The cosmic-ray events around AD 775 and AD 993 : assessing their causes and possible effects on climate

Miyake et al. (2012, 2013) discovered rapid increases of 14C content in tree rings dated to AD 774-5 and AD 992-3 which were attributed to unprecedented cosmic-ray events. These extreme particle events have no counterparts in the instrumental and historical record and consequently praised great interest. Indeed, many studies have tentatively associated the two events to solar proton events (SPE), supernovae, gamma-ray bursts (GRB) and to a cometary event which all differ in terms of their energy spectrum. Furthermore, such outbursts of energetic particles have the potential to deplete atmospheric ozone and impact atmospheric circulation and temperature. In consequence, the aims of this project were twofold. The first and most emphasized was to assess the likelihood for the different suggested causes. The second was to investigate the possible effects of the cosmic-ray events on climate. Cosmogenic radionuclides such as 10Be, 14C and 36Cl arise from the nuclear cascade which is triggered when cosmic-rays reach the atmosphere. These radio-isotopes are produced through different reaction pathways which have different energy dependencies. This discriminant feature could consequently help to better constrain the energy of the incident particles and thus the origin of the two events. Nevertheless, only 14C has been measured so far at annual resolution. In that light, new annually-resolved 10Be was measured from the NGRIP ice core and used in complement with available records of other radionuclides. An exhaustive and very highly-resolved dataset of ions and element compounds from the NGRIP ice core in addition to δ18O records from several Greenland ice cores were utilized in order to investigate the potential effects on climate. The results demonstrate that 10Be concentrations and flux from the NGRIP ice core also exhibit large increases in relation to both events and similar to those reported in tree rings 14C content. This symmetric increase in both radionuclides suggests solar proton events as a cause for both cosmic-ray events. Furthermore, the multiple cosmogenic radionuclide records show that both events were measured around the globe in both hemispheres which is also fully consistent with solar proton events. Calculations based on the different production yields of 10Be, 14C and 36Cl indicate that the two probable SPEs were characterized by a hard spectrum and by unprecedented fluences. As a matter of fact, it is found that the solar flare responsible for the larger of the two events (AD 774-5) was an order of magnitude stronger than the hardest instrumental SPE. More startlingly, it was substantially more energetic than the Carrington event of 1859 which is considered as the strongest reported historical solar flare. Coeval peaks in Pb, Cd and Na ice core concentrations suggest an atmospheric circulation response timed with the larger of the two events. The high Na concentrations are interpreted as increased vigor in marine air masses associated with sustained storminess in the North Atlantic synchronous with the exceptional SPE. Finally, the new NGRIP 10Be measurements from this study shed light on the existence of an unexpected early offset in the Greenland Ice Core Chronology 2005 (GICC05) time scale. Lags of 4 years at AD 993 and of 7 years at AD 775 in GICC05 are reported.Miyake et al. (2012,2013) upptäckte en snabb ökning av 14C i träringar daterade till 774-5 och 992-3 vilket tillskrevs exceptionalla kosmik strålnings händelser. Dessa extrema partikel händelser har inget motstycke i instrumentala eller hstoriska arkiv och blev följdaktigen mycket uppmärksammade. Många studier har försöt koppla samman dessa två händelser med sol protonstormar (SPE), supernovor, gamma strålnings utbrott och med att en komet passerat genom atmosfären, alla dessa skiljer sig ifråga om energi spektrum. Vidare har sådana utbrott av hög energi partiklar potential att utarma atmosfäriskt ozon och påverka atmosfärens cirkulation och temperature. Som konsekvens av detta har detta projekt två mål. Det första och mest betonade målet var att bestämma sannolikheten för de olika föreslagna orsakerna. Det andra var att utreda möjliga effekter av kosmik strålnings händelser på klimatet. Kosmiska radionuklider som 14Be, 14C och 36Cl uppstår från den nuclear cascade som startas av att kosmiska strålar når atmosfären. Dessa radioaktiva isotoper produceras genom olika reaktions vägar som har olika energi behov. Detta diskriminerade särdrag kan följdaktigen användas för att ringa in energin på moderpartiklarna och därigenom ursprunget till de två händelserna. Dock har endast 14C mätts med årlig upplösning än så länge. I ljus av detta gjordes nya 10Be mätningar med en årlig upplösning på NGRIP iskärnan och användes tillsamans med tillgänglig data över andra radionuklider. Ett uttömande och mycket högupplöst dataset för joner och grundämnen från NGRIP iskärnan sammt δ18O arkiv från flera Iskärnor från Grönland användes för att utreda den potentiella effekten på klimatet. Resultaten demonstrerar att 10Be concentrationer och flöde i NGRIP iskärnan också uppvisar stora ökningar i relation till båda händelserna liknande de förändringar i 14C som påvisats i träringar. Denna symetriska ökningen i båda radionukliderna indikerar att sol protonstormar var orsaken till båda kosmik strålnings händelserna. Vidare visar ett flertal arkiv över kosmogeniska radionuklider att båda händelserna uppmättes runt hela klotet i båda hemisfärerna också är konsekvent med sol protonstormar. Beräkningar baserade på produktionen av 10Be, 14C och 36Cl indikerar att de två troliga SPE karaktäriserades av ett hårt spektrum och saknade motstycke avseende fluenser. Faktum är att solutbrottet som orsakade den största av de två händelserna (774-5) var en magnitud större än den hårdaste instrumentellt uppmäta SPEn. Mer överaskande hade den avsevärt mycket högre energi än Carrington händelsen 1859 som anses vara den starkaste av de rapporterade historiska sol protonstormar. Sammtidiga toppar i Pb, Cd och Na i iskärnan indikerar en reaktion i den atmosfäriska cirkulationen simultant med den större av de två händelserna. Den höga Na koncentrationen tolkas som ökad styrka i luftmassor associerad med ökad stormighet över norra atlanten sammtidigt med den exceptionella SPE. Slutligen, de nya 10Be mätningarna i NGRIP iskärnan från denna studie påvisar existensen av en oförutsedd offset i the Greenland Ice Core Chronology 2005 (GICC05) tidskalan. Förseningar om fyra år vid år 993 och om sju år vid år 775 i GICC05 påvisas

