https://www.sciencedaily.com/releases/2024/02/240226204614.htm

Significant glacial retreat in West Antarctica began in 1940s
Published study reports Thwaites and pine island glaciers share common history of thinning
Date:
February 26, 2024
Source:
University of Houston

Among the vast expanse of Antarctica lies the Thwaites Glacier, the world’s widest glacier measuring about 80 miles on the western edge of the continent. Despite its size, the massive landform is losing about 50 billion tons of ice more than it is receiving in snowfall, which places it in a precarious position in respect to its stability. Accelerating ice loss has been observed since the 1970s, but it is unclear when this significant melting initiated — until now. A new study suggests that the significant glacial retreat of two glaciers on the west coast of Antarctica began in the 1940’s, likely spurred by climate change.
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Among the vast expanse of Antarctica lies the Thwaites Glacier, the world’s widest glacier measuring about 80 miles on the western edge of the continent. Despite its size, the massive landform is losing about 50 billion tons of ice more than it is receiving in snowfall, which places it in a precarious position in respect to its stability.

Accelerating ice loss has been observed since the 1970s, but it is unclear when this significant melting initiated — until now. A new study published in the journal PNAS, led by researchers at the University of Houston, suggests that significant glacial retreat began in the 1940s. Their results on the Thwaites Glacier coincide with previous work that studied retreat on Pine Island Glacier and found glacial retreat began in the ’40s as well.

“What is especially important about our study is that this change is not random nor specific to one glacier,” said Rachel Clark, corresponding author, who graduated from UH last year with a doctorate in geology. “It is part of a larger context of a changing climate. You just can’t ignore what’s happening on this glacier.”

Clark and the study authors posit that the glacial retreat was likely kicked off by an extreme El Niño climate pattern that warmed the west Antarctic. Since then, the authors say, the glacier has not recovered and is currently contributing to 4% of global sea-level rise.

“It is significant that El Niño only lasted a couple of years, but the two glaciers, Thwaites and Pine Island, remain in significant retreat,” said Julia Wellner, UH associate professor of geology and U.S. lead investigator of the Thwaites Offshore Research project, or THOR, an international collaboration whose team members are authors of the study.

“Once the system is kicked out of balance, the retreat is ongoing,” she added.

Their findings also make it clear the retreat at the glaciers’ grounding zone, or the area where the glaciers lose contact with the seabed and start to float, was due to external factors.

“The finding that both Thwaites Glacier and Pine Island Glacier share a common history of thinning and retreat corroborates the view that ice loss in the Amundsen Sea sector of the West Antarctic ice sheet is predominantly controlled by external factors, involving changes in ocean and atmosphere circulation, rather than internal glacier dynamics or local changes, such as melting at the glacier bed or snow accumulation on the glacier surface,” said Claus-Dieter Hillenbrand, U.K. lead investigator of THOR and study co-author.

“A significant implication of our findings is that once an ice sheet retreat is set in motion, it can continue for decades, even if what started it gets no worse,” added James Smith, a marine geologist at the British Antarctic Survey and study co-author. “It is possible that the changes we see today on Thwaites and Pine Island glaciers — and potentially across the entire Amundsen Sea embayment — were essentially set in motion in the 1940s.”

Dating of Sediment Cores Plays Key Role in Study

Clark and the team used three primary methods to reach their conclusion. One of those methods was marine sediment core collection that was closer to the Thwaites Glacier than ever before. They retrieved the cores during their trip to the Amundsen Sea near Thwaites in early 2019 aboard the Nathaniel B. Palmer icebreaker and research vessel. The researchers then used the cores to reconstruct the glacier’s history from the early Holocene epoch to the present. The Holocene is the current geological epoch that began after the last ice age, roughly 11,700 years ago.

CT scans were used to take x-rays of the sediment to gather details from its history. Geochronology, or the science of dating earth materials, was then used to reach the conclusion that significant ice melt began in the ’40s.

Clark used 210Pb (lead-210), an isotope that’s naturally buried in the sediment cores and is radioactive, as the most important isotope in her geochronology. This process is similar to radiocarbon dating, which measures the age of organic materials as far back as 60,000 years.

“But lead-210 has a short half-life of about 20 years, whereas something like radiocarbon has a half-life of about 5,000 years,” Clark said. “That short half-life allows us to build a timeline for the past century that’s detailed.”

This methodology is important because although satellite data exists to help scientists understand glacial retreat, these observations only go as far back as a few decades, a time frame that is too short to determine how Thwaites responds to ocean and atmosphere changes. Pre-satellite records are needed for scientists to understand the glacier’s longer-term history, which is why sediment cores are used.

Study Informs Future Modeling to Reduce Uncertainty of Sea-Level Rise

Thwaites Glacier plays a vital role in regulating the West Antarctic ice sheet stability and, thus, global sea-level rise, according to Antarctic researchers.

