ALBERT

Beschreibung: The stable isotope records for mid- and late- Holocene are based on two stalagmites, VEAJ collected in Alfredo Jahn cave and VECA collected in Caripe Cave, respectively. Both caves are located in northern Venezuela, adjacent to Cariaco Basin. The ẟ18O record was interpreted as a proxy for the proximity of the Intertropical Convergence Zone (ITCZ) to our study sites, and the ẟ13C record as a proxy for vegetation changes, as discussed in the paper 'Atlantic ITCZ variability during the Holocene based on high-resolution speleothem isotope records from northern Venezuela' (Medina et al., 2023). The ẟ18O and ẟ13C analyses were performed at the Stable Isotope Laboratory at the Institute of Geoscience of the University of São Paulo (Brazil) using a Thermo-Finnigan Delta Plus Advantage mass spectrometer. ẟ-notation in per mil units (‰) was used to express the sample isotopic ratios deviation from the Vienna Pee Dee Belemnite (VPDB) standard. Approximately 200 μg of CaCO3-powder subsamples for ẟ18O and ẟ13C stable isotopic analyses were collected using a manually controlled Sherline 5400 milling at a resolution of 0.4 mm for VEAJ and 0.5 mm for VECA. The ẟ18O and ẟ13C isotopic profiles of VEAJ-base, VEAJ-top left and VEAJ-top right are based on 530, 310 and 250 samples, respectively. VECA isotopic profiles consist of 670 samples. Since VEAJ-top left overlaps with some sections of the -top right record, we merged them through normalization (i.e., by subtracting the mean and dividing by the standard deviation) of the data inside the overlapping period, averaging both series and then reconstructing the shorter time series with the mean and standard deviation of the longer one. The geochronology was established by means of the U/Th dating method, using a multicollector inductively-coupled plasma mass spectrometers (MC-ICP-MS-Thermo-Finnigan NEPTUNE) at the Institute of Global Environmental Change, Xi'an Jiaotong University (China). The sampling for the U/Th dating was performed by extracting ~0.100 g of powdered carbonate with a handheld drill of the least porous and colored, most traceable layers along or at the side of each speleothem growth axis. A total of 42 U/Th ages were used to construct the age model for VEAJ and 25 for VECA, yielding an mean temporal stable isotope sampling resolutions of 3 and 23 years for VEAJ-base & top-composite, respectively, and 1.5 years for VECA. Some age reversals along the stalagmites were flagged as outliers using Bayesian statistics, and consequently removed from the age models. For other age inversions, an iterative procedure was applied to increase the range of uncertainty in order to fulfill the monotonicity criterion (Scholz and Hoffmann, 2011).