A team led by Pradeep K. Aggarwal, formerly of the Isotope Hydrology Section at the International Atomic Energy Agency in Vienna, together with Courtney Schumacher and Aaron Funk of Texas A&M University, Frederick J. Longstaffe of the University of Western Ontario, and Matthew D. Shupe of the University of Colorado and NOAA, examined what happens to d-excess when ice grows by a process called riming. In mixed-phase clouds, where supercooled liquid droplets, ice crystals and vapor coexist at temperatures above roughly minus 38 degrees Celsius, ice can grow in two distinct ways. In the Wegener–Bergeron–Findeisen process, liquid droplets never touch the ice; instead they evaporate, and the resulting vapor diffuses onto the ice crystals, which preferentially incorporate heavier isotopologues and end up with a d-excess as much as 30 per mil higher than the surrounding liquid. Riming is different: here, supercooled droplets collide directly with ice particles and freeze on their surfaces.

The long-standing assumption, embedded in isotope models since the early 1980s, was that riming occurs without isotopic fractionation—that rimed ice simply inherits the isotopic composition of the liquid it accretes. The new analysis shows this assumption is wrong. When droplets freeze onto a falling ice particle, the latent heat of fusion warms the particle surface, and under many conditions a liquid film forms that partially evaporates before freezing is complete. Because the semi-heavy isotopologue H2H16O diffuses more slowly than H218O in air, this evaporation preferentially removes oxygen-18 relative to deuterium from the accreted liquid, driving down the d-excess of the ice that ultimately forms. The result is rimed ice with a d-excess substantially lower than the parent liquid—by as much as 20 to 30 per mil in wet growth conditions.

To test this idea against real weather, the team needed an independent measure of riming intensity, and they found one in radar. Riming makes ice particles denser and rounder, which increases their terminal fall speed: a lightly rimed snowflake might fall at 0.5 to 1 meter per second, while dense graupel exceeds 1.5 meters per second. Vertically pointing Doppler radars measure the mean Doppler velocity of falling hydrometeors, and in stratiform clouds, where small upward and downward air motions cancel out when averaged over 20 to 30 minutes, this velocity approximates the terminal fall speed. The researchers correlated mean Doppler velocity with the d-excess of precipitation collected at six sites spanning the globe: Summit, Greenland; Ny-Ålesund and Andenes in Norway; Dumont d’Urville in Antarctica; Cazadero, California; and Rio Claro, Brazil.

The result was strikingly consistent. Across an observed d-excess range from minus 23 to plus 45 per mil, d-excess decreased as fall velocity increased at every location except winter precipitation at Summit. Pooling 211 samples from all sites except Summit, a standardized regression yielded a strong correlation coefficient of minus 0.68, with the slope negative at each individual site and tightly constrained at the best-sampled locations. The team converted fall velocities into rimed mass fractions using a published parameterization and found that each 10 percent increase in rimed mass corresponds to a d-excess decrease of roughly 8 per mil. Because the physics of droplet freezing is the same everywhere, this relationship holds from the tropics to the poles—a universality that argues the correlation reflects a genuine microphysical mechanism rather than a site-specific coincidence.

Skeptics might wonder whether sub-cloud evaporation of raindrops, which also lowers d-excess, could explain the pattern. The researchers addressed this head-on. For rainfall sites, Doppler velocities were taken from the snow region above the melting layer, well inside the cloud and untouched by sub-cloud processes. Calculations with an established raindrop evaporation model showed that evaporation could have lowered d-excess by only about 2 per mil during the key Cazadero event, and less than 1 per mil at Rio Claro where surface humidity exceeded 90 percent. Moreover, comparing fall velocities above and below the melting layer showed that the lowest d-excess rain samples plotted in the graupel and heavily rimed fields—exactly where riming, not evaporation, would place them.

Radiosonde profiles of temperature and humidity added independent atmospheric context. At Summit, winter temperatures throughout the precipitating column fell below minus 38 degrees Celsius, ruling out mixed-phase conditions and riming entirely; the low winter d-excess there instead arises from vapor deposition at very cold temperatures from vapor strongly depleted in oxygen-18, under high ice supersaturation. In summer, humidity near the cloud base approached liquid saturation at temperatures between minus 10 and minus 4 degrees Celsius, precisely the conditions for wet-growth riming. At Ny-Ålesund and Dumont d’Urville, the profiles revealed a two-layer structure: an upper, ice-supersaturated layer where vapor deposition dominates, and a lower, near-water-saturated layer where riming takes over. Case studies of individual storms traced the full spectrum, from a deposition-dominated event at Ny-Ålesund with d-excess of plus 34.5 per mil to a heavily rimed rainfall at minus 4.6 per mil.

