Denmark’s best-preserved 17th century wreck may have gone completely unnoticed if it hadn’t been lying close to the path of a construction project.
It was only discovered because researchers had been scouring the ocean floor with side sonar to check the seabed ahead of dredgers working on the world’s longest immersed tunnel between Denmark and Germany.
The remarkably intact Dutch ship, the ‘Zwaarte Arend’ – or ‘Black Eagle’ – still had much of its original contents – canons, officers’ chests, wine jugs and other items.
It raises the question of what else might lie undiscovered along Europe’s shores, whether it be shipwrecks or ancient settlements submerged by rising tides, and how they can be protected from treasure hunters.
A three-year EU-funded research project called SASMAP is looking at fast and cost-effective ways of locating shipwrecks and historical underwater settlements in northwest Europe and the Mediterranean.
From satellites to 3D sonar
The SASMAP project is using satellite imaging to chart the shallow underwater coastline to see where ancient human settlements may be located, and catch the first signs of wrecks that are at least partly exposed on the seafloor to depths of six to eight metres.
‘People think the marine environment is benign, but most sites are very dynamic: they can change from being completely covered to uncovered or washed away almost overnight.’
David Gregory, senior scientist, National Museum of Denmark, coordinator of the SASMAP project
Anything suspicious is investigated more closely from a boat using sonar to generate images of large objects, even if buried by sand and sediment. Divers then identify and assess the condition of the objects, for example, checking for signs of erosion or, in the case of wooden boats, destruction by wood-boring shipworm.
Besides satellite imaging, the consortium is testing a new sonar scanning device that generates images in 3D, and novel environmental sensors that will indicate whether conditions, such as low oxygen levels, beneath the sediment could have helped to preserve buried artefacts.
The project will demonstrate how archaeologists can focus their time and resources in places that are most likely to yield good results.
‘People think the marine environment is benign, but most sites are very dynamic: they can change from being completely covered to uncovered or washed away almost overnight,’ says David Gregory, senior scientist working on the conservation of marine archaeological sites for the National Museum of Denmark and coordinator of SASMAP.
Putting theory to the test
David Gregory, scientist in charge of the conservation of marine archaeological sites for the National Museum of Denmark and coordinator of SASMAP.The first test site for SASMAP is Tudse Hage, a Stone Age underwater settlement off the coast of Denmark. Here, an older coastline has been gradually submerged, enabling archaeologists to date artefacts according to their depth.
Artefacts at 7.5 metres belong to people who lived there around 7 000 years ago, while those in shallower waters are the possessions of those who retreated to higher ground as sea levels rose.
Four Stone Age sites are known to exist around Denmark. ‘There are more but we haven’t found them yet,’ explains Jørgen Dencker, Head of Maritime Archaeology at the Viking Ship Museum in Denmark, who led the project that discovered the ‘Zwaarte Arend.’
The SASMAP project is also testing the use of artificial sea grasses to protect sites by slowing down water currents and encouraging particles of sediment to settle. In some cases this may also lead to the formation of a thick protective layer of sand and sediment, which could stifle bacteria and prevent attacks on wood by shipworm. An exposed ship can otherwise be eaten by shipworm in less than 10 years.
The SASMAP approach could save both time and money. ‘In the field it’s very expensive to send a team of divers, and you have weather constraints. We want to be as well prepared as possible for when we do send divers down – it’s about optimising what we can do,’ says Gregory.
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