Peak winter extent was reached on Feb. 25, with 5.61 million square miles of Arctic waters having at least 15 percent ice coverage, the center said. That maximum was about 7 percent smaller than the average winter maximum of 6.04 million square miles recorded from 1981 to 2010, the center said.
The ice coverage peak -- and start of the melt season -- was also one of the earliest on record, 15 days earlier than the 1981-2010 average date of peak coverage, the center said.
The melt season now underway is starting out in "a deep hole," Mark Serreze, director of the National Snow and Ice Data Center, said in an email.
While ice extent at the end of this year's melt season will depend a lot of summer weather patterns, "we've set the stage for another extreme minimum," he said. "Will there be a new record low at the end of the coming melt season? While we'll have to wait and see; we've raised the odds of this happening."
Through this winter, sea ice extent has been below average almost everywhere in the Arctic but particularly in waters off Alaska and eastern Siberia, the center said. That was thanks in large part to warm conditions brought to the Pacific by an unusual pattern in the jet stream, the center said.
There was a slight buildup of thin ice in the Bering Sea earlier this month, occurring during the brief snap of cold weather that struck this part of the world, the center said. That new ice reversed the downward trend in overall Arctic ice extent that started after Feb. 25, but only incrementally and only for a short period.
Such brief freezing is common in the Bering Sea this time of the year, said Mary-Beth Schreck, a sea ice analyst with the National Weather Service in Anchorage.
"The seawater is still primed, even if the ice gets broken up," she said.
Bering Sea ice, which melts away every year, is very dynamic, and that was the case with this new ice that formed in early March, Schreck said. Within days, that ice coverage changed, she said.
"We had winds that were blowing offshore and it caused the ice to push away from shore, so we had open water," she said.
The earliest start to the annual melt season happened in 1996, when ice extent reached its peak on Feb. 24, according to the National Snow and Ice Data Center. The latest start was in 2010, when the winter maximum was reached on April 2, according to the center.