On the ice shelf, meltwater in the form of slush occurs more frequently than liquid meltwater accumulations in the Antarctic peak summer, but has not yet been sufficiently taken into account in climate models.
With the help of satellite images and artificial intelligence, an international research team led by the University of Cambridge mapped meltwater on 57 Antarctic ice shelves. The results of the study, which were published last week in Nature Geoscience, certainly raise concerns.
Firstly, the team discovered that the amount of meltwater that accumulates on the ice shelf in the height of the Antarctic summer is around twice as large as previously assumed. It was underestimated because almost all previous studies only considered meltwater lakes, but not slush. In the current study, the researchers found that 57 percent of the total meltwater in January is present as slush and the rest in ponds or lakes.
Secondly, their research revealed that the lower albedo of slush and meltwater lakes compared to ice or snow leads to snowmelt that is almost three times greater than predicted by standard climate models.
“This slush has never been mapped on a large scale across all of Antarctica’s large ice shelves, so over half of all surface meltwater has been ignored until now,” said Dr. Rebecca Dell, a scientist at the Scott Polar Research Institute (SPRI) in Cambridge and lead author of the study, in a university press release. “This is potentially significant for the hydrofracture process, where the weight of meltwater can create or enlarge fractures in the ice.”
According to Professor Ian Willis, also a scientist at SPRI and co-author of the study, slush, which is more solid than meltwater, will not cause hydrofractures in the ice shelf in the same way as water. However, slush can be a precursor to meltwater lakes and subsequently lead to hydrofractures, according to the study. It must therefore be taken into account when predicting how or whether an ice shelf will collapse, says Professor Willis.
However, determining what impact slush actually has on the stability of ice shelves is not so easy, as Dr. Dell explains: “We can use satellite imagery to map meltwater lakes across much of Antarctica, but it’s hard to map slush, because it looks like other things, such as shadows from clouds, when viewed from a satellite. But using machine learning techniques, we can go beyond what the human eye can see and get a clearer picture of how slush might be affecting ice in Antarctica.”
To document slush and meltwater lakes on the ice shelves, the researchers used optical data from NASA’s Landsat-8 satellite from 2013 to 2021 and trained a machine learning model that determined the different types of meltwater with a temporal resolution of one month.
“Machine learning allows us to use more information from the satellite, since it can work with more wavelengths of light than the human eye can see,” says Dr. Dell. “This allows us to determine what is and isn’t slush, and then we can train the machine learning model to quickly identify it across the whole continent.”
The amount of meltwater that collects on the ice shelf every summer will therefore increase faster than predicted in the future, with serious consequences for the stability of the ice shelves and the rise in sea level. Only recently, a study in which Professor Willis and Dr. Dell were also involved showed that ice shelves can sink under the weight of meltwater and cracks can form, which can lead to a sudden collapse.
Julia Hager, Polar Journal AG
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