The Heat Is Online

Old Arctic Sea Ice Gives Way to Newer, Thinner Ice

Thick, Old Arctic Ice Nearly Gone, Jan. 18, 2008 


Jan. 18, 2008 -- A new study using satellite measurements of Arctic sea ice have revealed that thinner ice that's only two or three years old now accounts for 58 percent of the ice cover -- up from 35 percent in the mid-1980s.


Meanwhile, ice older than nine years had all but disappeared by 2007.


The extinction of the older, thicker ice is effectively melting away the Arctic Ocean's hedge against complete summer meltdowns, say researchers.


"The thinning is consistent with long-term warming, " said ice researcher James Maslanik of the University of Colorado in Boulder.

Maslanik is the lead author of a paper reporting the thinning ice published in the latest issue of the journal Geophysical Research Letters.


The key difference in the new study from those done in the past is that the researchers were able, for the first time, to distinguish and measure different thicknesses of perennial ice -- that's ice which survives summer melts to grow thicker for multiple winters.


The result is that the researchers can better calculate the sea ice volume in addition to how much area the sea ice is covering.


Both are critical numbers for deciphering how the Arctic Ocean is responding to global warming.


"In our study, in the maps, there are a couple of places where the ice thickness has increased," said Maslanik, "but it doesn't balance out with the losses."


The thinner ice that's now dominating the Arctic is more vulnerable to ridging -- the crumpling into ridged rafts of ice -- or melting. Either way you get more open water which can absorb summer sunlight and warm up the Arctic even further.


The key to the new sea ice measurements is data from the laser altimeter onboard NASA's Ice, Cloud and Elevation Satellite (ICE-Sat). Using the altimeter data to measure the different heights of ice floating above the water, the researchers could distinguish between older, thicker perennial ice and younger, thinner perennial ice.


They then applied the new information to almost three decades of data from satellite imagery and drifting buoys, which had been used to estimate ice age. The result was a record of differently-aged perennial ice volumes going back to the early 1980s.


"They had a remarkably high correlation of age and ICE-Sat observation," commented ice researcher Ron Lindsay of the University of Washington in Seattle.


Even better, the changes Maslanik's team sees over the decades seem to mesh with models over the same period, Lindsay told Discovery News.