The team then built a process-weighted framework treating precipitation d-excess as a mass-weighted mixture of four end-members: vapor deposition, diamond dust, wet-growth riming and dry-growth riming. Mixtures containing 20 to 80 percent vapor deposition, with the remainder riming, reproduced the observed d-excess ranges at all the maritime polar, mid-latitude and tropical sites, while pure vapor deposition reached the highest observed values near plus 44 per mil. At Summit in winter, mixtures of vapor deposition and diamond dust accounted for the observed range without any riming at all. The calculations demonstrate that in-cloud microphysics alone can generate the full spread of d-excess values seen in precipitation worldwide.

The consequences reach deep into paleoclimate science. Lower d-excess in Greenland and Antarctic ice cores during the Last Glacial Maximum, and during abrupt climate swings, has been interpreted as evidence that the geographical source of moisture shifted dramatically. The new findings suggest an alternative: glacial conditions meant colder precipitating columns, more isotopically depleted vapor and higher ice supersaturation—precisely the combination that suppresses d-excess through in-cloud fractionation, no source shift required. Similarly, the north-to-south d-excess gradient across Greenland and the contrast between coastal and interior Antarctic snow, traditionally attributed to moisture origin, could partly reflect systematic differences in riming intensity and deposition conditions along those transects. Even the low d-excess of tropical rainfall, usually blamed on sub-cloud evaporation or the amount effect, may carry a riming signal born in the ice phase high above the surface.

Practically, the work hands climate scientists a new tool. Where radar and isotope observations coexist, the d-excess–riming relationship offers a way to test whether the microphysics schemes in climate models—which currently treat riming as isotopically neutral—produce realistic riming rates. Where only isotope data exist, d-excess can be inverted to estimate the rimed mass fraction, a quantity otherwise nearly impossible to obtain from the ground. After more than forty years of assuming that freezing droplets leave isotopes untouched, the field now has both a reason and a method to look again at one of paleoclimatology’s most trusted proxies.

Subject of Research: Isotopic fractionation during riming ice growth in mixed-phase clouds and its effect on the deuterium excess of precipitation

Article Title: Isotopic fractionation during ice growth by riming and its effect on the d-excess of precipitation

Article References: Aggarwal, P. K., Schumacher, C., Longstaffe, F. J., Funk, A., & Shupe, M. D. (2026). Isotopic fractionation during ice growth by riming and its effect on the d -excess of precipitation. Atmospheric Chemistry and Physics, 26(19), 13661-13692. https://doi.org/10.5194/acp-26-13661-2026

Image Credits: AI Generated

DOI: 10.5194/acp-26-13661-2026

Keywords: deuterium excess, riming, mixed-phase clouds, isotopic fractionation, ice cores, paleoclimate, Doppler radar, cloud microphysics, precipitation, vapor deposition, graupel, climate models

The research, published in The Cryosphere, was carried out by Dorothea Elisabeth Baur of the British Antarctic Survey and University of Cambridge, together with Andrea Spolaor and Federico Scoto of Italy’s Institute of Polar Sciences and Elizabeth R. Thomas of the British Antarctic Survey. Over eleven days in March 2023, the team conducted seventeen tracer percolation experiments in nine snow pits on the Gruvebadet slope, roughly a kilometre south of Ny-Ålesund. Their goal was deceptively simple: to simulate a small winter rain event, watch the water move, and then compare the chemical fingerprints of the snow before and after. What they found reshapes how scientists can read melt-affected ice cores, and it offers a measure of hope for archives that many feared were already lost.

