According to a new study in the journal Geophysical Research Letters, a major glacier in Antarctica is breaking up from the inside out, implying the surrounding ocean is deterioration ice on the edges of the continent.
The Pine Island Glacier, part of the ice shelf that borders the West Antarctic Ice Sheet, is one of a pair glaciers that scientists suspect are going through rapid shrinkage, shipping more and more ice from the interior of the ice sheet to the ocean, where its melting would sink coastlines around the planet.
An approximately 225-square-mile iceberg broke off from the glacier, an event known as calving, in 2015, but it wasn’t until scientists at The Ohio State University were testing out new image-processing software that they found something strange in satellite pictures taken before the calving event.
In the pictures, they saw evidence that a rift created in 2013 at the very base of the ice shelf almost 20 miles inland. The rift propagated upward over two years, until it broke through and set the iceberg adrift over 12 days in late July and early August 2015.
“It’s generally accepted that it’s no longer a question of whether the West Antarctic Ice Sheet will melt, it’s a question of when,” study author Ian Howat, associate professor of earth sciences at Ohio State, sadi in a news release. “This kind of rifting behavior provides another mechanism for the rapid retreat of these glaciers, adding to the probability that we may see a significant collapse of West Antarctica in our lifetimes.”
Although this is the first time scientists have noted a deep rift opening below the Antarctic ice, they have seen comparable breakups in the Greenland Ice Sheet – in locations where ocean water has bled inland along the bedrock and started to melt the ice from below.
Howat said the satellite pictures offer the first strong proof that these large Antarctic ice shelves react to variations at their ocean edge, in a manner also detected in Greenland.
“Rifts usually form at the margins of an ice shelf, where the ice is thin and subject to shearing that rips it apart,” he explained. “However, this latest event in the Pine Island Glacier was due to a rift that originated from the center of the ice shelf and propagated out to the margins. This implies that something weakened the center of the ice shelf, with the most likely explanation being a crevasse melted out at the bedrock level by a warming ocean.”
The study team also noted the rift happened in the bottom of the “valley,” where the ice had thinned. The valley is probably an indication of something scientists have long warned about: Since the bottom of the West Antarctic Ice Sheet sits below sea level, ocean water can stream inland and remain hidden to observers. New valleys developing on the top of the glacier would be one apparent sign that ice was melting away far below.
The source of the rift in the Pine Island Glacier would have gone hidden, too, except the Landsat 8 pictures Howat and his team were examining happened to be captured when the sun was low in the sky. Long shadows across the ice attracted the team’s attention to the valley that had formed.
“The really troubling thing is that there are many of these valleys further up-glacier,” Howat said. “If they are actually sites of weakness that are prone to rifting, we could potentially see more accelerated ice loss in Antarctica.”
Image credit: NASA/Nathan Kurtz
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