Control of oceanic circulation on sediment distribution in the southwestern Atlantic margin (23 to 55° S)

Michel Michaelovitch De Mahiques,Leticia Burone,Roberto Violante,Cesar Barbedo Rocha,Rubens Cesar Lopes Figueira,Bianca Sung Mi Kim,Marcia Caruso Bícego,Paula Franco-Fraguas,Leonardo Ortega,Rosangela Felicio Dos Santos

doi:10.5194/os-17-1213-2021

Abstract

Abstract. In this study, we interpret the role played by ocean circulation in sediment distribution on the southwestern Atlantic margin using radiogenic Nd and Pb isotopes. The latitudinal trends for Pb and Nd isotopes reflect the different current systems acting on the margin. The utilization of the sediment fingerprinting method allowed us to associate the isotopic signatures with the main oceanographic features in the area. We recognized differences between Nd and Pb sources to the Argentinean shelf (carried by the flow of Subantarctic Shelf Water) and slopes (transported by deeper flows). Sediments from Antarctica extend up to the Uruguayan margin, carried by the Upper and Lower Circumpolar Deep Water. Our data confirm that, for shelf and intermediate areas (the upper 1200 m), the transfer of sediments from the Argentinean margin to the north of 35∘ S is limited by the Subtropical Shelf Front and the basin-wide recirculated Antarctic Intermediate Water. On the southern Brazilian inner and middle shelf, it is possible to recognize the northward influence of the Río de la Plata sediments carried by the Plata Plume Water. Another flow responsible for sediment transport and deposition on the outer shelf and slope is the southward flow of the Brazil Current. Finally, we propose that the Brazil–Malvinas Confluence and the Santos Bifurcation act as boundaries of geochemical provinces in the area. A conceptual model of sediment sources and transport is provided for the southwestern Atlantic margin.

Highlights

Physical and oceanographic processes, including ocean current circulation, river discharge, marine fronts, wind patterns, and climate variability, have a crucial impact on sediment transport variability and fate (Storlazzi and Reid, 2010; Qiao et al, 2020)
Hydrodynamics are strongly influenced by the Río de la Plata (RdlP) outflow, the secondlargest river basin in South America, and by the encounter of subtropical and subantarctic water masses transported by the Brazil and Malvinas currents, which is known worldwide as Brazil—Malvinas Confluence (BMC); there is an influence by the BMC’s shelf extension, the Subtropical Shelf Front (STSF)
We use Nd and Pb radiogenic isotopes to recognize the role of ocean circulation in the sediment distribution of the southwestern Atlantic margin

Summary

Introduction

Physical and oceanographic processes, including ocean current circulation, river discharge, marine fronts, wind patterns, and climate variability, have a crucial impact on sediment transport variability and fate (Storlazzi and Reid, 2010; Qiao et al, 2020). At the BMC, water masses are transported eastwards as part of the southern limb of the basin-wide Anticyclonic Atlantic Subtropical Gyre (Boebel et al, 1997; Schmid et al, 2000). M. M. de Mahiques et al.: Control of oceanic circulation on sediment distribution where it splits into two branches, forming the Santos Bifurcation (SB; Boebel et al, 1999a; Legeais et al, 2013). The southward branch of the bifurcation feeds the Brazil Current (BC), flowing south until its eastward displacement at the BMC (Schmid et al, 2000). The northward branch flows as the Intermediate Western Boundary Current (IWBC) (Legeais et al, 2013), which is an important mechanism for the transport of the Antarctic Intermediate Water towards the Northern Hemisphere (Boebel et al, 1999b)

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Conclusion