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Cosmic‐ray event in 994 CE recorded in radiocarbon from Danish Oak
Abstract
We present measurements of radiocarbon in annual tree rings from the time period 980-1006 CE, hereby covering the cosmic-ray event in 994 CE. The new radiocarbon record from Danish oak is based on both earlywood and latewood fractions of the tree rings, which makes it possible to study seasonal variations in 14C production. The measurements show a rapid increase of c. 10%0 from 993 to 994 CE in latewood, followed by a modest decline and relatively high values over the ensuing ∼10 years. This rapid increase occurs from 994 to 995 CE in earlywood, suggesting that the cosmic-ray event most likely occurred the the period between April-June 994 CE. Our new record from Danish oak shows strong agreement with existing Δ14C records from Japan, thus supporting the hypothesis that the 994 CE cosmic-ray event was uniform throughout the northern hemisphere and therefore can be used as an astro-chronological tie-point to anchor floating chronologies of ancient history.
... Thus if Miyake events occur preferentially at solar maxima, this would support a solar origin. The radiocarbon data themselves contain the 11-year solar cycle, and several attempts have been made to determine its phase at the time of a Miyake event [15,21,[63][64][65]. In this paper, we will attempt a similar inference. ...
... We apply this code to an analysis of all publicly available 14 C data for the six events previously identified in the literature, gathering the COSMIC network data from many sites across both hemispheres for 774 CE and 993 CE from Büntgen et al. [23]; additional data, including early and late wood data, for 774 CE from Uusitalo et al. [112], and Danish oak over 993 CE from Fogtmann-Schulz et al. [64]; English oak over 993 CE from Rakowski et al. [113]; the discovery data for 7176 BCE and 5259 BCE from Brehm et al. [16]; earl tree-rings over 660 BCE from Park et al. [15], and early and late wood over 660 BCE from Sakurai et al. [24]; and data from the decades leading up to 5410 BCE from Miyake et al. [25]. We exclude the Japanese cedar from Miyake et al. [114], as it shows a delayed rise compared to the other 993 CE datasets, and for the purposes of the present work, we await a consensus on how to interpret this. ...
... As well as this, the physiology of each species determines the way it uses and/or reuses carbohydrates for growth-ring construction. This latter consideration lies at the core of an ongoing debate about whether whole rings or only late wood fractions should be analysed to achieve the highest quality data [64,115,116]. Furthermore, at per mille precisions intra-annual fluctuations in atmospheric radiocarbon concentrations also become significant, and in particular the coincidence of annual maxima and minima with the growing seasons of different species at different locations [117]. ...
Annually resolved measurements of the radiocarbon content in tree-rings have revealed rare sharp rises in carbon-14 production. These ‘Miyake events’ are likely produced by rare increases in cosmic radiation from the Sun or other energetic astrophysical sources. The radiocarbon produced is not only circulated through the Earth’s atmosphere and oceans, but also absorbed by the biosphere and locked in the annual growth rings of trees. To interpret high-resolution tree-ring radiocarbon measurements therefore necessitates modelling the entire global carbon cycle. Here, we introduce ‘ ticktack ’ ( https://github.com/SharmaLlama/ticktack/ ), the first open-source Python package that connects box models of the carbon cycle with modern Bayesian inference tools. We use this to analyse all public annual 14 C tree data, and infer posterior parameters for all six known Miyake events. They do not show a consistent relationship to the solar cycle, and several display extended durations that challenge either astrophysical or geophysical models.
... Since the discovery of extreme and rapid events in the radiocarbon record, several records based on single-year 14 C measurements have been produced in order to gain a better understanding of the origin and nature of these cosmic-ray events (Miyake et al., 2012(Miyake et al., , 2013(Miyake et al., , 2014(Miyake et al., , 2021Usoskin et al., 2013;Jull et al., 2014;Wacker et al., 2014;Güttler et al., 2015;Rakowski et al., 2015;Fogtmann-Schultz et al., 2017;Oppenheimer et al., 2017;Büntgen et al., 2018;Quarta et al., 2019). Rapid events are characterized by an extreme single-year increase in the atmospheric 14 C content caused by solar energetic particles (SEP) associated with solar super flares (Schaefer et al., 2000;Karoff et al., 2016;Uusitalo et al., 2018). ...
... The new data extend the existing Danish 14 C record with measurements between 1058 CE and 1250, hereby covering most of the Medieval Warm Period (950e1250 CE). This results in a continuous high-resolution 14 C time series spanning the time period 966e1378 CE (412 years) as well as two shorter records covering the periods 650e902 CE (252 years) and 1432e1578 CE (146 years) (Philippsen et al., 2022;Kudsk et al., 2020;Fogtmann-Schultz et al., 2017, 2021a. Four additional years were measured in the period 1050e1056 CE in order to examine SN1054 and the event in 1052 CE proposed by Brehm et al. (2021). ...
... All previously published and new 14 C data based on Danish oak trees are shown in Fig. 2A. The precision of the Danish dendrochronology has been confirmed by the two cosmic-ray events in 774 CE and 993 CE for the pieces covering these events (Fogtmann-Schultz et al., 2017;Kudsk et al., 2020), although the dendrochronological age of the 14 C measurements in Fogtmann-Schultz et al. (2017) had to be corrected by one year (Fogtmann-Schultz et al., 2017;Kudsk et al., 2020). Information (wood number, used tree rings, sample site and references) and statistics (Student-t values) concerning the dendrochronology of all previously measured Danish wood pieces are presented in Kudsk et al. (2020) and Fogtmann-Schulz et al. (2019, 2021a. ...
This study investigates solar variability between 650 CE and 1900 based on new and published ¹⁴C records with a time resolution of two years or higher. The new high-resolution ¹⁴C data presented here are derived from Danish oak and span the period 1058–1250 CE. We determine the durations of past solar minima and periods with moderate solar activity from the solar modulation potential calculated using a carbon-box model with the high-resolution ¹⁴C records as input. The observed intervals of solar minima and intermittent periods with moderate activity levels suggest that a Maunder-type minimum occurred in 656–707 CE. We tentatively propose to name this minimum the Horrebow Minimum after Christian Horrebow, an early Danish astronomer who studied the occurrence of sunspots and was the first to propose that they follow a cyclic behaviour. Changes in amplitude and cycle length of the 11-year solar cycle are investigated by bandpass filtering 23 individual ¹⁴C records. The filtered ¹⁴C data indicate that the length of the 11-year solar cycle may be prolonged before the onset of the Oort, Maunder, and Spörer minima. The amplitude of the 11-year solar cycle associated with solar minima and periods with moderate solar activity between 650 CE and 1900 is estimated to 1.1‰. A two-sample Kolmogorov-Smirnov goodness-of-fit test indicates that there is no significant difference between the amplitude distribution of 11-year solar cycles during solar minima and periods of moderate solar activity. A review of the high-resolution ¹⁴C records encompassing the near-Earth supernova events that occurred in 1006 CE, 1054, 1181, 1572, and 1604 suggests that these events were not accompanied by distinct changes in the ¹⁴C production rate. Nonetheless, an unusual increase of c. 10‰ in Δ¹⁴C between 1048 CE and 1055 is observed and discussed.
... This is consistent with the values presented by Miyake et al. (2013Miyake et al. ( , 2014. The systematical negative offset of -2.1 ± 1.0‰ for the LW and the Hinoki tree data and -5.1 ± 1.1‰ for the Danish oak and the Hinoki tree have also been reported (Fogtmann-Schulz et al. 2017). The magnitude of the Δ 14 C increase in the LW (for 993-994 CE) and the EW (994-995 CE) from Kujawy seems to be smaller. ...
... The EW and LW radiocarbon concentration data from the Danish oak were used to estimate the most probable period during which the phenomena occurred (most likely a SEP or a series of SEPs), which caused the abrupt increase in the atmospheric radiocarbon concentration. It was determined that the most probable time period for the occurrence of this global phenomena is between late autumn of 993 CE and early summer of 994 CE, but most likely between April-June 994 CE (Fogtmann-Schulz et al. 2017). The latter is based on the fact that no increase is seen in the radiocarbon concentration in the EW from that year. ...
... Graphs showing the (a) Δ 14 C values (in ‰) for the Kujawy whole wood, EW, and LW, alongside the EW and LW values for the Danish oak(Fogtmann- Schulz et al. 2017) and IntCal20(Reimer et al. 2020) and (b) δ 13 C values (in ‰ VPDB) for the EW and LW from Kujawy. ...
This article presents measurements of the radiocarbon ( ¹⁴ C) concentration in sub-annual tree rings. Samples of earlywood (EW) and latewood (LW) from dendrochronologically dated tree rings (English oak, Quercus robur ) from Kujawy, near Kraków (Poland), spanning the years of 990–997 CE, are extracted and their ¹⁴ C content is measured at the Center for Applied Isotope Studies at the University of Georgia, USA. The EW and LW data show a gradual increase in the Δ ¹⁴ C values between 991–995 CE, which are similar to those observed by Rakowski et al. (2018). An increase of 10.3 ± 2.6‰ in Δ ¹⁴ C for the EW data, and 8.6 ± 2.6‰ for the LW data has been recorded for this period. Using this data, it is possible to estimate the time period for when a major historical event occurred, which seems to have been in the late summer (September –2/+1 month) of 993 CE.
... Hence, it is of great importance that new tree-ring data submitted for future calibration curves are of sufficient quality in terms of the robustness of the dendrochronological age constraints, internal and external validation of 14 C measurements within each laboratory, and that the new 14 C ages are compared with existing 14 C data in order to ensure the calibrated ages are reliable and accurate. Furthermore, annual 14 C data have contributed to the findings of so-called solar cosmic-ray events, which are characterized by an abrupt increase in the amount of 14 C in Earth's atmosphere for one or several years (Miyake et al. 2012(Miyake et al. , 2013(Miyake et al. , 2014(Miyake et al. , 2017aUsoskin et al. 2013;Jull et al. 2014Jull et al. , 2018Wacker et al. 2014;Güttler et al. 2015;Rakowski et al. 2015;Fogtmann-Schulz et al. 2017;Wang et al. 2017;Park et al. 2017). Annually resolved 14 C records have also been used to search for similar excursions in the atmospheric 14 C content that may be caused by near-Earth supernova explosions, but so far no clear indications of such an event have been found (Damon et al. 1995;Menjo et al. 2005;Dee et al. 2017). ...
... The dendrochronological dating of the wood piece RE1 is verified by the AD 775 event, as the timing of the event recorded in this study is in full agreement with existing 14 C records from all over the world ( Figure measurements of late wood per reported year. The new data presented here appear to agree better with existing data for this period, and we therefore consider them more accurate than the data presented by Fogtmann-Schulz et al. (2017) for the years AD 1001-1006 ( Figure 3B). A rather striking difference between the AD 1000 dataset and published data by Fogtmann-Schulz et al. (2017) concerns the occurrence of the AD 994 cosmic-ray event. ...
... The new data presented here appear to agree better with existing data for this period, and we therefore consider them more accurate than the data presented by Fogtmann-Schulz et al. (2017) for the years AD 1001-1006 ( Figure 3B). A rather striking difference between the AD 1000 dataset and published data by Fogtmann-Schulz et al. (2017) concerns the occurrence of the AD 994 cosmic-ray event. ...
Single-year measurements of radiocarbon ( ¹⁴ C) in tree rings have led to the discovery of rapid cosmic-ray events as well as longer lasting anomalies, which have given new insights into the Sun’s behavior in the past. Here, we present two new single-year ¹⁴ C records based on Danish oak that span the periods AD 692–790 and 966–1057, respectively, and consequently include the two rapid cosmic-ray events in AD 775 and 994. The new data are presented along with relevant information on the dendrochronological dating of the wood pieces, implying that these new measurements may contribute towards generating the next international calibration curve. The new data covering the AD 966–1057 period suggest that the increase in atmospheric ¹⁴ C associated with the cosmic-ray event in AD 994 actually occurred in AD 993, i.e. one year earlier than the year reported in Fogtmann-Schulz et al. (2017) based on oak from southern Denmark. Careful reanalysis of the dendrochronology that underpins the new ¹⁴ C records based on oak material from southern Denmark reveals that the cosmic-ray event reported in Fogtmann-Schulz et al. (2017) actually took place in AD 993.
