New discovery about ice layer formation in ice sheets can improve sea level rise predictions

University of Texas at Austin

 

image: 

Meltwater streaming across the top of the Greenland ice sheet. A study led by researchers at The University of Texas at Austin examines the flow and freezing of meltwater within old snow on the ice sheet, which can help improve estimate of sea level rise.

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Credit: NASA Earth Observatory

A newly discovered mechanism for the flow and freezing of ice sheet meltwater could improve estimates of sea level rise around the globe.

Researchers from The University of Texas at Austin in collaboration with NASA’s Jet Propulsion Laboratory (JPL) and the Geological Survey of Denmark and Greenland (GEUS) have found a new mechanism that explains the process of how impermeable horizontal ice layers are formed below the surface, a process critical for determining the contribution of ice sheet meltwater to sea level rise.

The work by Mohammad Afzal Shadab a graduate student at UT’s Oden Institute for Computational Engineering and Sciences was published in Geophysical Research Letters. Shadab was supervised by study co-authors Marc Hesse and Cyril Grima at UT’s Jackson School of Geosciences.

The world’s two largest freshwater reservoirs, the Greenland and Antarctica ice sheets, are covered in old snow, known as firn, that’s not yet compacted into solid ice. Because the firn is porous, melted snow can drain down into the firn and freeze again rather than running into the sea. This process is thought to decrease meltwater runoff by about half.

However, it’s also possible to form impermeable ice layers that can serve as barriers for meltwater – and divert meltwater to the sea, said Shadab.

“So, there are cases where these ice layers in firn accelerate the rate of meltwater running into the oceans,” he said.

The potential for glacial meltwater to freeze in firns or flow off existing ice barriers makes understanding freezing dynamics within the firn layer an important part of estimating sea level rise, according to the researchers. Previous work on firn in mountains, which also contains ice layers, found that these ice layers are created when rainwater accumulates, or ponds, on older layers within the firn and then refreezes. But according to Hesse, it didn’t seem to work that way for ice sheets.

“When we looked at the data from Greenland, the actual amount of melt that’s being produced, even in an extreme melt event, is not enough to produce ponds,” said Hesse. “And that’s really where this study has come up with a new mechanism for ice layer formation.”

This new research presents ice layer formation as a competition between two processes: warmer meltwater flowing down through the porous firn (advection) and the cold ice freezing the water in place by heat conduction. The depth where heat conduction begins to dominate over heat advection determines the location where a new ice layer forms.

“Now that we know the physics of the formation of those ice layers, we will be able to better predict the meltwater retention capability of firn,” said study co-author Surendra Adhikari, a geophysicist at JPL.

Anja Rutishauser, a former UT postdoctoral researcher who is now a now at GEUS, also co-authored the study.

To ground truth this new mechanism, the researchers compared their models to a dataset collected in 2016 in which scientists dug a hole in Greenland’s firn and heavily equipped it with thermometers and radar that could measure the movement of meltwater. While previous hydrological models deviated from the measurements, the new mechanism successfully mirrored observations.

An unexpected finding of the new work was that the location of the ice layers may act as a record of the thermal conditions under which they formed.

“In the warming scenario, we found that the ice layers form deeper and deeper into the firn chronologically in a top-down fashion,” said Shadab. “And in a colder condition, ice layers form closer to the surface in a bottom-up scenario.”

Today, the amount of water running into the sea from Greenland currently outpaces Antarctica’s, about 270 billion tons per year compared to Antarctica’s 140 billion tons. Together, that’s more than two and a half Lake Tahoe’s worth each year. But future predictions of how much the two ice sheets will contribute to sea level rise are highly variable, fluctuating from 5 to 55 centimeters by 2100. And it’s clear ice layers play a key, and until now, poorly understood role.

“Things are much more complex in reality than what has been captured by existing models,” said Adhikari. “If we really want to improve our predictions, this is where we’re really advancing the state of the art.”

