Unbiased analysis of geomagnetic data sets and comparison of historical data with paleomagnetic and archeomagnetic records

Abstract

Reconstructions of the past geomagnetic field provide fundamental constraints for understanding the dynamics of the Earth's interior, as well as serving as basis for magnetostratigraphic and archeomagnetic dating tools. Such reconstructions, when extending over epochs that precede the advent of instrumental measurements, rely exclusively on magnetic records from archeological artifacts, and, further in the past, from rocks and sediments. The most critical component of such indirect records is field intensity because of possible biases introduced by material properties and by laboratory protocols, which do not reproduce exactly the original field recording conditions. Large biases are usually avoided by the use of appropriate checking procedures; however, smaller ones can remain undetected in individual studies and might significantly affect field reconstructions. We introduce a new general approach for analyzing geomagnetic databases in order to investigate the reliability of indirect records. This approach is based on the comparison of historical records with archeomagnetic and volcanic data, considering temporal and spatial mismatches with adequate weighting functions and error estimation. A good overall agreement is found between indirect records and historical measurements, while for several subsets systematic bias is detected (e.g., inclination shallowing of lava records). We also demonstrate that simple approaches to analyzing highly inhomogeneous and internally correlated paleomagnetic data sets can lead to incorrect conclusions about the efficiency of quality checks and corrections. Consistent criteria for selecting and weighting data are presented in this review and can be used to improve current geomagnetic field modeling techniques.

Global and Regional Assessments of Paleosecular Variation Activity Over the Past 100 ka

“…These were estimated by comparing the data with the gufm1 model predictions for the historical period (Korte et al, ) and later RMS deviations for directions were converted to α 95 values. Recently, Arneitz et al () introduced a new approach for analyzing archeomagnetic and volcanic data by comparison with historical records and applying temporal and spatial mismatches with weighting functions. Their posteriori estimates imply that reported measurement errors are underestimated.…”

One Hundred Thousand Years of Geomagnetic Field Evolution

“…In all cases when uncertainties are not available, or are smaller than a certain plausible threshold, it has become customary to allocate minimum uncertainties (e.g., Korte et al, ; Panovska, Constable, & Korte, ). Other methods include introducing a modeling error and adding it in quadrature to the original data uncertainty (Licht et al, ), assigning minimum errors based on the number of samples/specimens used to calculate the mean (Nilsson et al, ), grouping the data in different categories based on paleomagnetic quality criteria (Korte et al, ; Pavón‐Carrasco et al, ), and via comparison with historical data, considering error estimates for the difference (Arneitz et al, ).…”

The HISTMAG database: combining historical, archaeomagnetic and volcanic data

“…Generally, it has to be noted that the results have to be interpreted with caution because investigated data sets may have strong internal correlations, for example, due to geographical distribution, decreasing the effective sample size N D and statistical testing capabilities. Therefore, the cancellation of different effects, as observed by Arneitz et al (2017) for diverse indirect data sets, may not be ensured in this case.…”

“…∼ D represents an estimate for the uncertainty of individual records (see Arneitz et al (2017) for more details). Outliers were rejected in the evaluation for data sets marked with * (see Fig.…”

“…HISTMAG database provides the possibility to test specific historical data sets against other temporally and spatially surrounding records. We adopt the strategy of Arneitz et al (2017), who investigated the reliability of archaeomagnetic and palaeomagnetic records via comparison with historical data. Here, instead of indirect records, mining data (derived from adit directions and mining maps), historical maps and sundials are compared with all other remaining historical records.…”