The stakes are high because Svalbard is warming faster than almost anywhere on Earth. Mean temperatures on the archipelago rose by three to five degrees Celsius between 1971 and 2017, with winters warming at roughly 1.35 degrees per decade. Glaciers that were once cold throughout are turning temperate, and perennial meltwater aquifers have now been documented on the Holtedahlfonna, Lomonosovfonna and Austfonna ice caps, in some cases at elevations and times of year that would have been unthinkable a generation ago. During a drilling project on Holtedahlfonna in March 2023, researchers encountered liquid water in the firn before spring had even begun. Melt generally enriches snow in the heavy isotope oxygen-18, mixes neighbouring layers and smooths the seasonal cycles that ice-core scientists rely on, a deterioration already documented in nearby Austre Brøggerbreen and Holtedahlfonna and, more dramatically, in the alpine Corbassière glacier in Switzerland.

To catch melt in the act, the team designed an experiment that could work within the strict environmental protections of Brøggerhalvøya, using only harmless natural substances. They prepared a tracer of ultrapure water enriched with deuterium oxide, heavy hydrogen that is chemically identical to water but detectable in isotope measurements, and coloured it with blue food dye. Each experiment poured a known volume, between 250 and 2000 millilitres, equivalent to about 6.25 millimetres of water on the 40 by 20 centimetre test plot, onto a carefully characterised patch of snow. Before each pour, the researchers measured snow temperature profiles at five-centimetre resolution, mapped the full stratigraphy of grain size, shape and hardness, and took density measurements. After the water had drained and refrozen, they cut fresh faces into the pit wall and photographed, measured and sampled the blue-stained structures.

The structural results were strikingly diverse. In colder snow, the meltwater froze into a distinct, bubble-free surface crust, with sharply defined vertical preferential flow paths, fingers of dyed water up to 5.5 centimetres wide, connecting the surface to isolated melt lenses deeper down. In warmer snow, near the end of the campaign, the behaviour changed completely: there was no refrozen surface layer, and instead the water spread in a broad, partly undersaturated wetting front that compacted the snow and lowered the surface by four to eight centimetres. Most remarkably, the team documented internal layering within melt lenses on a millimetre scale, with white remnants of the original snow structure surviving between saturated blue segments. Such fine-scale heterogeneity had been seen in laboratory experiments and computer models before, but never observed forming in the field within a single melt event.

Statistical analysis of the experiments revealed what controlled this behaviour. A multiple linear regression of percolation depth against snow and water properties explained about 63 percent of the variance, and three factors stood out as significant: warmer surface snow allowed deeper infiltration, transitions from fine-grained to coarse-grained layers retarded vertical flow, and larger water volumes pushed the wetting front deeper. Stratigraphy could even override temperature entirely. In one experiment on 29 March, when the snowpack was comparatively warm, the tracer was trapped within the top 1.5 centimetres of fine-grained snow and spread sideways instead of sinking, ponding above the first hard layer. Capillary forces at fine-to-coarse grain transitions, not just dense ice layers, act as barriers to downward flow.

The chemical story, however, is where the study delivers its most consequential message. By sampling stable water isotope ratios, the oxygen-18 to oxygen-16 ratio expressed as δ18O and the deuterium-to-hydrogen ratio expressed as δD, before and after each experiment, the researchers could quantify exactly how much the meltwater had rewritten the snow’s climate record. Melt-affected samples were clearly enriched, with δ18O shifted by about plus 3 per mil and δD by about plus 39 per mil on average. But samples taken just outside the visible blue structures were essentially unchanged, with mean differences of plus 1 per mil for δ18O and plus 7 per mil for δD, within the range of measurement noise. In one vivid example, a dyed flow path carried an enriched δ18O value of minus 15.8 per mil, while samples taken a mere 1.5 centimetres to either side retained their original value of minus 19.5 per mil.

This localisation matters enormously for ice-core interpretation. It means that melt does not homogenise the entire annual layer; it carves enriched channels and lenses through it, leaving the surrounding snow intact. Where enough snow accumulates each year, sub-annual isotope information can still be recovered from the unaffected parts of the profile. The study also suggests a counterintuitive protective effect: refrozen melt layers can act as lids that prevent wind from scouring and mixing the surface, preserving the stratification, and the isotope record, beneath them. Previous work has described melt layers as diffusion-limiting in this way, and the new field observations support that picture. At the same time, the fine-scale heterogeneity that melt introduces is a warning: a single core profile may not capture the true variability of a melt-affected layer, and the number of ice layers in a core will not necessarily equal the number of rain events that occurred.

