Arctic sea ice moves and spreads in ways that wind alone cannot explain. A new UC Riverside-led study finds that collisions between individual pieces of ice provide a surprisingly simple explanation for these movements, potentially offering scientists a better way to predict where sea ice will travel as the Arctic warms.
The study, published in Physical Review Letters , was led by Bryan Shaddy, formerly a UC Riverside undergraduate and now at the University of Southern California, with UCR materials scientist Alex Greaney and Bhargav Rallabandi, associate professor of mechanical engineering at UCR.
Arctic sea ice is not a single, continuous sheet. It consists of individual slabs, called floes, ranging from several meters to a few kilometers across. Winds push these floes across the ocean, causing them to drift and gradually spread apart.
Scientists know that wind is a major force moving Arctic sea ice. But the ice doesn’t behave the way the wind alone would suggest. The speed at which the ice moves varies in unexpected ways, and it spreads much more slowly than simple wind-driven models predict.
Researchers have proposed several explanations for these discrepancies, including unusual wind patterns, ocean eddies, and fractures in the ice. The new study offers a unifying explanation: the ice floes are constantly bumping into one another.
“If you get a lot of ice floes together in the same place with some wind, they bump into each other and transfer energy to neighbors,” Rallabandi said. “We showed that that’s the only ingredient you need to explain these observations.”
To test the idea, the researchers built a computer simulation treating the ice somewhat like grains moving through a silo, except these grains float on water and are pushed by turbulent winds. The model accounts for drag from the ocean as well as collisions among the floes.
The team then compared its predictions with measurements of sea ice in the Fram Strait, a passage between Greenland and the Norwegian archipelago of Svalbard through which Arctic ice travels toward the Atlantic Ocean.
Using measured local wind and ice conditions, and only one additional parameter that had little influence on the overall results, the model reproduced three previously puzzling observations: how quickly ice spreads, the distribution of floe speeds, and how ice motion varies across timescales ranging from hours to days.
The reason collisions have such a large effect is that Arctic ice can be densely packed. In concentrated ice fields, floes run into their neighbors much more frequently than the wind changes. Each collision dissipates some of the energy supplied by the wind and shortens the distance a floe can travel freely before encountering another piece of ice.
That insight could eventually help scientists predict sea ice transport as Arctic conditions change. The amount of ocean covered by ice and the size of individual floes affect how frequently collisions occur, which in turn affects how rapidly ice spreads. The study provides a physical framework for connecting such small-scale interactions to movement over much larger distances.
The paper does not predict exactly how future warming will alter the destinations of Arctic ice. However, Rallabandi said the framework could ultimately help researchers investigate questions such as whether changing ice conditions allow floes to disperse more readily and reach warmer waters, where they could melt more quickly.
That could also make the work useful for climate modeling. Global models cannot individually track the enormous number of relatively small floes covering the Arctic. A physics-based description of their collective behavior could help represent processes happening out of immediate view.
For Rallabandi, the study’s value lies partly in demonstrating how a simple process explains a complex real-world motion.
The underlying physics used in this research may also extend beyond sea ice. Any system involving many objects colliding while being driven by an unpredictable environment could behave similarly. The paper points to possible applications including avalanches, landslides, materials science, and particle-filled inks used in 3D printing.
“The model is not restricted to ice,” Rallabandi said. “It just needs a noisy source of force and the things that are moving to experience collisions.”
Physical Review Letters
Anomalous Statistics of Sea Ice Transport are Explained by Collisional Rules
10-Sep-2026