Rapid increase in cosmogenic 14C in AD 775 measured in New Zealand kauri trees indicates short-lived increase in 14C production spanning both hemispheres

- Annually resolved, high precision 14C record of the Southern Hemisphere from AD 760-787.
- An identical distinct 14C increase compared to Northern Hemisphere data is found in AD 775.
- A cosmic event with a globally uniform impact is suggested as a potential cause for the increase.
- 14C data analysis is performed with a computer simulation deploying a carbon cycle box model.
- A globally averaged 14C production caused by the event of 2.2×108C14cm−2 is calculated.

In 2012, Miyake et al. reported a sudden and strong increase of the atmospheric radiocarbon (14C) content in Japanese cedar trees of 1.2% between AD 774 and 775. While their findings were quickly confirmed by a German oak chronology for the Northern Hemisphere (NH), the question remained if the effect was seen in both hemispheres. Here we present the first annually resolved Southern Hemisphere (SH) 14C record spanning the interval AD 760-787, using New Zealand kauri (Agathis australis) chronology wood. An almost identical distinct increase compared to Northern Hemisphere data was observed, suggesting a cosmic event with globally uniform impact as a potential cause for the increase. Deploying a carbon cycle box model a worldwide averaged net 14C production of 2.2×108C14atomscm−2 was estimated, which is 3.7 times higher than the average annual 14C production. The immediate appearance of the event in tree rings on both hemispheres suggests a short duration event of significantly less than 1 yr.