Signatures of cosmic-ray increase attributed to exceptional solar storms inferred from multiple cosmogenic radionuclide records

et al. 2013) discovered rapid increases of 14 C content in tree rings dated to AD 774-5 and AD 993-4 which they have attributed to cosmic-ray events. These extreme particle events have no counterparts in the instrumental record and have been tentatively associated with solar proton events, supernovae and short gamma-ray bursts, which have very different energy spectra. Cosmogenic radionuclides such as 14 C, 10 Be and 36 Cl arise from the interaction of cosmic rays with atmospheric nitrogen, oxygen and argon. These radio-isotopes are produced through different reaction pathways and vary with different energy dependencies of the production rate cross section. Owing to this, yield functions can be used to determine the energy level of incident particles. However, only 14 C has been measured at high resolution to quantify the energy and thus the origin of the outbursts. We present an annually resolved record of 10 Be from the NGRIP ice core for the two events. In addition, we also utilized the GRIP ice core 36