... Since the discovery of rapid cosmic-ray events (e.g. Miyake et al. 2012Miyake et al. , 2013Jull et al. 2014;Güttler et al. 2015;Rakowski et al. 2015;Fogtmann-Schulz et al. 2017;Wang et al. 2017), interest in high-precision annual radiocarbon ( 14 C) records has grown rapidly (e.g. Dee and Pope 2016). ...
... Miyahara et al. 2006;Beramendi-Orosco et al. 2010). However, even fewer studies have measured the 14 C content of both early-wood (EW) and late-wood (LW) fractions in an attempt to study sub-annual variations (Olsson and Possnert 1992;Rakowski et al. 2013;Xu et al. 2015;Fogtmann-Schulz et al. 2017). The origin and relative age of 14 C in EW therefore remain poorly understood, which limits the potential for resolving sub-annual variations in past atmospheric 14 C levels. ...
... This study indicated that incorporation of radiocarbon from the previous year in EW may occur, but no systematic differences between 14 C in α-cellulose extracted from EW and LW could be detected. Some studies, however, suggest that it might be possible to resolve subannual changes in the atmospheric 14 C level by measuring both components Xu et al. 2015;Fogtmann-Schulz et al. 2017). Data published by Xu et al. (2015) (cedar tree) and Rakowski et al. (2013) (pine tree) indicate that EW and LW record sub-annual 14 C variations in the atmosphere. ...
Substantial amounts of annual radiocarbon ( ¹⁴ C) data have recently been produced with the purpose of increasing the time resolution of ¹⁴ C records used for constructing the calibration curve and for studying the occurrence of abrupt cosmic-ray events. In this study, we investigate if it is possible to resolve sub-annual scale changes in the atmospheric ¹⁴ C content by measuring radiocarbon in early-wood and late-wood fractions from Danish oak. The tree-ring samples span the period 1954–1970 CE, hereby covering the peak of the bomb pulse. A least squares test comparing the atmospheric ¹⁴ C content and the new sub-annual ¹⁴ C record from Danish tree rings reveals that by measuring early-wood and late-wood fractions, it may be possible to resolve sub-annual variations in past atmospheric ¹⁴ C levels.
... Thus if Miyake events occur preferentially at solar maxima, this would support a solar origin. The radiocarbon data themselves contain the 11-year solar cycle, and several attempts have been made to determine its phase at the time of a Miyake event (Miyake et al., 2013b;Fogtmann-Schulz et al., 2017;Park et al., 2017;Scifo et al., 2019;Brehm et al., 2021), and in this Paper we will attempt a similar inference. ...
... As well as this, the physiology of each species determines the way it uses and/or reuses carbohydrates for growth-ring construction. This latter consideration lies at the core of an ongoing debate about whether whole rings or only late wood fractions should be analyzed to achieve the highest quality data (Fogtmann-Schulz et al., 2017;McDonald et al., 2019;Park et al., 2021). Furthermore, at per mille precisions intra-annual fluctuations in atmospheric radiocarbon concentrations also become significant, and in particular the coincidence of annual maxima and minima with the growing seasons of different species at different locations (Kromer et al., 2001). ...
Annually-resolved measurements of the radiocarbon content in tree-rings have revealed rare sharp rises in carbon-14 production. These 'Miyake events' are likely produced by rare increases in cosmic radiation from the Sun or other energetic astrophysical sources. The radiocarbon produced is not only circulated through the Earth's atmosphere and oceans, but also absorbed by the biosphere and locked in the annual growth rings of trees. To interpret high-resolution tree-ring radiocarbon measurements therefore necessitates modelling the entire global carbon cycle. Here, we introduce 'ticktack', the first open-source Python package that connects box models of the carbon cycle with modern Bayesian inference tools. We use this to analyse all public annual 14C tree data, and infer posterior parameters for all six known Miyake events. They do not show a consistent relationship to the solar cycle, and several display extended durations that challenge either astrophysical or geophysical models.
... These events have been demonstrated for AD 774-775, AD 994-995, 660 BC, and 3372-3371 BC (e.g. Miyake et al. 2012, 2017aUsoskin et al. 2013;Jull et al. 2014;Güttler et al. 2015;Fogtmann-Schulz et al. 2017;Park et al. 2017;Wang et al. 2017). These four events appear to have similar structures, with a rapid rise and slow decay, although different amplitudes. ...
... In the case of the most well-documented event at AD 774-775, Mekhaldi et al. (2015) and Miyake et al. (2015) have confirmed the nature of the event from studies of other radionuclides, by measuring 10 Be and 36 Cl in ice cores. Other smaller events at AD 993-994 have also been observed, initially by Miyake et al. (2013) and recently confirmed by Fogtmann-Schulz et al. (2017). In addition, other events at 5480 BC (Miyake et al. 2017a) and 660 BC (Park et al. 2017) have been reported. ...
Two radiocarbon ( ¹⁴ C) excursions are caused by an increase of incoming cosmic rays on a short time scale found in the Late Holocene (AD 774–775 and AD 993–994), which are widely explained as due to extreme solar proton events (SPE). In addition, a larger event has also been reported at 5480 BC (Miyake et al. 2017a), which is attributed to a special mode of a grand solar minimum, as well as another at 660 BC (Park et al. 2017). Clearly, other events must exist, but could have different causes. In order to detect more such possible events, we have identified periods when the ¹⁴ C increase rate is rapid and large in the international radiocarbon calibration (IntCal) data (Reimer et al. 2013). In this paper, we follow on from previous studies and identify a possible excursion starting at 814–813 BC, which may be connected to the beginning of a grand solar minimum associated with the beginning of the Hallstatt period, which is characterized by relatively constant ¹⁴ C ages in the period from 800–400 BC. We compare results of annual ¹⁴ C measurements from tree rings of sequoia (California) and cedar (Japan), and compare these results to other identified excursions, as well as geomagnetic data. We note that the structure of the increase from 813 BC is similar to the increase at 5480 BC, suggesting a related origin. We also assess whether there are different kinds of events that may be observed and may be consistent with different types of solar phenomena, or other explanations.
... Hare et al., 2019;Park et al., 2017;Sakurai et al., 2020) 774/775 CE(Büntgen et al., 2018;Güttler et al., 2015;Jull et al., 2014;Mekhaldi et al., 2015;Miyake et al., 2015Miyake et al., , 2012Park et al., 2017;Rakowski et al., 2015;Scifo et al., 2019;Sigl et al., 2015;Usoskin et al., 2013;Uusitalo et al., 2018) 992/993 CE(Büntgen et al., 2018;Fogtmann-Schulz et al., 2017;Mekhaldi et al., 2015;Miyake et al., 2019Miyake et al., , 2015Miyake et al., , 2013Rakowski et al., 2018;Scifo et al., 2019) 1055 CEEastoe et al., 2019; 1279 CE ...
Radiocarbon (14C) has an important role both in the environment and climate research as well as in radiocarbon dating. As a natural tracer, radiocarbon can be applied to differentiate fossil or modern derived inorganic and organic compounds. Although fossil materials do not contain radiocarbon, recent modern materials have a well-measurable radiocarbon content as they are closely related to the atmospheric carbon dioxide. In certain cases, different methods apart from the isotope analysis cannot be applied to discriminate the two sources, like in the case of the discrimination of fossil and modern CO2 emissions (Suess, 1955). The method is not only applicable for discrimination of emission sources, but also in industry for the investigation of materials containing fossil and bio components as well, like plastic and fuel samples (Oinonen et al., 2010). In addition, the 14C emission of nuclear facilities can be investigated, as the 14C/12C ratio of nuclear emission are easily distinguishable from the natural background (Zhang et al., 2021). Plants collect and fix the carbon from the atmospheric CO2 by the photosynthesis, for this reason, some plant organic material, like cellulose, well represent the local atmospheric 14C/12C ratio of CO2 in the year of the production (Rakowski, 2011; Richardson et al., 2013). Based on this, plant materials (tree rings and leaves) can be applied to high spatial and temporal resolution passive sampling in urban and rural areas or around nuclear power plants, for recent and retrospective investigations. By this method, areas can be investigated, where instrumental sampling is not possible or would be very costly. Furthermore, the method is applicable to signals of extraterrestrial events, that cannot be performed by ordinary instrumental sampling, like investigation of 14C fingerprints of the supernova explosions in tree ring samples, which are over a thousand years old (Miyake et al., 2012)
My presented PhD work was performed in the Eövtös Lóránd Research Network, Institute for Nuclear Research (ATOMKI), Isotope Climatology and Environmental Research Centre (ICER). In my research I was aiming to develop and apply accelerator mass spectrometry (AMS) based radiocarbon measurement methods that have not been applied in Hungary for environmental research. My aim was mapping the fossil carbon load in urban and background areas with high spatial resolution without instrumental air sampling, based on plant samples in Hungary (Debrecen) and Indonesia (Bali). In addition, I aimed to determine the effect of the Fukushima nuclear accident for the level of 14C in tree ring samples, 50 km west from the Fukushima Nuclear Power Plant. Beside nuclear emission, my research aim was also the investigation of the 14C fingerprints of natural cosmic events in tree ring samples. I tried to reproduce a previously published rapid 14C increase event in tree ring samples produced between 3351-3392 BCE. Furthermore, I wanted to expand the application of the applied 14C methods for such type materials that have not been investigated in Hungary before, such as fuel and honey samples. By these studies, in addition to radiocarbon dating, my aim was to open new perspectives in the Hungarian radiocarbon research, that can be the base of long-term researches in the future and open new research directions.
... For short-lived samples, such as grains that grew within one season, a calibration curve based on annual tree-ring samples is more appropriate. Furthermore, atmospheric 14 C concentrations can fluctuate rapidly (Jull et al. 2018;Miyake et al. 2017;Miyake et al. 2012;Park et al. 2017;Güttler et al. 2013;Usoskin et al. 2013;Fogtmann-Schulz et al. 2017;Kudsk et al. 2019), which would be blurred in calibration curves based on decadal samples. With annual calibrations, such short-term fluctuations can be used to calibrate radiocarbon dates with great precision, potentially to a single year in special circumstances (Wacker et al. 2014;Kuitems et al. 2020). ...
... For short-lived samples, such as grains that grew within one season, a calibration curve based on annual tree-ring samples is more appropriate. Furthermore, atmospheric 14 C concentrations can fluctuate rapidly (Jull et al. 2018;Miyake et al. 2017;Miyake et al. 2012;Park et al. 2017;Güttler et al. 2013;Usoskin et al. 2013;Fogtmann-Schulz et al. 2017;Kudsk et al. 2019), which would be blurred in calibration curves based on decadal samples. With annual calibrations, such short-term fluctuations can be used to calibrate radiocarbon dates with great precision, potentially to a single year in special circumstances (Wacker et al. 2014;Kuitems et al. 2020). ...
The aim of this chapter is to use Bayesian modelling to add an absolute chronology to the phases identified in the excavation at SJM3 Posthustorvet (Croix et al., this volume, Chapter 3). In previous excavations, the earliest levels in Ribe’s emporium showed good preservation of wood, which has provided material for dendrochronological dates from the period c. 710-741 (in the ASR 9 Posthuset excavation, cf. Feveile & Jensen 2006, 126). Later phases were only dated by a qualitative assessment of the character of the deposits and the typological cross-dating of coins and other artefact materials. This study, by contrast, uses radiocarbon dating to construct a site chronology.
We use large numbers of radiocarbon dates in combination with Bayesian modelling and high-precision calibration curves to fundamentally improve the accuracy and reliability of the site chronology. Urban historical archaeology requires dating precision that is unobtainable with individual radiocarbon dates. Recent advances in calibration techniques, however, have improved the resolution sufficiently to make the precision of radiocarbon dates comparable to those of written sources, coins, or other artefact chronologies. In terms of the results obtained and of method development, this study is thus of broader methodological significance to urban archaeology and radiocarbon studies.
