Canyons, plateaus and teardrop-shaped structures: An unmanned submersible has provided insights into the hidden blanket landscape on the underside of the floating ice shelf of Antarctica. These are structures that are due to the melting processes caused by the circulating warm water that gnaws at the ice from below. The results can now be used to improve predictions of ice shelf melting and the associated sea level rise, say the researchers.
They are the marine extensions of the gigantic glaciers: the ice shelves of the Antarctic are formed by the flow of ice from the land. At first the mass of the glacier pushes itself across the sea floor – but from a certain distance the ice is then eroded by sea water. This floating part is then called the ice shelf and can be several hundred meters thick. These ice surfaces have been the focus of concern for years. Some ice shelves are showing signs of increasing thinning, which is probably due to the complex consequences of climate change. It seems that increasingly warm water is getting under the ice and is eroding it more intensively. The problem is that the ice shelf has an important braking function against the flow of glacier ice from the Antarctic. An increased inflow into the sea could therefore lead to a significant rise in global sea levels, so the fear goes.
Icy blanket landscapes in sight
Research into the thinning processes of the ice shelf is therefore particularly important. However, so far there has been only limited insight into the undersides of the floating ice masses affected by the melting processes. Now an international research team led by Anna Wåhlin from the University of Gothenburg is presenting the results of the most detailed study to date of one of the icy cover landscapes. In spring 2022, the researchers deployed an unmanned submersible under the Dotson Ice Shelf in West Antarctica. The underwater vehicle “Ran” was programmed to dive into the cavity of the 350-meter-thick ice shelf and scan the ice above with sonar.
In 27 days, the submarine traveled more than 1,000 kilometers under the shelf, penetrating 17 kilometers into the cavity. Ran also recorded data on the salinity, temperature and currents of the water under the ice shelf. “We have previously used satellite data and ice cores to observe how ice shelves change over time. By navigating the submersible into the cavity, we were able to obtain high-resolution maps of the ice underside. It’s a bit like seeing the back of the moon for the first time,” says Wåhlin.
As the team reports, some results initially confirmed basic assumptions about the melting processes: For example, it became clear that the ice is shrinking particularly strongly where strong underwater currents are eroding its base. But the complexity of the icy landscape and some elements were surprising. It is partly characterized by intense terraces, deep gorges and rounded formations. “When Anna sent around the first pictures of the underside of the Dotson Ice Shelf, we were excited – no one had seen anything like it before and some things amazed us: There were cracks and swirls in the ice that we hadn’t expected. It looked more like art,” says senior author Karen Heywood from the University of East Anglia in Norwich.
Melting dynamics reflected in ice structures
The team was particularly amazed by the discovery of teardrop-shaped depressions 20 to 300 meters long that appeared at the western base of the ice shelf, where the melting rate is highest. These structures are apparently due to circular water movements. According to the researchers, the mapping results reflect surprisingly specific dynamics on the underside of the ice. “The study has provided us with new data that we now need to look at more closely. It seems clear that many previous assumptions about the melting of the undersides of glaciers are too simplistic. Current models cannot explain the complex patterns we see. But there is a chance of finding the answers,” says Wåhlin.
According to the authors, a better understanding of the complex processes that take place beneath the ice shelves is important for assessing their future development. “We need better models to predict how quickly the ice shelves will melt in the future,” says Wåhlin. Therefore, the researchers now also need to continue exploring the undersides of the ice masses. As they conclude, however, there was a setback this year: In January, the group returned to the Dotson Ice Shelf with Ran to repeat the investigations in the hope of documenting changes. However, they were only able to complete one dive before the precious submersible was lost. “These scientific advances have been made possible thanks to the unique submersible Ran. This research is necessary to understand the future of the Antarctic ice sheet, and we hope to be able to replace Ran and continue this important work,” says Wåhlin.
Source: University of East Anglia, professional article: Science Advances, doi: 10.1126/sciadv.adn9188