Large 14C excursion in 5480 BC indicates an abnormal sun in the mid-Holocene
Large 14C excursion in 5480 BC indicates an abnormal sun in the mid-Holocene
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DOI：
10.1073/pnas.1613144114
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发表时间：
2017-01-31
影响因子：
11.1
通讯作者：
Nakamura, Toshio
中科院分区：
文献类型：
--
作者：
Miyake, Fusa;Jull, A. J. Timothy;Nakamura, Toshio
年轮中的放射性碳含量可以很好地代表过去传入地球的宇宙射线强度。尽管过去的宇宙射线变化已经通过测量树木年轮中的 C-14 含量进行了研究，对于全新世的时间分辨率>= 10-y，但每年的 C-14 数据很少。过去，人们对 C-14 的年度变化知之甚少，除了少数时期（包括 AD 774-775 C-14 偏移）进行了年度测量之外。在这里，我们报告了使用狐尾松树年轮对公元前 5490 年至公元前 5411 年期间的 C-14 测量结果，分辨率为 1 至 2-y，并发现从公元前 5481 年到公元前 5471 年（公元前 5480 年事件），C-14 异常大幅增加（千分之二十）。这次事件的C-14增加率比正常的太阳大极小期的增加率要大得多。我们提出这一事件的可能原因是太阳大极小期的未知阶段，或者是连续的太阳质子事件和正常太阳大极小期的组合。
Radiocarbon content in tree rings can be an excellent proxy of the past incoming cosmic ray intensities to Earth. Although such past cosmic ray variations have been studied by measurements of C-14 contents in tree rings with >= 10-y time resolution for the Holocene, there are few annual C-14 data. There is a little understanding about annual C-14 variations in the past, with the exception of a few periods including the AD 774-775 C-14 excursion where annual measurements have been performed. Here, we report the result of C-14 measurements using the bristlecone pine tree rings for the period from 5490 BC to 5411 BC with 1- to 2-y resolution, and a finding of an extraordinarily large C-14 increase (20 parts per thousand) from 5481 BC to 5471 BC (the 5480 BC event). The C-14 increase rate of this event is much larger than that of the normal grand solar minima. We propose the possible causes of this event are an unknown phase of grand solar minimum, or a combination of successive solar proton events and a normal grand solar minimum.