A simple model of the patterns formed by ponds could help us make better predictions about how Arctic ice is melting.
Arctic sea ice has been melting faster than expected. One factor that might contribute to this is the way ponds trap heat. When ice melts and forms ponds on the surface of sea ice, it becomes less reflective, trapping more heat and making the ice melt faster. That leads to a positive feedback mechanism: melting creates ponds, which results in faster melting.
Previous studies have shown that the fraction of the ice covered by ponds in the spring can predict how much sea ice will be left at the end of the summer each year.
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The geometry of the ponds influences how the ice around them melts: for example, small, long ponds will grow sideways by melting more ice faster than large, symmetrical ponds. at the University of Chicago and colleagues modelled the patterns created by ponds by randomly drawing overlapping circles of varying sizes on a plane. They analysed hundreds of photographs of sea ice taken during helicopter flights to compare their model with real data.
A vicious circle
At first, they thought of the circles as representing ponds, but it turned out that the model worked better if the area within each circle represented ice, while the voids between the circles represented ponds. The model has only two parameters: the average size of the circles and the fraction of the total area covered by ponds.
This simple model successfully reproduced many geometric properties of the ponds. But it only matched up properly to the data when ponds covered about 31 per cent of the ice. “That tells us that pond coverage is constrained beyond just randomness,” says Popovic.
The mean pond coverage is important for climate models, since it tells you how much sunlight the ice will absorb and thus how quickly it will melt. The constraints from Popovic’s model will help us make better predictions about Arctic ice melting and the resulting implications for sea level rise and climate change.
Physical Review Letters
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