Deep-sea treasures unlocked in the Med
Image credit: Odyssey Marine Exploration for Enigma Recoveries
Shipwrecks discovered in the Mediterranean have given scientists a tantalising glimpse into life along one of the world’s most important trade routes, with underwater technology lending a helping hand.
Advances in underwater technology are enabling a golden age of exploration and discovery in the deep ocean worldwide. The ‘Enigma Shipwrecks Project’ (ESP) in the eastern Mediterranean is no exception, uncovering no fewer than 12 shipwrecks sleeping under silty mud 2km below the surface in international waters off the coast of Lebanon. The team has found wrecks that span over two millennia from ancient Greek and Roman times to the last days of the Ottoman Empire.
The most remarkable find was a huge and well-preserved Ottoman trader – dubbed the Ottoman ‘Colossus’ – 43m long and almost 11m wide, and with a cargo capacity of 700 tonnes. “When we found the Ottoman Colossus, we immediately realised that this was a spectacular find; nothing like it had been seen before,” says Tim McKechnie, co-director of Enigma Recoveries, and UK-based sponsor of the multiple expeditions.
“You can see ships like this in contemporary paintings and on fancy plates from Turkey, but none had ever been found as a well-preserved wreck like this, with much of the cargo intact,” adds Dr Sean Kingsley, director of the Centre for East-West Maritime Exploration and archaeologist on the project. “The Ottoman Colossus gives us a spectacular insight into the global nature of East-West trade of the time. Clearly global trade is far from a modern phenomenon.”
The immense trading ship was en route from Alexandria to Constantinople (now Istanbul) carrying an internationally sourced cargo from rare Chinese Ming dynasty porcelain of the highest quality, Indian peppercorns, Egyptian flax, and Italian pottery, when it sank in around 1630 in the Levantine Basin. These two ports were part of a transcontinental maritime trade route that linked north-west Europe with India and China via the Nile and the Red Sea.
The belongings of the crew and travelling merchants helped to date the demise of the unique vessel and included items from Belgium, Portugal and Spain, north Africa and the Ottoman Empire.
It’s likely that a winter storm sank the Ottoman Colossus. In that period, single storms often sank many vessels. It may even have been attacked by Christian pirates, the Knights of Malta, who preyed on Ottoman ships. We will likely never know exactly how the ship met its end – but it was prepared for piracy. The vessel was lightly armed with six cannon, five iron and one bronze, set up to fire stone cannonballs and ‘dirty bombs’ – wooden canisters filled with a nasty mix of pebbles, glass shards and lead shot, designed to cause maximum damage.
Ernie Tapanes was project manager aboard the Odyssey Explorer, the specialist vessel used by Enigma for the search and recovery phases of the project. In the search phase, he explains, “we used an Edgetech side-scan sonar to deliver an acoustic picture of the bottom topography, towed in tandem with a Geometrics magnetometer. We could look at the sonar picture overlaid with magnetic signals to maximise our chances of success.That combination is the best bet to differentiate between the mass of garbage dumped by modern shipping and to discover targets completely buried in the silt. Some targets jump out as being obviously ship-shaped and must-dive possibilities.”
He continues: “There is a bit of art in differentiating between modern dumped junk, modern shipwrecks and older wooden wrecks with rigging, hardware and potentially cannons. Ultimately, experience helps us to divide the readings into three groups: high, low and discounted categories. Then we dive the Zeus robot to ground-truth what lies below.”
Mapping the ocean depths
There are an estimated three million submerged wrecks around the world, and it is thought that only 0.5 per cent of them have been discovered. The Seabed 2030 project, backed by the Nippon Foundation and ocean-mapping body GEBCO, means to rectify that by mapping the entire seafloor of the planet by 2030 and making it freely available to all nations. Less than 20 per cent of the world’s ocean floor has been mapped and the project means to bring together all of the current maps, identify gaps in coverage and map the gaps.
At a Royal Society London meeting in 2019, the project announced plans to equip multiple vessels around the world with data loggers to record bathymetric information and increase global mapping capacity. Already data sets covering an area equivalent to the African continent have been donated to the project, including the mapping by Ocean Infinity of its huge search area (125,000km2) for downed jet MH370 in the Indian Ocean, much of which was previously unmapped.
Knowing the topography of the ocean floor does not just benefit the search for cultural artefacts and shipwrecks; it is vital to understanding ocean circulation patterns, tsunami forecasting, and mineral, oil and gas exploration to name a few. Seabed 2030 is the first coordinated international effort to map the largest unexplored part of our planet.
Over three seasons between 2006 and 2010, the team surveyed an area the size of London. But it was not until 2015 that they could return for a detailed investigation of the Ottoman Colossus site. The Zeus that Tapanes refers to is a remotely operated vehicle, or ROV, the 7.3-tonne eyes and hands of the marine archaeologists that has been transformed into one of the most sophisticated archaeologically tooled robots in the world.
As in any scientific archaeological investigation, the first job was to accurately map the area of the hull and debris field at the site of the Ottoman Colossus using multi-beam sonar prior to any disturbance or excavations. The ship had split open on its journey to the bottom or cracked open on impact with the seabed, spilling out some of its cargo. When it hit the bottom it threw up a colossal plume of mud, still visible clearly in sonograms of the bottom topography after almost 400 years as round-edged berms in the form of an impact crater 30m to the east and west of where the hull landed. Smaller mounds mark the build-up of material over crates thrown free of the hull.
After the site has been completely mapped, the ROV Zeus is tasked with the second phase of the investigation – excavation and recovery. Neil Cunningham Dobson was the offshore archaeology manager on the Enigma project. “Zeus is something of a marine archaeologist’s dream machine. Beneath the waves Zeus handles the most delicate of tasks while hovering above centuries-old fragile timbers. Its suite of tooling and systems are uniquely valuable to marine archaeologists,” he says.
