Beryllium ten production and relative paleointensity for the past 1.2 million years

Abstract

Composite curves of relative paleointensity document the evolution of the geomagnetic field intensity during the past 1.2 Million years. Several records of production of ¹⁰Be cosmogenic isotope from the ¹⁰Be/⁹Be ratio (referred to as Be-ratio) covering this period have also been acquired. We add here new ¹⁰Be records to the database and produce a first composite curve of beryllium production (Be-1200) for the past 1.2 Myr. We compare Be-1200 with Sint-2000 (Valet et al., 2005) and PISO-1500 (Channell et al., 2009) paleointensity curves. The three curves show similar patterns, but frequently different amplitudes. The variations in dipole moment values derived from the Sint-2000 and PISO-1500 relative paleointensity composite curves were then confronted with the geomagnetic dipole moment record derived from the Be-1200 record. The predicted amplitudes of dipole moment loss during geomagnetic excursions reconstructed from the measured in the Be-1200 record are generally compatible with those deduced from SINT-2000 and PISO-1500. More specifically, the three datasets indicate very low field intensities during the Laschamp, that are consistent with the existence of reverse directions, and to a lesser extent during other events (Iceland basin, Calabrian Ridge/West Eifel events). The two paleointensity curves show a decrease in field intensity of at least 80–90% during the reversals. The Be- derived dipole moment decreases meet the predictions for the Brunhes/Matuyama transition, but are significantly smaller than expected for the two Jaramillo transitions. Such limited variability may result from the impact of environmental factors on the Be ratios, as suggested in a previous study of the last reversal (Savranskaia et al., 2021). This comparative study of ¹⁰Be records and relative paleointensity records reveals that, in particular cases, Be ratio records can underestimate the amplitude of virtual geomagnetic dipole variation. With their respective strengths and weakness, these two approaches provide similar first-order patterns relevant to the common control by the geomagnetic moment variation.