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Sökning: WFRF:(Boswijk G.)

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1.
  • Buntgen, U., et al. (författare)
  • Tree rings reveal globally coherent signature of cosmogenic radiocarbon events in 774 and 993 CE
  • 2018
  • Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 9
  • Tidskriftsartikel (refereegranskat)abstract
    • Though tree-ring chronologies are annually resolved, their dating has never been independently validated at the global scale. Moreover, it is unknown if atmospheric radiocarbon enrichment events of cosmogenic origin leave spatiotemporally consistent fingerprints. Here we measure the 14C content in 484 individual tree rings formed in the periods 770–780 and 990–1000 CE. Distinct 14C excursions starting in the boreal summer of 774 and the boreal spring of 993 ensure the precise dating of 44 tree-ring records from five continents. We also identify a meridional decline of 11-year mean atmospheric radiocarbon concentrations across both hemispheres. Corroborated by historical eye-witness accounts of red auroras, our results suggest a global exposure to strong solar proton radiation. To improve understanding of the return frequency and intensity of past cosmic events, which is particularly important for assessing the potential threat of space weather on our society, further annually resolved 14C measurements are needed.
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2.
  • Guettler, D., et al. (författare)
  • Rapid increase in cosmogenic C-14 in AD 775 measured in New Zealand kauri trees indicates short-lived increase in C-14 production spanning both hemispheres
  • 2015
  • Ingår i: Earth and Planetary Science Letters. - : Elsevier BV. - 1385-013X .- 0012-821X. ; 411, s. 290-297
  • Tidskriftsartikel (refereegranskat)abstract
    • In 2012, Miyake et al. reported a sudden and strong increase of the atmospheric radiocarbon (C-14) content in Japanese cedar trees of 1.2% between AD 774 and 775. While their findings were quickly confirmed by a German oak chronology for the Northern Hemisphere (NH), the question remained if the effect was seen in both hemispheres. Here we present the first annually resolved Southern Hemisphere (SH) C-14 record spanning the interval AD 760-787, using New Zealand kauri (Agathis australis) chronology wood. An almost identical distinct increase compared to Northern Hemisphere data was observed, suggesting a cosmic event with globally uniform impact as a potential cause for the increase. Deploying a carbon cycle box model a worldwide averaged net C-14 production of 2.2 x 10(8) C-14 atoms cm(-2) was estimated, which is 3.7 times higher than the average annual C-14 production. The immediate appearance of the event in tree rings on both hemispheres suggests a short duration event of significantly less than 1 yr.
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