THIS week, a US Navy nuclear submarine finished an unusual tour of duty in the Mediterranean. The submarine, called the NR-1, has spent the past 10 days seeking out the remains of ships that sank between Rome and Carthage more than 2000 years ago.
Robert Ballard, the Massachusetts scientists best known for finding the wreck of the Titanic, borrowed the sub 鈥 which can dive to depths of 800 metres, scout along the seabed on retractable wheels and stay submerged for up to a month 鈥 to hunt for archaeological treasures scattered over 100 square kilometres on the floor of the Mediterranean. Though the sub was originally designed in the Cold War for deep-sea surveillance and recovery, it could be on the verge of a new career in archaeology. 鈥淚鈥檓 an explorer,鈥 says Ballard, 鈥渁nd the NR-1 couldn鈥檛 have been better designed for my application. It鈥檚 really spectacular what you can do.鈥
More than a thousand wrecks have been found in shallow Mediterranean waters since the invention of scuba gear in the early 1940s. Divers have excavated over a hundred of them, but cannot work below about 50 metres. In 1988, Ballard towed an underwater camera called Argo to the Mediterranean to search for deeper pickings. He struck gold, discovering a fourth-century shipwreck and a host of ancient artefacts 800 metres below the surface in the dark, cold, calm depths.
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Watery vignettes
Archaeologists were thrilled. On land, vital evidence about the ancients has been destroyed by subsequent generations, and in shallow waters, wrecks have been disturbed by storms and scavengers. But buried in the deep sea, along the many trade routes that crisscrossed the Mediterranean during Roman times, wrecked ships could answer many unresolved questions about the Romans, their allies and their enemies. They offer 鈥渧ignettes of in situ life, where people haven鈥檛 had time to clean up鈥, says Harvard archaeologist Fred Hiebert.
Sure enough, when Ballard returned the following year for a more detailed survey with a robotic vehicle called Jason, he recovered rare artefacts from at least five other periods, implying that there are more ancient wrecks in the same area. But neither Jason nor the underwater camera could find these wrecks in the time available 鈥 their range was just too limited, and the area too vast.
Now, six years later, Ballard has returned and this time he has the tool he needs. The NR-1鈥檚 reactor was refuelled between 1990 and 1992 and the US Navy took the opportunity to give the sub an extensive refurbishment. Now, they are making it increasingly available for undersea scientific missions (see 鈥淣uclear sub for hire鈥). Because the sub is so small, its inner capsule is very robust and can withstand huge pressures. Compared with the bigger nuclear missile-carrying and attack subs in the fleet, which are restricted to depths of around 300 to 450 metres respectively, the NR-1 can dive to 800 metres or so. Its nuclear reactor (the smallest in the world at around the size of a rubbish bin) means that it can stay underwater for up to a month 鈥 plenty of time to seek out important finds and study them in detail. Moreover, its advanced reconnaissance systems can search in far greater detail, and over a larger area, than Ballard managed in his earlier missions, which mapped less than five per cent of the area over which the artefacts were scattered. (see Diagram).
鈥淏allard has a wonderful technology for surveying a region that鈥檚 never been surveyed before 鈥 the bottom of the ocean,鈥 says Hiebert, who is hoping to join him on a future NR-1 mission. But the exact locations of any new finds will be a closely guarded secret. Afraid that scavengers and treasure-seekers will destroy his discoveries, Ballard would not release even the rough location of his researches 鈥 around the Skerki Bank off northwest Sicily 鈥 until this week, when he is steaming away from the region, and can no longer be tracked during his search. Now, armed with the data he has collected, he will work with Anna McCann, an independent archaeological consultant based in New York, to decide which of the wrecks should be examined in detail in 1997.
Ballard is currently director of the Center for Marine Exploration at the Woods Hole Oceanographic Institution in Massachusetts, but plans to retire in two years to head the $15 million Institute for Exploration being built at the Mystic Marinelife Aquarium in Connecticut; this month鈥檚 trip was his first under its auspices. Despite his credentials as an explorer, Ballard鈥檚 original training was in geology and geophysics, and he is a relative latecomer to marine archaeology.
In the 1970s, he used the manned submersible Alvin to study mid-ocean ridges. He then began developing unmanned undersea robots, controlled from the surface through high-capacity fibre-optic cables. The US Navy paid for the programme, and witnessed the first top-secret demonstrations. These were images of the two American nuclear submarines that sank during the Cold War 鈥 the Thresher (which foundered in April 1963 in 2.6 kilometres of water a few hundred kilometres east of Cape Cod) and the Scorpion (which sank in May 1968 in 3.5 kilometres of water south of the Azores).
