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.
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, meanwhile, are more accurate but are limited by lack of access. But the submarine can measure the thickness of the ice much more accurately.
Three locations around the Antarctic Peninsula were mapped – the Weddell, Bellingshausen and Wilkes Land sectors covering an area of 5.4 million square feet (500,000 square meters).
‘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 researchers wrote in their paper.
‘We suggest that thick ice in the near-coastal and interior pack may be under-represented in existing in situ assessments of Antarctic sea ice and hence, on average, Antarctic sea ice may be thicker than previously thought.’
“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.”
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”.
And Professor 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 also.
‘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.’
EFFECTS OF CLIMATE CHANGE ARE UNSTOPPABLE SAYS WORLD BANK
A report from the World Bank Group recently claimed that the world must brace itself for more extreme weather, as it is locked on a path to unstoppable warming. They said some effects of climate change will be unavoidable owing to past and predicted emissions from power plants, factories and cars. But they added the worst impacts could be avoided by cutting global emissions.
The report, entitled ‘Turn down the Heat: Confronting the New Climate Normal’, stated that the average temperature on Earth will be 1.5°C (2.7°F) above pre-industrial levels by 2050. Sea levels will also continue to rise as the vast ice sheets in Greenland and Antarctica thaw slowly, they said.