In common with most ROVs, the manipulator arms have a master/slave function, which allows the actions of the flying pilot on board the research ship to be mirrored by the slave arm aboard the robot. Piloting an ROV like this has been described as one of the most expensive and complex video games on the planet. The arms’ custom-built converter kits record precise positional data in three dimensions, critical for plotting the location of finds, vital for understanding an object’s relationship to others nearby, and to the wreck itself.
Zeus can also excavate stratigraphically, in layers of time, by meticulously slicing off small tranches of sediments to tease out their secrets. It has an integrated pump-operated dredge that works just like an archaeologist’s sieve would on land. The dredged sediments or silts pass through the robot’s filtration unit and any small items in the mud are collected in a tray at the back of the ROV, for checking by the archaeologists when the robot returns to the surface. “It’s a smart way of saving small finds that might be missed, such as the dates and the other seeds recovered from the Ottoman Colossus that tell us about the diet of the crew and its passengers,” Cunningham Dobson adds.
To retrieve delicate objects from the seafloor, the pilots deploy Zeus’s limpet suckers. Instead of having to gauge the pressure applied by a remote robotic arm, a small amount of suction can be applied to lift the most delicate and priceless porcelain cups or bowls without risk of breakage.
Everything that Zeus does is transmitted via fibre-optic cable from the robot’s seven observation, video and stills photographic camera systems to the two-person team controlling its activities. One pilot flies the machine, while a second controls its manipulator arms, both working under the direction of the marine archaeologist and the project managers.
The Odyssey Explorer is also equipped with a dynamic positioning system, allowing the vessel to hold a geostationary position above the ocean floor. This helps avoid putting undue stress on the long umbilical cable running between the vessel and the robot, when it works on the seabed some 2,000 metres below.
The Ottoman Colossus is a ship type never seen before, except in contemporary paintings or on decorated ceramic goods, so it is of immense historical significance. Much of its well-preserved ceramic cargo is as rare. The Chinese Great Ming dynasty porcelain from the kilns of Jingdezhen is of a quality destined for the tables of the Sultan and his ambassadors, and similar items can be seen in the Topkapi Palace Museum in Istanbul – hardly everyday tableware. The porcelain almost reached its destination in Constantinople, the culmination of a two-year journey dictated by the monsoons.
To date, Enigma has excavated some 45 per cent of the site and recovered 591 objects, leaving almost 400 other pieces on the seabed. Unlike on land, deep underwater the trenches made by Zeus will naturally backfill, and protect the treasures left at the wreck site. The Enigma team have no immediate plans to return to the secret location, but would like to be able to go back in the future and recover additional finds. The study of some of the Ottoman copperware would almost certainly reveal inscriptions confirming where they were made and the names of merchants – allowing the team to pinpoint when the ship sank, and who operated it.
The stories that can be pieced together by the painstaking detective work of the marine archaeologists and conservators have yielded insights into the lives of those unlucky seafarers and merchant travellers. Concealed among the cargo were 29 tobacco pipes, destined for the addicted of Constantinople. One of the humbler one-off finds from the wreck is a carved pipe in stone that takes the form of a rider on his camel, perhaps the treasured possession of one of the merchants or crew travelling aboard. Both the Sultan and the imams were highly suspicious of the new stimulants nicotine and caffeine, lumping them together with wine and opium. They viewed the cafes where people gathered to indulge in both coffee and a smoke as possible centres of sedition. Smoking was the subject of a fatwa issued by the religious authorities in Mecca.
Over 150 blue and green glazed Persian jars were also found, some packed with Indian peppercorns. Dr Kingsley suggests that this may have been a way to smuggle the valuable spice as contraband and avoid the payment of dues, though it may equally just have been a space-efficient means of transport. Only two other examples of jars like these have ever been discovered.
The last season of fieldwork took place at the end of 2015. After five years of painstaking post-excavation analysis of the finds, the results were publicised earlier this year and a book is due out soon. Kingsley sums up the discovery of the biggest ancient ship ever found. “For an archaeologist, it’s the equivalent of finding a new planet. There is an embarrassment of wonders here. Its major historical value eclipses any material monetary value.” The Enigma team hope that the entire collection will go on permanent display in a major public museum soon.
Creating a 3D model of the wreck
Photogrammetry is the software-assisted stitching together of many images to create a large and detailed composite 3D image. On the Ottoman Colossus wreck, the team used Pix4D software, more commonly used in topside surveys for a huge range of purposes from virtual reality to agriculture or mining.
Dr Gerhard Seiffert, data manager on the Enigma project team, explained the details: “The photogrammetry we used was a game-changer. It doesn’t just look impressive; it has the serious practical advantage of making contactless measuring a reality. Previously, the ROV measured point-to-point, taking a few dozen readings underwater in half a day. But now at a depth of 2,000m we were able to take a set of a few thousand photos at the same time, and process them into 3D overnight. Later you can take hundreds of precise measurements from the model.”
The process involves taking thousands of photos vertically and side-on using the dual stills cameras mounted on the ROV. “We became so efficient that we took photos for 3D modelling every couple of days to document the excavation’s progress. The magic is in the software’s ability to analyse and match points among overlapping photos and then reconstruct the geometry of the scene. Pix4D reads the photos into its software and compares each with one another for pixel matching. The end result can be either a point cloud that we use for measurements, a mesh to produce fly-through 3D video, or 2D orthophotos for GIS (geographic information systems).”
Length, area and volume measurements can be taken both horizontally and vertically from the 3D model. A line is drawn between two points and it gives you 3D and 2D projected lengths. This system created a high-density point cloud of 1-2cm resolution; a resolution ten times better than a multi-beam sonar.
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