The erosive power of the Malvinas Current: Influence of bottom currents on morpho-sedimentary features along the northern Argentine margin (SW Atlantic Ocean)

Abstract

Sediment deposits formed mainly under the influence of bottom currents (contourites) are widely used as high-resolution archives for reconstructing past ocean conditions. However, the driving processes of Contourite Depositional Systems (CDS) are not entirely understood.The aim of this study is to establish a clearer link between contourite features and the oceanographic processes that form them. The morphosedimentary characteristics of a large CDS were analysed together with the current dynamics along the northern Argentine continental margin. This study combines multibeam bathymetry, seismo-acoustic data, sediment samples, vessel-mounted Acoustic Doppler Current Profiler (VM-ADCP) data and numerical modelling of ocean currents. The contouritic features include large contourite terraces (La Plata Terrace, Ewing Terrace) and an abraded surface between the terraces, as well as smaller erosional and Preprint submitted to Marine Geology 2021 2 depositional features like moats, erosion surfaces on the Ewing Terrace, sediment waves and contourite drifts. Measured and modelled near-bottom currents are vigorous (up to 63 cm/s at 150 -200 m above the seafloor) where abraded surfaces and moats are present, and relatively weak (below 30 cm/s) on the La Plata Terrace and the Ewing Terrace. Generally, bottom currents follow the upper and middle slope morphology. Decreasing velocity of water masses flowing northward leads to less erosion and finer sediment deposits. ADCP data and the hydrodynamic model show the formation of eddies near the seafloor which probably lead to the small erosion surfaces on the Ewing Terrace, even though it is mainly a depositional environment. Overall, this study contributes to a better understanding of the formation of CDS and can help future reconstructions of past ocean conditions based on sedimentary structures.