See how Arctic sea ice is down its earthwork against warming summers

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Arctic Sea Ice Zoom Masti

Arctic sea ice, the vast sheath of cold seawater floating on the Arctic Ocean and its adjoining seas, has been hit with a double whammy over the past decades: as its extent shrank, the oldest and thickest ice has either thinned or melted away, leaving the sea ice cap more weak to the warming ocean and atmosphere

 

What we’ve seen over the years is that the big ice is disappearing,” said Walt Meier, a sea ice researcher at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “This older, thicker ice is like the earthwork of sea ice: a temperate summer will melt all the young, thin ice away but it can’t completely get clear of the older ice. But this older ice is becoming weaker because there’s less of it and the residual old ice is more broken up and thinner, so that fortification is not as good as it used to be.”

 

What we’ve seen over the years is that the big ice is disappearing,” said Walt Meier, a sea ice researcher at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “This older, thicker ice is like the earthwork of sea ice: a temperate summer will melt all the young, thin ice away but it can’t completely get clear of the older ice. But this older ice is becoming weaker because there’s less of it and the residual old ice is more broken up and thinner, so that fortification is not as good as it used to be.”

Direct capacity of sea ice width are irregular and incomplete across the Arctic, so scientists have developed estimates of sea ice age and tracked their development from 1984 to the present. Now, a new NASA dream of the age of Arctic sea ice shows how sea ice has been growing and shrinking, spinning, melting in place and drifting out of the Arctic for the past three decades.

“Ice age is a good analog for ice thickness because essentially, as ice gets older it gets thicker,” Meier said. “This is due to the ice usually growing more in the winter than it melts in the summer.”

In the early 2000s, scientists at the University of Colorado developed a way to monitor Arctic sea ice movement and the development of its age by using data from a diversity of sources, but primarily satellite passive microwave instruments. These instruments measure brightness temperature: a measure of the microwave energy emitted by sea ice that is partial by the ice’s temperature, salinity, surface texture and the layer of snow on top of the sea ice. Each floe of sea ice has a feature brightness temperature, so the researchers developed an move toward that would identify and track ice floes in consecutive passive microwave images as they moved across the Arctic. The system also uses information from drifting buoys as well as weather data

It’s like bookkeeping; we’re maintenance track of sea ice as it moves around, up until it melts in place or leaves the Arctic,” said Meier, who is a coworker of the group at the University of Colorado and the National Snow and Ice Data Center in Boulder, Colorado, the center that at present maintains the Arctic sea ice age data.

Ice in motion

Every year, sea ice forms in the winter and melts in the summer. The sea ice that survives the melt term thickens with each passing year: recently formed ice grows to about 3 to 7 feet of thickness during its first year, while multi-year ice (sea ice that has survived several melt seasons) is about 10 to 13 feet thick. The older and thicker ice is more opposed  to melt and less likely to get pressed around by winds or broken up by waves or storms.

The motion of sea ice is not limited to its cyclic expansion and shrinkage: Except for coastal regions where sea ice is attached to the coast, the sea ice cap is in approximately constant movement. The primary driver of sea ice movement in the Arctic is wind and there are two main features in the Arctic flow: the Beaufort Gyre, a clockwise ice flow that makes ice spin like a wheel in the Beaufort Sea, north of Alaska, and the Transpolar Drift brook, which transports ice from Siberia’s coast toward the Fram Strait east of Greenland, where the ice exits the Arctic basin and melts in the warmer waters of the Atlantic Ocean.

“On a week-to-week foundation, there are weather systems that come through, so the ice isn’t moving at a constant rate: sometimes the Beaufort Gyre reverses or breaks down for a couple weeks or so, the Transpolar Drift Stream shifts in its direction … but the overall pattern is this one,” Meier said. “Then the spring melt starts and the ice shrinks back, disappearing from the tangential seas.”

The new animation shows two main bursts of thick ice loss: the first one, starting in 1989 and lasting a few years, was due to a switch in the Arctic fluctuation, an atmospheric circulation pattern, which shrank the Beaufort Gyre and improved the Transpolar Drift Stream, flushing more sea ice than usual out of the Arctic. The second peak in ice loss started in the mid-2000s.

“Unlike in the 1980s, it’s not so much as ice being rosy out -though that’s still going on too,” Meier said. “What’s happening now more is that the old ice is melting within the Arctic Ocean during the summertime. One of the reasons is that the multiyear ice used to be a pretty consolidated ice pack and now we’re seeing relatively smaller chunks of old ice interspersed with younger ice. These isolated floes of thicker ice are much easier to melt.”

“We’ve lost the majority of the older ice: In the 1980s, multiyear ice made up 20 percent of the sea ice cover. Now it’s only about 3 percent,” Meier said. “The older ice was like the insurance policy of the Arctic sea ice pack: as we lose it, the likelihood for a mainly ice-free summer in the Arctic increases.”