Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Geophysical Union (AGU)  

Prominent excursions in the number of cosmogenic nuclides (e.g., 10Be) around 774 CE/775 document the most severe solar proton event (SPE) throughout the Holocene. Its manifestation in ice cores is valuable for geochronology, but also for solar-terrestrial physics and climate modeling. Using the ECHAM/MESSy Atmospheric Chemistry (EMAC) climate model in combination with the Warning System for Aviation Exposure to SEP (WASAVIES), we investigate the transport, mixing, and deposition of the cosmogenic nuclide 10Be produced by the 774 CE/775 SPE. By comparing the model results to the reconstructed 10Be time series from four ice core records, we study the atmospheric pathways of 10Be from its stratospheric source to its sink at Earth's surface. The reconstructed post-SPE evolution of the 10Be surface fluxes at the ice core sites is well captured by the model. The downward transport of the 10Be atoms is controlled by the Brewer-Dobson circulation in the stratosphere and cross-tropopause transport via tropopause folds or large-scale sinking. Clear hemispheric differences in the transport and deposition processes are identified. In both polar regions the 10Be surface fluxes peak in summertime, with a larger influence of wet deposition on the seasonal 10Be surface flux in Greenland than in Antarctica. Differences in the peak 10Be surface flux following the 774 CE/775 SPE at the drilling sites are explained by specific meteorological conditions depending on the geographic locations of the sites.

DOI： 10.1029/2021JD035658

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Other Link： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2021JD035658

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Frontiers Media SA  

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.

DOI： 10.3389/fspas.2022.886140

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Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Geophysical Union (AGU)  

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.

DOI： 10.1029/2021JA029378

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Scopus

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Proceedings of Science  

Ion-induced nucleation by cosmic rays influenced by solar modulation is of interest, and several studies with radioactive sources or accelerator beams have been performed. We focused on ionization with high-linear energy transfer (LET) particles, such as protons, neutrons, and ions, in secondary cosmic rays and the ion density of the secondary cosmic rays near the ground using the excel-based program for calculating atmospheric cosmic-ray spectrum (EXPACS). According to the calculation, not only muons but also protons and neutrons leave substantial traces of solar modulation at an altitude of 3 km from the ground. To verify the ion-induced nucleation by these secondary high-LET cosmic rays, a chamber experiment was conducted at the accelerator facility HIMAC. Using a chamber with a capacity of 75 L, experiments were conducted by irradiating protons and nitrogen ion beams with a constant energy of 180 MeV/u with varying intensity. The experimental results confirm that the ion density and aerosol density increased as the beam intensity increased. The aerosol density was found to be proportional to the ion density, but irrelevant to the ionization density. It was concluded that the ion-induced nucleation by high-LET secondary cosmic rays, such as protons and neutrons, provides no evidence of enhancement owing to ionization density and cannot account for the claimed variation of cloud formation due to the solar modulation.

Scopus

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Proceedings of Science  

Terrestrial cosmogenic nuclides (e.g., 14C, 10Be, and 36Cl) are primarily produced by galactic cosmic rays. However, a certain amount of these nuclides is also produced by solar energetic particles (SEPs) derived from sporadic solar events such as solar flares and coronal mass ejections. Cosmic ray increase events in AD 774/775, AD 993/994 (or AD 992/993), and ~BC 660 have been discovered using 14C data in tree rings (Miyake et al. 2012, 2013; Park et al. 2017). It is considered that the most plausible cause of these events was an extreme SEP events with very hard energy spectra based on 14C analyses of tree rings and 10Be and 36Cl analyses of ice cores (e.g., Mekhaldi et al. 2015; Miyake et al. 2015, 2019; Büntgen et al. 2018; O'Hare et al. 2019). These SEP events are estimated to be several dozens of times larger than the largest events seen in direct observations, and an event of that size might have a serious impact on modern society. Therefore, it is important to investigate the occurrence rate of past extreme events. In recent years, surveys of past SEP events have been actively conducted via cosmogenic nuclide measurements with high time resolution (~one-year resolution). Here the detected past SEP candidates and a further survey of similar events are reviewed.

Scopus

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

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.

