Cosmogenic radionuclides reveal an extreme solar particle storm near a solar minimum 9125 years BP - PubMed (original) (raw)

doi: 10.1038/s41467-021-27891-4.

Florian Mekhaldi 2 3, Florian Adolphi 4, Marcus Christl 5, Christof Vockenhuber 5, Philip Gautschi 5, Jürg Beer 6, Nicolas Brehm 5, Tobias Erhardt 4 7, Hans-Arno Synal 5, Lukas Wacker 5, Frank Wilhelms 4 8, Raimund Muscheler 2

Affiliations

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

Chiara I Paleari et al. Nat Commun. 2022.

Abstract

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.

© 2022. The Author(s).

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Conflict of interest statement

The authors declare no competing interests.

Figures

Fig. 1

Fig. 1. Cosmogenic radionuclide records for the 9125 years BP event.

NGRIP and EDML data are shown on the left, GRIP and EGRIP 10Be data and 14C production rate are shown on the right. The baseline (average radionuclide concentration excluding the peak values) is shown as a dashed line. The error bar of each data point includes the measurement uncertainty. The enhancement factors (ratio between integrated enhancements in the radionuclide production and the baseline value) are noted next to the peak for each record.

Fig. 2

Fig. 2. Event-integrated fluence spectra (assuming an average Φ = 650 MV).

The dashed curves represent the original spectra of the modern events that fit the 36Cl/10Be ratio of the 9125 years BP event. The scaled spectra are shown as continuous lines. The black line shows the average fluence spectrum. The fluences above 30, 200, and 430 MeV (F30, F200 and F430) of the average spectrum are reported. The uncertainties of the fluence estimates include the uncertainty of the 10Be enhancement factor and the standard deviation of the scaled spectra.

Fig. 3

Fig. 3. Relationship between the solar 11-year cycle and the occurrence of the solar energetic particle events of 9125 years BP and 774/5 CE.

a The normalized 10Be records from NGRIP and EGRIP from 9150 to 9105 years BP (see legend) compared to the normalized 10Be annual production rate modeled from neutron monitor data for the period 1963–2008 (black line), showing the best correlation coefficients (for details see main text, EGRIP: r = 0.45, p < 0.01; NGRIP: r = 0.51, p < 0.01). The top panel shows the group sunspot number corresponding to the period of the neutron monitor-based production rate. b The same comparison for the average 10Be data from ice cores from Greenland (NEEM S1, NGRIP, and Tunu) and Antarctica (WAIS) from 770 to 800 CE (blue line) to the period 1961–1991 (neutron-monitor based production rate, black line), showing the best correlation coefficient (for details see main text, r = 0.69, p < 0.01). NEEM, NGRIP, and Tunu from Greenland and WAIS from Antarctica were normalized to their baseline (average 10Be concentration excluding the peak). The red line indicates the estimated onset of the event. The timescales are independently matched,, i.e., not matched to get a fit for the 10Be peak.

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