Seafloor erosional processes within the Rio Grande Rise: Integrated results from past scientific expeditions

ABSTRACT The Rio Grande Rise is a submerged plateau that has received increasing interest due to the presence of critical minerals within ferromanganese crusts that partially cover the plateau. The formation, distribution and preservation of the crusts are partially controlled by the hydrodynamic processes that are active around the region. This study was carried out to describe the erosional and depositional processes that have shaped the geomorphology of the Rio Grande Rise in an area where three scientific cruises have recently occurred. Particularly, we investigated the role of ferromanganese crusts in seafloor erosional processes and their interaction with deep ocean currents. For that, we combined the analysis of multibeam bathymetry, sub-bottom profiles and ROV imaging data. Multibeam bathymetry reveals the heterogeneity of submarine morphologies, composed of escarpments, slope scars, submarine canyons, subcircular depressions and erosive channels. Sub-bottom profiles show that deep currents have eroded the plateau flanks, forming contourite drifts only where ferromanganese crusts are absent. ROV images show that current directions are variable, and obstacle scouring occurs widespread. Overall, we show that the presence of ferromanganese crust is crucial in preventing erosion. Lastly, outcrops of basaltic escarpments expose the various characters of volcanic deposits in the Rio Grande Rise, while sediment mass movements including debris flows occur along the scarps. The integrated results shed light on the nature of the seabed erosional processes that affect the region and how the presence of ferromanganese crusts is shaping the morphology of the Rio Grande Rise.