Canadian scientists discover new clues to rapid Arctic ice melt
by BOB WEBER
The Canadian Press
Last updated
A 500-kilometre walk over treacherous Arctic terrain has resulted in a possible explanation for why sea ice in northern waters is melting so much more rapidly than anyone thought it would.
“We're trying to understand why the ice is melting so fast,” said Simon Boxall of the Catlin Arctic Survey. “It's not just down to simple warming. There are more complicated processes.”
The speed at which sea ice is disappearing in the Arctic has far exceeded almost all predictions and alarmed climate scientists.
A 2007 paper from the National Snow and Ice Data Center in Boulder, Colo., found that the projections of the UN-sponsored Intergovernmental Panel on ClimateChange were already obsolete three years after they were published.
When projections from the panel were compared with actual observations, the authors found that between 1953 and 2006 the sea ice was retreating three times faster than it should have. Between 1979 and 2006, when satellite data was available, the actual retreat was twice as fast as climate models predicted.
The report concluded that sea ice retreat is 30 years ahead of where scientists thought it would be.
“Decay of the ice cover is proceeding more rapidly than expected based on the model simulations,” said the report published in Geophysical Research Letters.
The team at the Catlin Arctic Survey, sponsored by the Catlin Group insurance company, thought the answer might lie in different temperatures at different levels of Arctic seas.
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 Mr. 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.
Mr. 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 Mr. Boxall, may be part of the reason that sea ice is melting so much faster than anyone thought it would.
“What we're seeing is that (fresh meltwater) being taken away from the surface and replaced by slightly warmer water,” said Mr. Boxall. “The evidence is that the surface waters are (now) slightly warmer.”
Mr. Boxall cautions that his conclusions are based on a preliminary review of data that the team brought back from the ice.
“We need to compare our results with previous data and with groups from other areas.”
A paper is being prepared for publication.
The results do show that the effects of climate change and global warming are not always obvious, suggested Mr. Boxall.
“The evidence is that there's something interesting going on. The fact that (the climate) is getting warmer is one reason for the ice melting, but it's more complex than that.”
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6 comments:
And this would be also the reason why the THC won't shutdown without a massive burst of meltwater from Greenland, imo.
You know, there is some recent research that says that a very large pool of fresh water is accumulating in the Arctic Sea. This is also a partial explanation.
If that large pool for some reason or mechanism decides to come out rapidly into the North Atlantic, well...
the big fresher water pool could mix in the spring as the saltier layer (generated by 1st year ice) sinks, but on this I'm not certain, I'll give you that.
I was under the impression that it is not mixing and it is growing, but I could always be entirely wrong.
it seems we have a slight disagreement on this issue of the thermohaline circulation shutting down, but let's leave it at that, shall we? I guess neither of us is an expert on ocean circulation in the northern Atlantic or Arctic Ocean so it may be better to leave this thing to be solved by further research if it is possible to solve that way. OK? :-)
LOL - I'm not disagreeing with you, I'm just relating to you further (somewhat vague) information.
I sure don't want to find out though if it will shut down.
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