Just days after photographing the Scorpion, Ballard and his team were out again in the North Atlantic with their remote camera 鈥 called Argo 鈥 searching for the remains of the Titanic. Ten years ago this month he found it, and the following July, he returned with Alvin to explore the wreck. His find made Ballard a media star, and brought him 16 000 letters from children, many of them wanting to join him on his next trip. It also showed him, he says, how well preserved history is in the deep sea, and helped turn his personal course toward archaeology.
The Mediterranean is a logical place to look for hidden archaeological treasures. It was the main highway of the ancient world, where wooden ships carried goods between many ports, including Carthage, Athens, Syracuse, and Ostia (the port serving Rome). Many ships stayed near the coast, and shallow wrecks have provided archaeologists with new windows into ancient times. Excavations have shown how the ancients built their ships, and uncovered evidence of trade in a wide variety of goods, from food to statues.
Amphoras, the terracotta vessels that held fluids, are the most common marine artefacts. Others are more dramatic. 鈥淢ost great bronze statues of antiquity 鈥 about a dozen 鈥 came from the sea,鈥 says McCann. The famous life-sized charioteer in Delphi, from about the fifth century BC, is among the very few ancient bronzes that survived on land; most were melted for other uses. Fishermen have recovered some from the sea, including a statue of Zeus now in the National Archaeological Museum in Athens.
Bronzed Greeks
A snorkeller found two other ancient Greek bronzes more than a decade ago in shallow water near the town of Riace in southern Italy. Their discovery 鈥渞ocked the art world鈥, says McCann. The statues, she says, are 鈥渕agnificent 鈥 made by a master of the time鈥. Yet their origin remains a mystery because they were found isolated, and hauled from the sea by locals, with no record of their archaeological context. They may have been abandoned by smugglers or thrown from a troubled ship that left no other trace in the area.
Artefacts such as these, which came to rest in shallow waters, are more accessible than deeper ones. But therein lies the problem. Fishing trawlers destroy many artefacts as they drag their nets along the bottom. Scavengers and treasure-hunters collect others. 鈥淭here are so many sport divers in Italy that there鈥檚 hardly an amphora in sight,鈥 says McCann. And it is not only human activity that destroys shallow wrecks. Rocks, reefs and heavy swell can often inflict severe damage when ships sink in shallow water.
Also, shallow parts of the Mediterranean are warm, and receive enough light to support high levels of biological activity, speeding the decay of organic material and encrusting exposed durable surfaces. 鈥淪hipwrecks become reefs before long 鈥 after a period of time a ship is reduced to something that doesn鈥檛 resemble a ship at all,鈥 says Ballard. Other wrecks are buried by the rapid accumulation of sediments near the coast.
By contrast, ships that foundered far from the coast probably sank intact into the mud on the seabed, says Ballard. The deep sea is a highly preserving environment where the water temperature is just a few degrees centigrade and little light can penetrate. This combination of cold and dark would prevent the growth of the organisms that turn shallow wrecks into reefs, though oxygenated water at the bottom of the Mediterranean does support wood borers that devour any wood or other organic material protruding from the mud. Another advantage of the deep sea is that, far from land, the average rate of sedimentation is just a centimetre per millennium, so anything left behind by the wood borers would remain exposed on the sea bed. 鈥淵ou can鈥檛 bury ancient history [in the deep sea],鈥 says Ballard. 鈥淚t hasn鈥檛 been on the bottom long enough.鈥
But finding these deeper wrecks is not as easy as it sounds. Large areas of the Mediterranean have been scoured by trawlers, or lie far from trading routes. In the 1988 expedition, it took Ballard and his team about two weeks searching along what ought to have been very promising trade routes near Italy before they finally stumbled across the 4th-century wreck, dubbed Isis by McCann after the Roman goddess supposed to protect sailors. According to McCann it is a potentially very important find. 鈥淭here are very few wrecks from this later period of antiquity 鈥 and none has been well excavated,鈥 she says.
The following year, when Jason photographed the wreck area, it also recovered 48 objects from the ocean floor, including 10 rare intact amphoras, other pottery, previously unknown types of anchors and millstone, and three pieces of wood that were subsequently carbondated to 30, 331 and 401, with a margin of error of between 75 and 100 years. The archaeologists think that the older wood was salvaged from an earlier ship and re-used, or that it came from the heartwood of an older tree. A copper coin from some time in the last six years of the rule of the emperor Constantius II (in power from 337 to 361), and other evidence indicated the ship sank in the last quarter of the 4th century.
