Share on FacebookShare on Twitter+1Pin it on PinterestShare on LinkedInShare via email
Author: Andrew Darby
Date: 19 September, 2013

As the area of Antarctic sea ice grows to a record extent, blast freezer winds are emerging as a key to the riddle of how, in a warming world, this ice is expanding.

Each winter the sea ice area in Antarctica is much greater than total land-bound ice, but the vast white blanket floating over the Southern Ocean is peaking at increasing sizes.

It reached around 19.45 million square kilometre in extent on Monday, according to satellite data published by the US National Snow and Ice Data Centre on Wednesday.

This is up on last year’s 19.44 million square kilometres’ September record, and is part of a trend in recent years for the late winter maximum to grow.

A University of Washington oceanographer, Jinlun Zhang, said there was overwhelming evidence that the Southern Ocean was warming, so the increase in sea ice had been a puzzle to scientists.

Possible reasons for the increase included the greater melting of ice shelves and land-bound ice, pouring more very cold water into the ocean that would readily freeze in winter.

Dr Zhang found changes in water density could account for a small part of the increase, but in his latest study published in Journal of Climate he focussed on winds swirling around the Antarctic for the answer.

These winds have grown measurably stronger over the past 40 years in what may be a result of ozone depletion. Dr Zhang developed a computer model that simulated links between these winds and the sea, and found that they drove the creation of thicker, longer-lasting ice, which increased by about one per cent annually.

Under what Dr Zhang agreed were blast freezer-like conditions, the ice piled up, exposing surrounding waters and thinner ice to the blistering cold, and forcing ice growth.

“You’ve got more thick ice, more ridged ice, and at the same time you will get more ice extent because the ice just survives longer,” he said.

Despite this growth, overall the world is losing sea ice.

The snow and ice data centre said this year’s Arctic summer minimum ice extent was about 30 per cent below a 30-year average, and the 2012 record low extent was nearly 60 per cent down.

“This helps to highlight why scientists are more concerned by Arctic ice shrinkage than by Antarctic ice expansion,” the agency said.

Read article at the Sydney Morning Herald