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ABSTRACTPrehistoric 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.

ABSTRACTThe Radiocarbon Laboratory of the Fluminense Federal University was installed in 2009, and its NEC Single Stage Accelerator Mass Spectrometry system has been operational since 2012. As the first 14C-AMS facility in Latin America, the LAC-UFF became a reference center for radiocarbon (14C) dating in Brazil. Over the years we have implemented pretreatment protocols for several kinds of materials, such as cellulose, soil, bone, and biofuels. In the present paper we describe our current protocols for the preparation of these types of samples. Moreover, after 10 years of operation, with the aim of expanding the range of materials we are able to analyze, we report the results of several tests to improve accuracy, precision and background levels. For example, here we discuss how isotopic fractionation during the graphitization and measurement steps has been controlled. Concerning results interpretation, our research group has been using OxCal chronological models to analyze different contexts such as stromatolite growth, tree rings, soil deposition and marine reservoir effect (MRE) determination.

ABSTRACTIn paleoenvironmental research, several proxies are used to reconstruct climate and vegetation. The establishment of a chronological framework allows for the association of different proxies and correlation of events happening in different geographic areas. Cultural deposits, such as the shellmounds found along the coast of Brazil, play an important role in paleoenvironmental interpretations. Here, we have employed anthracological analysis in charcoal fragments from the Amourins shellmound, located at the margins of the Guanabara Bay, Rio de Janeiro. This allowed for the taxonomic identification and selection of short-lived trees and specific parts of plants for accurate radiocarbon dating. We recorded genera and families typical of the Atlantic Forest, restingaforest, open restingaand mangrove. The 14C ages of charred nuts from different occupational layers range from 3807 ± 35 to 3503 ± 70 BP and a sequential chronological model was built, relating the predominance of mangrove vegetation to the period between 4130–3960 cal BP.

ABSTRACTThe radiocarbon (14C) chronology of hunter-fisher-gatherers’ archaeological settlements along the Brazilian coast is usually based on mollusk shells, charcoal from hearths, and eventually human bones. However, fish otoliths are found in several archaeological contexts and may represent a reliable option as a chronological record. In this work, we compare the 14C dates of whitemouth croakers (Micropogonias furnieri) otoliths with dates obtained from other materials (shell and charcoal), collected from shellmounds on the coast of Rio de Janeiro, with the aim of improving the accuracy in the 14C dating of Brazilian shellmounds, strengthening the comprehension of the native populations’ occupational trends and the coeval palaeoceanographic context. Based on x-ray diffraction results for archaeological otoliths, their geochemical composition indicates minimal diagenesis effect over time even under burial conditions in the studied sites. The comparison between otolith dates and dates obtained from other proxies revealed similar results but with decreased deviations in otolith dates in all of the studied sites.

The study of relative sea level variations (RSLV) is crucial for understanding past fluctuations and predicting future environmental changes, especially in coastal areas. The Holocene epoch is of particular interest due to the greater preservation of its indicators, which come from various academic fields such as micropaleontology, archaeology, geomorphology, sedimentology, stratigraphy, and geochronology. As a result, methodologies can vary and have improved over time. This study aimed to discuss the main articles and authors that deal with RSLV on the coast of Rio de Janeiro state. We selected 44 articles from the Scopus database, using keywords such as 'Sea Level', 'Indicators', 'Holocene', and 'Rio de Janeiro' to conduct the search. Using the VOSViewer bibliometric software, we generated maps showing links between authors, articles, and keywords, as well as tables indicating the number of citations and publications. The software identified 140 authors from the selected articles. We found an increase in publications on the subject in recent years. From the number of citations and publications, we concluded that author J.W.A. Castro stands out in the field due to his works on constructing the state's RSLV curve. The most frequently appearing keywords in the articles were 'Holocene' and 'sea level change', which were expected. In addition, 'radiocarbon dating', 'beachrock', and 'paleoenvironment' were commonly used, indicating that the radiocarbon method is the most widely used for dating. However, we also found a lack of detail on the methodologies used for dating, from sample pre-treatment to age measurement, which could make it difficult for other researchers to use the data. Nevertheless, our analysis of bibliometric data and bibliographic review revealed many collaborations between authors from different fields, broadening the understanding of the subject and generating knowledge exchange within the academic community.

ABSTRACTConsidering the impact of coastal dynamics on the radiocarbon (14C) marine reservoir effect (MRE), upwelling has the potential of enhancing marine influence, usually 14C depleted. Freshwater input can contribute either to increased reservoir offsets, when dead carbon from rock weathering is available, but also towards an atmospheric 14C 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.

When a carbon reservoir has a lower radiocarbon content than the atmosphere, this is referred to as a reservoir effect. This is expressed as an offset between the radiocarbon ages of samples from the two reservoirs at a single point in time. The marine reservoir effect (MRE) has been a major concern in the radiocarbon community, as it introduces an additional source of error that is often difficult to accurately quantify. For this reason, researchers are often reluctant to date marine material where they have another option. The influence of this phenomenon makes the study of the MRE important for a broad range of applications. The advent of Accelerator Mass Spectrometry (AMS) has reduced sample size requirements and increased measurement precision, in turn increasing the number of studies seeking to measure marine samples. These studies rely on overcoming the influence of the MRE on marine radiocarbon dates through the worldwide quantification of the local parameter ΔR, that is, the local variation from the global average MRE. Furthermore, the strong dependence on ocean dynamics makes the MRE a useful indicator for changes in oceanic circulation, carbon exchange between reservoirs, and the fate of atmospheric CO2, all of which impact Earth's climate. This article explores data from the Marine Reservoir Databaseand reviews the place of natural radiocarbon in oceanic records, focusing on key questions (e.g., changes in ocean dynamics) that have been answered by MRE studies and on their application to different subjects. A detailed review of radiocarbon marine reservoir effect research and its applications is presentedThe influence of the global carbon cycle on marine radiocarbon ages is discussedSpatiotemporal variations in ocean radiocarbon concentration are discussed

AbstractAmong other zooarchaeological remains, terrestrial snails’ shells from the Thaumastusand Megalobulimusgenera are found in some Brazilian shellmounds, presenting a potential substitute for charcoal in radiocarbon dating analyses, as reliable representatives of the atmospheric carbon isotopic ratio. In this paper, we present statistically similar results of both charcoal and land snails samples from the same archaeological contexts in three settlements on the coast of Rio de Janeiro. The Manitiba I shellmound results range from 4.2 to 3.7 ka cal BP (95.4%), contemporary with the Saquarema shellmound, occupied during the period from 4.3 to 3.6 ka cal BP (95.4%). For the Usiminas shellmound, two groups of samples revealed different periods of time for two occupational layers from 2.3 to 2.1 ka cal BP (95.4%) and from 1.6 and 1.3 ka cal BP (95.4%). A model constraining each group of samples to within a single phase has a general agreement of 97% with only two outliers out of 22 dates, yielding minimum individual agreement of 74% and 7% posterior outlier probability for Saquarema shells. These are good examples of sites in which the occupation chronology can be successfully obtained by the radiocarbon dating of land snails.