Coastal methane emissions triggered by ship passages

Abstract

Estuarine and coastal areas are important sources of methane emitted to the atmosphere through diffusion or ebullition. These processes can be triggered by pressure changes and water column mixing, which can be induced by ships. However, the contribution of ship-triggered emissions is unknown and missing in current emission inventories. Here we show evidence of extensive ship-induced methane emissions and an estimated methane flux (11.1 mmol m−2 day−1) from Neva Bay shipping lane. The flux is 10–1000 times higher than reported global estuarine/coastal fluxes, and of similar magnitude as aquatic methane emission hotspots. Our results indicate that ship-induced pressure changes (30–60 mbar) trigger methane emission, comparable with observed emissions induced by tidal pressure changes. The ship-triggered methane emissions corresponded to a 22% increase of emitted carbon dioxide equivalents, compared to the combustion related exhausts. Our results demonstrate the need to include shipping lanes when assessing estuarine/coastal methane emissions. (Figure presented.)