Melting sea ice combines with Arctic ocean to make clouds

Scientists have uncovered a previously unknown natural process that dramatically increases the number of cloud-forming particles in the Arctic atmosphere - potentially altering cloud cover, sunlight reflection, and future climate change.

Publishing their findings in Nature Geoscience, an international research team led by the University of Birmingham - including partners from China and Spain - reveals the first real-world evidence that, where Arctic sea ice meets open ocean, marine life and sunlight combine to release a chemical mixture that seeds the sky with cloud-forming particles.

The team found that a combination of naturally occurring iodine, sulphur and organic compounds are emitted to create new atmospheric particles. Near the ice edge, the researchers watched the number of particles capable of forming cloud droplets rising fifty-fold in a day.

The warming atmosphere of the Arctic causes the ice to melt. This melting ice exposes more of the productive ice edge, which subsequently makes particles. Those particles can change cloud cover, which affects the Earth’s radiation balance.

Backed by funding from the Natural Environment Research Council (NERC), the team gathered the data during an expedition aboard the Royal Research Ship Discovery around Greenland and the Davis Strait in spring and summer 2022.

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.”

Researchers also identified a new class of atmospheric compounds known as iodine-containing oxygenated organic molecules (I-OOMs), which appear to play an important role in helping newly formed particles grow large enough to influence clouds.

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.”

Researchers discovered that new particles were forming on more than 80% of sunny days, showing that the process is common in this part of the Arctic. Their formation is driven by compounds that are emitted into the air and chemically transformed under sunlight, which include a combination of:

• Iodine compounds released from the ocean, sea ice, and coastal areas.
• Dimethylsulfide, from marine plants and algae.
• Organic compounds released naturally from the ocean or land.

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 influence 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."

The strongest effects came from the marginal ice zone, the narrow band where open ocean meets melting sea ice and where marine algae are at their most productive. During one event there, the number of cloud-seeding particles rose from roughly 50 to 1,500 per cubic centimetre.

That band is widening as Arctic sea ice retreats. Because the process is missing from current climate models, its influence on the region is not yet accounted for in projections, and the team is now working to build it in.