Declining temperature has been thought to explain the abandonment of Norse settlements in southern Greenland in the early 15th century CE, although limited evidence is available from the inner settlement region itself. In a new study, scientists from the University of Massachusetts Amherst and elsewhere reconstructed the temperature and hydroclimate history from lake sediments at a site adjacent to a former Norse farm; they found no substantial temperature changes during the settlement period but rather that the region experienced a persistent drying trend, which peaked in the 16th century.
Norse settlers developed the Eastern Settlement on southern Greenland in 985 CE, and other settlers subsequently expanded the settlements on the shores of the fjords to the south and southwest of Narsarsuaq.
The inhabitants relied primarily on raising livestock on cleared pastureland for sustenance, and the estimated population reached about 2,000 people.
Despite the success of the settlements, the region was largely abandoned by the early 15th century.
For decades, scientists have thought the Eastern Settlement’s demise was due to the onset of the Little Ice Age, a period of exceptionally cold weather, particularly in the North Atlantic, that made agricultural life in Greenland untenable.
“However, before this study, there was no data from the actual site of the Viking settlements. And that’s a problem,” said Professor Raymond Bradley, a researcher in the Department of Geosciences at the University of Massachusetts Amherst.
“Instead, the ice core data that previous studies had used to reconstruct historical temperatures in Greenland was taken from a location that was over 1,000 km to the north and over 2,000 m higher in elevation.”
“We wanted to study how climate had varied close to the Norse farms themselves. And when they did, the results were surprising.”
Professor Bradley and his colleagues traveled to a lake called Lake 578, which is adjacent to a former Norse farm and close to one of the largest groups of farms in the Eastern Settlement.
There, they spent three years gathering sediment samples from the lake, which represented a continuous record for the past 2,000 years.
“Nobody has actually studied this location before,” said Dr. Boyang Zhao, a postdoctoral researcher in the Department of Earth, Environmental, and Planetary Sciences at Brown University.
The researchers then analyzed that 2,000 year sample for two different markers: the first, a lipid called branched glycerol dialkyl glycerol tetraether (BrGDGT), can be used to reconstruct temperature.
“If you have a complete enough record, you can directly link the changing structures of the lipids to changing temperature,” said Professor Isla Castañeda, a researcher in the Department of Geosciences at the University of Massachusetts Amherst.
A second marker, derived from the waxy coating on plant leaves, can be used to determine the rates at which the grasses and other livestock-sustaining plants lost water due to evaporation. It is therefore an indicator of how dry conditions were.
“What we discovered is that, while the temperature barely changed over the course of the Norse settlement of southern Greenland, it became steadily drier over time,” Dr. Zhao said.
Norse farmers had to overwinter their livestock on stored fodder, and even in a good year the animals were often so weak that they had to be carried to the fields once the snow finally melted in the spring.
Under conditions like that, the consequences of drought would have been severe.
An extended drought, on top of other economic and social pressures, may have tipped the balance just enough to make the Eastern Settlement unsustainable.
“Drier climate would have notably reduced grass production, which was essential for livestock overwintering, and this drying trend is concurrent with a Norse diet shift,” the authors said.
“We conclude that increasingly dry conditions played a more important role in undermining the viability of the Eastern Settlement than minor temperature changes.”
The results appear in the journal Science Advances.
Boyang Zhao et al. 2022. Prolonged drying trend coincident with the demise of Norse settlement in southern Greenland. Science Advances 8 (12); doi: 10.1126/sciadv.abm4346