Geographic and temporal variations in atmospheric carbon isotopic ratios are recorded in environmental proxies. In temperate regions, this may assist in the construction of datasets for the calibration of radiocarbon ages. Over the tropics, the high growth rate of speleothems combined with high precision 230 Th dating provides potential records for atmospheric 14 C reconstruction. In this preliminary work, we investigate the isotopic composition (δ 18 O and δ 13 C) of a speleothem from central Brazil, precisely dated by the multi-collector inductively coupled plasma mass spectrometry technique (MC-ICP-MS). Radiocarbon Accelerator Mass Spectrometry (AMS) measurements were compared to the 14 C concentration in the atmosphere during the nuclear tests period based on the Bomb13SH1-2 curve. Our results show that the speleothem dead carbon proportion is less than 20% between 1932 and 1992 AD while δ 13 C values vary between −14 and −9‰. Given that the empirical radiocarbon calibration curves for the Southern Hemisphere were constructed based on limited records, we discuss the potential and limitations of Brazilian speleothems for the evaluation of atmospheric 14 C concentrations over the last millennia.
Bibliographical noteFunding Information:
The authors would like to thank Brazilian financial agencies CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico , grant 307771/2017-2 to K.D.M. and INCT-FNA , grant 464898/2014-5 ) and FAPERJ (Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro , grants E-26/110.138/2014 and E26/203.019/2016 ). This research was also directly benefited by the project PIRE NSF-FAPESP to F.W.C, grant 2017/50085-3 and FAPESP grants 2017/23687-2 and 2016/15807-5 to V.F.N. This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Finance Code 001 and CLIMATE-PRINT-UFF Project 88887.310301/2018-00 . We thank the editor and reviewers whose comments and suggestions helped to improve the quality of the manuscript.
- Bomb peak curve
- Southern hemisphere calibration curves
- Stable isotopes
- Th dating