Prehistoric sea level study begins

Sue Dawson taking a core sample from the Stenness loch.

Sue Dawson taking a core sample from the Stenness loch.

A project to study sea level change in Orkney over the millennia got under way last week, with initial work in Stenness and Burray.

Sue and Alistair Dawson, from the Universities of St Andrews and Aberdeen, travelled to Orkney, where, along with local archaeologist Caroline Wickham Jones, they retrieved core samples from the bottom of the Stenness loch and Echnaloch, in Burray.

Picture: Caroline Wickham Jones

Cleaning a sediment core from Voy on the Stenness loch.

Caroline Wickham Jones explained: “Through analysing the remains of the tiny creatures known as diatoms, preserved in the sediments of both sea and loch, the samples will allow the experts to pinpoint when the sea around the islands reached its present level.

Picture: Caroline Wickham Jones

Out on Echnaloch, in Burray.

“The diatoms preserve a record that shows both rise and fall of sea level: by taking cores of material from various sites it is possible to examine the changes between fresh water to marine diatoms, and once this is dated it is possible to see when and how sea level has changed.”

Picture: Caroline Wickham Jones

A sample core showing the variations in the type of sediment.

Although it is generally assumed that relative sea levels in prehistoric times were much lower than at present, there has been no detailed work to confirm exactly how much and we do not know when sea level reached its present levels.

The change in sea level is a complicated process that relates both to the release of water from the ice at the end of the last glaciation and the bounce back of the land, once the weight of ice upon it had gone.

Across Scotland, this varies due to the varying thickness of ice at different places.  In Orkney relative sea level is still rising, but very slowly.

The team were able to extract sediments that appear to show visible signs of changes in sea level but these have to be analysed and dated over the winter. Where the Stenness loch is concerned, this work will provide an indication of when the freshwater loch was inundated by the sea.

Echnaloch used to be an arm of the sea and the team hope to get a date for the creation of the storm beach (now topped by the road) which cut off the loch from the sea.

The project, which is still in the early stages, also hopes to use samples taken in the 1970s by the British Geological Society to calculate early sea level changes at the end of the Ice Age when relative sea level around Orkney may have been as much as 30 metres below that of the present day. The landscape of Orkney that greeted the earliest settlers would have been very different, possibly one or two large, hilly islands surrounded by sea.

The project is currently funded by The Crown Estate, Historic Scotland, and Orkney Islands Council

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