The research, led by ARC Future Fellow Dr Guy Williams and published in November 2014, provides the most complete picture yet of Antarctic sea ice thickness and structure.
The data was collected by an Autonomous Underwater Vehicle (AUV) deployed during a two-month exploration in late 2012 as part of an international collaboration between polar scientists, including the Antarctic Climate and Ecosystems CRC (ACE CRC). It’s hoped the work will help explain the ‘paradox’ of Antarctic sea ice extent, which has grown slightly during the past 30 years. This is in stark contrast to Arctic sea ice, which has shown a major decline.
Previously, measurements were made via drill holes in the ice and supplemented by visual observations made from icebreakers as they crashed and ploughed through the sea ice zone, said Williams.
In contrast, the AUV gathers information by travelling beneath the ice, producing 3D maps of the underside of the ice based on data captured by a multi-beam sonar instrument. Complex imagery of an area the size of several football fields can be compiled in just six hours.
The manual drill estimates of thickness have never exceeded 5–6 m, but the AUV regularly returned thicknesses over 10 m and up to 16 m.
“This sort of thick ice would simply never be sampled by drilling or observations from ships,” said Williams. “We measured the thickness of 10 double football fields, and found that our traditional method [manual drill lines] would have underestimated the volume by over 20%.”
The researchers can’t yet say that overall Antarctic sea ice thickness is underestimated by this amount. They’ll need to use the AUV over much longer scales – across distances of 1000 km, for example – and directly compare the results with those from traditional methods.
The AUV is one of two new innovative information sources being used by ACE CRC scientists to explore Antarctic sea ice processes and change. They’ve also begun tapping into environmental data gathered in the Southern Ocean by elephant seals. These marine mammals can dive deeper than 1500 m and travel thousands of kilometres in a season.
During the past decade, ecologists and biologists have been equipping them with specialised oceanographic equipment provided by Australia’s Integrated Marine Observing System, to observe where and when they forage.
“These seals had been going to places we could only dream of going with a ship,” said Williams. The first major breakthrough from the seal-gathered data came last year with the confirmation of a new source of Antarctic bottom water, the cold dense water mass created by intense sea ice growth that ultimately influences climate worldwide.
It’s the fourth source to be identified of this influential water mass, and scientists had been looking for it for more than 30 years.
– Karen McGhee