Cosmogenic 10Be and paleomagnetic records of the Earth’s magnetic field history : news and views.

Records of paleomagnetic activity (relative paleointensity, RPI) and cosmogenic Beryllium production (authigenic 10Be/9Be ratio) can be reconstructed from ocean sediment sequences (deposited at rates of 2 to 20 cm/kyr). These data can in turn be used to identify Geomagnetic dipole lows (GDL) associated with reversals of earth's magnetic field and geomagnetic excursions. 10Be production is enhanced (quasi-doubled) during both polarity reversals (e.g. the B/M transition at ca 772 ka) and excursions (e.g. the Laschamp event at 41 ka). Intercomparison of the two techniques has identified stratigraphic offsets (of a few cm to several dm) between the two expressions of a given GDL. This finding impacts the inferred precision/reliability of paleomagnetic markers for intercorrelation and dating of sedimentary archives.

The calibration of 10Be/9Be records using empirical and theoretical relationships between cosmogenic nuclide production and the geomagnetic dipole moment values, allows us to produce dipole moment records independent of RPI sedimentary paleomagnetic records. These provide useful time series of past geomagnetic moment across reversals and excursions, and offer a reliable pacing for the Earth’s geomagnetic dynamo, opening perspectives on the secular to millenial decay of the modern geomagnetic field.