The experiments also carry a caution about scale. The simulated events, at around 6.25 millimetres of water equivalent, represent small winter rain episodes typical of coastal Svalbard, not the extreme storms the region has seen, such as the 98-millimetre rainfall event of January 2012. The tracer liquid had to be warmed, averaging 11.7 degrees Celsius, to keep it from freezing in the sprinkler during fieldwork at temperatures as low as minus 25 degrees, and the team acknowledges that repeating the experiments through spring and under warmer conditions would broaden the picture. Still, the approach is deliberately simple and cheap, requiring no electricity or wireless equipment, which makes it reproducible at other melt-threatened drilling sites across the polar regions.

For the growing community of scientists racing to extract climate records from warming glaciers, the message is twofold. Melt is not a uniform eraser; it is a sculptor whose work depends on the temperature, texture and layering of the snow it passes through, and whose fingerprints can be read, and partly corrected for, if researchers sample carefully enough. But the study is also a reminder of urgency. Svalbard’s glaciers are among the key Arctic ice-core archives, and the conditions that allow seasonal signals to survive are themselves disappearing. As the authors note, the invaluable firn and ice-core records of melt-prone regions need to be retrieved before the local climate no longer permits their preservation.

Subject of Research: In-situ tracer percolation experiments quantifying how rain-on-snow melt affects snow structure and stable water isotope records in the Svalbard snowpack

Article Title: In-situ tracer percolation experiments to quantify the influence of near-surface melting on Svalbard snow signatures

Article References: Baur, D. E., Spolaor, A., Scoto, F., & Thomas, E. R. (2026). In-situ tracer percolation experiments to quantify the influence of near-surface melting on Svalbard snow signatures. The Cryosphere, 20(9), 5533-5558. https://doi.org/10.5194/tc-20-5533-2026

Image Credits: AI Generated

DOI: 10.5194/tc-20-5533-2026

Keywords: Svalbard, rain-on-snow, meltwater percolation, stable water isotopes, ice cores, snow stratigraphy, Ny-Ålesund, Arctic warming, preferential flow, climate proxies, firn, The Cryosphere

The team worked with two full-depth cores recovered from the accumulation zones of Tibetan glaciers. The first, 169.45 meters long, was drilled in November 2020 from the summit of the Weigeledangxiong Glacier on Mount Animaqing in the eastern Kunlun Mountains, at 5750 meters above sea level. The second, 77.6 meters long, came in November 2022 from the southern slope of Mount Bugyai Kangri in the eastern Tanggula Mountains, at 6180 meters. Both regions are dominated by the Asian monsoon and both glaciers have been retreating in recent decades, but they differ in a crucial way: the Animaqing site is warmer, with borehole temperatures ranging from about -0.22 to -6.84 degrees Celsius, while the Bugyai Kangri core is colder, spanning roughly -1.54 to -8.31 degrees Celsius. That temperature contrast turned out to be the key to interpreting everything the crystals had to say.

Measuring grain size continuously along an ice core is a formidable technical challenge, and the authors solved it with a Microstructure Mapping system adapted from protocols developed for polar cores. Vertical ice slices, cut with a band saw and shaved flat with a Leica microtome, were sublimated at -20 degrees Celsius for about fifteen hours until grain boundaries stood out in sharp relief. Each slice was then photographed under vertical coaxial illumination, in which air bubbles and grain boundaries appear dark against the translucent ice, producing panoramic images at a resolution of roughly eight micrometers per pixel. A U-Net neural network performed the binary segmentation of grain boundaries, and the ImageJ software package with its MorphoLibJ plugin extracted the area, position and shape of every grain. In total the researchers analyzed 1890 slices from Animaqing, covering 91 percent of the core, and 560 slices from Bugyai Kangri, covering 71 percent, a sampling density that captures centimeter-scale variations invisible to traditional discrete sampling.

The resulting profiles divide naturally into four depth zones that mirror, in modified form, the classic three-stage model established for polar ice cores. In the firn layer, extending to about 35 meters in both cores, snowflakes of roughly one square millimeter are slowly compressed as irregular pores close off; average grain areas remain small, below about two square millimeters at the surface, and grow gently with depth. Both cores reached the critical density of 0.830 grams per cubic centimeter for pore closure at approximately 35 meters, sealing the atmospheric archive in bubbles. Below that lies a ten-meter coarsening zone in which the firn becomes true ice and average grain areas rise rapidly, reaching 18.00 square millimeters in the Animaqing core and 8.06 square millimeters at Bugyai Kangri, as larger grains grow by consuming their smaller neighbors.

