T04_P03

MAG-C63: a tree-ring standard for AD 1586

Bayliss A¹, Canti M¹, Dee M², Howard R³, Miles D⁴, Tyers C¹, Wacker L⁵

¹Historic England, London, United Kingdom, ²Rijksuniversiteit Groningen, Groningen, The Netherlands, ³Nottingham Tree-ring Dating Laboratory, Nottingham, UK, ⁴Oxford Dendrochronology Laboratory, Mapledurham, UK, ⁵ETH Zürich, Zürich, Switzerland

Standard materials are fundamental for accurate radiocarbon dating, but must be available in sufficient quantities for all AMS facilities worldwide to use as required. MAG-C63 is a beam removed from the Great Tower at St Mary Magdalen College, Oxford (51.75°N, 1.24°W) during repair works in the 1960s. It is 6.1m long, by 0.3m square and weighs over a metric tonne. It has been securely dated by ring-width dendrochronology as spanning AD 1487-1629, and has been purchased in its entirety by Historic England.

The ring selected for use as a tree-ring standard is that for AD 1586. It is 2.76mm wide, and sufficiently close to the outside of the timber that dissection in quantity is feasible, yet far enough from the outside of the timber to minimise the potential for contamination. Whole rings (earlywood and latewood) have been dissected by professional dendrochronologists, each sample being split across the ring so that it contains roughly equal amounts of earlywood and latewood. Each sample weighs approximately 50mg. We estimate that MAG-C63 will supply 40,000 such samples.