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

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 ¹⁴ C, ¹⁰ Be and ³⁶ Cl 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 Δ¹⁴ C 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 ¹⁰ Be and ³⁶ Cl 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 ¹⁰ Be and ³⁶ Cl in the same samples, with sample sizes challenging for the ME samples. Preliminary ¹⁰ Be results at annual resolution spanning 30 years allowed an exact location of the events. We have clearly identified the expected ME774 and ME993 ¹⁰ Be 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 ¹⁰ Be 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 ³⁶ Cl AMS targets from the sub-annual ice core samples and the initial annual survey samples. No discernible ¹⁰ Be peak or ³⁶ Cl peak was found for CE1859 at annual resolution. © The Authors

Keywords

Isotopes, Antarctica, Solar atmosphere, Storms, Beryllium 10, Carbon 14, Weather, Space, Solar system

Citation

Smith, A., Curran, M., Fink, D., Dee, M., Kuitems, M., Levchenko, V., Moy, A., Scifo, A., Simon, K., & Wilcken, K. (2021). Cosmogenic radionuclides at Law Dome, East Antarctica, as signatures of past Solar storm events. Paper presented to the 15th International Conference on Accelerator Mass Spectrometry. ANSTO Sydney, Australia. November 15th – 19th, 2021. (pp. 92). Retrieved from: https://ams15sydney.com/wp-content/uploads/2021/11/AMS-15-Full-Program-and-Abstract-Book-R-1.pdf

URI

https://ams15sydney.com/wp-content/uploads/2021/11/AMS-15-Full-Program-and-Abstract-Book-R-1.pdf
https://apo.ansto.gov.au/dspace/handle/10238/14422

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