While flying over the eastern Beaufort Sea as part of NASA’s Operation IceBridge, mission scientist John Sonntag made photos of something he had never seen before on April 14: odd crater-like holes in the ice.

While experts agree the sea ice in the photograph is thin and likely young, since it is a grey color (indicating there is little snow), what made the holes is a mystery. “I have never seen anything like that before,” said IceBridge project scientist Nathan Kurtz. (See what the world would look like if all the ice melted.)

Now in its tenth year in the Arctic, Operation IceBridge is an airborne mission flown annually over both polar regions using various instruments to measure the changes to the ice sheets, ice shelves, and sea ice. And with global warming there are lots of changes in the polar regions. This past winter, the Arctic had 448,000 square miles (1.16 million square kilometers) less sea ice than it normally has in winter. In fact, the last four winters have had less sea ice than the 1981 to 2010 average winter maximum.

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These odd holes might be connected to the rapidly warming Arctic region, which has experienced unusually warm conditions for much of the winter. “The sea ice is more mobile now, and has more open areas that can re-freeze,” said Walt Meier, a scientist at the National Snow and Ice Data Center. Meier thinks it unlikely this is the result of a fragmented meteor strike, since the holes are so close together.

At first, one likely explanation was thought to be seals, since they are known to gnaw through the ice for breathing holes and sometimes haul themselves onto the ice to rest. “If those holes are less than 2 meters in size, then the encircling features may be due to waves of water washing out over the ice when the seals surface,” Meier said.

Another possibility is warm-water upwelling, because this part of the Beaufort is quite shallow. But Dartmouth College sea ice geophysicist Don Perovich doesn’t think so, because the effects would be broader, he says. On Monday, he went with the seal hypothesis: “My guess is a seal pushed ice out of the way to make a hole and thus also made the ice around the hole thicker.”

But after returning from another long day flying over the Arctic ice, Sonntag said on Tuesday that the mysterious holes are several meters in size, perhaps even tens of meters. That would seem to rule out the "seal hypothesis." Thus, given the size, they were more likely caused by bowhead whales punching up through the thin ice to breathe, says Sue Moore, senior scientist at the NOAA/Fisheries Office of Science and Technology.

“It is a fascinating picture,” Perovich concluded.