A varved lake sediment record of ¹⁰Be solar activity proxy for the Lateglacial-Holocene transition

Solar modulated variations in cosmogenic radionuclide production provide both information on past changes in the activity of the Sun and a global synchronization tool. However, to date the use of cosmogenic radionuclides for these applications is almost exclusively based on 10Be records from ice cores and 14C time-series from tree rings, all including archive-specific limitations. We present the first 10Be record from annually laminated (varved) lake sediments for the Lateglacial-Holocene transition from Meerfelder Maar. We quantify environmental influences on the catchment and, consequently, 10Be deposition using a new approach based on regression analyses between our 10Be record and environmental proxy time-series from the same archive. Our analyses suggest that environmental influences contribute to up to 37% of the variability in our 10Be record, but cannot be the main explanation for major 10Be excursions. Corrected for these environmental influences, our 10Be record is interpreted to dominantly reflect changes in solar modulated cosmogenic radionuclide production. The preservation of a solar production signal in 10Be from varved lake sediments highlights the largely unexplored potential of these archives for solar activity reconstruction, as global synchronization tool and, thus, for more robust paleoclimate studies

Cosmogenic radionuclides reveal an extreme solar particle storm near a solar minimum 9125 years BP

During solar storms, the Sun expels large amounts of energetic particles (SEP) that can react with the Earth’s atmospheric constituents and produce cosmogenic radionuclides such as 14C, 10Be and 36Cl. Here we present 10Be and 36Cl data measured in ice cores from Greenland and Antarctica. The data consistently show one of the largest 10Be and 36Cl production peaks detected so far, most likely produced by an extreme SEP event that hit Earth 9125 years BP (before present, i.e., before 1950 CE), i.e., 7176 BCE. Using the 36Cl/10Be ratio, we demonstrate that this event was characterized by a very hard energy spectrum and was possibly up to two orders of magnitude larger than any SEP event during the instrumental period. Furthermore, we provide 10Be-based evidence that, contrary to expectations, the SEP event occurred near a solar minimum

