The threat from Thwaites: The retreat of Antarctica's riskiest glacier

by British Antarctic Survey

Thwaites ice cliff. The glacier currently contributes four percent of annual global sea level 

rise. Credit: Rob Larter, BAS

Antarctica's Thwaites Glacier is retreating rapidly as a warming ocean slowly erases its ice from below, leading to a faster flow, more fracturing and a threat of collapse, according to an international team of scientists. The glacier currently contributes four percent of annual global sea level rise. If it does collapse, global sea levels would rise by several feet—putting millions of people living in coastal locations in danger from extreme flooding.

Dr. Peter Davis, Physical Oceanographer at British Antarctic Survey (BAS), says: "Thwaites Glacier in West Antarctica is a river of ice the size of Great Britain that has been changing dramatically over the past 30 years. The speed at which it flows into the ocean has doubled, and there are fears that a complete collapse of the glacier could raise sea levels by over 60cm. Critically, the glacier is currently held back by an ice shelf, a floating extension of the glacier that is held in place by an underwater mountain.

Recent research as part of the International Thwaites Glacier Collaboration has shown that this ice shelf is under attack from all sides. It is being melted from below by warm ocean waters, causing it to lose its grip on the underwater mountain. At the same time, massive fractures are forming and growing across the ice shelf surface. The research suggests that at the current rate of change, this critical ice shelf will begin to break apart within the next two decades, with severe consequences for the stability of Thwaites Glacier and ultimately sea level here in the UK."

Thwaites field camp. Thwaites Glacier is retreating rapidly as a warming ocean slowly

 erases its ice from below. Credit: BAS

The International Thwaites Glacier Collaboration is a collaboration between UK and US scientists, involving over 60 scientists and students. This five year project is aimed at collecting instrument data throughout the glacier and the adjacent ocean, and modeling ice flow and the future of the ice sheet. Their work has revealed major changes in the ice, the surrounding water and the area where it floats of the bedrock below. The ITGC It is one of BAS' flagship projects and several of our science and support staff are currently being deployed for the start of the 2021–2022 field research season.

Thwaites sits in West Antarctica, flowing across a 120km stretch of frozen coastline. A third of the glacier flows more slowly than the rest—it's braced by a floating ice shelf which prevents faster flow of the upstream ice. But the brace of ice slowing Thwaites won't last for long, said Erin Petitt, an associate professor at Oregon State University. Beneath the surface, warmer ocean water circulating beneath the floating eastern side is melting the ice directly from beneath. This floating extension of the Thwaites Glacier will likely only survive a few more years.

Peter Davis, whose team use hot water to drill access holes from the surface of the ice shelf to the ocean cavity hundreds of meters below, adds: "Warm water is also a threat for the so-called 'grounding zone,' the area where the glacier lifts off the seabed. The ocean waters in the grounding zone are warm, by polar standards, and salty, and this generates prime conditions for melting the ice shelf from beneath."

Credit: British Antarctic Survey

Peter Washam, a research associate at Cornell University, also studies the grounding zone. His team lowered a remote-controlled underwater robot through the borehole to take measurements of the ocean, ice and seafloor in this region. They mapped these properties up to the point where the ice and seafloor came in contact. Washam describes the grounding zone as "chaotic," with warm water, rugged ice, and a steep, sloping bottom that allows the water to quickly melt the ice sheet from below.

Upstream of here, researchers have found that water is pumped under the ice sheet by tides. Lizzy Clyne, an adjunct professor at Lewis and Clark College, and their team study the tidal pumping mechanism that physically forces warm water between the ice and bedrock at Thwaites. The floating portion of the glacier rises and falls with the tides—and that motion acts like a lever, pumping water under the ice sheet. Also, downstream of the grounding zone on the bottom of the floating ice shelf, constant stretching and melting is rapidly creating long channels through the ice where water can flow, impacting the long term stability of the ice shelf, said Clyne.

