Detection of solar events by using radiocarbon in tree-rings

Mr Nicolas Brehm1, Dr Marcus Christl1, Dr Florian Adolphi2, Prof Raimund Muscheler3, Prof Hans-Arno Synal1, Florian Florian Mekhaldi3, Mrs Chiara Paleari3, Dr Timothy Knowles4, Mr Emmanuelle Casanova4, Dr Lukas Wacker1

1ETH Zürich, Zürich, Switzerland, 2Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany, 3Lund University, Lund, Sweden, 4University of Bristol, Bristol, UK

The Sun irregularly expels large amounts of energetic particles into the interplanetary space and towards Earth which can be observed as so-called solar proton events (SPE). These large amounts of energetic particles can cause major damages to satellites and could even disrupt sensitive electronic systems at ground level. This rises the questions how often strong SPEs occur. Since sattalite observations of SPEs are limited to the last few decades, cosmogenic radionuclides are the most reliable tool to detect and study SPEs multiple millenia back in time.
The production rate of cosmogenic nuclides, such as radiocarbon, is primarily dependent on the incoming flux of highly energetic galactic cosmic rays (GCR). When the sun expels large amounts of highly energetic particles into the interplanetary space cosmogenic radionuclide production can suddenly be increased. There are findings of sharp increases in several radionuclide records (10Be, 36Cl, 14C) within less than one year, which can be attributed to SPEs.
Until now, only three strong SPEs could confidently be detected by using cosmogenic radionuclides. Analyzing annual 14C concentrations in tree-rings from Switzerland, Germany, Ireland, Russia, and the USA we discovered rapid increases in atmospheric 14C. The ~2% increases of atmospheric 14C recorded for both events exceed all previously known 14C peaks but after correction for the slowly varying geomagnetic field, they are comparable to the largest event of this type discovered so far at 775 CE. These strong events serve as accurate time markers for the synchronization with floating tree-ring and ice core records and provide critical information on the previous occurrence of extreme solar events which threaten modern infrastructure. Such sudden increases in radionuclide production also have the potential to be used to synchronize not precisely dated cosmogenic radionuclide records (e.g. 10Be and 36Cl in ice core records) with precisely dated records (14C in tree-ring records).



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Nov 15 2021


12:15 pm - 1:30 pm