Field incubation experiments were conducted at two stations in the Clarion-Clipperton Zone (CCZ) of the Eastern Pacific to simulate the discharge of polymetallic nodules (PMNs) slurry. After 24 hours of deck incubation, the acute and short-term effects of PMNs slurry discharge on marine picophytoplankton growth were evaluated by measuring chlorophyll a concentrations and monitoring picophytoplankton community changes. The results indicated significant differences in biomass and nutrient levels between the two stations, likely due to seamount effects. PMNs particles caused a maximum reduction of 61% in surface chlorophyll a concentration. However, the inhibitory effect decreased with the addition of sediments. Additionally, Synechococcus, Prochlorococcus, and picoeukaryotes (especially diatoms) exhibited different responses to PMNs slurry. Specifically, PMNs particles did not inhibit the growth of Synechococcus, while sediments did. PMNs particles inhibited the growth of Prochlorococcus, with smaller particle sizes and higher concentrations resulting in stronger inhibition; low concentrations of sediments could mitigate this inhibition and promote Prochlorococcus growth. Sediments promoted the growth of diatoms, with higher sediment concentrations leading to more pronounced effects. The physiological characteristics of different picophytoplankton and the trace metals and nutrients brought by particles and sediments are likely the main reasons for these differences.
 

Deep-sea mining; polymetallic nodules; SPH; sediment dispersion