C03_P01

Cosmogenic radionuclides at Law Dome, East Antarctica,

record the 774/5 AD and 993/4 AD Miyake Events.

Smith A¹, Curran M², Dee M⁴, Fink D¹, Kuitems M⁴, Levchenko V¹, Moy A², Scifo A⁴, Simon K¹, Wilcken K¹

¹ANSTO, Sydney, Australia, ²Australian Antarctic Division, Hobart, Australia, ³Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Australia, ⁴Centre for Isotope Research, University of Groningen, Gronigen, Netherlands

This project investigates increased atmospheric production of cosmogenic radionuclides in ice core records at Law Dome, East Antarctica, for three extreme events: the Carrington Event (CE) of 1859 AD and the Miyake Events (ME) of 774/5 AD and 993/4 AD. Ice samples for ¹⁰Be and ³⁶Cl analysis were taken from ice cores drilled near the summit of Law Dome, East Antarctica. This will be 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.

A survey of ¹⁰Be at annual resolution spanning 30 years allowed an exact location of the events in the ice cores. We clearly identified the expected ME774 and ME993 ¹⁰Be peaks, which were ~ 4 years earlier and ~ 2 years earlier, respectively, than the layer-counted ice core chronology, but within the margin of error. No discernible ¹⁰Be peak or ³⁶Cl peak was found for CE1859 at annual resolution.

A further set of ¹⁰Be samples at bi-monthly resolution were taken over ME774 and ME993 to better define the fine structure and amplitude of the signal. These sub-annual results confirm the survey results, showing additional structure and higher ¹⁰Be concentrations. High resolution ¹⁴C analysis has already been undertaken at Groningen over all three events and will be reported at this meeting. Finally, we will be combining the mobile phases from the sub-annual and annual 10Be processing to yield sufficient sample for ³⁶Cl AMS analysis across these two Miyake Events.