Multiyear ice is ice that has survived at least one melt season, has less brine than first-year ice, and is much more difficult for icebreakers to navigate through. It is much more common in the Arctic than in the Antarctic, partly because the Arctic is somewhat landlocked and circulating currents do not move ice around as much as in the Antarctic.

The expedition found no large multiyear ice packs, but encountered hundreds of miles of “rotten ice”—half-meter layers of fresh ice covering chunks of older ice, which the icebreaker could push through with relative ease at up to 13 knots. Without multiyear ice, the Arctic is much more likely to become ice-free in summer. “We are almost out of multiyear ice in the Northern Hemisphere”, Barber remarked. “I’ve never seen anything like this in my 30 years of working in the high Arctic.”

As more ice melts in the Arctic, the larger expanses of darker water reduce the albedo, or reflectivity, of the area, creating a positive feedback loop that accelerates the melting process. Last month, the US National Snow and Ice Data Center (NSIDC) announced that Arctic sea ice appeared to have reached its minimum extent for the year (earlier post), with less sea ice than all but two previous years since satellite measurements began in 1979. The two years with less minimum Arctic sea ice were 2007 and 2008.

At one point, the expedition found a 16-kilometer (10-mile) wide, 6 to 8 meter thick multiyear ice floe. However, the floe broke up in a period of five minutes after being hit by a series of waves.

Barber was one of the lead investigators on the 2002-2007 Canadian Arctic Shelf Exchange Study (CASES), which brought together 400 scientists from 11 countries to study causes and effects of thinning and disappearing sea ice in the Arctic.

In 2005, the National Science Foundation’s Arctic System Science Committee predicted (earlier post) that the Arctic would eventually become ice-free in summer, with no imaginable chance of “any interaction between the components that would act naturally to stop the trajectory to the new [ice-free] system.”

—Jack Rosebro