Abstract
Abstract. In this study, we use inorganic (metal) and organic (bulk and molecular) markers in sediment samples of the south-eastern Brazilian margin to investigate the response of geochemical fingerprints to the complex hydrodynamic processes present in the area. Results indicate the potential of export of terrigenous siliciclastic and organic constituents to the upper slope, even in an area with limited fluvial supply.Metal contents and especially the ln(Ti ∕ Al) and ln(Fe ∕ K) ratios make it possible to recognise the extension of shelf sediments toward the upper slope. Potassium, here expressed as ln(K ∕ Sc) and ln(K ∕ Al) ratios used as proxies of illite–kaolinite variations, proved to be an important parameter, especially because it allowed us to decipher the imprint of the northward flow of the Intermediate Western Boundary Current (IWBC) in comparison to the southward flows of the Brazil Current (BC) and Deep Western Boundary Current (DWBC). Using organic matter analyses, we were able to evaluate the extent of terrestrial contributions to the outer shelf and slope, even without the presence of significant fluvial input. In addition, molecular markers signify a slight increase in the input of C4-derived plants to the slope sediments, transported from distant areas by the main alongshore boundary currents, indicating that the terrestrial fraction of the organic matter deposited on the slope has a distinct origin when compared to shelf sediments.
Highlights
Sedimentary processes at continental margins are controlled by a complex interplay of factors that act on local, regional and global scales (Pratson et al, 2007)
Sedimentation along the south-eastern Brazilian continental margin (Fig. 1) is controlled by coastal hydrodynamic processes, which are strongly associated with the local winddriven current system, by the northward-directed plume of the Río de La Plata on the inner and mid shelf, and by the meandering eddy structure of the southward flowing Brazil Current on the outer shelf, which itself is a result of upwelling dynamics, occasionally driven by passing BC meanders and local wind conditions
It is worth noting that despite the value of the sedimentation rate obtained for core 65, the visual description of the sediments showed stained and oxidised bioclasts as well as limonite-covered quartz grains, which are indicative of relict sediment facies (Wilson, 2010)
Summary
Sedimentary processes at continental margins are controlled by a complex interplay of factors that act on local, regional and global scales (Pratson et al, 2007). Previous studies (de Mahiques et al, 2008; FrancoFraguas et al, 2014; Razik et al, 2015) provide different and contradictory interpretations for the sources and transport of sediment in the south-western Atlantic; this is especially due to a complex hydrodynamics of the Subtropical Gyre (Boebel et al, 1999; Schmid et al, 2000; Biló et al, 2014) between 23 and 35◦ S In this sense, considering the complex hydrodynamics of the south-eastern Brazilian margin north of 28◦ S, this study analyses a new data set of both organic and inorganic sediment parameters, collected from the inner shelf to the middle slope. – Is it possible to differentiate distinct geochemical signatures in the sediments that reflect the various ocean current systems on the south-eastern Brazilian slope, namely the BC, IWBC and DWBC?
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
