Antarctica Sea Ice Expansion - an explanation (or two?)

By ExpeditionsOnline / 03 April 2013

Antarctica Sea Ice Expansion - an explanation (or two?)

Global warming might actually be expanding Antarctica's sea ice levels, according to a Dutch study released by Nature Geoscience.

This unexpected phenomenon may be caused by cold streams of fresh water feeding back from melting occurring underneath Antarctic ice shelves. The cold melt water then accumulates near the top layer of the ocean because of its low density and is able to re-freeze more easily during Autumn and Winter. This explains the observed peak in sea ice during these seasons.

Scientists have observed that Antarctic sea ice has shown an expansion of almost 2% per decade since 1985, whereas Arctic sea ice has been shrinking over the same period.

The Dutch researchers predict that the "negative feedback" effect described in their study will continue into the future. In computer-based climate modelling, the sea ice expanded in response to the fresh, cool surface water layer, which floated over the denser, warmer salty sea water. This fresh water is sourced from increased melting at the base of Antarctica's ice shelves.

"Sea ice around Antarctica is increasing despite the warming global climate," said the study's lead author Richard Bintanja.

"This is caused by melting of the ice sheets from below," he told the Reuters news agency.

However there are other possible explanations for Antarctic sea-ice expansion.

Paul Holland of the British Antarctic Survey (BAS) repeated his suggestion of last year that a shift in winds linked to climate change was blowing ice away from the coast, allowing exposed water closer to the coast to refreeze and thereby increase the overall surface area of ice.

"The possibility remains that the real increase is the sum of wind-driven and melt water-driven effects, of course. That would be my best guess, with the melt water effect being the smaller of the two," he told the London Science Media Centre.

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