Oldest frozen DNA reveals a greener Greenland

Oldest frozen DNA reveals a greener Greenland
19:00 05 July 2007
NewScientist.com news service
Catherine Brahic

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Picture this: sweeping conifer forests, with pine, alder, spruce and yew trees, crawling with beetles, flies and spiders, and with butterflies fluttering through the sun-dappled branches.

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It does not sound like a description of Greenland, but scientists say this is what the island looked like half a million years ago. They were able to paint the picture by extracting what is probably the oldest-known DNA from the ice at the base of the Greenland ice sheet.

The approach fills a significant gap in knowledge, says lead researcher Eske
Willerslev at the University of Copenhagen in Denmark: "About 10% of Earth is
covered in ice, and we have really no idea of what the environment looked like
in these regions before the ice was formed."

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Willerslev and his
colleagues extracted hundreds of DNA samples from the ice 2000 metres down at
the very base of the southern Greenland ice sheet, in a
location known as Dye 3.

Comparing the recovered fragments with
the DNA sequences of modern plant and animal species revealed the presence of
alder, spruce, pine, and yew trees. They also found DNA from beetles, spiders,
flies and butterflies. The best modern-day analogue is the forest in eastern
Canada.

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Mammals possible
Willerslev does not exclude
finding frozen mammal DNA, if researchers were to process larger volumes of ice.
"We know from previous experiments to extract DNA from permafrost that plant DNA
survives better, probably because there is much more to start with," he told New
Scientist.

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In 2003, Willerslev extracted horse DNA from permafrost.

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Once the researchers extracted the frozen DNA, they set about
dating it - and more surprises followed.

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A well-regarded modelling study from 2006 by Bette Otto-Bliesner
of the US National Center for Atmospheric Research suggested that the Dye 3 site was not covered in ice during the last interglacial period -
about 120,000 years ago (Science, vol 311 p 1751).

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Disputed dates
But when Willerslev's team dated their recovered DNA, they found
that it was at least 450,000 years old. This would mean that the
Greenland site must have been completely covered in ice 120,000 years
ago.

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"We used four different dating
techniques," says Willerslev, which returned overlapping date ranges.
He adds that the samples were also sent to other labs, which returned the same
results. "All the dating experiments suggest the DNA is older than the last
interglacial period," he says.

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The researchers conclude that the ice at
the bottom of the ice sheet at Dye 3 is between 450,000 and 800,000
years old. This implies the 2006 modelling study is incorrect and Dye 3
was not ice-free 120,000 years ago.

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This suggests that
the Greenland ice sheet is more stable than currently thought.
Temperatures in the Arctic during the last interglacial period were
significantly warmer than they are today - between 3C and 5C higher, according
to the latest Intergovernmental Panel on Climate Change report.

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The IPCC
also says that sea levels are likely to have been between 4 and 6 metres
higher than today.

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Sea-level clues
"We know the sea
level was higher in past and we know [that the extra water] had to come from the
ice sheets," says David Vaughan of the British Antarctic Survey. Many
scientists think that this water probably came from Greenland, a
hypothesis that was strengthened by Otto-Bliesner's 2006 study.

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But if Willerslev's dates are correct, and the
Greenland ice cap extended all the way to southern Greenland during the last
interglacial period, then the sea-level rise could not have come from
melting ice in Greenland, at least not in its entirety. "If it
wasn't Greenland then it had to be Antarctica," says Vaughan.

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Eric Wolf, also at the British Antarctic Survey says this may mean
scientists have underestimated the stability of Greenland's ice sheet.

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"It may mean that we have been too dramatic about what is happening to
Greenland," he told New Scientist. "But the flipside is that if this
is true, then we have not been dramatic enough about what is happening to
Antarctica."

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Journal reference: Science (vol 317, p 111)

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They are going around in circles, not realizing that there dating techniques are the problem! Message 1

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