Seismic surprise on Totten Glacier

More of the Totten Glacier is floating on the ocean than previously thought, increasing its potential to contribute to global sea level rise.

Glaciologist, Dr Ben Galton-Fenzi, said the Totten Glacier is one of the fastest flowing and largest glaciers in Antarctica and, until now, satellite observations suggested that more of it was grounded on Antarctic bedrock.

As part of the Australian Antarctic Program*, Dr Galton-Fenzi’s team of researchers, including scientists from the Australian Antarctic Division, University of Tasmania’s Institute for Marine and Antarctic Studies, and the Central Washington University, spent the summer in Antarctica studying the glacier.

The team conducted a ground-based geophysical survey, using a hammer and plate system to send sound waves into the ice and geophones to ‘listen’ to the sound reflected back. The idea was to map the structure of the upper layers of ice, but the team got back more than they expected.

“We were surprised the technique allowed us to see through up to two kilometres of ice and into the ocean beneath,” Dr Galton-Fenzi said.

“When we conducted a geophysical test at a site on the glacier we’d previously thought was grounded on bedrock, we discovered there was ocean underneath — so the glacier was actually floating at that location.”

Professor Paul Winberry from Central Washington University said if more of the glacier is floating on a warming ocean, it may help explain recent periods of accelerated melting and flow.

“It also means the Totten might be more sensitive to climate variations in the future,” he said.

Dr Galton-Fenzi said the new geophysical data would improve the accuracy of models of the glacier’s (and the broader ice sheet’s) sensitivity to a warming climate. These models will in turn inform the placement of instruments on the Totten Glacier to best measure ice flow and thickness.

Next season the team plan to continue their geophysical survey using small quantities of explosives, rather than the hammer and plate system.

“Explosives will allow us to see right through to the bedrock below the glacier, so we can map the boundary where the ice sheet moves from being grounded, to a floating ice shelf,” Dr Galton-Fenzi said.

The Totten Glacier contains enough ice to raise global sea levels by about three metres if it all melted. Since the 1900s the global sea-level has risen by about 20 centimetres and by the end of the century the Intergovernmental Panel on Climate Change projects it could rise by up to one metre or more, if global emissions of carbon dioxide continue unabated.

“These precise measurements of Totten Glacier are vital to monitoring changes and understanding them in the context of natural variations, and the research is an important step in assessing the potential impact on sea level under various future scenarios,” Dr Galton-Fenzi said.

Instruments to measure the glacial flow, speed and thickness have been left on the glacier for another 12 months collecting data. The field season was supported by the Australian Antarctic Division and the Australian Research Council Antarctic Gateway Partnership.

Eliza Grey and Wendy Pyper
Australian Antarctic Division

*Australian Antarctic Science Project 4287