Enhanced cosmic‐ray production of <sup>10</sup>Be coincident with the Mono Lake and Laschamp Geomagnetic Excursions

McHargue, L. R.; Damon, Paul E.; Donahue, D. J.

doi:10.1029/95gl00169

Cited by 79 publications

(55 citation statements)

References 33 publications

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“…In recent years, time-dependent models of the main geomagnetic ®eld going back to 1690 have been produced (Bloxham and Jackson, 1992), using which, long term (b 10 2 y) variations in cuto rigidities of cosmic rays can be computed. Enhanced cosmic ray production of 10 fe coincident with the Mono Lake and Laschamp geomagnetic excursions have been reported in recent literature (McHargue et al, 1995). A mechanism which has been proposed for this enhancement, by these authors, is the change in galactic cosmic ray¯ux coincident with a supernova event.…”

Section: Resultsmentioning

confidence: 82%

Changes in cosmic ray cut-off rigidities due to secular variations of the geomagnetic field

Bhattacharyya¹,

Mitra

1997

Ann. Geophys.

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Abstract. An analytical expression is derived for the cuto rigidity of cosmic rays arriving at a point in an arbitrary direction, when the main geomagnetic ®eld is approximated by that of an eccentric dipole. This expression is used to determine changes in geomagnetic cuto s due to secular variation of the geomagnetic ®eld since 1835. E ects of westward drift of the quadrupole ®eld and decrease in the e ective dipole moment are seen in the isorigidity contours. On account of the immense computer time required to determine the cuto rigidities more accurately using the particle trajectory tracing technique, the present formulation may be useful in estimating the transmission factor of the geomagnetic ®eld in cosmic ray studies, modulation of cosmogenic isotope production by geomagnetic secular variation, and the contribution of geomagnetic ®eld variation to long term changes in climate through cosmic ray related modulation of the current¯ow in the global electric circuit.

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Section: Resultsmentioning

confidence: 82%

Changes in cosmic ray cut-off rigidities due to secular variations of the geomagnetic field

Bhattacharyya¹,

Mitra

1997

Ann. Geophys.

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“…These results reveal elevated and very variable 14 C between 45 and 33 ka BP. These fluctuations may correlate with peaks in cosmogenic 36 Cl and 10 Be isotopes [20], which have been observed in polar ice cores, as well as those observed for 10 Be in marine sediments [1]. Modeling results suggest that the major features of this record cannot be produced with solar or terrestrial magnetic field modulation alone, but may require significant changes in the carbon cycle [c.f.…”

Section: Extension Of the Radiocarbon Time Scale To ~45000 Years Bpmentioning

confidence: 98%

“…Sample preparation involves dissolution of the sample and addition of 1-mg Be carrier, extraction of Be using acetylacetone, and ion exchange chromotography, as discussed by McHargue et al [1] Be(OH) 2 is precipitated from the final solutions and is converted to BeO by heating in air. The BeO powder is then mixed with a silver powder as a binder and the mixture is pressed into a Cu target holder for the AMS measurements.…”

Section: Some Ams 10 Be Measurementsmentioning

confidence: 99%

“…The first machine is a 2.5-MV Tandetron (General Ionex Corporation), in operation since 1981, and the second, which was installed in spring 2000, is a 3-MV Pelletron (NEC, National Electrostatics Corporation). Most samples run in our laboratory are for radiocarbon measurements, though we have developed applications using 10 Be [1] and 129 I [2]. We have measured over 46,000 radiocarbon samples for a wide variety of applications over the last 20 years at our laboratory.…”

Section: Introductionmentioning

confidence: 99%

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Accelerator Mass Spectrometry at Arizona: Geochronology of the Climatic Record and Connections with the Ocean

