Mongolia is the most land locked country in the world, lying between China and Russia and framed by the Gobi Desert and the Siberian Steppe. It's a vast, dry and wind swept land with a climate that's not for the faint-hearted. It's haunting as much as it's unique.
Mongolia's uniqueness lies in the surrounding regions that influence it and the westerly winds which bring it moisture. The dynamics of this major wind system also affect the growth and shrinkage of glaciers which, for the first time, are providing unique new data about regional and global climate variability.
According to climate scientist Dr Henrik Rother, of ANSTO, who visited Mongolia's Khangay Moutnains in 2007 and 2008, mountain glaciers are sensitive climate indicators.
"The expansion or retreat of mountain glaciers mirror changes in temperature and precipitation as well as leave land formations and sediments to help scientists reconstruct past climates," he said.
"At ANSTO we are dating rocks and deposits from glacial moraines and this basic research will help improve models of past climate movements and ultimately help predict future climate."
Scientists have always known that glacial deposits preserve past climate information but making sense of them was extremely difficult, mainly because accurate geological dating of mountain glacial movements was not possible until recently.
Carbon dating is the leading dating technique but this requires organic matter, such as plants or animals, to produce the carbon-14 signal for measurement. The very conditions that make glaciers grow means that plant and animal remains are rarely preserved, so historically this has been a challenge.
ANSTO scientists have contributed to the development of a new geological dating method called Surface Exposure Dating' (SED) which has addressed this challenge. It utilises the long-lived radionuclides Beryllium-10 and Aluminium-26 to date glacial rocks and is opening new doors to providing high resolution climate records from mountain regions around the world.
Henrik explained that the dating technique uses Accelerator Mass Spectrometry via ANSTO's powerful particle accelerator, ANTARES, to measure minute quantities of these radionuclides.
"As large glaciers expand and retreat, fresh rock becomes exposed at the Earth's surface. These are bombarded by cosmic rays which in turn produces small amounts of Beryllium-10 and Aluminium-26 within the quartz minerals in the rocks," Henrik said.
"Over time these radionuclides build up so that the older the rock, the greater the isotopic concentration. By counting the atoms using ANTARES we can, for the first time, date the geological event that exposed the rocks to cosmic rays and from that establish a chronology of past glaciations going back as far as three to four million years and as short as a few thousand," he said.
Henrik recently returned from Mongolia on a field trip collecting rock samples from the Khangay mountains. He and ANSTO's head of Cosmogenic climate Archives of the Southern Hemisphere (CcASH) Project, Dr David Fink, are working in collaboration with Germany's Professor Frank Lehmkul from the University of Aachen, a world leader in glacial climate variability in Asia.
The latest trip was Henrik's second to Mongolia which was made possible through the collaboration with Professor Lehmkul. The idea was first conceived at a special scientific meeting in Tibet in China where he and David each gave invited talks and met the Professor. Henrik was then invited to join the first Mongolian expedition in 2007.
The samples collected on the latest expedition will add to data collected from the 2007 trip, which found three key results.
"First, we now know Mongolia experienced a major glacier advance 30-35,000 years ago, coinciding with an 'interstadial' or slightly warmer phase during the last ice age. Curiously at that time, glaciers in Europe and North America were shrinking, unlike Mongolia, which grew.
"Second we confirmed that a big advance occurred 18,000 years ago, several thousand years after what is known globally as the 'Last Glacial Maximum' about 22,000 years ago," he said.
"Finally, there was a third large glacial advance, almost as big as the first two, around 13,000 years ago. Once again this took place when European and North American glaciers did the opposite and were in full retreat."
Henrik explained that the data showed that Mongolia's major glacial advances occurred during the past 50,000 years but were not in sync with events recorded globally.
"To explain why, we have to look at the Westerly wind system. If it fails to give moisture, glaciers can't grow and we believe it's the lack of moisture, not the effects of colder temperature, which was the primary driver of glacial advances in the high mountains of central Asia.
"Overall these results also highlight the fact that past climate states, as deduced from ice and marine cores, only represent average global conditions while our work shows the important regional climate variability on the back of these global trends," he concluded.
As well as Mongolia, David and Henrik have conducted numerous field expeditions to Tasmania, New Zealand and Antarctica in collaboration with other scientists to collect glacial deposits for exposure age dating. This work is part of cutting edge research within the CcASH Project aimed at obtaining high-resolution records to better understand the variability of our past climate and environment.
Published: 02/12/2008