Posted on 01/10/2006 2:47:01 PM PST by blam
Broken ice dam blamed for 300-year chill
14:21 10 January 2006
NewScientist.com news service
Kurt Kleiner
A three-century-long cold spell that chilled Europe 8200 years ago was probably caused by the bursting of a Canadian ice dam, which released a colossal flood of glacial meltwater into the Atlantic Ocean.
Two new papers, using different computer models, show that the massive freshwater flood accounts for evidence of the sudden climate change, which cooled Greenland by an average of 7.4°C, and Europe by about 1°C. It was the most abrupt and widespread cool spell in the last 10,000 years.
Evidence for the cooling has been found in ice core samples, preserved pollen, evidence of shifting lake levels and ocean sediment. Some researchers think the cooling might have been caused by normal fluctuations in solar radiation.
In 1999 Don Barber, a geologist now at Bryn Mawr College in Pennsylvania, US, and colleagues suggested that the cooling was caused by flooding by glacial meltwater. Geological evidence shows that by about 11,000 years ago, retreating glaciers had left two huge freshwater lakes sprawling over Central Canada and parts of the northern US, bigger than all of today's Great Lakes combined.
Eventually, the lakes broke through an ice sheet that served as a dam and drained into Hudson Bay, and from there into the North Atlantic (Nature, vol 400, p 344).
Barber's idea was that the influx of fresh water changed salinity levels in the North Atlantic, and disrupted the thermohaline circulation – the currents that bring warm southern water north, helping to warm Europe and the Arctic regions.
"Strong confirmation"
In the new papers, one in the Proceedings of the National Academy of Sciences and the other in the current Quaternary Science Reviews, two teams of researchers using different computer models say that both models show that such a freshwater flood could shut down ocean circulation in a way that is consistent with temperature data from the time.
"We've shown the hypothesis generates the climate change that generates the data. It makes the story of the 8200-year event a much more well-rounded story," says Gavin Schmidt, a climatologist at NASA's Goddard Institute for Space Studies in New York City, US, a co-author of the PNAS paper.
"I would say it's a pretty strong confirmation of our understanding of that event," says Barber.
The work could have implications for the modern climate. Some researchers suggest that global warming and glacial melting might one day change ocean salinity enough to cause a similar disruption in ocean currents.
Journal references: Proceedings of the National Academy of Sciences (DOI: 10.1073/pnas.0510095103), Quaternary Science Reviews (vol 25, p 63)
The lake may have emptied within months. That's pretty good considering that the lake 11,000 ya that drained into the great lakes then into the Atlantic was larger than all the great lakes put together.
Yes, I agree with this assessment. There were most likely areas that were quite temperate, and probably even tropical at the equator. Or, there is the possibility that the ice age was not even that at all, but a product of the shifting of the earths axis and therefore the location of the polar regions. What if the polar regions of say 100,000 years ago were just a couple hundred miles south (referring to the arctic region of course) of where it is now. It has been determined that the polar regions are in a constant state of flux and the north pole's location is moving towards Russia. Could this explain both continental drift and temperal variations around the world throughout it's history?
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Well dah.
And here I was to blame Bush and our SUV.
Which would make my theory absolutely absurd. Well, you know I'm not a geologist, nor am I an anthropologist, so I can really just have a lightly educated opinion on the matter. Thanks for the info!!
Klingon? Surely that is not a logical conclusion. Fascinating. :)
No, *I* broke the dam!!
Albert Einstein was willing to consider that the earth might shift its axis now and then, and even that the crust might slip on the inner core.
I don't find the idea as foreign as I once did.
Thanks for the ping. Just what we were talking about the other day.
It looks like the ice sheet on North America melted from the top, leaving ice walls around the edges, and then broke through the ice walls in several places.
I wonder why the ice sheet on North America melted but the ice sheet on Greenland didn't.
Frozen Klingon
Like blam said, the biggest (final) flood went north, but prior to the last, there were several other flooding events, some of which flowed southward, some which were "domino" effect floods, ( i.e., glacial lakes emptied into others, then into Lake Aggassiz, then channeled down available outlets..
Here's a good link with history of Lake Agassiz..
( Grew up in North Dakota, proud member, Lake Agassiz Rock Club.. )
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