... The SEP event scenario for the 774-775 AD event is preferred over the main competing galactic GRB hypothesis for three reasons: (1) the latitudinal gradient and inferred global symmetry of the cosmogenic signal (Sukhodolov et al. 2017;Uusitalo et al. 2018;Büntgen et al. 2018) (if a GRB source were located near to Earth's equatorial plane, the expected latitudinal gradient would be opposite to the observed polar enhancement of the cosmogenic signal; Uusitalo et al. 2018), 17 (2) the significant response in 10 Be (e.g., Mekhaldi et al. 2015;Sukhodolov et al. 2017) which is not expected for a GRB (Pavlov et al. 2013a), and (3) the identification of four additional cosmogenic nuclide events in 993-994 AD (Miyake et al. 2013(Miyake et al. , 2014Fogtmann-Schulz et al. 2017;O'Hare et al. 2019), * 660 BC (Park et al. 2017;O'Hare et al. 2019), 7176 BC (Paleari et al. 2022;Brehm et al. 2022), and 5259 BC (Brehm et al. 2022). In addition to these five confirmed SEP events, three other candidates are known presently that need to be independently confirmed; 1052 AD and 1279 AD (Brehm et al. 2021) as well as 5410 BC (Miyake et al. 2021). ...
We trace the evolution of research on extreme solar and solar-terrestrial events from the 1859 Carrington event to the rapid development of the last twenty years. Our focus is on the largest observed/inferred/theoretical cases of sunspot groups, flares on the Sun and Sun-like stars, coronal mass ejections, solar proton events, and geomagnetic storms. The reviewed studies are based on modern observations, historical or long-term data including the auroral and cosmogenic radionuclide record, and Kepler observations of Sun-like stars. We compile a table of 100- and 1000-year events based on occurrence frequency distributions for the space weather phenomena listed above. Questions considered include the Sun-like nature of superflare stars and the existence of impactful but unpredictable solar "black swans" and extreme "dragon king" solar phenomena that can involve different physics from that operating in events which are merely large.
... The SEP event scenario for the 774-775 AD event is preferred over the main competing galactic GRB hypothesis for three reasons: (1) the latitudinal gradient and inferred global symmetry of the cosmogenic signal (Sukhodolov et al. 2017;Uusitalo et al. 2018;Büntgen et al. 2018) (if a GRB source were located near to Earth's equatorial plane, the expected latitudinal gradient would be opposite to the observed polar enhancement of the cosmogenic signal; Uusitalo et al. 2018), 17 (2) the significant response in 10 Be (e.g., Mekhaldi et al. 2015;Sukhodolov et al. 2017) which is not expected for a GRB (Pavlov et al. 2013a), and (3) the identification of four additional cosmogenic nuclide events in 993-994 AD (Miyake et al. 2013(Miyake et al. , 2014Fogtmann-Schulz et al. 2017;O'Hare et al. 2019), * 660 BC (Park et al. 2017;O'Hare et al. 2019), 7176 BC (Paleari et al. 2022;Brehm et al. 2022), and 5259 BC (Brehm et al. 2022). In addition to these five confirmed SEP events, three other candidates are known presently that need to be independently confirmed; 1052 AD and 1279 AD (Brehm et al. 2021) as well as 5410 BC (Miyake et al. 2021). ...
We trace the evolution of research on extreme solar and solar-terrestrial events from the 1859 Carrington event to the rapid development of the last twenty years. Our focus is on the largest observed/inferred/theoretical cases of sunspot groups, flares on the Sun and Sun-like stars, coronal mass ejections, solar proton events, and geomagnetic storms. The reviewed studies are based on modern observations, historical or long-term data including the auroral and cosmogenic radionuclide record, and Kepler observations of Sun-like stars. We compile a table of 100- and 1000-year events based on occurrence frequency distributions for the space weather phenomena listed above. Questions considered include the Sun-like nature of superflare stars and the existence of impactful but unpredictable solar "black swans" and extreme "dragon king" solar phenomena that can involve different physics from that operating in events which are merely large.
... So far, three confirmed solar energetic particle events (SEP 774 CE,993 CE,660 BCE,and 7176 BCE), one supernova (SN1056) and proposed solar-proton event (5259 BCE) have been confirmed with annual 14 C series from numerous geographical locations and different AMS radiocarbon laboratories (Jull et al. 2014;Fogtmann-Schulz et al. 2017;Büntgen et al. 2018;Terrasi et al. 2020;Sakurai et al. 2020;Brehm et al. 2021a;Paleari et al. 2022). Four other proposed 14 C excursions (1279 CE, 813 BCE, 5480 BCE, and 5410 BCE) need to be corroborated with data from multiple locations or need to be confirmed (Miyake et al. 2017(Miyake et al. , 2021Jull et al. 2018;Brehm et al. 2021b). ...
A signal of rapid changes in 14 C production is logged in annual series of 14 C derived from tree rings, which can be associated with diverse effects of cosmic-ray fluxes, including solar bursts and supernova events. These 14 C signatures may vary in time and space. The intensity and structure of the 14 C signal are multifaced, which complicates the understanding of the forcing and attribution of the underlying astrophysical events. It was suggested that Δ 14 C in 1052/53 CE and 1054/55 CE signatures at a 4‰-6‰ range over two years could be caused by the Crab Nebula supernova (SN1054) or/and solar perturbation. The temporal incoherence of the signals in the published 14 C series is investigated with dynamic time warping (DTW), a novel approach for matching time-behavioral patterns in multiple 14 C datasets. DTW analysis of four 14 C signatures from tree rings of California, Finland, and England suggests that 14 C spikes between 1052 CE and 1055 CE can be caused by a single event. The flickering fingerprint may result from cross-dating inconformity. Cross-checking tree-ring records from distant locations is impossible sometimes due to large differences in environmental conditions limiting tree growth. The methodology helps to align the signals and can be applied to other 14 C datasets.
... After the initial discovery, it has become evident that the historical atmospheric 14 C concentrations have occasionally changed more dramatically than what has been previously thought based on lower resolution measurements. So far, similar rapid events have been suggested around years AD 993 [2], 660 BCE [3][4][5], 5480 BCE [6], 800 BCE [7] and CE 1055 [8]. In addition to providing important insights into the causes of such events, rapid 14 C spikes can work as pointer years when anchoring and identifying geological phenomena such as volcanic eruptions and historical events [9][10][11][12]. ...
Annual and sub-annual tree-ring ¹⁴C measurements allow the study of past natural phenomena such as rapid ¹⁴C increases and solar behavior. In addition, they provide precise calibration data sets that help in improving the dating accuracy of past natural and cultural events. However, for the data to be comparable, it is important that laboratories describe the whole process from sample retrieval to eventual results. In this paper, we describe the full ¹⁴C measurement procedure adopted in the Finnish tree-ring consortium, including sample collection and preparation, dendrochronology, chemical pretreatment, combustion and graphitization, Accelerator Mass Spectrometry (AMS) measurements and data processing. In addition, we report the ¹⁴C background components for our traditional Closed-Tube Combustion (CTC) and Elemental Analyzer (EA) based processes, both yielding to high-quality data. Furthermore, we study the mass-dependence effects of tree-ring measurements and find them to be practically insignificant for ages up to several millennia but growing in significance when approaching the ¹⁴C limit.
... A new paradigm using annual samples is set by the calibration curve IntCal20, to which the present project has contributed data 1 . A key feature of IntCal20 is the recognition that atmospheric 14 C levels have fluctuated rapidly several times (for example, ad 993, ad 775 and 5480 bc) during the Holocene epoch due to solar particle events (SPEs) created by coronal mass ejections during extreme solar flares [2][3][4][5][6][7][8][9] . These appear about every 1,000 years 29 and can cause rapid spikes in the atmospheric 14 C content, significantly larger than the normal 2-3‰ fluctuations of the 11-year solar cycle 30,31 . ...
Recent discoveries of rapid changes in the atmospheric ¹⁴C concentration linked to solar particle events have spurred the construction of new radiocarbon annual calibration datasets1–13. With these datasets, radiocarbon dating becomes relevant for urban sites, which require dates at higher resolution than previous calibration datasets could offer. Here we use a single-year radiocarbon calibration curve to anchor the archaeological stratigraphy of a Viking Age trade centre in time. We present absolutely dated evidence for artefact finds charting the expansion of long-distance trade from as far away as Arctic Norway and the Middle East, which we linked to the beginning of the Viking Age at ad 790 ± 10. The methods developed here enable human interactions and cultural, climatic and environmental changes to be compared in archaeological stratigraphies worldwide.
... Rapid and large increases in 14 C concentration over one to a few years have been discovered in the annual 14 C measurements of various events: 774/775 CE (Miyake et al., 2012), 993/994 (992/993) CE (Miyake et al., 2013), ∼660 BCE (Park et al., 2017), 1052 CE , 1279 CE , and 5410 BCE (Miyake et al., 2021). Three of these events (774/775 CE, 993/994 (992/993) CE, and ∼660 BCE) have been confirmed in worldwide 14 C tree ring measurements (Büntgen et al., 2018;Fogtmann-Schulz et al., 2017;Güttler et al., 2015;Jull et al., 2014;Miyake et al., 2014;Rakowski et al., 2015Rakowski et al., , 2018Rakowski et al., , 2019Usoskin et al., 2013;Uusitalo et al., 2018;Sakurai et al., 2020;Scifo et al., 2019), and are corroborated by 10 Be and 36 Cl measurements in ice cores (Mekhaldi et al., 2015;Miyake et al., 2015Miyake et al., , 2019O'Hare et al., 2019;Sigl et al., 2015). The relative 36 Cl/ 10 Be ratio supports an extreme SPE origin of the three events discovered in 774/775 CE, 993/994 CE, and ∼660 BCE (Mekhaldi et al., 2015;O'Hare et al., 2019). ...
Cosmogenic nuclides in tree rings and polar ice cores record the information of past cosmic ray intensities and solar activities. A large ¹⁴C increase over 10 years has been discovered around 5480 BCE. The ¹⁴C variations in this event differ from those of other short‐term cosmic ray events and typical grand solar minima. To elucidate the cause of the ¹⁴C increase around 5480 BCE, we measured the ¹⁰Be and ³⁶Cl concentrations in the Antarctic Dome Fuji ice core at quasi‐annual and 4–5 years resolutions, respectively. Based on the combined ¹⁴C, ¹⁰Be, and ³⁶Cl data, the 5480 BCE event was probably not caused by a solar proton event (SPE) or a gamma‐ray event, because the ³⁶Cl concentration did not significantly increase as expected in these events. The incremented ¹⁰Be data were enhanced similarly to those of recent grand solar minima, but more rapidly increased (over ∼10 years). These results suggest that an unusual grand solar minimum occurred around 5480 BCE, characterized by a rapidly decreasing solar activity.
... This purpose could be achieved by taking advantage of the sudden increase in the radiocarbon ( 14 C) concentration in annual tree rings, described by Miyake et al. (2012Miyake et al. ( , 2013Miyake et al. ( , 2014Miyake et al. ( , 2017 and Park et al. (2017). Studies on the radiocarbon content in the annual growth of different tree species growing in both northern and southern hemispheres have demonstrated that the socalled "Miyake effects" dated to 661/660 BC, 774/775 AD and 993/994 AD are of a global extent (Usoskin et al. 2013;Jull et al. 2014;Güttler et al. 2015;Büntgen et al. 2016Büntgen et al. , 2018Fogtmann-Schulz et al. 2017). Similar results have also been determined in annual increments of oaks growing around Krakow (S Poland) (Rakowski et al. 2015(Rakowski et al. , 2019. ...