“The glacier is significant not only because of its contribution to sea-level rise but because it is acting as a cork in the bottle holding back a broader area of ice behind it,” Wellner said. “If Thwaites is destabilized, then there’s potential for all the ice in West Antarctica to become destabilized.”

If Thwaites Glacier were to collapse entirely, global sea levels are predicted to rise by 65 cm (25 in).

“Our study helps to better understand what factors are most critical in driving thinning and retreat of glaciers draining the West Antarctic ice sheet into the Amundsen Sea,” Hillenbrand said. “Therefore, our results will improve numerical models that attempt to predict the magnitude and rate of future Antarctic ice sheet melting and its contributions to sea levels.”

Researchers with THOR are part of an even larger initiative, the International Thwaites Glacier Collaboration, a joint U.S.-U.K. partnership to reduce uncertainty in the projection of sea-level rise from Thwaites Glacier.

The study’s authors are Clark, Wellner and Georgina Garcia-Barrera of the University of Houston; Hillenbrand, James Smith, Robert Larter and Kelly Hogan of the British Antarctic Survey; Rebecca Totten, Asmara Lehrmann and Victoria Fitzgerald of the University of Alabama; Lauren Simkins and Allison Lepp of the University of Virginia; Alastair Graham of the University of South Florida; Frank Nitsche of Columbia University; James Kirkham of the University of Cambridge and the British Antarctic Survey; Werner Ehrmann of the University of Leipzig; and Lukas Wacker of Ion Beam Physics.

Journal Reference:

Rachel W. Clark, Julia S. Wellner, Claus-Dieter Hillenbrand, Rebecca L. Totten, James A. Smith, Lauren E. Miller, Robert D. Larter, Kelly A. Hogan, Alastair G. C. Graham, Frank O. Nitsche, Asmara A. Lehrmann, Allison P. Lepp, James D. Kirkham, Victoria T. Fitzgerald, Georgina Garcia-Barrera, Werner Ehrmann, Lukas Wacker. Synchronous retreat of Thwaites and Pine Island glaciers in response to external forcings in the presatellite era. Proceedings of the National Academy of Sciences, 2024; 121 (11) DOI: 10.1073/pnas.2211711120

https://www.sciencedaily.com/releases/2023/05/230531145123.htm

Ground beneath Thwaites Glacier mapped
Date:
May 31, 2023
Source:
British Antarctic Survey
Summary:
The ground beneath Antarctica’s most vulnerable glacier has now been mapped, helping scientists to better understand how it is being affected by climate change. Analysis of the geology below the Thwaites Glacier in West Antarctica shows there is less sedimentary rock than expected — a finding that could affect how the ice slides and melts in the coming decades.
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FULL STORY
The ground beneath Antarctica’s most vulnerable glacier has been mapped for the first time, helping scientists to better understand how it is being affected by climate change. Analysis of the geology below the Thwaites Glacier in West Antarctica shows there is less sedimentary rock than expected — a finding that could affect how the ice slides and melts in the coming decades.

“Sediments allow faster flow, like sliding on mud,” says Dr Tom Jordan, a geophysicist with the British Antarctic Survey (BAS), who led the study.

“Now we have a map of where the slippery sediments are, we can better predict how the glacier will behave in future as it retreats.”

The distribution of sedimentary rocks beneath the Thwaites glacier is included in a new map of the geology of the region produced by the BAS researchers and published in the journal Science Advances. The findings are important because the glacier, which is the size of Great Britain or the US state of Florida, is one of the fastest changing ice-ocean systems in Antarctica.

The Thwaites glacier’s grounding zone — the point where it meets the seafloor — has retreated 14 km since the late 1990s.

Much of the ice sheet is below sea level and susceptible to rapid, irreversible ice loss that could raise global sea-level by over half a metre within centuries.

The new analysis is based on airborne surveys using aircraft equipped with radar which can see through the ice to the rocks below, as well as sensors which can map minute variations in gravity and magnetism hundreds to thousands of metres below the ground and seabed on which the glacier rests.

The researchers then use these multiple data sources to compile a 3D picture of features, including the type and extent of different rocks.

Jordan says: “The integrated nature of the airborne surveys was one of the keys to this research. Each sensor on the aircraft provided an important but incomplete part of the picture, but by bringing them all together we could provide the detailed map of the underlying geology.”

In doing so, the study effectively turns back the geological clock to examine what happened when New Zealand was ripped away from Antarctica about 100 million years ago — long before the Thwaites glacier was formed.

Because the base of Thwaites Glacier lies far below sea level, researchers had expected that thick sediments would have been deposited there over the subsequent millions of years Similar analysis has been done on some other Antarctic glaciers, showing that these other systems were predominantly underlain by thick sediments.

But the aircraft data suggests that only about a fifth of the ground below the glacier is sedimentary rock.

These lie in a series of basins between 80 and 200 km long and about 30 km wide.

The rest is made up of other types of geological bodies, including granite peaks and other hard rocks.

