A newly discovered feedback loop may be accelerating the melting of the West Antarctic Ice Sheet, according to a study published in Science Advances. This effect may be pushing up global sea levels as a result.
The West Antarctic Sheet has been losing ice for decades, causing the sea level to rise. If it melts completely, the global sea level will increase by about five meters. Researchers know that the Circumpolar Deep Water (CDW) — a water mass that is 4°C above freezing temperatures —flows directly beneath the ice shelves and melts them from below. Given that much of the West Antarctic Ice Sheet sits below sea level, it is highly vulnerable to these warmer waters and may further retreat in the future.
Previous models showed that undercurrents move this warm water to cavities under the ice shelves, but researchers didn’t really know how until now. Using high-resolution simulations, a team of researchers from the University of Southampton, UK, unveiled a positive feedback loop that increases the formation of more warm water.
“Our findings suggest a positive feedback loop: as the ice shelf melts more rapidly, more freshwater is produced, leading to a stronger undercurrent and more heat being transported toward the ice shelves. This cycle could speed up the melting of ice shelves, potentially making the West Antarctic Ice Sheet less stable in the future,” said Professor Alberto Naveira Garabato, from the University of Southampton, a coauthor of the paper.
“These simulations reveal that this deep current conveying warm waters toward the ice shelves is driven by the very same ice shelf melting that such warm waters cause,” added Dr Alessandro Silvano, also from the University of Southampton.
The new model suggests that when warm water interacts with the ice shelf, it melts the ice and mixes with the melted freshwater. Eventually, this water starts to rise and creates a swirling motion upwards. If there is a water trough — an underwater valley — near the coast, this swirling movement is carried away from the ice shelf cavity toward the edge. This movement then drives a current along the slope of the seafloor, directing more warm water toward the ice shelf. As more ice melts, the current gets stronger, carrying even more warm water toward the ice shelf.
“Scientific models that don’t include the cavities under ice shelves are probably overlooking this positive feedback loop. Our results suggest it’s an important factor that could affect how quickly ice shelves melt and how stable the West Antarctic Ice Sheet is over time,” concluded Dr Silvano.
Si Y et al. Antarctic Slope Undercurrent and onshore heat transport driven by ice shelf melting.Sci. Adv.10,eadl0601(2024).DOI:10.1126/sciadv.adl0601