Evidence for magmatic carbon bias in C dating of the Taupo and other major eruptions.

Prehistoric timescales, volcanic hazard assessment, and understanding of volcanogenic climate events rely on accurate dating of prehistoric eruptions. Most late Quaternary eruptions are dated by C measurements on material from close to the volcano that may be contaminated by geologic-sourced infinite-age carbon. Here we show that C ages for the Taupo (New Zealand) First Millennium eruption are geographically arrayed, with oldest ages closer to the vent. The current eruption wiggle match date of 232 ± 5 years CE is amongst the oldest. We present evidence that the older, vent-proximal C ages were biased by magmatic CO degassed from groundwater, and that the Taupo eruption occurred decades to two centuries after 232 CE. Our reinterpretation implies that ages for other proximally-dated, unobserved, eruptions may also be too old. Plateauing or declining tree ring cellulose δC and ΔC values near a volcano indicate magmatic influence and may allow forecasting of super-eruptions.