Particle Fluxes and Bulk Geochemical Characterization of the Cabo Frio Upwelling System in Southeastern Brazil: Sediment Trap Experiments between Spring 2010 and Summer 2012

Abstract

Physical and biogeochemical processes in continental shelves act synergistically in both transporting and transforming suspended material, and ocean dynamics control the dispersion of particles by the coastal zone and their subsequent mixing and dilution within the shelf area constrained by oceanic boundary currents, followed by their gradual settling in a complex sedimentary scenario. One of these regions is the Cabo Frio Upwelling System located in a significantly productive area of Southeastern Brazil, under the control of the nutrient-poor western boundary Brazil Current but also with a wind-driven coastal upwelling zone, inducing cold-water intrusions of South Atlantic Central Water on the shelf. To understand these synergic interactions among physical and biogeochemical processes in the Cabo Frio shelf, a series of four experiments with a total of 98 discrete samples using sediment traps was performed from November 2010 to March 2012, located on the 145 m isobath on the edge of the continental shelf. The results showed that lateral transport might be relevant in some cases, especially in deep layers, although no clear seasonal cycle was detected. Two main physical-geochemical coupling scenarios were identified: singular downwelling events that can enhance particles fluxes and are potentially related to the Brazil Current oscillations; and events of significant fluxes related to the intrusion of the 18°C isotherm in the euphotic zone. The particulate matter settling in the Cabo Frio shelf area seems to belong to multiple marine and terrestrial sources, in which both Paraiba do Sul River and Guanabara Bay could be potential land-sources, although the particulate material might subject intense transformation (diagenesis) during its trajectory to the shelf edge.

Branched GDGTs as Proxies in Surface Sediments From the South-Eastern Brazilian Continental Margin

“…accumulation of OM, mostly from autochthonous processes, was already demonstrated (Oliveira et al, 2013;Albuquerque et al, 2014;Cordeiro et al, 2018). Based on the sediment TOC contents reported by Cordeiro et al (2018), the total brGDGTs contents varied from 5 to 32 µg gTOC −1 , with a sharply decreasing gradient in contents from the coastal to deeper waters ( Figure 3A).…”

“…Two samples with the highest contents are close to the Paraíba do Sul River mouth (25 and 50 m depths, transect H), which confirm the role of this river as the main source of brGDGTs to the Campos Basin. In addition, relatively high contents of TOC-normalized brGDGTs (up to 31 µg gTOC −1 ) were also found at shallow stations from transects A and B, in the southern basin near Cabo Frio (Figure 1), suggesting coastal transport of continental materials delivered by small rivers along the coast, including contribution from the Paraíba do Sul river, located further north (Albuquerque et al, 2014).…”

“…As a consequence of the upwelling events, predominance of autochthonous OM in the basin's sediments on a regional scale is observed (Yoshinaga et al, 2008;Carreira et al, 2010;Cordeiro et al, 2018), a scenario also favored by a relatively low input of allochthonous OM (Carreira et al, 2015). The major contributor to continentally-derived materials to the Campos Basin is the Paraíba do Sul river, located to the north of the basin (Figure 2), as evidenced by isotopic and molecular markers (Souza et al, 2010;Albuquerque et al, 2014;Carreira et al, 2015), dissolved black carbon (Dittmar et al, 2012) and metals (Lacerda et al, 1993;Araujo et al, 2017). Even though the Paraíba do Sul River plays a minor role as source of material to the global oceans when compared to other rivers, the influence of Paraíba do Sul River is relevant on a regional scale .…”

Influence of estuarine dynamics on macrobenthos spatial variability along the southeast continental shelf of Brazil

“…Ocean dynamics control the dispersion of particles by riverine plumes and their subsequent mixing and dilution within coastal and oceanic boundary currents, followed by their gradual sedimentation within the shelf area (Albuquerque et al 2014). All of these sources and processes operate according to their own temporal and spatial constraints, creating a complex scenario for understanding the origins and fates of suspended particles at the ocean margin and their fluxes to the ocean floor (Liu et al 2010, Schmidt et al 2010 The Paraíba do Sul River (PSR) plays an important role in the ecosystem of the southeast continental shelf of Brazil.…”

Oceanographic and sedimentological influences on carbonate geochemistry and mineralogy in hypersaline coastal lagoons, Rio de Janeiro state, Brazil

“…These semiarid conditions are attributed to the occurrence of the coastal CFUS. This phenomenon is more intense around Cabo Frio than in the area north of the Cabo de São Tomé due to the change in the shoreline orientation from east–west to north–south, respectively (Albuquerque et al ; Palóczy et al ). Offshore Cabo Frio, the Brazilian Current separates from its bathymetric steering and disintegrates into a series of meso‐scale oceanic eddies, resulting in upwelling along the coast.…”