This early growth is governed by Normal Grain Growth, a textbook process in which grain boundaries migrate to reduce the total surface energy of the ice, and it is strongly temperature-dependent: warmer ice allows boundaries to migrate faster, so crystals grow larger. The data show this vividly. The Animaqing core, several degrees warmer than Bugyai Kangri, maintains substantially larger grains at every comparable depth even where it bears greater overburden stress. In the recrystallization zone that follows, the trend reverses. From about 45 meters down to 140 meters at Animaqing and 73 meters at Bugyai Kangri, average grain area stabilizes and declines below five square millimeters, small grains become more abundant, and micrographs fill with subgrain boundaries, the telltale signature of Rotation Recrystallization. Under accumulating stress, subgrain boundaries rotate and gradually mature into true grain boundaries, splitting large crystals into smaller ones and setting up a dynamic balance between stress-driven refinement and temperature-driven growth.

The deepest zone belongs to Strain-Induced Boundary Migration, a rapid recrystallization mechanism that flourishes when ice is warmer than about -10 degrees Celsius, a condition satisfied at the base of both cores. Here average grain areas surge, the population of large crystals grows roughly ten times faster than in the coarsening layer, and micrographs show interlocked grains with highly curved boundaries. At Animaqing the effect is spectacular: below 150 meters, where temperatures climb above -6.27 degrees Celsius, crystals balloon to more than 400 square millimeters, and near the very base they exceed 3000 square millimeters, their boundaries spilling beyond the edges of the prepared slices. There, the researchers infer, repeated freeze-thaw cycles in excessively warm ice generated a five-meter-thick bubble-free layer of refrozen ice with gigantic, nearly transparent crystals.

Between these hundred-meter trends lie two centimeter-scale troublemakers, and both are ultimately climatic in origin. The first is melt-refreezing. Because surface temperatures at Animaqing approach zero, summer meltwater percolates into the firn and refreezes, producing centimeter-scale ice layers in which liquid-mediated recrystallization drives crystal sizes upward in abrupt jumps. The colder Bugyai Kangri site rarely experiences this, following a classic cold-type ice formation without meltwater involvement. The second troublemaker is impurity. Both cores contain millimeter to centimeter bands rich in dust and soluble impurities, and within these bands crowds of small grains, typically under two square millimeters, pile into walls that drag average grain area sharply down. In the Animaqing core a dense zone of impurity layers between 120 and 140 meters contains up to 90 centimeters of impurity-bearing ice per meter of core, and impurity thickness correlates strongly and negatively with grain size, with a correlation coefficient of -0.715. The mechanism is thought to be pinning: impurity particles obstruct grain boundary migration, holding grains small in much the same way documented in polar cores from Greenland and Antarctica and in the Monte Perdido Glacier of the Pyrenees.

The decisive test of the study is whether grain size survives this barrage of confounding influences and still records temperature. To find out, the authors compared average grain area with the oxygen isotope ratio, expressed as δ18O, the workhorse paleoclimate proxy in Tibetan ice core research. In the interval between 45 and 51 meters, where vertical pressures are low enough that Rotation Recrystallization is negligible and Normal Grain Growth dominates, the Bugyai Kangri core shows a statistically significant correlation between grain area and δ18O, with r equal to -0.286, corresponding to ice dated between 1975 and 1985. The correlation at Animaqing is obscured by heavy refreezing, but in the dense impurity zone the Animaqing core instead delivers a significant positive correlation of 0.205, tying small crystals to cold, dusty periods on an inferred centennial scale. In both settings, the physical texture of the ice is keeping step with the chemical thermometer.

Comparisons with other mountain glaciers reinforce the temperature story. When the authors placed their cores alongside four others from the eastern Tibetan Plateau, the Tianshan Mountains and the European Alps, the ranking of grain sizes at 35 meters depth, where vertical pressures are broadly comparable, broadly tracked the ranking of ice temperatures. The Guliya core tops the grain size list and the Tsanfleuron core tops the temperature list, with Animaqing, Bugyai Kangri and the KCC core following in the expected order. The consistency, the authors argue, marks temperature as the dominant control on grain growth in mountain glaciers, outweighing even the greater stresses borne by deeper, warmer ice.

