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.

In 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, restinga forest, open restinga and 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.

Collagen extraction depends on the state of bone preservation, and the acidity of Brazilian soils often prevents the use of this material for radiocarbon dating. When available, however, bone samples constitute very important chronological records for both archaeological sites and natural depositional sites of specific animals. The extraction of collagen was performed using two filters, the first aiming to remove insoluble contaminants, and the second, a vivaspin ultrafilter 30KD to retain large molecular weight materials. The collagen was liofilized and converted to CO2 by combustion in sealed quartz tubes with CuO and Ag. The graphite was produced by zinc reduction in independently sealed Pyrex™ tubes. In order to verify the accuracy of this protocol, we analyzed a modern bone and four previously dated fragments, including those from the Sixth International Radiocarbon Intercomparison (SIRI), and a fragment of human bone from the Amourins site, a Brazilian shellmound. The results for the known age material are in agreement with the expected and the studied sector of Amourins shellmound was dated 4100–3900 years cal BP from a chronological model performed with charcoal dating found in different stratigraphic layers. Samples were dated at the radiocarbon laboratory of Universidade Federal Fluminense (LAC-UFF) in Brazil.

Throughout its 200 years, the Museu Nacional (National Museum) in Rio de Janeiro has been the principal museum of natural history in Brazil. It certainly has been among the most important research institutions in the Americas. Many of the greatest national and international scholars worked in or visited its collections, exhibitions, and laboratories. Botanists, zoologists, ecologists, geologists, paleontologists, anthropologists, archaeologists, and so many other scientists frequented the research facilities of the São Cristóvão Palace, its hallways, internal gardens, associated buildings, and park. They established friendships, scientific partnerships, and antagonisms, engaging in intense and productive exchanges that advanced science in each discipline yet with a multidisciplinary spirit. This thriving space, which we all always referred to as “our home,” was utterly destroyed by the tragedy of September 2018, when we watched in astonishment as the fire consumed our lives.

The Santa Elina rock shelter (Central Brazil) was recurrently occupied from the Late Pleistocene to the Late Holocene. We compare sets of previously published anthracological analyses with new data to reconstruct the landscape, vegetation, and climate over the several thousand years of occupation, providing information on firewood management from about 27,000 to about 1500 cal BP. Laboratory analyses followed standard anthracological procedures. We identified 34 botanical families and 84 genera in a sample of almost 5,000 charcoal pieces. The Leguminosae family dominates the assemblage, followed by Anacardiaceae, Bignoniaceae, Rubiaceae, Euphorbiaceae, and Sapotaceae. The area surrounding the shelter was forested throughout the studied period. The local landscape was formed, as it is today, by a mosaic of vegetation types that include forest formations and open cerrado. Some regional vegetation changes may have occurred over time. Our data corroborate the practice of opportunistic firewood gathering in all periods of site occupation, despite a possible cultural preference for some taxa. The very long occupation of Santa Elina may be due not only to its attractiveness as a rock shelter but also to the continuously forested vegetation around it. It was a good place to live.

The anthracological analyses of domestic and ceremonial contexts of proto-Jê archaeological sites in southern Brazil and Argentina have yielded data regarding landscape, fire technology, fuel economy, wood selection, and wood use from about 1200 to 250 years BP. The inhabitants of these sites built up the landscape that they occupied, actively constructing and experiencing their domestic and ceremonial places and possibly engaging in vegetation management practices. They gathered timber and firewood in the Araucaria Forest and in intensely modified areas covered by secondary vegetation. These practices likely included logging and gathering fallen deadwood. Our data indicate cultural selection of particular species. Inga sp., Jacaranda sp., and Araucaria angustifolia were probably selected because of the meaning of these woods in the cosmological dual system of proto-Jê societies. Bamboos and palm stems may have been used as kindling and for fire making. These results are an important contribution to our understanding of the proto-Jê occupation and the relationships that these groups maintained with their plant environment.

Considering 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.

The Saquarema archaeological site, on the Atlantic coast of the Rio de Janeiro State, is one of many shellmounds built on the Brazilian coast by hunter-gatherer populations during the Holocene. We used archaeological material from this site with the aim of evaluating the marine reservoir effect (MRE) in the region. Radiocarbon ages of 45 marine and 6 terrestrial samples from this shellmound provided data for assessing the MRE and the influences of freshwater and seasonal coastal marine upwelling in this specific locality. Samples of charcoal, fish otoliths, and mollusk shells were analyzed and the 14C dates were modeled in the OxCal platform to determine the marine reservoir correction. The result obtained is R = 265 ± 70 14C yr and the offset ΔR was found to be –140 ± 66 14C yr. To support the accuracy of this value for correcting conventional 14C marine ages, taxonomic analyses of the samples were performed.

Previous work has suggested that seasonal and interannual upwelling of deep, cold, radiocarbon-depleted waters from the South Atlantic has caused variations in the reservoir effect (R) through time along the southern coast of Brazil. This work aims to examine the possible upwelling influence on the paleoreservoir age of Brazilian surficial coastal waters based on paired terrestrial/marine samples obtained from archaeological remains. On the Brazilian coast, there are hundreds of shell middens built up by an ancient culture that lived between 6500 to 1500 yr ago, but there are few shell middens located on open-coast sites with a known upwelling influence. Three archaeological sites located in a large headland in Arraial do Cabo and Una de Cabo Frio on the southeastern coast of Brazil, with open-ocean conditions and a well-known strong and large upwelling of the Malvinas/Falkland current, were chosen for this study. The 14C age differences between carbonized seed and marine samples varied from 281 ± 44 to 1083 ± 51 14C yr. There are also significant age differences between carbonized seed samples (977 14C yr) and marine samples (200 and 228 14C yr) from the same archaeological layer that cannot be explained by a reservoir effect or an old-wood effect for charcoal. Therefore, the present data from the southeastern Brazilian coast are inconclusive for identifying an upwelling effect on R. To do so, it would be necessary to more precisely define the present–pre-bomb R in upwelling regions, and to analyze paired marine/terrestrial samples that are contemporaneous beyond doubt.