Study Reveals Shocking Impact of Ship Traffic on Methane Emissions in Shallow Waters

Ship traffic in shallow areas, such as ports, can trigger large methane emissions by just moving through the water. A recent study led by Chalmers University of Technology in Sweden has shed light on the significant impact of ships on methane release in marine environments. Researchers observed a staggering 20 times higher methane emissions in the shipping lane compared to nearby undisturbed areas.

According to Amanda Nylund, a researcher at Chalmers University of Technology and the Swedish Meteorological and Hydrological Institute, SMHI, ship passages cause clear pulses of high methane fluxes from the water to the atmosphere. These pulses are a result of pressure changes and water mass mixing. Despite being short-lived, the cumulative methane emissions during a day are substantial.

The study revealed that methane emissions are not dependent on the type of fuel used by ships. This means that all ships, regardless of their fuel selection, can contribute to greenhouse gas emissions. The researchers emphasized that the activity of ships can release significant amounts of methane into the atmosphere, even though methane naturally occurs in sediments.

The research focused on shallow marine areas with oxygen-free sediments rich in organic matter, where methane is formed. When ships pass through these areas, the pressure changes at the seafloor facilitate the release of methane bubbles from the sediments. Additionally, the mixing caused by ships accelerates the rise of methane to the surface, allowing it to escape into the atmosphere.

The discovery of extensive methane emissions in shallow waters was initially accidental, occurring during measurements in the Neva Bay in the Baltic Sea. Johan Mellqvist, Professor of Optical Remote Sensing at Chalmers, highlighted the importance of this finding for improving global estimates of methane emissions, especially considering the prevalence of similar conditions in major ports worldwide.

The study identified cruise and container ships as the primary triggers of frequent and substantial methane releases, with ropax vessels (freight and passenger ferries) also contributing significantly. Surprisingly, bulk carriers emitted lower levels of methane compared to other ship types, suggesting that factors beyond ship size influence methane emissions.

Professor Rickard Bensow, responsible for the study’s ship traffic modeling, suggested that the double propellers on ropax vessels could explain their high methane emissions. The researchers plan to further investigate the global implications of ship-induced methane emissions, focusing on major ports in China, Singapore, South Korea, and Europe.

Ida-Maja Hassellöv, Professor of Maritime Environmental Science at Chalmers, will lead the upcoming project to assess the extent of methane emissions in similar port environments. The findings emphasize the urgent need to address the overlooked impact of ship traffic on methane release in shallow waters.