Is an East Antarctic melt probable?

Does melting of the East Antarctic Ice Sheet (EAIS) pose a threat to sea level rise? Studies of the ice melt that fuels sea level rise often focus on the prominent warming and melting of glaciers in Greenland and western Antarctica. The massive East Antarctic Ice Sheet (EAIS) has been largely ignored, until recently. “It’s generally been assumed that it’s so big and so cold that it’s probably immune to some of the warming trends we’ve seen across the planet,” said Chris Stokes, a professor at Durham University. Two recent studies, however, paint a new picture of the world’s thickest, unwavering giant, suggesting the need to look deeper into eastern Antarctica.

Sensitivity to climate

Using 50 years of observed flight and satellite data of 175 glaciers along 5,400 kilometers (3355 miles) of coastline, Stokes and his team of researchers concluded that the EAIS is more sensitive to climate shifts than suspected. The results showed the glaciers rapidly responding to minor temperature shifts. For every degree increase, the glaciers retreated 0.5 kilometers (0.3 miles) per decade. “We detected a clear synchronization between what the glaciers were doing and what the climate was doing,” he said. The analysis found three trends: 63 percent of glaciers retreated from 1974 to 1990, when it was warmer; 72 percent advanced from 1990 to 2000, when it was cooler; and 58 percent advanced from 2000 to 2010, a period that experienced phases of warming and cooling.

These panels show satellite imagery of the retreating and advancing Vanderford Glacier, Wilkes Land, East Antarctica. The red lines on each image mark the terminus of the glacier in 1963. The arrow in the 1963 image shows the direction of ice movement. Credit: USGS Earth Resources Observation Science Center

These panels show satellite imagery of the retreating and advancing Vanderford Glacier, Wilkes Land, East Antarctica. The red lines on each image mark the terminus of the glacier in 1963. The arrow in the 1963 image shows the direction of ice movement. Credit: USGS Earth Resources Observation Science Center

At its highest, the EAIS is almost 5 kilometers (3 miles) thick, containing about 50 meters (164 feet) of sea level equivalent. Stokes is careful to point out, however, that this amount wouldn’t be dumped into the ocean in any short amount of time, and if it were to happen, it would probably take thousands of years. “The implication with our study,” said Stokes, “is that if we keep adding greenhouse gases into the atmosphere, we could expect to see changes similar to those taking place in Greenland and west Antarctica.”

A peak into the past

Another study suggest that the EAIS has melted once before, during the Pliocene Epoch some 5 to 2.5 million years ago, a period that is comparable in atmospheric CO2 concentrations and global temperatures to those predicted for the end of this century. The EAIS alone added about 10 meters (33 feet) to sea level rise. “This is already after a completely deglaciated West Antarctic Ice Sheet and deglaciated Greenland Ice Sheet,” said Carys Cook, a researcher at Imperial College London. “In total that accounts to be 22 meters (72 feet) of global sea level rise.”

The BedMap2 project has mapped Antarctic’s topography beneath ice sheets and glaciers. Scientists are examining the Wilkes Subglacial Basin to better understand glacial movement and potential contribution to rising sea levels. Credit: BedMap2, British Antarctic Survey

The BedMap2 project has mapped Antarctic’s topography beneath ice sheets and glaciers. Scientists are examining the Wilkes Subglacial Basin to better understand glacial movement and potential contribution to rising sea levels. Credit: BedMap2, British Antarctic Survey

To study this long-ago event, Cook and her team of researchers focused on the Wilkes Subglacial Basin, a large low-lying region where the ice sheet is up to 2.4 kilometers (1.5 miles) below sea level. Glacier systems below sea level are some of the fastest accelerating of the world. “If any retreat was to take place in the EAIS,” Cook said, “this would be the site.”

They analyzed marine sediment cores drilled off shore near East Antarctica and about 2.9 kilometers (1.8 miles) below sea level. The presence of a specific type of rock, only present in large quantities quite far and deep within the Wilkes Subglacial Basin, indicated serious ice sheet retreat. “Since most ice sheet erosion occurs at the margin of the ice sheet, that indicated times when the ice sheet retreated,” Cook said. Increasingly warming seawater sloshed exposed rocks about 161 kilometers (100 miles) inland of the current ice sheet edge.

Cook states that the next piece of the puzzle is to quantify the rate of change for these events. “If something similar happens today,” she said, “we really need to get a nail on how quickly it will happen.”

Stokes added, “We hope studies like these will help persuade other scientists to investigate glaciers in East Antarctica.”

References

Cook, Carys P. et al. 2013. Dynamic behaviour of the East Antarctic ice sheet during Pliocene warmth. Nature Geoscience 6, 765-769, doi:10.1038/ngeo1889.

Miles, B. W. J., C. R. Stokes, A. Vieli, and N. J. Cox. 2013. Rapid, climate-driven changes in outlet glaciers on the Pacific coast of East Antarctica. Nature 500, 563-566, doi:10.1038/nature12382.

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