New video shows Arctic Sea Ice depletion
The vast sheath of frozen seawater known as Arctic sea ice, has depleted over the past decades, as it’s surface area has shrunk the oldest and thickest ice has thinned or merely melted away. Subsequently the ice cap has been left vulnerable to the warming conditions of the ocean and the atmosphere.
Walt Meier, a sea ice researcher at NASA’s Goddard Space Flight Center in Greenbelt, Maryland said “What we’ve seen over the years is that the older ice is disappearing. This older, thicker ice is like the bulwark of sea ice: a warm summer will melt all the young, thin ice away but it can’t completely get rid of the older ice. But this older ice is becoming weaker because there’s less of it and the remaining old ice is more broken up and thinner, so that bulwark is not as good as it used to be.”
Sea ice direct measurements are sporadic and incomplete across the Arctic, to combat this lack of data scientists developed estimates of sea ice age and tracked their evolution from 1984 to now. This new NASA visualization of the Arctic sea ice shows the sea ice evolution over the past 3 decades.
“Ice age is a good analog for ice thickness because basically, as ice gets older it gets thicker,” Meier said. “This is due to the ice generally growing more in the winter than it melts in the summer.”
Scientists at the University of Colorado developed a way to monitor Arctic sea ice in the early 2000s. They pulled data from a variety of sources, but focused on the study of satellite passive microwave instruments.
These instruments gauge brightness temperature which is influenced by the ice’s temperature, salinity, surface texture and the layer of snow on top of the sea ice. The researchers developed an approach to identify and track ice floes in successive passive microwave images as they moved across the Arctic. They also use information from drifting buoys.
“It’s like bookkeeping; we’re keeping track of sea ice as it moves around, up until it melts in place or leaves the Arctic,” said Meier, who is a collaborator of the group at the University of Colorado and the National Snow and Ice Data Center in Boulder, Colorado, the center that currently maintains the Arctic sea ice age data.
Sea ice forms in the winter and melts in the summer annually. The sea ice which services thickens each year, older ice can be as much as 13 feet thick. This elderly ice is more resistant to melting and is less likely to be affected by weather conditions.
The sea ice cap is in constant movement with a few coastal exceptions. It’s primary driver is wind. In the Arctic circulation there are two major features: the Beaufort Gyre, which is a clockwise ice circulation that makes ice spin like a wheel, and the Transpolar Drift Stream, which transports ice from Siberia’s coast toward the Fram Strait east of Greenland.
“On a week-to-week basis, 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 peripheral seas.”
The new animation shows two main periods of ice loss:
“Unlike in the 1980s, it’s not so much as ice being flushed 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 most 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 largely ice-free summer in the Arctic increases.”
Read the full story about arctic sea ice depletion at NASA