Researchers have identified volcanic eruptions, likely in Iceland, as the source of a mysterious platinum spike in Greenland ice cores from 12,800 years ago. This finding rules out a comet or asteroid impact and occurred decades after the onset of the Younger Dryas cooling period. The study provides new insights into abrupt climate shifts.
A sharp rise in platinum levels in Greenland ice cores, dated to about 12,800 years ago, has puzzled scientists for years. Previously interpreted as evidence of a meteorite or comet strike, the anomaly coincides with the Younger Dryas Event, a sudden cold snap from roughly 12,870 to 11,700 years ago when northern hemisphere temperatures plummeted, including over 15°C colder in Greenland than today. This reversal interrupted the warming trend at the end of the last ice age, transforming European forests into tundra and altering rainfall patterns elsewhere. Leading theories attribute the cooling to freshwater influx from melting North American ice sheets disrupting ocean circulation, while others proposed an extraterrestrial impact over North America. In 2013, analysis of Greenland Ice Sheet Project (GISP2) cores revealed high platinum but low iridium levels, atypical for space rocks. New research rules out the Laacher See eruption in Germany, as its pumice showed negligible platinum. Updated dating places the spike 45 years after the Younger Dryas began, persisting for 14 years—too late and prolonged for an impact. The chemical signature best matches volcanic gas condensates from submarine or subglacial eruptions. Icelandic fissure eruptions, capable of lasting years, are the prime suspects, fueled by ice sheet melting that reduced crustal pressure and increased volcanism. Recent Icelandic events, like the 8th-century Katla and 10th-century Eldgjá eruptions, deposited metals in Greenland ice over long distances. A separate sulfate spike aligns exactly with cooling onset around 12,870 years ago, suggesting volcanic sulfur aerosols reflected sunlight, amplifying feedbacks like sea ice expansion. The study, published in PLOS One by Charlotte E. Green and colleagues, emphasizes volcanoes over impacts for this signal, aiding understanding of past climate disruptions.