Voice of the Sea Ice: Life!

6:32 am today

Two people stand next to a rectangular hole cut into the sea ice. The man on the left is wearing all black and he is bending over to insert a long coring drill into the hole. There is a spade and flag on the far left. On the right of the hole, a woman with a short blonde bob stands, holding a rod attached to cables. She is wearing an Antarctica New Zealand black-and-orange jacket. In the background, a flat expanse of white ice extends to low rocky, snow-strewn hills on the horizon, beneath a blue sky with a smear of cloud.

Dr Greg Leonard and Lizzy Skelton measure sea ice thickness. Photo: Claire Concannon / RNZ

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In some places, the underside of the sea ice looks like giant green clouds.

These are the 'grass meadows' of Antarctica, made up of phytoplankton, or microalgae - the foundation of the complex food web that powers all life here.

The 'charismatic microfauna'

Dr Jacqui Stuart is the self-described champion of these 'little guys'. Sitting in a heated shipping container that's kitted out as a mini laboratory, she pulls arranges a sample under the microscope lens, bringing into focus a tiny floating shape on the attached monitor screen.

A woman wearing a beanie over her brown hair sits at a bench in front of a laptop and a microscope, with a whiteboard on the wall covered with writing. She is looking down the microscope.

Dr Jacqui Stuart looking for microalgae. Photo: Claire Concannon / RNZ

It's a diatom. A long, thin type of microalgae that likes to group together to form a fan star array. But this is just one type of microalgae, amongst a whole community of them.

"You can get them in all shapes and sizes. And I think that's, that's one of the things that I underestimated for a very long time: the amazingness of algae," says Jacqui.

Food web foundations

She's investigating these microalgal communities in the sloshy layer found just under the sea ice of McMurdo Sound. In this 'sub ice platelet layer', big ice crystals known as platelets provide a safe haven from the currents for the algae to live.

Microalgae, or phytoplankton, can photosynthesise - just like plants on land do. When they take in energy from the sunlight and use it to make food, it's the first step in supporting some of the iconic Antarctic life that we think of: emperor and Adélie penguins, Weddell seals, skua, orca, and humpback whales.

A wide shot: in the mid-distance, two people wearing black-and-orange sit on camp chairs on a wide, flat expanse of white ice with a snow-covered volcano on the horizon, and a blue sky above.

Aimee and Salvatore seal-spotting after a work day, with Mt Erebus in the background. Photo: Claire Concannon / RNZ

In the warmer months, when the sea ice melts and there is an influx of nutrients, blooms of free-floating phytoplankton occur - massive patches of green that can be seen from space. It's the kick starter for the giant Antarctic buffet that attracts the world's largest whales to these waters each summer.

But in the dark winter and the shorter days of the year, the microalgae associated with sea ice is a vital food source for a host of tiny critters and fish.

Monitoring microalgae on ice

That's why NIWA's Dr Natalie Robinson and her team have been camping out on the land-fast sea ice. Each day they travel to one of their study sites to collect samples for investigation back in the makeshift biology lab.

Dr Natalie Robinson outside the sea ice camp. Photo: Claire Concannon / RNZ

Collecting 'platelet ice cores' is a difficult task, because it requires drilling down through the solid ice and then devising a way to recover the layers of these sloshing platelet crystals without mixing them all up.

The system that Natalie and her team have engineered took many years to devise and test. Now, it's used extensively as they try to figure out how microalgal communities change under ice of different structures.

A panorama of a field work site in action on the ice. In the foreground, three people in black-and-orange warm clothing gather around a small platform on the ice, where the drill is being inserted. They are in front of a green hagglund towing a carrier that is open with various gear stacked inside and outside. In the background, streaky clouds in a blue sky above snowy hills.

Platelet ice sampling. Photo: Claire Concannon / RNZ

Snow, solid ice, and that sloshy platelet ice can all occur in different thicknesses, which will impact the amount of light that gets through to the phytoplankton. This then impacts what the microalgal community looks like: some species like high light levels, others not so much.

And different types of pf phytoplankton provide different nutrients to those that eat them, says Jacqui. So as the sea ice cycle changes, there are microalgal winners and losers, and she's keen to figure out this ebb and flow.

This series was made with travel support from the Antarctica New Zealand Community Engagement Programme.

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