The link between wildfire smoke and Arctic algal blooms raises new questions
According to a new study, a wildfire in Siberia likely contributed to an unusually large and long-lasting algal bloom in the Arctic Ocean during the summer of 2014.
The work highlights an understudied impact of smoke, which could become more significant as climate change makes wildfires more frequent and severe.
Burning forests and peatlands are known to release a lot of carbon, but smoke plumes also carry a variety of aerosols, including nutrients such as phosphorus, nitrogen and iron.
Scientists have speculated that these aerosols could reach nutrient-limited parts of the ocean, where they could act as fertilizers and promote the growth of phytoplankton – microscopic plant-like organisms that form the basis of the food web. of the ocean.
Until recently, researchers had only predicted that this could happen in computer models.
“It’s one thing to do it in models,” said Douglas Hamilton, assistant professor of marine, terrestrial and atmospheric sciences at North Carolina State University in the United States. Hamilton co-led the study as a postdoctoral researcher at Cornell University.
“It’s a whole other thing to watch it in the real world,” they said.
Last year, another team of scientists linked a massive algal bloom off the coast of Antarctica to iron deposited by smoke from severe Australian wildfires in 2019-20, Forbes reported.
The new study, published in the journal Communications Earth & Environment in September, is the first to document the phenomenon in the Arctic Ocean, the researchers say.
“We think it’s happening in several places around the world, but it’s hard to detect,” said Joan Llort, a biogeochemical oceanographer at the Barcelona Supercomputing Center in Spain, who co-authored the algal bloom study. in the southern hemisphere. but has not participated in recent work.
While the new findings aren’t necessarily surprising, Llort said, the fact that researchers observed the phenomenon in the Arctic for the first time is relevant. It’s nice to see researchers putting the pieces together, he said.
Unlike other parts of the ocean, the Arctic is nitrogen rather than iron limited. So when Hamilton and their colleagues noticed an unexpectedly large algal bloom about 850 km south of the North Pole in 2014, they looked for potential explanations.
It was a bit like a Sherlock Holmes analysis, Hamilton said. The team first ruled out ocean mechanisms known to bring nitrogen, such as river inflows, upwellings and storms. Next, they looked at possible sources of nitrogen from the atmosphere.
Downwind of the algal bloom, a wildfire had burned about 1.5 million hectares in Siberia, an area about half the size of Vancouver Island. (It was also the same summer as the Northwest Territories’ 2014 “megafire” season.) The timing of the Siberian Fire aligned with the bloom, and satellite data revealed that the smoke had been transported to the bloom area.
The researchers performed computer simulations to estimate the amount of nitrogen deposited at the bloom site. These simulations are known to underestimate emissions from boreal fires, however, and they don’t include emissions from peat, which is high in nitrogen, Hamilton said. By adjusting their estimates to account for these factors, the researchers found that the Siberian wildfire contributed between 12 and 100 percent of the nitrogen needed to sustain the bloom.
Although the work does not prove that the bloom was caused entirely by wildfire, it does suggest that fire played an important role, the researchers reported.
As permafrost thaws and more peatlands burn in northern regions — including Canada — a more sustained supply of nitrogen could reach Arctic waters and increase phytoplankton production, Hamilton says.
“But what this actually means for the delicate balances of the Arctic ecosystem, we don’t yet know,” they said.
Like plants, phytoplankton produce oxygen and absorb carbon. That may have climate implications, said Sasha Kramer, a postdoctoral researcher at the Monterey Bay Aquarium Research Institute, who wasn’t involved in the research but looked at the effects of wildfires on phytoplankton in California.
A change in productivity could also affect food webs and ecosystems. But what blooms matters, Kramer said. “It’s really hard to theorize what might happen with the phytoplankton bloom, partly because there are thousands of species of phytoplankton.”
According to Llort, it is also difficult to know what is in the ashes that emanate from the forest fires. As a result, in the new work, the researchers had to rely on remote sensing and modeling, which meant they had to make certain assumptions. “It’s not ideal,” he said, but it’s currently the best they can do.
Many questions remain. For example, it’s still unclear whether the 2014 Arctic bloom was a rare event or a sign of how the ecosystem might change in a warming world, Hamilton said.
Researchers will need to study more of these events, they said, to draw firm conclusions about the link between algal blooms and wildfires, and begin to answer questions about their impacts.
This article is produced under a Creative Commons CC BY-ND 4.0 license through the Wilfrid Laurier University Climate Change Journalism Fellowship.