The scientists think that these sedimentary basins were once much larger, but they have been ground down to the bedrock by movement of the glacier.

It’s not yet clear how this new knowledge of the subglacial geology will affect estimates of ice flow and loss from Thwaites and other glaciers.

The study does show that the geological landscape has a direct control on the basal shear stress, which influences how fast ice can flow into the ocean.

Members of the research team will now carry out more detailed studies of these processes.

Modellers may also be able to use the new data to make more reliable projections of future ice loss.

Jordan says: “We hope that by showing the detailed geology, and how it correlates with the basal friction, future models of glacial retreat will have lower uncertainty, as the controls of the basal processes will be better understood.”

He adds: “No single scientific study could ever match she scale and challenge of climate change. But it is the incremental building of all the individual scientific studies like this that allows us to understand and tackle that challenge.”

Glaciologist Dr Sarah Thompson, co-author on the paper, said:

“The integrated approach used in this study has significant potential for successful application elsewhere in Antarctica, enabling us to explore other potentially vulnerable regions where current knowledge is sparse.”

monkey skipper said:

https://www.sciencedaily.com/releases/2023/05/230531145123.htm

Ground beneath Thwaites Glacier mapped
Date:
May 31, 2023
Source:
British Antarctic Survey
Summary:
The ground beneath Antarctica’s most vulnerable glacier has now been mapped, helping scientists to better understand how it is being affected by climate change. Analysis of the geology below the Thwaites Glacier in West Antarctica shows there is less sedimentary rock than expected — a finding that could affect how the ice slides and melts in the coming decades.
Share:

FULL STORY
The ground beneath Antarctica’s most vulnerable glacier has been mapped for the first time, helping scientists to better understand how it is being affected by climate change. Analysis of the geology below the Thwaites Glacier in West Antarctica shows there is less sedimentary rock than expected — a finding that could affect how the ice slides and melts in the coming decades.

“Sediments allow faster flow, like sliding on mud,” says Dr Tom Jordan, a geophysicist with the British Antarctic Survey (BAS), who led the study.

“Now we have a map of where the slippery sediments are, we can better predict how the glacier will behave in future as it retreats.”

The distribution of sedimentary rocks beneath the Thwaites glacier is included in a new map of the geology of the region produced by the BAS researchers and published in the journal Science Advances. The findings are important because the glacier, which is the size of Great Britain or the US state of Florida, is one of the fastest changing ice-ocean systems in Antarctica.

The Thwaites glacier’s grounding zone — the point where it meets the seafloor — has retreated 14 km since the late 1990s.

Much of the ice sheet is below sea level and susceptible to rapid, irreversible ice loss that could raise global sea-level by over half a metre within centuries.

The new analysis is based on airborne surveys using aircraft equipped with radar which can see through the ice to the rocks below, as well as sensors which can map minute variations in gravity and magnetism hundreds to thousands of metres below the ground and seabed on which the glacier rests.

The researchers then use these multiple data sources to compile a 3D picture of features, including the type and extent of different rocks.

Jordan says: “The integrated nature of the airborne surveys was one of the keys to this research. Each sensor on the aircraft provided an important but incomplete part of the picture, but by bringing them all together we could provide the detailed map of the underlying geology.”

In doing so, the study effectively turns back the geological clock to examine what happened when New Zealand was ripped away from Antarctica about 100 million years ago — long before the Thwaites glacier was formed.

Because the base of Thwaites Glacier lies far below sea level, researchers had expected that thick sediments would have been deposited there over the subsequent millions of years Similar analysis has been done on some other Antarctic glaciers, showing that these other systems were predominantly underlain by thick sediments.

But the aircraft data suggests that only about a fifth of the ground below the glacier is sedimentary rock.

These lie in a series of basins between 80 and 200 km long and about 30 km wide.

The rest is made up of other types of geological bodies, including granite peaks and other hard rocks.

The scientists think that these sedimentary basins were once much larger, but they have been ground down to the bedrock by movement of the glacier.

It’s not yet clear how this new knowledge of the subglacial geology will affect estimates of ice flow and loss from Thwaites and other glaciers.

The study does show that the geological landscape has a direct control on the basal shear stress, which influences how fast ice can flow into the ocean.

Members of the research team will now carry out more detailed studies of these processes.

Modellers may also be able to use the new data to make more reliable projections of future ice loss.

Jordan says: “We hope that by showing the detailed geology, and how it correlates with the basal friction, future models of glacial retreat will have lower uncertainty, as the controls of the basal processes will be better understood.”

He adds: “No single scientific study could ever match she scale and challenge of climate change. But it is the incremental building of all the individual scientific studies like this that allows us to understand and tackle that challenge.”

Glaciologist Dr Sarah Thompson, co-author on the paper, said:

“The integrated approach used in this study has significant potential for successful application elsewhere in Antarctica, enabling us to explore other potentially vulnerable regions where current knowledge is sparse.”

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