As Thwaites retreats upstream and into the ice sheet, it may form very tall ice cliffs at the ocean front. Anna Crawford, a postdoctoral researcher at the University of St. Andrews, and her team use computer modeling to study ice cliff failure: a process by which ice can break off the ends of the glacier into the open ocean. The process can take on many forms, but all of them could lead to very rapid retreat of the massive glacier. The bedrock shape of West Antarctica makes the region vulnerable to rapid retreat via ice-cliff failure, as increasingly tall cliffs could be exposed as the ice retreats. This could lead to a chain-reaction of fracturing, resulting in collapse, said Crawford. A challenge for the team is assessing if, when, and how fast this might occur, but major ice loss is possible within several decades to a few centuries.

Thwaites Glacier is one of Antarctica’s most unstable glaciers. Credit: Jeremy Harbeck

Ted Scambos, a senior research scientist at the Cooperative Institute for Research in Environmental Sciences (CIRES) says: "If Thwaites were to collapse, it would drag most of West Antarctica's ice with it, so its critical to get a clearer picture of how the glacier will behave over the next 100 years. "

ITGC research, including future sea-level projections, will be vital for policy makers in their efforts to mitigate and adapt to the impacts of global sea level rise.Scientists find record warm water in Antarctica, pointing to cause behind troubling glacier melt

More information: For more information, see thwaitesglacier.org/

Provided by British Antarctic Survey 

Warming seas are carving into glacier that could trigger sea level rise

New research provides a startling look at how warmer 

oceans, driven by climate change, are gouging the 

West Antarctic’s Thwaites Glacier

By Chris Mooney

Updated February 15, 2023

A robot called the Icefin operates under the sea ice near McMurdo Station, an Antarctic research station. (Schmidt-Lawrence/NASA PSTAR RISE UP)

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Rapidly warming oceans are cutting into the underside of the Earth’s widest glacier, startling new data and images show, leaving the ice more prone to fracturing and ultimately heightening the risk for major sea level rise.

Using an underwater robot at Thwaites Glacier, researchers have determined that warm water is getting channeled into crevasses in what the researchers called “terraces” — essentially, upside-down trenches — and carving out gaps under the ice. As the ice then flows toward the sea, these channels enlarge and become spots where the floating ice shelf can break apart and produce huge icebergs. If the remaining shelf is further undermined, Thwaites Glacier will flow into the ocean faster and boost global sea levels on a large scale.

A team deploys the Icefin at Thwaites Glacier in January 2020. (Andrew Mullen/International Thwaites Glacier Collaboration)

Warm water carves underwater crevasses into glacier

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Underwater video taken of the Thwaites Glacier in Antarctica in January 2020 shows carvings of potential break points beneath the glacier. (Video: International Thwaites Glacier Collaboration)

The results from overlapping teams of more than two dozen scientists, published Wednesday in two papers in the journal Nature, reveal the extent to which human-caused warming could destabilize glaciers in West Antarctica that could ultimately raise global sea level by 10 feet if they disintegrate over the coming centuries.

Scientists with the International Thwaites Glacier Collaboration, a historic scientific collaboration organized by the United States and the United Kingdom, arrived at one of the safest spots to land on the West Antarctic behemoth in 2019 and 2020, and used hot water to drill through nearly 2,000 feet of ice to the ocean below.

Here, in a region known as the eastern ice shelf, they deployed an ocean sensor at the base of the floating ice shelf and sent down an 11-foot-long pen-shaped robot called Icefin. The vessel collected data and images in an environment in which warm ocean water, in some places more than 2 degrees Celsius above the local freezing point, is weakening the glacier.

The biggest revelation was that the ice melt is very uneven, with relatively slow loss in flat areas on the underside of the glacier. But the warm water entering Thwaites Glacier’s crevasses poses a serious threat, according to Britney Schmidt, a Cornell University scientist who is the lead researcher behind Icefin and deployed it with a group of 12 other researchers who encamped on the ice.

“The warm water is getting into the weak spots of the glacier, and kind of making everything worse,” Schmidt said.

“It shouldn’t be like that,” Schmidt continued. “That’s not what the system would look like if it wasn’t being forced by climate change.”

The new observations emerge from what is the very definition of an extreme environment. In this part of Thwaites Glacier — perhaps its most stable region — 1,900-foot-thick ice lifts upward from the seafloor and spreads over the ocean. Where the ice first departs from the seafloor is called the “grounding line” — the three-dimensional intersection of ice, ocean and bedrock. Outward from there, the floating ice creates a dark cavity that warm seawater and some fish can enter — but that humans cannot.

