The core revealed a Younger Dryas Boundary (YDB) layer containing microspherules—tiny particles of melted material—and platinum-rich nanoparticles that the researchers interpret as possible evidence of an extraterrestrial event. Crucially, older, deeper layers in the same core contain volcanic ash from the Laacher See eruption, deposited roughly 150 years before the boundary layer formed. The younger, microspherule-rich layer lies immediately beneath sediments recording a shift to colder and wetter conditions at the start of the Younger Dryas. This stratigraphic ordering means the eruption and the boundary layer were separate events, spaced far enough apart in time that the eruption is an unlikely primary driver of the cooling.

Microscopic and chemical analyses of the boundary layer point to a mixed origin for its contents. Most of the melted particles appear to have formed from terrestrial material, but some of the platinum-rich nanoparticles show chemical ratios that overlap with those found in certain meteorites and other extraterrestrial material. The team also measured concentrations of several elements carried by the nanoparticles at roughly five to ten times higher levels in the YDB layer than in the surrounding sediments. That pattern was absent from the older volcanic ash and is consistent with fallout from a possible extraterrestrial impact or an atmospheric airburst—an explosion of a space object in the atmosphere rather than a ground collision.

The Swedish findings align with reports from numerous other Younger Dryas Boundary sites across the Americas, Europe, Africa and the Middle East, where researchers have previously identified unusual platinum enrichments and microscopic melted particles in sediments of comparable age. Such evidence has been cited in support of the Younger Dryas extraterrestrial impact hypothesis, though scientists continue to debate the origin of these particles and whether any such event actually contributed to the cooling. The new core does not settle that question, but it sharpens the timeline: at this site, the boundary layer precedes the environmental shift to colder, wetter conditions almost immediately, while the Laacher See ash sits clearly below it.

Lead author Christopher Moore, a research professor at the University of South Carolina, said the separation of events is the study’s central contribution. “This demonstrates that the volcanic eruption and the Younger Dryas Boundary were separate events,” Moore said. “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.” He noted that the work helps distinguish the Laacher See eruption, the deposition of the boundary layer, and the beginning of Younger Dryas cooling—three events that have often been conflated.

The timing argument against a volcanic trigger rests on both sequence and duration. Although the Laacher See eruption may have caused some short-term atmospheric cooling in Europe, large volcanic eruptions typically produce brief cooling episodes lasting years to decades, not the more than 1,000 years of near-glacial conditions experienced across much of the Northern Hemisphere during the Younger Dryas. With the ash deposited about 150 years before the boundary layer, the researchers argue the eruption’s climatic fingerprint would have faded long before the cooling began.

The researchers favor an extraterrestrial impact or atmospheric airburst as a possible trigger for the Younger Dryas, but they acknowledge alternatives. Another volcanic eruption around the same time cannot be ruled out, and it is also possible that volcanic activity and an extraterrestrial event occurred together. Notably, no distinct volcanic ash layer was identified at the Younger Dryas Boundary in the Swedish core itself, although the authors caution that ash from an eruption elsewhere might simply not have reached or been preserved at the site—a limitation that keeps other volcanic scenarios open.

The Younger Dryas has attracted competing explanations for decades. Among the leading alternatives is a large release of glacial meltwater that may have disrupted Atlantic Ocean circulation, a mechanism that could plausibly sustain long-term cooling in the Northern Hemisphere. The Swedish core clarifies the order of events in southern Scandinavia—eruption, then boundary-layer deposition, then environmental change—but, as the authors emphasize, it does not establish what caused the cooling. What it does provide is a cleaner European archive for testing the competing hypotheses, allowing researchers to evaluate volcanic, extraterrestrial, and ocean-circulation explanations against a stratigraphy in which the key events can finally be told apart.

Subject of Research: Sediment core evidence separating the Laacher See volcanic eruption from the Younger Dryas Boundary layer and onset of Younger Dryas cooling

Article Title: New sediment core analysis sheds light on 13,000-year-old ‘cold case’

Article References: New sediment core analysis sheds light on 13,000-year-old ‘cold case’. Original publication (Bibliographic details unavailable.)

