Antarctic ice floes up to 17 metres thick have been accurately measured for the first time using a submersible robot equipped with upward-looking sonar.
The high resolution 3D maps of Antarctic sea ice will help scientists investigating the dramatic polar changes caused by global warming.
Satellites can measure large-scale ice thickness, but their data is often difficult to interpret because of snow covering the ice.
Man-made measurements carried out by drilling holes and observations from ships are more accurate but are limited by lack of access.
An autonomous underwater vehicle (AUV) known as Seabed provides a new way of mapping sea ice − from below.
The two-metre long sub operates at a depth of 20 to 30 metres, bouncing sound waves off the under-surface of the ice.
Jeremy Wilkinson, from the British Antarctic Survey, said: “The AUV missions have given us a real insight into the nature of Antarctic sea ice − like looking through a microscope.
We can now measure ice in far greater detail and were excited to measure ice up to 17 metres thick.”
Seabed was built and operated by engineers from Woods Hole Oceanographic Institution in Massachusetts, US. Hanumant Singh, a member of the Woods Hole team, said: “Putting an AUV together to map the underside of sea ice is challenging from a software, navigation and acoustic communications standpoint.
The AUV missions have given us a real insight into the nature of Antarctic sea ice − like looking through a microscope. We can now measure ice in far greater detail
“Seabed’s manoeuvrability and stability made it ideal for this application where we were doing detailed floe-scale mapping and deploying, as well as recovering in close-packed ice conditions.
“It would have been tough to do many of the missions we did, especially under the conditions we encountered, with some of the larger vehicles.”
The research is reported in the journal Nature Geoscience.
Mike Meredith, deputy director of science at the British Antarctic Survey, said: “Sea ice is changing in both polar regions, with important consequences for climate and the ecosystem.
“In contrast to the Arctic, the changes around Antarctica vary from region to region, but full understanding of the causes and impacts of these changes requires detailed knowledge of how thick the ice is, which has historically proven very hard to get.
“Satellites can now give information about this over large areas, but proper interpretation of the satellite data requires direct measurements. This new paper presents important results obtained from a novel underwater vehicle that radically change our concepts of the structure of Antarctic sea ice, and the processes that influence it.
“Such understanding is key to improving our models of how sea ice will change into the future.”