Modeling the Transport and Deposition of Be-10 Produced by the Strongest Solar Proton Event During the Holocene

Prominent excursions in the number of cosmogenic nuclides (e.g., Be-10) around 774 CE/775 document the most severe solar proton event (SPE) throughout the Holocene. Its manifestation in ice cores is valuable for geochronology, but also for solar-terrestrial physics and climate modeling. Using the ECHAM/MESSy Atmospheric Chemistry (EMAC) climate model in combination with the Warning System for Aviation Exposure to SEP (WASAVIES), we investigate the transport, mixing, and deposition of the cosmogenic nuclide Be-10 produced by the 774 CE/775 SPE. By comparing the model results to the reconstructed Be-10 time series from four ice core records, we study the atmospheric pathways of Be-10 from its stratospheric source to its sink at Earth's surface. The reconstructed post-SPE evolution of the Be-10 surface fluxes at the ice core sites is well captured by the model. The downward transport of the Be-10 atoms is controlled by the Brewer-Dobson circulation in the stratosphere and cross-tropopause transport via tropopause folds or large-scale sinking. Clear hemispheric differences in the transport and deposition processes are identified. In both polar regions the Be-10 surface fluxes peak in summertime, with a larger influence of wet deposition on the seasonal Be-10 surface flux in Greenland than in Antarctica. Differences in the peak Be-10 surface flux following the 774 CE/775 SPE at the drilling sites are explained by specific meteorological conditions depending on the geographic locations of the sites.