Open to Talent

Going under the sea ice - Getting to the bottom of Antarctic mystery

Researchers are using revolutionary techniques to understand the depths of the frozen ocean

Dr Guy Williams
Polar pavlova: Sea ice is like "the doily
around the edge" of the Antarctic
land mass, says Dr Guy Williams.

By Peter Cochrane

University of Tasmania researchers are developing a "game-changing" strategy to measure the thickness of sea ice in Antarctica.

The plan, as outlined by polar oceanographer Dr Guy Williams at a Research Week showcase presented by the Institute for Marine and Antarctic Studies, will involve the use of both underwater robots and unmanned aerial vehicles.

Sea ice is the frozen ocean around a land mass such as Antarctica or Greenland. "Think of a pavlova – sea ice is the doily around the edge," Dr Williams explained.

"It's the canary in the coal mine. In the Arctic, Greenland is melting and our canary is dead."

Typically 1-2 metres thick, sea ice expands each winter and contracts during summer. This year, the maximum wintertime extent of Antarctic sea ice went beyond 20 million square metres, the largest in 35 years of satellite observations. Researchers suspect this could be the result of higher-intensity westerly winds and/ or increased melt-water from the Antarctic ice sheet, which both favour greater sea ice coverage.

"Sea ice has no impact on rising sea levels. So why is it important? Because we see it as an early warning system for the really big problem that is the melting of Antarctic land ice.

"It's the canary in the coal mine. In the Arctic, Greenland is melting and our canary is dead. Arctic sea ice is declining very rapidly – so it's a very clear signal from our warning system.

"It's a bit more confusing in the Antarctic – we do know that the ice sheet is losing mass, however the average area of sea ice is slightly increasing. And to get to the bottom of the total change in sea ice volume, we must examine its thickness – and that is actually quite hard to do."

In the past, researchers have relied on ship-based observations as vessels such as the Aurora Australis crunch through the ice.

"Maybe once every five years or more we are able to get off the ship and drill holes in the  ice but these too are crude measurements. So now we are very excited by the advent of the autonomous underwater vehicle (AUV) which we can use to map the bottom of the sea ice at a depth of about 20m. Over the last four years, working in three areas around Antarctica with scientists from the British Antarctic Survey and an AUV operated by the Woods Hole Oceanographic Institution, we have been amazed by this new view of sea ice from below. This data was previously unattainable and will provide an improved assessment of sea ice thickness estimates from satellites."

Dr Williams said next time researchers plan to use unmanned aerial vehicles – like the OktoKopter used by Dr Arko Lucieer's TerraLuma team in the University's School of Land and Food.

"We hope to have an aerial vehicle to follow the underwater robot, to map the top and the bottom of the sea ice at the same time."

www.utas.edu.au/channel-utas/general-interest/media/understanding-antarctic-sea-ice-expansion