C03_01

The ice core radionuclide perspective on past cosmic ray events

Muscheler R¹, Paleari C¹, Mekhaldi F^1,2, Nguyen L¹, Zheng M^1,4, Adolphi F³, Christl M⁴, Vockenhuber C⁴, Gautschi P⁴, Beer J⁵, Brehm N⁴, Erhardt T^3,6, Wacker L⁴, Nilsson A¹, Herbst K⁷

¹Lund University, Lund, Sweden, ²British Antarctic Survey, Cambridge, UK, ³Alfred-Wegener-Institut , Bremerhaven, Germany, ⁴ETH Zürich, Zürich, Switzerland, ⁵Swiss Federal Institute of Aquatic Science and Technology, Dübendorf, Switzerland, ⁶University of Bern, Bern, Switzerland, ⁷Christian-Albrechts-Universität zu Kiel, Kiel, Germany

The recent discovery of strong and rapid radionuclide production enhancements has opened up a whole new field of paleo space weather research. In this presentation we will give an overview of the present status of the ice-core based assessment of past cosmic ray events in comparison to radiocarbon records. We will review the present detection limit and show the comparison of the proposed radionuclide spikes in tree-ring radiocarbon with ice core ¹⁰Be and ³⁶Cl records. We will discuss unresolved issues in either the carbon cycle, ¹⁰Be and ³⁶Cl transport and deposition and/or their theoretical production rates. Furthermore, we will discuss the potential of these rapid production rate enhancements for climate research in general. 

C03_02

A Polar Bias in Ice Core ¹⁰Be-Data

Adolphi F¹, Herbst K², Nilsson A³, Panovska S⁴

¹Alfred Wegener Institute For Polar And Marine Research, Bremerhaven, Germany, ²Institut für Experimentelle und Angewandte Physik, Christian-Albrechts-Universität zu Kiel, Kiel, Germany, ³Department of Geology, Lund University, Lund, Sweden, ⁴GFZ German Research Centre for Geosciences, Helmholtz Centre Potsdam, Potsdam, Germany

Cosmogenic radionuclide records from polar ice cores provide unique insights into past cosmic ray flux variations. Besides allowing reconstructions of past solar activity, space weather, and geomagnetic field changes, they provide independent estimates of radiocarbon production rate changes in the past and are thus, an independent means to assess the radiocarbon calibration curve. However, all these applications rely on the proportionality of the ice core radionuclide records to the global mean production rate changes. This premise has been long debated from the model and data perspective. Here, we address this issue through atmospheric mixing model experiments and comparison to independent data. We find that all mixing scenarios that do not assume complete tropospheric mixing result in a polar bias. This bias is more prominent for geomagnetic field changes than solar modulation changes. Supported by independent geomagnetic field records and marine ¹⁰Be, the most likely scenario results in a dampening of geomagnetic field-induced changes by 23-37% and an enhancement of solar-induced changes by 7-8%. We propose a correction function that allows deconvolving the ice core to restore proportionality to the global mean signal and discuss the relevance for understanding past variations in Δ¹⁴C.

C03_03

Detection of solar events by using radiocarbon in tree-rings

Brehm N¹, Christl M¹, Adolphi F², Casanova E^3,4, Evershed R.P⁴, Muscheler R⁵, Synal H¹, Mekhaldi F⁵, Paleari C⁵, Knowles T⁴, Bayliss A⁶, Nicolussi K⁷, Pearson C⁸, Fonti P⁹, Nievergelt D⁹, Hanterimov R¹⁰, Wacker L¹

¹Eth Zürich, Zürich, Switzerland, ²Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany, ³Muséum National d’Histoire Naturelle, Paris, France ⁴University of Bristol, Bristol, UK, ⁵Lund University, Lund, Sweden, ⁶Historic England, London, UK, ⁷Universität Innsbruck, Innsbruck, Austria, ⁸University of Arizona, Tucson, USA, ⁹Eidgenössische Forschungsanstalt WSL, Birmensdorf, Switzerland, ¹⁰Laboratory of Dendrochronology, Institute of Plant and Animal Ecology, Ekaterinburg, Russia

The Sun irregularly expels large amounts of highly energetic particles into the interplanetary space and towards Earth which can be observed as so-called solar energetic particle (SEP) events. SEP events can potentially cause major damage to satellites and can even disrupt sensitive electronic systems at ground level. While direct observations of SEP events are limited to the last few decades, cosmogenic radionuclides such as ¹⁴C can be used to detect and study them much further back in time.

