Κυριακή, 23 Οκτωβρίου 2011

Shipwrecks, amphora and DNA offer clues to ancient trade

by Matt Villano (Woods Hole Oceanographic Institution)
Brendan Foley hunts for shipwrecks, but he’s not searching for gold or jewels. The sunken treasure he pursues comes not in chests, but mostly in curvaceous clay jars called amphorae—the cargo containers of the B.C. world. Holding remnants of goods and foodstuffs produced and traded by ancient civilizations, they are rare and valuable puzzle pieces, strewn and preserved on the seafloor, which scientists could piece together to reconstruct the agriculture, technologies, economies, art, and geopolitics of long-lost eras.

“Ships carry not only economic goods, but the ideas of people,” said Foley, researcher at Woods Hole Oceanographic Institution (WHOI). “Even today, something like 85 percent of all goods are carried across water at some point, and that proportion was higher as you go back in time, because there were few roads and no airplanes.”

Some proportion of those ships that set sail never made it back to port. So Foley believes the sea is full of shipwrecks too deep to be discovered by human divers. Over the past decade, advances in deep-sea vehicle engineering and DNA sequencing are giving scientists new abilities to search for, survey, and analyze these potentially fruitful archaeological sites, he said. Put another way, technological leaps forward are opening new vistas for scientists to make leaps into the past.

What launched the Bronze Age?


The Mediterranean Sea was the highway system of the ancient world.

In particular, Foley has set his sights on the Mediterranean Sea during the Bronze Age, a period from about 3,000 to 1,000 B.C. when human civilization swiftly blossomed. The era was named after a technological advance—the development of metallurgy to produce bronze, an alloy of copper and tin, to make more durable goods. But this relatively brief period in the span of human history also spawned advances in cities, art, architecture, agriculture, written language, and long-distance seaborne trade spanning Egypt, Phoenicia, Greece, and island states throughout the Mediterranean Sea, such as Crete, Santorini, and Cyprus.

Ironically, original artefacts made of the very metal that named the era are much more likely to be found under water than on land, Foley said. “All the great bronze artwork in the National Museum in Athens, Greece, was found under water—some of them from shipwrecks; some of them may have been thrown in lakes or just off shore in advance of invasion. Bronze on land isn’t preserved, because it’s valuable and easily melted down and converted into something else: shields and swords, or later on into cannons or church bells.”

“We shouldn’t be parked on land and confining our search. There’s too much to find out there,” he said, pointing on a map to a blue expanse of the Mediterranean.

“This area is a cradle of civilization,” he said. “With new techniques and tools for marine archaeology, we can start to look for answers to questions such as: What technological developments enabled the flowering of civilization? What was the nature of contact among ancient peoples? How, when, and where did trade networks first develop? How did trade affect cultural development throughout the Mediterranean world?

“Really, what I want to learn is the roots of our civilization—why we became what we are today,” he said.

Piecing together a picture of the past

Foley began working with archaeologists from the Hellenic Ministry of Culture in Greece in 2005, obtaining a list of wrecks that have been reported over the years by fishermen, divers, and other researchers. Many of these shipwrecks, ranging from 700 B.C to 400 A.D., are located near the islands of Chios and Oinousses in the eastern Aegean just off the coast of Turkey.

During that first summer, Foley and a team of Greek archaeologists aboard the research vessel Aagaeo dove on only a handful of wrecks. In crystal-clear visibility of up to 200 feet, they used digital cameras encased in special waterproof housings to take dozens of photographs of the wrecks. Then, they used a WHOI autonomous underwater vehicle named SeaBED to take additional images.


This photomosaic of a wreck from about 350 B.C. is composed of 350 individual photos systematically taken by a robotic vehicle called SeaBED. The wreck was found off the coast of the island of Chios. (Mosaic courtesy of Brendan Foley, Woods Hole Oceanographic Institution)



These ceramic vessels provide clues to who was trading what with whom and when. The 3-foot-tall amphora on the right was made in Chios and contained olive and oregano (probably used as either flavoring or a preservative). The origin of the amphora on the left is still unknown, but its DNA analysis showed that it contained terebinth, a resin from a shrub related to pistachios.

