Geomagnetic reversals at the edge of regularity

Geomagnetic field reversals remain as one of the most intriguing problems in geophysics and are regarded as chaotic processes resulting from a dynamo mechanism. In this article, we use the polarity scale data set for the last 170 Myr from the ocean's floor to provide robust evidence for an inverse relationship between the complexity of sequences of consecutive polarity intervals and the respective reversal rate. In particular the variability of sequences of polarity intervals reaches a minimum in the mid-Jurassic when a maximum reversal rate is found. This raises the possibility of epochs of high regularity in the reversal process geodynamo. To shed light on this process, We investigate the transition from regular to chaotic regime in a minimal model for geomagnetic reversals. We show that even in a chaotic regime, near to the transition the system retains the signature of regular behavior. We suggest that geomagnetic reversals have switched between different degrees of irregularity, with a dominant periodicity around 70 kyrs that results from a "ghost" limit cycle.