Alaska's coastal ice season has shrunk by up to 57 days in three decades

University of Alaska Fairbanks Geophysical Institute. Published in the Journal of Geophysical Research: Oceans, January 2026.

Fifty-seven days. That is how much ice season the Chukchi Sea has lost since 1996 — nearly two full months of stable, shore-attached ice that communities once relied on for travel, hunting, and coastal protection. The Beaufort Sea, long considered more resilient, has lost 39 days over the same period.

These numbers come from a new analysis by University of Alaska Fairbanks scientists that extends decades of monitoring into the most recent years, confirming that landfast sea ice — the frozen platform that stays anchored to the coastline rather than drifting with currents — is retreating on multiple fronts simultaneously.

Ice that people actually use

Most Arctic ice coverage gets discussed in terms of satellite images showing white expanse shrinking year over year. Landfast ice is different. It is the ice that intersects directly with human life along Alaska's northern coast.

Residents of coastal communities travel across landfast ice to reach hunting and fishing grounds. The oil and gas industry builds seasonal roads on its frozen surface to access nearshore facilities. And by remaining locked in place, the ice acts as a buffer, absorbing wave energy that would otherwise batter shorelines already vulnerable to erosion.

"Landfast ice is the ice that is used by people," said Andrew Mahoney, research professor at the UAF Geophysical Institute and lead author of the study, published in January in the Journal of Geophysical Research: Oceans. "It has a much more immediate connection with humans."

The shortening of the ice season may matter more than any loss of total ice area during that season, Mahoney added, because it leaves shorelines exposed to waves for longer stretches and makes hunting conditions far less predictable.

Later formation, not just earlier breakup

The dominant driver of the shrinking ice season is delayed formation in autumn. Even after air temperatures drop below freezing, the ocean retains enough warmth to prevent solid ice from developing along the coast. The water, in effect, remembers summer longer than it used to.

In the Chukchi Sea, the 57-day loss reflects both later ice attachment in fall and earlier detachment in spring — a squeeze from both ends. In the Beaufort Sea, the 39-day decline is almost entirely due to later formation. Spring breakup timing has remained relatively stable there, at least so far.

The study extends a 2014 analysis by Mahoney that covered 1996 through 2008. Co-authored by former UAF graduate student Andrew Einhorn, the new work pushes the record through 2023, using data from the National Ice Center and the National Weather Service Alaska Sea Ice Program.

The Beaufort's delayed decline

For years, the Beaufort Sea's landfast ice appeared to be holding steady while ice in other Arctic regions deteriorated. The new analysis shows that stability has ended.

The total landfast ice on the U.S. Outer Continental Shelf dropped from 3.8% of the total in the first nine years of the record to 2% in the final nine years (2014-2023). The ice is no longer extending as far offshore. It previously reached waters near 20 meters deep on an annual basis — a distinguishing feature of the Beaufort compared to other Arctic coastlines. That reach has contracted.

The researchers attribute the change to the overall thinning of Arctic sea ice, which produces fewer ice ridges with keels deep enough to ground on the seafloor. These grounded ridges are critical. Once a ridge touches bottom, it acts like a dam — additional ice piles up against it, growing the structure and anchoring the ice field to the coast. Without that initial grounding, the entire anchoring process stalls.

The ridge problem: a chicken-and-egg puzzle

Mahoney describes the loss of grounded ridges as a feedback loop with an uncertain trigger. The ridges form when drifting ice collides with stationary ice near shore, creating jumbled piles of ice blocks thick enough to sit on the seafloor. Thinner ice produces smaller ridges. Smaller ridges fail to ground. Without grounded ridges, there is no anchor for the broader ice sheet.

"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," Mahoney 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."

Disentangling cause from consequence here is one of the study's acknowledged open questions. The ice is thinner, the ridges are smaller, and the anchoring is failing — but the precise sequence remains unclear.

Consequences measured in exposure

The practical effects of a shorter landfast ice season are already visible. Longer stretches of open water in autumn and early winter mean more wave action against shorelines that, in many locations along Alaska's north coast, consist of permafrost bluffs. These bluffs erode rapidly when exposed to sustained wave energy, and several communities have faced accelerating coastal retreat in recent years.

For subsistence hunters, the uncertainty is equally concrete. Landfast ice provides a stable platform for accessing marine mammals. When the ice forms later and breaks earlier, the window for safe travel shrinks, and the ice that does form may be thinner and less predictable.

The study does not model future projections or attempt to predict when specific thresholds might be crossed. It is descriptive, not predictive — a careful accounting of what has already changed. But the trajectory is consistent with broader Arctic trends, and nothing in the data suggests a reversal.

"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."

Those new changes — particularly the Beaufort's shift from stable to declining — suggest that landfast ice may be entering a phase of accelerated loss after decades of relative persistence. Whether communities, industries, and coastlines can adapt to a substantially shorter ice season is an open question the data cannot answer.