Finding the treasures of trade

Back on land, they pieced together the photos to compose detailed photomosaics that offered panoramic perspectives of entire swaths of seafloor. As with most ancient wrecks in that region, the hulls, decks, masts, sails, and most of the other organic material on the ships had been consumed by marine organisms. What remained poking out of seafloor mud was all of the inorganic material—hundreds of empty ceramic amphorae. These had been stacked within the long-gone hulls to carry commodities such as wine, olive oil, olives, nuts, and a type of fish sauce called garum.

Various civilizations established their own “factories” to manufacture bulk quantities of amphorae to transport goods, Foley said.

“Different people in different areas and in different times had their own style of ceramic amphorae that you can discern at a glance—they way you can discern a Heinz ketchup bottle from a Coke bottle,” Foley said. “So these ceramic vessels are really good indicators of time and place and who was trading with whom.”

But that doesn’t provide much information about what the civilizations were producing or trading.

“Imagine if you were asked to analyse the American economy just by looking at the empty shells of 40-foot shipping containers,” Foley said.

Digging deeper with DNA

To find out what had been inside the amphorae, Foley turned to a close friend, Maria Hansson, a molecular biologist at Lund University in Sweden. She pioneered a sampling technique that enables researchers to swab the interior of ostensibly empty amphorae for traces of ancient DNA.




The team included (from left) Theotokis Theodoulou and Dimitris Kourkoumelis from the Hellenic Ministry of Culture, Maria Hansson from Lund University in Sweden, and Brendan Foley from Woods Hole Oceanographic Institution. (Petros Vezirtis, Hellenic Ministry of Culture)



“Even if it looks like everything has been washed off, we can still detect quite a number of things,” Hansson explained.

Hansson examined swabs from two amphorae recovered from a wreck off the coast of Chios, which the Greeks had discovered in 2004 and Foley and others examined the following year.

Hansson and Foley reported their findings in a 2007 article in the Journal of Archaeological Science. According to DNA data, one of the amphorae held an olive product (probably olive oil), flavoured or perhaps preserved with oregano. The other most likely contained wine, because it appeared to contain fragments of DNA from mastic, a plant that grows on Chios and was used to preserve wine. (Hansson notes that the team wasn’t certain of this latter hypothesis because the same DNA sequences are also found in pistachio nuts.)

Down the road, Foley hopes to apply this technique to other wrecks, combining DNA and other data to reconstruct the movement of crops and commodities across the Mediterranean region.

“If we can get an idea of how food was being preserved and prepared and what sort of value-added products were moving across the Mediterranean between cultures, it would be outstanding,” he said. “If you go back to the fundamental questions of how civilization grows and spreads, maybe a precondition for large populations living in marginal areas like the Greek Isles includes the importation of foodstuffs from other, more fertile spots.”

Robots go where people can’t

But first you have to find amphorae—and that’s where autonomous underwater vehicles (AUVs) have the potential to expand the field. Unlike humans, who can’t safely dive deeper than about 130 feet (40 meters), AUVs can reach into the depths. They can be programmed to conduct systematic sonar surveys covering many square miles of seafloor per day to search for wrecks.



New deep-diving robots expand scientists’ ability to find ancient shipwrecks. The ships’ wooden hulls decompose, but their ceramic amphorae will be preserved, holding clues to ancient civilizations. Above, a vehicle developed at WHOI called SeaBED was used to survey and systematically photograph a shipwreck off the Greek isle of Chios. (Photo by Tom Kleindinst, Woods Hole Oceanographic Institution)

That significantly ups the odds of finding more wrecks—including many in previously inaccessible deep-sea regions. Once wrecks are located, AUVs can map and survey the sites. In the future,they might be able to retrieve artefacts in places where divers cannot go or accomplish tasks more quickly than divers in shallower areas.

“We can get new information about ancient ships travelling long-distance routes, not just day-trippers staying close to shore,” Foley said. “We [humans] can never be there ourselves. We need these robotic vehicles to act as intermediaries linking us to these sites.

