COLUMBIA, S.C. – A new study led by an international research team including scientists at the University of South Carolina challenges the idea that the ancient Laacher See volcanic eruption in western Europe triggered a significant climate-cooling period affecting central Europe and the Arctic nearly 13,000 years ago. Their work expands the European archive for testing theories on what caused the millennium-long cooling event, known as the Younger Dryas.
An analysis of a new sediment core collected in southern Sweden revealed a Younger Dryas Boundary (YDB) layer containing tiny melted particles called microspherules and platinum-rich nanoparticles that the researchers interpret as possible evidence of an extraterrestrial event. Older, deeper layers contain volcanic ash from the Laacher See eruption, deposited about 150 years earlier. The younger microspherule-rich layer lies immediately below sediments showing a shift to colder, wetter conditions at the beginning of the Younger Dryas.
Microscopic and chemical analyses indicate that most of the melted particles formed from material on Earth, while some of the platinum-rich nanoparticles have chemical ratios that overlap with those found in some meteorites and other extraterrestrial material. Researchers also found that the amounts of several elements carried by nanoparticles were roughly five to ten times higher in the YDB layer than in surrounding sediments. This pattern was not found in the older volcanic ash and is consistent with fallout from a possible extraterrestrial impact or atmospheric airburst.
The finding is consistent with reports from numerous other Younger Dryas Boundary sites across the Americas, Europe, Africa and the Middle East, where researchers have identified unusual platinum enrichments and microscopic melted particles in sediments of similar age. These findings have been cited in support of the Younger Dryas extraterrestrial impact hypothesis, although scientists continue to debate their origin and whether such an event contributed to the cooling.
"This demonstrates that the volcanic eruption and the Younger Dryas Boundary were separate events," says study lead author and USC Research Professor Christopher Moore. "At our site in southern Sweden, we identified this boundary layer through tiny, melted particles called microspherules and unusually high concentrations of platinum-group elements. This layer is followed almost immediately by evidence for a sudden shift to colder and wetter conditions. This is important because it helps separate three events that have often been discussed together: the Laacher See eruption, deposition of the Younger Dryas Boundary layer and the beginning of Younger Dryas cooling."
Although the Laacher See eruption may have caused some short-term atmospheric cooling in Europe, its timing makes it unlikely to have been the primary driver of Younger Dryas cooling. Large volcanic eruptions commonly cause brief periods of cooling, rather than the more than 1,000 years of near-glacial conditions experienced across much of the Northern Hemisphere during the Younger Dryas.
The researchers favor an extraterrestrial impact or atmospheric airburst as a possible trigger for Younger Dryas cooling, although another volcanic eruption around the same time cannot be ruled out. It is also possible that volcanic activity and an extraterrestrial event occurred together. However, no distinct volcanic ash layer has been identified in the Swedish core at the Younger Dryas Boundary, although ash from an eruption elsewhere might not have reached or been preserved at the site.
Published Sept. 30 in ScienceOpen Research, the study adds new evidence about the timing of events surrounding the Younger Dryas. By identifying the volcanic ash, the younger particle-rich layer and the subsequent environmental change in the same core, researchers can distinguish events that have sometimes been linked.
Other proposed explanations for the Younger Dryas include large releases of glacial meltwater that may have disrupted Atlantic Ocean circulation. The Swedish core clarifies the order of events in southern Scandinavia, but it does not establish what caused the cooling.
