New archeomagnetic secular variation data from Central Europe, II: Intensities

Abstract

Variations of the geomagnetic field during the past millennia can be obtained by investigating archeological material. The spatial distribution of the available data across Europe is rather uneven and only about 15% of the sites provide a full vector record of the geomagnetic field. Here we report 39 new reliable paleointensity data for sites from Austria, Germany and Switzerland, with ages ranging between 1500 BCE and 1900 CE. For 31 of them, directional information is available, too. Paleointensities were determined with Thellier type techniques, with the multiple-specimen domain-state corrected paleointensity protocol or with both techniques. Corrections for anisotropy of thermoremanent magnetization were carried out for the structures, showing small variations of only a few per cent in most cases. Cooling rate dependence was tested for 16 structures. Often strong alteration during the experiments was observed. Seven successful cooling rate corrections were applied, which lowered the paleointensity values by about 10%. Values obtained from the multiple-specimen technique are generally somewhat lower than those from the Thellier experiments. Rock magnetic measurements revealed magnetite-type minerals mostly in pseudo single domain range as main magnetic carrier, but also high coercive mineral components like hematite or epsilon iron oxide are present. The new data are mostly in good agreement with published paleointensities. They support the presence of strong intensity variations around 800 CE and in the millennium BCE. The new full vector data reveal that the deep paleointensity minimum observed from German data around 850 BCE is accompanied by large variations in direction with declinations up to 50°.