During winter 2018 the sea ice in the Bering Sea reached record-low levels thanks to persistent warm southerly winds. These conditions caused the ice to retreat to the northern reaches of the 800,000 square mile body of water.
Scientists were amazed, “It was about half of what we usually have in winter,” said NOAA oceanographer Phyllis Stabeno, lead author of a new paper in the journal Geophysical Research Letters offsite linkanalyzing the event. “To be blunt, all of us were shocked. This isn’t how it’s supposed to work.”
At the end of April, 2018 Bering Sea ice covered 61,704 square kilometers. By contrast, sea ice extent on April 29, 2013, was 679,606 square kilometers, closer to the 1981 to 2010 average. By the end of April 2018, sea ice was about 10 percent of normal.
And then, much to the scientists’ surprise, 2019 just missed eclipsing the record set in 2018.
In the past, Stabeno explained, cycles of cold years with extensive sea ice would be succeeded by warm years with less sea ice. Climate models have predicted these warm, ice-eating winter winds would become common in the 2030s. “We did not expect to see these low-ice conditions for at least 10 to 15 years,” she said.
Scientists are now wondering if another cold cycle will recur, or if the Bering Sea has passed a tipping point. Complicating matters is the ongoing melt of the Chukchi Sea, to the north of the Bering Strait separating Alaska from Russia. Ice in the Bering Sea forms when cold winds over the Chukchi Sea come blasting down from the north.
“To get the frigid winds out of the north that freeze the Bering Sea, you have to freeze the Chukchi,” Stabeno said. “But now the Chukchi is not freezing until December. That means there’s less time for the Bering to freeze up.” Still, Stabeno isn’t ready to go out on a limb and predict that Bering Sea ice is history. She’s seen too much variability over her 30 years of research.
“There’s always year-to-year variability,” agreed Rick Thoman, Alaska climate specialist with the International Arctic Research Center. “But these kinds of winters are going to become more and more common.”
What does this mean for the ecosystem and Alaska? The Bering Sea is one of the largest and most valuable fisheries in the world, contributing about half of the nation's fish landings. The current distribution of fish stocks is dependent on a cold pool of water at the bottom of the shallow sea. Species like Arctic cod thrive in colder water, while the shift of just a couple of degrees allows Pacific species like pollock to replace Arctic cod. “This has tremendous implications for the ecosystem,” Stabeno said.
The conditions associated with warmer winters would disrupt not only the marine ecosystem but the conditions that generations of Alaskans have come to depend on. Sea ice dampens waves, making fishing safer. Subsistence hunters need ice to pursue seals and whales. Open water allows waves to hammer the coast, eroding beaches and threatening towns.
Stabeno, whose work is partially funded by the Joint Institute for the Study of the Atmosphere and Ocean, NOAA’s cooperative institute at the University of Washington, has mixed emotions at watching the impact of climate change unfold before her eyes. “As a scientist, it’s fascinating to see our predictions coming true,” Stabeno said. “As a human being, it’s not so good.”
Theo Stein, 303-497-6288