Flint stone sounds suggest a Stone Age settlement in Copenhagen’s Svanemøllen Harbour

Deep beneath the seabed just outside of Copenhagen’s Svanemøllen Marina, a several thousand-years-old Stone Age settlement is likely entombed within the seafloor sediment.

This is the thesis of a new study, published in the journal Remote Sensing, which includes the work of two Danish researchers. Using a new geophysical method, the researchers were able to register acoustic signals from shaped flint stones, known as knapped lithics, that were widely used for weapons and tools by Stone Age people roughly 4,000 years ago.

"Flint stone that has been knapped, i.e. reduced by flaking away, is nearly always the sign of a nearby Stone Age settlement," explains Lars Ole Boldreel, one of the researchers behind the study and an associate professor in the Geology Section of the Department of Geosciences and Natural Resource Management at the University of Copenhagen.

Together with his colleague Ole Grøn, an archaeologist and visiting researcher at the University of Copenhagen, as well as a group of fellow researchers from Switzerland, Sweden and the United States, the two Danes tested their theory by placing large amounts of both human-knapped and naturally-cracked flint into the sea at Amager Beach and other locations.

"Our seismic measuring instrument only detected a signal, in the form of unique acoustic phenomena, when we sailed over knapped flint. This makes us 90 percent sure that there is a Stone Age settlement in Svanemøllen Harbour, in precisely the area where we received a signal. For now, there is no "smoking gun" in the form of knapped flint, which we could only get by drilling for samples. We certainly hope to do just that," says Boldreel.

He notes that after colleagues in Florida registered similar acoustic signals, divers were able to confirm the presence of knapped flint arrowheads and other tools.

A Stone Age people from 6,000–9,000 years BC

The researchers' measurements of the acoustic signal suggest that the Stone Age site spans a large area of 80 x 120 meters, approximately 7.5 to 9 meters below sea level just outside of Svanemøllen Marina.

The depth from which the acoustic signals reverberate indicates the presence of a Stone Age site inhabited by people of Scandinavia’s Maglemosian culture, who lived from 6,000–9,000 BC. Ole Grøn explains:

"It was a hunter-gatherer culture in which one or two families gathered in bark huts. Tools such as knapped flint and quartz were used to craft spears, knives and arrowheads for hunting red deer, roe deer and aurochs. People also fished and ate hazelnuts, fruits, berries and seeds."

He adds: "An excavation of the site could reveal the remains of preserved mammal and fish bones, as well as remnants of axes, bows, arrows, spears and hut floors. This would add a new layer to the exciting story of these Stone Age people."

New method can bridge gaps in our knowledge about the past

Until now, underwater archaeologists had to rely on knowledge about geography, landscape formations and finds collected by divers as they pondered the presence of submerged settlements at a given site.

"However, existing methods are expensive, time-consuming and inefficient. That’s why our geophysical method is a welcome alternative. Without much funding, we seem to be able to locate Stone Age settlements based on the unique acoustic signals of flint," explains Ole Grøn. 

Historically, about 1,000 submerged Stone Age settlements have been located in Denmark. But according to Ole Grøn, this is probably "just the tip of the iceberg."

In Europe, underwater areas corresponding to 40 percent of the current day landmass exist. The study demonstrates that this is why a major piece of the puzzle to understand the history and culture of our ancestors remains a mystery.

"Our method holds great potential to map submerged settlement sites hidden around the world," concludes Lars Ole Boldreel.

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