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Head: Andrzej Rakowski, PhD hab. Eng.

Duration

2018-2021

Participants

Financial support

National Science Centre, Poland, grant UMO-2017/25/B/ ST10/02329

 Abstract

In year 2012 appeared in the Nature article showing a rapid increase in the concentration of radiocarbon in the atmosphere caused by the activity of our star. Recorded increase of radiocarbon concentration in samples of annual tree rings of Japanese cedar (Cryptomeria japonica) at the turn of years 774 and 775 A.D. was 12 ‰. A similar increase (11.3‰) was recorded at the turn of years 993 and 994 A.D. In literature this effect is called the effect Miyake from the name of the discoverer.

This effect is of great importance for radiocarbon dating. This method based on the decay of the isotope of carbon of mass 14 (radiocarbon), and is very important to know how the radiocarbon concentration has changed in the past, and what is the present concentration in the sample. Radiocarbon concentration in the atmosphere is not constant in time and therefore to obtain a calendar age of the sample it is necessary to use the calibration curve. It allows the determination of the interval in calendar years, which corresponds to the appropriate concentration of radiocarbon (radiocarbon age). This curve in the youngest period was built on the basis of radiocarbon concentrations in tree rings from trees which were previously dated dendrochronological. Each point on the curve represents mean average of 10 years, which means that the amplitude of changes (rapid increase or decrease of the concentration of radiocarbon in the atmosphere) is shallower. Many archaeological samples come from the period, in which occur rapid changes of radiocarbon due to the Miyake’s effect. Calendar age of such samples appear younger due to calibration with such constructed curve. It is therefore necessary to take into account these rapid changes in the curve used for the calibration of radiocarbon dates.

The aim of this project is, in addition to archive these rapid changes in the radiocarbon concentrations in annual tree rings, to use these changes to precise dating part of the floating chronology for pine in central Poland, which has 227 years. By using AMS technique (Accelerator Mass Spectrometry), it is possible to make precise measurements of samples containing ≥1mg of carbon. Measurements of radiocarbon concentration in the pine cores of pine (annual growth rings) will be compared with changes in the reference samples (dendrochronologically dated annual rings of sub-fossil oak) in order to determine the similarity between these two waveforms changes ("wiggle matching"). This will allow the absolute dating of tree rings from floating pine chronology, which has been so far unattainable using radiocarbon method. It will be one of the first applications of this discovery in absolute dating, which will build the longest chronology of pine trees in central Europe.

Research project objectives/ Hypothesis

The proposed project aims to provide new information about the increase in concentration of 14C (radiocarbon) in the period of abrupt solar activity in the AD 774/775 and 993/994 AD, known in literature as Miyake’s effect. These information are particularly important from the point of view of radiocarbon method, because of the calibration curve which is constructed based on measurements of samples, containing of ten annual rings each. This results in substantial flattening of the amplitude of this effect, which may cause younger ages of samples after its calibration. In addition to taking into account the effect of the calibration curve, the results of our research will be use to fix in time a part of the floating pine chronology for Poland, which can be used for dendrochronological dating. This can be achieved by comparing the changes in radiocarbon concentration in annual tree rings with its concentration in a period of rapid growth between AD 774/775 and AD 993/994.

Research methodology

The project is planned to undertake radiocarbon analyzes in single annual tree rings, previously dating using dendrochronological method, which include the two periods in which there was observed abrupt increase of radiocarbon concentration due to the Miyake’s effect. Standard chemical pretreatment of samples of annual tree rings will be extended to step aimed at obtaining α-cellulose, which should ensure the elimination of any contamination. Measurements will be performed for samples of oak and pine, in order to determine possible differences in the magnitude of increase of radiocarbon concentrations, depending on the tree species. The concentration of radiocarbon in annual tree rings will be determined based on measurement with accelerator mass spectrometry (AMS). This technique allows to perform precise measurements in samples with a carbon content of ≥ 1 mg.

Research project impact

Determination of changes in radiocarbon concentration caused by the Miyake’s effect, for trees from the area of Polish allow for a comparison of the magnitude of this effect between the obtained results and data available in the literature. This will determine if there are clear differences in the magnitude in different parts of the world. Finally, there appears a real possibility to extend pine chronology for Poland of a part of floating chronology. This will be possible by comparison of changes of radiocarbon concentration in annual tree rings (Wiggle matching) in our standard samples with those measured in pine cores (floating chronology). In this case is possible to obtain the age of each tree ring with precision of 1 year.

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