The editors of several major journals have recently asserted the importance of combating racism and sexism in science. This is especially relevant now, as the COVID-19 pandemic may have led to a ...widening of the gender and racial/ethnicity gaps. Implicit bias is a crucial component in this fight. Negative stereotypes that are socially constructed in a given culture are frequently associated with implicit bias (which is unconscious or not perceived). In the present article, we point to scientific evidence that shows the presence of implicit bias in the academic community, contributing to strongly damaging unconscious evaluations and judgments of individuals or groups. Additionally, we suggest several actions aimed at (1) editors and reviewers of scientific journals (2) people in positions of power within funding agencies and research institutions, and (3) members of selection committees to mitigate this effect. These recommendations are based on the experience of a group of Latinx American scientists comprising Black and Latina women, teachers, and undergraduate students who participate in women in science working group at universities in the state of Rio de Janeiro, Brazil. With this article, we hope to contribute to reflections, actions, and the development of institutional policies that enable and consolidate diversity in science and reduce disparities based on gender and race/ethnicity.
The radiocarbon dating method is supported by highly refined calibration data empirically obtained from environmental archives. Nevertheless, marine calibration remains problematic due to the ...spatiotemporally variable Marine Reservoir Effect (MRE). The currently accepted curve for radiocarbon calibration in the ocean is a global curve, partly derived by numerical modelling from its atmospheric counterpart. As such, this curve cannot account for the effects of local phenomena, strongly correlated with 14C signatures in seawater (e.g., ocean dynamics and continental input). Although the radiocarbon community has suggested the use of regional calibration curves that would better represent the heterogeneous ocean reservoir, a reasonable method for their construction has not yet been proposed. We directly address this longstanding issue in radiocarbon research by exploring the output of a model for the temporal evolution of the MRE. The limitations of this model are inherited by our method, and this hinders the use of the regional curves derived here in many regions of the world ocean. Nevertheless, the approach described in this paper remains valid regardless of the chosen model and our preliminary results show that, with the future development of accurate and highly resolved models for the MRE, this method may be a promising alternative to the use of ΔR values in the process of marine calibration.
•We propose a simple way to extract local marine calibration curves from MRA model outputs.•The output of a MRA model is compared with experimental data.•We assess the impact of a MRA model in the calibration of marine 14C ages.
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.
Given the difficulty in obtaining robust chronologies from tree rings in tropical regions, the search for appropriate species is very important. Both dendrochronology and radiocarbon (14C) ...measurements are required to validate the use of any specific tree. Some species have proved to be reliable for representing atmospheric 14C concentration over time, such as Cedrela fissilis and Araucaria angustifolia. However, not only the species have to be validated, but also different climatic conditions may result in different growth patterns for the same species. In this work, we study the annual growth rings of Cedrela fissilis from a dry tropical forest patch typical of a highly seasonal climate in central Brazil. 14C accelerator mass spectrometry (AMS) was used to compare the isotopic ratios of tree rings with the 14C concentrations in the atmosphere during the nuclear tests based on curve Bomb13SH 1-2. Results are similar to the bomb peak curve within the period from 1958 to 1980 AD and serve as a crucial test for the cross-dating analyses using the skeleton plot technique.
For environmental reasons, the production of plastic from renewable sources is gaining importance worldwide. In the case of polyethylene made from sugarcane-based ethanol, Brazil, being the world ...leader in sugarcane production, plays a fundamental role. Nevertheless, the absence of national regulations for monitoring the manufacturing process or verifying the biogenic fraction of what is already on the market raises concerns in Brazil. The main reason for the lack of such regulations is that the only approach fully capable of distinguishing identical chemical compounds of biogenic or fossil origin is the measurement of radiocarbon concentrations using an expensive and time-consuming method. Nevertheless, the measurement of stable carbon isotopes ratios has proven to be an acceptable approach to distinguish between C4 plant-derived plastics and petroleum-derived plastics. The present study compares the potential of the conventional mass spectrometry and radiocarbon accelerator mass spectrometry techniques as tools to determine the biogenic fraction of green polyethylene in Brazil. For plastics derived from either corn or sugarcane sources, δ13C values less negative than −20‰ indicate biofractions of 51% or higher. Other values would indicate the need to follow up to the radiocarbon accelerator mass spectrometry measurement, since it would not be possible to distinguish between lower biofractions and the presence of wheat or soy. The conventional mass spectrometry method can be employed for the preliminary screening of bio-based materials in manufacturing industries, representing a relatively cheap and accessible way of inspecting these products in developing countries.
•Plastic marketed as bio-based may have petroleum as a significant source.•Biofractions of plastics derived from C4 plants can be resolved via IRMS analyses.•Sugarcane based plastics were measured by both IRMS and 14C-AMS techniques.•IRMS represents a cheaper alternative to 14C-AMS analyses in biofraction studies.
In the present work, we assess the chronology of archaeological sites known as earthen mounds, commonly found at the Pampas biome, among the lowlands of Brazil, Uruguay, and Argentina. We focused on ...the Pontal da Barra settlement, which is a testimony of the long-term occupation of indigenous groups in the swamp and wet environment of Patos Lagoon, southern Brazil. A Bayesian chronological model based on the radiocarbon (14C) dating of 17 samples of fish otolith, 5 charcoal fragments, and 2 bones (human and dog) allowed determination of the beginning of the occupation as well as the occupational synchronism of the different mounds. The nature of the samples allows us to study the local 14C reservoir effect through the comparison between the group of marine and terrestrial samples, deriving a reservoir offset value of 63±53 14C yr for this particular area, indicating a strong freshwater influence in the lagoon system. We estimate the start of human intervention in the landscapes of southern Patos Lagoon to be around 2200 cal BP, with the most intense activity between 1800 and 1200 cal BP.