DOI： 10.1029/2021GL093419

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PubMed

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Applied Physics  

DOI： 10.11470/jsapmeeting.2020.2.0_356

Language：Japanese   Publishing type：Research paper (scientific journal)  

© 2020 Cambridge University Press. All rights reserved. The radiocarbon (C) calibration curve so far contains annually resolved data only for a short period of time. With accelerator mass spectrometry (AMS) matching the precision of decay counting, it is now possible to efficiently produce large datasets of annual resolution for calibration purposes using small amounts of wood. The radiocarbon intercomparison on single-year tree-ring samples presented here is the first to investigate specifically possible offsets between AMS laboratories at high precision. The results show that AMS laboratories are capable of measuring samples of Holocene age with an accuracy and precision that is comparable or even goes beyond what is possible with decay counting, even though they require a thousand times less wood. It also shows that not all AMS laboratories always produce results that are consistent with their stated uncertainties. The long-term benefits of studies of this kind are more accurate radiocarbon measurements with, in the future, better quantified uncertainties.

DOI： 10.1017/RDC.2020.49

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：UNIV ARIZONA DEPT GEOSCIENCES  

Radiocarbon (C-14) ages cannot provide absolutely dated chronologies for archaeological or paleoenvironmental studies directly but must be converted to calendar age equivalents using a calibration curve compensating for fluctuations in atmospheric C-14 concentration. Although calibration curves are constructed from independently dated archives, they invariably require revision as new data become available and our understanding of the Earth system improves. In this volume the international C-14 calibration curves for both the Northern and Southern Hemispheres, as well as for the ocean surface layer, have been updated to include a wealth of new data and extended to 55,000 cal BP. Based on tree rings, IntCal20 now extends as a fully atmospheric record to ca. 13,900 cal BP. For the older part of the timescale, IntCal20 comprises statistically integrated evidence from floating tree-ring chronologies, lacustrine and marine sediments, speleothems, and corals. We utilized improved evaluation of the timescales and location variable C-14 offsets from the atmosphere (reservoir age, dead carbon fraction) for each dataset. New statistical methods have refined the structure of the calibration curves while maintaining a robust treatment of uncertainties in the C-14 ages, the calendar ages and other corrections. The inclusion of modeled marine reservoir ages derived from a three-dimensional ocean circulation model has allowed us to apply more appropriate reservoir corrections to the marine C-14 data rather than the previous use of constant regional offsets from the atmosphere. Here we provide an overview of the new and revised datasets and the associated methods used for the construction of the IntCal20 curve and explore potential regional offsets for tree-ring data. We discuss the main differences with respect to the previous calibration curve, IntCal13, and some of the implications for archaeology and geosciences ranging from the recent past to the time of the extinction of the Neanderthals.

DOI： 10.1017/RDC.2020.41

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Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATURE PUBLISHING GROUP  

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.

DOI： 10.1038/s41598-019-57273-2

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PubMed

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1088/2514-3433/ab404ach6

Web of Science

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1088/2514-3433/ab404ach5

Web of Science

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1088/2514-3433/ab404ach7

Web of Science

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1088/2514-3433/ab404ach1

Web of Science

Language：English   Publishing type：Research paper (scientific journal)  

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)  

Extreme cosmic radiation events occurred in the years 774/5 and 993/4 CE, as revealed by anomalies in the concentration of radiocarbon in known-age tree-rings. Most hypotheses point towards intense solar storms as the cause for these events, although little direct experimental support for this claim has thus far come to light. In this study, we perform very high-precision accelerator mass spectrometry (AMS) measurements on dendrochronological tree-rings spanning the years of the events of interest, as well as the Carrington Event of 1859 CE, which is recognized as an extreme solar storm even though it did not generate an anomalous radiocarbon signature. Our data, comprising 169 new and previously published measurements, appear to delineate the modulation of radiocarbon production due to the Schwabe (11-year) solar cycle. Moreover, they suggest that all three events occurred around the maximum of the solar cycle, adding experimental support for a common solar origin.

DOI： 10.1038/s41598-019-53296-x

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PubMed

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

Auroral records found in historical archives and cosmogenic isotopes found in natural archives have served as sound proxies of coronal mass ejections and solar energetic particles (SEPs), respectively, for dates prior to the onset of telescopic sunspot observations in 1610. These space weather events constitute a significant threat to a modern civilization, because of its increasing dependency on an electronic infrastructure. Recent studies have identified multiple extreme space weather events derived from SEPs in natural archives, such as the event in 660 BCE. While the level of solar activity around 660 BCE is of great interest, this had not been within the coverage of the hitherto-known datable auroral records in historical documents that extend back to the 6th century BCE. Therefore, we have examined Assyrian astrological reports in the 8th and 7th centuries BCE, identified three observational reports of candidate aurorae, and dated these reports to approximately 680 BCE-650 BCE. The Assyrian cuneiform tablets let us extend the history of auroral records and solar activity by a century. These cuneiform reports are considered to be the earliest datable records of candidate aurorae and they support the concept of enhanced solar activity suggested by the cosmogenic isotopes from natural archives.