Image Credits: AI Generated

DOI: Not provided

Keywords: Younger Dryas, Laacher See eruption, sediment core, microspherules, platinum anomaly, extraterrestrial impact hypothesis, airburst, paleoclimatology, southern Sweden, volcanic ash, Quaternary climate, sediment

The iron hypothesis, proposed by oceanographer John Martin in the late 1980s, rests on a simple biological fact. In vast stretches of ocean known as High-Nutrient Low-Chlorophyll regions, which cover up to twenty percent of the ocean surface, phytoplankton starve for lack of iron even though nitrate and phosphate abound. These microscopic plants use iron as a co-factor in the enzymes of photosynthesis and nitrogen fixation, so when iron arrives, blooms follow. Martin argued that during cold, dusty glacial periods, windblown dust delivered extra iron to these waters, stimulating marine productivity and drawing down atmospheric carbon dioxide, which was eighty to one hundred parts per million lower during ice ages than today. Subsequent research confirmed the mechanism but steadily shrank its estimated contribution, with models attributing perhaps twenty parts per million of the glacial decline to iron-driven fertilization.

To test the hypothesis where it should have mattered most, the team turned to the EGRIP ice core, drilled within the Northeast Greenland Ice Stream about 360 kilometers from the Greenland Summit. The ice they analyzed spans the Pleistocene-Holocene transition, from 13,000 to 10,300 years before present, capturing the Younger Dryas cold event, the warmer Bølling-Allerød interval before it, and the Early Holocene after. Crucially, much of the dust that settled on Greenland during the Younger Dryas originated in the Gobi and Taklamakan deserts of Asia and the Sahara, and a large share of it traveled across the North Pacific before reaching the ice sheet. That geography means Greenland ice records changes in atmospheric iron deposition over the iron-starved Subarctic North Pacific, the very region where marine sediment cores show that productivity stubbornly refused to rise during dusty cold periods.

The technical challenge lies in measuring not just iron, but the right kind of iron. The researchers used the Bern Continuous Flow Analysis system, which melts ice at 2.8 centimeters per minute and channels the meltwater from the pristine inner core of each sample to an array of detectors. Two iron fractions emerged from this pipeline. The first, called Fe_ICP, was quantified by single-particle inductively coupled plasma time-of-flight mass spectrometry and captures most of the atmospheric iron pool, excluding only iron locked inside refractory silicate minerals. The second, dubbed labile iron or LFe, was measured by online acidification of the meltwater at a pH of roughly 1.6 followed by spectrophotometric detection. This mild acid treatment releases iron bound in colloids, hydroxides and organic complexes, the forms most easily grabbed by the siderophore molecules that phytoplankton deploy to scavenge iron from seawater. Labile iron is therefore an upper bound on the iron potentially available to marine life.

The contrast between the two fractions is the heart of the discovery. Median Fe_ICP concentrations surged seventeen-fold between the Early Holocene and the Younger Dryas, rising from 1.76 micrograms per liter to 30.16 micrograms per liter, a signal consistent with the known dustiness of the cold period. Yet labile iron climbed only twenty-nine percent, from a median of 0.51 to 0.66 micrograms per liter after excluding volcanic horizons, a statistically robust difference confirmed by a Wilcoxon rank sum test on more than 21,000 data points. As a result, the labile share of total iron collapsed from roughly forty percent during the Holocene to a mere two percent during the Younger Dryas. In other words, the ocean received vastly more dust, but almost none of the extra iron came in a form plankton could use.

The culprit, the researchers argue, was chemistry. Ice-core acidity measurements reveal that Greenland snow was mildly acidic during the Early Holocene, at a median of 1.06 micro-equivalents per liter, but turned distinctly alkaline during the Younger Dryas, at minus 4.93 micro-equivalents per liter, because carbonate-rich dust from the deserts neutralized the aerosol. Iron solubility is exquisitely sensitive to pH: theoretical calculations show that a single unit increase in pH can reduce dissolved iron(III), the thermodynamically stable form, by nearly two orders of magnitude. That swing matches the gap between the seventeen-fold rise in total iron and the modest rise in labile iron almost exactly. The Bølling-Allerød, still slightly alkaline, showed even lower labile iron concentrations than the Holocene, reinforcing the link between alkalinity and iron lock-up.

The hemispheric comparison makes the case even more striking. In Antarctic ice from EPICA Dome C, labile iron rose as much as twelve-fold between the Holocene and the Antarctic Cold Reversal, contributing up to sixty-four percent of the total iron content during that cold interval. Antarctica stayed acidic even during glacial times, likely because abundant biogenic sulfur dioxide emissions prevented complete neutralization of the aerosol, keeping iron dissolved and potentially bioavailable. This chemical divergence helps explain why sediment records show that iron fertilization boosted productivity in the Subantarctic zone of the Southern Ocean during ice ages, while the North Pacific, bathed in alkaline dust, saw no comparable response over the past 800,000 years.

