Seismic events drive pollution in Japan Trench hadal basins

Abstract Hadal trenches, the deepest regions of the ocean, have long been considered remote sinks for organic matter and pollutants. However, recent evidence suggests these environments are more dynamic, influenced by both natural events and human activity. Here we present a geochemical assessment of organic and inorganic pollutants in surface sediments from seven basins along the Japan Trench axis, at depths greater than 7000 metres below sea level. We show that earthquake-triggered sediment flows are a major mechanism delivering anthropogenic pollutants, including polycyclic aromatic hydrocarbons, dichlorodiphenyltrichloroethane metabolites, hopanes, and trace metals, into the trench. While slow background transport contributes to deep-sea contaminant accumulation, episodic, high-energy sediment-gravity flows appear to dominate pollutant delivery in this ultra-deep environment. These findings reveal that pollution in hadal trenches is not simply passive accumulation but can be driven by seismic events, linking human activity on land to biogeochemical processes in tectonically active marine settings.