Soil study shock for scientists

Southern Alps found to fight climate change

SARAH-JANE O'CONNOR
Last updated 09:02 17/01/2014
Isaac Larsen
Krista Larsen

Isaac Larsen collects a sand sample at the Rapid Creek test site.

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The fast-growing Southern Alps also appear to be fighting climate change.

In a Science magazine article published online today, scientists from the United States and New Zealand said Southern Alps rocks were transformed into soil twice as fast as previously thought possible.

The new soil is then exposed to chemical weathering, the process by which carbon dioxide in the air reacts with soil. The carbon is locked into the soil, meaning there is less in the atmosphere contributing to climate change.

Researchers from the University of Washington and Lincoln University assessed rates of soil weathering in the Southern Alps.

Visiting sites along the western side of the mountain range, from Hokitika south to Karangarua, the team took soil samples to measure the removal of certain elements.

The research was part of Isaac Larsen's PhD work at the University of Washington. He and co-author Andre Eger, a postgraduate student at Lincoln University, were dropped to remote mountaintops by helicopter to collect soil samples.

By measuring the amount of Beryllium-10, an isotope that only forms at the Earth's surface, Larsen and his colleagues showed soil was being produced on the ridge tops at rates between 0.1 millimetres and 0.25mm a year.

The peak rate was more than twice what had been previously suggested as the "speed limit" for soil production.

Co-author Professor David Montgomery, also from the University of Washington, said "a couple of millimetres a year sounds pretty slow to anybody but a geologist".

"That's shockingly fast . . . because the conventional wisdom is it takes centuries," he said.

Vegetation growing high on the slopes of the Southern Alps could be responsible for the rapid soil production.

Plant roots reaching down into rocks may assist in breaking rocks apart to expose them to rainwater and chemical weathering.

GNS Science tectonic geologist Rupert Sutherland said parts of the Southern Alps were uplifted at rates of more than a centimetre a year - one of the fastest rates of mountain uplift in the world. This rapid uplift, driven by the Alpine Fault, meant there was a lot of young surface exposed to processes such as weathering.

Sara Mikaloff-Fletcher, an atmosphere-ocean modeller at Niwa, said the results could be important in understanding the fate of carbon dioxide in the atmosphere. "This type of result might be really important to understanding over the long term how long it's going to take to get back to a pre-industrial level of atmospheric carbon dioxide," she said.

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- The Press

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