Three decades have passed since the publication in 1991 of the first use of stable isotope analysis applied to a Brazilian archaeological context. Despite being still mainly applied to palaeodietary ...research, stable isotope analysis in archaeology has been diversified in Brazil. In the last five years, an increasing number of studies has addressed various issues. Such issues are related to population mobility, social differentiation, health and children care, changes and resilience of cultural practices, and identification of the origin of enslaved populations brought by force from the African continent, among others. However, research in this area is still incipient when compared to the large territory of Brazil (WGS 84: -33˚ to 5°N, -73˚ to -34˚E), the diversity of socio-cultural contexts of pre-colonial and indigenous societies, and the country's historical formation process. In terms of radiocarbon dates, data are also sparse and lack essential information as the material used for dating, as this information could be related to necessary corrections, e.g., the marine reservoir effect. The first radiocarbon dates of Brazilian archaeological material are reported, however, since the 1950s and have been more frequently reported in publications across Brazil since the installation of the first Brazilian radiocarbon laboratory (CENA/USP) in 1990 and the first Latin American 14C-AMS facility (LAC-UFF) in 2012. Thus, the purpose of this compilation was to gather all dispersed, and often fragmented, data from analyses of stable and radioactive (focusing on radiocarbon) isotopes carried out in Brazilian archaeological contexts. We compiled data from 1991 until the end of November 2021. The data included here contain information from 71 archaeological sites, 556 humans, 219 animals and 2 plants. Isotopic analyses were performed on 832 organic samples, mainly paired δ13C and δ15N plus δ34S measurements, and on 265 mineral samples, mainly δ13C, δ18O and 86Sr/87Sr measurements. Sr concentrations for 49 mineral samples were also compiled. Radiocarbon or relative dates span from 18 kyr BP to the present. All data from this compilation are deposited in open access on the IsoArcH platform (https://doi.isoarch.eu/doi/2021.005). This extensive work aims to point out the gaps in stable isotopes and radiocarbon dates provided for Brazilian archaeological contexts that could be further explored. Besides, it aims to promote easy access to numerous analyses that, otherwise, would be hard to obtain. Lastly, it seeks to broaden the interdisciplinary collaboration in Brazil and strengthen the international collaboration among peers.
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.
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.
In this paper, we summarize the sample preparation methods currently used at the Radiocarbon Laboratory of the Universidade Federal Fluminense (LAC-UFF) in Brazil. We also report on a series of ...results with regards to the graphitization protocol. Tests with different temperatures and baking times were performed, and carbon stable isotope ratios of graphite were measured by an EA–IRMS (elemental analyzer coupled with an isotopic ratio mass spectrometer) to infer the completeness of the graphitization reaction. We monitored the muffle furnace temperature using an independent thermocouple and found a −60°C offset, which may have caused the lower graphitization yields (detected from the large isotopic fractionation on several reference materials targets). At a temperature of 520°C, the isotopic fractionation in the graphitization reaction was systematically lower (−5‰ in average) and the overall scattering was reduced. As long as isotopic fractionation corrections are made using the online stable isotopes ratios provided by the AMS system, the accuracy of the 14C results should be maintained.
Despite the great extent of the Brazilian coast, there are very few studies on the marine radiocarbon reservoir correction local offset (ΔR) for this region.
In the present study, we used marine ...shells from the malacological collection of the National Museum of Brazil to obtain values of ΔR for different locations on the Brazilian coast. According to the museum records, the mollusks were collected alive from the coasts of Rio de Janeiro, Rio Grande do Sul, São Paulo and Bahia, prior to the 14C bomb-peak. The exact year of collection for each shell is known.
The samples were chemically prepared and measured at the Radiocarbon Laboratory of the Universidade Federal Fluminense (LAC-UFF) in Brazil. The conventional ages were calibrated using the Marine13 curve and the ΔR values were calculated using the OxCal software. The values range from 17 ± 56 14C yr in São José do Norte, Rio Grande do Sul to 96 ± 48 14C yr in Cabo Frio, Rio de Janeiro.
•Pre-bomb shells from a museum collection were radiocarbon dated.•We obtained the first radiocarbon reservoir corrections for some regions on the Brazilian coast.•The values range from 17 ± 56 14C yr in São Jose do Norte, Rio Grande do Sul to 96 ± 48 14C yr in Cabo Frio, Rio de Janeiro.
Among other zooarchaeological remains, terrestrial snails’ shells from the Thaumastus and Megalobulimus genera 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.
Abstract
The response of terrestrial ecosystems to increased atmospheric CO
2
concentrations is controversial and not yet fully understood, with previous large‐scale forest manipulation experiments ...exhibiting contrasting responses. Although there is consensus that increased CO
2
has a relevant effect on instantaneous processes such as photosynthesis and transpiration, there are large uncertainties regarding the fate of extra assimilated carbon in ecosystems. Filling this research gap is challenging because tracing the movement of new carbon across ecosystem compartments involves the study of multiple processes occurring over a wide range of timescales, from hours to millennia. We posit that a comprehensive quantification of the effect of increased CO
2
must answer two interconnected questions: How much and for how long is newly assimilated carbon stored in ecosystems? Therefore, we propose that the transit time distribution of carbon is the key concept needed to effectively address these questions. Here, we show how the transit time distribution of carbon can be used to assess the fate of newly assimilated carbon and the timescales at which it is cycled in ecosystems. We use as an example a transit time distribution obtained from a tropical forest and show that most of the 60% of fixed carbon is respired in less than 1 year; therefore, we infer that under increased CO
2
, most of the new carbon would follow a similar fate unless increased CO
2
would cause changes in the rates at which carbon is cycled and transferred among ecosystem compartments. We call for a more frequent adoption of the transit time concept in studies seeking to quantify the ecosystem response to increased CO
2
.
