Seafloor dynamics: sediment-ocean interactions in the Diamantina Fracture Zone (SE Indian Ocean)

Diamantina Fracture Zone in the SE Indian Ocean is one of the less unexplored hadal zones (>6000 m) of our planet without human visits until recently. This study incorporates shallow sediments, submarine videos, and multibeam bathymetry data at a wide range of water depth and geomorphology to fully assess the sediment dynamics of the Diamantina Fracture Zone and their major causative factors. Grain size and organic geochemical analyses confirmed a primary marine source. Australian terrigenous input was indicated by an increasing silty contribution to the eastern hadal section of the fracture zone. Importantly, in the western to middle section, angular volcanic-rich sediments with a peak at 200-300 μm covered the underlying fine pelagic sediments and calcareous oozes, which were likely initiated during the Last Glacial Maximum. Susceptibility to slope failure was high due to localized topographical constraints, rather than earthquakes. The occurrence of sediment ripples at the west and densely-covered manganese nodules at the east implied the ocean bottom circulation with increasing current intensity, which also enhanced the possibility of the gravity-driven slope deposition. This research provides the first knowledge of the highly spatial heterogeneity of sediment dynamics in the remote deep Indian Ocean where continuous but fluctuating downslope and alongslope processes were developed.