Based on 27 years of data analyzed by scientists at the University of Alaska Fairbanks, the length of time that sea ice remains on Alaska’s northern coastline is getting shorter and shorter each year.
This type of ice, known as fast ice because it remains fixed to the shore rather than drifting away with wind or ocean currents, has started covering smaller areas in recent winters.
The study, led by Professor Andrew Mahoney of the University of Alaska Fairbanks Geophysical Institute, was published in January in the Journal of Geophysical Research: Oceans. Former UAF graduate student Andrew Einhorn contributed as a co-author.
The latest study builds on Mahoney’s earlier work in 2014, which looked at data from 1996 to 2008, and extends the timeline to 2023. The analysis focuses on the Chukchi and Beaufort Seas.
Decline extends to the Beaufort Sea
Land ice in the Chukchi Sea has been decreasing for decades. The new findings show that the Beaufort Sea is now experiencing a similar decline after remaining relatively stable from the 1970s to the early 2000s.
“Landfast ice is the ice that people use,” Mahoney said. “It has a more direct connection to humans.”
Communities rely on this stable ice to go hunting and fishing. It also supports seasonal ice roads used by the oil and gas industry to access coastal infrastructure. In addition, land ice acts as a natural barrier, reducing the impact of waves on shorelines and allowing river water to spread offshore.
“For coastal regions, the shortening of the ice season may be more important than the loss of ice cover during it, because it makes coastlines more exposed to waves and makes hunting conditions more unstable,” Mahoney said.
Subsequent freezing prompts change.
The main cause of the reduced season is ice formation later in the year. Even when temperatures drop below freezing in the fall, the ocean retains heat longer, slowing the formation of solid ice along the coast.
From 1996 to 2023, the land ice season shortened by 57 days in the Chukchi Sea and 39 days in the Beaufort Sea. In Chukotka, this change reflects both late ice formation and early ice collapse. In Beaufort, the reductions are primarily related to formation delays.
Why is landfast ice important?
Land ice attaches to coasts in several ways. It may freeze directly to the shoreline, anchor in shallow areas of the ocean floor, or attach to grounded ice ridges. These ridges form when chunks of sea ice are pushed toward the coast and build up until they are thick enough to stay on the ocean floor.
“Land ice is decreasing along with the rest of the Arctic ice,” Mahoney said. “In some ways, we’re following the same trends that we see in other parts of the Arctic, but we’re also seeing some new changes.”
The ice gets thinner and there are fewer anchors.
The decline in Beaufort Sea land ice is also reflected in its share of total land ice on the entire outer U.S. continental shelf. That percentage 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 Beaufort Sea ice does not extend as far offshore as it once did. Previously, they regularly reached waters around 20 meters deep, which set them apart from other Arctic regions where land ice was already receding.
The researchers suggest that this change may be related to overall thinning of the Arctic sea ice. As the ice becomes thinner, there are fewer grounding ridges with foundations deep enough to anchor the ice to the ocean floor.
“We see evidence that the grounding ridge is not forming where it once was,” Mahoney said.
Unanswered questions about ice formation
Mahoney noted that more research is needed to understand exactly why these changes occur.
“This is where the chicken-and-egg part comes in, because once the ridge falls to the ground, it acts like a traffic jam. More ice accumulates there, and it gets bigger and bigger,” he says.
“But we still don’t know whether the movement at the beginning of the ridge is simply not occurring, or whether the subsequent traffic congestion is not occurring,” he said. “For some reason, we don’t see any evidence of it touching down where the ridge was forming, which is an expected result of thinning ice.”
The study utilized data from the National Ice Center and the National Weather Service Alaska Sea Ice Program.
