ASSESSING THE ¹⁴C MARINE RESERVOIR EFFECT IN ARCHAEOLOGICAL CONTEXTS: DATA FROM THE CABEÇUDA SHELL MOUND IN SOUTHERN BRAZIL

Abstract

Prehistoric shell mounds can be useful for the quantification of the radiocarbon marine reservoir effect (MRE) and, at the same time, knowledge about the MRE allows for the establishment of robust chronologies for these sites. This creates a loop in which the archaeological setting has a dual role: it is part of both the method and the application. Therefore, it is paramount to address these sites from both archaeological and environmental perspectives, investigating their origin and diagenesis in order to overcome biases caused by post-depositional alterations. In this study, samples of bone, charcoal and shell from a Late Holocene shell mound in Southern Brazil, the Sambaqui de Cabeçuda, were analyzed following a multidisciplinary approach to disentangle the complex relationships between archaeology and the environment. We performed X-ray diffraction, radiocarbon dating, stable isotopes (δ13C, δ18O, δ15N) and anthracology analyses as well as Bayesian Chronological Models and Isotope Mixing Models to assess the local MRE and to reconstruct the diet of Cabeçuda builders. Our results reveal a negative local correction for the MRE (ΔR = –263 ± 46 14C yr), expected for the lagoon next to the site, and diets with considerable intakes of marine proteins. We examine the implications of these results for the chronology of the site and discuss a series of complications when performing MRE studies using shell mound sites.

Late shellmound occupation in southern Brazil: A multi-proxy study of the Galheta IV archaeological site

“…The δ 13 C and δ 15 N obtained from human bones and teeth confirm the substantial reliance on marine resources by the inhabitants of Galheta IV, as previously mentioned by Colonese and colleagues [28], considering both stable isotopes and lipids analysis on pottery sherds. Marine protein appears to have played a crucial role in their diets, similar to other coastal sites of Santa Catarina [63,[118][119][120][121][122][123][124][125][126][127], a pattern also observed on the southeastern coast of Brazil [128][129][130][131][132].…”

“…For the human bone calibrations, the marine curve Marine20 [58] and the atmospheric curve SHCal20 [59] were used (50/ 50% each, considering a mixed diet between marine and C 3 consumption expected for shellmounds populations as quantified by Scheel-Ybert et al [60]). To account for the marine reservoir effect, which carbon is incorporated in to bone tissues from the consumption of marine resources [61], we calculate a ΔR mean of -87±38 14 C years [62,63]. For the fur seal bone, which was previously dated [13], only the marine curve and reservoir effect was considered.…”

“…Other coastal sites of the region also rely on aquatic resources, but with species that could be found both at the estuary and the sea [101,[118][119][120][123][124][125][126][127]. However, when comparing the carbon and nitrogen isotopic ratios of humans from the non-ceramic sites Jabuticabeira II (~2400 years cal BP) [28,124,125,134] and Cabec ¸uda (~4000 to 2800 years cal BP) [63,124,135], there is significant dietary overlap among most individuals. Faunal deposition differs between Galheta IV and Jabuticabeira II, with the latter showing a higher concentration of fish near human burials [125], while Galheta IV has a different distribution pattern (see next discussion session).…”

The Potential of Biogenic Fraction Analysis by Radiocarbon in Food, Drug, and Cosmetic Products

“…This 100 pMC is valid for the terrestrial biosphere, but this value may vary in the aquatic biosphere. Due to the mixture with pre-aged carbon pools, the carbon sources for fishes and aquatic animals in the sea and ocean typically have a lower 14 C/ 12 C ratio, which can cause them to appear older than their true age, presenting different specific radiocarbon activity compared to the atmospheric value (marine reservoir effect or MRE) (Philippsen 2013; Fernandes et al 2016; Larsen et al 2018; Alves et al 2022; Svyatko et al 2022).…”