How Bottom Trawling Turns the Ocean Floor Into a Carbon Bomb

For decades, bottom trawling—dragging heavy nets across the seafloor—has been criticized for destroying marine ecosystems. Now, new research reveals another devastating consequence: it’s turning the seabed into a major source of CO₂ emissions.

The Hidden Carbon Reservoir

A study from the GEOMAR Helmholtz Centre for Ocean Research in Kiel exposes how trawling disrupts the delicate balance of carbon stored in fine-grained sediments. Analyzing samples from Kiel Bight in the Baltic Sea, researchers found these muddy deposits act as critical carbon reservoirs. But when disturbed, they don’t just release organic carbon—they trigger a chemical chain reaction that pumps CO₂ into the atmosphere.

“Pyrite oxidation, not just organic decay, is the primary driver of CO₂ release,” says lead author Habeeb Thanveer Kalapurakkal. “It’s a previously overlooked feedback loop accelerating emissions.”

Acid, Bicarbonate, and Escaping CO₂

In lab experiments, the team simulated trawling’s effects by resuspending different sediment types—from sandy to muddy—under varying oxygen conditions. The results were stark. When pyrite (iron sulfide) in the sediment oxidizes, it generates acid, which reacts with bicarbonate in seawater. This chemical cascade converts dissolved bicarbonate into CO₂ gas, much of which escapes into the air instead of staying sequestered.

Worse, the process reduces the seafloor’s ability to absorb CO₂ long-term. “The ocean isn’t just losing stored carbon—it’s losing its capacity to capture more,” Kalapurakkal explains.

A Sink Becomes a Source

Modeling from the study shows that sediment resuspension can flip seafloors from carbon sinks to temporary carbon sources. While organic carbon breakdown contributes, pyrite oxidation amplifies the effect, creating a double hit to the climate. The Baltic Sea findings likely apply to other continental shelves where fine sediments accumulate—regions heavily targeted by industrial trawling.

The implications are urgent. Protecting these muddy carbon vaults could be as critical as preserving forests. Yet trawling churns up 1.5 million square miles of seabed annually, equivalent to twice the area of India. With each pass of the net, another pulse of CO₂ may be bubbling into an already overheated atmosphere.