Catastrophic bushfires ‘caused an explosion in ocean life’

Smoke from the 2019-20 bushfires in Australia caused an explosion of life in the Southern Ocean that was equivalent to turning the ­entire Sahara desert green.

Bushfire smoke rising high and far across the atmosphere. Picture: NASA

Smoke from the 2019-20 bushfires in Australia caused an explosion of life in the Southern Ocean that was equivalent to turning the ­entire Sahara desert green.

Research published on Thursday in Nature journal has found that total carbon dioxide emissions from the bushfires was 715 million tonnes, twice as much as previously thought.

Another paper, also published in Nature, says an equivalent amount of CO2 was sucked up by a phytoplankton bloom in the ocean between New Zealand and South America caused by fertilisation of the ocean by smoke from the fires.

The bushfires caused catastrophic damage on land, killing billions of creatures, but Pete Strutton from the Institute for Marine and Antarctic Studies at the University of Tasmania, a contributing author on the second paper, said the phytoplankton bloom had positive impacts at sea.

Part of the bloom would have sunk to the ocean floor, locking the CO2 out of the atmosphere. In addition, as a critical building block in the aquatic food chain, the phytoplankton would have been eaten by other species, storing the carbon and dramatically increasing ocean productivity.

Professor Strutton said the bloom was not the same as a “toxic” algal bloom that starved the ocean of oxygen and was detrimental to life.

“It is not like the kind of thing that causes deoxygenation when it decomposes”, he said.

The unknown is exactly how much of the additional CO2 from the bushfires was captured and lock away.

The researchers, led by Weiyi Tang from Duke University, said more research was needed to properly understand the im­plications of there potentially being more wildfires as a ­consequence of climate change.

Professor Strutton said the team had studied 22 years of satellite data to assess the impact of the 2019-20 fires. “Nothing like the increase in productivity we saw has been observed in that 22 years in that part of the ocean”, he said.

Using satellites and autonomous profiling floats, researchers “observed a greening in the south Pacific sector of the Southern Ocean that exceeded the size of Australia.”

The research paper said feedbacks between climate and wildfires were complex and often poorly represented in climate models, leading to high uncertainty in future projections. “There is increasing evidence that wildfires may have had an important role modulating atmospheric CO2 during glacial – interglacial periods”, the paper said.

“Given the increasing risk of wildfires with climate change (for example, in southeast Australia, the Amazon, and the western US), their central role in our global climate in the geological past, at present, and in future therefore ­argues for a more comprehensive representation of wildfires in climate models”, it said.

“Among other things, extensive measurements of wildfire aerosols and targeted studies of their effects on marine ecosystems are needed to further elucidate the wide-ranging impacts, especially for an event of the magnitude of the 2019-20 Australian wildfires”, the paper concluded.