BEXCO - Room F(201/202/203/204)
[SH133] How did solar activity cause Δ14C peaks in AD 775?
Since the AD 775 Δ14C peak (henceforth M12) was first measured by Miyake et al. (2012), globally M12 had been confirmed, but although SEP is supposed to be main cause, the cause and mechanism remains to be debating. Here we present Δ14C values from AD 770-780 Pinus edulis annual tree-ring samples from Mummy cave, Chinle, Arizona, USA, and from AD 721-820 Sequoiadendron giganteum annual tree-ring samples from Sequoia National Park in California, USA. Two data sets confirm that a sharp Δ14C peak exists at AD 775 and long year range result from AD721-820 shows that this spike was preceded by several decades of rapidly decreasing Δ14C, suggesting that solar activity was very strong just prior to M12 and may be causally related. During periods of peak solar activity there is increased probability for Coronal Mass Ejection (CME) events of various types. We strain to look at Multiple-CME sequences, which the magnetic field from an initial CME partially reduces the geomagnetic field and during a window of reducing geomagnetic field a significantly larger fraction of the atmosphere is exposed to solar particles accelerated by a shockwave from one or more subsequent CME’s, leading to enhanced production of 14C and other cosmogenic isotopes.