Utida, Giselle; Cruz, Francisco William; Vuille, Mathias; Ampuero, A; Novello, Valdir Felipe; Maksic, Jelena; Sampaio, Gilvan; Cheng, Hai; Zhang, Haiwei; De Andrade, Fabio Dias; Edwards, R Lawrence (2024): Oxygen and carbon isotopes data obtained in stalagmites from Northeastern Brazil for the last 3 millennia: spatiotemporal ITCZ dynamics and related impacts in modern human history [dataset bundled publication]. PANGAEA, https://doi.pangaea.de/10.1594/PANGAEA.969137 (DOI registration in progress)

In order to reconstruct precipitation for the last 3200 years in Northeast Brazil (NEB) region we analyze U/Th ages and oxygen isotopes in four stalagmites of Trapiá (TRA5 and TRA7) and Furna Nova (FN1 and FN2) caves from Rio Grande do Norte state that serve as a faithful proxy for the past location of the southern margin of the ITCZ. Chronological studies on speleothems were based on U–Th geochronology performed at the Laboratories of the Department of Earth and Environmental Sciences, College of Science and Engineering, University of Minnesota (USA), and at the Isotope Laboratory of the Institute of Global Environmental Change, Xi'an Jiaotong University (China), according to Cheng et al. (2013). Subsamples of around 100 mg were obtained in clear layers, close to the growth axis trying to keep a maximum thickness of 1.5 mm, 10mm wide, and no more than 3mm depth. Age models of speleothem TRA5 and FN2 were based on 12 and 10 U/Th dates, respectively. The FN1 chronology is based on 10 previously published U/Th (Cruz et al., 2009) plus 8 additional new dates obtained for this study. Speleothem TRA7 has 27 U/Th ages (Utida et al., 2020). The U/Th ages are given at the Suplementary material of Utida et al. (2023). The individual age models for all speleothems were constructed by the software COPRA (Breitenbach et al., 2012) through a set of 2000 Monte Carlo simulations, where a random age within the ±1σ age interval was chosen each time. For oxygen and carbon isotope analysis of the speleothems, around 200 μg of powder was drilled for each sample, consecutively at intervals of 0.1mm (TRA5), 0.3mm (TRA7), and 0.15mm (FN2), with a Micromill micro-sampling device. The samples were analyzed in a GasBench interfaced linked to a Thermo Finnigan Delta V Advantage at the Laboratory of Stable Isotopes (LES) at the Geoscience Institute of the University of São Paulo. Isotopes are reported in delta notation (δ18O and δ13C) relative to the Vienna Pee Dee Belemnite (VPDB) standard, with uncertainties in the reproducibility of standard materials <0.1 ‰. The isotopic profiles of TRA5, TRA7, FN1, and FN2 stalagmites consist of 443, 885, 1215, and 651 isotope samples, respectively. These datasets provide an average resolution of 1 year per sample for TRA5 and 4 years for the other speleothem records. Complementary results are presented by Utida et al. (2020) (TRA7 δ13C and U/Th results) and by Cruz et al. (2009) (FN1 δ18O and U/Th results) that were produced by using the same methods. The intra-site correlation model (iscam) was used to construct a composite record (Fohlmeister, 2012) by combining the four stalagmites data to obtain a unique age model and oxygen isotopic record. The age–depth modeling software was adjusted to calculate 1000 Monte Carlo simulations, 2000 first-order autoregressive processes (AR1) for each record. The age data were assumed to have a Gaussian distribution and were calculated pointwise. The composite result was detrended and normalized according to the iscam method. The following intervals were removed from the stalagmite records before constructing the RN Composite: FN1 0–12mm and 187–202 mm, FN2 0– 6 mm, TRA5 0–37 mm, and TRA7 222–227 mm. In addition, the FN1 record was divided into two portions: FN1a 12.14– 136.99mm and FN1b 140.15–186.87mm that are separated by a hiatus. The composite calculation rearranges the proxies in order to obtain the optimal calculated age and then calculates the average of the proxy data after normalizing the records.

Age BP = 1950