Montiel, Mauricio: Biennial tree-ring chemical concentrations of Araucaria araucana from Mirador El Roble, Tolhuaca National Park, Chile (1985-2020) [dataset]. PANGAEA, https://doi.pangaea.de/10.1594/PANGAEA.994009 (dataset in review)

This dataset contains biennial concentrations of Na, Mg, K, Ca, Al, Mn, Ni, Cu, Zn, Mo, and Ba (µg/g) measured in tree rings of Araucaria araucana from Parque Nacional Tolhuaca, Mirador El Roble sector, Región de La Araucanía, Chile (38°12′04″ S, 71°47′55″ W; 1200 m a.s.l.). Increment cores were collected on 27 and 28 January 2021. The dataset spans the period 1985-1986 to 2019-2020 and was compiled to document chemical variability in tree rings in relation to fire history records. Samples were obtained from increment cores collected with increment borers. The analyzed material consisted of pooled biennial ring samples. For each two-year period, the corresponding rings were identified and cut from all selected trees, and the material was combined into a single composite sample for each biennium and tree group. Tree-ring dating followed standard dendrochronological procedures. Cores were sanded and crossdated against a regional chronology and among series. Rings were separated at two-year intervals, and instruments were cleaned with isopropyl alcohol between cuts to minimize cross-contamination. Samples were weighed in pre-cleaned, metal-free polypropylene centrifuge tubes. A volume of 3 mL of 70% nitric acid was added for a 24-hour predigestion at room temperature, followed by complete digestion at 90°C for 1 hour using a thermal block digestion system. After digestion, tubes containing the digestate were reweighed to calculate dilution factors. Ultrapure water (18.2 MΩ·cm, Milli-Q system) was then added to reach 15 mL, followed by a second dilution step to obtain a final dilution factor of approximately 10. For major cations, a dilution factor of approximately 100 was applied. Element concentrations were measured by ICP-MS at the Arizona Laboratory for Emerging Contaminants (ALEC), University of Arizona. Analytical precision was assessed using NIST standard pine needles (1575a) and a procedural blank.