The implications reach well beyond crystallography. Ice cores from the polar sheets have long used grain size as a supplementary climate archive, with abrupt changes in crystal dimensions marking cold-warm transitions, but mountain glaciers were widely considered too warm, too fast-flowing and too contaminated to preserve such signals. This study demonstrates that a mountain glacier ice core can, in specific layers where stress-driven grain refinement is suppressed, hold onto temperature information despite melt layers, impurities and rapid flow. That matters for the Third Pole, where observational records are short and paleoclimate archives are scarce, and it suggests that physical properties of ice, from grain size to bubble number density, could eventually complement isotope chemistry in reconstructing how High Mountain Asia responded to past warming. As glaciers across the Tibetan Plateau retreat under modern climate change, their crystals may prove to be among the last witnesses of the climates that built them, recording in millimeter-scale geometry the temperatures of decades, centuries and perhaps millennia gone by.

Subject of Research: Temperature-dependent grain size variation and climate signal preservation in Tibetan Plateau ice cores

Article Title: Temperature dependence of grain size in Tibetan ice core

Article References: He, Z., & Xu, B. (2026). Temperature dependence of grain size in Tibetan ice core. The Cryosphere, 20(10), 5745-5759. https://doi.org/10.5194/tc-20-5745-2026

Image Credits: AI Generated

DOI: 10.5194/tc-20-5745-2026

Keywords: ice cores, Tibetan Plateau, grain size, recrystallization, paleoclimate, glaciology, oxygen isotopes, Third Pole, The Cryosphere, ice microstructure, mountain glaciers, climate change

The research centered on a careful comparison of two sets of ice cores drilled from the Guliya ice cap, one recovered in 1992 and the other in 2015. When the team analyzed the oxygen isotope patterns preserved in both samples, they found strikingly similar signatures, indicating that the environmental signals locked within the ice are consistent and reproducible across a gap of more than two decades. This kind of internal agreement is a cornerstone of paleoclimate science, because it demonstrates that the record has not been distorted by melting, refreezing, or other processes that can scramble the layered history of a glacier. Lonnie Thompson, lead author of the study, professor of earth sciences and senior research scientist at the Byrd Polar Research Center at The Ohio State University, emphasized the significance of this match, noting that reproducibility of records within a given ice cap is extremely important and that obtaining an identical record a quarter of a century later reveals a great deal about the behavior of the ice over time.

Determining the true age of ancient ice is one of the most technically demanding challenges in glaciology. Ice cores serve as vital climate archives of the locations and time periods they represent, but deciphering these flash-frozen treasure troves requires an accurate knowledge of the core’s timescale. Without reliable dating, the chemical and physical signals within the ice cannot be confidently matched to specific climatic events. To overcome this obstacle, the research team deployed advanced dating techniques capable of detecting two radioactive isotopes, beryllium and chlorine, whose half-lives make them reliable tools for capturing large-scale environmental changes across deep time. These cosmogenic isotopes are produced when cosmic rays interact with the atmosphere and are then deposited onto the ice surface, where their concentrations can serve as chronological markers for extraordinary events in Earth’s history.

The pivotal marker used in this study was the Laschamp Geomagnetic Excursion, a dramatic reversal of Earth’s magnetic field that occurred more than 41,000 years ago. During this event, the planet’s protective magnetic shield weakened substantially, allowing greater fluxes of cosmic radiation to reach the atmosphere. That surge in cosmic ray intensity produced elevated concentrations of cosmogenic isotopes such as beryllium-10 and chlorine-36, which were subsequently deposited and preserved in the accumulating snow of the Guliya ice cap. By identifying this distinctive isotopic spike within the cores and anchoring it to the well-established timing of the Laschamp event, the team was able to construct a robust chronological framework for the ice, effectively pinning a known date onto the deep layers of the glacier and allowing the ages of overlying and underlying ice to be constrained with far greater confidence.

