Aust bushfires sparked massive ocean bloom

Research shows Australia's Black Summer bushfires sparked a massive ocean phytoplankton bloom.
Research shows Australia's Black Summer bushfires sparked a massive ocean phytoplankton bloom.

Australia's devastating bushfires two summers ago spewed millions of tonnes of carbon dioxide into the atmosphere, but in an unexpected twist, sparked a rare and massive ocean phytoplankton bloom which removed the same amount of gas.

The unusual phenomenon could point to a way to tackle climate change in the future.

New research has found the bloom, between New Zealand and South America, spanned an area larger than Australia, with its emergence tracking the progress of the fires which hit multiple states including NSW, Victoria and South Australia.

It was estimated the fires emitted 715 million tonnes of carbon dioxide, with the smoke turning New Zealand glaciers brown and travelling across the ocean to South America and beyond.

In a study published in Nature, researchers from the ARC Centre of Excellence for Climate Extremes and the University of Tasmania's Institute for Marine and Antarctic Studies, said the phytoplankton bloom was unprecedented in the 22-year satellite record, and lasted about four months.

"What made it more extraordinary is that the part of the season when the bloom appeared is usually the seasonal low point in phytoplankton, but the smoke from the Australian bushfires completely reversed that," chief investigator Peter Strutton said.

As part of their research, the scientists tracked the path of the smoke using satellite and ground-based measurements.

They then confirmed the increased concentration of phytoplankton in the ocean by combining satellite data with floats deployed across the region.

The smoke from the fires included low but significant concentrations of iron vital for photosynthesis and phytoplankton growth, with the researchers estimating the iron was deposited at a rate three times more than normal levels.

"The acceleration in phytoplankton growth as the fires took hold in Australia was so quick that it only lagged the blazes by a few weeks and in some cases just days," PhD student and study contributor Jakob Weis said.

"This was even as the impact of the smoke was felt in fits and starts rather than appearing as a constant rain of smoke on the ocean."

Ironically, the phytoplankton growth, removed significant amounts of carbon dioxide from the air, absorbing the gas as part of the photosynthesis.

It was estimated the bloom removed about the same amount of CO2 as the fires released, though whether such a process could help the permanent sequestration of carbon from the atmosphere was difficult to determine.

"With increasing risks of bushfires in some areas, and the potential impact on climate, this research shows that we need to turn our attention to the consequences of fires at a global scale," Prof Strutton said.

"We need a far more comprehensive representation of wildfires in climate models and targeted studies to understand their influence on marine ecosystems.

"Our capacity to adapt to future climate change depends on it."

Australian Associated Press