New SOCOL:14C-Ex model reveals that the Late-Glacial radiocarbon spike in 12350 BC was caused by the record-strong extreme solar storm

The Sun rarely produced extreme solar particle events (ESPEs), orders of magnitude stronger than everything directly observed. Their enormous power can greatly distort the production of cosmogenic isotopes, e.g., radiocarbon ¹⁴C, in the terrestrial system, leaving clear signatures in natural terrestrial archives including dateable tree rings. Eight such events were known to occur during the past 12 millennia of the Holocene, with the strongest one being that of 775 AD. Recently, a new and the only ESPE candidate beyond the Holocene has been discovered as the largest known ¹⁴C peak dated to ca. 12350 BC, nearly twice as big as that of 775 AD. However, it could not be analysed earlier due to the lack of appropriate models applicable to glacial climate conditions. We have developed a brand-new state-of-the-art chemistry-climate model SOCOL:14C-Ex to study fast changes in ¹⁴C. It was tested on the well-studied event of 775 AD and applied to the ESPE of 12350 BC. We found that it was stronger by 18±11% than by 775 AD and likely occurred between January – April 12350 BC with the most probable date in early March. This makes the ESPE of 12350 BC the record strongest known event, pushing the bounds of the extreme solar-terrestrial events even further, forming the new worst-case scenario paradigm and providing the global tie point for dendrochronological dating before the Holocene. The newly developed model lifts the existing limitation to the Holocene and extends our ability to analyse radiocarbon data even for glacial climate conditions.