If not iron, what did control North Pacific productivity during the last glacial transition? The study points to sea ice and ocean stratification. Sediment records from the eastern and western Subarctic Pacific and the Bering Sea indicate extensive spring sea-ice cover during the Last Glacial Maximum, precisely when iron fluxes peaked, and sea ice acts as a physical barrier that blocks both light and direct iron deposition. Productivity rose as perennial ice retreated, peaked during the largely ice-free Bølling-Allerød, and dipped again amid variable ice during the Younger Dryas. Meanwhile, nitrogen isotope measurements from foraminifera show that nitrate consumption was more complete during the Younger Dryas despite low productivity, a paradox explained by stronger stratification: cold, fresh surface waters suppressed vertical mixing, cutting off the upwelling of nutrient-rich deep water even as iron arrived from above.

There is one dramatic exception to the iron drought, and it comes from volcanoes. By identifying ten volcanic horizons through spikes in acidity and electrical conductivity, the team found that labile iron soared to as high as 17 micrograms per liter during eruptions, more than twenty-five times background levels. Acidic volcanic gases react with ash surfaces to create soluble iron salts such as iron chlorides, fluorides and sulfate hydrates, and ash also carries phosphorus, silica, zinc, manganese and copper. At least three interhemispheric eruptions, dated to 10,481, 12,917 and 13,028 years before present, could have triggered transient phytoplankton blooms in the North Pacific, though such blooms would last only a few years and leave no trace in sediment cores. The authors also note a modern echo: rising aerosol pH from changing industrial emissions may have locally altered iron availability in recent decades.

The study does carry caveats. Microbial activity in ice can reduce insoluble iron(III) to more soluble iron(II), and post-depositional mineral weathering can form jarosite and other poorly soluble secondary minerals, but the authors judge these effects limited and broadly uniform across the shallow, 150-meter depth interval examined, leaving the relative changes intact. Even so, the implications are significant for climate science and for any future proposals to fertilize the ocean deliberately. The iron hypothesis, the work suggests, is not a simple matter of dumping dust on the sea; whether iron nourishes plankton depends on the acidity of the atmosphere that carries it, the chemistry of the aerosol, and the physical state of the ocean below. During the Younger Dryas, the Northern Hemisphere failed that test on every count, and the North Pacific stayed hungry despite a seventeen-fold feast of dust.

Subject of Research: Atmospheric iron bioavailability and its role in North Pacific marine productivity during the Younger Dryas

Article Title: Limited atmospheric iron availability increase during the Younger Dryas in the Northern Hemisphere

Article References: Burgay, F., Derrod, H., Erhardt, T., Scoto, F., Segato, D., Maffezzoli, N., Dallo, F., Zannoni, D., Spagnesi, A., Kjær, H.-A., Fischer, H., Varin, C., Barbante, C., & Spolaor, A. (2026). Limited atmospheric iron availability increase during the Younger Dryas in the Northern Hemisphere. Climate of the Past, 22(9), 1675-1689. https://doi.org/10.5194/cp-22-1675-2026

Image Credits: AI Generated

DOI: 10.5194/cp-22-1675-2026

Keywords: iron hypothesis, EGRIP ice core, Younger Dryas, North Pacific, labile iron, aerosol acidity, phytoplankton, HNLC regions, marine productivity, volcanic ash, sea ice, Climate of the Past

The size of the particles an eruption produces is not a trivial detail. It is the single most important factor controlling how far pyroclasts travel, how long they remain aloft, and what hazards they pose once they land. Coarse bombs and lapilli fall close to the vent, while fine ash can drift for hundreds or thousands of kilometers, fouling jet engines, coating crops, and settling into water supplies. Yet despite decades of study, volcanologists have lacked a complete picture of exactly how and where these particles form inside and around an erupting volcano. A new study published in Geology, led by Jacopo Taddeucci, a volcanologist at Italy’s Istituto Nazionale di Geofisica e Vulcanologia, now offers the most detailed microtextural evidence yet that the answer is far more complicated than simplified eruption models have assumed.

The stakes are easy to underestimate. As Taddeucci explains, volcanic ash and larger pyroclasts interfere with nearly every aspect of life downwind of an eruption. They disrupt air traffic and road traffic, and once the eruption is over the work has only begun: the material must be removed, and its effects on crops, plants, vegetation in general, and wildlife must be assessed. Understanding how these particles are formed, he argues, is essential precisely because the formation process controls their features—their size, shape, density, and ultimately their behavior in the atmosphere and on the ground.

To interrogate that process, the research team turned to techniques more often associated with materials science than with volcanology. Using scanning electron microscopy and X-ray microtomography, they analyzed pyroclasts collected from three mafic, or basaltic, volcanoes: Etna and Stromboli in Italy, and Cumbre Vieja in Spain. These instruments allowed the researchers to peer inside individual particles at microscopic scales, resolving features far too small to see with the naked eye but large enough to record the physical history of the magma that produced them. Scanning electron microscopy reveals surface textures and fine-scale fractures, while X-ray microtomography builds three-dimensional images of a particle’s interior without cutting it open, preserving the spatial relationships between crystals, voids, and welded fragments.

