How explosives, a robot and a sled expose an ‘apocalyptic’ glacier – Mother Jones

Part of the Thwaites Glacier.

Erin Pettit

This story was originally posted by Wired and is reproduced here as part of the Climate office collaboration.

Two Decembers ago Erin Pettit layered up, donned goggles, recorded an audiobook and hiked across the Thwaites Glacier in Antarctica. Behind her, she dragged a sled loaded with ground-penetrating radar, which sent pulses through a thousand feet of ice and analyzed radio waves bouncing off the seawater below, building a detailed picture of the glacier. under his feet. Pettit, a glaciologist and climatologist at Oregon State University, walked alone in the snow, sometimes avoiding headphones for the utter aural silence of Earth’s most remote landscape. “It was actually kind of an amazing, meditative field season,” she says, “I just bundled up, got out and pulled my sled, and just walked miles and miles .”

In case you were worried, his colleagues always knew Pettit’s whereabouts; occasionally someone would ride on a snow machine to bring him supplies or to replace the radar battery. Of course, the team could have covered more ground by towing the radar behind the vehicle, but the vibrations would have introduced noise into the data. And by walking slowly, Pettit was able to maximize the resolution of the radar images. Every night she returned to the camp, downloaded this data and began to analyze it. “And then the next day, I’d go out and do the same thing — take this peaceful, quiet walk,” Pettit says. She walked up to 12 miles a day for over two weeks, for a total of 135 miles. “I was thinking: I’m walking on 300, 400 meters of ice that’s above the ocean, and on this piece of ice that wasn’t likely to be there any longer.”

That’s because Thwaites – aka the Doomsday Glacier – is rapidly deteriorating, losing 50 billion tonnes of ice to the sea every year. Stretching 75 miles along the Antarctic coast, encompassing an area the size of Florida, it is currently responsible for 4% of global sea level rise. (It straddles land and sea: the piece on land is known as an “ice cap,” but where it floats is an “ice shelf.”) If it melted completely, the glacier would not only contribute more than two feet of sea level rise, but as it slid through the ocean, it would also pull on the glaciers around it, further destabilizing them. This would add another eight feet of sea level rise.

Scientists are racing to figure out how Thwaites is decaying and to figure out how long humanity has before it causes disastrous sea level rise. which will greatly accelerate the decline of the rest of the glacier. Each new satellite image of Thwaites shows deeper, longer fractures growing up to six miles a year, and they’re heading into thinner ice.

But the view from above only tells half the story. That’s why Pettit and 100 other scientists from the five-year Thwaites Glacier International Collaboration, funded by the US and UK governments, are also studying the glacier’s hard-to-reach belly. At a meeting of the American Geophysical Union last month, they updated the public on their recent findings. And yes, things are not looking good.

Radar measurements based on Pettit’s sled give an idea of ​​the strength of the underside of the glacier. The radar travels well in solid water but not in liquid water, so when the pulses reached the sea – the relatively warm water that melts the bottom of the glacier – they bounced off the sled. “The place I walk around feels like an endless flat landscape,” says Pettit. “But when you look underneath, it’s a very intricate, intricate landscape that has cliffs and gullies and fractures, and it’s much thinner than the rest of the pack ice.”

Unlike the fractures that satellites have spotted on the surface, these lower cracks don’t appear to be growing rapidly right now, Pettit says, “but they could easily be triggered to spread faster.” That’s because the pack ice loses its grip on an undersea mountain about 30 miles offshore, which acts as a dam, or “pinning point,” holding back the rest of the glacier. But soon this dam will break and the pack ice will break up into icebergs. It will be like a car hitting a pothole, allowing a gash in the windshield to propagate into a network of cracks.

Without a cohesive ice shelf holding it back, the ice sheet on land will hasten its own seaward march, and that of its neighbors. “As the Thwaites Glacier loses mass and flows faster into the ocean, it will pull on nearby glaciers,” Pettit says. Hence the name “Doomsday Glacier”.

