A 12,000-mile scientific research cruise that traversed the North Pole and sampled conditions across the Arctic Ocean found some of the thinnest floes yet observed at such high latitudes — offering a unique reality check on the diminished polar pack during one of the most severe seasonal melts on record.
"In the central Arctic, the proportion of old, thick sea ice has declined significantly," according to this report posted last week by the Alfred Wegener Institute for Polar and Marine Research. "Instead, the ice cover now largely consists of thin, one-year-old floes."
These latest observations from researchers aboard the German icebreaker Polarstern come only a few weeks after U.S. and European scientists declared the summer loss of sea ice put 2011 on par with the previous record minimum extent seen in 2007.
Satellite monitoring by the National Snow & Ice Data Center found sea ice cover shrank to the second smallest area yet observed during the age of satellites. But other measurements using rival satellites found the ocean-wide surface footprint of floes did dip into record territory, according to this dispatch by the European Space Agency.
Scientists say it's important not to get hung up on the differences — a reflection of trying to measure conditions across millions of square miles with satellites of slightly different capabilities. Both methods unveiled the same, unrelenting trend of sea ice destruction that has accelerated during the past 10 years.
Estimates of the total volume of sea ice — size of the surface footprint plus all the ice hidden beneath the surface — were 66 percent lower than the 30-year average and 75 percent lower than the maximum seen in 1979, according to the September analysis posted by the Polar Science Center at the University of Washington.
Now comes the eyewitness measurements taken during the institute's "TransArc" mission to document changes in water, air and ice across the polar sea.
With 150 scientists from six countries, the 387-foot Polarstern spent 16 weeks cruising the Arctic this summer and fall — traveling along a 11,800-nautical-mile-long route from Franz Josef Land to the western Canadian Basin. The vessel drove through floes at the geographic North Pole at exactly 11:42 p.m. ADT on Aug. 21 — its third visit to Earth's most northern spot.
"One of the most important research questions was: Did sea ice melt to a greater extent this summer, making it thinner than in past years?" explained this story about the trip.
To find out, sea ice physicists Marcel Nicolaus and Stefan Hendricks hauled a 13-foot-long, torpedo-shaped probe called the "EM Bird" beneath a helicopter over about 1,500 miles of tracts. The instrument produces electromagnetic induction — a magnetic field — that allows the scientists to measure the thickness of ice as it passes beneath. Its findings were stunning.
Much of the multi-year, royal-blue ice that once dominated the central Arctic has been replaced by brittle ice formed the previous winter with an average thickness of about 3 feet.
The Polarstern team concluded that 2011 sea extent was basically identical to record minimum seen in 2007.
"The ice has not recovered," Hendricks said. "This summer it appears to have melted to exactly the same degree as in 2007. Yes, it is exactly as thin as in the record year."
It gets worse. During the 2007 cruise, the team found thin, new ice in the Laptev Sea off the northern coast of Siberia. Not so during a visit to the same area about the same date in 2011.
"There was no sign of ice formation anywhere," said Ursula Schauer, chief scientist during that portion of the voyage. "The water temperature at a depth of (about 32 feet) was (about 37 degrees Fahrenheit) — that is how much the sun had heated the ice-free water surface."