Decoding dangers of Arctic sea ice with seismic, radar method
As drifting sea ice menaces coastal communities, a tool from researchers at Penn State lends new insight
Penn State
image:
Sea ice was visible in the Arctic Ocean along the coast of Utqiaġvik, Alaska, on Aug. 2, 2024. A tool developed by researchers at Penn State identifies seismic activities linked to different types of shifting ice.
view moreCredit: Provided by Gabriel Rocha Dos Santos
UNIVERSITY PARK, Pa. — Sea ice coverage in the Arctic Ocean is at one of its lowest levels on record, yet there’s no unanimity on when that ice will disappear completely during summer months. Understanding the traits and movements of the remaining ice is a persistent challenge for scientists, but a study by researchers at Penn State has provided a new tool to explore ice characteristics and interactions along with coastal conditions. Using radar images, fiber-optic sensing and seismic sensors, the team in the College of Earth and Mineral Sciences (EMS) identified different seismic activities linked to the types of ice that are shifting.
The work was published in the journal Geophysical Research Letters.
Drifting sea ice threatens Arctic communities, including infrastructure, as it can crash into stable formations that underpin where people live and work.
The new method can help coastal communities understand the scope, strength and hazards of these ice movements during different seasons, said Tieyuan Zhu, associate professor of geosciences and corresponding author on the study.
“This work creates a foundation to assess threats from particular kinds of sea ice that drift at different times of year,” said Zhu, who is also affiliated with the EMS Energy Institute. “April tends to see smaller but more chunks of ice. In January, they tend to be the strongest.”
Zhu and Gabriel Rocha Dos Santos, doctoral candidate in geosciences and the first author on the paper, centered their study near Utqiaġvik, a town with a population of about 4,900 in northern Alaska. The region is known informally as the land of fast ice — a reference to landfast ice that attaches to the ground as smaller sea ice travels on wind and ocean currents. The researchers collected seismic and radar data from two large interactions of chunks of sea ice striking landbound, stationary ice — one each on Jan. 4, 2022, and April 8, 2022.
To determine seismic activity during the strikes, the team used data from two mechanisms: broadband seismometers that capture ground motion and fiber-optic cables laid across the tundra. The latter employed acoustics to record longer-distance seismic patterns. Merging the insights with radar-derived visual observations allowed researchers to identify different types of ice-to-ice impacts and associate them with distinct seismic tremors.
The team said they believe those tremors can help reveal traits and threats posed by shifting sea ice where conventional monitoring is limited by harsh Arctic conditions. During the April 2022 event, tremors generated by smaller ice chunks were more intermittent and short-lived despite robust overall ice cover. Three months earlier, when large, more dense ice packs accumulated, the researchers found harmonic tremors, or more constant vibrations.
Zhu described the findings as the first evidence linking types of Arctic ice — and individual ice interactions — to specific seismic signals. Converting the seismic data to audio gave researchers an alternative way to interpret, understand and share the seismic activity in tandem with radar images.
“We could hear the vibration, the tremor,” Dos Santos said. “It’s a very eerie sound when you speed up the recordings to 200 times the ice’s actual rate of movement.”
Accelerating playback helps distinguish variations in ice friction and gliding, which happen over hours-long periods, the researchers said. Some lower-frequency recordings in April 2022 appeared to correlate with lower-velocity movement when drifting and stationary ice had locked up. The more sustained harmonic in January 2022 mirrored larger-mass impacts and the transfer of more ice-to-ice momentum.
“Radar images provide useful visuals, but we needed the seismic data to show what’s happening away from the surface, away from the camera lens,” Zhu said.
Merging seismic and radar data serves as a new research tool that can drive future studies to help protect coastal communities, the researchers said. Zhu estimated that Utqiaġvik residents live as close as 100 feet to the coast, leaving them especially vulnerable to erosion and waves created by drifting ice.
“In the context of a rapidly changing Arctic, this multi-sensor approach could help the communities better evaluate immediate hazards as Arctic ice continues to break apart and strike coastal areas, as the drifting ice can be tough to characterize otherwise,” Zhu said.
The new insights also can be useful for residents and those who make their livelihood in the area. Fishermen, for example, depend on sea ice as a fishing platform, so they need to know whether it’s stable, Dos Santos said.
“What we’ve found is very applicable in different regions — in Antarctica, in Greenland, in Russia,” Dos Santos said, explaining that the work would be replicable with similar use of radar images and readily available seismic sensors.
Zhu said that his team, along with other collaborators at Penn State, plan to explore 20 years of prior seismic readings and ice movements in the Arctic region to see how the integrated data assessment approach holds up against the 2022 evaluations in the paper.
