The Isles of Scilly were once a single large landmass, but new research has shown how rapidly rising seas created the many separate islands present today and caused its prehistoric inhabitants to abandon many of their settlements. (IMAGE: Historic Environment Record, Cornwall Council)

The Isles of Scilly are known for their sandy beaches and shallow tidal waters, but the archipelago was not always like this. A collaboration between researchers is investigating how the islands and their surrounding sea have changed over the millennia, reconstructing the ways in which our prehistoric ancestors adapted to a changing landscape – and examining how current climate patterns are likely to affect the islands in the future.

The Lyonesse project – encompassing the Cornwall archaeology unit, the Cornwall and Isles of Scilly Maritime archaeology society, the Islands Maritime archaeology group, Historic England, and the universities of Aberystwyth, Cardiff, and Exeter – examined foraminifera, single-celled organisms which survive as fossils. In so doing, as a report published by Historic England (https://historicengland.org. uk/whats-new/research/pastas- key-to-future/) describes, the team was able to ‘pinpoint the elevation of the deposit in which [the foraminifera] were found, relative to the sea-level at the time of their formation’. In this way, they were able to reconstruct changing sea-levels. Their results showed that until around 7,000 BC, Scilly was one large landmass, but by 4,000 BC the sea level began to rise rapidly, and the island of St Agnes as well as some of the smaller western isles were separated from the whole.

The northern islands appear to have separated around 3,000 BC as a consequence of tidal flooding, although Tresco, Bryher, and Samson remained joined. It was not until between 2,500 and 2,000 BC, however, that the most dramatic changes to the island landscape occurred, when roughly two-thirds of the previous landmass became intertidal. The current configuration of islands was mostly achieved by 1,500 BC.

A notable aspect of the Scillonian coastal environment today is the presence of prehistoric roundhouses and field walls below high water, abandoned when the low-lying land was submerged by rising sea levels. This demonstrates how reconstructing palaeoclimates is essential for interpreting archaeological evidence.

Assessments for future sea-level changes in the region suggest that by 2100 it is likely that further areas of land will become submerged, while parts that remain above the surface will be more prone to flooding. Still, despite these drastic changes, the team found that they are unlikely to be as profound as the ones seen in the second half of the 3rd millennium BC. How will humans adapt this time?

This article appeared in CA 341.

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