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“The conventional picture of Antarctic sea ice being a thin veneer over the ocean is probably only true for some portion of it,” says Ted Maksym, an ice researcher at Woods Hole Oceanographic Institution in Massachusetts (WHOI).  “We need to do a better job of surveying the overall ice cover.”

Previous observations of the thickness of Antarctic sea ice produced a mean draught — the depth between the waterline and the bottom of the ice sheet — of around 1 metre; the new work gives a mean draught of over 3 metres.  And a previous maximum recorded ice-sheet thickness of 10 metres has now been increased to 16 metres.

Stephen Ackley, who studies sea ice at the University of Texas at San Antonio, says there have been a few previous observations of thicker ice in Antarctica.  “We’ve always felt we have some difficulties in making observations of this very thick ice.  What they’ve done is to qualify it well,” he says.  “It is clearly [because] the ships haven’t been operating in these areas.”

The more data that scientists can gather about Antarctic sea ice, the more they can unpick why climate models struggle to accurately predict its extent.  Although researchers have been generally successful at modelling the huge declines in Arctic sea ice, the extent of Antarctic sea ice has actually increased in recent years, contrary to the predictions of models.  More under-ice AUV (autonomous underwater vehicle) surveys could calibrate satellite measurements of ice thickness, allowing researchers a better understanding of what is really going on around the frozen continent.

Olivier Lecomte, who works on sea-ice modelling at the Catholic University of Louvain in Belgium, says that much of the analysis of the discrepancy between models and observations focuses on the extent and coverage of the ice sheets.  Having accurate measurements of the thickness as well provides another angle on the issue.  “It’s invaluable data,” he says.

For more information, see the item on the Nature News website or read the original article in Nature Geoscience.

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