New analysis shows continued loss of Arctic landfast sea ice
Sea ice is sticking to Alaska’s northern coast for less time each year, according to 27 years of data analyzed by University of Alaska Fairbanks scientists.
Such landfast ice, which stays attached to the shoreline instead of drifting with winds and currents, also has covered less total area in recent winters.
The work led by research 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 is a co-author.
The new assessment extends the timeframe of a 2014 study by Mahoney that covered 1996-2008. It focuses on the Chukchi and Beaufort seas.
Landfast sea ice has been declining in the Chukchi Sea for decades. The new analysis found that the extent of Beaufort Sea landfast sea ice has also begun to decline in recent years after remaining relatively stable between the 1970s and early 2000s.
“Landfast ice is the ice that is used by people,” Mahoney said. “It has a much more immediate connection with humans.”
Residents travel across the stable ice to reach hunting and fishing areas. The oil and gas industry uses the frozen surface to build seasonal ice roads that connect to nearshore facilities. By remaining fixed in place, landfast ice also helps shield the shoreline from strong waves and allows 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.”
The landfast ice season has shrunk mostly because the ice is forming later in the year. Even after air temperatures drop below freezing in the fall, the ocean is staying warm longer, so it takes more time for solid ice to develop along the coast.
From 1996-2023, the landfast season has shortened by 57 days in the Chukchi Sea and 39 days in the Beaufort Sea. In the Chukchi, that’s due to later ice attachment and earlier ice detachment. In the Beaufort, it’s due to later ice attachment only.
Sea ice can attach to land in several ways. Newly formed sea ice can freeze directly to the coastline, anchor to a shallow seafloor or bond with grounded ice ridges. These ridges are jumbles of sea ice blocks pushed to the coast, where they pile up and become thick enough to sit 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.”
The decline in Beaufort Sea landfast ice is reflected in the percentage of total landfast sea ice on the U.S. Outer Continental Shelf. The total decreased from 3.8% in the first nine years of Mahoney and Einhorn’s 27-year record to 2% in the final nine years, 2014–2023.
The two scientists found that the Beaufort’s landfast sea ice was not extending as far from shore in recent years. It previously could reach waters near 20 meters deep annually, distinguishing the Beaufort Sea from other regions of the Arctic where landfast ice retreat had already been observed.
They speculate the recent decline is related to the overall thinning of Arctic sea ice, which results in the creation of fewer ice ridges with bottoms deep enough to become grounded on the seafloor and anchor the ice.
“We are seeing evidence that grounded ridges are not forming where they used to,” Mahoney said.
Additional research is needed to better understand why, Mahoney said.
“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 new extended work uses data from the National Ice Center and the National Weather Service Alaska Sea Ice Program.
CONTACTS:
• Andrew Mahoney, University of Alaska Fairbanks Geophysical Institute, armahoney@alaska.edu
• Rod Boyce, University of Alaska Fairbanks Geophysical Institute, 907-474-7185, rcboyce@alaska.edu
Journal
Oceans
Article Title
The Evolving Decline of Landfast Sea Ice in Northern Alaska and Adjacent Waters: Results from an Updated Climatology
Research provides timely views of warming’s impact on Alaska glaciers
Alaska’s glaciers respond to climate change by melting for three additional weeks with every 1 degree Celsius increase in the average summer temperature, data from satellite-mounted radars show.
A single degree Celsius equates to 1.8 degrees Fahrenheit.
Work by scientists at Carnegie Mellon University and the University of Alaska Fairbanks also shows that synthetic aperture radar, or SAR, can consistently and automatically monitor glaciers and their snowlines year-round. Those are usually only gauged at the end of the melt season using optical instruments.
SAR data is also more reliable than traditional surface-based optical instruments.
The findings were published Feb. 4 in Nature.
The lead author is recent Ph.D. graduate Albin Wells of Carnegie Mellon University. Co-authors are assistant professor David Rounce of Carnegie Mellon and Mark Fahnestock of the UAF Geophysical Institute. Rounce previously was a Geophysical Institute postdoctoral fellow and research associate.
The scientists used the radar data to track the number of glacier “melt days.” A single melt day can be one 24-hour period in which an entire glacier is melting, or it can consist of multiple days where portions of the glacier melt and eventually reach the glacier’s total surface area equivalent.
An increase in melt days over time signals a longer melt season and accelerates a glacier’s net loss of ice.
Using European Sentinel-1 radar satellite data, the researchers tracked changes throughout each melt season at nearly all Alaska glaciers larger than about half a square mile from mid-2016 through 2024.
Synthetic aperture radar works by sending microwave pulses toward the ground from a moving aircraft or satellite and combining the returning echoes to create detailed images, even through clouds and in darkness.
Sentinel-1 passes over the same location every 12 days, covering more than 3,000 Alaska glaciers.
The team also found that short-term heat waves caused Alaska’s glaciers to lose up to 28% more of their protective snow cover than in typical years. That percentage is at the scale of individual mountain ranges rather than applying uniformly to each glacier within a mountain range.
“Our ability to quantify these changes is really important,” Wells said. “Melt extents and snowlines are proxies for glacier mass balance.”
Glacier mass balance is the difference between how much snow and ice a glacier gains and how much it loses over time.
“These correlations with temperature begin to give a sense for how much melt or snowline retreat we can anticipate under future, warmer climates across the region,” Wells said.
The snowline marks the division between a glacier’s accumulation zone, where snow builds up and adds mass, and its ablation zone, where melting removes snow and ice.
Glaciologists typically use optical equipment to assess snowlines at the end of the melt season, usually in late summer or early fall.
“In optical data, the snowline can be really hard to observe,” Fahnestock said. “If you’re a day late taking your picture, it might have snowed on the entire glacier, and you can’t see where the bare glacier ice is down below and where the snow and firn is above.”
Firn is partially compacted granular snow that forms the surface part of the upper end of a glacier and can eventually become ice.
Fahnestock noted that optical instruments can be affected by variable lighting conditions, shading, clouds and whether firn is clean or dirty.
SAR overcomes that and can also provide regular in-season snowline updates.
“What Albin has done is operationalize the tracking of surface conditions on the glaciers in a way that can be applied anywhere,” Fahnestock said.
The research paid close attention to a June 23-July 10, 2019, Alaska heat wave that encompassed all glaciated regions of Alaska except the Brooks Range.
Temperatures rose to 20 to 30 degrees above average at many locations for nearly two weeks. Several days set all-time records, including 90 degrees Fahrenheit at Ted Stevens Anchorage International Airport. Anchorage’s typical summer highs are in the mid-60s.
The excessive heat caused glacier snowlines to retreat nearly 350 feet in elevation, according to the researchers. Snowlines do not retreat that high in a typical year until about two months later.
The change lengthened exposure of bare ice and firn, leading to increased mass loss.
The authors write that this underscores “the sensitivity of glaciers to short-term climatic variability.”
Wells said the research also revealed consistent differences in the number of melt days between glaciers on the coastal side of mountain ranges and those farther inland. The pattern suggests the glaciers operate differently even though many are losing ice at broadly similar rates.
“This is an important finding,” Wells said, “because it corroborates prior knowledge that glaciers in Alaska on the coastal side of mountains have more melt in summer and more accumulation in winter than those on the continental side of the ranges.”
CONTACTS:
• Albin Wells, albin.wells@geo.uzh.ch
• Mark Fahnestock, University of Alaska Fairbanks Geophysical Institute, 907-687-6371, mfahnestock@alaska.edu
Journal
Nature
Article Title
Seasonal progression of melt and snowlines in Alaska from SAR reveals impacts of warming
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