Cosmogenic radionuclides at Law Dome, East Antarctica, as signatures of past Solar storm events.

Dr Andrew Smith1, Dr Mark Curran2,3, Dr David Fink1, Dr Michael Dee4, Dr Margot Kuitems4, Dr Vladimir Levchenko1, Dr Andrew Moy2,3, Dr Andrea Scifo4, Dr Krista Simon1, Dr Klaus Wilcken1

1ANSTO, Lucas Heights, Australia, 2Australian Antarctic Division, Kingston, Australia, 3Australian Antarctic Program Partnership, Institute for Marine and Antarctic Studies, Hobart, Australia, 4Centre for Isotope Research, University of Groningen, Groningen, Netherlands

This project investigates evidence for increased atmospheric production of cosmogenic radionuclides in ice core records at Law Dome, East Antarctica, during three extreme events. These events are the Carrington Event (CE) of 1859 AD [1], the largest solar storm of modern times, and two recently discovered cosmic radiation events of even greater magnitude, the Miyake Events (ME) of 774/5 AD [2] and 993/4 AD [3]. Our intention is to determine ¹⁴C, ¹⁰Be and ³⁶Cl profiles, with the highest sub-annual temporal resolution to date, across these events to determine whether or not all three events are manifestations of the same phenomena. Understanding the frequency, origin and magnitude of these events is essential for future-proofing modern communication infrastructure against such high magnitude radiation impacts from space. Identification of the events also provides an independent check on the Law Dome ice chronology.
New annual Δ¹⁴C measurements in tree rings, in combination with earlier published data, show that the ME774 and the ME993 events occurred in close proximity to the point of maximum activity of the 11-year solar cycle [4]. Although it did not leave any radiocarbon signature, the CE1859 event was already known to have occurred around the point of maximum activity of the solar cycle from sunspot records.
Ice samples for ¹⁰Be and ³⁶Cl analysis are derived from ice cores drilled near the summit of Law Dome, East Antarctica. This is 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. Both ME samples were taken from sections of core where the amount of available ice was limited, and the CE samples were taken from a section where more ice was available. AMS measurements involved some method development at ANSTO, measuring both ¹⁰Be and ³⁶Cl in the same samples, with sample sizes challenging for the ME samples.
Preliminary ¹⁰Be results at annual resolution spanning 30 years allowed an exact location of the events. We have clearly identified the expected ME774 and ME993 ¹⁰Be peaks, which were ~ 4 years and ~ 2 years, respectively, within the error of when the layer-counted DSS ice core chronology had suggested. Accordingly, a further set of ¹⁰Be samples at sub-annual seasonal resolution have been taken to better define the fine structure and amplitude of the signal but are currently not processed. We will also prepare a set of ³⁶Cl AMS targets from the sub-annual ice core samples and the initial annual survey samples. No discernible ¹⁰Be peak or ³⁶Cl peak was found for CE1859 at annual resolution.
1. Carrington, R.C., Monthly Notices of the Royal Astronomical Society, 1859. 20(1): p. 13-15.
2. Miyake, F., et al., Nature (London, U. K.), 2012. 486(7402): p. 240-242.
3. Miyake, F., K. Masuda, and T. Nakamura, Nat Commun, 2013. 4: p. 1748.
4. Scifo, A., et al., Scientific Reports, 2019. 9(1).


Biography:

Andrew is a Physicist with 32 years experience in Accelerator Mass Spectrometry [AMS] and 45 years experience with particle accelerator systems. Andrew leads research activity in the Environment theme and Centre for Accelerator Science platform at ANSTO, with interests in the applications of 7Be, 10Be and 14C to environmental and climate change studies. Andrew has made six scientific expeditions to Antarctica for sample collection, supported by the Australian Antarctic Division, one to Summit, Greenland, and another to Taylor Glacier, Antarctica; the latter two were supported by the National Science Foundation (USA).

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Date

Nov 15 2021

Time

MONDAY
12:15 pm - 1:30 pm