Rising bedrock could slow down the melting Antarctic ice sheet

Image credit: DT

The West Antarctic Ice Sheet, which is at risk of floating away due to global warming, may be halted in its tracks by bedrock that is rising as the weight of the melting ice lowers, scientists have said.

The research provides a rare bit of good news in global climate studies as it could slow the melting of the whole shelf and the subsequent rise in sea levels.

The study was completed by an international team, led by DTU Space at the Technical University of Denmark with Colorado State University (CSU).

“We studied a surprising and important mechanism, glacial isostatic adjustment, that may slow the demise of the massive West Antarctic Ice Sheet by lifting up the bedrock and sediments beneath the ice sheet,” explained CSU Professor Rick Aster, a co-author of the study.

Scientists have been concerned that this ice sheet is particularly precarious in the face of a warming climate and ocean currents, because it is grounded hundreds to thousands of feet below sea level – unlike the ice sheets of East Antarctica or Greenland – and its base slopes inland.

This bowl-like topography makes it susceptible to runaway destabilisation and even complete collapse over centuries to thousands of years.

The entirety of West Antarctica contains enough ice that, if it were to melt, would contribute more than 10ft of average global sea level rise. In addition, the ice sheet is so massive that it gravitationally attracts an ocean bulge that, if released, would lead to an additional increase of 3ft or more to sea level in parts of the northern hemisphere.

The West Antarctic Ice Sheet is currently contributing approximately 25 per cent of global melting land-based ice each year, and recent satellite-based studies have shown that this amount has increased in recent decades.

This figure is equivalent to about 37 cubic miles or a cube of over three miles on each side, the scientists said.

They have led the installation of sensitive GPS stations on rock outcrops around the remote region to measure the regional uplift of the Earth in response to the thinning ice sheet.

Measurements showed that the bedrock uplift rates near the coast of West Antarctica were as high as 1.6in (4cm) per year, one of the fastest rates ever recorded in glacial areas.

“This very rapid uplift may slow the runaway wasting and eventual collapse of the ice sheet,” said Aster. “The uplift tends to stabilise the critical grounding line where the ice sheet loses contact with underlying bedrock or sediment and goes afloat,” he explained. This grounding line then counteracts the process of the ice sheet collapsing.

Researchers also found that the uplift is accelerating and predicted that it will continue to do so into the next century.

“Our research indicates that recent and ongoing ice loss in the region has been underestimated by approximately 10 per cent in past studies, because this bedrock uplift was inadequately accounted for in satellite measurements,” said Aster.

Lead author Valentina Barletta said that this uplift is occurring very rapidly, when compared with other regions of the Earth where glaciers are melting.

“Normally we would see this type of uplift happening slowly, over thousands of years after an ice age,” she said. “What we found tells us that Earth’s underlying viscous mantle is relatively fluid and flows relatively quickly when the weight of the ice is taken off,” she added.

The researchers have deployed a large network of sensitive seismographs across Antarctica to produce seismic tomographic images – analogous to a gigantic CAT scan – of the deep Earth below Antarctica.

This work assisted in the interpretation and modelling of the GPS uplift data by providing detailed mapping of a vast region of the Earth’s mantle up to 400 miles below West Antarctica.

Previous and related studies conducted by the research team have also revealed that some hotter features below Antarctica extend still deeper, over 600 miles, into the Earth.

Aster said that while the research does provide room for a positive outcome, if future global warming is extreme, the entire West Antarctic Ice Sheet will still melt.

“To keep global sea levels from rising more than a few feet during this century and beyond, we must still limit greenhouse gas concentrations in the atmosphere, which can only occur through international cooperation and innovation,” he said.

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