Impact or eruptions? Geologists have been arguing for decades about what caused a cold snap around 12,900 years ago. Some believe a comet or asteroid impact was the cause, while others believe it was caused by frequent volcanic eruptions. Analyzes from Florida and Texas now provide new evidence for the latter. Deposits from the Younger Dryas showed increased concentrations of osmium and other iron-loving elements, whose isotopic patterns are more consistent with a volcanic origin, as the team reports in Science Advances.
Around 12,900 years ago, the climate in the northern hemisphere experienced a kind of regression: after the ice age was actually over, the North Atlantic Overturning Current (AMOC) weakened and temperatures fell by a few degrees Celsius. This so-called Younger Dryas Age lasted about a thousand years and almost threw Europe back into the Ice Age. The prehistoric Clovis culture in North America may also have experienced its decline as a result.
But the trigger for this post-glacial cold snap is still controversial. Some researchers believe the impact of meteorites or comets is the cause. Possible indications for this include nanodiamonds, melt spherules and the accumulation of certain elements in sediments and ice cores from this period. Scientists have also discovered striking metal enrichments and melt globules on the seabed of Baffin Bay between North America and Greenland.
Dispute over who caused the cold snap
The problem, however, is that many potential indicators of impact could also have arisen from purely terrestrial events, such as frequent volcanic eruptions – this is what other geologists argue. In their opinion, the accumulation of siderophilic, iron-loving elements such as osmium, iridium, ruthenium, platinum, palladium or rhenium in the deposits indicates a volcanic origin of the cold period.
To clarify the controversial issue, Lucien Nana Yobo from Texas A&M University and his colleagues examined a rock formation from the Younger Dryas in Florida in more detail. This Page-Ladson site on the coast of the USA shows an undisturbed layer sequence and is one of the best and most frequently dated archaeological sites in the New World, as the researchers explain. For their study, they analyzed the isotope ratios of osmium and other siderophilic elements in the layers around the beginning of the Younger Dryas.
Telltale element enrichments
And indeed: the layer that marks the beginning of the Younger Dryas Period showed an abrupt shift in isotope ratios from osmium-187 to osmium-188. This indicates an accumulation of non-radiogenic osmium not produced by cosmic rays, as Yobo and his team explain. The concentrations of rhenium and other siderophilic elements also increased at the beginning of the cold period.
The crucial thing, however, is that this enrichment and isotopic change correspond to the pattern typical of volcanic eruptions. “The fractionation patterns of the highly siderophilic elements fit better with enrichment in volcanic aerosols than with the pattern generated by extraterrestrial inputs,” write Yobo and his colleagues. Something similar was found when comparing the analysis values from two other sites in Texas.
More like volcanic aerosols than impact
According to the team, this suggests that there must have been several strong volcanic eruptions at the beginning of the Younger Dryas period. Their gases and aerosols were distributed in the upper atmosphere of the northern hemisphere and thereby abruptly cooled the climate. “The spatial consistency of the anomalies suggests far-reaching transport mechanisms of the aerosols,” report the geologists. It fits that there were several eruptions in the northern hemisphere around 13,000 years ago, including the Laacher Lake eruption in the Eifel 12,880 years ago.
In fact, in an earlier study, researchers identified 30 volcanic eruptions before the start of the Younger Dryas, including four eruption clusters between 12,987 and 12,980 years ago. “Sulfur values from ice cores in Greenland and Antarctica also indicate a cluster of increased volcanic activity lasting around 110 years shortly before the start of the Younger Dryas,” write Yobo and his team. “This may have triggered cascading climate effects consistent with the abrupt onset of the Younger Dryas.”
Trigger for long-lasting feedback
However, geologists also admit that volcanic eruptions alone cannot explain why the Younger Dryas cold phase lasted for around 1,300 years. In their opinion, the climate disruption caused by the volcanic eruptions, which lasted a good hundred years, could have been enough to set a self-reinforcing process in motion: “Long-term feedbacks through the renewed growth of ice surfaces and the disruption of ocean circulation represent a plausible and coherent mechanism for the Younger Dryas cold phase,” emphasizes the team.
Yobo and his colleagues therefore see their results as further confirmation of a purely terrestrial cause of the cold snap in the Younger Dryas. “This offers a robust alternative to impact-based explanations and underscores that clustered volcanic eruptions can also trigger abrupt climate change,” they write.
Source: Lucien Nana Yobo (Texas A&M University, College Station, Texas) et al., Science Advances, 2026, doi: 10.1126/sciadv.aec9030