MADRID, 16 Sep. (EUROPA PRESS) –
Clouds of smoke and ash from the fires that devastated Australia in 2019 and 2020 triggered algal blooms in the Southern Ocean thousands of miles downwind to the east.
A new international study led by Duke University, published in Nature, is the first to conclusively link a large-scale response in marine life to pyrogenic iron aerosol fertilization (or made by fire) from a forest fire.
It shows that tiny aerosol iron particles in the windblown smoke and ash fertilized the water as they fell into it, providing nutrients to feed the blooms to a unprecedented scale in that region.
The discovery raises intriguing new questions about the role wildfires can play in stimulating the growth of microscopic seaweeds known as phytoplankton, which absorb large amounts of carbon dioxide from Earth’s atmosphere that warms the climate through photosynthesis and they are the basis of the oceanic food web.
“Our results provide strong evidence that pyrogenic iron from wildfires can fertilize the oceans, which could lead to a significant increase in carbon uptake by phytoplankton,” he said. it’s a statement Nicolas Cassar, professor of biogeochemistry at Duke’s Nicholas School of the Environment.
The algal blooms triggered by the Australian bushfires were so intense and extensive that the subsequent increase in photosynthesis may have temporarily offset a substantial fraction of the CO2 emissions from the fires, he said. But it is not yet clear how much of the carbon absorbed by that event, or by algal blooms triggered by other wildfires, remains safely stored in the ocean and how much is released into the atmosphere. Determining that is the next challenge, Cassar said.
Large wildfires, such as the unprecedented fires that devastated parts of Australia between 2019 and 2020 and the fires now raging in the western US, Siberia, the Amazon, the Mediterranean and elsewhere, are predicted to will occur with increasing frequency with climate changesaid Weiyi Tang, a postdoctoral fellow in geosciences at Princeton University, who co-led the study as a doctoral candidate in Cassar’s lab at Duke.
“These fires represent an unexpected and previously poorly documented impact of climate change on the marine environment, with possible feedbacks on our global climate“Tang said.
Pyrogenic aerosols are produced when trees, shrubs, and other forms of biomass are burned. Aerosol particles are light enough to be carried by smoke and ash from a fire for months, often over great distances.
While the new study focused on the impacts of wildfires in the Southern Ocean, other regions, including the North Pacific, and areas near the equator where the deeper, colder waters rise to the surface, “They should also respond to iron additions from wildfire aerosols,” said Joan Llort, a postdoctoral fellow in marine biogeochemistry at the Barcelona Supercomputing Center, who co-led the study as a researcher at the Institute for Marine and Antarctic Studies at the University of Tasmania.
The scientists used satellite observations, robotic ocean floats, atmospheric transport models, and measurements of atmospheric chemistry to track the spread of pyrogenic iron aerosols from Australian wildfires and measure their impacts on marine productivity.
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