The autonomous underwater vehicle, Ran, was sent beneath the Dotson ice shelf in West Antarctica to scan the ice using advanced sonar technology. Over 27 days, Ran traveled more than 1,000 kilometers beneath the glacier, reaching 17 kilometers into the ice shelf cavity. Ice shelves are floating masses of glacial ice fed by land-based glaciers.

"We have previously used satellite data and ice cores to observe how glaciers change over time. By navigating the submersible into the cavity, we were able to get high resolution maps of the ice underside. It's a bit like seeing the back of the moon," says lead author Anna Wahlin, Professor of Oceanography at the University of Gothenburg.

In a recent Science Advances paper, the team detailed their findings. Predictably, the glacier melts faster where strong underwater currents erode its base. Using the submersible, scientists measured these currents beneath the glacier for the first time, explaining why the western part of Dotson Ice Shelf melts so rapidly. They also found significant melting at vertical fractures extending through the glacier.

Unexpectedly, the glacier's base featured peaks, valleys, plateaus, and dune-like formations, likely shaped by flowing water influenced by Earth's rotation.

Complex areas
Karen Alley, a glaciologist from the University of Manitoba and co-author of the study, emphasized the importance of these findings:

"The maps that Ran produced represent a huge progress in our understanding of Antarctica's ice shelves. We've had hints of how complex ice-shelf bases are but Ran uncovered a more extensive and complete picture than ever before. The imagery from the base of Dotson Ice shelf helps us interpret and calibrate what we see from the satellites," says Karen Alley.

Future missions will explore the numerous processes beneath glaciers that remain unknown.

"The mapping has given us a lot of new data that we need to look at more closely. It is clear that many previous assumptions about melting of glacier undersides are falling short. Current models cannot explain the complex patterns we see. But with this method, we have a better chance of finding the answers," says Anna Wahlin.

Dotson Ice Shelf, part of the West Antarctica ice sheet, significantly impacts future sea level rise due to its size and location.

"Better models are needed to predict how fast the ice shelves will melt in the future. It is exciting when oceanographers and glaciologists work together, combining remote sensing with oceanographic field data. This is needed to understand the glaciological changes taking place - the driving force is in the ocean," says Anna Wahlin.

A daunting experience
Anna Wahlin continues: "There are not many uncharted areas left on Earth. To see Ran disappear into the dark, unknown depths below the ice, executing her tasks for over 24 hours without communication, is of course daunting. Experience from over 40 missions below ice gave us confidence but in the end the challenging environment beat us."

The fieldwork took place in 2022, and the team returned in January 2024 to repeat the surveys with Ran, hoping to document changes. However, after one successful dive, Ran disappeared.

"Although we got valuable data back, we did not get all we had hoped for. These scientific advances were made possible thanks to the unique submersible that Ran was. This research is needed to understand the future of Antarctica's ice sheet, and we hope to be able to replace Ran and continue this important work," says Anna Wahlin.

Research Report:Swirls and scoops: Ice-base melt revealed by multibeam imagery of an Antarctic ice shelf

Related Links
University of Gothenburg
Beyond the Ice Age