Physics on ice

Stories of physics research in Antarctica - into, under, and from within the ice. Claire finds out about measuring sea ice thickness and supercooling. Katy Gosset learns how scientists detect neutrinos from outer space.

The frozen continent of Antarctica is defined by its snow and ice. On land, freshwater ice sheets kilometres thick sit on top of rock. In the ocean, an area of sea ice twice the size of Australia forms each winter, to break up in summer.

Though distant and intangible to most of us, what happens to Antarctic ice has global impacts, hence researchers want to find the best ways to monitor it in a warming world.

But for others, Antarctic ice presents unique and ideal conditions to catch glimpses of elusive subatomic particles from space.

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How thick is that ice?

What happens to Antarctic sea ice affects the global climate and ocean circulation. But measuring its thickness is hard.

Not only does it change every year, but in some places, it can change every day. On top of that, it forms over a massive area, much of which is inaccessible. Added to that, radar from satellites has difficulty finding the bottom of the ice because of the salt and a soft mushy layer that confuses it.

Instead, satellites can only measure the distance between the top of the snow and ice and the water. Which is maybe only 10 - 20 cm thick, on the most volatile patch of ocean on the globe.

So, tricky to do.

Emeritus Professor Pat Langhorne started her career trying to use radar to measure sea ice thickness. But when she and colleagues discovered that the salt and 'warm' mushy layer under the ice prevented this, she put that research aside and went on to investigate other aspects of sea ice.

Now, 35 years later, she has returned to this problem.

Langhorne and her collaborators now use electromagnetic (EM) induction to identify the bottom of the ice layer by flying a torpedo like piece of equipment, called Rosie, low over the ice.

This 'EM bird' gives more accurate measurements, which can be ground-truthed by drilling holes in the ice and checking the thickness manually. Eventually the plan is to use Rosie's measurements to calibrate the satellites. And, though retired, this is what excites Langhorne, and keeps her coming in to her office at the University of Otago Physics department.

Supercooling and crystals

But the ice in Antarctica has even more mysteries to it…

Go to this episode on rnz.co.nz for more details