A signature of cosmic-ray increase in ad 774–775 from tree rings in Japan

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Increases in 14C concentrations in tree rings could be attributed to cosmic-ray events1, 2, 3, 4, 5, 6, 7, as have increases in 10Be and nitrate in ice cores8, 9. The record of the past 3,000 years in the IntCal09 data set10, which is a time series at 5-year intervals describing the 14C content of trees over a period of approximately 10,000 years, shows three periods during which 14C increased at a rate greater than 3‰ over 10 years. Two of these periods have been measured at high time resolution, but neither showed increases on a timescale of about 1 year (refs 11 and 12). Here we report 14C measurements in annual rings of Japanese cedar trees from ad 750 to ad 820 (the remaining period), with 1- and 2-year resolution. We find a rapid increase of about 12‰ in the 14C content from ad 774 to 775, which is about 20 times larger than the change attributed to ordinary solar modulation. When averaged over 10 years, the data are consistent with the decadal IntCal 14C data from North American and European trees13. We argue that neither a solar flare nor a local supernova is likely to have been responsible.

At a glance


  1. Measured radiocarbon content and comparison with IntCal98.
    Figure 1: Measured radiocarbon content and comparison with IntCal98.

    The concentration of 14C is expressed as Δ14C, which is the deviation (in ‰) of the 14C/12C ratio of a sample with respect to modern carbon (standard sample), after correcting for the age and isotopic fractionation30. a, Δ14C data for tree A (filled triangles with error bars) and tree B (open circles with error bars) for the period ad 750–820 with 1- or 2-year resolution. The typical precision of a single measurement of Δ14C is 2.6‰. Most data were obtained by multiple measurements, yielding smaller errors. Error bars, 1 s.d. b, The decadal average of our data (filled diamonds with error bars) compared with the IntCal98 data13 (open squares with error bars), which is a standard decadal Δ14C time series. Six standard samples (NIST SRM4990C oxalic acid, the new NBS standard) were measured in the same batch of samples. Because Δ14C is calculated as the deviation of the 14C/12C ratio of a sample with respect to an average of 14C/12C of the six standard samples, the errors are the resultant of error propagation. An error for a sample is a statistical one from a Poisson distribution, and an error for the standard sample is the greater of either averaged statistical error from a Poisson distribution of Δ14C for the six standard samples or the s.d. of values of 14C/12C for six standard samples.

  2. Comparison of our data with a four-box carbon cycle simulation.
    Figure 2: Comparison of our data with a four-box carbon cycle simulation.

    Filled diamonds represent the Δ14C values of our data, and lines represent an expected change by a four-box carbon cycle simulation. Various lines represent different cosmic-ray input durations of 0.1, 0.5, 1, 2 and 3 years. The Δ14C value of the simulation in ad 773 is fixed at a value calculated by the weighted average of the three data from ad 770 to 772. Error bars, as in Fig. 1 legend.


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Author information


  1. Solar-Terrestrial Environment Laboratory, Nagoya University, Chikusa-ku, Nagoya 464-8601, Japan

    • Fusa Miyake,
    • Kentaro Nagaya &
    • Kimiaki Masuda
  2. Center for Chronological Research, Nagoya University, Chikusa-ku, Nagoya 464-8601, Japan

    • Toshio Nakamura


K.M. conducted the research. F.M. prepared samples. T.N. measured 14C content by AMS at Nagoya University. F.M., K.M. and K.N. discussed the result. F.M. prepared the manuscript. K.M. and T.N. commented on the manuscript.

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    This file contains Supplementary Text and Data 1-6, Supplementary Figures 1-2, Supplementary Tables 1-3 and additional references.


  1. Report this comment #62717

    Fusa Miyake said:

    In this paper, we calculated the best fitted production rate for the 775 event as 6×10^8^ atoms/cm^2^. After our paper was published, Usoskin et al. [2012, 2013] has revisited the AD 775 event and calculated a ^14^C production rate for this event using other carbon cycle models. They claimed that the biggest difference between theirs and our model is having the deep ocean box or not. They concluded that the production rate is (1.3 ± 0.2)×10^8^ atoms/cm^2^ which corresponds to 5 times smaller than our result.
    However, the reason of the different result is the definition of the production rate. That is, we calculated the production rate as ^14^C atoms/(?R^2^), while, they calculated as ^14^C atoms/(4?R^2^). If we calculated using ^14^C atoms/(4?R^2^), the production rate becomes (1.5 ± 0.3)×10^8^ atoms/cm^2^, and this value is consistent with the result of Usoskin et al. 2013. In this case, the total global production of ^14^C is almost same as their calculation.

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