Scientists aboard the research vessel Reuben Lasker were conducting surveys of marine life off the Southern California coast in early January when ash from the Los Angeles wildfires began to rain down on the ship. "It's like a winter day with big, fluffy snowflakes falling around you, except these weren’t snowflakes,” said oceanographer Rasmus Swalethorp. "It didn’t smell like burned wood; it smelled very synthetic, like burned electronics.”

Being in "the right place at a horrible time,” said Swalethorp, has given researchers a rare opportunity to collect real-time data on catastrophic urban wildfires’ effects on ocean ecosystems and commercially valuable fisheries. Even as climate change-driven wildfires burn ever-larger swathes of California, their impact on the ocean remains little studied. Increasingly fast-moving infernos can burn tens of thousands of acres within hours, but it can take months to launch expensive ocean-going scientific expeditions.

The few existing studies mainly focus on marine effects from forest fires that combust organic matter. One paper on the 440-square mile (1,140 square kilometer) Thomas Fire in Southern California found that woodland ash that fell in the Santa Barbara Channel in 2017 promoted the growth of plankton. The more than 15,000 structures that burned in the LA fires, on the other hand, incinerated unknown amounts of plastic, pesticides, asbestos, herbicides and lithium-ion batteries, releasing carcinogenic clouds of ash that blew far out to sea.