To further validate and extend this timescale, the researchers compared their isotope-based results with oxygen-isotope records obtained from cave deposits in nearby regions of the Tibetan Plateau. Speleothems, the mineral formations that grow in caves, carry their own independent records of past climate and can be dated with high precision using uranium-series methods. The alignment between the Guliya ice core signals and these cave records led the team to estimate that the age of the Guliya record may stretch back well over 128,000 years, a span that reaches into or beyond the last interglacial period. This cross-verification between two entirely independent paleoclimate archives represents a powerful convergence of evidence, strengthening the case that the deepest ice at Guliya predates the Holocene by a wide margin.

The significance of this finding becomes especially clear when placed in a global context. Thompson pointed out that outside of the polar regions, this is the only ice core from the mountaintops that reaches back that far. He contrasted the Guliya record with that of Huascarán in the Peruvian Andes, another celebrated high-altitude drilling site where the ice record extends back only over 30,000 years rather than over 100,000. That comparison makes Guliya a very unique record, preserving a continuous or near-continuous account of climate variability across a stretch of time that no other mountain glacier on Earth has been shown to retain. For scientists seeking to reconstruct how monsoons, temperature regimes, and atmospheric circulation patterns behaved across multiple glacial cycles in Asia, the Guliya cores now stand as an irreplaceable resource.

The new evidence also settles a persistent scientific controversy. Previous work had suggested that the Guliya record stopped at the Mid-Holocene, an era that began nearly 12,000 years ago, implying that the ice cap contained only relatively young ice. If that interpretation had been correct, it would have meant that the large ice sheets of the last ice age did not persist through the early Holocene on the Tibetan Plateau. The evidence from this work lays those doubts to rest, confirming that some of the ice is in fact much older than the Holocene. As Thompson explained, if only Holocene-era ice existed in Tibet, it would indicate that the great ice masses of the last glacial period failed to survive into the current warm epoch, but the data demonstrate that they did. This confirmation reshapes scientific understanding of glacial persistence in one of the most climatically sensitive regions on the planet, often described as the water tower of Asia because its glaciers feed major river systems serving billions of people.

Guliya’s distinctive topography likely plays an important role in its extraordinary ability to preserve such ancient paleoclimate records. The ice cap sits at extreme altitude, where frigid temperatures limit surface melting, and its geometry may shield deeper layers from the deformation and basal processes that typically destroy old ice. Yet the value of constructing a more accurate timescale for the ice cap extends beyond validating its antiquity. A precise chronology opens the door to answering bigger environmental questions, such as when Earth’s intense periods of glaciation began and ended. Thompson framed the challenge in stark terms, asking when ice started forming on the planet and what the natural processes of ice loss looked like, and observing that the only way to truly demonstrate these dynamics is with accurate timescales on these records. In an era when scientists are working to distinguish natural climate variability from human-driven change, benchmarks of past glacial behavior drawn directly from ice are indispensable.

Because these results open new pathways for detailed scientific investigations of the Guliya ice cores, the team plans to use future samples to determine how other key climate and environmental indicators may change in light of this revised understanding of Earth’s geologic history. Dust concentrations, trapped atmospheric gases, microbial communities, and a host of geochemical tracers preserved in the ice can now be interpreted against a trustworthy timeline, potentially yielding insights into past atmospheric composition and ecosystem responses at altitudes above six kilometers. The international collaboration behind the study included Ohio State co-authors Mary Davis and Ellen Mosley-Thompson, along with Juerg Beer from the Swiss Federal Institute of Aquatic Science and Technology, Christof Vockenhuber and Marcus Christl from ETH Zurich in Switzerland, Tandong Yao from the Chinese Academy of Sciences, and Ninglian Wang and Ling Fang from Northwest University in China, with support from the U.S. National Science Foundation. Reflecting on the work, Thompson observed that the results tell a very consistent story, and that if the science is done right, it is consistent, adding that it is human understanding of what the ice is trying to tell us that has to catch up.

Subject of Research: Dating of ancient ice cores from the Guliya ice cap on the Tibetan Plateau

Article Title: Digging deep, researchers find high-altitude glacier endured last ice age

Article References: Digging deep, researchers find high-altitude glacier endured last ice age. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: Guliya ice cap, Tibetan Plateau, ice cores, paleoclimatology, Laschamp Geomagnetic Excursion, cosmogenic isotopes, beryllium-10, chlorine-36, oxygen isotopes, last ice age, glaciology, Science Advances