An international race is on to retrieve the first million-year-old sample from deep within Antarctica's ice to discover what drives major changes in Earth's climate. This 10-nation consortium completed two ice cores penetrating right through the Antarctic ice sheet; one of them, over 3000 meters long, is the oldest ice core in the world, containing a continuous record of the climate and environment of the last 800,000 years.
"It's a real head spinner," says Tas van Ommen at the Australian Antarctic Division in Hobart, Tasmania. But climatologists are keen to find an explanation. "If we don't understand the switch, then we cannot claim to understand why we have the climate we have today," according to Eric Wolff of the British Antarctic Survey in Cambridge, UK. Dr Wolff has been the chair of the scientific group in the European Project for Ice Coring in Antarctica (EPICA).
The current science believes that the shifts between ice ages and warm interglacial phases are thought to be influenced by three cyclical changes to Earth's motion: The Earth's axis wobbles or "precesses" on a 26,000-year cycle; changes its tilt on a 41,000-year cycle; and shifts its orbit from a somewhat circular to more elliptical on a 100,000-year cycle.
These three cyclical changes alter the intensity of sunlight hitting the Earth at high latitudes, affecting the state of glaciation. The big mystery about the shift that occured a million years ago is that there was no obvious change to any of these cycles. So what caused it?
One possible explanation is that there was a slow decline in the concentration of carbon dioxide in the atmosphere, starting around 3 million years ago, which could have tamped the greenhouse effect and cooled the Earth so much that the tilt towards the sun every 41,000 years no longer provided enough heat to melt the glaciers that formed in between.
But confirmation of this theory requires a direct record of the ancient atmosphere from analysis of the air that became trapped in tiny bubbles within ice as the snow it formed from fell to Earth.
EPICA has been joined in the chase for the million-year-old core at Dome C on east Antarctica's plateau by three other teams: one from the Australian Antarctic Division; a US contingent; and one from the Chinese Arctic and Antarctic Administration.
"China is there already, at Dome A," in east Antarctica, according to Dr Tas van Ommen (left), Principal Research Scientist Ice Cores and Climate of the Australian Antarctic Division in an interview with New Scientist. But despite their lead, the Chinese may have run into problems. Last month, Robin Bell of the Lamont-Doherty Earth Observatory in Palisades, New York, and her colleagues found that ice sheets in Dome A are growing from the bottom up. This could mean that any ancient ice that was once there may have melted and been replaced.
Despite these issues, Eric Wolff remains sanguine that the million-year-old ice core will be found. It is only recently that very deep cores have been drilled -- and three of them contain ice more than 160,000 years old. "It would be surprising if we happened to have already collected the oldest ice available," Wolff told New Sciemtist.
The Daily Galaxy via newscientist.com , antarctica.gov.au and epa.ie