Did you know that there are at least 20,000 historic shipwrecks and ancient settlements beneath the Baltic Sea? And more are still being found.
“The Baltic Sea is a truly unique treasury,” says Professor of Conservation Charlotte Björdal.
Few people are likely to be aware that there are quite so many shipwrecks at the bottom of the sea, probably because they simply aren’t visible to most of us. There are not that many wrecks remaining off Sweden’s west coast, since shipworms thrive in the waters here and can eat their way through entire wooden boats in just a few decades. However, the brackish waters of the Baltic Sea are a less favourable environment for the shipworm, meaning that old wrecks dating back to the 17th century are still relatively well preserved.
“Wood decomposes slowly in waterlogged environments, since there is very little oxygen,” explains Charlotte. “The water provides indirect protection, which we can also see in mosses and wetlands, for example.”
But despite this, some degree of decomposition does take place under water and in the most oxygen-deficient environments such as in sediment. Until the late 1980s, it was thought that this was due to a chemical process. But now we know better. It is fungi and in particular bacteria that cause wood to break up and soften under water, and Charlotte is a leading expert when it comes to these so-called erosion bacteria. Within the framework of several EU projects, the most recent of which has just been completed, she has worked together with researchers from other countries and different disciplines to study these archaeological underwater sites.
“For me, it’s a matter of conserving and preserving our cultural heritage for future generations. And in order to do this, we must first understand the threat – a bit like with medicine. An accurate diagnosis is needed in order to find the right medicine.”
The latest project, SASMAP, has focused on identifying new methods and techniques for finding wrecks, assessing their condition, stabilising the area and ultimately monitoring and preserving these historically interesting locations. This is quite a tricky working environment, in which researchers want to take samples while also trying to avoid disturbing these sensitive areas. Method development is therefore an important part of the project. Private companies are involved as partners, developing various different prototypes for obtaining sediment samples, for example, or ascertaining the status of the wood.
Charlotte has been out into the field on a couple of occasions, but her work is normally confined to dry land.
“I leave the diving to others. I prefer my microscope,” she laughs as she shows fantastic enlarged images of wood structures and attacks on them.
She is something of an expert on wood, and by studying wood samples from wrecks she can work out how quickly the decomposition is occurring. Different types of wood are broken down at different rates. Oak, which was used to build most ships at this time, lasts longer than pine, for example, which was often used for ships’ floors.
Despite the fact that decomposition takes place more slowly in water, this is a complex environment to protect. But preserving wrecks by raising them and exhibiting them in museums is not something that is currently done. As Charlotte explains, this costs too much.
“A UNESCO directive states that maritime cultural heritage should ideally be preserved in situ, in other words where it already is. But we don’t know how to achieve this yet. We’ve developed simple methods for smaller wreck fragments, but we don’t know how to protect the large ships in the Baltic Sea from ongoing microbial attack. Here, we really need help from engineers, designers and marine scientists.”
SASMAP was a project within the EU’s 7th framework programme, and was carried out during 2012-2015. The participants were from Denmark, Germany, the UK, the Netherlands, Italy and Greece.
SASMAP stands for Development of tools and techniques to Survey, Assess, Stabilise, Monitor and Preserve underwater archaeological sites.