Sea ice is remaining attached to Alaska’s northern coastline for shorter periods each year, based on 27 years of data analyzed by scientists at the University of Alaska Fairbanks.
This type of ice, known as landfast ice because it stays fixed to the shore rather than drifting with winds and currents, has also covered a smaller area in recent winters.
The research, led by University of Alaska Fairbanks Geophysical Institute professor Andrew Mahoney, was published in January in the Journal of Geophysical Research: Oceans. Former UAF graduate student Andrew Einhorn contributed as a co-author.
The updated study builds on Mahoney’s earlier work from 2014, which examined data from 1996 to 2008, and expands the timeline through 2023. The analysis focuses on the Chukchi and Beaufort seas.
Declines Spread to the Beaufort Sea
Landfast ice in the Chukchi Sea has been decreasing for decades. The new findings show that the Beaufort Sea is now experiencing similar declines after remaining relatively stable from the 1970s through the early 2000s.
“Landfast ice is the ice that is used by people,” Mahoney said. “It has a much more immediate connection with humans.”
Communities depend on this stable ice to travel to hunting and fishing areas. It also supports seasonal ice roads used by the oil and gas industry to access coastal infrastructure. In addition, landfast ice acts as a natural barrier, reducing the impact of waves on the shoreline and allowing river water to spread farther offshore.
“The shortening of the landfast ice season may matter even more for coastal communities than any loss of ice area during that season,” Mahoney said, “because it leaves shorelines more exposed to waves and makes hunting conditions much more uncertain.”
Later Freeze-Up Is Driving Change
The shrinking season is largely due to ice forming later in the year. Even when air temperatures fall below freezing in autumn, the ocean retains heat longer, delaying the formation of solid ice along the coast.
Between 1996 and 2023, the landfast ice season shortened by 57 days in the Chukchi Sea and 39 days in the Beaufort Sea. In the Chukchi, this change reflects both later ice formation and earlier breakup. In the Beaufort, the reduction is tied mainly to delayed formation.
Why Landfast Ice Matters
Landfast ice can attach to the coast in several ways. It may freeze directly to the shoreline, anchor to shallow areas of the seafloor, or connect with grounded ice ridges. These ridges form when chunks of sea ice are pushed toward the coast, piling up until they become thick enough to rest on the seafloor.
“Landfast ice is diminishing with the rest of the ice in the Arctic,” Mahoney said. “In some ways it is following the same trends as we see in the rest of the Arctic, but we are also seeing some new changes.”
Thinning Ice and Fewer Anchors
The decline in Beaufort Sea landfast ice is also reflected in its share of total landfast ice across the U.S. Outer Continental Shelf. That share dropped from 3.8% in the first nine years of the 27-year dataset to 2% in the most recent nine years (2014-2023).
Researchers also found that the ice in the Beaufort Sea is no longer extending as far offshore as it once did. Previously, it regularly reached waters about 20 meters deep, a feature that set it apart from other Arctic regions where landfast ice had already retreated.
The team suggests that this shift may be linked to the overall thinning of Arctic sea ice. Thinner ice leads to fewer grounded ridges with deep enough bases to anchor the ice to the seafloor.
“We are seeing evidence that grounded ridges are not forming where they used to,” Mahoney said.
Unanswered Questions About Ice Formation
More research is needed to determine exactly why these changes are happening, Mahoney noted.
“This is where the chicken and egg part of it comes in,” he said, “because once a ridge becomes grounded, it acts like a traffic jam; additional ice piles up into it and it becomes larger and larger.”
“But we don’t yet know whether the action that starts the ridge just isn’t happening or whether the traffic jam afterward isn’t happening,” he said. “For one reason or another, we don’t see evidence of grounded ridges where they had been forming, and that’s the outcome you would expect if the ice is getting thinner.”
The study draws on data from the National Ice Center and the National Weather Service Alaska Sea Ice Program.