“Instead of concentrating resources on a single site over many years as has been the practice in underwater archaeology, soon we will be able to survey dozens of sites in a single field season,” Foley said. “Eventually AUVs will be deployed from shore, reducing project costs by eliminating the support ship.”

Foley hopes to try that experiment, deploying WHOI-developed AUVs called REMUS (Remote Environmental Monitoring UnitS) from the Egyptian shoreline.

“The Egyptian Mediterranean coast in particular is probably one of the least-explored coasts in the whole Mediterranean region,” said Emad Khalil, director of the Centre for Maritime Archaeology and Underwater Cultural Heritage at Alexandria University. “The use of advanced methods and techniques, as well as cooperation between institutions which are interested in the region, will certainly reveal a lot.”

Foley is also teaming with WHOI engineer Dana Yoerger and WHOI geophysicist Jian Lin on a project with the Algerian government to mount a multibeam sonar on an Algerian naval vessel and map the entire Bay of Algiers in the western Mediterranean.

The scientific goals are twofold: to map submerged active seismic faults to assess Algeria’s vulnerability to major earthquakes and tsunamis and help the government better prepare for them, and also to seize the opportunity to find shipwrecks and rediscover the country’s rich maritime history, which extends at least as far back as the 10th century B.C., Foley said.

Shipwrecks farther afield

Meanwhile, as plans for Mediterranean expeditions continue to unfold, Foley has also pursued an underwater archaeology project in the Stockholm Archipelago in Sweden. There, with help from archaeologists representing the Swedish National Maritime Museum and the University of Southampton in England, Foley plans to build a small diver sled, with a thruster, for shallow-water investigations.



In the future, autonomous underwater vehicles, such this WHOI-developed vehicle called REMUS, could be deployed right from shore to search for shipwrecks, avoiding the need to use costly ships. (Photo by Chris Linder, Woods Hole Oceanographic Institution)

The sled will have a Doppler velocity log for relative navigation and a multibeam sonar for precise and accurate mapping of seafloor features. Eventually, Foley hopes to equip the vehicle with a stereo-pair colour-camera system and use it as an AUV to create photomosaics of Viking-era shipwrecks.

Many of these ships are much more intact than their counterparts in the Mediterranean, because the low-salinity Baltic Sea lacks zooplankton that eat wood. Many of the wrecks have decks, masts, and bowsprits still standing and barrels full of cargo between the decks.

“It’s the sort of vision of a shipwreck that Hollywood directors have in mind—ghost ships sitting on the seafloor,” Foley said.

The big challenge in this environment will be visibility. On good days, researchers report visibility of no more than five feet—a green-shifted, dark, and gloomy place to try to image a shipwreck.

“With this technology, any shipwreck within diver-depth we can map to a high quality in maybe less than half an hour,” Foley said.

If they can prove the concept in the Baltic, they will take the technology back to the balmier Mediterranean.

Article by —Matt Villano (Woods Hole Oceanographic Institution) reproduced by kind permission (all images are copyright)


Article update

Since this article was written, further work has been carried out and is published in the Journal of Archaeological Science – Aspects of Ancient Greek trade re-evaluated with amphora DNA.

The researchers have not only found grape and olive DNA as might be expected from wine and olive oil, but also DNA from legumes, ginger, walnut and juniper and from herbs such as mint, thyme and oregano.

Of the thousands of amphorae found in wrecks all over the Mediterranean Sea some of them contain residues of food, such as olive pits and fish bones, but the vast majority of them are discovered empty and unmarked.

Foley says historians tend to assume that these containers were used mainly to transport wine — in a survey of 27 peer-reviewed studies describing 5,860 amphorae, he found that 95% of the jars were described as having carried the beverage – but his work with colleagues is changing this view suggesting that amphorae were commonly reused, and that they may have contained more complex foodstuffs.

The study of DNA from underwater artefacts is still in its infancy, but in theory, this approach could also be used on tableware, or even on small bottles and jars that might have held cosmetics or medicines, says Foley. “This opens up an entirely new view of this early market,” he says. “Now we can start to record what was actually being traded.”



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