DOI： 10.3847/2041-8213/ab42e4

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Scopus

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：Japanese   Publishing type：Research paper (other academic)  

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Geophysical Union ({AGU})  

DOI： 10.1029/2018GL080475

Web of Science

Scopus

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Proceedings of Science  

Terrestrial cosmogenic nuclides (e.g., 14C, 10Be, and 36Cl) are primarily produced by galactic cosmic rays. However, a certain amount of these nuclides is also produced by solar energetic particles (SEPs) derived from sporadic solar events such as solar flares and coronal mass ejections. Cosmic ray increase events in AD 774/775, AD 993/994 (or AD 992/993), and ~BC 660 have been discovered using 14C data in tree rings (Miyake et al. 2012, 2013; Park et al. 2017). It is considered that the most plausible cause of these events was an extreme SEP events with very hard energy spectra based on 14C analyses of tree rings and 10Be and 36Cl analyses of ice cores (e.g., Mekhaldi et al. 2015; Miyake et al. 2015, 2019; Büntgen et al. 2018; O'Hare et al. 2019). These SEP events are estimated to be several dozens of times larger than the largest events seen in direct observations, and an event of that size might have a serious impact on modern society. Therefore, it is important to investigate the occurrence rate of past extreme events. In recent years, surveys of past SEP events have been actively conducted via cosmogenic nuclide measurements with high time resolution (~one-year resolution). Here the detected past SEP candidates and a further survey of similar events are reviewed.

Scopus

Language：English   Publishing type：Research paper (international conference proceedings)  

Ion-induced nucleation by cosmic rays influenced by solar modulation is of interest, and several studies with radioactive sources or accelerator beams have been performed. We focused on ionization with high-linear energy transfer (LET) particles, such as protons, neutrons, and ions, in secondary cosmic rays and the ion density of the secondary cosmic rays near the ground using the excel-based program for calculating atmospheric cosmic-ray spectrum (EXPACS). According to the calculation, not only muons but also protons and neutrons leave substantial traces of solar modulation at an altitude of 3 km from the ground. To verify the ion-induced nucleation by these secondary high-LET cosmic rays, a chamber experiment was conducted at the accelerator facility HIMAC. Using a chamber with a capacity of 75 L, experiments were conducted by irradiating protons and nitrogen ion beams with a constant energy of 180 MeV/u with varying intensity. The experimental results confirm that the ion density and aerosol density increased as the beam intensity increased. The aerosol density was found to be proportional to the ion density, but irrelevant to the ionization density. It was concluded that the ion-induced nucleation by high-LET secondary cosmic rays, such as protons and neutrons, provides no evidence of enhancement owing to ionization density and cannot account for the claimed variation of cloud formation due to the solar modulation.

Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATURE PUBLISHING GROUP  

DOI： 10.1038/s41467-018-07636-6

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Scopus

PubMed

Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATURE PUBLISHING GROUP  

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 C-14 content in 484 individual tree rings formed in the periods 770-780 and 990-1000 CE. Distinct C-14 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 C-14 measurements are needed.

DOI： 10.1038/s41467-018-06036-0

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PubMed

Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)  

Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：UNIV ARIZONA DEPT GEOSCIENCES  

Two radiocarbon (C-14) 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 C-14 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 C-14 ages in the period from 800-400 BC. We compare results of annual C-14 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.

DOI： 10.1017/RDC.2018.53

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：UNIV ARIZONA DEPT GEOSCIENCES  

The so-called Millennium Eruption of Baitoushan Volcano is one of the largest of the Common Era but its date has been uncertain. Recently, Oppenheimer et al. (2017) reported the eruptive year as late AD 946 using a new method called carbon-14 spike matching. However, it is necessary to verify their result to confirm the eruptive year, since only one wood sample was used in their study. We verified the eruptive year by measuring C-14 contents in tree rings from another wood sample buried during the Baitoushan eruption. We succeeded in reproducing the AD 774-775 C-14 spike (Miyake et al. 2012), and counted the number of rings from the outermost ring accompanied by bark to the ring possessing the AD 774-775 C-14 spike. We found the outermost ring was formed in AD 946. Our study supported the result of Oppenheimer et al. (2017), which makes the eruptive year conclusive. Also, we suggest that the C-14 spike-matching method can be a prominent dating tool applicable to ancient woods that are difficult to date using the usual dendrochronology techniques.

