UA research suggests ocean collapse triggered ancient wildfires

TUSCALOOSA, Ala. - Research led by The University of Alabama found that widespread wildfires during one of Earth's ancient environmental crises did not trigger an ocean collapse but was a consequence of it.

The study, published in Science Advances in April, revisits the Late Devonian period, when large parts of the coastal ocean became oxygen-depleted, disrupting marine ecosystems on a global scale. This period is considered one of the five great extinction events in Earth's history.

Some have proposed that wildfires, also evidenced in the geological record, might have caused the massive die-off of marine life. In theory, wildfire can mobilize nutrients from terrestrial ecosystems into coastal waters.

The new findings point to a different sequence.

Timing reshapes the story

By analyzing chemical signals preserved in sedimentary records from a shale deposit in Tennessee, the research team reconstructed the sequence of environmental changes for the first time. The study draws in part on fossil biomarkers - organic molecules derived from past organisms and preserved in rocks - to trace processes across land and ocean systems.

Lu's team sampled at one location at an exceptionally high temporal resolution, so they finally had enough detail to confirm the sequence of events.

Oxygen fuels fire beyond the mass extinction interval

The study links the rise of wildfires to a long-term shift in Earth's carbon cycle. When these marine anoxic events and the mass extinctions of ocean life happen, the organic material sinks to the ocean floor. The carbon in those life forms is buried instead of being released into the atmosphere.

In a normal cycle, this carbon would eventually bind with atmospheric oxygen to create carbon dioxide. When it is instead buried under ocean sediment, the amount of oxygen in the atmosphere is out of balance.

Elevated oxygen levels increase vegetation flammability and promote more frequent, intense fires. Wildfire activity thus rose - not as a trigger, but as a response to marine anoxia. The research also shows that this response is delayed and non-linear.

Importantly, this oxygen-driven increase in wildfire activity persisted beyond the mass extinction itself, suggesting a long-lasting shift in atmospheric conditions.

Why it matters today

Although these events occurred ~370 million years ago, the study offers insights into how tightly coupled Earth's systems are. Changes in ocean chemistry, atmospheric composition and terrestrial ecosystems can reinforce one another over long timescales.

As modern climate change alters carbon cycling and wildfire regimes, understanding these deep-time feedbacks will help scientists anticipate future environmental responses.

This study was primarily supported by the American Chemical Society Petroleum Research Fund New Directions. The first author, Dr. Man Lu, carried out the research as a doctoral student under the supervision of Dr. Yuehan Lu in the Molecular Eco-Geochemistry Laboratory at The University of Alabama. Man Lu is currently an associate professor at the China University of Petroleum. The work also involved contributions from researchers at Zhejiang University and the Geological Survey of Alabama.