How oceans and algae are affected by fires fueled by climate change

Two years ago, in the South Pacific Ocean, an algae explosion grew to more than 2,000 kilometers wide, roughly the width of Australia.

Giant algae flowers are often linked to soil pollution, such as runoff from farmland, which is full of nutrients like nitrogen they need to thrive on these plant-like organisms. But there were no farms or factories nearby here in the middle of the ocean.

The flourishing expansion was fueled by something distant and unexpected: wildfires thousands of miles to the west.

In a new study published in the journal Nature, the researchers concluded that the smoke from the historic Australian wildfires of 2019 went out to sea and fertilized vast communities of algae. The smokers, which contained the nutritious iron, resulted in algae blooms that were together larger than Australia, the authors write.

“We know these fires have catastrophic impacts on local ecosystems,” said Nicolas Cassar, co-author of the study and professor of biogeochemistry at Duke University. But by spreading nutrients, “they also impact ecosystems that are thousands of miles away.”

Courtesy of the National Institute of Information and Communication Technology of Japan

As regions from the American West to the Mediterranean face another devastating fire season, the study adds a new dimension to our understanding of how climate-driven disasters are transforming the planet. We are learning that the impacts of fires go far beyond the number of human deaths, leveled homes and charred forests. Extreme forest fires are also disrupting underwater ecosystems away from flames.

How the smoke from forest fires can fertilize the ocean

As anyone living in the western United States knows, fire smoke is full of all sorts of things that are toxic to inhalation, including carbon monoxide and nitrogen oxides. Dirty air is one of the most serious threats to public health and is known to shave years out of life expectancy.

But while it is harmful to humans, wildfire smoke (which typically contains nutrients such as iron and phosphorus) can help algae and plants grow, just as fertilizer can help rescue a floor of the withered house. Some of these nutrients come directly from burning forests or meadows, while others are found in powder that ignites and sinks into the air, said Douglas Hamilton, a researcher at Cornell University who led a recent review of how aerosols affect ocean biogeochemistry.

Weiyi Tang et al./Nature

In some cases, the smoke settles on the ground, as is usual in the United States, where the wind tends smoke blows rising from the western states to the east coast. That’s why the sky over New York was cloudy this summer as wildfires were raging in California and Oregon.

In other regions, however, drafts send it to the sea. This is what happened during Australia’s devastating wildfire season that began in 2019, according to the study. The smoke from the fires, which burned 21 percent of the country’s temperate and broadleaf forests, traveled west to the southern Pacific Ocean, where it settled in waters with iron levels. relatively low. There, cap a large source of iron is believed to be “an essential engine of primary ocean production,” the authors wrote.

As a result, researchers argue that the smoke caused huge algae blooms, concentrated in patches in southern Australia and far from the west coast of South America. The flowers, shown in red on the map below, peaked in January 2020 and lasted about four months, the authors said.

Weiyi Tang et al./Nature

The results are especially striking considering that in a typical year, the abundance of algae in these regions is actually lower during the Australian summer (North American winter), according to the study.

Scientists have known for years that wind-borne dust is a source of nutrients for algae, Hamilton said, but they only had one “idea” that fire also played an important role. They said this study is the first to connect large fires with large flowers, which is what makes the work “innovative”.

Are there fires in California that are damaging the Pacific Ocean?

Massive wildfires have already burned hundreds of thousands of acres in California, the Brazilian Amazon and Siberia this year. They have destroyed houses, wiped out wildlife and flooded the air with greenhouse gases. Will the biology of the nearby oceans also change? According to experts, this depends on several factors, such as the size of the flame and the direction of the wind.

Occasionally, for example, smoke from western forest fires will come out over the Pacific Ocean. This happened during the 2017 Thomas Fire in Southern California, then the largest in the state’s history. The smoke ran down the Santa Barbara Canal and research suggests it may have altered the marine ecosystem there. When the authors tested the water during the fire, they found an abnormally high number of some seaweed called dinoflagellates, said Sasha Kramer, the study’s lead author and doctoral student at the University of California, Santa Barbara. It’s not clear what exactly this means for ecosystem health, but different types of algae are known to be better or worse at the carbon sequestration they absorb, he said. (The authors found no more algae in general.)

Al Seib / Los Angeles Times via Getty Images

Courtesy of Sasha Kramer

Elsewhere in the world, research has found a stronger connection between fire and phytoplankton. In 2003, a particularly notable document related to a 1997 red tide that suffocated oxygen on a coral reef in Sumatra, killing fish and the reef itself. – forest fires in Indonesia. “Iron fertilization by the 1997 Indonesian fires was enough to produce the extraordinary red tide,” the authors wrote, “which caused the death of the reefs by suffocation.”

Fire smoke can also cause algae to appear in freshwater rivers and lakes. “It usually causes a very large flowering response because [the algae] it is just sitting there fertilized in the sun, “Kramer said. In these cases, however, algae usually need to bloom, rather than make phosphorus rather than iron, Hamilton said.

Fire smoke has even been shown to fertilize plants in the ground. A notable 2019 study found that phosphorus from wildfires in southern Africa traveled as far as the Amazon Basin, where it fertilized the rainforest.

How an increase in serious fires will shape the future of our oceans

Although forest fires are becoming more frequent and severe due to climate change, scientists are still unsure of what this means for the future of our oceans.

Like the Nature study shows, fires can stimulates large algae blooms, but depends heavily on the local environment. If the ecosystem already has many nutrients, for example, the entry of iron or phosphorus may not produce any flowering.

Even if there is a bloom, it is not always clear whether it is good or bad. Phytoplankton, like plants, is photosynthetic and absorbs carbon dioxide (CO2) as it grows. In a basic sense, more algae means less carbon emissions. That is why some people have proposed fertilizing the ocean with iron as a way to combat climate change. But even large algae may not absorb enough carbon to compensate for the CO2 from the fires that feed them. Some types of algae can also release the carbon they store back into the atmosphere when they decay, while others, such as diatoms, are more likely to block them permanently, Kramer said.

“It’s best not to rely on this carbon reduction in phytoplankton, but to stop emitting CO2,” Hamilton said.

David Gray / Bloomberg via Getty Images

Algae blooms can also wreak havoc on wildlife and unbalance ecosystems. Blooms in Florida, for example, have killed thousands of fish and even manatees. They have also caused “dead zones” around the world, including parts of the Gulf of Mexico and Chesapeake Bay, where there is not enough oxygen to survive the animals. If nothing else, they are likely to be disrupting the food chain, Hamilton said.

This research raises many new questions, such as how fire-fed phytoplankton affect ocean biology and carbon sinks, and further complicates future climate models. It also highlights an awkward juxtaposition: both the science of catastrophe can surprise us and be very concerned about what it tells us. It’s baffling that fires in Australia are fertilizing the oceans off the coast of South America, and it’s troubling to think about what it might mean for the marine animals that live there.