Regional differences in sediment oxygen uptake rates in polymetallic nodule and co-rich polymetallic crust mining areas of the Pacific Ocean

The potential impact of manganese mining on benthic remineralization in the Pacific Ocean was assessed in this study. We estimated total sediment oxygen uptake rates (TOU) using in situ autonomous benthic chambers at the polymetallic nodule and Co-rich polymetallic crust mining sites of Korea: at the Clarion-Clipperton Fracture Zone (PILOT site) in the eastern Pacific and the open-sea seamounts (OSM) 9-1 and OSM17 in the western Pacific, respectively. The TOU rates in the shallow seamount areas (0.58 ± 0.01–2.22 ± 0.04 mmol O₂ m⁻² d⁻¹) were significantly higher than in the PILOT station (0.21 ± 0.05 mmol O₂ m⁻² d⁻¹), indicating that relatively labile organic matter could be deposited according to the regional oceanographic features and water depth. The highest TOU found among the seamount areas was in the wide summit area at OSM9-1, which may be due to environmental conditions such as seasonal wind-driven mixing, upwelling around the seamount slope, and topography, which can increase productivity seasonally. Our findings suggest that organic carbon quality and hydrodynamics can be closely linked to benthic carbon mineralization in the targeted polymetallic mining areas of the Pacific.