Algae offers answers
Ahyperspectral camera and snow gardens have become tools in learning how Antarctic sea ice algae will likely respond to climate change.
Both techniques were used near Scott Base this summer and the results are encouraging enough to likely send Dr Ken Ryan, an associate professor of biology at Victoria University, and colleagues from the University of Tasmania back to the ice next season for more work.
Algae are like the grass of the Ross Sea, explains Ryan. They are eaten by krill, which are eaten by fish, which are eaten by penguins and seals, and so forth through various food webs.
To understand how climate change will affect Ross Sea’s life, algae are a good place to start because changes that affect them also affect larger species.
Until recently, researchers collected sea algae data by extracting drill cores from the sea ice in which algae live. This classic technique is limited by the relatively spotty coverage possible. Travel on sea ice is limited to a few months a year and cores are about 10 centimetres wide.
Hyperspectral cameras promise to significantly increase the coverage.
These researchers’ camera was attached to a rig that was winched along the underside of the sea ice, where many sea algae live, with the camera pointed upwards. It was the first time such a camera had been put under sea ice, Ryan says.
Their hyperspectral camera captured upwards of 200 colours a pixel. In a simplified comparison, colour schemes like RGB capture three colours a pixel and CMYK capture four colours a pixel.
This sensitivity allowed the researchers to ‘‘quantify biomass variability at unprecedented spatial scales’’, according to Ryan. They can separate out chlorophyll, for example, and hope to identify individual algal species.
The four camera transects accomplished this season were 10 metres by 1 metre, still tiny by reference to the Antarctic continent but better than core samples, Ryan says.
Ryan and colleagues hope one day to attach the hyperspectral camera to a remotely operated vehicle – an underwater drone, in effect – and drive it around much larger area while taking photos.
One point of this work is that is the thickness of the ice and snow layers directly affects how much light penetrates to the underside of the sea ice, thus affecting how much algae – and which species of algae – grow there.
In food webs, some algae are better eating than others.
Snow layer thickness was also queried more directly by Ryan and colleagues with snow gardens.
They marked out 5m x 5m plots and added 30cm of snow to some, 10cm to others and no snow to yet others. They measured how the algae responded, then changed the snow thickness and measured again, and so forth.
While the full data have not been analysed yet, there were ‘‘dramatic changes’’, Ryan says.
They were interested in whether algae stress levels changed as the snow thickness changed, as measured by the amount of hydrogen peroxide present, for example.
When the snow layer was thin and therefore more light was penetrating the ice, there were higher levels of hydrogen peroxide, indicating high stress.
The algae quickly adapted to the new conditions and stress fell off. But different species acclimatised differently to the changing circumstances.
It’s thought that warming will result in more precipitation in the Antarctic. When it falls as snow, it will have different impacts than when it falls as rain. How these differences will affect algae are still not understood.