Complete list of δ18O determinations on tree ring cellulose at the Centre for Isotope Research (CIO), University of Groningen as a supplement to the work done by John du Plessis, Dipayan Paul, Margot Kuitems, Anita Aerts-Bijma, Neil J.Loader, Harro A.J. Meijer, and Michael Dee.

The purpose of this research was to establish a working protocol and a performance baseline for δ18O determination on tree-ring α-cellulose at the Centre for Isotope Research (CIO) of the University of Groningen, and to investigate the efficacy of on hand reference materials to correct cellulose δ18O values and accurately calibrate cellulose QC standards including IAEA-C3. To achieve this, a variety of tree ring samples, along with QC standards and certified references were selected and analysed for δ18O via continuous flow Pyrolysis-IRMS in order to determine precision, accuracy and repeatability.

Three number of trees were sampled in order to have their rings collected and subjected to cellulose extraction. One of each: oak (Quercus sp. felled 2022, Lauwersoog, Netherlands), ash (Fraxinus sp. felled 2021, Ens, Netherlands), and pine (Pinus sp. collected 2023, Assen, Netherlands). The names within the dataset corresponding to ring x of each tree are “LML Rx”, “ASH2 Rx”, and “P2 Rx” for the oak, ash and pine samples respectively. Also measured was the known-age (CE 1503) radiocarbon standard “Windsor castle” (Quercus robur).

Samples were subject to α-cellulose extraction and ultrasonic homogenisation before measurement by continuous flow pyrolysis-IRMS. Pyrolysis was performed using a vario PYRO cube elemental analyser (Elementar, Langenselbold, Germany) and precisION isotope ratio mass spectrometer (Elementar, Langenselbold, Germany).