Scientists find new marine source of carbon emissions

Bottom trawling, the act of dragging a heavy fishing net across the ocean floor and resuspending some of the carbon in the seafloor sediment, is a previously unaccounted for source of atmospheric carbon emissions, scientists reveal in a recent study.

The new research has revealed that 55-60 per cent of the CO2 produced underwater by bottom trawling will make it into the atmosphere within nine years.

Additionally, the amount of carbon released by bottom trawling into the atmosphere each year is estimated to double the annual emissions from fuel combustion of the entire global fishing fleet, said to be about 4 million vessels.

In a statement, Dr Trisha Atwood, Utah State University and National Geographic Pristine Seas, said: “We have long known that dragging heavy fishing nets — some as large as ten 747 jets — across the ocean floor destroys sea life and habitats.

“Only recently, we have discovered that bottom trawling also unleashes plumes of carbon, which otherwise would be safely stored for millennia in the ocean floor. Our study is the very first to show that over half the carbon released by bottom trawling eventually escapes into the atmosphere as carbon dioxide over the span of about ten years, contributing to global warming.

“Much like destroying forests, scraping up the seafloor causes irreparable harm to the climate, society and wildlife.”

The study was conducted by a global team of climate and ocean experts from Utah State University, NASA Goddard Institute for Space Studies, the University of California Santa Barbara, Columbia University, James Cook University and National Geographic Pristine Seas.

The researchers used data on bottom trawling carried out globally between 1996-2020 and sophisticated models to calculate how much of the CO2 produced by bottom trawling ultimately enters the atmosphere.

This study builds on recent foundational research finding that the amount of CO2 released into the ocean from bottom trawling is larger than most countries’ annual carbon emissions and on the same order of magnitude as annual CO2 emissions from global aviation.

Researchers identified ocean areas where carbon emissions from bottom trawling are especially high, including the East China Sea, the Baltic and the North Seas, and the Greenland Sea.

“Right now, countries don’t account for bottom trawling’s significant carbon emissions in their climate action plans,” said Dr Enric Sala, National Explorer in Residence and Executive Director of Pristine Seas.

“Our research makes it clear that tackling these and other ocean emissions is critical to slowing the warming of the planet, in addition to restoring marine life.

“The good news is that reducing bottom trawling carbon emissions will deliver immediate benefits. The bad news is, delaying action ensures that emissions from trawling will continue seeping into the atmosphere a decade from now.”

The study also assessed what happens to carbon that remains trapped in ocean waters after bottom trawling takes place, concluding that between 40-45 per cent of the total carbon dislodged from the ocean floor by trawling remains in the water, leading to greater localised ocean acidification and damage to plant and animal life in the area where the fishing activity takes place.

The research, published in Frontiers in Marine Science, can be read in full here.