DOI： 10.1017/RDC.2017.75

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：GEOCHEMICAL SOCIETY OF JAPAN  

<p>Recently, the increase of cosmic ray flux was found around 5480 BC using the ¹⁴C measurements for tree rings with 1- to 2-y resolution. It is assumed that it may be caused by the large solar flares but we cannot specify the detail cause of this event. In this study, we aim to elucidate the cause of 5480 BC cosmic ray event by measuring ¹⁰Be and ³⁶Cl in the ice core which was drilled at the Dome Fuji Station in Antarctica, and investigate the variation of cosmic ray flux around 5480 BC. The result of ³⁶Cl concentration variation using the Accelerator Mass Spectrometry (AMS) system in the University of Tsukuba is reported in this presentation. In addition, the performance of ¹⁰Be-AMS and the future plan is also presented.</p>

DOI： 10.14862/geochemproc.65.0_230

CiNii Research

Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)  

Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)  

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：UNIV ARIZONA DEPT GEOSCIENCES  

Single-year spikes in radiocarbon production are caused by intense bursts of radiation from space. Supernovae emit both high-energy particle and electromagnetic radiation, but it is the latter that is most likely to strike the atmosphere all at once and cause a surge in C-14 production. In the 1990s, it was claimed that the supernova in 1006 CE produced exactly this effect. With the C-14 spikes in the years 775 and 994 CE now attributed to extreme solar events, attention has returned to the question of whether historical supernovae are indeed detectable using annual C-14 measurements. Here, we combine new and existing measurements over six documented and putative supernovae, and conclude that no such astrophysical event has yet left a distinct imprint on the past atmospheric C-14 record.

DOI： 10.1017/RDC.2016.50

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：UNIV ARIZONA DEPT GEOSCIENCES  

Two radiocarbon excursions (AD 774-775 and AD 993-994) occurred due to an increase of incoming cosmic rays on a short timescale. The most plausible cause of these events is considered to be extreme solar proton events (SPE). It is possible that there are other annual C-14 excursions in the past that have yet to be confirmed. In order to detect more of these events, we measured the C-14 contents in bristlecone pine tree-ring samples during the periods when the rate of C-14 increase in the IntCal data is large. We analyzed four periods every other year (2479-2455 BC, 4055-4031 BC, 4465-4441 BC, and 4689-4681 BC), and found no anomalous C-14 excursions during these periods. This study confirms that it is important to do continuous measurements to find annual cosmic-ray events at other locations in the tree-ring record.

DOI： 10.1017/RDC.2016.54

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Scopus

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：NATURE PUBLISHING GROUP  

Sporadic solar energetic particle (SEP) events affect the Earth's atmosphere and environment, in particular leading to depletion of the protective ozone layer in the Earth's atmosphere, and pose potential technological and even life hazards. The greatest SEP storm known for the last 11 millennia (the Holocene) occurred in 774-775 AD, serving as a likely worst-case scenario being 40-50 times stronger than any directly observed one. Here we present a systematic analysis of the impact such an extreme event can have on the Earth's atmosphere. Using state-of-the-art cosmic ray cascade and chemistry-climate models, we successfully reproduce the observed variability of cosmogenic isotope Be-10, around 775 AD, in four ice cores from Greenland and Antarctica, thereby validating the models in the assessment of this event. We add to prior conclusions that any nitrate deposition signal from SEP events remains too weak to be detected in ice cores by showing that, even for such an extreme solar storm and sub-annual data resolution, the nitrate deposition signal is indistinguishable from the seasonal cycle. We show that such a severe event is able to perturb the polar stratosphere for at least one year, leading to regional changes in the surface temperature during northern hemisphere winters.

DOI： 10.1038/srep45257

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PubMed

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATL ACAD SCIENCES  

Radiocarbon content in tree rings can be an excellent proxy of the past incoming cosmic ray intensities to Earth. Although such past cosmic ray variations have been studied by measurements of C-14 contents in tree rings with &gt;= 10-y time resolution for the Holocene, there are few annual C-14 data. There is a little understanding about annual C-14 variations in the past, with the exception of a few periods including the AD 774-775 C-14 excursion where annual measurements have been performed. Here, we report the result of C-14 measurements using the bristlecone pine tree rings for the period from 5490 BC to 5411 BC with 1- to 2-y resolution, and a finding of an extraordinarily large C-14 increase (20 parts per thousand) from 5481 BC to 5471 BC (the 5480 BC event). The C-14 increase rate of this event is much larger than that of the normal grand solar minima. We propose the possible causes of this event are an unknown phase of grand solar minimum, or a combination of successive solar proton events and a normal grand solar minimum.

