Modeling atmospheric transport of cosmogenic radionuclide ¹⁰Be using GEOS-Chem 14.1.1 and ECHAM6.3-HAM2.3: implications for solar and geomagnetic reconstructions

A prerequisite to applying ¹⁰Be in natural archives for solar and geomagnetic reconstructions is to know how ¹⁰Be deposition reflects atmospheric production changes. However, this relationship remains debated. To address this, we use two state-of-the-art global models GEOS-Chem and ECHAM6.3-HAM2.3 with the latest beryllium production model. During solar modulation, both models suggest that ¹⁰Be deposition reacts proportionally to global production changes, with minor latitudinal deposition biases (<5%). During geomagnetic modulation, however, ¹⁰Be deposition changes are enhanced by ~15% in the tropics and attenuated by 20%-35% in subtropical and polar regions compared to global production changes. Such changes are also hemispherically asymmetric, attributed to asymmetric production between hemispheres. For the extreme solar proton event in A.D. 774/5, ¹⁰Be shows a 15% higher deposition increase in polar regions than in tropics. This study highlights the importance of atmospheric mixing when comparing ¹⁰Be from different locations or to independent geomagnetic field records.