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Journal

Geophysical Research Letters

DOI

10.1029/2024GL109893 

Article Title

A Mechanism for Ice Layer Formation in Glacial Firn

 

Greenland landslide-induced tsunami produced global seismic signal that lasted 9 days

American Association for the Advancement of Science (AAAS)

In 2023, a massive rockslide in East Greenland, driven by glacial melt, triggered a towering tsunami and a rare global seismic signal that resonated for nine days, according to a new study. The study provides insights into how climate change-induced events like glacial thinning can lead to significant geophysical phenomena with impacts extending throughout the Earth system. Due to climate change, steep slopes are increasingly vulnerable to landslides. In Arctic regions – which are undergoing the most rapid warming globally – landslides can be driven by glacial debuttressing, permafrost degradation, and altered precipitation patterns. These landslides can trigger large and destructive tsunamis, particularly when they occur in confined water bodies like fjords. Such events have been recorded around the globe, including recently in West Greenland. Large tsunamigenic landslides produce long-period seismic waves, which can be detected remotely, and their tsunamis may create standing waves known as seiches, in which water sloshes back and forth at a specific resonant frequency. Seiches create long-period, monochromatic signals useful for studying energy transfer between the hydrosphere and the solid Earth. However, current observations of seiches have been limited to short-duration effects recorded by local seismometers. What’s more, numerical modeling of tsunami-induced seiches is limited, leaving a gap in understanding of how climate change can cause cascading, hazardous feedbacks between the cryosphere, hydrosphere, and lithosphere. Here, Kristian Svnnevig and colleagues report data from a significant landslide event in East Greenland that occurred in September 2023, which produced a very-long-period seismic signal that was detected globally for nine days. The event, which was triggered by glacial thinning, led to a massive rock-ice avalanche into Dickson Fjord, generating a 200-meter-high tsunami. This tsunami stabilized into a 7-meter-high long-duration seiche with a 90-second period, which produced a 10.88 millihertz (mHz) global seismic signal that resonated for nine days. Using a variety of geophysical techniques, Svennevig et al. show that the observed seismic signal was driven by the seiche. The findings further reveal that seiches in narrow fjords can produce long-duration seismic signals without persistent external driving forces, like strong winds or storm events.

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Journal

Science

DOI

10.1126/science.adm9247 

Article Title

A rockslide-generated tsunami in a Greenland fjord rang the Earth for 9 days

Article Publication Date

13-Sep-2024

Climate-change-triggered landslide caused Earth to vibrate for nine days

A landslide in a remote part of Greenland caused a mega-tsunami that sloshed back and forth across a fjord for nine days, generating vibrations throughout Earth, according to a new study involving UCL (University College London) researchers

University College London

 

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From left: before (August 2023) and after (September 2023) photos of the mountain peak and glacier, taken from the fjord. 

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Credit: Søren Rysgaard / Danish Army

A landslide in a remote part of Greenland caused a mega-tsunami that sloshed back and forth across a fjord for nine days, generating vibrations throughout Earth, according to a new study involving UCL researchers.

The study, published in the journal Science, concluded that this movement of water was the cause of a mysterious, global seismic signal that lasted for nine days and puzzled seismologists in September 2023.

The initial event, not observed by human eye, was the collapse of a 1.2km-high mountain peak into the remote Dickson Fjord beneath, causing a backsplash of water 200 metres in the air, with a wave up to 110 metres high. This wave, extending across 10km of fjord, reduced to seven metres within a few minutes, the researchers calculated, and would have fallen to a few centimetres in the days after.

The team used a detailed mathematical model, recreating the angle of the landslide and the uniquely narrow and bendy fjord, to demonstrate how the sloshing of water would have continued for nine days, with little energy able to escape.

The model predicted that the mass of water would have moved back and forth every 90 seconds, matching the recordings of vibrations travelling in the Earth’s crust all around the globe.

The landslide, the researchers wrote, was a result of the glacier at the foot of the mountain thinning, becoming unable to hold up the rock-face above it. This was ultimately due to climate change. The landslide and tsunami were the first observed in eastern Greenland.

