The Thwaites Glacier’s fractures were identified in satellite imagery.Credit: NASA
Giant fractures in the floating ice of Antarctica’s massive Thwaites Glacier — a fast-melting formation that has become an icon of climate change — could shatter part of the shelf within five years, research suggests. If that happens, in what had been considered a relatively stable part of Thwaites, the glacier could release an armada of icebergs and begin flowing much faster into the ocean, funnelling ice that had been resting on land into the sea, where it would contribute to sea-level rise.For decades, scientists have carefully tracked changes in the Thwaites Glacier, which already loses around 50 billion tonnes of ice each year and causes 4% of global sea level rise. The recently identified fractures are deep, fast-moving cracks in Thwaites’ eastern ice shelf (see ‘Cracking up’). They appeared in satellite images over the past few years and their growth seems to be accelerating.’I visualize it somewhat similar to that car window where you have a few cracks that are slowly propagating, and then suddenly you go over a bump in your car and the whole thing just starts to shatter in every direction,’ said Erin Pettit, a glaciologist at Oregon State University in Corvallis, at the American Geophysical Union (AGU) meeting on 13 December. If Thwaites’ eastern ice shelf collapses, ice in this region could flow up to three times faster into the sea, Pettit says. And if Thwaites were to collapse completely, it would raise sea levels by 65 centimeters.
Brink of changePettit will describe the work on 15 December at the AGU meeting in New Orleans, Louisiana. It is the latest finding from the five-year, US$50-million International Thwaites Glacier Collaboration, an initiative funded by the US and UK governments to study and understand the threat of how Thwaites might contribute to rising sea levels in a warming world.’We have been expecting that ice shelf to fail, and that’s one of the reasons that there has been such a coordinated international effort to study Thwaites — it’s big and important, but it’s also been clearly poised on the brink of change,’ says Kirsty Tinto, a geophysicist at the Lamont-Doherty Earth Observatory in Palisades, New York, who has studied Thwaites. The latest work, she says, reveals more about how ice shelves fail. ‘Understanding those processes helps us to understand not just Thwaites, but also all the rest of Antarctica, past, present, and future,’ she says.Mountain braceThwaites flows off the Antarctic continent into the Southern Ocean. At 120 kilometres across, it is the world’s widest glacier. Across about two-thirds of that expanse, ice flows relatively quickly into the ocean. The remaining one-third is the eastern ice shelf, where ice had been flowing relatively slowly1. In part, that’s because the ice grinds to a halt when it reaches an underwater mountain about 40 kilometers offshore. The submerged mountain holds back the ice flow like a cork in a bottle.Earlier this year, members of the Thwaites collaboration reported that the glacier is becoming unstuck from that mountain, causing cracking and fracturing across other parts of the ice shelf23. Previous studies4,5 have also shown hints of instability across Thwaites’ eastern ice shelf. ‘It’s been something to keep an eye on for a long time,’ says Matthew Siegfried, a glaciologist at the Colorado School of Mines in Golden, Colorado.The fractures caught the attention of Pettit and her colleagues two years ago, as they were looking through satellite images to figure out where to set up camp for the season. One crack, nicknamed ‘the dagger’, was even headed straight towards the proposed camp site. It wasn’t moving fast enough for the scientists to relocate their work, but ‘we actually all just had to take a pause’, said Pettit. ‘It still was hugely surprising to me that this was rapidly changing that fast.’The fractures are propagating through the ice at speeds of several kilometres per year. They are heading into weaker and thinner ice, where they may accelerate and lead to the demise of this part of the Thwaites ice shelf within five years, Pettit estimates.’There’s going to be a dramatic change in the front of the glacier,’ said Ted Scambos, a glaciologist at the Cooperative Institute for Research in Environmental Sciences in Boulder, Colorado. ‘It will accelerate the pace and effectively widen the dangerous part of the glacier.’Warm water flowsHow exactly the changes might happen isn’t clear, says Siegfried, because many factors influence how ice shelves fall apart. Those include how rapidly warm water melts the bottom of the floating part of the glacier, and the geometry of how ice, land and water interact.One of the collaboration’s recent discoveries at Thwaites is that ocean tides cause the floating part of the glacier to rise up at high tide and drop down at low tide. That up-and-down ‘tidal pumping’ — long suspected but rarely observed in detail — causes the glacier to flex further upstream, including in the region where it flows off land and into the water. Seismic and radar data from the Thwaites work have shown that because of this flexing, warm water might be able to intrude beneath the glacier more easily, said Lizzy Clyne, a glaciologist at Lewis & Clark College in Portland, Oregon. ‘The existence and possible rapid formation of these features could have implications for the long-term stability of the ice shelf,’ they said.The Thwaites collaboration completed its most extensive field research season in 2019–20, before the COVID-19 pandemic interrupted the project last year. This Antarctic winter, which is under way, several research teams are again descending onto the ice to take measurements at different locations across the glacier.A major research cruise in February aboard the US icebreaker Nathaniel B. Palmer will also study the ocean directly in front of the glacier’s floating edge.Each visit underscores how fast Thwaites is changing. Seeing this huge ice shelf moving at you at about a mile every year is unsettling, said Scambos. ‘And all by itself, this one glacier is big enough to impact sea level significantly.’ 1.Alley, K. E. et al. Cryosphere 15, 5187–5203 (2021). Google Scholar 2.Benn, D. I. et al. Preprint at Cryosphere Discuss. (2021).3.Wild, C. T. et al. Preprint at Cryosphere Discuss. (2021).4.Tinto, K. J. & Bell, R. E. Geophys. Res. Lett. 38, L20503 (2011). Google Scholar 5.Kim, J.-W. et al. GIScience & Remote Sens. 52, 498–509 (2015). Google Scholar Download references
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