Technology The West Antarctic Ice Sheet Seems to Be Good at Collapsing

21:11  13 june  2018
21:11  13 june  2018 Source:   nationalgeographic.com

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The West Antarctic Ice Sheet , which holds enough water to raise global seas by several feet, is thinning. The good news is that while the word " collapse " implies a sudden change, the fastest scenario is 200 years, and the longest is more than 1,000 years.

“The retreat of this ice seems to be unstoppable.” And the collapse of the Thwaites and its bordering glaciers could lead to the loss of the entire West Antarctic Ice Sheet , like removing the keystone from a bridge.

Scientists have discovered that the West Antarctic Ice Sheet underwent a major retreat between 10,000 and 12,000 years ago, at a time when the world was actually cooler than it is today. The collapse happened at the close of the last Ice Age, and it left the ice sheet 135,000 square miles smaller than it is today – a difference nearly as large as the state of Montana.

“That the ice sheet could retreat beyond where it is today, in a climate that was likely quite a bit colder than today, points to extraordinary sensitivity,” says Robert DeConto, a glaciologist at the University of Massachusetts Amherst, who was not involved in the research.

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16 thoughts on “ Is the West Antarctic Ice Sheet collapsing ?” Nice post overall, but your use of conditional language seems hard to justify given the findings of the two papers. Neither lead author has been so hesitant about the irreversibility.

Explore further: West Antarctic Ice Sheet collapse is under way. But you're right --since the fact of AGW has been established, even presenting the denier argument seems like troll-baiting. rwinners. 2.3 / 5 (3) May 26, 2014.

Most researchers had believed that the West Antarctic ice sheet hadn’t been much smaller than it is now for at least 120,000 years. “We were really surprised,” says Reed Scherer, of Northern Illinois University in DeKalb, who co-authored the new paper, published today in the journal Nature, with nine other scientists.

West Antarctica is considered the most vulnerable of Earth’s three major ice sheets. It rests in a deep, broad bowl that dips thousands of feet below sea level – exposing it to warm ocean currents. It would raise sea level by 11 feet if it collapsed.

(Read more here about the threat from melting Antarctic ice.)

Scientists hope that by reconstructing the past advances and retreats of the West Antarctic ice sheet, they can predict its future fate amid global warming.

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What's more, its disappearance will likely trigger the collapse of the rest of the West Antarctic ice sheet , which comes with a sea level rise of between three and five metres. Such an event will displace millions of people worldwide. Two centuries – if that is what it takes – may seem like a long time

Anyway, it just seems to me that even for those who do not believe this is man made, it seems to me, it is just healthier to have cleaner air and cleaner water Global Warming, Pollution, and Politics - Discussion by Theaetetus. Forums. » West Antarctic Ice Sheet Is Collapsing .

Another paper published in the same issue of Nature confirmed the urgency: It found that Antarctica as whole lost more than 3 trillion tons of ice between 1992 and 2017. Most of that came from West Antarctica, where the rate of ice loss has tripled in the last quarter century.

A Half-Mile Deep Hole

Axl Rose et al. sitting in the snow: In 2013 scientists drilled through the West Antarctic ice sheet into a subglacial lake—and found evidence that the ice sheet had once been much smaller.© Photograph by JT Thomas, SwiftTern Productions In 2013 scientists drilled through the West Antarctic ice sheet into a subglacial lake—and found evidence that the ice sheet had once been much smaller. The new evidence of West Antarctic fragility stems from two research expeditions that visited the region in the last several years. Scherer was part of the first one. It began in January 2013, as a convoy of tractors, towing a million pounds of equipment on massive sleds, arrived at a remote spot on the ice sheet, just 380 miles from the South Pole. The place seemed unremarkable – nothing but flat, wind-sculpted snow in every direction.

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‘Unstoppable collapse ’ of the west antarctic ice sheet is not happening. Dr. Don J. Easterbrook, Western Washington University, Bellingham, WA. May 19, 2014.

Their collapse threatens the entire West Antarctic Ice Sheet . Rising seas. The good news is that sea-level rise will be relatively small in the coming centuries, according to the Thwaites Glacier model published today in the journal Science.

The expedition’s true objective lay half a mile beneath the surface: a body of water, called Lake Whillans, sealed under the ice sheet. The lake’s outline had been mapped with ice-penetrating radar. No human had ever laid eyes on it. But that January, the equipment on those sleds was assembled into a monstrous drill that, with a jet of hot water, melted a hole, 20 inches wide and 2,600 feet deep – straight through the ice, and into the lake.

Scherer and his colleagues plunged a hollow cylinder into the bottom of the lake, and hoisted up 18 inches of mud – gritty stuff, full of the fragments of Antarctic bedrock, pulverized by sliding ice. When Scherer viewed that mud through a microscope, he found it littered with delicate shards of curved, dimpled glass: the ancient shells of diatoms, tiny marine creatures that had lived in this place at a time when it was covered not by ice, but by ocean – perhaps with a bit of ice floating on top.

