Thawed In Prehistoric
By Steve Connor
10 August 2006
last time massive amounts of greenhouse gases were released into the
atmosphere, the North Pole was an ice-free expanse of open ocean that
was teeming with tropical organisms, a study has found.
Scientists have discovered
that the complete disappearance of the Arctic sea ice, 55 million years
ago, coincided with a dramatic increase in concentrations of carbon
dioxide or methane in the atmosphere - which must have caused global
After analysiing the sediments
on the floor of the Arctic Ocean, an international team of researchers
working for the Arctic Core Expedition (Acex) came to the conclusion
that the region was once extremely warm, unusually wet, and ice-free.
The scientists also found
that the Arctic is currently experiencing one of the fastest temperature
rises on record, with more sea ice melting each summer than at any time
in hundreds and possibly thousands of years.
The Acex research team drilled
frozen sedimentary cores from the ocean floor, which can be dated to
55 million years ago, a period known as the palaeocene-eocene thermal
maximum (PETM). Surface temperatures in some parts of the world were
then 8C (15F) higher than now.
"Building a picture
of ancient climatic events is a lot like putting together a jigsaw puzzle,
and what Acex allowed us to do was fill in a black section of the PETM
picture," said Gerald Dickens, a geochemist at Rice University
in Houston, Texas.
"It's difficult to overestimate
the importance of this kind of experimental evidence. The Acex cores
clearly show that the Arctic got very warm and wet during the PETM.
Even tropical marine plants thrived in the balmy conditions [of the
Arctic]," he said. The ice cores were drilled from the Lomonosov
Ridge, an under-sea mountain range that stretches from northern Greenland,
across the Polar Sea, to Siberia in northern Russia.
The task involved three icebreaker
ships: a drilling vessel and two further ice-breakers, which protected
the drilling operation from being crushed by drifting ice floes and
metre-thick pack ice. This was the first time that scientists have had
access to sedimentary cores drilled deep from under the Arctic.
Dr Dickens said the fossils
of some microscopic plants, which can trigger algal blooms, suddenly
become commonplace in the parts of the cores that are about 55 million
years old. These organisms lived only in the tropics prior to the PETM
warm period, suggesting the Arctic was also warm and ice-free during
Scientists are not sure what
caused the warming, which occurred over a relatively rapid geological
period of 100,000 years. But they think it may have been due either
to the release of vast deposits of carbon-containing methane stored
on the sea floor, or the massive release of carbon dioxide from volcanic
"The magnitude of the
carbon input at the PETM outset is truly enormous. If it were all volcanic,
you'd need something like a Vesuvius-sized eruption each day for centuries,
which seems very unlikely," Dr Dickens said.
Another possibility is that
there was a sudden release of massive amounts of methane and carbon
dioxide that had been locked away in the deep ocean in a frozen form
known as ocean gas hydrates. Even today, it is estimated that there
is more carbon locked away as ocean gas hydrates than all of the oil
and gas reserves of the world combined.
The latest study suggests
this huge reservoir of carbon has been released in the past with devastating
effects on the climate.
The last time massive amounts
of greenhouse gases were released into the atmosphere, the North Pole
was an ice-free expanse of open ocean that was teeming with tropical
organisms, a study has found.
© 2006 Independent News and Media Limited