Research by three New Zealand scientists may have solved the mystery of why glaciers behave differently in the Northern and Southern Hemispheres.
Geologist David Barrell of GNS Science, Victoria University geomorphologist Andrew Mackintosh and glaciologist Trevor Chinn of the Alpine and Polar Processes Consultancy have helped provide definitive dating for changes in glacier behaviour.
They were part of a team of nine scientists, led by Joerg Schaefer of the Lamont-Doherty Earth Observatory at Columbia University in New York, who used an isotope-dating technique to get very precise ages for glacial deposits near Mt Cook.
They measured the build-up of beryllium-10 isotopes in surface rocks bombarded by cosmic rays to pinpoint dates when glaciers in the Southern Alps started to recede. The technology is expected to be widely applied to precisely date other glaciers around the world.
Glaciers are sensitive indicators of climate changes, usually advancing when it cools and retreating when it warms.
The first direct confirmation of differences in glacier behaviour between the Northern and Southern Hemispheres, the new work topples theories based on climate in the Northern Hemisphere changing in tandem with the climate in the Southern Hemisphere.
The research argues that at times the climate in both hemispheres evolved in sync and at other times it evolved differently in different parts of the world.
Dr Barrell said their research presented "new data of novel high precision", though the team has so far chosen not to roll out wider interpretations too quickly.
He said much of it reinforced work done 30 years ago by Canterbury University researcher Professor Colin Burrows, who used NZ glacier data to highlight some of the similarities and differences between northern and southern records over the past 12,000 years.
The paper published in Science magazine yesterday showed the Mt Cook glaciers advanced to their maximum length 6500 years ago, and have been smaller ever since.
But glaciers in the Swiss Alps advanced to their maximum only in the past 700 years - during the Northern Hemisphere's "Little Ice Age", which ended about 1860.
During some warm periods in Europe, glaciers were advancing in New Zealand. At other times, glaciers were well advanced in both areas.
In a commentary which accompanied the research, Greg Balco, from the Berkeley Geochronology Centre in California, said the conclusion that glacier advances in the Northern and Southern Hemispheres were not synchronised was "unexpected".
Dr Barrell said the paper presented only the first instalment of the dating work, and more would be revealed at an international workshop on past climates to be held at Te Papa on May 15.
"The New Zealand findings point to the importance of regional shifts in wind directions and sea surface temperatures," he said.
Regional weather patterns such as the El Nino Southern Oscillation were superimposed on the global climate trends reflected in the behaviour of glaciers.