Search for Annual 14C Excursions in the Past

Title of Publication: 
Search for Annual 14C Excursions in the Past
Miyake, Fusa, Masuda, Kimiaki, Nakamura, Toshio, Kimura, Katsuhiko, Hakozaki, Masataka, Jull, A.J. Timothy, Lange, Todd E., Cruz, Richard Panyushkina, Irina P., Baisan, Chris, and Salzer, Matthew W.
Publication Info: 
Radiocarbon, 2016, p. 1–6 DOI:10.1017/RDC.2016.54

Two radiocarbon excursions (AD 774775 and AD 993994) occurred due to an increase of incoming cosmic rays on a short timescale. The most plausible cause of these events is considered to be extreme solar proton events (SPE). It is possible that there are other annual 14C excursions in the past that have yet to be confirmed. In order to detect more of these events, we measured the 14C contents in bristlecone pine tree-ring samples during the periods when the rate of 14C increase in the IntCal data is large. We analyzed four periods every other year (24792455 BC, 40554031 BC, 44654441 BC, and 46894681 BC), and found no anomalous 14C excursions during these periods. This study confirms that it is important to do continuous measurements to find annual cosmic-ray events at other locations in the tree-ring record.

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Figure 2 Bristlecone pine samples for this study. These samples came from the White Mountains of California, USA (37.3794°N, 118.1654°W).