The AD 775 cosmic ray event shown in beryllium-10 data from Antarctic Dome Fuji ice core

Abstract

Cosmogenic nuclides such as 14C or 10Be are produced by cosmic rays to the Earth. It is known that their concentration in tree rings or in ice cores record the past cosmic ray intensities. A large annual excursion in 14C content from AD 774 to AD 775 was firstly found in Japanese tree rings. After that this event has been confirmed by several verifications using some other tree samples from all over the world. Also quasi decadal 10Be concentration data in the Antarctic ice core show rapid increase around AD 775. However, annual 10Be variations have not been revealed. We measured 10Be concentrations in the Antarctic Dome Fuji ice core with quasi-annual resolution for the period approximately from AD 763 to AD 794, and found a clear 10Be increase around AD 775 against a background variations. Since our quasi-annual 10Be data and Na+ ion data which obtained from the same ice core show similar variations, the background variation in 10Be concentration is considered as a climatic noise. It is possible that the large 10Be increase is occurred by the AD 775 cosmic ray event. This manuscript is based on our published paper, Miyake et al. [2015] to GRL.