East Antarctic Ice Sheet not as stable as thought

The East Antarctic Ice Sheet, which locks away enough water to raise sea level by an estimated 53 metres - more than any other ice sheet on the planet - may not be as stable as thought, scientists say.

A study, published in the journal Nature, found that the ice sheet has a long history of expanding and shrinking - a finding that indicates the ice sheet may contribute substantially to global sea level rise as Earth's climate warms.

Data collected during the first-ever oceanographic survey of East Antarctica's Sabrina Coast shows that this region may be particularly susceptible to climate change because the glaciers flow from the Aurora Basin, a region of East Antarctica that mostly lies below sea level.
 

Sean Gulick, a research professor at the University of Texas Institute for Geophysics (UTIG) said that glaciers from the Aurora Basin have been stable only for the past few million years.

"It turns out that for much of the East Antarctic Ice Sheet's history, it was not the commonly perceived large stable ice sheet with only minor changes in size over millions of years," Gulick said.

"Rather, we have evidence for a very dynamic ice sheet that grew and shrank significantly between glacial and interglacial periods," he said.

"There were also often long intervals of open water along the Sabrina Coast, with limited glacial influence," he said.

Using marine seismic technology deployed from an icebreaker, researchers were able to reconstruct how glaciers on the Sabrina Coast have advanced and retreated during the past 50 million years.

The team also took core samples of mud from one to two metres below the seafloor and analysed ancient pollen to determine the age of the samples.

The Sabrina Coast, and nearby Aurora Basin, are particularly important because regional glaciers are presently thinning and retreating as nearby ocean waters warm.

If the ice sheet in the Aurora Basin melted, global sea levels would rise more than three to five metres.

According to the team's data, ice advanced from the Aurora Basin and retreated back again at least 11 times during the first 20 million years of the ice sheet's history.

Researchers also found that the young ice sheet was much wetter than it is today, with meltwater from the surface flowing into a network of channels beneath the ice.

These channels were eroded into the rock below the ice, leaving distinctive formations known as "tunnel valleys."

This dynamic time for East Antarctic glaciers occurred when atmospheric temperatures and atmospheric carbon dioxide levels were similar to or higher than present day.

"We shouldn't view this as one ice sheet that suddenly grew to its present size, but rather one that was a transient ice sheet that expanded every couple million years or so," Gulick said.