In Brazilian archaeological shellmounds, many species of land snails are found abundantly distributed throughout the occupational layers, forming a contextualized set of samples within the sites and ...offering a potential alternative to the use of charcoal for radiocarbon dating analyses. In order to confirm the effectiveness of this alternative, one needs to prove that the mollusk shells reflect the atmospheric carbon isotopic concentration in the same way charcoal does. In this study, 18 terrestrial mollusk shells with known collection dates from 1948 to 2004 AD, around the nuclear bombs period, were radiocarbon dated. The obtained dates fit the SH1-2 bomb curve within less than 15 years range, showing that certain species from the Thaumastus and Megalobulimus genera are reliable representatives of the atmospheric carbon isotopic ratio and can, therefore, be used to date archaeological sites in South America.
Interactions between invader species and the local biota may lead to disequilibria in regional ecosystems. For such reason, the cultivation of nonnative species may be prohibited in specific regions, ...as a means of protecting native species. On the other hand, the question of whether a species is a bioinvader or not may not be straightforward. This is the case of the mollusc Perna perna, presently naturalized and widely distributed along Brazilian coast, from the Bay of Vitória, in the state of Espírito Santo (ES), to the state of Rio Grande do Sul (RS). Following previous works that explored the hypothesis that P. perna invaded the coast of Brazil at the colonial period, attached to slave ships, we discuss zooarchaeological data, radiocarbon dating, and molecular genetics analyses. Out of the 578 archeological shellmounds investigated, 542 (93.8%) had no records of P. perna. From the radiocarbon dating results, it is possible to infer that the presence of the two P. perna specimens from the Saquarema shellmound, in Rio de Janeiro, as well as the other shells from the top layer, is likely related to a recent occupation of the site in the colonial period, with a great probability of being from the XVII or XVIII centuries. Data on genetic population structure of P. perna along the Brazilian coast showed higher genetic identities between the African and the Brazilian populations than among the Brazilian populations, while haplotypic diversity shows a pattern which relates to trade routes of slaves (XVII and XVIII centuries) between Africa and Brazil. These data reinforce the argument that the appearance of P. perna along the Brazilian coast is due to invasion during historical time.
ABSTRACT
Identifying and tackling recrystallization is a critical factor in the reliable radiocarbon (
14
C) dating of carbonates, since exogenous carbon can be incorporated and thus mask the real ...age of the samples. Vermetids are among the most important bioindicators used for paleo sea-level reconstruction, and the accuracy of their chronology can significantly impact sea-level curves. Age differences larger than 1
14
C kyr before and after acid etching, combined with X-ray diffraction (XRD) analysis that indicates a significant amount of calcite still remains in the shell, led us to apply the previously developed carbonate density separation protocol (CarDS). Using a solution of sodium polytungstate, with density of 2.80 g/cm
3
, we successfully separated different carbonate fractions for a set of 10 vermetid samples from the coast of Rio de Janeiro, southeast of Brazil. Each separation was verified by XRD analysis and the
14
C concentrations of different fractions were compared. The results show that the calcite fraction in the studied vermetid samples varied from 12 to 63% and aragonite fraction ages are up to 2
14
C kyr older than the raw samples, thus confirming the efficacy of CarDS in removing young carbonates and the importance of density separation to vermetids prior to accelerator mass spectrometry (AMS) dating.
Foraminifera are widely used in paleoclimatic and paleoceanographic studies, providing information about past ocean conditions. However, in order to use these tracers, it is essential to obtain an ...accurate chronology. Radiocarbon has proven to be a powerful tool in developing robust chronologies. Sample sizes of a few milligrams of carbonate material are needed for precise radiocarbon determination using accelerator mass spectrometry (AMS). In the specific case of paleoceanographic and paleoenvironmental studies, Foraminifera microfossils are the most important indicator of oceanic conditions. However, for establishing the chronology of deposition, sample availability is often limited. In AMS facilities using solid ion sources, such as the Radiocarbon Laboratory of the Universidade Federal Fluminense (LAC-UFF), in Brazil, CO2 samples need to be converted to graphite after physical and chemical pre-treatment to remove contamination. Reducing the sample sizes increases the relative contribution of contamination and can favor increased background levels. In this work, we tested different amounts of 14C-free carbonate samples as a means to evaluate the pattern of contamination. For the sealed tube Zn/TiH2 graphitization method, we tested prebaking the graphitization tubes and compared storage procedures. As a result, the background for regular-sized samples was decreased, and accurate measurement of carbonate samples containing ca. 0.5 mg C could be performed. Prebaked graphitization tubes can safely be stored in desiccator cabinets for up to 4 weeks. Foraminifera samples with mass as low as 1 mg (ca. 0.1 mg C) can now be measured at the LAC-UFF AMS facility, provided that C contamination can be estimated and corrected. The developments presented in this work allowed for the study of species-specific Foraminifera and other small-sized carbonate samples.
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