Science

Black Summer bushfires believed to have triggered huge algae bloom

New research has linked the 2019-2020 Black Summer bushfires with unusually large algal blooms in the Southern Ocean.

In just a few months, the Black Summer bushfires burned over 1.8 million hectares across south-east Australia in 2019-20, killing 33 people and an estimated 3 billion animals.

While the bushfires devastated the landscape and wildlife of south-east Australia, they seemed to have helped bloom new life in the ocean.

Algal blooms shown from a satelite Image: Himawari-8

A new research paper from Nature reports that algae blooms in the Southern Ocean between New Zealand and South America benefitted from the smoke and iron-rich ash dropping into the water.

At their largest the blooms covered an area larger than Australia according to the report, growing to a width of over 3500 kilometres.

The blooms began showing up in the usually desolate Southern Ocean in October 2019, reaching huge quantities between December and March 2020.

These mega blooms were large enough to be seen by satellites, which were measuring the amount of green pigment in algae — called chlorophyll — in the water.

But by March 2020, almost all fires in NSW and Victoria were extinguished or contained, and as the smoke and ash decreased, so did the algal blooms.

Another paper published in Nature by Dutch researchers estimated around 715 million tonnes of carbon dioxide was released between November 2019 and January 2020 by the Black Summer fires – almost double what was previously thought.

This is around 200 million tonnes more than the amount of carbon dioxide produced by human activities in Australia in the whole of 2018.

Richard Matear, an oceans and climate scientist with the CSIRO and co-author of the study, talked to the ABC, calculating that the ensuing algal bloom potentially offset almost all of the carbon dioxide emissions emitted by the fires between November and January.

“You don’t have to add much iron to have a massive carbon uptake response,” Dr Matear said.