Co-author Dr Stephen Hicks, of UCL Earth Sciences, said: “When I first saw the seismic signal, I was completely baffled. Even though we know seismometers can record a variety of sources happening on Earth’s surface, never before has such a long-lasting, globally travelling seismic wave, containing only a single frequency of oscillation, been recorded. This inspired me to co-lead a large team of scientists to figure out the puzzle.

“Our study of this event amazingly highlights the intricate interconnections between climate change in the atmosphere, destabilisation of glacier ice in the cryosphere, movements of water bodies in the hydrosphere, and Earth’s solid crust in the lithosphere.

 “This is the first time that water sloshing has been recorded as vibrations through the Earth’s crust, travelling the world over and lasting several days.”

The mysterious seismic signal – coming from a vibration through the Earth’s crust – was detected by seismometers all over the globe, from the Arctic to Antarctica. It looked completely different to frequency-rich ‘rumbles’ and ‘pings’ from earthquake recordings, as it contained only a single vibration frequency, like a monotonous-sounding hum.

When the study’s authors first discovered the signal, they made a note of it as a “USO”: unidentified seismic object. 

At the same time, news of a large tsunami in a remote northeast Greenland fjord reached authorities and researchers working in the area.

The researchers joined forces in a unique multidisciplinary group involving 68 scientists from 40 institutions in 15 countries, combining seismometer and infrasound data, field measurements, on-the-ground and satellite imagery, and simulations of tsunami waves.

The team also used imagery captured by the Danish military who sailed into the fjord just days after the event to inspect the collapsed mountain-face and glacier front along with the dramatic scars left by the tsunami.

It was this combination of local field data and remote, global-scale observations that allowed the team to solve the puzzle and reconstruct the extraordinary cascading sequence of events.

Lead author Dr Kristian Svennevig, from the Geological Survey of Denmark and Greenland (GEUS), said: “When we set out on this scientific adventure, everybody was puzzled and no one had the faintest idea what caused this signal. All we knew was that it was somehow associated with the landslide. We only managed to solve this enigma through a huge interdisciplinary and international effort.”

He added: “As a landslide scientist, an additional interesting aspect of this study is that this is the first-ever landslide and tsunami observed from eastern Greenland, showing how climate change already has major impacts there.”

The team estimated that 25 million cubic metres of rock and ice crashed into the fjord (enough to fill 10,000 Olympic-sized swimming pools).

They confirmed the size of the tsunami, one of the largest seen in recent history, using numerical simulations as well as local data and imagery.

Seventy kilometres away from the landslide, four-metre-high tsunami waves damaged a research base at Ella Ø (island) and destroyed cultural and archaeological heritage sites across the fjord system.

The fjord is on a route commonly used by tourist cruise ships visiting the Greenland fjords. Fortunately, no cruise ships were close to Dickson Fjord on the day of the landslide and tsunami, but if they had been, the consequences of a tsunami wave of that magnitude could have been devastating.

Mathematical models recreating the width and depth of the fjord at very high resolution demonstrated how the distinct rhythm of a mass of water moving back and forth matched the seismic signal.

The study concluded that with rapidly accelerating climate change, it will become more important than ever to characterise and monitor regions previously considered stable and provide early warning of these massive landslide and tsunami events.

Co-author Thomas Forbriger, from Karlsruhe Institute of Technology, said: “We wouldn’t have discovered or been able to analyse this amazing event without networks of high-fidelity broadband seismic stations around the world, which are the only sensors that can truly capture such a unique signal.”

Co-author Anne Mangeney, from Université Paris Cité, Institut de Physique du Globe de Paris, said: “This unique tsunami challenged the classical numerical models that we previously used to simulate just a few hours of tsunami propagation.  We had to go to an unprecedentedly high numerical resolution to capture this long-duration event in Greenland. This opens up new avenues in the development of numerical methods for tsunami modelling.”

Before and after the landslide: annotated image 

 

 before (August 2023) and after (September 2023) photos of the mountain peak and glacier, taken from the fjord. 

