Directional and intensity paleosecular variation data from Japan during the last three millennia: an overview

Reconstructing the past geomagnetic field variations is a key point for understanding the dynamo processes that take place in the Earth’s outer core and for deciphering the field’s behavior over centennial and millennial scales. For this purpose, well-dated paleomagnetic data from volcanic rocks and archeological artifacts is used, coming from different parts of the world and contributing to the calculation of regional and global geomagnetic field models. Japan, located in the eastern part of Asia and characterized by intense volcanic activity and long cultural heritage, represents a precious source of data for geomagnetic field reconstructions. This study aims to provide an updated overview of all the available paleo- and archeo-magnetic data from Japanese volcanos and archeological sites. Particular focus is given on the quality of the data, mainly regarding the paleointensity records, which present higher dispersion in respect to the directional data. A total of 303 directional and 135 intensity data are available for the last 3,000 years, most of them coming from archeological material such as kilns and pottery while 45 records come from volcanic rocks. Only 24 data offer full geomagnetic field determinations, including both direction and absolute intensity, most of them coming from in situ lava flows. The majority of the paleointensity data are obtained through the classical Thellier-Thellier method and its modifications, but in their great majority miss cooling rate and anisotropy corrections. The Japanese data are compared with data from nearby countries and geomagnetic field model predictions and are used to identify geomagnetic field characteristics such as abrupt changes and anomalies.

This study has been partially financed by the European Union’s Horizon 2020 Research and Innovation Programme Excellent Science, under the Marie Skłodowska-Curie RISE Action ‘BEYOND ARCHAEOLOGY’ (no. 823826).