Mountain 'dipsticks' reveal past ice history

Media Release: 25 May 2007

Mountain 'dipsticks' reveal past ice history

Researchers from New Zealand and Australia have used mountains as gigantic 'dipsticks' to probe the frozen history of the world's largest ice sheet.

The study by researchers at Victoria University of Wellington, Macquarie University in Sydney and the Australian Nuclear Science & Technology Organisation (ANSTO) was published this week in the prestigious American journal, Geology. It throws new light on the size of the East Antarctic Ice Sheet—which is centred on the South Pole and lies on the Indian Ocean side of the Transantarctic Mountains—during the last ice age.

Dr Andrew Mackintosh, Senior Lecturer in Victoria's School of Geography, Environment & Earth Sciences, says past changes in the volume of the East Antarctic Ice Sheet were not previously well known.

"The East Antarctic Ice Sheet, the world's largest, contains enough water to increase sea levels by 60m and is one of the most significant features in the Earth's global climate system. But we knew little of its size and mass 20,000 years ago during the last ice age, when sea levels were 120m lower than they are now. If we're to predict the response of the ice sheet to modern climate change, it is essential we understand how it reacted to the last major change in global temperatures."

Dr Mackintosh says it had been suggested that during the last ice age, the East Antarctic Ice Sheet was massively bigger in both height and breadth.

"Some researchers had hypothesised that this ice sheet was up to a kilometre higher with a significantly bigger surface area. But trying to understand what had occurred is difficult because the geological record is presently buried beneath the ice.

"To understand the ice sheet's size during the last ice age, we used mountains that pierce the ice sheet in Mac. Robertson Land as geological 'dipsticks.' Rocks were gathered and analysed to determine how long ago they were deposited while their height showed how thick the ice sheet was in the past."

Dr Mackintosh says the Victoria and Macquarie team, along with scientists at the Australian Nuclear Science & Technology Organisation found that the East Antarctic Ice Sheet has remained relatively stable for the last 20,000 years. The new findings are based on ‘cosmogenic exposure age dating’ “which is like radiocarbon dating of rock surfaces.”

"The small changes that did occur in the ice sheet's volume were probably due to changing global sea levels driven by the waxing and waning of the Northern Hemisphere ice sheets. In effect, the East Antarctic Ice Sheet reached its present volume about 6,000 years ago when global sea levels stabilised. Its sluggish response is in dramatic contrast to the West Antarctic ice sheet which has retreated continuously since this time and is a significant risk today."

Dr Mackintosh says the research also points to East Antarctic Ice Sheet's role in sea level changes caused by climate change.

"Our research suggests changes in sea levels due to global warming will not be caused by changes in East Antarctic Ice Sheet – yet. Most sea level rise in the short term will instead be sourced from the melting of valley glaciers, thermal expansion of the oceans, and from retreat of the Greenland and West Antarctic ice sheets."

ENDS

© Scoop Media