Researcher helps crack the mysteries of sea ice

Dr Ruzica Dadic says there are complicated relationships between Antarctic snow and ice with feedback loops that need to be better understood as climate warms.

The mysteries of how snow affects Antarctic sea ice remain largely unknown, something Te Herenga Waka—Victoria University of Wellington researcher Dr Ruzica Dadic is working to change.

International research in recent years has increasingly delved into the links between snow and ice cover in the Arctic. But the intricate connections between the two in Antarctica have not been as intensively studied.

A year ago, Dr Dadic, a senior research fellow in the University’s Te Puna Pātiotio–Antarctic Research Centre, was part of the biggest polar expedition in history.

She was the only scientist from Aotearoa New Zealand invited to join the high-profile MOSAiC programme to the Arctic, which involved hundreds of researchers from 20 countries.

Dr Dadic says that although it sounds counter-intuitive there’s a warmth to snow. “If you have ever been in a snow cave, you’ll remember it is really warm inside.”

Snow’s insulating properties are well known to those who live and work with it. This insulation and the high albedo (reflectivity) of snow can change the energy availability in sea ice on which it lies and either accelerate ice melt or increase ice growth.

Dr Dadic says these are complicated relationships with feedback loops that need to be better understood as Earth’s climate continues to warm.

Born in Bosnia and raised in Switzerland, Dr Dadic grew up with a lot of snow.

“Snow is something I’ve always been interested in. It’s really fascinating—snow is actually a warm material, always close to its melting point. Once you start digging into it, you realise there’s more to snow than just snowballs and skiing. Which is really cool.”

The MOSAiC expedition aimed to better understand how climate change is affecting the Arctic and the subsequent effects on the world’s climate.

Dr Dadic says the differences between the Arctic and the Antarctic are stark.

“One is a continent, one isn’t. One is surrounded by oceans, one by land masses. Antarctica behaves differently. Antarctic sea ice is mostly snow-covered even in summer, whereas in Arctic summer we get these melt ponds that have strong feedbacks on the system. These melt ponds are dark and therefore have a much lower albedo and absorb more sunlight.

“It is clear the amount of sea ice in the Arctic has been declining, while the sea ice in Antarctica is just going up and down without a clear trend.”

There are complex relationships between snow and ice in the Antarctic. For example, if snow on sea ice starts melting, its albedo decreases, allowing the surface to absorb more energy and accelerate the melting, decreasing the albedo further and increasing the melting.

“Once those feedbacks start, it’s hard to stop them. The Southern Ocean keeps Antarctica relatively cool, but again, if we do increase the temperature, if we change the amount of snow on the sea ice, that could trigger changes we don’t see, or understand, yet.”

Most computer models represent sea ice crudely as a surface with high albedo. But this does not reflect the complex reality.

It is possible for small changes in the albedo of sea ice to cause relatively large changes in the global energy balance and the heat budget, says Dr Dadic.

“If you have snow on top of sea ice, that small amount of snow will insulate the sea ice below. If you have no insulation, no snow, your ice will grow thicker. But also if you have more snow, as currently in many parts of Antarctica,  it will be heavy on the sea ice and suppress it, contributing to sea-ice growth from above.

“So it is complex, with interactions where more snow might lead to less melt and thicker sea ice because of a higher albedo, or to a thinner sea-ice cover because of higher insulation from the relatively cold air, or to a thicker sea-ice cover because of the formation of ice from submerging snow.”

Dr Dadic wants to collect better measurements in the Antarctic to improve sea-ice models.

“A lot of what we know about sea ice comes from remote sensing, but for remote sensing to get the correct numbers we need to know exactly what we are measuring in terms of the surface and the physical properties of the snowpack.”

Dr Dadic is involved in the Antarctic Research Centre’s Girls on Ice programme to encourage Year 11 and 12 girls who have had little exposure to the outdoors to undertake fieldwork and become life-long advocates for the environment and environmental science.

“It’s about getting girls into the outdoors who don’t have a chance from their backgrounds. I only got interested in glaciology because I had friends who were members of this alpine club that had a youth section where they just took us to the mountains every week for free.

“My kids will go to the mountains because we will take them, but many other children never have the opportunity to explore the great outdoors New Zealand has to offer. So it’s really about empowering girls to gain confidence in the outdoors so they can go out and do anything they want.