The production rate of cosmogenic nuclides, such as ¹⁴C, is primarily dependent on the incoming flux of highly energetic galactic cosmic rays. Normally solar particles expelled into the interplanetary space have not sufficient energy to cause radionuclide production in the Earth atmosphere, but SEP events may cause sudden increases in radionuclide production.

Analyzing ¹⁴C concentrations in annual tree-rings from Switzerland, Germany, Ireland, Russia, and the USA, we recently discovered two new spikes in atmospheric ¹⁴C in 7176 and 5259 BCE. The ~2% increases of atmospheric ¹⁴C recorded for both events exceed all previously known ¹⁴C peaks. Here we summarize and characterize all the found ¹⁴C production events that are attributed to SEP events. We find that the two newly found events are comparable to the largest event of this type discovered so far at 775 CE.

C03_04

Annual dating of Late Glacial trees from the French Alps. Implications of a spike at ca. 14.3 cal kyr BP

Bard E¹, Miramont C², Capano M¹, Guibal F², Marschal C², Rostek F¹, Tuna T¹, Fagault Y¹

¹CEREGE, Aix-en-provence, France, ²IMBE, Aix-en-Provence, France

We present new ¹⁴C results measured on subfossil Scots pines recovered in the eroded banks of the Drouzet watercourse in the region of the middle course of Durance River in the Southern French Alps. Recent fieldwork enabled us to complement previous studies starting with Miramont et al. (2000 Radiocarbon). Dendro-matching of wood sequences allowed to construct 3 chronologies with durations ranging between 200 and 400 years, each including between 23 to 59 individual trees. Selected trees were sampled at annual resolution and every third ring was pretreated by using methods previously developed for trees from the nearby site of Barbiers (Capano et al. 2018, 2020 Radiocarbon included in IntCal20 Reimer al. 2020 Radiocarbon). So far, about 400 new ¹⁴C ages were measured on 15 trees, which allowed to construct a ≈ 700-yr long chronology. Preliminary matching with the Late Glacial German pine chronology shows that the Drouzet chronology reaches ca.14.4 cal kyr BP. The resulting ∆¹⁴C record exhibits a century-long event between 14 and 13.9 cal kyr BP and a large and abrupt spike occurring in a single year around 14.3 cal kyr BP (evidenced in 2 dendro-matched trees). We will compare our record with that obtained in a floating tree from Northern Italy (Adolphi et al. 2017 QSR). The abrupt spike around 14.3 cal kyr BP, together with the length of the Drouzet record and its long overlap with the German pine chronology should be helpful to refine the comparison and tuning between the Greenland ice and IntCal chronologies.

C03_05

Toward detections of ¹⁴C spikes: regional differences in ¹⁴C data

Miyake F¹, Hakozaki M², Kimura K³, Tokanai F⁴, Nakamura T¹, Takeyama M⁴, Moriya T⁴, Panyushkina I⁵, Hantemirov R⁶, Helama S⁷, Jull A⁵

¹Nagoya University, Nagoya, Japan, ²National Museum of Japanese History, Sakura, Japan, ³Fukushima University, Fukushima, Japan, ⁴Yamagata University, Yamagata, Japan, ⁵University of Arizona, Tucson, USA, ⁶Institute of Plant and Animal Ecology, Ekaterinburg, Russia, ⁷Natural Resources Institute Finland, Rovaniemi, Finland

Annual ¹⁴C data in tree rings is a good proxy for past extreme solar energetic particle (SEP) events. As far, several signatures of extreme SEP events have been found in ¹⁴C data, such as 774 CE, 993 CE, 660 BCE, and 5259 BCE events. Although these events are characterized by a rapid ¹⁴C increase and a following decrease, ¹⁴C data recorded worldwide do not always show similar variations. Such regional differences in ¹⁴C data hinder a consistent understanding of the event and a detection of small 14C spikes, and affect a dating using ¹⁴C spikes. Here, we focus on a timing of rapid ¹⁴C increases and discuss a possible relationship with the atmospheric transport effect.

