A new applied mathematical theory could help improve accuracy of predictions about how sea ice impacts polar climate changes.
Dr Noa Kraitzman is a senior lecturer in Applied Mathematics at Macquarie University and lead author of the study recently published in the Proceedings of the Royal Society A journal.
She says the research addresses a key gap in current climate modelling and provides fresh insights into the way heat travels through sea ice – a key factor in regulating Earth’s polar climate.
“Sea ice covers about 15 per cent of the ocean’s surface during the coldest season,” Kraitzman says. “It’s a thin layer that separates the atmosphere and the ocean and is responsible for heat transfer between the two.”
Predicting climate change
Sea ice acts as an insulating blanket on the ocean, reflecting sunlight and moderating heat exchange. As global temperatures rise, understanding how sea ice behaves will become increasingly important for predicting climate change.
The study – conducted by mathematicians from Macquarie University in Australia, the University of Utah and Dartmouth College, New Hampshire in the U.S – was supported by funding from the US National Science Foundation.
Kraitzman says the unique structure of sea ice, as well as its sensitive dependence on both salinity and temperature, makes measuring and predicting its properties – specifically its thermal conductivity – challenging.
“When you look at sea ice on a small scale, what makes it interesting is its complex structure because it’s made up of ice, air bubbles, and brine,” she says.
“As the atmosphere above the ocean becomes extremely cold, below minus 30 degrees Celsius, while the ocean water remains at about minus two degrees, this creates a large temperature difference. This means the water freezes from the top down.
“As the water freezes rapidly, it pushes out the salt, creating an ice matrix of purely frozen water which captures air bubbles and pockets of very salty water, called brine inclusions, surrounded by nearly pure ice.”
Mathematics plays key role in climate science
Sea ice in the Arctic has been rapidly declining in recent decades. The loss can lead to a feedback loop – as more dark ocean water is exposed, more sunlight is absorbed, leading to further warming and ice loss that can affect ocean circulations, weather patterns, and marine ecosystems far beyond the polar regions.
Kraitzman says that understanding sea ice’s thermal conductivity is a vital part of predicting its future.
Her team’s research builds on earlier field work dating back to 1999, which suggested that fluid flow within sea ice might enhance its thermal conductivity. Kraitzman and her team have now provided mathematical proof of this phenomenon.
“Our mathematics definitely shows that such an enhancement should be expected once convective flow within the sea ice begins,” she says.