McCann says that the ship was probably sailing from Carthage to Rome because the majority of the cargo can be traced to Tunisia. Although most amphoras recovered elsewhere are found broken, archaeologists have identified the distinctive shapes made in different ports and used for different cargoes. No traces of their original contents remained in the Isis artefacts, but McCann says narrow-necked amphoras with pitch lining probably contained wine. Others with wide necks probably held dried material such as fish sauce.
Although the 1989 expedition demonstrated the feasibility of deep-sea archaeology, it literally only scratched the surface of the potential discoveries. Jason collected artefacts from the sea floor, but was unable to excavate below the surface, or to measure the size of the Isis. In a typical wooden shipwreck, the only parts of the ship to survive will be those buried beneath the seabed, where ship worms cannot reach the timber. But buried material was inaccessible to Jason.
More importantly,with the limited capabilities of the equipment that he had at the time, Ballard was unable to make a detailed map of the artefact-rich region, and locate other, perhaps more interesting wrecks. The NR-1 is a different matter, and is fitted with souped up sonars that have never been available to Ballard before. He says he鈥檚 鈥渢hrilled鈥 to be able to sweep out nearly 7000 metres on each side because he鈥檚 used to only 500 metres. Also, the sonars look all around the submarine, instead of just to the sides. This means operators can spot objects ahead, then alter their course to get a closer view, impossible with side-looking sonars.
Cameras on the sub can photograph the seabed, while scientists on board can look out of portholes to examine artefacts first-hand. The NR-1 also carries a 鈥渟ub-bottom profiler鈥, a sonar that can penetrate the sea floor to detect buried artefacts. The sonar can profile only the area lying directly beneath the sub, but the NR-1 can be moved into place once possible wrecks are located, to see what lies beneath the surface. Once they have a detailed map, Ballard and McCann will spend more than a year choosing the wreck they will excavate in 1997. 鈥淭he worst case is we excavate Isis,鈥 says Ballard, but he hopes the NR-1 will locate even more interesting wrecks. 鈥淲e might run right into the Punic Wars,鈥 he notes in which Rome eventually conquered Carthage, or find a wreck from the earlier Bronze Age.
The 1997 expedition will take archaeologists to the bottom, where they will control the excavation, working with a crew member who will operate the manipulator arm. The sub鈥檚 digital camera will document the excavation. When artefacts are exposed, Jason 鈥 controlled from the surface 鈥 will collect them and deliver them to an 鈥渆levator鈥 which will take them to the surface.
Round the clock
A big advantage of the submarine for the 1997 mission is its ability to remain submerged for up to a month, so excavation can continue 24 hours a day. That鈥檚 a significant improvement over Alvin 鈥 when it dived to explore the Titanic it took 2.5 hours to descend to the bottom and 2.5 hours to rise to the surface 鈥 leaving its three human occupants only 3.5 hours to explore the wreck.
The 1997 mission will also venture into the Black Sea 鈥 the location, according to Greek legend, of the quest by Jason and the Argonauts to capture the Golden Fleece. Connected to the Mediterranean through the narrow Bosphorus, the Black Sea is shaped like a bathtub, with steep sides dropping to depths of about 2000 metres. The NR-1 can鈥檛 dive that deep, but it can map the bottom, and robotic vehicles like Jason can give people on the surface a 鈥渢elepresence鈥 at the bottom.
Both the Black Sea and the Mediterranean are remnants of the ancient Tethys Sea, destroyed by the collisions of Africa and India with Eurasia. However, their hydrologies differ greatly. Fresh water that flows into the Black Sea floats on a denser salt layer, stratifying the water, which turns over only once in 2500 years. This feature means oxygen penetrates only the upper 200 metres of water, leaving the depths devoid of oxygen and animal life 鈥 including the ship worms that devour wooden ships.
The Black Sea has not seen as much commerce as the Mediterranean, but Ballard notes that the Jason legend indicates 鈥渢here was maritime travel and commerce about 2000 BC鈥 along the northern coast of Turkey. The absence of wood borers 鈥渕eans that there should be a tremendous amount of human history there鈥, he explains. 鈥淭he Mediterranean is sort of a sure bet, and you need those sort of things in a programme, but you also need to stretch.鈥 That stretch will take him into the Black Sea, where he has no guarantees of finding anything, in an American submarine that just a few years ago would have been decidedly unwelcome in waters then surrounded on three sides by the Soviet Union and its allies (see Map).