The Extreme Space Weather Event in 1903 October/November: An Outburst from the Quiet Sun

While the Sun is generally more eruptive during its maximum and declining phases, observational evidence shows certain cases of powerful solar eruptions during the quiet phase of the solar activity. Occurring in the weak Solar Cycle 14 just after its minimum, the extreme space weather event in 1903 October -- November was one of these cases. Here, we reconstruct the time series of geomagnetic activity based on contemporary observational records. With the mid-latitude magnetograms, the 1903 magnetic storm is thought to be caused by a fast coronal mass ejection (~1500 km/s) and is regarded as an intense event with an estimated minimum Dst' of ~-513 nT The reconstructed time series has been compared with the equatorward extension of auroral oval (~44.1{\deg} in invariant latitude) and the time series of telegraphic disturbances. This case study shows that potential threats posed by extreme space weather events exist even during weak solar cycles or near their minima.Comment: 20 pages, 5 figures, 1 table, and accepted for publication in the ApJ

Tree-rings reveal two strong solar proton events in 7176 and 5259 BCE

The Sun sporadically produces eruptive events leading to intense fluxes of solar energetic particles (SEPs) that dramatically disrupt the near-Earth radiation environment. Such events have been directly studied for the last decades but little is known about the occurrence and magnitude of rare, extreme SEP events. Presently, a few events that produced measurable signals in cosmogenic radionuclides such as 14C, 10Be and 36Cl have been found. Analyzing annual 14C concentrations in tree-rings from Switzerland, Germany, Ireland, Russia, and the USA we discovered two spikes in atmospheric 14C occurring in 7176 and 5259 BCE. The ~2% increases of atmospheric 14C recorded for both events exceed all previously known 14C peaks but after correction for the geomagnetic field, they are comparable to the largest event of this type discovered so far at 775 CE. These strong events serve as accurate time markers for the synchronization with floating tree-ring and ice core records and provide critical information on the previous occurrence of extreme solar events which may threaten modern infrastructure

Extreme Solar Events: Setting up a Paradigm

The Sun is magnetically active and often produces eruptive events on different energetic and temporal scales. Until recently, the upper limit of such events was unknown and believed to be roughly represented by direct instrumental observations. However, two types of extreme events were discovered recently: extreme solar energetic particle events on the multi-millennial time scale and super-flares on sun-like stars. Both discoveries imply that the Sun might rarely produce events, called extreme solar events (ESE), whose energy could be orders of magnitude greater than anything we have observed during recent decades. During the years following these discoveries, great progress has been achieved in collecting observational evidence, uncovering new events, making statistical analyses, and developing theoretical modelling. The ESE paradigm lives and is being developed. On the other hand, many outstanding questions still remain open and new ones emerge. Here we present an overview of the current state of the art and the forming paradigm of ESE from different points of view: solar physics, stellar–solar projections, cosmogenic-isotope data, modelling, historical data, as well as terrestrial, technological and societal effects of ESEs. Special focus is paid to open questions and further developments. This review is based on the joint work of the International Space Science Institute (ISSI) team #510 (2020–2022)

Cosmogenic radionuclides in environmental archives – A paleo-perspective on space climate and a synchronizing tool for climate records

