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

Abstract

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