Australian wildfires caused massive algal blooms

A recent study led by Duke University has found that the wildfires that ravaged Australia in 2019 and 2020 triggered massive algal blooms in the Southern Ocean. According to the scientists, small aerosol particles of iron from the windborne smoke and ash fertilized the ocean waters, providing a large amount of nutrients that fueled large-scale algal blooms. 

Pyrogenic aerosol particles are produced when trees, brush or other types of biomass are burned. They are light enough to be carried easily by smoke and ash over large distances, during long periods of time. This study, published in the journal Nature, is the first to discover a strong correlation between these aerosols and the emergence and growth of marine life.

Through robotic ocean floats, satellite observations, atmospheric transport modelling, and measurements of atmospheric chemistry, scientists tracked the spread of pyrogenic iron aerosols caused by the Australian wildfires and measured their impact on marine productivity.

“Our results provide strong evidence that pyrogenic iron from wildfires can fertilize the oceans, potentially leading to a significant increase in carbon uptake by phytoplankton,” said Nicolas Cassar, a professor of Biogeochemistry at Duke University’s Nicholas School of the Environment.

According to Cassar, the algal blooms caused by the Australian wildfires were so extensive that the subsequent increase in photosynthesis might have temporarily offset an important fraction of the environmentally damaging CO₂ emissions caused by the fires. However, it is not yet clear how much of the carbon absorbed by the algae remains safely stored in the waters and how much is released back in the atmosphere, negatively impacting life on Earth. 

Large wildfires, such as the Australian ones, or the more recent devastating fires in the American West, the Mediterranean area, the Amazon, or even Siberia, are becoming more frequent and intense due to climate change. Further research is needed to investigate their complex impact on the environment.

According to study co-author Weiyi Tang, who worked as a doctoral student in Professor Cassar’s lab, “these fires represent an unexpected and previously under-documented impact of climate change on the marine environment, with potential feedbacks on our global climate.”

If until now, only their negative role has been explored, further research is needed to assess the entire gamut of environmental effects that wildfires produce.

—

By Andrei Ionescu, Earth.com Staff Writer