Sea-level rise in southwest Greenland as a contributor to Viking abandonment

Newswise —

The Norsemen inhabited Greenland for around five centuries, from approximately 985 to 1450, engaging in agriculture and establishing communities before inexplicably abandoning their settlements and disappearing without a trace. The enigma of their sudden disappearance has confounded historians for years, but a recent study conducted by the Department of Earth and Planetary Sciences (EPS) proposes that a significant factor contributing to their vanishing act was the gradual rise in sea level.

Marisa J. Borreggine, the primary author of the study titled "Sea-Level Rise in Southwest Greenland as a Contributor to Viking Abandonment," which was recently published in the Proceedings of the National Academy of Sciences (PNAS), highlighted that there are numerous theories regarding the Vikings' departure from Greenland. She stated that the prevailing narrative has shifted from the notion that the Vikings simply failed to adapt to their environment, to considering a multitude of challenges they faced, such as social unrest, economic turmoil, political issues, and environmental changes. Borreggine, who is a doctoral candidate in the Harvard Griffin GSAS in EPS, emphasized the complexity of the factors that may have contributed to the Vikings' mysterious disappearance.

According to Borreggine, the evolving landscape would have posed an additional challenge to the Viking community in Greenland, alongside the other issues they faced. Working in the Mitrovica Group under the leadership of Jerry X. Mitrovica, the Frank B. Baird, Jr. Professor of Science, Borreggine suggests that these cumulative challenges may have eventually reached a tipping point, leading to the ultimate abandonment of the settlement by the Vikings. The changing environment, including the rising sea levels, likely played a significant role in this tipping point, further adding to the mystery of the Vikings' disappearance from Greenland.

The Viking settlers left Greenland during the onset of the Little Ice Age, a historical period characterized by cooler temperatures and freezing conditions in the North Atlantic. However, contrary to the expected outcome of lower sea levels due to cooling and freezing, a combination of factors actually led to the opposite effect in Greenland. Complex factors such as glacial meltwater runoff and changes in ocean currents contributed to an increase in sea levels during the Little Ice Age in Greenland, further complicating the challenges faced by the Viking settlers and contributing to their eventual departure from the region. The relationship between the Little Ice Age and sea level changes in Greenland adds a layer of intricacy to the mystery of the Vikings' disappearance from the region.

Borreggine pointed out that intuition might suggest that sea levels should have decreased during the Little Ice Age due to the new ice volume from the waters of the North Atlantic. However, a closer examination of previously published geomorphological and paleoclimate data, as well as the researchers' ice-sheet growth modeling, revealed that the opposite occurred in Greenland, specifically in the Vikings' Eastern Settlement. Borreggine explained that their group focuses on studying glacial isostatic adjustment, a process that involves changes in the gravitational field, rotation axis, and crustal deformation as ice grows or melts. This complex process likely contributed to the rise in sea levels in Greenland during the Little Ice Age, further adding to the intricacies of the Vikings' disappearance from the region.

In a first for this kind of research “we were able to apply that analysis of non-uniform sea-level change and more accurate sea-level physics to this longstanding archeological question of, ‘Why exactly did Vikings abandon the Eastern Settlement?’”

What the researchers found was striking: Not only were sea levels drawn up by gravity, other factors – including the subsidence of Greenland’s land mass – made the settlement more prone to flooding.

During the period of Viking habitation in Greenland from 1000 to 1450, there was already a background trend of sea-level rise in the Eastern Settlement, which had been ongoing for thousands of years, according to the researchers. However, there was also a local effect that further exacerbated the sea-level rise: crustal subsidence, which refers to the sinking of land and the gravitational pull of water towards the growing ice sheet. This combination of factors, including the background sea-level rise and the local crustal subsidence, likely contributed to the challenges faced by the Viking settlers in Greenland, further complicating their ability to adapt to the changing environment and eventually leading to their departure from the region.

“Not only do you have the ground being pushed down, you also have the sea surface going up,” Borreggine noted. “It’s a double whammy.”

During this period, researchers found that the settlers experienced “up to 3.3 meters of sea-level rise throughout their occupation.” For comparison’s sake, “that’s two to six times the rate of 20th-century sea-level rise. So it was pretty intense,” they said.

The archaeological research into the lives of the Vikings who settled in Greenland, combined with the novel application of sea-level science, has shed light on this compelling story. As researchers examined the partially drowned ruins of a Viking warehouse, Borreggine highlighted that their analysis revealed that 75 percent of Viking sites were located within a thousand meters of areas that experienced flooding. This widespread flooding was pervasive, indicating the significant impact of rising sea levels on the Viking settlements in Greenland. Such findings provide further evidence of the challenges faced by the Viking settlers as they grappled with the changing environmental conditions, including the rising sea levels, which likely played a role in their eventual abandonment of the region.

The impact of rising sea levels on the Vikings in Greenland is also evident in their changing diet. As their agricultural fields became saturated with salt or flooded due to rising seas, the Vikings were forced to shift from relying on their own agricultural products to more marine-based foods. This dietary shift, as observed by Borreggine, indicates that the Vikings were attempting to adapt to the changing environmental conditions, including the rising sea levels. It provides further evidence of the challenges they faced and their efforts to cope with the impact of sea-level rise during their occupation of Greenland.

Mitrovica highlighted the significance of interdisciplinary research, as demonstrated in this paper. By bringing ideas from different fields together, Borreggine's research sheds light on new insights regarding the challenges faced by the Vikings in Greenland. Mitrovica acknowledged Borreggine's expertise in sea-level physics, which allowed her to uncover the pervasive flooding that the Vikings faced in addition to the challenges posed by the changing climate during the ice age. This underscores the importance of interdisciplinary approaches in unraveling complex historical and environmental mysteries, and how diverse expertise can contribute to a more comprehensive understanding of the past.

Borreggine drew parallels between the lasting impact of sea-level rise during the Viking era and current efforts to mitigate climate change. However, one major difference is that the Vikings did not have a choice as they were locked into the changes brought by the Little Ice Age. In contrast, modern society has the opportunity to take action to mitigate climate change through proactive measures. This highlights the importance of addressing climate change now to avoid irreversible consequences in the future, unlike the situation faced by the Vikings in Greenland.