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article imageUnderwater robot sheds new light on Antarctic sea ice

By Robert Myles     Nov 24, 2014 in Environment
Cambridge - A collaborative effort involving scientific teams from the UK, U.S. and Australia has produced the first detailed, high-resolution 3-D maps of Antarctic sea ice with the help of an underwater robot.
The new survey, which took ice thickness measurements in areas that were previously too difficult to access, has important implications for better understanding the dramatic sea ice changes currently taking place in the polar regions as a result of climate change.
The underwater robot, an Autonomous Underwater Vehicle (AUV) known as SeaBED, fills a gaping hole in the ice, as it were.
Previously, although scientists used a range of sources to measure ice thickness, difficulties were always experienced in accessing thicker areas of sea ice, so leaving gaps in the scientific data. Satellite data was useful, up to a point, in measuring large-scale ice thickness from space but snow cover on the ice often made interpreting such data problematic. Equally, while additional data could be gleaned from measurements made by drilling holes in the sea ice or from visual observations from ships, both of had limitations when it came to thicker areas of sea ice.
Now, the additional data provided by SeaBED should give a more complete picture of what’s happening to sea ice as global temperatures rise.
SeaBED deployment from the RRS James Clark Ross under the midnight sun
SeaBED deployment from the RRS James Clark Ross under the midnight sun
Permission British Antarctic Survey
The two meter long SeaBED robot, weighing in at 200 kilograms, differs from most oceanographic survey instruments. Most of these instruments look down at the seafloor. SeaBED, however, was fitted with upward looking sonar that measured and mapped sea ice floes from below. This was done by operating the AUV at a depth of between 20 and 30 meters. Ice floes were then surveyed as the AUV traced a pattern, much like a lawnmower mowing a lawn, up and down the length of the floe. The robot’s twin hulled design gave it enhanced stability, ideal for low-speed photographic surveys.
These ‘lawnmower’ stripes, effectively lines of data, were then merged. The result was high-resolution 3D bathymetric surveys of the underside of the ice.
"Putting an AUV together to map the underside of sea ice is challenging from a software, navigation and acoustic communications standpoint," commented Hanumant Singh, an engineering scientist at the Massachusetts-based Woods Hole Oceanographic Institution (WHOI) whose lab designed, built and operated the AUV.
"SeaBED's maneuverability 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,” Singh added.
According to co-author Dr Guy Williams from Australia’s Institute of Antarctic and Marine Science, this full 3-D topography of the underside of the ice provides a wealth of new information about the structure of sea ice and the processes that created it. That, said Dr Williams, “is key to advancing our models particularly in showing the differences between Arctic and Antarctic sea ice."
By combining the data from SeaBED with airborne measurements of sea-ice surface elevation, ice core surveys, and satellite observations, scientists studying polar ice should be able to obtain far better estimates, not just of ice thickness, but also total sea ice volume.
The research team deployed AUVs as part of two Antarctic survey missions that took place during spring in the southern hemisphere in 2010 and 2012. The first deployment was from the British Antarctic Survey's Royal Research Ship (RRS) James Clark Ross, named after the pioneering, British, 19th century Arctic and Antarctic explorer. Two years later, an AUV was launched from the Australian icebreaker and Australia’s Antarctic flagship, the Aurora Australis, as part of operations conducted by 50 scientists during the Sea Ice Physics and Ecosystem eXperiment 2012 (SIPEX-2).
The two AUV mapping missions encompassed three locations around the Antarctic Peninsula — that northernmost part of Antarctica stretching out like a tentative finger trying to touch South America. Areas of the Weddell and Bellinghausen Seas and the waters off Wilkes Land were surveyed. In total the AUVs mapped an area of 500,000 square meters — roughly the size of 100 football pitches.
The ambitious plan is to use the AUVs to conduct large-scale surveys that will then be compared to similar large-scale observations from aircraft and satellites. These measurements, though routine, will constitute an important step towards obtaining a better understanding of what’s happening with the ice and the large scale changes currently taking place.
The scientific team’s results are published Nov. 24 in the journal Nature Geoscience.
More about Antarctic, British Antarctic Survey, Antarctic sea ice, sea ice extent, Globalwarming
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