[1] This paper presents a compilation of intensity data covering the past 10 millennia (ArcheoInt). This compilation, which upgrades the one of Korte et al. (2005), contains 3648 data and incorporates additional intensity and directional data sets. A large majority of these data ($87%) were acquired on archeological artifacts, and the remaining $13% correspond to data obtained from volcanic products. The present compilation also includes important metadata for evaluating the intensity data quality and providing a foundation to guide improved selection criteria. We show that $50% of the data set fulfill reasonable reliability standards which take into account the anisotropic nature of most studied objects (potsherds), the stability of the magnetization, and the data dispersion. The temporal and geographical distributions of this sub-data set are similar to those of the main data set, with $72% of the data dated from the past three millennia and $76% obtained from western Eurasia. Approximately half of the selected intensity data are associated with at least an inclination value. To constrain the axial and full dipole evolution over the past three millennia requires that we avoid any overrepresentation of the western Eurasian data. We introduce a first-order regional weighting scheme based on the definition of eight widely distributed regions of 30°width within which the selected data are numerous enough. The regional curves of virtual axial dipole moments (VADM) and of mixed VADM-virtual dipole moments (VDM) averaged over sliding windows of 200 years and 500 years testify for strong contributions from either equatorial dipole or nondipole components. The computation of global VADM and mixed VADM/VDM variation curves, assuming an equal weight for each region, yields a dipole evolution marked by a distinct minimum around 0 B.C./A.D. followed by a maximum around the third-fourth century A.D. A second minimum is present around the eighth century A.D. This variation pattern is compatible with the one deduced from earlier, more sophisticated analysis based on the inversion of both intensity and directional data. In particular, there is a good agreement among all VADMs and dipole moment estimates over the historical period, which further strengthens the validity of our weighting scheme.

[1] Paleointensity determinations based on double heating techniques (in-field/zero-field cooling, zerofield/in-field cooling, and two in-field steps with opposite laboratory fields) are generally considered to be functionally interchangeable producing equally reliable paleointensity estimates. To investigate this premise, we have developed a simple mathematical model. We find that both the zero-field first and infield first methods have a strong angular dependence on the laboratory field (parallel, orthogonal, and antiparallel) while the two in-field steps method is independent of the direction of the laboratory-produced field. Contrary to common practice, each method yields quite different outcomes if the condition of reciprocity of blocking and unblocking temperatures is not met, even with marginal (10%) tails of partial thermoremanence. Our calculations suggest that the zero field first method with the laboratory-produced field anti-parallel to the natural remanence (NRM) is the most robust paleointensity determination technique when the intensity of the lab-induced field is smaller than ancient field. However, the zero field first method with the laboratory-field parallel to the NRM is the optimum approach when the intensity of the lab-induced field is larger than the ancient field. By far the best approach, however, is to alternatethe infield-zerofield (IZ) steps with zerofield-infield (ZI) steps.

[1] We studied 14 groups of French pottery fragments dated between the 4th and 16th centuries. The potsherds were analyzed using the Thellier and Thellier [1959] method, revised by Coe [1967]. Intensity values were corrected for thermoremanent magnetization (TRM) anisotropy and cooling rate dependence of TRM acquisition. We first analyzed modern ceramics produced following ancient techniques and fired in a wood-burning kiln inside of which field intensity was measured. The recovered mean intensity is within $3% of the expected value, which proves the reliability of our experimental procedure. Thermal experiments carried out at rapid and slow cooling rates clearly indicate that the cooling rate correction is critical in archeointensity studies. Our data indicate that large variations in intensity occurred in France over the last 2000 years. Two relative maxima in intensity are observed, one between the 8th and 10th centuries and the second between the 14th and 15th centuries. Similarities are observed between the archeointensity data from France and Ukraine, yielding some evidence for eastward drift of geomagnetic sources between western and eastern Europe from A.D. 800 to A.D. 1700. We also show that the dipole moment evolution proposed by McElhinny and Senanayake [1982] and Yang et al. [2000] for the last two millennia is likely biased toward higher values, mainly because of the absence of correction for the cooling rate dependence of TRM acquisition in most published archeointensity studies. We finally underline a possible relationship, valid at least in western Europe, between changes in direction and intensity of the geomagnetic field.