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

Mekhaldi, Florian LU (2014) In Dissertations in Geology at Lund University GEOR02 20141
Department of Geology
Abstract
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... (More)
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. (Less)
Abstract (Swedish)
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... (More)
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. (Less)
Please use this url to cite or link to this publication:
author
Mekhaldi, Florian LU
supervisor
organization
alternative title
Kosmisk strålnings händelsena runt år 775 och år 993 : utvärdera orsaker och möjliga effekter på klimatet
course
GEOR02 20141
year
type
H2 - Master's Degree (Two Years)
subject
keywords
cosmic-rays, cosmogenic radionuclides, GICC05, NGRIP, solar proton event, storminess
publication/series
Dissertations in Geology at Lund University
report number
412
language
English
id
4584299
date added to LUP
2014-08-25 13:58:42
date last changed
2016-08-25 04:07:39
@misc{4584299,
  abstract     = {{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.}},
  author       = {{Mekhaldi, Florian}},
  language     = {{eng}},
  note         = {{Student Paper}},
  series       = {{Dissertations in Geology at Lund University}},
  title        = {{The cosmic-ray events around AD 775 and AD 993 : assessing their causes and possible effects on climate}},
  year         = {{2014}},
}