Scientists find explosive method to measure ice

David Prior and his team are in Antarctica for a survey at the Priestley Glacier, some 400km from...
David Prior and his team are in Antarctica for a survey at the Priestley Glacier, some 400km from Scott Base.PHOTO: SUPPLIED
NZME  science reporter Jamie Morton, who is at Scott Base covering New Zealand research in the Antarctic, talks to David Prior of the University of Otago.

New Zealand scientists have found a clever way to investigate how climate change impacts in the Antarctic will touch the rest of the world.

This summer, a University of Otago-led team is working at the Priestley Glacier, some 400km from Scott Base, where it will attempt to glean insights that could tell us what the best satellite monitoring cannot.

Getting a clearer picture of what several degrees of global warming might mean for the frozen continent - and the 60m of global sea level rise it holds - has become an increasingly urgent mission for scientists.

"In both Antarctica and Greenland, ice flows from the land to the sea and an increase in the rate of flow of ice from the land to the sea will cause global sea levels to rise," study leader David Prior said.

"It is clear that global climate change will have this effect. What is less certain is the rate of sea level change that will occur in the next few decades."

That made understanding how ice flow would respond to the changing climate critically important.

A big driver of ice flow is ice deformation, which happens along the edges of the fast-moving Priestley Glacier, where it meets slow-moving ice at what is called the shear margin.

"At the edge of the Priestley Glacier, ice is being sheared and stretched out, in the same way a ball of pastry gets stretched with a rolling pin," Associate Prof Prior said.

"How fast the ice shears depends on how hard it is being pushed and on the temperature of the ice.

"We will treat the Priestley Glacier shear zone as a natural experiment to calibrate how ice might speed up as the world gets warmer."

In the project, supported by the Marsden Fund and Antarctica New Zealand, team members are producing seismic waves to image the large-scale structure of the rapidly shearing ice at the glacier's edge.

They record these low-frequency sound waves using an array of seismometers spread across the 10km-wide area in which the ice deforms.

"We detonate explosives at each of about 10 locations to generate seismic waves that pass through the shearing ice before being recorded on our seismometer array," Prof Prior said.

"We have to drill holes up to 25m deep with hot water, to place the explosives in hard ice.

"This ensures that the source signal is strong. Some of the seismometers are also frozen into holes, up to 50m deep, to improve the receiver signal."

By combining this data with laboratory work, they would be able to put together an extrapolation describing ice flow behaviour - which could ultimately be used in ice sheet modelling.

"The end goal is to be able to predict how fast ice flow will respond to warming temperatures and stress changes related to ice shelf collapse." 

 - Jamie Morton is hosted at Scott Base by Antarctica New Zealand.

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