The glaciers Pine Island in Thwaites on the west coast of Antarctica are among the largest on the continent. Together they have an area of more than 120,000 square kilometers, or 4 times the area of Belgium.
The Amundsen Sea where the Pine Island and Thwaite glaciers come out, source: NASA
Under the pressure of global warming
In recent decades they have come under increasing pressure due to global warming. Scientists currently estimate their share of the sea level rise at 5 percent, or 5 millimeters over 40 years. But if they continue to calve, the entire west coast of Antarctica can become disrupted. This could lead to a much greater rise in sea level, up to a few meters even.
The piece of ice that the Pine Island glacier has lost in recent years is outlined in yellow. Source: ESA
The glaciers are lined by pack ice that acts as a buffer or a brake. “You can compare it to a slow car on the highway that stops traffic,” explains research leader Stef Lhermitte from. But that buffer is weakening. Cracks appear in the ice shelf in front of the glacier. The cracks and fissures form further from the edge of the ice so that larger and larger pieces crumble. This makes the glacier less stable.
2 degrees above freezing
That process has become very clear in the last twenty years with the help of satellite technology. “We know that these glaciers are important for the future,” says Stef Lhermitte, “but these images show ice shelves in a very bad condition.” One of the mechanisms is that relatively warm water flows underneath the ice shelves and gnaws at the plates from below, causing them to become thinner and cracked.
Cracks at the edge of the Pine Island Glacier, source: NASA
That relatively warm water flows under the ice shelf has been discovered by British and American scientists. They have drilled a hole 600 meters deep in the Thwaites glacier. At the bottom, the temperature of the water turned out to be 2 degrees above freezing. For such a depth in such a place it is exceptionally warm.
“With your feet in the water”
In addition, the bottom on which the glaciers rest is below sea level. “The glaciers have their feet in the water and that makes them less stable,” says Lhermitte. The glaciers are thus under pressure on the coastline, but also at the bottom, at the base.
satellite images of the ever-growing crumbling of the ice shelves around Pine Island and Thwaite Glacier, source: NASA
The speed with which the crumbling takes place is also striking. In 1972, the Pine Island glacier slowly began to retreat. But from 2000 that process accelerated. The glacier lost icebergs every six years. After that it went even faster, with calving every two years.
The quality of the ice has also changed. Video images show how icebergs immediately crumble as if they were sugar cubes: “In six years, the glacier has shrunk by almost a third, an area the size of Los Angeles. We are seeing the first signs of the disappearance of the Pine Island ice shelf. The damage will be difficult to repair ”, Lhermitte concludes.
The study led by Stef Lhermitte with glaciologist Frank Pattyn (VUB), among others, was published in Proceedings of the National Academy of Sciences.