Bottom Trawling: Scientists Find a Previously Unaccounted For Marine Source of Carbon Emissions

A new study has revealed a previously unaccounted for marine source of carbon emissions in the atmosphere: bottom trawling.

Underwater Carbon Dioxide

This discovery comes as global efforts focus on slashing fossil fuel emissions, deforestation, and other emission sources. The study has found that bottom trawling, which involves dragging a heavy fishing net through the ocean floor and resuspending some carbon in the sediments of the seafloor, is a significant atmospheric carbon source. This was detailed in the "Atmospheric CO2 emissions and ocean acidification from bottom-trawling" study.

An earlier study discovered that a portion of the sediment that got disturbed became carbon dioxide in the water. Now, the new study has discovered that 55% to 60% of the carbon dioxide produced due to bottom trawling underwater will reach the atmosphere within a span of nine years.

The carbon quantity released each year into the atmosphere due to bottom trawling is projected to double the annual fuel combustion emissions of the whole flushing fleet worldwide, which comprises roughly 4 million vessels. Dr. Trisha Atwood from Utah State University and National Geographic Pristine Seas explains that they have known for a long time that dragging fishing nets that are heavy through the ocean flood can destroy habitats and sea life. However, it is only recently that they discovered that the method also leads to carbon plume releases that could have been safely stored in the seafloor.

The study is the first to reveal that more than half of the bottom-trawling-released carbon eventually reaches the atmosphere as carbon dioxide in a span of nearly a decade. This resultantly contributes to global warming.

Bottom Trawling as a Carbon Emission Source

The scientists made use of bottom-trawling data all over the world from 1996 to 2020. They also utilized intricate models to calculate the quantity of CO2 produced by bottom trawling that goes into the atmosphere.

The efforts build on the foundational research finding that the quantity of CO2 released into the waters due to bottom trawlers exceeds the annual carbon emissions of most countries. It also builds on how it belongs to the same order of magnitude as global aviation's annual CO2 emissions.

The researchers were able to identify various areas in the ocean where bottom-trawling-caused carbon emissions were notably high. These include the Baltic and North Seas, the East China Sea, and the Greenland Sea. The study also finds that the Bay of Bengal, parts of Europe, the Gulf of Mexico, the Arabian Sea, and Southeast Asia could also be major carbon emission sources because of trawling. However, data pertaining to bottom trawling's intensity and extent in this area remains insufficient.

At present, the significant carbon emissions brought about by bottom trawling are not accounted for in the climate action plans of countries. With this, the researchers argue that the study clearly shows that addressing these emissions and other marine emissions is crucial to slowing global warming down, on top of restoring life in marine ecosystems.

The good news is that reducing carbon emissions from bottom trawling can lead to immediate benefits. However, the bad news is that delaying actions will make sure that trawling will keep on entering the atmosphere in roughly a decade.

The study also looks into what happens to the trapped carbon in ocean waters post-bottom-trawling. It finds that roughly 40% to 45% of the total dislodged carbon stays in water, resulting in heightened ocean acidification that is localized. This heightened acidity could lead to damage to animal and plant life where the fishing activity occurs.

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