Rebound of Earth’s Mantle May Slow West Antarctic Ice Melt
In a rare piece of good news about the West Antarctic ice sheet, researchers have discovered that far beneath its undeniably melting glaciers, the Earth’s mantle is correspondingly rebounding—an effect which may actually help slow further loss of ice, reports the Washington Post.
“At least since 2014,” writes Post climate reporter Chris Mooney, the news about the ice sheet “has been dire,” with ice loss “nearly tripling in the past 10 years alone.”
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So last week’s discovery of a “possible mitigating factor, one that could slow or even prevent the ice sheet’s full collapse into the ocean,” delighted the American, Dutch, and Danish scientists who went to West Antarctica to measure mantle rebound.
‘It has long been known that the Earth’s crust rebounds as glacial ice lifts from it,” notes the Post: what surprised the researchers was how fast such glacial isostatic adjustment is happening.
Using GPS, the scientists were able to determine that mantle rebound beneath the melting ice sheet is happening very quickly, “at a rapid rate of 41 millimeters per year, or just over 1½ inches.”
This rate of rebound is “way more than we expected,” said Technical University of Denmark researcher and project lead Valentina Barletta.
Barletta and her colleagues contend that this rapid rebound may help counteract the forces driving the ice sheet’s collapse in three ways: reduced contact between the ice sheet and the ocean will mean less ice floating away; elevated underwater surfaces will become sources of friction that catch at melting ice; and, “easing the downward slope of the sea floor beneath the ice could slow its retreat.”
This last counterweight to ice sheet collapse is particularly important, the Post explains, given that the significant pitch of the submarine slope on which the ice sheet sits had been “one reason that West Antarctica was thought to be in unstoppable retreat.”
“In such a situation,” Mooney writes, “the process of ice melting from warm ocean water and retreating backward has a tendency to just keep going.”
That mantle rebound may cause a significant levelling of the submarine slope is “amazing” cause for hope, Barletta noted.
But “precisely how much this uplift will protect ice remains to be seen,” the Post notes, because “West Antarctica’s massive glaciers are being melted by a thick, deep layer of warm ocean water that touches them at their bases,” and far more than an inch or two of rebound per year would be needed to lift them beyond the reach of its melting power.
Still, scientists remain intrigued and hopeful about what the competing forces of melting ice and rebounding mantle will produce. At very least, said University of Arizona geoscientist Christopher Harig, the as yet unknown interaction between “positive feedbacks to the ice itself, such as how surface melt will increase over time,” and “negative feedback from the solid Earth,” makes the future of West Antarctica over the next century “a very complex question.”
Then again, no amount of rebound will “impact the large acceleration in ice loss we’ve seen over the past decade,” Harig cautioned. “This model does change with time, but the changes in the ice we’ve seen are still much greater.”