Paleoproductivity changes during the Late Quaternary in the southeastern Brazilian upper continental margin of the Southwestern Atlantic

Abstract

A B S T R A C TChanges in the Brazilian continental margin's oceanic productivity and circulation over the last 27,000 years were reconstructed based on sedimentological and microfaunal analyses. Our results suggest that oceanic paleoproductivity and the supply of terrigenous sediments to the Brazilian continental margin were higher during the Last Glacial Maximum (LGM) than during the Holocene. These changes may have been primarily influenced by significant sea level fluctuations that have occurred since the late Pleistocene. During the LGM, the lower sea level, higher productivity and lower sea-surface paleotemperatures may have been the result of the offshore displacement of the main flow of the Brazil Current. However, during the Holocene, the warm waters of the Brazil Current were displaced toward the coast. This displacement contributed to the increase in water temperature and prevented an increase in oceanic productivity. The decrease in terrigenous supply since the LGM could be related to the increase of the extension of the continental shelf and/or drier climatic conditions. R E S U M OMudanças na produtividade e circulação oceânica da margem continental Brasileira foram reconstituídas a partir de análises sedimentológicas e microfaunísticas realizadas em sedimentos de um testemunho representativo dos últimos 27 000 anos. Nossos dados sugerem maior produtividade oceânica e suprimento de sedimento terrígeno na área de estudo no Último Máximo Glacial (UMG) do que no Holoceno. Estas mudanças foram principalmente influenciadas por flutuações do nível relativo do mar. Durante o UMG, num cenário de nível relativo do mar mais baixo, a maior produtividade oceânica e menor temperatura da superfície do mar, podem ter sido produtos do deslocamento para o largo da Corrente do Brasil. No Holoceno, o deslocamento para a costa das águas quentes da Corrente do Brasil contribuiu para o aumento na temperatura da água e menor produtividade oceânica. A diminuição do aporte de sedimentos terrígenos desde o UMG pode estar relacionado ao aumento da extensão da plataforma continental e/ou a condições climáticas mais secas no continente.

Organic biomarker records spanning the last 34,800 years from the southeastern Brazilian upper slope: links between sea surface temperature, displacement of the Brazil Current, and marine productivity

“…The decrease in productivity during the Holocene can be attributed to a progressive strengthening of the BC as a result of the southward displacement of the Intertropical Convergence Zone caused by changes in insolation related to the precessional cycle (Toledo et al 2008). Nagai et al (2010) studied the foraminiferal signatures of a sediment core collected from the same region as that of the present study, and also reported increased benthic productivity during MIS 2. Those authors proposed that the presence of species considered to be indicative of high food availability (Bulimina marginata and Uvigerina peregrina) reflected a higher input of organic matter.…”

“…This has confirmed the important role of major reorganization of Atlantic thermohaline circulation in abrupt climate change (Mahiques et al 2005(Mahiques et al , 2007Toledo et al 2007aToledo et al , 2008Nagai et al 2010;Pivel et al 2010Pivel et al , 2013Leonhardt et al 2013;Mendoza et al 2014;Chapori et al 2015). For the southwestern Atlantic, study of planktonic foraminiferal records has suggested that productivity was higher during deglaciation than in the last glacial maximum (LGM) and the Holocene (Toledo et al 2007b), although other studies have shown that productivity peaked during the LGM and the Younger Dryas in the same region (Mahiques et al 2007;Toledo et al 2008).…”

Chapter 5 The southern Brazilian shelf

“…Hydrodynamic changes in the Brazilian continental margin, derived from sea-level fluctuations, have been explored previously (Mahiques et al 2007;Nagai et al 2010). According to these authors, low sea-level conditions promote offshore displacement of the BC, resulting in a less intense action of this current on the shelf.…”

Climatic evolution of eastern South America during the last deglaciation: a paleoceanographic approach

“…Only a few studies investigated changes in paleoproductivity in the oligothrophic 305 western South Atlantic Ocean (i.e., Mahiques et al, 2007;Nagai et al, 2010;Toledo, 2008;306 Toledo et al, 2007). Toledo (2008) …”

“…Mahiques et al (2007) and Nagai et al (2010) found increased 310 productivity during the Last Glacial Maximum (LGM, 23 to 19 ka, and 311 relatively stable paleoproductivity values during Termination 1. Even during the LGM our 312…”