Model correctly identifies glaciers at risk of collapse due to climate change – Is it increasing because of it?
Meltwater seeps beneath Arctic glaciers making the risk of sudden collapse the thickest and fastest
UNIVERSITY OF CALIFORNIA, BERKELEY
CREDIT: WHYJAY ZHENG, UC BERKELEY
As climate change warms the planet, glaciers are melting faster, and scientists fear that many will collapse by the end of the century, raising sea levels and flooding coastal cities. seas and islands.
A University of California, Berkeley scientist has now created an improved model of glacier motion that can help pinpoint which Arctic and Antarctic glaciers are more likely to slide rapidly downhill and fell into the ocean.
New model, published last week in the magazine Cryosphere, which combines the effects of meltwater into the glacier’s bottom and lubricates its downhill runoff. The new physical model predicts that the most vulnerable glaciers are the thickest with a history of faster flows, even if that rapid flow is cyclic.
“The model shows that thick, fast-flowing glaciers are more sensitive to lubricating oil than thin, slow glaciers,” Whyjay Zheng, a postdoctoral fellow in the UC Berkeley Department of Statistics. “Data from the Greenland glaciers support this new finding, suggesting that those fast and thick glacial monsters may be more unstable than we thought under global warming.”
Zheng built the new model to incorporate a more important mechanism for global warming: meltwater seeps into the bottom of glaciers and lubricates their downhill movement across the bedrock. The Arctic and Antarctic have warmed more than the rest of the world – in March, Antarctica saw a record 70 degrees Fahrenheit above normal, while parts of the North The pole is 60 degrees warmer than average. Warmer weather causes melt lakes to form on many glaciers, especially in Greenland. Lakes can penetrate the bottom of glaciers by a process called hydraulic fracturing, or escape to the bottom through nearby openings.
Glaciologists have found that the rate at which glaciers rise and fall is related to what is happening in front of the glaciers, where the ice mixes into the ocean and meets warmer water. Observations show that for so many sea-terminal glaciers, as the front glaciers melt, or emptied into the ocean, the remaining glaciers tend to accelerate. As the facades enter the ocean, the glaciers slow down. Therefore, the focus is mainly on what is happening at the terminal.
But basic lubrication with molten water appears to be creating a feedback loop that accelerates glaciers that have accelerated for other reasons, such as terminal changes.
“In Greenland, the speed of the glacier is mostly controlled by the terminus position: If the terminus is retreating, the glacier will accelerate; if the terminus advances, the glacier will slow down,” said Zheng. “People think this is probably the main reason why the glaciers in Greenland can speed up or slow down. But now, we’re starting to think there’s another and possibly faster way to slow glaciers or speed them up – that’s basic lubrication.”
So Zheng set out to modify the common perturbation model of glacier flow to account for the lubrication of molten water, using standard equations for fluid flow.
He tested the model’s predictions on glaciers in Greenland, a part of Denmark, and in Svalbard, an archipelago of Norway. The prediction that thicker, faster-moving glaciers tend to thin out and empty into the ocean is consistent with observations of glacier flow over a 20-year period, from 1998 to 2018.
“Basic lubrication creates a positive feedback loop,” says Zheng. “Faster glaciers are more likely to respond more quickly to basic lubrication, and the subsequent rapid rise makes them more susceptible to future lubrication. For example, if a glacier flows 3 km per year and there is sudden ground lubrication, it will react so quickly that you can see fluctuations in speed, maybe just days later, compared to Another glacier will flow at 100 meters per year. ”
The implication is that thick, fast-moving glaciers around the North and South Poles should be regularly monitored, just as glaciers are now monitored for terminus changes, to predict the release of icebergs. into the ocean can affect sea levels. Zheng says there needs to be better ways to measure base lubricity.
“If the glacier has the potential to break down in the short term and draw a lot of ice into the ocean, perhaps within a year or two, that could be something we have to worry about,” he said.
Zheng, who has a background in geophysics, planetary science and remote sensing, was first interested in the basic lubrication of glaciers after studying an ice cap in the Siberian Arctic – the Vavilov Ice Cap on Russian island of Severnaya Zemlya – suddenly collapsed. In the past few years, there was a time in 2015 that accelerated to 9 km / year. After analyzing the event, he determined that the stationary ice cap’s transition to an ice stream – a fast-flowing glacier – in such a short period of time was due to basic lubrication and the sending of the terminal into the ocean. , reducing friction at the front. of the glacier is holding the glacier back. About 11% of the ice flowed into the ocean between 2013 and 2019.
“This is the first time we’ve seen such a large ice cap collapse,” he said. “Once it started accelerating, it maintained speed for a long time. We think one of the most likely reasons is that it creates a lot of cracks in the surface, and those cracks are pipes that carry surface meltwater down to the bottom of the glacier. The water now descends more easily and effectively reduces friction, so the glacier can continue to slide rapidly and even faster if the climate warms.”
Zheng plans to test the new model on several sea-ending glaciers in Antarctica. Meanwhile, through a new online platform called Jupyter Book, anyone can run Zheng’s data through model equations and Python code to reproduce his results – a standard. publishing standard that he hopes will become commonplace for big data research in the future.
Work supported in part by Jupyter meets the Earth projectfunded by the EarthCube program of the National Science Foundation (1928406, 1928374).
JOURNEYS
Cryosphere
DOI
RESEARCH METHODS
Simulation / computational modeling
RESEARCH SUBJECTS
Do not apply
ARTICLE TITLE
Glacier shape and flow rate determine how Arctic sea-terminating glaciers respond to lubricated strata
ARTICLE PUBLICATION DATE
April 21, 2022
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