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Andes tropical glaciers smallest for 6000 years

By John Parnell

The largest ice cap in the tropics is smaller now that it has been in the last 6000 years, researchers from Ohio State University have discovered.

As the ice retreats it reveals the debris of plants it consumed as it advanced more than six millenia ago, indicating that the Quelccaya ice cap in the Andes is melting fast.

“The ages of the plants tell us that over the last 25 years the ice cap has retreated 65 times faster than it advanced more than 6000 years ago,” said Lonnie Thompson, distinguished university professor of earth sciences at Ohio State and lead author of the study.

Thompson has been studying Quelccaya and taking ice core samples since 1983 and told RTCC that the ice cap provides valuable climate information in two ways.

“It serves both as a high resolution recorder of climate change through the ice core history as well as an indicator of [ongoing] climate change.

“The Quelccaya ice cap has lost 25% of its surface area since I was a graduate student in the mid-1970s,” he said.

“In 1991 the ice core records started to be compromised by surface melting at the summit of this ice cap and the percolation of melt water through the upper layers of snow and firn, which alters both the isotope and chemistry records.”

An ice core from the Quelccaya Glacier has provided the final piece in the puzzle to recreating the climate record in the tropics (Creative Commons/Edubucher)

‘Rosetta Stone’

The scientists also believe that ice cores from Quelccaya are the ‘Rosetta Stone’ for the climate record of the tropics.

They found that ice cores taken from the ice cap in 2003, matched perfectly with those taken from glaciers half the world away in the Himalayas and Tibet.

The composition of oxygen and hydrogen isotopes in ice cores can be used to infer the temperature from the time that that layer of ice was laid down.

The deepest ice cores from the poles can stretch back hundreds of thousands of years. The obvious lack of ice in tropical regions means the same volume of data is not available. The discovery fills an important hole in the climate record.

“These ice cores provide the longest and highest-resolution tropical ice core record to date,” said Thompson.

“In fact, having drilled ice cores throughout the tropics for more than 30 years, we now know that this is the highest-resolution tropical ice core record that is likely to be retrieved,” he added.

The findings from the Quelccaya and new observations of its retreat appear in the journal Science Express.

“We have been able to derive a proxy for sea surface temperatures that reaches back long before humans were able to make such measurements, and long before humans began to affect Earth’s climate,” Thompson said.

These sea surface temperature estimates also deliver important information on the El Niño phenomenon in the Pacific that drives short term climate changes.

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