Robot submarine shows Antarctic sea ice thicker than believed

The AUV SeaBED robot under the Antarctic sea ice.

Scientists have been able to take accurate measurements of the thickness of Antarctic sea ice for the first time, using an underwater robot to map it in high resolution and 3D.

The work is a breakthrough in understanding the changing ice patterns in the light of climate change.

Initial findings show the ice is much thicker than previously thought and ranges from 1.4 to 5.5 metres up to 16 metres.

The ice was also "deformed", where slabs had crashed together, forging new thicker formations.

"We also find that, on average, 76% of the ice volume is deformed ice," the study, published in Nature Geoscience, said. "Our surveys indicate that the floes are much thicker and more deformed than reported by most drilling and ship-based measurements of Antarctic sea ice."

The scientists used the Autonomous Underwater Vehicle (AUV) known as SeaBED, which was fitted with a unique upward-looking sonar that could measure and map the underside of sea ice floes. It operated at a depth of 20 to 30 metres and was driven in a lawnmower pattern. These lines of data were merged to form high-resolution 3D bathymetric surveys of the underside of the ice.

The yellow SeaBED robot, which is approximately two meters long and weighs nearly 200 kilograms, has a twin-hull design that gives the robot enhanced stability for low-speed photographic surveys.

"Putting an AUV together to map the underside of sea ice is challenging from a software, navigation and acoustic communications standpoint," says Hanumant Singh, an engineering scientist at the Woods Hole Oceanographic Institution (WHOI) whose lab designed, built and operated the AUV.

"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 SeaBED AUV being deployed in the Antarctic.
Hanu Singh, Woods Hole Oceanographic Institution

Co-author Dr Guy Williams from Institute of Antarctic and Marine Science said the imaging "provides a richness of new information about the structure of sea ice and the processes that created it. This is key to advancing our models particularly in showing the differences between Arctic and Antarctic sea ice".

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