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In this illustration, seawater flows deep below the surface toward an actively opening ice shelf crack in Antarctica. New research shows that these cracks can open very quickly and that incoming seawater helps control the rate of ice shelf breakup. Credit: Rob Soto
There is enough frozen water in the glaciers of Greenland and Antarctica that, if they melted, global seas would rise by many feet. What will happen to these glaciers in the coming decades is the biggest unknown in the future of sea level rise, in part because the physics of glacier fracture is not yet fully understood.
A critical question is how warmer oceans could cause glaciers to break up more quickly. University of Washington Researchers have demonstrated the fastest known large-scale breakup along an Antarctic ice shelf. The study, recently published in AGU Advances, shows that a 10.5-kilometer (6.5-mile) crack formed in the Pine Island Glacier, a retreating ice shelf that retains the largest ice sheet in West Antarctica, in about 5 minutes and half. That means the crack opened at about 35 meters (115 feet) per second, or about 80 miles per hour.
“To the best of our knowledge, this is the most rapid crack-opening event ever observed,” said lead author Stephanie Olinger, who conducted the work as part of her doctoral research at the University of Washington and Harvard University. and is now a postdoctoral researcher at Stanford University. . “This shows that, under certain circumstances, an ice shelf can break up. “It tells us to be on the lookout for this kind of behavior in the future and tells us how we might describe these fractures in large-scale ice sheet models.”
The importance of crack formation
A crevasse is a crack that runs through the approximately 300 meters (1,000 feet) of floating ice on a typical Antarctic ice shelf. These cracks are the precursors to ice shelf calving, in which large chunks of ice break off from a glacier and fall into the sea. These events often occur on the Pine Island glacier: the iceberg observed in the study has long since separated from the mainland.
Satellite images taken on May 8 (left) and May 11 (right), three days apart in 2012, show a new crack forming a “Y” branching to the left of the previous crack. Three seismic instruments (black triangles) recorded vibrations that were used to calculate crack propagation speeds of up to 80 miles per hour. Credit: Olinger et al./AGU Advances
“Ice shelves have a really important stabilizing influence on the rest of the Antarctic ice sheet. If an ice shelf breaks up, the ice on the glacier behind it really accelerates,” Olinger said. “This breakup process is essentially how Antarctic ice shelves give birth to large icebergs.”
In other parts of Antarctica, fissures often develop over months or years. But it may happen more quickly on a rapidly evolving landscape like the Pine Island Glacier, where researchers believe the West Antarctic Ice Sheet has already passed a turning point in its collapse into the ocean.
Challenges in observing glacial changes
Satellite images provide continuous observations. But satellites in orbit pass by each point on Earth only every three days. What happens during those three days is harder to pin down, especially in the dangerous landscape of a fragile Antarctic ice shelf.
For the new study, the researchers combined tools to understand the formation of the crack. They used seismic data recorded by instruments placed on the ice shelf by other researchers in 2012 with radar observations from satellites.
Glacier ice acts like a solid on short time scales, but is more like a viscous liquid on long time scales.
“Is crack formation more like breaking glass or breaking Silly Putty? That was the thing,” Olinger said. “Our calculations for this event show that it is much more like breaking glass.”
The role of seawater and future research
If the ice were simply a brittle material, it should have broken down even faster, Olinger said. Additional research pointed to the role of seawater. Seawater in the crevices keeps the space open against the internal forces of the glacier. And since seawater has viscosity, surface tension and mass, it cannot fill the void instantly. Instead, the rate at which seawater fills the opening crack helps slow the crack’s expansion.
“Before we can improve the performance of large-scale ice sheet models and projections of future sea level rise, we must have a good physics-based understanding of the different processes that influence shelf stability. of ice,” Olinger said.
Reference: “Ocean coupling limits the breakup rate of the fastest observed ice shelf breakup propagation event” by Stephanie D. Olinger, Bradley P. Lipovsky and Marine A. Denolle, February 5, 2024, AGU Advances.
DOI: 10.1029/2023AV001023
The research was funded by the National Science Foundation. Co-authors are Brad Lipovsky and Marine Denolle, both members of the Earth and Space Sciences faculty at the University of Washington who began advising on the work while at Harvard University.