C03_06

On Proposed New Single-Year Radiocarbon Production Events and the Limits of Event Detectability

Scifo A¹, Abi Nassif T¹, Zhang Q², Sharma U², Bayliss A⁴, Marshall P⁴, Pope B^2,3, Dee M¹

¹Centre For Isotope Research (CIO), University of Groningen, Groningen, the Netherlands, ²School of Mathematics and Physics, The University of Queensland, St Lucia, Australia, ³Centre for Astrophysics, University of Southern Queensland, Toowoomba, Australia, ⁴Historic England, London, United Kingdom

Over the last decade, the field of radiocarbon analysis has been revolutionised by the discovery of single-year production anomalies, sometimes called Miyake events, as they are both indicators of extreme space weather phenomena, and useful as anchors for exact-year dating. Brehm et al. (2021) proposed two new candidate events in the years 1052 and 1279 CE. Their data showed annual ∆¹⁴C increases over these years of 5.9‰ and 6.5‰, respectively. We have also recently analysed dendrochronologically dated samples spanning these two periods of time, from Furness Abbey and Apethorpe Church, England. Our results, although statistically consistent (at 2σ) with those presented by Brehm et al. (2021), show much less obvious increases of around 4.5‰ and 3‰, respectively. Furthermore, we have also modelled our new datasets, as well as those of Brehm et al. (2021), in ticktack, the first open-source Python package that connects box models of the carbon cycle with modern Bayesian inference tools (Zhang et al., forthcoming). The radiocarbon production rates we obtain pose questions about the actuality of cosmic ray events at these times, and the limits of detectability of such phenomena more generally.

Brehm et al. (2021). Eleven-year solar cycles over the last millennium revealed by radiocarbon in tree rings. Nature Geoscience 14: 10–15.

Zhang et al. (forthcoming). Bayesian inference of radiocarbon production from tree-ring data.

C03_07

New records of ¹⁴C excursions at 664/62 BCE and 1279/81 CE from Inner Eurasia examine signal timing

Jull A^1,2, Panyushkina I³, Molnar M², Varga T², Livina V⁴, Sljusarenko I⁵, Myglan V⁶, Miyake F⁷

¹University Of Arizona, Tucson, United States, ²Institute for Nuclear Research, Debrecen, Hungary, ³Laboratory for Tree-Ring Research, Tucson, USA, ⁴National Physical Laboratory, Teddington, UK, ⁵Institute of Archaeology and Ethnography, Novosibirsk, Russia, ⁶Siberian Federal University, Krasnoyarsk, Russia, ⁷Institute for Space-Earth Environmental Research, Nagoya, Japan

Excursions in the annual ¹⁴C production rate in the atmosphere are manifest in an excess of up to 20 ‰ in tree rings, caused by transient increases in the ¹⁴C production rate. These signals rise rapidly over a period of 1-2 yr and has a decay time of about 15-20 yr. These events are generally explained as a rapid increase of incoming cosmic rays or gamma rays. Only a few have been reproduced in multiple tree-ring records from many locations around the globe, particularly at 7176BCE, 5259BCE, ~660BCE, 774-775CE and 993-994CE reported by different laboratories. These excursions are positively connected to the impact of strong Solar Energetic Particles (SEP) events and are also observed from ¹⁰Be and ³⁶Cl excursions in polar ice cores. Other proposed events show different structures and either coincide with Grand Solar Minima or other effects of a lesser magnitude. These include reported events at 815BCE, 5480BCE, 5410BCE, 1052/1054CE and 1279CE events. We focus on a new detailed record of the 664-662BCE event from the Altai Mountains. It appears that the intensity and structure of the ¹⁴C signal is multifaced in space and time, which complicates understanding of the forcing and attribution to the underlying astrophysical events. Timing of these events is important to register the recurrence intervals of these events for past and future ¹⁴C excursions. We investigated the time concordance of a number of these events and possible explanations.

C03_08

Finding smaller solar particle events from tree-ring ¹⁴C time-series data

Uusitalo J^1,2,3, Hackman T^1,3, Oinonen M^1,2

¹University Of Helsinki, Helsinki, Finland, ²Finnish Museum of Natural History, Helsinki, Finland, ³Department of Physics, Helsinki, Finland

Tree-ring ¹⁴C measurements are an excellent way for studying past solar particle events (SPEs) and other anomalous astronomical phenomena. Following the discovery of the AD 774 solar storm by Miyake et al. in 2012, the number of annually resolved tree-ring ¹⁴C measurements have grown significantly. Since then, these annually resolved measurements have led to new discoveries that are similar in magnitude with the Miyake event. However, assuming a power-law distribution for SPEs, one would expect there to be many more less intense particle events causing smaller ¹⁴C spikes, yet only few such candidates have been found. One reason for this could be that it is hard to separate the signal from the statistical noise and short-term natural variability, caused mainly by the 11-year solar cycle, so many smaller events might end up being missed. However, it should be possible to spot new and so far unrecognized events using time-series methods specifically built for this purpose. In this work, we present one such new method that takes into account the respective ¹⁴C baseline, the sudden increase and the full shape of the event. Furthermore, we analyze and discuss how the longer-scale structures in ¹⁴C records, such as steep downslopes or uphill’s affect the general detectability of such small events.