Nuclear sub for hire
WITH just $8000 dollars a day 鈥 and the right contacts 鈥 you can hire your own nuclear submarine from the US Navy fleet. The NR-1, recently seeking Roman artefacts in the Mediterranean, is itself an artefact of another era 鈥 the height of the Cold War in the 1960s, when the US spent freely on military technology. Admiral Hyman Rickover, the strong-willed officer who supervised the building of the nuclear submarine fleet, asked his engineers to develop the smallest possible nuclear reactor. Then he directed them to build a compact submarine around it that could dive hundreds of metres deeper than larger nuclear attack or missile-carrying subs.
Designed for undersea surveying, search and recovery, the NR-1 can dive to about 800 metres. The US Navy won鈥檛 talk about most of its missions, but they have included recovering debris from the space shuttle Challenger, which exploded off Florida. Because its top speed is five knots, the sub is towed to sites by a faster surface vessel, which also houses crew members on rotation from the cramped quarters of the little sub. Conventional subs avoid the ocean floor, but the NR-1 has two retractable wheels in its base so it can work there.
杏吧原创s and crew view the undersea world by lying on the floor and looking through three 10-centimetre acrylic portholes which can withstand pressures at depths over 900 metres. One person can control an external manipulator, which can pick up objects up to 20 centimetres in size and deposit them in a basket to be transported to the surface. A recovery claw can also be fitted to pick up slightly larger objects 鈥 up to 35 centimetres in size and weighing up to 226 kilograms.
Lights, cameras and other equipment are mounted on the outside of the 44.4-metre sub. Several onboard sonars can operate in a total of 11 different modes, including Doppler measurements of velocity, surveying broad areas around the sub, measuring elevation above the sea floor, and profiling structures buried in the mud below. Because the submarine is nuclear-powered, its range is limited not by fuel, but by supplies for its human occupants. The quarters are cramped even by submarine standards, but the NR-1 can hold supplies for 330 man-days 鈥 a month for nine crew members and two scientists. This avoids the frequent ascents and descents needed with smaller manned submersibles.
Ian MacDonald of the geochemical and environmental research group at Texas A&M University has used the NR-1 to study natural oil seeps in the Gulf of Mexico since 1987. MacDonald and his team used the sub鈥檚 bottom-hugging capabilities to search large areas for organisms such as tube worms and clams that colonise oil seeps, and seem similar to the life that surrounds deep-ocean vent systems. MacDonald hopes to learn how organisms establish themselves at seeps, how they detoxify the oil, and how much productivity they contribute to the continental slope ecosystem.
The reactor gives the NR-1 power to spare for extra equipment 鈥 a big plus for experiments like one conducted last November by MacDonald鈥檚 group and Westinghouse. Ocean water scatters light strongly, so images must normally be recorded up close. Westinghouse has developed a system that minimises scattering by using a narrow laser beam to scan the scene sequentially, like the raster scan on a TV camera. This makes it possible to record images from up to 24 metres above the ocean floor, a capability MacDonald used to make mosaic images of the bottom.
Robert Steneck of the Darling Marine Center in Walpole, Maine, used the NR-1 for the more prosaic task of assessing lobster populations. Lobster fishing is an important industry in northern New England, and there is wide concern that stocks are being depleted. 鈥淲e know virtually nothing about how lobster populations regenerate,鈥 he explains. The largest numbers are along the shore, but the animals are widely dispersed along the continental shelf.
Counting is complicated because lobsters congregate in certain areas, while ignoring others. Steneck and a student cruised waters up to 200 metres deep from Rhode Island to Canada, counting lobsters and surveying the extents of the habitats.
With the end of the Cold War, the US Navy welcomes scientists who want to use the sub when it is not being deployed for classified missions. The sponsors not only pay the US Navy for extra operating costs, but scientific missions pose challenges that help train the crew 鈥 manoeuvring the vessel within tight constraints, for instance, and learning more about how to find hidden objects in the deep ocean. However, science remains a second priority when duty calls 鈥 even when a scientific mission is in progress. In April, after spending 24 hours towing the NR-1 to a region Steneck wanted to study, the Navy abruptly dispatched the sub to a site where a fighter plane had crashed. Like a standby airline passenger, the scientist was dumped in favour of the customer paying full fare.