Intensity-Inclination Correlation for Long-Term Secular Variation of the Geomagnetic Field and Its Relevance to Persistent Non-Dipole Components

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Yamazaki and Oda [2002] reported long-term secular variation in inclination with ∼100 kyr periodicity and coherency between paleointensity and inclination variations using a sediment core from the western equatorial Pacific. In this paper, we first conducted a paleomagnetic study of another core taken nearby (∼120 km away) to examine the reproducibility of the records. The new core covers the last 1.1 Myr. Long-term inclination variations from the new core are almost identical to those of the previous core after conversion to a common age scale by inter-core correlation based on relative geomagnetic paleointensity. Mutually consistent long-term inclination records were also obtained from two cores of Brunhes age in the north central Pacific after inter-core correlation using relative paleointensity. Next, we compared intensity-inclination correlations of cores in the western equatorial Pacific (WEP) with those in the north central Pacific (NCP). A cross-correlation analysis showed that the coherency between intensity and inclination is strong in the WEP but weak in the NCP. Another remarkable difference in inclinations of the two regions is that the cores in the WEP have a large negative inclination anomaly (ΔI), whereas the cores in the NCP have a small ΔI. These observations support the model of Yamazaki and Oda [2002] that long-term secular variations in inclination are controlled by changes in the relative strength of the geocentric axial dipole and persistent non-dipole components. This model predicts that the intensity-inclination correlation should be obvious in regions where ΔI is large, but not where ΔI is small.