Vikings may have been basking in pleasant summer weather when they settled in Greenland, according to a study which debunks the pop-culture belief that the Norse people braved subzero temperatures in fur pelts and iron helmets.
After reconstructing southern Greenland's climate record over the past 3,000 years, researchers at Northwestern University in the US found that it was relatively warm when the Norse lived there between 985 and 1450 CE, compared to the previous and following centuries.
"People have speculated that the Norse settled in Greenland during an unusually, fortuitously warm period, but there weren't any detailed local temperature reconstructions that fully confirmed that," said Yarrow Axford, senior author of the study published in the journal Geology.
To reconstruct past climate, the researchers studied lake sediment cores collected near Norse settlements outside of Narsaq in southern Greenland.
Since lake sediment forms by an incremental buildup of annual layers of mud, these cores contain archives of the past. By looking through the layers, researchers can pinpoint climate clues from eons ago.
For the study, researchers analysed the chemistry of a mix of lake fly species, called chironomids, trapped inside the layers of sediment.
By looking at the oxygen isotopes within the flies' preserved exoskeletons, the team pieced together a picture of the past.
This method allowed the team to reconstruct climate change over hundreds of years or less, making it the first study to quantify past temperature changes in the so-called Norse Eastern Settlement.
"The oxygen isotopes we measure from the chironomids record past lake water isotopes in which the bugs grew, and that lake water comes from precipitation falling over the lake," said G Everett Lasher, a PhD candidate at Northwestern University.
"The oxygen isotopes in precipitation are partly controlled by temperature, so we examined the change in oxygen isotopes through time to infer how temperature might have changed," Lasher said.
Since recent studies concluded that some glaciers were advancing around Greenland and nearby Arctic Canada during the time Vikings lived in southern Greenland, researchers expected their data to indicate a much colder climate.
Instead, they found that a brief warm period interrupted a consistent cooling climate trend driven by changes in Earth's orbit.
Near the end of the warm period, the climate was exceptionally erratic and unstable with record high and low temperatures that preceded Viking abandonment of Greenland.
Overall, the climate was about 1.5 degrees Celsius warmer than the surrounding cooling centuries. This warmer period was similar to southern Greenland's temperatures today, which hover around 10-degrees Celsius in summer.
"We went in with a hypothesis that we wouldn't see warmth in this time period, in which case we might have had to explain how the Norse were hearty, robust folk who settled in Greenland during a cold snap," Lasher said.
"Instead, we found evidence for warmth. Later, as their settlements died out, apparently there was climatic instability. Maybe they weren't as resilient to climate change as Greenland's indigenous people, but climate is just one of many things that might have played a role," she said.
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