[Aqualist] Quaternary in the news
Tim.Barrows at anu.edu.au
Fri Oct 5 15:34:40 EST 2007
SCIENCE media office
5 October 2007
Nearly 12,900 years ago as the world was warming after the last ice
age it was suddenly plunged back into the cooler for another 1300
years. Temperatures dropped by as much as 12C and ice sheets
advanced. The sudden changes were thought to be global in scale, but
now research is suggesting that the Southern Hemisphere was spared.
The cooling episode, known as the Younger Dryas event, was likely
linked to a disruption of ocean circulation in the Atlantic. If this
cycle were disrupted, as researchers think it might be if the
Greenland Ice Sheet were to rapidly melt, it would have big
implications for the climate. The important question is "how big."
The Younger Dryas was definitely felt in the Northern Hemisphere, but
whether its effects were global is a matter of debate. At the Waiho
Loop site in New Zealand, wood has been found in glacial debris
dating to the time when the cooling took place, suggesting that
glaciers responded to the Younger Dryas event.
But palaeoclimatologist Tim Barrows at The Australian National
University has his doubts. He has previously dated the remains of
glaciers in Australia and found no evidence for cooling after the
last Ice Age. Using a new method for dating glacial sediments similar
to radiocarbon dating, he measures radioactive elements in rock
surfaces that are produced by nuclear reactions between minerals and
cosmic rays. Barrows and colleagues now report in Science that
boulders from the Waiho Loop, date to 10,500 years, more than 1000
years after the Younger Dryas event had ended.
They support their finding with a new sea surface temperature record
from a core off the coast of New Zealand. The record from the core
shows no sign of the Younger Dryas cooling. In fact, the core data
suggests that temperatures actually warmed during the time period.
"Heat accumulating in the Southern Hemisphere as the North cooled is
precisely what we expected to see if the ocean conveyor belt were
shut down in the North Atlantic", comments Barrows.
"This study that shows no obvious cooling in the Southern Hemisphere,
suggesting that previous theories of the hemispheres being
climatically synchronous is questionable" comments geomorphologist
Derek Fabel at the University of Glasgow. "It is good to see
re-examination of critical Earth history events using new techniques,
and this particular study shows that there is still a lot about the
time period of the Younger Dryas that we still do not understand"
adds geologist Ken Verosub at UC Davis.
On the bright side, if global warming triggers a collapse of an ice
sheet which triggers another ice age, Australia and New Zealand will
be toasty warm.
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