Below the dark blue waters of the Bay of Aarhus in northern Denmark, archaeologists have searched for coastal settlements swallowed by rising sea levels more than 8,500 years ago.
This summer, divers descended about eight metres below the waves close to Aarhus, Denmark's second-biggest city, and collected evidence of a Stone Age settlement from the seabed.
It is part of a $15.5 million, six-year international project to map parts of the seabed in the Baltic and North Seas. The initiative, funded by the EU, involves researchers from Aarhus, as well as the UK's University of Bradford and the Lower Saxony Institute for Historical Coastal Research in Germany.
The goal is to explore sunken landscapes and search for lost Mesolithic settlements as offshore wind farms and other sea infrastructure expand.
Rising tides
Most evidence of such settlements has so far been found inland from the Stone Age coast, said Peter Moe Astrup, an underwater archaeologist leading the excavations in Denmark.
“Here, we actually have an old coastline. We have a settlement that was positioned directly at the coastline,” he said. “What we actually try to find out here is how was life at a coastal settlement.”
After the last Ice Age, huge ice sheets melted and global sea levels rose, submerging Stone Age settlements and forcing the hunter-gatherer human population to move inland.
About 8,500 years ago, sea levels rose by about two metres every century, Mr Moe Astrup said. He and colleagues at the Moesgaard Museum in Hojbjerg, about 10km south of Aarhus, have excavated an area of about 40 square metres of the small settlement discovered off the coast.
Underwater sites 'like time capsules'
Early dives uncovered animal bones, stones tools, arrowheads, a seal tooth and a small piece of worked wood, probably a simple tool. Researchers are combing the site metre by metre using a kind of vacuum cleaner to collect material for analysis.
They hope further excavations will unearth harpoons, fish hooks or traces of other fishing materials. “It’s like a time capsule,” Mr Moe Astrup said. “When sea level rose, everything was preserved in an oxygen-free environment … time just stops.
“We find completely well-preserved wood. We find hazelnut. Everything is well-preserved.”
Excavations in the relatively calm and shallow Bay of Aarhus and dives off the coast of Germany will be followed by work at two locations in the less hospitable North Sea.
Rising sea levels thousands of years ago submerged, among other things, a vast area known as Doggerland that connected Britain with continental Europe and now lies under the southern region of the North Sea. To build a picture of the rapid rise of the waters, Danish researchers are using dendrochronology, the study of tree rings.
Submerged tree stumps preserved in mud and sediment can be dated exactly, revealing when rising tides covered coastal forests. “We can say very precisely when these trees died at the coastlines,” Moesgaard Museum dendrochronologist Jonas Ogdal Jensen said. “That tells us something about how the sea level changed through time.”
As today's world faces rising sea levels driven by climate change, researchers hope to shed light on how Stone Age societies adapted to shifting coastlines more than eight thousand years ago.
“It’s hard to answer exactly what it meant to people,” Mr Moe Astrup added. “But it clearly had a huge impact in the long run because it completely changed the landscape.”
