What pancake ice tells us about the climate
Thursday, Oct 26, 2017, 12:03 AM | Source: Pursuit
Jason Monty, Grant Skidmore
Standing for six hours in a minus 15-degree room while watching ice form sounds like a colder version of the old saying ‘watching grass grow’. But researchers in the Melbourne School of Engineering at the University of Melbourne are doing just that.
Associate Professor Jason Monty and Dr Grant Skidmore are creating very specific ice formations in a huge indoor wave tank to investigate how they interact.
Over the past 20 years research has confirmed an increase in wind speeds and wave heights in our oceans. Researchers are now using the Sea-Ice-Wind-Wave-Interaction (SIWWI) facility, the first fresh-water tank of its kind in the world, to understand how certain types of ice form, melt, and respond to wind and waves.
“You can study how waves interact with ice in the field, but there are more unknowns than you can deal with,” says Dr Skidmore. “So we’ve created a very controlled experiment to look at each different variable.”
Continuous sea ice cover is diminishing because of climate change, and as larger areas ice become loose, waves can penetrate deeper into the ice cover. With wave action, this loose floating ice can turn into ‘pancake ice’.
These strange-looking formations resemble a lily pad, hockey puck or, as the name would suggest, a pancake. They are a common type of ice found floating in polar oceans and in large fresh water rivers and lakes in cold climates, such as the River Dee in Scotland.
“Research shows that extremely cold temperatures and reasonably large waves driven by the wind, disturb the ice-formation process on the water surface, resulting in small disks of ice (pancake ice) appearing before the formation of continuous sheets,” says Dr Skidmore.
“Understanding how pancake ice forms, melts and responds in a controlled environment helps better predict how they will move when storms hit and how waves interact with the ice shelves behind them.”
The research is a two-stage investigation.
The first involves studying what conditions generate this type of ice by separating the wind, wave and temperature events.
“Certain types of floating ice need waves to grow, but the conditions greatly determine what type of ice you get – grease ice, ice pans or pancake ice,” says Dr Skidmore.
So, what’s the difference?
Grease ice is a loose collection of ice crystals that never quite form a cohesive group.
“It got its name from whalers who thought this type of ice resembled floating whale fat - it’s so loose that you can’t grab it with your hand,” says Dr Skidmore.
“Ice pans are similar, but the air is cold enough that the top layer freezes. It has a soft underside though, so they break apart when you try to grab them.
“But pancake ice is hard. It grows with a cone-like shape under the surface and you can pick it up, and, provided the disk is large enough, even stand on it.”
Once the pancake ice forms, Associate Professor Monty and Dr Skidmore use a mechanical wave generator to explore how different waves interact with it.
“In the second stage, we try to understand how the ice breaks up, how much energy is lost in collisions of ice floes, as well as how the waves reduce in size as they propagate through the ice pack,” says Associate Professor Monty. “There are very few controlled studies of these effects.”
All this helps improve how changes to the Arctic and Antarctic are modelled and therefore, contribute to better climate models.
Ice shelves cover 74 per cent of the Antarctic coast, and as the Weddell Sea in the Southern Ocean warms the ice is disintegrating. But according to Dr Skidmore it is breaking up faster than predicted.
“Weddell Sea is what meets with the Larsen A, B and C ice shelves. Larsen A disintegrated in 1995. B began its decay in early 2002 when 3250 square kilometres disintegrated in a 35-day span, which was far quicker than anyone could have imagined.
“And C suffered a major break off in July of this year that was roughly the size of Delaware – forming an iceberg that weighed over a trillion tonnes. This was in an area that, up until recently, had been identified as stable since 1975.”
Associate Professor Monty’s and Dr Skidmore’s research is conducted in the Michell Hydrodynamics Laboratory on main Parkville campus at the University of Melbourne, but Associate Professor Monty says the new facilities at Fishermans Bend in the city’s south west will have a dramatic impact on what they can do.
“Our biggest challenge is space,” says Associate Professor Monty. “At our new campus at Fishermans Bend, we will make the wave tank larger, which will allow us to run longer simulations and acquire more data. We will also build a separate freezer room to make test pieces of ice, carefully controlled for thickness and mechanical strength.”
“A temperature controlled environment will also make a huge difference,” adds Dr Skidmore. “At the moment, it’s a lot of trial and errorthat is complicated by the outside temperature – whether or not the sun is shining on the facility, as well the laboratory/building temperature.
“In the summertime with everything running, we start to approach 40 degrees inside the laboratory. We can set the ice room to its minimum temperature at minus fifteen but can still struggle to make ice on the ends of the tank. It’s an ongoing battle.”
Banner image: Flickr/NOAA Photo Library