30 Sep 2021

Physics on ice

From Our Changing World, 5:00 am on 30 September 2021

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.

Rosie the EM bird being flown over sea ice

Rosie the EM bird being flown over sea ice Photo: Gemma Brett

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How thick is that ice?

Emeritus Professor Pat Langhorne in Antarctica

Emeritus Professor Pat Langhorne in Antarctica Photo: Supplied

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.

Pat Langhorne on an early Antarctic research trip

Pat Langhorne on an early Antarctic research trip Photo: Supplied

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.  

1943 Basler BT-67 aircraft with Rosie (green-nosed torpedo-shaped object)

1943 Basler BT-67 aircraft with Rosie (green-nosed torpedo-shaped object) Photo: Supplied

Supercooling and crystals

Dr. Inga Smith

Dr. Inga Smith Photo: Supplied

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

When freshwater ice comes off the land into the ocean it forms floating ice shelves. Where ice shelf and sea ice meet you can often find the interesting phenomenon of supercooled water – water still liquid below the local freezing point.

When supercooled water snap freezes it results in ice crystals forming. These make for tricky conditions for standard oceanographic equipment, so senior lecturer Dr. Inga Smith has been working on making specific under-ice-shelf sensors.

Smith is just getting ready to head to Antarctica for her 5-week expedition to test the equipment she and her colleagues have designed. Her sensors will be placed in the remotely operated vehicle Icefin, created by her international collaborators.

Getting accurate measurements under the ice shelves will help determine the health of Antarctic ice - an important thing to monitor in a continual warming world.

The Icefin remotely operated vehicle

The Icefin remotely operated vehicle Photo: Supplied

Powerful particles

Jenni Adams with one of the IceCube optical sensors.

Jenni Adams with one of the IceCube optical sensors. Photo: Duncan Shaw-Brown

We learn about protons and electrons in high school yet many people have never heard of neutrinos.

But an international team of scientists believes these high energy particles could carry key information about some of the farthest parts of the universe.

Neutrinos are tiny, subatomic particles with no electric charge and almost no mass. They rarely interact with matter, making them very hard to measure.

Where better to look out for them then, than within the darkness and purity of subsurface ice in Antarctica?

The IceCube neutrino detector is made up of a big array of optical sensors placed at depts between 1,450 and 2,450 meters into holes melted in the ice using a hot water drill. There they lay in wait for the circumstantial occurrence of a neutrino colliding with another particle.

University of Canterbury Professor, Jenni Adams, has just won the Dan Walls Medal for her work on the project, the first woman to be awarded the prestigious physics prize.

She talks to Katy Gosset about the research she's doing in Antarctica and the role of women in physics.

The IceCube array, the world's largest neutrino observatory.

Photo: AFP / HO / NSF / F. DECAMPS

Listen to more:

Our Changing World has two award winning series based on Antarctic research and ice for you to enjoy!

  • Voice of the Iceberg - Artist Joseph Michael and his team record the characters and sounds of icebergs in Antarctica. Produced by Alison Ballance.
  • Voices from Antarctica - Alison Ballance finds out what it takes to live in and do science in Antarctica, in a podcast series recorded on the frozen continent in November 2019.

Dr Inga Smith's project to develop HiPSMI - High Precision Supercooling Measurement Instrument for supercooling measurements under ice shelves is funded through the New Zealand Marsden Fund's Engineering and Interdisciplinary Sciences Panel.

The soundart used in this piece is from the audiovisual project One Data Day, composed of Beneath_Above - Playing with listening by Elissa Goodrich and featuring field recordings by artist Gabby O'Connor.


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