The Sun is the primary source for Earth’s climate system. Its fluctuations in irradiance are also known to have an impact on climate. In addition, changes in solar activity modulate the atmospheric production rates of cosmogenic radionuclides (e.g. 10Be, 14C, 36Cl) that all eventually deposit to different environmental archives. The signal of the changing solar activity through time can thus be retrieved and measured from these archives, such as ice cores, tree rings, or lake sediments. The Sun can also display a more chaotic behavior by erupting flashes of light, plasma and magnetic fields whereby energetic particles can be accelerated, and sometimes hit Earth. These all can damage our spacecraft technologies, harm astronauts, and also affect transformer, electric, and electronic infrastructures on the ground. In the case of extreme events, they may also pose a challenge to air-travel safety. At the same time, when solar energetic particles enter the atmosphere, they can enhance the production rate of cosmogenic radionuclides. The objectives of this thesis are twofold. First, the potential of using 10Be, 14C, and 36Cl as tracers of extreme solar storms is explored in depth. Second, the common production signal of 10Be and 14C caused by the longer term changes in solar activity is used to synchronize climate records from different environmental archives from different regions in order to assess the relative timing of a prominent climate oscillation, over 11,000 years before present. Two large signatures of cosmic-ray increase date to AD 774/5 and AD 993/4 are conclusively attributed to extreme solar energetic particle events that have hit Earth and left a clear imprint on the production rates of 14C as measured in tree rings all around the world, and of 10Be and 36Cl in ice cores from Greenland and Antarctica. The inferred energy spectrum and flux of particles of these events indicate that they were an order of magnitude stronger than any solar high-energy event observed during the space era. To infer the energy spectrum of ancient events, it is shown that the relative differences in the energy dependency of the production rates of 10Be and 36Cl by solar particles can be used. An additional, and similarly extreme, solar storm is also suggested to have hit Earth 2,610 years BP. The events from AD 774/5 and AD 993/4 are further explored to test, and thereafter reject, the hypothesis that nitrate enhancements in ice cores can be reliably linked to the occurrence of solar storms or to assess their magnitude. Two high resolution and continuous records of ice-core 36Cl concentration spanning the past several centuries are also presented. They show several increases in 36Cl possibly linked to solar energetic particle events including one that is coeval with the geomagnetic storm of September 1909 CE. These records also show that there is no enhancement in 36Cl production rate following the Carrington event of 1859 CE. A theoretical experiment also proposes that it is possible that major solar storms with a large flux of lower energy particles could lead to a significant increase in ice-core 36Cl concentrations but not in 10Be. Finally, it is shown that wiggles in cosmogenic radionuclides caused by longer-term changes in solar activity can be used to synchronize lake sediment records from Europe to Greenland ice cores. The investigation of both archives on the same time-scale suggests that the climate oscillations observed in Greenland, and subsequently in Western Europe could be attributed, in part, to solar forcing

Evaluating the 11-year solar cycle and short-term 10Be deposition events with novel excess water samples from the East Greenland Ice-core Project (EGRIP)

10Be is produced by the interaction between galactic cosmic rays (GCRs) and solar energetic particles (SEPs) with the Earth's atmospheric constituents. The flux of GCRs is modulated by the varying strength of the magnetic fields of the Earth and the Sun. Measurement of 10Be concentrations from polar ice cores is thus a valuable tool to reconstruct the variations in the geomagnetic field and solar activity levels. The interpretation of 10Be records is, however, complicated by non-production-related effects on the 10Be deposition rate caused by climate- or weather-induced variability. Furthermore, volcanic eruptions have been proposed to lead to short-term 10Be deposition enhancements. In this study, we test the use of excess meltwater from continuous flow analysis (CFA) to measure 10Be, allowing less time-consuming and more cost-effective sample preparation. We compare two records obtained from CFA and discrete samples from the East Greenland Ice core Project (EGRIP) S6 firn core, reaching back to 1900 CE. We find that the two records agree well and that the 10Be record from CFA samples agrees as well as the discrete samples with other records from Greenland. Furthermore, by subtracting the theoretically expected GCR-induced signal, we investigate the high-frequency variability in the 10Be records from Greenland and Antarctica after 1951 CE, focusing on SEP events and volcanic eruptions. Finally, we use the 10Be records from Greenland and Antarctica to study the 11-year solar cycles, allowing us to assess the suitability of the CFA samples for the reconstruction of solar activity. This result opens new opportunities for the collection of continuous 10Be records with less time-consuming sample preparation, while saving an important portion of the ice cores for other measurements.</p