Geomagnetic field intensity, excursions, reversals and the 41,000-yr obliquity signal

The possibility that precession provides power to the geodynamo has been tested by comparing variations in field intensity and the occurrence of excursions and reversals with the obliquity signal. The strongest minima in the paleomagnetic intensity records for the past 800,000 yr correlate with obliquity minima. The distribution of the length of polarity intervals less than 100,000 yr peaks between 30 and 40,000 yr, i.e., marginally shorter than the obliquity period. Reversals preferentially occur when the average amplitude of the obliquity signal is low. The most recent reversals occur close to the point of inflection during the decrease from the maximum of the obliquity signal. These results suggest that precession provides some power to the geodynamo.