A North Pacific Anomaly around 700BC: a potential analogy to the present day geomagnetic field

Recent advances in geomagnetic field modelling of palaeomagnetic data have led to significant improvements of our understanding of the geomagnetic field and how it varies on millennial timescales. Among other things, palaeomagnetic field reconstructions have shown that large-scale non-dipolar field anomalies, similar to or even larger than the present day South Atlantic Anomaly (SAA), have occurred several times in the past, implying that such structures are not necessarily associated with polarity reversals or excursions. A recent study even suggests that such large-scale field asymmetries could be periodically recurrent features of the field. Here we present results from a new Holocene geomagnetic field model, pfm9k.2, constructed using a novel Bayesian approach to account for chronologic uncertainties and address problems with potential smoothing induced by post-depositional remanent magnetisations. We focus our attention on a particular time period, around 700BC, where our new model shows a large-scale field asymmetry in the northern hemisphere with a weak field anomaly in the North Pacific accompanied with strong field intensities in Europe. The field evolution predicted by the model during this time period shares many similarities with the present day field, including a rapid decay of the dipole moment, suggesting that there may be common driving processes. We discuss the physical implications of these results.