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Elsewhere in the world, research has found a stronger connection between fires and phytoplankton. In 2003, a particularly notable paper linked a 1997 red tide — which choked a coral reef in Sumatra of oxygen, killing fish and the reef itself — to wildfires in Indonesia. “Iron fertilization by the 1997 Indonesian wildfires was sufficient to produce the extraordinary red tide,” the authors wrote, “leading to reef death by asphyxiation.”
Wildfire smoke can also cause algae to balloon in freshwater rivers and lakes. “It usually causes a really big bloom response because [the algae] is just sitting there getting fertilized in the sun,” Kramer said. In these cases, however, it’s typically phosphorus rather than iron that the algae need to bloom, Hamilton said.
Smoke from wildfires has even been shown to fertilize plants on land. One remarkable study from 2019 found that phosphorus from fires burning in southern Africa traveled all the way to the Amazon Basin, where it fertilized the rainforest.
How an increase in severe fires will shape the future of our oceans
While wildfires are becoming more frequent and severe due to climate change, scientists still aren’t sure what that means for the future of our oceans.
As the Nature study shows, fires can spur large algal blooms, but a lot depends on the local environment. If the ecosystem already has plenty of nutrients, for example, an influx of iron or phosphorus might not produce a bloom.
Even if there is a bloom, it’s not always clear if it’s good or bad. Phytoplankton, like plants, are photosynthetic, absorbing carbon dioxide (CO2) as they grow. In a basic sense, more algae mean fewer carbon emissions. That’s why some people have proposed fertilizing the ocean with iron as a way to combat climate change. But even big algal blooms may not absorb enough carbon to offset the CO2 stemming from the wildfires that fuel them. Some kinds of algae are also likely to release the carbon they store back into the atmosphere when they decay, whereas others, such as diatoms, are more likely to lock it up permanently, Kramer said.
“The best thing is to not rely on this carbon drawdown from phytoplankton, but to stop emitting CO2 in the first place,” Hamilton said.
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