Scientists ride a boat on a lake in Greenland.
The research team collects bathymetry data from a lake in southern Greenland. Credit: Isla Castañeda

It’s a mystery scientists have long been investigating. Why, after more than 450 years, did a colony of medieval Norse farmers disappear from their remote Greenland settlement?

In attempting to uncover what may have happened, researchers have returned again and again to climate—and to a seemingly obvious scenario. Having turned up on the island during the centuries-long Medieval Warm Period, the settlers were then gradually ushered out by the arrival of the Little Ice Age in the 14th century.

But a new study has found that drought, not plunging temperatures, may have pushed an already fragile community to its breaking point.

“We started looking at another technique to reconstruct relative humidity, and there we saw a pretty significant change.”

“There’s been a lot of focus on temperature when we think about climate change in the Arctic, and there are some good reasons for that,” said Isla Castañeda, coauthor of the study, published in Science Advances. Her team, however, found little temperature variability directly at the Norse settlement sites in southern Greenland. “So we started looking at another technique to reconstruct relative humidity, which gives an indication of drought,” she said, “and there we saw a pretty significant change.”

The Viking (Ice) Age

Around 985 CE, at the height of the Viking era, a group led by exiled explorer Erik the Red sailed west from Iceland and established the first European settlement on Greenland. The Norse farmed the land and hunted walrus for the ivory trade. It’s estimated that at its peak, Greenland’s Norse community numbered around 2,200 inhabitants. They made their homes in the small Western Settlement, near the modern-day capital of Nuuk, and the somewhat misnomered Eastern Settlement in the south. Over the centuries, they weathered social and economic changes, agricultural challenges, and, evidence suggests, the weather itself. Though they inhabited Greenland concurrently with Indigenous Dorset and Thule populations, archaeological findings show that the Norse never adopted effective Indigenous sea ice hunting practices or tools. Other evidence indicates conflict between the two populations.

According to radiocarbon dating, by 1450, the Norse settlers were gone.

The Little Ice Age, a period of cooling temperatures, began around 1300 and affected different parts of the globe at different times until the mid-19th century. Yarrow Axford, a paleolimnologist at Northwestern University who was not involved in the new study, said researchers have tended to extrapolate Little Ice Age climate effects in western Europe and Iceland and, perhaps erroneously, relate them to the fate of the Norse in North America.

“I’m really excited to see any new data that we can bring to bear on this mystery,” she said.

Going Local

There have been relatively few temperature reconstructions in Greenland, according to Castañeda, and many of those come from ice core samples taken far from the settlement sites and at a higher elevation. To figure out what happened to the Norse, she said, “we really needed records from closer to where they were living.”

Castañeda is an organic chemist and an associate professor in the Department of Geosciences at the University of Massachusetts Amherst. She and her colleagues applied organic geochemical tools to reconstruct the temperature more locally, taking sediment samples from Lake 578, which is adjacent to an Eastern Settlement farming site. Some bacteria found in the lake adjust their membrane lipids in response to temperature, and analysis of these compounds in dated sediment cores provided a quantitative reconstruction of historic temperatures. The research team then extracted plant leaf waxes from the same sediment cores and analyzed their hydrogen isotope levels, which indicate moisture levels at time of growth.

Boyang Zhao (left) and Tobias Schneider assemble a gravity corer at a lake in southern Greenland. Credit: Isla Castañeda

In looking at both temperature and hydroclimate, the researchers made two surprise findings. “We were expecting to see this dramatic temperature drop at the end of the Norse settlement period, if temperature was indeed the main factor that caused them to leave,” Castañeda said.

Instead, the leaf waxes revealed that Greenland had experienced a relatively wet period just before the settlers arrived, and conditions became drier over time, peaking in the century after the Norse abandoned the site. According to study authors, this long-term drying trend would have decreased summer grass yields, a critical source of winter fodder for livestock.

Supporting these findings, said the study, are two pieces of archaeological evidence—irrigation channels at a Norse farming site in Igaliku and transition to a marine-based diet, which suggests that the Norse came to rely more heavily on seal hunts as drought limited the availability of meat from livestock.

To gain insight into modern Greenlandic agriculture, the team spoke with local farmers and learned that even today drought conditions are a top concern. These farmers are “living in the same spot as the Vikings,” said Boyang Zhao, a paleoclimatologist and postdoctoral research associate at Brown University who coauthored the study as a Ph.D. candidate at Amherst. According to locals, he said, “it’s OK if the summer is a little bit cooler. However, if there is less rainfall in summer, they won’t have enough hay to overwinter [livestock].” Under these circumstances, modern Greenlanders rely on imports. The Norse could not.

Science Surprises Us

The team’s study, said Axford, “highlights how important it is to look at hydroclimate, to look at changes in precipitation and evaporation…and how those affected societies in the past.” But, she added, “I don’t think it’s going to be the last word. We need more data.”

“The real challenge is to actually draw a very close connection between what we see in terms of prevailing trends at the settlement scale and the human activities that reflect a cause-and-effect response.”

Commenting on the findings, Rowan Jackson, a geographer and archaeologist at the University of Edinburgh, agreed. “We do need more evidence locally to corroborate these records,” he said. “And although we can look at evidence of climate such as this, the real challenge is to actually draw a very close connection between what we see in terms of prevailing trends at the settlement scale and the human activities that reflect a cause-and-effect response.”

In considering the study’s evidence of adaptive strategies, Jackson pointed to irrigation channels at the Eastern Settlement site of Gardar. “We can interpret irrigation systems as evidence of adaptation to a drier climate,” he said. “But you need to infer that across other farms as well.”

Jackson’s research looks at whether the Norse settlers may have clung to a cultural identity that was closely tied to farming, which may explain why they apparently failed in the face of climatic challenges while the nomadic Indigenous populations survived. Combined with farming, he said, Norse hunting strategies would have become increasingly inefficient.

Marisa Borreggine, a Ph.D. candidate in the Department of Earth and Planetary Sciences at Harvard University, is studying the effects of rising sea levels on Greenland’s Norse population. Their research argues that an advance of the southern Greenland Ice Sheet during the Little Ice Age led to local sea level rise and an inundation of coastal areas that would have affected Norse settlements.

“Past studies…have been focused on trying to find a singular environmental cause as to why Vikings might have left southern Greenland, and in the past, that’s been really, really focused on temperature,” Borreggine said. Their research and that of the study team at Amherst are both trying to contribute a more in-depth look at the environmental factors at play, Borreggine explained. “There’s a wide array of social and political and environmental factors that could have contributed to Viking out-migration, and we’re able to [provide] more specific details on why a certain environmental factor could have been part of that story.”

“I would be surprised if temperature trends were that spatially variable. But science surprises us all the time.”

Could multiple findings on climate during the settlement period be accurate? It may come down to where researchers are looking. “I would be surprised if temperature trends were that spatially variable,” said Axford. “But science surprises us all the time.”

Zhao and his team acknowledge that many other factors were at play toward the end of the settlement period—disruptions to the ivory trade and plague in Europe among them. “We’re trying to highlight that this drying trend could have been another disadvantage of being in Greenland during that time,” he said.

Though deeper research into fluctuations in temperature and precipitation, in addition to social and economic conditions, offers a more nuanced picture, the puzzle is still incomplete. But the pieces, when put together, may provide insight into a future in which climate and cultural adaptation are bound to increasingly intersect.

—Korena Di Roma Howley (@KDRHowley), Science Writer

Citation: Howley, K. D. R. (2022), Evidence of drought provides clues to a Viking mystery, Eos, 103, https://doi.org/10.1029/2022EO220375. Published on 4 August 2022.
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