Credit

Søren Rysgaard, Danish Army

Pre- (30 minutes before) and post-landslide (7 minutes after) Planet Labs satellite image

Credit

Planet Labs

ground motion visualisation animation and simulation of tsunami and seiche 

Ground motion visualisation animations showing the very long-period seismic wave propagating around the globe. The left panel shows a ground motion visualisation, showing the seismic wave from the Greenland seiche spreading out around the planet. Each circle shows the data from an individual seismic monitoring station. The right panel shows a numerical simulation of the 16 September 2023 tsunami and seiche in Dickson fjord.

Credit

Music credit: Isabelle Ryder https://isabellerydermusic.weebly.com/; animation credit: Stephen Hicks; Kristian Svennevig; Alexis Marbeouf.

Drone footage following landslide showing destroyed mountain peak 

Drone footage taken high above the fjord after the 16 September 2023 event showing the destroyed mountain peak and glacier.

Credit

Credit: Wieter Boone, Flanders Marine Institute.

Journal

Science

DOI

10.1126/science.adm9247 

Method of Research

Computational simulation/modeling

Subject of Research

Not applicable

Article Title

A rockslide-generated tsunami in a Greenland fjord rang the Earth for 9 days

Article Publication Date

12-Sep-2024

Climate change-triggered landslide unleashes a 650-foot mega-tsunami

Wave created a seismic signal that lasted for nine days

University of California - San Diego

 

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'Before' image of landslide site taken on Aug. 12, 2023

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Credit: Søren Rysgaard

In September 2023, scientists around the world detected a mysterious seismic signal that lasted for nine straight days. An international team of scientists, including seismologists Alice Gabriel and Carl Ebeling of UC San Diego’s Scripps Institution of Oceanography came together to solve the mystery.

A new study published today in Science provides the stunning solution: In an East Greenland fjord, a mountaintop collapsed into the sea and triggered a mega-tsunami about 200 meters (650 feet) tall. The giant wave rocked back and forth inside the narrow fjord for nine days, generating the seismic waves that reverberated through Earth’s crust, baffling scientists around the world. This rhythmic sloshing is a phenomenon known as a seiche. Fortunately, no people were hurt, but the waves destroyed some $200,000 in infrastructure at an unoccupied research station on Ella Island.

“When we set out on this scientific adventure, everybody was puzzled and no one had the faintest idea what caused this signal,” said Kristian Svennevig, a geologist at the Geological Survey of Denmark and Greenland (GEUS) and the study’s lead author. “All we knew was that it was somehow associated with the landslide. We only managed to solve this enigma through a huge interdisciplinary and international effort.”

Climate change set the stage for the landslide by melting the glacier at the base of the mountain, destabilizing the more than 25 million cubic meters (33 million cubic yards) of rock and ice – enough to fill 10,000 Olympic-sized swimming pools – that ultimately crashed into the sea. As climate change continues to melt Earth’s polar regions it could lead to an increase in large, destructive landslides such as this one.

“Climate change is shifting what is typical on Earth, and it can set unusual events into motion,” said Gabriel, whose work on this study was supported by the European Research Council, Horizon Europe, the National Science Foundation (NSF) and NASA.

When seismic monitoring networks first detected this signal in September 2023, it was puzzling for two main reasons. First, the signal looked nothing like the busy squiggle that earthquakes produce on seismographs. Instead, it oscillated with a 92-second-interval between its peaks, too slow for humans to perceive. Second, the signal stayed strong for days on end, where more common seismic events weaken more rapidly.

The global community of Earth scientists started buzzing with online discussion of what could be causing the strange seismic waves. The discussion turned up reports of a huge landslide in a remote Greenland fjord that occurred on Sept. 16, around the time the seismic signal was first detected.

To figure out if and how these two phenomena might be connected, the team, led by Kristian Svennevig of the Geological Survey of Denmark and Greenland, combined seismic recordings from around the world, field measurements, satellite imagery and computer simulations to reconstruct the extraordinary events.

The team, comprised of 68 scientists from 41 research institutions, analyzed satellite and on-the-ground imagery to document the enormous volume of rock and ice in the landslide that triggered the tsunami. They also analyzed the seismic waves to model the dynamics and trajectory of the rock-ice avalanche as it moved down the glacial gully and into the fjord.

