LAUSR

Abstract Frost rings can provide direct evidence of anomalously cold summertime conditions on hemispheric scales. Here we report frost rings in subfossil pinewood from Finnish Lapland dated dendrochronologically to AD 536 and 1627 BC. These exact calendar dates have been vividly discussed in the literature in the respective contexts of a cold climate anomaly/dust veil/crop failure/famine/Justinianic Plague and the Minoan eruption of Thera (Santorini). Coinciding anomalies in growth and carbon isotope ratios (δ13C) indicate cold and overcast conditions in these years in Finnish Lapland, typical to conditions induced by volcanic dust veils. This evidence reinforces the view of multiple climatic drivers strongly effecting contemporary societies around AD 536 and provides important new evidence regarding the 1627 BC event. We report a frost ring for this year, and also consider evidence from Lapland for other Thera candidate eruptions in the 16th century BC. The marker years 1560 BC and 1546 BC in bristlecone pine tree rings in North America are positioned within negative departures in our δ13C data. Most likely, the frosts occurred somewhere in July and were driven by dust veils from Northern Hemisphere. Although not indicative of volcanic provenance, frost rings and other dendroclimatic proxies dated to exact calendar years offer important time markers for chronological frameworks which can synchronize archaeological, historical and environmental data to further our understanding of environmental changes at scales that matter to human societies.