This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: 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 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 that treated 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.
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