Carbon-dating of the mud showed that some of those diatoms had been deposited in what is now Lake Whillans as recently as 10,000 years ago—which was startling enough. But Scherer and his colleagues tested mud from nine other holes inland from Lake Whillans, as far as 120 miles from the present ice edge. They found young material in every single one. “That was the real shocker,” says Scherer.

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Modelling result: West Antarctic Ice Sheet collapsed during last interglacial. While this might seem obvious, it is no matter of course for the

Hence, they concluded "there is good evidence that the strongly negative trends at these outlet glaciers, the mass balance of the corresponding drainage basins, and the overall mass balance of the west Antarctic ice sheet may be related to increased basal melting caused by ocean temperature

It suggested that the West Antarctic ice sheet had pulled back at least 120 miles. But even that is “just a lower limit,” says glaciologist Slawek Tulaczyk of the University of California at Santa Cruz, who co-led the drilling expedition.

Since glaciers constantly drag along the mud at their base as they flow toward the coastline, he explains, the young mud in the boreholes could have come from as far as 300 to 400 miles inland—meaning that 10,000 years ago the edge of the ice sheet may have been as far inland as that.

Tell-tale Scars

Even as Scherer, Tulaczyk and their colleagues grappled with these surprises, another scientist, unbeknownst to them, was making his own discovery.

Jonathan Kingslake, a young glaciologist now at the Lamont-Doherty Earth Observatory in New York, spent two months in late 2014 camping on the opposite side of West Antarctica, 800 miles from Lake Whillans. Driving snowmobiles roped together in a single line—lest one of them plunge into a crevasse—he and his guide towed a sled carrying an ice-penetrating radar. As they traveled, sometimes 15 hours a day, the radar traced internal layers and cracks hidden thousands of feet down in the ice.

In his tent one night, reviewing the day’s data on his laptop, Kingslake saw something intriguing. The radar’s black and white traces showed a series of bright lines rising from the bottom of the ice.

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As Eugene WR Gallum points out, the West Antarctic ice sheet most certainly did NOT collapse during those earlier warm periods –… So now someone has to subtract the additional snow that seems to be fall in East Antarctica . http

And here's a 2005 article from the magazine: [2]: The massive west Antarctic ice sheet , previously assumed to be stable, is starting to collapse , scientists warned on Tuesday. It might be a good idea to label the satellite picture that's currently there. Otherwise, what's the point?

Those lines, he ultimately decided, were the scars of old cracks that had opened, long ago, at the bottom of the ice sheet—at a time when it wasn’t thick and sitting on bedrock, as it is now at that place, but thinner and floating on the ocean. The cracks had formed as the ice skidded and juddered over a subglacial mountain. Then they had filled with seawater and refrozen.

On the far side of West Antarctica from where Scherer and Tulaczyk worked, Kingslake had found independent evidence that the ice sheet had once retreated far inland. Reviewing all the evidence, Torsten Albrecht of the Potsdam Institute for Climate Impact Research in Germany estimated that the retreat happened 10 to 12 thousand years ago. Compared with the present, Albrecht calculates, West Antarctica contributed roughly 30,000 cubic miles of ice to sea level rise— equal to 130 trillion tons.

Rebound Won't Save Us

How fast sea level rises in the next century will depend a lot on how fast the West Antarctic ice sheet crumbles.© Photograph by Mario Tama, Getty Images How fast sea level rises in the next century will depend a lot on how fast the West Antarctic ice sheet crumbles.

At that time, the ice sheet was already in the midst of shrinking from its Ice Age maximum, when it extended 600 miles further out to sea than it does today. And the ocean floor sat at least 1,300 feet lower than it does today—because the weight of the massive ice sheet had pressed down on the Earth’s crust.

As the ice retreated, thinned, and floated, this allowed warm ocean currents to slither in along the deep ocean floor. That melted the ice ever more rapidly, sending the ice sheet into full-blown collapse. It roared right past its present-day boundaries, retreating at least 120 miles further inland than today.

This runaway collapse was eventually halted by slow changes in the Earth’s crust. The removal of all that ice allowed the crust to rebound upward. Researchers calculate that the seafloor under the ice sheet rose as quickly as 7 inches per year, or more than 1,300 feet over the course of several thousand years. This sheltered the remaining ice from the deep ocean currents that were melting it, allowing it to stabilize, re-advance, and eventually reach its present-day size—perhaps as little as 2,000 years ago.

As the planet warms today, will this sort of glacial rebound protect us from a wholesale collapse of the West Antarctic ice sheet, and the catastrophic sea-level rise that would result? Since temperatures and atmospheric carbon dioxide levels are already far higher than they were 10,000 years ago, and still rising, Tulaczyk warns, the glacial retreat and rebound observed back then can’t simply be extrapolated to the future.

But in any case, glacial rebound is too slow a process to be a comfort to humans. It would not rescue coastal cities from sea level rise, Tulaczyk says, “unless we are willing to hold our breath for thousands of years underwater.”

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