Geomorphology of Ona Basin, southwestern Scotia Sea (Antarctica): Decoding the spatial variability of bottom-current pathways

Ona Basin, the westernmost oceanic basin in the southern Scotia Sea, is affected by the opposite flows of Circumpolar Deep Water (CDW) and Weddell Sea Deep Water (WSDW); thus, it represents a key location for exploring seafloor morphologies influenced by bottom currents. The present study aims to capture the spatial arrangement of recent subsurface contourite features, assuming a latitudinal influence of water masses and the interactions between along- and downslope processes, in order to contribute to the knowledge of regional deepwater flow pathways and to the sedimentary model of small sediment-starved oceanic basins. To this end, the investigation combines an interpretation of multibeam bathymetry and parametric echo sounder seismic data complemented with hydrological data. The distribution of morpho-sedimentary features in Ona Basin reveals two major domains. The southern margin of the basin can be regarded as a mixed/hybrid system containing abundant sediment drifts with channels and contourite moats and a lateral continuity interrupted by downslope morphologies. In contrast, the northern abyssal setting comprises relatively homogeneous large sheeted drifts with superimposed sediment waves, mounded drifts, and several scattered erosive features, likely reflecting the more distinct influence of deepwater contourite processes. Our work demonstrates that tectonic features in the southern basin control the interaction between deepwater along- and downslope processes, as the westward flow of the WSDW is deflected, channelized, and intensified along its westward route. In the northern region, the study indicates an overall clockwise rotation of the WSDW flow, with the spatial and vertical variability of CDW and WSDW affecting the distribution of bottom-current features around seamounts and/or structural highs. The results underscore the importance of sloping interphases in the water mass vertical structure, the degree of basin confinement, and the influence of local bathymetric elevations in sedimentation models of small sediment-starved oceanic basins.

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