Sediment plumes (near bottom and near surface plumes)

A significant environmental concern with deep-sea mining comes in the form of a ‘plume’ at the seafloor. A sediment plume, or simply plume, occurs with the combination of bottom sediments and turbidity in the water column. In the mining process, sediment plumes are created by the action of the mining device and during transport of mined materials. Plumes created by the mining device at the ocean floor are called near bottom plumes, and those created through transportation at the surface are called near surface plumes.With every ton of manganese nodule mined, 2.5-5.5 tonnes of sediment will be brought up into the water column. These suspended loads of sediment persist for long periods and travel laterally, potentially causing devastating effects to marine ecosystems. Near bottom plumes could bury and suffocate benthic flora and fauna (the organisms inhabiting the ocean floor – see definition), as well as clog their filter feeding mechanisms. Near surface plumes might cause even more damage, affecting extensive areas because they spread over greater distances with currents. These could affect the pelagic community (see definition of pelagic zone) by, for example, clogging the filter feeding mechanisms of zooplankton (see definition of zooplankton) and blocking sunlight for a range of photosynthetic organisms, preventing photosynthesis and decreasing biological activity long-term.