Dipole strength during the Matuyama-Brunhes reversal reconstructed from the deconvolution of magnetic and climatic modulation of 10Be/9Be records

The global production rate of the cosmogenic isotope ¹⁰Be by cosmic ray spallation is modulated by the activity of the sun and the intensity of the far-reaching component of the Earth magnetic field, which is in turn dominated by the dipolar term. Therefore, sedimentary ¹⁰Be records can be used to reconstruct past variations of the geomagnetic dipole moment. However, several environmental factors affect the transfer of ¹⁰Be atoms from the high atmosphere and soils, where it is produced, to the sediment, introducing a significant climatic modulation that can, in worst cases, completely obscure the paleomagnetic signal. These factors include variations of the continental runoff, oceanic circulation, sediment fluxes, and sediment scavenging effi­ciency. The latter is largely removed by normalizing the ¹⁰Be record with the concentration of authigenic ⁹Be, which is accumulated by sediment particles in the same manner as the cosmo­genic isotope. Even with this correction in place, individual ¹⁰Be/⁹Be records are significantly influenced by climate, to the point that only major geomagnetic events, such as the MB reversal, can be recognized. We present a model, which, for the first time, enables to deconvolve, at least partially, the climatic and magnetic components of ¹⁰Be/⁹Be records on a set of cores from the Atlantic, Indian, and Pacific Ocean. The climatic modulation is composed of an additive term, which reflects Be recycling through diagenetic release from sediments, and a multiplicative term, which is dominated by oceanic current patterns. Knowledge of these terms enables to remove, at least partially, site-specific environmental effects, obtaining a corrected ¹⁰Be/⁹Be stack that can be inverted to reconstruct variations of the dipole moment during the last geomagnetic reversal.