Radiocarbon ( ¹⁴ C) analyses are commonly used to determine the absolute age of floating tree-ring chronologies. At best, with the wiggle-matching method, a precision of 10 years could be achieved. For the early Middle Ages, this situation has been markedly improved by the discovery of rapid changes in atmospheric ¹⁴ C concentrations in tree-rings dated to 774/775 and 993/994 AD. These high-resolution changes can be used to secure other floating tree-ring sequences to within 1-year accuracy. While a number of studies have used the 774 even to secure floating tree-ring sequences, the less abrupt 993 event has not been so well utilized. This study dates a floating pine chronology from Ujście in Wielkopolska (Greater Poland) (NW Poland), which covers the 10th century period and is critical for studies on the beginning of the Polish State to the calendar years 859–1085 AD using the changes in single year radiocarbon around 993/4 AD.
... replicate type c) above; Table 1). Following the application of the relevant error Table 1 Whole-process intra-laboratory replicates on tree-ring samples reported for IntCal20 (*quoted errors are counting errors on samples and standards only (Stuiver 1982: 5;Stuiver et al. 1986: 969); § these replicate groups were used in calculating the QL-radon offset (Stuiver et al. 1998b(Stuiver et al. : 1128(Stuiver et al. -1129; † earlywood/latewood replicates (Fogtmann-Schulz et al. 2017;Büntgen et al. 2018 multiplier where appropriate (Stuiver et al. 1998a(Stuiver et al. : 1044(Stuiver et al. -1045, 31 replicate groups (out of the 339) are statistically inconsistent at the 5% significance level. This is in line with statistical expectation. ...
We undertook a strengths, weaknesses, opportunities, and threats (SWOT) analysis of Northern Hemisphere tree-ring datasets included in IntCal20 in order to evaluate their strategic fit with the demands of archaeological users. Case studies on wiggle-matching single tree rings from timbers in historic buildings and Bayesian modeling of series of results on archaeological samples from Neolithic long barrows in central-southern England exemplify the archaeological implications that arise when using IntCal20. The SWOT analysis provides an opportunity to think strategically about future radiocarbon (14C) calibration so as to maximize the utility of 14C dating in archaeology and safeguard its reputation in the discipline.
... Since the phenomenon of rapid increase in CR intensity in 775 CE was solved 1-3 , 14 C analysis in annual rings has played a major role in searching for another rapid 14 C increase event 4,5 . While such events have been suggested to originate from an extreme SPE [6][7][8][9][10] , the other type with a rather long period of 14 C increase has recently been reported in German oak tree rings 11 . ...
Annual rings record the intensity of cosmic rays (CRs) that had entered into the Earth’s atmosphere. Several rapid 14C increases in the past, such as the 775 CE and 994CE 14C spikes, have been reported to originate from extreme solar proton events (SPEs). Another rapid 14C increase, also known as the ca. 660 BCE event in German oak tree rings as well as increases of 10Be and 36Cl in ice cores, was presumed similar to the 775 CE event; however, as the 14C increase of approximately 10‰ in 660 BCE had taken a rather longer rise time of 3–4 years as compared to that of the 775 CE event, the occurrence could not be simply associated to an extreme SPE. In this study, to elucidate the rapid increase in 14C concentrations in tree rings around 660 BCE, we have precisely measured the 14C concentrations of earlywoods and latewoods inside the annual rings of Japanese cedar for the period 669–633 BCE. Based on the feature of 14C production rate calculated from the fine measured profile of the 14C concentrations, we found that the 14C rapid increase occurred within 665–663.5 BCE, and that duration of 14C production describing the event is distributed from one month to 41 months. The possibility of occurrence of consecutive SPEs over up to three years is offered.
... We only used late wood since it is the most reliable component for tracing past variations in atmospheric radiocarbon (Fogtmann-Schulz et al., 2017;Kudsk et al., 2018;McDonald et al., 2019). We only used the -cellulose fraction, as this is the most stable part of the wood (Nemec et al., 2010). ...
Several aspects concerning the origin and nature of grand solar minima remain unclear, and more high‐resolution ¹⁰Be and ¹⁴C records are needed to improve our understanding of these phenomena. Here, we report 137 new high‐precision, annually resolved radiocarbon concentrations based on oak from the Danish dendrochronology. The new record covers a period (CE 1432–1578) that encompasses most of the penultimate grand solar minima known as the Spörer Minimum. A detailed comparison between the Spörer and Maunder (CE 1640–1720) minima shows that the Spörer Minimum is associated with enhanced Δ¹⁴C variability in a band centered around the 11‐year Schwabe cycle from CE 1450 to 1479 and between CE 1545 and 1578, whereas little 11‐year variability is observed from CE 1479 to 1539. In contrast, we only observe enhanced 11‐year variability after the end of the Maunder Minimum at CE 1722–1744, which could indicate that the nature and origin of the two minima were different.
... The anomalous concentration of 14 C in 774/775 in tree rings (Miyake et al., 2012) called for intensive discussions of its origin. Further surveys were conducted on the concentration of 14 C in tree rings around the world and 10 Be in ice cores from the polar regions, to confirm the spike in 774/775 and another one in 993/994 (Miyake et al. 2013(Miyake et al. , 2015Usoskin and Kovaltsov, 2012;Usoskin et al., 2013;Jull et al., 2014;Mekhaldi et al., 2015;Sigl et al., 2015;Fogtmann-Schulz et al., 2017;Uusitalo et al., 2018;Büngten et al., 2018). The origin of these spikes attracted various hypotheses, including a nearby supernova (Allen, 2012), a gamma ray burst (Pavlov et al., 2013;Hambaryan and Neuhäuser, 2013), a cometary impact with the Earth (Liu et al., 2014), and an extreme solar proton event (Thomas et al., 2013;Usoskin et al., 2013;Miyake, Masuda, and Nakamura, 2013;Cliver et al., 2014). ...
The anomalous concentration of radiocarbon in 774/775 attracted intense discussion on its origin, including the possible extreme solar event(s) exceeding any events in observational history. Anticipating such extreme solar events, auroral records were also surveyed in historical documents and those including the red celestial sign after sunset in the Anglo-Saxon Chronicle (ASC) were subjected to consideration. Usoskin et al. (Astron. Astrophys. 55, L3, 2013: U13) interpreted this record as an aurora and suggested enhanced solar activity around 774/775. Conversely, Neuhäuser and Neuhäuser (Astron. Nachr. 336, 225, 2015a: N15a; Astron. Nachr. 336, 913, 2015b: N15b) interpreted “after sunset” as during sunset or twilight; they considered this sign as a halo display and suggested a solar minimum around 774. However, so far these records have not been discussed in comparison with eyewitness auroral records during the known extreme space weather events, although they were discussed in relationship with potential extreme events in 774/775. Therefore, we reconstruct the observational details based on the original records in the ASC and philological references, compare them with eyewitness auroral observations during known extreme space weather events, and consider contemporary solar activity. We clarify the observation was indeed “after sunset”, reject the solar-halo hypothesis, define the observational time span between 25 March 775 and 25 December 777, and note that the parallel “drawing of lunar halo display” in 806 in the ASC shown in N15b was not based on the original observation in England. We show examples of eyewitness auroral observations during twilight in known space weather events, and this celestial sign does not contradict the observational evidence. Accordingly, we consider this event to have happened after the onset of the event in 774/775, but to have shown relatively enhanced solar activity, with regard to other historical auroral records in the mid-770s, as also confirmed by the ¹⁰ Be data from ice cores.
... Our results show a sharp increase in the 14 C concentration in 993 CE corresponding to 11.3 ± 3.8‰ in the Δ 14 C scale. This change-value compares well with those published by others for this Miyake-event, for instance for Denmark (10.5 ± 3.4‰) and Japan (11.3 ± 3.5‰) (Miyake et al. 2014;Fogtmann et al. 2017). Also the shape of the observed increase is consistent with what is generally observed by others, namely a slight decline before 993 CE, a sharp increase, and a slow decline over the following years probably because of the exchanges with the terrestrial carbon pools. ...
Combined dendrochronology and accelerator mass spectrometry radiocarbon (AMS ¹⁴ C) dating analyses were used in order to date an old living tree named Italus , growing in the Pollino massif in Southern Italy. Wiggle match AMS ¹⁴ C dating analysis was performed on a 320-yr-long floating chronology obtained by cross-dating four wood cores extracted from the exposed roots of the tree. Following this approach, an age for the tree of ≈1230 yr was estimated. This age makes Italus the oldest living tree in Europe. High-resolution ¹⁴ C dating analyses performed on single rings extracted from the tree stem allowed us to identify the 993–994 CE large excursion in atmospheric ¹⁴ C concentration (Miyake event) revealing for the first time its presence in the Mediterranean basin.
... These sudden increases were subsequently coined Miyake Events and their amplitude can vary. The first Miyake Event, illustrated in Fig. 1, has since been confirmed by other 14 C laboratories on dendrochronogical archives from Germany [5], the USA, Russia [6] and New Zealand [7]; and the second, by teams in Denmark and Poland [8]. Another similar event has been identified by Wang et al. [9] in 3372 -3371 BCE, and an analogous but slightly slower uplift has also been found around 660 BCE by Park et al. [10]. ...
Extreme bursts of radiation from space result in rapid increases in the concentration of radiocarbon in the atmosphere. Such rises, known as Miyake Events, can be detected through the measurement of radiocarbon in dendrochronological archives. The identification of Miyake Events is important because radiation impacts of this magnitude pose an existential threat to satellite communications and aeronautical avionics and may even be detrimental to human health. However, at present, radiocarbon measurements on tree-ring archives are generally only available at decadal resolution, which smooths out the effect of a possible radiation burst. The Miyake Events discovered so far, in tree-rings from the years 3372-3371 BCE, 774-775 CE, and 993-994 CE, have essentially been found by chance, but there may be more. In this paper, we use signal processing techniques, in particular COSFIRE, to train filters with data on annual changes in radiocarbon (Δ
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C) around those dates. Then, we evaluate the trained filters and attempt to detect similar Miyake Events in the past. The method that we propose is promising, since it identifies the known Miyake Events at a relatively low false positive rate. Using the findings of this paper, we propose a list of 26 calendar years that our system persistently indicates are Miyake Event-like. We are currently examining a short-list of five of the newly identified dates and intend to perform single-year radiocarbon measurements over them. Signal processing techniques, such as COSFIRE filters, can be used as guidance tools since they are able to identify similar patterns of interest, even if they vary in time or in amplitude.
... The 775 event was identified even in the decadal 14 C data (INTCAL) and 10 Be data (Dome Fuji [DF] ice core) as a rapid change (Usoskin & Kovaltsov, 2012). The 775 and 994 events were confirmed by subsequent independent annual 14 C measurements using worldwide tree samples (Büntgen et al., 2018;Fogtmann-Schulz et al., 2017;Güttler et al., 2015;Jull et al., 2014;Miyake et al., 2012Miyake et al., , 2013Miyake et al., , 2014Park et al., 2017;Rakowski et al., 2015;Usoskin et al., 2013;Uusitalo et al., 2018). Carbon-14 is a nuclide produced by cosmic rays (CR), which are high energy particles with origins in outside the solar system (Galactic CR: GCR) or an eruption of the sun (Solar Energetic Particles). ...
Cosmogenic nuclides are good indicators of past cosmic ray events and variations. To verify such phenomena, it is important to evaluate them using multiple nuclides from different archives. The cosmic ray event in 993–994 Common Era (CE) has already been confirmed with ¹⁴C and ¹⁰Be data, which show rapid increases in the concentrations. However, the ¹⁰Be data were obtained from the Greenland ice cores in the Northern Hemisphere. To investigate the extent of the ¹⁰Be increase in the Southern Hemisphere, we measured quasi-annual ¹⁰Be concentrations between 980 and 1,011 CE in the Antarctic Dome Fuji ice core. We observed a ~50% increase in ¹⁰Be concentration around 994 CE, consistent with the Greenland data. Increases in ¹⁰Be concentrations in both hemispheres support a solar origin of the 994-CE event. In addition, we propose a method of evaluating the so-called “system effect” for ¹⁰Be deposition by extracting common components from ¹⁰Be and Na⁺ data.
