Storms Turn Arctic Sea Ice From Aerosol Sink Into Particle Source

The Arctic Ocean has long been treated in climate models as a quiet place for aerosols: a vast, snow-covered expanse where particles drifting down from the atmosphere are absorbed and removed, rather than a surface capable of launching new ones skyward. A five-week measurement campaign aboard the Swedish icebreaker Oden has now upended that simple picture. During the spring of 2023, an international team of researchers recorded continuous, direct measurements of the turbulent exchange of aerosol particles between the surface and the air over the High Arctic, and found that under strong winds the supposedly inert ice pack can flip from a particle sink into a significant particle source, most likely through the mobilization and sublimation of blowing snow.

The study, led by Theresa Mathes of the Technische Universität Berlin and the Leibniz Institute for Tropospheric Research, together with colleagues from the University of Leeds, Stockholm University, Uppsala University and TROPOS in Leipzig, was carried out as part of the ARTofMELT expedition, which sailed from Svalbard between 8 May and 15 June 2023. The campaign’s broader goal was to understand how atmospheric rivers, narrow corridors of warm, moist air, trigger the onset of sea ice melt. But the flux measurements collected along the way, published in the journal Atmospheric Chemistry and Physics, provide one of the longest continuous eddy covariance records of particle exchange ever obtained over the Arctic Ocean, and they carry implications that reach well beyond the expedition’s original purpose.

Aerosol particles matter enormously in the Arctic. They scatter and absorb sunlight directly, and they act as cloud condensation nuclei and ice nucleating particles, shaping the formation, brightness and lifetime of clouds. Because particle concentrations in the polar boundary layer are often very low, particularly in autumn, even small changes in the particle budget can ripple through cloud microphysics and the regional radiation balance. The Arctic is warming two to seven times faster than the global average since 1979, a phenomenon known as Arctic amplification, and shifts in the sources and sinks of aerosols are one of the feedbacks that models struggle to capture. Yet direct observations of turbulent particle fluxes over sea ice have been strikingly scarce, with most previous ship-based campaigns lasting only days to a couple of weeks.

The technical challenge of making these measurements from a moving ship is considerable. Eddy covariance, the gold-standard technique, requires capturing rapid fluctuations in vertical wind speed and particle concentration simultaneously, at sampling rates of around 10 hertz. The team mounted a sonic anemometer 20.3 meters above the surface on Oden’s foremast, alongside a heated inlet feeding a mixing-type condensation particle counter capable of detecting particles down to 7 nanometers. Because the instrument sampled air through a long tube, the researchers had to correct carefully for the time lag between wind and concentration fluctuations, for particle losses to the tubing walls, and for the motion and flow distortion of the ship itself, using motion sensors and computational fluid dynamics corrections developed for Oden. Ship exhaust contamination, an ever-present hazard on a vessel, was rigorously screened out, removing 17 percent of the data.

To interpret the fluxes, the team classified the surface upwind of the ship into three categories: closed ice, leads, and open water. This was done automatically using a machine-learning image segmentation algorithm, a random forest classifier, applied to hourly photographs taken by cameras on the ship’s decks, with the relevant camera chosen according to the prevailing wind direction. The approach allowed the researchers to attribute each 20-minute flux measurement to the type of surface it had sampled, something few previous studies have done systematically.

The headline result is a study in contrasts. Under low to moderate turbulence, closed ice behaved as expected: it was a net sink for particles, with a median deposition flux of −0.02 × 10⁶ particles per square meter per second, and deposition dominated roughly 70 percent of the intervals measured over ice. But when the wind picked up, the picture reversed. During eight high wind speed events identified during the campaign, five showed net particle emission, and during the longest of these, a storm on 24 to 26 May with winds reaching 19 meters per second, the team recorded net emission fluxes of up to 0.98 × 10⁶ particles per square meter per second, a statistically robust figure with a 95 percent confidence interval excluding zero. The inferred emission strength, calculated by subtracting a modeled deposition flux from the measured net flux, peaked at 1.57 × 10⁶ particles per square meter per second during a second storm at the end of May.

The most likely culprit is blowing snow. Strong winds lift snow grains from the surface, and because Arctic snow contains sea salt, sulfate, nitrate, organic matter and even black carbon, the sublimation of these wind-blown particles releases aerosols into the boundary layer. The particle size distributions measured during the storm events support this interpretation: elevated concentrations appeared across a broad range of diameters, roughly 30 to 300 nanometers, rather than showing the narrow nucleation-and-growth signature expected from new particle formation driven by precursor gases. The researchers also found that the strength of the particle flux correlated strongly with friction velocity, a measure of near-surface turbulence, with a correlation coefficient of 0.88, reinforcing the link between turbulent wind stress and particle exchange. The threshold wind speed for blowing snow is not fixed; it depends on temperature and snow properties, and at low temperatures mobilization could begin at winds as gentle as 6 meters per second.

Over leads and open water, the story was more nuanced. Both surfaces showed a mixture of emission and deposition events, with median fluxes close to zero, suggesting that while open ocean and cracks in the ice can act as particle sources, through mechanisms such as bubble bursting and sea spray, their net contribution during the campaign was modest. The researchers note that whitecaps in pack ice regions are smaller and less frequent than in the open ocean, which may explain the weak net emission observed. They also caution that open water periods were underrepresented in the filtered dataset because the ship was typically underway when open water was present, and surface classification was restricted to periods of slow drift.

What makes these findings consequential is the trajectory of the Arctic itself. Climate models project continued sea ice loss and a corresponding expansion of open water, which is expected to change the frequency and intensity of the particle exchange processes documented here. As the ice retreats, local particle sources, whether from leads, open water or wind-blown snow, are likely to play a growing role in the regional aerosol budget, with knock-on effects for cloud formation and the surface energy balance. Whether the net climatic effect is cooling, through brighter clouds reflecting more sunlight, or warming, through changes in cloud lifetime and phase, remains poorly constrained, and competing source and sink processes make the outcome genuinely uncertain.

By providing hard observational constraints on particle fluxes over three distinct surface types, the ARTofMELT dataset gives modelers something they have long lacked: direct numbers against which to test deposition schemes and emission parameterizations in the High Arctic. The team’s data are publicly available through the PANGAEA repository. As the researchers conclude, quantifying particle deposition on closed ice and emissions from leads and storm-whipped snowfields is a step toward reducing the stubborn uncertainties that still surround Arctic aerosol-cloud-climate interactions, in a region where the stakes of getting the feedbacks right could not be higher.

Subject of Research: Turbulent aerosol particle exchange between the atmosphere and sea ice, leads and open water in the High Arctic

Article Title: Turbulent atmospheric particle fluxes in the High Arctic: surface type dependence and variability

Article References: Mathes, T., Brooks, I., Murto, S., Tjernström, M., Kojoj, J., Zieger, P., Prytherch, J., Wehner, B., & Held, A. (2026). Turbulent atmospheric particle fluxes in the High Arctic: surface type dependence and variability. Atmospheric Chemistry and Physics, 26(19), 14507-14530. https://doi.org/10.5194/acp-26-14507-2026

Image Credits: AI Generated

DOI: 10.5194/acp-26-14507-2026

Keywords: Arctic, aerosol particles, eddy covariance, sea ice, blowing snow, particle fluxes, cloud condensation nuclei, Arctic amplification, leads, sea spray aerosol, ARTofMELT, dry deposition