Subseasonal δ13C and δ18O of tree-ring cellulose of an African baobab (Adansonia digitata) tree from Oman

Carbon and oxygen stable isotope data of tree-ring cellulose covers the period from 1941 to 2005CE. Tangential wood slices of approximately 1 mm were cut parallel to the fiber orientation, in radial direction from the cambial zone towards the pith resulting in resolutions from 1 up to 11 samples per year. Visible rays and other identified parenchymatous structures were removed from the wood slices to minimize possible contamination. Cellulose was extracted from wood samples after Wieloch et al. (2011). After extraction cellulose samples were homogenized by ultrasonic treatment (Laumer et al., 2009), and freeze-dried for at least 48 h. 130 180 μg of cellulose were packed in silver capsules and stored over night at 100 °C in a vacuum drying oven (ThermoFisher Heraeus VT 6060) prior to isotope ratio mass spectrometry. δ13C and δ18O were measured simultaneously by reduction of cellulose samples to carbon monoxide in a high temperature TC/EA converter (1400 °C) coupled online to an IRMS Delta V Plus (Thermo Fisher Scientific, Bremen, Germany). Values are referred to VPDB and VSMOW, respectively with a reproducibility of ≤ 0.15 for δ13C and ≤ 0.25 for δ18O.