- The first detailed maps from underneath an ice shelf in Antarctica have revealed previously unknown shapes and melting patterns.
- While researchers are yet to fully understand what causes the patterns in ice erosion, they say it indicates new information about how oceans are melting ice.
- The scientists involved in the study deployed an autonomous vehicle that traveled underneath the ice and used multibeam sonars to map the underside of the ice shelf.
- Ice shelves are floating masses of ice attached to land mass; while their melting doesn’t directly contribute to sea level rise, it can destabilize glaciers and cause them to flow faster.
When Anna Wåhlin and her colleagues deployed a submersible vehicle to go under the ice in Antarctica, they meant for it to serve as a proof of concept for the technology.
Instead, what they found has left them more mystified than ever.
The first detailed maps from the underside of the Doston Ice Shelf in Antarctica revealed patterns that couldn’t be explained by existing models. On one side of the ice shelf, areas where the ice had melted were shaped like teardrops. The other side, however, resembled landscapes on ice.
“When we saw the first teardrop, we thought ‘Oh, that’s a really funny shape,’ but then we saw more and more and they were everywhere in the western side,” Wåhlin, an oceanographer and professor at the University of Gothenburg in Sweden, told Mongabay in a video interview. On the eastern side, Wåhlin said it was much more dramatic, with “thick shapes carved into the ice that looked a little bit like the Grand Canyon where the water had eaten away into the ice.”
A study co-authored by Wåhlin and published in the journal Science Advances documents how the team developed and deployed the autonomous underwater vehicle that traveled more than 1,000 kilometers (620 miles) back and forth under the Doston Ice Shelf over the course of 27 days in 2022. The study was conducted as part of a project monitoring how atmospheric and oceanic processes impact ice shelves.
Ice shelves are floating masses of ice attached to glaciers or ice sheets on land. Simply put, they are protrusions from the landmass that have water flowing underneath them. Since they have more contact with the air above and water below, they melt faster than glaciers and ice sheets. Their melting doesn’t directly contribute to sea level rise since they’re already floating on the sea. However, it does cause the glaciers they’re attached to on land to destabilize and flow faster, which in turn leads to rising sea levels. A study published in 2004 showed that glaciers melt up to six times faster following the collapse of an ice shelf. Therefore, figuring out how ice shelves are melting is imperative to understanding and predicting sea level rise.
“They’re like cork in a bottle,” Wåhlin said. “If we can understand how that cork is getting looser, that will help us understand how sea level rise will happen in the future.”
Traditionally, ice shelves have been studied and monitored using satellites or radar technology, both of which give very scant data about the underside of the ice shelves. While submersible vehicles have previously been deployed to map ice shelves, Wåhlin’s work has yielded possibly the most detailed and high-resolution data yet.
The work commenced in 2015 and it took the team years and several trials to develop the sensor-equipped vehicle. Named Ran, the vehicle had sensors measuring temperature, salinity and dissolved oxygen. The highlight, however, was the two multibeam sonars: one pointed toward the seabed and the other pointed up toward the bottom side of the ice shelf. “When it moves over, it’s like illuminating a dark room with a flashlight, but with sound instead,” Wåhlin said.
The multibeam sonars helped the scientists create maps and understand what the ice shelves were shaped like underneath, including shedding light on the teardrop-shaped areas where ice had melted, as well as the other shapes carved into the ice. “If it had been all flat, we wouldn’t have learned so much,” Wåhlin said. “But what we saw tells us something about the way the ocean melts the ice.”
Ice melts when there’s relatively warmer water moving underneath it. As it melts, the freshwater that’s produced acts like a protective layer between the ice and the warmer, saline water underneath. Turbulence caused by other factors mixes the freshwater with the saltwater, causing the ice to melt further.
“What we have learned [from the patterns] is that there’s something else happening as well,” Wåhlin said. “In addition to the turbulence-driven melt, there appears to be some other type of melt going on where the heat gets into the ice without that big, large-scale turbulence.”
While it requires further research, the team has hypothesized that the teardrop-like erosions in the ice shelf — ranging from 20-300 meters (66-990 feet) in length — are shaped by fast ocean currents that flow near the ice, as well as by the Earth’s rotation. Wåhlin said they would need more data and better computer models and laboratory experiments to figure out the exact cause of these patterns.
Earlier this year, the researcher deployed the underwater vehicle again to gather more data on the ice shelf. However, during the process, the vehicle disappeared under the ice, underscoring the challenges of conducting research in the region.
Wåhlin, however, said she’s hopeful about similar missions that are preparing to carry the work forward. She also emphasized the huge trove of data and samples collected by her team during the mission which, she said, can further improvise how ice shelves are studied and analyzed.
“We have loads of data that will take several years to process and analyze,” she said. “Our hope is that this data will be taken by many other scientists and be used to develop newer models.”
Banner image: An ice shelf and the sea in Greenland. Image by Bob Brewer via Unsplash (Public domain).
Abhishyant Kidangoor is a staff writer at Mongabay. Find him on 𝕏 @AbhishyantPK.
Antarctic warming alters atmosphere, ice shelves, ocean & animals
Citations:
Wåhlin, A., Alley, K. E., Begeman, C., Hegrenæs, Ø., Yuan, X., Graham, A. G., … Heywood, K. J. (2024). Swirls and scoops: Ice base melt revealed by multibeam imagery of an Antarctic ice shelf. Science Advances, 10(31). doi:10.1126/sciadv.adn9188
Scambos, T. A., Bohlander, J. A., Shuman, C. A., & Skvarca, P. (2004). Glacier acceleration and thinning after ice shelf collapse in the Larsen B embayment, Antarctica. Geophysical Research Letters, 31(18). d>oi:10.1029/2004gl020670
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