Underwater robot deployed beneath Antarctic glacier

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The Icefin underwater robot was deployed beneath the Thwaites Glacier in Antartica in January 2020 to measure ice melt beneath the surface of the glacier. (Video: International Thwaites Glacier Collaboration)

That’s why the observations from Icefin — which scientists pulled back up the borehole after the experiments and can be deployed again — are so unprecedented and revealing. “That’s the first time we’ve had data from that kind of environment, for Thwaites or any other glacier,” Schmidt said.

They give breathtaking details of what it looks like beneath the glacier.

Near the grounding line, video from the robot shows an underside of the ice that is dark and grainy because seafloor mud and sediment is frozen into it. Further downstream, the robot observed sand and pebbles falling out of the ice as it melted.

Within the crevasses and terraces, the robot captured video of scalloped side walls that resemble a round coffered ceiling.

“The technical achievement of getting this amazing range of data in a very difficult environment, and getting out safely, is just wonderful,” said Richard Alley, a glaciologist at Penn State who was not directly involved in the research.

The unique data and images come from what is arguably the most important ocean-facing glacier of them all — at least so far as humans are concerned.

The Icefin at Kamb Ice Stream after being pulled from the water. (Schmidt-Lawrence/NASA PSTAR RISE UP)

Antarctica’s Thwaites Glacier in 2019. (Jeremy Harbeck/OIB/NASA)

Thwaites is some 80 miles across and is the exit point for an area of ice larger than Florida. It is, essentially, the heart of West Antarctica, so large that if lost, it could be replaced only by a new Thwaites Sea.

Thwaites has been losing ice at an accelerating pace, based on data provided by Eric Rignot, one of the studies’ co-authors, at the University of California at Irvine.

The rate of loss overall since 1979 has been a little less than 20 billion tons per year, but that has increased to more than 40 billion tons since 2010, according to the data Rignot provided.

“This robot is getting to the hard places where we need to go to understand the future of the continent,” Rignot said. “We cannot understand what we cannot observe and measure.”

The terraced and scalloped features are generally not included in the simulations, or models, which attempt to forecast what the all-important Thwaites Glacier system will do in the future, the new research noted.

That’s critical because as the ice flows outward over the ocean — that is why this part of the glacier is called an ice shelf — crevasses that begin at the grounding line grow and develop over the course of this motion.

“This melting that starts right at the grounding line in crevasses is really important for what happens downstream,” Schmidt said. “Downstream, where it’s falling apart, these crevasses become these giant features.”

In the main trunk of Thwaites — where the seafloor is deeper and the glacier’s movement much faster, and which is difficult to safely reach — the floating ice shelf has largely collapsed. In the calmer eastern region, where the research took place, it is still intact but features large cracks.

In both regions, the grounding line of the glacier is retreating toward the center of Antarctica. And in both regions the glacier is out of balance, meaning it is getting thinner, and losing more ice to the ocean than is being replaced by flow from the inland parts of Antarctica.

A borehole drilling site on the Thwaites Glacier is seen in 2022. (Peter Davis/British Antarctic Survey)

When it comes to the Icefin robot, “my hope is that we will have a chance to take it to [the] main trunk of Thwaites, which is harder to get to, but also more important (deeper, warmer, moving faster, etc.),” Rignot said in an email. “These studies show it can be done and that we learn enormously from it.”

There was some good news in the research: In areas measured beneath Thwaites that were not characterized by crevasses and terraces, the melt rates were fairly slow. That’s because cold fresh meltwater created a protective layer that insulated the ice from the warmer water below — which could mix up into the crevasses but was thwarted in the more linear environment. Thus, nearly a third of melting occurred in the crevasses, the scientists calculated.

And the slower melt rate outside of them is not much consolation, considering that this slow rate may not be characteristic of the faster-changing part of Thwaites, and at any rate does not change the fact that the glacier is losing ice and retreating.

