Normally ice-bound this time of year, the Bering Sea is mostly open water

Open water has replaced sea ice in much of the Bering Sea off Alaska's west coast, leaving villages vulnerable to powerful winter storms and adding challenges to Alaska Native hunters seeking marine mammals, an expert said Monday.

Rick Thoman of the Alaska Center for Climate Assessment & Policy at the University of Alaska Fairbanks said that winter storms over five weeks obliterated thin ice that had formed since December.

Wind blew ice to Russian beaches in the west and to the south side of Norton Sound south of Nome but left open water all the way to Chukchi Sea north of the Bering Strait.

"You can take your sailboat from Dillingham to Diomede today," he said.

Sea ice historically covers much of the Bering Sea throughout the winter with maximum coverage through March. Kotzebue Sound, a great bay northeast of the Bering Strait, already has open water, an occurrence normally seen in June.

It's the second consecutive winter for low sea ice. Last year, it was low all season. This winter, a warm November was followed by a cold December and January, Thoman said.

"Then the weather pattern changed and the ice has just collapsed," he said. He suspects that heat in the ocean played a factor.

The ice is now similar in extent to what it was last year at this time and last year had the lowest maximum ice extent ever observed.- Phyllis Stabenow,  National Oceanic and Atmospheric Administration

Phyllis Stabeno, a physical oceanographer at the Pacific Marine Environmental Laboratory, part of the U.S. National Oceanic and Atmospheric Administration, said Monday that storms played a large role in the extreme low ice.

Winds from November to April typically blow out of the north or northwest and are cold, driving ice southward, she said by email. The year, warm winds in a series of storms blew out of the southwest in mid-January and especially February.

Not labelled as climate change

"These storms broke the ice up and pushed it north. Also some of the ice melted. So the ice is now similar in extent to what it was last year at this time and last year had the lowest maximum ice extent ever observed," she said.

Thoman and Stabeno did not label the unusual ice event as climate change. The Bering Sea has been warm for several years, Thoman said. The ice loss can be attributed to a warm ocean and combination of an unusual but not unprecedented weather pattern.

However, some events are unlikely to occur without climate change, he said.

Stabeno said no single event can be attributed to climate change.

"What can be said is that some climate models predict more southerly winds, which will reduce ice extent," she said. "Also, an increase in southerly winds in the northern Bering Sea during the fall and winter has been observed since 2016."

Sea ice is an important feature of the ecosystem. Its absence has implications above and below the ocean surface.

Coastal communities historically could rely on a barrier of sea ice after Labour Day to protect them from the pounding of fierce winter storms. Without an ice cover, waves erode beaches and sometimes flood villages, Thoman said.

Residents of coastal villages traditionally hunt and butcher marine mammals such as walruses and seals when the animals "haul out" on ice. Residents of St. Lawrence Island last year had to try to hunt in open water far from shore, Thoman said.

"Now instead of going out one mile, you have to go out 50. There's that increased cost," Thoman said. "It's much more difficult to butcher an animal the size of a walrus in a boat as opposed to on ice. Much greater chance of injury to the people. Much greater chance of losing the animal altogether."

Sea ice historically has formed a "cold pool" in the central Bering Sea, a barrier of cold water that sets the structure for fish. The cold pool acts as a thermal wall, keeping valuable commercial fish such walleye pollock and Pacific cod, in the southern and central Bering Sea.

In the absence of sea ice last year, federal fish biologists conducting surveys found that a 2018 cold pool had not formed and that southern species had migrated north in far greater numbers.