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The First Geological Evidence for Past Glacier Retreat in Antarctica

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Posted November 30, 2015

A new study by a team of geoscientists from New Zealand, led by Richard Jones, a postdoctoral research fellow at Victoria University, provides the very first geological evidence of rapid glacier retreat in Antarctica’s past that was caused by minor climate warming, and lasted for several hundred years.

First geological evidence of rapid retreat of Antarctica’s Mackay Glacier in the past suggests that even a very slight and relatively short-lived warming of the oceans could cause a large-scale runaway event, capable of reaching a point of no return. Image credit: Wetenschatje via Wikipedia.org, CC BY-SA 3.0.

First geological evidence of rapid retreat of Antarctica’s Mackay Glacier in the past suggests that even a very slight and relatively short-lived warming of the oceans could cause a large-scale runaway event, capable of reaching a point of no return. Image credit: Wetenschatje via Wikipedia.org, CC BY-SA 3.0.

The team collected and analysed rocks from different elevations along the Mackay Glacier, which drains the massive East Antarctic Ice Sheet (EAIS), thought to be more stable than the West Antarctic Ice Sheet, where melting of several glaciers has now reached the point of no return, according to a NASA study published last year.

Chemical analysis of the rocks revealed the glacier had retreated and thinned rapidly about 7,000 years ago, proving it’s not the sleeping giant it was once thought to be. According to Jones, the rate of thinning was nearly identical to that seen today in glaciers of West Antarctica that lose more than 150 cubic kilometres of ice each year due to a warming ocean.

“Before Richard’s study, we had a theory about how ice sheets might respond and we had computer models that encapsulate this theory, but we had no direct geological evidence that this had occurred in the past,” said study co-author Andrew Mackintosh. “This gives us an example of how this can occur, the period of time that this might extend over, and the rate at which the ice might be lost.”

The concept of marine ice sheet instability, proposed to be a major factor in the rapid retreat of glacial ice in the past, describes how part of Antarctica’s ice sheet grounded below sea level will react to warming.

As an ice sheet grows and develops, it slowly invades the land that sits below sea level, thereby displacing the sea. This creates a fundamental vulnerability – whenever the glacier starts retreating backwards, thicker parts of ice flow with greater stress, potentially causing a runaway feedback loop. “A little bit of ice retreat leads to much greater rates of ice loss.”

All that was needed to trigger this was a couple of years of warmer ocean temperatures that initiated the initial retreat, which then accelerated as it reached the deeper trough.

The team will return to Antarctica in January to study a much larger glacier, which also drains the East Antarctic Ice Sheet, to look at its past thinning history.

The research was published in the journal Nature Communications.

Source: radionz.co.nz.

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