Intensity of the geomagnetic field in Europe for the last 3 ka: Influence of data quality on geomagnetic field modeling

One of the main challenges of paleomagnetic research is to obtain high-resolution geomagnetic
field intensity reconstructions. For the last millennia, these reconstructions are mostly based on archeomagnetic
data. However, the quality of the intensity data available in the databases is very variable, and
the high scatter observed in the records clearly suggests that some of them might not be reliable. In this
work we investigate how the geomagnetic field intensity reconstructions and, hence, our present knowledge
of the geomagnetic field in the past, are affected by the quality of the data selected for modeling the
Earth’s magnetic field. For this purpose we rank the European archeointensity data in four quality categories
following widely accepted paleomagnetic criteria based on the methodology used during the laboratory
treatment of the samples and on the number of specimens retained to calculate the mean intensities. Four
geomagnetic field regional models have been implemented by applying the revised spherical cap harmonic
analysis to these four groups of input data. Geomagnetic field models strongly depend on the used data
set. The model built using all the available data (without any preselection) appears to be the less accurate,
indicating some internal inconsistencies of the data set. In addition, some features of this model are clearly
dominated by the less reliable archeointensity data, suggesting that such features might not reflect real variations
of the past geomagnetic field. On the contrary, the regional model built on selected high-quality
intensity data shows a very consistent intensity pattern at the European scale, confirming that the main
intensity changes observed in Europe in the recent history of the geomagnetic field occurred at the continental
scale.