Influence of bottom currents on morpho-sedimentary features along the northen Argentine margin shows the erosive power of the Malvinas current

TILMANN SCHWENK; ALBERTO PIOLA; VOLKHARD SPIESS; SABINE KASTEN; ELDA MIRAMONTES; WENYAN ZHANG; CHRISTINE PROVOST; MERET FELGENDREHER; HENRIETTE WILCKENS; CAMILA ARTANA; BAQUÉS, M.; F. JAVIER HERNÁNDEZ-MOLINA

New Orleans, LA & Online

Congreso; AGU Fall Meeting; 2021

AGU

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. During RV SONNE cruise SO260 (January-February 2018), a large CDS together with the current dynamics along the continental margin off northern Argentina were analysed. This study combines multibeam bathymetry, seismo-acoustic data, sediment cores, Acoustic Doppler Current Profiler (ADCP) data and numerical modelling of ocean currents. Several sedimentary features have been interpreted together with the ocean currents. These features include large contourite terraces (La Plata Terrace, Ewing Terrace) and an abraded surface connecting the terraces, as well as smaller features like moats, erosion surfaces on the terrace, sediment waves and contourite drifts. Measured and modelled bottom-currents are strong (up to 63 cm/s at 150 - 350 m above the seafloor) where abraded surfaces and moats are present, and weak (below 30 cm/s) on the La Plata Terrace and the Ewing Terrace. Generally, the bottom-currents follow the upper and middle slope morphology. Decreasing velocity of surface and intermediate water masses flowing northward leads to less erosion and finer sediment deposits. ADCP data and the hydrodynamic model show the formation of eddies at the seafloor which probably lead to small erosion surfaces on the Ewing Terrace, even though it is mainly a depositional environment. Furthermore, modelled data show that the Malvinas Current continues flowing northwards at the seafloor (~36°S) than at the sea surface. 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.