The study received support from the U.S. National Science Foundation, the U.S. Department of Energy and UIC Science LLC. The authors also thanked several colleagues for field support that made the effort possible: Penn State graduate students Min Liew, Xiaohang Ji, Ziyi Wang, Matt Hallissey and Nolan Roth; Ming Xiao, professor of civil engineering at Penn State; Anne Jensen and Dmitry Nicolsky, faculty members at the University of Alaska Fairbanks; and Eileen Martin and Ahmad Tourei, a faculty member and a graduate student, respectively, at the Colorado School of Mines.
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Journal
Geophysical Research Letters
Method of Research
Computational simulation/modeling
Subject of Research
Not applicable
Article Title
Seismic Tremors From Sea-Landfast Ice Interactions Near Utqiaġvik, Alaska
The Southern Ocean’s low-salinity water locked away CO2 for decades, but...
An AWI study gives a potential explanation as to why the ocean around Antarctica is defying climate model projections and continuing to absorb CO2, despite the effects of climate change
image:
An iceberg in the Weddell Sea, Southern Ocean
view moreCredit: Alfred Wegener Institute / Mario Hopmmann
Climate models suggest that climate change could reduce the Southern Ocean’s ability to absorb carbon dioxide (CO2). However, observational data actually shows that this ability has seen no significant decline in recent decades. In a recent study, researchers from the Alfred Wegener Institute have discovered what may be causing this. Low-salinity water in the upper ocean has typically helped to trap carbon in the deep ocean, which in turn has slowed its release into the atmosphere – until now, that is, because climate change is increasingly altering the Southern Ocean and its function as a carbon sink. The study is published in the journal Nature Climate Change.
Oceans absorb around a quarter of all anthropogenic CO2 emissions released into the atmosphere. Of this total, the Southern Ocean alone stores roughly 40 per cent, making it a key region for containing global warming. The Southern Ocean’s important role comes about due to the ocean circulation in the region, whereby water masses upwell from deeper levels, are renewed and then return to the depths. This process releases natural CO2 from the deep ocean and absorbs and stores anthropogenic CO2 from the atmosphere. How well the Southern Ocean is able to absorb anthropogenic CO2 depends on how much natural CO2 comes to the surface from the deep ocean: the more natural CO2 that rises to the surface from the deeper levels, the less anthropogenic CO2 the Southern Ocean is able to absorb. This process is controlled by ocean circulation and the stratification of different water masses.
The water that upwells from the depths in the Southern Ocean is extremely old, having not been at the surface for hundreds or thousands of years. Over time, it has accumulated large amounts of CO2 which naturally return to the surface through the upwelling process. Model studies show that strengthening westerly winds, caused by climate change, will cause more and more of this CO2-rich deep water to rise to the surface. In the long term, this would reduce the Southern Ocean’s capacity to absorb human-made CO2. However, contrary to climate model projections, observational data from recent decades has shown no reduction in its capacity as a CO2 sink. A new study from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) now provides an explanation as to why, despite strengthening westerly winds, the Southern Ocean has continued to act as a CO2 sink in recent decades and therefore been able to slow down climate change.
“Deep water in the Southern Ocean is normally found below 200 metres,” says Dr. Léa Olivier, AWI oceanographer and lead author of the study. “It is salty, nutrient-rich and relatively warm compared to water nearer the surface.” The deep water contains a large amount of dissolved CO₂ that entered the deep ocean from the surface a long time ago. Near-surface water, on the other hand, is less salty, colder and contains less CO₂. As long as the density stratification between deep and surface water remains intact, CO₂ from the deeper layers cannot easily rise to the surface.
Cold, low-salinity water keeps carbon-rich water contained – however, climate change brings CO₂ dangerously close to the surface
“Previous studies suggested that global climate change would strengthen the westerly winds over the Southern Ocean, and with that, the overturning circulation too,” says Léa Olivier. “However, that would transport more carbon-rich water from the deep ocean to the surface, which would consequently reduce the Southern Ocean's ability to store CO₂.” Although strengthening winds have already been observed and attributed to human-made change in recent modelling and observational studies, there is no evidence pointing to the Southern Ocean absorbing less CO₂ – at least at this point.
Long-term observations by the AWI and other international research institutes suggest that climate change may be affecting the properties of surface and deep water masses. “In our study, we used a dataset comprising biogeochemical data from a large number of marine expeditions in the Southern Ocean between 1972 and 2021. We looked for long-term anomalies, as well as changes in both circulation patterns and the properties of water masses. In doing so, we only considered processes related to the exchange between the two water masses, namely circulation and mixing, and not biological processes, for example,” explains Léa Olivier. “We were able to determine that, since the 1990s, the two water masses have become more distinct from one another.” The Southern Ocean’s surface water salinity has reduced as a result of increased input of freshwater caused by precipitation and melting glaciers and sea ice. This “freshening” reinforces the density stratification between the two water masses, which in turn keeps the CO₂-rich deep water trapped in the lower layer and prevents it from breaking through the barrier between the two layers.