... If of sufficient amplitude, abrupt changes in the Earth's atmospheric radiocarbon ( 14 C) abundance 4,5 are recorded in tree rings owing to the short mixing time of the atmosphere 6 , including stratosphere-troposphere exchanges. Often attributed to extreme fluxes of high-energy solar particles 7,8 , distinct 14 C anomalies in 774/5 and 992-4 CE 4,5,[9][10][11][12][13] , as well as possibly much earlier in 660 and 3372/1 BCE 14,15 have been identified in local proxy archives. These so-called Cosmic Events also yield anomalies in records of other cosmogenic radionuclides, such as 10 Be and 36 Cl that are measured in ice cores 7 . ...
The original version of this Article contained an error in the Data Availability section, which incorrectly read ‘All data will be freely available via https://www.ams.ethz.ch/research.html.’ The correct version states ‘http://www.ams.ethz.ch/research/published-data.html’ in place of ‘https://www.ams.ethz.ch/research.html’. This has been corrected in both the PDF and HTML versions of the Article.
... If of sufficient amplitude, abrupt changes in the Earth's atmospheric radiocarbon ( 14 C) abundance 4,5 are recorded in tree rings owing to the short mixing time of the atmosphere 6 , including stratosphere-troposphere exchanges. Often attributed to extreme fluxes of high-energy solar particles 7,8 , distinct 14 C anomalies in 774/5 and 992-4 CE 4,5,[9][10][11][12][13] , as well as possibly much earlier in 660 and 3372/1 BCE 14,15 have been identified in local proxy archives. These so-called Cosmic Events also yield anomalies in records of other cosmogenic radionuclides, such as 10 Be and 36 Cl that are measured in ice cores 7 . ...
Though tree-ring chronologies are annually resolved, their dating has never been independently validated at the global scale. Moreover, it is unknown if atmospheric radiocarbon enrichment events of cosmogenic origin leave spatiotemporally consistent fingerprints. Here we measure the 14C content in 484 individual tree rings formed in the periods 770-780 and 990-1000 CE. Distinct 14C excursions starting in the boreal summer of 774 and the boreal spring of 993 ensure the precise dating of 44 tree-ring records from five continents. We also identify a meridional decline of 11-year mean atmospheric radiocarbon concentrations across both hemispheres. Corroborated by historical eye-witness accounts of red auroras, our results suggest a global exposure to strong solar proton radiation. To improve understanding of the return frequency and intensity of past cosmic events, which is particularly important for assessing the potential threat of space weather on our society, further annually resolved 14C measurements are needed.
The article presents results of measurements of radiocarbon ( ¹⁴ C) concentration in sub-annual dendrochronologically dated tree rings of English oak ( Quercus robur L.) from Grabie village near Kraków (southern Poland). Samples of early wood (EW) and late wood (LW) spanning the years 664–658 BCE. α-cellulose was extracted from each sample and their radiocarbon content was measured at the ATOMKI laboratory in Debrecen, Hungary. The EW and LW data confirm a prolonged increase in Δ ¹⁴ C values around 665–663 as was observed by Park et al. (2017), Rakowski et al. (2019), or Sakurai et al. (2020). In addition, we found that this event may consist of two relatively small events, as was proposed by Sakurai et al. (2020). Based on obtained in this and previous study data we estimate that the occurrence of the two events were between 665 and 664 BCE (Rakowski et al. 2019), and in late spring of 663 BCE (May–June, before beginning of LW formation).
Cosmogenic nuclides such as 14C from tree rings and 10Be and 36Cl from ice cores are excellent proxies for the past extremely large solar energetic particle (SEP) events, which are dozens of times larger than the largest SEP event in the history of observation. So far, several rapid 14C increases have been discovered, which are considered to have originated from extreme SEP events (or set of successive SEP events) from verifications using multiple cosmogenic nuclide analyses in natural archives. Although these events are characterized by a rapid increase in cosmogenic nuclide concentrations, 14C data recorded worldwide do not always show similar variations, especially during the 993 CE event, where a rapid increase was recorded in either 992–993 CE or 993–994 CE in several records. We present new 14C data of the Japanese cedar sample for the 993 CE event. Although the latest data show no significant increase in 1 year, an overall increase pattern is consistent with the previously reported 14C data of the Japanese cedar, which supports that a significant 14C increase occurred from 993 to 994 CE in the Japanese sample. Given the dominant 14C production in high latitudes by SEPs, the difference in timing of increase may be a transport effect in the atmosphere. Moreover, the difference in the timing of the 14C increase can cause a 1-year age-determination error using the 993 CE radiocarbon spike. Compared with the 14C data between tree samples from high latitude and midlatitude, including Japan, high-latitude data can capture 14C changes originating from SEP events more quickly and clearly and may be more suitable for a SEP event exploration in the past.
A laboratory intercomparison project was carried out on 20 annually resolved late-wood samples from the Danish oak record. The project included the following three laboratories: (1) the University of Arizona AMS Laboratory, University of Arizona, USA (AA); (2) HEKAL AMS Laboratory, MTA Atomki, Hungary (DeA); and (3) Aarhus AMS Centre (AARAMS), Aarhus University, Denmark (AAR). The large majority of individual data points (96%) lie within ±2σ of the weighted mean. Further assessment of the accuracy associated with the individual laboratories showed good agreement, indicating that consistent and reliable ¹⁴ C measurements well in agreement with each other are produced at the three laboratories. However, the quoted analytical uncertainties appear to be underestimated when compared to the observed variance of differences from the geometric mean of the samples. This study provides a general quality check of the single-year tree-ring ¹⁴ C measurements that are included in the new calibration curve.
The annual 14C data in tree rings is an outstanding proxy for uncovering extreme solar energetic particle (SEP) events in the past. Signatures of extreme SEP events have been reported in 774/775 CE, 992/993 CE, and ∼660 BCE. Here, we report another rapid increase of 14C concentration in tree rings from California, Switzerland, and Finland around 5410 BCE. These 14C data series show a significant increase of ∼6‰ in 5411-5410 BCE. The signature of 14C variation is very similar to the confirmed three SEP events and points to an extreme short-term flux of cosmic ray radiation into the atmosphere. The rapid 14C increase in 5411/5410 BCE rings occurred during a period of high solar activity and 60 years after a grand 14C excursion during 5481-5471 BCE. The similarity of our 14C data to previous events suggests that the origin of the 5410 BCE event is an extreme SEP event.
Aims. The 11-year solar cycle (Schwabe cycle) is the dominant pattern of solar magnetic activity reflecting the oscillatory dynamo mechanism in the Sun’s convection zone. Solar cycles have been directly observed since 1700, while indirect proxy data suggest their existence over a much longer period of time, but generally without resolving individual cycles and their continuity. Here we reconstruct individual solar cycles for the last millennium using recently obtained ¹⁴ C data and state-of-the-art models.
Methods. Starting with the ¹⁴ C production rate determined from the so far most precise measurements of radiocarbon content in tree rings, solar activity was reconstructed in the following three physics-based steps: (1) correction of the ¹⁴ C production rate for the changing geomagnetic field; (2) computation of the open solar magnetic flux; and (3) conversion into sunspot numbers outside of grand minima. All known uncertainties, including both measurement and model uncertainties, were straightforwardly accounted for by a Monte-Carlo method.
Results. Cyclic solar activity is reconstructed for the period 971–1900 (85 individual cycles) along with its uncertainties. This more than doubles the number of solar cycles known from direct solar observations. We found that the lengths and strengths of well-defined cycles outside grand minima are consistent with those obtained from the direct sunspot observations after 1750. The validity of the Waldmeier rule (cycles with fast-rising phase tend to be stronger) is confirmed at a highly significant level. Solar activity is found to be in a deep grand minimum when the activity is mostly below the sunspot formation threshold for about 250 years. Therefore, although considerable cyclic variability in ¹⁴ C is seen even during grand minima, individual solar cycles can hardly be reliably resolved therein. Three potential solar particle events, ca. 994, 1052, and 1279 AD, are shown to occur around the maximum phases of solar cycles.
Conclusions. A new approximately 1000-year-long solar activity reconstruction, in the form of annual (pseudo) sunspot numbers with the full assessment of all known uncertainties, is presented based on new high-precision Δ ¹⁴ C measurements and state-of-the-art models, more than doubling the number of individually resolved solar cycles. This forms a solid basis for new, more detailed studies of solar variability.
We present a new biennial record of radiocarbon ( ¹⁴ C) measured in Danish oak. The new record covers the years 1251–1378 CE, thereby spanning the Grand Solar Minimum known as the Wolf Minimum. Two oak samples from every other year were measured at the AMS facility at Aarhus University (Denmark), resulting in an average precision of 1.4‰ for the record. Spectral analysis of the new record revealed two peaks at 27 and 9.1 years, which could indicate the Hale cycle was lengthened and the Schwabe cycle shortened during the Wolf Minimum, but it is also possible that the amplitude of the Schwabe cycle was too small to be accurately identified with the acquired precision of this record. The record was bandpass filtered to investigate the variability of the amplitude in different bands, which showed a dampening of the amplitude during the second half of the Wolf Minimum in bands centered on the Schwabe and the Hale cycle, respectively. A reconstruction of the solar modulation function, Φ, also showed a periodicity of ca. 9 years, and indicated that the Wolf Minimum was preceeded by one cycle of decreased solar activity.
We here present a comparison of methods for the pretreatment of a batch of tree rings for high-precision measurement of radiocarbon at the Aarhus AMS Centre (AARAMS), Aarhus University, Denmark. The aim was to develop an efficient and high-throughput method able to pretreat ca. 50 samples at a time. We tested two methods for extracting α-cellulose from wood to find the most optimal for our use. One method used acetic acid, the other used HCl acid for the delignification. The testing was conducted on background ¹⁴ C samples, in order to assess the effect of the different pretreatment methods on low-activity samples. Furthermore, the extracted wood and cellulose fractions were analyzed using Fourier transform infrared (FTIR) spectroscopy, which showed a successful extraction of α-cellulose from the samples. Cellulose samples were pretreated at AARAMS, and the graphitization and radiocarbon analysis of these samples were done at both AARAMS and the radiocarbon dating laboratory at Lund University to compare the graphitization and AMS machine performance. No significant offset was found between the two sets of measurements. Based on these tests, the pretreatment of tree rings for high-precision radiocarbon analysis at AARAMS will henceforth use HCI for the delignification.
Miyake et al. (2012, 2013, 2014) described a sudden increase of radiocarbon ( ¹⁴ C) concentration in annual tree rings of Japanese cedar ( Cryptomeria japonica ) and Hinoki cypress ( Chamaecyparis obtusa) between AD 774 and 775 and between AD 993 and 994. In both analyzed periods, the sudden increase was observed almost in a single year. The increase in the ¹⁴ C content was about 12‰ in the period AD 774–775 (Miyake et al. 2012) and about 11.3‰ in the period AD 993–994 (Miyake et al. 2013, 2014; Fogtmann-Schultz et al. 2017; Rakowski et al. 2018). A similar increase was observed in 660 BC, with a peak height of about 10‰ (Park et al. 2017). Single-year samples of dendrochronologically dated tree rings of deciduous oak ( Quercus robur ) from Grabie, a village near Krakow (SE Poland), spanning the years 670–652 BC, were collected and their ¹⁴ C content was measured using an AMS technique. The results clearly show a rapid increase in the ¹⁴ C concentration in tree rings around 660 BC similar to this observed in Park et al. (2017).
