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Wildfire ash fertilizes the ocean and boosts marine life

In late 2017, the Thomas Fire in Santa Barbara County became one of the most destructive wildfires in California’s history. The fire led to the unprecedented closure of classes at UC Santa Barbara and widespread use of N95 masks. 

This catastrophic event, however, presented a unique opportunity for scientists at the university. Huge amounts of wildfire ash had settled into the oceans, and the experts wanted to investigate what effect it might have on marine life.

Significant discovery 

The team embarked on a mission to understand the effects of wildfire ash on ocean ecosystems – a subject that has been relatively unexplored compared to freshwater systems.

The researchers made a significant discovery: wildfire ash can actually fertilize marine ecosystems. This is in stark contrast to its toxic effects in freshwater environments. 

Research expedition 

The team, led by Tanika Ladd, had to rapidly adapt their pre-planned expedition. “With a research cruise already on the calendar, the team jumped on the opportunity to investigate. “We planned this out in just a few weeks,” said Ladd.

“The fire broke out Dec. 4; our cruise was scheduled to go out on Dec. 17, and this clearly wasn’t in our plans for all of the cruise prep before the fire started.” The group quickly pivoted the entire cruise itinerary. Senior scientists sent off a flurry of grant applications, and the team revised the schedule a couple weeks before setting sail.”

How the research was conducted 

Study co-author Eleanor Arrington collected ash samples from car windshields across Santa Barbara, creating a saltwater solution with the ash and then filtering out solid particles. 

This solution was added to seawater cultures, which were incubated on deck of the research vessel. 

Key nutrients 

The team’s measurements indicated a significant increase in particulate organic carbon in samples with added ash leachate, suggesting enhanced plankton growth and increased carbon drawdown from the atmosphere through photosynthesis.

Further analysis showed that the ash was enriching the seawater with key nutrients like nitrate, nitrite, ammonium, and silicic acid, which are essential for the growth of phytoplankton such as diatoms. 

Potentially toxic metals

The ash also introduced metals like copper and iron to the seawater. While essential in small quantities, these metals can be toxic at higher concentrations in freshwater ecosystems. 

However, the vastness of the ocean dilutes these elements, reducing their potential harm.

Study implications 

This study sheds light on the complex interactions between terrestrial and marine ecosystems, particularly in the context of increasing wildfires. 

The nutrients carried by wildfire ash into the ocean may boost primary production in coastal areas, especially in nutrient-limited regions like the Santa Barbara Channel. 

“Coastal ecosystems may have increased primary production during these wildfires, but we need to know what this actually means on a global scale,” said Ladd.

The study is published in the journal Proceedings of the Royal Society B Biological Sciences.

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