Jull

Burr

Beck

et al. 2002

The Scientific World JOURNAL

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There are many diverse uses of accelerator mass spectrometry (AMS). 14 C studies at our laboratory include much research related to paleoclimate, with 14 C as a tracer of past changes in environmental conditions as observed in corals, marine sediments, and many terrestrial records. Terrestrial records can also show the influence of oceanic oscillations, whether they are short term, such as ENSO (El Niño/Southern Oscillation), or on the millennial time scale. In tracer applications, we have developed the use of 129 I as well as 14 C as tracers for nuclear pollution studies around radioactive waste dump sites, in collaboration with IAEA. We discuss some applications carried out in Tucson, AZ, for several of these fields and hope to give some idea of the breadth of these studies.KEY WORDS: accelerator mass spectrometry, carbon-14, paleoclimate, radiocarbon dating, beryllium-10, corals, forest fires, ENSO DOMAINS: environmental chemistry, freshwater systems, global systems, isotopes in the environment INTRODUCTIONIn this paper, we describe our new accelerator mass spectrometry (AMS) system and also summarize some aspects of AMS applications at the University of Arizona facility. Over the last 2 decades, AMS has gradually evolved into the standard method of radionuclide measurements, especially for 1580 Jull et al.: Arizona: Geochronology of the Climatic Record TheScientificWorldJOURNAL (2002) 2, 1579-1593 radiocarbon. At the University of Arizona, we now operate two AMS machines. The first machine is a 2. AMS RADIOCARBON MEASUREMENTS PretreatmentIt is important to consider the careful pretreatment of samples for radiocarbon dating, since improper cleaning can affect the results. Although basic procedures are uniform, pretreatment can vary between different radiocarbon laboratories. The processing of an AMS radiocarbon sample at Arizona follows several well-defined steps, which are summarized below for different types of samples:1. Organic materials such as charcoal, wood, cellulose, plant material, and animal tissue: after physical inspection, the samples are cleaned with 1 N HCl acid, 0.1% NaOH, and 1 N HCl (acid-base-acid [ABA] pretreatment), washed with distilled water, dried, and combusted at 900°C with CuO. 2. Carbonates: samples are etched with 100% H 3 PO 4 to remove 50 to 85% of the carbonate, dried, and hydrolyzed with H 3 PO 4 . An alternative is to use selective etching [3]. 3. Marine and lacustrine sediments: after cleansing in 1 N HCl and drying, the sample is combusted at 400°C in ~0.3 atm oxygen gas. We will discuss specific problems of sediment dating later in this paper. 4. Textiles, parchment, canvas, art works, and artifacts: the samples are given the ABA pretreatment and, after washing and drying, they are Soxhlet extracted with hexane, then ethanol, and finally methanol. After washing in distilled water and drying, they are combusted at 900°C with CuO[4]. 5. Ivory: samples are given a light acid pretreatment or a light ABA pretreatment. Dried samples are combusted at 900°C with CuO.Once the gr...

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“…The low geomagnetic field of the Laschamp event, which was first discovered in a lava flow of the Massif Central, France (Bonhommet and Zähringer 1969), and dated to ~40 ka cal BP (see Valet et al 2007 for a review) and more recently to 40.65 ± 0.65 ka cal BP (Singer et al 2009), has been discussed as the most likely cause of these changes. In the 1990s, measurements of 10 Be concentrations in deep-sea sediments became available showing enhanced 10 Be levels around 40 ka cal BP (McHargue et al 1995(McHargue et al , 2000Robinson et al 1995). Finally, reconstructions of geomagnetic field intensity in deep-sea sediments (Laj et al , 2002 and correlation with the ice-core record of cosmogenic isotopes 10 Be and 36 Cl has shown that the intervals of low geomagnetic field coincided with periods of increased flux of cosmogenic isotopes (Baumgartner et al 1998;Wagner et al 2000).…”

Section: Study Backgroundmentioning

confidence: 99%

Anomalous Radiocarbon Ages Found in Campanian Ignimbrite Deposit of the Mediterranean Deep-Sea Core CT85-5

Hajdas¹,

Taricco²,

Bonani³

et al. 2011

Radiocarbon

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ABSTRACT.A detailed radiocarbon chronology has been established for the deep-sea core CT85-5 from the Tyrrhenian Sea. This chronology, which is based on the analysis of foraminifera shells, shows a set of reversed 14 C ages for sediments deposited during the eruption of the Campanian Ignimbrite (~40 ka cal BP). The anomalous young 14 C ages coincide with elevated concentrations of 10 Be measured in the same core. Although reversals in 14 C ages have been previously found in other records at 40 ka cal BP, such extreme changes have not been observed elsewhere. The enhancement in 14 C concentration in CT85-5 sediments associated with the Campanian Ignimbrite is equivalent to an apparent age ~15 ka younger than the age for the sediments deposited shortly before the eruption. Here, we present consistent results of repeated measurements showing no analytical problems that can explain the observed rapid changes in 14 C of this particular record.

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Enhanced cosmic‐ray production of ¹⁰Be coincident with the Mono Lake and Laschamp Geomagnetic Excursions

Cited by 79 publications

References 33 publications

Changes in cosmic ray cut-off rigidities due to secular variations of the geomagnetic field

Changes in cosmic ray cut-off rigidities due to secular variations of the geomagnetic field

Accelerator Mass Spectrometry at Arizona: Geochronology of the Climatic Record and Connections with the Ocean

Anomalous Radiocarbon Ages Found in Campanian Ignimbrite Deposit of the Mediterranean Deep-Sea Core CT85-5

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Enhanced cosmic‐ray production of 10Be coincident with the Mono Lake and Laschamp Geomagnetic Excursions

Cited by 79 publications

References 33 publications

Changes in cosmic ray cut-off rigidities due to secular variations of the geomagnetic field

Changes in cosmic ray cut-off rigidities due to secular variations of the geomagnetic field

Accelerator Mass Spectrometry at Arizona: Geochronology of the Climatic Record and Connections with the Ocean

Anomalous Radiocarbon Ages Found in Campanian Ignimbrite Deposit of the Mediterranean Deep-Sea Core CT85-5

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Enhanced cosmic‐ray production of ¹⁰Be coincident with the Mono Lake and Laschamp Geomagnetic Excursions