The anomalous concentration of radiocarbon in 774/775 attracted intense discussion on its origin, including the possible extreme solar event(s) exceeding any events in observational history. Anticipating such extreme solar events, auroral records were also surveyed in historical documents and those including the red celestial sign after sunset in the Anglo-Saxon Chronicle (ASC) were subjected to consideration. Usoskin et al. (2013: U13) interpreted this record as an aurora and suggested enhanced solar activity around 774/775. Conversely, Neuhauser and Neuhauser (2015a, 2015b: N15a and N15b) interpreted "after sunset" as during sunset or twilight; they considered this sign as a halo display and suggested a solar minimum around 774. However, so far these records have not been discussed in comparison with eyewitness auroral records during the known extreme space-weather events, although they were discussed in relationship with potential extreme events in 774/775. Therefore, we reconstruct the observational details based on the original records in the ASC and philological references, compare them with eyewitness auroral observations during known extreme space-weather events, and consider contemporary solar activity. We clarify the observation was indeed "after sunset", reject the solar halo hypothesis, define the observational time span between 25 Mar. 775 and 25 Dec. 777, and note the parallel halo drawing in 806 in the ASC shown in N15b was not based on the original observation in England. We show examples of eyewitness auroral observations during twilight in known space-weather events, and this celestial sign does not contradict the observational evidence. Accordingly, we consider this event happened after the onset of the event in 774/775, but shows relatively enhanced solar activity, with other historical auroral records in the mid-770s, as also confirmed by the Be data from ice cores.
An increase in atmospheric radiocarbon ( ¹⁴ C) content of about 11.3‰ in the period AD 993–994 was observed in annual tree rings from Japanese cedar ( Cryptomeria japonica ) and Hinoki cypress ( Chamaecyparis obtusa) (Miyake et al. 2013, 2014). Single-year samples of dendrochronologically dated tree rings (English oak, Quercus robur ) from Kujawy, a village near Krakow (SE Poland), spanning the years AD 981–1000, were collected, and their ¹⁴ C content was measured using the AMS system in the Leibniz Laboratory. The results clearly show an increase of 6.2±1.6‰ in the ¹⁴ C concentration in tree rings between AD 993 and 994, with a maximum increase of 10.9±1.7‰ between AD 991 and 994.
Aims . Historical records provide evidence of extreme magnetic storms with equatorward auroral extensions before the epoch of systematic magnetic observations. One significant magnetic storm occurred on February 15, 1730. We scale this magnetic storm with auroral extension and contextualise it based on contemporary solar activity.
Methods . We examined historical records in East Asia and computed the magnetic latitude (MLAT) of observational sites to scale magnetic storms. We also compared them with auroral records in Southern Europe. We examined contemporary sunspot observations to reconstruct detailed solar activity between 1729 and 1731.
Results . We show 29 auroral records in East Asian historical documents and 37 sunspot observations.
Conclusions . These records show that the auroral displays were visible at least down to 25.8° MLAT throughout East Asia. In comparison with contemporary European records, we show that the boundary of the auroral display closest to the equator surpassed 45.1° MLAT and possibly came down to 31.5° MLAT in its maximum phase, with considerable brightness. Contemporary sunspot records show an active phase in the first half of 1730 during the declining phase of the solar cycle. This magnetic storm was at least as intense as the magnetic storm in 1989, but less intense than the Carrington event.
The discovery of past spikes in atmospheric radiocarbon activity, caused by major solar energetic particle events, has opened up new possibilities for high-precision chronometry. The two spikes, or Miyake Events, have now been widely identified in tree-rings that grew in the years 775 and 994 CE. Furthermore, all other plant material that grew in these years would also have incorporated the anomalously high concentrations of radiocarbon. Crucially, some plant-based artefacts, such as papyrus documents, timber beams and linen garments, can also be allocated to specific positions within long, currently unfixed, historical sequences. Thus, Miyake Events represent a new source of tie-points that could provide the means for anchoring early chronologies to the absolute timescale. Here, we explore this possibility, outlining the most expeditious approaches, the current challenges and obstacles, and how they might best be overcome.
The origin of two large peaks in the atmospheric radiocarbon ((14)C) concentration at AD 774/5 and 993/4 is still debated. There is consensus, however, that these features can only be explained by an increase in the atmospheric (14)C production rate due to an extraterrestrial event. Here we provide evidence that these peaks were most likely produced by extreme solar events, based on several new annually resolved (10)Be measurements from both Arctic and Antarctic ice cores. Using ice core (36)Cl data in pair with (10)Be, we further show that these solar events were characterized by a very hard energy spectrum with high fluxes of solar protons with energy above 100 MeV. These results imply that the larger of the two events (AD 774/5) was at least five times stronger than any instrumentally recorded solar event. Our findings highlight the importance of studying the possibility of severe solar energetic particle events.
Count rates, representing the rate of 14 C decay, are the basic data obtained in a 14 C laboratory. The conversion of this information into an age or geochemical parameters appears a simple matter at first. However, the path between counting and suitable 14 C data reporting (table 1) causes headaches to many. Minor deflections in pathway, depending on personal interpretations, are possible and give end results that are not always useful for inter-laboratory comparisons. This discussion is an attempt to identify some of these problems and to recommend certain procedures by which reporting ambiguities can be avoided.
Volcanic eruptions contribute to climate variability, but quantifying these contributions has been limited by inconsistencies in the timing of atmospheric volcanic aerosol loading determined from ice cores and subsequent cooling from climate proxies such as tree rings. Here we resolve these inconsistencies and show that large eruptions in the tropics and high latitudes were primary drivers of interannual-to-decadal temperature variability in the Northern Hemisphere during the past 2,500 years. Our results are based on new records of atmospheric aerosol loading developed from high-resolution, multi-parameter measurements from an array of Greenland and Antarctic ice cores as well as distinctive age markers to constrain chronologies. Overall, cooling was proportional to the magnitude of volcanic forcing and persisted for up to ten years after some of the largest eruptive episodes. Our revised timescale more firmly implicates volcanic eruptions as catalysts in the major sixth-century pandemics, famines, and socioeconomic disruptions in Eurasia and Mesoamerica while allowing multi-millennium quantification of climate response to volcanic forcing.
bstract The calibration of radiocarbon dates by means of a master calibration curve has been invaluable to Earth, environmental and archeological sciences, but the fundamental reason for calibration is that atmospheric radiocarbon content varies because of changes in upper atmosphere production and global carbon cycling. Improved instrumentation has contributed to high-resolution (interannual) radiocarbon activity measurements, which have revealed sudden and anomalous activity shifts previously not observed at the common resolution of 5–10 years of most of the calibration scale. One such spike has been recently reported from tree rings from Japan and then again in Europe at A.D. 774–775, for which we report here our efforts to both replicate its existence and determine its spatial extent using tree rings from larch at high latitude (northern Siberia) and bristlecone pine from lower latitude (the White Mountains of California). Our results confirm an abrupt ~ 15‰ 14C activity increase from A.D. 774 to 776, the size and now the hemispheric extent of which suggest that an extraterrestrial influence on radiocarbon production is most
likely responsible.
An explanation is offered for the impulsive increase in the
concentration of cosmogenic radiocarbon in annual tree rings
(Δ14C ˜ 12‰) from AD ≃775. A possible
cause of such an increase could be the high-energy emission from a
Galactic gamma-ray burst. It is shown that such an event should not lead
to an increase in the total production of 10Be in the
atmosphere, as distinct from the effect of cosmic-ray fluxes on the
atmosphere. At the same time, the production of an appreciable amount of
36Cl, which can be detected in Greenland and Antarctica ice
samples of the corresponding age, should be expected. This allows the
effects caused by a gamma-ray burst and anomalously powerful proton
events to be distinguished.
We explore requirements for a solar particle event (SPE) and flare
capable of producing the cosmogenic nuclide event of 775 A.D., and
review solar circumstances at that time. A solar source for 775 would
require a >1 GV spectrum ~45 times stronger than that of the intense
high-energy SPE of 1956 February 23. This implies a >30 MeV proton
fluence (F 30) of ~8 × 1010 proton
cm–2, ~10 times larger than that of the strongest 3
month interval of SPE activity in the modern era. This inferred F
30 value for the 775 SPE is inconsistent with the occurrence
probability distribution for >30 MeV solar proton events. The best
guess value for the soft X-ray classification (total energy) of an
associated flare is ~X230 (~9 × 1033 erg). For
comparison, the flares on 2003 November 4 and 1859 September 1 had
observed/inferred values of ~X35 (~1033 erg) and ~X45 (~2
× 1033 erg), respectively. The estimated size of the
source active region for a ~1034 erg flare is ~2.5 times that
of the largest region yet recorded. The 775 event occurred during a
period of relatively low solar activity, with a peak smoothed amplitude
about half that of the second half of the 20th century. The ~1945-1995
interval, the most active of the last ~2000 yr, failed to witness a SPE
comparable to that required for the proposed solar event in 775. These
considerations challenge a recent suggestion that the 775 event is
likely of solar origin.
We have compared accelerator mass spectrometry (AMS) radiocarbon results on wood samples at or near the limit of 14C dating, pretreated with a standard acid-base-acid (ABA) protocol, with those obtained from cellulose prepared from the same samples by several modifications of the Jayme-Wise cellulose extraction method (Green 1963). These tests were carried out to determine the most efficient way to ensure low backgrounds in 14C measurements of well-preserved ancient wood samples. © 2010 by the Arizona Board of Regents on behalf of the University of Arizona.
A large and sudden increase in radiocarbon ((14)C) around AD 773 are documented in coral skeletons from the South China Sea. The (14)C increased by ~ 15‰ during winter, and remain elevated for more than 4 months, then increased and dropped down within two months, forming a spike of 45‰ high in late spring, followed by two smaller spikes. The (14)C anomalies coincide with an historic comet collision with the Earth's atmosphere on 17 January AD 773. Comas are known to have percent-levels of nitrogen by weight, and are exposed to cosmic radiation in space. Hence they may be expected to contain highly elevated (14)C/(12)C ratios, as compared to the Earth's atmosphere. The significant input of (14)C by comets may have contributed to the fluctuation of (14)C in the atmosphere throughout the Earth's history, which should be considered carefully to better constrain the cosmic ray fluctuation.
The IntCal09 and Marine09 radiocarbon calibration curves have been revised utilizing newly available and updated data sets from 14C measurements on tree rings, plant macrofossils, speleothems, corals, and foraminifera. The calibration curves were derived from the data using the random walk model (RWM) used to generate IntCal09 and Marine09, which has been revised to account for additional uncertainties and error structures. The new curves were ratified at the 21st International Radiocarbon conference in July 2012 and are available as Supplemental Material at www.radiocarbon.org. The database can be accessed at http://intcal.qub.ac.uk/intcal13/. © 2013 by the Arizona Board of Regents on behalf of the University of Arizona.
We compare radiocarbon accelerator mass spectrometry (AMS) ages of wood samples subjected to a conventional acid-base-acid pretreatment with stepped combustion (ABA-SC) with results from the same samples subjected to an acid-base-wet oxidation pretreatment with stepped combustion (ABOX-SC) and cellulose extraction with stepped combustion (CE-SC). The ABOX-SC procedure has been shown previously to lead to lower backgrounds for old charcoal samples. Analyses of relatively uncontaminated “ ¹⁴ C-dead” samples of wood suggest that backgrounds of 0.11 ± 0.04 pMC are obtainable for both the ABOX-SC and ABA-SC procedures. Where wood is significantly contaminated the ABOX-SC technique provides significantly better decontamination than either the ABA-SC technique or cellulose extraction alone, although CE-SC can produce comparably low backgrounds to the ABOX-SC procedure.
We also report the application of the ABOX-SC, ABA-SC and CE-SC procedures to wood samples associated with the chronologically controversial Rotoehu Ash eruption, New Zealand. New ¹⁴ C-AMS dates from wood sampled from below the Rotoehu Ash span an age range of 43–50 ka BP consistent with recently presented OSL dates of 42–44 ka obtained for palaeosols beneath the ash.
Miyake et al. (henceforth M12) recently reported, based on 14C data, an
extreme cosmic event ca. AD775. Using a simple model, M12 claimed that the
event was too strong to be caused by a solar flare within the standard theory.
