Seasonal shift begins in northern latitudes
By Summit Voice
FRISCO — It’s just the very start of the melt season in the Arctic, but sea ice has already dropped below last year’s level, which ended with a record low extent in September.
In the early April update, the National Snow and Ice Data Center reported that levels of multiyear ice remain extremely low. Satellite data suggests that first-year ice may now cover the North Pole area for the first time since the winter of 2008.
For March, the average extend was about 5.81 million square miles, which is about 274,000 square miles below the 1979 to 2000 average extent, and about 236,000 square miles above the record low for the month, set in 2006. March sea ice extent is declining at a rate of about 2.5 percent each decade, losing about 15,300 square miles per year, (about the size of Maryland and Delaware combined).
The overall changes in March are often small, with gains early in the month until the melting starts.Air temperatures at about 3,000 feet were 5 to 11 degrees higher than average over the central Arctic Ocean, with cooler-than-average readings over the Kara and Barents seas.
The NSIDC researchers said the Arctic Oscillation reached an extreme negative phase in the second half of the month, associated with unusually high sea level pressure covering nearly the entire Arctic Ocean, capping several months of a persistently negative phase of the Arctic Oscillation.
Historically, the pattern has favored retention of thick ice in the Arctic Ocean and more extensive sea ice at the end of the summer, but that trend has been reversed the past few years, with summer ice dwindling even after a winter dominated by a negative Arctic Oscillation.
Extensive fracturing of sea ice in the Beaufort and Chukchi seas north of Alaska is also consistent with wind patterns associated with the strong negative pattern of the AO.
As thicker, multiyear ice melts, the boundary between primarily first-year ice and multiyear ice is now near the North Pole marking the first time since the winter of 2008 that a substantial amount of first-year ice may be covering the pole as we enter the melt season.
The percentage of multiyear ice in the Arctic Ocean has declined from 60 percent to about 30 percent in recent years, with the the oldest ice now comprising only 5 percent of the ice. This is a slight uptick from last winter’s record low of 3 percent, but still far less than during the 1980s when old ice covered roughly 25 percent of the region.
The newest data available, from the European Space Agency’s CryoSat-2 satellite, launched in April 2010, shows an overall thinning of the ice cover. CryoSat-2 compares thickness with data from NASA’s ICESat satellite, which operated from 2003 to 2009, especially along the north coast of Greenland, formerly a stronghold for thick, multi-year ice.