As Arctic sea ice melts away, it may be doing more than exposing open ocean. Scientists have found that the retreating ice could also help create many of the tiny particles needed to form clouds.
Scientists have discovered a previously unknown natural process in the Arctic that can rapidly increase the number of particles capable of forming clouds. Observed near the boundary between melting sea ice and open ocean, the process is driven by marine emissions and sunlight and could influence cloud cover, sunlight reflection, and the pace of future climate change.
The discovery adds a previously missing piece to an already complicated Arctic climate system. Clouds can change how much solar energy reaches the ocean and ice below while also affecting the escape of heat back toward space. Their overall effect depends on factors including season, location, cloud properties, and the surface beneath them. Scientists are still working to understand how these interactions will evolve as Arctic sea ice disappears.
Published in Nature Geoscience, the study was led by the University of Birmingham with an international team that included researchers from China and Spain. The scientists found that the boundary between open ocean and sea ice acts as an especially active source of the chemical ingredients needed to make new atmospheric particles.
How Arctic Cloud-Forming Particles Develop
Cloud droplets do not usually appear from water vapor alone. They form around tiny airborne particles known as cloud condensation nuclei. Sources can include sea spray, dust, pollution, and particles created through chemical reactions in the atmosphere.
In this newly documented Arctic pathway, iodine, sulfur compounds, and organic chemicals released from the ocean and surrounding environment react in sunlit air. The resulting molecules can first create extremely small particles and then help them grow until some become large enough to seed cloud droplets. Laboratory research had already shown that iodine oxoacids and other compounds can participate in atmospheric particle formation, but the new study demonstrates the mechanism under real Arctic conditions.
Co-author Dr. James Brean, Assistant Professor in Atmospheric Science at the University of Birmingham, said, “Our findings provide the first real-world validation of a recently identified atmospheric chemistry mechanism involving iodine oxoacids and sulfuric acid. Until now, this process had only been demonstrated in laboratory experiments at the CLOUD chamber at CERN.”
The measurements came from an expedition aboard the Royal Research Ship Discovery around Greenland and the Davis Strait during spring and summer 2022. The research was supported by the Natural Environment Research Council (NERC).
Sunlight and Marine Emissions Drive Particle Formation
What the team saw was not an isolated curiosity. New particles appeared on more than 80% of the sunny days studied, indicating that this chemistry occurs frequently in the region.
The new particles form when sunlight transforms a mixture of naturally emitted chemicals, including:
- Iodine compounds released from the ocean, sea ice, and coastal environments.
- Dimethylsulfide, produced by marine plants and algae.
- Organic compounds released naturally from the ocean or land.
Previous Arctic measurements had already linked new particle formation to substances including sulfuric acid, ammonia, marine organic compounds, and, in some cases, iodine. The new findings reveal how strongly several of these chemical pathways can work together near the sea ice boundary.
Newly Discovered Molecules Help Particles Grow
The researchers also identified a new category of atmospheric compounds called iodine-containing oxygenated organic molecules (I-OOMs).
These molecules appear to solve an important part of the particle formation puzzle. Creating a microscopic particle is only the beginning. It must survive and grow substantially before it can serve as a nucleus for a cloud droplet. The newly detected organic molecules appear to assist that growth.
Dr. James Brean added, “These newly identified compounds help small particles grow into larger particles that can seed clouds – we believe this is the first time such molecules have been observed and implies important new pathways for iodine chemistry.”
Marginal Ice Zone Becomes a Particle Hotspot
The most dramatic activity occurred in the marginal ice zone, the shifting band where open seawater meets melting sea ice. This environment is also highly biologically productive, providing abundant marine emissions that can feed atmospheric chemistry.
During one event, researchers measured cloud-seeding particle concentrations rising from roughly 50 to 1,500 per cubic centimeter.
That location is particularly significant because the marginal ice zone changes as the Arctic loses ice. Satellite observations have documented a major long-term decline in Arctic sea ice, exposing increasing areas of open water during the melt season. Snow-covered sea ice is also highly reflective, sending roughly 50% to 70% of incoming solar energy back upward, while darker ocean water absorbs far more of that energy.
What the Discovery Could Mean for Arctic Climate
The newly identified particle pathway introduces another potential consequence of that transformation. As ice retreats, more biologically active ocean and ice edge environments may become exposed to sunlight and the atmosphere, potentially changing the supply of particles available for cloud formation.
Corresponding author Zongbo Shi, Professor of Atmospheric Biogeochemistry at the University of Birmingham, who led the study, said, “Our discovery is important because these new particles can influence clouds, which play a critical role in determining how much heat is retained or reflected. More clouds or thicker clouds in the warming season could potentially accelerate ice melt while cooling down the open ocean.
“The Arctic has warmed more than three times faster than the global average over the past 40 years, making it one of the most sensitive regions on Earth to climate change. Understanding how natural emissions influences clouds is critical for predicting climate changes in this region. Our discovery will help climate models to improve understanding of how climate change is affecting the Arctic and how the region itself influences global climate.”
Because current climate models do not yet include this process, its potential impact on the Arctic remains absent from projections. The team is now working to incorporate the newly identified mechanism into future modeling.
Reference: “Arctic cloud condensation nuclei enhanced by iodine, sulfur and organic precursors” by Mao Du, James Brean, Douglas R. Worsnop, Congbo Song, Yangmei Zhang, Vipul Lal Chandani, Deepchandra Srivastava, David C. S. Beddows, W. Joe F. Acton, Darrel Baumgardner, Jo Browse, Anna B. Callaghan, Manjula Canagaratna, Yuqing Dai, Pete M. Edwards, Jingkun Jiang, Thomas M. Jordan, James D. Lee, Roberto Sommariva, Harald Stark, Mark D. Tarn, Loren G. Temple, Gavin H. Tilstone, Mingxi Yang, William J. Bloss, Roy M. Harrison, Manuel Dall’Osto and Zongbo Shi, 5 August 2026, Nature Geoscience.
DOI: 10.1038/s41561-026-02062-6
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