[M-ZZ44] Marine manganese deposits - Genesis, exploration and development

[MZZ44-03] Observation and simulation of flows in a seamount with cobalt-rich ferromanganese crusts

*Naoki Saito¹, Masayuki Nagao¹, Atsushi Suzuki¹ (1.National Institute of Advanced Industrial Science and Technology)

Keywords:Flow model, Numerical simulation, Tidal current, Tidal residual current

Under the influence of topography, tides, and stratification, complex flow regimes are formed on seamounts. Characterization of the flow regime is important for environmental impact assessment in the development of cobalt-rich ferromanganese crusts. In this study, observation and simulation of the flow regime were conducted on a flat-topped seamount in the Northwest Pacific Ocean, where cobalt-rich ferromanganese crusts are distributed. Observations were obtained at the top, slope, and base of the seamount for one year. A three-dimensional numerical flow model, Delft3D, was used to construct the simulation model. Observations showed that flow velocities at the top of the seamount (scalar mean 10.2 cm/s) were higher than those at the slope (7.2 cm/s) and base (6.8 cm/s), and there was no bias in the flow direction. Semidiurnal tidal currents had a dominant influence on the flow regime at the top. The simulation reproduced the observed currents with high accuracy. The simulation showed that the tidal currents were strong throughout the flat-topped area, with the strengthening extending to approximately 400 m above the seafloor. The simulation also suggested the existence of vertical circulating currents (mean <0.06 cm/s), which downwell in the center of the flat-topped area and upwelling near the margin. These findings will provide a basis for understanding the seamount environment and estimating the dynamics of the possible sediment plume produced by excavation.