Mysterious warm periods found in Antarctic history
20 November 2009, by Tamera Jones
Temperatures in Antarctica during the warm periods between ice ages, called interglacials, may have been higher than previously thought. The findings, reported in Nature today, could help researchers better understand more about how the climate can quickly change on the continent.
Antarctica
Until now, scientists thought maximum temperatures during interglacials were a little warmer than today's temperatures. But they now think they may have been up to 6ºC warmer.
'Our results suggest that Antarctica warmed rapidly in the past, but at the moment we don't know why,' says lead author, Dr Louise Sime from the British Antarctic Survey. 'It might be that at higher CO2 levels Antarctic temperatures are more sensitive to small variations, due to regional warming feedbacks.'
Climate has flipped
Scientists have known that the climate has flipped between ice ages and interglacials over the last few million years for some time. Fossils of animals that lived during warm or cool climates in deep-sea sediments and rocks reflect changing temperatures.
'Our results suggest that Antarctica warmed rapidly in the past, but at the moment we don't know why.'
Dr Louise Sime, British Antarctic Survey
Ice cores tell a similar story. Changes in the proportion of different types of atoms of the same chemical element, or isotope, in ancient ice give researchers detailed information about how temperatures varied.
When it's cold, water made with the heavy version, or isotope, of hydrogen - deuterium - falls out of the sky as snow sooner than water made with normal hydrogen, because it's heavier than normal water. Ice cores containing ancient ice record this, so they tell scientists what the temperature was thousands of years ago.
'Isotopes in ice cores are a very neat temperature proxy, because you're using fairly simple physics,' says Sime.
To figure out average changes in temperature each year, scientists have assumed that the way snowfall records annual temperatures each year hardly varies over East Antarctica.
But when Sime and scientists from the Open University and the University of Bristol analysed ice cores from three regions of East Antarctica containing 340,000-year-old ice, they found differences in the way snowfall records annual temperature.
Sime says, 'It's unlikely that all of the differences in ice cores depend on temperature. Instead there are also likely to be some changes in snowfall.'
'Further data on interglacial climates from Greenland would be invaluable to help understand what's going on,' she adds.
The world has seen cycles of glaciation with ice sheets advancing and retreating on 100,000-year time scales. These periods are called glacials and interglacials respectively. We're currently in an interglacial, which started around 11,000 years ago.
Evidence for warmer interglacials in East Antarctic ice cores
L C Sime, E W Wolff, K I C Oliver & J C Tindall
Nature
doi:10.1038/nature08564
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