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Cosmogenic nuclides are good indicators of past cosmic ray events and variations. To verify such phenomena, it is important to evaluate them using multiple nuclides from different archives. The cosmic ray event in 993-994Common Era (CE) has already been confirmed with C-14 and Be-10 data, which show rapid increases in the concentrations. However, the Be-10 data were obtained from the Greenland ice cores in the Northern Hemisphere. To investigate the extent of the Be-10 increase in the Southern Hemisphere, we measured quasi-annual Be-10 concentrations between 980 and 1,011CE in the Antarctic Dome Fuji ice core. We observed a 50% increase in Be-10 concentration around 994CE, consistent with the Greenland data. Increases in Be-10 concentrations in both hemispheres support a solar origin of the 994-CE event. In addition, we propose a method of evaluating the so-called system effect for Be-10 deposition by extracting common components from Be-10 and Na+ data.

Plain Language Summary New quasi-annual beryllium-10 measurements were made with the Dome Fuji ice core from Antarctica over the period in which the 994 cosmic ray event would be expected. We observed an approximately 50% increase in beryllium-10 concentrations, which is consistent with the beryllium-10 increases observed in the Greenland ice cores. This lends support to a solar origin of the 994 event. We propose a phenomenological method for evaluating a common deposition component between quasi-annual beryllium-10 and sodium ion data.