“What the results show is that you don’t need a large increase in melting to drive rapid retreat,” said Peter Davis, a researcher with the British Antarctic Survey who led a second paper published with Schmidt’s by a largely overlapping team of scientists. “You just need to shift it out of equilibrium.”

Scientists consulted by The Washington Post had different readings of what the new research means for our overall understanding of what Thwaites Glacier will do to coastlines in our coming lifetimes.

For Ted Scambos, a glaciologist at the University of Colorado, the results from the International Thwaites Glacier Collaboration dampen somewhat the fear of catastrophic collapse of the glacier any time soon. It is retreating and that may not be stoppable, Scambos said, but the pace will still be manageable in coming decades.

“While we might see only a moderate add-on to sea level rise in the next 50 years, the processes are real, and the triggers for accelerating the collapse are bound to occur,” he said. “But we have also seen how to apply the brakes, what parts of the climate and ocean system are the main drivers, and what makes them drive. … We have some time to get this under control. Otherwise, the century of our grandchildren’s children will be very, very difficult.”

Alley, the glaciologist at Penn State, had a somewhat different overall outlook — that at least we are finally learning how these gigantic glaciers work.

“Overall, these papers don’t really change my level of worry about Thwaites collapse or not,” Alley said. “But the papers increase my optimism that we can make sense of this incredibly difficult and important system, and improve our ability to project what it may do in the future.”

New results provide close-up view of melting underneath Thwaites Glacier

New data from an international expedition and underwater robot Icefin beneath the remote Thwaites Glacier in Antarctica

Peer-Reviewed Publication

BRITISH ANTARCTIC SURVEY

The rapid retreat of Thwaites Glacier in West Antarctica appears to be driven by different processes under its floating ice shelf than researchers previously understood. Novel observations from where the ice enters the ocean show that while melting beneath much of the ice shelf is weaker than expected, melting in cracks and crevasses is much faster. Despite the suppressed melting the glacier is still retreating, and these findings provide an important step forward in understanding the glacier’s contribution to future sea-level rise.

Two papers in the journal Nature this week (15 February 2023) provide a clearer picture of the changes taking place under the glacier, which is the size of Great Britain or the US state of Florida and is one of the fastest changing ice-ocean systems in Antarctica. Results show that although melting has increased beneath the floating ice shelf, the present rate of melting is slower than many computer models currently estimate.

A layer of fresher water between the bottom of the ice shelf and the underlying ocean, slows the rate of melting along flat parts of the ice shelf.  But the authors were surprised to see the melting had formed stair-case-like topography across the bottom of the ice shelf. In these areas, as well as in cracks in the ice, rapid melting is occurring. 

Thwaites Glacier is one of the fastest changing glaciers in Antarctica: the 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 data were collected as part of the MELT project, one of the projects in the UK-US International Thwaites Glacier Collaboration, one of the largest international field campaigns ever undertaken in Antarctica. The MELT team undertook observations of the grounding line (where the ice first meets the ocean) beneath the Thwaites Eastern Ice Shelf in order to understand how the ice and ocean interacts in this critical region.

Dr Peter Davis of the British Antarctic Survey (BAS) took ocean measurements through a 600m deep borehole around two kilometres from the grounding line, created by a hot water drill in late 2019. These measurements were compared with melt rate observations taken at five other sites underneath the ice shelf. Over a nine-month period, the ocean near the grounding line became warmer and saltier but the melt rate at the ice base averaged 2-5 m per year: less than previously modelled.

Dr Peter Davis, who’s an oceanographer at BAS and lead author on one of the studies, says:

“Our results are a surprise but the glacier is still in trouble. If an ice shelf and a glacier is in balance, the ice coming off the continent will match the amount of ice being lost through melting and iceberg calving. What we have found is that despite small amounts of melting there is still rapid glacier retreat, so it seems that it doesn’t take a lot to push the glacier out of balance.”

Dr Britney Schmidt, of Cornell University in the US, and a team of scientists and engineers deployed a robot called Icefin through the 600m deep borehole.  The vehicle is designed to access such grounding zones that were previously almost impossible to survey. The observations Icefin made of the seafloor and ice around the grounding zone provide more detail on the picture of how melting varies beneath the ice shelf. They found the staircases, called terraces, as well as crevasses in the ice base are melting rapidly. Melting is especially important in crevasses, as water funnels through them heat and salt can be transferred into the ice, widening the crevasses and rifts.

