The oceanographer was far out in the Pacific, off the coast of San Diego, when he saw a high yellow cloud floating toward him. It was smoke from the Los Angeles wildfires.
Rasmus Swalethorp and others on a routine month-long sampling mission aboard a government research vessel sprang into action. The presence of wildfire smoke dozens of miles offshore was unexpected. But they knew that where there was smoke, there was also ash. And data to collect.
The 209-foot boat, the Reuben Lasker, changed course and piloted toward Manhattan Beach, California.
“We were heading into an apocalyptic sky,” said Swalethorp, who studies changes in ocean environments at the Scripps Institution of Oceanography. They stopped about 60 miles offshore on Jan. 8.
“It was like being out in a calm snowy day in the winter except it was not snowflakes, it was ash particles raining down on us,” he said.
As the blazes that have consumed swaths of L.A. are being contained after destroying some 40,000 mostly residential acres and killing at least 27 people, experts say harmful hazards will persist in the land and in the air long after the flames are extinguished. Scientists fear that could also be true for the sea, as the forceful Santa Ana winds whip ash and wreckage far into the Pacific.
“There’s for sure going to be a lot of toxins associated with this debris,” Swalethorp said. “We don’t know the exact effects, because this is more or less unprecedented. But it’s likely to have an effect on the organisms living there.”
Research into the impact of wildfire ash on oceans is a newer scientific field, said biogeochemical oceanographer Joan Llort, “because it’s kind of related to this new generation of fires, mega-fires.”
Studies show extreme wildfires that are hotter and harder to control are happening more often. The fires release huge plumes of smoke and ash that can get blown out to the ocean.
But the debris is not always harmful, said Morgane Perron, a researcher in marine trace element biogeochemistry at Brest University. She and Llort were part of a team that studied the effects on marine life in the wake of Australia’s “black summer” from 2019 to 2020, when wildfires, fueled by extreme drought, ripped through forests across the country, releasing ash and smoke particles into the ocean.
They found that the nutrients, including nitrogen and iron, in the ash and soil that were swept out to sea may actually have helped some marine life there. They observed phytoplankton blooms – a sign small algae are feeding and rapidly reproducing – during and shortly after the fires.
But, Perron added, “The Australia fires were a forest fire. The L.A. fires aren’t.”
Sifting through the floating sea muck this month to collect his samples, a sour stench filled Swalethorp’s nostrils.
“It’s not like the ash you’d smell after camping and a bonfire,” he said. “It smelled like burned electronics.”
The L.A. blazes have burned through homes, cars, televisions and power lines, raising fears of the harmful chemicals that could be present in the air and the soil. ASCENT Network, a group funded by the National Science Foundation that measures aerosols and pollutants in the air, found high levels of lead and chlorine in L.A. after the fires.
Llort said it was likely these chemicals could end up in the ocean. “This is a big concern,” he said. “We’re not sure what happens when you add chemicals like the ones we use to clean our houses.”
Some scientists have tried to find out. In Maui, after devastating wildfires consumed Lahaina in August 2023, researchers studied how the urban blaze affected nearby coral reefs. They found elevated levels of copper, lead and zinc, peaking in October 2023, said Nicholas Hawco, an assistant professor and oceanographer at the University of Hawaii at Manoa.
The levels have since declined, but Hawco said the effects on the wildlife in the area could be ongoing.
“I wouldn’t call it a devastation zone in the same way that the land is,” he said. “That doesn’t mean there aren’t slower accumulative effects that don’t need monitoring.”
“It’s not something that goes away as fast as the fire is extinguished,” he added, noting it could take years for the repercussions to travel up the marine food chain.
In the nearly two weeks since the team on the Reuben Lasker saw that first plume of yellow smoke, they have continued to collect data, sampling and resampling the seawater. The goal in the coming months, said Swalethorp, is to map out where the ash has distributed and its impact on coastal and marine communities.
The boat returned to the area over the weekend and found the levels of ash and debris are declining, he said, but they are still waiting for the first rainfall. Water could push more residue down the slick, burn-scarred hills of L.A. into streams and, eventually, the ocean.
Swalethorp sees his team’s work as vital to understanding what the future holds for California’s coast, especially if fires continue to become more frequent and extreme.
“The California ecosystem is a biodiversity hotspot essential to fisheries so we need to understand the short-to-long-term impacts of this fallout on ecosystem health,” he said.
“Wildfires with urban areas at risk are predicted to increase in frequency and strength,” Swalethorp added. “So the L.A. fires represent a unique opportunity for us to understand the ecosystem risks and impacts from such urban fire events.”