How will the LA fires affect the ocean? These researchers are racing to find out
Scientists aboard a research ship collected ash and debris to assess wildfire pollutants
A quarterly research voyage to study the Pacific Ocean coincided with the Palisades and Eaton fires in the Los Angeles area. Samples gathered during the January trip will help scientists understand the natural disaster’s effects on the ocean.
Robyn Beck/AFP/Getty Images
The ship was more than 160 kilometers offshore when biological oceanographer Rasmus Swalethorp spotted yellow smoke billowing above Los Angeles.
Swalethorp and nearly 40 others had set sail less than a week earlier to survey water and marine life off California’s coast. But on January 7, reports of erupting wildfires — including the Palisades and Eaton fires — began popping up on the television in the ship’s galley. The flames’ ferocity didn’t register with Swalethorp until he saw smoke the next day.
“These were bigger than anything I’ve seen before, and we were just heading straight towards those smoke plumes,” says Swalethorp, of the University of California, San Diego’s Scripps Institution of Oceanography. “That’s when the scope of this fire really started to hit.”
Swalethorp was on a research vessel as part of the California Cooperative Oceanic Fisheries Investigations, or CalCOFI, program. Each quarter, scientists spend weeks gathering data, including seabird counts and water from multiple depths, at around 100 sites in a grid pattern. Gathered since 1949, this information has helped scientists detect shifts in marine ecosystems. CalCOFI voyages currently collect around 85 different types of samples at each site, which track about 1,000 distinct measures over time, says Swalethorp, CalCOFI’s director of ship operations.
Now the voyages will aid scientists’ understanding of how the Los Angeles fires may alter the ocean.
The winter 2025 data-gathering mission occurred at “the perfect opportunity in a pretty tragic time,” says Scripps marine biologist Julie Dinasquet, who leads the institution’s investigation of how fires affect the ocean. As the flames raged, Dinasquet, who was not on the ship, urged the researchers at sea to collect samples beyond what they had planned. Using nets and other tools available on board, Swalethorp and the others scooped up ash and extra water samples to see what toxins may have seeped into the Pacific.
The stench of burnt electronics choked the air. The amount of human-made materials set ablaze — batteries, cars, plastics, building materials — means the LA fires may affect the environment in unprecedented ways compared with other wildfires, Swalethorp and Dinasquet say.
As Swalethorp and his colleagues worked through the night, they watched the hills burn as ash floated around them like snowflakes. It was “very surreal,” he says.
After a January 18 stop to get specialized equipment, the vessel returned to the waters off Los Angeles. The team used those new tools to gather water and aerosol samples, which will reveal any heavy metals carried by smoke and ash, and took snapshots as particles sank underwater. Once finished, the ship resumed its pattern and docked on January 31.
Although Dinasquet hasn’t started studying January’s samples yet, she’s already shocked by the size of the ash pieces that landed in the sea, some as long as a thumb. The strong winds — a reason for the fires’ rapid spread — blew smaller bits as far as 160 kilometers offshore. Current models of aerosol movement during fires don’t account for hunks of burnt materials, so this discovery may lead to revisions in the models, she says.
Dinasquet worries about pollutants driven into the water by the fires and debris flows from heavy rains that followed. “The ocean is already so stressed,” she says. Fires add another layer of complexity to increasing temperatures and longtime pollutants. “How resilient is the ecosystem going to be, especially if this kind of stress is increasing in the future?”
Scientists who board CalCOFI cruises plan to keep gathering data on the LA fires’ effects for the remainder of this year, depending on funding.
During the spring 2025 trip that ended on April 20, no ash or smoke was visible to the naked eye, says marine biologist Nicolas Concha Saiz of the National Oceanic and Atmospheric Administration’s Southwest Fisheries Science Center in San Diego. “The water and the air look completely ‘normal’ now,” says Concha Saiz, who was also on the winter trip. But “we will have to wait and see what our new collected samples reveal.”