“Our study shows that this fresher surface water has temporarily offset the weakening of the carbon sink in the Southern Ocean, as model simulations predicted. However, this situation could reverse if the stratification were to weaken,” summarises Léa Olivier. There is a risk of this happening, as the strengthening westerly winds push the deep water ever closer to the surface. Since the 1990s, the upper boundary of the deep water mass has shifted roughly 40 metres closer to the surface, where CO₂-rich water is increasingly replacing the low-salinity winter surface water. As the transition layer between surface and deep water moves closer to the surface it becomes more susceptible to mixing, which could be primarily caused by the strengthening westerly winds. Such mixing would release the CO₂ that had accumulated beneath the surface water layer.
A recently published study suggests that this process may have already begun. The result would be that more CO₂-rich deep water could reach the surface, which would in turn reduce the Southern Ocean’s capacity to absorb anthropogenic CO₂ and therefore further drive climate change. “What surprised me most was that we actually found the answer to our question beneath the surface. “We need to look beyond just the ocean's surface, otherwise we run the risk of missing a key part of the story,” says Léa Olivier. “To confirm whether more CO₂ has been released from the deep ocean in recent years, we need additional data, particularly from the winter months, when the water masses tend to mix,” explains Prof. Alexander Haumann, co-author of the study. “In the coming years, the AWI is planning to carefully examine these exact processes as part of the international Antarctica InSync programme, and gain a better understanding of the effects of climate change on the Southern Ocean and potential interactions.“
Journal
Nature Climate Change
Method of Research
Observational study
Subject of Research
Not applicable
Article Title
Southern Ocean freshening stalls deep ocean CO2 release in a changing climat
Article Publication Date
17-Oct-2025
New study finds large fluctuations in sea level occurred throughout the last ice age, a significant shift in understanding of past climate
Oregon State University
CORVALLIS, Ore. — Large changes in global sea level, fueled by fluctuations in ice sheet growth and decay, occurred throughout the last ice age, rather than just toward the end of that period, a study publishing this week in the journal Science has found.
The findings represent a significant change in researchers’ understanding of how the Pleistocene – the geological period from about 2.6 million to 11,700 years ago and commonly known as the last ice age – developed, said Peter Clark, a paleoclimatologist at Oregon State University and the study’s lead author.
“This is a paradigm shift in our understanding of the history of the ice age,” said Clark, a university distinguished professor in OSU’s College of Earth, Ocean, and Atmospheric Sciences.
During the last ice age, Earth experienced cycles of dramatic shifts in global sea level caused by the formation and melting of large ice sheets over northern areas of North America and Eurasia. These changes are recorded in the shell remains of microscopic marine organisms called foraminifera, which are found in ocean sediment and collected by drilling cores, giving scientists an important record of past climate history.
When the first reconstruction of global sea level over the last ice age was published nearly 50 years ago, the science suggested there was a transition period about 1.25 million to 700,000 years ago, known as the middle Pleistocene transition, when the size of the ice sheets and the cycle of forming and melting changed.
“Before that transition, the glaciation cycles occurred about every 41,000 years, and after the transition, the cycles were every 100,000 years and were larger in amplitude,” said Clark. “All theories developed to explain this transition were focused on an increase in the size of the ice sheets through this transition. Every sea level reconstruction since that initial study produced the same storyline until now.”
Researchers had two leading hypotheses to explain why the transition occurred. One suggests that global cooling from decreasing carbon dioxide levels contributed to the cycle change and the other suggested that changes in how ice sheets move played a role.
In the new study, researchers reconstructed sea level changes for the past 4.5 million years. They found that many of the glaciation cycles during the early Pleistocene, when the cycles were 41,000 years in duration, were as large as the more recent cycles.
“Having those large ice sheets present throughout that time means that their formation and decay were likely influenced by internal feedbacks in the climate system, rather than external dynamics,” Clark said. “This finding challenges the conventional wisdom on the middle Pleistocene transition and forces us to develop new explanations.”
The research builds on previous work by Clark and colleagues to reconstruct global atmospheric temperatures and mean ocean temperatures, a project that began in 2017 to further understand past climate dynamics.
“Our ability to understand the past gives us a greater understanding of ice sheet-climate interactions and provides context for what we might experience in the future,” Clark said. “We have two big ice sheets today, in Antarctica and Greenland, and it’s important to think about how ice sheets like this can exist under a variety of conditions.”
Co-authors of the study are Steven W. Hostetler and Nicklas G. Pisias of Oregon State University; Jeremy D. Shakun of Boston College; Yair Rosenthal of Rutgers University; David Pollard of Pennsylvania State University; Peter Kohler of the Alfred-Wegener Institute of Germany; Patrick J. Bartlein of University of Oregon; Jonathan M. Gregory of University of Reading of the United Kingdom; Chenyu Zhu of the Chinese Academy of Sciences; Daniel P. Schrag of Harvard University; and Zhengyu Liu of Ohio State University.
Journal
Science
Article Title
Global mean sea level over the past 4.5 million years
Article Publication Date
16-Oct-2025
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