Vikings left Greenland after growing ice sheet caused sea level rise
The sea level around Greenland rose more than 3.3 metres from AD 1000 to 1450, contributing to the woes of Viking settlers and to their eventual abandonment of the island, researchers have found.
In AD 985, Erik the Red established a colony in Greenland after being exiled from Iceland. At the time, the North Atlantic region was unusually warm – the so-called medieval warm period – but after a massive volcanic eruption in Indonesia in 1257, conditions became much colder for several centuries, a period known as the little ice age.
That led to the expansion of the Greenland ice sheet, say Marisa Borreggine at Harvard University and their colleagues, causing the land adjacent to the ice sheet to subside because of the increased weight. The bigger ice sheet also had a greater mass and so exerted a stronger gravitational pull on the waters around Greenland. These two factors had roughly equal effects on sea level there.
The growth of the Greenland ice sheet reduced global sea level by 7 millimetres during this time as it locked away water, but due to other factors, there was a small overall rise on average across the world. All of this contributed to the 3.3-metre rise around Greenland.
It was already known that the sea rose in Greenland when Vikings lived there, but Borreginne’s team is the first to calculate the effect. The findings show that the coast would have retreated hundreds of metres, with the water swamping more than 200 square kilometres of land and impinging on many farms and homes.
That must have had a major impact on the settlers. There is evidence that their diet shifted from land-based to sea-based, says Borreginne.
The settlers – including Erik the Red’s son Leif Erikson, who sailed to North America some 500 years before Christopher Columbus – were also grappling with colder weather making farming more difficult, conflict with Inuit peoples and reduced demand for walrus ivory as more elephant ivory reached Europe. By around 1450, all the settlements were abandoned.
“What we found is that sea level rise did indeed play a role in the Viking abandonment,” says Borreginne. “But it was not necessarily the number one cause.”
Greenland’s ice sheet is now shrinking fast. Local sea level is already falling around Greenland as the gravity effect weakens and the reduced weight of ice allows land to rise. If the entire ice sheet there melts, as may soon become inevitable, local sea level will fall by more than 100 metres over coming centuries– but rise globally by around 6 metres on average.