In 2018, when winter ice in the Bering Sea was scarcer than at any time since records began in the mid-1800s, the effects cascaded.
Warmer-water fish like Pacific cod swam north into the Bering Strait area, crowding out and preying on colder-water fish like juvenile king crab. High-fat zooplankton disappeared and was replaced by lower-quality plankton at the bottom of the food web. Masses of birds, seals and whales perished in widespread die-offs that were linked to starvation. Harmful algal blooms proliferated, and high levels of the toxins they produce were documented for the first time in Bering Strait-area clams. Diomede, the village on the tiny Alaska island at the U.S-Russian maritime border in the middle of the normally frozen Bering Strait, remained exposed to open water well into the winter and was inundated when a February storm pushed waves to flood the community.
Now scientists who have crunched the climate and weather numbers have a warning about the Northern Bering Sea: Expect the then-unprecedented 2018-like conditions to be repeated one to three times per decade through the end of the 2030s.
The forecast is in a newly published study by scientists from the National Oceanic and Atmospheric Administration.
The reason is the combination of Arctic warming, which is occurring at nearly four times the global rate, and the randomness of the Aleutian Low, a perennial low-pressure system that sets weather patterns around the North Pacific.
“In the past, the Arctic is really dominating the Northern Bering Sea every year. And that’s sort of gone away,” said James Overland, a research oceanographer with NOAA’s Pacific Marine Environmental Laboratory and lead author of the new study.
Whether there is warmth flowing into the Northern Bering from southerly winds now depends not on the less-cold Arctic but on the location of the Aleutian Low, which varies year-to-year at random, Overland said.
“If it’s far to the west, then you have southerly winds and warmer temperatures and less sea ice,” Overland said. “So the real loss of sea ice that we’d never really seen before, in 2018, was one of these cases where the Aleutian Low was far to the west.”
His study, coauthored with NOAA colleague Muyin Wang, a Pacific Marine Environmental Laboratory meteorologist, tracked the wandering movements of the Aleutian Lows back to 1948.
The Aleutian Low, a low-pressure system around which winds flow counterclockwise, influences weather patterns over a wide swath of the globe, from monsoons and dry spells in East Asia to storms in the midlatitudes of North America. It strengthens in the winter and fades in the summer, and it varies in location and intensity from year to year.
It is typically centered about at the middle of the North Pacific by the Aleutian Islands. When it is there, or farther to the east or south, it allows north winds from the Arctic to sweep over the Bering Sea and bring on the freeze, Overland said. But if it is far to the west, as it was in 2018, it sends warm winds up from the south, hindering Bering Sea freeze, he said.
The forecast of one to three 2018-like low-ice years is based on past wanderings of the Aleutian Low, which was west of the International Dateline 18 times over the seven decades and Overland and Wang reviewed. In the past, the western location did not matter much because the influence of the cold Arctic dominated, Overland said. But now, with the Arctic less cold, the random western movements of the Aleutian Low will have big impacts on the Northern Bering, as they did in 2018, he said.
“We should have several of these events. But we won’t have them every year,” he said.
Overland and Wang also factored in results of a climate-modeling study led by Rick Thoman, a scientist at the University of Alaska Fairbanks’ Alaska Center for Climate Assessment and Policy. That study, published in 2020, combined several climate models and concluded that by the 2040s, the extremely low ice conditions of 2018 could be the average condition.
Alaska’s Bering Sea communities and fishers should prepare
The take-home message of the new study is that communities and people dependent on the Northern Bering Sea’s natural resources need to prepare for repeats of the 2018 heatwave conditions through the end of the 2030s.
“Communities need to plan for a response to intermittent occurrence of 2018-like extreme sea-ice loss and their ecosystem impacts over the coming decades,” the new study says.
That means preparing for more coastal erosion and flooding, like the disastrous conditions that occurred in Western Alaska during Typhoon Merbok in the fall of 2022, the study said.
It also means preparing for future disruptions to fish stocks that could linger over multiple years and generations. The 2018 record-low ice winter affected not only the fish and other marine life present at that time but also, because of poor or failed reproduction, the offspring of those year groups, according to scientists studying Alaska’s ocean ecosystems.
An example is the Bering Sea snow crab collapse that led to unprecedented harvest closures for two years, starting in late 2022. The snow crab population has started to recover, and harvesting was opened in October, though at a level much smaller than in the past.
Planning for repeats of the 2018 conditions also means that subsistence harvesters and wildlife managers need to be on alert for harmful algal blooms and the toxins they produce, as well as repeats of the bird and mammal die-offs.
While the influence of the Aleutian Low varies each year, the long-term warming of the wider Arctic is well documented – as are long-term changes in the Northern Bering Sea.
Several are summarized in a report newly released by the Alaska Center for Climate Assessment and Policy call. The report, “ Alaska’s Changing Environment,” updates a version issued in 2019
One trend documented in the updated report is a Bering Sea ice season that is 41 days shorter on average than it was in the 1970s.
The report also shows how Alaska’s marine waters have warmed since 1982, with some notable trends in the Northern Bering Sea region. Average surface temperatures in the Chukchi Sea, which is connected through the Bering Strait to the Bering Sea, are now 3 degrees Fahrenheit warmer in summer than they were in the 1980s, the report said. Surface temperatures in Kotzebue Sound, just north of the strait, are now 12.1 degrees warmer on average, the report said.
Ocean acidity has increased dramatically in Alaska’s marine waters, the updated report said, including in the Bering Sea. Acidity rises when atmospheric carbon from fossil fuel burning is absorbed into the water, increasing the corrosive qualities. In 2022, about half of the bottom water in the Bering Sea was acidic enough to hinder juvenile king crab development, the report said. That compares to 10% in the 1970s and 1980s, the report said.
The 2018 conditions were layered atop those long-term changes. They did not disappear quickly.
Surprisingly to Overland and others, the Aleutian Low in 2019 was also located to the west, resulting in yet another winter of warmer southerly winds flowing into the Bering Sea and the spinoff effects, with ice extent that was almost as low as in the year prior.
But four years ago, the Aleutian Low reverted to more eastern locations, and the Bering Sea began cooling and returning to a more normal state, Overland said.
That does not mean the Bering Sea should now be considered to be in a cold phase, an expert warned officials with the North Pacific Fishery Management Council on Monday.
Elizabeth Siddon of NOAA Fisheries’ Auke Bay Laboratory, presenting the agency’s annual Bering Sea ecosystem report, told the council’s scientific and statistical committee that there are signs of recovery, notably in the northern part of the sea.
“The Bering Sea has cooled to average thermal conditions,” Siddon told the committee, which is in Anchorage as part of the council’s December meeting. She added a warning: “It’s a common misconception to think that the Bering Sea as having cooled to ‘cool’. It has only cooled to average.”
The Bering Sea is still coming out of its overheated period, which was unprecedented both in warmth and duration, Siddon said. There are mixed signals that make it difficult to predict what is in store this year, she said.
“We are in a transition between a warm and a cool” sea phase, she told the committee on Monday. “So it becomes very important what any individual species’ thermal preference is, or envelopes are, in terms of who we’re going to see in this new Bering Sea, who’s going to be out there.”
The North Pacific Fishery Management Council, which oversees commercial fisheries in federal waters off Alaska, uses the annual ecosystem reports for the Bering Sea, Aleutian Islands and Gulf of Alaska to help guide decisions on harvest limits for pollock, Pacific cod and other fish species.