For several years now climatologists have puzzled over an apparent conundrum: why is Antarctic sea ice continuing to expand, albeit at the relatively slow rate of about one to two percent per decade, while Arctic sea ice has been declining rapidly (by some 13% per decade in late summer)?
Just a few weeks ago the Antarctic saw a third consecutive record year of sea ice coverage. The two previous records were set in 2012 and 2013.
To help get to the bottom of this mystery, one team of scientists have enlisted an underwater robot to help measure the thickness of the ice. Their vehicle, known as SeaBED, has an upwards looking sonar which maps the underside of ice floes and provides novel, highly-detailed three-dimensional maps of Antarctic sea ice. The researchers present their findings in the journal Nature Geoscience.
Measuring a total of ten ice floes covering more than 500,000 square metres, they found mean ice thicknesses of 1.4 to 5.5 metres. In some places the ice was up to 16 metres thick. This is much thicker than has been gauged by previous more limited field-based (mainly ship-based) measurements, possibly because ships tend to avoid the areas of thicker sea ice, so there may very well be a sampling selection bias.
Satellites would ideally be able to assess ice thickness over a much wider area. However, although they have had some success in the Arctic, at the other end of the world satellites are severely hampered by our poor knowledge of how much snow there is on top of any given area of Antarctic sea ice.