This implied a new paradigm of either an impossibly strong solar flare or a
very strong cosmic ray event of unknown origin occurred ca. AD775. We show that
the strength of the event was significantly overestimated by M12. Several
subsequent works have attempted to find a possible exotic source for such an
event, but they are all based on incorrect estimates by M12. We revisit this
event with analysis of new datasets and consistent theoretical modelling. We
verified the experimental result for the AD775 event using independent datasets
including 10Be series and newly measured 14C annual data. We surveyed available
historical chronicles for astronomical observations for the AD770s to identify
potential sightings of aurorae or supernovae. We interpreted the 14C
measurements using an appropriate carbon cycle model. We show that: (1) The
reality of the AD775 event is confirmed by new measurements of 14C; (2) by
using an inappropriate carbon cycle model, M12 strongly overestimated the
event's strength; (3) The revised magnitude of the event is consistent with
different independent datasets (14C, 10Be, 36Cl) and can be associated with a
strong, but not inexplicably strong, SEP event (or a sequence of events), and
provides the first evidence for an event of this magnitude (the fluence >30 MeV
was about 4.5*10^{10} /cm2) in multiple datasets; (4) This is in agreement with
increased auroral activity identified in historical chronicles. This point to
the likely solar origin of the event, which is the greatest solar event on a
multi-millennial time scale, placing a strong observational constraint on the
theory of explosive energy releases on the Sun and cool stars.
Atmospheric 14C production is a potential window into the energy of
solar proton and other cosmic ray events. It was previously concluded
that results from AD 774-775 are orders of magnitude greater than known
solar events. We find that the coronal mass ejection energy based on 14C
production is much smaller than claimed, but still substantially larger
than the maximum historical Carrington Event of 1859. Such an event
would cause great damage to modern technology, and in view of recent
confirmation of superflares on solar-type stars, this issue merits
attention.
In the last 3000 yr, one significant and rapid increase in the concentration
of 14C in tree rings was observed; it corresponds to a gamma-ray energy input
of 7x10^24 erg at Earth within up to one year in AD 774/5 (Miyake et al. 2012).
A normal supernova and a solar or stellar flare are unlikely as cause (Miyake
et al. 2012), so that the source remained unknown. Here, we show that a short
gamma-ray burst (GRB) in our Galaxy is consistent with all observables: Such an
event is sufficiently short and provides the necessary energy in the relevant
spectral range of $\gamma$-rays. Its spectral hardness is consistent with the
differential production rates of 14C and 10Be as observed. The absence of
reports about a historic sighting of a supernova in AD 774/5 or a present-day
supernova remnant are also consistent with a short GRB. We estimate the
distance towards this short GRB to be ~ 1 to 4 kpc - sufficiently far away, so
that no extinction event on Earth was triggered. This is the first evidence for
a short GRB in our Galaxy.
To investigate the radiocarbon concentration of atmospheric CO 2 over the past few millennia in Japan, we measured the ¹⁴ C age of annual rings from 3 Japanese trees with calendar dates ranging from ∼2000 yr old to present, and we compared the tree-ring ¹⁴ C age with the corresponding ¹⁴ C age from IntCal09. In some instances, the ¹⁴ C ages of the annual rings of Japanese trees are not consistent with the IntCal09 data sets. Often, the ¹⁴ C ages of tree rings are older than those from IntCal09, but younger than those from the SHCal04 data sets. The average shifts in the Nagoya ¹⁴ C age from IntCal09 data sets and 1σ errors were determined to be +26 ± 36, +24 ± 30, +16 ± 22, +5 ± 21, and +14 ± 22 ¹⁴ C yr for the intervals AD 72– 382, 589–1072, 1413–1615, 1617–1739, and 1790–1860, respectively. The Japanese Archipelago is situated near the boundary of the Intertropical Convergence Zone in summer, and the ¹⁴ C concentration of atmospheric CO 2 over Japan can be influenced by air masses of the Southern Hemisphere with lower ¹⁴ C concentrations during periods of higher solar activity and heightened East Asian summer monsoons. Our results suggest that the Japanese Archipelago is located in a critical zone where it is difficult to calibrate the ¹⁴ C age of tree-ring samples using existing calibration data sets. It should be noted that calibration of the ¹⁴ C dates of Japanese samples with IntCal09 may induce additional systematic shifts of calibrated ages toward older ages by about 30 yr compared with the sample optimum calendar ages.
We report here on the radiocarbon performance on the AARAMS HVE 1MV Tandetron. ¹⁴ C analysis is carried out in charge state 2+. We have avoided Li interference by appropriate settings of the high-energy electrostatic analyzer and the 30° second high-energy magnet. The ¹⁴ C machine background is determined using unprocessed graphite, which yielded 58,650±2032 ¹⁴ C yr determined as the average and standard deviation of four measurements. International standards, which are used to monitor the long-term performance of the ¹⁴ C measurements, agree with the reported consensus values.
To investigate the radiocarbon concentration of atmospheric CO2 over the past few millennia in Japan, we measured the C-14 age of annual rings from 3 Japanese trees with calendar dates ranging from similar to 2000 yr old to present, and we compared the tree-ring C-14 age with the corresponding C-14 age from IntCal09. In some instances, the C-14 ages of the annual rings of Japanese trees are not consistent with the IntCal09 data sets. Often, the 14C ages of tree rings are older than those from IntCal09, but younger than those from the SHCal04 data sets. The average shifts in the Nagoya C-14 age from IntCal09 data sets and 1 sigma errors were determined to be +26 +/- 36, +24 +/- 30, +16 +/- 22, +5 +/- 21, and +14 +/- 22 C-14 yr for the intervals AD 72-382, 589-1072, 1413-1615, 1617-1739, and 1790-1860, respectively. The Japanese Archipelago is situated near the boundary of the Intertropical Convergence Zone in summer, and the C-14 concentration of atmospheric CO2 over Japan can be influenced by air masses of the Southern Hemisphere with lower C-14 concentrations during periods of higher solar activity and heightened East Asian summer monsoons. Our results suggest that the Japanese Archipelago is located in a critical zone where it is difficult to calibrate the C-14 age of tree-ring samples using existing calibration data sets. It should be noted that calibration of the C-14 dates of Japanese samples with IntCal09 may induce additional systematic shifts of calibrated ages toward older ages by about 30 yr compared with the sample optimum calendar ages.
The 14 C activity in rings from an oak tree grown in a suburb of Uppsala, Sweden has been studied for the period, AD 1938 to 1981. We compare the results with the atmospheric carbon dioxide records from Abisko, northern Sweden, where local or regional contamination from fossil-fuel combustion can be disregarded. We assess the influence from different chemical pretreatment procedures in use and compare HCl-NaOH-HCl treatment with cellulose extraction. We split each ring into two samples corresponding to early (spring) and late wood. A more refined partitioning has been applied to the years 1963 and 1964.
A 30-year-old Japanese cedar (Cryptomeria japonica), collected from Iwaki, Fukushima in 2014, was analyzed for the long-lived radionuclide (14)C. Values of Δ(14)C varied from 211.7‰ in 1984 to 16.9‰ in 2013. The temporal Δ(14)C variation can be described as an exponential decline, indistinguishable from the general Northern Hemisphere Zone 2 (NH Zone 2) values in the atmosphere, until at least 1994. Values of Δ(14)C for 1999 and 2004 are slightly depleted compared with NH Zone 2 values, while from 1999 to 2013 the data suggest a clear depletion with a 2-8 ppmV additional CO2 contribution from a (14)C-free (i.e. fossil carbon) source. This change coincides with local traffic increases since two nearby expressways were opened in the 1990's. In addition, the small but visible (14)C pulse observed in the 2011 tree-ring might be caused by release from the damaged reactors during the Fukushima nuclear accident.
Copyright © 2015. Published by Elsevier Ltd.
In the best case, radiocarbon measurements allow artificial objects to be dated with a precision of 10 calendar years when conventional wiggle-matching onto the IntCal09 calibration curve is applied. More precise dating can only be achieved by using annually resolved ¹⁴C calibration data, particularly in timespans when there are rapid changes in atmospheric ¹⁴C concentration. The recently observed jump in atmospheric ¹⁴C concentration of 1.5% between AD 774 and 775, though expected to be rare, is a good example for such a rapid change. We demonstrate by example that is possible to precisely ¹⁴C date the cutting year of a timber in the historically important and well-preserved Holy Cross chapel of the convent St. John the Baptist in Val Müstair, Switzerland.
DOI: 10.2458/56.17634
A rapid yearly increase in the radiocarbon content has been detected for the period from AD 993 to 994. However, this event is supported by the C-14 measurements of only one cedar tree sample, and verification is necessary to confirm this event more reliably. For this purpose, this study measured the C-14 content in Japanese Hinoki tree rings corresponding to the period from AD 988 to 997 using the accelerator mass spectrometry system at Yamagata University (YU-AMS). The result shows a significant C-14 increase from AD 993 to 994, and is consistent with the previously measured data for the Japanese cedar tree. This marks the second case detecting an increased C-14 level corresponding to the AD 994 event.
14C content in tree rings and 10Be concentration records in polar ice core provide information about past cosmic ray intensities. The AD 774–775 cosmic ray event has been identified by 14C measurement in several tree rings from all over the world. Although the quasi-decadal 10Be Dome Fuji data in the Antarctic ice core also shows a sharp peak around AD 775, annual 10Be variations in the Dome Fuji core or in other cores have not been revealed. We have measured quasi-annual 10Be concentrations from approximately AD 763–794 in the Dome Fuji ice core, and detected a clear increase (~80% above the baseline) in 10Be concentration around AD 775. However, an accurate height of this increase is not straightforwardly estimated due to the background variation in 10Be concentration. The 10Be increase can be due to the same cosmic ray event as shown in the 14C content in AD 774–775.
The strong 14C increase in the year AD 774/5 detected in one German and two
Japanese trees was recently suggested to have been caused by an impact of a
comet onto Earth and a deposition of large amounts of 14C into the atmosphere
(Liu et al. 2014). The authors supported their claim using a report of a
historic Chinese observation of a comet ostensibly colliding with Earth's
atmosphere in AD 773 January. We show here that the Chinese text presented by
those authors is not an original historic text, but that it is comprised of
several different sources. Moreover, the translation presented in Liu et al. is
misleading and inaccurate. We give the exact Chinese wordings and our English
translations. According to the original sources, the Chinese observed a comet
in mid January 773, but they report neither a collision nor a large coma, just
a long tail. Also, there is no report in any of the source texts about "dust
rain in the daytime" as claimed by Liu et al. (2014), but simply a normal dust
storm. Ho (1962) reports sightings of this comet in China on AD 773 Jan 15
and/or 17 and in Japan on AD 773 Jan 20 (Ho 1962). At the relevant historic
time, the Chinese held that comets were produced within the Earth's atmosphere,
so that it would have been impossible for them to report a "collision" of a
comet with Earth's atmosphere. The translation and conclusions made by Liu et
al. (2014) are not supported by the historical record. Therefore, postulating a
sudden increase in 14C in corals off the Chinese coast precisely in mid January
773 (Liu et al. 2014) is not justified given just the 230Th dating for AD 783
\pm 14.
