A new report published in the journal Geophysical Research Letters reveals how the ocean is weakening ice on the edges of Antarctica and how the Pine Island Glacier is breaking apart from the inside out.
Back in 2015 a nearly 225-square-mile iceberg broke off from the Pine Island Glacier and it was not until now that scientists found the reason behind this. Researchers at Ohio State University saw evidence of a rift formed at the very base of the ice shelf nearly 20 miles inland in 2013 using a new image-processing software. This particular rift propagated upward over the two years from 2013 to 2015 before eventually breaking the ice surface and setting the iceberg adrift.
Researchers say that the images provide one of the first evidence that these large Antarctic ice shelves respond to changes at their ocean edge in a similar way as observed in Greenland. Similar breakups have been observed in Greenland Ice Sheet-in spots where ocean water has seeped inland along the bedrock and begun to melt the ice from underneath.
Authors of the study say that while such rifts are a common occurrence at the margins of an ice shelf, this is the first time that such a rift has been seen originating at the center of the ice shelf and propagating out to the margins. This rift at middle of the ice shelf indicates that there is something that 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.
Another thing worth noting is that the rift opened in the bottom of a “valley” in the ice shelf where the ice had thinned compared to the surrounding ice shelf. The valley is likely a sign of something researchers have long suspected: Because the bottom of the West Antarctic Ice Sheet lies below sea level, ocean water can intrude far inland and remain unseen. New valleys forming on the surface would be one outward sign that ice was melting away far below.
The origin of the rift in the Pine Island Glacier would have gone unseen, too, except that the Landsat 8 images the team were analyzing happened to be taken when the sun was low in the sky. Long shadows cast across the ice drew the team’s attention to the valley that had formed there.
More than half of the world’s fresh water is frozen in Antarctica. The Pine Island Glacier and its nearby twin, the Thwaites Glacier, sit at the outer edge of one of the most active ice streams on the continent. Like corks in a bottle, they block the ice flow and keep nearly 10 percent of the West Antarctic Ice Sheet from draining into the sea.
Studies have suggested that the West Antarctic Ice Sheet is particularly unstable, and could collapse within the next 100 years. The collapse would lead to a sea-level rise of nearly 10 feet, which would engulf major U.S. cities such as New York and Miami and displace 150 million people living on coasts worldwide.
The Pine Island Glacier, part of the ice shelf that bounds the West Antarctic Ice Sheet, is one of two glaciers that researchers believe are most likely to undergo rapid retreat, bringing more ice from the interior of the ice sheet to the ocean, where its melting would flood coastlines around the world.