Freeze frame: Isotope science studies climate change
At our Department of Imaging and Applied Physics, the Isotope Science Research Group has been determining sources of pollution from major civilisation and industrialisation episodes by analysing lead in ice-cores from Antarctica and Arctic regions. Led by Professor of Isotope Science Kevin Rosman, the team has, since 1990, been measuring the isotopic ratios of lead in ice-core samples which provides a fingerprint of the pollutants’ presence and its origin.
Air samples from around the globe have shown that lead in the atmosphere varies isotopically depending on its origin. Lead-containing particles can travel thousands of kilometres, be collected in snowflakes and then deposited onto the ice sheets of Greenland and Antarctica. The team has been analysing ice-core samples, identifying the source of the lead in the samples by using a lead isotope register (which is being continually expanded), thereby tracing the Earth’s pollution history.
‘Lead never goes away – once released it’s there forever, and by analysing the elemental and isotopic patterns of the lead we obtain a fingerprint of the pollutants’ origin,’ Rosman explained.
‘For example, the Antarctic ice sheet was free of lead pollution until just over a century ago when lead mining and processing began in eastern Australia. The pollution record also shows the impact of leaded petrol in the Southern Hemisphere from the 1950s.’
Funded by Australian Research Council (ARC) Discovery Grants, the project has benefited, and continues to benefit, from research links with the Laboratory for Glaciology and Geophysics of the Environment in Grenoble (France), the Korea Ocean Research and Development Institute, the University of Venice and the Australian Antarctic CRC.
Climate change is the latest focus for the Isotope Science Research Group; their work on pollution has been extended to exploring aspects of climate change by analysing lead isotopes and isotopes of other trace metals such as strontium in ice-cores.
Analysis of the ice record is a rapidly advancing field and the potential of using lead and strontium isotope variations as proxies for climate changes is essentially unexplored. At our world-class John de Laeter Centre of Mass Spectrometry, the team is now analysing lead and strontium isotopes within Greenland and Antarctic ice stretching back over six complete glacial cycles and almost 700,000 years.
‘Permanent icecaps can trap comprehensive samples of the atmosphere. More recent ice provides evidence of human impact, while ancient ice reflects climatic changes,’ Rosman said. ‘Using this, we may be able establish a record of environmental changes caused by natural phenomena and increase our understanding of past climate change.’
The work could determine whether there is a link between temperature and isotopic composition (and the identified source regions) which could provide knowledge about the extent of glaciation, changing vegetation cover, desert formation and other factors that may have played a role in the character of dust reaching polar regions.
The research is pioneering in its development of sensitive measurement techniques for lead isotopes, performed at the recently constructed Advanced ultraClean Environment (ACE) – the world’s most advanced facility for decontaminating ice and processing ultra-clean samples. The new techniques are enabling measurements of lead isotopes in dust contained in the ice at very low concentrations.
‘We measure the isotopic fingerprint in as little as two picogram of lead. By comparison, a small grain of soil might typically contain about 5000 picogram of lead,’ Rosman explained.
Tracing the dust back to its source and measuring the changing ‘isotopic tracer’ in the ice enables the changing climatic conditions at the source regions to be interpreted and could, Rosman believes, simultaneously signal the timing and location of past episodes of climate change.
‘Analyses of ice-cores stretching back over almost one million years of deposition can provide baseline data showing climatic fluctuations in the ancient past for comparison with more recent studies of climate change,’ he said.
‘We’re trying to establish what events were linked to climate change by providing another measure of change – and the development of highly sensitive techniques is the key to it all. Without them nothing can be done.’
You can find this and other research-related articles in the latest issue of R&D Now.
'Lead never goes away... by analysing the elemental and isotopic patterns of the lead we obtain a fingerprint of the pollutants' origin.'