Prehistoric communities off the coast of Britain embraced rising seas – what this means for today’s island nations


  • Prehistoric communities off the coast of Britain embraced rising seas – what this means for today’s island nations

    The Isles of Scilly – then and now. Showing land (green), water (blue, darker for deeper water) and the intertidal zone (orange).

    Relative sea level around Scilly was rising fast 12,000 years ago, a response to the melting of both local and far-field ice sheets. During the Last Glacial Maximum, a large ice sheet occupied Scotland, Ireland and much of northern Britain. When this melted, the land it occupied started to rebound – a great mass of ice had been lifted. This caused the land in the south to sink as the Earth’s crust flexed back to its original position. This process is still ongoing today – the land in south-west Britain is currently sinking by around 1 mm each year (mm/yr) while Scotland continues to rise.

    We found that a high rate of relative sea-level rise (nearly 3 mm/yr) continued around Scilly up until 4,000 years ago. At this point, the rate slowed down. Only the ice sheets over Greenland and Antarctica remained, and land subsidence in south-west Britain was lessening. Already, the one large island of Scilly had diminished in size, having lost 100 km² of land to the sea over the 8,000 years up until then.

    But the island was still transforming. We found that even though the rate of relative sea-level rise decreased between 5,000 and 4,000 years ago (from nearly 3 mm/yr to less than 1 mm/yr), the land was still being inundated by the sea. This is because the coastline was low-lying, with much of the land area that remained only a few metres above sea level. As the sea level continued to rise, even at the modest rate of 1 mm/yr, dramatic coastal changes were taking place.

    Land area was being lost at a rate of around 10,000 m² each year, equivalent to the area of a large international rugby stadium. About half of the lost land was turning into intertidal regions - the area of coastline which is intermittently flooded and exposed during the rising and falling of the tide. In fact, between 5,000 and 4,000 years ago, the amount of intertidal area across Scilly nearly doubled.

    A view from Bryher, Isles of Scilly, today. Annie Spratt/Unsplash, FAL
    Despite this large-scale coastal reorganisation of Scilly, the formation of widespread intertidal habitats means that the changes may not have been entirely negative for coastal communities.