Sea ice in Antarctica is home to an upside-down garden that is the powerhouse at the bottom of Antarctic food webs.
But what will happen to this remarkable ecosystem in a warming world?
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Less than one percent of ambient light makes it through the sea ice but it is enough to trigger a bloom of ice algae in spring. Snow on the ice surface creates the darker patches. Photo: CC BY-SA 4.0 Andrew Thurber - Deep-Sea and Polar Biology
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Microscopic plants bloom on the underside of the Antarctic sea ice in spring, as soon as the sun returns.
Less than one percent of ambient light makes it through the sea ice, which averages 1.7 to 2 metres thick at Cape Evans, but it is enough light to trigger the plants to begin photosynthesis.
Microscopic algae called diatoms, as well as bacteria and viruses, form complex communities on the underside of Antarctic sea ice. Photo: CC BY-SA 4.0 Andrew Thurber - Deep-Sea and Polar Biology
These ice algae, along with bacteria and viruses, live in tiny pockets and channels in the bottom few centimetres of the ice. These pockets between the ice crystals are created by brine which is excreted as seawater freezes.
The tiny algae and microbes are grazed on by young krill and forms a vital part of their diet.
Krill underpin the Antarctic food web, and seals, penguins and whales all rely on the huge pulse of krill that follows the annual spring algae bloom.
Researchers lifting coloured perspex panels used in an experiment on the algae that grows under the sea ice. Mt Erebus in the background. Photo: RNZ / Alison Ballance
New Zealand and Australian researchers have been studying this under-ice community for many years at Cape Evans, on Ross Island.
Andrew Martin, from the University of Tasmania, says the current research, funded by the New Zealand Antarctic Research Institute, aims to understand what might happen to Antarctica in the future as global temperatures rise.
He says that in the next 80 years, Antarctic sea ice is predicted to shrink in area and thickness by a third. As well, increasing snow and wind will change how much light gets through the ice.
Andrew and colleagues are trying to measure and predict how these changes will affect life in Antarctica, especially the ‘grass of the sea’ under the ice.
The University of Tasmania's remote operated vehicle, nicknamed the TIE Fighter, contains a hyperspectral camera to scan the brown ice algae living on the underside of the sea ice. The skis help the ROV glide under the ice Photo: RNZ / Alison Ballance
In November 2019, the researchers used coloured perspex panels screwed onto the ice to mimic changing light conditions. Vanessa Lucieer and the On Thin Ice team from the Institute of Marine and Antarctic Studies at the University of Tasmania, used hyperspectral scanning and remote operated vehicles, as well as ice cores, to measure how microscopic life responded.
A hyperspectral camera composes an image that uses the full spectrum of light and goes beyond the range visible to the human eye.
Emiliano Cimoli watches data coming in from a hyperspectral camera deployed under the sea ice. Vanessa Lucieer, at the back of the tent, feeds out cable through a hole cut in the ice. Photo: RNZ / Alison Ballance
Andrew says they were surprised to discover that there was more abundant microbial life under the red, green and blue acrylic panels than under the surrounding sea ice. The make-up of the communities had also changed.
Microscopic life grows as a thick mat on the underside of Antarctica's sea ice, coloring the ice brown. Photo: RNZ / Alison Ballance
He says it is too soon to know what this means, although he speculates that there will be winners and losers amongst different species which will mean that some kind of microbial community will survive. One result might be an increase in phytoplankton living in the water column, rather than under the ice.
However, he says the loss of sea ice will have significant consequences for krill populations, as the juvenile krill are so dependent on the growth of ice algae early in spring.
Klaus Meiners, from Australian Antarctic Division, holds a sea ice core. Photo: RNZ / Alison Ballance
At the moment the annual sea ice around Antarctica covers 20 million square kilometres in winter, shrinking to 4 million square kilometres by late summer. It covers such a large area that Andrew says the under ice microbial and plant community is one of the most significant microbial communities on earth.
Antarctic krill scraping ice algae growing on the underside of sea ice. Photo: CC BY-SA 3.0
Voices from Antarctica – listen to the full series
Voices from Antarctica 1: Ice Flight
Voices from Antarctica 2: Scott Base
Voices from Antarctica 3: Flags to physics
Voices from Antarctica 4: Best journey in the world
Voices from Antarctica 5: Waiting for Emperors
Voices from Antarctica 6: Seal songs
Voices from Antarctica 7: What the ice is saying
Voices from Antarctica 8: Under the ice
Our Changing World’s Antarctic collection
Listen to a wide range of stories recorded in and about Antarctica from our archives.