To understand the tsunami and resulting seiche, the researchers used supercomputers to create high-resolution simulations of the events.

“It was a big challenge to do an accurate computer simulation of such a long-lasting, sloshing tsunami,” said Gabriel.

Ultimately, these simulations were able to closely match the real-world tsunami’s height as well as the long-lasting seiche’s slow oscillations.

By integrating these diverse data sources, the researchers determined that the nine-day seismic signal was caused by the massive landslide and resulting seiche within Greenland’s Dickson Fjord.

“It was exciting to be working on such a puzzling problem with an interdisciplinary and international team of scientists,” said Robert Anthony, a geophysicist with the United States Geological Survey’s Earthquake Hazards program and co-author of the study. “Ultimately, it took a plethora of geophysical observations and numerical modeling from researchers across many countries to put the puzzle together and get a complete picture of what had occurred.”

The study’s findings demonstrate the complex, cascading hazards posed by climate change in polar regions. While no people were in the area when the landslide and mega-tsunami occurred, the fjord is close to a route commonly used by cruise ships, highlighting the need to monitor polar regions as climate change accelerates. For example, a landslide in western Greenland’s Karrat Fjord in 2017 triggered a tsunami that flooded the village of Nuugaatsiaq, destroying 11 houses and killing four people.

Gabriel said the results could also inspire researchers to comb back through the seismic record to look for similar events now that scientists know what to look for. Finding more seiches could help more clearly define the conditions that give rise to the phenomenon.

“This shows there is stuff out there that we still don’t understand and haven’t seen before,” said Ebeling, who co-authored the study with support from NSF and helped manage a network of seismic sensors that detected the seiche’s vibrations. “The essence of science is trying to answer a question we don’t know the answer to – that’s why this was so exciting to work on.” 

'After' image of landslide site 

Image of landslide site taken on Sept. 19, 2023 following Sept. 16, 2023 event.

Credit

Danish Army

Video recorded of the landslide area three days after the landslide in Dickson fjord.

Credit

Danish Army, Joint Arctic Command

Drone video of landslide site (VIDEO)

Drone video of landslide site (VIDEO)

Seismic waves and seiche simulation (VIDEO)

Credit

Music credit: Isabelle Ryder https://isabellerydermusic.weebly.com/ 

Animation credit: Stephen Hicks/University College London

University of California - San Diego

Caption

Left panel shows a ground motion visualization, showing the seismic wave from the Greenland seiche spreading out around the planet. Each circle shows the data from an individual seismic monitoring station. The right panel shows a numerical simulation of the Sept. 16, 2023 tsunami and seiche in Dickson fjord.

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Journal

Science

DOI

10.1126/science.adm9247 

Method of Research

Data/statistical analysis

Subject of Research

People

Article Title

A rockslide-generated tsunami in a Greenland fjord rang the Earth for 9 days

Article Publication Date

12-Sep-2024

 

Antarctica’s receding sea ice could impact seabirds’ food supply

Durham University

 

image: 

Close-up of a southern giant petrel.

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Credit: Professor Richard Phillips

Antarctica’s rapidly receding sea ice could have a negative impact on the food supply of seabirds that breed hundreds of miles away from the continent.

Most of the world's albatrosses, and their close relatives, petrels, breed on islands in the Southern Ocean, which surrounds Antarctica.

Now new research led by Durham University, UK, and the British Antarctic Survey (BAS) has used satellite technology to track the movement of these seabirds.

They found that the birds fly huge distances to parts of the ocean affected by sea ice – called the Antarctic seasonal sea ice zone.

It is thought they travel to either feed in the nutrient enriched waters left behind when Antarctica’s sea ice melts each summer or, in the case of southern giant petrels, to scavenge on seals found on the ice itself.

Until recently, Antarctica had not suffered the big losses in sea ice seen in the Arctic, but over the past five years Antarctic sea ice has begun to recede at a quicker rate.

