NASA: Sea ice minimum / summer 2007
Arctic Ocean ice has thinned dramatically during the past few years, with vast quantities of stable multi-year ice flushing into oblivion out in the Atlantic Ocean.
Replacing these reliable royal-blue floes built over many years — the literal bedrock of the Arctic ice habitat — are weak pans formed during one or two seasons at a time.
As this older ice increasingly “gives way” to the younger and thinner ice, the Arctic becomes more prone to another unprecedented meltback similar to the 2007 season, when ice cover set an all-time minimum record, according to a new study by scientists at the University of Colorado at Boulder.
“This thinner, younger ice makes the Arctic much more susceptible to rapid melt,” said Research Professor James Maslanik in an online story. “Our concern is that if the Arctic continues to get kicked hard enough toward one physical state, it becomes increasingly difficult to reestablish the sea ice conditions of 20 or 30 years ago.”
The impact on marine mammals may be devastating, because the melting consumes their habitat for hunting, resting and breeding. Native hunters and others who use sea ice for travel also find conditions more unpredictable and dangerous.
“North of Alaska, the ocean now is receiving more than twice the amount of heat from the sun every year than in the early 1980s,” University of Alaska Fairbanks ice specialist Hajo Eicken told people listening to a climate teleconference this week, sponsored by the Alaska Center for Climate Assessment and Policy. (Here is a PDF slide show of Eicken’s presentation.)
“We find that some of this warm water survives the winter and actually moves up into shallow water near Barrow, and this has a very big impact by melting ice from below and destabilizing the coast-line cover,” Eicken said.
The UCB study, published in Geophysical Research Letters, basically confirmed the worry that the Arctic is fast approaching a “tipping point” where sea ice will irreversibly disappear during summer.
Using satellites, the scientists developed an estimate of ice thickness from 1982 to 2007 — and found the old ice in stunning decline.
“These data show that in addition to the well-documented loss of perennial ice cover as a whole, the amount of oldest and thickest ice within the remaining multiyear ice pack has declined significantly,” the scientists wrote in the paper’s abstract.
“The oldest ice types have essentially disappeared, and 58 percent of the multiyear ice now consists of relatively young 2- and 3-year-old ice compared to 35 percent in the mid-1980s.
Ice coverage in summer 2007 reached a record minimum, with ice extent declining by 42 percent compared to conditions in the 1980s. The much-reduced extent of the oldest and thickest ice, in combination with other factors such as ice transport that assist the ice-albedo feedback by exposing more open water, help explain this large and abrupt ice loss.
An online story from UCB explained further:
The researchers used passive microwave, visible infrared radar and laser altimeter satellite data from the National Oceanic and Atmospheric Administration, NASA and the U.S. Department of Defense, as well as ocean buoys to measure and track sections of sea ice.
The team developed “signatures” of individual ice sections roughly 15 miles square using their thickness, roughness, snow depth and ridge characteristics, tracking them over the seasons and years as they moved around the Arctic via winds and currents, Emery said. “We followed the ice in sequential images and track it back to where it had been previously, which allowed us to infer the relative ages of the ice sections.”
The replacement of older, thicker Arctic ice by younger, thinner ice, combined with the effects of warming, unusual atmospheric circulation patterns and increased melting from solar radiation absorbed by open waters in 2007 all have contributed to the phenomenon, said researcher Sheldon Drobot.
“These conditions are setting the Arctic up for additional, significant melting because of the positive feedback loop that plays back on itself,” he said.
“Taken together, these changes suggest that the Arctic Ocean is approaching a point where a return to pre-1990s ice conditions becomes increasingly difficult and where large, abrupt changes in summer ice cover as in 2007 may become the norm,” the research team wrote in Geophysical Research Letters.