Washington: For more than a century scientists have known that Earth`s ice ages are caused by the wobbling of the planet`s orbit, but a new research has revealed that Antarctic warming began at least two, and perhaps four, millennia earlier than previously thought.
A West Antarctica Ice Sheet Divide project researcher stands in a snow pit next to an ice core with data from 68,000 years ago. The prominent line across the middle of the ice separates one year`s ice and snow accumulation from the next years.
A US-led research team studying a new ice core from West Antarctica found that warming there was well under way 20,000 years ago.
"Sometimes we think of Antarctica as this passive continent waiting for other things to act on it. But here it is showing changes before it `knows` what the north is doing," said T.J. Fudge, a University of Washington doctoral student in Earth and space sciences and lead corresponding author of the paper.
The findings come from a detailed examination of an ice core taken from the West Antarctic Ice Sheet Divide, an area where there is little horizontal flow of the ice so the data are known to be from a location that remained consistent over long periods.
Fudge identified the annual layers by running two electrodes along the ice core to measure higher electrical conductivity associated with each summer season. Evidence of greater warming turned up in layers associated with 18,000 to 22,000 years ago, the beginning of the last deglaciation.
He noted that the warming in West Antarctica 20,000 years ago is not explained by a change in the sun`s intensity. Instead, how the sun`s energy was distributed over the region was a much bigger factor.
It not only warmed the ice sheet but also warmed the Southern Ocean that surrounds Antarctica, particularly during summer months when more sea ice melting could take place.
The research is published in journal Nature.