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)
Better white wine.
Cool.
There's a place near me in Wash state (near Black Diamond) that has alot of sandstone with fossilized maple leaf impressions.
Maybe I'll get ambitious one of these days and go get some.
How is that a model that shows that global warming caused global cooling is proof that humans are now causing global warming?
um.. no kidding...
These lakes were held in place by ice?
What is that picture?
Yeah, kinda like evolution.
How "sudden" is sudden?
Just Dam(n).
I like comets.
Scientists at Cardiff University, UK, believe they have discovered the cause of crop failures and summer frosts some 1,500 years ago. The answer? A comet colliding with Earth.
http://www.50connect.co.uk/index.asp?main=http%3A//www.50connect.co.uk/50c/articlePages/genealogy_index.asp%3Fsc%3Dhist%26aID%3D9555
I believe the scientific term is ">1 VU rocks"
(VU - Volkswagen units)
In upper Manhattan there's exposed mica schist also with the glacial striations.
I do too.
Professor Stephen Oppenheimer believes it was a comet impact that began the end of the last Ice Age.
I broke the dam.
"We coulda had a V8!"
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