So, although the vertical melting along the base of the ice shelf was less than expected, melting along sloped ice in these cracks and terraces is much higher and may be a significant factor in ice loss across Thwaites Glacier, especially as major rifts are progressing across the ice shelf and may become the primary trigger for ice shelf collapse.

Dr Britney Schmidt, who’s an Associate Professor at Cornell University and lead author of the second study, says:

“These new ways of observing the glacier allow us to understand that it’s not just how much melting is happening, but how and where it is happening that matters in these very warm parts of Antarctica. We see crevasses, and probably terraces, across warming glaciers like Thwaites.  Warm water is getting into the cracks, helping wear down the glacier at its weakest points.”

Issued by the Press Office at British Antarctic Survey for the International Thwaites Glacier Collaboration (ITGC)

Emily Newton, communications officer, mobile +44 (0) 7517 466407; emiton@bas.ac.uk

Athena Dinar, UK ITGC communications lead, mobile: +44 (0)7909 008516; email: amdi@bas.ac.uk

Notes to Editors

There are a lot of great images and footage to accompany these papers and to illustrate these results. This includes the MELT camp on Thwaites Glacier from the 2019/20 field season, the hot water drill rig, the Icefin robot being deployed, moving images down the borehole through the ice shelf and footage of under the ice near the grounding line showing the ‘staircase’ like topography of the ice. It’s all saved here: https://files.bas.ac.uk/photo/Thwaites-Glacier/Icefin-robot/ and caption information is included in this folder. Images should include the name of the photographer and should be credited as ‘Pete Davis, ITGC’ or similar. There is an animation showing the grounding line that was produced by ITGC but can be used to illustrate how the glacier is melting from below.

Heterogeneous melting near the Thwaites Glacier grounding line by B. E. Schmidt1,2 ✉, P. Washam1,2, P. E. D. Davis3 , K. W. Nicholls3 , D. M. Holland4,5, J. D. Lawrence6 , K. L. Riverman7 , J. A. Smith3 , A. Spears6 , D. J. G. Dichek1,2, A. D. Mullen1,2, E. Clyne8,9, B. Yeager5 , P. Anker3 , M. R. Meister1,2, B. C. Hurwitz6 , E. S. Quartini1,2, F. E. Bryson1,2,6, A. Basinski-Ferris4 , C. Thomas3 , J. Wake3 , D. G. Vaughan3 , S. Anandakrishnan8 , E. Rignot10, J. Paden11 & K. Makinson3 is published in the journal Nature.

Suppressed basal melting in the eastern Thwaites Glacier grounding zone by Peter E. D. Davis1 ✉, Keith W. Nicholls1, David M. Holland2,3, Britney E. Schmidt4, Peter Washam4, Kiya L. Riverman5,6, Robert J. Arthern1, Irena Vaňková1, Clare Eayrs3, James A. Smith1, Paul G. D. Anker1, Andrew D. Mullen4, Daniel Dichek4, Justin D. Lawrence7, Matthew M. Meister4, Elisabeth Clyne8,9, Aurora Basinski-Ferris2, Eric Rignot10,11, Bastien Y. Queste12, Lars Boehme13, Karen J. Heywood14, Sridhar Anandakrishnan8 & Keith Makinson1 is published in the journal Nature.

This mission is part of the International Thwaites Glacier Collaboration (ITGC), a five-year, $50 million joint U.S. and U.K. mission to learn more about Thwaites Glacier, its past, and what the future may hold. Find out more here: www.thwaitesglacier.org

Thwaites Glacier, covering 192,000 square kilometres (74,000 square miles)—an area the size of Florida or Great Britain—is particularly susceptible to climate and ocean changes. Computer models show that over the next several decades, the glacier may lose ice rapidly, as ice retreats. Already, ice draining from Thwaites into the Amundsen Sea accounts for about four percent of global sea-level rise. A run-away collapse of the glacier would contribute around an additional 65cm (25 inches) to sea-level rise over the coming centuries.

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