We have developed techniques for accurately and precisely measuring samples containing less than a few hundred micrograms of carbon, using a compact AMS system (NEC 0.5 MV 1.5SDH-1). Detailed discussions of the sample preparation, measurement setup, data analysis and background corrections for a variety of standard samples ranging from 0.002 to 1 mgC are reported. Multiple aliquots of small amounts of CO2 were reduced to graphite with H2 over pre-baked iron powder catalyst. A reduction reaction temperature of 450 �C was adopted for graphite samples below 0.05 mgC, rather than the usual 550 �C used on samples of 0.1–1 mgC. In our regular reactors (�3.1 cm3), this reduction in temperature improved the graphite yield from �60 to 90–100% for samples ranging from 0.006– 0.02 mgC. The combination of lower reaction temperature with a reduced reactor volume (�1.6 cm3) gave yields as high as 100% on graphite samples <0.006 mgC. High performance measurements on ultra-small samples are possible also due to a modified NEC MC-SNIC ion-source that generates C� currents of 1 lA per lg of carbon for samples in the 0.002 to 0.010 mgC range, combined with on-line measurement of 12C and 13C (AMS d13C) to correct machine-induced isotopic fractionation. Source efficiencies are in excess of 10%, which enables 4–5% of the radiocarbon atoms in 0.005–0.010 mgC samples to be measured. Examination of the background samples revealed two components: (a) 0.2–1 lg of modern carbon and (b) 0.1–0.5 lg of dead carbon. The latter component can be ignored when measuring unknown samples paired to small standards of precisely identical size (matching size normalizing standard method). Otherwise, one must make corrections for both background components. Ultra-small samples from 0.002 to 0.01 mgC can be measured with accuracy and precision of a few percent, based on scatter in results for multiple aliquots of a primary standard and deviations of secondary standards from their known values.
A mysterious increase of radiocarbon 14C ca. 775 AD in the Earth's atmosphere
has been recently found by Miyake et al. (Nature, 486, 240, 2012). A possible
source of this event has been discussed widely, the most likely being an
extreme solar energetic particle event. A new exotic hypothesis has been
presented recently by Liu et al. (Nature Sci. Rep., 4, 3728, 2014) who proposed
that the event was caused by a comet bringing additional 14C to Earth. Here we
calculated a realistic mass and size of such a comet to show that it would have
been huge (~100 km across and 10^{14}-10^{15} ton of mass) and would have
produced a disastrous impact on Earth. Such an impact could not remain
unnoticed in the geological records and chronicles. The absence of an evidence
for such a dramatic event makes this hypothesis invalid.
The main methods applied to clean plant material for radiocarbon dating are not compound-specific and generally remove only the easily exchangeable components by an acid-base-acid sequence and additional optional steps like Soxhlet extraction to remove resins and oxidative bleaching with NaClO2. The products are normally clean enough for standard 14C measurement, but in some cases it is desirable to have pure cellulose, which remains unchanged and immobile over longer time ranges, better representing the original plant material. In this work, 2 more compound-specific but still simple methods were tested to separate the cellulose from wood. The viscose method is based on the xanthification process used in the textile industry, where the alkali-cellulose with CS2 forms a soluble cellulose xanthate, which is then extracted and cellulose is recovered. The second procedure is based on the wood/cellulose dissolution in ionic liquid 1-butyl-3-methylimidazolium chloride [BMIM]Cl, when the dissolved cellulose could be precipitated again by simply adding a water-acetone mixture. This process was recently reported, but still not used in sample preparation procedures for 14C dating. © 2010 by the Arizona Board of Regents on behalf of the University of Arizona.
The NOAA listings of solar flares in cycles 21 – 24, including the GOES soft X-ray magnitudes, enable a simple determination of the number of flares each flaring active region produces over its lifetime. We have studied this measure of flare productivity over the interval 1975 – 2012. The annual averages of flare productivity remained approximately constant during cycles 21 and 22, at about two reported M- or X-flares per region, but then increased significantly in the declining phase of cycle 23 (the years 2004 – 2005). We have confirmed this by using the independent RHESSI flare catalog to check the NOAA events listings where possible. We note that this measure of solar activity does not correlate with the solar cycle. The anomalous peak in flare productivity immediately preceded the long solar minimum between cycles 23 and 24.
We explore the idea that detectable excursions in 26Al may arise from direct
deposition by any bolide, and excursions in 14C and 10Be abundances in the
atmosphere may result from long-period comet impacts. This is very different
from the usual processes of production by cosmic rays within Earths atmosphere.
Long-period comets experience greatly increased cosmic ray flux beyond the
protection of the suns magnetic field. We report the computed amount of 14C,
10Be, and 26Al present on long-period comets as a function of comet mass. We
find that the amount of nuclide mass on large long-period comets entering the
Earths atmosphere may be sufficient for creating anomalies in the records of
14C and 10Be from past impacts. In particular, the estimated mass of the
proposed Younger Dryas comet is consistent with its having deposited sufficient
isotopes to account for recorded 14C and 10Be increases at that time. The
26Al/10Be ratio is much larger in extraterrestrial objects than in the
atmosphere, and so, we note that measuring this ratio in ice cores is a
suitable definitive test for the Younger Dryas impact hypothesis, even if the
hypothetical bolide is not a long-period comet and/or did not contribute to the
14C and 10Be increases.
The cosmogenic nuclide beryllium-10 (10Be), recovered from ice cores, is often used to study solar activity on long timescales. However, the 10Be signal is also influenced by factors other than the Sun. To identify and quantify various contributions to the 10Be signal, two Antarctic snow records from the Vostok and Concordia sites spanning the last 60years were studied at a sub-annual resolution. Three factors that contribute to the 10Be signal were identified. First, a significant period of approximately 11yr that can be associated with the modulation of 10Be production by solar activity was detected in both records. The solar imprint constitutes 20–35% of the variance within the total signal. The 11-yr 10Be snow component was attenuated by a factor of ∼0.5 and was delayed by ∼1.4yr compared to the 10Be production expected within the polar atmosphere. The result could be interpreted as the composite response of a stratospheric 10Be reservoir with an 11-yr modulation that was attenuated and delayed (with respect to 10Be polar production) and to a tropospheric 10Be reservoir with an 11-yr modulation that was not attenuated or delayed. Then, peaks in 10Be concentrations that were ∼66% and ∼35% higher than the average concentration were observed during the stratospheric volcanic eruptions of Agung (in 1963) and Pinatubo (in 1991), respectively. In light of these new results, published 10Be ice core records could be reinterpreted because spikes in 10Be concentration appear at the time of several stratospheric events. The data indicate that stratospheric volcanic eruptions can impact 10Be transport and deposition as a result of the roles played by the sedimentation of sulfate aerosols and the formation and rapid settling of polar stratospheric clouds (PSC). Also, an interannual variability of ∼4yr was determined in both 10Be records, corresponding to ∼26% of the variance within the signal at Vostok. As with species of marine origin (sodium), this 4-yr variability is interpreted as a tropospheric modulation. The 4-yr variability could be associated with atmospheric circulation associated with the coupled Southern Ocean ocean–atmosphere system. The results presented here, from sites within the high Antarctic plateau, open new possibilities for ice core dating over the last few centuries and for the reconstruction of past solar activity in relation to climate.
High-resolution stable isotope analyses were carried out on a sample of oak (Quercus petraea) from Cultra, Co Down, UK. A sampling strategy of unparallelled resolution was adopted in an attempt to reconstruct short-term climatic changes during the growing season. The results display a surprising clarity of signal and suggest a significant relationship between δ 13C and relative humidity and, to a lesser extent, temperature. This preliminary study proposes possible reasons for the isotopic profile observed and highlights the perceived future value of intra-ring isotope studies ('microdendroclimatology').
Solar (heliomagnetic), geomagnetic and oceanic forcing all play a role in atmospheric 14CO2 change. Here we assign the variance associated with certain periodicities in a single year (0-450 cal. BP) and a Holocene bidecadal (0-11400 cal. BP) 14CO2 record to specific forcing factors. In the single-year time series the variance in the 2-6-year periodicity range is attributable to El Niño-Southern Oscillation (ENSO) ocean perturbations. A 10-11-year component is partially tied to solar modulation of the cosmic ray flux, and multidecadal variability may relate to either solar modulation or instability of the North Atlantic thermohaline circulation. For the early Holocene bidecadal 14C record we derive a 512-year atmospheric 14C periodicity which relates to instabilities in North Atlantic thermohaline circulation. North Atlantic deep water formation increased near the start, instead of the termination, of the Younger Dryas interval. The ubiquitous 206-year 14C cycle is assigned either to solar modulation, or to solar modulation modified by a climate (ocean) response. The latter modification is discussed as part of a hypothetical mechanism explaining postulated climate-14C relationships in which a minor solar- induced Maunder Minimum climate change is amplified by salinity effects on North Atlantic thermoha line circulation.
The chronology of ancient Egypt can only be recovered (and then, inexactly) by combining several approaches. These include the sequences of kings and reigns, grouped into dynasties and larger periods. Original documents and interstate synchronisms (plus genealogical data) permit considerable control. To some extent, if their ambiguities can be overcome, lunar and ‘Sothic’ dates from astronomy can help. Other science‐based techniques (e.g., radiocarbon) are not precise enough to help, except in the prehistoric epoch. The margin of error of c. 200 years in early third millennium BC sinks to 20/10 years during the second millennium, and to zero in 664 BC.
New results of radiocarbon concentration in tree rings from the City of Valladolid (Spain) covering a growth period of 22year have been measured using an AMS. Samples were taken using a hollow drill from a living tree, and α-cellulose was extracted from each of annual rings (early and late wood separately). The set of data shows lower radiocarbon concentration than that reported for “clean air” at the reference station, indicating a remarkable input of “dead” CO2 of fossil fuel origin. Using data of carbon dioxide and 14C concentrations from Schauinsland, the corresponding summer and winter values of the fossil component (cf) in carbon dioxide were calculated for the City of Valladolid. By fitting exponential and linear functions to the experimental data, the exchange time was calculated, and the expected future 14C concentration in the atmosphere was estimated.
Measurements of /14C/13C ratios were made on samples of Oxalic Acid and 14C ``dead'' materials spanning the mass range from 10 mug to ~ 1 mg. These measurements have allowed the determination of both the amount, and the 14C content, of the contaminant carbon introduced during sample processing in our laboratory. These data were used to corner measured /14C/13C ratios obtained from ANU Sucrose and `` ~ one-half-life old'' test samples for the influence of the contaminant. The test samples spanned the 10 mug to ~ 1 mg mass range and the corrections were made using three different formulae. The results obtained from these calculations allow the accuracy of these background correction formulae to be evaluated.
Previously, we have observed that the atmospheric (14)C content measured in tree rings showed a strong increase from AD 774 to 775. Although the cause of this event can be explained by a large solar proton event or a short gamma-ray burst, a more detailed discussion of the cause is difficult because the rate of occurrence of such rapid (14)C events remains unknown. Here we report new (14)C measurements from AD 822 to 1020, and the discovery of a second rapid increase of (14)C content from AD 992 to 993. The (10)Be flux in the Antarctic ice core shows peaks corresponding to these two (14)C events. The proportions of flux increase ((14)C/(10)Be) of the two events are consistent with each other. Therefore, it is highly possible that these events have the same origin. Considering the occurrence rate of (14)C increase events, solar activity is a plausible cause of the (14)C increase events.
We examine possible sources of a substantial increase in tree ring 14C
measurements for the years AD 774-775. Contrary to claims regarding a coronal
mass ejection (CME), the required CME energy is not several orders of magnitude
greater than known solar events. We consider solar proton events (SPEs) with
three different fluences and two different spectra. The data may be explained
by an event with fluence about one order of magnitude beyond the October 1989
SPE. Two hard spectrum cases considered here result in moderate ozone
depletion, so no mass extinction is implied, though we do predict increases in
erythema and damage to plants from enhanced solar UV. We are able to rule out
an event with a very soft spectrum that causes severe ozone depletion and
subsequent biological impacts. Nitrate enhancements are consistent with their
apparent absence in ice core data. The modern technological implications of
such an event may be extreme, and considering recent confirmation of
superflares on solar-type stars, this issue merits attention.
The $^{14}$C production of shock-accelerated particles is calculated in terms
of the total energy released in energetic particles. The recently reported 1.2%
jump in the $^{14}$C content of the atmosphere in the year C.E. 775, it is
found, would require $\gtrsim 10^{34}$ erg in energetic particles, less than
first estimates but far more than any known solar flare on record. It is noted
that the superflare from a large comet (comparable to C/Hale-Bopp) colliding
with the sun could produce shock-accelerated GeV cosmic rays in the solar
corona and/or solar wind, and possibly account for the CE 775 event. Several
additional predictions of cometary encounters with the sun and other stars may
be observable in the future.