The Fimbulwinter myth in the context of Nordic tree-ring climate proxy data

High-magnitude Late-Holocene volcanic eruptions contributed to the climate-related hardships of past societies. It has been theorised that memories of one of the volcanic events and its terrible consequences are recorded in the Old Norse traditions of the Fimbulwinter and Ragnarök (possibly also in the Old Kalevala). This Fimbulwinter theory suggests that the eruption (or double-eruption) responsible for the calamity was the one that caused the AD 536 dust veil and led to strong reductions in incoming sunlight and in summer temperatures especially over the next decade. The theory is explored here with tree-ring records from Sweden, Finland, Norway and Denmark, historical data on dust veils, ice core evidence for major volcanic eruptions, and North Atlantic proxy records. Very low summer temperatures and reduced irradiance are evident across the study region over the duration of the AD 536/540s event. Alternative cold events (656–655 BC, 420–419 BC, 42–41 BC, AD 800–801 and AD 1127–1128) were less prominent than the AD 536/540s event. A cold event in AD 1601 serves as an interesting counterpart for the prehistoric events as it occurred, akin to the 536/540s event, at the height of the North Atlantic pulses of drift ice. This suggests that the coupled sea ice-ocean mechanism needed to deepen the anomaly is sensitive to the initial climate state and emphasises the importance of longue durée structures when reconstructing the human past. Overall, the AD 536/540s event appears a climate-related natural catastrophe to be remembered by following generations, which accords with the Fimbulwinter theory.