During the peak of summer, slush, which is water-soaked snow, constitutes over 50% of the total meltwater on the Antarctic ice shelves. However, regional climate models inadequately consider its presence.
A team of researchers, spearheaded by the University of Cambridge, utilized artificial intelligence methods to chart the distribution of slush on Antarctic ice shelves. Their findings indicate that 57% of all meltwater exists in the form of slush, while the remaining portion is present in surface ponds and lakes.
With the rising temperatures, the surface of ice shelves generates more meltwater. These ice shelves, which surround Antarctica and serve as a support against glacier ice from the interior, can become unstable or collapse due to increased meltwater. Consequently, this can lead to a rise in sea levels.
The scientists also discovered that slush and gathered meltwater lead to 2.8 times greater meltwater formation than anticipated by standard climate models, as it absorbs more heat from the sun compared to ice or snow. The findings, published in the journal Nature Geoscience, could have significant implications for the stability of ice shelves and the rise in sea levels.
Every summer, as the temperature rises, water accumulates on the surfaces of Antarctica’s floating ice shelves. Previous studies have indicated that surface meltwater lakes can contribute to the fracturing and collapse of ice shelves, as the weight of the water can cause the ice to bend or break. However, determining the role of slush in ice shelf stability is more challenging.
“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,” said lead author Dr. Rebecca Dell from Cambridge’s Scott Polar Research Institute (SPRI). “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.”
The researchers at Cambridge, in collaboration with teams from the University of Colorado Boulder and the Delft University of Technology, utilized optical data from NASA’s Landsat 8 satellite. They employed a machine learning model to extract monthly data on slush and meltwater lakes from 57 Antarctic ice shelves spanning the period from 2013 to 2021.
“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,” said 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.”
“We’re interested in learning how much slush is present during the Antarctic summer and how it’s changed over time,” said co-author Professor Ian Willis, also from SPRI.
The researchers utilized their machine learning model to discover that during the peak of the Antarctic summer in January, a majority (57%) of the meltwater on Antarctica’s ice shelves exists as slush, while the remaining 43% forms as meltwater lakes.
“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 Dell. “This is potentially significant for the hydrofracture process, where the weight of meltwater can create or enlarge fractures in the ice.”
Meltwater has an impact on the stability of the floating ice shelves bordering the Antarctic coastline. With rising temperatures and increased melt rates in Antarctica, meltwater, whether in the form of lakes or slush, has the potential to seep into cracks in the ice, leading to their expansion. This process can result in the formation of fractures in the ice shelf, potentially causing vulnerable ice shelves to collapse. This collapse could subsequently lead to inland glacier ice flowing into the ocean, contributing to the rising sea levels.
“Since slush is more solid than meltwater, it won’t cause hydrofracture in the same way that water from a lake does, but it’s definitely something we need to consider when attempting to predict how or whether ice shelves will collapse,” said Willis.
The impact of slush on hydrofracture has significant implications, and it also influences the rate of melting. Due to their lower reflectivity compared to snow or ice, slush and lakes absorb more solar heat, leading to increased snowmelt. This additional melting is not currently considered in climate models, potentially resulting in underestimated forecasts for ice sheet melting and ice shelf stability.
“In the future, it’s likely that places in Antarctica that currently don’t have any water or slush will start to change,” said Willis. “As the climate continues to warm, more melting will occur, which could have implications for ice stability and sea level rise.”
Journal reference:
- Rebecca L. Dell, Ian C. Willis, Neil S. Arnold, Alison F. Banwell & Sophie de Roda Husman. Substantial contribution of slush to meltwater area across Antarctic ice shelves. Nature Geoscience, 2024; DOI: 10.1038/s41561-024-01466-6