When sea ice goes missing in the Arctic, every part of the ecosystem feels the effects.
Peggy’s data were a bit of a shock.
Peggy is a floating buoy attached to sensors that monitor the temperature, saltiness and other properties of the Arctic’s Bering Sea. These sensors reach down more than 70 meters (about 230 feet) below the water and are anchored to the seafloor west of Alaska.
Here, the coming and going of floating sea ice follows a seasonal pattern. Peggy’s data normally show that pattern. But in the winter of 2017–2018, they didn’t. The sea ice never appeared!
At their closest point, Alaska and Russia are separated by the Bering Strait. This stretch of water is 82 kilometers (51 miles) wide. To the north lies the Chukchi Sea, which is on the edge of the Arctic Ocean. Below the strait is the Bering Sea, which extends south to Alaska’s Aleutian Islands.
In summer, the Bering Sea is largely ice-free. In winter, ice forms in its northern reaches. Ice also migrates southward through the strait from the Chukchi. Scientists consider the waters frozen over when at least 20 percent of their surface is ice-covered.
Satellite maps of the Bering Sea from April 2013 through April 2018 show dwindling ice cover. Last year, the Bering Sea was basically ice-free. Credit: Joshua Stevens/NASA Earth Observatory, National Snow and Ice Data Center
Most years, sea ice shows up in the Bering Sea by November. As that ice forms, it causes a large mass of cold, salty water to pool near the seafloor. In the spring, algae bloom under the ice and around it. By early summer, the sea ice begins to melt away. But the cold pool near the seafloor, with an average temperature of just belowfreezing, lingers through the summer.
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The deep cold pool is central to the Bering Sea’s ecosystem. It is where Arctic cod take refuge. These fish hide from predators such as Pacific cod and pollock (which don’t like the cold as much.) The Arctic cod also get fat on large, shrimplike copepods (KOH-peh-podz), then spawn. In turn, these fish keep polar bears and seals well-fed.
Peggy’s data, along with that of other packages of sensors, revealed that the cold, near-seafloor pool was missing. That and the absent sea ice alarmed ocean scientists. Researchers gathered in Washington, D.C., at the American Geophysical Union’s annual meeting in December 2018. Many shared new data, traded stories and pondered what the changes may mean.
Were these findings a fluke? “We don’t yet have enough data,” says Jacqueline Grebmeier. She works at the University of Maryland’s Center for Environmental Science in Solomons. But Grebmeier, who has studied seafloor life in the Arctic for more than 30 years, has a gut feeling that the ice-free winter is not a one-off event: “I think it’s the beginning of change,” she says.
If last year’s events signal a new normal for the Bering Sea (and the very low sea ice cover as of March this year signals they might), then a cascade of changes are in store for its complex ecosystem — from the algae at the bottom of the food web to humans at the top.
