Sydney, Jan 24: Scientists have found clues to climate changes in radioactive fallout from nuclear bombs detonated in the atmosphere more than 50 years ago, in limestone cave stalagmites around Australia.
Researchers from the Australian National University, Newcastle University and the Australian Nuclear Science and Technology Organisation proposed harnessing stalagmites as ancient rain gauges to map past climate patterns. They found that in dry years, rainwater, dripping into caves to grow stalagmites, would seep in so slowly it would have plenty of time to soak up rare metals and natural isotopes from the soil.
But in wet years the water would gush in so fast it would have no time to leach out the elements.
According to the researchers, varying levels of isotopic and rare metal concentrations deposited in stalagmites should point to droughts and deluges in Australia as far back as 500,000 years.
Dr Ed Hodge, a carbon-dating specialist and speleologist at Lucas Heights, said yesterday the radioactive material would have settled on the surface before seeping into the caves with rainwater, dripping down to become part of the stalagmites.
He said, ''What really surprised me was the amount of radioactive carbon that was deposited in the stalagmites.'' Our research showed that stalagmites could be used to reveal past weather patterns, the age quoted him as saying.
The scientists were confident they can date stalagmites up to 500,000 years old by dating their ratios of natural uranium and thorium.