Impact of ferromanganese ore pollution on phytoplankton CO₂ fixation in the surface ocean

Because ferromanganese polymetallic crusts can become a global resource of valuable elements the ecological impact of seafloor crust mining requires evaluation. Whilst the detrimental impact on deep-ocean benthos is established, experimental evidence about the mining hazard to surface-ocean is sparse. When retrieved, mined crusts can leach elements potentially harmfull to the core oceanic CO₂-fixers – phytoplankton. To directly assess the magnitude of this potential hazard at ocean-basin scale, we examine the impact of ore slurry on phytoplankton CO₂ fixation along a meridional transect through the South Atlantic Ocean. Within 12 h crust slurry additions caused a 25% decrease of CO₂ fixation in the subtropical region and 15% in the temperate-polar region. Such moderate susceptibility of phytoplankton indicates limited release of harmful elements from tested polymetallic powder. Although this implies that environmentally sustainable seafloor mining could be feasible, longer-term complex studies of the mining impact on the surface ocean are required.