Global analysis of the geomagnetic field: Time variation of the dipole moment and the geomagnetic pole in the holocene.

Global features of the geomagnetic field over the past 10, 000 years were studied. Reliable data set of inclination and declination at twelve localities were prepared by combining paleomagnetic data with archaeomagnetic data. We estimated the time variation of the geomagnetic dipole moment by analyzing the virtual geomagnetic pole (VGP) positions calculated from this data set. The geomagnetic poles were calculated for every 100-year interval by averaging the VGP. The distribution of the geomagnetic poles has an elliptic shape and westward movement was predominant throughout the interval. The obtained time sequence of the movement of the geomagnetic pole can be divided into three intervals: during the period between ca. 7000 and ca. 3700 B.P. (B.P.: before 1950 A.D.), the movement of the geomagnetic pole was inactive, and it was active before and after this period, fluctuating over 10 degrees. Continuous time variation of the dipole moment was inferred from the angular dispersion of the VGP, by investigating the relationship between the angular dispersion of the VGP and the dipole moment. The result suggests that the dipole moment had sharp peaks of high intensity around. 8500 B.P., 4200 B.P. and 1200 B.P.