Other scientists have turned their attention to the Thwaites Grounding Area, where the glacier transitions from land to floating on water. Peter Washam, oceanographer and climatologist at Cornell University, presented at the conference the results of his last years of work. His team gets an even more detailed image of the underside of the ice with a robot called Icefin, essentially an 11-foot-long science torpedo that a crew lowers through a drilled hole. Tethering the robot allows it to travel more than 2 miles, using sonar and lasers to map the seafloor and the belly of the glacier in three dimensions. It has sensors that measure salinity, temperature, and oxygen, and it uses acoustic pings that bounce off particles in the water column to measure the speed of currents. Basically, Icefin can track down anything scientists want to know about the Thwaites Grounding Area. “It’s your typical on-board instrumentation, all slammed into a small vehicle,” says Washam.

Get a view of any the grounding area is a rarity. “The fact that it was Thwaites was like a gold star on top of that,” he continues. “It gives us an idea as we start to look around Antarctica elsewhere, and Greenland, of what we might expect in those kinds of areas.”

But the news from Icefin does not bode well. Waters warm enough to melt glaciers swirl around Thwaites Anchor Line – the exact point where ice meets land – and that line has receded more than a mile since 2011. This means there now has more seawater in contact with the bottom of the glacier, which means more melting. The ice, Washam says, “is the most chaotic part of it all — it has these sort of really cool wavy, wavy features near the baseline.” These features are melting hotspots.

If Thwaites’ underside were flat, fresh water melting from the ice would collect under it like a lid, insulating it from being further melted by warmer seawater. “It will basically fight the movement of heat from the ocean into the ice,” says Washam. Instead, the undulating and sloping features disrupt the freshwater cover, allowing warmer waters to come into contact with the ice.

The revelation gives glaciologists critical insight into how glaciers anywhere in the world could be degrading – and it’s a factor they haven’t yet factored into modeling. “That kind of other way of melting along these tilted ice surfaces just isn’t in the ice sheet models,” Washam says. “What this shows us is that this is something that needs to be considered if we are to more accurately project Antarctica’s contribution to sea level rise.”

Lizzy Clyne, a geophysicist and glaciologist at Lewis and Clark College, and fellow lecturer, found even more trouble in the grounding area – using explosives, which crews lower into a 20-foot-deep hole in the ice. (“It’s kind of like a firework,” Clyne says. “It would hurt if it exploded in your hand, but it’s not like a giant bomb.”) A network of seismometers at the surface measures how the energy of the explosion bounces off what lies beneath the ice. Using this data, Clyne can see if it is water or solid ground. It works like Pettit’s ground penetrating radar, and indeed Clyne also marries seismic data with radar data.

The data, which Clyne has been collecting since 2018, shows that because part of the Thwaites sea ice floats on the sea, it tilts as the tide rises and falls. As it lifts, warmer water slides through the grounding area and under the ice sheet that sits on land, causing even more melting. This is yet another critical dynamic that is not represented in glacial melt modeling. “There’s this kind of action where you could pull that sea water a few degrees above freezing a little further inland than we initially thought,” Clyne says. “It could be like a few centimeters of water, a little thin layer going further inland. But that’s all it takes to melt the ice.

Now that scientists are piecing together these patterns — ice shelf fractures, the complexity of the glacier’s underside, and tidal pumping — they’ve come up with a grim assessment of Doomsday Glacier: It’s breaking down in more ways that they understood before. If it melted entirely and took the surrounding glaciers with it, the sea level would rise a total of 10 feet. “In my opinion,” Clyne says, “if we’re going to have very rapid sea level rise over the next few decades, that can only happen if Thwaites contributes a lot to it.”

By dragging radars on sleds, piloting torpedo robots and setting off explosives, scientists are building an ever-clearer picture of Earth’s largest glacier. “I don’t have the ability to control sea level rise, and I can’t fix global warming on my own,” Clyne says. “But what we can do is study and understand what is happening, what is going to happen and how to mitigate as much as possible.”

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