Let the annual Arctic Ocean meltdown commence.
After a brutally frigid winter that jammed Alaska's Bering Sea with big-dog floes, the spread of sea ice across the Far North likely hit its winter peak last week and has slowly begun its slow shrink toward another season of open water, according to the latest report posted by the National Snow & Ice Data Center.
"The maximum marks the point when the Arctic shifts from a freezing period into the summer melting period," said NSIDC scientist Walt Meier in this post.
The area covered by at least 15 percent ice floes topped out at 5.88 million square miles on March 18. In 34 years of satellite monitoring, only eight winters have seen less. At the same time, the sea ice covered about 4 percent more ocean than the maximum seen last year.
"As of March 23, ice extent has declined for five days," the NSIDC reported here. "However, there is still a chance (it) could expand again. February and March tends to be quite variable, because ice near the edge is thin and often quite dispersed."
The North Pacific's severe winter, which delivered cold snaps and deep snow to mainland Alaska, boosted the ice pack in the Chukchi Sea, Bering Sea and Arctic Ocean. The ice pack spread much farther than usual near Alaska, virtually filling the Bering Sea and causing problems with late winter snow crab fishery, according to this March 18 map. Greater-than-normal ice was also documented on the Russian side of the Bering and in some areas off western Greenland.
But sea ice remained far below average above Scandinavia and European Russia, possibly breaking all-time minimum records in the Barents and Kara seas. Novaya Zemlya — an island north of Russia that usually spends March deep inside the ice pack — remained ice free with open water between it and the Siberian coast until only a few weeks ago.
The nine smallest winter maximums on record are the last nine years.
Here's why it matters: The existence of an ice cap over the polar sea helps stabilize the world's climate. The melting of sea ice in summer also means destruction of habitat for populations of polar bears, walruses and seals, and speeds up climate warming because darker open water absorbs more solar energy than reflective white floes. In 2011, sea ice shrank to one of the smallest summer extents of the past 30 years, and a record number of large ships crossed the Bering Strait on voyages from Europe to the Far East.
The polar pack is always changing, and tracking it over the course of the year has become an important tool for scientists.
"Arctic sea ice melts and regrows in an annual cycle, freezing throughout the winter months and melting in the spring and summer," explained NSIDC's Katherine Leitzell in this Icelights story. "The ice cover generally reaches its maximum extent sometime in late February or March. After that, ice melts through the summer, hitting a low point in early or mid-September."
To put the figures in perspective, consider that at its height this winter, polar ice was 240,000 square miles smaller than the the average maximum between 1979 to 2000. An area nearly the size of Texas failed to re-freeze this winter.
On the other hand, this winter's ice coverage was 4 percent larger than last year, the lowest on record at about 5.65 million square miles. This winter, Arctic ice covered an additional 230,000 square miles of ocean, much of it in the Bering Sea.
What are our prospects for the coming summer meltdown? Difficult to say, according the sea ice scientists.
"At the beginning of the melt season, scientists look at data on sea ice extent, ice thickness and other factors that influence how much the ice cover will retreat during the coming summer," Leitzell said here. "For example, the amount of thick ice that has survived multiple melt seasons plays a big role in how much ice melts away. Researchers also look at the date on which the maximum occurs, and how quickly the ice declines after the maximum extent."
Expect the satellite jockeys at NSIDC to post a detailed analysis sometime in the next week or two. For those who must whet their appetite immediately, here's a discussion posted last April.
Contact Doug O'Harra at doug(at)alaskadispatch.com