Researchers elucidate sea ice variations

A team of researchers from Japanese universities and the University of Alaska Fairbanks has determined that heat input through open water is the primary driver behind annual variations in Arctic sea ice retreat, according to a paper published in Scientific Reports.

Using data from the Pacific Arctic collected from satellite observations between May and August from 1979 to 2014, the researchers found that in regions where the ice cover is seasonal, rather than multiyear, the ice melt volume strongly correlates with the area of open water. As the ice breaks apart when the summer melt gets underway, the increasing area of open water tends to accelerate the melt rate, the researchers determined.

The cause of this phenomenon is the fact that the ice tends to reflect solar energy, while open water absorbs the energy and hence warms up, melting the ice. Moreover, because the melting of the underside of thin first-year ice causes that ice to melt completely, thus increasing the surface area of open water, the bottom melting of the ice as well as the melting of the sides of ice floes contributes to the overall decrease in sea ice area. Conversely, the presence of thick, multiyear ice can constrain the overall melt rate.

The findings also point to the importance of the early melt season divergence of ice floes and resulting uncovering of the sea surface as a critical factor in determining the variation from one year to the next in the overall extent of the Arctic sea ice retreat. A relatively small change in ice floe divergence early in the season becomes magnified later in the season, through the multiplier effect of ever increasing areas of open water. The importance of this phenomenon has become particularly noticeable in Pacific Arctic since the early 2000s, the researchers say.

- ALAN BAILEY