When Andreas Fickner painted fiber options cables into deep holes in Greenland's ice, he didn't expect to discover an entirely new way that glaciers could move. Even when Cable began sending data, his initial response was skeptical.
“Garbage” and Dr. Fichtner, professor of seismology and wave physics at the University of Switzerland, remembers the idea. “Some electronic noise.”
This was August 2022. Greenland's field season is almost over. Cold, altitude, long hours – all of that was worn by Dr. Fichtner and his fellow researchers. However, they had saved one of the cables for the last one experiment. It allowed us to measure small movements deep inside the vast rivers of ice as they flow towards the ocean.
What they find raises questions about scientists' assumptions about how the Greenland and Antarctic ice sheets are operating and are being added to sea levels around the world.
That last cable picked up a tiny cascade of “ice trembling.” Some of them echoed hundreds of feet, Dr. Fichtner and his colleagues reported in Journal Science on Thursday.
These earthquakes appeared to have started near impurities in the ice that had been deposited by the volcanic eruptions, Dr. Fichtner said. When these particles are sitting, the ice is weak and easily cracked. Along these cracks, ice moves, slips and trembles, creating small earthquake disturbances.
This is not something scientists would normally imagine it happening in deep ice mountains that cover Earth's polar regions. Usually they think this ice flows like syrup. Slow, smooth, fluid.
But he said if the ice really moved like uniform honey, Dr. Fichtner's cable would have picked up “complete silence.” Instead, he recorded these “really, really strange events,” he said. “That was a surprise here.”
By sending laser pulses through fiber optic cables and measuring how they scatter, scientists can reconstruct fine movements along the entire length of the cable. This has been proven to be useful for monitoring seismic activity, deep sea currents, glacial ice, and more.
In Greenland, Dr. Fichtner and his colleagues hand-down the cables nearly a mile down the borehole. The cable lay there for 14 hours, picking up vibrations.
If you are wrapping and rewinding a cable, let Dr. Fichtner know first, if it doesn't sound particularly challenging. It was “serious physical work.” The boreholes were filled with a special kind of vegetable oil, so they were not closed, so the cables were slow to sink, heavier, and lifted. Furthermore, the cable has become brittle due to the Sub-Zero cold. This means that it had to be handled with the utmost care.
When Dr. Fichtner began to watch the recitation of his return, he had to be certain of himself that they weren't “trash.” What happens if you show vibrations from the cable itself? Or from a crack formed in the wall of a borehole?
Eventually he and his team concluded that they had recorded something unique to the ice. Still, Dr. Fichtner acknowledged that only by taking more measurements in more places can scientists really say how these earthquakes occur within ice sheets.
Getting adequate measurements is a constant challenge, says Hélène Seroussi, an engineering professor at Dartmouth University in New Hampshire, who is not involved in new research. When oceanographers want to collect data, they can drop their instruments into the deep sea in just a few hours. Glacier researchers must dig deep into the ice.
“That's why all of these new principles and mechanisms continue to find all the mechanisms that seem relatively basic,” Dr. Seroussi said. “Every time you have a new observation, a new ice core, a new method of measuring, you learn something new.”
Andy Ashwanden, a glaciologist at the University of Alaska Fairbanks University, said the discoveries of Dr. Fichtner and his colleagues provide a glimpse into the complexity of ice physics. But he said it's too early for scientists to know if a melted ice sheet will help scientists to predict more quickly how quickly the world's ocean levels will rise. According to Dr. Aschwanden, the ice still carries other mysteries that are likely to improve modeling.
Richard B. Ally, a professor of geoscience at Pennsylvania State University, said new discoveries could help scientists better understand how sheets of ice fall apart at their edges.
Existing defects or ice damage can cause them to break rapidly when they run off land and exit into the ocean. It's easy to open fast food ketchup packets when you do it from a small notch, but it's very difficult to try to tear it elsewhere, he said.
“All us who study ice,” Dr. Ally said, “We'll build on this new paper for a long time.”
