A Bizarre Platinum Spike in Greenland’s Ice May Rewrite a Famous Climate Mystery

A long-debated platinum spike in Greenland ice is best explained by volcanic activity rather than a cosmic impact, reshaping ideas about what triggered the Younger Dryas cooling.

An unusual platinum signal preserved in Greenland ice has puzzled scientists for over a decade. New evidence hints that volcanic activity, rather than an impact from space, may be responsible.

Deep within Greenland’s ice sheet, scientists have uncovered an unusual chemical signal that has fueled years of debate. An ice core (a cylinder of ice drilled out of ice sheets and glaciers) revealed a pronounced rise in platinum levels dated to about 12,800 years ago, a finding that some researchers have taken as evidence of a rare meteorite or comet striking Earth at that time.

Our new study points to a far less dramatic source. The platinum anomaly, we argue, is more likely the result of a volcanic fissure eruption in Iceland rather than an object from space.

When the spike appeared is crucial. It coincides closely with the onset of the Younger Dryas Event, the most recent major cold interval in Earth’s history. This period, which lasted from roughly 12,870 to 11,700 years ago, brought a sharp drop in temperatures across much of the northern hemisphere.

The cooling began just as the planet was emerging from the last ice age and starting to warm. Pinpointing what caused this sudden reversal could offer valuable insight into how Earth’s climate system responds to abrupt disturbances.

Based on the available evidence, we suggest that this cold phase was triggered by a major volcanic eruption, possibly from the Laacher See region in Germany or from another volcano that has yet to be identified.

A climate mystery

Ice cores show that during the millennium-long Younger Dryas Event, temperatures across Greenland dropped to more than 15°C colder than they are today. Europe returned to near glacial conditions, with tundra replacing forests that had begun to flourish. Low-latitude rainbelts shifted to the south.

The traditionally accepted explanation involves a massive release of freshwater from melting North American ice sheets. This freshwater pulse disrupted the ocean circulation, affecting temperatures. However, other researchers have proposed that the event was triggered by a comet or asteroid impact over North America.

In 2013, researchers analyzing ice cores drilled as part of the Greenland Ice Sheet Project (GISP2) discovered platinum concentrations that were well above normal levels. The ratio of platinum to an element called iridium was also unusual because space rocks usually have high levels of iridium, while the ice core spike does not. The ice core signature was very different from anything seen in known meteorites or volcanic rocks.

The authors of the space impact paper suggested that perhaps the unusual ice chemistry reflected the impact of an unusual asteroid made up of iron.

A subsequent paper proposed that the ice chemistry could reflect the German Laacher See volcanic eruption, which had an unusual geochemistry and occurred around that time. To test this idea, we collected and analyzed 17 samples of volcanic pumice from deposits left behind by the Laacher See eruption. We measured platinum, iridium, and other trace elements to create a chemical fingerprint of the eruption.

Our results were clear: the Laacher See pumices contain virtually no platinum, with concentrations below or barely at detection limits. Even though some platinum may have escaped to the atmosphere before being trapped in the rock, the eruption was clearly not the source of Greenland’s platinum spike.

Additionally, when we examined the timing carefully, using updated ice core chronologies, we found the platinum spike actually occurred about 45 years after the Younger Dryas began – too late to have triggered the cooling.

This result was arrived at independently, but was consistent with previous research finding the same thing. Importantly, the elevated platinum concentrations lasted for 14 years, suggesting a prolonged event rather than an instantaneous asteroid or comet impact.

A volcanic signal emerges

We compared the ice core’s chemical signature with various other geological samples and found the closest match was with volcanic gas condensates (the products formed when gases released from a volcano cool from a gas to a liquid or solid state) particularly from submarine volcanoes.

Iceland’s volcanoes can produce fissure eruptions lasting years or even decades, matching the 14-year duration of the platinum spike. During the melting phase that preceded the Younger Dryas, Iceland’s volcanic activity increased dramatically as melting ice sheets reduced pressure on the Earth’s crust.

Crucially, submarine or subglacial eruptions interact with water in ways that could explain the unusual chemistry. Seawater can strip away sulfur compounds while concentrating other elements like platinum in volcanic gases. These platinum-rich gases could then travel to Greenland and be deposited on the ice sheet, explaining the odd geochemistry.

Recent research on historical Icelandic eruptions supports this mechanism. The 8th-century Katla eruption produced a 12-year spike in heavy metals like bismuth and thallium in Greenland ice cores. The 10th-century Eldgjá eruption resulted in a cadmium spike within glacial ice. Although platinum was not measured in those studies, these examples show Icelandic volcanoes regularly deliver heavy metals to the Greenland ice sheet.

A smoking gun?

Because of the chronological mismatch, whatever mechanism was responsible for the platinum spike didn’t trigger the Younger Dryas. Our research does, however, highlight previous results showing a massive volcanic sulphate spike in multiple ice cores coinciding precisely with the onset of cooling 12,870 years ago.

This eruption, whether from the Laacher See eruption or an unknown volcano, injected enough sulphur into the atmosphere to rival the largest eruptions in recorded history. Volcanic eruptions can trigger cooling by releasing sulphur into the stratosphere, reflecting incoming sunlight and potentially setting off a cascade of positive feedbacks including sea ice expansion, changed wind patterns, and disruption of ocean currents, though future research needs to explore this further.

The substantial volcanic forcing around the Younger Dryas onset – a time when climate was already sitting between a glacial and an interglacial (the periods between cold snaps) – may have provided the nudge that tipped Earth’s climate back into a cold state.

It is important to note that our research focused on the platinum spike and did not consider other evidence, such as spherules (spherical fragments of melted rock) and black mats (mysterious dark layers in soil), for an extraterrestrial impact. That said, based on our analysis of the new results and existing data, a large northern hemispheric volcanic eruption seems to be the most straightforward explanation for the Younger Dryas Event.

Understanding past climate triggers is vital for anticipating what lies ahead. Although the chance of a large meteorite impact or volcanic eruption in any given year is low, such events are virtually certain to occur eventually. Knowing how Earth’s climate responded in the past is therefore crucial for preparing for the consequences of the next major event.

Reference: “A possible volcanic origin for the Greenland ice core Pt anomaly near the Bølling-Allerød/Younger Dryas boundary” by Charlotte E. Green, James U. L. Baldini, Richard J. Brown, Hans-Ulrich Schmincke, Marie Edmonds and Thomas C. Meisel, 18 September 2025, PLOS ONE.
DOI: 10.1371/journal.pone.0331811

Adapted from an article originally published in The Conversation.

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