tih-kul ar-kee-OL-low-jee) is the science of finding, collecting, preserving, and studying human objects that have become lost or buried under water. It is a fairly modern field of study since it depends primarily on having the technology both to locate submerged objects and to be able to remain underwater for some time to do real work. Whether it is conducted in freshwater or in the sea, and whether it finds sunken ships, submerged cities, or things deliberately thrown into the ocean, nautical archaeology is but another way of exploring and learning more about the human past.
Archaeology done underwater
Although some use the words nautical archaeology to mean a specialized branch of underwater archaeology, which is concerned only with ships and the history of seafaring, most consider the term to mean the same as the words underwater archaeology, undersea archaeology, marine archaeology, or maritime archaeology. All of these interchangeable terms mean simply that it is the study of archaeology being done underwater. Archaeology is the scientific study of the artifacts or the physical remains of past human cultures. By studying objects that ancient people have made, we can learn more about how they lived and even what they were like. In fact, studying ancient artifacts is the only way to learn anything about human societies that existed long before the invention of writing. For those later societies that are studied, being able to examine the actual objects made and used by those people not only adds to the written records they left behind, but allows us to get much closer to the reality of what life was like when they lived. Also, if we pay close attention to how the objects were made and used and what were their purposes, we begin to get a much more realistic picture of what these people were really like.
Underwater repositories of human history
Ever since the beginning of civilization and mankind's ability to move over water, the bottoms of nearly all oceans, lakes, and rivers became the final resting place for whatever those vessels were carrying. Once real trade began, it is safe to say that nearly every object made by humans was probably transported over water at some point in time, and just as frequent were mishaps and accidents of all sorts that resulted in those objects sinking to the bottom. Vessels of all types—from canoes, rafts, and barges to seafaring ships—became victims of every imaginable disaster. Vessels were sunk by severe weather and fierce storms, by construction defects and collisions, by robbery and warfare, by hidden sandbars and jagged reefs, and probably just as often by simple human error and misjudgment. Some cultures may have thrown things into the sea, perhaps to appease an angry god, while others conducted burials at sea. Finally, entire coastal cities are known to have been totally and permanently submerged as the result of an earthquake. All of these and more resulted in the creation of what might be called underwater repositories of human history.
Destroyed or preserved
Not all of these objects survived either the trip down to, or their stay on, the bottom. Their fate depended on where they landed. If an object sank near the seashore, chances are that it would have been broken by wave action. Even if it sank far below the action of waves, it still might not have survived, since it could have landed on submerged rocks and been broken by ocean currents. Sometimes underwater creatures, like snails and worms, burrowed inside and ate them, while others like coral or barnacles may have cemented themselves on the surface of an object and rotted or rusted away its inside.
Words to Know
Archaeology: The scientific study of material remains, such as fossils and relics, of past societies.
Artifact: In archaeology, any human-made item that relates to the culture under study.
Scuba: A portable device including one or more tanks of compressed air used by divers to breathe underwater.
However, besides hiding or destroying objects, the sea can also preserve them. Objects that sank into deep layers of mud were hidden from sight but were usually well-preserved. Often the saltiness of the water discouraged the growth of bacteria that can rot organic materials like wood. Other times, metals were buried in mud that allowed little or no air to get in, thus preventing them from corroding. It is not unusual, therefore, to discover ancient ships that have been deeply buried whose parts—from their wood boards to their ropes, masts, and nails—and cargos of pottery or weapons or even leather and cloth have been perfectly preserved.
Underwater technology
People have been finding submerged objects of all sorts for as long as they have been able to get and stay below the surface. Early sponge divers were probably among the first, since they were expert at holding their breath and working underwater. Although primitive diving suits were used as early the sixteenth century, it was not until the nineteenth century that helmet diving gear was invented that allowed a person to "walk" on the bottom and explore it. Connected to the surface by an air hose and wearing what must have felt like a heavy suit of armor, the diver was clumsy and very slow and could never get very much done during his short trips to the bottom.
Nautical archaeology did not become a feasible pursuit until the invention in 1943 of an underwater breathing device by French naval officer and ocean explorer Jacques-Yves Cousteau (1910–1997) and Emile Gagnan, also of France. Called scuba gear for self-contained underwater breathing apparatus (and trademarked under the name Aqua-Lung), it revolutionized diving and allowed a person to swim freely down to about 180 feet (55 meters) wearing only a container of highly compressed air on his back. It was later improved by using a mixture of oxygen and helium rather than normal air (which is oxygen and nitrogen), and this allowed a diver to descend as deep as 1,640 feet (500 meters). Until this invention, actual underwater exploring had been done mostly by professional divers who were directed by archaeologists. With this new scuba gear, however, archaeologists could explore themselves. From this, modern nautical archaeology was born.
Improving technology
The first underwater site to be excavated (exposed by digging) by diving archaeologists was a Bronze Age (c. 1200 b.c.) ship wrecked off the coast of Turkey. It was explored by Americans Peter Throckmorton and George Bass, who became pioneers in the field. They and all others to follow used nearly the same techniques that archaeologists on land always
follow, although working underwater made their job one of the most difficult and demanding of all scientific activities.
Today, nautical archaeologists employ a variety of technologies and techniques that make their job easier. They sometimes use aerial photographs to get detailed pictures of shallow, clear water. They often use metal detectors or a magnetometer (pronounced mag-neh-TAH-meh-ter) to find metal objects. Sonar devices send waves of sound through the water that bounce off solid objects and return as echoes, which are recorded by electronic equipment. Underwater cameras are regularly used, as are remotely operated vehicles that can penetrate to extreme depths where severe cold, high pressure, and total darkness would prevent humans from going. Finally, before excavating, nautical archaeologists carefully study and map a site (the location of a deposit or a wreck). This is probably the most time-consuming part of the job, as each artifact is drawn on a map to note its exact location. Only after the entire site is mapped will removal begin. This is done using several different methods. Balloons or air bags are often used to raise large or heavy objects. Vacuum tubes called airlifts are used to suck up smaller objects or pieces. Certain objects brought to the surface must be properly cared for or they can fall apart in a matter of days. Nautical archaeologists must therefore have ready a thorough plan to preserve these fragile objects once they are raised.
Nautical archaeology is still a young science, but it has achieved some spectacular results. Entire ships, like the Swedish warship Vasa, which sank in 1628, and the even older English ship Mary Rose, have been raised. The Vasa took five years to raise; the Mary Rose took nearly twice that long. The wreck of the Titanic, which sunk in 1912 after hitting an iceberg, has been thoroughly explored ever since it was first located by a remote-control submarine in 1985. As technology improves, so does the ability of nautical archaeologists to explore the hidden museum under the sea that holds more clues about our human past.
[See also Archaeology ]