High-Resolution Be-10 and Cl-36 Data From the Antarctic Dome Fuji Ice Core (similar to 100 Years Around 5480 BCE): An Unusual Grand Solar Minimum Occurrence?

Cosmogenic nuclides in tree rings and polar ice cores record the information of past cosmic ray intensities and solar activities. A large C-14 increase over 10 years has been discovered around 5480 BCE. The C-14 variations in this event differ from those of other short-term cosmic ray events and typical grand solar minima. To elucidate the cause of the C-14 increase around 5480 BCE, we measured the Be-10 and Cl-36 concentrations in the Antarctic Dome Fuji ice core at quasi-annual and 4-5 years resolutions, respectively. Based on the combined C-14, Be-10, and Cl-36 data, the 5480 BCE event was probably not caused by a solar proton event (SPE) or a gamma-ray event, because the Cl-36 concentration did not significantly increase as expected in these events. The incremented Be-10 data were enhanced similarly to those of recent grand solar minima, but more rapidly increased (over similar to 10 years). These results suggest that an unusual grand solar minimum occurred around 5480 BCE, characterized by a rapidly decreasing solar activity.