Home   News   Article

Subscribe Now

Evidence of how West Antarctic Ice Sheet shrunk rapidly at end of Last Ice Age uncovered by Cambridge researchers





The first direct evidence that the West Antarctic Ice Sheet shrunk suddenly and dramatically at the end of the Last Ice Age has been uncovered by researchers at the University of Cambridge and the British Antarctic Survey.

The evidence, unearthed using an ice core, shows the ice sheet thinned in one location within 200 years by an astonishing 450 metres - more than the height of the Empire State Building.

Tents at Skytrain Ice Rise. The nearest tent is the drilling tent with part of the winch mechanism protruding from the roof. Living tents are behind. Picture: University of Cambridge / British Antarctic Survey.
Tents at Skytrain Ice Rise. The nearest tent is the drilling tent with part of the winch mechanism protruding from the roof. Living tents are behind. Picture: University of Cambridge / British Antarctic Survey.

There is concern that rising temperatures could destablise the West Antarctic Ice Sheet in future and pass a tipping point that leads to a runaway collapse.

“We now have direct evidence that this ice sheet suffered rapid ice loss in the past,” said Prof Eric Wolff, senior author of the new study from Cambridge’s Department of Earth Sciences. “This scenario isn’t something that exists only in our model predictions and it could happen again if parts of this ice sheet becomes unstable.”

There is enough freshwater in the Antarctic ice sheets, from west to east, to raise global sea levels by about 57 metres.

Scientists consider the West Antarctic ice sheet to be more vulnerable because much of it sits on bedrock, below sea level.

Inside the drilling tent at Skytrain Ice Rise, a scientist prepares the drill for its next drop into the borehole. Picture: University of Cambridge / British Antarctic Survey.
Inside the drilling tent at Skytrain Ice Rise, a scientist prepares the drill for its next drop into the borehole. Picture: University of Cambridge / British Antarctic Survey.

There are already model predictions that suggest a large part of the West Antarctic ice sheet could disappear within the next few centuries, but when that might happen - and how fast - is not known.

Data from ice loss during periods of previous warming can be used to improve the models.

Antarctic ice covers a larger area than today at the peak of the Last Ice Age, 20,000 years ago, but as the planet thawed and temperatures climbed, the West Antarctic Ice Sheet contracted to something like its extent today.

“We wanted to know what happened to the West Antarctic Ice Sheet at the end of the Last Ice Age, when temperatures on Earth were rising, albeit at a slower rate than current anthropogenic warming,” said Dr Isobel Rowell, study co-author from the British Antarctic Survey. “Using ice cores we can go back to that time and estimate the ice sheet’s thickness and extent.”

Inside the drilling tent at Skytrain Ice Rise, engineers and scientists separating the inner barrel of the drill from the outer barrel between drilling runs. Picture: University of Cambridge / British Antarctic Survey.
Inside the drilling tent at Skytrain Ice Rise, engineers and scientists separating the inner barrel of the drill from the outer barrel between drilling runs. Picture: University of Cambridge / British Antarctic Survey.

Ice cores comprise layers of ice that formed as snow fell and was then buried and compacted into ice crystals over thousands of years.

Bubbles of ancient air and contaminants that mixed with each year’s snowfall are trapped within the cores, providing evidence on the changing climate and ice extent.

In 2109, a 651-metre long ice core was drilled in the Skytrain Ice Rise - a mound that sits at the edge of the ice sheet, near to where grounded ice flows into the floating Ronne Ice Shelf.

The ice cores were carefully transported back to Cambridge at -20C for analysis to reconstruct the ice thickness.

They measured stable water isotopes to learn the temperature at the time the snow fell. Since temperature decreases at higher altitudes, warmer temperatures are associated with lower-lying, thinner ice.

A piece of ice showing the air bubbles. Picture: University of Cambridge / British Antarctic Survey.
A piece of ice showing the air bubbles. Picture: University of Cambridge / British Antarctic Survey.

The pressure of trapped air bubbles was also measured. Lower-lying, thinner ice contains higher pressure air bubbles.

The findings, published in Nature Geoscience, showed the ice thinned rapidly 8,000 years ago.

“Once the ice thinned, it shrunk really fast,” said Prof Wolff. “This was clearly a tipping point — a runaway process.”

The researchers think this thinning was probably triggered by warm water getting underneath the edge of the West Antarctic Ice Sheet, which usually normally sits on bedrock.

It is thought this untethered a section of the ice from the bedrock so that it suddenly floated and formed what is now the Ronne Ice Shelf. The neighbouring Skytrain Ice Rise was no longer restrained by grounded ice so thinned rapidly.

Map showing the location of the Skytrain Ice Rise ice core. Picture: University of Cambridge / British Antarctic Survey.
Map showing the location of the Skytrain Ice Rise ice core. Picture: University of Cambridge / British Antarctic Survey.

The sodium content of the ice, which originated from salt in sea spray, was found to have increased about 300 years after the ice thinned.

This revealed that, after the ice thinned, the ice shelf shrunk back, so the sea was hundreds of kilometres nearer.

Dr Rowell explained: “We already knew from models that the ice thinned at around this time, but the date of this was uncertain. We now have a very precisely dated observation of that retreat which can be built into improved models,” said Rowell.

Insulated boxes full of ice cores being loaded into the Twin Otter aircraft, Skytrain Ice Rise. Picture: Eric Wolff
Insulated boxes full of ice cores being loaded into the Twin Otter aircraft, Skytrain Ice Rise. Picture: Eric Wolff

Ice sheet models had placed the retreat at anywhere between 12,000 and 5,000 years ago and it was not clear how quickly it happened.

While the West Antarctic Ice Sheet retreated quickly 8,000 years ago, it did stabilise at roughly its current extent.

“It’s now crucial to find out whether extra warmth could destabilise the ice and cause it to start retreating again,” said Prof Wolff.



This site uses cookies. By continuing to browse the site you are agreeing to our use of cookies - Learn More