Most concerns about ice melting in Antarctica have focused on the west coast, where ice is enough to raise sea levels by up to 4.3 feet. But new research suggests that the huge Ross ice shelf, which has been considered stable, may be at risk as well – potentially leading to a slower sea-level rise of up to 38 feet, such as the glaciers previously held by the platform . quickly into the ocean. Researchers suspect that other crucial ice shelves may also be at risk.
"My main concern is that the melting and collapse potential of large ice shelves is not taken seriously," said Laurie Padman, a physical oceanographer in Corvallis, Oregon, who works at a Seattle-based non-profit organization called Earth and Space . Search. "They are being treated as less important because they are not currently showing much signs of change, but over a 100-year period, they have the potential for major changes."
The fragile Antarctic support system
The Ross Ice Shelf is the world's largest ice shelf. Located next to Antarctica closest to New Zealand, it occupies an area the size of Spain and has an average thickness of approximately 1,300 feet. It is one of many ice shelves that extend into the ocean from the edge of Antarctica, with about 90% of its volume submerged.
The melting of these ice shelves has no direct effect on global sea levels as ice is already in equilibrium with the surrounding water. But ice shelves greatly slow the flow of glaciers on the continent that would otherwise slide faster into the ocean, causing water levels to rise.
The idea that ice shelves hold ice is not just theoretical. In 2002, Antarctica's Larsen B ice shelf collapsed in less than a month, and then some of the adjacent glaciers accelerated by up to eight times.
The collapse of Larsen B shocked scientists, as no one had realized that an ice shelf could disappear so quickly, said Anna Hogg, a glaciologist at the University of Leeds in England. It was triggered by puddles of water that formed on the surface of the ice shelf. The water leaked into fissures and forced them to open in a process known as hydrofracture.
Hydrofracture is one of two mechanisms considered to be responsible for most of the ice loss in Antarctica. The other mechanism happens when deep, warm ocean currents flow away under an ice shelf, eroding the "earth line," where it connects to earth.
That is what is happening with the small ice shelves of the Amundsen Sea on the west coast of Antarctica, Padman said. Measurements by satellites over the last 26 years have shown that these ice shelves have sank, indicating that some are shrinking by as much as 7 meters (about 23 feet) a year. As a result, the glaciers they support – which contain enough ice to raise global sea levels by more than one meter and four – are flowing rapidly into the sea.
A new way to melt
Satellite measurements suggest that the Ross ice shelf has remained stable over the past decades, even growing thicker in certain regions. But over the past four years, Padman has co-led a multi-institutional collaboration called ROSETTA-Ice to study Ross Ice Shelf more closely. Last month, at the meeting of the American Geophysical Union in Washington, he presented some of the first discoveries of various studies that are part of the project.
ROSETTA-Ice researchers have constructed a computerized model of the interconnected factors that control the Ross ice shelf, including seasonal conditions, ocean currents, and the structure of ice and rock bed on the adjacent continent. The model is based on data collected by the ROSETTA-Ice team using instruments mounted on aircraft and submarine robots.
The findings suggest that a point on the northwest side of the ice shelf is melting in a way that researchers have not seen before – neither hydrocracking nor deep currents in the ground line. Instead, Ross's problem is seasonal masses of warm water near the surface of the ocean in front of the ice shelf.
In winter, a sea ice crust – much thinner than the ice shelf itself – covers the ocean in front of the shelf. But in summer, sea ice melts and dark water absorbs solar energy and warms water down. This surface of warm water then erodes the northwest corner of Ross's ice shelf, corroding the ice under the lip and causing small icebergs to collapse from its edge.
"What [Padman’s] What has been shown is that on the Ross ice shelf there are some regions that have very high melt rates at the front, on the front of the ice shelf, as opposed to the ground line where we could normally look, "Hogg said. was not involved in the research.
What does this mean for sea level
The lost ice is currently being replaced by ice flowing down from the mainland, so the shelf is still not getting thinner. But it can easily begin to decrease as the weather continues to warm up, and current projections do not take into account the processes that the ROSETTA-Ice team has observed, Padman said.
Most of the ice from the grounded glacier being trapped by the Ross ice shelf should not melt so soon, in part because it is also held in place by the shape of mountains and valleys, Padman said. But the melted corner of the Ross is located right in front of a particularly vulnerable range of ice on the mainland.
"It turns out it's in the right area, where if you dilute the ice shelf you will have an effect on the amount of grounded ice coming into the ocean," Padman said.
Even in the worst case scenario, the Ross melt will not cause a sudden jump in sea level over the next few decades, Padman said. But over the centuries or millennia, the changes can be massive. Researchers are working to estimate how fast they can occur.
It is possible that other ice shelves in Antarctica also have stains that are melting rapidly due to the warming of the summer surface, Padman said. For example, no one has yet sought such a process on the Filchner-Ronne Ice Shelf, a giant ice shelf that presently prevents the formation of glaciers that could raise sea levels by about 45 feet if they melt completely.
"We're seeing a new process that we really did not think was a problem before," Hogg said. "There's no reason why the things they're seeing on Ross's ice shelf are not applicable elsewhere."
[This story was originally published on Inside Science]