Mid- to late-Holocene paleoceanographic changes on the southeastern Brazilian shelf based on grain size records

Abstract

High-resolution grain size analyses of three AMS 14C-dated cores from the Southeastern Brazilian shelf provide a detailed record of mid- to late-Holocene environmental changes in the Southwestern Atlantic Margin.The cores exhibit millennial variability that we associate with the previously described southward shift of the Inter Tropical Convergence Zone (ITCZ) average latitudinal position over the South American continent during the Holocene climatic maximum. This generated changes in the wind-driven current system of the SW Atlantic margin and modified the grain size characteristics of the sediments deposited there. Centennial variations in the grain size are associated with a previously described late-Holocene enhancement of the El Niño-Southern Oscillation (ENSO) amplitude, which led to stronger NNE trade winds off eastern Brazil, favouring SW transport of sediments from the Paraiba do Sul River. This is recorded in a core from off Cabo Frio as a coarsening trend from 3000 cal. BP onwards. The ENSO enhancement also caused changes in precipitation and wind pattern in southern Brazil, allowing high discharge events and northward extensions of the low-saline water plume from Río de la Plata. We propose that this resulted in a net increase in northward alongshore transport of fine sediments, seen as a prominent fine-shift at 2000 cal. BP in a core from ~24°S on the Brazilian shelf. Wavelet- and spectral analysis of the sortable silt records show a significant ~1000-yr periodicity, which we attribute to solar forcing. If correct, this is one of the first indications of solar forcing of this timescale on the Southwestern Atlantic margin.

Magnetic fingerprint of the late Holocene inception of the Río de la Plata plume onto the southeast Brazilian shelf

“…Cavallotto et al, 2004;Mahiques et al, 2009;Nagai et al, 2009;Chiessi et al, 2010;Gyllencreutz et al, 2010;Bender et al, 2013;Razik et al, 2013). The hydrological dynamics off the mouth of the Rio de la Plata (RdlP) is dominated by the plume of its discharge waters, which is transported northward by the Brazilian Coastal Current (BCC) to the SE Brazilian continental shelf (Souza and Robinson, 2004;Piola et al, 2005).…”

“…The penetration of the BCC onto the SE Brazilian continental shelf presently reaches latitudes of about 28°S (Piola et al, 2000), and wind stress is considered to be the main factor controlling its northward penetration (Möller et al, 2008;Piola et al, 2008). Before the full development of the RdlP plume, the SE Brazilian shelf could have received sediments from the Argentinean shelf (Mahiques et al, 2008;Gyllencreutz et al, 2010), but the causes and timing of this change in sediment sourcing are still poorly constrained.…”

“…Because sedimentation in the SE Brazilian continental shelf is weakly influenced by adjacent terrigenous input, the northward extension of the RdlP plume plays an important role as a source of sediments to the SE Brazilian continental shelf (Mahiques et al, 2008;Gyllencreutz et al, 2010). The RdlP drainage basin comprises a catchment area of 3.2 × 10 6 km 2 , which encompasses a large surface of the Paraná flood basalts and the subordinated acidic volcanics.…”

Surficial sediment texture database for SW Iberia Atlantic Margin

“…sediments (Vandenberghe, 2013), changes in the strength of continental shelf currents and precipitation regimes over time (Gyllencreutz et al, 2010), or to infer driver-related energy gradients (Rosa et al, 2013).…”

Integridade biótica dos ecossistemas na região do Arquipélago dos Alcatrazes, São Sebastião - SP

“…Porém, Castro (1996) (Campos et al, 1999;Souza & Robinson, 2004). A presença desse fluxo atua nos processos de sedimentação naárea de estudo, transportando sedimento do Río de La Plata para a plataforma continental de São Paulo (Mahiques et al, 2008;Gyllencreutz et al, 2010;Mahiques et al, 2011). …”