A groundbreaking study led by researchers at Chalmers University of Technology has revealed a surprising and significant source of methane emissions—ship traffic in shallow coastal waters. Focusing on the Neva Bay in the Baltic Sea, an oxygen-depleted marine environment rich in organic sediments, scientists discovered that the passage of ships through these waters triggers pronounced pulses of methane gas escaping from the seabed into the atmosphere. Remarkably, methane emission rates in the shipping lanes were found to be up to twenty times higher than in neighboring undisturbed areas, highlighting a previously overlooked contributor to global greenhouse gas emissions.
Methane is a powerful greenhouse gas, with a global warming potential 27 times greater than that of carbon dioxide over a 100-year period. Despite this potency, the role of methane emissions associated with shipping activities has remained largely underestimated in climate impact assessments. Prior to this study, concerns over methane release largely centered on vessels powered by liquefied natural gas (LNG), but the Chalmers-led research establishes that the physical movement of ships themselves, regardless of fuel type, can substantially elevate methane fluxes from marine sediments.
The key physical mechanism driving these enhanced emissions relates to pressure fluctuations at the seabed and subsequent water column mixing caused by passing vessels. Underlying sediments in shallow coastal zones often harbor methane generated by anaerobic microbial decomposition of organic matter. This methane accumulates within sediment pores or forms gas bubbles under pressure. When a ship moves above, altered hydrostatic pressures and the turbulent wake disturb the water and sediment interface. These disturbances allow trapped methane to be released upward more efficiently, rapidly transferring the gas from sediment to surface water, and ultimately to the atmosphere.
Such episodic methane release events manifest as brief but intense pulses of high fluxes. Although transient, their cumulative effect throughout daily ship traffic remains significant when scaled over time and across busy ports. The Chalmers team’s careful field measurements employed novel observational methods capable of capturing these rapid emission events, overcoming limitations of conventional measurement techniques that often miss short-lived methane plumes.
This discovery emerged serendipitously during unrelated environmental monitoring in the Neva Bay, a heavily trafficked waterway characterized by shallow waters with anoxic bottom sediments. The realized importance of ship-induced methane emissions in this region underscores the potential for similar phenomena in other port areas worldwide, especially where environmental conditions resemble those in the Baltic Sea. Coastal zones adjacent to major global trade hubs often feature comparable sediment composition and hydrodynamic settings, suggesting that methane emissions from ship passages could represent a widespread but unrecognized global source.
Further investigation revealed that not all vessels contribute equally to these methane pulses. Large passenger cruise ships and container vessels were identified as the most frequent and significant triggers of methane discharge, while ropax ferries, combining freight and passenger transport and equipped with double propellers, also produced substantial emissions. Intriguingly, bulk carriers, despite their size, generated comparatively lower methane release, indicating that factors other than sheer vessel size—such as propulsion type and hull design—may influence the extent of methane flux enhancement.
Resolving these dynamics requires sophisticated hydrodynamic and environmental modeling, blending fluid mechanics with biogeochemical processes. Chalmers researchers applied detailed simulations and observational data to unravel how ship-induced pressures and turbulent wakes interact with sediment gas reservoirs. This interdisciplinary approach has provided new insight into methane transport pathways in coastal systems under anthropogenic disturbance.
The study’s findings carry profound implications for methane budget accounting and climate change mitigation strategies. Previous inventories of greenhouse gas emissions from maritime transport underestimated shipping’s total methane output by neglecting this physical release mechanism. Incorporating methane flux pulses induced by vessel activity into climate models will refine projections of future warming and better inform regulatory frameworks targeting shipping emissions.
Moving forward, the research team plans to extend monitoring efforts to other major port regions known for their shallow, organically rich sediments and heavy traffic volumes. Cities such as Rotterdam, Antwerp, and those in China, South Korea, and Singapore possess environmental conditions analogous to Neva Bay and likely experience elevated ship-driven methane emissions. Characterizing and quantifying methane pulses globally will be critical to assessing shipping’s true climate impact and identifying mitigation opportunities.
Moreover, the study advocates rethinking existing methane measurement methodologies in coastal environments. Traditional sampling techniques may miss the transient nature of methane pulses resulting from ship passages. Implementing real-time, high-frequency monitoring in ports and surrounding waters can capture these emissions more accurately, enabling comprehensive evaluation of anthropogenic influences on marine greenhouse gas dynamics.
Beyond immediate policy relevance, these discoveries emphasize the intricate interplay between human maritime activities and natural biogeochemical processes in coastal zones. They underscore the importance of integrating oceanographic, atmospheric, and engineering perspectives to understand and tackle emerging environmental challenges. The research adds a new dimension to the complex narrative of global methane sources, particularly highlighting unrecognized mechanisms in human-dominated coastal ecosystems.
The original article, published in Nature Communications Earth & Environment, documents this unprecedented finding and represents a collaborative effort among environmental scientists, hydrodynamic modelers, and atmospheric researchers. It demonstrates how chance observations can lead to paradigm-shifting insights, revealing underappreciated pathways of greenhouse gas emissions linked to everyday human activity.
The study’s authors emphasize the urgency of expanded research, especially in the context of escalating global trade and port expansions. As maritime traffic grows, so too may the scale of methane emissions induced by ship passages, stressing the need for integrated assessments and mitigation initiatives. Ultimately, this research informs policies aimed at decarbonizing shipping while safeguarding coastal environments from unintended environmental side effects.
In conclusion, methane emissions triggered by ship traffic in shallow coastal areas represent an overlooked but impactful climate forcing agent. By uncovering the physical and biological processes behind this phenomenon, the Chalmers-led study opens new avenues for environmental monitoring, climate modeling, and sustainable maritime management worldwide.
Subject of Research: Not applicable
Article Title: Coastal methane emissions triggered by ship passages
News Publication Date: 15-May-2025
Web References:
- https://doi.org/10.1038/s43247-025-02344-8
- https://communities.springernature.com/posts/solving-the-mystery-of-unexpected-methane-plumes-in-the-neva-bay-shipping-lane
References:
Amanda T. Nylund, Johan Mellqvist, Vladimir Conde, Kent Salo, Rickard Bensow, Lars Arneborg, Jukka-Pekka Jalkanen, Anders Tengberg, Ida-Maja Hassellöv. “Coastal methane emissions triggered by ship passages.” Nature Communications Earth & Environment, 2025.
Image Credits: Chalmers University of Technology | Amanda Nylund
Keywords: methane emissions, ship traffic, greenhouse gases, coastal environment, methane flux, sediment mixing, maritime emissions, climate change, hydrodynamics, shipping lane, organic sediments, Neva Bay
