Studying Stone Age forest under the sea

Off the coast at Haväng, forests several thousands of years old are hidden below the sea. When researchers dive down to examine the well-preserved tree-trunks, they are literally diving deep into human history.

Haväng 3 LITEN

Arne Sjöström gets ready for another sea dive.

The morning sun is glittering on the calm surface of the Baltic Sea at Haväng in Österlen. Down on the beach, the researchers are preparing for yet another dive. Archaeologists Björn Nilsson and Arne Sjöström climb into the boat, while geologists Dan Hammarlund and Anton Hansson remain on dry land to tell LUM about their interdisciplinary research project.

“Our aim is to understand both the development of the landscape and how human beings exploited it. For example, we want to know how fast the sea-level rose”, says Dan Hammarlund, Professor of Quaternary Geology.

His doctoral student, Anton Hansson, points towards the sea and describes the well-preserved remains of pine forests several thousand years old which rest on the seabed. Many of the tree trunks are lying down, but some of them are still in the same upright position as they were when they were alive. The most ancient forest has been dated back to 11 000 years BCE. It is located about two and a half kilometres from the beach, at a depth of between 15 and 20 metres. Anton Hansson observes that the ancient coastline was located there 11 000 years ago. Thus, the sea-level at that time was considerably lower than it is today.

Much closer to the shore, about 400 metres from the beach, lies another area of ancient forest on the sea bed, at a depth of 6 to 8 metres. That forest consisted of both evergreens and deciduous trees, which grew there about 9 000 years ago. Thus by then, the sea level had risen compared to a couple of thousand years previously, and the shoreline had moved approximately two kilometres closer to the edge of the present-day beach. The researchers’ theory is that the wooded areas drowned as the sea-level rose – an effect of the major deglaciation of the Ice Age and the changing outlet of the Baltic Sea basin.

“We brought this pine log up yesterday”, says Anton Hansson, showing us a log about a metre long which the research team raised from a depth of about 17 metres.

The brown log is in excellent condition and has clear annual rings. It is a slightly dizzying feeling to run your fingers over its surface and think that it was once actually growing in a forest where Stone Age humans lived. Anton Hansson explains that the find was a four-metre long trunk which they sawed into suitable pieces. Using the measurement of the annual rings, the quaternary geologists can extract facts about when the trees lived and how the weather and climate affected their growth. It is also possible to compare the order in which the trees died, which helps the researchers to reconstruct the progression of the rise in sea level.

“It is interesting for the archaeologists to get information on how changeable the landscape was in the Stone Age”, says Dan Hammarlund.

The quaternary geologists also use other methods to gather facts about the landscape of the Stone Age. These include drilling several metres down into the layer of sediment on the seabed where the drowned forests are located, as well as into the sludge layer on land, close to the nearby Verkeå stream. The analysis of these various drilled cores shows researchers how quickly the sediment formed. The analyses also provide a picture of the salt content at the time, and how fast the water flowed.

To help them understand the changes in the landscape, the researchers also have various high-tech methods at their disposal, such as high resolution depth data, gathered with various sonar methods. Various types of echosounders are used to generate a topographical or bathymetric map of the seabed. Anton Hansson and Dan Hammarlund roll out just such a map, covering the current area of investigation. It clearly shows the changes in the levels of the ancient layer of sludge formed over thousands of years, which now lies on the seabed in compact and delimited mudbanks. It is close to these layers of sludge that the drowned forests once grew.

“Here you can see where the stream ran out. And we have interpreted this part as lagoon formation. And out here are the most ancient trees and the shoreline from 11 000 years ago”, says Anton Hansson, pointing out the sludge formations revealed by the bathymetric map.

Then we all look out to sea, towards the rest of the research team in the boat. Dark clouds are gathering in the sky, and there is a worrying rumble in the air. Suddenly it starts to pour with rain and we are forced to shelter under the eaves of one of the thatched fishing huts. Even modern-day humans sometimes have to adapt to weather and wind.

Text: Lena Björk Blixt

Photo: Gunnar Menander

PROJECTS FACTS: Landscapes Lost

Previously, both archaeologists and geologists have separately taken an interest in investigating traces of the Stone Age on the seabed outside Haväng. Four years ago, archaeologists found a stationary fishing installation which is about 9000 years old, one kilometre from the current shoreline. This is the world’s oldest known fixed fishing installation. Sweden’s oldest processed aurochs bone is one of the finds; tar torches used for night fishing are another artefact from the site.

Archaeologist Björn Nilsson was recently awarded a three-year grant from the Swedish National Heritage Board for the interdisciplinary project Landscapes Lost, which is a collaboration between the Departments of Archaeology and Geology in Lund. The project aims to increase knowledge about the heritage of the coastal areas of Skåne and Blekinge primarily, as well as the human settlement sites that may be found there. The research findings are also valuable in relation to planning needs for coastal areas before investment into sea-based wind energy. Björn Nilsson presented his research on 7 October in the new LUX building.