Researchers contend increase in Antarctic sea ice due to summer melt

(Phys.org) —A team of researchers from the Netherlands, led by Richard Bintanja, has published a paper in the journal Nature Geoscience, contending that the reason the amount of annual Antarctic sea ice is increasing is because of increased ice sheet melting during the summer months. They suggest that the increased melt creates a cold layer of fresh water on the ocean surface that is easily frozen when the next winter arrives.

Over the past several years, scientists have found something that appears to go against common sense—as the planet undergoes global warming, sea ice expansion around Antarctica has been growing each year instead of contracting as has been the case with sea ice around the Arctic. The reason for this has not been clear and researchers have been offering a variety of possible explanations—last year ocean modelers at the British Antarctic Survey in Cambridge, published a paper suggesting that changes in wind patterns in the area were responsible.

In this new effort, the group from the Netherlands suggests it's more likely due to increased heat in the summer leading to an increase in offshore ocean temperatures. That warmer water, they theorize, causes melting of the ice sheets from below. Then, because the water from the ice that melts has little salt in it, it tends to float, creating a layer of cold water sitting on top of the warmer saltier water below, which easily freezes when cold winter temperatures return. The researchers suggest that the cold layer of water created offshore may also be responsible for lower than average snowfall in Antarctica, as it cools the air above it—cooler air holds less moisture.

The researchers came to these conclusions by using existing models that simulate conditions in Antarctica to build new models based on what would likely happen in the sea should the ocean experience warming. Their model, they claim, indicates that increased ice expansion around the continent is most likely due to summer melt, though they acknowledge that some might also be due to changes in wind patterns due to global warming as well. They note also that despite the increase in surface ice expansion each winter, the total mass of ice around Antarctica is continuing to shrink (by about 250 billion metric tons a year) because of the underside melting of the sheet ice.