Browsing by Subject "tree rings"

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  • Miyake, Fusa; Panyushkina, Irina; Jull, Tim; Adolphi, Florian; Brehm, N; Helama, Samuli; Kanzawa, K; Moriya, T; Muscheler, Raimund; Nicolussi, K; Oinonen, Markku; Salzer, M; Takeyama, M; Tokanai, F; Wacker, Lucas (2021)
    The annual C-14 data in tree rings is an outstanding proxy for uncovering extreme solar energetic particle (SEP) events in the past. Signatures of extreme SEP events have been reported in 774/775 CE, 992/993 CE, and similar to 660 BCE. Here, we report another rapid increase of C-14 concentration in tree rings from California, Switzerland, and Finland around 5410 BCE. These C-14 data series show a significant increase of similar to 6 parts per thousand in 5411-5410 BCE. The signature of C-14 variation is very similar to the confirmed three SEP events and points to an extreme short-term flux of cosmic ray radiation into the atmosphere. The rapid C-14 increase in 5411/5410 BCE rings occurred during a period of high solar activity and 60 years after a grand C-14 excursion during 5481-5471 BCE. The similarity of our C-14 data to previous events suggests that the origin of the 5410 BCE event is an extreme SEP event.
  • Stivrins, Normunds; Aakala, Tuomas; Ilvonen, Liisa; Pasanen, Leena; Kuuluvainen, Timo; Vasander, Harri; Galka, Mariusz; Disbrey, Helena R.; Liepins, Janis; Holmstrom, Lasse; Seppa, Heikki (2019)
    Fire is a major disturbance agent in the boreal forest, influencing many current and future ecosystem conditions and services. Surprisingly few studies have attempted to improve the accuracy of fire-event reconstructions even though the estimates of the occurrence of past fires may be biased, influencing the reliability of the models employing those data (e.g. C stock, cycle). This study aimed to demonstrate how three types of fire proxies - fire scars from tree rings, sedimentary charcoal and, for the first time in this context, fungal spores of Neurospora - can be integrated to achieve a better understanding of past fire dynamics. By studying charcoal and Neurospora from sediment cores from forest hollows, and the fire scars from tree rings in their surroundings in the southern Fennoscandian and western Russian boreal forest, we produced composite fire-event data sets and fire-event frequencies, and estimated fire return intervals. Our estimates show that the fire return interval varied between 126 and 237 years during the last 11,000 years. The highest fire frequency during the 18th-19th century can be associated with the anthropogenic influence. Importantly, statistical tests revealed a positive relationship between other fire event indicators and Neurospora occurrence allowing us to pinpoint past fire events at times when the sedimentary charcoal was absent, but Neurospora were abundant. We demonstrated how fire proxies with different temporal resolution can be linked, providing potential improvements in the reliability of fire history reconstructions from multiple proxies.