Sea ice in the Antarctic may be thicker than previously thought, according to a study published online in Nature Geoscience.
Although the aerial extent of Antarctic sea ice is easily tracked by satellites, estimating the thickness of the ice from above has proven challenging.
Researchers from Australia, the US and the UK used an autonomous underwater vehicle to map the thickness of sea ice across several coastal regions of Antarctica in 2010 and 2012 . The researchers found that, on average, the thickness of the ice beneath sea level was 1.4 to 5.5 metres, with the thickest sea ice measured at 16 metres. Although submarines have been used to document Arctic sea-ice thicknesses in previous studies, Antarctic measurements have been limited to shipboard observations and drill holes. Those limited studies had suggested that most sea ice is thinner than a metre.
“What this effort does is show that observations from AUVs under the ice are possible and there is a very rich data set that you can get from them,” says Ted Maksym, a Wood’s Hole Oceanographic Institute scientist and co-author of the paper. “This work is an important step toward making the kinds of routine measurements we need in order to really monitor and understand what’s happening with the ice and the large scale changes that are occurring.”
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Dr David Ferreira, Oceanographer at the University of Reading, said:
“The quality and density of these observations are truly outstanding. This literally adds a new dimension to our knowledge of the Antarctic sea ice. The frustration is that we do not have more measurements like these.
“Because Antarctic sea ice melts and refreezes every year, we tend to think of it as relatively thin and smooth, a view that was not challenged by the few measurements available up to now. This latest discovery reveals a much richer and more exciting picture, one of a more dynamically active ice pack than previously thought.
“These findings call for a rethinking of the interaction between ocean and atmosphere around Antarctica and how it is represented in our climate models. Several processes, such as the movements of winds, and the transfer of heat from the ocean to the atmosphere, go through the sea ice and are critically dependent on its thickness.
“This research provides a formidable benchmark to evaluate our climate models in this region. We strongly depend on the simulation of the sea ice in these models to test possible causes of the Antarctic sea ice expansion. Effects of the ozone hole, of melt water from the Antarctic ice sheet, or of sea ice movements are among the plausible candidates, but we are limited by the quality of our models in this poorly observed region of the world to discriminate between them.”
Prof 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.”