The Radiocarbon Laboratory of the Universidade Federal Fluminense, in Brazil, has been successfully applying the zinc reduction method for graphitization of carbon samples since the development of ...its early protocols in 2009. Successive methodological research aiming to improve and, ultimately, optimize the precision and accuracy of our results indicates that graphitization temperatures as low as 460°C promote erratic 13C isotopic fractionation, but an approximately constant fractionation of about –5‰ is achieved at 520°C. In this work, we present isotope ratio mass spectrometry (IRMS) δ13C results for 14C reference materials graphitized at 550°C with variable amounts of zinc. Based on the results obtained from the addition of 20, 35, and 50 mg of zinc, we conclude that a slightly lower variation in 13C isotope fractionation during graphitization is obtained with less zinc. Moreover, the average isotopic fractionation is not altered by increasing the graphitization temperature from 520°C to 550°C.
The response of terrestrial ecosystems to increased atmospheric CO2 concentrations is controversial and not yet fully understood, with previous large‐scale forest manipulation experiments exhibiting ...contrasting responses. Although there is consensus that increased CO2 has a relevant effect on instantaneous processes such as photosynthesis and transpiration, there are large uncertainties regarding the fate of extra assimilated carbon in ecosystems. Filling this research gap is challenging because tracing the movement of new carbon across ecosystem compartments involves the study of multiple processes occurring over a wide range of timescales, from hours to millennia. We posit that a comprehensive quantification of the effect of increased CO2 must answer two interconnected questions: How much and for how long is newly assimilated carbon stored in ecosystems? Therefore, we propose that the transit time distribution of carbon is the key concept needed to effectively address these questions. Here, we show how the transit time distribution of carbon can be used to assess the fate of newly assimilated carbon and the timescales at which it is cycled in ecosystems. We use as an example a transit time distribution obtained from a tropical forest and show that most of the 60% of fixed carbon is respired in less than 1 year; therefore, we infer that under increased CO2, most of the new carbon would follow a similar fate unless increased CO2 would cause changes in the rates at which carbon is cycled and transferred among ecosystem compartments. We call for a more frequent adoption of the transit time concept in studies seeking to quantify the ecosystem response to increased CO2.
Terrestrial ecosystems remove CO2 from the atmosphere via photosynthesis and convert it into biomass and soil organic matter. This carbon is returned to the atmosphere via decomposition and respiration, processes that depend on climatic conditions, microbial community structure and function, and nutrient availability. When ecosystems are exposed to increased CO2, the photosynthesis rate increases, but it is not clear how much carbon remains in the system and for how long. The transit time concept can be used to assess the fate of newly assimilated carbon and the timescales at which it is cycled in ecosystems. Modified after Steiner (2008).
Tropical forests fix large quantities of carbon from the atmosphere every year; however, the fate of this carbon as it travels through ecosystem compartments is poorly understood. In particular, ...there is a large degree of uncertainty regarding the time carbon spends in an ecosystem before it is respired and returns to the atmosphere as CO2.
We estimated the fate of carbon (trajectory of photosynthetically fixed carbon through a network of compartments) and its transit time (time it takes carbon to pass through the entire ecosystem, from fixation to respiration) for an old‐growth tropical forest located in the foothills of the Andes of Colombia.
We show that on average, 50% of the carbon fixed at any given time is respired in <0.5 years, and 95% is respired in <69 years. The transit time distribution shows that carbon in ecosystems is respired on a range of time‐scales that span decades, but fast metabolic processes in vegetation dominate the return of carbon to the atmosphere.
Synthesis. The transit time distribution integrates multiple ecosystem processes occurring at a wide range of time‐scales. It reconciles measurements of the age of respired CO2 with estimates of mean residence time in woody biomass, and provides a new approach to interpret other ecosystem level metrics such as the ratio of net primary production to gross primary production.
Resumen
Los bosques tropicales fijan grandes cantidades de carbono atmosférico cada año; sin embargo, el destino o trayectoria de este carbono a medida que viaja por los compartimentos del ecosistema es poco conocido. En particular, existe un gran grado de incertidumbre en cuanto al tiempo que el carbono pasa en un ecosistema antes de ser respirado y vuelve a la atmósfera en forma de CO2.
Estimamos el destino del carbono (trayectoria del carbono fijado fotosintéticamente a través de una red de compartimentos) y su tiempo de tránsito (tiempo que tarda el carbono en pasar por todo el ecosistema, desde su fijación hasta su respiración) para un bosque tropical antiguo situado en las estribaciones de los Andes de Colombia.
En este articulo mostramos que, en promedio, el 50% del carbono fijado en un momento dado se respira en menos de 0,5 años, y el 95% se respira en menos de 69 años. La distribución del tiempo de tránsito muestra que el carbono en los ecosistemas se respira en un continuo de escalas temporales que abarcan décadas, pero procesos metabólicos rápidos en la vegetación dominan el retorno del carbono a la atmósfera.
Síntesis. La distribución del tiempo de tránsito integra múltiples procesos ecosistémicos que operan en una amplia gama de escalas temporales. Concilia las mediciones de la edad del CO2 respirado con las estimaciones del tiempo medio de residencia en la biomasa leñosa, y proporciona un nuevo enfoque para interpretar otras métricas a nivel de ecosistema, como la relación entre la producción primaria neta y la producción primaria bruta.
The transit time distribution quantifies the time it takes for photosynthates to appear in the respiration flux. For a tropical forest in Colombia, it predicts that 50% of fixed carbon is respired in <0.5 years, and 95% in <69 years.
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