The Marine Reservoir Effect on the Coast of Rio de Janeiro: Deriving ∆R Values from Fish Otoliths and Mollusk Shells

Abstract

Considering the impact of coastal dynamics on the radiocarbon (14C) marine reservoir effect (MRE), upwelling has the potential of enhancing marine influence, usually14C depleted. Freshwater input can contribute either to increased reservoir offsets, when dead carbon from rock weathering is available, but also towards an atmospheric14C signal, when the presence of terrestrial organic matter from catchment prevails. An overview of the MRE studies based on shellmounds on the coast of Rio de Janeiro reveals a pattern of negative local corrections for Saquarema and Rio das Ostras but positive values for Cabo Frio island, suggesting the presence of cold upwelling waters in Cabo Frio at 1.6–1.2 cal kBP. New results for a shellmound on the Ilha Grande island, in the western portion of the Rio de Janeiro coast, revealed a negative value at about 3 ka. We discuss distribution of MRE values and temporal variability in the region and their relation to ocean dynamics, continental input and the choice of marine organisms used for ∆R determination. A comparison of local reservoir offsets for the Saquarema region obtained from fish otolith and mollusk shells revealed similar ΔR distributions, showing that both materials can be equally used.

Otolith-Based Chronology of Brazilian Shellmounds

“…Based on the importance of this species in terms of prehistoric fisheries and its well-known natural history, we have selected M. furnieri otoliths for 14 C analysis. For comparison, we used the data on whitemouth croaker otoliths from the Saquarema shellmound published in Alves et al (2015b) plus shell and charcoal data from Kneip et al (1981, 2001), Lima et al (2003, 2004), Macario et al (2014, 2015a, 2018), Alves et al (2015b), and Carvalho et al (2015).…”

“…In these sites, despite the proximity with a seasonal upwelling area evidenced by the Usiminas shellmound, in llha de Cabo Frio, with ∆R of 67 ± 33 14 C yr, the contrasting negative reservoir offsets disclose the competing freshwater influence in this lagoon system (Macario et al 2016a). For the Acaiá, Algodão, Caieira, Bigode, Major, and Peri shellmounds located in the Ribeira Bay a ∆R of –80 ± 87 14 C yr (Macario et al 2018) was used. For the other sites, where no specific study on the MRE is available, we used the pre-bomb mean value 32 ± 44 14 C years (Alves et al 2015a) for the coast of Brazil.…”

“…The establishment of the Radiocarbon Laboratory of the Universidade Federal Fluminense (LAC-UFF), the first radiocarbon ( 14 C) accelerator mass spectrometry (AMS) dedicated facility in South America (Anjos et al 2013; Macario et al 2013, 2015a), and subsequent research about the marine reservoir effect (MRE), particularly on the southeastern Brazilian coast (Macario et al 2015b, 2016a, 2018; Carvalho et al 2015; Alves et al 2015a, 2015b), have contributed to improve 14 C-based studies on archaeological shellmounds. The materials that have traditionally been used for 14 C analysis are charcoal, seed, shell (Lima et al 2004; Angulo et al 2007; Macario et al 2014, 2015b; Alves et al 2015a; Carvalho et al 2015) and human bones (e.g.…”

“…Previous research involved the use of otolith for 14 C chronology (Piner and Wischniowski 2004; Alves et al 2015b), reservoir effect calculations (Kalish 1993; Alves et al 2015b; Milheira et al 2017; Macario et al 2018), isotope-derived paleotemperature (Thorrold et al 1997; Ghosh et al 2007; Darnaude et al 2014; Bertucci et al 2018), fish growing (Cook et al 2009; Andrews et al 2011), isotope fish migration signals (Holbach et al 2012; Darnaude et al 2014), environmental geochemistry (Albuquerque et al 2012; Stanley et al 2015) and palaeoceanography (Schloesser et al 2009; Grammer et al 2015). Following these works, we discuss the use of otolith for improving the accuracy in the 14 C dating of Brazilian shellmounds.…”

Marine Reservoir Corrections for the Brazilian Northern Coast Using Modern Corals

“…Research on the marine reservoir effect (MRE) on the coast of Brazil has increased over the last few years (Alves at al. 2015a, 2015b, 2018; Carvalho et al 2015; Macario et al 2015, 2016, 2018). Nevertheless, due to its extensive area and varied geomorphological features, the available estimates for ΔR offsets between local and global oceans are far from ideal.…”