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Such data is usually obtained from ships. But during the spring, when melting is greatest, there's still too much sea ice for ships to make it through.
So the scientists walked from Borden Island to Ellef Ringnes Island and also from near the North Pole all the way down to the northern tip of Ellesmere Island, slogging about 10 kilometres a day in below-deep-freeze temperatures over rugged, uneven ice. What they found was a surprise — a layer of seawater about 200 metres below the surface that was actually colder than when it had been measured by previous expeditions.
"That's counterintuitive," said Boxall. "We would expect to see, with global warming, warming conditions generally." But when they realized that the colder water was also saltier than they expected, an explanation began to suggest itself.
Boxall points out that the older sea ice is, the less salt it contains. Ice that's two or three years old already contains very little salt. Year-old ice, however, remains fairly salty. And when it melts, it produces meltwater that's denser than the relatively fresh water from older ice.
As multi-year ice declines throughout the Arctic, more of the saltier meltwater from younger ice is mixing into the ocean. That colder, denser water sinks more quickly and forces less dense water from deeper in the ocean up to the surface. Because fresh meltwater is colder than seawater, that means relatively warm water is being forced upwards. And that, said Boxall, may be part of the reason that sea ice is melting so much faster than anyone thought it would.
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http://www.winnipegfreepress.com/arts-and-life/life/greenpage/124625789.html