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Arctic Ice Maximum: Earth Image of the Week April 6, 2012
Arctic ice graphic
Arctic sea ice reached its maximum extent for the winter of 2011–2012 on March 18.
The closing days of the 2011-2012 Arctic winter saw the pack of sea ice around the polar region reach its greatest coverage of the season.

With a total extent of 5.88 million square miles, sea ice was below the 1979–2000 average, but slightly above the record low recorded during the winter of 2010–2011.

The map graphic to the right was created from satellite observations and shows sea ice concentration on March 18, the day it peaked.

The brightest white indicate the greatest concentration of ice and blue indicates open water. The dull yellow line around the periphery of the ice pack shows the median, or basically the average, extent of the annual sea ice maximum.

That maximum usually occurs around March 6 each year, but has tended to arrive later during recent years.

While the cause of the later peak has not yet been determined, some researchers believe it might be related to the greater summer melting that has been occurring over the past few years.

“There are constraints (longer days and a sun higher in the sky) on how long Arctic sea ice can keep growing in late March,” said Walt Meier, of NOAA’s National Snow and Ice Data Center. “But since Arctic sea ice has melted so much in the summers, it could be that the ice has more room to grow at the end of the season.”

Over the last decade, Arctic sea ice extents in September have set record lows three times. The 2011 minimum nearly tied the 2007 record low. Meier points out something else about Arctic sea ice extent.

“The nine lowest maximum extents have occurred in the last nine years, since 2004,” he says. Although Arctic sea ice has continued to grow later in the season, the ice has been thin—only about 4 to 12 inches thick at most, Meier explains. “So it will all melt away very quickly. I don’t expect the late-season growth spurt to have a big effect on sea ice extent next summer.”

Full story and image: NASA