Ships releasing a large amount methane from the seafloor

A groundbreaking study from Chalmers University of Technology in Sweden has unveiled a surprising source of methane emissions linked to maritime activity. Researchers found that large vessels navigating shallow waters are inadvertently releasing significant amounts of methane from the seafloor, rather than from their engines. This discovery highlights the urgent need to reassess the environmental impact of shipping in busy maritime routes.

Unexpected Findings in Methane Emissions

The research indicates that methane emissions in heavily trafficked shipping lanes can be up to twenty times greater than in nearby undisturbed waters. This increase is attributed to the physical disturbances caused by ships as they traverse shallow seabeds rich in methane. In coastal areas and ports, the seabed often contains oxygen-poor sediments filled with decomposing organic matter, which generates methane. When a ship passes over these areas, it creates pressure changes and turbulence that disturb the sediment, allowing methane bubbles to escape into the water column.

As the ship moves, the turbulence in its wake facilitates the rapid ascent of methane to the surface, where it is released into the atmosphere. This phenomenon was discovered serendipitously during measurements conducted in Neva Bay, located in the Baltic Sea. Johan Mellqvist, a professor of Optical Remote Sensing at Chalmers, emphasized the significance of this finding, stating, “The discovery of the hitherto unknown impact of ships is important for improving global estimates of methane emissions, especially considering that nine of the world’s ten largest ports are situated in similar conditions as Neva Bay.”

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Implications for Global Methane Emissions

The study also revealed that the size and type of vessel influence methane release. While large cruise and container ships were responsible for many of the highest emissions, smaller RoPax vessels—ferries that carry both passengers and freight—also contributed significantly. Interestingly, bulk carriers, despite their larger size, produced comparatively lower emissions, suggesting that a ship’s design and propulsion systems play a crucial role in methane release. Rickard Bensow, a professor of Hydrodynamics at Chalmers, speculated that the high emissions from RoPax vessels might be due to their double propellers.

Researchers plan to extend their investigation to major ports in Asia and Europe, where similar environmental conditions could lead to overlooked methane emissions on a global scale. Ida-Maja Hassellöv, a professor of Maritime Environmental Science at Chalmers, will lead this follow-up project. She noted, “The next step is to estimate how large these effects can be globally. Major ports in China, Singapore, and South Korea, as well as European ports like Rotterdam and Antwerp, have conditions akin to Neva Bay. It is very likely that we underestimate methane emissions there as well.”