Authigenic Be-10/Be-9 ratio signatures of the cosmogenic nuclide production linked to geomagnetic dipole moment variation since the Brunhes/Matuyama boundary

Geomagnetic dipole moment variations associated with polarity reversals and excursions are expressed by large changes of the cosmogenic nuclide beryllium-10 (Be-10) production rates. Authigenic Be-10/Be-9 ratios (proxy of atmospheric Be-10 production) from oceanic cores therefore complete the classical information derived from relative paleointensity (RPI) records. This study presents new authigenic Be-10/Be-9 ratio results obtained from cores MD05-2920 and MD05-2930 collected in the west equatorial Pacific Ocean. Be ratios from cores MD05-2920, MD05-2930 and MD90-0961 have been stacked and averaged. Variations of the authigenic Be-10/Be-9 ratio are analyzed and compared with the geomagnetic dipole low series reported from global RPI stacks. The largest Be-10 overproduction episodes are related to dipole field collapses (below a threshold of 2 x 1022 Am-2) associated with the Brunhes/Matuyama reversal, the Laschamp (41 ka) excursion, and the Iceland Basin event (190 ka). Other significant Be-10 production peaks are correlated to geomagnetic excursions reported in literature. The record was then calibrated by using absolute dipole moment values drawn from the Geomagia and Pint paleointensity value databases. The Be-10-derived geomagnetic dipole moment record, independent from sedimentary paleomagnetic data, covers the Brunhes-Matuyama transition and the whole Brunhes Chron. It provides new and complementary data on the amplitude and timing of millennial-scale geomagnetic dipole moment variations and particularly on dipole moment collapses triggering polarity instabilities.