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article imageScientists argue reasons for Antarctic sea ice expansion

By Robert Myles     Mar 31, 2013 in Science
With records going back to 1979, there is little dispute that Arctic ice is in retreat but up till now scientists have had difficulty in reconciling an expansion of Antarctic sea ice with global warming.
A new study by Dutch researchers may point to an answer but not all scientists are convinced.
An expansion of Antarctic sea ice at first glance seems to be contrary to theories of global warming. Various explanations have been put forward in the past. Digital Journal earlier reported on a joint NASA/ British Antarctic Survey study which found significant growth in Antarctic sea ice drift caused by changes in the wind currents around Antarctica observed over the past 20 years.
The new study which was published today in the journal Nature Geoscience suggests that freshwater from melting tongues of ice that extend the continental ice cap into the Southern Ocean surrounding Antarctica is accumulating a layer of colder surface water. In effect, Antarctic continental ice melt is presently causing a reverse feedback effect in the surrounding ocean. Water from the freshwater ice tongues, which has a higher freezing point than the ocean salt water is promoting the formation of sea ice, a more reflective and therefore cooler surface than liquid water.
Although scientists have known for some time that meltwater from polar ice sheets can produce a cold ‘cocoon’ that protects sea ice on the surface from warmer ocean currents below, they were uncertain whether that could explain the observed expansion of Antarctic sea ice as suggested by the new study.
Quoted on Nature Geoscience, Richard Bintanja, a climate researcher at the Royal Netherlands Meteorological Institute in Utrecht, said, “The paradox is that global warming leads to more cooling and more sea ice around Antarctica.”
In the study, Bintanja and his fellow researchers demonstrate that faster melting of the Antarctic ice sheet has probably been the principal cause of a small but statistically measurable expansion of sea-ice around Antarctica.
Speaking to the New Zealand Herald, French paleoclimatologist Valérie Masson-Delmotte the Laboratory of Climate and the Environment said, “This is a major, new piece of work with wide implications for assessing Antarctica's ice mass in the coming decades.” She went on to highlight a worrying rise in sea levels in 2011 and 2012, due partly to expansion of the ocean through warming and through glacial runoff — the ice caps of Greenland and Antarctica together make a one third contribution to rising sea levels, with the remaining two-thirds comprising thermal expansion of the oceans and the melting of mountain glaciers in equal measure.
One of the authors who contributed to the earlier study on the effects of polar winds on Antarctic sea ice was unconvinced. Paul Holland, an oceanographer at the British Antarctic Survey, said the new study showed no formal link between the melting of ice tongues in Antarctica, according to 20 minutes.
Speaking to Nature Geoscience, Paul Holland said, “The mechanism could be completely true, but this study does not demonstrate that increased melting has made a significant contribution to the increase in sea-ice cover.”
Bintanja countered, conceding that wind effects are important locally but arguing that meltwater influences sea-ice expansion in a regional context. Holland argued that ice melt is not uniform around the Antarctic coastline, as the authors of the new study assume, but is concentrated in some locations.
The answer may be, as Holland conceded, that both wind patterns and meltwater may be expanding the sea-ice around the Antarctic continent. For the moment, the elephant in the room remains the anomaly of an expansion of Antarctic sea ice, when factors such as contraction in Arctic sea ice and permafrost thaw may point to global warming.
More about Antarctic ice, Ice melt, polar ice melt, volume of polar ice, Global warming
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