A Late Quaternary geomagnetic secular variation record from Lake Waiau, Hawaii, and the question of the Pacific nondipole low

Abstract

A continuous paleomagnetic record for the last 13,000 years was obtained from the sediments of Lake Waiau, located near the summit of Mauna Kea Volcano on the island of Hawaii. The secular variation (SV) of the geomagnetic field was studied using spectral analysis and precession analysis of the magnetic vector. The hypothesis that there has been anomalously low geomagnetic SV in the central Pacific was tested using angular dispersion analysis. The inclination record has a mean value of 27° that is much lower than the 35° predicted by the geocentric axial dipole hypothesis. The spectrum obtained from spectral analysis shows major inclination peaks at periodicities of approximately 3600 and 7900 years and major declination peaks at periodicities of approximately 1100, 2000, 3300, and 7800 years. The approximately 8000‐ and 3500‐year periodicities shown in both inclination and declination spectrums may represent the dipole and nondipole variation, respectively. The approximately 1100‐ and 2000‐year periodicities are probably derived from either the sources that affect declination only or the offsets between the core sections. In addition, Bauer plots of the magnetic vector are dominated by clockwise motion. The angular dispersion calculated from lake sediments is 5.9° with respect to the mean virtual geomagnetic pole (VGP) and 9.1° with respect to the geographic pole. Both values are much lower than the 13.5° expected from paleosecular variation model G which separates the angular dispersion into components from the dipole and the quadruple families. Our results support the hypothesis that an anomalously low secular variation is a characteristic feature of the central Pacific. Furthermore, this geomagnetic behavior persists on time scales of 104 years. Regional anomalies in temperature, topography or electrical conductivity at the core‐mantle boundary are inferred to cause the low SV.