A team of international scientists has uncovered new evidence that sheds light on a dramatic climate event in the Early Middle Ages—one that may have played a role in reshaping Europe after the collapse of the Roman Empire.
Researchers from the University of Southampton, working alongside colleagues from Queen’s University in Canada and the Chinese Academy of Sciences, have traced unusual rocks found on Iceland’s west coast back to Greenland. Their findings, published in Geology, suggest that these rocks were carried to Iceland by icebergs during a previously underestimated cold period known as the Late Antique Little Ice Age.
This short-lived but intense cooling period began around 540 AD and lasted for up to three centuries. According to the researchers, it may have been triggered by a series of volcanic eruptions that spewed ash into the atmosphere, dimming the sun and causing a drop in global temperatures.
“When it comes to the fall of the Roman Empire, this climate shift may have been the straw that broke the camel’s back,” said Tom Gernon, Professor of Earth Science at the University of Southampton and co-author of the study.
Historians have long debated the causes behind the Roman Empire’s decline, including economic instability, invasions, and disease. This new research adds weight to theories that environmental upheaval may have intensified existing pressures and helped spark the mass migrations that reshaped Europe in the post-Roman world.
The rocks in question were discovered on a raised beach terrace—land that rose after the retreat of the last ice sheets. These cobbles, about the size of a human fist, were notably different from Iceland’s typical basalt landscape.
“We knew these rocks seemed somewhat out of place because the rock types are unlike anything found in Iceland today, but we didn’t know where they came from,” said Dr Christopher Spencer, Associate Professor at Queen’s University in Kingston, Ontario, and lead author of the research.
Fingerprints of a Frozen Past
“On one hand, you’re surprised to see anything but basalt in Iceland; but having seen them for the first time, you instantly suspect they arrived by iceberg from Greenland,” added Professor Ross Mitchell, a co-author from the Chinese Academy of Sciences.
To confirm the rocks’ origins, the team crushed them and extracted hundreds of zircon crystals—tiny mineral grains that can reveal a rock’s geological history. “Zircons are essentially time capsules that preserve vital information including when they crystallised as well as their compositional characteristics,” said Dr Spencer.
Using these “time capsules,” the scientists traced the rocks back to various regions of Greenland. “The fact that the rocks come from nearly all geological regions of Greenland provides evidence of their glacial origins,” explained Professor Gernon.
The timing of the deposits—around the 7th century—aligns with what scientists call the Bond 1 event, a major episode of iceberg activity in the North Atlantic. “This is the first direct evidence of icebergs carrying large Greenlandic cobbles to Iceland,” Dr Spencer noted.
Professor Gernon added: “This timing coincides with a known major episode of ice-rafting, where vast chunks of ice break away from glaciers, drift across the ocean, and eventually melt, scattering debris along distant shores.”
“What we’re seeing is a powerful example of how interconnected the climate system is,” concluded Dr Spencer. “When glaciers grow, icebergs calve, ocean currents shift, and landscapes change. Climate-driven iceberg activity may have been one of the many cascading effects of rapid cooling.”
The article, “Greenlandic debris in Iceland likely tied to Bond event 1 ice rafting in the Dark Ages,” by Christopher J. Spencer, Thomas M. Gernon and Ross N. Mitchell, published in Geology. Click here to access it
Top Image: Icebergs off of Iceland – photo by AntaniTapioca / Flickr
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