Something is happening to the floating sea ice of the Arctic, other than the well-documented retreat in its surface coverage each summer. Scientists are finding that Arctic sea ice is getting younger and thinner, which is set to continue in March, when US research reveals the winter maximum, and September, when it reveals the summer minimum, making it more vulnerable to a catastrophic and unprecedented break-up.
Nasa researchers have found that the thicker multi-year ice, which has survived several summer melt seasons, is being rapidly replaced by thinner, more ephemeral one-year ice formed over a single winter. This change makes the polar region increasingly vulnerable to storms that could smash their way through the final remnants of thinner, one-year sea ice, making a completely ice-free summer in the Arctic increasingly likely.
An unpublished study of changes to the multi-year ice over the past few decades has revealed that a part of the Arctic that should be a “nursery” for older ice has in recent years turned into a “graveyard”. Instead of multi-year ice forming within the Beaufort Gyre, a huge circular movement of ice off the coast of northern Alaska and Canada, it is now melting away within this critical region.
The result is that while older, multi-year ice typically made up more than 20% of Arctic sea ice in the 1980s, it now comprises just 3% and what little multi-year ice is left behind is behaving like the crushed ice of a cocktail, more prone to being pushed about and melting compared to a solid ice cube.
The loss of multi-year ice is important because it forms an important bulwark against further ice loss as the region gets warmer, says Walt Meier, a sea ice specialist at Nasa’s Goddard Space Flight Center in Greenbelt, Maryland, who studies the loss of multi-year ice with the help of satellite imagery.
“In the past, the seasonal ice loss in summer would tend to stop when it got to the multi-year ice because it’s three to four metres thick. You couldn’t melt that much ice in summertime, but now what’s happening is that things are getting more broken up,” Meier said.
“Multi-year ice is more fragmented so now you are getting warm water attacking it from all sides. Previously, it was a consolidated ice pack, like a wall of multi-year ice where warm water may melt it a little bit at the edges. But now you are getting big chunks of individual floes sitting there, floating round, surrounded by water that has been warmed by summer sunlight.
“The ice is getting thinner and the winds can more easily break it up. Once broken up, the winds can push it more easily. That just breaks things even further.”
Arctic sea ice, the vital seal-hunting platform of the polar bear, is considered important for the wider climate because it reflects sunlight back into space. The more it melts, the more open ocean there is to soak up sunlight, raising regional temperatures even further.
The Beaufort Gyre is traditionally where much of the multi-year ice forms, Meier said. Its circular winds and currents spin in a clockwise direction, keeping sea ice confined within the colder Arctic region, preventing it from slipping out into the warmer north Atlantic via the Fram Strait, separating Greenland and Svalbard.
Since about the mid-2000s, the circular movement of sea ice in the Beaufort Gyre has speeded up, indicating that this multi-year ice is more “slushy” and fragmented. At the same time, older ice within the gyre has melted, attacked in different directions by warm water.
“Now we’re seeing the thicker, multi-year ice melting out completely, particularly in the Beaufort and Chukchi seas, so it’s getting harder for that multi-year ice to survive. The Beaufort Gyre was like a nursery for the older ice and now it has become sort of like a graveyard where the ice is spinning… surrounded by warm water,” he said.
Computer models in the past predicted the first sea ice-free summers in the Arctic occurring mid-century, but these models have assumed a smooth loss of ice as it melts, rather than a catastrophic break-up. Now many scientists predict the first summers free of Arctic sea ice could occur within the next 10 to 15 years.
“You’re going to get the first ice-free summer when you have an extreme summer, almost by definition. But with this break-up of ice cover and loss of multi-year ice, the system is becoming more vulnerable to extreme summers,” Meier said.
“The ice has become more vulnerable to the weather and so more vulnerable to extremes. In that sense, things have definitely changed and it makes things less predictable in many ways because you can’t predict when or where the next storm is going to hit.
“We’re obviously heading for a sea ice-free Arctic at some point, but which year it happens may very much depend on a big enough storm happening in the right year at the right time.”
Although we may not see a sea ice-free Arctic this summer, we are likely to see the continued loss of multi-year ice that makes that event more and more imminent.