The findings suggest that Antarctica’s shrinking sea ice could force seabirds to travel further from their breeding grounds to find food or it could alter the patterns of where that food can be found. In turn, this could affect the ecosystems these birds are a part of.

The study is published in the journal Progress in Oceanography.

Lead author Dr Ewan Wakefield, in the Department of Geography, Durham University, said: “Every winter the sea freezes around Antarctica, with sea ice covering tens of millions of square miles.

“We found that albatrosses and large petrels travel hundreds of miles, some far into the area covered by this sea ice and we think that they do this to feed.

“In that case, Antarctica’s receding sea ice, driven by climate change, could affect not just the penguins, familiar to many people, that breed on the continent, but also huge numbers of seabirds breeding hundreds or thousands of miles away.”

The researchers analysed data showing the movements of seven species of albatross and large petrel from the sub-Antarctic island of South Georgia, which is about 1,000 miles from Antarctica.

These species were the northern giant petrel, southern giant petrel, white-chinned petrel, light-mantled albatross, black-browed albatross, grey-headed albatross and the wandering albatross.

In total they looked at 2,497 foraging trips made by 1,289 of the seabirds from satellite data collected between 1992 and 2023.

They found that all seven species used sea ice-affected parts of the ocean, but in different ways.

For example, albatrosses largely avoided ice-covered areas, probably because they find it difficult to fly or land there. However, in late summer and autumn, albatrosses fed in areas where the ice had melted weeks or months earlier and released concentrated nutrients into the sea.

In contrast, during the spring, southern giant petrels flew hundreds of miles into the pack ice, which researchers think they do to scavenge on the seals that breed on the ice.

On a bigger scale, researchers also found a remarkable pattern of birds moving north and south with the seasons, which they think is caused by birds following plankton blooms in the oceans – known as green wave surfing.

Antarctic sea ice was relatively stable during the period when the satellite data was recorded, but in recent summers seasonal sea ice has retreated earlier and reached record lows.

Study co-author Professor Richard Phillips, leader of the Higher Predators and Conservation Group at the British Antarctic Survey, said: “Given that all seven species of albatross and petrel we looked at travelled to the Antarctic seasonal sea ice zone, it is likely that they, and many other sub-Antarctic breeding seabirds, are linked to sea ice dynamics.

“Declines in Antarctic sea ice predicted under climate change could exacerbate the already unsustainable human impacts being experienced by these populations.”

The researchers said there were some limitations to their study.

While their analysis showed that the birds used sea ice affected habitats, they do not exactly know what the birds are eating. They hope this will be shown by follow-up tracking and dietary studies to give a better idea of how changing sea ice might affect different species.

The resolution of the sea ice and tracking data was not sufficient to tell how birds interacted with sea ice at fine scale and the researchers hope fine scale tracking could resolve this.

For several of the species, the beginning and end of the breeding period was not covered by tracking, so the researchers do not know how they might use sea ice habitats during that time.

The research also included BirdLife International, the University of Barcelona, the University of Helsinki, Stony Brook University and the University of Coimbra. 

It was funded by the Leverhulme Trust, the European Research Council H2020, the Natural Environment Research Council (NERC), Darwin Plus, the National Science Foundation and the GSGSSI.

The study also benefited from the strategic programme of the Marine and Environmental Sciences Centre (MARE), financed by the Foundation for Science and Technology (FCT) and represents a contribution to the Ecosystems component of the BAS Polar Science for Planet Earth Programme, funded by NERC.

ENDS

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Journal

Progress In Oceanography

DOI

10.1016/j.pocean.2024.10333 

Method of Research

Data/statistical analysis

Subject of Research

Animals

Article Title

Seasonal resource tracking and use of sea-ice foraging habitats by albatrosses and large petrels

Article Publication Date

12-Sep-2024

Close-up of a southern giant petrel.

Close-up of a wandering albatross spreading its wings.

Nesting wandering albatross.

A white-chinned petrel in flight against an icy mountain backdrop.

Close-up of a white-chinned petrel in flight.

Credit

Professor Richard Phillips