What the team found inside these particles was a record of violence and repair. By identifying and quantifying characteristic microtextures—including broken crystals, sutures, and incorporated clasts—the researchers demonstrated that fragmentation does not occur at a single depth and a single moment, as many simplified eruption models assume. Instead, the process is protracted, unfolding across several distinct stages. As Taddeucci puts it, this is not a process occurring at a single point in space and time; it covers a span of time and a span of spaces that reaches from inside the volcano to outside it. The particles that rain down on cities like Catania are, in effect, archives of a prolonged sequence of breaking and healing events that began deep within the plumbing system.

Some of this protracted behavior had already been documented in the open air. Volcanologists have long observed bombs and lapilli breaking apart in flight, shattering into smaller fragments as they arc away from the vent. What has remained invisible is everything that happens before the magma exits the volcano, where direct observation is impossible. The new study provides the first microtextural evidence that fragmentation is also protracted inside a volcano, extending the known sequence of breaking events from the observable exterior into the hidden interior of the edifice. The microscopic scars preserved in pyroclasts—fractured crystals, sutured contacts, embedded fragments of earlier generations of magma—now serve as a proxy for processes no camera can reach.

Perhaps the most consequential finding concerns the opposite of breaking. The team showed that crack healing and the welding together of pyroclasts can be just as important as fragmentation in controlling the final particle size distribution. Taddeucci notes that researchers are accumulating more and more evidence that not only the breaking of the magma controls the size of the particles, but also the fact that different particles can stick together after they are broken. In other words, an eruption’s ash output is not simply the residue of how thoroughly the magma shattered; it is the net result of a dynamic competition between fracturing and reassembly. Cracks can close, and fragments that separate can fuse back together, particularly in hot, low-viscosity basaltic systems where freshly exposed surfaces remain plastic enough to weld.

This reframing has direct implications for hazard modeling. Particle size governs how pyroclasts are dispersed through the atmosphere, and computer models of eruptions rely on assumptions about that size distribution to forecast ash cloud trajectories, ground deposition, and aviation impacts. If fragmentation is protracted and healing is significant, then models that treat fragmentation as a single instantaneous event at a fixed depth may systematically misestimate the grain size of the erupted material—and with it, the reach of the hazard. Incorporating the full break-and-heal history into eruption models could therefore sharpen forecasts of how far ash will travel and how long airports, roads, and agricultural areas will remain affected.

The microtextures identified in the study are not unique to the three volcanoes examined. Asked whether the same features would appear in material from Etna’s eruption this summer, Taddeucci did not hesitate: yes, of course, he says, adding that most basaltic eruptions that are explosive in nature will produce these kinds of features. That generality is what makes the finding powerful. Rather than a quirk of one volcano or one eruption, the break-and-heal signature appears to be a common feature of explosive basaltic volcanism worldwide, from the pulsing fountains of Stromboli to the sustained activity of Cumbre Vieja on La Palma.

There is also a retrospective dimension to the work. Because these microtextures can be preserved in rocks from past eruptions, researchers can use them to reconstruct the fragmentation conditions of events that occurred centuries or millennia ago, extending the observational record far beyond the era of modern monitoring. Taddeucci highlights this as a significant advantage volcanology holds over other geophysical hazards: unlike earthquakes, which leave no comparable physical archive of their internal dynamics, eruptions preserve a durable record of the conditions under which their products formed. Reading that record could improve models of future eruptions at well-studied volcanoes and at sites whose behavior is known only from ancient deposits. Taddeucci also emphasizes that the research depended on collaboration, comparing eruptions across different volcanoes and countries—a scope possible only through cooperation with colleagues at observatories and institutions, including researchers beyond the paper’s official list of co-authors. As ash clouds continue to test the resilience of aviation and communities, the microscopic scars inside volcanic particles are proving to be one of the most informative records science has of what really happens when magma comes apart.

Subject of Research: Microtextural evidence for protracted magma fragmentation and healing during basaltic explosive eruptions

Article Title: Scientists find microscopic evidence that magma repeatedly breaks and heals during eruptions

Article References: Scientists find microscopic evidence that magma repeatedly breaks and heals during eruptions. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: volcanology, pyroclasts, magma fragmentation, Mount Etna, Stromboli, Cumbre Vieja, scanning electron microscopy, X-ray microtomography, volcanic ash, basaltic eruptions, Geology journal, eruption modeling