学术文献库

Excursions in the carbon-14 record measured in tree rings are attributed to various high energy but short-lived cosmic effects. So far, rapid changes at 774-775 CE, 993-994 CE and 660 BCE have been convincingly interpreted as due to rapid changes in solar cosmic-ray flux, usually accredited with reproduction of the events in trees at different locations and different laboratories, and followed with equivalent peaks of other cosmogenic isotopes in polar ice cores. In 2017, Wang et al. proposed a new event at 3372-3371 BCE based on a single set of annual 14C data measured on a floating series of tree rings sampled from a buried specimen of Chinese wingnut tree (Pterocarya stenoptera). We attempted to reproduce this event in tree rings of an absolutely dated bristlecone pine specimen (Pinus longaeva) from the White Mountains, California USA and a subfossil European oak (Quercus sp.) from the Moselle River Valley in France. Unfortunately, we are unable to determine whether there is any rapid 14C excursion during this time, although the regular 11-year Schwabe cycle is clearly observable. Therefore, the presence of a cosmic-ray event as suggested at 3372-3371 BCE cannot be confirmed. It is possible the exposed 14C spike occurred at some other time, the absolute age of which we cannot determine unless the precise calendar age of the Chinese wingnut wood is properly crossdated, although the other data of Wang et al. (2017) is not inconsistent with our records. In either case, this is important because the frequency of such extreme cosmic events needs to be well-documented to assess the likelihood of similar high-energy effects occurring in the future.