Transient Offset in 14C After the Carrington Event Recorded by Polar Tree Rings

• Published in: Geophysical research letters 2024-03, Vol.51 (5), p.n/a
• Main Authors: Uusitalo, Joonas, Golubenko, Kseniia, Arppe, Laura, Brehm, Nicolas, Hackman, Thomas, Hayakawa, Hisashi, Helama, Samuli, Mizohata, Kenichiro, Miyake, Fusa, Mäkinen, Harri, Nöjd, Pekka, Tanskanen, Eija, Tokanai, Fuyuki, Rozanov, Eugene, Wacker, Lukas, Usoskin, Ilya, Oinonen, Markku
• Format: Article
• Language: English
• Subjects: Atmospheric dynamics; Atmospheric models; Atmospheric transport; Atmospheric transport models; Carbon 14; Carrington event; Energetic particles; Eruptions; Latitude; Photosynthesis; solar eruptions; Solar flares; Solar phenomena; space weather; Statistical analysis; Stratosphere; stratosphere‐troposphere exchange; Tree rings; Trees; Troposphere
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2023GL106632

The Carrington event of 1859 has been the strongest solar flare in the observational history. It plays a crucial role in shedding light on the frequency and impacts of the past and future Solar Energetic Particle (SEP) events on human societies. We address the impact of the Carrington event by measuring tree‐ring 14C with multiple replications from high‐latitude locations around the event and by comparing them with mid‐latitude measurements. A transient offset in 14C following the event is observed with high statistical significance. Our state‐of‐the‐art 14C production and transport model does not reproduce the observational finding, suggesting features beyond present understanding. Particularly, our observation would require partially fast transport of 14C between the stratosphere and troposphere at high latitudes. The observation is consistent with the previous findings with the SEP events of 774 and 993 CE for which faster integration of 14C into tree rings is observed at high latitudes. Plain Language Summary Strong Earth‐directed solar eruptions can cause 14C concentration spikes in the atmosphere. Large enough events may leave a signal in the annually grown tree‐rings as they capture the isotopic carbon fingerprint through photosynthesis. Such rapid 14C increases have been detected, for instance, starting in years 774 and 993 CE. However, no increase has been observed following the Carrington event of 1859, despite it being the largest solar eruption of the modern era. Notably, all prior 14C measurements covering the Carrington event come from mid‐latitude trees. To achieve a broader geographical coverage, we have measured the event from several high‐latitude locations. After comparing the high‐ and mid‐latitude measurements, we have found a statistically significant difference lasting for several years post‐Carrington. To better understand the difference, we have adopted a 14C production and atmospheric transport model capable of simulating regional differences. Despite the improved model, we found it unable to reproduce the observational results, which suggests features beyond current understanding. Ultimately, the observation emphasizes the role of subtle 14C differences in tree‐ring 14C studies, potentially opening new ways to study past solar phenomena and atmospheric dynamics. Key Points A transient offset in 14C from high‐latitude Finnish Lapland tree rings was observed between years 1861 and 1863 The Carrington event and the stratosphere‐trop