Samples provide first pieces in giant algae puzzle

Scientists at the ACE CRC have begun analysing samples taken from the massive algal bloom first sighted by satellite off East Antarctica’s Cape Darnley in late February. Information on species composition is likely to be significant in determining the cause of the bloom. Marine glaciologist Dr Jan Lieser said there were now about 15 scientists collaborating on the bloom, which he first sighted off Cape Darnley at the end of February via the MODIS satellite. Dr Lieser was surprised by the size and brightness of the bloom, which was clearly visible through thin cloud via the satellite 650km away in space. Those now working on the “big green slime” include scientists from the ACE CRC, Australian Antarctic Division, CSIRO, the Institute for Marine and Antarctic Studies at UTAS as well as visiting scientists from Laboratoire d'Oceanographie et du Climat and the University of Brittany in France. The great boon for scientists was that the Antarctic supply ship Aurora Australis was in the area at the time and was able to divert and collect samples. “This means that we are not sitting here wondering and arguing about the composition of this bloom – we will actually know,” Dr Lieser said. On March 18 NASA’s Earth Observatory website noted that there were slightly different theories among scientists of what the bloom contained. “The slightly differing interpretations of one satellite image are not seeds of a scientific controversy. They are, instead, a reminder of the limits of what we can see and say with satellite imagery. They are also a reminder of how science works: incrementally and collaboratively,” the site said. Dr Lieser said the bloom appeared to be about 200 kilometres (E-W) by 100 kilometres (N-S) when he first saw it. It then grew to cover at least 45,000 square-kilometres, an area about half the size of Tasmania, before it began to dissipate after about three weeks. ACE CRC/Australian Antarctic Division glaciologist Dr Mark Curran said there was reasonable agreement among colleagues he had spoken to that the cause of the bloom was delivery of iron to the surface waters. He described three main theories for how this delivery could have happened: •    strong offshore winds blowing across the ocean surface and changing the ocean circulation so that sediment containing iron from the ocean floor was disturbed and resuspended •    as a result of fast ice from the eastern side of Cape Darnley decaying, melting and releasing its nutrient load (Fast ice is type of sea ice (frozen ocean) that become "fastened" to the shore or to grounded icebergs.) •    via strong offshore winds blowing snow, containing iron, from the Antarctic continent onto the open ocean surface.

Authorised by the CEO of the Antarctic Climate and Ecosystems Cooperative Research Centre October 2019.

The ACE CRC was established and supported under the Australian Government’s Cooperative Research Centres Program.

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