C03_P01

Cosmogenic radionuclides at Law Dome, East Antarctica,

record the 774/5 AD and 993/4 AD Miyake Events.

Smith A¹, Curran M², Dee M⁴, Fink D¹, Kuitems M⁴, Levchenko V¹, Moy A², Scifo A⁴, Simon K¹, Wilcken K¹

¹ANSTO, Sydney, Australia, ²Australian Antarctic Division, Hobart, Australia, ³Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Australia, ⁴Centre for Isotope Research, University of Groningen, Gronigen, Netherlands

This project investigates increased atmospheric production of cosmogenic radionuclides in ice core records at Law Dome, East Antarctica, for three extreme events: the Carrington Event (CE) of 1859 AD and the Miyake Events (ME) of 774/5 AD and 993/4 AD. Ice samples for ¹⁰Be and ³⁶Cl analysis were taken from ice cores drilled near the summit of Law Dome, East Antarctica. This will be the first time these radionuclides have been measured at the same site for these events, allowing a direct comparison of ME774, ME993 and CE1859 under similar transport conditions.

A survey of ¹⁰Be at annual resolution spanning 30 years allowed an exact location of the events in the ice cores. We clearly identified the expected ME774 and ME993 ¹⁰Be peaks, which were ~ 4 years earlier and ~ 2 years earlier, respectively, than the layer-counted ice core chronology, but within the margin of error. No discernible ¹⁰Be peak or ³⁶Cl peak was found for CE1859 at annual resolution.

A further set of ¹⁰Be samples at bi-monthly resolution were taken over ME774 and ME993 to better define the fine structure and amplitude of the signal. These sub-annual results confirm the survey results, showing additional structure and higher ¹⁰Be concentrations. High resolution ¹⁴C analysis has already been undertaken at Groningen over all three events and will be reported at this meeting. Finally, we will be combining the mobile phases from the sub-annual and annual 10Be processing to yield sufficient sample for ³⁶Cl AMS analysis across these two Miyake Events.

C03_P02

The potential for using Δ¹⁴C excursions to accurately date floating pine chronologies from the Hallstatt period

Damian W¹, Rakowski A², Krapiec M¹, Pawlyta J¹, Barniak J¹, Szychowska-Krąpiec E¹

¹AGH, Kraków, Poland, ²SUT, Gliwice, Poland

In Central Europe, the dendrochronological method in absolute dating is widely used, but a significant difficulty in its application is the lack of pine (Pinus sylvestris) chronologies reaching back more than tenth century CE. Recently, long floating pine chronologies covering the last thousand years of the BCE were compiled at the Dendrochronological Laboratory of AGH University of Science and Technology in Krakow. These are mean curves developed from hundreds of trunks of subfossil trees found in Polish peatlands. They were preliminarily dated using the wiggle-matching method. Later, rapid Δ¹⁴C changes at 660 BCE and at 814-813 BCE were used for their precise dating with annual precision.

C03_P03

Variations in the radiocarbon calibration curves around known and suspected Δ¹⁴C excursions

Rakowski A¹, Pawlyta J², Krąpiec M², Huels M³, Molnar M⁴

¹SUT, Gliwice, Poland, ²AGH, Kraków, Poland, ³Uni Kiel, Kiel, Germany, ⁴ATOMKI, Debrecen, Hungary

The search for and analysis of rapid Δ¹⁴C changes in the past has received much attention in recent years. In this paper, we will present the results of searching for rapid Δ¹⁴C changes in the raw data used to build radiocarbon calibration curves: IntCa20 and SHCal20 and attempts to identify them in rings of single trees from Poland. We collected information on the periods of occurrence of rapid changes identified by other authors and within our own review of Δ¹⁴C variability in raw data of calibration curves. For some of the periods we found, we were able to find research material in the form of tree trunks from areas of Poland. We determined the concentration of ¹⁴C in tree rings. In this paper we present a comparison of the obtained Δ¹⁴C for our samples and raw data and the IntCal20 curve itself.