DOI： 10.1073/pnas.1613144114

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PubMed

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.quaint.2015.04.014

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/2014GL062218

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.2458/56.17769

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/2012JA018320

Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publisher：The Japan Society of Applied Physics  

DOI： 10.11470/jsapmeeting.2020.1.0_595

Language：Japanese   Publisher：The Japan Society of Applied Physics  

DOI： 10.11470/jsapmeeting.2020.1.0_602

Language：Japanese   Publisher：The Japan Society of Applied Physics  

DOI： 10.11470/jsapmeeting.2020.1.0_603

Other Link： https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-20K20918/

Language：Japanese   Publisher：The Japan Society of Applied Physics  

DOI： 10.11470/jsapmeeting.2019.2.0_542

Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.74.1.0_466

J-GLOBAL

Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.74.2.0_407

Language：Japanese   Publisher：The Japan Society of Applied Physics  

DOI： 10.11470/jsapmeeting.2018.2.0_54

Language：Japanese  

J-GLOBAL

Language：Japanese   Publisher：The Volcanological Society of Japan  

DOI： 10.18940/vsj.2018.0_230

Language：Japanese   Publisher：GEOCHEMICAL SOCIETY OF JAPAN  

Recently, the increase of cosmic ray flux was found around 5480 BC using the ¹⁴C measurements for tree rings with 1- to 2-y resolution. It is assumed that it may be caused by the large solar flares but we cannot specify the detail cause of this event. In this study, we aim to elucidate the cause of 5480 BC cosmic ray event by measuring ¹⁰Be and ³⁶Cl in the ice core which was drilled at the Dome Fuji Station in Antarctica, and investigate the variation of cosmic ray flux around 5480 BC. The result of ³⁶Cl concentration variation using the Accelerator Mass Spectrometry (AMS) system in the University of Tsukuba is reported in this presentation. In addition, the performance of ¹⁰Be-AMS and the future plan is also presented.

DOI： 10.14862/geochemproc.65.0_230

CiNii Research

Language：Japanese   Publishing type：Internal/External technical report, pre-print, etc.  

Language：Japanese  

To investigate the 14C concentration of atmospheric CO2 over the past few millennia in Japan, we measured the 14C age of annual rings from several Japanese trees with calendar dates ranging from ca. 2000 yr old to present, and we compared the tree-ring 14C age with the corresponding 14C age of IntCal13. It was revealed that the 14C age of the annual rings of Japanese trees are not consistent with IntCal13 datasets in some instances. Many cases of 14C age of tree rings are older than those of IntCal13, but younger than those of SHCal13 datasets. The average shift in Nagoya 14C age from IntCal13 datasets and one-sigma errors were obtained to be +26±36, +24±30, +16±22, +5±21, and +14±22 14C yr for the intervals AD72-382, AD589-1072, AD1413-1615, AD1617-1739, and AD1790-1860, respectively. In addition, a wood sample collected from northern end of the mainland of Japan also showed a value of +35±22 14C yr shifted older than IntCal13. We also analyzed 14C age data obtained for trees grown up in Korea, and yielded the values of +17±35 and +6±35 14C yr for the intervals AD1250-1650 and AD 1650-1850, respectively. The Japanese archipelago is situated near the boundary of the inter-tropical convergence zone in summer, and the 14C concentration of atmospheric CO2 over Japan can be influenced by air masses of the Southern Hemisphere with lower 14C concentrations during periods of higher solar activity and heightened East Asian summer monsoons. Korean Peninsula is also influenced by air masses of the Southern Hemisphere. Present results suggest that the southeast end of Eurasian Continent is located in the critical zone from where it is difficult to calibrate the 14C age of tree ring samples using existing calibration datasets. At the moment, it should be noted that calibration of the 14C dates of Japanese samples with IntCal13 induces additional systematic shifts of calibrated ages toward older ages by about 10-30 yr compared with the sample optimum calendar ages.

DOI： 10.18999/nagubc.1.108

Other Link： http://hdl.handle.net/2237/00028479

Language：English   Presentation type：Oral presentation (keynote)  

Language：English   Presentation type：Oral presentation (general)  

Language：English   Presentation type：Oral presentation (general)  

Language：English   Presentation type：Oral presentation (general)  

Language：English   Presentation type：Oral presentation (general)  

Language：English   Presentation type：Oral presentation (general)  

Language：English   Presentation type：Oral presentation (general)  

Language：English   Presentation type：Oral presentation (general)  

Language：English   Presentation type：Oral presentation (general)  

Language：English   Presentation type：Oral presentation (general)  

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