Fractionation in the graphitization reaction for  14 C-AMS analysis: The role of Zn  ×  the role of TiH 2

Macario, Kita D.; Alves, Eduardo Queiroz; Moreira, Vinícius N.; Oliveira, Fernanda Midori de; Chanca, Ingrid; Jou, Renata M.; Diaz, Maikel

doi:10.1016/j.ijms.2017.10.005

Cited by 8 publications

(7 citation statements)

References 22 publications

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“…CO 2 samples were then transferred to 9 mm Pyrex tubes previously prepared with titanium hydride and zinc on the bottom and iron powder inside a 6-mm inner tube. Tubes were sealed with an oxy-acetylene torch and heated to 550°C for 7 h so that CO 2 could be reduced to graphite (Macario et al, 2015, 2017; Xu et al, 2007). Graphite samples were pressed in aluminium cathodes and their radiocarbon concentration was measured at the Center for Applied Isotope Studies at the University of Georgia (Cherkinsky et al, 2010).…”

Section: Methodsmentioning

confidence: 99%

Palaeoenvironmental dynamics of Holocene shoreface bryoliths from the southern coast of Brazil

et al. 2019

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Beds of free-living coated nodules (coralline algae, bryozoans, acervulinid foraminifera) create shallow-water carbonate biogenic benthic habitats, which are sensitive to human disturbance and slow to recover. Holocene bryoliths, ranging from sub-spheroidal, sub-discoidal to sub-ellipsoidal in shape, were found scattered in the foredunes in ca. 30-km stretch along the Hermenegildo and Concheiros do Albardão beaches on the southernmost coast of Brazil (Santa Vitória do Palmar municipality, Rio Grande do Sul State). The dominating bryozoan species forming the bryolith is Biflustra holocenica Vieira, Spotorno-Oliveira and Tâmega sp. nov. The inner bryolith arrangement, generally asymmetrical, shows multilamellar and circumrotatory growth of colonies that envelop the bivalve Ostrea puelchana. Bryozoans and subordinate corals characterize the outer bryolith surfaces. The ichnogenera Gastrochaenolites (made by the boring bivalve Lithophaga patagonica) and Caulostrepsis occur throughout the bryoliths, from the inner part up to the outer surface. The studied bryoliths, originated in a shoreface setting at ca. 7910–7620 cal. yr BP and during subsequent storm waves, were resedimented onto the foreshore and foredunes (to ca. 5700 cal. yr BP) where the bryoliths were finally fossilized.

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Section: Methodsmentioning

confidence: 99%

Palaeoenvironmental dynamics of Holocene shoreface bryoliths from the southern coast of Brazil

et al. 2019

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“…Chemical treatment of the otolith and mollusk samples followed standard procedures with etching in 0.1M hydrochloric acid followed by hydrolysis in 85% phosphoric acid. The carbon dioxide produced was purified and graphitized in independently sealed Pyrex tubes at 550ºC (Macario et al 2015b, 2017). Fossil calcite and C2 IAEA reference samples were prepared together with unknowns for quality control.…”

Section: Methodsmentioning

confidence: 99%

The Marine Reservoir Effect on the Coast of Rio de Janeiro: Deriving ∆R Values from Fish Otoliths and Mollusk Shells

et al. 2018

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Considering the impact of coastal dynamics on the radiocarbon (14C) marine reservoir effect (MRE), upwelling has the potential of enhancing marine influence, usually14C depleted. Freshwater input can contribute either to increased reservoir offsets, when dead carbon from rock weathering is available, but also towards an atmospheric14C 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.

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“…These tubes were previously prepared with titanium hydride and zinc on the bottom and iron powder inside a 6-mm inner tube. Tubes were sealed with an oxy-acetylene torch and heated to 550ºC for 7 hr so that CO 2 could be reduced to graphite (Xu et al 2007;Macario et al 2015Macario et al , 2017. Graphite samples were pressed in aluminum cathodes and their 14 C concentration was measured at the Center for Applied Isotopes Studies at the University of Georgia (samples A01, A02 and A10) or at the NEC SSAMS system of the Fluminense Federal University (samples A03-A09).…”

Section: Accelerator Mass Spectrometrymentioning

confidence: 99%

Aragonite Fraction Dating of Vermetids in the Context of Paleo Sea-Level Curves Reconstruction

et al. 2020

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Identifying and tackling recrystallization is a critical factor in the reliable radiocarbon (14C) 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 14C 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/cm3, 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 14C 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 14C 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.

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Fractionation in the graphitization reaction for 14 C-AMS analysis: The role of Zn × the role of TiH 2

Cited by 8 publications

References 22 publications

Palaeoenvironmental dynamics of Holocene shoreface bryoliths from the southern coast of Brazil

Palaeoenvironmental dynamics of Holocene shoreface bryoliths from the southern coast of Brazil

The Marine Reservoir Effect on the Coast of Rio de Janeiro: Deriving ∆R Values from Fish Otoliths and Mollusk Shells

Aragonite Fraction Dating of Vermetids in the Context of Paleo Sea-Level Curves Reconstruction

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