Ships trigger hidden methane emissions on the seabed

Ship traffic in shallow waters in coastal waters produces huge methane emissions simply through the movement of water, a previously undeemed source of greenhouse gas pollution that could impact global climate calculations.

Researchers in Sweden found that the ship channel triggers methane release twenty times, twenty times as much as undisturbed areas, and its emissions are caused by pressure changes and water mixing rather than ship fuel selection.

The results show that all vessels lead to methane emissions through the physical presence in methane-rich water regardless of fuel type. This challenges the current understanding of the impact of transport climate and reveals gaps in greenhouse gas accounting approaches.

Pressure connection

Researchers at Chalmers University University observed that as the ship passes through shallow water, clear pulses of methane escape from the water into the atmosphere. The mechanism is like this: When ships move in water, they create pressure changes on the seabed, making methane more likely to emerge from the sediment.

“Our measurements show that the ship’s passage triggers a clear pulse of high methane flux from water to the atmosphere,” explained Amanda Nylund, a researcher at the Chalmers Technical University and a researcher at the Swedish Institute of Meteorology and Levels.

The study measured pressure changes of 30-60 mbar under the vessel, similar to the pressure changes known to trigger methane release in other marine environments. Combined with the turbulent mixing in the vessel’s wake, these pressure drops create the ideal conditions for methane escape.

Surprising emissions meter

The team studied ship traffic in the Bay of Neva, Russia and found significant emission levels:

• Daily methane emissions reach 120 kg from just 5.5 km of transport lanes
• Methane flux is 11 times higher than typical coastal areas in the world
• Containers and cruise ships trigger the most common large emissions
• Even smaller ferry containers produce a large amount of methane release

All ships are the culprit

Unlike methane slip of LNG engines (which only affects known issues that only certain containers), these emissions regardless of fuel type. Any ship passing through a methane-rich sediment area can trigger issuance, thus becoming a common transport impact.

The study shows that the size, speed and design of the ship all affect the emission amplitude. Vessels over 250 meters always trigger emissions, while vessels below 125 meters rarely trigger. Speed ​​is also important – the speed of traveling faster than 12 knots produces the largest methane pulse.

Interestingly, this study found technical details not highlighted in the initial report: passenger ferries (such as passenger ferries) generate particularly large emissions, which may be because the twin propellers affect greater water volume and increase gas exchange efficiency.

Climate impact

The warming potential of methane packaging is 27 times that of carbon dioxide over a century, making these emissions climate-relevant. The researchers calculated that ship-triggered methane represents 22% additional warming compared to the ship’s fuel combustion emissions.

“Even if the pulse is short, the total amount of the day is obvious,” Nylund noted. This phenomenon was discovered by chance in other measurements, highlighting the ease of this emission being easily overlooked.

Schedule is more relevant than that. As transporting is transported at zero emissions by 2050, these newly identified methane sources will represent an increasing number of methane cargoes, especially as current emission reduction strategies do not address their problems.

Global hot spots

This discovery has global implications, as nine of the world’s top ten ports are located in waters similar to Neva Bay. Major ports in European hubs such as China, Singapore, South Korea, and Europe’s hubs such as Rotterdam and Antwerp may experience comparable methane emissions.

“The next step is to estimate that these impacts can be significant globally,” said Ida-Maja Hassellöv, Chalmers Maritime Environmental Sciences professor, who will lead the follow-up research starting this fall.

The study shows that the current methods used to measure coastal methane emissions systematically underestimate the total by avoiding transport lanes, which are some of the largest emissions.

As global transport flows continue to grow, understanding and mitigating these hidden emissions is critical to accurate climate accounting and effective environmental policies.

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